Collaborative Research: Ice sheet erosional interaction with hot geotherm in West Antarctica

南极玛丽伯德地（MBL）海岸附近的沉积物记录表明，在过去的短（数万年）和长（数百万年）时间框架内，南极西部冰盖（WAIS）的大小发生了频繁而剧烈的变化。目前，WAIS覆盖了MBL的大部分地区，覆盖了崎岖不平的基岩景观。当出口冰川从大陆内部流入海洋时，冰盖雕刻出狭窄的线状沟槽，深达海平面以下二三千米。结果，大量破碎的大陆基岩被带到海底。冰川向下切入结晶岩（即花岗岩）区域，其温度随岩石深度的变化恰好是显著的。基岩中这种强烈的地热梯度有利于确定基岩何时经历了快速挖掘或“暴露”。分析被侵蚀岩石中矿物（锆石和磷灰石）的化学成分将提供有关冰川从南极大陆带走基岩的速度和时间的信息。这项研究解决了以下问题：什么时候陆地变得足够高，可以形成一个大冰盖？冰期前的区域地形是怎样的？在什么样的气候条件下，在冰盖生长的什么时候，冰川开始急剧切割基岩，形成流向海洋的狭窄沟槽？这项研究将有助于更好地了解过去南极冰盖的波动，并确定冰川切割的精确时间。这些结果将完善冰盖历史，并有助于国际社会对当代冰盖变化及其全球后果的反应。该项目将有助于培养STEM领域的两名研究生和两名本科生。目的是明确WAIS冰川切口的起始时间，评价新生代古地形的演化。低温(T)热年代学和Pecube三维热运动学模型将应用于确定冰川侵蚀切口的日期和特征。锆石和磷灰石的单粒、双粒和三粒定年将揭示该地区地壳热演化的详细情况，使研究小组能够确定始新世到现在构造/岩浆作用对冰川和基岩隆升的比较地形影响。横跨Marie Byrd Land （MBL）的高t矿物温度计在~100 Ma的温度下从800摄氏度到8804；300℃，这一特征形成了一个参考层，即古地温层，通过这个参考层，可以使用低温度温度计来探索新生代的景观历史。MBL的地热梯度在新生代持续升高，为敏感的磷灰石和锆石低t温度计记录与冰川切口有关的基岩冷却创造了有利条件。学生将接受培训，使用亚利桑那州和明尼苏达州最先进的分析设备，从基岩样品和近海沉积沉积物中扩展MBL的地质和热年代学历史。他们获得的温度和时间数据将提供古地形、均衡和MBL热演化的约束条件，这些数据将使用Pecube模型模拟在3D中建模。在热地壳中，只需较少的切口即可暴露基岩，其中包含独特的热时剖面；这一预测将通过反向Pecube三维热场模型进行验证，基岩和碎屑样品通过该模型冷却。利用Pecube的结果，ICI-Hot团队将检查随侵蚀速率、地形起伏、地热梯度和/或弯曲等静力刚度变化而形成的时变地形。这些影响是WAIS动态过程的表现，包括冰盖负荷、冰体积波动、地壳断层上的相对运动以及与岩浆作用相关的MBL穹丘海拔升高。该项目利用了美国极地岩石储存库、IODP的墨西哥湾海岸核心储存库和南极海洋地质研究设施中已有的样本。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Sediment records off the coast of Marie Byrd Land (MBL), Antarctica suggest frequent and dramatic changes in the size of the West Antarctic Ice Sheet (WAIS) over short (tens of thousands of years) and long (millions of years) time frames in the past. WAIS currently overrides much of MBL and covers the rugged and scoured bedrock landscape. The ice sheet carved narrow linear troughs that reach depths of two to three thousand meters below sea level as outlet glaciers flowed from the interior of the continent to the oceans. As a result, large volumes of fragmented continental bedrock were carried out to the seabed. The glaciers cut downward into a region of crystalline rocks (i.e. granite) whose temperature change as a function of rock depth happens to be significant. This strong geothermal gradient in the bedrock is favorable for determining when the bedrock experienced rapid exhumation or "uncovering". Analyzing the chemistry of minerals (zircon and apatite) within the eroded rocks will provide information about the rate and timing of the glacier removal of bedrock from the Antarctic continent. The research addresses the following questions: When did the land become high enough for a large ice sheet to form? What was the regional pre-glacial topography? Under what climate conditions, and at what point in the growth of an ice sheet, did glaciers begin to cut sharply into bedrock to form the narrow troughs that flow seaward? The research will lead to greater understanding of past Antarctic ice sheet fluctuations and identify precise timing of glacial incision. These results will refine ice sheet history and aid the international societal response to contemporary ice sheet change and its global consequences. The project will contribute to the training of two graduate and two undergraduate students in STEM.The objective is to clarify the onset of WAIS glacier incision and assess the evolution of Cenozoic paleo-topography. Low-temperature (T) thermochronology and Pecube 3-D thermo-kinematic modeling will be applied to date and characterize episodes of glacial erosional incision. Single-grain double- and triple-dating of zircon and apatite will reveal the detailed crustal thermal evolution of the region enabling the research team to determine the comparative topographic influences on glaciation versus bedrock uplift induced by Eocene to present tectonism/magmatism. High-T mineral thermochronometers across Marie Byrd Land (MBL) record rapid extension-related cooling at ~100 Ma from temperatures of 800 degrees C to ≤ 300 degrees C. This signature forms a reference horizon, or paleogeotherm, through which the Cenozoic landscape history using low-T thermochronometers can be explored. MBL's elevated geothermal gradient, sustained during the Cenozoic, created favorable conditions for sensitive apatite and zircon low-T thermochronometers to record bedrock cooling related to glacial incision. Students will be trained to use state-of-the-art analytical facilities in Arizona and Minnesota, expanding the geo- and thermochronologic history of MBL from bedrock samples and offshore sedimentary deposits. The temperature and time data they acquire will provide constraints on paleotopography, isostasy, and the thermal evolution of MBL that will be modeled in 3D using Pecube model simulations. Within hot crust, less incision is required to expose bedrock containing the distinct thermochronometric profile; a prediction that will be tested with inverse Pecube 3-D models of the thermal field through which bedrock and detrital samples cooled. Using results from Pecube, the ICI-Hot team will examine time-varying topography formed in response to changes in erosion rates, topographic relief, geothermal gradient and/or flexural isostatic rigidity. These effects are manifestations of dynamic processes in the WAIS, including ice sheet loading, ice volume fluctuations, relative motion upon crustal faults, and magmatism-related elevation increase across the MBL dome. The project makes use of pre-existing sample collections housed at the US Polar Rock Repository, IODP's Gulf Coast Core Repository, and the Antarctic Marine Geology Research Facility.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.