鲁西地区中生代高镁闪长岩角闪石成分变化特征及其对矽卡岩型铁矿成矿作用的启示

Compositional Variations of Amphiboles from Mesozoic High-Mg Diorite in Western Shandong:Implications for the Mineralization of Skarn-type Iron Deposits

矽卡岩型铁矿床是我国最重要的铁矿床类型之一,在华北克拉通东部广泛发育,时空上与中生代高镁闪长岩体紧密伴生,研究其物质来源和成岩成矿过程具有重要的意义。本文对鲁西地区与金岭铁矿床具有成因联系的中生代高镁闪长岩中的角闪石进行了详细的成分研究,限定高镁闪长岩的岩浆演化过程及其物理化学条件变化,探讨高镁闪长岩的岩石成因机制及其与矽卡岩型铁矿床成矿作用之间的联系。金岭高镁闪长岩的角闪石斑晶边部与基质角闪石具有一致的主量元素成分,记录了相似的T-P-fO_(2)-H_(2)O条件,显著不同于角闪石斑晶核部。角闪石斑晶核部的平衡岩浆来源于地幔部分熔融,而角闪石斑晶边部与基质角闪石的平衡岩浆中则存在地壳组分的贡献。高镁闪长岩-矽卡岩型铁矿床体系为极其复杂的成岩成矿系统,起源于高氧逸度和高水含量的地幔源区,并经历了包括结晶分异、同化混染、岩浆混合以及流体出溶、迁移和淋滤在内的诸多复杂岩浆热液演化过程。这些源区特征和岩浆-热液过程记录了不同深度岩石圈对华北克拉通破坏的构造响应。

Skarn-type Fe deposit is among the most important types of iron deposits in China.Such deposits widely occur in the eastern North China Craton and are spatially and temporally associated with Mesozoic high-Mg diorites.It is of great significance to investigate the petrogenesis and mineralization processes and the material sources of the skarn-type Fe deposits and associated high-Mg diorites.This paper presents detailed compositional variations of amphiboles in the Mesozoic high-Mg diorite that is genetically related to the Jinling Fe deposit in Western Shandong,with the aims of constraining the magmatic processes and associated changes in the physical-chemical conditions and investigating the petrogenesis of the Jinling high-Mg diorite.This may provide insights into the genetic relationships between high-Mg diorite and skarn-type Fe deposit.The rims of the amphibole phenocrysts and the matrix amphiboles show similar major element compositions and record similar T-P-fO_(2)-H_(2)O conditions of magmatism,both of which are significantly different from those of the cores of amphibole phenocrysts.The melts in equilibrium with the cores of amphibole phenocryst would be mainly derived from the partial melting of a mantle source,whereas continental crust components might have been involved in the genesis of melts in equilibrium with the rims of the amphibole phenocryst and the matrix amphiboles.The association between high-Mg diorite and skarn-type Fe deposit is a complex magmatic and metallogenetic system.The magma might have originated from mantle sources with high oxygen fugacity and high H_(2)O content and experienced complicated magmatic-hydrothermal processes,such as fractional crystallization,assimilation,and contamination,magma mixing,fluid exsolution,and transportation and infiltration.These source characteristics and magmatic-hydrothermal processes record the tectonic responses of the lithosphere at different depths to the destruction of the North China Craton.