Mesozoic Granitoids Research Articles

Pyrite in-situ S–Fe isotope constraints on the ore-forming sources and mineralization processes of gold and polymetallic deposits in the Liaodong Peninsula, North China Craton

Plenty of gold and polymetallic deposits are widespread in the eastern part of the North China Craton. They are associated with mafic to felsic dikes and hosted by Precambrian basement or Mesozoic granitoids. However, the sources of gold and other metals in the ore-forming fluids remain controversial. Here we present in-situ S and Fe isotopes and trace element contents of pyrites from various gold and Pb–Zn–(Ag) deposits in the Liaodong Peninsula, China. Pyrites from quartz vein-type gold deposit hosted by Mesozoic granites in the Wulong deposit have relatively homogeneous magmatic-like S isotopes (δ34S values of 0.9 ‰ to 2.5 ‰) and Co/Ni ratios, indicating derivation of sulfur and, by inference, of ore fluids/materials most likely from Mesozoic magmas. In contrast, pyrites from gold and Pb–Zn–(Ag) deposits in the Qingchengzi orefield hosted by Precambrian basement have high and variable δ34S values (9.7 ‰ to 12.7 ‰ for the Wandigou altered rock-type gold deposit and 4.7 ‰ to 8.5 ‰ for the Xiquegou Pb–Zn deposit and the Zhenzigou Pb–Zn–Ag deposit), identical to those of host rocks, indicating the important contributions of gold and other metals from wall rocks to the ore deposits. Pyrites from the various deposits have variable δ56Fe values of 0.08 ‰ to 0.63 ‰ for the Pb–Zn–Ag deposit, –0.58 ‰ to 1.23 ‰ for the altered rock-type gold deposit, and –0.68 ‰ to 0.77 ‰ for the quartz vein-type gold deposit, indicating distinct mineralization processes. Rapid precipitation of pyrites (with negative δ56Fe values) in the alteration rock and subsequent deposition of pyrites (with positive δ56Fe values) from the residual fluids in an Fe-open hydrothermal system during intensive ore-forming fluid-wall rock interaction account for the Pb–Zn–Ag mineralization, while weak fluid-rock interaction and pyrites precipitation from a Fe-closed hydrothermal system contribute to gold mineralization. Our observations provide a robust S–Fe isotope evidence for the contribution of various sources and metallogenic processes for distinct gold and polymetallic deposits.

Zircon U-Pb Ages of the Granitoids in Shanxi and Its Significance for Tectonic Evolution of North China Craton in Mesozoic

Mesozoic granitoid formations offer crucial insights into the tectonic history of the North China Craton. New zircon U-Pb ages of two Mesozoic granitoids in the Huai’an terrane yield ages of 226.4 ± 1.1 Ma for the Yihe (YH) granite and 156.3 ± 2.9 Ma for the Zhujiagou (ZJG) granodiorite. The negative Nb, Ta, and Ti anomalies; high Nb/Ta ratios (20.4 to 24.1); high (La/Yb)N (30–84); low initial 87Sr/86Sr ratios (0.707725–0.708188); and negative ƐNd(t) values of the Yihe complex suggest that it originated from the partial melting of the lower crust and lithospheric mantle. However, the geochemical and Sr-Nd isotopic results of the ZJG granodiorite are characterized by I-type granites: Na2O + K2O values of 7.27 to 7.94 wt%, negative Nb anomalies, positive Pb anomalies, higher initial 87Sr/86Sr ratios (0.710979–0.714841), and much lower ƐNd(t) values (−27.1 to −30.1). The Late Jurassic Zhujiagou complex was derived from partial melting of a thickened low crust, and during the Late Triassic, magmatic rocks were formed under a post-collisional extensional regime. Multiple upwellings of the asthenosphere facilitated the mixing of magmas derived from partial melting of the lithospheric mantle and lower crust. These mixed magmas then ascended to the upper crust after undergoing fractional crystallization, leading to the formation of the YH complex. In the Late Jurassic, the tectonic regime of the NCC shifted from compression to extension. The Late Jurassic intrusion identified in this study developed within a compressional setting linked to the subduction of the Paleo-Pacific Ocean.

