Petrologic Constraints on Subduction Termination From Lamprophyres, Ross Orogen, Antarctica

南极洲罗斯造山带灯岩对俯冲终止的岩石学约束

• 批准号: 1443296
• 负责人: John Cottle
• 金额: $ 25.71万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1443296&HistoricalAwards=false
• 关键词: Petrologic; Constraints; Subduction; Termination; Lamprophyres

Subduction takes place at convergent plate boundaries and involves sinking of one tectonic plate underneath another. Although this process is a key aspect of plate tectonics that shapes the planet over geologic time, and is a primary cause of earthquakes, it is not known what causes subduction to cease, and what effect it has on the deepest portions of the crust and the upper part of the mantle. By studying the age and composition of igneous rocks emplaced at the very end of the subduction cycle, this project seeks to understand what causes subduction to cease, and how this changes the composition and structure of the crust and upper mantle. Because this process occurs deep within the earth, the project will focus on rocks in the root of an ancient subduction zone, now exposed in the Transantarctic Mountains of Antarctica. In addition, Antarctica remains relatively poorly understood, and this project will contribute directly to increasing our understanding of the geologic history of this region. The project will focus on training graduate and undergraduate students - incorporating hands-on experience with an array of state-of-the-art analytical instrumentation. Students will also gain a range of more general skills including Geographic Information Systems (GIS), written and oral communication, and data management - strengths that are highly relevant to careers both in the academic and Geosciences industry. Each summer, high school students will be incorporated into aspects of the laboratory-based research through the UCSB research mentorship program. The PI and graduate students will engage the general public through a purpose-built iPhone App and multimedia website. Activities will include live phone and video conversations from the field between elementary school students and members of the team in Antarctica. The mechanisms by which the deep crustal delaminates or "founders" and is returned to the mantle remains a fundamental problem in earth science. Specifically, little is known about the temporal and spatial scales over which this process occurs or the mechanisms that trigger such catastrophic events. Igneous rocks highly enriched in potassium, called lamprophyres, are often emplaced during, and immediately after, termination of subduction and therefore potentially provide direct insight into foundering. These enigmatic rocks are important because they represent near-primary mantle melt compositions and therefore their age, geochemistry and petrologic evolution reveal key information on both the composition of the upper mantle and its thermal state. Of equal importance, they reveal how these key parameters vary through both space and time. By evaluating lamprophyres along a subduction zone margin it is possible to extract: 1) local-scale information, such as the timing and duration of melting and the role of igneous crystallization processes in generation of isotopic heterogeneities; 2) along-strike variations in mantle source composition, temperature, and depth of melting 3) the plate-scale forces that control foundering and termination of subduction. This project will study a suite of lamprophyres along the axis of the Transantarctic Mountains, emplaced during the latest stages of the Neoproterozoic - Ordovician Ross orogeny, Antarctica (roughly 505 to 470 million years before present). High-precision geochronology (age determinations) will be combined with geochemical measurements on the rocks and minerals to understand the mechanisms and timing of deep crustal foundering/delamination.

俯冲作用发生在会聚板块边界处，涉及一个构造板块下沉到另一板块下方。尽管这一过程是板块构造的一个关键方面，它在地质时期塑造了地球，并且是地震的主要原因，但目前尚不清楚是什么导致俯冲停止，以及它对地壳最深部分和地球的最深处有什么影响。地幔的上部。 通过研究俯冲周期末期火成岩的年龄和成分，该项目旨在了解导致俯冲停止的原因，以及这如何改变地壳和上地幔的成分和结构。由于这一过程发生在地球深处，因此该项目将重点关注古代俯冲带根部的岩石，该俯冲带现已暴露在南极洲的横贯南极山脉中。此外，人们对南极洲的了解相对较少，该项目将直接有助于增加我们对该地区地质历史的了解。该项目将重点培训研究生和本科生——将实践经验与一系列最先进的分析仪器相结合。学生还将获得一系列更通用的技能，包括地理信息系统（GIS）、书面和口头交流以及数据管理——这些优势与学术和地球科学行业的职业高度相关。每年夏天，高中生将通过 UCSB 研究指导计划参与实验室研究的各个方面。 PI 和研究生将通过专门构建的 iPhone 应用程序和多媒体网站与公众互动。活动将包括小学生和南极洲团队成员之间的现场电话和视频对话。深层地壳分层或“奠基”并返回地幔的机制仍然是地球科学中的一个基本问题。具体来说，人们对这一过程发生的时间和空间尺度或触发此类灾难性事件的机制知之甚少。富含钾的火成岩（称为煌斑岩）通常在俯冲终止期间和俯冲终止后立即形成，因此有可能提供对沉没的直接了解。这些神秘的岩石很重要，因为它们代表了近原始地幔熔体的成分，因此它们的年龄、地球化学和岩石演化揭示了上地幔的成分及其热状态的关键信息。同样重要的是，它们揭示了这些关键参数如何随空间和时间变化。通过评估沿俯冲带边缘的煌斑岩，可以提取：1）局部尺度信息，例如熔化的时间和持续时间以及火成岩结晶过程在同位素异质性产生中的作用； 2) 地幔源成分、温度和熔化深度的沿走向变化 3) 控制俯冲沉没和终止的板块尺度力。该项目将研究沿横贯南极山脉轴线的一系列煌斑岩，它们位于南极洲新元古代 - 奥陶纪罗斯造山运动的最新阶段（距今大约 505 至 4.7 亿年前）。高精度地质年代学（年龄测定）将与岩石和矿物的地球化学测量相结合，以了解深层地壳沉没/分层的机制和时间。