A tectonic model for Cenozoic igneous activities in the eastern Indo-Asiancollision zone

Geochronologic dating and compilation of existing age data suggest that Cen ozoic activities in the eastern Indo Asian collision zone of southeast Chin a 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 sy nchronously with transpression. The younger rocks are widely distributed in rift basins and are coeval with east-west extension of Tibet and eastern A sia. 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 gay bet ween the two magmatic sequences represents an important geodynamic transiti on in the evolution of the eastern Indo-Asian collision zone, From processe s controlled mainly by crustal deformation to that largely dominated by man tle tectonics. (C) 2001 Elsevier Science B.V. All rights reserved.