Compositional diversity of late Mesozoic granites rooting from the subducted crust in the Qinling–Dabie orogenic belt

Continental subduction has been identified in many orogens, such as the Alps, the Himalayas, and the Dabie; however, better understanding of the mechanism and outcome of different subduction processes remains desirable. The Qinling–Dabie orogen in Central China shows an asymmetric distribution of Triassic ultrahigh-pressure metamorphic rocks and syn- and post-tectonic granitoid plutons, thereby providing an excellent means by which to probe the diverse processes of continental subduction. Many late Mesozoic granitoid plutons that formed in post-orogenic or even anorogenic settings are widely distributed in both the Qinling and Dabie tectonic units and can be useful for studying the composition of materials beneath the crust because of their conspicuous compositional diversity. In the present study, we report zircon ages and NdHf isotopic compositions for the Shangcheng and Heyu granite plutons, which represent late Mesozoic plutons in Dabie and Qinling. When compared with those of the Shangcheng pluton, the wide range of Nd isotopic values and the slightly depleted Hf isotopic compositions of the Heyu pluton indicate that there may be juvenile crust beneath the Qinling tectonic unit that is not present beneath the southern margin of North China. The currently undetectable juvenile material in this region may be an important candidate source of the late Mesozoic magmatism and metal mineralization in the southern margin of North China. The compositional diversity of these granites, as indicated by the NdHf isotopic compositions, is attributed to the nature of the deep crust within the orogenic belt, and the magmatic origins of this region are discussed in the present study.

He-Ar isotopic signatures of the Mesozoic granitoids in South Korea: implications for genesis of the granitic magma and crustal evolution in NE continental margin of the Eurasian plate

He-Ar isotopic signatures of the Mesozoic granitoids in South Korea: implications for genesis of the granitic magma and crustal evolution in NE continental margin of the Eurasian plate

Isotopic distribution of bioavailable Sr, Nd, and Pb in Chungcheongbuk-do Province, Korea

BackgroundMapping the distribution of bioavailable isotope ratios across landscapes serves as an efficient geochemical tool for delineating the origins and migration trajectories of humans and animals. Chungcheongbuk-do Province in central Korea, known for its geological diversity and inland location isolated from coastal influences, provides an ideal area to study the contributions of geological and environmental factors to the isotope landscape (isoscape). This study analyzed the distribution of bioavailable Sr, Nd, and Pb isotopes in the province using plant and soil data obtained in this study and from previous works.FindingsChungcheongbuk-do features diverse geological elements, including Precambrian basement, Paleozoic metasedimentary rocks, and Mesozoic granitoids and volcano-sedimentary sequences. The 87Sr/86Sr ratios of bulk soil samples from 44 sites primarily range from 0.781 to 0.706, with two ratios exceeding 0.9 originating from Precambrian basement and Cretaceous granitoid areas. Fractions of soils treated with 1 M ammonium nitrate and acetic acid exhibit indistinguishable 87Sr/86Sr ratios (R2 = 0.99, except for one point), spanning from 0.804 to 0.707. Plant 87Sr/86Sr ratios demonstrate a robust positive correlation with leachate ratios (for ammonium nitrate data, (87Sr/86Sr)plant = 0.938 × (87Sr/86Sr)leachate + 0.045, R2 = 0.98). The εNd values of bulk soils from Precambrian basement areas (–18 to –30) plot against Sm/Nd ratios around the reference line corresponding to 3 Ga, while other bulk soil samples (εNd = –1 to –21) align with a younger (~ 2 Ga) reference line. Plant εNd values, ranging from –4 to –24, exhibit a prominent positive correlation with ammonium nitrate leachates (plant εNd = 0.77 × leachate εNd – 3.83, R2 = 0.89). Plant samples do not show consistent variation between 87Sr/86Sr and εNd. The 206Pb/204Pb and 207Pb/204Pb ratios of bulk soils show a ~ 2 Ga trend, typical for Korean basement rocks. The Pb isotopic ratios of ammonium nitrate and acetic acid leachates match perfectly with each other (R2 = 0.99). The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of plant samples vary narrowly (19.2–17.9; 15.8–15.5; 39.0–38.0) and are distinctly different from those of bulk soils (24.4–17.9; 16.5–15.6; 42.5–37.9) and their leachates (23.1–17.7; 16.2–15.6; 41.0–38.1). Plant and soil data from this study and previous works were used to construct Sr and Nd isoscapes, employing interpolation models based on inverse distance weighting, simple kriging, empirical Bayesian kriging, and geology and topography-considered empirical Bayesian kriging regression prediction. These maps await validation through analysis of additional archives.ConclusionsThe isotope data obtained in this study highlight a strong geological control over bioavailable Sr and Nd, in contrast to a dominant environmental influence on bioavailable Pb. The Sr and Nd isoscapes presented here are potentially valuable for addressing archaeological or forensic inquiries in their current state. Nevertheless, the maps would benefit from additional refinement with increased sample density and enhanced interpolation models.

