Origin of C type adakite magmas in the NE Xing＇an block, NE China and tectonic implication

In this paper, we report new whole-rock geochemical and zircon U-Pb data for monzogranites in the NE Xing＇an block. These data constrained the petrogenesis of C type （high Sr/Y） adakitic rocks and showed the spatial extent of the influence of the Mongol-Okhostsk ocean tectonic regime and the collision between the Jiamusi Massif and Songliao Terrane. New zircon laser-ablation inductivity coupled plasma mass spectrometry （LA-ICP-MS） U-Pb data indicated that the monzogranites in the studied area were emplaced in the Early Jurassic （～ 180 Ma）. These rocks were characterized by unusally high SiO2 （≥67.49）, and Sr （461-759 ppm）, but strikingly low Y （4.63-8.06 ppm） and HREE （∑HREE = 3.83-6.49 ppm, Yb = 0.5-0.77 ppm） contents, with therefore high Sr/Y （67.2-119） and （La/Yb）N （29.7-41.5） ratios, showing the geochemical characteristics of C type adakitic granite. The data displayed negligible Eu anomalies （Eu/Eu^＊ =0.77-1.08）, LREE-enriched and pronounced negative Nb and Ta anomalies. The C-type adakites in the studied area were most likely derived from the partial melting of a thickened lower continental curst. The magma source is most likely dominated by amphibolites and garnet amphibolites. In combination with previously-reported data from igneous rocks from the Mesozoic in NE China, we conclude that the Xing＇ an block was influenced by the Mongol-Okhotsk subduction tectonic system, and experiences compressive settings from the amalgamation of the Jiamusi block in the east of the CAOB.

Age and geochemistry of Early Ordovician A-type granites in the Northeastern Songnen Block,NE China

Early Ordovician A-type granites in the northeastern(NE) Songnen Block NE China were studied to better understand the geodynamic settings in this region.This research presents new zircon U–Pb ages and wholerock geochemical data for the Early Ordovician granites in the NE Songnen Block. Zircon U–Pb dating indicates that the granite in the Cuibei, Hongxing, and Meixi areas in the NE Songnen Block formed in the Early Ordovician with ages of 471–479 Ma. The granites show geochemical characteristics of high SiO2 and K2 O compositions and low FeOT, MgO, CaO, and P2 O5 compositions. They belong to a high K calc-alkaline series and display a weak peraluminous featurPe with A/CNK values of 0.98–1.14. The rocks have aREE composition of 249.98–423.94 ppm,and are enriched in LREE with(La/Yb)Nvalues of2.87–9.87, and display obvious Eu anomalies(d Eu =0.01–0.29). Trace elements of the studied granites are characterized by enrichment in Rb, Th, U, Pb, Hf, and Sm,and depletion of Ba, Nb, Ta, and Sr. They display geochemical features of high Zr +Y + Nb+Ce values(324–795 ppm) and Ga/Al ratios consistent with A-type granites. Based on particular geochemical features, such as high Rb/Nb(7.98–24.19) and Y/Nb(1.07–3.43), the studied A-type granites can be further classified as an A2-type subgroup. This research indicates that the Early Ordovician A-type granites were formed by the partial melting of ancient crust in an extensional setting. Lower Sr/Y and(Ho/Yb)Nratios indicate that plagioclase and amphibole are residual in the source, and garnet is absent, implying that the magma was generated at low levels of pressure. By contrast, the contemporaneous granites in the SE Xing'an Block suggest a subduction-related tectonic setting, and its adakitic property indicates a thickened continental crust.We suggest that the Paleo-Asian Ocean plate between the Xing'an and Songnen blocks subducted northward during the Early Ordovician. Meanwhile, the NE Songnen Block was exposed to a passive continental margin tectonic setting.

Multiple metal sources in polymetallic W-Sn ore deposits revealed by mercury stable isotopes

Granite-related W-Sn ore systems are commonly associated with coeval Pb-Zn mineralization. It remains unclear whether these metals are derived from the same sources or not. Mercury(Hg) is a common minor component in such systems. Hg isotopes undergo unique mass-independent fractionation(expressed as Δ^(199)Hg values), which is mainly generated during Hg photochemical reactions on Earth's surface and not affected by magmatic-hydrothermal processes, offering an excellent opportunity to trace metal sources in hydrothermal systems. We observed near-zero Δ^(199)Hg values in wolframite(-0.10‰ to0.08‰, n=11), and in skarn-(-0.17‰ to 0.12‰, n=48) and greisen-type(-0.12‰ to 0.10‰, n=11) bulk tin-tungsten ore from eight major ore deposits in South China. These values are identical to those of coeval highly evolved granites(-0.13‰ to 0.12‰,n=49), supporting that Hg in W-Sn ores were sourced from granite. However, sulfides(e.g., pyrite, chalcopyrite, arsenopyrite,galena, and sphalerite) in these deposits exhibit negative to near-zero Δ^(199)Hg values(-0.42‰ to 0.09‰, n=124), which indicates a contribution of Hg and by inference other metals from both Precambrian basement rocks(Δ^(199)Hg<0) and ore-related granites.The study demonstrates that multiple sources of metals were involved in the formation of the polymetallic W-Sn deposits, and further highlights that extraction of metals from basement rocks may be a critical control on the formation of economically important mineralization of base metal sulfides(e.g., Pb, Zn) in granite-related magmatic-hydrothermal systems.

