京西海坨山岩体的期次划分、成因类型及构造环境

Intrusive Stages Division,Genetic Types and Tectonic Setting of Haituoshan Pluton in Western Beijing

海坨山岩体位于北京市延庆区与河北省怀来县的交界处,为一大型复式深成岩基,前人研究工作程度较低。在1∶5万区域地质调查工作的基础上,对该岩体进行了岩性、岩相及侵入期次划分,并对其成因类型和形成环境进行了研究和探讨。结果表明,海坨山岩体的主要岩性为石英二长岩、二长花岗岩以及花岗岩,分三个期次侵入,总体属钙碱性系列的中—酸性岩,具有K、Rb、Ba及轻稀土元素相对富集,Zr、Yb、Y及重稀土元素相对亏损等特点,其成因类型属幔、壳混源的I型花岗岩,形成环境应为活动性大陆边缘的造山带环境,岩浆活动发生于晚造山期。

The Haituoshan pluton is located in the junction between Yanqing District of Beijing and Huailai County of Hebei Province.It is a large composite plutonic batholith,of which the previous research work level was relatively low.In this paper,the author focused the research on lithology,lithofacies and intrusive stage division about this pluton on the basis of 1∶50 000 regional geological survey,further,its genetic type and tectonic setting were studied and discussed.The results show that the main lithology of the Haituo Mountain pluton is quartz monzonite,monzonitic granite and granite,and it was the product of three intrusion stages.It belongs to the neutral-acid rocks of the calc-alkaline series,and has the characteristics that K,Rb,Ba and light rare earth elements are relative enrichment while Zr,Yb,Y and heavy rare earth elements are relative depleted.Thus,its magma type belongs to the crust-mantle mixing I-type granite,and it originated in the active continental margin of the orogenic belt,which magmatic activity occurred in the late-orogenic phase.