Crustal Material Research Articles

Petrogenesis and Geodynamic Mechanisms of Porphyry Copper Deposits in a Collisional Setting: A Case from an Oligocene Porphyry Cu (Au) Deposit in Western Yangtze Craton, SW China

The Xifanping deposit is a distinct Cenozoic porphyry Cu (Au) deposit located in the Sanjing porphyry metallogenic belt 100–150 km east of the JinshajFiang fault in the western Yangtze craton. We present new zircon U–Pb–Lu–Hf isotopic studies and geochemical data of the ore-bearing quartz monzonite porphyry from the Xifanping deposit to determine their petrogenesis and geodynamic mechanisms. LA–ICP–MS zircon U–Pb dating yielded precise emplacement ages of 31.87 ± 0.41 Ma (MSWD = 0.86) and 32.24 ± 0.61 Ma (MSWD = 1.8) for quartz monzonite porphyry intrusions, and 254.9 ± 5.1 Ma (MSWD = 1.7) for inherited zircons of the monzonite porphyry. The ore-bearing monzonite porphyry is characterized by high-K calc–alkaline to shoshonite and peraluminous series, relatively enriched in light over heavy REEs, with no distinct Eu anomalies, as well as enrichment in LILEs and depletion of HFSEs, with adakitic affinities. The zircon Lu–Hf isotope data ranged from εHf(t) values of −2.94 to +3.68 (average −0.47) with crustal model (TDM2) ages ranging from 0.88 to 1.30 Ga, whereas the inherited zircons displayed positive εHf(t) values ranging from +1.83 to +7.98 (average +5.82), with crustal model (TDM2) ages ranging from 0.77 to 1.17 Ga. Results suggest that the Xifanping porphyry Cu (Au) deposit is related to two periods of magmatic activities. Early magmas were generated from the Paleo-Tethys oceanic subduction during the Late Permian. The subsequent porphyry magma was likely formed by the remelting of previously subduction-modified arc lithosphere, triggered by the continental collision between the Indian and Asian plates in the Cenozoic. The deep magmas and late hydrothermal fluids took advantage of the early magma transport channels along tectonically weak zones during the transition from an extrusive to an extensional–tensional tectonic environment. Early dikes from remelted and assimilated crust contributed to the two age ranges observed in the porphyry intrusions from the Xifanping deposit. The juvenile lower crust materials of the early magmatic arc were potential sources of the Cenozoic porphyry magmas, which has significant implications for mineral exploration and the geological understanding of porphyry Cu deposits in this region.

Pan-African and Early Paleozoic Orogenic Events in Southern Tibet: Evidence from Geochronology and Geochemistry of the Kangbuzhenri Gneissic Granite in the Zhegu Area

The Zhegu area in southern Tibet is situated in the central and eastern part of the Tethys Himalayan tectonic belt, with the Kangbuzhenri area being abundant in gneissic granites. This study examines the petrology, chronology, and geochemistry of the Kangbuzhenri gneissic granite, providing insights into its Pan-African and Early Paleozoic geological evolution. The zircon U-Pb chronology indicates an upper intercept age of ~539 Ma, reflecting Pan-African orogenic events in the eastern part of the Tethys Himalayan tectonic belt, and a lower intercept age of ~144 Ma, representing a late tectonic–thermal event. Geochemically, the gneissic granites are calc-alkaline peraluminous rocks with high SiO2 and Al2O3 contents and low TiO2, P2O5, MgO, and FeOT contents. The gneissic granites are enriched in LREE and LILEs (Rb, Pb, Th, U, etc.), but relatively depleted in HREE and HFSEs (Nb, Ti, P, etc.). Most of them show a weak negative δEu anomaly, except for two samples which show a significant negative δEu anomaly due to the crystallization of plagioclase. Based on the above study, most of the gneissic granites exhibited the characteristics of an I-type granite, while two of the samples were a highly differentiated I-type granite with S-type affinities. All the above characteristics indicate that the gneissic granite likely originated from the partial melting of crustal materials and sediments with a minor involvement of mantle-derived materials. Combined with the previous chronological studies, the Kangbuzhenri gneissic granites were formed in an extensional tectonic environment during post-collision orogeny and then they were influenced by the Kerguelen mantle plume tectonic–thermal event around ~144 Ma and the subsequent Southern Tibet Detachment System (STDS).

Structural Controls on Fault Slip Models of the 6 February 2023 Kahramanmaraş, Türkiye Earthquake Doublet With Finite Element Analyses

AbstractTwo major earthquakes of Mw7.8 and Mw7.5 ruptured the Southern East Anatolian Fault (SEAF) and the Savrun‐Çardak‐Sürgü fault (SCSF), devastating southeast Türkiye and northwest Syria on 6 February 2023. We adopt innovative nonlinear and linear approaches to analyze the coseismic ground displacements and estimate the complex slip geometry. Unlike conventional analytical solutions that simplify crust heterogeneity, finite‐element fault models invert the displacement data and simulate the dual‐fault geometry with non‐uniformly distributed shallow crustal materials. Our results suggest the west‐dipping SEAF and north‐dipping SCSF accommodate earthquake slips of >10 m. Their respective slip distributions and proximal aftershocks correlate spatially with local seismic velocity anomalies (i.e., ΔVp and ΔVs), which implies differences in structural control along these two faults and provides insights into assessing the seismic hazard of mixed incipient‐mature fault systems.

