Element geochemistry and geologic significance of the basanite and its xenoliths in the Maguan Area, Yunnan Province

摘要

There are kinds of xenoliths in volcanic breccia rocks at Maguan Area, Yunnan Province. Systemically petrological and geochemical studies of the host rocks and their xenoliths show that they can be classified into three groups, basanlte and ultrapotassic rocks as cements of volcanic breccia rocks, and spinel mantle peridotite which can be further divided into two groups. The one is primitive peridotite which stands for residues of highly melted primitive mantle, and the other one is metasomatied peridotite which origins from depleted mantle and contaminates with slab fluid. Besides, an altersted basic-ultrabasic rock, whose protolith is not known still, and some metamorphic xenoliths are discovered. They develop black opaque materials and various alterations, such as chloritization, carbonatation, serpentinization and uralitization, companied by metalliferous mineralization and sulfidization. The geochemical similarities of altersted basic-ultrabasic rock, metamorphic xenoliths and metasomatied peridotite suggests that mantle fluid from lateral asthenosperic mantle flow resulted by collision and subduction of India—Eurasia initiates alterations, and contaminated with slab fluid, which makes the mantle fluid change from melt of high temperature to hydrothermal fluid of relative low temperature. The mechanism of alkaline magma and mantle fluid can be manifested metalliferous mineralization and sulfidization in microcosmic, and have something to do with polymetal ores related to alkaline porphyry and long-distance middle-low hydrothermal deposits. So, studies of volcanic breccia rocks, basanlte and mantle xenoliths are of great significance for deep mineralization principles at western Yunnan Province.