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

南极马里伯德岛(MBL)海岸的沉积物记录表明，在过去的短(数万年)和长(数百万年)时间范围内，西南极冰盖(WAIS)的大小发生了频繁和戏剧性的变化。WAIS目前覆盖了MBL的大部分，覆盖了崎岖和冲刷的基岩地貌。当出口冰川从大陆内部流入海洋时，冰盖上刻出了狭窄的线形凹槽，深达海平面以下两三千米。因此，大量破碎的大陆基岩被带到海底。冰川向下切割成结晶岩石(即花岗岩)的区域，其温度随着岩石深度的变化恰好是显着的。基岩中这种强烈的地温梯度有利于确定基岩经历了快速折返或“暴露”的时间。对侵蚀岩石中矿物(锆石和磷灰石)的化学分析将提供有关南极大陆基岩冰川移动的速度和时间的信息。这项研究解决了以下问题：陆地什么时候变得足够高，可以形成大冰盖？区域前冰川地貌是什么？在什么气候条件下，在冰盖生长的什么时候，冰川开始急剧切割基岩，形成向海洋流动的窄槽？这项研究将有助于更好地了解南极冰盖过去的波动，并确定冰川切割的准确时间。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。该项目将帮助培养两名STEM研究生和两名本科生。目的是澄清WAIS冰川切割的开始，并评估新生代古地形的演化。低温(T)热年代学和Pecube 3-D热运动学模拟将用于确定冰川侵蚀切割的年代和特征。锆石和磷灰石的单颗粒双测年和三重测年将揭示该地区详细的地壳热演化，使研究小组能够确定相对地形对冰川作用和基岩抬升的影响，这些抬升是由始新世引起的，以呈现构造/岩浆作用。整个玛丽伯德岛(MBL)的高温矿物测温仪(MBL)记录了大约100 Ma时与伸展相关的快速冷却，温度从800摄氏度到300摄氏度。这一特征形成了一个参照层，即古地温，通过它可以探索使用低T测温仪的新生代地貌历史。MBL在新生代持续的高地温梯度，为敏感的磷灰石和锆石低T温度计时仪记录与冰川切割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施，从基岩样本和近海沉积矿床扩展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对古地形、均衡和MBL的热演化的约束，这些将使用Pecube模型模拟在3D中模拟。在炎热的地壳中，暴露包含不同热时间剖面的基岩所需的切割较少；这一预测将通过基岩和碎屑样品冷却时所通过的热场的逆Pecube 3-D模型进行验证。利用Pecube的结果，ICI-HOT团队将研究随着侵蚀速度、地形起伏、地温梯度和/或弯曲均衡刚性的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、冰量波动、地壳断层上的相对运动以及与岩浆作用有关的跨MBL穹顶的海拔上升。该项目利用了美国极地岩石储存库、IODP的墨西哥湾沿岸核心储存库和南极海洋地质研究设施的现有样本收集。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.