The Margin of a Gneiss Dome: Development of the Waqia Half-Graben, Southeast Pamir

Previous research on the evolution of compressional gneiss domes largely focus on the highly sheared footwalls, with less emphasis on the hanging walls of these structures. The Waqia Valley is located along the southeast margin of the easternmost Central Pamir Gneiss Dome (the Mustaghata Gneiss Dome) and provides an excellent location to study the spatial and temporal relationships of extension and basin formation along the margin of a gneiss dome. The ~50 km long Waqia half-graben is oriented northwest-southeast and is bound to the northeast by the southwest dipping Waqia Fault. This normal fault appears to be kinematically linked with the Shen-ti and Kuke faults which bound the metamorphic core of the Muztaghata Gneiss Dome. Deformation within the hanging wall is limited to the Bandi'er Monocline in the north, which runs for ~4 km, and the Rebu-te Fault in the south, which runs for ~10 km and has ~40 m of throw. Initial results from kinematic analyses, of measurements taken from fault surfaces along the Waqia Fault, show dip slip motion. The oldest deposits in the basin are likely late Neogene in age and occur proximal to the bounding fault. These deposits consist of 200-1000 m of bedded pebble to boulder conglomerates derived from the surrounding bedrock which fine basinward and are interpreted as alluvial fan deposits. The late Neogene deposits are deeply incised and partially refilled by younger Quaternary sediments, which consist of diamict and bedded conglomerates, sandstones, and mudstones. Structural and stratigraphic observations suggest the evolution of the basin is kinematically linked to the tectonic exhumation of the Mustaghata gneiss dome beginning in the late Miocene rather than interaction with the left slip Karakax fault which has been interpreted to continue into the valley. In our model, the Waqia valley developed on the flank of the Mustaghata gneiss dome in response to high magnitudes of extension beginning in the late Miocene.