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    U-Pb zircon geochronology, geochemistry and Nd isotopic study of Neoproterozoic bimodal volcanic rocks in the Kangdian Rift of South China implications for the initial rifting of Rodinia [查看] Xian-huaLi、Zheng-XiangLi、HanwenZhou、YingLiu、PeterD.Kinny
    SHRIMP U–Pb zircon age, geochemical and Nd isotopic data are reported for the Neoproterozoic Suxiong volcanic rocks in the Kangdian Rift, western South China. These volcanic rocks are bimodal, consisting mainly of mildly alkaline basalts and trachydacites to rhyolites. SHRIMP U–Pb zircon age determination indicates that they were erupted at 803±12 Ma. Most basaltic rocks are characterized by high positiveεNd(T) values (+5 to +6),pronounced enrichment in Th, Ta, Nb, LREEs, Sr, P, Zr, Hf, Ti, smooth LREE-enriched patterns and generally‘humped’ trace element spidergrams. They resemble the alkali basalts of the Hawaiian oceanic island basalts (OIB) and the Ethiopian continental flood basalts (CFB). These features suggest that the basaltic rocks were most probably derived from an OIB-like mantle source without appreciable crustal/lithospheric contamination. Differentiated basalt and trachyandesite samples show relatively lowεNd(T) values (+1.7 to +2.4) and Nb-Ta depletion due to contamination by the mafic lithosphere and/or crustal materials. The rhyolite and dacite samples have small positiveεNd(T) values (+1.1 to +2.6), general enrichment in most incompatible trace elements (K, Rb, Th, Zr, Hf and REEs) but significant depletion in Nb, Ta, Sr, P, Eu and Ti. They share geochemical characters of A2-type granites, and are likely generated by shallow (P≤4 kbar) dehydration melting of hornblende-bearing granitoids. Geochemical and Nd isotopic characters and high-volcanicity of the Suxiong bimodal volcanic successions are consistent with their formation in a continental rift environment, such as the Ethiopian rift. The Kangdian Rift is considered as part of a wider continental rift system produced by a starting mantle plume beneath South China during the Neoproterozoic breakup of Rodinia.
    Grenvillian continental collision in south China New SHRIMP U-Pb zircon results and implications for the configuration of Rodinia [查看] Zheng-XiangLi、Xian-huaLi、HanwenZhou、PeterD.Kinny
    The timing of continental collision between the Yangtze and Cathaysia blocks of south China is an issue that bears on the accretion of Asia, as well as on the assembly and configuration of the Neoproterozoic supercontinent Rodinia. We report in this paper SHRIMP (sensitive high-resolution ion microprobe) evidence that suggests a Grenvillian continental collision in south China, including (1) evidence for 1.3–1.0 Ga metamorphism on both sides of the Sibao orogen between the Yangtze and Cathaysia blocks and (2)sedimentary provenance of possible foreland-basin deposits on the Yangtze side of the orogen that were derived from the Cathaysia block and the Sibao orogen during the continental collision. The occurrence of ca. 1430 Ma granodiorites in southern Cathaysia, along with ca. 1800 Ma basement and Archean protoliths in northern Cathaysia, makes Cathaysia a possible western extension of the Mojave province in southwestern Laurentia.Together with regional data, we suggest that the Sibao orogen could be one of the Grenvillian sutures at the center of Rodinia assembly that brought Australia, Yangtze, and Cathaysia-Laurentia together by ca. 1000 Ma.
    U–Pb ages and Hf–O isotopes of zircons from Late Paleozoic mafic–ultramafic units in the southern Central Asian Orogenic Belt Tectonic implications and evidence for an Early-Permian mantle plume [查看] Ben-XunSu、Ke-ZhangQin、PatrickAsamoahSakyi、Xian-HuaLi、Yue-HengYang、HeSun、Dong-MeiTang、Ping-PingLiu、Qing-HuaXiao、SanjeewaP.K.Malaviarachchi
    U–Pb age and Hf–O isotope data of zircons fromthe mafic–ultramafic complexes and their related rhyolites and granites in the Eastern Tianshan and Beishan regions were obtained by SIMS and LA-ICPMS. The Hf–O isotopic composition and Hf model age of the zircons are closely related to their tectonic setting and formation age. The zircons from the mafic–ultramafic complexes in the Bogeda–Haerlike and Jueluotage belts have higher εHf(t)(+8–+17) and lower δ18O (+4‰–+6‰), whereas most of the zircons in the gabbros, granites and rhyolite from theMiddle TianshanMassif and Beishan Rift display lower εHf(t) (0–+8) and higher δ18O (+5‰–+8‰).The positive εHf(t) and relatively lower δ18O values suggest that thesemafic–ultramafic complexes were derived from depleted mantle which was subjected to subduction-related modification processes. The Hf isotopic composition of zircons in the granites has revealed that the growth of juvenile crust was also very significant in the southern margin of the Central Asian Orogenic Belt during the Paleozoic. The Hf model ages of the analyzed zircons, together with the regional geology suggest that the Beishan area had a northward subduction, possibly fromca. 900 Ma to ca. 400 Ma,whereas the Eastern Tianshan had a south-directed subductionmost likely fromca.600 Ma to ca. 310 Ma. Additionally, zircons with ca. 280 Ma U–Pb ages display wider and more scattered εHf(t) and δ18O variations than the relatively older and younger ones, which further support the Early Permian mantle plume model.
