东天山自然铜矿化带玄武岩的起源、演化及成岩构造背景

新疆东天山地区与玄武岩有关的自然铜矿化带位于东天山觉罗塔格构造带内,自西向东有十里坡、黑龙峰、长城山、东尖峰等主要矿(化)点,自然铜矿化主要发育在玄武岩、杏仁状玄武岩及凝灰岩夹层中。本文基于玄武岩的地球化学特征,研究东天山自然铜矿化带玄武岩是否与地幔柱有关、岩浆源区性质、岩浆演化、成岩构造背景等问题。研究显示,东天山自然铜矿化带玄武岩与地幔柱岩浆活动无直接关系,整个天山地区是否存在石炭-二叠纪地幔柱岩浆活动也需要进一步的研究; 玄武岩起源于亏损岩石圈地幔,是演化岩浆的产物; 演化的玄武质岩浆形成后,在岩浆房中或上升至地表的过程中没有发生明显的分离结晶作用,也没有受到明显的地壳物质混染; 与玄武岩对应的地幔橄榄岩平衡原生岩浆演化的高镁岩浆的产物,可能为东天山地区与铜镍硫化物成矿有关的基性-超基性岩,指示这些铜镍硫化物矿床可能与地幔柱岩浆活动也没有关系; 玄武岩形成于新疆北部后碰撞构造阶段的伸展期,是在拉张应力体制下,由于软流圈上涌导致岩石圈地幔部分熔融而形成。

Source, evolution and tectonic setting of the basalts from the native copper mineralization area in eastern Tianshan, Xinjiang

The native copper mineralization area is located in Jueluotage tectonic belt, eastern Tianshan, Xinjiang, China. There are 4 main mineralized districts (Shilipo, Heilongfeng, Changchengshan and Dongjianfeng) from west to east. The metallization of native copper occurred in the basalts, amygdaloidal basalts and tuff. Based on the geochemical characteristics, this paper studied the relationship between basalts and mantle plume, the source of basaltic magma, the evolution of magma, and the tectonic setting of diagenesis in the native copper mineralized belt. The results indicated that, there was no connection between the basalts and the mantle plume in the study area, and there wasn't mantle plume magmatism at Carboniferous- Permian in Tianshan area probably. The basalts originated from the depleted lithospheric mantle and were the production of evolutional magma. After built-up, the evolutional basaltic magma did not occur the apparent fractional crystallization and contamination with crustal materials in the magma chamber or during the rising process of magma. Corresponding to the basalts, the high-Mg igneous rocks evolved form the primary magma should exist, and they might be the basic-ultrabasic rocks with Cu-Ni sulphide mineralization in eastern Tianshan area. And these Cu-Ni sulphide deposits had no connection with the mantle plume magmatism probably. The basalts formed at the extensional stage of post-collisional tectonic setting in North Xinjiang. Under the extensional regime, the upwelling of asthenosphere caused the partial melting of lithosphere mantle, and then the primary magma formed.