Study On Cenozoic Tectonic And Geomorphic Processes Of Typical Regions Of Qilian Mountains

Qilian Mountains are located in the northeastern margin of the Tibetan Plateau. The uplifting of Qilian Mountains are only the remote effect from India- Asia collision, but also the product of Altyn and Haiyuan stick-slip faults moved during Cenozoic tectonic which are the main boundary of the northern margin of the Tibetan Plateau.On the basis of discussion of the Qilian Mountains topographic feature, this paper selected the planation surface developed areas in southern Qilian and the basin-mountain areas confined by Altyn and Haiyuan strick-slip faults in northern Qilian as the research objects, and the differences between the two tectonic geomorphologies as the starting point, combining Cenozoic sedimentary strata, tectonic deformation and low-temperature thermochronlogy history simulation, to restore the tectonic geomorphic evolution progress of the two typical areas of planation surface developed area and the basin-mountain area in Qilian mountains. This paper draws the following conclusions:(1) Cenozoic tectonic geomorphological evolution processes of the planation surface developed areas in southern Qilian: After the crustal shortening and uplifting in Cretaceous, the southern Qilian was in a stable configuration leveled stage to the Late Cretaceous – Eocene. Until Eocene- early Oligocene, there was a limited scale crustal shortening and regional uplifting in southern Qilian, leading to the early planation surface disintegrated. From Oligocene to early Miocene the southern Qilian was razed again. To the late Miocene, the southern Qilian uplifted in overall stage, but the crustal movement mode in the southern Qilian had a major shift, from the near the north and south by an earlier way to squeeze transforming into a crust eastward extrusion of the tectonic movements. Since the Pliocene, after several stages of rapid overall uplift, eventually planation surface maintained and the southern Qilian was raised to the current height level.(2) Cenozoic tectonic geomorphological processes of the basin-mountain area in northern Qilian: Since Cretaceous to Miocene, early evolution of the tectonic geomorphology processes of northern Qilian was basically the same way as it was of the southern. But to the late Miocene(since 13Ma), controlled by the Altyn and Haiyuan stick-slip faults’ activities, the basin-mountain areas in northern Qilian developed a series of NWW thrusts, causing the formation of basin and mountain. Since the Pliocene, the north Qilian restarted to rapid uplift and subjected to multi-stage rapid uplift sharply, because of the activity intensity of Altyn and Haiyuan faults, and built the present tectonic geomorphology pattern of basin-mountain.(3) According to the ESR ages of fluvial gravels calcareous cement which cutting planation surface in southern Qilian, and the Sedimentary facies variation of Oligocene Group Baiyanghe(E3N1b), we conclude that the main planation surface formed of the Qilian Mountains in Eocene, and was disintegrated in about 34 Ma.(4) During late Miocene(13-12Ma), the crustal movement mode in the Qilian mountain had a major shift, from the near the north and south by an earlier way to squeeze transforming into a crust eastward extrusion of the tectonic movements., influenced by the Altyn and Haiyuan strike-slip faults’ activity,...