黑龙江省东部跃进山增生杂岩的形成时代和构造意义

The formation time and tectonic significance of Yuejinshan accretionary complex in eastern Heilongjiang Province

那丹哈达地体中的跃进山和饶河增生杂岩对于重建古太平洋板块的俯冲—增生过程以及揭示古太平洋和古亚洲洋之间的构造体制转换过程提供了重要地质证据。然而古太平洋板块俯冲至欧亚大陆下的起始时间以及跃进山增生杂岩相关的古洋盆属性存在较大争议。笔者等对跃进山增生杂岩的野外地质调查显示其具有“基质+岩块”的物质组成特征,对其中的基质变泥质粉砂岩碎屑锆石U-Pb定年结果显示其沉积时代不早于233.1±5.1 Ma,绿片岩岩块的锆石U-Pb定年结果显示其原岩的结晶年龄为194.7±4.8 Ma,并具有洋岛玄武岩的地球化学属性。结合前人新近发表的跃进山地区和区域上增生杂岩的岩块和基质的年代学资料,表明跃进山增生杂岩的增生时代主体为三叠纪,而最终就位时代为早侏罗世早期,它为古太平洋板块俯冲—增生的物质记录。

Objectives and Methods:The Yuejinshan and Raohe accretionary complexes in the Nadanhada Mountains terrane can provide important geological evidence to reconstruct the subduction—accretion process of the PaleoPacific Plate and reveal the tectonic transformation process between the Paleo-Pacific Ocean and Paleo-Asian Ocean.However,the time of the initial subduction of the Paleo-Pacific slab under Eurasia Plate and the properties of the ancient ocean related to the Yuejinshan accretionary complex are still controversial.Based on the field geological survey of the Yuejinshan accretionary complex,zircon U-Pb geochronology and geochemical tests of the matrix and rocks were carried out.Combined with the existing research results,the accretion and in-situ age of the Yuejinshan accretionary complex was further limited,providing evidence for the subduction—accretion process of the paleo-Pacific Plate.Results:This field survey shows the Yuejinshan accretionary complex has a typical structure of"matrix and block"in terms of rock assemblage.Through this study,The geochemical compositions of the green schist block are similar to those of ocean the island basalt.The U-Pb zircon age of the green schist is 194.7±4.8 Ma,and the UPb age of detrital zircons of the meta-argilaceous siltstone in matrix show that the depositional age is not earlier than 233.1±5.1 Ma.Combined with the published geochronological data on the region,it is believed that the accretionary age of the Yuejinshan accretionary complex is mainly Triassic.Conclusions:Combined with previous research results,it is believed that the accretionary age of the Yuejinshan accretionary complex is mainly Triassic,its sediment source is mainly from the rocks in Jiamusi block and sillar in accretionary complex,the final location age is Early Jurassic,it is the product of subduction—accretion of the paleo-Pacific plate and records the process of subduction—accretion of the paleo-Pacific plate.