The Early Neoproterozoic Andean-Type Orogenic and Within-Plate Magmatic Events in the Northern Margin of the Yangtze Craton during the Convergence of the Rodinia Supercontinent

Although considered a crucial component of the Rodinia supercontinent, it remains uncertain how the Yangtze craton relates to the accretion and breakup of Rodinia. Here, the Huanglingmiao granitic complex (HGC), an intermediate-acid rock series that intruded on the southern Kongling terrane of the northern Yangtze craton margin, is investigated to help resolve this conundrum. Our analysis indicates that these rocks consist of tonalite, trondhjemite, granodiorite, oligoporphyritic granodiorite, porphyric biotite granodiorite, and fine- to medium-grained granodiorite dyke compositions. Collectively, this assemblage is further subdivided into two categories by their temporal, spatial, and geochemical features into early TTG-like and later granitic–dioritic units, which are composed of tonalite, trondhjemite, granodiorite, porphyritic granodiorite, and the fine- to medium-grained granodiorite dykes, respectively. Zircon U-Pb dating yields ages of 865~850 Ma for the TTG-like rocks, 844~825 Ma for the porphyritic granodiorites, and ~800 Ma for the granodiorite dykes. Combined with geochemical evidence, the data suggest that the early- and late-series rocks were formed by a partial melting of Mesoproterozoic and Paleoproterozoic crustal materials, respectively, suggesting that the vertical layering of the crust controlled the composition of the independent units. In addition, isotopic evidence points to different sources for the various rocks in the Kongling terrane and that mantle-derived materials influenced the early-series lithologies. Combined with previous studies on the northern margin of the Yangtze craton, it is inferred that the early-series rocks formed in an active continental margin environment, while the late-series rocks display within-plate boundary formation characteristics. The multiple magmatic activities revealed by this study record sequential partial melting with tectonic transition characteristics from an Andean-type to within-plate magmatism in the northern margin of the Yangtze craton. Taken together, these observations point to a strong association between these rocks, convergence, and incorporation of the northern Yangtze craton margin into the Rodinia supercontinent during the Tonian Period.

Constraints on the Growth and Evolution of Continental Crust in the Northeast Cathaysia Block: Insights from Detrital Zircon U-Pb Age and Hf-O Isotope Analysis in Tingjiang Sediments

Fluvial detrital zircons provide crucial insights into the early Precambrian crustal evolution. In this study, we utilize U-Pb geochronology and Hf-O isotopic compositions of detrital zircons from the Tingjiang River to comprehend the provenance and continental crustal evolution of the northeast Cathaysia Block. Zircon U-Pb ages display seven major populations at 105-177 Ma, 200-262 Ma, 376-520 Ma with a striking peak at ca. 422 Ma, 606-775 Ma, 836-1457 Ma, 1710-2042Ma, and 2300-2661Ma, corresponding to the documented tectonic-thermal events in the South China Block. Episodic magmatism was the response to the formation and breakup of the Columbia and Rodinia supercontinent. The episode of 422 Ma matches with the ages of widely spread early Paleozoic intraplate orogenic events in the South China Block. The isotopic signatures of Hf and O in the detrital zircons indicate that the majority of Precambrian zircons likely originated from the re-melted ancient continental crust, with contributions from juvenile mantle-derived magmas. Phanerozoic zircons, on the other hand, were formed through partial melting of recycled crustal material. Analysis of crustal growth rates, based on the two-stage Hf model ages, suggests a significant presence of juvenile crustal growth during the Paleoproterozoic era. Specifically, it is estimated that approximately 40% and 90% of the present crust within the northeastern Cathaysia Block were formed around 2.3 Ga and 1.6 Ga, respectively.

Garnet Pyroxenite Cumulates from Cretaceous Alkaline Intraplate Magmas Underplate the Zealandia Mantle Lithosphere

