黑龙江黑河地区早侏罗世岩浆弧的火成岩记录及其成因

Igneous Rock Records and Genesis of the Early Jurassic Magmatic Arc in Heihe Area of Heilongjiang Province

黑河地区广泛发育中生代火成岩类,但是其形成时代、不同阶段的火成岩组合、岩石成因以及形成的大地构造背景还有争议.对黑河卧牛湖一带的侵入岩开展详细的野外地质学、岩石学、地球化学、年代学等研究,以揭示岩石的时代、成因等.对卧牛湖附近产出的闪长岩及二长花岗岩开展的LA-ICP-MS锆石测年结果表明其形成于175.53±0.53 Ma和177.25±0.45Ma,即早侏罗世.该区这一时期火成岩主要为深成相侵入岩、少量脉岩,岩石类型主要为(二长)花岗岩、花岗闪长岩及少量的二长岩类,脉岩主要为花岗质、闪长质岩脉等,是含有英云闪长岩(T1)-奥长花岗岩(T2)-花岗闪长岩(G1)的T1T2G1G2岩石组合,上述岩石在TAS图上主要是亚碱性系列,硅钾图上主要为高钾钙碱系列,Peacock指数为钙碱性或碱钙性,准铝质-过铝质,硅镁图中多为MA系列,微量元素蛛网图一般富集Rb、K、Pb等大离子亲石元素,亏损Nb、Ta、La、Ce、Ti等元素,稀土元素配分曲线为右倾型,轻稀土较陡,重稀土较平缓.上述岩石组合及其特征均指示岛弧岩浆岩的特征.结合构造环境判别认为该花岗岩类形成于与洋俯冲有关的环境,岩浆可能形成于俯冲玄武质洋壳的局部熔融并与上覆地幔楔发生过反应以及兴安弧下地壳的局部熔融,认为与北部蒙古-鄂霍次克洋的演化有关.

Mesozoic igneous rocks are widely developed in Heihe area,but the age of formation,igneous rock assemblages at different stages,petrogenesis,and the geotectonic background of the formation are still controversial.This article conducts detailed field,petrology,geochemistry,and chronology studies on intrusive rocks around the Woniu Lake in Heihe area to reveal the age and genesis of the rocks.LA-ICP-MS zircon dating of diorite and monzogranite shows that they formed at 175.53±0.53 Ma and 177.25±0.45 Ma.Igneous rocks in this area during this period were mainly intrusive rocks and some dike rocks,intrusive rocks are mainly granite,granodiorite,and a small amount of monzonite,dike rocks are mainly granitic dikes and dioritic dikes.Plutonic facies rocks were T1 T2 G1 G2 rock assemblage contained some Tonalite(T1)-Trondhjemite(T2)rocks and more Granodiorite(G1)-Granite(G2)rocks.The rock assemblage were mainly subalkaline series on SiO2-(Na2 O+K2 O)diagram and on SiO2-K2 O diagram were mainly high-potassium calcium-alkali series,were calcium alkali or alkali calcium series on SiO2-(Na2 O+K2 O-CaO)diagram.They were metaluminums-peraluminous series rocks.Most of the rocks in SiO2-MgO diagram were similar to magnesium andesite(MA)series.Trace elements spider diagrams were generally enriched in LILE,such as Rb,K,Pb,depleted in Nb,Ta,La,Ce,Ti.The REE patterns were right-inclined,LREE were steeper and HREE were gentler.The rock assemblages and their characteristics all indicated the characteristics of island arc magmatic rocks.Based on the discrimination of the tectonic environment,it is considered that the rock assemblages were formed in the environment related to ocean subduction.Magma may have formed in the local melting of the subducting basaltic crust reacted with the overlying mantle wedge and the local melting of the crust under the Xing′an arc.It is considered to be related to the evolution of the northern Mongolia-Okhotsk Ocean.