藏南邛多江地区二长花岗岩^(40)Ar-^(39)Ar同位素年龄及其地质意义  

^(40)Ar-^(39)Ar isotope age dating on biotite samples of two monzogranite bodies occurring in the Qiongduojiang area,southern Tibet and their geological significances

作　　者：聂凤军[1] 胡朋[1] 江思宏[1] 刘妍[1] 

机构地区：[1]中国地质科学院矿产资源研究所,北京100037

出　　处：《岩石学报》2006年第11期2704-2710,共7页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(973)(2002CB412606)资助。

摘　　要：本文以藏南邛多江变质核杂岩中花岗岩类侵入岩体为研究对象,分别对仲格耐和倾日二长花岗岩环(株)中的新鲜黑云母样品进行了^(40)Ar/^(39)Ar 同位素年龄测定。仲格耐二长花岗岩环黑云母样品的坪年龄和等时年龄分别为(13.30±0.32)Ma 和(12.90±2.90)Ma,而倾日二长花岗岩株黑云母样品的坪年龄和等时年龄则为(12.35±0.14)Ma 和(12.37±0.26)Ma。与倾日岩株相比,仲格耐岩环黑云母样品的坪年龄值相对较高些,暗示了其相对较早的形成时间。考虑到倾日二长花岗岩株形成之后基本未遭受到明显构造-岩浆活动影响,因此,12Ma 也许代表了黑云母的结晶时间,属中喜马拉雅时期构造-岩浆活动的产物。确切地讲,邛多江变质核杂岩及有关花岗岩类侵入岩的形成时间不是老第三纪的渐新世,而是新第三纪的中新世。本区花岗岩类侵入岩形成时代的确定,对于探讨本区中酸性岩浆岩的形成过程和揭示藏南拆离构造体系的动力学机制均具有重要意义。Located at easternmost part of the Tethyan-Himalayan tectonic belt, the Qiongduojiang is one of the most important part of southern Tibet metallogenic province, and has been considered as one of the key parts of the southern Tibet detachment system. Precambrian-Paleozoic metamorphic core complxe and Phanerozoic granitoid intrusions are widely distributed. Geochronological study of these granitoids associated with these metamorphic core complexes has attracted geologists＇ attention both at home and abroad. ^40Ar/^39Ar isotope data for biotite separates, that come from Zhonggenai monzogranite ring and Qingri monzogranite stock of the Qiongduojiang metamorphic core complex, southern Tibet, are presented in this paper. Eleven stepwise heating Ar data of the biotite separates of the Zhonggenai monzogranite ring give an ^40Ar/^39Ar plateau age of （ 13.30 ± 0. 32 ） Ma and an isoehron age of（ 12.90 ± 2.90） Ma （2σ） , respectively. The ^40Ar/^39Ar initial value is of 331 ± 240（2σ） and slightly differ from the Nier＇ s value, indicating the disturbance of the Ar isotopic system by post-intrusion hydrothermal event. In contrast, Thirteen stepwise heating Ar data of the biotite separates of the Qingri monzogranite stock give an ^40Ar/^39Ar plateau age of （ 12. 35 ±0. 14） Ma and an isochron age of （ 12. 37 ±0. 26） Ma （2σ） , respectively. The ^40Ar/^36Ar initial value is of 293 ± 11 （2σ）, and showes no differences with the Nier＇ s value. This age may represent the crystallization time of the biotite of the Qingri monzogranite stock from the Qiongduojiang metamorphic core complex, and has been considered as the age of major tectonic-magmatic event occurring within the Qiongduojiang area. Although the early Zhonggenai monzogranite ring has been overprinted by late hydrothermal event and show a slightly disturbed Ar isotopic system, the late Qingri monzogranite has not been effected by late tectonic-magmatic activities, and has been considered as ideal target for isotopic age dating.

关 键 词：^40AR/^39AR同位素年龄 中新世 二长花岗岩 邛多江 藏南 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]