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Petrologic consequences of non-hydrostatic stress during subduction zone metamorphism

俯冲带变质作用过程中非静水应力的岩石学后果

基本信息

批准号：
2208229
负责人：
Jay Ague
金额：
$ 35.05万
依托单位：
Yale University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2022
资助国家：
美国
起止时间：
2022-07-01 至 2025-06-30
项目状态：
未结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2208229&HistoricalAwards=false
关键词：
Petrologic consequences non hydrostatic stress

项目摘要

Rocks deep below Earth’s surface are subjected to high temperatures and intense pressures. The chemical compositions of the minerals in rocks can record the temperature–pressure conditions under which the rocks form. Different geologic environments are characterized by distinct temperature–pressure regimes. Consequently, geoscientists can use the chemical histories preserved in minerals to reveal geologic environments of rock formation, such as within a subduction zone or mountain belt. The traditional approach to reading the temperature–pressure record is to assume that the pressure on a rock was equal in all directions when it formed. However, emerging research demonstrates that pressure (or stress) on a rock may vary considerably with direction. For example, earthquakes and the existence of mountains that stand high above sea level are settings where directional stresses play an essential role by exerting fundamental controls on the reactions that take place among minerals. These include reactions that release water (dehydration reactions). This water can weaken rocks and facilitate seismic activity, or drive the rock melting that produces dangerous volcanoes such as Mt. Rainier as well as many of the world’s great ore deposits. The natural hazards are particularly acute in and around Earth’s subduction zones, regions where one tectonic plate descends beneath another (for example, in Oregon, Washington State, and Alaska). In summary, to obtain a better understanding of the rock record, we must be able to quantitatively assess the impact of unequal stresses on geologic processes. This study will entail Ph.D. and undergraduate student research as well as public outreach programs through the Yale University Peabody Museum of Natural History.Four key interrelated concepts relevant for metamorphic rocks in subduction zones will be tested. (1) Solid solution mineral compositions and crystallographic orientations record stress fields. (2) Stress variations at the grain scale can produce compositional zoning in minerals. (3) Diffusion within minerals can generate stresses that affect diffusion profile shapes and thus diffusion-based estimates for the timescales of metamorphic and tectonic processes. (4) Normal stress can trigger dehydration reactions, rock weakening, and potential seismic moment release. These tests will involve theoretical development of the thermodynamic and kinetic equations needed to quantitatively describe unequal stress in minerals, together with applications to natural samples from exhumed subduction complexes in the Alps, Germany, Greece, and Norway. The landmark contributions of materials scientists F. C. Larché and J. W. Cahn will be the basis for the theoretical development. Field work and sample collection will be done in the Bergen Arcs, Norway; samples from the other localities are already in the petrologic collections of Yale University. A wide array of laboratory techniques will be used, including thin section petrography, electron backscatter diffraction analysis of mineral crystallographic orientations, and electron-probe microanalysis of mineral chemistry. Ultimately, the research will evaluate the impact of non-hy¬drostatic stress on mineral interface stability, solid solution mineral compositions, and intracrystalline diffusion rates. This, in turn, will have broad implications for diffusion-based time¬scale estimation, reconstructing deformation, cooling, and exhumation histories, and fluid generation in subduction zones.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.

地球表面深处的岩石会受到高温和高压的影响。岩石中矿物的化学成分可以记录岩石形成的温度-压力条件。不同的地质环境具有不同的温压关系。因此，地球科学家可以利用保存在矿物中的化学史来揭示岩石形成的地质环境，例如在俯冲带或山带内。阅读温度-压力记录的传统方法是假设岩石形成时在各个方向上的压力都是相等的。然而，新的研究表明，岩石上的压力(或应力)可能会随着方向的不同而有很大的不同。例如，地震和海拔较高的山脉的存在，是方向性应力通过从根本上控制矿物之间发生的反应而发挥关键作用的环境。这些反应包括释放水分的反应(脱水反应)。这些水可以削弱岩石，促进地震活动，或者推动岩石融化，从而产生危险的火山，如芒特山。雷尼埃以及世界上许多伟大的矿藏。自然灾害在地球俯冲带及其周围尤为严重，俯冲带是指一个构造板块俯冲到另一个板块之下的地区(例如，在俄勒冈州、华盛顿州和阿拉斯加)。总之，为了更好地了解岩石记录，我们必须能够定量地评估不均匀应力对地质过程的影响。这项研究将通过耶鲁大学皮博迪自然历史博物馆进行博士和本科生研究以及公共推广项目。将测试与俯冲带变质岩相关的四个关键概念。(1)固溶体矿物成分和晶体取向记录了应力场。(2)颗粒尺度上的应力变化可以在矿物中产生成分分带。(3)矿物内部的扩散作用会产生影响扩散剖面形状的应力，从而对变质作用和构造作用的时间尺度进行基于扩散的估计。(4)正常应力可引发脱水反应、岩石弱化和潜在的地震矩释放。这些测试将涉及定量描述矿物中不同应力所需的热力学和动力学方程的理论发展，以及对阿尔卑斯山、德国、希腊和挪威挖掘出的俯冲杂岩中的自然样品的应用。材料科学家F·C·拉奇和J·W·卡恩的里程碑式贡献将成为理论发展的基础。野外工作和样品采集将在挪威卑尔根弧进行；来自其他地方的样品已经在耶鲁大学的岩石学收藏中。将使用广泛的实验室技术，包括薄片岩相学、矿物晶体取向的电子背散射衍射分析和矿物化学的电子探针显微分析。最终，该研究将评估非水力应力对矿物界面稳定性、固溶体矿物成分和晶体内扩散速率的影响。这反过来将对基于扩散的时间尺度估计、重建变形、冷却和折返历史以及俯冲区的流体生成产生广泛的影响。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。