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    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 Zircon U-Pb and Molybdenite Re-Os Datings of the Superlarge Donggou Porphyry Molybdenum Deposit in the East Qinling,China,and Its Geological Implications [查看] YEHuishou、MAOJIngwen、LIYongfeng、GuoBaojian、ZHANGChangqing、LIUJun、YANQuanren、LIUGuoyin
    Located in the eastern part of the East Qinling molybdenum belt,the Donggou deposit is a superlarge porphyry molybdenum deposit discovered in recent years.The authors performed highly precise dating of the mineralized porphyry and ores in the Donggou molybdenum deposit.A SHRIMP U-Pb zircon dating of the Donggou aluminous A-type granite-porphyry gave a rock-forming age of 112±1Ma,and the ICP-MS Re-Os analyses of molybdenite from the molybdenum deposit yielded Re-Os model ages ranging from 116.5±1.7to 115.5±1.7Ma for the deposit.The ages obtained by the two methods are quite close,suggesting that the rocks and ores formed approximately at the same time.The Donggou molybdenum deposit formed at least 20Ma later than the jinduicheng,Nanihu,Shangfanggou and Leimengou porphyry molybdenum deposits in the same molybdenum belt,implying that these deposits were formed in different tectonic settings.
    SHRIMP zircon U-Pb dating for volcanic rocks of the Dasi Formation in southeast Hubei Province, middle-lower reaches of the Yangtze River and its implications [查看] XIEGuiqing、MAOJingwen、LIRuiling、ZHOUShaodong、YEHuishou、YANQuanren、ZHANGZusong
    Abstract The Jinniu Basin in southeast Hubei,located at the westernmost part of middle-lower valley of the Yangtze River, is one of the important volcanic basins in East China. Volcanic rocks in the Jinniu Basin are distributed mainly in the Majiashan Formation, the Lingxiang Formation and the Dasi Formation, consisting of rhyolite, basalt and basaltic andesite, (trachy)-basalt and basaltic trachy-andesite and (trachy)-andesite and (trachy)-dacite and rhyolite respectively, in which the Dasi volcanism is volumetrically dominant and widespread. The Dasi volcanic rocks were selected for SHRIMP zircon U-Pb dating to confirm the timing of volcanism. The results indicate that there exist a large amount of magmatic zircons characterized by high U and Th contents in the volcanic rocks. The concordia ages for 13 points are 128 ± 1Ma (MSWD = 3.0). On account of the shape of zircons and Th/U ratios, this age is considered to represent the crystallization time of the Dasi volcanism.The volcanic rocks in the Dasi, Majiashan and Lingxiang Formations share similar trace element and REE partition patterns as well as Sr-Nd isotopic compositions. In combination with the regional geology,it is proposed that the southeast Hubei volcanic rocks were formed mainly during the Early Cretaceous, just like other volcanic basins in middle-lower Yangtze valley. A lithospheric extension is also suggested for tectonic regime in this region in the Cretaceous Period.
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