Rheology of Orthopyroxene

斜方辉石的流变学

• 批准号: 1045820
• 负责人: Caleb Holyoke
• 金额: $ 28万
• 依托单位: Texas A&M Research Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-01-15 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1045820&HistoricalAwards=false
• 关键词: Rheology; Orthopyroxene

Heat dissipation by convection of the Earth's mantle drives plate tectonics and deformations in the Earth's crust. These deformations cause earthquakes and fertile mantle to conditions which cause melting and, therefore, volcanoes, both of which have a significant impact on society. Therefore, it is important to understand the mechanisms that enable heat dissipation of the Earth's mantle. The Earth's upper mantle is a polyphase system, composed in bulk of approximately 55% olivine, 25% orthopyroxene, 15% clinopyroxene and 5% aluminous phases (Ringwood, 1975). However, secondary phases (primarily clinopyroxene and aluminous phases) are preferentially removed during partial melting of the lithospheric mantle, leaving a residue of olivine and orthopyroxene (e.g. dunites and harzburgites). As a result, understanding the deformation mechanisms of the most dominant mineral, olivine, and how its rheology is affected by various environmental conditions (pressure, temperature and chemical environment) and physical factors (grain size and distribution) has been a priority of field-based, experimental and modeling studies. However, to date, little work has been performed to determine the strength of orthopyroxene, which if significantly stronger or weaker than olivine, would impact the viscosity of the mantle, and thereby affect rates of convection and plate displacement. This project will use an experimental approach to investigate how strain rate, water content, temperature and pressure affect the strength of orthopyroxene aggregates. The experiments will be performed in two different high pressure rock deformation apparatus, one located at Texas A&M University and another capable of higher confining pressures located at the National Synchrotron Light Source at Brookhaven National Laboratory. Data from these experiments can be used by field-based and numerical simulations of the viscosity of the mantle at plate boundaries and may aid in our understanding of the processes that cause the deformations in the mantle that causes earthquakes and volcanic activity. This study will also provide salary and mentoring for an early-career scientist and provide at least one undergraduate student with a hands-on research experience.The overall goals of this project are to use experimental techniques to investigate the rheology of orthopyroxene aggregates deforming by dislocation creep and how this rheology is affected by the chemical environment (water fugacity or hydroxyl content and activity of silica), pressure and temperature in an axial compression deformation geometry. We will also investigate how microstructures evolve as a function of strain by performing experiments using a shear deformation geometry. These goals will be accomplished by performing experiments in both water-present and dry conditions over a wide range of temperatures, pressures and strain rates in a Griggs-type piston-cylinder rock deformation apparatus using a molten salt cell for precise determination of mechanical data and the deformation DIA operated by COMPRES located at the National Synchrotron Light Source at Brookhaven National Laboratory.

地幔的对流散热驱动着板块构造和地壳的变形。这些变形导致地震和肥沃的地幔，从而导致融化，从而产生火山，这两者都对社会产生重大影响。因此，了解使地幔散热的机制是很重要的。地球上地幔是一个多相体系，主要由大约55%的橄榄石、25%的正辉石、15%的斜辉石和5%的铝相组成（Ringwood, 1975）。然而，在岩石圈地幔的部分熔融过程中，次级相（主要是斜辉石和铝相）被优先去除，留下橄榄石和正辉石的残留物（如dunite和harzburgites）。因此，了解最主要矿物橄榄石的变形机制，以及各种环境条件（压力、温度和化学环境）和物理因素（粒度和分布）对其流变性的影响，一直是现场实验和建模研究的重点。然而，迄今为止，确定正辉石强度的工作很少，如果它明显强于橄榄石或弱于橄榄石，就会影响地幔的粘度，从而影响对流和板块位移的速率。本项目将采用实验方法研究应变速率、含水量、温度和压力如何影响正辉石骨料的强度。实验将在两个不同的高压岩石变形设备中进行，一个位于德克萨斯农工大学，另一个位于布鲁克海文国家实验室的国家同步加速器光源，能够承受更高的围压。这些实验的数据可以用于板块边界处地幔黏度的现场模拟和数值模拟，并有助于我们理解导致地幔变形的过程，这些变形导致了地震和火山活动。这项研究还将为一名早期职业科学家提供薪水和指导，并为至少一名本科生提供实践研究经验。该项目的总体目标是使用实验技术来研究位错蠕变变形的正辉石聚集体的流变学，以及这种流变学如何受到化学环境（水逸度或羟基含量和二氧化硅活性）、压力和温度在轴向压缩变形几何中的影响。我们还将通过使用剪切变形几何进行实验来研究微观结构如何演变为应变的函数。这些目标将通过在有水和干燥的条件下进行实验，在广泛的温度、压力和应变速率下，在格里格斯型活塞缸岩石变形装置中进行实验，使用熔盐电池精确测定机械数据和变形DIA，由位于布鲁克海文国家实验室的国家同步辐射光源的comppres操作。