The tectonic evolution of Southeast China during Late Mesozoic is a prominent topic. Numerous tectonic models on Late Mesozoic evolution ofSoutheast Chinahave been published in the past 50 years. We synthesized many up-to-date and precise zircon U-Pb ages, sedimentary strata, and regional structures and discussed the oxygen fugacity of magmas and related ore deposits. We also analyzed the most current tectonic models published by some scholars. A multistage tectonic stress evolution history during Late Mesozoic was constructed, which included the following stages: 1) Early-Middle Jurassic (196 - 175 Ma) extension, in which many bimodal volcanics formed; 2) Middle-Late Jurassic (165 - 140 Ma) compression, which generated largescale gneissic granites, garnet-bearing granites, stratigraphic hiatus, and nappe structures; 3) Early Cretaceous (140 ± 5 - 120 Ma) extension, which formed weakly deformed or undeformed granites, alkali granites, metamorphic core complexes, graben basins, and basic dike swarms; 4) Early Cretaceous (120 - 110 Ma) compression, which generated nappe structures, volcanic hiatuses, and garnet-bearing granites; and 5) Early-Late Cretaceous (110 - 80 Ma) extension, which generated largescale bimodal volcanics, basic dike swarms, alkali granites, and graben basins. The Late Mesozoic tectonic evolution ofSoutheast Chinamay be attributed to the drifting history of the Paleo-Pacific plate. The drifting direction of the Paleo-Pacific plate has changed several times since 140 Ma, which led to major changes in the tectonicphenomena from Jurassic to Cretaceous and to the formation of Late Mesozoic mineral deposits.
Sediment-hosted Cu–Co deposits in the Zhongtiao Mountains are hosted by the metasedimentary rocks of the Paleoproterozoic Zhongtiao Group in the southern part of the trans-North China orogen, North China Craton. The ore genesis is still disputed with proposed genetic models including metamorphosed sedimentary exhalative (M−SEDEX), metamorphosed sediment-hosted stratiform copper (M−SSC) and metamorphogenic mineralization type. Pyrite occurs as a ubiquitous mineral throughout all ore-forming stages and is ideal for clarifying this issue via the integration of in situ (LA–ICP–MS and EPMA) elemental and LA–MC-ICP–MS sulfur isotope composition analyses. Two main types of pyrite are identified based on petrographic and SEM observations: fine- to medium-grained, variably deformed and inclusion-rich Py1 (including Py1a and Py1b subtypes) in the disseminated–veinlet mineralization stage (S1), and coarse-grained, fractured Py2 (including Py2a and Py2b subtypes) in the fracture-controlled vein-type mineralization stage (S2, main ore stage). Deformed and inclusion-rich Py1a is overgrown by inclusion-poor Py1b, and nonporous Py2a is rimed by porous Py2b. Geochemical results show that the studied pyrite samples have considerable contents of Co (mean > 1000 ppm) and Ni (mean > 100 ppm). These features could be related to both the Co and Ni-rich sedimentary environment (e.g., a volcaniclastic-rich sulfidic marine) and metamorphic enrichment. The content of Se (mean > 200 ppm) in Py2 is significantly higher than that in Py1, indicating the extensive interaction of mineralizing fluids with Se-bearing graphite schist. LA–ICP–MS mapping and textural studies indicate the presence of coupled dissolution-reprecipitation (CDR) reactions that could lead to trace metal compositions (e.g., Co, Ni, Se, Pb, Bi) in the product phases (Py1b, Py2b) that differ from those of their parent phases (Py1a, Py2a). These variations were most likely controlled by fluid temperature and precipitation of specific minerals. The grain-scale chemical zoning of Py2a revealed by elemental mapping indicates fluctuating fluid parameters (e.g., temperature, fS2, and/or parent fluid compositions). The bimodal distributions in Py1 (10–14 ‰ and 18–24 ‰) are consistent with the inheritance of sulfur from sedimentary pyrite and the input of thermochemical sulfate reduction (TSR) -related sulfur from reworked evaporite sulfates in an increasingly open system. The relatively lighter and wider variation in δ34S values (3.2–22.4 ‰, mean = 15.1 ‰) of Py2 implies that the evolution of the ore fluid in S2 was far more complicated, probably as a result of fluid–rock interactions and fluid cooling. During this process, hydrothermal rims with lighter δ34S values (8.4 ‰) grew on older metamorphic pyrite cores with relatively heavier δ34S values (17.4–18.2 ‰). Chalcopyrite displays overlapping S isotopic compositions with pyrite from different mineralization stages, suggesting that copper sulfides inherited reduced sulfur from earlier formed pyrite. Cooling and fluid–rock interactions serve as the critical controls triggering Cu precipitation from the fluid. The combined textural and compositional data of pyrite and chalcopyrite are suggestive of a syn-orogenic copper deposit model, in which all the ore-grade copper was introduced during the Zhongtiao orogeny.
