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.

俯冲发生在收敛的板块边界，包括一个板块下沉到另一个板块下面。虽然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，也是地震的主要原因，但人们还不知道是什么原因导致俯冲停止，以及它对地壳最深处和地幔上部有什么影响。通过研究位于俯冲周期末期的火成岩的年龄和组成，该项目试图了解导致俯冲停止的原因，以及这是如何改变地壳和上地幔的组成和结构的。由于这一过程发生在地球深处，该项目将把重点放在古代俯冲带根部的岩石上，这些岩石现在暴露在南极洲的南极横贯山脉中。此外，对南极洲的了解相对较少，而这个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，并结合一系列最先进的分析仪器的实践经验。学生还将获得一系列更通用的技能，包括地理信息系统（GIS）、书面和口头沟通以及数据管理——这些都是与学术和地球科学行业的职业高度相关的优势。每年夏天，高中学生将通过UCSB研究指导计划参与实验室研究的各个方面。项目负责人和研究生将通过专门设计的iPhone应用程序和多媒体网站与公众互动。活动将包括小学生与南极考察队成员之间的现场电话和视频对话。深层地壳分层或“创立者”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以及引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，通常在俯冲结束期间或之后立即就位，因此可能提供对沉没的直接了解。这些神秘的岩石很重要，因为它们代表了接近原始的地幔熔体成分，因此它们的年龄、地球化学和岩石学演化揭示了上地幔成分和热状态的关键信息。同样重要的是，它们揭示了这些关键参数是如何随时间和空间变化的。通过对俯冲带边缘煌斑岩的评价，可以提取：1)局部尺度的信息，如熔融的时间和持续时间以及火成岩结晶过程在同位素非均质性形成中的作用；2)地幔源组成、温度和熔融深度的沿走向变化3)控制沉降和俯冲终止的板块尺度力。该项目将研究横贯南极山脉轴线上的一套煌斑岩，这些煌斑岩位于南极洲新元古代-奥陶纪罗斯造山运动的最新阶段（距今约5.05亿至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，以了解深部地壳沉降/分层的机制和时间。