Collaborative Research: Formation of the Dry Valleys, Antarctica: Linking Thermochronometric (U-Th/He) and Cosmogenic Constraints on Landscape Development

9910880该奖项由极地计划办公室南极地质和地球物理计划提供，支持对横贯北极山脉的干旱山谷段的隆起和地貌演变的调查。山脉形成为地形特征的时间是了解它们作为地壳变形重力驱动力的作用以及评估它们对气候变化的影响或依赖的关键因素。然而，造山作用的这一方面仍然缺乏文献记载，因为与地表高度增加相关的地貌表现或沉积记录可能会被后来的侵蚀所改变。同样，用于跟踪侵蚀和地貌发育的地球化学工具(例如，地表暴露年代测定)很少用于这一目的，因为它们通常只提供最近(100万年)历史的信息。因此，我们对山脉带的时间和地形/构造演化的理解仍然存在很大差距。在没有对不断演化的山脉的地貌进行直接限制的情况下，由磷灰石裂变径迹测温等技术得出的快速降温事件通常被归因于山脉地带的地形隆起。这种做法假设，从冷却数据推断出的折返(岩石相对于地表向上移动)和基岩抬升(岩石相对于大地水准面向上移动)代表着地球表面海拔(和地形)的同等增加，即使工作人员已经证明这种相关性并不总是成立的。解决长期景观演变问题的一种方法是将低温热计时与表面暴露测年相结合。横贯北极山脉的干旱山谷地区是进行这种活动的理想地点，因为该地区的许多现代地表可能有15 Ma的历史，自中新世中期以来，显然需要非常低的侵蚀率。磷灰石裂变径迹表明，直到大约45 Ma，干燥山谷中的岩石冷却了大约105℃，留下了大约30 Ma的差距，我们对这条山脉的演化的认识。新开发的磷灰石(U-Th)/氦温度计时仪(闭合温度为70摄氏度)的应用可以进一步缩小这一差距，因为该技术对更低的温度很敏感，更重要的是，磷灰石氦年龄可以提供地形起伏形成时间的唯一灵敏记录。该项目是一项重点严密的研究，旨在将河谷切割的温度计时指标与宇宙射线暴露年龄相结合，以更好地约束干燥山谷地区的形成和地貌演变。将收集的磷灰石(U-Th)/He和暴露年龄数据将在磷灰石裂变径迹研究中关于基岩抬升和折返的大量数据与地形演变之间提供亟需的联系。特别是，通过限制干燥山谷的形成年龄，该项目将确定横贯北极的山脉作为地形特征形成的时间。这项工作的结果应该对该区域的地球动力学演化具有普遍意义，并将有助于关于新生代古气候变化影响南极东部冰盖的生长和稳定的辩论。

9910880EncarnacionThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports an investigation of uplift and landscape evolution of the Dry Valleys segment of the Transantarctic Mountains. The time when mountains form as topographic features is a crucial factor for understanding their role as gravitational driving forces for crustal deformation, as well as for assessing their influence or dependence on climate variations. Yet, this aspect of orogenesis remains poorly documented because the geomorphologic expressions or sedimentation record associated with increasing surface elevations may be modified by later erosion. Similarly, geochemical tools used for tracking erosion and landform development (e.g., surface exposure dating) are seldom useful for this purpose because they usually provide information on only the most recent (1 million year (Ma)) history. As a result, a large gap in our understanding of the temporal and physiographic/tectonic evolution of mountain belts remains. In the absence of direct constraints on the geomorphology of evolving mountain ranges, episodes of rapid cooling deduced from techniques like apatite fission track thermochronometry are often attributed to the topographic rise of mountain belts. This practice assumes that exhumation (movement of a rock upward with respect to the earth's surface) and bedrock uplift (movement of the rock upward with respect to the geoid) inferred from cooling data represent an equivalent increase in elevation at the earth's surface (and relief), even though workers have shown that such a correlation does not always hold. One way to address the problem of long-term landscape evolution is to combine low-temperature thermochronometry with surface exposure dating. The Dry Valleys region of the Transantarctic Mountains is an ideal place for such an exercise because many of the modern land surfaces in the region may be as old as 15 Ma, clearly requiring very low erosion rates since the mid-Miocene. Apatite fission tracks indicate that rocks in the Dry Valleys cooled through approximately 105 degrees C as recently as about 45 Ma, leaving a gap of about 30 Ma in our knowledge of the evolution of this mountain range. Application of the newly developed apatite (U-Th)/He thermochronometer (closure temperature of 70 degrees C) can further close this gap because the technique is sensitive to even lower temperatures and more importantly apatite helium ages can provide a uniquely sensitive record of the time at which topographic relief develops. This project is a tightly focused study designed to combine thermochronometric indications of river valley incision with cosmic-ray exposure ages to better constrain the formation and geomorphologic evolution of the Dry Valleys region. The apatite (U-Th)/He and exposure age data that will be collected will provide a much-needed link between the large amounts of data already available from apatite fission track studies on bedrock uplift and exhumation on the one hand, and landscape evolution on the other. In particular, by constraining the formation age of the Dry Valleys, this project will determine when the Transantarctic Mountains formed as a topographic feature. The results of this work should have general implications for the geodynamic evolution of the region, and will contribute to the debate regarding Cenozoic paleoclimate changes influencing the growth and stability of the East Antarctic ice sheet.