Geochemical Investigation of Xenoliths From the Central Rio Grande Rift and Colorado Plateau: Constraints on Lithosphere Evolution and Possible Delamination

里奥格兰德裂谷中部和科罗拉多高原捕虏体的地球化学调查：对岩石圈演化和可能的分层的限制

• 批准号: 0911253
• 负责人: John Lassiter
• 金额: $ 21.41万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-15 至 2013-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911253&HistoricalAwards=false
• 关键词: Geochemical; Investigation; Xenoliths; Central; Rio

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Intellectual Merit: This proposal seeks funding to study the evolution of the lithospheric mantle beneath the central Rio Grande Rift and Colorado Plateau margin. The project will provide insights into a variety of questions related to the tectonic and volcanic evolution of this province, including the role of Farallon plate subduction and dehydration in generation of "enriched" mantle sources of Rio Grande Rift lavas. However, this proposal seeks primarily to answer one simple question: Has the original Proterozoic-age lithospheric mantle beneath the central Rio Grande Rift and Colorado Plateau margin been actively removed by delamination or convective erosion, as suggested by several recent geophysical studies? If correct, these studies suggest that lithosphere delamination, previously recorded beneath the Sierra Nevada, may be more prevalent than currently recognized and may be triggered by extensional as well as compressional tectonic regimes. Correlation of Hf- and Os-isotope variations in peridotite xenoliths with mineralogic constraints on degree of melt depletion will allow constraints on the timing of melt depletion recorded in xenoliths from the Rio Grande Rift and Colorado Plateau. Also, peridotite clinopyroxene trace element abundances combined with Sm-Nd isotope compositions will constrain the age of metasomatic overprints observed in portions of the Colorado Plateau and Rio Grande Rift. Together, these data will allow us to distinguish between Proterozoic, melt-depleted and possibly metasomatized lithospheric mantle and young, fertile asthenosphere. This study will thus provide a direct test of the lithosphere delamination model proposed by Gao et al. (2004) and Song & Helmberger (2007) to explain the presence of anomalously low seismic velocities in the shallow mantle beneath the central rift and plateau margin and complementary, anomalously high velocities within a slab-like structure dipping beneath the Central Plains lithosphere. Identification of asthenosphere-derived peridotite at the relatively shallow depths (~40-60 km) represented by peridotite xenolith suites throughout the region would support the proposed delamination models, and would be inconsistent with simple passive thinning of the lithosphere in response to extension. In contrast, identification of ancient lithosphere at these depths would suggest significantly less lithosphere removal and would require reevaluation of current interpretations of the available seismic tomographic data. Insights gained from this study on the chemical and physical evolution of lithospheric mantle prior to and during continental rifting will expand our understanding of the triggers and mechanisms involved in continental rifting and continental break-up. This remains a fundamental question in plate tectonics.Broader Impacts: Students at the graduate and undergraduate level will participate in all aspects of this project, from data acquisition to interpretation and dissemination of results at national conferences and through peer-reviewed publications. Undergraduate student involvement in fieldwork and analytical aspects of the proposed research will allow the selected student to discover the excitement of scientific research outside the classroom. One undergraduate has already completed an honors thesis examining the petrology of xenoliths from our study area. We plan to extend the success of this initial pilot project by incorporating additional undergraduates into all aspects of the research program. This proposal will foster cross-discipline collaboration and partnerships through organization of interdisciplinary workshops focused on the evolution of the Rio Grande Rift and Colorado Plateau.

“该奖项是根据2009年的《美国复苏与再投资法》（公法111-5）资助的。“知识分子：该提案寻求资金来研究中央里奥格兰德裂谷和科罗拉多高原余地层下岩石圈地幔的演变。该项目将为与该省的构造和火山演化有关的各种问题提供见解，包括法拉隆板俯冲和脱水在里奥格兰德裂谷熔岩的“丰富”地幔来源中的作用。但是，该建议主要是要回答一个简单的问题：正如最近的一些地球物理学研究所暗示的那样，在里奥格兰德裂谷中部和科罗拉多高原边缘下方的原始原始古生代岩石圈地幔和科罗拉多高原边缘是否被积极地消除了？如果正确的话，这些研究表明，先前记录在内华达山脉下方的岩石圈分层可能比目前认识的更为普遍，并且可能是由延伸和压缩构造政权触发的。橄榄石异构石中的HF-和OS-同位素变化与矿物质学耗尽程度的矿物质学约束的相关性将允许对从里奥格兰德·里夫（Rio Grande Rift）和科罗拉多高原（Colorado Plateau）记录的熔体耗竭时间的限制。同样，橄榄岩斜晶岩痕量元素丰度与SM-ND同位素组成相结合将限制在科罗拉多高原和里奥格兰德裂谷的部分中观察到的上质层面的年龄。总之，这些数据将使我们能够区分植物学，融化且可能的岩石圈地幔和年轻，肥沃的软圈。因此，这项研究将提供对Gao等人提出的岩石圈分层模型的直接检验。 （2004年）和Song＆Helmberger（2007），解释了中央裂谷和高原边缘和互补的浅层地幔中异常低的地震速度的存在，在平原层底层下方倾斜的平板状结构中，异常高的速度异常高。在相对较浅的深度（〜40-60 km）中鉴定在整个地区橄榄岩异种石套件代表的相对较浅的深度（约40-60 km）处的鉴定会支持所提出的分层模型，并且与岩石圈的简单被动稀疏相反。相比之下，在这些深度上对古代岩石圈的识别将表明岩石圈的去除幅度要少得多，并且需要重新评估对现有地震层析成像数据的当前解释。这项研究从岩石圈地幔的化学和物理演变中获得的见解将扩大我们对大陆裂谷和大陆裂解涉及的触发因素和机制的理解。这仍然是板块构造中的一个基本问题。公民影响：研究生和本科级别的学生将参与该项目的各个方面，从数据获取到国家会议的解释和通过同行评审的出版物的解释和传播。拟议的研究的本科生参与了野外工作和分析方面，将使选定的学生能够在课堂外发现科学研究的兴奋。一位本科生已经完成了荣誉论文，研究了我们研究领域的异种石的质学。我们计划通过将额外的本科生纳入研究计划的各个方面来扩展该最初的试点项目的成功。该提案将通过组织跨学科的研讨会来促进跨学科的合作和合作伙伴关系，该研讨会着重于里奥格兰德裂谷和科罗拉多高原的演变。