    Precisely dating Paleozoic kimberlites in the North China Craton and Hf isotopic constraints on the evolution of the subcontinental lithospheric mantle [查看] Qiu-LiLi、Fu-YuanWu、Xian-HuaLi、Zhi-LiQiu、YuLiu、Yue-HengYang、Guo-QiangTang
    Kimberlite, a deep-sourced ultramafic potassic rock, carries not only diamond, but also invaluable mantle xenoliths and/or xenocrysts,which are important for tracking the evolution of subcontinental lithosphericmantle(SCLM). However, it is challenging to accurately determine the emplacement age of kimberlite and its compositions of primary magma because of modifications by crustal and/or mantle contamination and postemplacement alteration. This paper reports emplacement ages of diamondiferous kimberlites in Mengyin and Fuxian of the North China Craton (NCC) using three different dating methods. For Mengyin kimberlite, singlegrain phlogopite Rb–Sr dating yields an isochron age of 485±4 Ma, U–Th–Pb analyses on perovskite give a 238U–206Pb age of 480.6±2.9 Ma and a 232Th–208Pb age of 478.9±3.9 Ma, and baddeleyite yields a 207Pb–206Pb age of 480.4±3.9 Ma. For Fuxian kimberlite, baddeleyite gives a 207Pb–206Pb age of 479.6±3.9 Ma, indicating that the Paleozoic kimberlites in the NCC were emplaced at ~480Ma. Numerous lines of evidence indicate that the studied baddeleyites are xenocrysts fromthe SCLM, and can be used to constrain Hf isotope compositions (εHf(t)~−6) of the SCLM when kimberlite erupted. Combined with data from Mesozoic–Cenozoic mantle-derived rocks and xenoliths, the Hf isotope evolution trend of the SCLM beneath NCC before craton destruction was tentatively constructed, which suggested that the Archean SLCM was enriched by metasomatism at ~1.3 Ga.Further Hf isotope investigations on additional SCLM-derived materials could be used to compare with the constructed Hf isotope evolution trend before craton destruction to determine when lithospheric thinning occurred.
    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.
    A Permian large igneous province in Tarim and Central Asian orogenic belt, NW China,Results of a ca.275 Ma mantle plume [查看] Chuan-LinZhang、Zheng-XiangLi、Xian-HuaLi、Yi-GangXu、GangZhou、Hai-MinYe
    New sensitive high-resolution ion microprobe(SHRIMP) U-Pb zircon ages, geochemical data, and a synthesis of existing stratigraphic, geochronologic, and geochemical results from the Tarim block and the Central Asian orogenic belt in northwestern China suggest the presence of a Per mian (ca. 275 Ma) large igneous province (the Bachu large igneous province). The large igneous province consists predominantly of coeval mafic rocks (basalts and mafic-ultramafic intrusions) having an aerial coverage of more than 600,000 km2, and its formation was accompanied by voluminous emplacement of A-type granites. This large igneous province,interpreted to be of mantle plume origin, is~15 m.y. older than the ca. 260 Ma Emeishan large igneous province in southwestern China and ~25 m.y. older than the 251 Ma Siberian Trap in Russia. Such a sudden fl air up of plume activity in the Permian may represent the early stage of the Pangean superplume event. The Permian plumes likely played a role in late Paleozoic rapid continental crustal growth in the Central Asian orogenic belt. In addition, there appear to be two types of mantle geochemical provinces (domains) in the region, a long-term enriched Tarim province and a subduction-metasomatized and depleted Central Asian orogenic belt province.