Abstract The elemental and isotopic properties of garnet pyroxenites can yield information on lithospheric mantle composition, thermal state, and evolution. The 34Ma Kakanui Mineral Breccia in New Zealand contains spectacular but little-studied mantle peridotite and pyroxenite xenoliths that yield new insights into the evolution of a portion of the underlying mantle lithosphere of a former Gondwana margin. The moderately depleted and metasomatized spinel peridotites, as judged from spinel and olivine compositions and bulk rock major and platinum group element abundances, give mineral equilibration temperatures <1020°C and are derived from the middle to shallow (~35 to 50 km) lithospheric mantle when projected onto a 70 mW∙m−2 geotherm. These residues have low Re/Os and Re-depletion 187Os/188Os model ages that range from Eocene (0.05 Ga) to Paleoproterozoic (1.9 Ga), consistent with extraction from a lithospheric mantle comprising fragments with complex depletion histories. Although the peridotites have restricted δ18O (olivine +5.2 to 6.2), evidence for an isotopically heterogeneous mantle column in addition to the 187Os/188Os is seen in clinopyroxene 87Sr/86Sr (0.70244 to 0.70292), εNd (+4.1 to 18.8), 206Pb/204Pb (17.8 to 20.3), and εHf (+10 to +101). Higher metamorphic equilibrium temperatures of the garnet pyroxenites (Fe–Mg exchange of >1150°C) compared to the peridotites indicate their Eocene extraction was from towards the base of this isotopically heterogeneous mantle lithosphere. Pyroxenite bulk compositions point to cumulate origins, and the mineral isotope ratios of 87Sr/86Sr (0.70282 to 0.70294), εNd (+5.5 to 8.0) and 206Pb/204Pb (18.1 to 19.3) match many of the Zealandia metasomatized mantle peridotite xenoliths as well as the primitive intraplate basalts but not the garnet pyroxenite host magmas. In contrast to many global pyroxenite studies, the garnet pyroxenite 87Sr/86Sr and δ18O (+5.2 to 5.8) data provide no evidence for subducted crustal material in the primary magma source region, and Sm–Nd and Lu–Hf isotope data yield mid-Cenozoic ages that are probably related to isotope closure during eruption. An exception is one sample that yields a Lu–Hf isochron age of 111.9 ± 9.1 Ma, which corresponds to the convergence of the Lu–Hf isotope evolution curves of three other samples. Liquids calculated to have been in equilibrium with these cumulates have trace element compositions comparable to primitive alkaline intraplate basalts like those found at the surface of Zealandia. The new data, therefore, indicate that a pulse of intraplate magmatism occurred during or directly after the cessation of long-lived subduction on the former Zealandia Early Cretaceous forearc Gondwana margin, despite any volcanic surface exposure having been long eroded away. The lower lithospheric mantle emplacement of the garnet pyroxenites suggests that the source of the alkaline parent magmas was probably the convecting mantle, which supports conclusions that intraplate magmas in Zealandia have asthenospheric and lithospheric mantle sources.

From an accretionary margin to a sediment-rich collision: Spatiotemporal evolution of the magmatism during the closure of the Mongol-Okhotsk Ocean

The closure of the Mongol-Okhotsk Ocean (MOO) marks the final suturing of the Central Asian Orogenic Belt, one of the largest accretionary orogens on Earth and a region that is considered an archetype for crustal growth during the Phanerozoic. Abundant Permian to Triassic magmatism in Mongolia extended into the Jurassic on the eastern side of the Mongol-Okhotsk Belt (MOB), the orogenic belt produced by the closure of the MOO. Magmatic belts formed north and south of the suture along the MOB provide insight into the dynamics of the subduction system and the magmatic, crustal, and mantle processes pre-, syn- and post- collision within this accretionary margin. One of the main questions regarding the magmatism in the region is: Was the magmatism formed during active subduction or during the collision and closure of the basin? Here we compile geochemical data (major and trace elements, and isotopes) from the Permian to Jurassic magmatic rocks in the MOB and analyze their spatiotemporal characteristics. Our goal is to assess how magmatism changed in time and space during the closure of the Mongol-Okhotsk Ocean and how those changes relate to first-order tectono-magmatic processes right before or during the collisional event that closed the basin. Our results show a general enrichment in fluid mobile elements, LILE, and LREE and depletion in HFSE, and HREE in mafic and felsic rocks, which indicates a mantle metasomatized by subduction-related fluids regardless of crustal contamination. Our analysis supports higher enrichment in sediment melts, especially along its western and older extent, and the assimilation of juvenile crustal components without producing abundant S-type peraluminous magmatism which indicates mantle and crustal contributions. Thus, we conclude that magmatism formed above a sediment-rich retreating margin was able to recycle and stabilize young and compositionally evolved crustal material in the Central Asian Orogenic Belt.

Comparative mineralogy, geochemistry and petrology of the Beloziminsky Massif and its aillikite intrusions

The Beloziminsky Massif (BZM) is an alkaline ultramafic carbonatite complex that includes carbonatites, ijolites, meltegites, and syenites (abbreviated as the CIMS suite) as well as aillikite intrusions that range in age from 645–621 Ma. Aillikite intrusions also occur in the Yuzhnaya Pipe (YuP), located about 16 km eastward of the BZM. Over 5400 analyses in total were conducted to compare mineralogy and geochemistry of different rock types in this study; of these, 24 CIMS samples (>1100 analyses) and about 16 aillikites (>2300 analyses) were collected from within the BZM; the rest are aillikite mineral samples from pipes and dykes outside the massif (>2000 analyses). The results suggest significant differences in sources for rock-forming minerals, less so for the accessories. The pyroxenes in aillikite correspond either to mantle Cr-diopside xenocrysts or megacrystic augites. Low-Na Ti-augites and diopsides as well as aegirines are prevalent in the CIMS intrusive suite. Amphiboles show a considerably long compositional trend, from hornblendes to richterites. Dolomitic carbonatites include admixtures of Na, K, and Ba while calcium carbonatites often contain Sr. The carbonate-rich aillikitics are enriched either in Mg or Ca. The CIMS rocks, particularly the Ca-Mg carbonatites, often include siderites. Thermobarometry for the YuP samples, collected from outside the BZM and containing Cr-diopsides, Cr-phlogopites and Cr-spinels, suggest a formation pressure of 2–4 GPa and a temperature of 800–1250°C; augite xenocrysts with elevated HFSE, U, Th, and Al-augites trace a 90 mW/m2 geotherm.The huge thermal impact of the plume that triggered the break-up of Rodinia also created a series of ultramafic–alkaline–carbonatite massifs. Initially, the aillikites in the mantle were likely produced by the plume-induced melting of carbonated metasomatites containing ilmenite, perovskites, apatites, amphiboles and phlogopites which, in turn, were created by subduction-related melts. Any additional enrichment in the ore components might have occurred subsequentlty in the lower crust, due to liquation. The aillikites inside the BZM contain low-temperature clinopyroxenes tracing a steep advective geotherm (0.4–1.5 GPa); they also contain clots, related to intermediate depth magma chambers, together with CIMS pyroxenes and amphiboles. This suggests that the liquation of aillikites was accompanied by density separation and assimilation and fractional crystallization (AFC) fractionation with the participation of crustal material. Trace elements (especially REEs) in silicate minerals, carbonates, apatites, and accessories (perovskites, pyrochlores, monazites, columbites, zircons, ancylites, etc.) show a general rise in REE levels and La/Ybn ratios from aillikites to ijolites, and later to Fe- carbonatites. The presence of zircons, monazites, columbite-tantalites, and other Zr-Hf and Ta-Nb minerals like perovskites and tantalites in the BZM aillikites occurred due to the mixing of the silicate melts with carbonate-rich magmas at deeper levels in the crust and later, in the massif. In the aillikites, xenocrysts. Further, apatites and perovskites show high REE levels. The carbonate-silicate magmas likely passed through a system of polybaric magmatic chambers and liquated carbonatites. Consequently, the later-formed aillikites captured and mixed all varieties of xenocrysts.

