新疆东天山黑白山镁铁超镁铁岩地球化学、U-Pb年代学、Hf同位素特征及地质意义

黑白山镁铁超镁铁岩位于新疆中天山地块与觉罗塔格构造带的分界断裂——阿其克库都克大断裂南侧约4 km处.该岩体主要由阳起石化橄榄辉石岩、辉橄岩、辉石岩、蚀变细粒辉长岩组成,对岩体的主微量及稀土元素地球化学特征研究表明,岩体属铁质镁铁超镁铁岩,具低钾拉斑玄武质岩的分异特征;岩石具相对较低SiO2(43.90％～52.80％...

Geochemistry,U-PB chronology,Hf isotope Characteristics and Geological Significance of the Heibaishan Mafic Ultramafic Rocks of East Tianshan,Xinjiang

The Heibaishan mafic ultramafic rock is located about 4 km south of the Akkekuduk fault,the boundary fault between the Middle Tianshan block and the Jelotag tectonic belt in Xinjiang province.The rock mass is mainly composed of anolitic pyroxenite,pyroxenite,pyroxenite and altered fine gabbro.The study on the geochemical characteristics of the main,trace and rare earth elements of the rock mass shows that the rock mass belongs to ferromagnesian ultramafic and has the differentiation trend of low potassium tholeiite.Rocks with relatively low SiO₂(43.90%~52.80%),relatively rich Na₂O(0.38%~2.97%),poor K₂O(0.11%~0.47%)and Na₂O>K₂O,the characteristics of the MgO style change of value and higher(4.25%~32.49%),high Mg#(63.94~82.98),the relative enrichment of light rare earth(La/Yb N 2.03~5.76),the enrichment of large ion lithophile Rb,Ba,U,La,loss of high field strength elements Nb,Ta,Ce,Ti,strong enrichment of Pb,It shows that the rocks have mantle-derived characteristics and island arc magmatic characteristics.The zircon LA-ICP-MS U-PB age(392.7±4.5Ma)indicates that the rock mass is a product of early Devonian magmatic activity.The geochemical characteristics of hafnium isotopes and petrology show that the magma originated from the asthenosphere with the loss of the subducted oceanic crust at the early stage,and was mixed by the crust and surrounding rocks during the magma evolution,but the mixing was weak.The discovery of the Heibaishan rock mass provides a new evidence for the southern subduction of the Northern Tianshan Ocean along the Akhikkuduk fault in the early Paleozoic.