太行山南段平顺杂岩体成因:岩石学、年代学和地球化学证据

Petrogensis of the Pingshun Complexes in the Southern Taihang Mountains: Petrology, Geochronology and Geochemistry

太行山南段平顺杂岩体主要由橄榄角闪辉长岩,角闪辉长-闪长岩和闪长岩组成,锆石SHRIMP U-Pb测年显示,橄榄角闪辉长岩体和闪长岩体年龄分别为123.4±1.7 Ma和125.3±2.3 Ma,说明岩体形成于早白垩世。平顺杂岩体SiO2含量介于42.82%~63.54%之间,以高 Mg#,富 Na,高 Sr、Cr、Ni,以及富集 LILE、LREE,亏损 HFSE、HREE 为特点,并具有相对低的87Sr/86Sr初始比值和明显偏低的εNd（125 Ma）值,表明岩浆具有壳幔双重属性。结合辉长岩中地幔包体已有的研究成果,认为辉长岩是由富硅流体交代的亏损地幔橄榄岩经低程度部分熔融形成；高 Mg 闪长岩起源于下地壳部分熔融,并与一定规模的幔源岩浆发生混合；角闪辉长-闪长岩形成于辉长质岩浆与高Mg闪长质岩浆的混合作用。

The Pingshun complexes in the southern Taihang Mountains mainly consists of olivine hornblende gabbro, hornblende gabbro-diorite and diorites. The zircon SHRIMP U-Pb dating results show that the olivine hornblende gabbro and diorites are 123.4±1.7 Ma and 125.5±2.3 Ma, respectively, which suggests that the Pingshun complexes was formed in the Early Cretaceous within a short time. The Pingshun complexes has the following characteristics： SiO2 mostly 42.82%-63.54%, high Mg# values and Na, Sr, Cr, Ni contents, and high abundances of LILE and LREE, low abundances of HFSE, relative low initial ratio of 87Sr/86Sr and strikingly lowεNd（125 Ma） values, which showed that the magma originated from the mixing between magma derived from refractory peridotite and crustal magma. Combined with the nature of the mantle dunite xenoliths from olivine hornblende gabbro, we suggest that the primary magma for the olivine hornblende gabbro should derive from the partial melting of the refractory peridotite source modified by SiO2-rich melt. High-MgO diorite was derived from the partial melting of the lower continental crust from the central orogenic belt, and then mixed with some mantle magma. The hornblende gabbro-diorite formed in the process of mixing between gabbro magma and high-MgO diorite magma.