Collaborative Research: Exhumation of the Transantarctic Mountains: Constraints from (U-Th)/He Dating of Apatites

9909436法利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升历史的调查。总体目标是通过使用新开发的磷灰石(U-Th)/He测年方法对垂直剖面上收集的样品进一步限制横贯北极山脉的折返历史。这一方法与现有的磷灰石裂变径迹信息相结合，将限制横贯北极山脉的折返速度和模式，因为它们在早新世作为裂谷侧翼隆起。该项目将补充其他项目，并建立在以前利用磷灰石裂变径迹热年代学确定的折返和构造历史解释的基础上。它将弥合根据裂变径迹热年代学和宇宙起源表面暴露年代确定的侵蚀速率信息之间的差距，并将山脉的剥露历史与其地貌演变结合起来。因此，该项目的成果将解决南极科学中的一个悬而未决的问题；即南极东部冰盖的稳定性，以及从“温暖的”动态冰盖向寒冷的极地冰盖过渡的时间。与这一问题高度相关的是横贯北极山脉的地貌演化，因为许多关于地貌演化速度的不同证据被用来论证直到上新世(“动态”冰盖模型)或中新世中期(“稳定”冰盖模型)都存在动态冰盖。了解南极东部冰盖过去的稳定性或相对于气候记录的动态波动，对于了解现在的冰盖可能如何响应全球变暖当然很重要。该项目的具体目标是确定横跨南极山前和整个山脉结构颗粒的一些垂直剖面的磷灰石(U-Th)/He年龄/海拔趋势。所有这些剖面的裂变径迹数据都已经存在，磷灰石裂变径迹年龄在150-30 Ma之间。(U-Th)/He技术的较高精度和它在较低温度(闭合温度为~70℃；He部分保留带的限度为40-85℃)下记录的信息将使我们能够更详细地研究约130 Ma至20 Ma的的折返历史。另一个方面是研究记录了白垩纪折返作用的地区，以及裂变径迹剖面表明整个白垩纪处于热稳定和构造稳定以及最小侵蚀时期的地区。还将研究早期新生代横贯北极山脉的抬升和形成过程中更快速的折返开始的时间的变化。

9909436 FarleyThis award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, supports an investigation of the uplift history of the Dry Valleys segment of the Transantarctic Mountains. The overall goal is to further constrain the exhumation history of the Transantarctic Mountains by using the newly developed apatite (U-Th)/He dating method on samples collected in vertical profiles. This approach, combined with existing apatite fission track information will constrain the rate and patterns of exhumation across the Transantarctic Mountains since their inception as a rift-flank uplift in the early Cenozoic.This project will complement other projects and build on previous interpretations of the exhumation and tectonic history determined using apatite fission track thermochronology. It will bridge the gap between information on erosion rates determined from fission track thermochronology and from cosmogenic surface exposure dating and integrate the exhumation history of the mountains with their landscape evolution. As such, the results from this project will address an outstanding problem in Antarctic science; namely the stability of the East Antarctic Ice Sheet, and the timing of the transition from a "warm" dynamic ice sheet to a cold polar ice sheet. Highly relevant to this issue is the landscape evolution of the Transantarctic Mountains because many diverse lines of evidence for the rate of landscape evolution have been used to argue for a dynamic ice sheet up until either the Pliocene (the "dynamic" ice sheet model) or the middle Miocene (the "stable" ice sheet model). Understanding the past stability or dynamic fluctuations of the East Antarctic ice sheet with respect to the climate record is, of course, important for understanding how the present ice sheet may respond to global warming.The specific objective of this project is to determine apatite (U-Th)/He age versus elevation trends for a number of vertical profiles from locations within the Transantarctic Mountain front and across the structural grain of the range. Fission track data already exist for all of these profiles, with apatite fission track ages ranging from 150-30 Ma. The greater precision of the (U-Th)/He technique and the fact it records information at lower temperatures (closure temperature of ~70 degrees Celsius; limits of 40-85 degrees Celsius for the He partial retention zone) will allow examination of the exhumation history of the TAM in more detail from ca 130 Ma to ~20 Ma. Another facet is to examine areas where Cretaceous exhumation is recorded and areas where the fission track profiles indicate periods of thermal and tectonic stability and minimal erosion throughout the Cretaceous. The variation of timing of the onset of more rapid exhumation accompanying uplift and formation of the Transantarctic Mountains in the early Cenozoic will also be examined.