Late Jurassic granitoids in Mufushan complex and their significance for the Mesozoic tectonic evolution of eastern South China

The Mesozoic tectono-thermal evolution of eastern South China plays an important role in forming the abundant magmatic rocks and associated giant polymetallic deposits. The middle-late Mesozoic granitoids in Mufushan and adjacent regions (e.g., Lianyunshan, Wangxiang, Taohuahsan, etc.) represent the western front of the southeast China magmatic province. However, the tectonic regimes and petrogenesis of the magmatic rocks are still elusive. Here, we report zircon UPb ages, geochemistry, and Sr-Nd-Hf-Pb isotopic data for the granitic rocks in the Mufushan region, in combination with data available from the literatures, to discriminate the middle-late Mesozoic tectono–magmatic history of the Mufushan complex in north-central South China Block. New zircon UPb dating suggests that the Mufushan two-mica monzogranites were emplaced at 149–144 Ma, a short time after the 153–151 Ma granodiorites. These late Jurassic felsic magmas share broad similarities in geochemical-isotopic characteristics, with significant enrichment in LREEs and LILEs (e.g., Ba, Rb, Th, and K), depletion in some HFSEs (e.g., Nb, Ta, Ti, and P) and positive Pb anomalies, similar to those of arc-type rocks. The common existence of Neoproterozoic zircons within the magmatic rocks indicates a certain amount of ancient material involved in the genesis of the magma. The two-mica monzogranites have εHf(t) values ranging from −13.4 to +3.5, overlapping with those of the granodiorites (−11.3 to +6.6), but both are lower than contemporaneous diorites (−2.4 to +0.59), suggesting a greater incorporation of enriched materials into the source for the granitoids. The two-mica monzogranites and granodiorites have εNd(t) values ranging from −7.9 to −8.8 and − 10 to −7.9, with corresponding two-stage Nd model ages of 1.7–1.6 Ga and 1.6 Ga, respectively, falling within their two-stage Hf model ages of 2.0–1.4 Ga and 1.8–1.4 Ga, respectively. Compared with the geochemical and isotopic compositions of the coeval magmatic rocks in eastern South China, we favor that the late Jurassic Mufushan granodiorites evolved from variable mixing and differentiation of the diorites and granitoids, accompanied by a continuous magma assimilation. The presence of late Jurassic highly fractionated granites suggests an extensive magma differentiation in eastern South China and the well-developed early Cretaceous A-type granites in eastern South China reflect a dominant extensional tectonic regime induced by slab roll-back of the Izanagi plate. The involvement of subduction-related melts facilitated the underplating of mantle-derived magma and crustal heating, triggering intensive partial melting of the lithosphere and magma enrichment, as well as the polymetallic deposits in eastern South China.

First identification of late Mesozoic intraplate magmatism in the Chinese north Tianshan: implications for the orogenic architecture and crustal evolution