Late Palaeozoic high-K calc-alkaline to shoshonitic series magmatism and related W(–Mo–Cu–Au) metallogeny of the Kyrgyz Tien Shan, Central Asia

In the Kyrgyz Tien Shan, numerous high-K calc-alkaline to shoshonitic series intrusions are associated with the large fault system known as the ‘Major structural line of Tien Shan’, or ‘Nikolaev Line’. During the Carboniferous, this lineament represented a zone of intracontinental, possibly back-arc rifting associated with a north-dipping subduction, whereas in the Late Carboniferous to Permian it was part of a larger continental collision structure. These Late Paleozoic high-potassic intrusions comprise numerous intrusive phases that vary in composition from the early mafic (monzogabbro, monzodiorite) through intermediate (monzonite, syenite, quartz syenite) to late stage and more evolved (quartz monzonite, granodiorite, monzogranite, leucogranite–alaskite) members locally intersected by monzodiorite–porphyry and lamprophyre dykes. They can be related to low degrees (from ∼1–2 to 2–2.5 vol%) of partial melting of metasomatically enriched upper mantle followed by magma fractionation and emplacement at shallower crustal levels. In summary, the high-K magmas formed in continental- and post-collisional arc settings with a progressive input of crustal material. From the west to the east, the potassic intrusions contain progressively higher Nb and Y concentrations, reflecting their derivation in a post-collisional setting. The A-type granite signatures also become more distinct in this direction. This is consistent with the tectonic model implying the ‘scissor-like’ closure of the Late Paleozoic Turkestan palaeo-ocean from east to west. These high-potassic intrusions are accompanied by W–Mo–Cu–Au skarn/porphyry to Au(–W) replacement-style deposits, which are part of the extended Au (Au–W–Mo–Cu) metallogenic belt of Tien Shan. The association of skarn and porphyry-style W–Mo to Mo–Cu–Au–W mineralization defines these ‘porphyry–skarn’ systems as a distinct group containing strongly oxidized andradite-dominant skarns. An early W partitioning into magmatic–hydrothermal fluid, together with Mo and Cu, is typical of this magmatic–hydrothermal system and can be explained by an early H 2 O saturation of the parental magma. The late-stage mafic dykes including lamprophyres probably reflect the presence of another, but concealed, mafic intrusion releasing CO 2 and metals, such as Au, As, Sb, Bi and Te, into the hydrothermal mineral system.

Trace element geochemistry of mantle xenoliths from Zarnitsa kimberlite pipe, Daldyn field, Yakutia: Complex history of melts interactions with lithospheric mantle

Mantle xenoliths from Zarnitsa pipe studied in gray eruptive breccias (early) brown autholitic breccia (BAB) and black macrocrystic kimberlites (last dike; BMK), include garnet and spinel dunites-harzburgites, pyroxenites, eclogites, glimmerites and megacrysts. PT reconstructions using xenoliths reveal sharply layered structure (8 levels), estimated with the single grain mineral estimates mark hot (Cpx, Ilm) and cold (OPx, Gar) inflected geotherm. The interaction with plume melts is found at the lithosphere asthenosphere boundary (LAB), pyroxenite layer (3-4 GPa), Gar-Sp transition and Moho. Eclogites reveal Fe# growth from LAB to middle pyroxenites layer. Clinopyroxenes and ilmenite estimates marks melt refertilisations in interlayers between coupled subduction slabs. Source of capture from first to third stage deepening to LAB and Cr- rich garnets (to 19.5 Cr2O3) are below the LAB.The grey erupted breccia (GEB) includes mainly depleted and deformed peridotites. The later BAB includes pyroxenites, eclogites, and refertilised, deformed, and veined peridotites in BMK. Geochemistry of minerals changes from primary mid ocean ridge basalts (MORB) and back arc peridotites with low REE and large ion lithophile elements (LILE) and deeps in high field strength elements (HFSE) to metasomatized by alkaline (high Na and LILE) and adakitic melts (high Al, Na, Sr, and elevated HFSE) varieties and refertilised lherzolites due to plume at last stage. Mantle column metasomatized with scattered phlogopites in early grey eruptive breccia to amphibole-phlogopite ilmenite veins at last stages. Amphiboles trace mantle from lithosphere – asthenosphere boundary to Moho.Growth of the diamond grade from early eruptive breccia to later kimberlite phases refer to decreasing of the crust material and deepening of the xenoliths capture level. Metasomatism dissolve the diamonds but growth of megacrystic diamond crystals increase diamond grade.

