国家科技基础条件平台
  • 你好,请
  • 登录
    • logotext
    Geochemical and Hf–Nd isotope data of Nanhua rift sedimentary and volcaniclastic rocks indicate a Neoproterozoic continental flood basalt provenance [查看] Xuan-CeWang、Zheng-XiangLi、Xian-HuaLi、Qiu-LiLi、Qi-RuiZhang
    Geochemical and Hf–Nd isotope studies of Neoproterozoic sedimentary and volcaniclastic rocks in the Nanhua Rift Basin, South China, demonstrate that their source provenances contained large proportions of mafic rocks and various amounts of granites. A significant proportion of the studied Neoproterozoic rift sedimentary and volcaniclastic rocks have initial εNd(t) values higher than those of Neoproterozoic granites, but fall within the range of ca. 825–750 Ma basaltic rocks. Their initial εNd(t) values correlate with ratios of La/Sc, La/Cr, La/V, La/Co and La/Ni. The Nd isotope and trace element data, in combination with existing in-situ U–Pb and hafnium–oxygen isotope data fromthe detrital zircon grains indicate a dominant ca. 825–800 Mamafic provenance. Furthermore,the studied samples formed a linear array and plot within the field defined by the remanent of ca. 825–810 Ma continental flood basalts in the Hf–Nd isotopic space. Thus, the inferred large proportions of mafic rocks in the source provenance of the Neoproterozoic rift sedimentary and volcaniclastic rocks likely signify an eroded continental flood basalt province, similar to that reported for the Neoproterozoic sedimentary rocks in Australia. This work thus provides further evidence for the possible once existence of a common large igneous province between South China and eastern Australia as adjacent parts of the supercontinent Rodinia.
    Geochemical and geochronological study of early Carboniferous volcanic rocks from the West Junggar Petrogenesis and tectonic implications [查看] HongyanGeng、MinSun、ChaoYuan、GuochunZhao、WenjiaoXiao
    A series of early Carboniferous volcanic rocks, i.e., basalt, andesite, and dacite, occur in the West Junggar.Zircon U–Pb isotopic data indicate that these rocks coevally erupted at 331–344 Ma. These volcanic rocks have comparable trace element patterns, characterized by the enrichment of large ion lithophile elements (LILE) and the depletion of high field strength elements (HFSE). Isotopically, they display consistently depleted Sr–Nd isotopic compositions (initial 87Sr/86Sr ratios = 0.7034–0.7054, eNd(t) = 4.2–7.7).These rocks are interpreted to be derived from a slightly metasomatized depleted mantle in a normal subduction environment. In the context of a previously proposed ridge subduction model, this study constrains that ridge subduction, if it indeed occurred, commenced between 331 and 310 Ma in the central West Junggar.
    Eclogite origin and timings in the North Qinling terrane,and their bearing on the amalgamation of the South and North China Blocks [查看] H.WANG、Y.-B.WU、S.GAO、X.-C.LIU、H.-J.GONG、Q.-L.LI、X.-H.LI、H.-L.YUAN
    The amalgamation of South (SCB) and North China Blocks (NCB) along the Qinling-Dabie orogenic belt involved several stages of high pressure (HP)-ultra high pressure (UHP) metamorphism. The new discovery of UHP metamorphic rocks in the North Qinling (NQ) terrane can provide valuable information on this process. However, no precise age for the UHP metamorphism in the NQ terrane has been documented yet, and thus hinders deciphering of the evolution of the whole Qinling-Dabie-Sulu orogenic belt. This article reports an integrated study of U–Pb age, trace element, mineral inclusion and Hf isotope composition of zircon from an eclogite, a quartz vein and a schist in the NQ terrane. The zircon cores in the eclogite are characterized by