    Amalgamation between the Yangtze and Cathaysia Blocks in South ChinaConstraints from SHRIMP U-Pb zircon ages, geochemistry and Nd-Hf isotopes of the Shuangxiwu volcanic rocks [查看] Xian-HuaLi、Wu-XianLi、Zheng-XiangLi、Ching-HuaLo、JianWange、Mei-FangYe、Yue-HengYang
    South China was formed through the amalgamation of the Yangtze Block with the Cathaysia Block, but the timing of this amalgamation is controversial, ranging from Mesoproterozoic to Mesozoic. We report here SHRIMP U–Pb zircon ages, geochemistry and Nd–Hf isotopes of the Shuangxiwu Group volcanic rocks from the southeastern Yangtze Block. These rocks were strongly deformed, metamorphosed to greenschist-facies, intruded by 849±7Ma dolerites, and unconformably overlain by Neoproterozoic rift successions of no older than ca. 820 Ma. The Beiwu and Zhangcun volcanic rocks from the middle and uppermost Shuangxiwu Group were dated at 926±15Ma and 891±12 Ma, respectively. All the studied rocks are characterized by highly positive Nd(T) (5.4–8.7) and Hf(T) (11.0–15.3) values. The Pingshui basaltic and andesitic rocks from the lower Shuangxiwu Group, whichwere previously dated at ca. 970 Ma, are high in Al2O3 (15–20%) but low in MgO (<8%), and are characterized by enrichments in Th and LREE but depletions in Nb, Ta, Zr, Hf and Ti, broadly similar to high-Al basaltic rocks in many volcanic arcs. The Beiwu andesitic to rhyolitic rocks have higherMgOthan the experimental melts of basaltic rocks, and their Al2O3 content decreases with increasing SiO2, similar to the regional coeval tonalites and granodiorites,suggesting their formation by crystal fractionation of basaltic parent magma. The Zhangcun volcanic rocks are high in SiO2 (mostly >69%), low in MgO (0.35–1.2%), and have nearly constant Al2O3 contents of 14–15%and relatively uniform trace element concentrations. Theywere generatedby remelting of juvenile mafic to intermediate arc rocks. Overall, the Shuangxiwu Group volcanic rocks and associated intrusive tonalites and granodiorites constitute a typical calc-alkaline magmatic assemblage of a 970–890Maactive continental margin. These results and the 849±7Ma zircon U–Pb age for the undeformed doleritic dikes intruding the Shuangxiwu Group suggest that the tectonic regime of the study region transformed from plate convergence to intracontinental rifting in the time period between ca. 890Ma and ca. 850 Ma.Previously reported 1.04–0.94Ga metamorphic and deformation ages from the nearby Tianli Schists and evidence for the final closure of the back-arc basin at ca. 880Ma (ophilitic obduction at Xiwan), further suggest that the amalgamation between the Yangtze and Cathaysia Blocks, likely through “soft docking”at the eastern segment of the Sibao orogen, was completed at ca. 880Ma or soon after.
    SHRIMP zircon U–Pb geochronology, elemental, and Nd isotopic geochemistry of the Neoproterozoic mafic dykes in the Yanbian area, SW China [查看] Wei-GuangZhua、HongZhong、Xian-HuaLi、Hai-LinDeng、De-FengHe、Kong-WenWu、Zhong-JieBai
    Sensitive High-Resolution Ion Microprobe (SHRIMP) U–Pb zircon ages, geochemical and Nd isotopic data are reported for two groups of Neoproterozoic mafic dykes in the Yanbian area of Sichuan Province, SW China. The Group 1 and Group 2 dykes were dated at 792±13Ma and 761±14 Ma, respectively. While Group 1 and Group 2 rocks are commonly high in Fe2O3 and TiO2 contents with similar MgO contents and Mg numbers, they exhibit distinct trace element features. Group 1 rocks with high εNd(T) values (+5.8 to +7.2) and total rare earth element (REE) contents (109–171 ppm), are characterized by LREE-enriched and “humped” trace-element patterns with slightly negative Nb–Ta anomaly, similar to typical alkaline basalts associated with continental rifts.Group 2 rocks have relatively lowtotal REE contents (50.4–103 ppm) with relatively flat REE patterns and can be further divided into two sub-types. Group 2a rocks showMORB-like trace element patterns depleted in highly incompatible elements such as Th, Nb, Ta, La and Ce, whereas the Group 2b rocks exhibit flatter REE patterns than those of the Group 2a. The εNd(T) values of the Group 2a and Group 2b rocks are +5.4 to +7.2 and +4.5 to +5.3, respectively.The Group 1 and Group 2 dykes display different magma crystallization trends. Group 1 rocks were crystallized from a high-Ti alkaline basaltic magma that was generated by low degrees of partial melting of OIB-like mantle source in the garnet-bearing field. In contrast, the parental magma of Group 2 rocks is similar to those parental to low-Ti tholeiitic basaltic melt generated by relatively higher degrees of partial melting of the asthenospheric mantle source in the spinel-stable field. Group 1 and Group 2a rocks show the intraplate basalts affinity. It is therefore suggested that they originated from an intra-continental rift regime, which was likely related to a mantle plume underneath the supercontinent Rodinia.
