SHRIMP Zircon U-Pb Dating of the Tongshi Magmatic Comlex in Western Shandong and Its Geological Implications
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
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.
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