西天山CuNi-VTiFe复合型矿化镁铁-超镁铁杂岩——哈拉达拉岩体成岩成矿背景特殊性讨论

摘要

西天山哈拉达拉镁铁-超镁铁杂岩为一CuNi-VTiFe复合型矿化岩体,主要由橄长岩、橄榄辉长岩、角闪辉长岩、辉长岩和辉绿岩组成.获得岩体中橄榄辉长岩SHRIMP锆石U-Pb年龄为308.8±1.9Ma,辉长岩SHRIMP锆石U-Pb年龄307.3±8.2Ma.岩石具堆晶结构、辉长-辉绿结构,岩体韵律层发育;各类岩石稀土和微量元素配分曲线模式相似,多具Eu,Sr正异常,它们可能为同一岩浆结晶分异演化的产物;Sr-Nd同位素特征(87Sr/86Sr初始比值=0.703913～0.705259,εNd(t)=4.00～8.42)表明原始岩浆来自于亏损地幔源区.推测哈拉达拉岩体形成于后碰撞造山早期伸展环境、叠加近同期地幔柱活动的特殊地质背景中.%Haladala pluton, a mafic-ultramafic complex related to CuNi-VTiFe composite mineralization in western Tianshan, consists of troctolite, olivine gabbro, hornblende gabbro and diabase. The SHRIMP zircon U-Pb age of 308. 8 ?1. 9Ma, 307. 3 ?8. 2Ma for olivine gabbro and gabbro of the Pluton were obtained. The major rock types in the Haladala pluton show cumulate texture, gabbro-ophitic textures, and the pluton exhibits well-developed rhythmic layering. All the different types rock of the plutong have rather similar trace-element distribution and REE patterns with positive Eu, Sr abnormity mostly, and it suggests they were the results of crystallization differentiation of the similar or same magma. The geochemical characteristics of Sr-Nd isotope compsition, initial "St/ Sr values =0.703913 -0.705259, em(t) =4.00-8.42, show that the original magma came from depleted mantle source. The study proposes that the Haladala pluton was formed in an early post-collisional orogenic stage, overlaying the possible mantle plume in the same time.