T21B-2824
Uplift and growth of the northwest Pamir
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Edward R Sobel1, Rasmus C Thiede2, Paolo Ballato2, Konstanze Stübner3, Mustafo Gadoev4, Ilhomjon Oimahmadov4, Todd Alan Ehlers5 and Manfred R Strecker2, (1)University of Potsdam, Institute of Earth and Environmental Sciences, Potsdam, Germany, (2)University of Potsdam, Potsdam, Germany, (3)University of Tübingen, Institut für Geowissenschaften, Tübingen, Germany, (4)Tajik Academy of Science, Institute of Geology, Dushanbe, Tajikistan, (5)University of Tübingen, Tübingen, Germany
Abstract:
The Pamir is the most prominent mountainous region within Central Asia, forming the northwestern tail of the Tibetan plateau. Although many large-scale tectonic features are thought to be understood, the details of uplift and orogenic growth are still too poorly constrained to evaluate first order geodynamic models. To assess the impact of tectonic uplift on the geomorphic evolution of the plateau, we performed several standard morphometric analyses. We have also begun Apatite (AHe), Zircon U-Th-Sm/He (ZHe) and apatite fission track dating to obtain the timing of upper crustal cooling related to rock uplift. Here we focus on the western and northwestern unglaciated margin of the Pamir, Darvaz and Peter the 1st Range. Drainage pattern and DEM analysis indicate that the Panj River forms the base level that controls the river network draining the entire central and western margin of the Pamir. Fluvial network constraints indicate that it has been established in the geologic past, has facilitated deep valley incision when crossing Darvaz Range, but not been uplifted significantly. Within the Darvaz Range, bounded by the Darvaz fault zone in the northwest and Badakhshan fault zone in the southeast, we discovered extensive low-relief landscapes with gentle, concave longitudinal upstream river profiles. These are interrupted by major knick points and steep downstream segments, draining towards the deeply incised Panj River. Prior to uplift, this landscape was eroded to a low relief and was partly covered by upper Neogene sediments. Preliminary ZHe and AHe ages indicate that uplift of the Darvaz Range was underway by 15 Ma and may have accelerated since then. We suggest that the western flank of the Pamir has had 1 to 2 km of surface uplifted starting during the middle Miocene. Focused precipitation in the internal portion of the western Pamir facilitated deep valley incision during late Cenozoic. The base level of the major Panj drainage has remained at its low elevation.