Osmium and oxygen isotope constraints on magma-crust interactions and the transport of copper at the roots of arcs

The formation of copper-rich cumulates at the base of arc crusts has been proposed as a key process modulating the geochemical evolution of the continental crust and the genesis of giant ore deposits of copper. Despite the importance of these phenomena, the degree to which the lower crustal evolution of magmatic systems is influenced by open-system interaction and the assimilation of pre-existing crustal materials remains unclear. To tackle this issue, we provide direct isotopic constraints on the evolution of deep magmatic systems in arcs by measuring the osmium and oxygen isotope composition of hydrous copper-rich (∼730 μg·g−1 Cu) ultramafic cumulates formed at the base of the Acadian orogen (∼40 km deep) in the New England Appalachians (northeastern USA). The radiogenic 187Os/188Os initial ratios (ranging from 0.31 to 0.67) and the elevated δ18O values (8.97 ± 0.42 ‰ for orthopyroxene; 9.25 ± 0.26 ‰ for phlogopite) suggest a significant role of open-system magmatic differentiation, involving crustal assimilation, in the formation of these cumulates. Modeling of the 187Os/188Os and δ18O composition of the cumulates suggests that the observed isotopic compositions result from the initial evolution of parental magmas under sulfide-undersaturated conditions, followed by saturation after approximately 15% to 20% of assimilation and fractional crystallization progression. These results suggest that the assimilation of crustal material led to a drop in the magmatic system's fO2 (∼ΔFMQ < −1), triggering sulfide segregation and the formation of copper-rich cumulates. Our findings align with the hypothesis that magma-crust interactions can lead to the formation of lower crustal domains enriched with Cu, which may constitute a pre-stage in the formation of some porphyry copper deposits, particularly in collisional orogens.

Chaotic Mixing Experiments: Unravelling Contamination Processes on Dacitic Melts

Magmas are the ultimate source of volcanism on Earth. At high-temperatures these complex silicate melts may easily chaotically mix, on their way towards the surface of the planet.The Paraná-Etendeka Magmatic Province (PEMP), one of the largest volcanic provinces of our planet, serves as the focus of this experimental study. The investigation simulates the contamination of high-Ti dacites passing through the continental crust. Our final aim is to contribute to the origin of the high-Ti Chapecó dacites from PEMP, with particular attention to the genesis of Chapecó-Ourinhos dacites (COD).The experimental apparatus is based on the Journal Bearing System. All experimental runs have been operated at atmospheric pressure and a temperature of 1500 °C. A dacitic magma chamber under the assimilation of crustal material has been simulated. The resulting experimental products (dry/bubble free glasses) exhibit concentric folded and stretched filaments of contrasting compositions. The calculated fractal dimension for a representative section is Dbox = 1.60(3), confirming the achievement of chaotic dynamics. Electron Microprobe Analysis (EMPA) from the experimental glasses clearly shows SiO2-contamination, while Al2O3-data indicate lower contamination levels. As a consequence, different elements depict dissimilar curves in chemical transects. We used the parameter σn2 (normalized variance) to quantify the mixing efficiency and differential elemental mobilities. In addition, our data reproduced the chemical behaviour of some elements in COD- dacites, especially the network formers such as Fe, Al, Ti and Si. EMPA reveals clear deviations from the linear mixing model. Our experiments and data replicate a selective contamination process. Differential elemental mobilities could be calculated. Comparisons with natural data depict how the mixing involving Chapecó-Guarapuava (CGD) and Chapecó-Ourinhos (COD) dacitic end-members may have contributed to the generation of more evolved COD from the interaction of CGD pre-existing melts with crustal rocks from the PEMP basement via chaotic dynamics.

Geochronology and Geochemistry of Paleoproterozoic Mafic Rocks in Northern Liaoning and Their Geological Significance

