A tectonic model for Cenozoic igneous activities in the eastern Indo–Asian collision zone

Abstract

Geochronologic dating and compilation of existing age data suggest that Cenozoic activities in the eastern Indo–Asian collision zone of southeast China and Indochina occurred in two episodes, each with distinctive geochemical signatures, at 42–24 Myr and 16–0 Myr. The older rocks are localized along major strike–slip faults such as the Red River fault system and erupted synchronously with transpression. The younger rocks are widely distributed in rift basins and are coeval with east–west extension of Tibet and eastern Asia. Geochemical data suggest that the early igneous phase was generated by continental subduction while the late episode was caused by decompression melting of a metasomatically altered, depleted mantle. The magmatic gap between the two magmatic sequences represents an important geodynamic transition in the evolution of the eastern Indo–Asian collision zone, from processes controlled mainly by crustal deformation to that largely dominated by mantle tectonics.