The formation and dynamics of granitoids in an intra-continental setting are crucial for understanding the architecture and evolution of continental crust. Here, we report geochronological, geochemical and Sr–Nd–Hf isotopic data for newly discovered late Mesozoic granitic intrusions in the Tianshan belt, northwestern China. These granitoids are I-type granites derived from an igneous precursor and were emplaced at c . 145–132 Ma. They have positive ε Nd ( t ) values and young Nd model ages, together with relatively low Sr/Y ratios, indicating that they might have originated from partial melting of the juvenile lower crust. There is a prominent decoupling between zircon Hf and bulk-rock Nd isotopes, which may have resulted from the early crystallization of Ti-rich minerals. These granitic intrusions also display subduction-related geochemical characteristics, which are probably inherited from Paleozoic crustal sources that were metasomatized by subduction-related fluids. We conclude that these late Mesozoic granitoids were emplaced in an intra-continental setting, and were probably triggered by thermal relaxation owing to crustal shortening and thickening. These data further imply that the Tianshan changed into crustal reworking during the Mesozoic from its prominent crustal growth in the Paleozoic. Supplementary material: LA-ICP-MS zircon U–Pb dating results, whole-rock major and trace element compositions, whole-rock Sr–Nd isotopic data and zircon Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.7167890 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Geodynamic Settings of Late Paleozoic–Early Mesozoic Granitoid Magmatism at the Arctic Continental Margins: Insights from New Geochronological and Geochemical Data from the Taimyr Peninsula

Despite significant progress in Arctic geological studies, a number of principal questions concerning the Paleozoic collisional events remain unanswered. Therefore, the Taimyr Peninsula, representing the only outcropped high Arctic region where magmatic complexes, formed by Hercynian collision between the Siberian Craton and the Kara Block, are well exposed, is crucially important. In this paper we report new geochemical and geochronological data for intrusions in the poorly studied northeastern part of the Taimyr Peninsula. The obtained results in combination with published data show that supra-subduction magmatism at the southern active margin of the Kara Block continued from ca. 345 to 285 Ma (Early Carboniferous to Early Permian), and was followed by a post-collisional magmatic pulse that affected the whole Taimyr across terrane boundaries at ca. 280 Ma in the Early Permian. After cessation of the post-collisional magmatism at ca. 265 Ma, the Taimyr experienced extension, and voluminous magmatic series associated with a Siberian mantle plume were formed between 251 and 228 Ma during the Triassic. The studied post-collisional and plume-related intrusions of the Northeastern Taimyr are generally classified as evolved high-K I-type granites with adakitic affinity. The latter is a regional feature because the majority of the analyzed plume-related granitoids are geochemically similar to high potassium continental adakites. It is suggested that the adakitic geochemical characteristics of the plume-related granitoids resulted from melting of hydrated mafic lower crustal protoliths and were controlled by the source lithology. Comparison of the new results with data available for adjacent areas allows for correlation of terranes on a regional scale and sheds light on the evolution of the Arctic continental margins in general. In the Early–Middle Paleozoic, the Kara Block was part of a continental terrane that formed at the northern edge of Baltica as a result of Neoproterozoic Timanian orogeny. In the Early Carboniferous, the southern margin of Kara turned into an active margin, while its inferred continuation in the eastern Uralian margin of Baltica remained a passive margin until the Early Permian. This discrepancy can be explained by dextral displacement of Kara relative to Baltica that took place in the Early Carboniferous and was later accommodated by the formation of the Taimyr collisional belt in the course of the Early Permian collision between Kara and Siberia. After collision, the Taimyr was incorporated into the northern Eurasian margin as an uplifted block that experienced surface erosion and supplied clastic material in surrounding basins.

Regional variation of biotite composition of granitoid and its significance to deep crust component and mineralization: A case study on biotite from Early Mesozoic granitoid in the Qinling orogen

Regional variation of biotite composition of granitoid and its significance to deep crust component and mineralization: A case study on biotite from Early Mesozoic granitoid in the Qinling orogen

Preservation of Archean mafic lower continental crust worldwide

Mafic granulite xenoliths found in Archean cratons have generally been inferred to form from post-Archean basaltic underplating, implying that the Archean mafic lower crust was removed perhaps via delamination. Here based on an integrated study of granulite terrain, granulite xenoliths and lower crustal-derived granitoids, we make a compelling case that most of the Tertiary alkali basalt-entrained mafic granulite xenoliths from the northern North China craton are restites left after partial melting of the late Archean mafic lower crust to produce the Mesozoic granitoids. This runs counter to archetypical Mesozoic basaltic underplating as commonly believed. We further show that the Archean mafic lower crust persists on a cratonic scale in the North China craton presently. Re-examination of mafic granulite xenoliths from many other cratons that were considered to be products of Proterozoic underplating shows that most of them have similar genetic mechanism to the present case, suggesting that they may form in the Archean. This attests to preservation of the Archean mafic lower crust globally, contrary to the widely held concept that much of the Archean mafic lower crust has delaminated. We predict preservation of such mafic lower crust beneath all Archean cratons. It suggests that the quantity of Archean rocks in the lower crust may be much greater than that exposed.