oscillatory zoning or weak zoning, high Th ⁄U and 176Lu ⁄ 177Hf ratios, pronounced Eu anomalies and steep heavy rare earth element (HREE) patterns. The zircon cores yield an age of 796 ± 13 Ma, which is taken as the protolith formation age of the eclogite,and implies that the NQ terrane may belong to the SCB before it collided with the NCB. The eHf(t) values vary from )11.3 to 3.2 and corresponding two-stage Hf model ages are 2402 to 1495 Ma,suggesting the protolith was derived from an enriched mantle. In contrast, the metamorphic zircon rims show no zoning or weak zoning, very low Th ⁄U and 176Lu ⁄ 177Hf ratios, insignificant Eu anomalies and flat HREE patterns. They contain inclusions of garnet, omphacite and phengite, suggesting that the metamorphic zircon formed under eclogite facies metamorphic conditions, and their weighted mean 206Pb ⁄ 238U age of 485.9 ± 3.8 Ma was interpreted to date the timing of the eclogite facies metamorphism. Zircon in the quartz vein is characterized by perfect euhedral habit, some oscillatory zoning, low Th ⁄U ratios and variable HREE contents. It yields a weighted mean U–Pb age of 480.5 ± 2.5 Ma, which registers the age of fluid activity during exhumation. Zircon in the schist is mostly detrital and U–Pb age peaks at c. 1950 to 1850, 1800 to 1600, 1560 to 1460 and 1400 to 1260 Ma with an oldest grain of 2517 Ma, also suggesting that the NQ terrane may have an affinity to the SCB.Accordingly, the amalgamation between the SCB and the NCB is a multistage process that spans c. 300 Myr, which includes: the formation of the Erlangping intra-oceanic arc zone onto the NCB before c. 490 Ma, the c. 485 Ma crustal subduction and UHP metamorphism of the NQ terrane, the c. 430 Ma arc-continent collision and granulite facies metamorphism, the 420 to 400 Ma extension and rifting in relation to the opening of the Palaeo-Tethyan ocean, the c. 310 Ma HP eclogite facies metamorphism of oceanic crust and associated continental basement, and the final 250 to 220 Ma continental subduction and HP–UHP metamorphism.
    Early Cretaceous volcanism in the northern Songliao Basin, NE China, and its geodynamic implication [查看] F.Q.Zhang、H.L.Chen、X.Yua、C.W.Dong、S.F.Yang、Y.M.Pang、G.E.Batt
    The Songliao Basin is characterized by episodic rifting and intense volcanism during its early development,and forms a key concealed part of the Late Mesozoic magmatic province of NE China. Few precise geochronological and geochemical data were previously available for the volcanic elements of this basin,restricting understanding of its geodynamic setting and evolution. We present new SHRIMP U–Pb zircon ages and geochemical data for the volcanic rocks from the northern Songliao Basin, which limit this volcanism to the Early Cretaceous period (115–109 Ma). Although dominated by rhyolite, the rocks cover a wide compositional spectrum encompassing trachyandesite, basaltic trachyandesite, trachyte and dacite.This suite exhibits a range of geochemical signatures characteristic of subduction-related genesis, falling into a high-K calc-alkaline series, with enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), and weak depletion in high field strength elements (HFSE) and heavy rare earth elements (HREE). The suite also shares a common isotopic composition, consistent with derivation from partial melting of a single depleted mantle source. This Early Cretaceous volcanism occurred in an extensional backarc setting associated with the subduction of the Paleo-Pacific plate, large scale upwelling of the asthenosphere, and intensive lithospheric thinning of the eastern continental margin of NE China which may have lasted until ca. 109 Ma.
