Cenozoic intraplate volcanism in central Asia: Mantle upwelling induced by India-Eurasia collision

Most of Earth's volcanism occurs at tec-tonic plate boundaries associated with sub-duction or rifting processes. The mantle plume hypothesis is an important supple-ment to plate tectonics for explaining some high-volume intraplate volcanic fields. How-ever, many intraplate magmatic provinces occur as low-volume, monogenetic basaltic -suite fields that are neither associated with plate-boundary processes nor attributable to mantle plumes, and the origin of such mag-matism has long been debated. Identification of their source characteristics and possible mechanisms that trigger mantle melting will provide essential insights into Earth's mantle heterogeneity and also develop our knowl-edge of tectonic plate movement through time. Here, we report new geochronology, mineral chemistry (especially olivine), and whole-rock chemical and Sr-Nd-Pb-Hf isoto-pic compositions on Cenozoic intracontinen-tal alkaline basalts from the northwestern Tarim craton (central Asia), aiming to better assess the origin of Earth's low-volume effu-sive intraplate volcanic fields. The basalts (ca. 42 Ma) have olivine (e.g., mean Ni abundances of -2250 ppm, mean Mn/Zn ratios of 13.7) and whole-rock chemistry consistent with their derivation from a mixed peridotite-py-roxenite source. Moderately depleted Sr-Nd-Pb-Hf isotopes (87Sr/86Sr = 0.7039-0.7053; & epsilon;Nd = +4.0 to +5.5; 206Pb/204Pb = 18.247-18.535; & epsilon;Hf = +8.1 to +8.7) require a young (ca. 500 Ma) oceanic crust recycled into the source, possibly related to subduction events during the assembly of Pangea. Estimated thermal-chemical conditions indicate that the original melting occurred in a relatively dry (H2O = 1.4 & PLUSMN; 0.9 wt%) and reduced (logfO2 & UDelta;FMQ = -0.97 & PLUSMN; 0.21, where FMQ is fayalite-magnetite-quartz) asthenosphere under a mantle potential temperature of -1420 & DEG;C and a pressure of -3.7 GPa (corre-sponding to a depth of -120 km). Combining these data with regional tectonic history and geophysical data (high-resolution P-wave tomography), we propose that the long-lasting India-Eurasia collision triggered asthenospheric upwelling, focusing melts along translithospheric zones of weakness; this model provides a robust explanation for the observed Cenozoic intracontinental vol-canism in central Asia. The integrated geo-chemical and geophysical evidence reveals that plate subduction-induced mantle up -welling represents a likely mechanism for the generation of many regions of plume-absent intraplate magmatism within continents.