小兴安岭西北部科洛杂岩的岩石学与年代学

目前业内学者对于科洛杂岩的认识一致缺乏系统的年代学数据与之相匹配，且关于科洛杂岩原岩的物质组成和形成时代也缺少年代学资料的约束，为查明小兴安岭西北部科洛杂岩的原岩组成和变质期次，利用LA-ICP-MS锆石U-Pb测年方法，在系统分析锆石特征及成因的基础上，对科洛杂岩中3种变质岩（弱片麻状角闪石岩、黑云斜长片麻岩和黑云角闪斜长片麻岩）中不同成因锆石进行年代学研究.岩浆型锆石年龄数据显示，碎屑锆石可分为古-中元古代、晚泥盆世晚期-早石炭世早期和晚石炭世晚期-早二叠世早期3组，3个样品中最年轻的锆石年龄分别为286.3±3.6 Ma、284.3±3.1 Ma和345.3±4.8 Ma，而变质锆石年龄数据分为早-中三叠世（峰值年龄248.5 Ma）和早-中侏罗世（峰值年龄173.1 Ma）两期.结合区域资料和年龄数据分析，科洛杂岩中包含下二叠统和下石炭统碎屑沉积岩，物源可能分别来自于区域上的前寒武纪基底残块和石炭统-二叠统岩浆岩，且在成岩之后至少经历了两期变质作用，早期的变质作用可能是蒙古-鄂霍茨克板块南向俯冲作用的远程效应；晚期变质作用受蒙古-鄂霍茨克洋南向俯冲和古太平洋西向俯冲的叠加作用控制. 

Petrological and Geochronological Study of Keluo Complex in Northwestern Lesser Xing'an Range

Due to the lack of chronological data to constrain the material composition and protolithic age of the Keluo complex, and the lack of chronological date matching the knowledge of the industry scholars, in this study, based on the systematic analysis of different genesis zircon characteristics, genesis and isotopic chronologic results of metamorphic rocks from Keluo complex in northwestern Lesser Xing'an Range, the protolith and metamorphic period of Keluo complex was studied. The LA-ICP-MS magmatic zircon U-Pb ages of three metamorphic rocks (including weak gneissic amphibolite, biotite plagioclase gneiss and biotite amphibole plagioclase gneiss) show that the youngest clastic zircons ages are 286.3±3.6 Ma, 284.3±3.1 Ma and 345.3±4.8 Ma, respectively, which means they formed in Early Permian and Early Carboniferous instead of the Precambrian. Age data also show that the source of clastic sedimentary rocks in Keluo complex is regional basement debris with widely developed two-stage magmatic rocks. Meanwhile, the LA-ICP-MS U-Pb ages of metamorphic zircons indicate that the protolith of Keluo complex underwent at least two-stage metamorphism after diagenesis, the Early-Middle Triassic(peak age 248.5 Ma) and the Early-Middle Jurassic (peak age 173.1 Ma) respectively. The early metamorphism may be a long-range effect of the southward subduction of the Mongolia-Okhotsk plate, while the late metamorphism was controlled by the superposition of the southward subduction of the Mongolia-Okhotsk Ocean and the westward subduction of the paleo-Pacific Ocean.