    Early Cretaceous stratigraphy and SHRIMP U-Pb age constrain the Valanginian-Hauterivian boundary in southern Tibet [查看] XIAOQIAOWAN、ROBERTSCOTT、WENCHEN、LIANFENGGAOANDYIYIZHANG
    The Late Jurassic to the Early Cretaceous marine strata are extensively distributed in southern Tibet. In Gyangze, the strata are divided into the Weimei and Jiabula formations.In Nagarze, they are divided into the Weimei and Sangxiu formations. Previous work has reported diverse ammonite species of Haplophylloceras and Himalayites in the Weimei Formation, and a few species of Spiticeras in the lower Jiabula and Sangxiu formations.The present study has found the bivalve Inoceramus and nannofossil assemblages in the lower Jiabula and Sangxiu formations. The nannofossil assemblage of Nannoconus steimannii steinmannii, N. steinmannii minor and Watznaueria barnesae indicates Berriasian age, and the Calcicalathina oblongata–Speetonia colligata assemblage is Valanginian in age. Numerical ages for the Jiabula and Jiabula-goukou sections in Gyangze have been interpolated by comparing the fossil ranges with ages calibrated in other sections. The correlation experiment plots fossil ranges in the two sections to the CRET1 Database. The estimated rate of sediment accumulation of the lower Sangxiu Formation is 22.6 m⁄ myr. The Jurassic–Cretaceous (J/K) boundary is at the bottom of the Jiabula Formation in Gyangze, and the base of the Sangxiu Formation in Nagarze.The boundary is marked by the appearance of the ammonite Spiticeras and the nannofossil assemblage of Nannoconus st. steinmannii–N. st. minor–Watznaueria barnesae. The radiometric age in Tibet is the first to be integrated with upper Valanginian fossils. The volcanic rocks of the upper Sangxiu Formation are dated at 136 ± 3.0 Ma deduced from zircon SHRIMP age of rhyolite. By consideration of the rate of sediment accumulation of the underlying sedimentary deposits, the J/K boundary in the Gyangze–Nagarze area is approximately 145 Ma as suggested by the newly issued International Stratigraphic Chart, and the Valanginian ⁄Hauterivian boundary lies between 134 Ma and 136 Ma.
    Detrital Zircon Dating of Meso-and Neoproterozoic Rocks in North China and Its Implications [查看] GAOLinzhi、LIUPengju、YINChongyu、ZHANGChuanheng、DINGXiaozhong、LIUYanxue、SONGBiao
    New dates from Meso-and Neoproterozoic strata contribute to the recently defined Orecambrian stratigraphical timescale of China agreed by the Subcommission on the Precambrian System,and the National Commission on Stratigraphy of CHina on Nov.24,2009.First,the age range of the Chingcheng System,including the Changzhougou,Chuanlinggou,Tuanshanzi and Dahongyu formations has been constrained to 1.8-1.6Ga.second,the Jinxian System including the Gaoyuzhuang,Yangzhuang,Wumishan,HOngshuizhuang and Tieling formations has been constrained to 1.6-1.4Ga.Third,an as-yet unnamed(undefined)system(1.4-1.0Ga)is only developed in the Xiamaling Formation at JIxian section,Tianjing.OFrth,the Qingbaikou System,including the Luotuoling and jing'eryu formationshas been constrained to 1.0-0.78Ga.Fifth,the Nanhuan System ranges betwwen 780-635Ma，and the Sinian System is within 635-542Ma,However,according to a series of SHRIMP U-Pb dates from the late Precambrian in the JIangnan Orogen Belt in South China Platform,the constrained strata will be redefined as in the upper part of the Qingkaikou SYstem.To aid global geodynamics,it is useful to denote a late Precambrain section with unified,precise and high-precision chronological dating;this is here defined in North China Block and Jiaoliao-Korean Block. However,the Neoproterozoic Qingkaikou study in North China will be influence in whole Meso-and Neoproterozoic in the Jiangnan Orogenic Belt in betwwen the Yangtze Block and the Cathaysia Block in South China.
