Structural evolution of the Neogene Gar Basin, western Tibet: Implications for releasing bend development and drainage patterns

Abstract

We investigated the interaction among basin-bounding faults, basin fi ll, and geomorphic features of the southern Gar Basin, one of only two known releasing double-bend basins along the Karakoram fault, to better understand their structural evolution and role in basin development. The southern Gar Basin is bounded by an ~44-km-long, N20°Wstriking central fault segment fl anked by two N40°W-striking segments that parallel the regional strike of the Karakoram fault system. The central fault segment is composed of a system of strike-slip and normal faults that young basinward and incorporate basin fi ll in their uplifted footwalls. The oldest faults along the extensional portion of the bend are dominantly strike-slip, and they strike ~15°W from the main strike of the Karakoram fault. Basin fi ll is broadly folded about a NNWtrending axis and can be explained by E-SEdirected slip along a listric normal fault. Cross sections across the basin and associated faults suggest the geometry is best described as an extensional fl ower structure. Forward structural modeling of the intrabasinal faults shows that the system has accommodated ~8 km of east-west extension. We interpret the bend to have formed from linking of R and P shears into a through-going principal displacement zone. At shallow levels in the crust (low confi ning pressures), R shears are exploited; at deeper levels, these faults merge with the principal displacement zone, forming the extensional fl ower structure geometry. We estimate that the shear zone is 50-35 km wide based on the aerial distribution of P and R shears. Restoration of R shears on the west and east sides of the Gar Valley indicates ~55 km of right-lateral separation along the Karakoram fault, which is a minimum slip estimate for the Karakoram fault system.

Karakoram fault activity defined by temporal constraints on the Ayi Shan detachment, SW Tibet

“…The new Zircon U-Pb ages reported in this study confirm that the Proterozoic to Ordovician rocks in the footwall of the Ayi Shan detachment are part of the Ayilari Ranges (Xizang BGMR 2005;Sanchez et al 2010;Zhang et al 2011;Wang et al 2013). Previous research has shown that the Ayilari Range consisted mainly of three episodes of granites at ∼60 Ma, 45-50 Ma, and 32-25 Ma (Lacassin et al 2004;Valli et al 2007Valli et al , 2008Wang et al 2009Wang et al , 2011.…”

“…Notes: GCT, Great Counter thrust; KKF, Karakoram Fault System; MBT, Main Boundary Thrust; MCT, Main Central Thrust; MFT, Main Frontal Thrust; STD, South Tibetan Detachment. Map is compiled from Murphy et al (2000), Xizang BGMR (2005), Sanchez et al (2010), and Wang et al (2011). fault system, with lenses of serpentinized mafic rocks hundreds of metres long and ultramafic rocks that crop out locally along the fault zone, which defines the surface trace of the Indus-Yalu suture zone. The strata involved in the hanging wall of the GCT are mainly of the PalaeozoicMesozoic Tethyan sedimentary sequence, and mélange from the Indus-Yalu suture (Xizang BGMR 2005).…”

Timing of metamorphism, melting and exhumation of the Leo Pargil dome, northwest India

“…The dome extends northeast to the Ayi Shan that is bound by the Karakoram fault system (Valli et al. , 2007; Sanchez et al. , 2010) (Fig.…”

“…Metamorphic isograds are from this study and Chambers et al (2009). Mineral abbreviations after Kretz (1983). dome extends northeast to the Ayi Shan that is bound by the Karakoram fault system (Valli et al, 2007;Sanchez et al, 2010) (Fig. 1).…”

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“…However, Valli et al (2007) suggest it was continuously active since the Early Miocene, based on U-Pb zircon ages and petrofabric analyses of rocks exposed on its south side (footwall). The Karakoram fault is presently active as it offsets Quaternary surfi cial deposits (Armijo et al, 1989;Chevelier et al, 2005;Brown et al, 2002;Murphy and Burgess, 2006;Sanchez et al, 2010).…”