太行山南段矿山杂岩体LA-ICP-MS锆石U-Pb年代学、地球化学及其地质意义

Geochemistry and chronology characteristics of Kuangshan complex in the southern Taihang Mountain and the geological significance

太行山南段矿山杂岩体主要由闪长岩、石英闪长岩及二长闪长岩组成,LA-ICP-MS锆石U-Pb测年显示,闪长岩形成于125.2 Ma±1.4 Ma—126.9 Ma±1.3 Ma,说明该岩体形成于早白垩世。矿山杂岩体具有高w(Sr)(557×10^(-6)~985×10^(-6))和w(Sr)/w(Y)(30.9~61.8)值,低w(Y)(11.52×10^(-6)~22.10×10^(-6))和w(Yb)(1.30×10^(-6)~2.00×10^(-6))值的特征,这和埃达克岩相似。Th、U和大离子亲石元素(Rb、Ba、K)富集,高场强元素(Nb、Ta、Zr、Hf)亏损。稀土元素配分曲线近乎一致,均显示为轻稀土富集、弱正铕异常的右倾型的特点。综合岩性组合、岩相特点、地球化学特征和锆石年代学特征认为,矿山杂岩体是在下地壳大规模拆沉基础上,经过连续俯冲的影响,拆沉下来的物质诱发软流圈上涌而部分熔融,并交代上覆亏损地幔岩体使其发生部分重熔为高Mg的类似埃达克岩浆而形成的。

Kuangshan complex in the South Taihangshan mountain mainly consists of diorite,quartz diorite and monzodiorite.The LA-ICS-MS dated zircon U-Pb age of the diorite is 125.2 Ma±1.4 Ma to 126.9 Ma±1.3 Ma corresponding to Early Cretaceous Period.The complex is similar to adakite with high w(Sr)(557×10^(-6)-985×10^(-6))and w(Sr)/w(Y)(30.9-61.8),and low w(Y)(11.52×10^(-6)-22.10×10^(-6))and w(Yb)(1.30×10^(-6)-2.00×10^(-6)).Th,U and large ion element(Rb,Ba,K)are enriched,high field strong element(Bb,Ta,Zr,Hf)lost.The REE pattern curve is almost the same declined to right with LREE enrichment and weakly positive Eu anomaly.Comprehensively considering characteristics of litho logic combination,lithofacies,geochemistry and zircon U-Pb chronology the complex is originated from continuous subduction and large scale delamination of the lower crust by which some of the delaminted material in duce upwell of asthnosphere to produce partially melted magma which in turn replace the overlying depleted mantle rock mass and partially rememelt them to produce the Mg-rich adakite-like rock.