An Early Cretaceous slab window beneath central Tibet, SW China: Evidence from OIB-like alkaline gabbros in the Duolong area

The geodynamic mechanism of the late Early Cretaceous magmatic flare-up in the collisional zone between the Lhasa and Qiangtang terranes in Tibet is controversial because of a scarcity of robust evidence. To address this problem, we report geochronological, geochemical and Hf isotopic data for the newly discovered Gufeng gabbros from the Duolong Cu-Au mineral district of the western Bangong-Nujiang Suture Zone (BNSZ). The gabbro samples, dated at 126.3 +/- 1.8 Ma, show geochemical similarities to typical ocean island basalt (OIB) and have positive epsilon Hf(t) values of +3.3 to +6.9. The gabbros were generated by decompression melting of deep upwelling asthenosphere. This event is best explained by slab break-off and the resultant development of a slab window beneath central Tibet.