Collaborative Research: Assessment of the Role of Water in Cratonic Roots and their Post-Archean Margins on the Strength and Longevity of Continental Lithosphere

合作研究：评估克拉通根部及其太古代边缘中的水对大陆岩石圈强度和寿命的作用

• 批准号: 1118388
• 负责人: Alan Brandon
• 金额: $ 9.63万
• 依托单位: University of Houston
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-10-01 至 2016-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1118388&HistoricalAwards=false
• 关键词: Collaborative; Research; Assessment; Role; Water

Intellectual merit: This collaborative proposal requests funds for 3 years to analyze water by Fourier transform infrared spectrometry (FTIR) in minerals from peridotite xenoliths brought up by kimberlite magmas in cratons and their margins. The key physical property evoked in this project is the hydrolytic weakening of olivine (and potentially pyroxene and garnets) that occurs when hydrogen (H) is incorporated as a trace element in mineral defects of these ?nominally anhydrous? minerals. The main purpose is to test in the Slave craton (Canada) and the Siberian craton (Russia) whether the olivines at the bottom of the lithosphere have low water contents (amount of H calculated as ppm H2O) similar to what may be observed beneath the Kaapvaal craton (Peslier et al., 2010a). If this is the case, the hypothesis that dry olivines at the base of the lithosphere are in part responsible for a high viscosity contrast between a strong lower lithosphere and a more deformable asthenosphere would be confirmed as a general mechanism for craton longevity. If cratons other than the Kaapvaal do not have dry olivines at the bottom of their lithosphere, then other mechanisms will have to be proposed for craton longevity and the role of water in cratonic root survival will have to be re-assessed. A second part of this proposal is to explore the water distribution in mantle minerals at craton margins, using xenoliths from post-Archean mobile belts surrounding the Kaapvaal craton (Proterozoic Namaqua-Natal and Rehoboth terranes, South Africa and Namibia), and at Kilbourne Hole (Phanerozoic continental rift, southern New Mexico, USA), and decipher the role of water in the preservation of these terrains? mantle roots. In all parts of the proposal, all peridotite minerals (not only olivine) will be analyzed for water on well-characterized xenoliths in terms of petrography, major and trace elements, and radiogenic isotopes. Ten samples per xenolith suite will be selected, spanning the widest possible range of equilibration pressures. The effect on water content of melting, metasomatism or refertilization in the mantle, and water loss or gain during host magma ascent will be assessed. This work will also provide information on hydrogen speciation in mantle minerals. The water contents will then be incorporated into laws of viscous creep of olivine assemblages to estimate their effect on mantle rheology. This project will provide crucial data and constraints on Earth geodynamics and continental lithosphere history and longevity. Broader impacts. The analyses will be performed on a NSF-funded FTIR. Two graduate students, and two undergraduate students will benefit from this study. The graduate students will have enhanced their skills for future employment in the geosciences by performing complex analytical tasks in combination with comprehensive modeling of the data. Undergraduate students will be included in the research via various available internship, senior thesis, and work-study programs. Students from underrepresented populations (a large portion of enrolled students at the University of Houston) will have important access to state-of-theart equipment and cutting-edge research in petrology and geochemistry. The collaboration is cross-institutional and international, work will be presented at international conferences, and peer-reviewed papers will come out of this study. The results from this work will be crucial for our understanding of Earth?s mantle dynamics and will bring fundamental data to scientists interested in geodynamic modeling, rock deformation, seismology, mantle thermal conductivity and electrical resistivity, volcanology, and the history of continents.

智力价值：该合作提案要求提供三年资金，通过傅里叶变换红外光谱法 (FTIR) 分析克拉通及其边缘金伯利岩岩浆产生的橄榄岩捕虏体矿物中的水。该项目中引起的关键物理性质是橄榄石（以及潜在的辉石和石榴石）的水解弱化，当氢（H）作为微量元素掺入这些“标称无水”的矿物缺陷中时，就会发生水解弱化。矿物质。主要目的是在斯拉夫克拉通（加拿大）和西伯利亚克拉通（俄罗斯）测试岩石圈底部的橄榄石是否具有低含水量（以 ppm H2O 计算的 H 量），类似于在岩石圈下方观察到的情况。 Kaapvaal 克拉通（Peslier 等人，2010a）。如果是这样的话，那么岩石圈底部的干燥橄榄石在一定程度上造成了强烈的下部岩石圈和更容易变形的软流圈之间的高粘度对比的假设将被证实为克拉通长寿的一般机制。如果卡普瓦尔以外的克拉通岩石圈底部没有干橄榄石，那么就必须提出其他机制来延长克拉通的寿命，并且必须重新评估水在克拉通根部生存中的作用。该提案的第二部分是利用 Kaapvaal 克拉通周围的太古代移动带（南非和纳米比亚的元古代纳马夸-纳塔尔和 Rehoboth 地体）以及 Kilbourne Hole 周围的太古代移动带中的捕虏体来探索克拉通边缘地幔矿物中的水分布。 （显生宙大陆裂谷，美国新墨西哥州南部），并破译水在保存这些地形中的作用？地幔根。在该提案的所有部分中，所有橄榄岩矿物（不仅是橄榄石）都将根据岩相学、主要元素和微量元素以及放射性同位素对特征良好的捕虏体上的水进行分析。每个捕虏体套件将选择十个样品，涵盖尽可能广泛的平衡压力范围。将评估地幔中的融化、交代作用或再施肥对含水量的影响，以及宿主岩浆上升过程中的失水或增加。这项工作还将提供有关地幔矿物中氢形态的信息。然后将含水量纳入橄榄石组合的粘性蠕变定律中，以估计其对地幔流变学的影响。该项目将为地球地球动力学和大陆岩石圈历史和寿命提供重要数据和约束。更广泛的影响。分析将在 NSF 资助的 FTIR 上进行。两名研究生和两名本科生将从这项研究中受益。研究生将通过结合数据的综合建模执行复杂的分析任务，提高未来在地球科学领域的就业技能。本科生将通过各种可用的实习、高级论文和勤工俭学项目参与研究。来自弱势群体的学生（休斯顿大学就读学生的很大一部分）将有机会获得最先进的设备以及岩石学和地球化学领域的前沿研究。这项合作是跨机构和国际性的，工作将在国际会议上展示，同行评审的论文将来自这项研究。这项工作的结果对于我们了解地球地幔动力学至关重要，并将为对地球动力学建模、岩石变形、地震学、地幔热导率和电阻率、火山学和大陆历史感兴趣的科学家提供基础数据。