Generation of hydrous-carbonated plumes in the mantle transition zone linked to tectonic erosion and subduction

• P-type convergent margins supply crust material to the mantle transition zone (MTZ).
• Hydrated and carbonated rocks of oceanic slabs supply H2O and CO2 to the mantle.
• U-Th-K–rich crustal material can accumulate in the MTZ and serve a source of heat.
• H2O and CO2 can metasomatize the mantle and generate hydrous-carbonated plumes (HCPs).
• HCPs are manifested on the surface as rift basins and intra-plate volcanic fields.

This paper presents a model for the generation of hydrous-carbonated plumes (HCPs) in the mantle transition zone (MTZ) linking (i) the Pacific-type convergent margins; (ii) melt generation in the MTZ under the influence of volatiles (water, carbon dioxide) and subducted granitic material and oceanic slabs and (iii) the Meso-Cenozoic intra-plate magmatism in Central Asia. The model is based on four groups of evidences obtained from geology, petrology, seismic tomography and numerical simulations. The double-sided subduction at the Pacific-type margins around post-Miocene Asia supplies hydrated-carbonated oceanic crust and continental crust materials down to the deep mantle, which accumulate in the MTZ at 410–660 km. The delivery of crustal material to the MTZ is provided by the direct subduction of intra-oceanic arcs in the Western Pacific and by the tectonic erosion of convergent margin hanging walls. The U-Th-K–enriched continental material accumulated in the MTZ can serve an additional source of heat. Evidence for the subduction of continental crust materials comes from seismic tomography and numerical modelling data. The subducting oceanic slab consisting of serpentinites, hydrated sediments, carbonates and carbonatized basalts can supply water and carbon dioxide to the deep mantle and metasomatize it. The presence of volatiles, which can reduce melting temperature, and the presence of the subducted crustal material, which may serve an additional heater, can synergistically trigger the generation of HCPs. Those HCPs can induce mantle upwelling, melting of the metasomatized mantle and subducted MORB slabs, ascent of melts, surface rifting and formation of mafic and bimodal volcanic series. In addition, they can contribute to the supercontinent cycle. The HCPs generated in the MTZ beneath Central and East Asia resulted in a shift of the tectonic regime from transpression to transtension and in the formation of numerous Meso-Cenozoic intra-plate volcanic fields.