Earth and Planetary Sciences › Geophysics

Geological and Geochemical Analysis

Works Count: 228454

Wikipedia

Description

This cluster of papers focuses on the tectonic evolution and geochronological analysis of orogenic processes, with a particular emphasis on zircon geochemistry, isotopic composition, and thermodynamic modeling. It covers topics such as subduction zones, mantle evolution, plate tectonics, and the growth of continental crust.

Keywords

Zircon; Geochronology; Tectonics; Granitic Rocks; Isotopic Composition; Subduction Zones; Mantle Evolution; Plate Tectonics; Thermodynamic Modeling; Continental Growth

An internally consistent thermodynamic data set for phases of petrological interest

1998-05-01

T. J. B. Holland , Roger Powell

The thermodynamic properties of 154 mineral end‐members, 13 silicate liquid end‐members and 22 aqueous fluid species are presented in a revised and updated data set. The use of a temperature‐dependent … The thermodynamic properties of 154 mineral end‐members, 13 silicate liquid end‐members and 22 aqueous fluid species are presented in a revised and updated data set. The use of a temperature‐dependent thermal expansion and bulk modulus, and the use of high‐pressure equations of state for solids and fluids, allows calculation of mineral–fluid equilibria to 100 kbar pressure or higher. A pressure‐dependent Landau model for order–disorder permits extension of disordering transitions to high pressures, and, in particular, allows the alpha–beta quartz transition to be handled more satisfactorily. Several melt end‐members have been included to enable calculation of simple phase equilibria and as a first stage in developing melt mixing models in NCKFMASH. The simple aqueous species density model has been extended to enable speciation calculations and mineral solubility determination involving minerals and aqueous species at high temperatures and pressures. The data set has also been improved by incorporation of many new phase equilibrium constraints, calorimetric studies and new measurements of molar volume, thermal expansion and compressibility. This has led to a significant improvement in the level of agreement with the available experimental phase equilibria, and to greater flexibility in calculation of complex mineral equilibria. It is also shown that there is very good agreement between the data set and the most recent available calorimetric data.

The 176Lu decay constant determined by Lu–Hf and U–Pb isotope systematics of Precambrian mafic intrusions

2004-02-12

Ulf Söderlund , P. Jonathan Patchett , Jeffrey D. Vervoort +1 more

Tectonic discrimination of granitoids

1989-05-01

P.D. Maniar , Philip M. Piccoli

Research Article| May 01, 1989 Tectonic discrimination of granitoids PAPU D. MANIAR; PAPU D. MANIAR 1Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 Search for other … Research Article| May 01, 1989 Tectonic discrimination of granitoids PAPU D. MANIAR; PAPU D. MANIAR 1Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 Search for other works by this author on: GSW Google Scholar PHILIP M. PICCOLI PHILIP M. PICCOLI 1Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 Search for other works by this author on: GSW Google Scholar Author and Article Information PAPU D. MANIAR 1Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 PHILIP M. PICCOLI 1Department of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1989) 101 (5): 635–643. https://doi.org/10.1130/0016-7606(1989)101<0635:TDOG>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation PAPU D. MANIAR, PHILIP M. PICCOLI; Tectonic discrimination of granitoids. GSA Bulletin 1989;; 101 (5): 635–643. doi: https://doi.org/10.1130/0016-7606(1989)101<0635:TDOG>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Granitoids as categorized by tectonic environment are (1) island arc granitoids (IAG), (2) continental arc granitoids (CAG), (3) continental collision granitoids (CCG), (4) postorogenic granitoids (POG), (5) rift-related granitoids (RRG), (6) continental epeirogenic uplift granitoids (CEUG), and (7) oceanic plagiogranites (OP). Of these, the IAG, CAG, CCG, and POG are considered orogenic granitoids, and the RRG, CEUG, and OP are considered anorogenic granitoids.The discrimination of granitoids is based on the major-element chemistry. Various discrimination plots are presented which sequentially discriminate the different tectonic environments. OP are separated from all other granitoids on the K2O versus SiO2 plot. Discrimination between group I (IAG + CAG + CCG), group II (RRG + CEUG), and group III (POG) granitoids can be achieved by using plots of Al2O3 versus SiO2, FeO(T)/ [FeO(T) + MgO] versus SiO2, and AFM and ACF ternary diagrams. In the figures, group I and group II plot in individual fields. Identification of group III is different, in that group III does not have a unique field in which it plots. Group III is identified because it consistently displays characteristics of both group I and group II. Further discrimination within group I can be accomplished on the basis of Shand's index. Only CCG have A/CNK [AL2O3/(CaO + Na2O + K2O)] values greater than 1.15. It is not possible to discriminate between IAG and CAG. Further discrimination within group II is done using the TiO2 versus SiO2 plot.The proposed discrimination scheme is applied to the Proterozoic granitoids of the midcontinent of the United States. It is shown that the Arbuckle granitoids are not anorogenic as previously thought. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Nature and composition of the continental crust: A lower crustal perspective

1995-08-01

Roberta L. Rudnick , David M. Fountain

Geophysical, petrological, and geochemical data provide important clues about the composition of the deep continental crust. On the basis of seismic refraction data, we divide the crust into type sections … Geophysical, petrological, and geochemical data provide important clues about the composition of the deep continental crust. On the basis of seismic refraction data, we divide the crust into type sections associated with different tectonic provinces. Each shows a three‐layer crust consisting of upper, middle, and lower crust, in which P wave velocities increase progressively with depth. There is large variation in average P wave velocity of the lower crust between different type sections, but in general, lower crustal velocities are high (>6.9 km s −1 ) and average middle crustal velocities range between 6.3 and 6.7 km s −1 . Heat‐producing elements decrease with depth in the crust owing to their depletion in felsic rocks caused by granulite facies metamorphism and an increase in the proportion of mafic rocks with depth. Studies of crustal cross sections show that in Archean regions, 50–85% of the heat flowing from the surface of the Earth is generated within the crust. Granulite terrains that experienced isobaric cooling are representative of middle or lower crust and have higher proportions of mafic rocks than do granulite terrains that experienced isothermal decompression. The latter are probably not representative of the deep crust but are merely upper crustal rocks that have been through an orogenic cycle. Granulite xenoliths provide some of the deepest samples of the continental crust and are composed largely of mafic rock types. Ultrasonic velocity measurements for a wide variety of deep crustal rocks provide a link between crustal velocity and lithology. Meta‐igneous felsic, intermediate and mafic granulite, and amphibolite facies rocks are distinguishable on the basis of P and S wave velocities, but metamorphosed shales (metapelites) have velocities that overlap the complete velocity range displayed by the meta‐igneous lithologies. The high heat production of metapelites, coupled with their generally limited volumetric extent in granulite terrains and xenoliths, suggests they constitute only a small proportion of the lower crust. Using average P wave velocities derived from the crustal type sections, the estimated areal extent of each type of crust, and the average compositions of different types of granulites, we estimate the average lower and middle crust composition. The lower crust is composed of rocks in the granulite facies and is lithologically heterogeneous. Its average composition is mafic, approaching that of a primitive mantle‐derived basalt, but it may range to intermediate bulk compositions in some regions. The middle crust is composed of rocks in the amphibolite facies and is intermediate in bulk composition, containing significant K, Th, and U contents. Average continental crust is intermediate in composition and contains a significant proportion of the bulk silicate Earth's incompatible trace element budget (35–55% of Rb, Ba, K, Pb, Th, and U).

Mantle geochemistry: the message from oceanic volcanism

1997-01-01

Albrecht W. Hofmann

A-type granites: geochemical characteristics, discrimination and petrogenesis

1987-04-01

J B Whalen , Kenneth L. Currie , B. W. Chappell

View PDF Chat

Derivation of some modern arc magmas by melting of young subducted lithosphere

1990-10-01

Marc J. Defant , Mark S. Drummond

Zircon chemistry and magma mixing, SE China: In-situ analysis of Hf isotopes, Tonglu and Pingtan igneous complexes

2002-04-01

William L. Griffin , Xiang Wang , Simon E. Jackson +4 more

The chemical composition of subducting sediment and its consequences for the crust and mantle

1998-04-01

Terry Plank , C. H. Langmuir

Subducted sediments play an important role in arc magmatism and crust–mantle recycling. Models of continental growth, continental composition, convergent margin magmatism and mantle heterogeneity all require a better understanding of … Subducted sediments play an important role in arc magmatism and crust–mantle recycling. Models of continental growth, continental composition, convergent margin magmatism and mantle heterogeneity all require a better understanding of the mass and chemical fluxes associated with subducting sediments. We have evaluated subducting sediments on a global basis in order to better define their chemical systematics and to determine both regional and global average compositions. We then use these compositions to assess the importance of sediments to arc volcanism and crust–mantle recycling, and to re-evaluate the chemical composition of the continental crust. The large variations in the chemical composition of marine sediments are for the most part linked to the main lithological constituents. The alkali elements (K, Rb and Cs) and high field strength elements (Ti, Nb, Hf, Zr) are closely linked to the detrital phase in marine sediments; Th is largely detrital but may be enriched in the hydrogenous Fe–Mn component of sediments; REE patterns are largely continental, but abundances are closely linked to fish debris phosphate; U is mostly detrital, but also dependent on the supply and burial rate of organic matter; Ba is linked to both biogenic barite and hydrothermal components; Sr is linked to carbonate phases. Thus, the important geochemical tracers follow the lithology of the sediments. Sediment lithologies are controlled in turn by a small number of factors: proximity of detrital sources (volcanic and continental); biological productivity and preservation of carbonate and opal; and sedimentation rate. Because of the link with lithology and the wealth of lithological data routinely collected for ODP and DSDP drill cores, bulk geochemical averages can be calculated to better than 30% for most elements from fewer than ten chemical analyses for a typical drill core (100–1000 m). Combining the geochemical systematics with convergence rate and other parameters permits calculation of regional compositional fluxes for subducting sediment. These regional fluxes can be compared to the compositions of arc volcanics to asses the importance of sediment subduction to arc volcanism. For the 70% of the trenches worldwide where estimates can be made, the regional fluxes also provide the basis for a global subducting sediment (GLOSS) composition and flux. GLOSS is dominated by terrigenous material (76 wt% terrigenous, 7 wt% calcium carbonate, 10 wt% opal, 7 wt% mineral-bound H2O+), and therefore similar to upper continental crust (UCC) in composition. Exceptions include enrichment in Ba, Mn and the middle and heavy REE, and depletions in detrital elements diluted by biogenic material (alkalis, Th, Zr, Hf). Sr and Pb are identical in GLOSS and UCC as a result of a balance between dilution and enrichment by marine phases. GLOSS and the systematics of marine sediments provide an independent approach to the composition of the upper continental crust for detrital elements. Significant discrepancies of up to a factor of two exist between the marine sediment data and current upper crustal estimates for Cs, Nb, Ta and Ti. Suggested revisions to UCC include Cs (7.3 ppm), Nb (13.7 ppm), Ta (0.96 ppm) and TiO2 (0.76 wt%). These revisions affect recent bulk continental crust estimates for La/Nb and U/Nb, and lead to an even greater contrast between the continents and mantle for these important trace element ratios. GLOSS and the regional sediment data also provide new insights into the mantle sources of oceanic basalts. The classical geochemical distinction between `pelagic' and `terrigenous' sediment sources is not valid and needs to be replaced by a more comprehensive understanding of the compositional variations in complete sedimentary columns. In addition, isotopic arguments based on surface sediments alone can lead to erroneous conclusions. Specifically, the Nd/Hf ratio of GLOSS relaxes considerably the severe constraints on the amount of sediment recycling into the mantle based on earlier estimates from surface sediment compositions.

