Cenozoic uplifting and exhumation process of the Altyn Tagh mountains

The Altyn Tagh mountains define the northern boundary of the Qinghai-Tibet plateau. This paper presents apatite fission-track dating that are used to infer the uplifting and exhumation process of the mountain range. This analysis is crucial for understanding the deformation and northward growth history of the plateau during the Indo-Asian collision. Fission-track dating of apatite from 34 samples of granite, granodiorite, and gneiss produced exhumation ages ranging from 61 Ma to 1.8 Ma, and suggesting that the range experienced five stages of uplifting process during the Cenozoic, i.e., 61-34 Ma, 42-11 Ma, 10.2-7.3 Ma, 5.5-4.5 Ma, and 2.1-1.8 Ma. Measurements show that uplift and exhumation of the EW-trending Lapeiquan-Hongliugou range, in the northern Altyn Tagh mountain, was initiated as early as 61 Ma, and lasted until 34 Ma. That of the NE-trending Qiemo-Mangya range occurred from the late Eocene (42 Ma) to the middle Miocene (10 Ma). The youngest uplift and exhumation within the Altyn Tagh mountains took place near the main Altyn Tagh fault, where three exhumation events, i.e., 10.2-7.3 Ma, 4.6-4.5 Ma, and 2.1-1.8 Ma are interpreted. Analyses of regional fission-track data, regional deformation events, and left-slip displacement of the Altyn Tagh fault, indicate that the original uplift and exhumation of the Altyn Tagh mountains probably occurred in the late Cretaceous. Paleogene exhumation was limited to the EW-trending portion of the northern Altyn Tagh range, but three later periods of exhumation, from late Eocene to mid-Miocene (42-11 Ma), mid-Pliocene (5.5-4.5 Ma), and early Pleistocene (1.8-2.1 Ma), were widespread in all mountains along the northern margin of the Tibetan plateau; and 8 Ma was one of the most important periods for the deformation and evolution of the plateau. Studies on the sedimentation in the foreland basin and intra-mountain basins suggest that mountain uplift, and sedimentation and evolution of related basins were coupled with the strike-slip motion of the Altyn Tagh fault.