缅甸中部抹谷早白垩世构造岩浆作用及对特提斯演化的启示  

The Early Cretaceous Tectonic Magmatism in the Mogok District,Central Myanmar,and Its Implication for the Evolution of Tethys

作　　者：陈希节[1] 许志琴[1] Kyaing Sein 孟元库[1] 蔡志慧[1] 

机构地区：[1]中国地质科学院地质研究所,大陆构造与动力学重点实验室,北京100037 [2]缅甸地质学会,Hlaing大学,缅甸仰光

出　　处：《地质学报》2016年第11期3060-3080,共21页Acta Geologica Sinica

基　　金：中国地质科学院地质研究基本科研业务费(编号J1621);国家自然科学基金项目(编号41403029,41302166);中国博士后科学基金会项目(编号2015T080114)联合资助成果

摘　　要：本文系统报道了缅甸抹谷变质带中部Yinmabin花岗闪长岩体及其基性岩墙的主量元素、微量元素及锆石U-Pb年龄和Lu-Hf同位素组成,重点讨论了花岗闪长岩和基性岩墙的岩石成因、物质来源及其地质意义。抹谷Yinmabin花岗闪长岩体主量元素显示富钠(N2O/K2O=1.5~1.75)、准铝(ACNK=0.94~0.97)和钙碱性岩石系列的地球化学特征。样品富集轻稀土(LREE)元素、大离子亲石元素(LILE),相对亏损高场强元素(HFSE)。岩体的主、微量元素地球化学特征均显示其具有活动陆缘I型花岗岩的地球化学属性。抹谷Yinmabin花岗闪长岩的锆石U-Pb年龄为131~135 Ma,其εHf(t)值在-15.66^-2.99之间,平均值为-8.77,单阶段模式年龄(tDM)为795~1569 Ma;而后期侵位的辉绿岩的锆石U-Pb年龄为120~118 Ma,其εHf(t)值在-13.72^+5.82之间,平均值为-2.72,单阶段模式年龄(tDM)为570~1341 Ma,表明这些岩石可能主要来源于古老下地壳部分熔融但同时也受到地幔物质的加入混染。与滇西以及北拉萨岩浆带的Lu-Hf同位素特征十分相近,暗示抹谷-毛淡棉地块早白垩世岩浆岩带与波密-察隅-高黎贡-拉萨岩浆岩带形成环境相似,可能是腾冲岩浆岩带向南延伸的一部分。结合岩石成因、源区性质和区域构造演化,认为抹谷花岗闪长岩体及基性岩墙的形成与中特提斯洋板块的俯冲作用密切相关,同时俯冲-碰撞转换的时限应该在120 Ma左右。这对于研究抹谷地体在中生代期间中特提斯洋俯冲碰撞过程具有重要的地质意义。This study systemically presents the geochemical features and zircon U-Pb and Lu-Hf isotopic compositions of Yinmabin plutons and mafic dykes in the central Mogok metamorphism belt, Myanmar, with an emphasis on their petrogenesis and sources and geological implications. The Yinmabin granodiorites are geochemically characterized by medium SiO2 （64.3% -65.5%） and high Na, with N2O/ K2O=1.5-1.75 and A/CNK=0.94-0.97, enrichment in LREE （Sr and Ba〉500×10.6） and high field strength elements （HFSE） such as Nb, Ta, Zr and HI, nd depleted in HFSE. These geochemical features of the Yinmabin granodiorites are of attribute of active continental margin calc-alkaline I-type granite. The LA-ICP-MS analysis yielded an age of 131-135 Ma for the zircon from Yinmabin granodiorite and 120- 118 Ma for diabases. The Yinmabin granodiorite are heterogeneous in zircon εHf （t） values （-15. 66-2. 99） with a mean of -8.77, yielding younger zircon Hf crustal modal ages of 795-1569 Ma. While zircons from diabases dykes show εHf （t） values from -13. 72 to ＋5. 82 （averaging -2. 72） and a corresponding mean tDM age of 570- 1341 Ma. This suggests that the rocks mainly derived from partial melting of ancient crust with the addition of depleted mantle material. The similar Lu-Hf isotopic compositions to that of the Tengchong and North Lasha magmatism belt indicate that early Cretaceous magmatic belt in the Mogok-Maodanmian block formed in the similar geological background as the Bomi-Chayu-Gaoligong-Lasha magmatic belt. This suggests it be part of southward extension of the Tengchong magmatic rock belt. Combined with petrogenesis, source characteristics and the previous research results, it can he concluded that the formation of Early Cretaceous Yinmabin granodiorite and marie dyke were closely related to the subduction of the Luxi-Mogok oceanic plate and that the ocean-continent transformation occurred at about 120Ma. The research has important geological significance in understanding the process of subduction an

关 键 词：缅甸抹谷 早白垩世 花岗闪长岩及基性岩墙 特提斯 

分 类 号：P588.1[天文地球—岩石学] P542[天文地球—地质学]