Petrological characteristics of lithospheric mantle beneath Nui Nua and Ba Ria areas, southern Vietnam

摘要

Spinel peridotites from the Nui Nua and Ba Ria volcanic suites of southern Vietnam were investigated to interpret mantle processes and geochemical evolution of the lithospheric mantle beneath southern Vietnam. Spinel peridotites from both study areas consist of lherzolites and harzburgites displaying porphyroclastic textures. The spinel peridotites may have experienced a low degree (1-13%) of fractional melting. The variation of light rare earth elements (LREEs) and other incompatible elements in clinopyroxenes indicates that most of the spinel peridotites have undergone silicate metasomatism. The spinel peridotite xenoliths of both areas originated at depths between 35 and 52 km with equilibrium temperatures ranging from 714-1211 degrees C (+/- 15 degrees C). Correlations between Sr, Nd, and Pb isotopic compositions of the clinopyroxenes suggest that the spinel peridotites originated from mixing of depleted (DM) and enriched (EM2) mantle sources. The spinel peridotites from Nui Nua gave a Pb-Pb isochron age of 3.6 +/- 0.3 Ga which suggests the formation time of lithospheric mantle beneath southern Vietnam due to initial melt extraction.