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.

知识分子的优点：该协作提案要求资金3年来通过金伯利特岩浆在克拉顿及其利润率的牛皮岩异甲岩矿物质的矿物质变换红外光谱法（FTIR）分析水。该项目中引起的关键物理特性是橄榄石（以及潜在的辉石和石榴石）的水解削弱时，当氢（H）作为痕量元素纳入这些矿物质缺陷中时发生的痕量元素吗？矿物质。主要目的是在奴隶克拉顿（加拿大）和西伯利亚克拉顿（俄罗斯）中测试岩石圈底部的橄榄石是否具有与可以在kaapvaal craton下观察到的相似的水含量（h计算为ppm h2o）（PPM H2O的数量）（Peslier等人，Peslier等人，2010a，2010a）。如果是这种情况，那么岩石圈底部干橄榄石的假设部分是导致强质岩石圈和更可变形的运动层之间高粘度对比度的，这将被证实是Craton longevity的一般机制。如果Kaapvaal以外的其他克拉通在其岩石圈的底部没有干橄榄石，则必须提出其他机制以延长克拉顿的寿命，并且必须重新评估水在克拉通根中的作用。该提案的第二部分是使用围绕Kaapvaal Craton（Protereroxoic Namequa-Natal and Rehoboth Terranes，South Africa and Namibia and Namibia和Namibia）以及米米布尔（Phannorne southtorne southton Contronter）的近代居住在墨西哥群岛的Kaapvaal Craton（Protereroxoic Namequa-Natal and Rehoboth Terranes）探索Craton边缘地幔矿物的水分分配。破译水在保存这些地形中的作用？地幔根。在提案的所有部分中，所有橄榄岩矿物（不仅是橄榄石）将根据岩石学，主要元素和痕量元素以及放射性同位素的特征化异义石进行分析。将选择每个异种石套件的十个样本，涵盖最宽的平衡压力范围。将评估对地幔中融化，交代或介引性化以及宿主岩浆上升过程中的水分流失或增益的影响。这项工作还将提供有关地幔矿物质氢形成性的信息。然后，水含量将被纳入橄榄石组合的粘性蠕变定律中，以估计其对地幔变性的影响。该项目将提供有关地球地球动力学以及大陆岩石圈历史和寿命的关键数据和约束。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。研究生将通过与数据的全面建模结合执行复杂的分析任务来提高他们在地球科学的未来就业技能。本科生将通过各种可用的实习，高级论文和勤学计划包括在研究中。来自代表性不足人群的学生（休斯顿大学的大量注册学生）将有重要的访问良好的设备和岩石学和地球化学领域的尖端研究。该合作是跨机构和国际的，将在国际会议上进行工作，并将在这项研究中提出同行评审的论文。这项工作的结果对于我们对地球地幔动态的理解至关重要，并将为对地球动力学建模，岩石变形，地震学，地幔导热率和电阻率，火山学和大陆历史感兴趣的科学家带来基本数据。