Melt inclusions in phenocrysts track enriched upper mantle source for Cenozoic Tengchong volcanic field, Yunnan Province, SW China

Abstract

The Tengchong Volcano Field (TVF), located at the southeastern margin of the Tibetan Plateau, is the only Cenozoic volcanic-related geothermal region around the Himalayan geothermal belt that extends from southwestern Tibet to western Yunan along the Indo-Asian suture zone. The volcanic rock suites from this field are important proxies for the India-Eurasia convergence since the Late Cretaceous. Here, we investigate the melt inclusions hosted in the Tengchong volcanoes from different locations including Qingliangshan, Heikongshan and Dayingshan based on petrological and geochemical data with a view to gain insights on the magma sources and petrogenesis. Olivine (Ol), clinopyroxene (Cpx), orthopyroxene (Opx) and plagioclase (Pl) phenocrysts from basalts and andesites of the Tengchong volcanic rocks carry abundant melt inclusions. These melt inclusions are high in silica and alkali contents, and enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) such as Rb, Th, U, K, Pb, but depleted in high field strength elements (HFSEs) including Nb, Ta, Ti, P, with arc-like signature. The geochemical features of the melt inclusions suggest that the TVF volcanic rocks are possibly cogenetic, but with a progressive increase in the degree of magma evolution from Qingliangshan, through Heikongshan to Dayingshan. Melt and trace element modeling indicates that the magmas probably originated through variable degrees of partial melting of LREE-enriched upper mantle within garnet stability field with significant contributions from subducted oceanic crust. The melts were contaminated with continental crustal during ascent, followed by fractional crystallization.The volcanic activity was controlled by major Late Cenozoic dextral strike-slip faults within an extensional setting related to the geodynamic evolution of India plate. Our study provides insights into the tectonics accompanying the India-Eurasia collision.