Xialu N-MORB gabbros and diabases in the Xigaze ophiolite: Record of subduction initiation of the Yarlung Zangbo Tethyan Ocean at Early Cretaceous

The 130~120 Ma ophiolite is the most widely distributed in the Yarlung Zangbo suture zone, however, its formation environment remains controversial.Based on zircon U-Pb ages, whole-rock geochemical date of Xialu gabbros and diabases, and a large number of data of Xigaze ophiolite, the tectonic environment and dynamic significance of Early Cretaceous ophiolite were discussed.LA-ICP-MS zircon U-Pb dating of the Xialu gabbro yields weighted mean age of 123.8 ± 1.1 Ma(MSWD = 0.97), indicating one of the 130~120 Ma Xigaze ophiolite relics.Some gabbro samples are characterized by high Cao, low SiO₂ and very low K₂O and Na₂O contents, which can be attributed to a rodingitization process, whereas diabases suffer from minimal affection of fluid.Xialu gabbros and diabases show N-MORB type characteristics and more depleted in light rare earth elements than normal N-MORB, suggesting high degree partial melting of a depleted mantle of spinel lherzolite source.The N-MORB basic rocks of the 130~120 Ma ophiolite in Xigaze were generated from a mantle source with inhomogeneous mixture of subduction components, and characterized by the transition from MORB to VAB, with a minimal adding of continental crust, which suggest that the Xigaze ophiolite was formed in an intra-oceanic arc system.Combined with regional geology, it is suggested that the 130~120 Ma ophiolite in Xigaze is similar to the IBM fore-arc ophiolite in development time, lithology and geochemistry, representing a subduction initiation in the Yarlung Zangbo Tethys Ocean.