山西平顺西安里铁矿区中生代闪长岩年代学及地球化学特征

摘要

山西平顺地区位于大型宽缓的太行山复式背斜的西翼,大地构造位置属吕梁-太行断块的太行块隆的东南部,是华北地区重要的矽卡岩铁矿矿集区,中生代闪长质岩石是本区矽卡岩型铁矿重要的成矿母岩.本研究对其进行锆石SHRIMP年龄测定和地球化学分析,结果显示辉长岩和闪长岩的锆石年龄分别为123Ma和126 Ma,两者侵位时代基本一致.地球化学分析显示区内岩浆岩主要为准铝质高钾钙碱性系列岩石,所有样品(二峰山闪长岩、西安里辉长岩和闪长岩)均有非常相似的稀土配分模式,富集轻稀土元素(∑LREEs平均值分别为94.64 μg/g、110.73 μg/g、118.63 μg/g),轻重稀土分馏不是很强烈,(La/Yb)N平均值分别为9.47、9.17、9.70；Eu异常不明显(δEu平均值分别为1.00、0.96、1.04),富集Ba、Th、U等大离子亲石元素,具有高Sr特征,所有岩性强烈亏损Nb、Ta等高场强元素.研究认为岩体主要来自幔源岩浆与壳源酸性岩浆的混合作用,样品高的Nb/Ta(17 ～22,平均19)以及Zr/Hf值(35 ～ 40,平均37)是继承了岩浆源区高Nb/Ta和Zr/Hf比值特征,表明地幔源区受到俯冲板片熔融体/流体的交代.其地球动力学背景为华北克拉通中生代破坏和岩石圈减薄事件,但是应该注意华北克拉通破坏和岩石圈减薄机制的多样性.%The Shanxi Pingshun region is located in the west limb of a large-scale anticline of Taighang Mountain and is to the southeast of the Taihang upwell of Liiliang-Taihang fault block. It is one of the most important skarn iron ore concentration areas in North China. The Mesozoic dioritic rock was the source rock for skarn Fe deposits. In this paper, the work carried out on zircon SHRIMP dating and geochemical analysis of Mesozoic magmatic rocks is described. The results of zircon ages for the gabbro and diorite were 123 Ma and 126 Ma, respectively (within the same intrusion periods). Magmatic rocks in the region were metaluminous high-K calc-alkaline series rocks and all the samples ( Erfengshan diorite, Xi' anli gabbro and diorite) were characterized by similar REE patterns with enriched LREE (ΣLREE on average is 94.64μg/g, 110.73 μg/g and 118.63 μg/g). The fractionation between LREE and HREE was not very strong since (La/Yb)N on average were 9.47, 9.17 and 9.70. The Eu anomaly was not obvious as δEu on average were 1.00, 0.96 and 1.04. The gabbro and diorite were enriched Ba, Th, U, and other LILEs had the characteristic of high Sr and strongly depicted HFSEs ( Nb, Ta). Combined with previous research results, indications are that the magmatic rocks were mainly from the mixing members between mantle-derived magma and the low crust-derived magma. High Nb/Ta (17 to 22, on average is 19) and Zr/Hf values (35 to 40, on average is 37) were inherited from the magmatic source features. This indicated that the mantle source was replaced by subducted slab melt/fluid. The geodynamic setting is Mesozoic destruction and a lithospheric thinning event in the North China Craton. However, the diversity of the mechanism should also be noted.