EXTENSION, UPLIFT AND EROSIONAL UNROOFING OF THE YULONG MOUNTAINS ANTIFORM, CHINA

The Yulong Xueshan (Jade Dragon Snow Mountains) range are an isolated range of anomalously high and steep mountains bisected by the Jinsha (Yangzi) river in western Yunnan province, south and east of Tibet. The range is defined by a closed network of active transtensional faults, the most recent major rupture of which was a M 7.0 quake in 1997. Some of the deepest structural and stratigraphic levels of the Yangzi platform and Three Rivers foldbelts are exposed in the footwalls of these faults and in the nearly 4km deep gorge cut by the Jinsha river through this range. Within the bounding faults, hillslopes are steep and characterised by frequent large magnitude landslides. The Jinsha river itself becomes extremely narrow and anomalously steep within the range, suggesting adjustment to anomalously high rates of surface uplift. While elastic flexure is often appealed to to explain the uplift of rift-flanks in extensional settings, in this region, high, steep topography and exposure of deep structural levels are only observed in association with the dramatic incision of the Jinsha river. In this range, surface processes have a first-order effect in setting the style and pace of unroofing, and we suspect that at least some of the faults only passively accommodate anomalous exhumation rates.