Apatite geochemical composition of Mesozoic granitoids in the eastern Jiangnan Orogen, S. China: insights into petrogenesis and intrinsic magmatic variables

ABSTRACT The geochemical compositions of apatite are commonly used to provide reliable constraints on the intrinsic magmatic variables of the parental magma. There is a widespread distribution of Mesozoic granitic rocks in the eastern Jiangnan Orogen (EJNO), which include I-type and A-type granitoids. This study aims to investigate the geochemical composition of apatite in 11 representative I-type and A-type granitic intrusions from the EJNO to understand their petrogenesis, intrinsic magmatic variables, and polymetallic mineralization potential. The results show that apatites in these granitoids were characterized by oscillatory zonation and homogeneous texture, and exhibited high F, and low Cl contents, as well as high REE, Y, and Th contents, indicating magmatic origin. These apatites were divided into two groups depending on their geochemical characteristics and original rock types. In Group I apatites (in the I-type granitoids), the absence of an abrupt change in major and trace element concentrations from the core to the rim of the apatite crystals, combined with their low levels of MgO, Sr, and HREY (HREE+Y), serves as evidence to classify the I-type granitoids as low Sr-Y adakitic granitoids with a low Mg#, which can be attributed to the partial melting of the thickened lower crust. In Group A apatites (in the A-type granites), the normal increase in incompatible elements from the core to the rim, as well as the presence of a flat REE pattern with pronounced Eu anomalies, can be attributed to crystal fractionation of plagioclase, allanite, and zircon. Furthermore, Group I apatites have higher SO3, Cl, and molar OH/F and Cl/F ratios compared to Group A apatites. Quantitative calculation by apatite-melt partitioning and modelling suggests that the I-type granitic magmas were more volatile-rich and more oxidized than A-type granitic magmas. Taken together, based on the relationship between the intrinsic magmatic variables and the behaviour of ore-forming elements, our study demonstrates that early I-type granitoids of the EJNO have a strong W-Mo-Cu polymetallic mineralization potential, while late A-type granites may possess rare metal mineralization potential.

Multiple stages of continental rifting in Eastern Peninsular Malaysia: new insights from Jurassic–Cretaceous granitoids

Mesozoic granitoids in Peninsular Malaysia provide crucial information on the temporal–spatial relationship between the Tethyan and Palaeo-Pacific domains. This paper presents new ages and geochemical data for newly identified Jurassic–Cretaceous granites and meta-granites from East Malaya. These granitoids can be divided into three groups. Group 1 consists of high-K calc-alkaline granites and granodiorites (171–162 Ma) with variable ε Nd ( t ) values of −7.4–+0.5, zircon ε Hf ( t ) values of −7.4–+8.6, and high initial ratios for 206 Pb/ 204 Pb (20.04–20.65), 207 Pb/ 204 Pb (15.73–15.79) and 208 Pb/ 204 Pb (39.80–40.20). The melting of metasedimentary rocks with a juvenile mafic component formed Group 1 samples. Group 2 granite porphyries ( c. 131 Ma) with A-type affinities and Group 3 granitic gneisses ( c. 130 Ma) with I-type affinities share similar ε Nd ( t ) values (−7.2 to −5.5), zircon ε Hf ( t ) values (−10.1–+6.5), and initial ratios for 206 Pb/ 204 Pb (18.81–19.02), 207 Pb/ 204 Pb (15.71–15.77) and 208 Pb/ 204 Pb (38.95–39.59). Although Group 2 and 3 samples were derived from an ‘ancient’ meta-mafic source region, Group 2 shows evidence for the involvement of a juvenile mafic component. All these granitoids are akin to the Permian–Triassic igneous rocks in East Malaya. The Jurassic–Cretaceous igneous rocks in Eastern Peninsular Malaysia were formed during multiple stages of continental rifting in response to Palaeo-Pacific slab rollback pulses rather than by Tethyan evolutionary processes. Supplementary material : Data for the Middle Jurassic–Early Cretaceous granitoids of East Malaya are available at https://doi.org/10.6084/m9.figshare.c.6689085 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Sources and petrogenesis of Late Triassic granitoids in the Yajiang gneiss dome group (eastern Songpan-Ganze orogenic belt) with tectonic implications

