冈底斯带东段墨脱地区早侏罗世辉长岩的成因及其构造意义  

Genesis and geological significance of Early Jurassic gabbro in Medog area,the eastern part of the Gangdese magmatic belt

作　　者：董汉文[1] 许志琴[1] 李源[1] 刘钊[2] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质科学院矿产资源研究所,北京100037

出　　处：《岩石学报》2016年第12期3624-3634,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41502196;40921001);中国地质调查局地质调查项目(DD20160022);中国地质科学院基本科研业务费项目(J1623);大陆构造与动力学实验室自主基金(Z1301-a12)联合资助

摘　　要：本文系统地报道了冈底斯岩浆岩带东段墨脱地区辉长岩的LA-MC-ICP-MS锆石U-Pb年龄、LA-MC-ICP-MS锆石Hf同位素成分分析、全岩地球化学及全岩Sr-Nd同位素组成。结果表明,墨脱辉长岩形成于185.97±0.33Ma,SiO_2含量(48.19%~54.93%),MgO和Mg#变化较大(MgO=4.53%~12.76%,Mg~#=50.0~67.4)。具有高CaO(7.44%~12.11%),低碱(Na_2O=0.93%~2.36%,K_2O=0.49%~2.21%)的特征。辉长岩稀土元素球粒陨石标准化配分模式与E-MORB相似;微量元素上,样品具有富集Sr、Sc等元素,亏损高场强元素Zr-Hf、Nb-Ta等的特征。墨脱辉长岩ε_(Nd)(t)值介于-3.06和2.84之间,^(87)Sr/^(86)Sr(t)值为0.7059~0.7103。锆石的ε_(Hf)(t)值为-4.1~0,和相对古老的Hf模式年龄(866~1036Ma)。上述特征表明墨脱辉长岩经历了不同程度的大陆地壳的混染作用。结合对区域地质、年代学、岩石地球化学以及同位素等资料的全面分析,笔者认为冈底斯东段在早侏罗世应处于新特提斯洋板片俯冲的构造背景。This paper reports whole-rock major and trace element, LA-MC-ICP-MS zircon U-Pb ages, zircon Hf isotopic and Sr-Nd isotopic compositions from the gabbro occurring in Medog area, the eastern part of the Gangdese magmatic belt. LA-MC-ICP-MS zircon U-Pb isotopic dating indicates that the Medog gabbro emplaced at 185.97 ±0. 33Ma. It contains SiO2 of 48.19% - 54. 93%, MgO of 4. 53% - 12.76% and Mg of 50. 0 - 67.4. It is characterized by its high content of CaO （7.44% - 12. 11% ）, low content of alkali （Na20 = 0. 93 % - 2. 36% and K20 = O. 49% -2. 21% ）. The REE distribution patterns are quite similar to that of the E-MORB. The trace elements such as Sr, V, Sc is enriched, while the HFSE such as Nb, Ta, Zr, Hf is depleted. The gabbro has higher 6Nd （t） values （ -3.06- 2. 84） and lower initial 875r/S6Sr ratios （0. 7059 -0. 7103）. The Medog gabbro is heterogenous in zircon cHf（t） values （ - 4. 1 - 0） , yielding relatively ancient zircon Hf crustal modal ages of 866 - 1036Ma. Combining with regional geology, geochronological, geochemical and isotopic data, we propose that the eastern part of the Gangdese magmatic belt was under the Neotethyan subduction setting during the Early Jurassic.

关 键 词：辉长岩 岩石成因 新特提斯洋俯冲 冈底斯岩浆岩带 墨脱地区 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]