吉黑东部晚古生代构造体制转换:来自佳木斯-兴凯地块的双增生杂岩及岛弧岩浆岩带的制约

The transition of the Late Paleozoic tectonic regime in eastern Jilin and Heilongjiang provinces:Constraints from the double accretionary complex and island arc magmatic rock belts in the Jiamusi-Khanka Block

佳木斯-兴凯地块是吉黑东部地区至关重要的地质组成单元,其东缘和西缘分别平行对称分布着两条晚古生代岛弧岩浆岩带和中生代增生杂岩带,它们是古亚洲洋闭合向古太平洋俯冲-增生构造体制转换的关键地质记录。本文对佳木斯-兴凯地块西缘吉黑高压带中的青龙村群斜长角闪岩进行了系统的岩石学、锆石年代学和全岩地球化学研究,结果表明青龙村斜长角闪岩原岩为拉斑系列玄武岩,其原岩时代为~260Ma,具有富集型洋中脊玄武岩(E-MORB)的地球化学特征。同时结合前人对佳木斯地块东缘和西缘分布的大量晚古生代岛弧岩浆岩以及增生杂岩的研究,本文识别出佳木斯-兴凯地块东、西缘的“双带双弧”结构。“双带”即东缘和西缘平行对称分布的那丹哈达增生杂岩带和吉黑高压变质带,“双弧”则是东缘和西缘同样平行对称分布的早-中二叠世和中-晚二叠世岛弧岩浆岩带。通过对双带双弧的组成、形成时代以及构造背景的研究,进一步为吉黑东部地区晚古生代时期的古大洋构造体制转换提供新的证据,并重建了中亚造山带东缘晚古生代到早中生代的构造演化历史。

The Jiamusi-Khanka Block is a key geological unit in eastern Jilin and Heilongjiang provinces.The Late Paleozoic island arc magmatic belts and Mesozoic accretionary complex belts are distributed in parallel and symmetry along the western and eastern margins of the block,respectively,which are critical records of the transitional process from the closure of the Paleo-Asian Ocean to the subduction of the Paleo-Pacific Ocean.Here we reported a new combined study of petrological,geochemical and geochronological characteristics of the Qinglongcun Complex amphibolites within the southern part of Ji-Hei high pressure belt from the west Jiamusi-Khanka Block.The results show that the protoliths of these amphibolites are tholeiitic basalts with an affinity to the enriched mid ocean ridge basalt(E-MORB),and they have protolith ages of ca.260Ma.By integrating our new results with previous studies on the Late Paleozoic island arc magmatic rocks and Mesozoic accretionary complexes in the eastern and western margins of the block,we defined a“double complex belts and double island arcs”model of the Jiamusi-Khanka Block.The“double complex belts”is referred to the Nadanhada accretionary complex and the Ji-Hei high-pressure metamorphic belt distributed parallelly and symmetrically along the eastern and western edges of this block;while the“double island arcs”is referred to the Early-Middle Permian and Middle-Late Permian island arc magmatic rock belts distributed in the same way with the two complex belts.The study of the compositions,formation ages and tectonic settings of the two complex belts and island arcs further provide new evidence for the Late Paleozoic tectonic regime transition of the paleo-oceanic domain in the eastern part of Jilin and Heilongjiang provinces,and contributes much to the reconstruction of the tectonic evolution history of the eastern margin of the Central Asian Orogenic Belt from the Late Paleozoic to the Early Mesozoic.