班公湖—怒江缝合带西段酸性侵入岩LA-ICP-MS锆石U-Pb年龄与地球化学特征  

LA-ICP-MS zircon U-Pb age and geochemical characteristics of the acid intrusive rocks in the western part of Bangong Lake-Nujiang River suture zone

作　　者：张向飞 李佑国[2] 曹晓民 曲晓明[3] 辛洪波[3] 王健[4] 杜德道[5] 

机构地区：[1]云南省地质调查院矿产所,云南昆明650041 [2]成都理工大学地球科学学院,四川成都610059 [3]中国地质科学院矿产资源研究所,北京100037 [4]核工业北京地质研究院,北京100029 [5]中国石油勘探开发研究院,北京100083

出　　处：《地质通报》2014年第7期984-994,共11页Geological Bulletin of China

基　　金：中国地质调查局项目(编号:1212010818097)

摘　　要：针对班公湖—怒江中特提斯洋盆闭合的时间问题,选择西藏日土县班公湖畔蛇绿岩中的小型酸性侵入岩体为研究对象,探讨其岩石成因和构造环境。研究区酸性岩体的岩性为斜长花岗斑岩。地球化学分析显示,岩石SiO2含量介于65.78%～68.76%之间,（K2O＋Na2O）含量为6.39%～6.86%;具有轻稀土元素富集、分馏程度高、Eu正异常不明显的特点;富集大离子不相容元素Sr、Ba、Rb,亏损高场强元素Ta、Ti、Nb,并有Ta、Nb元素谷形,显示出典型的岛弧岩浆岩特征。2个斜长花岗斑岩体的LA-ICP-MS锆石^206Pb/^238U年龄加权平均值分别为96.08Ma±0.22Ma和96.05Ma±0.30Ma,均属于中生代晚白垩世。To investigate the closure time of the Bangong-Nujiang Middle Tethys Ocean, the authors chose small acid rock masses in the ophiolitic zone near the Bangong Lake in Rutog County of Tibet as the study object to investigate their petrogenesis and structural environment. The rock type is plagioclase granite-porphyry. Chemically the rocks consist mainly of SiO2and（K2O＋Na2O）,with their content being 65.78%～68.76% and 6.39%～6.86% respectively. In addition, the rocks have high LREE enrichment, high degree of fractionation and positive Eu anomalies They are rich in LREE such as Sr, Ba and Rb, but are depleted in high field strength elements（HFSE） like Ta, Ti and Nb, assuming a ＂valley＂ form. The depletion of Nb and Ta suggests that they have the typical characteristics of arc magmatite. LA-ICP-MS（inductively coupled plasma-mass spectrometer and a laser ablation system） dating shows that the zircon ^206Pb/^238U weighted mean ages of two plagioclase granite-porphyry samples are 96.08Ma±0.22 Ma and 96.05Ma±0.30 Ma respectively, implying that they both belong to the Late Cretaceous period of Mesozoic.

关 键 词：斜长花岗斑岩 岛弧岩浆岩 地球化学特征 LA-ICP-MS锆石U-PB年龄 班公湖—怒江 特提斯 

分 类 号：P597.3[天文地球—地球化学]