1:250 000 Mainba Sheet in Xizang

Stratigraphically, the previously Late Permian Mengla Formation is redefined as the pre-Ordovician Songduo Group Complex. The Pangduo Group is redivided into Nuoco, Laigu and Luobadui Formations, and the previously Sangba Group into the Mali and Sangkalayong Formations. The Duoni Formation is recognized within the Lhari fault. Petrologically, the ultramafic-mafic rocks within the Lhari fault are redefined as the ophiolites dated back to the Late Triassic in age. There occur the Late Triassic granites along the Gangdise magmatic arc, Late Jurassic two-mica granites in the Sebrong-Bagar zone, shonshonitic hypabyssal intrusive rocks in the Zaxoi region, and Eocene volcanic rocks in the Zaxoi region, Lhunzhub. The metamorphism may be discriminated into two phases:the Caledonian and Yanshanian, with the temperatures of metamorphism ranging between 450℃ and 605℃ and pressures between 0.93 GPa and 1.15 Gpa. Tectonically, the investigation of the structural features permits the identification of the Zaxoi-Mainba ductile deformational zone and Sebrong-Bagar brittle-ductile deformational zone. There exist at least four phases of structural deformations throughout the surveyed area.