Geochemical discrimination of different magma series and their differentiation products using immobile elements

1977-01-01

J. A. Winchester , P.A. Floyd

Tectonic models for accretion of the Central Asian Orogenic Belt

2006-12-07

Brian F. Windley , D. V. Alexeiev , Wenjiao Xiao +2 more

The Central Asian Orogenic Belt ( c . 1000–250 Ma) formed by accretion of island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges, oceanic plateaux and microcontinents in a manner comparable … The Central Asian Orogenic Belt ( c . 1000–250 Ma) formed by accretion of island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges, oceanic plateaux and microcontinents in a manner comparable with that of circum-Pacific Mesozoic–Cenozoic accretionary orogens. Palaeomagnetic and palaeofloral data indicate that early accretion (Vendian–Ordovician) took place when Baltica and Siberia were separated by a wide ocean. Island arcs and Precambrian microcontinents accreted to the active margins of the two continents or amalgamated in an oceanic setting (as in Kazakhstan) by roll-back and collision, forming a huge accretionary collage. The Palaeo-Asian Ocean closed in the Permian with formation of the Solonker suture. We evaluate contrasting tectonic models for the evolution of the orogenic belt. Current information provides little support for the main tenets of the one- or three-arc Kipchak model; current data suggest that an archipelago-type (Indonesian) model is more viable. Some diagnostic features of ridge–trench interaction are present in the Central Asian orogen (e.g. granites, adakites, boninites, near-trench magmatism, Alaskan-type mafic–ultramafic complexes, high-temperature metamorphic belts that prograde rapidly from low-grade belts, rhyolitic ash-fall tuffs). They offer a promising perspective for future investigations.

View PDF Chat

Major and trace element composition of the depleted MORB mantle (DMM)

2005-01-25

R. Workman , Stanley R. Hart

Naming materials in the magma/igneous rock system

1994-12-01

Eric A. K. Middlemost

The application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U–Pb zircon geochronology

2004-09-21

Simon E. Jackson , Norman J. Pearson , William L. Griffin +1 more

A Guide to the Chemical Classification of the Common Volcanic Rocks

1971-05-01

Τ. N. Irvine , W R A Baragar

A system is presented whereby volcanic rocks may be classified chemically as follows:I. Subalkaline Rocks:A. Tholeiitic basalt series:Tholeiitic picrite-basalt; tholeiite; tholeiitic andesite.B. Calc-alkali series:High-alumina basalt; andesite; dacite; rhyolite.II. Alkaline Rocks:A. … A system is presented whereby volcanic rocks may be classified chemically as follows:I. Subalkaline Rocks:A. Tholeiitic basalt series:Tholeiitic picrite-basalt; tholeiite; tholeiitic andesite.B. Calc-alkali series:High-alumina basalt; andesite; dacite; rhyolite.II. Alkaline Rocks:A. Alkali olivine basalt series:(1) Alkalic picrite–basalt; ankaramite; alkali basalt; hawaiite; mugearite; benmorite; trachyte.(2) Alkalic picrite–basalt; ankaramite; alkali basalt; trachybasalt; tristanite; trachyte.B. Nephelinic, leucitic, and analcitic rocks.III. Peralkaline Rocks:pantellerite, commendite, etc.

Magmatism at rift zones: The generation of volcanic continental margins and flood basalts

1989-06-10

R. S. White , Dan McKenzie

When continents rift to form new ocean basins, the rifting is sometimes accompanied by massive igneous activity. We show that the production of magmatically active rifted margins and the effusion … When continents rift to form new ocean basins, the rifting is sometimes accompanied by massive igneous activity. We show that the production of magmatically active rifted margins and the effusion of flood basalts onto the adjacent continents can be explained by a simple model of rifting above a thermal anomaly in the underlying mantle. The igneous rocks are generated by decompression melting of hot asthenospheric mantle as it rises passively beneath the stretched and thinned lithosphere. Mantle plumes generate regions beneath the lithosphere typically 2000 km in diameter with temperatures raised 100–200°C above normal. These relatively small mantle temperature increases are sufficient to cause the generation of huge quantities of melt by decompression: an increase of 100°C above normal doubles the amount of melt whilst a 200°C increase can quadruple it. In the first part of this paper we develop our model to predict the effects of melt generation for varying amounts of stretching with a range of mantle temperatures. The melt generated by decompression migrates rapidly upward, until it is either extruded as basalt flows or intruded into or beneath the crust. Addition of large quantities of new igneous rock to the crust considerably modifies the subsidence in rifted regions. Stretching by a factor of 5 above normal temperature mantle produces immediate subsidence of more than 2 km in order to maintain isostatic equilibrium. If the mantle is 150°C or more hotter than normal, the same amount of stretching results in uplift above sea level. Melt generated from abnormally hot mantle is more magnesian rich than that produced from normal temperature mantle. This causes an increase in seismic velocity of the igneous rocks emplaced in the crust, from typically 6.8 km/s for normal mantle temperatures to 7.2 km/s or higher. There is a concomitant density increase. In the second part of the paper we review volcanic continental margins and flood basalt provinces globally and show that they are always related to the thermal anomaly created by a nearby mantle plume. Our model of melt generation in passively upwelling mantle beneath rifting continental lithosphere can explain all the major rift‐related igneous provinces. These include the Tertiary igneous provinces of Britain and Greenland and the associated volcanic continental margins caused by opening of the North Atlantic in the presence of the Iceland plume; the Paraná and parts of the Karoo flood basalts together with volcanic continental margins generated when the South Atlantic opened; the Deccan flood basalts of India and the Seychelles‐Saya da Malha volcanic province created when the Seychelles split off India above the Réunion hot spot; the Ethiopian and Yemen Traps created by rifting of the Red Sea and Gulf of Aden region above the Afar hot spot; and the oldest and probably originally the largest flood basalt province of the Karoo produced when Gondwana split apart. New continental splits do not always occur above thermal anomalies in the mantle caused by plumes, but when they do, huge quantities of igneous material are added to the continental crust. This is an important method of increasing the volume of the continental crust through geologic time.

Correction of common lead in U–Pb analyses that do not report 204Pb

2002-12-01

Tom Andersen

Trace element and isotopic effects of combined wallrock assimilation and fractional crystallization

1981-04-01

Donald J. DePaolo

Atlas of Zircon Textures

2003-01-01

Fernando Corfú

Research Article| January 02, 2003 Atlas of Zircon Textures Fernando Corfu; Fernando Corfu Institute of Geology, University of Oslo, P B 1047 Blindern, N-0316 Oslo, Norway Search for other works … Research Article| January 02, 2003 Atlas of Zircon Textures Fernando Corfu; Fernando Corfu Institute of Geology, University of Oslo, P B 1047 Blindern, N-0316 Oslo, Norway Search for other works by this author on: GSW Google Scholar John M. Hanchar; John M. Hanchar Department of Earth and Environmental Sciences, The George Washington University, Washington, D.C. 20006 Search for other works by this author on: GSW Google Scholar Paul W.O. Hoskin; Paul W.O. Hoskin Institut für Mineralogie, Petrologie und Geochemie, Albert-Ludwigs-Universität Freiburg, D-79104 Freiburg, Germany Search for other works by this author on: GSW Google Scholar Peter Kinny Peter Kinny Department of Applied Geology, Curtin University of Technology, Perth WA 6845, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Fernando Corfu Institute of Geology, University of Oslo, P B 1047 Blindern, N-0316 Oslo, Norway John M. Hanchar Department of Earth and Environmental Sciences, The George Washington University, Washington, D.C. 20006 Paul W.O. Hoskin Institut für Mineralogie, Petrologie und Geochemie, Albert-Ludwigs-Universität Freiburg, D-79104 Freiburg, Germany Peter Kinny Department of Applied Geology, Curtin University of Technology, Perth WA 6845, Australia Publisher: Mineralogical Society of America First Online: 03 Mar 2017 © The Mineralogical Society Of America Reviews in Mineralogy and Geochemistry (2003) 53 (1): 469–500. https://doi.org/10.2113/0530469 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Fernando Corfu, John M. Hanchar, Paul W.O. Hoskin, Peter Kinny; Atlas of Zircon Textures. Reviews in Mineralogy and Geochemistry 2003;; 53 (1): 469–500. doi: https://doi.org/10.2113/0530469 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search The mineral zircon is extremely variable both in terms of external morphology and internal textures. These features reflect the geologic history of the mineral, especially the relevant episode(s) of magmatic or metamorphic crystallization (and recrystallization), strain imposed both by external forces and by internal volume expansion caused by metamictization, and chemical alteration. The paper presents a selection of both the most typical, but also of the less common, features seen in zircon, categorized according to the different geological processes responsible for their formation. The atlas is intended as a general guide for the interpretation of zircon characteristics, and of related... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

THREE NATURAL ZIRCON STANDARDS FOR U‐TH‐PB, LU‐HF, TRACE ELEMENT AND REE ANALYSES

1995-04-01

Michael Wiedenbeck , Paul Allé , Fernando Corfú +6 more

We report here the results of a study to develop natural zircon geochemical standards for calibrating the U‐(Th)‐Pb geochronometer and Hf isotopic analyses. Additional data were also collected for the … We report here the results of a study to develop natural zircon geochemical standards for calibrating the U‐(Th)‐Pb geochronometer and Hf isotopic analyses. Additional data were also collected for the major, minor and trace element contents of the three selected sample sets. A total of five large zircon grains (masses between 0.5 and 238 g) were selected for this study, representing three different suites of zircons with ages of 1065 Ma, 2.5 Ma and 0.9 Ma. Geochemical laboratories can obtain these materials by contacting Geostandards Newsletter.

Oblique Stepwise Rise and Growth of the Tibet Plateau

2001-11-23

Paul Tapponnier , Xu Zhiqin , Françoise Roger +4 more

Two end member models of how the high elevations in Tibet formed are (i) continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and … Two end member models of how the high elevations in Tibet formed are (i) continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and (ii) time-dependent, localized shear between coherent lithospheric blocks. Recent studies of Cenozoic deformation, magmatism, and seismic structure lend support to the latter. Since India collided with Asia ∼55 million years ago, the rise of the high Tibetan plateau likely occurred in three main steps, by successive growth and uplift of 300- to 500-kilometer-wide crustal thrust-wedges. The crust thickened, while the mantle, decoupled beneath gently dipping shear zones, did not. Sediment infilling, bathtub-like, of dammed intermontane basins formed flat high plains at each step. The existence of magmatic belts younging northward implies that slabs of Asian mantle subducted one after another under ranges north of the Himalayas. Subduction was oblique and accompanied by extrusion along the left lateral strike-slip faults that slice Tibet's east side. These mechanisms, akin to plate tectonics hidden by thickening crust, with slip-partitioning, account for the dominant growth of the Tibet Plateau toward the east and northeast.

Chemical mass transfer in magmatic processes IV. A revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures

1995-03-01

M. S. Ghiorso , Richard O. Sack

Tethyan evolution of Turkey: A plate tectonic approach

1981-06-01

A. M. Celâl Şengör , Yücel Yılmaz

Zircon saturation revisited: temperature and composition effects in a variety of crustal magma types

1983-08-01

E. Bruce Watson , T. Mark Harrison

Assembly, configuration, and break-up history of Rodinia: A synthesis

2007-06-26

Zheng‐Xiang Li , Svetlana Bogdanova , Alan S. Collins +7 more

The Hf isotope composition of cratonic mantle: LAM-MC-ICPMS analysis of zircon megacrysts in kimberlites

2000-01-01

William L. Griffin , Norman J. Pearson , Елена Белоусова +4 more

Composition of the Continental Crust

2013-11-07

Roberta L. Rudnick , Shan Gao

The geochemical evolution of the continental crust

1995-05-01

Stuart Ross Taylor , S. M. McLennan

A survey is given of the dimensions and composition of the present continental crust. The abundances of immobile elements in sedimentary rocks are used to establish upper crustal composition. The … A survey is given of the dimensions and composition of the present continental crust. The abundances of immobile elements in sedimentary rocks are used to establish upper crustal composition. The present upper crustal composition is attributed largely to intracrustal differentiation resulting in the production of granites senso lato. Underplating of the crust by ponded basaltic magmas is probably a major source of heat for intracrustal differentiation. The contrast between the present upper crustal composition and that of the Archean upper crust is emphasized. The nature of the lower crust is examined in the light of evidence from granulites and xenoliths of lower crustal origin. It appears that the protoliths of most granulite facies exposures are more representative of upper or middle crust and that the lower crust has a much more basic composition than the exposed upper crust. There is growing consensus that the crust grows episodically, and it is concluded that at least 60% of the crust was emplaced by the late Archean (ca. 2.7 eons, or 2.7 Ga). There appears to be a relationship between episodes of continental growth and differentiation and supercontinental cycles, probably dating back at least to the late Archean. However, such cycles do not explain the contrast in crustal compositions between Archean and post‐Archean. Mechanisms for deriving the crust from the mantle are considered, including the role of present‐day plate tectonics and subduction zones. It is concluded that a somewhat different tectonic regime operated in the Archean and was responsible for the growth of much of the continental crust. Archean tonalites and trond‐hjemites may have resulted from slab melting and/or from melting of the Archean mantle wedge but at low pressures and high temperatures analogous to modern boninites. In contrast, most andesites and subduction‐related rocks, now the main contributors to crustal growth, are derived ultimately from the mantle wedge above subduction zones. The cause of the contrast between the processes responsible for Archean and post‐Archean crustal growth is attributed to faster subduction of younger, hotter oceanic crust in the Archean (ultimately due to higher heat flow) compared with subduction of older, cooler oceanic crust in more recent times. A brief survey of the causes of continental breakup reveals that neither plume nor lithospheric stretching is a totally satisfactory explanation. Speculations are presented about crustal development before 4000 m.y. ago. The terrestrial continental crust appears to be unique compared with crusts on other planets and satellites in the solar system, ultimately a consequence of the abundant free water on the Earth.

