@Article{Kapp2:2003, author = {P.A. Kapp and A. Yin and C.M. Manning and T.M. Harrison and M.H. Taylor and L. Ding}, title={Tectonic evolution of the early {M}esozoic blueschist-bearing {Q}iangtang metamorphic belt, central {T}ibet}, journal={Tectonics}, year={2003}, volume={22}, number={}, month={Aug}, pages={1043}, note={}, annote={}, keywords={}, url={http://sims.ess.ucla.edu/PDF/kapp_et_al_TECT_2003.pdf}, doi={10.1029/2002TC001383}, abstract={A $>$500-km-long east-west trending metamorphic belt in the Qiangtang terrane of central Tibet consists of tectonic melange that occurs in the footwalls of Late Triassic-Early Jurassic domal low-angle normal faults. The melange is comprised of a strongly deformed matrix of metasedimentary and mafic schists that encloses lesser-deformed blocks of metabasites, Carboniferous-Triassic metasedimentary rocks, and early Paleozoic gneiss. Both the blocks and melange matrix exhibit greenschist, epidote-blueschist, and locally, epidote-amphibolite facies mineral assemblages. Thermobarometry reveals that the metamorphic belt experienced pressures of $>$10 kbar. Maximum equilibration temperatures for mafic schists in the melange matrix decrease from east to west, from $\sim$660$^{\circ}$C near Shuang Hu (33$^{\circ}$N, 89$^{\circ}$E), $\sim$500$^{\circ}$C near Rongma (33$^{\circ}$N, 87$^{\circ}$E), to $\sim$425$^{\circ}$C near Gangma Co (34$^{\circ}$N, 84$^{\circ}$E). Equilibration at consistently high pressures over a large range of temperatures is compatible with metamorphism of Qiangtang melange within a low-angle subduction zone beneath a continental margin. Coupled structural, thermobarometric, and $^{40}$Ar/$^{39}$Ar studies suggest that Qiangtang melange was exhumed in an intracontinental setting from depths of $>$35 km to upper crustal levels in $<$12 Myr by Late Triassic-Early Jurassic crustal-scale normal faulting. Detrital zircons from metasandstones within the melange matrix yield U-Pb ion-microprobe ages that range from early Paleozoic to Early Archean, and could have been sourced from terranes to the north of the Jinsha suture. Our results support a model in which Qiangtang melange was underthrust $\sim$200 km beneath the Qiangtang terrane during early Mesozoic flat-slab southward subduction of Paleo-Tethyan oceanic lithosphere along the Jinsha suture. This model predicts that significant portions of the central Tibetan continental mantle lithosphere were removed during early Mesozoic low-angle oceanic subduction and that the present-day central Tibetan deeper crust includes large volumes of underthrust early Mesozoic melange.} }