山东省栖霞牙山花岗闪长岩岩石地球化学特征及成因探讨

The Petrogeochemistry and Genesis of Granodiorite in Yashan Qixia,Shandong Province

栖霞牙山地区地处华北地台东部,对该区的似斑状花岗闪长岩体所作的岩石地球化学研究表明,该区岩石为钙碱性偏铝质岩石;微量元素MORB标准化蛛网图显示富集大离子亲石元素Ba、Sr,亏损高场强元素Nb、Ta、Hf、Y;K/Rb比值为295.34388.88,Rb/Sr比值为0.210.29;稀土元素蛛网图表现为较平滑的具微弱负Eu异常向右陡倾的稀土元素配分模式曲线,∑LREE/∑HREE为9.1412.22,显示轻重稀土元素分异较好。结合构造背景分析,认为牙山花岗闪长岩体为早白垩世太平洋板块向欧亚板块俯冲诱发的地幔柱活动,造成地幔底辟,引起地壳部分熔融,形成壳幔混合岩浆并进一步侵入形成。

Qixia Yashan area is located at the east of the North China platform.The geochemical studies about the porphyritic granodiorites in this area shows that the rocks belong to calc-akaline and metalumious series.The MORB-normalized spider diagram of trace elements reveals enriching LILE of Ba and Sr,and lacking of HFSE of Nb,Ta,Hf and Y.The ratio of K/Rb is 295.34388.88 and Rb/Sr is 0.210.29.The spider diagram of rare earth element,show relative smooth,weak negative abnormal of Eu and right steep patterns.∑ LREE/∑ HREE is 9.1412.22.They all indical well differentiation between LREE and HREE.Through the analysis of strural factors the genesis of Yashan granodiorite is that sabduction of Pacific plate to Eurasian plate causes mantle plume activlty,which produces mantdiapir and crust partial melting,then form crust-mantle magma,and the furture invasion form the granodiorite.