Evolution of the Altaid tectonic collage and Palaeozoic crustal growth in Eurasia

1993-07-01

A. M. Celâl Şengör , Boris A. Natal’in , В. С. Буртман

The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crust system

1997-04-01

Janne Blichert‐Toft , Francis Albarède

The Composition of Zircon and Igneous and Metamorphic Petrogenesis

2003-01-01

P. W. O. Hoskin , Urs Schaltegger

Research Article| January 02, 2003 The Composition of Zircon and Igneous and Metamorphic Petrogenesis Paul W. O. Hoskin; Paul W. O. Hoskin Institut für Mineralogie, Petrologie und Geochemie, Albert-Ludwigs-Universität Freiburg … Research Article| January 02, 2003 The Composition of Zircon and Igneous and Metamorphic Petrogenesis Paul W. O. Hoskin; Paul W. O. Hoskin Institut für Mineralogie, Petrologie und Geochemie, Albert-Ludwigs-Universität Freiburg D-79104 Freiburg, Germany Search for other works by this author on: GSW Google Scholar Urs Schaltegger Urs Schaltegger Section des Sciences de la Terre, Départment de Minéralogie, Rue des Maraîchers 13 CH-1211 Genève 4, Switzerland Search for other works by this author on: GSW Google Scholar Reviews in Mineralogy and Geochemistry (2003) 53 (1): 27–62. https://doi.org/10.2113/0530027 Article history first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paul W. O. Hoskin, Urs Schaltegger; The Composition of Zircon and Igneous and Metamorphic Petrogenesis. Reviews in Mineralogy and Geochemistry 2003;; 53 (1): 27–62. doi: https://doi.org/10.2113/0530027 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Zircon is the main mineral in the majority of igneous and metamorphic rocks with Zr as an essential structural constituent. It is a host for significant fractions of the whole-rock abundance of U, Th, Hf, and the REE (Sawka 1988, Bea 1996, O'Hara et al. 2001). These elements are important geochemically as process indicators or parent isotopes for age determination. The importance of zircon in crustal evolution studies is underscored by its predominant use in U-Th-Pb geochronology and investigations of the temporal evolution of both the crust and lithospheric mantle. In the past decade an increasing... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

View PDF Chat

Abbreviations for names of rock-forming minerals

2009-12-23

Donna L. Whitney , Bernard W. Evans

Research Article| January 01, 2010 Abbreviations for names of rock-forming minerals Donna L. Whitney; Donna L. Whitney * 1Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, U.S.A. … Research Article| January 01, 2010 Abbreviations for names of rock-forming minerals Donna L. Whitney; Donna L. Whitney * 1Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, U.S.A. *E-mail: [email protected] Search for other works by this author on: GSW Google Scholar Bernard W. Evans Bernard W. Evans 2Department of Earth and Space Sciences, Box 351310, University of Washington, Seattle, Washington 98185, U.S.A. Search for other works by this author on: GSW Google Scholar Author and Article Information Donna L. Whitney * 1Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, U.S.A. Bernard W. Evans 2Department of Earth and Space Sciences, Box 351310, University of Washington, Seattle, Washington 98185, U.S.A. *E-mail: [email protected] Publisher: Mineralogical Society of America Received: 11 Aug 2009 Accepted: 13 Aug 2009 First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X © 2010 American Mineralogist American Mineralogist (2010) 95 (1): 185–187. https://doi.org/10.2138/am.2010.3371 Article history Received: 11 Aug 2009 Accepted: 13 Aug 2009 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Donna L. Whitney, Bernard W. Evans; Abbreviations for names of rock-forming minerals. American Mineralogist 2010;; 95 (1): 185–187. doi: https://doi.org/10.2138/am.2010.3371 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Nearly 30 years have elapsed since Kretz (1983) provided the mineralogical community with a systematized list of abbreviations for rock-forming minerals and mineral components. Its logic and simplicity have led to broad acceptance among authors and editors who were eager to adopt a widely recognized set of mineral symbols to save space in text, tables, and figures. Few of the nearly 5000 known mineral species occur in nature with a frequency sufficient to earn repeated mention in the geoscience literature and thus qualify for the designation "rock-forming mineral," but a reasonable selection of the most common and useful rock-forming minerals... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

View PDF Chat

Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic Rocks

1984-11-01

Julian A. Pearce , Nigel Harris , A. G. Tindle

Granites may be subdivided according to their intrusive settings into four main groups—ocean ridge granites (ORG), volcanic arc granites (VAG), within plate granites (WPG) and collision granites (COLG)—and the granites … Granites may be subdivided according to their intrusive settings into four main groups—ocean ridge granites (ORG), volcanic arc granites (VAG), within plate granites (WPG) and collision granites (COLG)—and the granites within each group may be further subdivided according to their precise settings and petrological characteristics. Using a data bank containing over 600 high quality trace element analyses of granites from known settings, it can be demonstrated using ORG-normalized geochemical patterns and element-SiO2 plots that most of these granite groups exhibit distinctive trace element characteristics. Discrimination of ORG, VAG, WPG and syn-COLG is most effective in Rb−Y−Nb and Rb−Yb−Ta space, particularly on projections of Y−Nb, Yb−Ta, Rb−(Y + Nb) and Rb−(Yb + Ta). Discrimination boundaries, though drawn empirically, can be shown by geochemical modelling to have a theoretical basis in the different petrogenetic histories of the various granite groups. Post-collision granites present the main problem of tectonic classification, since their characteristics depend on the thickness and composition of the lithosphere involved in the collision event and on the precise timing and location of magmatism. Provided they are coupled with a consideration of geological constraints, however, studies of trace element compositions in granites can clearly help in the elucidation of post-Archaean tectonic settings.

View PDF Chat

Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic crust

1988-11-01

Albrecht W. Hofmann

View PDF Chat

The composition of the continental crust

1995-04-01

K. H. Wedepohl

Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes

1989-01-01

Shen‐Su Sun , W. F. McDonough

Summary Trace-element data for mid-ocean ridge basalts (MORBs) and ocean island basalts (OIB) are used to formulate chemical systematics for oceanic basalts. The data suggest that the order of trace-element … Summary Trace-element data for mid-ocean ridge basalts (MORBs) and ocean island basalts (OIB) are used to formulate chemical systematics for oceanic basalts. The data suggest that the order of trace-element incompatibility in oceanic basalts is Cs ≈ Rb ≈ (≈ Tl) ≈ Ba(≈ W) > Th > U ≈ Nb = Ta ≈ K > La > Ce ≈ Pb > Pr (≈ Mo) ≈ Sr > P ≈ Nd (> F) > Zr = Hf ≈ Sm > Eu ≈ Sn (≈ Sb) ≈ Ti > Dy ≈ (Li) > Ho = Y > Yb. This rule works in general and suggests that the overall fractionation processes operating during magma generation and evolution are relatively simple, involving no significant change in the environment of formation for MORBs and OIBs. In detail, minor differences in element ratios correlate with the isotopic characteristics of different types of OIB components (HIMU, EM, MORB). These systematics are interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone. Niobium data indicate that the mantle sources of MORB and OIB are not exact complementary reservoirs to the continental crust. Subduction of oceanic crust or separation of refractory eclogite material from the former oceanic crust into the lower mantle appears to be required. The negative europium anomalies observed in some EM-type OIBs and the systematics of their key element ratios suggest the addition of a small amount (⩽1% or less) of subducted sediment to their mantle sources. However, a general lack of a crustal signature in OIBs indicates that sediment recycling has not been an important process in the convecting mantle, at least not in more recent times (⩽2 Ga). Upward migration of silica-undersaturated melts from the low velocity zone can generate an enriched reservoir in the continental and oceanic lithospheric mantle. We propose that the HIMU type ( eg St Helena) OIB component can be generated in this way. This enriched mantle can be re-introduced into the convective mantle by thermal erosion of the continental lithosphere and by the recycling of the enriched oceanic lithosphere back into the mantle.

Continental and Oceanic Crust Recycling-induced Melt-Peridotite Interactions in the Trans-North China Orogen: U-Pb Dating, Hf Isotopes and Trace Elements in Zircons from Mantle Xenoliths

2009-12-16

Yongsheng Liu , Shunbao Gao , Zhaoping Hu +3 more

We present the first finding of continental crust-derived Precambrian zircons in garnet/spinel pyroxenite veins within mantle xenoliths carried by the Neogene Hannuoba basalt in the central zone of the North … We present the first finding of continental crust-derived Precambrian zircons in garnet/spinel pyroxenite veins within mantle xenoliths carried by the Neogene Hannuoba basalt in the central zone of the North China Craton (NCC). Petrological and geochemical features indicate that these mantle-derived composite xenoliths were formed by silicic melt^lherzolite interaction. The Precambrian zircon ages can be classified into three age groups of 2·4^2·5 Ga, 1·6^2·2 Ga and 0·6^1·2 Ga, coinciding with major geological events in the NCC. These Precambrian zircons fall in the field of continental granitoid rocks in plots of U/Yb vs Hf and Y. Their igneous-type REE patterns and metamorphic zircon type CL images indicate that they were not crystallized during melt^peridotite interaction and subsequent high-pressure metamorphism.The 2·5 Ga zircons have positive eHf(t) values (2·9^10·6), whereas the younger Precambrian zircons are dominated by negative eHf(t) values, indicating an ancient continental crustal origin.These observations suggest that the Precambrian zircons were xenocrysts that survived melting of recycled continental crustal rocks and were then injected with silicate melt into the host peridotite. In addition to the Precambrian zircons, igneous zircons of 315 3 Ma (2 ), 80^170 Ma and 48^64 Ma were separated from the garnet/spinel pyroxenite veins; these provide evidence for lower continental crust and oceanic crust recycling-induced multi-episodic melt^peridotite interactions in the central zone of the NCC. The combination of the positive eHf(t) values (2·91^24·6) of the 315 Ma zircons with the rare occurrence of 302^324 Ma subduction-related diorite^granite plutons in the northern margin of the NCC implies that the 315 Ma igneous zircons might record melt^peridotite interactions in the lithospheric mantle induced by Palaeo-Asian oceanic crust subduction. Igneous zircons of age 80^170 Ma generally coexist with the Precambrian metamorphic zircons and have lower Ce/Yb and Th/U ratios, higher U/Yb ratios and greater negative Eu anomalies.The eHf(t) values of these zircons vary greatly from ^47·6 to 24·6.The 170^110 Ma zircons are generally characterized by negative eHf(t) values, whereas the 110^100 Ma zircons have positive eHf(t) values.These observations suggest that melt^peridotite interactions at 80^170 Ma were induced by partial melting of recycled continental crust. The 48^64 Ma igneous zircons are characterized by negligible Ce anomalies, unusually high REE, U and Th contents, and positive eHf(t) values.These features imply that the melt^peridotite interactions at 48^64 Ma could be associated with a depleted mantle-derived carbonate melt or fluid.

Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks

1979-01-01

Julian A. Pearce , Michael J Norry

Tectonic setting of basic volcanic rocks determined using trace element analyses

1973-06-01

Julian A. Pearce , J. R. Cann

A Chemical Classification of Volcanic Rocks Based on the Total Alkali-Silica Diagram

1986-06-01

M. J. Le Bas , R. W. Le Maitre , A. Streckeisen +1 more

This contribution summarizes and brings up to date the recommendations made by the IUGS Subcommission on the Systematics of Igneous Rocks for the classification of volcanic rocks when modal analyses … This contribution summarizes and brings up to date the recommendations made by the IUGS Subcommission on the Systematics of Igneous Rocks for the classification of volcanic rocks when modal analyses are lacking. The classification is on a non-genetic basis using the total alkali-silica (TAS) diagram, and is as nearly consistent as possible with the QAPF modal classification. The diagram is divided into 15 fields, two of which contain two root names which are separated according to other chemical criteria, giving the following 17 root names: basalt, basaltic andesite, andesite, dacite, rhyolite, trachybasalt, basaltic trachyandesite, trachyandesite, trachyte, trachydacite, picrobasalt, basanite, tephrite, phonotephrite, tephriphonolite, phonolite and foidite. Using Na-K criteria, trachybasalt may be further divided into the sub-root names hawaiite and potassic trachybasalt, basaltic trachyandesite into the sub-root names mugearite and shoshonite, and trachyandesite into the sub-root names benmoreite and latite.

Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust

2007-08-01

Julian A. Pearce

A Geochemical Classification for Granitic Rocks

2001-11-01

Carol D. Frost , Calvin G. Barnes , William J. Collins +2 more

This geochemical classification of granitic rocks is based upon three variables. These are FeO/(FeO + MgO) = Fe-number [or FeOtot/(FeOtot + MgO) = Fe*], the modified alkali–lime index (MALI) (Na2O … This geochemical classification of granitic rocks is based upon three variables. These are FeO/(FeO + MgO) = Fe-number [or FeOtot/(FeOtot + MgO) = Fe*], the modified alkali–lime index (MALI) (Na2O + K2O – CaO) and the aluminum saturation index (ASI) [Al/(Ca – 1·67P + Na + K)]. The Fe-number (or Fe*) distinguishes ferroan granitoids, which manifest strong iron enrichment, from magnesian granitoids, which do not. The ferroan and magnesian granitoids can further be classified into alkalic, alkali–calcic, calc-alkalic, and calcic on the basis of the MALI and subdivided on the basis of the ASI into peraluminous, metaluminous or peralkaline. Because alkalic rocks are not likely to be peraluminous and calcic and calc-alkalic rocks are not likely to be peralkaline, this classification leads to 16 possible groups of granitic rocks. In this classification most Cordilleran granitoids are magnesian and calc-alkalic or calcic; both metaluminous and peraluminous types are present. A-type granitoids are ferroan alkali–calcic, although some are ferroan alkalic. Most are metaluminous although some are peraluminous. Caledonian post-orogenic granites are predominantly magnesian alkali–calcic. Those with <70 wt % SiO2 are dominantly metaluminous, whereas more silica-rich varieties are commonly peraluminous. Peraluminous leucogranites may be either magnesian or ferroan and have a MALI that ranges from calcic to alkalic.

View PDF Chat

Porphyry Copper Systems

2010-01-01

Richard H. Sillitoe

Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate boundaries, including porphyry deposits centered on intrusions; skarn, carbonate-replacement, and sediment-hosted Au deposits in increasingly … Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate boundaries, including porphyry deposits centered on intrusions; skarn, carbonate-replacement, and sediment-hosted Au deposits in increasingly peripheral locations; and superjacent high- and intermediate-sulfidation epithermal deposits. The systems commonly define linear belts, some many hundreds of kilometers long, as well as occurring less commonly in apparent isolation. The systems are closely related to underlying composite plutons, at paleodepths of 5 to 15 km, which represent the supply chambers for the magmas and fluids that formed the vertically elongate (>3 km) stocks or dike swarms and associated mineralization. The plutons may erupt volcanic rocks, but generally prior to initiation of the systems. Commonly, several discrete stocks are emplaced in and above the pluton roof zones, resulting in either clusters or structurally controlled alignments of porphyry Cu systems. The rheology and composition of the host rocks may strongly influence the size, grade, and type of mineralization generated in porphyry Cu systems. Individual systems have life spans of ~100,000 to several million years, whereas deposit clusters or alignments as well as entire belts may remain active for 10 m.y. or longer. The alteration and mineralization in porphyry Cu systems, occupying many cubic kilometers of rock, are zoned outward from the stocks or dike swarms, which typically comprise several generations of intermediate to felsic porphyry intrusions. Porphyry Cu ± Au ± Mo deposits are centered on the intrusions, whereas carbonate wall rocks commonly host proximal Cu-Au skarns, less common distal Zn-Pb and/or Au skarns, and, beyond the skarn front, carbonate-replacement Cu and/or Zn-Pb-Ag ± Au deposits, and/or sediment-hosted (distal-disseminated) Au deposits. Peripheral mineralization is less conspicuous in noncarbonate wall rocks but may include base metal- or Au-bearing veins and mantos. High-sulfidation epithermal deposits may occur in lithocaps above porphyry Cu deposits, where massive sulfide lodes tend to develop in deeper feeder structures and Au ± Ag-rich, disseminated deposits within the uppermost 500 m or so. Less commonly, intermediate-sulfidation epithermal mineralization, chiefly veins, may develop on the peripheries of the lithocaps. The alteration-mineralization in the porphyry Cu deposits is zoned upward from barren, early sodic-calcic through potentially ore-grade potassic, chlorite-sericite, and sericitic, to advanced argillic, the last of these constituting the lithocaps, which may attain >1 km in thickness if unaffected by significant erosion. Low sulfidation-state chalcopyrite ± bornite assemblages are characteristic of potassic zones, whereas higher sulfidation-state sulfides are generated progressively upward in concert with temperature decline and the concomitant greater degrees of hydrolytic alteration, culminating in pyrite ± enargite ± covellite in the shallow parts of the litho-caps. The porphyry Cu mineralization occurs in a distinctive sequence of quartz-bearing veinlets as well as in disseminated form in the altered rock between them. Magmatic-hydrothermal breccias may form during porphyry intrusion, with some of them containing high-grade mineralization because of their intrinsic permeability. In contrast, most phreatomagmatic breccias, constituting maar-diatreme systems, are poorly mineralized at both the porphyry Cu and lithocap levels, mainly because many of them formed late in the evolution of systems. Porphyry Cu systems are initiated by injection of oxidized magma saturated with S- and metal-rich, aqueous fluids from cupolas on the tops of the subjacent parental plutons. The sequence of alteration-mineralization events charted above is principally a consequence of progressive rock and fluid cooling, from >700° to <250°C, caused by solidification of the underlying parental plutons and downward propagation of the lithostatic-hydrostatic transition. Once the plutonic magmas stagnate, the high-temperature, generally two-phase hyper-saline liquid and vapor responsible for the potassic alteration and contained mineralization at depth and early overlying advanced argillic alteration, respectively, gives way, at <350°C, to a single-phase, low- to moderate-salinity liquid that causes the sericite-chlorite and sericitic alteration and associated mineralization. This same liquid also causes mineralization of the peripheral parts of systems, including the overlying lithocaps. The progressive thermal decline of the systems combined with synmineral paleosurface degradation results in the characteristic overprinting (telescoping) and partial to total reconstitution of older by younger alteration-mineralization types. Meteoric water is not required for formation of this alteration-mineralization sequence although its late ingress is commonplace. Many features of porphyry Cu systems at all scales need to be taken into account during planning and execution of base and precious metal exploration programs in magmatic arc settings. At the regional and district scales, the occurrence of many deposits in belts, within which clusters and alignments are prominent, is a powerful exploration concept once one or more systems are known. At the deposit scale, particularly in the porphyry Cu environment, early-formed features commonly, but by no means always, give rise to the best ore-bodies. Late-stage alteration overprints may cause partial depletion or complete removal of Cu and Au, but metal concentration may also result. Recognition of single ore deposit types, whether economic or not, in porphyry Cu systems may be directly employed in combination with alteration and metal zoning concepts to search for other related deposit types, although not all those permitted by the model are likely to be present in most systems. Erosion level is a cogent control on the deposit types that may be preserved and, by the same token, on those that may be anticipated at depth. The most distal deposit types at all levels of the systems tend to be visually the most subtle, which may result in their being missed due to overshadowing by more prominent alteration-mineralization.

Plešovice zircon — A new natural reference material for U–Pb and Hf isotopic microanalysis

2007-12-10

Jiří Sláma , Jan Košler , Daniel J. Condon +7 more

Volcanic rock series in island arcs and active continental margins

1974-04-01

Akiho Miyashiro

View PDF Chat

Dehydration Melting of Metabasalt at 8-32 kbar: Implications for Continental Growth and Crust-Mantle Recycling

1995-08-01

Robert P. Rapp , E. Bruce Watson

We report the results of partial melting experiments between 8 and 32 kbar, on four natural amphibolites representative of metamorphosed Archean tholeiite (greenstone), high-alumina basalt, low-potassium tholeiite and alkali-rich basalt. … We report the results of partial melting experiments between 8 and 32 kbar, on four natural amphibolites representative of metamorphosed Archean tholeiite (greenstone), high-alumina basalt, low-potassium tholeiite and alkali-rich basalt. For each rock, we monitor changes in the relative proportions and composition of partial melt and coexisting residual (crystalline) phases from 1000 to 1150°C, within and beyond the amphibole dehydration reaction interval. Low percentage melts coexisting with an amphibolite or garnet amphibolite residue at 1000–1025°C and 8–16 kbar are highly silicic (high-K2O granitic at ∼5%; melting, low-Al2O3 trondhjemitic at ∼5–10%). Greater than 20% melting is only achieved beyond the amphibole-out phase boundary. Silicic to intermediate composition liquids (high-Al2O3 trondhjemitic-tonalitic, granodioritic, quartz dioritic, dioritic) result from ∼20–40% melting between 1050 and 1100°C, leaving a granulite (plagioclase + clinopyroxene ± orthopyroxene ± olivine) residue at 8 kbar and garnet granulite to eclogite (garnet + clinopyroxene) residues at 12–32 kbar. Still higher degrees of melting ( ∼40–60%) result in mafic liquids corresponding to low-MgO, high-Al2O3 basaltic and basaltic andesite compositions, which coexist with granulitic residues at 8 kbar and edogitic or garnet granulitic (garnet + clinopyroxene + plagioclase ± orthopyroxene) residues at higher pressures (12–28 kbar). As much as 40% by volume high-Al2O3 trondhjemitic-tonalitic liquid coexists with an eclogitic residue at 1100–1150°C and 32 kbar. The experimental data suggest that the Archean tonalite-trondhjemite-granodiorite (TTG) suite of rocks, and their Phanerozoic equivalents, the tonalite-trondhjemite-dacite suite (including 'adakites' and other Na-rich granitoids), can be generated by 10–40% melting of partially hydrated metabasalt at pressures above the garnet-in phase boundary (≥12 kbar) and temperatures between 1000 and 1100°C. Anomalously hot and/or thick metabasaltic crust is implied. Although a rare occurrence along modern convergent plate margins, subductionrelated melting of young, hot oceanic crust (e.g. ocean ridges) may have been an important (essential) element in the growth of the continental crust in the Archean, if plate tectonic processes were operative. Coupled silicic melt generation-segregation and mafic restite disposal may also occur at the base of continental or primitive (sub-arc?) crust, where crustal overthickening is a consequence of underplating and overaccretion of mafic magmas. In either setting, net growth of continental crust and crustmantle recycling may be facilitated by relatively high degrees of melting and extreme density contrasts between trondhjemitictonalitic liquids and garnet-rich residues. Continuous chemical trends are apparent between the experimental crystalline residues, and mafic migmatites and garnet granulite xenoliths from the lower crust, although lower-crustal xenoliths in general record lower temperatures (600–900°C) and pressures (5–13 kbar) than corresponding residual assemblages from the experiments. However, geo-thermobarometry on eclogite xenoliths in kimberlites from the subcontinental mantle indicates conditions appropriate for melting through and beyond the amphibole reaction interval and the granulite-eclogite transition. If these samples represent ancient (eclogitized) remnants of subducted or otherwise foundered basaltic crust, then the intervening history of their protoliths may in some cases include partial melting.

