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

这个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的干谷段的隆起历史进行调查。总体目标是利用新发展的磷灰石(U-Th)/He定年法对垂直剖面采集的样品进一步限定横贯南极山脉的发掘历史。这种方法，结合现有的磷灰石裂变径迹信息，将限制横贯南极山脉在新生代早期作为裂谷翼隆升形成以来的挖掘速度和模式。该项目将补充其他项目，并建立在以前对挖掘和构造历史的解释基础上，利用磷灰石裂变径迹热年代学确定构造历史。它将弥合裂变径迹热年代学和宇宙地表暴露年代测定的侵蚀速率信息之间的差距，并将山脉的发掘历史与景观演变结合起来。因此，该项目的成果将解决南极科学中的一个突出问题；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。与这个问题高度相关的是横极山脉的景观演变，因为在上新世（“动态”冰盖模型）或中新世中期（“稳定”冰盖模型）之前，许多关于景观演变速度的不同证据都被用来论证一个动态冰盖。当然，根据气候记录了解南极东部冰盖过去的稳定性或动态波动，对于了解目前的冰盖如何对全球变暖作出反应非常重要。该项目的具体目标是确定横跨南极山脉锋面和整个山脉结构颗粒的许多垂直剖面的磷灰石(U-Th)/He年龄与海拔趋势。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技术的更高精度以及它在较低温度下记录信息的事实（关闭温度为~70摄氏度；He部分保留区限制为40-85摄氏度）将允许更详细地检查TAM的挖掘历史，从约130 Ma到~20 Ma。另一个方面是检查白垩纪挖掘记录的区域，以及裂变轨迹剖面显示整个白垩纪的热构造稳定和最小侵蚀时期的区域。此外，还将探讨在新生代早期，随着横贯南极山脉的隆升和形成，更快速的挖掘开始时间的变化。

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.