Late Cenozoic cooling history of the Xigaze fore-arc basin along the Yarlung-Zangpo suture zone (southern Tibet): New insights from low-temperature thermochronology

The Tibetan Plateau is currently the widest and highest elevation orogenic plateau on Earth. It formed as a response to the Cenozoic and still ongoing collision between the Indian and Eurasian plates. The Xigaze fore-arc basin is located along the suture zone of both plates, i.e. the Indus Yarlung suture zone in southern Tibet. This area preserves important information related to the late Cenozoic tectonic and topographic evolution of the Tibetan plateau. In this study, apatite fission track (AFT) thermochronology was carried out on twelve sandstone samples from the middle segment of the Xigaze basin and additionally on four sedimentary rocks from the neighboring Dazhuka (Kailas) and Liuqu Formations. Inverse thermal history modeling results reveal that the fore-arc basin rocks experienced episodic late Oligocene to Miocene rapid cooling, which we interpret as the exhumation of these rocks. Taking into account regional geological data, it is suggested that the late Oligocene-early Miocene (~27-18 Ma) cooling recognized in the northern part of the basin was related to fault activity along the Great Counter thrust, while mid-to-late Miocene-accelerated exhumation was facilitated by strong incision of the Yarlung and Buqu rivers, which probably resulted from enhanced East Asian summer monsoon precipitation. Sandstone and conglomerate samples from the Dazhuka and Liuqu Formations yielded comparable Miocene AFT apparent ages to those of the Xigaze basin sediments, indicative of (mid-to-late Miocene) exhumation soon after their deep, early Miocene burial (> ~3-4 km). Additionally, our new and published low-temperature thermochronological data indicate that enhanced basement cooling during the Miocene prevailed in vast areas of central southern Tibet when regional exhumation was triggered by both tectonic and climatic contributing factors. These events ultimately led to the formation of the high-relief topography of the external drainage area in southern Tibet, including the Xigaze fore arc basin.