辽宁兴城尖山早白垩世火山机构及岩石地球化学特征

Early Cretaceous volcanic mechanism in Jianshan of Xingcheng area,Liaoning and its lithogeochemical characteristics

对辽宁兴城尖山火山机构的岩性--岩相学特征进行了分析,并对角闪安山岩进行了岩石地球化学研究。结果表明角闪安山岩SiO_2=58.42%~60.42%,Al_2O_3=16.17%~17.5%,MgO=1.39%~3.08%,Mg~#=31~50,Sr=(387~1 325)×10^(-6),Yb=(1.15~1.57)×10^(-6),Y=(12.1~16.8)×10^(-6)。岩石富集轻稀土元素及大离子亲石元素,亏损高场强元素,高Sr和Sr/Y比值,低Y和Yb,显示出埃达克岩的地球化学特征,但其Mg~#较低,表明该类火山岩可能是加厚的基性下地壳部分熔融的产物,可能与早白垩世太平洋板块的俯冲构造背景有关。

The petrology and petrography of Jianshan volcanic mecganism in Xingcheng, Liaoning have been analyzed, and the geochemistry of hornblende andesites were studied. The results show that the hornblende andesites are characterized by Si02 = 58. 42% ?60. 4 2 % , MgO = 1. 39% ?3. 0 8 % ,Mg# = 31 ?50,A120 3 = 16. 17%-1 7 .5 % , Sr= (387 -1 325) x lO '6, Yb= (1 .1 5 -1 .5 7 ) x lO '6, Y = (1 2 .1 -1 6 .8 ) x 10~6, respectively.In addition, the volcanic rocks are enrichment in LREE and LILE and depletion in HREE, with high Sr and Sr/ Y values and low Y and Yb values, showing the geochemical characteristics of adakite. However, they are low in Mg#, indicating the volcanic rocks may originate by partial melting of the thickened mafic lower crust, and could be related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.