SGER: Integrated Petrophysical and Seismological Investigation of Crustal Fabric and Seismic Anisotropy of a Major Crustal Suture Zone, the Cheyenne Belt, Wyoming

SGER：怀俄明州夏安带地壳结构和主要地壳缝合带地震各向异性的综合岩石物理和地震学调查

• 批准号: 0750035
• 负责人: Kevin Mahan
• 金额: --
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-09-15 至 2010-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0750035&HistoricalAwards=false
• 关键词: SGER; Integrated; Petrophysical; Seismological; Investigation

Detection of seismic anisotropy in deep continental crust is a powerful new tool for mapping 3-dimensional crustal fabric in a variety of tectonic settings and in both modern and ancient orogens. Recent results, using improved receiver function analysis methods, reveal detailed information about km-scale subsurface fabric geometry that promises new insight into the active and long-term dynamic history of orogenic systems. Such analysis will also undoubtedly be an important component in future EarthScope projects aimed at understanding North American lithospheric structure and evolution. However, most crustal anisotropic receiver function studies to date lack geological and laboratory ground truth. Consequently, the gap between our ability to image detailed crustal structure and to accurately interpret these observations is widening due to continued uncertainty about the details of how crustal seismic anisotropy is developed, preserved, and destroyed. While conventional knowledge is that deep crustal anisotropy is fundamentally controlled by deformation-induced crystallographically preferred orientation (CPO) of highly anisotropic mica, there are still many unanswered questions about other potentially important factors such as (i) the role of other silicate minerals and the effects of their constructive and/or destructive interference; (ii) the contribution of fabric components other than the commonly assumed single foliation, such as lineation and composite shear fabrics; (iii) crustal metamorphic processes and deformation mechanisms; and (iv) alignment and length scale of anisotropic fabric compared to seismic wavelengths. The researchers will begin addressing these questions through an integrated seismic and petrophysical pilot study of a major crustal-scale suture zone in North America, the Proterozoic Cheyenne Belt in southern Wyoming. Several important advantages make this belt an ideal candidate for the proposed study: (1) it is a deeply exhumed (15 km paleodepth), crustal-scale zone of highly strained tectonite that is likely to have developed significant fabric-induced seismic anisotropy; (2) abundant published geological and geophysical results from the area provide a base; and (3) an excellent existing data set of broadband seismic waveforms from dense networks spanning the region is available and has yet to be analyzed for crustal anisotropy.The project will also involve evening presentations for Front Range science teachers during the academic year, followed by a one-day K-12 teacher workshop on earthquakes, faults, and the geology related to the project. The presentations and workshops, to be developed with the CIRES outreach group, will cover (1) geologic observations of faults and (2) seismology and earthquakes. Other broader impacts include research involvement of undergraduates, support of two junior career scientists, and the project's cross-disciplinary nature.

大陆地壳深部地震各向异性探测是研究现代和古代造山带三维地壳组构的一种新的有力工具。最近的结果，使用改进的接收函数分析方法，揭示了详细的信息公里尺度的地下结构的几何形状，承诺新的洞察造山系统的活动和长期的动态历史。这种分析无疑也将是地球镜未来旨在了解北美岩石圈结构和演变的项目的一个重要组成部分。然而，迄今为止，大多数地壳各向异性接收函数的研究缺乏地质和实验室的地面真相。因此，由于对地壳地震各向异性如何发展、保存和破坏的细节仍不确定，我们对详细地壳结构成像的能力与准确解释这些观测结果的能力之间的差距正在扩大。虽然传统知识认为地壳深部各向异性基本上是由高度各向异性的云母的变形诱导的晶体学优选取向（CPO）控制的，但关于其他潜在的重要因素仍有许多未回答的问题，例如（i）其他硅酸盐矿物的作用及其相长和/或相消干涉的影响;（ii）除了通常假设的单一面理之外的组构成分的贡献，例如线理和复合剪切组构;（iii）地壳变质过程和变形机制;以及（iv）与地震波长相比的各向异性组构的排列和长度尺度。研究人员将开始通过对北美一个主要的地壳规模缝合带--怀俄明州南部的元古宙夏延带--进行综合地震和岩石物理试点研究来解决这些问题。几个重要的优势使该带成为拟议研究的理想候选者：（1）它是一个深掘的（2）该地区丰富的地质和地球物理成果提供了依据;以及（3）从跨越该地区的密集网络获得的宽带地震波形的优秀现有数据集是可用的，并且还有待于对地壳各向异性进行分析。该项目还将包括在学年期间为Front Range科学教师进行的晚间演讲，随后是为期一天的K-12教师研讨会，内容涉及地震、断层和与该项目相关的地质学。将与CIRES外展小组一起制定的介绍和讲习班将涵盖（1）断层地质观测和（2）地震学和地震。其他更广泛的影响包括本科生的研究参与，两个初级职业科学家的支持，以及该项目的跨学科性质。