【摘要】 碱性花岗岩分布于西藏羌塘北部的花岗岩带内,岩石K2O+Na2O含量达11.27%～12.02%,具高铝、高碱、低铁镁组分的特征,属碱性花岗岩类。地球化学特征表明,该碱性岩形成于后碰撞期。形成该岩体的物质主要来源于加厚陆壳的中下部,反映了研究区古特提斯闭合后经历了陆内造山阶段。霞石正长岩同位素锆石U-Pb年龄为248.7Ma±2.6Ma,相当于早三叠世晚期。碱性花岗岩的出现是西藏西北部古特提斯造山带崩塌开始的岩石学标志。更多还原

【Abstract】 Alkaline granites are distributed in the granite belt in northern Qiangtang, Tibet. They contain up to 11.27-12.02% of K2O+Na2O and have high-Al and -alkali and low-Fe and -Mg features, belonging to alkaline granitoids. Geochemical characteristics indicate that the alkaline rocks formed in the post-collision stage. The material forming the intrusion was mainly derived from the middle and lower parts of the thickened crust, reflecting that the closing of the Paleo-Tethys in the study area went through the intracontinental orogenic stage. The nepheline syenite has a zircon U-Pb age of 24.87±2.6 Ma, indicating a late Early Triassic age. The appearance of the alkaline granitoids is a petrological indication for the onset of collapses of the Paleo-Tethys orogenic belt in northwestern Tibet.更多还原