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

地幔岩石圈与陆壳的拆离是一个基本的构造过程，研究难度较大。该项目的目标是研究从内华达山脉下方移除地幔岩石圈的情况。PI断言，Sierras是一个很好的观察地点，因为分层似乎发生得很近，而且可能仍然在发生。初步研究表明，塞拉山脉两端可能存在地幔“水滴”。该提案(S)试图确定剥离部分的去除过程和命运……即滴漏。通过结合大地电磁、地球化学、地貌研究和地球动力学模拟，结合现有和拟议的被动地震数据，个人资料试图了解地幔岩石圈是如何去除的，以及促进这种去除的条件。希望这种理解可以应用于其他地方。地幔岩石圈的剥离可能在具有不同历史和结构的地区发挥了关键作用，这些地区包括内华达山脉南部、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、喀尔巴底山脉、前寒武纪南非、北中国克拉通以及盆地和山脉。然而，在许多其他地区，地幔岩石圈可能已经被清除，清除工作要么太老了，要么环境太复杂，要么后勤上太困难，无法期待像在塞拉利昂那样清晰的记录。拟议的项目将建立在两个以前资助的CD项目的基础上，即南塞拉利昂大陆动力学项目(发现山脉南部不是由厚地壳支撑，而是由热、低密度的上地幔支撑)和西尔兰悖论实验(发现榴辉岩在最近的中新世或上新世从地壳底部移走)。该项目的一个优势是PI打算对大地电磁数据和地震数据进行联合分析。如上所述，这项联合分析将根据产生可观测数据的基本物理性质(例如，带水和不带水的地幔橄榄石和辉石基岩的岩石物理行为)，使用MT和地震结果更定量的耦合。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合作用的措施，将提高对地幔岩石圈进行地球物理成像的能力。该项目与EarthScope(内华达山脉地球望远镜项目-SNEP)资助的一个项目配对，该项目利用内华达山脉中部的EarthScope的FlexAray组件进行地震调查。SNEP的PI是G.Zandt、T.Owens和C.Jones。地震学工作目前侧重于已知岩石圈已被清除的区域的北缘，将对岩石圈清除的程度加以限制，并勾画出由于岩石圈清除而产生的地震构造。这一CD项目探索同一区域内地质和其他地球物理观测的变化，目的是查明那些明显与岩石圈清除有关的特征。尽管这些研究中的每一个都会产生有用的结果，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.