Antarctic Peninsula Exhumation and Landscape Development Investigated by Low-Temperature Detrital Thermochronometry

中纬度地区高山景观的极端山地地形（如欧洲阿尔卑斯山、巴塔哥尼亚、阿拉斯加）被认为是由冰川的侵蚀作用形成的，但我们对这些地形何时以及如何形成的确切了解有限。如果冰川的冰是它们形成的原因，那么这些地貌一定是在过去的2-3百万年中形成的，当时这些纬度地区有冰；这个时间直到最近才被观测证实。相比之下，南极半岛有着同样壮观的地形起伏，早在3700万年前就有高山冰川，目前被冰覆盖。因此，如果是由冰川侵蚀引起的，那么半岛的高地应该比在中纬度地区观察到的要早得多，但我们对其发展的时间几乎一无所知。这项研究的主要好处是通过对近海收集的沉积物进行最先进的化学分析，研究南极半岛地形发育的时间。这项研究很重要，因为研究高纬度地区的地点可以与中纬度地区的地点进行比较，并测试目前关于冰川景观发展的假设。本项目旨在利用磷灰石(U-Th)/He体系的低温热时测定技术，研究南极半岛中部地区的挖掘历史、现今地形的发展和冰川侵蚀模式。最近的一些研究使用这种方法来研究温带地区更新世高山冰川侵蚀形成的引人注目的高地形景观：新西兰、阿尔卑斯山、不列颠哥伦比亚省、阿拉斯加和巴塔哥尼亚。这些研究不仅揭示了这些景观形成的时间，而且还为冰川侵蚀的物理机制提供了新的见解。南极半岛与温带高山景观大体相似，主要地貌是巨大的冰川槽。然而，我们对南极冰川历史的了解表明，冰川侵蚀的时间和历史很可能与温带高山环境非常不同：南极半岛自始新世以来一直被冰川覆盖，更新世的气候冷却被认为抑制了冰川侵蚀，而不是增强了冰川侵蚀。我们的目标是通过开发一种直接的热时计记录来评估这些假设，该记录记录了现在的冰川谷地形何时以及如何形成的。我们建议通过对半岛主要冰川接地线附近收集的冰川沉积物进行磷灰石(U-Th)/He和4He/3He测量，了解冰川谷形成的时间和过程。实际上，由于我们不能直接对目前被冰覆盖的基岩取样，我们将依靠这些冰川来为我们做这件事。

The extreme mountain topographies of alpine landscapes at mid latitudes (e.g., European Alps, Patagonia, Alaska) are thought to have formed by the erosive action of glaciers, yet our understanding of exactly when and how those topographies developed is limited. If glacial ice was responsible for forming them, then those landscapes must have developed primarily over the last 2-3 million years when ice was present at those latitudes; this timing has only recently been confirmed by observations. In contrast, the Antarctic Peninsula, which contains similarly spectacular topographic relief, is known to have hosted alpine glaciers as early as 37 million years ago, and is currently covered by ice. Thus, if caused by glacial erosion, the high relief of the peninsula should have formed much earlier than what has been observed at mid latitude sites, yet we know nearly nothing about the timing of its development. The primary benefit of this research will be to study the timing of topography development along the Antarctic Peninsula by applying state of the art chemical analyses to sediments collected offshore. This research is important because studying a high latitude site will enable comparison with sites at mid latitudes and test current hypotheses on the development of glacial landscapes in general.This project aims to apply low-temperature thermochronometry based on the (U-Th)/He system in apatite to investigate the exhumation history, the development of the present topography, and the pattern of glacial erosion in the central Antarctic Peninsula. A number of recent studies have used this approach to study the dramatic, high-relief landscapes formed by Pleistocene alpine glacial erosion in temperate latitudes: New Zealand, the Alps, British Columbia, Alaska, and Patagonia. These studies have not only revealed when these landscapes formed, but have also provided new insights into the physical mechanisms of glacial erosion. The Antarctic Peninsula is broadly akin to temperate alpine landscapes in that the dominant landforms are massive glacial troughs. However, what we know about Antarctic glacial history suggests that the timing and history of glacial erosion was most likely very different from the temperate alpine setting: The Antarctic Peninsula has been glaciated since the Eocene, and Pleistocene climate cooling is hypothesized to have suppressed, rather than enhanced, glacial erosion. Our goal is to evaluate these hypotheses by developing a direct thermochronometric record of when and how the present glacial valley relief formed. We propose to learn about the timing and process of glacial valley formation through apatite (U-Th)/He and 4He/3He measurements on glacial sediment collected near the grounding lines of major glaciers draining the Peninsula. In effect, since we cannot sample bedrock directly that is currently covered by ice, we will rely on these glaciers to do it for us.