Numerous Mesozoic granitoid plutons with a substantial variety of petrologic and geochemical signatures intrude the Triassic metasedimentary rocks of the Songpan-Ganze accretionary-orogenic wedge in the eastern Tibetan Plateau. These granitoid rocks generally exhibit sharp contact with the Triassic sedimentary rocks. To better understand the genesis and emplacement of magmas associated with tectonic accretion along convergent plate boundaries, we present new LA-ICP-MS zircon U-Pb geochronology, major and trace elements, and Sr–Nd–Pb–Hf isotopic compositions for intermediate-to-felsic plutons in the Yajiang gneiss dome group (YGDG), including the Changzheng pluton, the Jiajika (Majingzi) pluton, the Rongxuka pluton, the Xiya pluton, the Xinduqiao pluton, and the Waduo diorite dikes in the eastern margin of the Songpan-Ganze orogenic belt (SGOB). By their typical petrological and geochemical characteristics, these plutons are classified as I-type granodiorite-diorite (Rongxuka, Xiya, Xinduqiao plutons, Waduo dikes) or S-type granite (Changzheng and Jiajika plutons). I-type granodiorite-diorites exhibit a high Mg# (average 49), medium-K cala-alkiline signature and are enriched in large-ion lithophile elements (e.g., Rb, Th, and U) but depleted in high field strength elements (e.g., Nb, Ta, and Ti), and with lower initial 87Sr/86Sr values (0.70622 to 0.70863) but a relatively high and concentrated εHf(t) (−27 to −1.9) and εNd(t) (−4.02 to −7.51); while S-type granites exhibit a high silica, high-K cala-alkiline signature with strong negative Eu anomalies (Eu/Eu* = 0.17–0.64), and possess high initial 87Sr/86Sr values but low εHf(t) (−40.1 to −0.9) and εNd(t) (−8.72 to −12.14) signatures, forming through partial melting of metasedimentary rocks from an ancient crust source. LA–ICP–MS zircon U-Pb dating indicates that they were emplacement between 207.2 ± 1.4 and 223.6 ± 2.2 Ma. Both types of granitoid rock were formed by the crustal partial melting followed by extensive fractional crystallization under high-temperature (700–850 °C), low-pressure (<15 kb) conditions. In combination with previous studies, our data provide evidence for an affinity between the eastern Songpan-Ganze andthe Yangtze craton basements, and suggest that the granitoid plutons formed in a syn-collisional to post-collisional setting at ca. 207–223 Ma.

Petrogenesis of the Triassic Dongjiangkou pluton in the South Qinling orogenic belt, Central China: Insufficient magma mixing of mafic and felsic magmas

Magma mixing or mingling between mafic and felsic magmas is a common phenomenon in granitoid magmatism, and chemical and mechanical interactions between the magmas are frequently observed in granitic rocks. The Dongjiangkou pluton is an example of magma mixing among the numerous early Mesozoic granitoid plutons that are exposed in eastern South Qinling. This pluton is predominantly composed of granodiorite and contains abundant mafic/intermediate microgranular enclaves (MMEs) and is sporadically intruded by mafic dykes. Both the granodiorite and MMEs were crystallized at 224–214 Ma and have inherited zircons of similar age ranges. The granodioritic rocks had metaluminous to weak peraluminous features and adakitic signatures and belong to the high-K calc-alkaline series, whereas the MMEs and dioritic dykes had low SiO2 contents and metaluminous features and belong to the high-K calc-alkaline to shoshonite series. All of the rocks had high Mg# values and similar geochemical characteristics regarding trace elements and Sr isotopes, but they had diverse whole-rock Nd-Pb and zircon Hf isotopic compositions. The Dongjiangkou granodiorite was produced by partial melting of old basement rocks and Paleozoic juvenile crust beneath South Qinling triggered by asthenospheric upwelling. Magma(s) of the Dongjiangkou MMEs may have been derived from deep mantle and injected into and mixed with the magma(s) of the granodiorite, but chemical and isotopic homogenization was not achieved during the magma mixing process. Clastic rocks may have played a major role in the formation of crust-derived magma(s), causing strong Nd-Hf isotopic decoupling of several granitoid plutons in South Qinling.