Composition of the Continental Crust

2003-01-01

Roberta L. Rudnick , Shan Gao

Proceedings of the American philosophical society

1838-10-01

Mössbauer spectroscopy for dolerite provenance characterization in Valencia region: A proof of concept

2025-06-25

Joaquín Jiménez‐Puerto , E. Devlin , Gianni Gallello +2 more | Journal of Archaeological Science Reports

Enhancing, Disseminating, and Preserving the Rio Almansor Migmatites Geosite (Montemor-o-Novo, SW Portugal)

2025-06-25

Manuel Francisco Pereira , Ícaro Días da Silva , Cristina Gama +1 more | Geoheritage

Geochemistry and tectonic evolution of Neoproterozoic Wadi Kid Dokhan volcanics, Southeast Sinai, Egypt

2025-06-25

Hatem M. El-Desoky , Ahmed M. Abdel-Rahman , Wael Fahmy +4 more | Mineralogy and Petrology

The role of magma differentiation in optimizing the fluid-assisted extraction of copper to generate large porphyry-type deposits

2025-06-25

Shunda Yuan , Anthony E. Williams‐Jones , Robert J. Bodnar +4 more | Science Advances

Porphyry copper deposits (PCDs) are the main source of copper globally, with the metals transported in and deposited from aqueous magmatic fluids. Processes that define the volume of magma and … Porphyry copper deposits (PCDs) are the main source of copper globally, with the metals transported in and deposited from aqueous magmatic fluids. Processes that define the volume of magma and concentration of copper in the magma required to form PCDs, however, are not well understood. Here, we present the results of quantitative modeling of the behavior of Cu and Cl during magma evolution in the upper crust. We show that fractional crystallization is the most important process promoting efficient Cu extraction, and that high concentrations of Cu in the ore-forming hydrothermal fluids can be reached with moderate Cl concentrations. Unusually high concentrations of Cl and Cu in the magma and large magma volumes are not required. Arc magmas of modest volume (<103 km3) and modest initial Cu and Cl concentrations can generate large PCDs, if a sufficient mass of magmatic fluid is exsolved at an advanced stage of crystallization.

Mafic magmatism triggered the Mesoproterozoic oxygenation event: Re-Os-PGE evidence from the Xiamaling Formation in North China and Velkerri Formation in North Australia

2025-06-24

Xuli Yang , Zhu‐Yin Chu , Shuan‐Hong Zhang +4 more | Earth and Planetary Science Letters

Coupling Phase Equilibrium Modelling and Apatite‐in‐Garnet Elastic Barometry to Unravel the P–T Path of the Micaschist Unit From the Zicavo Metamorphic Complex (Corsica, France)

2025-06-24

Lorenzo Dulcetta , Xin Zhong , Gabriele Cruciani +4 more | Journal of Metamorphic Geology

ABSTRACT To gain insights into the pressure–temperature evolution of a scarcely studied portion of the Variscan basement of Corsica in southern Europe, we combined phase equilibrium modelling, Zr‐in‐rutile thermometry and … ABSTRACT To gain insights into the pressure–temperature evolution of a scarcely studied portion of the Variscan basement of Corsica in southern Europe, we combined phase equilibrium modelling, Zr‐in‐rutile thermometry and apatite‐in‐garnet elastic barometry. We investigated Grt‐St micaschist rocks containing garnet grains of several millimetres in size hosting chloritoid + rutile inclusions. Garnet was found to be wrapped by a foliated matrix made up of muscovite, staurolite, chlorite, biotite and ilmenite. Intersecting compositional isopleths for garnet core, chloritoid and muscovite yielded P – T conditions for garnet core formation of 1.05–1.35 GPa and 430°C–535°C. These conditions were further constrained by Zr‐in‐rutile thermometry (470°C) and apatite‐in‐garnet elastic barometry, which intersect at 1.10 GPa and 455°C. We interpreted these conditions to be the beginning of garnet growth coinciding with the D 1 deformation. After decompression and heating, the thermal peak was reached during the main D 2 deformation, coeval with a dextral shearing; these conditions, constrained through garnet rim and matrix mineral isopleths, were found to be at 0.5–0.9 GPa and 540°C–580°C in the staurolite stability field. After (retrograde) D 3 deformation, isothermal decompression associated with granitoid intrusion caused contact metamorphism at shallower crustal levels. Overall, the combination of this P – T path with available ones from southern Corsica and NE Sardinia allows us to hypothesize a possible new geodynamic scenario. We hypothesize that Corsica and Sardinia were on opposite sides of the Lower Palaeozoic Mid‐Variscan Ocean before the Variscan Orogeny occurred, after which they welded, leading to the current configuration of the Corsica–Sardinia block.

Alpine Tethys rift-related OIB-type magmatism preserved on Elba Island (Northern Apennines, Italy)

2025-06-24

Federico Lucci , Andrea Brogi , John C. White +2 more | International Geology Review

Provenance of the Carboniferous Clastic Rocks in the Eastern Tibetan Plateau: Insights Into the Palaeogeography and Tectonic Evolution of the Northern Margin of East Gondwana

2025-06-24

Junwei Qiao , Xiuwen Fu , Xiaochen Zhao +4 more | Geological Journal

ABSTRACT The terranes in the eastern Tibetan Plateau are regarded as the key position in reconstructing the evolutionary history of the Paleo‐Tethys Ocean and the break‐up of East Gondwana. However, … ABSTRACT The terranes in the eastern Tibetan Plateau are regarded as the key position in reconstructing the evolutionary history of the Paleo‐Tethys Ocean and the break‐up of East Gondwana. However, the tectonic affinities of these terranes during the late Palaeozoic, as well as the position of Gondwana's northern margin at that time, remain contentious, owing principally to inadequate investigation of the provenance characteristics and tectonic setting of the constituent strata. The late Palaeozoic strata (especially Lower Carboniferous) exposed in the eastern Tibetan Plateau terranes provide crucial constraints for understanding their tectonic affinities and for more precisely defining Gondwana's northern margin during this time interval. This study presents a systematic provenance analysis of the Carboniferous strata from Kaqiong (Bangda Fm.), Zuogong (Kagong Fm.) and Qamdo (Machala Fm.) terranes in the eastern Tibetan Plateau, via new U–Pb dating of the detrital zircons. The detrital zircon U–Pb age data of Bangda Fm. yielded ages ranging from 336 to 2837 Ma with major age peaks at ~1000 Ma. The detrital zircon U–Pb age data of Kagong and Machala formations revealed obviously different age patterns, featured by predominant late Palaeozoic zircon ages (ca. 320 ~ 380 Ma), which were similar to the timing of synsedimentary magmatic arc activities. The U–Pb age spectra of the Bangda Formation are consistent with those of the lower Carboniferous in the southern Qiangtang, Lhasa and Himalaya blocks to the south. It indicates that the sediments of the Bangda Formation shared the same sources with these blocks. In contrast, the U–Pb age spectra of the Kagong and Machala formations indicate plentiful input of the late Palaeozoic zircons, which were probably derived from arc magmatic rocks distributed in the North Qiangtang, Qamdo terranes along the Longmucuo–Shuanghu–Lancangjiang suture zone. Furthermore, the differences in paleobiogeographic assemblages, stratigraphic sequence and tectonic setting of the lower Carboniferous from the Kaqiong and Zuogong–Qamdo terranes indicate the existence of an ancient ocean along the Longmucuo–Shuanghu suture zone. From this study, we infer that the Kaqiong terrane might have been located at the northern margin of East Gondwana, while Zuogong–Qamdo terranes were located at the southern margin of the Eurasia Blocks.

Magmatic Response to Closure of the Hegenshan Ocean and Subsequent Post‐Orogenic Extension: Insights From Middle Triassic A‐Type Granites in the Meilaotewula Ophiolitic Belt, Central Inner Mongolia, China

2025-06-24

Shuai Wang , Yingjie Li , Guochen Dong +6 more | Geological Journal

ABSTRACT The timing of closure of the Hegenshan Ocean and the evolution of post‐orogenic extension in the southeastern Central Asian Orogenic Belt (CAOB) are debated. To address this, we investigated … ABSTRACT The timing of closure of the Hegenshan Ocean and the evolution of post‐orogenic extension in the southeastern Central Asian Orogenic Belt (CAOB) are debated. To address this, we investigated the petrography, whole‐rock geochemistry and zircon U–Pb geochronology and Hf isotopic composition of the Harigentai granites that intrude the Meilaotewula ophiolitic belt in the Hegenshan ophiolite‐arc‐accretionary complex, central Inner Mongolia. These granites are monzogranites with Middle Triassic ages of 239.3 ± 1.4 and 238.7 ± 1.3 Ma. The monzogranites are weakly peraluminous and highly alkaline, and are enriched in Rb, Th, U, K and Ta, and depleted in Ba, Sr, P and Ti. They have flat chondrite‐normalised rare earth element (REE) patterns with negative Eu anomalies ( δ Eu = 0.15–0.38) and high Y/Nb ratios (1.42–2.72). They have positive ε Hf ( t ) values (7.5–12.0) and young two‐stage Hf isotopic model ages (788–500 Ma), with high zircon saturation temperatures (792°C–817°C). These characteristics suggest the monzogranites are A 2 ‐type granites that formed under high‐temperature and low‐pressure conditions by partial melting of juvenile mafic‐intermediate crust. The results of this study, combined with the spatial distribution of Carboniferous‐Triassic ophiolites and igneous rocks within the Hegenshan ophiolite‐arc‐accretionary complex, indicate that the Hegenshan Ocean closed at the end‐Permian, followed by a post‐orogenic extensional setting during the Triassic.

High‐Titanium Zircon Rims in Rhyolite – A Reflection of Adiabatic Ascent?

2025-06-24

Carson Kinney , H W Little , Chris Yakymchuk | Geological Journal

ABSTRACT Autocrystic zircon formed during magma crystallisation provides crucial information for understanding the long‐term evolution of Earth's crust. Due to the factors that control zircon solubility in silicate melt (e.g., … ABSTRACT Autocrystic zircon formed during magma crystallisation provides crucial information for understanding the long‐term evolution of Earth's crust. Due to the factors that control zircon solubility in silicate melt (e.g., temperature and melt composition), zircon crystallisation may occur during magma ascent, emplacement, and eruption. Zircon sourced from volcanic rocks can have rims with elevated concentrations of titanium relative to zircon cores; this has been linked to temperature changes associated with recharge events in magma chambers. An alternative cause of temperature shifts in subvolcanic systems is adiabatic ascent without magma mixing or recharge. Here, we simulate adiabatic ascent of rhyolitic magmas to model the growth and dissolution of zircon during ascent from the mid‐crust to sub‐volcanic depths – decompression melting and system expansion drive cooling prior to fluid saturation. Sub‐volcanic boiling induces magma crystallisation. Zircon growth is predicted throughout ascent for both A‐ and S‐type magmas. Our results suggest that high‐titanium rims of autocrystic zircon can form through the protracted evolution of a single magmatic pulse without the need for magmatic recharge.

