Abstract
The Himalayan orogen is a type example of continent–continent collision. Knowledge of the timing of India–Asia collision is critical to the calculation of the amount of convergence that must have been accommodated and thus to models of crustal deformation. Sedimentary rocks on the Indian plate near the suture zone can be used to constrain the time of collision by determining first evidence of Asian-derived material deposited on the Indian plate. However, in the Himalaya, for this approach to be applied successfully, it is necessary to be able to distinguish between Asian detritus and detritus from oceanic island arcs that may have collided with India prior to India–Asia collision. Zircons from the Indian plate, Asian plate and Kohistan–Ladakh Island arc can be distinguished based on their U–Pb ages combined with Hf signatures. We undertook a provenance study of the youngest detrital sedimentary rocks of the Tethyan Himalaya of the Indian plate, in the Western Himalaya. We show that zircons of Asian affinity were deposited on the Indian plate at 54 Ma. We thus constrain terminal India–Asia collision, when both sutures north and south of the Kohistan–Ladakh Island arc were closed, to have occurred in the Western Himalaya by 54 Ma.
Highlights
Knowledge of the timing of India–Asia collision is critical to models of Himalayan orogenesis, in particular to the determination of the amount of plate convergence that must have been accommodated
Using data from this region, a number of workers have proposed a ca. 60–50 Ma age for collision between India and the Kohistan–Ladakh intra-oceanic island arc (KLIA), with the KLIA already sutured to, and representing the southern margin of, Asia to the north. This is based on various factors including the time of elimination of marine facies in the Tethyan Himalaya and intervening Indus suture that provides a minimum age of collision (e.g. Green et al, 2008), age of eclogites indicative of onset of Indian continental subduction (e.g. Donaldson et al, 2013), and first evidence of detritus from north of the suture zone deposited on the Indian plate (e.g. Clift et al, 2002 but see ; Henderson et al, 2011) or sedimentary rocks containing both Indian and Asian provenance (Tripathy-Lang et al, 2013)
Whereas traditionally ∼60–50 Ma has been taken as the time of terminal India–Asia collision, there is increasing debate as to whether the collisional event at this time reflects collision between India and Asia, or between India and an oceanic island arc, with terminal collision between India and Asia occurring later
Summary
Knowledge of the timing of India–Asia collision is critical to models of Himalayan orogenesis, in particular to the determination of the amount of plate convergence that must have been accommodated. Hu et al, 2016 and references therein), a more recent suggestion has been proposed whereby the above quoted age represents a collision between India and an intra-oceanic island arc or Tethyan microcontinent, with later terminal suturing between India and Asia perhaps as late 40 Ma (Bouilhol et al, 2013), 34 Ma (Aitchison et al, 2007) or 23 Ma (van Hinsbergen et al, 2012) Such a degree of difference in the time of final suturing of India with Asia results in differences of >1000 km in the calculation of the amount of continental crust that needs to be accommodated during convergence. The NW Himalaya, where the Kohistan–Ladakh intra-oceanic island arc (KLIA; labelled as K and L in Fig. 1) is wedged between the Indian and Asian plates, provides the ideal location to study the relative timings of arc and continent collisions due to the excellent preservation and exposure of the arc Using data from this region, a number of workers have proposed a ca. This is based on various factors including the time of elimination of marine facies in the Tethyan Himalaya and intervening Indus suture that provides a minimum age of collision (e.g. Green et al, 2008), age of eclogites indicative of onset of Indian continental subduction (e.g. Donaldson et al, 2013), and first evidence of detritus from north of the suture zone deposited on the Indian plate (e.g. Clift et al, 2002 but see ; Henderson et al, 2011) or sedimentary rocks containing both Indian and Asian provenance (Tripathy-Lang et al, 2013)
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