Collaborative Research: Determining Mantle Rheology from Field and Microstructural Observations of Naturally-deformed Peridotites

合作研究：通过自然变形橄榄岩的现场和微观结构观察确定地幔流变性

• 批准号: 0409567
• 负责人: Julie Newman
• 金额: --
• 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: 2004
• 资助国家: 美国
• 起止时间: 2004-07-01 至 2009-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0409567&HistoricalAwards=false
• 关键词: Collaborative; Research; Determining; Mantle; Rheology

A crucial and unsolved question in global earth science is the relative strength of the different lithospheric layers that make up the tectonic plates. Rheology, the term used to describe material behavior, quantifies the relation between the observed deformation (strain) and the applied forces (stress). The principal investigators of this grant combine quantitative, field-based geologic studies with data from experimental rock deformation studies to constrain the rheology of naturally-deformed mantle rocks. The fieldwork provides analysis of deformation at geologic strain-rates, spatial scales, and levels of compositional heterogeneity, while laboratory studies provide data from controlled deformation experiments at known stresses and strain-rates for monophase materials. The lithospheric (uppermost) mantle is the focus of this study for three reasons. First, mantle rocks have a relatively simple mineralogy (typically only three minerals, volumetrically dominated by the mineral olivine). Second, a large amount of experimental data has been conducted on olivine, allowing calibration of the field studies. Third, because of the high strength of olivine in experimental studies, many current models assume that the lithospheric mantle dominates the material behavior of the tectonic plates. Two extremely well-exposed sections of upper mantle rocks, the Dun Mountain ophiolite body (Red Hills section) in New Zealand and the Twin Sisters dunite in Washington State, USA are investigated in this study. The two field areas provide different, but complimentary, constraints on mantle rheology. The Twin Sisters dunite is an ideal field locality to: 1) Quantify deformation in a mantle section, by using geological markers known as dikes; 2) Observe spatial variations in mantle deformation; and 3) Determine the effect of the 2nd mineral phase (orthopyroxene) on the bulk rheology of natural peridotites. The Red Hills section of the Dun Mountain ophiolite, New Zealand, allows the PIs to investigate two additional aspects of mantle deformation: 1) The rheological implications of large-scale structures (e.g., folds) present in naturally deformed mantle bodies; and 2) Why localization, as inferred from ductilely sheared markers, takes place in the mantle. From these data sets, the bulk rheology of lithospheric mantle will be constrained. The grant supports a graduate student and multiple undergraduate students at two universities. The funding forms the basis for international cooperation with a New Zealand university, allowing students to visit both universities.

全球地球科学中一个关键且尚未解决的问题是构成构造板块的不同岩石圈层的相对强度。 流变学是用于描述材料行为的术语，它量化了观察到的变形（应变）和施加的力（应力）之间的关系。 该资助的主要研究人员将定量的实地地质研究与实验岩石变形研究的数据结合起来，以约束自然变形的地幔岩石的流变性。 现场工作提供了地质应变率、空间尺度和成分异质性水平下的变形分析，而实验室研究提供了单相材料已知应力和应变率下的受控变形实验的数据。 岩石圈（最上层）地幔是本研究的重点，原因有三个。 首先，地幔岩具有相对简单的矿物学（通常只有三种矿物，体积上以橄榄石矿物为主）。 其次，对橄榄石进行了大量的实验数据，可以对现场研究进行校准。 第三，由于实验研究中橄榄石的高强度，许多当前模型假设岩石圈地幔主导了构造板块的物质行为。本研究对两个极其充分暴露的上地幔岩石部分进行了研究，即新西兰的邓山蛇绿岩体（红山部分）和美国华盛顿州的双姐妹纯岩。 这两个领域对地幔流变学提供了不同但互补的约束。 Twin Sisters 纯岩是理想的现场地点，可用于： 1) 通过使用称为岩脉的地质标记来量化地幔部分的变形； 2）观察地幔变形的空间变化； 3) 确定第二矿物相（斜方辉石）对天然橄榄岩整体流变的影响。 新西兰邓山蛇绿岩的红山部分使 PI 能够研究地幔变形的另外两个方面：1）自然变形地幔体中存在的大型结构（例如褶皱）的流变学意义； 2）从延性剪切标记推断，为什么定位发生在地幔中。 根据这些数据集，岩石圈地幔的整体流变学将受到限制。该赠款支持两所大学的一名研究生和多名本科生。 该资金构成了与新西兰大学进行国际合作的基础，允许学生访问两所大学。