Petrology and Sr–Nd Isotopes of High–Grade Amphibolites From Bankim Area (Central Cameroon Shear Zone), Cameroon: Constraints on Petrogenesis and Geodynamic Implications

2025-06-24

Tcheumenak Kouémo Jules , Maurice Kwékam , Eric Martial Fozing +3 more | Geological Journal

ABSTRACT The Bankim area is located in the Tikar Plain, on the N50E branch of the Central Cameroon Shear Zone (CCSZ) where amphibolites occur, but their relationship with the general … ABSTRACT The Bankim area is located in the Tikar Plain, on the N50E branch of the Central Cameroon Shear Zone (CCSZ) where amphibolites occur, but their relationship with the general Pan–African metamorphism history is poorly known. The petrography, mineral chemistry, geochemistry and Sr–Nd isotope systematics of amphibolites from the Bankim area are presented in this paper in order to constrain their petrogenesis and geodynamic setting during the Pan–African orogeny. They are garnet amphibolites (GA), pyroxene amphibolites (PA) and biotite amphibolites (BA) occurring as metric flagstones showing relic of S 1 foliation, lense–like, or as sheared sinistral and dextral and/or boudinaged enclaves. In GA, garnet occurs as lobate porphyroblasts (Alm 54‐58 Gr 25‐27 Pyr 10‐12 ∙ Sp 3‐5 ). It is usually surrounded by a corona made up of hornblende, plagioclase [andesite (Ab 67‐59 An 32‐46 Or 0.5 ) to oligoclase (Ab 72 An 27 Or 0.6 )], quartz and ilmenite; the whole defining a kelyphitic microstructure (characterised by garnet + amphibole + plagioclase + opaques mineral (ilmenite) parageneses). In PA, clinopyroxene (diopside; Ca 49‐50 Mg 29‐30 Fe 19‐22 ) is mostly relic–like and displays hornblende or plagioclase (andesine (Ab 65‐67 An 32‐34 Or 0.6‐0.8 ) to oligoclase (Ab 69‐70 An 29‐30 Or 1‐1.2 )) corona showing hornblende + clinopyroxene + plagioclase + opaque minerals paragenesis. Field and microstructural data indicate that these rocks recorded a polyphase prograde–peak followed by retrograde metamorphism. The metamorphic prograde phase and peak P–T conditions exceeding 5.2 kbar/789°C occurring during the D 1 deformation phase (613–600 Ma) correspond to the collisional stage of the Pan–African orogeny within the granulite facies. Retrograde metamorphism occurred from the granulite facies to the amphibolite facies under P–T conditions of 1.4–5.2 kbar/789°C–513°C. These changes were synchronous with the early sinistral syn–D 2 (590–580 Ma) and the late dextral syn–D 3 (580–545 Ma) ductile shear deformation phases. These deformation phases, which occurred as a result of exhumation during the crustal re–equilibration related to relaxation and erosion during the post‐collisional evolution of Western Gondwana. The geochemical data indicate that the above amphibolites derived from the metamorphism of mafic protolith which represents an ancient Proterozoic crust with model ages of T DM = 1.9–1.6 Ga and initial 87 Sr/ 86 Sr 600 ratios of 0.70626–0.70894. At the end of the prograde and retrograde metamorphism of this ancient crust, it was stretched, sheared, dismembered and scattered along the Pan–African mobile zone during the CCSZ reactivations.

Metallogeny of subduction initiation revealed by chalcophile element behaviour in the Samail ophiolite

2025-06-24

Thomas M. Belgrano , James A. Milton , Larryn W. Diamond +3 more | Earth and Planetary Science Letters

Rocks: Description, Identification, Nomenclature, Genesis by W. V. Maresch and H.-P. Schertl. Schweizer-bart Science Publishers, Stuttgart, Germany. 408 pages; 2024; €34.90 (softbound).

2025-06-24

Carl A. Francis | Rocks & Minerals

Late Carboniferous Slab Rollback in the Southern Altaids: Evidence from a Slab-Derived Adakitic Granodiorite in the South Tianshan

2025-06-24

Nijiati Abuduxun , Wenjiao Xiao , Wei Zhang +4 more | Minerals

The South Tianshan records the latest accretionary and collisional events in the southwestern Altaids, but the internal subduction-related processes are controversial. This study provides an integrative analysis of a newly … The South Tianshan records the latest accretionary and collisional events in the southwestern Altaids, but the internal subduction-related processes are controversial. This study provides an integrative analysis of a newly identified Late Carboniferous adakitic granodiorite from the South Tianshan, incorporating geochronological, zircon U-Pb and Lu-Hf isotopic, whole-rock geochemical, and Sr-Nd isotopic data. Zircon U-Pb analysis indicates that the granite was emplaced at 310 ± 2.5 Ma. Based on major element compositions, the granodiorite belongs to medium-K calc-alkaline weakly peraluminous series (A/CNK = 0.95–1.09). The samples exhibit typical high-silica adakitic affinity, as evidenced by the elevated contents of SiO2 (67.75–69.27 wt.%), Al2O3 (15.29–15.90 wt.%), Sr (479–530 ppm), and Ba (860–910 ppm); low concentrations of Yb (0.43–0.47 ppm) and Y (7.12–7.44 ppm); high Sr/Y ratios (67–72); and slight Eu anomalies (δEu = 0.89–1.03). The sodium-rich composition (K2O/Na2O = 0.48–0.71) is comparable to adakitic rocks from slab-derived melts. Elevated concentrations of Ni (22.12–24.25 ppm), Cr (33.20–37.86 ppm), Co (6.32–6.75 ppm), and V (30.33–32.48 ppm), along with high Mg# values (55–57), suggest melt–mantle interaction during magma ascent. The slightly enriched isotopic signatures, characterized by higher initial 87Sr/86Sr ratios (0.706086–0.706205) and lower εNd(t) (−3.09 to –2.47) and εHf(t) (−3.11 to +7.66) values, point to notable sedimentary contributions, potentially through source contamination and/or shallow-level crustal contamination. By integrating the new results with previously published data, we consider that the adakitic granodiorite was generated by partial melting of the subducted oceanic crust, triggered by asthenospheric upwelling associated with the southward rollback of the north-dipping South Tianshan oceanic lithosphere. Our data provide new insights into Late Carboniferous retreating subduction along the southern active margin of the Yili-Central Tianshan and the accretionary architecture of the southern Altaids.

Prediction of Buried Cobalt-Bearing Arsenides Using Ionic Leach Geochemistry in the Bou Azzer-El Graara Inlier (Central Anti-Atlas, Morocco): Implications for Mineral Exploration

2025-06-24

Yassine Lmahfoudi , Houssa Ouali , Saïd Ilmen +6 more | Minerals

The Aghbar-Bou Azzer East mining district (ABED) is located between the Bou Azzer East and Aghbar deposits. It is an area of approximately 7 km long towards ENE–WSW and 2 … The Aghbar-Bou Azzer East mining district (ABED) is located between the Bou Azzer East and Aghbar deposits. It is an area of approximately 7 km long towards ENE–WSW and 2 km wide towards N–S. In this barren area, volcano-sedimentary rocks are attributed to the Ouarzazate group outcrop (Ediacarian age): they are composed of volcanic rocks (ignimbrite, andesite, rhyolite, dacite, etc.) covered by the Adoudou detritic formation in angular unconformity. Given the absence of serpentinite outcrops, exploration investigation in this area has been very limited. This paper aims to use ionic leach geochemistry (on samples of soil) to detect the presence of Co-bearing arsenides above hidden ore deposits in this unexplored area of the Bou Azzer inlier. In addition, a detailed structural analysis allowed the identification of four families of faults and fractures with or without filling. Three directional major fault systems of several kilometers in length and variable orientation in both the Cryogenian basement and the Ediacaran cover have been identified: (i) ENE–WSW, (ii) NE–SW, and (iii) NW–SE. Several geochemical anomalies for Co, As, Ni, Ag, and Cu are aligned along three main directions, including NE–SW, NW–SE, and ENE–WSW. They are particularly well-defined in the western zone but are only minor in the central and eastern zones. Some of these anomalies correlate with the primary structural features observed in the studied area. These trends are consistent with those known under mining exploitation in nearby ore deposits, supporting the potential for similar mineralization in the ABED. Based on structural analysis and ionic leach geochemistry, drilling programs were conducted in the study area, confirming the continuity of serpentinites at depth beneath the Ediacaran cover and the presence of Co–Fe-bearing arsenide ores. This validates the ionic geochemistry technique as a reliable method for exploring buried ore deposits.

Petrogenesis and metamorphism of mafic rocks, Atlantis Massif, IODP Expedition 357: Implications of two episodes of magmatism

2025-06-24

Scott Whattam , Jan C.M. De Hoog , Sabyasachi Chattopadhyay +2 more | Journal of the Geological Society

The petrogenesis and metamorphism of IODP Expedition 357 (Atlantis Massif, MAR) mafic rocks is the focus of this communication. At least two phases of magmatism are identified. Later Phase I … The petrogenesis and metamorphism of IODP Expedition 357 (Atlantis Massif, MAR) mafic rocks is the focus of this communication. At least two phases of magmatism are identified. Later Phase I metamorphosed mafic intrusives (MMI) are moderately to extremely chloritized recording LOI of 3.33-9.99 wt. % and latest Phase II basalts are exceptionally fresh with LOI of 0.09-1.03 wt. %.Phase I MMI have Fe-chromite identical to Atlantis Massif serpentinite that have undergone melt-impregnation and Phase II basalt Cr-spinel are analogous to those of Atlantis Massif peridotite that have not undergone secondary melt-impregnation. . Whole rock Cr/Y relations that the Phase II basalt records melt fractions ( F ) of ∼16-25% and melt-liquid equilibria established for Phase II basalt olivine yield crystallization temperatures of 1173-1219 °C similar to MORB (∼1125-1290 °C). Trivariant plots of Na 2 O-CaO-MgO and XRD analysis confirm extreme chloritization of the Phase I MMI. Phase I MMI spinel are predominantly Fe-chromite that formed under amphibolite facies conditions (∼500 °C). Subsequent to peridotite exhumation, serpentinization and Phase I magmatism, an episode (or episodes) of asthenospheric upwelling resulted in contact metamorphism caused by Phase II magmatism.

The role of halogens and sulfur in apatite in assessing the potential ore content of granitoids of the Tigertysh complex (Kuznetsk Alatau)

2025-06-24

Ekaterina Nastavko , Timofey Leshukov , Alexeï Slesarev +1 more | Vestnik of Geosciences

The study of the halogen (F and Cl) and sulfur contents in apatite from granodiorites and leucogranites of the Tigertysh complex (Є-O1t) was carried out, which may indicate the potential … The study of the halogen (F and Cl) and sulfur contents in apatite from granodiorites and leucogranites of the Tigertysh complex (Є-O1t) was carried out, which may indicate the potential ore content of granitoids. Apatites of granodiorites are confined mainly to amphibole grains, less often located in quartz and feldspars, and correspond in composition to fluorapatite (F = 2.45–2.76 wt. %, Cl = 0.02–0.03 wt. %). In leucogranites, apatite is confined to feldspars and biotite, and corresponds in composition to hydroxyl- and fluorapatite (F = 1.50–1.80 wt. %, Cl = 0.33–0.52 wt. %). In apatite from granodiorites, the sulfur content is maximum in grains confined to amphibole and is 0.05–0.11 wt. %, while in apatite from quartz and feldspars it is no more than 0.04 wt. %. The sulfur content in apatite from leucogranites does not depend on its confinement to different minerals and is 0.04–0.07 wt. %. Based on the F, Cl and S contents in apatites of granitoids of the Tigertysh complex, it can be assumed that gold-sulfide-quartz mineralization may be associated with granodiorites, and Cu-porphyry mineralization with leucogranites.

Diancangshan Complex in SE Tibet: An Oligocene granitic pegmatitic volcanic edifice

2025-06-23

Tiannan Yang , Xin Di , Chuandong Xue +3 more | Geological Society of America Bulletin

The Cenozoic tectonic record of southeastern Tibet includes WNW-ESE−trending, large-scale ductile shear zones that are inconsistent with the lithospheric structure revealed by seismic data. The Diancangshan Complex is a major … The Cenozoic tectonic record of southeastern Tibet includes WNW-ESE−trending, large-scale ductile shear zones that are inconsistent with the lithospheric structure revealed by seismic data. The Diancangshan Complex is a major segment of the WNW-ESE−trending Ailaoshan−Red River “ductile shear zone” that contains voluminous granitic gneiss, augen mylonite, and sheared schists, which exhibit microtextures resembling those of typical mylonites. We investigated these mylonite-like rocks using TESCAN Integrated Mineral Analyzer, electron backscattered diffractometer, microscopic, and microprobe techniques to reassess the origin of these rocks. The analyses revealed that these mylonite-like rocks are actually granitic pegmatitic volcanic or subvolcanic rocks that did not undergo ductile deformation after solidification. The sequential mineral assemblages, large range of grain sizes for all minerals, and unidirectional solidification textures indicate dynamic crystallization related to a high degree of undercooling of the granitic pegmatitic melt. Dynamic crystallization during magma flow generated mylonite-like textures. Thus, the so-called Ailaoshan−Red River ductile shear zone does not exist. Detailed U-Pb dating revealed that &gt;90% of the zircons in the pegmatitic rocks were inherited from their source rocks, and &lt;10% were newly formed during the Oligocene (31−25 Ma). Heating of high-temperature, H2O-rich fluids derived from crystallized, mantle-derived magmas, which had accumulated beneath the upper crust, rapidly partially melted the upper-crustal rocks and generated hydrous granitic melts. Both real granitic mylonite and mylonite-like pegmatitic rock are common in most ancient orogenic belts, and their origins are critical to understanding their tectonic evolution.

