中文摘要：

运用岩石学的研究方法对出露于北祁连造山带中段北大坂一带的北大坂岩体进行岩石及元素分析结果表明：其岩性为斑状粗粒二长花岗岩、粗中粒二长花岗岩及中细粒二长花岗岩,含少量黑云母、角闪石及榍石,属钾质钙碱性花岗岩类;主量元素w（SiO2）=63.66%～74.38%,w（K2O）/w（Na2O）=2.61～3.31,总体为高钾钙碱性弱过铝质花岗岩,岩石富集LILE元素（Rb,Th,K等）,亏损HFSE元素（Y,Yb,Ta,Nb等）,稀土元素分配模式为轻稀土富集型,具中等负Eu异常（δEu=0.59～0.82）。微量、稀土元素分配模式与北祁连西段的金佛寺岩体（碰撞型花岗岩）基本一致。单颗粒锆石U-Pb年龄为414Ma±4Ma,综合分析认为北大坂岩体形成于同碰撞末-后碰撞初期的构造转换期,岩浆源区为下地壳。

英文摘要：

Baidaban granite pluton in the Baidaban area of North Qilian Mountain mainly consisted of monzonite granite.Chemical analysis of rocks showed that these rocks are characteristic of high SiO2（63.66%～74.38%）and K2O/Na2O（2.61～3.31）,and low aluminous,belonging to high K calc-alkaline granite series.The normalized REE-patterns revealed LREE enrichment with unconspicuous Eu negative abnormity（δEu=0.61～0.82）.Multi-element normalized spider diagrams showed that they were rich in LILE（Rb,Th,K）and poor in HFSE（Y,Yb,Ta and Nb）,similar to the typical continent-continent syn-collisional granite.These geochemical characteristics were similar to syn-collisional granites of occurred in Jinfosi of northern Qilian with a U-Pb ages of 414 Ma±4 Ma.It was considered that the tectonic setting of this pluton belonged to syn-collision accompanied by granite melting from lower crust.