安徽铜陵凤凰山石英二长闪长岩和花岗闪长岩锆石SHRIMP U-Pb年龄及其地质意义

SHRIMP U-Pb Dating of Zircon from the Fenghuangshan Quartz Monzodiorite and Granodiorite in Tongling Area,Anhui Province and Its Geological Implication

为建立矿区内岩浆演化序列、探讨成岩成矿关系,选取凤凰山石英二长闪长岩和花岗闪长岩进行锆石SHRIMP U-Pb精确定年。石英二长闪长岩样品测年获得年龄数据为(136.0±2.0)～(143.0±2.4)Ma,加权平均值为(139.4±1.2)Ma(n=15,MSWD=0.76);花岗闪长岩样品测年获得年龄数据为(136.7±2.0)～(145.3±2.4)Ma,加权平均值为(141.0±1.1)Ma(n=17,MSWD=1.5)。岩体侵位年代为晚侏罗世、燕山晚期,与铜陵矿集区主要成矿岩体的形成时代一致。辉钼矿Re-Os等时线年龄与花岗闪长岩侵位年龄一致,老于石英二长闪长岩侵位年龄,说明花岗闪长岩为凤凰山矽卡岩型铜矿床的主成矿岩体,成岩成矿关系密切,它们为同期产物。同位素组成表明,幔源岩浆分异的深部流体参与了成矿作用。岩体侵位、岩石圈整体加厚产生的伸展作用和软流圈地幔、上覆地壳减压熔融产生玄武岩浆底侵作用有关。

In order to study the magmatic evolution and relationship between magmatism and mineralization,the SHRIMP U-Pb dating of zircon in Fenghuangshan quartz monzodiorite and granodiorite in Tongling area,Anhui Province are carried out.The SHRIMP U-Pb age of zircon from the quartz monzodiorite changes from （136.0±2.0） to （143.0±2.4） Ma,and the weighted mean age is （139.4±1.2） Ma （n=15,MSWD=0.76）.Results of SHRIMP U-Pb zircon dating of granodiorite is from （136.7±2.0） to （145.3±2.4） Ma,and the weighted mean age is （141.0±1.1） Ma （n=17,MSWD=1.5）.The emplacing age of the Fenghuangshan intrusion is the Late Jurassic.Moreover,the molybdenite Re-Os isochrone age is accordant with that of the granodiorite and older than the age of quartz monzodiorite.The copper mineralization has the closer relationship with the granodiorite and they are formed contemporaneously.Isotopic data indicate that the mineralization is related to the deep fluids derived from mantle magma differentiation.The extensional process resulted from the whole lithosphere thickening and the basaltic magma approaching,caused by from the aesthenosphere mantle and upper crust decompression and melting,played an important role in forming of the Fenghuangshan intrusion.