Collaborative Research: Lithospheric removal: The Sierra Nevada as the prototype of a fundamental process in mountain building

[6074558]克拉地幔岩石圈与大陆地壳的分离是一个基本的构造过程，研究起来比较困难。这个项目的目标是检查内华达山脉下地幔岩石圈的移除。PIs断言，塞拉山脉是一个绝佳的考察地点，因为分层现象似乎是最近才发生的，而且可能仍在发生。初步研究表明，在塞拉山脉的两端可能有地幔“滴水”。该提案旨在确定移除过程和分层部分的命运……，即点滴。通过结合大地电磁（MT）、地球化学、地貌研究和地球动力学建模，结合现有和拟议的被动地震数据，pi试图了解地幔岩石圈是如何被移除的，以及促进这种移除的条件。希望这种理解可以应用到其他地方。地幔岩石圈的移动可能在历史和结构各不相同的地区发挥了关键作用，如南内华达山脉、阿尔博兰海、青藏高原、亚平宁山脉、阿巴拉契亚山脉、安第斯山脉中部、喀尔巴阡山脉、前寒武纪南非、华北克拉通、盆地和山脉。然而，在地幔岩石圈可能被移走的许多其他地区，这种移走要么太古老，要么环境太复杂，要么在逻辑上太困难，无法期望得到像塞拉那样清晰的记录。该计划将建立在两个先前资助的CD项目的基础上，一个是南部塞拉大陆动力学项目（该项目发现山脉的南部不是由厚地壳支撑，而是由热的、低密度的上地幔支撑），另一个是塞拉悖论实验（该项目发现榴辉岩在中新世或上新世时期从地壳底部移走）。该项目的一个优势是PI打算对大地电磁学和地震数据进行联合分析。如前所述，这一联合分析将基于产生可观测结果的底层物理性质（例如，地幔橄榄石和辉石基岩石的岩石物理行为有水和无水），对MT和地震结果进行更定量的耦合。pi试图通过泊松比、衰减和各向异性将地震速度和电阻率联系起来。这种联合反演方法，特别是如果它能提供一些地幔水化的测量，将提高地球物理成像地幔岩石圈的能力。该项目与EarthScope资助的一个项目（Sierra Nevada EarthScope project - SNEP）相配合，该项目利用EarthScope的FlexAray组件在内华达山脉中部进行地震学调查。SNEP的pi是G. Zandt， T. Owens和C. Jones。目前，地震学工作的重点是已知岩石圈已被移走的地区的北部边缘，地震学工作将对岩石圈移走的程度进行限制，并描绘出由于岩石圈移走而产生的地震学结构。该CD项目探讨了同一地区地质和其他地球物理观测的变化，目的是确定与岩石圈移动明显相关的特征。虽然这些研究中的每一个都将产生有用的结果，但它们的结合应该超过单独部分的总和。

0607458ClarkThe delamination of mantle lithosphere from continental crust is a fundamental tectonic process that is difficult to study. The goal of this project is to examine the removal of mantle lithosphere from under the Sierra Nevada. The PIs assert that the Sierras are an excellent place to look because delamination appears to have happened rather recently, and may still be happening. Preliminary studies indicate possible mantle "drips" at both ends of the Sierra. The proposal(s) seeks to identify the removal process and the fate of the delaminated portion ..., i.e. the drips. Through combined magnetotelluric (MT), geochemistry, geomorphic studies and geodynamic modeling, integrated with existing and proposed passive seismic data, the PIs seek to gain understanding of how mantle lithosphere is removed, and the conditions that facilitate such removal. The hope is that this understanding can be applied elsewhere. Removal of mantle lithosphere may have played a key role in regions with histories and structures as diverse as the southern Sierra Nevada, the Alboran Sea, the Tibetan Plateau, the Apennines, the Appalachians, central Andes, the Carpathians, Precambrian South Africa, the North China Craton, and the Basin and Range. However, in many of these other regions where mantle lithosphere may have been removed, the removal is either too old or in an environment too complex, or logistically too difficult to expect a record as clear as in the Sierra. The proposed project will build on the results of two previously funded CD projects, the Southern Sierra Continental Dynamics Project (that found that the southern part of the range was supported not by thick crust, but by a hot, low-density upper mantle) and the Sierran Paradox Experiment (that discovered that eclogite had been removed from the base of the crust in the latest Miocene or Pliocene time).A strength of the project is the PI's intent to conduct a joint analysis of MT and seismic data. As stated, this joint analysis will use a more quantitative coupling of MT and seismic results based on the underlying physical properties which produce the observables (e.g. petrophysical behavior of mantle olivine and pyroxene based rocks with and without water). The PIs seek to tie seismic velocities and electrical resistivity via poisson's ratio, attenuation, and anisotropy. Such a joint inversion method, particularly if it can provide some measure of mantle hydration, would advance the ability to geophysically image the mantle lithosphere. This project is paired with a project that has been funded by EarthScope (Sierra Nevada EarthScope Project - SNEP) to conduct a seismological investigation with the FlexAray component of EarthScope in the central Sierra Nevada. The PIs of SNEP are G. Zandt, T. Owens, and C. Jones. Currently focused on the northern edge of the region where lithosphere is known to have been removed, the seismological work will place limits on the extent of lithosphere removal and delineate the seismological structures resulting from that removal. This CD project explores the variations in geological and other geophysical observations across the same region with the goal of identifying those features clearly associated with removal of the lithosphere. Although each of these studies will yield useful results without the other, the combination of them should exceed the sum of the separate parts.