Tertiary structural evolution of the Gangdese Thrust System, southeastern Tibet

Abstract

Abstract. Structural and thermochronological investigations of southern Tibet (Xizang) suggest that intracontinental thrusting has been the dominant cause for formation of thickened crust in the southernmost Tibetan plateau since late Oligocene. Two thrust systems are documented in this study: the north dipping Gangdese system (GTS) and the younger south dipping Renbu-Zedong system ( RZT). West of Lhasa, the Gangdese thrust juxtaposes the Late Cretaceous forearc basin deposits of the Lhasa Block (the Xigaze Group) over the Tethyan sedimentary rocks of the Indian plate, whereas east of Lhasa, the fault juxtaposes the Late Cretaceous-Eocene, Andean-type arc (the Gangdese batholith) over Tethyan sedimentary rocks. Near Zedong, 150 km southeast of Lhasa, the Gangdese thrust is marked by a >200-m-thick mylonitic shear zone that consists of deformed granite and metasedimentary rocks. A major south dipping backthrust in the hanging wall of the Gangdese thrust puts the Xigaze Group over Tertiary conglomerates and the Gangdese plutonics north of Xigaze and west of Lhasa. A lower age bound for the Gangdese thrust of 18.3±0.5 Ma is given by crosscutting relationships. The timing of slip on the Gangdese thrust is estimated to be 27-23 Ma from 40 Ar/ 39 Ar thermochronology, and a displacement of at least 46±9 km is indicated near Zedong. The age of the Gangdese thrust (GT) is consistent with an upper age limit of -24 Ma for the initiation of movement on the Main Central thrust. In places, the younger Renbu-Zedong fault is thrust over the trace of the GT, obscuring its exposure. The RZT appears to have been active at circa 18 Ma but had ceased movement by 8±1 Ma. The suture between India and Asia has been complexly modified by development of the GTS, RZT, and, locally, strike-slip and normal fault systems.

Simulating the evolution of the Asian and African monsoons during the past 30 Myr using an atmospheric general circulation model

“…The uplift of the Rocky Mountain range and of the Colorado plateau occurred after 24 Ma, as deduced from paleodrainage systems suggesting an opposite flow direction since the Miocene [Scott, 1977]. We have assigned a mean height close to 1500 m for the Miocene topography [Yin et al, 1994]. The rest of the future Tibetan plateau ' We kept the relief nearly unchanged with respect to the present remained a low land (about 500 m), with probably smooth relief day (Figures la and lb).…”

Applications of morphochronology to the active tectonics of Tibet

“…Interpreting these thrust systems as termination or branching faults of the ATF, they conclude that the ATF must have been active since ~49 Ma, and that, combined with the 475 ± 75 km offset of Paleozoic plutons in the western Kunlun, the long-term slip rate is ~ 9 mm/yr. However, the temporal constraints must be viewed as somewhat controversial as the proposed initiation of slip on the ATF would predate that initiation of slip on the Red River Shear Zone, ~36 Ma (Gilley et al, 2003), and slip on the Gangdese Thrust system, ~27 Ma (Yin et al, 1994). Both features lie significantly closer to the Indo-Asian boundary and the proposed chronology would imply an "out-of-sequence" onset of continental deformation.…”

Oligocene-Miocene middle crustal flow in southern Tibet: geochronology of Mabja Dome

“…The Tethyan Himalaya is structurally complex, exhibiting Cretaceous to Quaternary reverse faults and folds (e.g. Le Fort 1975;Searle 1983;Ratschbacher et al 1994;Yin et al 1994Yin et al , 1999Quidelleur et al 1997;Searle et al 1997a;Godin et al 1999) and extensional structures (e.g. Molnar & Tapponnier 1975;Armijo et al 1986;Mercier et al 1987;Burchfiel et al 1992;Ratschbacher et al 1994) in a variety of orientations.…”