    Age, geochemistry and tectonic setting of the Neoproterozoic (ca 830 Ma) gabbros on the southern margin of the North China Craton [查看] Xiao-LeiWan、Shao-YongJiang、Bao-ZhangDai、W.L.Griffin、Meng-NingDai、Yue-HengYang
    Many studies have addressed the Paleozoic to Triassic collisional processes along the southern margins of the North China Craton (NCC), but little is known about the evolution of this margin during Precambrian time. This paper examines the geochronology and geochemistry of gabbros from the Luanchuan Group,which is located on the southern margin of the NCC. These gabbros are dated at ca 830 Ma by SHRIMP and LA–ICP-MS zircon U–Pb methods. They are characterized by high contents of TiO2 (2.21–4.45 wt%) and light-REEs (rare earth elements) ((La/Yb)N = 9.54–7.71). The gabbros have overall OIB (ocean island basalts)-like trace element patterns, without the positive Pb and Sr anomalies and negative Nb–Ta anomalies. In addition, they have low La/Nb (<1.5) and La/Ta (<30) ratios, indicating an origin in the asthenospheric mantle. The depletions of HFSEs (high field strength elements) (e.g. Zr–Hf and Ti) probably suggest that their source has been metasomatized by carbonates. The gabbros show negative εNd(t)(−1.5 to −3.0), suggesting crustal contamination or mixing with metasomatized lithospheric mantle. However, the low Th and U contents, constant incompatible-element ratios (e.g. Zr/Nb, La/Nb, La/Sm) and the absences of correlations of εNd(t) with MgO, Nb/Nb*, SiO2 or 1/Nd preclude significant crustal contamination. Alternatively, the wide range of Hf–isotope ratios in zircons (εHf(t) from −3.6 to +6.3) may imply the interaction between asthenosphere-derived melts and the metasomatized lithospheric mantle. Petrological modeling suggests that the gabbros may have been generated from the low-degree(2–3%) partial melting of lherzolite with 2% garnet at depths greater than 85 km. The gabbros may have been generated in a within-plate rift setting. The gabbros may best be correlated with the Neoproterozoic magmatic rocks in the NQB (North Qinling Belt), representing the relicts onto the southern margin of the NCC following the Neoproterozoic rifting between the NCC and the NQB. Therefore, the NCC and NQB may have been connected at ca 830 Ma. Moreover, the occurrence of the gabbros implies that the present southern margin of the NCC may have been mixed with late Mesoproterozoic to Neoproterozoic crustal materials from the NQB. The new findings imply that the southern margin of the NCC has been the locus of at least three extension-convergence cycles, and the reactivation of such tectonic margins may be more common in the geological record than previously recognized.
    Petrogenesis of late Triassic post-collisional basaltic rocks of the Lancangjiang tectonic zone, southwest China, and tectonic implications for the evolution of the eastern Paleotethys Geochronological and geochemical [查看] YuejunWang、AimeiZhang、WeimingFan、ToupingPeng、FeifeiZhang、YanhuaZhang、XiawuBi
    The Xiaodingxi and Manghuihe volcanic sequences represent key components of the Lancangjiang igneous zone in southwest China. Their petrogenesis provides important constraints on the tectonic evolution of the eastern Paleotethys ocean. The basaltic rocks from the Xiaodingxi and Manghuihe sequences yield SHRIMP zircon U–Pb weighted mean ages of 214±7 Ma and 210±22 Ma, respectively, which is 15–20 Ma younger than the ages of the syn-collisional granite magmatism (230–241 Ma). Samples from the volcanic sequences are dominated by alkaline basalts and basaltic andesites, and can be geochemically classified into two groups. Group 1 samples, mainly from the Xiaodingxi sequence and the lower part of the Manghuihe sequence, are characterized by low MgO(1.49–7.50 wt.%) and Zr/Nb (9.4–15.3), and high Al2O3 (15.95–18.39 wt.%). They are enriched in LILE and LREE contents and depleted in HFSE, and have 87Sr/86Sr(t) ratios of 0.705473–0.706972,εNd(t) of −1.47–0.75, and similar Pb isotopic compositions to the global average composition of pelagic sediments. In contrast, Group 2 samples from the middle–upper parts of the Manghuihe sequence have similar Al2O3 (16.62–18.23 wt.%) but higher MgO (8.08–11.74 wt.%) and Zr/Nb (15.9–23.9) than those of Group 1 samples. They exhibit relatively flat REE patterns, significantly negative Nb–Ta and Th–U anomalies and positive Sr anomalies. In comparison with Group 1, Group 2 samples show higher Cr, Ni contents and εNd(t) values (1.17–5.02), and lower 87Sr/86Sr(t) and Pb isotopic ratios (Δ8/4=43.2–59.8 andΔ7/4=11.8–19.8). The geochemical data suggest that Group 1 samples might be the differentiated product of primitive high MgO and low Al2O3 melts originating from a refractory modified mantle with the involvement of 5–10% recycled pelagic sediments. The parental magma for Group 2 samples may have been derived from a plagioclase-rich,garnet-free source comprising 80–85% fluid-metasomatized and 15–20% asthenospheric components. Based on all available data, a tectonic model involving eastward subduction in the Permian and collision in the Triassic can be proposed for the evolution of the eastern Paleotethys ocean. During the late Triassic, the progressive upwelling of the asthenospheric mantle, shortly after slab detachment, may have led to the melting of the metasomatized mantle wedge, resulting in the post-collisional Group 1 and Group 2 magmas.
