Hydrous upper mantle above the stagnant Pacific slab: evidence from the intra-continental alkali basalts from the Longgang volcanic field, NE China

Abstract

In northeast China, intra-continental magmatism is active, and some studies suggest the relations with subducted Pacific slab which is stagnant at the mantle transition zone beneath NE China. High pressure experiments and electrical conductivity studies indicate the existence of wet mantle above the stagnant slab, but the amount of water has not been estimated yet. In this study, the water content of mantle beneath NE China has been estimated by elucidating the conditions of melting. Temperature and depth of magma generation are estimated from thermodynamic constraints and REE compositions to be 1300 - 1310 degree C, 75 - 100 km depth. With hydrous mantle solidus calculation by Adiabat_1ph software, 220 - 600 ppm of water is required for generating partial melt beneath NE China.