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.
出处
《地质通报》
CAS
CSCD
北大核心
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)