Prolonged mantle metasomatism in the Neoproterozoic continental arc: Insights from mafic magmatism in the western Yangtze Block, South China

2025-06-23

Zhe-hao Zhong , Shaocong Lai , Yu Zhu +4 more | Acta Geochimica

Effects of melt-mush reaction on the lower oceanic crust and MORB chemistry: constraints from 53° E Southwest Indian Ridge

2025-06-23

Xiaohan Huang , Alexandra Yang Yang , Taiping Zhao | Earth and Planetary Science Letters

Relict landscape evolution and fault reactivation in the eastern Tian Shan: insights from the Harlik Mountains

2025-06-23

Zihao Zhao , Tianyi Shen , Guocan Wang +3 more | Solid Earth

Abstract. Relict low-relief surfaces, formed during tectonically quiescent periods and later modified by factors such as increased tectonic activity, are prevalent within the active mountain ranges of central Asia. However, … Abstract. Relict low-relief surfaces, formed during tectonically quiescent periods and later modified by factors such as increased tectonic activity, are prevalent within the active mountain ranges of central Asia. However, their formation, preservation, and subsequent evolution within the Mesozoic–Cenozoic tectonic framework remain poorly understood. This study examines the low-relief surfaces of the Harlik Mountains, located in the easternmost Tian Shan, integrating digital terrain analysis, fluvial geomorphic analysis, structural geology, and low-temperature thermochronology to reconstruct their long-term geomorphic evolution. Our results reveal that these surfaces are segmented by WNW–ESE-striking faults, which initially experienced right-lateral transtensional movement followed by left-lateral strike-slip reactivation. Apatite fission-track (AFT) thermochronology of samples from relict surfaces yields AFT ages ranging from ∼110 to ∼100 Ma, while samples from fault zones record ages of 90–70 Ma. Thermal modeling of these samples indicates a period of moderate cooling in the mid- to late Early Cretaceous, followed by a prolonged slow cooling phase for the relict surfaces. In contrast, fault zones show rapid cooling during the 90–70 Ma interval. By integrating these results with previous findings, we propose that the mid- to late Early Cretaceous (∼110-100Ma) cooling event corresponds to extensional collapse following building of the Mongol–Okhotsk orogen. This process, coupled with increased humidity, enhanced erosion, and relief reduction, facilitated the formation of low-relief surfaces. The influence of Mongol–Okhotsk orogenic collapse likely persisted into the Late Cretaceous (90–70 Ma), during which right-lateral transtensional faulting further segmented the landscape without generating significant topographic contrasts. By the Oligocene (∼30 Ma), far-field effects from the India–Eurasia collision reactivated major faults in a left-lateral sense, driving regional uplift, surface tilting, and drainage incision. This uplift phase marked the end of landscape stability, as evidenced by increased sediment input into adjacent basins. Despite active faulting and fluvial incision, generally low erosion rates allowed the preservation of large-scale Mesozoic low-relief surfaces.

Volcanic Rocks from Western Limnos Island, Greece: Petrography, Magnetite Geochemistry, and Magnetic Susceptibility Constraints

2025-06-23

Christos L. Stergiou , Vasilios Melfos , Lambrini Papadopoulou +2 more | Minerals

This study contributes new mineralogical, whole-rock geochemical, and magnetic susceptibility data to the well-established petrogenesis of the Miocene of Limnos volcanic rocks in the Aegean region. The combined examination of … This study contributes new mineralogical, whole-rock geochemical, and magnetic susceptibility data to the well-established petrogenesis of the Miocene of Limnos volcanic rocks in the Aegean region. The combined examination of volcanic samples from the Katalakon, Romanou, and Myrina units demonstrates that they belong to a genetically related high-K calc-alkaline to shoshonitic suite that was formed by fractional crystallization in a continental arc setting and derived from a subduction-modified mantle source, contaminated by continental sediments. Different magmatic processes and crystallization conditions are reflected in modest compositional differences in magnetite (Ti, Al substitution) and ilmenite (Mg, Al, Fe–Ti ratios), as well as variations in trace elements between the units (e.g., elevated Nb–Zr in Romanou, high LREE in Myrina, and Ba in Katalakon). According to the magnetic data, bulk magnetic susceptibility is largely determined by magnetite abundance, whereas magnetic domain states are influenced by the grain size and shape, as euhedral grains are associated with stronger responses. The coupled geochemical and magnetic results indicate the diversified and transitional character of the Agios Ioannis Subunit in the Katalakon Unit.

Mineralogy and Fluid Inclusion Constraints on the Genesis of the Recently Discovered Ag-(Ni-Co-Sb-As-Hg ± Bi) Vein Ore Shoot Mineralization in the Aouli Pb-Zn District (Upper Moulouya, Morocco)

2025-06-22

Khadra Zaid , Mohammed Bouabdellah , Gilles Lévresse +7 more | Minerals

Unusual Ag-(Ni-Co-Sb-As-Hg ± Bi)-bearing fault-fill vein ore shoot mineralization set in a gangue of quartz, fluorite, and barite has been identified in Morocco’s Aouli deposit. The Paleozoic host rocks consist … Unusual Ag-(Ni-Co-Sb-As-Hg ± Bi)-bearing fault-fill vein ore shoot mineralization set in a gangue of quartz, fluorite, and barite has been identified in Morocco’s Aouli deposit. The Paleozoic host rocks consist of a succession of Cambrian to Ordovician-aged folded and low- to medium-grade metasediments and metavolcaniclastic rocks with tuff interbeds and amphibolite sills, locally intruded by late Visean calc-alkaline to alkaline granitoid intrusions. Paragenetic relationships indicate that the sequence of ore precipitation comprises a succession of Ni-Co-Fe arsenides, followed by Pb-Sb-As-Ag-Hg sulfarsenides/sulfosalts and then Zn-Pb-Fe sulfides. Results indicate that the ore shoot mineralization formed from episodic stages of fracturing and subsequent fluid migration. Precipitation of ore phases is thought to have occurred as a result of isothermal mixing and subsequent fluid–rock interactions. The timing of mineralization is thought to have occurred between Late Triassic and Late Miocene, coinciding with major crustal extension and Middle Jurassic–Upper Cretaceous alkaline magmatism. Thermal convection and seismic pumping are proposed as the main driving force for the large-scale migration of the ore-forming brines. This research bears directly upon the potential for new exploration targets in Pb-Zn ± fluorite ± barite deposits hosted in Variscan inliers throughout North Africa.

Crust–mantle interactions and remelting of mica-rich residues in the lower crust: a new petrogenetic model for the southern Jinshajiang–Red River K-rich igneous belt, SW China

2025-06-21

Feng-Bao Ji , Peng Song | International Geology Review

Copper isotope evidence for recycled crustal sulfides in deep mantle plume source

2025-06-21

Junhua Yao , Wei Yuan , Zhengrong Wang +5 more | Communications Earth & Environment

Revealing the early geological history of the Istanbul Zone (Far-East Avalonia) through zircon U-Pb-Hf isotopic data

2025-06-21

Sinan Yılmazer , Gültekin Topuz , Marcel Guillong +3 more | Precambrian Research

Origin of the Harappan Ernestites: Geochemical Insights into Provenance and Fabrication

2025-06-20

Milan Kumar Mahala , Jyotiranjan S. Ray , Alok Kumar Kanungo +7 more | Research Square (Research Square)

<title>Abstract</title> Advancements in stone bead technology, particularly in drilling techniques, emerged during the Indus Valley (Harappan) civilization. Long-constricted cylindrical drill bits, made from a unique stone called Ernestite, were a … <title>Abstract</title> Advancements in stone bead technology, particularly in drilling techniques, emerged during the Indus Valley (Harappan) civilization. Long-constricted cylindrical drill bits, made from a unique stone called Ernestite, were a distinctive feature of this culture. The origin of Ernestite is a mystery due to the lack of a natural analogue and an unknown manufacturing process. This study presents a mineralogical and geochemical investigation of Ernestite stones and drill bits from several Harappan and contemporaneous sites in Gujarat, India, to uncover their origin. The isotopic ratios of Sr and Nd link the drills to the Ernestites. The texture and presence of pseudo-mullite (SiO2 > 40 wt%) with high Al-Ti-bearing hematite suggest that Ernestites are synthetic, created through a sintering process at ~ 1100°C. An abundance of sand to silt-sized detrital quartz, along with Fe-Ti-Zr-rich minerals, indicates the use of crudely powdered sandstones and laterites as raw materials, with geochemical ties to regional sources.

Deeply Recycled Origins of Mantle Heterogeneity at the Northern East Pacific Rise

2025-06-20

Molly Anderson , Gabriel Johnston , M. R. Perfit +6 more | Research Square (Research Square)

<title>Abstract</title> Compositionally diverse lavas from the 8°20’ N seamount chain near the East Pacific Rise (EPR) record greater geochemical heterogeneity than observed along the entire northern EPR, including evidence for … <title>Abstract</title> Compositionally diverse lavas from the 8°20’ N seamount chain near the East Pacific Rise (EPR) record greater geochemical heterogeneity than observed along the entire northern EPR, including evidence for a 4-component mantle, and the first discovery of high-µ (high time-integrated 238U/204Pb) mantle source at the northern EPR. The amplitude of Pb, Sr, and Nd isotopic heterogeneity is on the scale of the Galapagos plume but in an area distal to a mantle plume. Our study combines isotopic and trace element compositions of near-EPR seamounts with recent mantle particle tracking models to identify deeply subducted origins for northern EPR mantle heterogeneity. We show that geochemical models (using He, Pb, Sr, Nd isotopes and trace elements) and geodynamic models (using time-dependent mantle flow simulations based on tomography) are self-consistent with tectonically recycled material feeding the northern EPR asthenosphere. These models provide a rare opportunity to assess geographic origins of mantle heterogeneity, tying the chemical and isotopic variability at the northern EPR to a paleo subduction zone at ~ 130 Ma, and reveal that one of the fastest spreading ridges on Earth samples deeply recycled components associated with whole mantle convection.

Immiscibility in Magma Conduits: Evidence from Granitic Enclaves

2025-06-20

Ya Tian , Guanglai Li , Yongle Yang +4 more | Minerals

Many granitic enclaves are developed in the volcanic channel of the Xiangshan volcanic basin. To explore their genesis, this study examined the petrography, geochemistry, LA-ICP-MS zircon U–Pb chronology, and zircon … Many granitic enclaves are developed in the volcanic channel of the Xiangshan volcanic basin. To explore their genesis, this study examined the petrography, geochemistry, LA-ICP-MS zircon U–Pb chronology, and zircon Hf isotopes of the granitic enclaves and compared them with the porphyroclastic lavas. In general, the granitic enclaves and porphyroclastic lavas have similar structures, and the rock-forming minerals and accessory minerals have relatively close compositions. In terms of rock geochemical characteristics, the granitic enclaves are richer in silicon and alkalis but have lower abundances of aluminum, magnesium, iron, and calcium than the porphyroclastic lavas. Rb, Th, K, Sm, and other elements are more enriched, whereas Ba, Ti, Nb, P, and other elements are more depleted. The granitic enclaves have lower rare earth contents (195.53 × 10−6–271.06 × 10−6) than the porphyroclastic lavas (246.67 × 10−6–314.27 × 10−6). The rare earth element distribution curves of the two are generally consistent, both right-leaning, and enriched with light rare earth patterns. The weighted average zircon U–Pb ages of two granitic enclave samples were 135.45 ± 0.54 Ma (MSWD = 0.62, n = 17) and 135.81 ± 0.60 Ma (MSWD = 0.40, n = 20), respectively, which are consistent with the weighted average age of a single porphyroclastic lava sample of 134.01 ± 0.53 Ma (MSWD = 2.0, n = 20). The zircons of the two kinds of rocks crystallize at almost the same temperature. The consistent trend of the rare earth element distribution curve of zircons in the granitic enclaves and the porphyroclastic lava samples indicates that the zircons of the two samples were formed in the same stage. The formation process of granitic enclaves may be that the lower crustal melt is induced to rise, and the crystallization differentiation occurs in the magma reservoir and is stored in the form of crystal mush, forming a shallow crystal mush reservoir. The crystal mush reservoir is composed of a large number of rock-forming minerals such as quartz, feldspar, and biotite, as well as accessory mineral crystals such as zircon and flowable intergranular melt. In the later stage of magma high evolution, a small and short-time magmatic activity caused a large amount of crystalline granitic crystal mush to pour into the volcanic pipeline. In the closed system of volcanic pipeline, the pressure and temperature decreased rapidly, and the supercooling degree increased, and the immiscibility finally formed pale granitic enclaves.

