黑龙江省中东部地区二叠纪—早侏罗世洋陆演化过程及成矿动力学背景探讨

Permian—Early Jurassic ocean—continent evolution and metallogenic dynamic setting in the central and eastern part of Heilongjiang Province

我国东北古生代—中生代洋陆构造演化存在较大争议。黑龙江省中东部地区二叠纪—早侏罗世岩浆活动强烈、矿床发育,这些为我们认识中国东北晚古生代至早中生代洋陆转换过程以及成矿地质背景提供了重要素材。笔者等在系统总结黑龙江省中东部的蛇绿岩、岛弧岩浆岩和矿床学研究成果基础上,分析并识别出洋内弧前弧玄武岩、富铌玄武(安山)岩和英云闪长岩—奥长花岗岩—花岗闪长岩(TTG)等岩石类型,并将研究区二叠纪—早侏罗世洋陆演化与成矿划分为二叠纪、早—中三叠世、晚三叠世—早侏罗世三个阶段。①早二叠世佳木斯地块东侧的前弧玄武岩、富铌玄武岩和TTG岩类记录了古太平洋初始俯冲和洋陆汇聚,由于该西向俯冲导致佳木斯地块和松嫩地块间弧后拉张形成牡丹江洋,这期间佳木斯地块上的金矿围岩花岗岩类为与古太平洋俯冲背景有关的I型花岗岩。②早—中三叠世牡丹江洋发生双向俯冲消减,其中与牡丹江洋西向俯冲板片后撤相关的成矿序列为斑岩型钼矿。③晚三叠世—早侏罗世佳木斯地块东缘受到古太平洋持续俯冲,以及晚三叠世末期—早侏罗世早期牡丹江洋闭合,形成松嫩地块和佳木斯地块同碰撞、碰撞后伸展以及古太平洋俯冲相关的岩浆事件,该时期主要形成早侏罗世斑岩型钼矿床和矽卡岩型多金属矿床。

The Paleozoic and Mesozoic tectonic evolution of ocean—continentrealm in the northeast China is still controversial.The Permian—Early Jurassic multiple magmatic activities and homochromous ore deposits development in the central and eastern part of Heilongjiang Province provide crucial evidences to understand the ocean—continent transition process and metallogenic geological tectonic setting from Late Paleozoic to early Mesozoic in Northeast China.Based on the systematic summary of ophiolitic mélanges,igneous rocks and ore deposits in the central and eastern part of Heilongjiang province,we recognize intra-oceanic forearc basalt,Nbenriched basaltic andesite and an assemblage of tonodiorite,trondhjemite granodiorite(TTG).Themetallogenic and ocean—continent tectonic evolution in study area is divided into three stages of Permian,Early—Middle Triassic and Late Triassic—Early Jurassic.①The forearc basalt and Nb-enriched basalt in the eastern margin of the Permian Jiamusi block recorded the initial westward subduction of the Paleo-Pacific slab.This westward subduction resulted in opening of the Mudanjiang ocean through a backarc stretched between the Jiamusi block and the Songnen block.During this period,the wallrock granites of Permian gold deposits in the Jiamusi block are igneous(I)-type granitoid rocks that are related to the subduction of the Paleo-Pacific.②The Mudanjiang ocean subducted westward in the Early—Middle Triassic,and formed porphyry-type molybdenum deposits related to the rollback of the Mudanjiang oceanic lithosphere subduction slab.③In the Late Triassic—Early Jurassic,the eastern margin of the Jiamusi block was continuously influenced by the paleo-Pacific subduction.Concurrently,the Mudanjiang ocean was closed during Late Triassic to Early Jurassic,and produced intense magmatic events caused by Paleo-Pacific subduction,syn-collision,post-collision and late extension between the Songnen block and Jiamusi block.In this period,the porphyry-type molybdenum and skarn-type multi-metallogenic deposits were mainly formed in the Early Jurassic.