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

陆壳深部地震各向异性探测是绘制各种构造背景、现代造山带和古造山带三维地壳组构的有力新工具。最近的结果，利用改进的接收函数分析方法，揭示了关于千米尺度地下组构几何的详细信息，有望对造山系统的活动和长期动力学历史提供新的见解。这种分析无疑也将是未来旨在了解北美岩石圈结构和演化的EarthScope项目的重要组成部分。然而，到目前为止，大多数地壳各向异性接收函数研究缺乏地质和实验室地面事实。因此，我们成像详细地壳结构和准确解释这些观测结果之间的差距正在扩大，因为关于地壳地震各向异性是如何发展、保存和破坏的细节仍然存在不确定性。虽然传统知识认为地壳深层各向异性从根本上是由高度各向异性云母的变形诱导晶体择优取向(CPO)控制的，但关于其他潜在重要因素仍有许多悬而未决的问题，例如(1)其他硅酸盐矿物的作用及其建设性和/或破坏性干扰的影响；(2)不同于通常假设的单一面理的组构成分的贡献，如线理和复合剪切组构；(3)地壳变质过程和变形机制；以及(4)各向异性组构相对于地震波长的排列和长度。研究人员将通过对北美一个主要的地壳规模的缝合带-怀俄明州南部的元古界夏延带-进行综合地震和岩石物理初步研究来解决这些问题。几个重要的优势使这条带成为建议研究的理想候选者：(1)它是一个深度出土(古深度15公里)的地壳尺度的高应变构造岩带，可能已经发育了显著的组构引起的地震各向异性；(2)从该地区公布的丰富的地质和地球物理结果提供了基础；以及(3)来自该地区密集网络的宽带地震波形的优秀现有数据集，尚未分析地壳各向异性。该项目还将包括在学年期间为前沿科学教师做晚间报告，随后是为期一天的K-12教师研讨会，内容是地震、断层和与该项目相关的地质学。将与CIRES外联小组一起开展的专题介绍和讲习班将涵盖(1)断层的地质观测和(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，对两名初级职业科学家的支持，以及该项目的跨学科性质。

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.