Experimental and Natural Deformation of Magnesian Carbonates

碳酸镁的实验和自然变形

• 批准号: 0911586
• 负责人: Julie Newman
• 金额: $ 39.99万
• 依托单位: Texas A&M Research Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-01 至 2013-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911586&HistoricalAwards=false
• 关键词: Experimental; Natural; Deformation; Magnesian; Carbonates

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Shallow marine carbonate rocks that are deposited at continental margins are subjected to intense deformation at convergent plate boundaries, and a growing body of evidence indicates that these carbonate rocks are entrained in subduction zones to significant mantle depths. By comparison with rocks composed of silicate minerals, rocks composed of carbonates are weak, so that their deformation exerts a strong influence on the structures that develop in mountain belts resulting from continental collisions, and they may also influence deformation in the mantle during subduction. Carbonate rocks are composed largely of the minerals calcite, dolomite, and magnesite. These minerals have similar crystal structures, but are compositionally and mechanically different. While the rheology of calcite has been well established, the rheology of dolomite is less well constrained by experiments, and almost nothing is known about the rheology of magnesite, which is stable to greater depths in the mantle than calcite or dolomite. In order to accurately model deformation processes within the crust and mantle during subduction and mountain building processes, the rheology of dolomite needs to be refined, the rheology of magnesite determined, and then compared to the rheology of calcite. This project will use both experimental and observational approaches to achieve the following: (1) determine the rheology for dislocation creep of dolomite through experiments, in a triaxial rock deformation apparatus, to establish the temperature and strain rate dependence of this deformation mechanism in dolomite; (2) determine the mechanical properties of magnesite through experiments, in a triaxial rock deformation apparatus, over a wide range of pressures, temperatures and strain rates to establish the ranges of temperature and strain rate over which different deformation mechanisms operate; (3) investigate the microstructures and fabrics formed in experimentally shortened and sheared dolomite; and (4) compare the microstructures and fabrics formed during experimental deformation with those observed in natural dolomite shear zones to provide the foundation to apply laboratory determined rheologies to nature.This research will investigate, through deformation experiments and analyses of rocks deformed in nature, the strength and deformation processes of the carbonate minerals, dolomite and magnesite. Carbonate-bearing rocks make up a significant portion of the rocks that are deformed during mountain building at convergent plate boundaries. Therefore, the strength and deformation behavior of these rocks will strongly influence the structures that develop in mountains, which are responsible for the accumulation of natural resources. The data generated through this study will be used by theoretical modelers and field geologists to determine how and where resources accumulate. Carbonate rocks are also carried to significant depths in the earth?s interior within subduction zones, and their strengths and deformation behavior will thus exert a strong influence on processes such as subduction and mantle convection. Data on the deformation behavior of these rocks will enable theoretical modelers to more accurately predict the dynamics of these long-term geologic processes, including a better understanding of the dynamics of deep earthquakes.

该奖项根据 2009 年美国复苏和再投资法案（公法 111-5）提供资金。沉积在大陆边缘的浅海碳酸盐岩在会聚板块边界处遭受剧烈变形，越来越多的证据表明这些岩石碳酸盐岩被夹带在俯冲带中，到达重要的地幔深度。 与硅酸盐矿物岩石相比，碳酸盐岩石较弱，其变形对大陆碰撞造山带发育的构造影响较大，也可能影响俯冲过程中地幔的变形。碳酸盐岩主要由方解石、白云石和菱镁矿矿物组成。这些矿物具有相似的晶体结构，但成分和机械性能不同。虽然方解石的流变学已经很成熟，但白云石的流变学受实验限制较少，并且对菱镁矿的流变学几乎一无所知，菱镁矿在地幔中比方解石或白云石更稳定。 为了准确地模拟俯冲和造山过程中地壳和地幔内的变形过程，需要细化白云石的流变性，确定菱镁矿的流变性，然后与方解石的流变性进行比较。该项目将采用实验和观测方法来实现以下目标：（1）通过实验在三轴岩石变形装置中确定白云石位错蠕变的流变性，建立白云石中这种变形机制的温度和应变率依赖性； (2) 通过实验，在三轴岩石变形装置中，在较宽的压力、温度和应变速率范围内确定菱镁矿的力学性能，以确定不同变形机制运行的温度和应变速率范围； (3) 研究实验缩短和剪切白云石中形成的微观结构和织物； （4）将实验变形过程中形成的微观结构和织物与天然白云石剪切带中观察到的微观结构和织物进行比较，为实验室确定的流变学应用于自然界提供基础。本研究将通过变形实验和对自然界变形的岩石进行分析，研究碳酸盐矿物、白云石和菱镁矿的强度和变形过程。含碳酸盐岩石占会聚板块边界造山过程中变形岩石的很大一部分。因此，这些岩石的强度和变形行为将强烈影响山区发育的结构，而这些结构负责自然资源的积累。通过这项研究生成的数据将被理论建模者和现场地质学家用来确定资源积累的方式和地点。碳酸盐岩也被带到俯冲带内的地球内部相当深的地方，因此它们的强度和变形行为将对俯冲和地幔对流等过程产生强烈影响。这些岩石变形行为的数据将使理论建模者能够更准确地预测这些长期地质过程的动态，包括更好地了解深层地震的动态。