Geological Characteristics,Types And Geological Significance Of Ophiolite Tectonic Melange In Jifeng-Gaxian Area,North Of The Great Xing'an Range

On the basis of fully collecting and summarizing the previous research results,this paper takes the Ophiolite tectonic melange in Jifeng tree farm and Gaxian area of Oroqen Autonomous Banner in the north of the Great Xing'an Range as the research object,guided by the latest classification scheme of ophiolites in orogenic belt and Dilek(2011)ophiolites,and referring to the latest relevant research results of ophiolites,using a combination of petrology,petrography,petrogeochemistry,isotopic chronology,etc.,the main research methods are field investigation,geological profile measurement,LA-ICP-MS U-Pb dating of zircon and geogeochemical analysis,the rock assemblages,petrographic features and classification of ophiolite in Jifeng-Gaxian area,north of the Great Xing'an Range are determined.There are Neoproterozoic ophiolites in Jifeng-Gaxian area,which are mantle plume ophiolites and hanging side of subduction-belt SSZ ophiolites.According to LA-ICP-MS U-Pb dating of gabbro zircon age is 646.9 � 5.3Ma in Jifeng area(Feng zhiqiang et al.,2014),the age of pyroxenite SHRIMP is 626.7 � 9.7Ma in Gaxian area(She hongquan,2012),and the age of LA-ICP-MS U-Pb dating of gabbro zircon is 696.8 � 2.9Ma(Du bingying et al.,2017),the formation time of the ophiolite in Jifeng-Gaxian area is Neoproterozoic,combine LA-ICP-MS U-Pb dating of zircon was 618 �14Ma,which was obtained from the matrix sericite quartz schist of Gaxian ophiolitic melange,it is believed that the mixed age of the ophiolitic melange is Neoproterozoic-early Cambrian.In combination with Neoproterozoic granite in Dayangqi area LA-ICP-MS U-Pb isotope age is 557.2 �2.2 Ma(Liu Yuwei etc.,2017)and universal existence of typical early Paleozoic post-orogenic granites set in Tahe area of the Ergun block,the age is 480 ~ 490 Ma,and thus limit the Ergun block and Xing'an block collision occurred in at least 490 Ma ago.