Experimental and Natural Deformation of Magnesian Carbonates

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。沉积在大陆边缘的浅海相碳酸盐岩在会聚板块边界处受到强烈变形，越来越多的证据表明，这些碳酸盐岩被夹带在俯冲带中达到显著的地幔深度。 与硅酸盐矿物组成的岩石相比，碳酸盐组成的岩石较弱，因此它们的变形对大陆碰撞形成的山脉带中的构造产生了强烈的影响，并且它们还可能影响俯冲过程中的地幔变形。碳酸盐岩主要由方解石、白云石和菱镁矿等矿物组成。这些矿物具有相似的晶体结构，但成分和机械性质不同。虽然方解石的流变学已经得到很好的建立，但白云石的流变学不太受实验的约束，而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深的地方稳定。 为了精确模拟俯冲和造山过程中地壳和地幔的变形过程，需要细化白云石的流变学，确定菱镁矿的流变学，然后与方解石的流变学进行比较。本计画将采用实验与观察相结合的方法，以达成下列目标：（1）在三轴岩石变形装置中，借由实验来确定白云岩位错蠕变的流变性，以建立白云岩位错蠕变变形机制的温度与应变率相关性;（2）通过在三轴岩石变形仪中在宽压力范围内的实验来确定菱镁矿的力学性质，温度和应变速率，以确定不同变形机制的温度和应变速率范围：（3）研究实验性短切和剪切白云石中形成的显微结构和组构;以及（4）将实验变形过程中形成的显微结构和组构与天然白云岩剪切带中观察到的显微结构和组构进行比较，将实验室测定的流变学应用于自然界，本研究将通过岩石在自然界中变形的实验和分析，研究碳酸盐矿物、白云石和菱镁矿的强度和变形过程。含碳酸盐岩构成了在会聚板块边界造山过程中变形的岩石的重要部分。因此，这些岩石的强度和变形行为将强烈影响在山区发展的结构，这是负责自然资源的积累。通过这项研究产生的数据将被理论建模者和实地地质学家用来确定资源如何以及在哪里积累。碳酸盐岩也被带到地球的很深的地方？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的影响。关于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，包括更好地了解深源地震的动态。

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.