QUATERNARY GLACIAL GEOMORPHOLOGY AND CHRONOLOGY OF THE EASTERN SLOPE OF MT. GONGGA, CHINA

Mt. Gongga is the largest center of modern glaciation in the Hengduan Mountains and, with a summit elevation of 7,556 m, is the highest mountain on the eastern part of the Qinghai-Tibetan Plateau. During the Quaternary glacial-interglacial cycles Mt. Gongga was extensively and repeatedly glaciated, and glacial landforms and outwash deposits from multiple glaciations are well-preserved in valleys, in basins, and on piedmonts. To constrain the glacial chronology of the eastern slope of Mt. Gongga, sample sites were selected based on the distribution and weathering of glacial tills, relationships among glacial deposits, and soil development on moraines. Dating of the tills and glaciofluvial deposits was undertaken with electron spin resonance (ESR) and optically stimulated luminescence (OSL). The ages of the glacial deposits can be divided into three clusters: 11.9±0.6, 35.9±2.7–58.0±6.3, and 215.2±24.0–362.8±48.3 ka. Five glacial advances in this region have been identified, which are equivalent in age to the Little Ice Age (LIA), Neoglaciation, marine oxygen isotope stage (MIS) 2, mid-MIS3, and MIS6 or earlier. The largest local last glacial maximum (LGM_L) occurred on Mt. Gongga during MIS3 rather than the global Last Glacial Maximum (LGM_G) of MIS2. The Gongga, Nanmenguan and Yajiageng Glaciations occurred during the late part of the last glacial cycle, the middle of the last glacial cycle and the penultimate glacial cycle or an earlier glacial cycle, respectively. On the basis of geomorphological, sedimentological, and compositional characteristics, landforms of the Moxi Platform and terraces can be grouped in terms of facies and geochronology. In combination with the dating results, this analysis indicates that the basal part of the Moxi Platform between Xinxin and the Moxi Hotel is correlative with the till of the Nanguanmen Glaciation (mid-MIS3). This basal unit has occasional lens of glaciofluvial sandy gravel and lacustrine sediments. The remainder of the Moxi Platform and the terraces beside the platform are glaciofluvial deposits mixed occasionally with debris flow deposits and with a chronological range from MIS3 to Holocene.