Petrological, geochronological, and geochemical analyses of mafic rocks in northern Liaoning were conducted to constrain the formation age of the Proterozoic strata, and to further study the source characteristics, genesis, and tectonic setting. The mafic rocks in northern Liaoning primarily consist of basalt, diabase, gabbro, and amphibolite. Results of zircon U-Pb chronology reveal four stages of mafic magma activities in northern Liaoning: the first stage of basalt (2209 ± 12 Ma), the second stage of diabase (2154 ± 15 Ma), the third stage of gabbro (2063 ± 7 Ma), and the fourth stage of magmatic protolith of amphibolite (2018 ± 13 Ma). Combined with the unconformity overlying Neoproterozoic granite, the formation age of the Proterozoic strata in northern Liaoning was found to be Paleoproterozoic rather than Middle Neoproterozoic by the geochronology of these mafic rocks. A chronological framework of mafic magmatic activities in the eastern segment of the North China Craton (NCC) is proposed. The mafic rocks in northern Liaoning exhibit compositional ranges of 46.39–50.33 wt% for SiO2, 2.95–5.08 wt% for total alkalis (K2O + Na2O), 6.17–7.50 wt% for MgO, and 43.32–52.02 for the Mg number. TiO2 contents lie between 1.61 and 2.39 wt%, and those of MnO between 0.17 and 0.21 wt%. The first basalt and the fourth amphibolite show low total rare earth element contents. Normalized against primitive mantle, they are enriched in large ion lithophile elements (Rb, Ba, K), depleted in high field strength elements (Th, U, Nb, Ta, Zr, Ti), and exhibit negative anomalies in Sr and P, as well as slight positive anomalies in Zr and Hf. The second diabase and the third gabbro have similar average total rare earth element contents. The diabase shows slight negative Eu anomalies (Eu/Eu* = 0.72–0.88), enrichment in large ion lithophile elements (Ba), depletion in Rb, and slight positive anomalies in high field strength elements (Th, U, Nb, Ta, Zr, Hf, Ti), with negative anomalies in K, Sr, and P. The gabbro is enriched in large ion lithophile elements (Rb, Ba, K), depleted in high field strength elements (Th, U, Nb, Ta, Zr, Hf), and exhibits positive anomalies in Eu (Eu/Eu* = 1.31–1.37). The contents of Cr, Co, and Ni of these four stages of mafic rocks are higher than those of N-MORB. The characteristics of trace element ratios indicate that the mafic rocks belong to the calc-alkaline series and originate from the transitional mantle. During the process of magma ascent and emplacement, it is contaminated by continental crustal materials. There are residual hornblende and spinel in the magma source of the first basalt. The other three magma sources contain residual garnet and spinel. The third gabbro was formed in an island arc environment, and the other three stages of mafic rocks originated from the Dupal OIB and were formed in an oceanic island environment. The discovery of mafic rocks in northern Liaoning suggests that the Longgang Block underwent oceanic subduction and extinction in both the north and south in the Paleoproterozoic, indicating the possibility of being in two different tectonic domains.

Geochronology, Geochemical Characterization and Tectonic Background of Volcanic Rocks of the Longjiang Formation in the Lengjimanda Plate Area, Middle Da Hinggan Mountains

The Lengjimanda plate is situated in the middle section of the Da Hinggan mountains, in the eastern section of the Tianshan Xingmeng orogenic belt. To determine the formation age of the volcanic rocks in the Longjiang formation in this area, to explore their origin and tectonic background, and to reconstruct the geodynamic evolution of the region, this study conducted petrological, zircon U–Pb geochronological, geochemical, and isotopic analyses of the volcanic rocks in the Longjiang formation. The Longjiang formation’s volcanic rocks are primarily composed of trachyandesite, trachyte trachydacite, and andesite, which are intermediate basic volcanic rocks. They are enriched in large-ion lithophile elements, are depleted in high-field-strength elements, are significantly fractionated between light and heavy rare earth elements, and exhibit a moderate negative Eu anomaly in most samples. The results of the LA–ICP–MS zircon U–Pb dating indicate that the volcanic rocks in this group were formed in the Early Cretaceous period at 129.1 ± 0.82 Ma. The zircon εHf(t) ranges from +1.13 to +43.77, the tDM2 ranges from +655 to +1427 Ma, the initial Sr ratio (87Sr/86Sr)i ranges from 0.7030 to 0.7036, and the εNd(t) ranges from +2.1 to +6.6. Based on the geochemical compositions and isotopic characteristics of the rocks, the initial magma of the volcanic rocks in the Longjiang formation originated from the partial melting of basaltic crustal materials, with a source material inferred to be depleted mantle-derived young crustal. These rocks were formed in a superimposed post-collisional and continental arc environment, possibly associated with the Mongol-Okhotsk Ocean closure and the oblique subduction of the Pacific plate. This study addresses a research gap regarding the volcanic rocks of the Longjiang formation in this area. Its findings can be applied to exploration and prospecting in the region.

Identification of the EMII-type mantle end-member of the Kerguelen mantle plume and its implications for the initial breakup of eastern Gondwana: New constraints from the Cretaceous diabase in the Tethyan Himalaya

