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《Geochimica》 2017-05
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Geochemistry of the Baoshan pluton in the Tongling region of the Lower Yangtze River Belt

NING Si-yuan;WANG Fang-yue;XUE Wei-dong;ZHOU Tao-fa;School of Resources and Environmental Engineering, Hefei University of Technology;Ore Deposit and Exploration Centre, Hefei University of Technology;University of Science and Technology of China;China University of Geosciences (Beijing);  
The petrogenesis of adakitic intrusions in the Lower Yangtze River Belt has been hotly debated for the past decade. The Baoshan pluton is located in the southwest of the Tongling district. Here we conducted a systematic mineralogical, petrological and geochemical study on the Baoshan rocks and mafic microgranular enclaves to understand their petrogenesis. The results indicate:(1) the Baoshan pluton is composed of several kinds of magmatic rocks, e.g., pyroxene diorite to granodiorite;(2) the mafic rocks are usually enrolled by felsic magma, with or without distinctive boundaries;(3) U-Pb dating on zircons by LA-ICPMS suggests that granodiorite and pyroxene diorite enclaves were emplaced at(143.8±3.2) Ma(2σ, MSWD=2.3) and(142.9±2.9) Ma(2σ, MSWD=2.2), respectively;(4) the Baoshan pluton is similar to adakite in geochemical affinity, e.g., a wide-range of SiO_2(Si O2 52.88%-63.66%), high Al_2O_3(averaging 16.03%), high Sr/Y(33.4-102, average 72.9) and Sr/La ratios, low Y and Yb, low(La/Yb)N(14.6-26.6, averaging 21.4) and K_2O/Na_2O(averaging 0.39) ratios;(5) the field contact relationship between mafic and felsic rocks and the geochemical characteristics of the Baoshan rocks indicate they were derived from magma mixing. The two end members of the Baoshan pluton are high-silica and low-silica end-members. High-silica end-member was formed by partial melting of subducted oceanic crust, followed by fractional crystallization of magnetite in varying degrees while upwelling. The other is the lithospheric mantle, which has high Ni, Cr, V and Co contents. The Baoshan rocks may indicate that the magmatism and mineralization in Tongling, even the LYRB, were formed in a subduction system during the Mesozoic time.
【Fund】: 国家自然科学基金(41373035 41203028);; 合肥工业大学中央高校基本科研业务费专项资金(112-4115102017)
【CateGory Index】: P584;P618.41;P618.51
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