Permian tectonic evolution and continental accretion in the eastern Central Asian Orogenic Belt:A perspective from the intrusive rocks

The tectonic evolution and history of continental accretion of the eastern Central Asian Orogenic Belt(CAOB)are not yet fully understood.In this study,we investigate Permian intrusive rocks from the Jiamusi Block of the eastern CAOB to constrain the tectonic evolution and continental accretion of this region during the late-stage evolution of the Paleo-Asian Ocean.Our new data show that Early Permian gabbro-diorites were derived from the partial melting of depleted mantle metasomatized by oceanic-slab-released fluids.Middle Permian adakitic granites have low Na2O and MgO and high K2O contents,indicating a thickened-lower-crust source.Late Permian S-type granites were derived from the partial melting of continental crust.A compilation of the available geochronological data for Permian intrusive rocks(including adakitic and A-,S-,and I-type granites and mafic rocks)from the eastern CAOB reveals that the A-type granites formed mainly during the Early–Middle Permian,S-type and adakitic granites mostly during the Middle–Late Permian,and I-type granites and mantle-derived mafic rocks throughout the Permian.The A-type granites,which are proposed to have been sourced from thinned continental crust,indicate an extensional setting in the eastern CAOB during the Early Permian.The Middle–Late Permian adakitic granites imply a thickened continental crust,which indicates a compressional setting.Therefore,the eastern CAOB underwent a transition from extension to compression during the Middle Permian,which was probably triggered by the late-stage subduction of Paleo-Asian oceanic crust.Considering the petrogenesis of the intrusive rocks and inferred regional tectonic evolution of the eastern CAOB,we propose that vertical underplating of mantle-and oceanic-slabderived magmas contributed the materials for continental crust accretion.

Roller-coaster atmospheric-terrestrial-oceanic-climatic system during Ordovician-Silurian transition:Consequences of large igneous provinces

The Ordovician-Silurian transition(OST)hosted profound and frequent changes in the atmospheric-terres trial-oceanic-climatic system(ATOCS).Previous studies have found contrasting stages for such changes,primarily based on hiatus-interrupted sections.However,the dominant driving factors and mechanisms reconciling such frequent changes remain controversial.Mercury isotopes,which undergo both massdependent and mass-independent fractionation,can provide critical insights into the deep-time ATOCSs,especially for those impacted by large igneous provinces(LIPs)events.Here,we build a highresolution multi-proxy record of Hg(concentrations and isotopic compositions)combined with organic carbon isotopes(δ^(13)Corg)and whole-rock geochemical data(including trace elements and phosphorus)from continuous cores in the Yangtze Platform,South China.Our data,combined with reported ones,indicate the occurrence of LIP eruptions against localized volcanism,and four successive,yet contrasting stages of ATOCSs during the OST.Moreover,we identified the coupling between two-pulse LIP magmatism and extreme ATOCSs,each with special pCO_(2),weathering rate,primary productivity,redox condition,climatic mode,and biotic evolution.For stage I,the first pulse of LIP magmatism triggered global warming,enhanced terrestrial weathering,oceanic acidification,eutrophication,anoxia,P recycling,and thereby widespread deposition of black shales.During stage II,the Hirnantian glaciation and oxygenation arose from the intense chemical weathering and black shale deposition of stage I;slashed terrestrial weathering and oceanic oxygenation facilitated CO_(2) accumulation.In stage III,another pulse of LIP magmatism triggered the de-glaciation,and the ATOCS was largely similar to that of stage I.This led to another round of oxygenation and positive d13Corg excursion in stage IV.Compared with the environmental pressure by the peculiar ATOCS of each stage,their transitions might have been more devastating in triggering the prolonged Late Ordovician Mass Extinction(LOME).Moreover,limited biotic recovery was possible in the later portion of stages I and III.The multi-proxy study of continuous strata of the OST provides an excellent framework for better illuminating LIPs’essential role in driving the“roller-coaster”behavior of the ATOCS and thus biotic crisis during the pivotal period of the OST.

Mercury isotope constraints on the genesis of late Mesozoic Sb deposits in South China

The late Mesozoic antimony(Sb)mineralization belt in South China hosts a large portion of the world’s Sb reserves.However,the source and mineralization processes of these Sb deposits remain controversial.Here,we measured mercury(Hg)concentrations and isotopic compositions of stibnite in the Banpo Sb-only and Woxi Sbpolymetallic ore deposits,as well as associated rocks in the Yangtze Block in order to constrain the metal sources and ore formation processes in the South China Sb mineralization belt.Stibnite samples from both deposits exhibit significant enrichment in Hg(4.23–50.6 ppm)and have higher δ^(202)Hg values(−0.47‰to 2.03‰)than the studied Precambrian basement rocks(−1.42‰to 0.59‰),Paleozoic sedimentary rocks(−2.40‰to−0.32‰),and other natural Hg reserves(e.g.,marine and continental systems).This indicates that significant mass-dependent fractionation of Hg isotopes occurred during hydrothermal processes.Negative to slightly positive Δ^(199)Hg values of−0.17‰to 0.02‰were obtained for stibnite from the studied deposits,similar to values for the Precambrian basement rocks,but different from those of the Paleozoic sedimentary rocks and data previously reported for mantle materials.This suggests that Precambrian basement rocks were the source of Hg and associated metals.Our data and the tectonic evolution of South China indicate that late Mesozoic asthenospheric upwelling,in response to the Paleo-Pacific oceanic slab foundering,generated heat that drove the circulation of fluids in the basement and crustal basinal rocks.These fluids leached Sb,Hg,and other metals from the Precambrian basement rocks and formed the world-class Sb mineralization belt in South China.