Identification of carbonated eclogitic source for Cenozoic intraplate alkaline basalts from western Central Asia and its geodynamic implication

Abstract

Carbonated eclogite has been identified as a significant component in the formation of intraplate alkaline basalts, typically attributed to stagnated subducted oceanic slabs, such as the Pacific plate beneath eastern China. However, it is unclear whether this component exists in other tectonic settings. Here, we present new zircon UPb geochronology, mineral chemistry, and geochemical analyses of Cenozoic Tuoyun basanites and alkaline basalts from western Central Asia, where stagnated subducted oceanic slabs are absent, to elucidate the source properties and associated geodynamic processes. Olivine compositions (e.g., moderate Ni concentrations, low Mn/Fe and Ni/(Mg/Fe) ratios) and whole-rock chemistry (e.g., high Fe/Mn, Ca/Al, and Zr/Hf ratios, TiO₂ contents, and weak anomalies of Zr-Hf-Ti) suggest a carbonated eclogite in the mantle source of the Tuoyun basanites. Trace elements (positive NbTa anomalies and absence of positive Eu anomaly) and depleted to slightly enriched Sr-Nd-Hf isotopic compositions indicate that the basanites originated from mantle sources composed of variable proportions of altered oceanic crust (AOC) and carbonates. Synthesizing regional geochemical, geophysical studies and tectonic history, we propose that the continuous India-Eurasia collision triggered mantle upwelling, leading to the formation of a widespread carbonated eclogitic mantle source beneath western Central Asia. Our findings suggest that carbonate-rich mantle sources may also be present in areas without stagnated subduction slabs.