冈底斯朱诺地区中新世板内热隆伸展成矿

位于冈底斯构造成矿带中段西侧的朱诺地区具有良好的成矿前景,已发现有朱诺大型斑岩铜矿床和铁雅铁铜矿点。野外基础地质和矿床地质调查、构造分析和岩石化学的研究表明,朱诺斑岩铜矿床在构造上受近EW向和近SN向伸展断裂控制,时间上属于中新世青藏高原南部板内构造过程,含矿斑岩具有典型的埃达克质岩特征。朱诺及其所在的冈底斯构造成矿带在中新世处于板内构造环境,板内伸展构造—埃达克质岩—斑岩铜矿系统叠加在早期的俯冲—碰撞构造岩石组合之上。与埃达克质岩形成直接相关的下地壳流动导致冈底斯上地壳及下地壳显著加厚,发生部分熔融作用,下地壳物质可能源于地壳减薄的锡瓦利克盆地,流经喜马拉雅,穿过并改造了雅鲁藏布江缝合带中挤入地壳的洋壳地幔岩石,造成被混入洋壳地幔成分的冈底斯下地壳发生部分熔融,形成埃达克质岩浆,上升并顶托冈底斯上地壳,致使冈底斯上地壳先后发生近EW向和近SN向的伸展,在上地壳伸展扩容空间中含矿埃达克质岩浆沿伸展断裂上升、侵位,并富集成矿。

Miocene Intraplate Thermo-Upwelling Extension of Zhunuo Porphyry Copper Deposits in Gangdese

Zhunuo area located in western Gangdese metallogenic belt reveals good metallogenic prospects, where Zhunuo large-scale porphyry copper deposit and the Tieya iron-copper polymetallic ore spot have been discovered recently. Based on the field deposit-geological investigations, structural analysis and petrochemistry studies, this paper presents a Miocene intraplate thermo-upwelling extensional metallogenic model of the Zhunuo porphyry copper deposit which is tectonically controlled by the nearly east-west and north-south extensive faults related to lower crustal flow. The ore-bearing porphyries have the characteristics of typical adakitic rock. The Zhunuo area and Gangdese belt belonged to intraplate tectonic setting in Miocene, where the earlier subduction-collision tectonics was superimposed by the intraplate extensional tectonics, adakitic rocks, and porphyry copper system. The lower crustal flow and partial melting produced adakitic rocks and lead to Gangdese crustal thickening. The flowing material of lower crust may originate from the Himalayan foreland basin with crust thinning, flowing through Himalayas and the Brahmaputra Suture Zone, and reforming the mantle rocks of Neo-Tethys oceanic crust. Therefore,the Gangdese lower crust mixed Neo-Tethys mantle materials and generated adakitic magma by partial melting. The lower crustal flow leads to nearly east-west trend and north-south trend extension successively in the Gangdese upper crust, the ore-bearing adakitic magma rose and emplaced the normal faults from lower crust, and controlled ore formation processes.