南秦岭白马山金矿区石英闪长岩地球化学特征及其构造意义

Geochemical Characteristics and its Tectonic Significance of Quartz Diorite in Baimashan Gold Field,Southern Qinling Mountains

白马山小岩体位于白马山金矿区内,构造位置上属南秦岭成矿亚带,岩体与矿床具有密切的空间关系。岩体的岩性以石英闪长岩为主,边缘为少量的黑云母二长花岗岩。地球化学特征表明,白马山Ⅰ型石英闪长岩属于高钾钙碱性岩石系列,为"C"型埃达克岩。早—中三叠世南秦岭地区处于板内伸展阶段,埃达克岩和喜马拉雅型花岗岩在空间上共存,说明三叠纪白马山岩体与俯冲洋壳关系不大,可能源于陆陆碰撞造成的加厚基性下地壳。下地壳发生变质作用转变为榴辉岩相,岩石圈地幔拆沉,造成软流圈上涌、岩石圈伸展和下地壳部分熔融,岩浆混合形成白马山埃达克岩岩浆,对寻找金铜矿产具有一定的指导意义。

Baimashan small rock,related to the gold deposit in spacial,is located in the Baimashan gold deposit area,the South Qinling ore-forming sub-belt.It is dominanted by the granodiorite and minor biotite monzonite at the marginal part.Geochemical characters indicate that Baimashan quartz diorite belong to the high K calc-alkalic series,however,they also have more similar geochemical characters to the＂C＂type adakite than the＂O＂type adakite.The tectonic nature of lithosphere in South Qinling was characterized by transition from compression to extention in the Early-Middle Triassic period.The granites of adakite in the South Qinling area may resulted from partial melting of the mafic lower crust（basalts）in the thickened lower crust,and mixing with the mafic magma,due to the lithospheric stretching and the asthenosphere upwelling,which can provide some clues to the collision between the North China Plate and the Qinling micro-plate,and also direct copper-gold prospecting.