    SHRIMP zircon U-Pb geochronological and whole-rock geochemical evidence for an early Neoproterozoic Sibaoan magmatic arc along the southeastern margin of the Yangtze Block [查看] Mei-FangYe、Xian-HuaLi、Wu-XianLi、YingLiu、Zheng-XiangLi
    It has been generally accepted that the South China Block was formed through amalgamation of the Yangtze and Cathaysia Blocks during the Proterozoic Sibaoan orogenesis, but the timing and kinematics of the Sibao orogeny are still not well constrained. We report here SHRIMP U–Pb zircon geochronological and geochemical data for the Taohong and Xiqiu tonalite–granodiorite stocks from northeastern Zhejiang, southeastern margin of the Yangtze Block. Our data demonstrate that these rocks, dated at 913±15 Ma and 905±14 Ma, are typical amphibole-rich calcalkaline granitoids formed in an active continental margin. Combined with previously reported isotopic dates for the ∼1.0 Ga ophiolites and ∼0.97 Ga adakitic rocks from northeastern Jiangxi, the timing of the Sibao orogenesis is thus believed to be between ∼1.0 and ∼0.9 Ga in its eastern segment. It is noted that the Sibao orogeny in South China is in general contemporaneous with some other early Neoproterozoic (1.0–0.9 Ga) orogenic belts such as the Eastern Ghats Belt of India and the Rayner Province in East Antarctica, indicating that the assembly of Rodinia was not finally completed until ∼0.9 Ga.
    Early history of the eastern Sibao Orogen (South China) during the assembly of Rodinia New mica 40Ar39Ar dating andSHRIMP U–Pb detrital zircon provenance constraints [查看] Zheng-XiangLi、Jo-AnneWartho、SandraOcchipinti、Chuan-LinZhang、Xian-HuaLi、JianWang、ChaominBao
    The Sibao Orogen in South China is one of the poorest known Grenville-aged orogenic belts through which the Neoproterozoic supercontinent Rodinia assembled. We report here the first UV laser spot 40Ar/39Ar mica and SHRIMP U–Pb zircon ages from a rare Grenville-aged metamorphic complex, the Tianli Schists, in the eastern Sibao Orogen. Our U–Pb zircon provenance ages indicate that the protolith of the Tianli Schists was a clastic sedimentary succession most likely derived from the Yangtze Block.The depositional age of the protolith is younger than 1530 Ma, as constrained by the youngest detrital zircon grains, but is older than 1040 Ma as constrained by the oldest 40Ar/39Ar muscovite ages. The Yangtze Block provenance for the Tianli Schists suggests that the Sibaoan ophiolitic complexes in northeastern Jiangxi, the ca. 970 Ma Xiwan adakitic granite intrusions, and the ca. 900 Ma(?) Xiwan blueschists, all to the northwest of the study region, were likely formed during the closure of a back-arc basin along the margin of the Yangtze Block. Our in situ UV laser 40Ar/39Ar results from S1 and S2 muscovites suggest that the Tianli Schists underwent metamorphism and deformation at 1042±7Ma to 1015±4 Ma, the oldest known metamorphic event in the easternSibao Orogen. Muscovite/biotite cooling ages of ca. 968±4 and 942±8Ma are recorded by deformed and recrystallised muscovite and biotite, respectively, indicating tectonic reactivation before 900 Ma, during the later stages of the Sibao Orogeny. Together with previous results from the western Sibao Orogen, our work suggests that the closure of the ocean between the Yangtze and Cathaysia Blocks during the assembly of Rodinia was diachronous: ≥1000 Ma at the western Sibao Orogen and ca. 900 Ma at the eastern Sibao Orogen.
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