Petrogenesis of Mesozoic granitoids in the northeastern North China Craton: Constraints from apatite trace elements and in-situ Nd isotopic data

Petrogenesis of Mesozoic granitoids in the northeastern North China Craton: Constraints from apatite trace elements and in-situ Nd isotopic data

Crustal architectural controls on critical metal ore systems in South China based on Hf isotopic mapping

Abstract There is increasing demand for critical metals (e.g., W-Sn, Li-Be-Nb-Ta, and rare earth elements [REEs]) to sustain the transition to green energy, yet it is unclear what controls the formation of such critical metal ore systems. Here, we focus on South China, which is well endowed with critical metals, and imaged its crustal architecture by zircon Hf isotopic mapping using 1096 zircon Hf isotope data sets for 1457 samples of Mesozoic granitoids and silicic volcanic rocks. We demonstrate that the crust is isotopically heterogeneous, characterized by spatial juxtaposition of ancient, reworked, and juvenile crustal domains. The granite-related W-Sn-Nb-Ta and REE deposits occur mainly in reworked crustal domains, where multiple stages of reworking and Mesozoic melting events likely resulted in the release of these metals into crust-derived magmas. Compared with W-Sn deposits, REE deposits occur mostly in strongly reworked crustal blocks with a juvenile input. The porphyry Cu-Au deposits are spatially confined to Cu-fertilized juvenile crustal domains, whereas U and Ag-Pb-Zn deposits occur predominantly in old crustal domains and at their margins. This study demonstrates the importance of isotopic mapping as a tool for characterizing crustal architecture and processes that lead to the formation of metal ore systems.

New Geochronological and Isotope Data on Mesozoic Granitoids of Eastern Transbaikalia

New Geochronological and Isotope Data on Mesozoic Granitoids of Eastern Transbaikalia

Igneous Records of Mongolia–Okhotsk Ocean Subduction: Evidence from Granitoids in the Greater Khingan Mountains

Large-scale Mesozoic granitoids are exposed in the Greater Khingan Mountains. Their relationship with the Mongolia–Okhotsk and the Paleo-Pacific Ocean is still under discussion and a matter of debate. In this study, field observations were made and a total of 18 granitoids exposed in the vicinity of the Heihe–Baishilazi area in the northern part of the Greater Khingan Mountains were sampled for petrological, geochronological, and geochemical research. In addition, to complement this study, 90 granitic samples from the Xinghua, Dajinshan, Yili, Chabaqi, and Sankuanggou areas in the Greater Khingan Mountains were compiled in order to reveal rock assemblages, magma sources, and then inquire into the tectonic background. Zircon LA–ICP–MS U–Pb dating indicates that two samples from the Heihe area were formed in the Early Jurassic period (194.2 ± 1.4 Ma and 183.1 ± 1.3 Ma), and the εHf(t) values and TDM2 of the zircons were mainly +5.8 to +10.7 and 528 Ma to 834 Ma, respectively, with a large variation range. The intrusive rocks from the Greater Khingan Mountains (108 in total) belonging to the T1T2G1G2 assemblage contained tonalites (T1), trondhjemites (T2), granodiorites (G1), and granites (G2). These granitoids are presented as subalkaline series in a plot of total alkali versus SiO2 (TAS diagram), medium-K calc-alkaline and high-K calc-alkaline series on SiO2 versus K2O diagram, with metaluminous to peraluminous characteristics on an A/CNK versus A/NK diagram. These are shown as a MA (magnesium andesite) series and LMA (lower (or non) magnesium andesite) series on a SiO2 versus MgO diagram, which can be further divided into the higher-pressure TTG subtype of the MA (corresponding to high-SiO2 adakite (HSA)) series and the lower-pressure TTG subtype of LMA (corresponding to typical calc-alkaline suprasubduction zone rocks). In addition, granitoids were enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs), corroborating a suprasubduction zone environment. Regional correlations as well as geochemical characteristics indicate that the rocks from the Greater Khingan Mountains formed in a subduction zone environment during the Early Jurassic; primary magma had presumably originated from the melting of young and hot oceanic crust under eclogite to amphibolite facies conditions. According to the spatial variation in rock assemblages (T1T2G1 to G1G2 and G2), we speculate that the northeastern Heihe, Baishilazi, and Xinghua areas as well as the westward Dajinshan area were adjacent to the ocean and formed an outer subduction zone, whereas the southwestward Sankuanggou, Yili, and Chabaqi areas were adjacent to the continent, forming an inner subduction zone. The distribution sites of the inner and outer subduction zones indicate southward and southwestward ocean subduction. Therefore, we propose a direct connection with southward subduction of the Mongolia–Okhotsk Ocean.

