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The Dayingzi detachment fault system in Liaodong Peninsula and its regional tectonic significance [查看] SHENLiang、LIUJunLai、HULing、JIMo、GUANHuiMei、GregoryADAVIS

Large scale lithosphere thinning is an important characteristic of the destruction of the North China Craton (NCC) during the late Mesozoic. A series of extensional structures were developed under extensional setting, among which is the Dayingzi detachment fault system (DFS). The DFS is constituted by three parts, volcano-sedimentary basins at the hanging wall, the Dayingzi-Huanghuadian detachment fault zone, and Paleoproterozoic metamorphic rock series and Mesozoic plutons at the footwall.In the section across the detachment fault zone, there is a sequence of tectonites including fault gouge, microbreccia, cataclastic-mylonites, mylonites, and gneissic biotite monzonite granite. Microstructural characteristics of tectonites and electron backscatter diffraction (EBSD) patterns of quartz indicate that the rocks from the footwall experienced a process from upper greenschist facies to lower greenschist facies. SHRIMP and LA-ICP MS U-Pb dating of zircons from the volcanic rocks in the basins, the tectonic evolution of the DFS is summarized as follows: 1) regional extension started at 135.0±1.2 Ma ago, when the detachment fault cut through the middle crust. Faulting induced the upwelling of magma and eruption of volcanic rocks and deformed a series of medium-acid volcanic rocks; 2) after 135.0±1.2 Ma, a large scale detachment faulting was active cross-cutting the mid-upper crust. The western margin of Jurassic and Triassic granite was ductilly and brittly sheared; besides,the Cretaceous volcano-sedimentary rocks were tilted when the master fault approached the surface; 3) at around 127±1 Ma,the detachment fault stopped its activity and was intruded by the unsheared Cretaceous granite near Chaoyang. Comparison with the Liaonan metamorphic core complex (MCC) and other extensional structures in Liaodong Peninsula led to a general trend of including three zones in the Peninsula: MCC zone, detachment fault systems (DFS) zone, and half graben zone. MCC commonly cuts through the mid-lower crust, DFS through the mid-upper crust, and half graben through the upper crust.Therefore, development of the extensional structures in Liaodong Peninsula indicates that they are the results of crustal extension and thinning at different crustal levels. They may provide a deep insight into the dynamic mechanism, history of destruction and lithosphere thinning of the North China Craton (NCC).

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.

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