TECTONIC GEOMORPHOLOGY ANALYSIS OF SOUTH-CENTRAL TIBET RIFTS USING REMOTE SENSING AND GEOGRAPHIC INFORMATION SYSTEMS

A kinematic model for the active tectonics in south-central Tibet shows that conjugate strike- slip faults are representative of both E-W extension and N-S contraction. This regional motion in the E-W and N-S directions may correlate with the magnitude of slip of major structures along the India-Asia suture zone.

The Lopukangri rift cuts across the India- Asia suture zone located in south-central Tibet. The rift is one of six structures previously presented to function as a trailing extensional imbricate fan system that are hypothesized to accommodate southward decreasing horizontal E-W extension. The area is bounded by the northern Bangong-Nujiang suture zone and the southern India-Asia suture zone.

Our observations indicate the range-front faults strike N-NW and are predicted to have a similar slip history based on geometry, although with variable magnitude. The spacing between the basins ranges from ~35 km in the west to 55 km in the east measured on a N60W trend along their southern tip. Only the Lopukangri rift cuts through the India-Asia suture zone. The other rifts to the east terminate before reaching the suture zone. The rift valleys show a decrease in size eastward of the Lopukangri rift. This means that the magnitude of E-W extension in the west was at a greater scale compared to the east. Lakes are present in at least four of the basins. Their geometry displays a crescent-shape throughout the region reflecting the enclosure resulting from merging faults at the tips of the basins. The axial rivers trend N- NW in the interior of the basins. We suggest that drainage reorganization resulting from slip along basin-bounding faults (and thus creation and/or reduction of relief) is an active phenomenon in controlling lake-filled versus unfilled basins.

In order to assess the extension component across the trailing system, we will incorporate remote sensing analyses of the tectonic geomorphology of the constituent rifts. These methods will include using Landsat, SPOT, and SRTM imagery to locate the rifts and in conjunction with GIS Hydrotools, map stream networks, drainage divides, and drainage basin areas. Active fault maps covering the rifts will be used to map range-front deposits and interpret cross-cutting relationships.