Late Paleozoic and early Mesozoic granitoids in the northwestern Bureya Massif, Central Asian Orogenic Belt: Timing and tectonic significance

ABSTRACT The Bureya Massif is an important massif in the eastern Central Asian Orogenic Belt (CAOB), and contains voluminous late Palaeozoic–early Mesozoic granitoids that are ideal for investigating the tectonic evolution of the eastern CAOB. Here we report whole-rock geochemical, and zircon U–Pb geochronological and Lu–Hf isotope data for several granite intrusions in the northwestern Bureya Massif, with the aim of constraining the timing of magmatism and late Palaeozoic–early Mesozoic tectonism in the eastern CAOB. The zircon U–Pb dating results indicate that granitoids with ages of 306 ± 4, 243 ± 3, 191 ± 2, and 189 ± 4 Ma occur in the Bureya Massif. These, and previously published data, reveal that at least four stages of magmatism occurred in the northwestern part of the massif: ~306 Ma, ~243 Ma, 219–212 Ma, and ~201-189 Ma. The late Carboniferous (306 ± 4 Ma) gneissic monzogranites have an S and A-type granite affinity, and were derived with significant contribution of the mantle component in a syn- to post-collisional setting between the Bureya and Xing’an massifs. The Middle Triassic (243 ± 3 Ma) porphyritic I-type monzogranites, Early Jurassic (191 ± 2 Ma) porphyritic S-type syenogranites, and Early Jurassic (189 ± 4 Ma) gneissic S-type monzogranites have a supra-subduction zone geochemical signature. These granitoids formed in an active continental margin setting associated with southward subduction of the Mongol–Okhotsk oceanic plate.

Giant Mesozoic gold ores derived from subducted oceanic slab and overlying sediments

Orogenic gold deposits account for more than 30 % of the global gold resources. To understand the genesis of orogenic gold deposits and ultimately target new orogenic gold deposits, it is important to determine the origin of gold. However, there has been a continuing debate surrounding gold source reservoirs. The Jiaodong gold province, comprising ore hosted within Mesozoic granitoids that intruded Archean metamorphic rocks, together with other gold occurrences in the North China block, collectively constitute the only Mesozoic world-class gold resource in a Precambrian basement. This geological setting, with young deposits in ancient rocks, offers a great opportunity to better determine the gold source because it allows us to fingerprint the isotopically distinct reservoirs. Specifically, it is possible to determine whether the mass-independent isotopic fractionation sulfur (MIF-S)-bearing Archean supracrustal rocks that form the lower crust are a permissive source. We present multiple sulfur isotope (δ34S and Δ33S) measurements of pyrite grains (n = 161) from 18 gold deposits in the six main districts of the Mesozoic Jiaodong gold province. Gold-associated pyrite grains yield non-MIF-S signatures (Δ33S = 0 ‰), indicating that Archean metasedimentary rocks are not a source reservoir of sulfur and gold. The isotopically heavy S (average δ34S = +9.0 ± 3.7 ‰, 2SD) demonstrates a sulfur contribution from a subducted oceanic slab and, in particular, its overlying sediments while excluding mantle and magmatic sources. The subduction-related metamorphism released appreciable gold and sulfur from the top of the downgoing slab into aqueous-carbonic fluids that ascended into the upper plate along crustal structures traversing a tectonically thinned crust. Here, we demonstrate that these giant Mesozoic orogenic gold deposits sourced gold and sulfur during subduction-related devolatilization reactions.