The breakup of eastern Gondwana during the Early Cretaceous has been well-documented. However, the relationship between Cretaceous mafic magma and the Kerguelen mantle plume has not been well-constrained. It is also unknown if the Kerguelen mantle plume in the Tethyan Himalaya played a key role in triggering the breakup of eastern Gondwana. The petrogenesis and geodynamic processes of the coeval magmatism in the Tethyan Himalaya might provide value insights into this issue. In this study, we conducted petrological, geochronological, and geochemical investigations on a recently identified diabase from the Yamdrok Lake. The diabase contains zircon grains with a U-Pb age of 138 ± 8 Ma, suggesting the emplacement at the Early Cretaceous. Geochemically, the studied samples display OIB-like trace elemental features that are enriched in light rare earth elements (LREEs) but no significant depletion in high field strength elements (HFSEs), such as Nb, Ta, and Ti. Furthermore, they have relatively uniform Sr-Nd-Pb-Hf-O isotopic compositions with initial 87Sr/86Sr ratios varying from 0.70563 to 0.70623, εNd(t) and εHf(t) values range from 0.6 to 0.8 and 1.0–2.4, respectively, whole-rock δ18O values of 6.42 ‰ to 7.50 ‰, and (208Pb/204Pb)i = 38.995 ∼ 39.285, (207Pb/204Pb)i = 15.673 ∼ 15.698, and (206Pb/204Pb)i = 18.689 ∼ 18.914, similar to an EMII-type enriched mantle. And recycled shallow continental crustal materials into the OIB-like mantle source might account for the EMII-type mantle features observed in this study. Considering the Kerguelen mantle plume locating beneath the triple junction of Australia, Antarctica, and Greater India, we propose that the mafic rocks in this study might be genetically related to the early activity or even initiation of the Kerguelen plume during the Early Cretaceous. Our study further indicates that the Kerguelen mantle plume contains EMI- and EMII-type isotopic compositions, which are characterized by geochemical complexity and variation.

Ore–forming potential of the Wubaduolai monzogranite porphyry, western Gangdese copper belt, Tibet: Insights from geochronology and petrogeochemistry

The Wubaduolai deposit is a newly discovered porphyry copper deposit in the Zhunuo-Beimulang ore-concentrated area of the Gangdese belt. The monzogranite porphyry is the causative intrusion in the deposit with a zircon U-Pb age of ∼16 Ma. Monzogranites have high Sr (332–673 ppm) and Sr/Y ratios (35–69), typical of adakite affinity. They have initial 87Sr/86Sr ratios of 0.7083–0.7093 and εNd(t) values between −9.2 and −7.1. The zircon εHf(t) values range from −6.45 to −2.09 and zircon δ18O values have a narrow range of 7.4 to 8.1 ‰ for the porphyry. These geochemical characteristics indicate that the parental magma was derived from juvenile Tibetan lower crust, with contributions from Indian plate-released fluids and metasomatized mantle-derived mafic magmas. The porphyry shows high values of log w(Fe2O3/FeO) (>0) and V/Sc (mostly > 12) in whole rock and high values of △FMQ (4.13–5.79), 10000 × (δEu)/Y(>4), and low Dy/Yb (<0.3) in zircons, suggesting that the magma was oxidized and hydrous. The oxidized and hydrous parental magma is consistent with those evaluated for the Zhunuo and Beimulang deposits. The three-component mixing model result shows that compared with the ore-related porphyries in the Zhunuo and Beimulang deposits, the Wubaduolai intrusion has higher proportion of Indian plate-released fluids and mafic magmas and lower proportion of juvenile Tibetan lower crust. Therefore, we suggest that although the causative intrusions have similar oxygen fugacity and water content, the source has more Indian continental crust and mantle-derived materials and fewer juvenile Tibetan lower crust materials at Wubaduolai, implying that the Wubaduolai monzogranite porphyry has lower potential for mineralization.

Active Tectonic Deformation of the Qilian Shan, Northeastern Tibetan Plateau

Abstract —The Qilian Shan (or Qilian Mountains), located on the northeastern margin of the Tibetan Plateau, is an actively growing orogenic belt resulting from the far-field impact of the India–Eurasia collision. The northward penetration of the Indian Plate is responsible for intense crustal shortening in the Qilian Shan. However, the tectonic deformation pattern in response to the crustal shortening remains unclear. In this study, we present the regional seismicity, fault activity, and GPS crustal movement velocity field to characterize the active tectonic deformation of the Qilian Shan based on historical data over the past two decades. The results suggest that the western Qilian Shan is characterized by distributed north–south crustal shortening, while the eastern Qilian Shan is dominated by blocklike eastward extrusion of crust along major strike-slip faults coupled with clockwise rotation. North–south crustal shortening and east–west lateral extrusion, two deformation modes responding to the India–Eurasia convergence, match the crustal deformation in the Qilian Shan. The tectonic deformation of the western Qilian Shan is largely in agreement with the former, while the eastern Qilian Shan corresponds closely to the latter. Lower crustal flow beneath the central Tibetan Plateau provides the potential driving force to induce the eastward extrusion of crustal material out of the plateau and the growth of some boundary mountain ranges, such as the Qilian Shan.

Xenolith petrography for identification of substratum lithology of an active volcano: a case study of Lava Kekep, Sundoro Volcano, Central Java

