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

9910880恩卡纳西翁该奖项由极地项目办公室的南极地质和地球物理项目提供，支持对横贯南极山脉干谷部分的隆起和景观演变进行调查。山脉作为地形特征形成的时间是理解其作为地壳变形的重力驱动力的作用以及评估其对气候变化的影响或依赖性的关键因素。然而，这方面的造山作用仍然很少记录，因为地貌的表达或沉积记录与增加表面海拔可能会修改后来的侵蚀。同样，用于跟踪侵蚀和地貌发育的地球化学工具（例如，表面暴露年代测定法（英语：Surface exposure dating）很少用于此目的，因为它们通常只提供最近（100万年（Ma））历史的信息。因此，在我们的理解的时间和地形/构造的山区带的演变仍然存在很大的差距。在没有直接的限制不断变化的山脉的地貌，情节的快速冷却推断技术，如磷灰石裂变径迹热年代学往往归因于山区的地形上升。这种做法假设从冷却数据推断出的剥露（岩石相对于地球表面向上移动）和基岩隆起（岩石相对于大地水准面向上移动）代表地球表面（和地形）高度的相等增加，尽管工作人员已经表明这种相关性并不总是成立。解决长期景观演变问题的一种方法是将联合收割机低温热年代测定法与地表暴露年代测定法结合起来。横贯南极山脉的干谷地区是进行这种研究的理想地点，因为该地区许多现代陆地表面的历史可能长达15 Ma，显然自中新世中期以来需要非常低的侵蚀速率。磷灰石裂变径迹表明，干谷中的岩石在大约45 Ma时冷却了大约105摄氏度，这在我们对这条山脉演化的认识中留下了大约30 Ma的空白。应用新开发的磷灰石（U-Th）/He热时计（闭合温度为70摄氏度）可以进一步缩小这一差距，因为该技术对更低的温度敏感，更重要的是，磷灰石氦年龄可以提供地形起伏发展时间的独特敏感记录。该项目是一项重点突出的研究，旨在将联合收割机热年代学指示与宇宙射线暴露年龄相结合，以更好地限制干旱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关于基岩隆起和剥露的研究所提供的大量数据与景观演变之间提供急需的联系。特别是，通过限制干旱山谷的形成年龄，该项目将确定跨南极山脉作为地形特征形成的时间。这项工作的结果应具有普遍意义的地球动力学演变的区域，并将有助于辩论新生代古气候变化影响的增长和稳定的东南极冰盖。

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.