胶东半岛艾山岩体岩石地球化学特征及成因意义

摘 要]艾山岩体位于胶东半岛的栖霞和蓬莱之间,主要岩性为二长花岗岩。岩石(地球)化学特征表明,艾山岩体为高硅(SiO₂=68.01%～75.85%)、高钾(K₂O/ Na₂O>1)、高镁和铁(MgO+Fe₂O₃+FeO+TiO₂>2%)、准铝-过铝质(A/ CNK=0.916～1.012)的钙碱性花岗岩,属I 型花岗岩。Rb、Ba、K、Sr 等大离子亲石元素(LILE)明显富集,Y、Hf、Zr、Yb、Nb、Ta 等较不活泼的高场强元素(HFSE) 相对亏损,显示负的Nb 异常和高的正Pb 异常,表明岩浆起源于下地壳,且地幔物质参与了岩浆作用过程。轻稀土元素相对富集,具弱的Eu 异常,SiO₂与ΣREE、δEu 相关性表明岩石主要受部分熔融控制。构造环境图解判别显示,艾山岩体的形成与岩石圈的消减和古太平洋板块俯冲有密切的联系。

Petrogeochemical Characteristics and Genetic Significance of the Aishan Pluton in Jiaodong Peninsula

The Aishan pluton is located between the Qixia and Penglai cities in Jiaodong Peninsula.It mainly consists of monzogranites,and is a typical late Yashanian granite pluton.Petrochemical characteristics indicate that it is calcium alkaline granite with high silicon(Si2O=68.01~75.85),high potassium(K2O/Na2O>1),high magnesium and iron(MgO+Fe2O3+FeO+TiO2>2%),and metaluminium-peraluminium(A/CNK=0.916~1.012).It belongs to type-I granite,and originates from the crust.The LILE elements,including Rb,K,Ba and Sr,are significantly enriched,while depleted for those inactive HFSE elements including Y,Hf,Zr,Yb,Nb and Ta.Generally,the rocks display negative Nb and positive Pb anomalies.This may imply that the magma originated from upper mantle or lower crust with crust substance involved in.The light REE is apparently enriched with weak Eu anomalies.Correlation between SiO2 and ΣREE or δEu indicates it is mainly controlled by partial melting.Combined with tectonic background,the Aishan pluton has a very close relation with the suduction of lithosphere and the underthrusting of the ancient Pacific plate.Strong mantle metasomatism partial melting caused by asthenosphere upwelling is the main reason for the generation of the Aishan pluton.