Tephrochronology Applied to Late Cenozoic Paleoclimate and Geomorphic Evolution of the Central Transantarctic Mountains

该奖项支持一项研究横贯北极山脉的干旱山谷地区地貌演变的计划。火山灰沉积的同位素年龄和面积分布将被用来限制地貌发育的年代学和速度，并帮助量化地貌表面的年龄。火山灰的沉积环境和风化程度也将有助于限制火山灰沉积期间和之后的区域古气候条件。这项工作将集中在库特曼山脉、阿斯加德山脉、奥林匹斯山脉和麦凯尔维山谷，因为这些地区众所周知包含一些火山灰矿床，而且它们在相当高的海拔范围内包含各种地貌背景。该项目将尝试检验以下假设：干旱河谷地区是在中新世中期大陆冰盖形成之前形成的残存的半干旱地貌，随后的坡度修改仅限于集中在谷头、冰川汇合处和深谷谷槽的轻微冰川冲刷。这些假设包括：1)目前的地貌过程是无效的剥蚀剂；2)构造均匀的地块内广泛的陆面反映了横贯北极山脉前缘的基准面变化；3)表面上类似于美国西南部箱形峡谷、悬崖、台地和沙漠地区的干燥山谷的地貌地貌是由目前在科罗拉多高原进行的剥蚀过程形成的。该项目产生的同位素年龄信息将对寒冷沙漠地区地貌演化模型提供制约，并将对横贯北极山脉的地貌发育和隆升历史模型产生影响。如果古半干旱侵蚀和小冰川切割的假说在干燥的山谷地区被证明是正确的，那么由山谷中的同位素测年地表所定义的基准面的变化将提供晚新生代山脉演化和抬升的年代学，而不依赖于已经完成的热年代学研究。这一点很重要，因为热年代学研究虽然很适合确定长期的隆升速率，但不太适合区分新生代早期和晚期的隆升。在本研究过程中开发的火山灰数据库也将有助于麦克默多火山省的研究。

This award supports a program to study the geomorphic evolution of the Dry Valleys region of the Transantarctic Mountains. The isotopic ages and areal distribution of volcanic ash deposits will be used to constrain the chronology and rates of landform development and to help quantify the age of geomorphic surfaces. The depositional setting and degree of weathering of the ash will also help to constrain regional paleoclimatic conditions during and after deposition of the volcanic ash. This work will focus on the Quartermain Mountains, Asgaard Range, Olympus Range, and McKelvey Valley because these regions are known to contain some volcanic ash deposits and because they contain a variety of geomorphic settings over a substantial elevation range. This project will attempt to test assumptions that underlie the hypothesis that the Dry Valleys region represents a relict, semi- arid landscape that formed prior to build up of the continental ice sheets during middle Miocene time and that subsequent slope modification has been limited to minor glacial scouring concentrated at valley heads, glacier confluences, and deep- valley troughs. Among these assumptions are 1) that present geomorphic processes are ineffective denudation agents, 2) that widespread land surfaces within tectonically uniform blocks reflect base-level changes at the Transantarctic Mountains front, and 3) that geomorphic landforms of the Dry Valleys that superficially resemble box canyons, escarpments, mesas, and buttes of desert regions in the American southwest formed by denudation processes now operating in the Colorado Plateau. The isotopic age information generated by this project will provide constraints for models of geomorphic evolution in cold- desert regions and will have implications for models of landscape development and uplift history of the Transantarctic Mountains. If the hypothesis of ancient semi-arid erosion followed by minor glacial incision proves correct for the Dry Valleys re gion, then changes in base level, as defined by isotopically dated land surfaces in the Valleys, will provide a chronology of late Cenozoic mountain evolution and uplift independent of thermochronological studies that have been completed. This is important because the thermochronology studies, although well suited for determining long-term uplift rates, are not well suited to distinguishing early from late Cenozoic uplift. The volcanic ash data base developed in the course of this study will also be useful for studies of the McMurdo volcanic province.