Geochemical and Mineralogical Investigation on Different Types of Cenozoic Basalts in the Sanshui Basin: Implications for Magma Mixing Processes

Abstract

Two kinds of basalts with different chemical compositions were obtained in the Sanshui Basin, they share the same eruption period. Although they have significant differences in major and trace element concentrations, their isotopic ratios suggest a similar magma source. Based on mineral geochemical analysis, orthopyroxene with reaction rim and zoned clinopyroxene are observed in Zidong (ZD) basalts, but not found in Wangjiegang (WJG) basalts. Linear scanning of these minerals suggests compositional variation between within-plate tholeiite and within-plate alkali-basalt. Presence of a double-layer magma chamber under the Sanshui Basin, and occurrence of magma mixing between upper and lower chambers is proposed. This magma mixing leads to different chemical composition and mineral constitution of two kinds of basalts, as well as reaction rim and compositional variation of minerals in ZD basalts.

Keywords

Sanshui Basin / alkali basalt / tholeiite / magma mixing / magma chamber / geochemistry

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