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The Dabie Orogen as the early Jurassic sedimentray provenanceConstraints from the detrital zircon SHRIMP U-Pb dating [查看] LIRenwei、WANYusheng、CHENGZhenyu、ZHOUJianxiong、XUYunhua、LIZhong、JIANGMaosheng

Abstract The SHRIMP U-Pb ages of detrital zircon from the oldest Mesozoic strata, the Fanghushan Fomation, in the Hefei Basin range from 200 Ma to ca. 2500 Ma, which indicates that the Dabie Orogen as the early Jurassic sedimentary provenance was complex. The composition of the Dabie Orogen includes: the Triassic high pressure-ultrahigh pressure metamorphic rocks, of which the detrital zircon ages are from 234 Ma to 200 Ma; the rocks possibly related to the Qinling and Erlangping Groups representing the southern margin of the Sino-Korean craton in the Qinling and Dabie area, of which the detrital zircon has an age of 481±378 Ma; the Neoproterozoic rocks originated from the Yangtze croton, of which the detrital zircon ages are 799±721 Ma old; and the rocks with the detrital zircon ages of ca. 2000 Ma and ca. 2500 Ma, which could be the old basement of the Yangtze craton.

Sm-Nd and zircon SHRIMP U-Pb dating of Huilanshan mafic granulite in the Dabie Mountains and its zircon trace element geochemistry [查看] HOUZhenhui、LIShuguang、CHENNengsong、LIQiuli、LIUXiaoming

Abstract The mafic granulites from Huilanshan are outcropped on the center of the Luotian dome in the northern Dabie Mountains. The Sm-Nd isochron defined by granulite-facies metamorphic minerals (garnet + clinopyroxene + hypersthene) yields an age of 136 ± 18 Ma indicating the early Cretaceous granulite-facies metamorphism. The cathodoluminescence (CL) images of zircons from the granulite show clearly core-mantle-rim structures. The zircon cores are characterized by typical oscillatory zoning and highly HREE enriched patterns, which suggests their magma origin. Some zircon cores among them with little Pb loss give SHRIMP U-Pb ages ranging from 753 to 780 Ma, which suggests that the protolith of Huilanshan granulite is Neoproterozoic mafic rocks. The zircon mantles usually cut across the oscillatory zone of the zircon cores have 3―10 times lower REE, Th, U, Y, Nb and Ta contents than the igneous zircon cores but have high common Pb contents. These characteristics suggest that they were formed by hydrothermal alteration of the igneous zircons. The part of zircon mantles with little Pb loss give a similar SHRIMP U-Pb age (716―780 Ma) to the igneous zircon cores, which implies that the hydrothermal events occurred closely to the magmatic emplacement. In view of the strong early Cretaceous magmatism in the Luotian dome, consequently, the Huilanshan mafic granulite was formed by heating of the Neoproterozoic mafic rocks in mid-low crust, which caused the granulite-facies metamorphism underneath the Dabie Mountains. The similarity between the granulite metamorphic age (136 ± 18 Ma defined by Sm-Nd isochron and K-Ar age of 123―127 Ma given by amphible from the gneiss in Luotian dome suggests a rapid uplifting of the Luotian dome,which may result in further exhumation of the ultrahigh pressure metamorphic rocks in the Dabie Mountains.

Silurian A-type granitoids in the southern margin of the Tongbai-DabieshanEvidence from SHRIMP zircon geochronology and geochemistry [查看] MAChangqian、SHEZhenbing、XUPin、WANGLingyan

Abstract SHRIMP U-Pb dating on magmatic zircons extracted from a riebeckite quartz syenite in the Huangyangshan pluton in Suizhou, the southern margin of Tongbai-Dabieshan yielded an age of 439±6Ma. According to the morphology and high Th/U ratios of the zircons, the age is interpreted as crystallization timing of the pluton. The Huangyangshan pluton is composed of peralkaline quartz syenite, alkaline granite and syenite. All of the rocks are characterized by high agpaitic index (A.I.=(Na+K)/Al, molar ratio) and Fe-number [FeOT/(FeOT+MgO)], low CaO and MgO contents, enrichment of high field strength elements (i.e. Nb, Zr, Ga, Y, Hf) and light REEs,evidently negative Eu anomalies and high Ga/Al ratios, which are consistent with anorogenic A-type granitoids. Being part of the South Qinling-South Dabieshan Paleozoic alkaline rock belt,the Huangyangshan A-type granitoid pluton results from the Paleozoic extension-initial rifting in the northern margin of the Yangtze Craton related to the opening of the eastern Paleo-Tethyan Ocean.

