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

合作研究：南极洲西部冰盖侵蚀与热地温的相互作用

• 批准号: 1917009
• 负责人: Stuart Thomson
• 金额: $ 13.55万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1917009&HistoricalAwards=false
• 关键词: Collaborative; Research; Ice; sheet; erosional

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.

南极洲玛丽伯德地（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）的大小发生了频繁和戏剧性的变化。 WAIS目前覆盖了MBL的大部分地区，覆盖了崎岖和冲刷的基岩景观。冰盖切割出狭窄的线性槽，当出口冰川从大陆内部流向海洋时，这些槽达到海平面以下两三千米的深度。因此，大量破碎的大陆基岩被带到海底。冰川向下切入结晶岩石（即花岗岩）区域，其温度随岩石深度的变化恰好很大。这种强烈的地温梯度有利于确定基岩何时经历快速折返或“暴露”。分析侵蚀岩石中的矿物（锆石和磷灰石）的化学成分将提供有关冰川从南极大陆移除基岩的速度和时间的信息。这项研究解决了以下问题：陆地何时变得足够高，足以形成大冰盖？冰川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，冰川开始急剧切入基岩，形成流向大海的狭窄槽？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的历史，并有助于国际社会对当代冰盖变化及其全球后果的反应。该项目将有助于培训两名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变。低温（T）热年代学和Pecube 3-D热动力学建模将应用于日期和冰川侵蚀切割的特点。锆石和磷灰石的单颗粒双重和三重定年将揭示该地区详细的地壳热演化，使研究小组能够确定比较地形对冰川作用的影响与始新世到目前的构造/岩浆作用引起的基岩隆起。横跨玛丽伯德地（MBL）的高温矿物热计时器记录了在~100 Ma时从800摄氏度到300摄氏度的与伸展相关的快速冷却。这个标志形成了一个参考层位，或古地温，通过它可以利用低温热时计探索新生代的景观历史。MBL的地热梯度升高，持续在新生代，创造了有利的条件，敏感的磷灰石和锆石低温热时计记录基岩冷却有关的冰川切割。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，从基岩样品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、等渗线和MBL热演化的约束，这些约束将使用Pecube模型模拟在3D中建模。在热地壳内，需要较少的切口，以暴露基岩包含不同的thermochronometric配置文件;预测，将测试与逆Pecube 3-D模型的热场，通过该基岩和碎屑样品冷却。利用Pecube的结果，ICI-Hot团队将研究随侵蚀速率、地形起伏、地热梯度和/或弯曲均衡刚度变化而形成的随时间变化的地形。这些影响是WAIS中动态过程的表现，包括冰盖加载、冰量波动、地壳断层上的相对运动以及与岩浆活动相关的整个MBL穹丘的高程增加。该项目利用了存放在美国极地岩石储存库、IODP墨西哥湾沿岸岩心储存库和南极海洋地质研究设施中的现有样本。该奖项反映了NSF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。