Basalts from the Mazhala area in southern Xizang: Geochemistry, petrogenesis and geological implications

The basalts from the Mazhala area are widespread in the Middle Jurassic Zhela Formation(J₂z) in the eastern part of the Tethyan Himalayas in southern Xizang. The present paper focuses on the geochemical signatures of the basalts aiming at improving our knowledge of tectonic settings of the study area during the Jurassic. The geochemical signatures of major and trace elements have disclosed that the basalts are characterized by SiO₂ contents ranging between 47.50% and 50.61%, high K(an average 0.61% for K₂O), high Ti((an average 4.02% for TiO 2, high P(an average 0.52% for P₂O₅, highly differentiated light/heavy REE ratios(ΣLREE/ΣHREE=7.30-7.58), and an average 7.94 for(La/Yb)_N ratios, enriched large-ion lithophile elements such as Ba and Th and high field strength elements Nb, Ta, Zr and Hf, indicating the geochemical signatures of the oceanic-island basalts. The basaltic magmas were originated from the partial(10%) melting of the garnet peridotite-dominated enriched mantle, and were not subjected to noticeable crustal contamination during the ascending of the magmas. The Mazhala basalts are interpreted to be generated on the Himalayan passive continental margin or derived from the mantle plume.