A Reversible Rheology for Water-Weakened Quartz

水弱化石英的可逆流变学

• 批准号: 1321882
• 负责人: Andreas Kronenberg
• 金额: $ 42.01万
• 依托单位: Texas A&M University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-08-01 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1321882&HistoricalAwards=false
• 关键词: Reversible; Rheology; Water; Weakened; Quartz

The overall goals of this project are to use experimental techniques to investigate : 1) the effect of chemical environment (water fugacity), strain rate, and temperature on the strength of quartz single crystals deformed in an axial compression; 2) the effect of the same parameters on the strength of synthetic quartzites (quartz aggregates) made from the same starting material as the single crystals; and 3) the fundamental relationship between the strengths of single crystals and polycrystals. These goals will be accomplished by performing experiments on annealed synthetic quartz single crystals and synthetic quartzites over a wide range of temperatures, water fugacities, and strain rates in a Griggs-type piston-cylinder rock deformation apparatus using a molten salt cell for precise determination of mechanical data. Specifically, the researchers will: 1) perform temperature-,strain rate-, and pressure-stepping experiments on single crystal cores in of synthetic quartz crystals, which have been heat-treated to establish a constant density and uniform distribution of freezable fluid inclusions, to investigate basal a, prism a and prism c slip systems; 2) reverse the sequence of experimental temperature, strain rate, and water fugacity conditions to test whether these rate laws are reversible; 3) hot-press polycrystalline quartz aggregates made of powders fabricated from the same heat-treated synthetic quartz materials, and subject these polycrystalline quartz samples to temperature-, strain rate-, and pressure-stepping experiments, testing for reversibility, and comparing the results with T, strain rate, and water fugacity sensitivities of basal and prism slip. The mechanical data from these experiments will be used to develop predictive models of deformation of natural quartzites at tectonic rates.Displacements of middle to lower crustal thrust faults and low-angle normal detachments associated with collisional tectonics and channel flow are commonly localized within quartz-rich lithologies. Postseismic visco-elastic relaxations in quartzo-feldspathic rocks below plate-scale continental fault zones are therefore thought to be governed by quartz strength. Motivated by the importance of quartz deformation to tectonics and rheology of the continental lithosphere, many experimental studies have been performed to investigate the deformation and recovery mechanisms of quartz, and quantify mechanical relations that can be applied to tectonic loading of the crust. Yet, the mechanism(s) of water weakening of quartz continues to be unresolved and little work has been performed to determine the effects of water fugacity, strain rate and temperature on the strength of the common slip systems in quartz. This project uses new experimental methods to address these problems. Simple models can be constructed that relate the strengths of the individual slip systems to the strengths of the quartzites over the range of experimental conditions and extrapolate the results to naturally deformed quartzites. Data from these experiments can be used in field-based research and numerical simulations of the viscosity of the continental crust at plate boundaries and may aid in the understanding of the processes in the continental crust that cause the deformations related to earthquakes.

本计画的主要目的是利用实验技术来探讨：1）化学环境的影响（水逸度）、应变速率和温度对石英单晶轴向压缩变形强度的影响; 2）相同参数对合成石英岩强度的影响（石英聚集体）由与单晶相同的起始材料制成;和3）单晶和多晶的强度之间的基本关系。这些目标将通过退火合成石英单晶和合成石英岩在很宽的温度范围内进行实验，水逸度，并在格里格型活塞缸岩石变形装置的应变率使用熔盐电池精确测定力学数据。具体来说，研究人员将：1）对人造石英晶体的单晶芯进行温度、应变率和压力步进实验，这些石英晶体已经过热处理，以建立恒定密度和均匀分布的可冻结流体包裹体，以研究基底A、棱柱A和棱柱C滑移系统; 2）颠倒实验温度、应变速率和水逸度条件的顺序，以测试这些速率定律是否可逆; 3）热压由相同热处理的合成石英材料制造的粉末制成的多晶石英聚集体，并使这些多晶石英样品经受温度、应变速率、和压力步进实验，测试的可逆性，并比较结果与T，应变率，和水逸度的敏感性的基础和棱柱体滑移。从这些实验中获得的力学数据将被用于建立天然石英岩在构造速率下变形的预测模型。与碰撞构造和河道流动有关的中下部地壳逆冲断层和低角度正断层的位移通常局限于富含石英的岩性中。因此，板状大陆断裂带下石英-石英质岩石的震后粘弹性弛豫被认为是由石英强度决定的。 由于石英变形对大陆岩石圈构造和流变学的重要性，人们开展了大量的实验研究，以探讨石英的变形和恢复机制，并量化可应用于地壳构造载荷的力学关系。然而，石英的水弱化的机制仍然没有得到解决，并且几乎没有进行工作来确定水逸度、应变速率和温度对石英中常见滑移系的强度的影响。该项目使用新的实验方法来解决这些问题。可以构建简单的模型，将各个滑移系的强度与石英岩在实验条件范围内的强度相关联，并将结果外推到自然变形的石英岩。这些实验的数据可用于对板块边界处大陆地壳粘性的实地研究和数值模拟，并有助于了解大陆地壳中引起与地震有关的变形的过程。