Eocene uplift and exhumation in Gangdese area: Evidence from zircon U-Pb ages and Al-in-biotite geobarometer

1.Objective The surface uplift history of the Tibetan Plateau is a hot topic in geosciences.The evidence from stratigraphy,geochronology of potassium-rich lava and studies of apatite fission tracks indicated that the Lhasa and southern Qiangtang terranes were at or close to their modern elevation since 40 Ma and formed the proto-Tibetan Plateau(Wang CS et al.,2008).However,uplifting mechanism of the southern margin of the proto-Tibetan Plateau is not well understood(Wang CS et al.,2008;Fig.1a).Lhasa-Woka ductile shear zone(LWDS),the eastern part of Xietongmen-Lhasa-Woka ductile shear zone,is a large-scale E-trending belt in Gangdese and is located in the southern margin of the proto-Tibetan Plateau.LWDS characterized by typical ductile shear zone at the easternmost part,whereas crop out as southward thrusting fault system at the western part,namely the Jiama-Qulong ore district and adjacent area(Fig.1b).