Examining temperatures and microgeochemical processes on fault slip surfaces with synchrotron methods

GSTDTAP

项目编号	1824852
	Examining temperatures and microgeochemical processes on fault slip surfaces with synchrotron methods
	James Evans
主持机构	Utah State University
项目开始年	2018
	2018-07-01
项目结束日期	2021-06-30
资助机构	US-NSF
项目类别	Standard Grant
项目经费	187363(USD)
国家	美国
语种	英语
英文摘要	Earthquakes result from slip along faults at depth in the Earth's crust, and faults typically form in rocks at depth that are strong. Opportunities to examine the effects of earthquakes in rocks are limited; sometimes the effects of earthquakes can be observed in rocks that are exhumed from depth and these exhumed faults can be used to learn about processes that occur at depth. Earthquake rupture should leave evidence for high temperatures and the effects of high heat in these faults. Because of the heat and the presence of fluids, a range of rock transformations occur in and around faults, and fault slip surfaces form. Some of these slip surfaces are very thin; determining the temperatures of fault slip, and the processes that occur during slip, are important for determining how earthquake fault slip works. Furthering this understanding can lead to better understanding of the physics of earthquakes. In order to determine the temperatures and processes of fault slip, this study uses a range of methods to examine rocks at very small scales. These methods include microscopic studies with standard microscopy methods (optical light and scanning electron microscopy) and geochemical methods of study. In addition, high-energy X-ray based methods will be used to look into fault-related rocks. These X-ray methods show how elements are distributed in the fault zones, how some of the elements might have been transformed by fault heating, and how minerals are transformed in the fault zones. The applications of these X-ray methods are novel in the study of deformed rocks. The project advances desired societal outcomes through research training in analytical methods for graduate and undergraduate students and development of short courses and teaching modules for undergraduate students that use X-ray analyses applied to geological questions and teach students a range of physics concepts. The aims are to provide fundamental concepts to the students and to provide an introduction into materials science analysis. Seismic slip should produce high temperatures in the focal region of earthquakes due to the high frictional strength of rocks and the stresses required to overcome these strengths. For some faults, seismic slip is focused on very narrow slip surfaces along which high temperatures are localized. Thus, these narrow slip surfaces should exhibit evidence for high temperatures that result from seismic slip. Yet, few methods exist to determine the peak temperatures of fault slip developed at seismogenic conditions in crystalline rocks. Estimating peak fault temperatures, documenting the evidence for coseismic slip localization, and determining the temporal and spatial distribution of high temperatures, deformation mechanisms, and fluid-rock interactions in natural fault zones are critical for assessing fault slip mechanics and energy distribution during earthquakes. The objectives of this project are to: 1) test the hypothesis that high slip temperatures are generated and preserved on slip surfaces, 2) develop methods of determining fault temperatures with transition element thermometry, 3) determine the physics and chemistry of the conditions of deformation that result in slip-localization and weakening, and 4) examine fluid-rock interactions in and near slip surfaces. Peak fault slip temperatures will be estimated using transition element thermometry, a new and novel method of investigating fault temperatures and fault-related deformation. Transition element thermometry is based on X-ray Absorption Near Edge Spectroscopy of transition elements (Fe, Mn, V) along faults that experience temperature-induced reduction. Synchrotron-based X-ray fluorescence mapping and spectroscopy will be integrated with scanning-electron and whole-rock geochemical analyses of fault slip surfaces from exhumed and cored parts of the San Andreas, Wasatch, Hurricane, and the West Salton detachment faults, and the Paris thrust fault. Peak slip-related temperatures will be determined and evidence of high-temperature fluid-rock interactions that lead to slip localization and fault evolution will be sought. The transformative nature of this work lies in the efforts to determine peak slip temperatures on slip surfaces, to decipher the possible temperature distribution in faults, and to identify slip localization and weakening mechanisms. These efforts require examination of complexly deformed rocks at scales typically below most optical resolution techniques. High-resolution, synchrotron-based high-energy X-ray fluorescence mapping and spectroscopy will be used to examine micrometer- to millimeter-thick slip surfaces within exhumed faults and from cored faults at depths ranging from 150 meters to 4 kilometers. Thin 'mirrored' or polished transition element-coated slip surfaces from exhumed normal faults to evaluate thermally activated processes responsible for these narrow slip surfaces. The use of highly focused short-wavelength X-ray fluorescent mapping and spectroscopy introduces an innovative approach of examining extremely narrow slip surfaces where geochemistry and textures cannot be discerned through conventional forms of microscopy. The results of the study will enable determination of the conditions of fault slip and examination of the manifestation of co- and post-seismic slip related deformation in these faults, providing benchmarks of deformation mechanisms and textures against which experimental rock deformation results can be compared, helping constrain theoretical models of fault zone heating and slip localization. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/72810
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	James Evans.Examining temperatures and microgeochemical processes on fault slip surfaces with synchrotron methods.2018.