山西塔儿山-二峰山含矿闪长质岩石年代学和地球化学特征及对深部动力学过程约束

Petrology,Geochemistry and Constraint for the Geodynamic Process of Ore-bearing Diorites in Ta’Ershan-Erfengshan,Shanxi

塔儿山-二峰山矽卡岩型铁矿床位于山西省临汾市,构造上位于华北板块中部太行山陆块南部。笔者对与该矽卡岩型铁矿床相关的闪长岩体,即二峰山和塔儿山岩体进行锆石LA-ICPMS U-Pb定年,结果表明,岩体侵位年龄为(128.7±3.0)~(131.2±2.2)Ma,这与华北地区其他矽卡岩型铁矿床中岩体年龄基本一致,指示它们可能与同一区域构造事件有关。岩石样品地球化学数据显示,塔儿山闪长质岩石属于钙碱性准铝质闪长岩,二峰山闪长质岩石属于碱性准铝质闪长岩;2个岩体具有相似的地球化学特征,如较低的SiO_(2)含量(57.17%~65.51%),高碱含量(Na_(2)O=5.07%~6.72%,K_(2)O=7.92%~11.73%),较低的Mg#,富集LILEs(Sr、Ba)和LREE,亏损Ni、Ta、Ti等高场强元素的特点。2个岩体的地球化学特征表明,岩体的初始岩浆分别由同一源区不同程度的部分熔融产生。结合平顺西安里、河南安林及山东莱芜地区闪长岩类年代学、地球化学数据对比研究,笔者认为华北克拉通中部未发生类似其东部的拆沉作用,古老下地壳熔融的岩浆在矽卡岩型铁矿床形成过程中发挥了重要的作用。

The Ta'ershan-Erfengshan iron skarn deposit,is located in the south Taihang mountains,central North China Craton(NCC).The diorites that hosted Ta'ershan-Erfengshan deposits,namely Ta'ershan and Erfengshan intrusions,yielded zircon U-Pb ages of(128.7±3.0)Ma~(131.2±2.2)Ma,which are in accordance with other Fe-skarn-related intrusions in eastern NCC,suggesting that they were related to same tectonic events.The geochemical data of ore-bearing diorites indicate that Ta'ershan diorite belongs to calc-alkalic aluminum diorite and Erfengshan diorite belongs to alkaline aluminum diorite.The Harker diagram and Rb/Nd-Rb diagram of the Ta'ershan-Erfengshan diorites indicate they are derived from one common source by different degrees of partial melting.At the same time,they also have similar geochemical characteristics,such as low contents of SiO_(2)(57.17%~65.51%),high contents of alkaline(Na_(2)O=5.07%~6.72%,K_(2)O=7.92%~11.73%),low Mg^(#) values,enriched in LILEs(Sr、Ba)and LREEs and depleted in HFSEs(Ni、Ta、Ti).In comparison with the chronology and geochemistry data of Pingshun-Xi'anli、Anlin and Laiwu diorites,this paper suggests that the central part of the North China Craton has not undergone delamination similar to the eastern part,and that the melting magma of the ancient lower crust has played an important role in the formation of iron skarn deposits.