The Xingmeng Orogenic Belt evolved through a long-lived orogeny involving multiple episodes of subduction and accretion. However, there is a debate on its tectonic evolution during the Late Paleozoic. Here, we report geochemical, geochronological, and isotopic data from strongly peraluminous granites and gabbro-diorites from the Sunidzuoqi–Xilinhot region. Zircon U–Pb ages suggest that the intrusive rocks were emplaced during the Early Carboniferous (333–322 Ma). The granites exhibit geochemical characteristics similar to S-type granites, with high SiO2 (72.34–76.53 wt.%), Al2O3 (12.45–14.65 wt.%), and A/CNK (1.07–1.16), but depleted Sr, Nb, and Ta contents. They exhibit positive εNd(t) and εHf(t) values (−0.3 to 2.8 and 2.7–5.7, respectively) and young Nd and Hf model ages (TDM2(Nd)=853–1110 Ma and TDM2(Hf)=975–1184 Ma), suggesting that they may be the partial melting products of heterogeneous sources with variable proportions of pelite, psammite, and metabasaltic rocks. The meta-gabbro-diorites from the Maihantaolegai pluton have low SiO2 (47.06–53.49 wt.%) and K2O (0.04–0.99 wt.%) contents, and demonstrate slight light rare earth element (REE) depletion in the chondrite-normalized REE diagrams. They have high zircon εHf(t) values (14.41–17.34) and young Hf model ages (TDM2(Hf)= 230–418 Ma), indicating a more depleted mantle source. The variations of the Sm/Yb and La/Sm ratios can thus be used to assess the melting degree of the mantle source from 5% to 20%, suggesting a quite shallow mantle melting zone. We propose that the petrogenesis and distribution of the strongly peraluminous granites and gabbro-diorites, as well as the tectonic architecture of the region, can be explained by a ridge subduction model. Based on these results, and previous studies, we suggest a southward ridge subduction model for the Sunidzuoqi–Xilinhot region.
We undertake zircon U–Pb dating, Hf isotopes, and geochemical analyses of the Houtoumiao pluton in the Xilinhot microcontinent (XLMC) in the central Inner Mongolia with an aim of determining their ages, petrogenesis, and sources, which are important for understanding the late Palaeozoic tectonic evolution of the Xing’an-Mongolia Orogenic Belt. The Houtoumiao pluton consists of medium-grained granodiorite, coarse- and medium-grained syenogranite. Mafic microgranular enclaves (MMEs) are common in the Houtoumiao pluton. Zircon U–Pb dating has yielded ages of 303 ± 2 and 301 ± 2 Ma for the granodiorite, 295 ± 2 Ma for the syenogranite, and 292 ± 1 Ma for the MMEs. The granodiorite and syenogranite have features of high-K high silica content, rich in Rb, U, and Th, but low content of HFSE, belong to calc-alkaline series. The P2O5 concentration decreases with the increasing SiO2 content, suggesting I-type affinity. The MMEs, which are characterized by low SiO2, relatively high and variable TiO2, Al2O3, FeOT, MgO, CaO, Ni, and Cr contents, also have much higher total rare earth element concentrations that the REE patterns are subparallel to those of the host rocks. Zircons from the host rocks have εHf(t) values from +3.91 to +7.73 and TDM2 values of 820–1067 Ma, suggesting that the granitoids were probably dominated by remelting of juvenile crust materials. The MMEs are of εHf(t) value ranging from +6.23 to +11.04 and TDM1 values from 490 to 693 Ma, suggesting that the primary magma probably was derived from partial melting of a depleted lithospheric mantle, the mafic mineral fractional crystallization and crustal contamination occurred during the magma evolution. Combined with previous studies on the contemporaneous magma-tectonic activities in the Uliastai Continental Margin and XLMC, we suggest that the Houtoumiao pluton formed in a post-orogenic setting.
The lives lost and economic costs of viral zoonotic pandemics have steadily increased over the past century. Prominent policymakers have promoted plans that argue the best ways to address future pandemic catastrophes should entail, “detecting and containing emerging zoonotic threats.” In other words, we should take actions only after humans get sick. We sharply disagree. Humans have extensive contact with wildlife known to harbor vast numbers of viruses, many of which have not yet spilled into humans. We compute the annualized damages from emerging viral zoonoses. We explore three practical actions to minimize the impact of future pandemics: better surveillance of pathogen spillover and development of global databases of virus genomics and serology, better management of wildlife trade, and substantial reduction of deforestation. We find that these primary pandemic prevention actions cost less than 1/20th the value of lives lost each year to emerging viral zoonoses and have substantial cobenefits.
We conducted zircon U–Pb dating and geochemical analyses for the Qianjinchang (QJC) pluton in the Xi Ujimqi, Northeast China, with an aim to determine their ages, petrogenesis, and sources. The QJC pluton consists of coarse/medium‐grained biotite monzogranite in the core and fine‐grained biotite granodiorite in the rim; those rocks intrude into quartz diorite but are intruded by minor intrusive phases, including small biotite syenogranite, diorite bodies, late diorite, granodiorite, granite, and pegmatite dykes. Our new laser ablation inductively coupled plasma mass spectrometry zircon U–Pb data indicate that the QJC composite pluton composed of 2 phases of magmatic activities, with the ages of 301~313 Ma for the quartz diorite, 283 ± 1 Ma for the biotite granodiorite, 280 ± 1 Ma for the biotite syenogranite, and 280 ± 2 Ma for the diorite dyke. Hf isotopic analyses for the quartz diorite sample show ε Hf (t) = 3.75 to 11.72, with 2‐stage Hf model age ( T DM2 ) ranging 568–1,078 Ma. The biotite syenogranite sample also shows a depleted ε Hf (t) = 4.47 to 8.71, with T DM2 ranging 745–1,015 Ma, suggesting the major involvement of juvenile crustal components. The various ε Hf values of the QJC pluton indicate a hybrid magma source of juvenile material with old crustal component, and the T DM2 values increase from the Carboniferous to Permian, which suggests an increasing proportion of old continental material during this period. Petrological and geochemical characteristics of the biotite granodiorite and biotite monzogranite samples suggest that they are S‐type granites and derived from partial melting of the clay‐poor, plagioclase‐rich psammitic source, produced at low‐medium pressure. The biotite syenogranite sample belongs to alkaline and shoshonitic series and probably formed by a hybridization process between basaltic magma and old continental components. Combined with previous studies on the contemporaneous magma‐tectonic activities in the Xilinhot microcontinent, we suggest that the QJC pluton formed in a postcollisional setting.
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