Microstructure in Marble: Comparison of Dislocation and Grain Structure Produced in Natural and Laboratory Deformation

大理石的微观结构：自然变形和实验室变形产生的位错和晶粒结构的比较

• 批准号: 0711139
• 负责人: Brian Evans
• 金额: $ 30万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-01 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0711139&HistoricalAwards=false
• 关键词: Microstructure; Marble; Comparison; Dislocation; Grain

In this project, researchers will make a detailed comparison of the dislocation and grain microstructure of natural samples (collected from the Morcles Nappe, a thrust fault in the Swiss Alps) with those in samples deformed in laboratories at MIT and at the Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum GFZ in Potsdam, Germany. The first suite of Carrara marble samples will be deformed in conventional triaxial compression at strain rates of 0.001 per second to 0.000001 per second, confining pressures between 100 and 300 Megapascals, and temperatures between 300 to 700 Kelvin, conditions that span the transition from cataclastic failure to dislocation creep. The second set of experiments includes synthetic and natural marbles deformed by dislocation flow, but extends to conditions at which diffusion creep also occurs (temperatures between 700 and 1000 Kelvin, grain sizes between 5 and 50 micrometers, strain rates and pressures as above). Experiments include simple shear, torsion, and conventional triaxial loading. For deformation at laboratory strain rates, confining pressures less than 300 Megapascals, and temperature less than 700 Kelvin, dislocation interactions at twin boundaries may cause hardening that eventually lead to brittle failure. Above 700 Kelvin, dislocation cell size may be an important state variable in the constitutive law. Detailed observations of this microstructure and its evolution will be made using optical microscopes, scanning and transmission electron microscopes, and Electron Backscatter Diffraction to correlate structure with the production of lattice preferred orientation, dynamic recrystallization, and the evolution of strength. Similar microstructure observations will be made for suites of natural calc-mylonites collected along traverses perpendicular to the Morcles thrust (Swiss Helvetic Nappes) at several different locations along the dip of the fault. Previous field studies provide detailed information of microstructure, geothermometry, and geochemistry that can be used to constrain the large-scale mechanical history of this. This setting provides two distinct opportunities: 1) to investigate the influence of temperature on the localization of strain into the main thrust plane of the Morcles Nappe, and 2) to investigate the influence of varying quartz and dolomite content on strain localization within the carbonates.Localization of natural rock deformation is ubiquitous, at all scales of observation, under a broad range of natural temperatures and pressures. In collisional mountain belts, shear zones and faults are often found within carbonates, and the extreme localization implies that the mechanical properties of those rocks are critical in determining the strength of the large scale rock mass. Understanding the mechanical properties of rocks deforming under natural conditions is a difficult problem because natural processes occur at extreme pressure and temperatures and at very slow strain rates. To back-calculate the mechanical behavior of rocks under conditions that are not accessible to direct experimentation requires careful experimentation, a thorough knowledge of the kinetics of the processes involved, observations of the microstructure of naturally deformed rocks, and comparison of the natural and experimental microstructures. The ultimate goal is to understand natural tectonic processes including mountain building, faulting, earthquake mechanics, and the overall mechanical budget of the crustal deformation cycle.

在该项目中，研究人员将详细比较天然样品的位错和微观结构（从Morcles Nappe收集，瑞士巨大的推力故障）与在MIT和Helmholtz-Zentrum deutsdam deutsdam deutsches geoforschungungschungschungschungschungszentrum gfarany gfaM的实验室中的样品中的样本中的样本中的插头进行了详细比较。第一套卡拉拉大理石样品将以每秒0.001至0.000001的应变速率在常规三轴压缩中变形，将压力限制在100至300兆帕之间，温度在300至700 kelvin之间，条件在破坏失败失败的蠕动中的过渡。第二组实验包括脱位流量变形的合成和天然大理石，但延伸到也发生扩散蠕变的条件（700至1000 kelvin之间的温度，晶粒尺寸在5至50微米之间，应变速率和压力如上所述）。实验包括简单的剪切，扭转和常规三轴载荷。对于实验室应变速率的变形，限制压力少于300兆帕，温度小于700 kelvin，双边界处的脱位相互作用可能会导致硬化，最终导致脆弱的失败。高于700开Kelvin的位错细胞大小可能是本构定律中重要的状态变量。对该微观结构及其演变的详细观察将使用光学显微镜，扫描和透射电子显微镜以及电子反向散射衍射，以将结构与晶格优选方向，动态重新结合化以及强度的演化相关联。对于沿着垂直于Morcles推力（瑞士螺旋尿布）在沿断层倾角的几个不同位置收集的遍历的天然钙基岩套件，将进行类似的微观结构观测。先前的现场研究提供了微观结构，地热学和地球化学的详细信息，可用于限制其大规模机械历史。这种环境提供了两个不同的机会：1）调查温度对应变在摩克纳普的主要推力平面以及2）的影响，以及2）研究各种石英和白云岩含量对碳酸盐菌株中应变定位的影响。在所有天然范围内，自然岩石变形的范围是普遍存在的自然岩石变形，在所有范围内，范围广泛。在碰撞山带中，经常在碳酸盐中发现剪切区和断层，极端定位意味着这些岩石的机械性能对于确定大型岩石质量的强度至关重要。理解在自然条件下岩石变形的机械性能是一个困难的问题，因为自然过程在极端压力和温度下发生，并以非常缓慢的应变速率发生。为了在无法直接实验的条件下对岩石的机械行为进行后计，需要仔细的实验​​，对所涉及过程的动力学的透彻了解，对自然变形岩石的微观结构的观察以及自然和实验微结构的比较。最终目标是了解自然的构造过程，包括山区建筑，断层，地震力学以及地壳变形周期的总体机械预算。