黑龙江东部滚突岭地区斜长角闪岩的原岩性质与变质作用演化

Protolith Property and Metamorphic Evolution of Amphibolites in Guntuling Area,Eastern Heilongjiang

黑龙江杂岩主要出露于牡丹江断裂以东,并沿其呈南北向带状展布于佳木斯地块西缘.有关于该杂岩的矿物成分和变质作用演变方面的报道很少,且前人的研究多集中在变质程度为绿片岩相-蓝片岩相的典型黑龙江杂岩.通过对出露于黑龙江东部滚突岭地区的斜长角闪岩进行了地球化学与变质演化研究,其岩石类型主要包括石榴黝帘斜长角闪岩和石榴黑云角闪片岩,结果表明该地区石榴黝帘斜长角闪岩样品明显富集元素K、Ti,亏损Hf,Ta/Yb比值低(0.09~0.16),轻稀土(LREE)相对重稀土(HREE)稍有弱亏损,稀土元素配分曲线为平坦型,类似于MORB的特征.石榴黑云角闪片岩样品微量元素K、Th、Ti明显富集,轻稀土(LREE)相对重稀土(HREE)弱富集,稀土元素配分曲线为右倾型,与洋岛玄武岩相似.斜长角闪岩的原岩既有形成于洋中脊环境的大洋拉斑系列玄武岩,也有少量形成于板内(大陆边缘)或洋岛环境的钙碱性系列玄武岩.斜长角闪岩经历了3个变质演化阶段,分别为高绿片岩相的进变质阶段(T=400~500℃,P=400~500MPa)、低角闪岩相的峰期变质阶段(T=550~640℃,P=590~630MPa)和高绿片岩相的退变质阶段(T=530~560℃,P=530~560MPa),记录了从早期升温升压到后期近等温降压的顺时针P-T演化过程,表明斜长角闪岩的变质作用可能与佳木斯地块与松嫩地块的碰撞有关.

The Heilongjiang complex which mainly outcrops to the east of Mudanjiang fault,is distributed in band trending north-south along the western margin of Jiamusi massif.However,there are few reports about the mineral composition and evolution of the metamorphism of the Heilongjiang complex,and the previous studies are mostly concentrated in the typical Heilongjiang complex with metamorphic degree of greenschist facies to blueschist facies.Therefore,geochemical characteristics and metamorphic evolution of amphibolite are studied in this paper.Amphibolites consist mainly of garnet-zoisite-bearing amphibolite and garnet-biotite-amphibole-bearing schist outcopped in Guntuling area,eastern Heilongjiang.Garnet-zoisite-bearingamphibolite is characterized by the enrichment of K and Ti,distinctly depleted Hf,and low ratio of Ta/Yb at（0.09-0.16）.Furthermore,LREE has weakly negative anomalies relative to HREE,chondrite-normalized REE diagram shows a flat pattern and has no obvious abnormality,which is similar to the features of MORB.Garnet-biotite-amphibole-bearing schist is characterized by the enrichment of K,Th and Ti;furthermore,LREE has weakly enrichments relative to HREE in the chondritenormalized REE pattern and has no obvious abnormality,which is almost consistent with OIB.Geochemistry and metamorphic evolution of amphibolites show that majority of them are oceanic tholeiite originated from the environment of the mid-ocean ridge,and minority of them are calc-alkaline basalt originated from the environment of intraplate（continental margin）or oceanic island.The amphibolites have undergone three successive stages：the progressive metamorphic phase of the high greenschist facies（T=400-500℃,P=400-500 MPa）,peak metamorphic stage of low amphibolite facies（T=550-640℃,P=590-630 MPa）and near isobaric cooling stage of high-greenschist facies（T=530-560℃,P=530-560 MPa）.It records a clockwise P-Tpath from early increased temperature and pressure to late isothermal depressurization.It is inferred that the metamorphism of amphibolite is probably associated with the collision between the Jiamusi Massif and the Songnen Massif.