Gangdese culmination model: Oligocene–Miocene duplexing along the India-Asia suture zone, Lazi region, southern Tibet

Abstract

The mechanisms for crustal thickening and exhumation along the Yarlung (India-Asia) suture in southern Tibet are under debate, because the magnitudes, relative timing, and interaction between the two dominant structures-the Great Counter thrust and Gangdese thrust-are largely unconstrained. In this study, we present new geologic mapping results from the Yarlung suture zone in the Lazi region, located ~350 km west of the city of Lhasa, along with new igneous (5 samples) and detrital (5 samples, 474 ages) U-Pb geochronology data to constrain the crystallization ages of Jurassic-Paleocene Gangdese arc rocks, the provenance of Tethyan Himalayan and Oligocene-Miocene Kailas Formation strata, and the minimum age (ca. 10 Ma) of the Great Counter thrust system. We supplement these data with a compilation of 124 previously published thermochronologic ages from Gangdese batholith, Kailas Formation, and Liuqu Formation rocks, revealing a dominance of 23-15 Ma cooling contemporaneous with slip across the Great Counter thrust system and other potentially linked structures. These data are systematically younger than 98 additional compiled thermo chronologic ages from the northern Lhasa terrane, recording mainly Eocene cooling. Structural and thermochronologic data were combined with regional geological constraints, including International Deep Profiling of Tibet and the Himalaya ( INDEPTH) seismic reflection data, to develop a new structural model for the Oligocene-Miocene evolution of the Tethyan Himalaya, Yarlung suture zone, and southern Lhasa terrane. We propose that a hinterland-dipping duplex beneath the Gangdese mountains, of which the Gangdese thrust is a component, is kinematically linked with a foreland-dipping passive roof duplex along the Yarlung suture zone, the Great Counter thrust system. The spatial and temporal convergence between the proposed duplex structures along the Yarlung suture zone and the South Tibetan detachment system indicate that they may be kinematically linked, though this relationship is not directly addressed in this study. Our interpretation, referred to as the Gangdese culmination model, explains why the Gangdese thrust system is only locally exposed (at relatively deeper structural levels) and provides a structural explanation for early Miocene crustal thickening along the Yarlung suture zone, relief generation along the modern Gangdese Mountains, early Miocene Yarlung River establishment, and creation of the modern internal drainage boundary along the southern Tibetan Plateau. The progression of deformation along the suture zone is consistent with tectonic models that implicate subduction dynamics as the dominant control on crustal deformation.

Low‐Temperature Thermochronology of the Indus Basin in Central Ladakh, Northwest India: Implications of Miocene‐Pliocene Cooling in the India‐Asia Collision Zone

“…Kirstein et al (2009) support a >20 Ma age for the GCT that led to the burial of the southern edge of the Ladakh batholith. Recent studies from south Tibet also assert that the slip on the GCT initiated at~23 Ma (Laskowski et al, 2018) and ceased by~15 Ma in most locations (Carrapa et al, 2014;Laskowski et al, 2018;Orme, 2019;Zhang et al, 2011).…”

“…Sinclair and Jaffey (2001) and Clift et al (2002) suggest that this episode of crustal thickening and uplift in the Himalayan wedge at~28-23 Ma provided the mechanical force to initiate movement along the GCT at~23-20 Ma, thereby inverting the IBSRs. Recent studies from south Tibet, based on geochronology and/or thermochronology data sets and cross-cutting relationships among Neogene intrusive rocks, also indicate that motion along the GCT initiated at~23 Ma and largely ended by~15 Ma (Carrapa et al, 2014;Laskowski et al, 2018;Orme, 2019;Zhang et al, 2011).…”

Long‐term exhumation history of the Gangdese magmatic arc: Implications for the evolution of the Kailas Basin, western Tibet

“…The eroded rocks would be transported and deposited in the Kailas basin since the Oligocene (earlier than 26 Ma), and then the Kailas Formation was rapidly exhumed since~17 Ma (Carrapa et al, 2014). The latter rapid exhumation was not exclusive for the conglomerates, but also observed at the Gangdese batholith along the southern margin of Lhasa Terrane (e.g., Dai, Wang, Hourigan, Li, & Zhuang, 2013;Ge et al, 2017;Laskowski, Kapp, & Cai, 2018;Tremblay et al, 2015). The Kailas Formation exposed at the surface today experienced approximately 4-7 km of burial between 21 and 17 Ma (Carrapa et al, 2014).…”

Supplemental Material: Active Uplift of Southern Tibet Revealed

“…Low temperature thermochronology data came from a variety of published sources compiled in Thiede & Ehlers (2013) and Laskowski et al, (2018). To produce panels C and D of Fig.…”