中文摘要：

改则格列戈阿尔辉长岩侵入于羌塘地体南缘木嘎岗日群,为研究班公湖—怒江缝合带在改则地区的演化提供新的强有力的约束。本文对辉长岩进行了LA-ICP-MS锆石U-Pb定年,结果显示格列戈阿尔辉长岩锆石UPb年龄加权平均值为122.9±1.6Ma,表明该辉长岩体形成时代为早白垩世中晚期。岩石地球化学研究表明,该区早白垩世辉长岩具有高Al2O3（15.39%~16.83%）、低Ti O2（0.78%~0.92%）、贫P2O5（0.09%~0.17%）和低碱（Na2O＋K2O=3.93%~4.41%）的特点。稀土元素总量（ΣREE）为63.37×10^-6~73.76×10^-6,平均为68.84×10^-6,稀土元素配分曲线呈右倾型,（La/Yb）N介于2.43~3.09之间,δEu=0.89~1.03,表现弱的负铕异常,具有明显的轻稀土富集,重稀土亏损特征。岩石微量元素总体上富集大离子亲石元素（LILE）Rb、Ba、Th、U等,显著亏损高场强元素（HFES）Nb、Ta、P、Ti等,Nb/Ta、Zr/Hf比值接近或略低于原始地幔组成。根据地球化学特征和微量元素构造判别图结果表明,该辉长岩源区为被俯冲改造的岩石圈地幔源岩浆,岩浆在演化过程中遭受了上地壳物质的同化混染,并经历一定程度的结晶分异作用。格列戈阿尔辉长岩形成于班公湖—怒江洋向北俯冲构造环境下的岛弧环境,表明至少在122.9±1.6Ma期间班公—怒江洋盆正在向北俯冲。结合区域资料,研究区班公—怒江洋盆闭合时间应介于110~85Ma之间。

英文摘要：

Bangong Co--Nujiang River （Bangong Lake--Nujiang River） suture is one of the largest sutures in the Qinghai--Xizang （Tibet） Plateau and it is situated between the Qiangtang terrance and the Lhasa terrance. With its complex tectonic settings,there are existed many disputes on the Bangong Co--Nujiang River suture, especially in Gaize area, which are mainly about two basic and key issues, which restrict our researches on the geological settings and the evolution of the Xizang. They are the polarity of subduction and the timing of opening. Based on the petrology, geochemistry and chronology of the Gelegear gabbro in Gaize area, we focus on its formation age, petrogenesis,tectonic settings and the evolution process of the subduction to closing. The gabbro sample separation and target preparation of zircons was carried out at the Lab Test Center of the Hebei Institute＇ s Regional Geology ＆ Mineral Survey. The samples were processed by contaminant free crushing. The zircon grains were obtained by selection under a binocular eyepiece after magnetic and electrical separation. Representative zircon grains were then selected for target preparation, and transmission and reflected light photography was used to investigate the zircons by cathode luminescence. Zircon U-Pb dating was performed by LAICP-MS at the Mineral Resource Institute of the Chinese Academy of Geological Sciences,with a Newwave UP 213 laser ablation system and the FinniganNeptune ; U, Th, Pb, and other elements had an integration time of 20s. Data processing was performed using Isoplot 3.0 software and the data was with a high concordance degree was eliminated. The major elements testing is in School of Geosciences and Info-Physics, Central South University. It used powder direct compression with instrument of ZSX Primus Ⅱ X-ray fluorescene. Spectrometer with analytical precision less than 1%. Trace elements testing is completed in Institute of Tibetan Plateau Research Chinese Academy of Sciences with instrument of X series ICP-MS. The tes