陕西柞水地区小茅岭复式岩体东段LA-ICP-MS锆石U-Pb定年

摘要

小茅岭复式岩体东段主要由早期宋家屋场蚀变角闪辉绿(辉长)岩体和晚期迷魂阵蚀变闪长岩体、磨沟峡蚀变石英闪长岩体、叶家湾蚀变二长闪长岩体组成.经LA-ICp-MS锆石U-Pb同位素测年,分别获得宋家屋场岩体侵位年龄864.4Ma±1.7Ma,迷魂阵岩体846.7Ma±2.7Ma,磨沟峡岩体为859.4Ma±1.7Ma,叶家湾岩体861.1Ma+1.8Ma,确证该复式岩体形成于新元古代.鉴于在小茅岭-陡岭隆起带的早前寒武系变质岩中曾获得与北秦岭造山事件(1000-848Ma)相一致的变质年龄,结合该复式岩体自身的特征,认为小茅岭复式岩体东段形成于后造山应力松弛的构造环境.%The eastern part of the Xiaomaoling composite intrusives in the Qinling Mountains is considered to consist mainly of the early Songjiawuchang altered proterobase or bojite, the late Mihunzhen altered diorite, Mogouxia altered quartz diorite and Yejiawan altered monzodiorite.The LA-ICP-MS U-Pb isotope dating for zircons from the rock masses above yields four ages: 864.4Ma±1.7Ma from Songjiawuchang, 846.7Ma±2.7Ma from Mihunzhen, 859.4Ma±1.7Ma from Mogouxia and 861.1Ma±1.8Ma from Yejiawan.All the data suggest that the eastern part of the Xiaomaoling composite intrusives belongs to the Neoprotozoic in age.The metamorphic age obtained from the early Precambrian metamorphic rocks of the Xiaomaoling-Douling uplift belt is close to the age of the North Qinling orogenic event (1000Ma～848Ma) based on the previous materials and combining with the intrusives' own character, the authors infer that the eastern part of the Xiaomaoling composite intrusives forms in the post-collisional stress relaxation environment.