Geochemistry of late Miocene-Pleistocene basalts from a coastal area of Vietnam: Implication for small-scale mantle heterogeneities

Abstract

This study presents a comprehensive analysis of late Miocene to Pleistocene basaltic samples collected from a coastal area of central Vietnam. The investigation involved various analytical methods, including eruption age determination, petrographic examination, geochemical characterization, and assessment of Sr-Nd-Hf-Pb isotopic compositions. The sampled basalt types include silica-undersaturated mantle xenolith-bearing basalts (∼1 Ma), olivine-bearing phyric alkaline, and sub-alkaline basalts (∼7 to 1 Ma). These basalt varieties display typical intraplate geochemistry and a wide range of radiogenic isotope variations, indicating mantle and crustal influences. Interestingly, despite these variations, there is no evidence of crustal contamination. Spatial analysis reveals distinct differences in geochemical and isotopic signatures across the sampled areas, suggesting spatial controls on mantle source composition. The isotopic compositions align with depleted mantle (DM) and enriched mantle types 1 and 2 (EM1 and EM2), closely associating with the Indian DUPAL lead isotopic signature. The localized heterogeneity within the subcontinental lithospheric mantle (SCLM) is attributed to metasomatism from mafic lenses or magmatic melts from the asthenosphere. Furthermore, elemental characteristics resembling typical ocean island basalts and elevated Pb and Sr isotopic ratios suggest a potential involvement of ancient, subducted sediments within the mantle.