Early Cretaceous volcanic rocks in northern Baingoin, Tibet: Magmatic record of the closure of the Bangong-Nujiang Ocean

The petrological, zircon U-Pb dating, whole-rock geochemical, and zircon Hf isotopic data of the Early Cretaceous andesites and dacites in the Maqianxiang area of Baingoin County, Tibet, are reported. The zircon U-Pb ages of andesite are (108.0±1.5)Ma and (113.6±0.9) Ma, and those of dacite are (106.7±1.9) Ma and (113.6±0.8) Ma. The andesites are enriched in Th and U and depleted in Nb, Ta, and Ti, have variable Mg^# values (25-63), and show mainly negative zircon ε_Hf(t) values (-8.6 to +1.5). They are probably generated by mixing of mantle- and crust-derived melts. Dacite shares similar trace element features with the coeval andesite, and has negative zircon ε_Hf(t) values (-12.3 to -8.1). It is interpreted as a product of partially melting crust. The andesite and dacite are interpreted as a product of the ca.110 Ma magmatism along the Bangong-Nujiang suture zone, and may be related to the continent-continent collision process after the closure of the Bangong-Nujiang Ocean.