Apatite fission-track records of the tectonic uplift of the central segment fo the Kunlun Mountains on the northern margin of the Qinghai-Tibet Plateau

Abstract： Three groups of apatite fission-track ages indicate three tectonic uplift events： the uplift of the Altyn Tagh block at the end of the Cretaceous (69.5±2.9 Ma BP) and the uplifts of the front of the Kunlun Mountains and rear zone of the Kunlun Mountains (on the northern margin of the plateau region) in the late Pliocene (4.2±0.8 Ma BP and 3.9±0.6 Ma BP) and in the middle Early Pleistocene (1.66±0.31 Ma BP). The paleo-altitudes of the apatite fission-track samples are calculated on the basis of the paleo-burial depths of the samples and paleo-altitudes of the surface inferred according previous relevant data, and then the absolute tectonic uplift amount is calculated, which is equivalent to the altitude difference and the absolute rate of tectonic uplift is equivalent to the ratio of the absolute uplift amount to the difference of apatite fission-track ages. The results of the calculation are as follows：the northern margin of the Altyn Tagh has risen 4 940 m since 69 Ma BP, with an average uplift rate of 0.072 mm/a; the front zone of the Kunlun Mountains has risen 1 380 m from 4.15 to 1.66 Ma BP, with an average uplift rate of 0.55mm/a, and risen 4 140 m since 1.66 Ma BP, with an average uplift rate of 2.49 mm/a; the rear zone of the Kunlun Mountains has risen 1 500 m from 3.85 to 1.66 Ma BP, with an average uplift rate of 0.70 mm/a, and it has risen 5 140 m since 1.66 Ma BP, with an average uplift rate of 3.19 mm/a. In combination with the relevant terrace features and ages, it may be estimated that the average uplift rate of the rear zone of the Kunlun Mountains may have reached 11 mm/a since the end of the late Pleistocene (21 ka BP). The rear zone of the Kunlun Mountains may have risen 1 120 m relative to the front zone of the Kunlun Mountains since 4 Ma BP and the ratio of the average uplift rates of the two zones is about 1.2.