新疆吐哈盆地南缘铜矿带含矿斑岩的地球化学及形成环境  

Geochemistry and tectonic setting of copper-bearing porphyries on the southern margin of Tuha basin,Xinjiang.

作　　者：张连昌[1] 万博[1] 李文铅[2] 唐红峰[3] 

机构地区：[1]中国科学院地质与地球物理研究所矿产资源重点实验室,北京100029 [2]中国科学院广州地球化学研究所,广州510640 [3]中国科学院地球化学研究所,贵阳550002

出　　处：《岩石学报》2006年第1期225-235,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金(40473028);国家重点基础研究计划项目(2001CB409805);中国科学院创新项目(KZCX3-SW-137)资助

摘　　要：吐哈盆地南缘斑岩铜矿带位于中亚造山带东天山的中段。研究表明该铜矿带含矿斑岩的形成时代可分早石炭世和晚石炭世一早二叠世两期,前者以土屋-延东含矿斜长花岗斑岩为例,形成于与洋壳俯冲有关的岛弧环境,后者以赤湖和三岔口斜长花岗斑岩为例,形成于同碰撞造山的中一晚期。主量、微量元素和Sr-Nd同位素地球化学数据表明,吐哈盆地南缘铜矿带大多数斑岩具有钙碱性和岛弧花岗岩的特征,初始锶比值一般小于0．7046,δ_Nd(t)值为5．3～7．6,反映成岩物质的深源性；进一步可将斑岩划分为埃达克岩和非埃达克岩,其中延东-土屋和三岔口含矿斑岩具有埃达克岩的特征,而赤湖、灵龙、卡拉塔格和垅西矿化斑岩和成矿后斑岩不具埃达克岩特征。埃达克岩成因有两种：土屋-延东埃达克岩为洋壳板片熔融成因,三岔口埃达克岩为加厚下地壳的熔融成因。土屋-延东洋壳熔融埃达克岩的确定,进一步肯定了晚古生代石炭纪吐哈盆地南缘的岛弧环境。研究表明侵位于中亚造山带晚古生代岛弧环境和洋壳熔融成因的埃达克岩最有利于形成大型斑岩铜矿。The eastern Tianshan porphyry copper belt is located on the southern margin of Tuha basin. Based on isotopic dating, the intrusive ages of copper-bearing porphyries were divided into two stages： early Carboniferous （i. g. Tuwu-Yandong porphyry） and late Carboniferous to early Permian （ i. g. Sanchakou, Chihu and Linglong porphyry）. The Contents of SiO2 （64.92 - 73.05% ）, Al2O3 （14.24-17.08%）, MgO （0.92-2.16%）, Y （6.03×10^-6-15.98×10^-6）, Yb （0.48×10^-6-1.43×10^-6） andSr （347× 10^-6 - 920 × 10^-6） and positive Eu anomalies of the plagiogranite porphyries indicate that Tuwu-Yandong and Sanchakou porphyries possess adakitic characteristics. The rocks also exhibit positive εNd （t） values （ ＋ 5.3 - ＋ 7.6） and low initial ^87Sr/^86Sr values （0. 70330-0.70416）. Such features are similar to those of adakites derived from partial melting of a subduction-related oceanic slab. Based on our study of the geology and geochemistry, we suggest that Tuwu-Yandong adakitic magma in the Dananhu island was formed by direct melting of an obliquely-subducting early Carboniferous oceanic slab, but Sanchakou adakitic magma was formed by partial melting of thickening lower crust in late-collisional orogen processes. Our studies indicate that large porphyry copper deposits are related to adakitic rocks, and small porphyry copper deposits （ or ore spots） have normal calc-alkaline affinity. We propose that large porphyry copper deposits are related to adakitic, highly oxidized, and water-rich melts, their melts are eventually derived from slab melting during flat subduction.

关 键 词：晚古生代 岛弧 斑岩铜矿 埃达克岩 东天山 

分 类 号：P588.122[天文地球—岩石学]