Paleoproterozoic sediment recycling leads to LOMU signature in hydrous asthenospheric mantle

Abstract

This study presents new geochemical and petrological data from the Higashi-Matsuura alkali basalts and demonstrates the presence of a LOMU-type mantle in southwest Japan. Radiogenic isotope ratios measured at the Hiroshima University (TIMS MAT-262) show low 206Pb/204Pb ratios (17.72 - 18.04) and moderate 87Sr/86Sr ratios (0.7041- 0.7044), indicating similarities with LOMU-type alkali basalts found in East Asia (e.g., Changbaishan, Wudalianchi, Xiaogulihe etc.).Petrological studies indicate that primary magma was generated in the hydrous asthenospheric mantle. Previous studies established that a hydrous asthenospheric mantle (> 1.8 GPa) derived from the stagnant Pacific Plate was responsible for the origin of southwest Japan alkali basalts. However, this model cannot explain LOMU-type isotopic ratios of Higashi-Matsuura basalts.In this study, we modelled the lead isotopic evolution for the generation of LOMU-type magmas, suggesting mixing of two independent Paleoproterozoic magma sources.