SHRIMP Zircon U-Pb Dating of the Tongshi Magmatic Comlex in Western Shandong and Its Geological Implications [查看] HUHuabin、MAOJingwen、LIUDunyi、NIUShuyin、WANGYanbin、LIYongfeng、SHIRuruo

Abstract The SHRIMP U-Pb zircon dating result of the Tongshi magmatic complex in western Shandong is presented in this paper. The Tongshi magmatic complex comprises fine-grained porphyritic diorite and syenitic porphyry. Eighteen analyses for fine-grained porphyritic diorite gave two concordia ages, in which ten analyses constitute the young age group,giving 206Pb/238U ages ranging from 167.9 Ma to 183 Ma with a weighted mean age of 175.7 ± 3.8 Ma, and the other eight yielded 207Pb/206Pb ages of 2502 Ma to 2554 Ma with a weighted mean 2518 ± 11 Ma. Two analyses for syenitic porphyry gave ages of 2485 Ma and 2512 Ma, respectively. The age of 175.7 ± 3.8 Ma indicates that the crystallization of the Tongshi magmatic complex occurred in the Middle Jurassic, whereas that of 2518 ± 11 Ma is interpreted as the age of inherited magmatic zircons in the Neoarchean Wutai period.

SHRIMP U-Pb zircon dating for the dacite of the Sangxiu Formatin in the central segment of Tethyan Himalaya and its implications [查看] ZHUDicheng、PANGuitang、MOXuanxue、WANGLiquan、LIAOZhongli、JIANGXinsheng、GENGQuanru

Abstract Petrology and SHRIMP U-Pb zircon chronology are reported for the dacite of the Sangxiu Formation in the central segment of Tethyan Himalaya to the southeast of Yangzuoyong Co. Twenty-one measured zircon grains from a dacite sample of the Sangxiu Formation can be divided into two groups, which include long columnar magmatic zircons of 133±3.0 Ma, representing the age of volcanism in the Sangxiu Formation, and inherited zircons consisting of core and overgrowth rim, in which ages of the three cores are 2244±16,1153±33 and 492±25 Ma respectively; and the age of one overgrowth rim is 132.7±5.2 Ma. These ages are considered to represent the remelting of accretionary crust at different periods resulting from the volcanism of Sangxiu Formation. These volcanic rocks in the Sangxiu Formation,for which age is close to that of Bunbury basalt in southwestern margin of Australia, and older than that of Rajmahal basalt in northeastern India, maybe considered as the products of early activity of the hotspot represented by the Rajmahal basalt.

SHRIMP U-Pb zircon dating for Qiashikansayi granodiorite,the Northern Altyn Tagh Mountains and its geological implications [查看] QIXuexiang、LIHaibing、WUCailai、YANGJingsui、ZHANGJianxin、MENGFancong、SHIRendeng、CHENSongyong

Abstract The Qiashikansayi granodiorite is foliated resulting in a granodioritic gneiss. Its geochemical features,such as alumina saturation index(A/CNK) of 0.81—0.99,Na2O/K2O values>1, TiO2 contents <1.0%, LREE enrichment with high fractionation factors, weakly negative or no Eu anomalies, and significant Ba and Ti negative anomalies,suggest that it is similar to a typical island arc pluton. The trace elements of the Qiashikansayi granodiorite are plotted in the island arc field in the tectonic setting discrimination diagrams as well. Cathodoluminescence images demonstrated that the zircons have clear rhythmic crystallized zoning, without any remnant core and new crystallized rim,suggesting the zircons be magmatic ones. Their U and Th contents vary in the range of 574—870 μg/g, and 279—556 μg/g respectively, with the Th/U ratio in the range of 0.52—0.68. SHRIMP zircon U-Pb dating yielded the 481.5±5.3 Ma age for the intrusion of the granodiorite, which is coeval with the island arc volcanic rocks in the northern Qilian Mountain, and confirms that there is an early Paleozoic island arc in the Hongliugou- Lapeiquan area.

