东天山-北山镁铁-超镁铁质岩特征、成矿意义及构造背景

Characteristics,Metallogenic Significance and Tectonic Setting of Maficultramafic Intrusions in East Tianshan and Beishan

东天山-北山地区镁铁-超镁铁质岩体成群成带分布,明显受区域内主干断裂控制,主要分布于东天山、中天山地块和北山裂谷。镁铁-超镁铁质岩体与Cu-Ni矿化密切相关,小岩体成大矿为普遍现象。含矿岩相多集中在橄榄辉长岩、角闪橄榄岩、辉橄岩和各岩相接触带上。岩体低Ti高Mg,高m/s和m/f是评价其含矿性的良好指标。SrNd同位素显示镁铁-超镁铁质岩体整体上源于亏损地幔,在演化过程中经历了同化混染作用,中天山和北山地区较东天山地区混染程度较小。成岩成矿集中在早二叠世约280 Ma,指示其可能是统一地球热力学的产物。镁铁-超镁铁质岩体的构造背景复杂,争议较多,单一的构造背景不能解释所有问题,后碰撞伸展和地幔柱的共同作用可能诱发大规模成岩成矿事件。

Mafic-ultramafic intrusions exposed in East Tianshan and Beishan Mountains ,evidently controlled by region-al fractures,are distributed as clusters and occurred in three belts:East Tianshan,Middle-Tianshan Block and Beishan Rift. The Cu-Ni mineralization is closely related to mafic-ultramafic intrusions and it’s common that large deposits yield to the small intrusions.In terms of petrography,the ore-bearing intrusions are mainly olivine gabbro,hornblende peridotite, harzburgite and the contact zone,with low in Ti while high in Mg,m/s and m/f.Sr-Nd isotope reveal that the mafic-ultra-mafic intrusions originate from depleted mantle,then experience crustal assimilation and contamination in different ex-tent during evolution, while intrusions exposed in Middle-Tianshan and Beishan suffer lesser contamination than in East Tianshan.The age of intrusions and deposits all approximately focus on 280 Ma,i.e. the early Permain, indicating that they may come of the unified earth thermodynamics.The tectonic setting of these intrusions is complicated with much controversy,and any single one can not explain all problems.The interaction between post-collisional extension and man-tle plume may induce events of a large-scale diagenesis and mineralization.