青藏高原东南部稻城古冰帽末次冰盛期冰底热状态空间结构及其控制因素

The basal thermal regime of ice sheets and ice caps exerts a fundamental control on ice dynamics，sub⁃ glacial erosion，and the preservation or modification of glacial landforms. Whether the ice is cold-based or warm-based directly determines the efficiency of basal sliding，meltwater production，and erosion intensity，thereby profoundly influencing long-term geomorphic evolution. Therefore，determining the spatial structure of the basal thermal regime and its controlling factors is essential for understanding Quaternary glacial-geomorphic processes. However，although research on large continental ice sheets has advanced in recent years，understand⁃ ing of the basal thermal regime of local ice caps，such as paleo-Daocheng Ice Cap（P-DIC）on the Qinghai-Xi⁃ zang Plateau（QXP），remains relatively limited. This study focused on the main coverage area（high planation surface）of the P-DIC in the Haizishan area of the southeastern QXP. In-situ cosmogenic ¹⁰Be and ²⁶Al surface ex⁃ posure dating was applied to widely distributed bedrock surfaces and glacial erratics in the area. Along the main axis of the planation surface from west to east，nine ¹⁰Be exposure ages［ranging from（15. 1±1. 0）ka to （148. 3±9. 3）ka］and two paired ²⁶Al exposure ages［（147. 3±13. 7）ka and（17. 8±1. 6）ka］were obtained，and the paired ²⁶Al ages were consistent with their corresponding ¹⁰Be ages within 1σ error. Combined with previ⁃ ously published exposure ages that were uniformly recalculated，this study compiled an exposure age dataset cov⁃ ering the planation surface，consisting of 33 ¹⁰Be ages and 11 ²⁶Al ages. The results exhibited a pronounced spa⁃ tial differentiation in exposure ages. Samples from the western part of the planation surface were mainly concen⁃ trated in Marine Isotope Stage（MIS）6. Samples from the central part spanned MIS5 to MIS2，whereas samples from the eastern part were predominantly concentrated in the late MIS2. The paired ¹⁰Be-²⁶Al results indicated that samples in the study area generally showed simple exposure histories，without significant later burial or com⁃ plex exposure/burial processes. This suggested that the spatial differences in exposure ages were unlikely to re⁃ sult from differences in the exposure histories of the samples. Regional glacial-geomorphic and chronological studies consistently indicated that the Haizishan high planation surface was entirely covered by the P-DIC during MIS6 and the Last Glacial Maximum（LGM）. Therefore，during this period，there was no scenario of gradual west-to-east deglaciation of the planation surface. Meanwhile，the lithology of the study area was relatively uni⁃ form，dominated by biotite monzogranite，and lithological differences were also insufficient to cause the spatial partitioning of exposure ages. These constraints indicated that the spatial distribution of exposure ages was more likely to reflect spatial differences in the basal thermal regime at the base of the ice cap. On this basis，by inte⁃ grating the regional glacial evolution context with existing chronological data，geomorphic features，and erosion rate results，this study identified the polythermal spatial structure of the basal regime of P-DIC in its main area during the LGM. From west to east，it was characterized by three types of basal thermal zones. The western part of the planation surface was characterized by old exposure ages concentrated in MIS6，well-preserved land⁃ forms，and low erosion intensity，indicating a stable cold-based preservation zone where ice was largely frozen to the bedrock. The central part exhibited ages spanning MIS5 to MIS2，together with preserved weathering crusts and localized abrasion landforms，with comparable erosion rates. This suggested a mixed cold-warm tran⁃ sitional zone dominated by warm-based conditions with locally residual cold-based patches. The eastern part of the planation surface was characterized by young exposure ages concentrated in the late MIS2，widely developed cirques and strongly abraded landforms，and relatively high erosion rates，indicating effective resetting of cosmo⁃ genic nuclides. This was consistent with a warm-based erosion zone during the LGM. Further analysis indicated that this spatial heterogeneity was primarily caused by the ice thickness distribution and heat accumulation capaci⁃ ty，which were controlled by the underlying topography. Combined with long-term differential erosion，these factors further shaped the topographic relief and reinforced the differentiation between the cold- and warm-based structures. This study is of great significance for a deeper understanding of the basal thermal structure，glacial dynamics，and geomorphic responses of local paleo-ice caps on the QXP，and provides key constraints for quan⁃ tifying the spatial differentiation of paleo-glacial erosion in the region and for evaluating the basal boundary con⁃ ditions in ice-cap models.