SHRIMP U-Pb zircon Geochronology of the Xiaotongguanshan and Shatanjiao Intrusions and Its Petrological Implications in the Tongling Aear,Anhui [查看] DIYongjun、WUGanguo、ZHANGDa、SONGBiao、ZANGWenshuan、ZHANGZhongyi、LIJinwen

Abstract This paper determines the crystallization ages of the Xiaotongguanshan quartz monzodiorite and Shatanjiao quartz monzonite porphyry from the Tongling area using the SHRIMP zircon U-Pb method. The crystallization age of the former is 142.8±1.8 Ma; that of the latter is 151.8±2.6 Ma. These data indicate that they were formed during the Late Jurassic (142.8 to 151.8 Ma). Zoned magma chamber was formed because of double diffusive convection. Therefore, the intrusive sequence of magma is generally from quartz monzonite through quartz monzodiorite to pyroxene monzodiorite, i.e. an inverted sequence.

Petrogenesis and dating of the Kangding complex,Sichuan Province [查看] CHENYuelong、LUOZhaohua、ZHAOJunxiang、LIZhihong、ZHANGHongfei、SONGBiao

Abstract An analysis of major and trace element geochemistry and SHRIMP U-Pb zircon dating of mafic, intermediate, and felsic rocks from the Mianning metamorphic complex of Sichuan Province was conducted. One of our conclusions is that a majority of the zircons crystallized between 721 and 773 Ma in a magmatic regime. The complexes contain early to late Paleo- proterozoic relict zircons from ancient continental crust. The oldest age, 2468 Ma, may represent the basement of the Yangtze block. Overgrowth zircon rims and palingenetic zircons have been observed and dated, and are believed to have formed after crystallization, during Paleozoic and Mesozoic metamorphic-anatexis. We also conclude that depletion of Nb, Ta, HREE, in a spider-diagram normalized to primitive mantle and calc-alkaline association, implies that they formed in island-arc or under-plating settings.

Opening of the Tethys in southwest China and its significance to the breakup of East Gondwanalang in late PaleozoicEvidence from SHRIMP U-Pb zircon analyses for the Garze ophiolite block [查看] YANQuanren、WANGZongqi、LIUShuwen、LIQiugen、ZHANGHongyuan、WANGTao、LIUDunyi、SHIYuruo、JIANPing、WANGJianguo、ZHANGDehui、ZHAOJian

Abstract SHRIMP U-Pb zircon analyses for a gabbro sample from the Garzê ophiolite block yielded a mean 206Pb/238U age of 292±4 Ma, which indicated that the spreading time of the Garzê-Litang Tethys was most likely at the earliest Permian. Combined with previous studies, we suggest that the opening of the Tethys in southwest China was derived from breakup of the East Gondwanaland in the late Paleozoic.

Mineral inclusions in zircon domains and geological significance of SHRIMP U-Pb dating for coesite-bearing zircons of paragniess in Sulu terrane,eastern China [查看] LIUFulai、YANGJingsui、XUZhiqin

Abstract Laser Raman spectroscopy and cathodoluminescence (CL) image reveal that zircons separated from paragneisses in the southwestern Sulu terrane (eastern China) preserve multi-stage mineral assemblages in different zircon domains. In the same paragneiss zircon sample, some zircon grains retain inherited (detrital) cores with abundant low-pressure mineral inclusions of Qtz + Phe + Ap + impurities and Qtz + Phe impurities. The ultrahigh-pressure (UHP) metamorphic overgrowths mantles of these zircons preserve Coe, Coe + Phe and other UHP mineral inclusions, indicating that these inherited (detrital) zircons from protoliths experi-enced metamorphic recrystallization during the Sulu UHP metamorphic event. However, other zircon grains preserve UHP mineral inclusions of Coe, Coe + Ap and Coe + Phe in the cores and mantles, whereas the outmost rims contain quartz (Qtz) and other low-pressure mineral inclusions. These phenomena prove that the second group zircons were crystallized at UHP metamorphic stage and overprinted by the late retrogressive metamorphism related to the Sulu terrane exhumation. SHRIMP U-Pb dating reveals that zircons separated from the paragneisses recorded complicated geochronological traces. Some zircons retain inherited cores with the 206Pb/238U ages of 284 754 Ma, indicating the complexity of the detrital zircons in protoliths.Coesite-bearing zircon domains recorded 238 266 Ma (with the average age of 245r14 Ma) for the UHP metamorphic event. The retrogressive rims of zircons recorded 213 223 Ma (with the average age of 217r15 Ma) for the late-stage amphibolite facies metamorphic event, indicating that the rapid exhumation time for the Sulu UHP terrane is about 220 Ma.