Intraplate extension of the Indochina plate deduced from 26 to 24 Ma A-type granites and tectonic implications

In recent years, abundant Cenozoic potassic magmatic rocks from eastern Tibet and the Indochina Block have been studied extensively; however, until now, knowledge of Cenozoic A-type granites from the interior of the Indochina Block has been limited. U-Pb zircon ages for six samples of the Salei granite pluton within the Indochina Block range from 26 to 24 Ma. In situ Lu-Hf and Sr-Nd isotope data indicate that the Salei pluton was sourced mostly from Mesoproterozoic basement rocks of the Indochina Block, mixed with a small volume of juvenile crust derived from the underplated mantle. Whole-rock major element geochemistry indicates that the six samples are peraluminous high-K calc-alkaline granites. The trace and rare earth element patterns are typical of within-plate A-type granites. In combination with previous research, the present results suggest that the late Oligocene Salei granite formed from the convective removal of thickened lower continental lithospheric mantle. Moreover, the presence of 26-24 Ma A-type granites in the Indochina Block indicates within-plate extension in the interior of the block during the late Oligocene.