Abstract Sundoro volcano is an active Quaternary stratovolcano in Central Java, located approximately 50 km west of the Merapi volcano. It is attributed to parasitic cones producing basaltic lava flow. We present our findings of sedimentary and igneous xenoliths embedded in the basaltic lava of the Kekep parasitic cone. Xenolith is one of the key materials to help identify various lithologies composing the substratum of a volcano. Twelve thin sections were analysed through detailed petrographic observation. We identified variations of xenolith lithology consisting of sedimentary rock, particularly siltstone, and igneous rocks such as dunite, pyroxenite and lherzolite. Detailed accounts of substratum lithologies comprises of (a) siltstone composed of &gt;0.125-0.5 mm size plagioclase crystals and silicic fine-grained matrix, (b) pyroxenite consists of massive interlocking 1-5 mm size clinopyroxene and few &lt;1 – 1 mm orthopyroxene, (c) dunite consists of 1 - 2 mm phenocryst of plagioclase, pyroxene, and olivine, embedded in a minor groundmass of plagioclase and pyroxene, (d) lherzolite consists of massive interlocking olivine crystals 1-5 mm in size. The analysis results identify gradual or groundmass and sharp contact between basaltic host rock and xenoliths (pyroxenite, lherzolite, dunite and siltstone). Other characteristics of the twelve samples includes (a) &lt;1 mm minerals fragments embedded in silt to clay-grained lithic sandstone, (b) siltstone showing chilled-baked margin in hand sample specimen, (c) identified disequilibrium textures in basaltic lava, and contact between xenolith and host rock. Substratum lithology along the Java arc is likely composed of Tertiary sedimentary rock in the upper part, transitions of granitoid – gabbroic diorite crustal material in the lower part, with ultramafic crustal material under Sundoro.

Geochronology, geochemistry, and isotope signatures of porphyries from the dabate Mo—Cu deposit, Western Tianshan, China: Implications for petrogenesis and geodynamic setting

The Dabate deposit in the West Tianshan Orogenic Belt is a large porphyry Mo-Cu deposit with obvious zoning feature. The Dabate pluton is closely related to mineralization associated with the rhyolite and granite porphyries. Copper (Cu) mineralization occurs on the margin of the rhyolite porphyry, and molybdenum (Mo) mineralization occurs in the interior of the rhyolite porphyry. Petrology, zircon U-Pb isotopic data, whole-rock geochemistry, and Sr-Nb-Hf-Pb isotopic data of the rhyolite and granite porphyries in the Dabate Mo-Cu mining zone and to discuss the properties, sources, evolution, and tectonic environment of the magma. Zircon U-Pb age dating shows that the rhyolite porphyry and granite porphyry were formed in 300.1 ± 1.3 Ma and 290.4 ± 5.2 Ma, respectively, and they are geochemically similar. Both are characterized by negative Eu anomalies (δEu = 0.09–0.15 and 0.10–0.11, respectively) and are slightly rich in light rare earth elements (LREE) but depleted in high-field-strength elements (HFSE), which indicates that they are both A2 type granites that underwent high differentiation. The Sr isotope (ISr) values for the rhyolite and granite porphyries range from 0.70564 to 0.70658 and 0.70833–0.70954, respectively. The Nd isotopic composition [εNd(t)] values for both are negative but close to zero (−0.25 to −0.46 and −0.65 to −1.10, respectively), and the two-stage depleted mantle Nd model ages (TDM2(Nd)) are 1.07–1.10 Ga and 1.11–1.14 Ga, respectively. Zircon εHf(t) values are 7.29–11.97 and 6.26–11.08 for rhyolite porphyry and granite porphyry, respectively, and the two-stage Hf model ages (TDM2(Hf)) are 550–848 Ma and 605–916 Ma, respectively. The initial Pb isotope ratios for the rhyolite and granite porphyry are close at (206Pb/204Pb)i = 18.26–18.65, (207Pb/204Pb)i = 15.54–15.64, and (208Pb/204Pb)i = 38.19–38.57. These results indicate that the two porphyries have a mixed source, likely originating from the partial melting of mantle blended with some recently formed lower crust material. The geochronology, geochemistry, and Sr-Nd-Hf-Pb isotope data of existing intrusions in the West Tianshan imply that the Late Carboniferous to Early Permian Dabate area was underplated in a post-collisional extensional setting, and A2-type granite intrusions with related Mo-Cu mineralization were formed.

New Research Results on U-Pb Zircon Isotope Age of Ta Cu Granodiorite in Dalat Zone and Geological Significance

Ta Cu granodiorites from the Dalat Zone, Southern Vietnam, have typical composition of granodiorite, coinciding with the Dinh Quan complex. The granodiorites are composed of plagioclase (45–50%), quartz (20–25%), orthoclase (15–20%), hornblende (5–7%), and biotite (5–7%). Geochemically, they are met aluminous with an average A/CNK value of 0.89- 0.96, low SiO2 (61.68-62.14) and high Na2O/K2O&gt; 1. Petrographical and geochemical characteristics of Ta Cu granodiorites are classified as I-type granite generated from arc-related magmas. Zircons selected from these rocks are characterized by prismatic shape, oscillatory zoning, no luminescent rim, and have high ratio Th/U (0.35–1.11) that are indications of the magmatic origin. We report the first LA-ICP-MS 206Pb/238U zircon ages of 116 Ma for the Ta Cu granodiorite in the Southeastern Dalat Zone in Southern Vietnam. This age value is temporally coeval with Early Cretaceous magmatism previously reported in the Dalat Zone. Zircon ꜪHf(t) values +4.0 to+13.0, whole-rock ꜪNd(t) values -2.0 to +0.2, and average model ages (TDM2) 652 Ma to 957 Ma indicate that the Ta Cu granodiorites were derived from the remelting of Neoproterozoic mantle-derived melt with a minor input of crustal materials. Together with other Late Mesozoic magmatic complexes along the Dalat Zone, the Ta Cu granodiorites are a representative of magmatism linked to Pacific Ocean subduction beneath the Indochina block during the Early Cretaceous.