    Zircon U-Pb geochronology, Hf isotopic composition and geological implications of the rhyodacite and rhyodacitic porphyry in the xiangshan uranium ore field,jiangxi province,China [查看] YANGShuiYuan、JIANGShaoYong、JIANGYaoHui、ZHAOKuiDong、FANHongHai
    The Xiangshan uranium ore field is the largest volcanic rock hosted uranium deposit in China. The host rock is a volcanic intrusive complex, including rhyodacite, porphyroclastic lava and late stage sub-volcanic rocks. In this study, zircons from an early stage rhyodacite and a late stage rhyodacite porphyry were dated by SHRIMP and LA-ICP-MS U-Pb methods, and their Hf isotopic compositions were measured by LA-MC-ICP-MS. 206Pb/238U ages of 135.1±1.7 and 134.8±1.1 Ma were obtained for the rhyodacite and rhyodacitic porphyry, respectively. These accurate ages indicate that the Xiangshan volcanic-intrusive complex formed in the Early Cretaceous rather than in the Late Jurassic, as concluded in some previous studies. By the Early Cretaceous, the tectonic setting of the area has evolved into a back-arc extensional setting, possibly related to subduction of the paleo-Pacific plate. The close ages of the (early) eruptive rhyodacite and the (late) hypabyssal rhyodacitic porphyry shows that the Xiangshan volcanism was intensive and concentrated in a short time. Zircons from the rhyodacite show negative εHf(t) values of –5.7 to –8.5, with Hf depleted mantle model ages between 1550 and 1720 Ma, whereas zircons from the rhyodacitic porphyry yield εHf(t) values of –6.9 to –10.1 and Hf model ages between 1621 and 1823 Ma. These zircon Hf model ages are similar to the whole rock Nd model ages (1486 to 1911 Ma). Combined with other geochemical characteristics, the Xiangshan rhyodacite and rhyodacitic porphyry may have been derived from partial melting of the Paleo-Mesoproterozoic metamorphic rocks from the Xiangshan basement, without any significant addition of mantle-derived magma. Contribution of basement of this age is also supported by finding a Paleoproterozoic xenocrystic zircon core in the rhyodacite sample
    Zircon SHRIMP U-Pb dating for gabbro at Chaotiehe in the Haicheng area- eastern Liaoning [查看] MIAOLaiCheng、ZHANGFuQin、LIUDunYi、SHIYuRuo、XIEHangQiang
    Chaotiehe gabbroic intrusion in the eastern part of Liaoning Province was dated by the zircon SHRIMP U-Pb technique. The results gave an emplacement age of 126±4 Ma, indicating that the intrusion thus formed during the lithospheric thinning of the North China Craton (NCC) in the Early Cretaceous rather than in a rifting setting during the Paleoproterozoic as previously thought. The gabbroic intrusion contains abundant old zircons with Paleoproterozoic (2.10–2.46 Ga and ca. 1.87 Ga) and Neoproterozoic(747–969 Ma) ages. The Paleoproterozoic zircons were probably derived from NCC itself, whereas the Neoproterozoic ones were likely from materials of the Yangtze Craton that had previously been subducted beneath NCC. These geochronological dates are of important implications for understanding the Mesozoic crustal evolution of NCC.
    © BJSHRIMP 2013 - bjshrimp.cn