Constraining the age of Liuqu Conglomerate, southern Tibet: Implications for tectonic evolution of the Indus-Yarlung Suture Zone

Abstract:

The depositional age and provenance of the Liuqu Conglomerate (LC), distributed along the Indus-Yarlung suture zone (IYSZ) in South Tibet, remain controversial, leading to different interpretations, such as a Paleogene basin deposited during India-Asia collision (Wang et al., 2010) or the result of the collision between India and an intra-oceanic arc (Aitchison et al., 2007). Here, we report low-temperature thermochronometry data (apatite fission track, apatite and zircon U-Th/He) for the LC in the Xigaze area, to constrain its depositional age, provenance and burial-exhumation history. Five samples from Liuqu yielded consistent AFT ages of ~6-8Ma, and dispersed single-grain AFT ages of six samples range from ~ 140 to 5 Ma, and single grain AFT ages for grains with >0.4 Cl (wt%) content was calculated three age-peaks of ~16.4 ±3.0, 37.3 ± 6.4 and 89.5 ± 22.2 Ma. Four groups of detrital ZHe ages, including 18 scattered single grain ages in the range of ~20 - 107.9 Ma, yielded four age peaks of ~20, 37, 66 and 104 Ma. We interpret the AHe ages of the LC as having been completely thermally reset, while AFT ages have been partially annealed and ZHe ages have not been thermally reset, suggesting that the post-depositional maximum temperature of the LC was > 80 °C and < 110°C. Collectively, our results indicate that the Liuqu Conglomerate was probably deposited in the Early Miocene time, similar to the Qiuwu-Dazhuka conglomerates which are located in the northern part of the IYSZ, as one component of the Gangrinboche Group, and was derived from the Xigaze forearc basin, Yarlung-Zangbo suture zone, as well as the Tethyan Himalaya. Furthermore, the Liuqu Conglomerate was exhumed to the surface by post-depositional incision of a tributary of the Yarlung Zangbo river by the Late Miocene time.
Aitchison, J. C.; Ali, J. R., and Davis, A. M. 2007, When and where did India and Asia collide?: J. Geophys. Res. v. 112: B05423, doi:10.1029/2006JB004706.
Wang, J.G., Hu, X.M., Wu, F.Y., and Jansa, L., 2010, Provenance of the Liuqu Conglomerate in southern Tibet: A Paleogene erosional record of the Himalayan–Tibetan orogen: Sedimentary Geology, v. 231, p. 74–84, doi:10.1016/j.sedgeo.2010.09.004.