Petrogenesis and tectonic evolution of tourmaline- bearing leucogranites, Sikait area, Southeastn desert of Egypt utilizing mineralogical and bulk rock analysis

2025-06-20

Gehad M. Saleh , Mohamed S. Kamar , Farrage M. Khaleal +3 more | Scientific Reports

Abstract The current research discuss in detail the tourmaline distribution in Sikait leucogranites in order to deduce its genesis and type. We conduct new detailed geological, petrographical, mineralogical, and geochemical … Abstract The current research discuss in detail the tourmaline distribution in Sikait leucogranites in order to deduce its genesis and type. We conduct new detailed geological, petrographical, mineralogical, and geochemical examinations to understand the Arabian Nubian Shield development by investigation of such the examined leucogranites. Tourmaline occurs as disseminated or cluster nodular within coarse-grained leucogranites. Geochemically, the examined leucogranites have high contents of SiO 2 (69.44–75.87 wt%), and total alkalis (mean > 7) with low mean CaO (0.4 wt%), Fe 2 O 3 (1.93 wt%), and Mg# (14.59) values. They share features of calc-alkaline, strongly peraluminous (A/CNK > 1.1), with high contents of Zn (av. 266.68 ppm), Pb (av. 29.13 ppm), Rb/Sr (av. 22), Al 2 O 3 /TiO 2 (av. 832.6), FeO/MgO (av. 12.24). They are remarkably enriched in semi-volatile elements (Pb = 12–235 ppm), and LILEs (Rb = 192–679 ppm) relative to HFSEs (e.g. Zr, U and Nb) with notable strong Ba, Sr and Ti negative anomalies. They are depleted in ∑REEs (av. 19.1 ppm) and reveal parallel, uniform patterns slightly notable depletion of HREEs in comparison with LREEs. They reveal extreme pronounced Eu (av. Eu/Eu*= 0.02) negative and Ce/Ce* (0.76–1.12) positive anomalies. The examined rocks have prominent tetrad effect (M-type) as indicated by Irber and Lambda methods. Based up on conventional geochemical diagrams, the examined rocks are post-collisional S-type granites derived by partial degree of the clay-rich pelite rocks melting followed by extreme fractional crystallization processes during post-collisional extension episode at temperatures (663 –786 °C) based on saturation temperature of zircon. The investigated tourmaline nodules are of alkali group and foitite end-member.

Grenvillian S-type granites in the North Qaidam orogenic belt, NW China: Implications for the geodynamic evolution of the Rodinia supercontinent

2025-06-20

Haitao Ma , Pengjie Cai , Dongyang Lian +1 more | Precambrian Research

Petrological Exploration of Magma Storage and Evolution Conditions at the Eastern Virunga Volcanic Province (Rwanda, East African Rift System)

2025-06-20

Fabio Colle , Teresa Trua , Serena Giacomelli +2 more | Minerals

The Virunga Volcanic Province (VVP), located in the western branch of the East African Rift System, hosts a variety of alkaline lavas erupted from closely spaced volcanic centers. However, the … The Virunga Volcanic Province (VVP), located in the western branch of the East African Rift System, hosts a variety of alkaline lavas erupted from closely spaced volcanic centers. However, the magmatic system of this region, particularly in its eastern sector, remains insufficiently constrained. In this study, we present a petrological and geochemical investigation of basaltic to trachytic lavas from the eastern VVP. Thermobarometric analysis of mineral phases indicates that basalts originated from magma storage zones between 4 and 30 km deep, with crystallization temperatures of ~1200 °C and melt H2O contents lower than 1 wt%. In contrast, more evolved magmas crystallized at similar depths, but at lower temperatures (~1050 °C) and higher H2O contents, ranging from 2 to 4 wt%. Thermodynamic modelling suggests that extensive (up to 70%) fractional crystallization of an assemblage dominated by olivine, clinopyroxene, and plagioclase can produce the more evolved trachytic derivatives from basaltic parental melts. When integrated with previous studies from other VVP volcanoes, our findings deepen the understanding of the architecture of the magmatic system beneath the region, suggesting it resembles a well-developed multi-level plumbing system.

Zircon out, Elpidite in: Deformation-Driven Zirconosilicate Evolution in Peralkaline Granites: A Case Study of the Papanduva Pluton (Brazil)

2025-06-20

Larissa P. Grangeiro , Frederico Castro Jobim Vilalva , Sílvio Roberto Farias Vlach +1 more | Minerals

The peralkaline granites of the Papanduva Pluton (South Brazil) display a remarkable facies dichotomy, with zircon dominant in massive facies and diverse zirconosilicates (Zr-Si) in foliated facies. This study employs … The peralkaline granites of the Papanduva Pluton (South Brazil) display a remarkable facies dichotomy, with zircon dominant in massive facies and diverse zirconosilicates (Zr-Si) in foliated facies. This study employs petrography and mineral chemistry (major and trace elements) to elucidate the textural diversity and compositional evolution of these minerals. Three discrete zirconosilicate groups were identified: Na-rich elpidite ( euhedral, vein-like, and granular varieties), Na-poor (Na,K)Zr-Si-I, and silica-rich (Na,K)Zr-Si-II. Contrary to the expected crystallization sequences, trace element data reveal that REE enrichment correlates with deformation intensity rather than paragenetic order, with vein-like aggregates along deformation features showing the highest REE concentrations. Statistical analysis demonstrates significant correlations between REE contents and alkali exchange patterns. We propose a three-stage evolutionary model involving magmatic crystallization, deformation-enhanced fluid interaction, and late-stage recrystallization, with a progressive evolution from Na-dominated to K-dominated conditions. This study provides new insights into closed-system fluid evolution in agpaitic environments and highlights deformation as a primary control on element mobility in peralkaline granitic systems.

The role of mineralizing fluids in the formation of the Erentaolegai Ag deposit, Great Hinggan Range, Northeast China: Insights from geology, fluid inclusions, and C–H–O isotope systematics

2025-06-20

Xiangguo Guo , Mingqian Wu , Fu Xu +4 more | Hydrogeology Journal

Fragments of ancient continental lithospheric mantle in the Mogok metamorphic Belt, Northern Myanmar: Re–Os isotope and platinum group element constraints

2025-06-20

Qinghua Zhang , Bin Su , Yi Chen +6 more | Precambrian Research

Mafic-ultramafic intrusions of Matokulma, Palojärvi, and Hongonniittu within the Central Finland Granitoid Complex with special reference to their petrogenesis and ore potential

2025-06-19

Seppo Karvinen , Hannu Makkonen , Perttu Mikkola +3 more | Bulletin of the Geological Society of Finland

We describe three previously unknown or poorly studied mafic-ultramafic intrusions (Matokulma, Palojärvi, Hongonniittu) from the south-central part of the Paleoproterozoic Central Finland Granitoid Complex (CFGC). The ore potential and petrogenesis … We describe three previously unknown or poorly studied mafic-ultramafic intrusions (Matokulma, Palojärvi, Hongonniittu) from the south-central part of the Paleoproterozoic Central Finland Granitoid Complex (CFGC). The ore potential and petrogenesis of the intrusions, with the focus on Matokulma and Palojärvi, are discussed based on petrography and geochemistry and, possible relationships with the Ni-Cu ore potential Vammala–Kotalahti type intrusions are examined. The poorly exposed Hongonniittu intrusion is likely genetically related to the Palojärvi intrusion. Median Mg-numbers for Matokulma and Palojärvi are 72 and 49, respectively. They consist of cumulus clinopyroxene, orthopyroxene and plagioclase, in case of Palojärvi also Fe-Ti oxide, and oikocrystic magmatic amphibole enclosing the cumulus phases. In Matokulma, mafic dikes cut the surrounding granitoids. A late leucogabbro dike with a U-Pb zircon age of 1882 ± 5 Ma constrains the minimum age for the Palojärvi intrusion. The Palojärvi leucogabbro has relatively radiogenic Nd isotope composition and is, in this respect, similar to Kotalahti-type mafic-ultramafic intrusions farther northeast. The parental magmas of the Matokulma and Palojärvi intrusions contained approximately 4–6 wt.% and 2–4 wt.% MgO, respectively. Magmatic amphibole, enrichment in large ion lithophile elements (LILE) and depletion in high field strength elements (HFSE) indicate crystallization from hydrous, evolved basaltic magmas. Owing to their evolved nature, the intrusions are not potential for magmatic Ni-Cu mineralizations, but Palojärvi could potentially host a Fe-Ti-V mineralization in deeper, concealed parts of the intrusion.

Assumptions about the dynamics sources and mechanisms of plate tectonic activities

2025-06-19

Ziyun Chen , Tianbin Li , Meiben Gao +1 more | Frontiers in Earth Science

The problem of the driving source and power mechanism of plate motion remains a major scientific issue in urgent need of resolution. Based on the isostatic hypothesis model proposed by … The problem of the driving source and power mechanism of plate motion remains a major scientific issue in urgent need of resolution. Based on the isostatic hypothesis model proposed by G.B. Airy in 1855, this study puts forward the crustal isostatic model based on the self-weight stress field and the assumption of the dynamic source of plate movement. It is believed that the plate movement in the crustal layer is the result of deep magma activities, and the mode of activity is mainly laminar flow. In terms of the dynamic mechanism, the assumption of the magma flow mechanism is proposed. It is believed that the magma flow is driven by the magma density gradient, and the magma density varies with depth. By using the model and assumptions in this paper, the two mechanical mechanisms of surface rupture and block movement are analyzed. Taking the Chengdu block in Western Sichuan as an example, the correlation between magma flow, regional stress field, large-scale displacement and tectonic activities is analyzed. The analysis results are in good agreement with the actual situation, effectively explaining the morphology and activities of typical fault activity structures in this region. The research results are helpful for people to further understand the tectonic activities of the Earth.

1865 Ma tholeiitic magmatism during an extensional episode of the Svecofennian orogeny: the Kaiplot gabbros in Nagu (Nauvo), southwestern Finland

2025-06-19

Anna Johnson , Olav Eklund , Jussi S. Heinonen | Bulletin of the Geological Society of Finland

The Svecofennian orogeny in southern Finland has traditionally been divided into two broadly defined compressional stages, the 1.89–1.87 Ga “synorogenic” stage and the ca 1.84–1.81 Ga “lateorogenic” stage. The term … The Svecofennian orogeny in southern Finland has traditionally been divided into two broadly defined compressional stages, the 1.89–1.87 Ga “synorogenic” stage and the ca 1.84–1.81 Ga “lateorogenic” stage. The term “intraorogenic” is used to describe a less studied stage that occurred between these two, with some overlap with both. Mafic and intermediate intrusions collectively named as the Kaiplot gabbros are situated on a number of islands and islets in Nagu (Nauvo) in the southwestern archipelago of Finland. The outcrops occur as dykes as well as plutonic bodies and have been emplaced in at least two separate pulses. Net-veining and other structures suggesting incomplete mixing between mafic and felsic magmas are found. The main plutonic body is a hornblende gabbronorite. U-Pb dating (TIMS, zircon) gives it an age of 1865 ± 2 Ma. Geochemically, the most primitive Kaiplot gabbros are tholeiitic and show affinity to back-arc basin basalts, indicating generation in an extensional tectonic environment. Their parental magmas appear to have originated from relatively high-degree partial melting of a shallow spinel-bearing and slightly subduction-modified depleted mantle. During transport and emplacement, both differentiation and assimilation of crustal material have taken place. The Kaiplot gabbros endorse an extensional tectonic episode of the Svecofennian orogeny at around 1865 Ma, possibly as a result of tectonic switching propagating southwestwards.

Polyphase intracontinental deformation of ancient suture zones correlated to multiple far-field collisions: A case study from the Xieyuguan Shear Zone, Northern Qinling Orogen

2025-06-19

Shengsi Sun , Yunpeng Dong , Bo Hui +5 more | Global and Planetary Change