Test Between Thermal and Tectonic Hypotheses for North Atlantic Seafloor Spreading Geometry Reorganization

北大西洋海底扩张几何重组的热假说和构造假说之间的检验

• 批准号: 1154071
• 负责人: Richard Hey
• 金额: $ 45.02万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1154071&HistoricalAwards=false
• 关键词: Test; Between; Thermal; Tectonic; Hypotheses

There is a massive ongoing reorganization of North Atlantic seafloor spreading geometry occurring at present south of Iceland. The previous orthogonal ridge/transform staircase geometry typical of slow-spreading ridge systems is being progressively changed to the present non-segmented oblique spreading geometry on the Reykjanes Ridge as transform faults are successively eliminated. This reorganization is presently interpreted as a thermal phenomenon, with a pulse of warmer mantle expanding away from the Iceland plume causing a progressive change in subaxial mantle rheology from brittle to ductile, so that transform faults can no longer be maintained. This explanation is nearly universally assumed to be true & is used to infer important conclusions about deep Earth & lithospheric geodynamics that are also nearly universally assumed to be true.The PI will undertake a month-long marine geophysical expedition to collect the multibeam, magnetics & gravity data that would provide a definitive test between the fundamentally different thermal & tectonic hypotheses for exactly how the Iceland plume (or whatever form of mantle convection or heterogeneity creates Iceland) caused the reorganization of the Mid-Atlantic Ridge south of Iceland. An important result of this test will be that modelers will either be confident that their thermal Reykjanes Ridge reorganization models are providing accurate information about Earth's behavior, or that they can confidently begin to model the correct mechanism instead. An additional benefit of this project will be the first accurate map of the Bight transform fault/fracture zone complex, known to be an important pathway for westward flow of North Atlantic mid-water circulation across the Reykjanes Ridge boundary, an important control on global climate change.Broader Impacts: Education and Human ResourcesResolving the origin of this large-scale plate boundary reorganization has important implications beyond testing a long-held fundamental assumption of Iceland mantle plume geodynamics. Thermal plume pulses have been interpreted as leading to regional uplift/subsidence events that modulate ocean currents and affect climate and sedimentation patterns throughout the North Atlantic. The proposed study will examine alternative tectonic explanations related to the mechanism and timing of the sequential elimination of transform faults in this area and thus has implications for inferred links among these phenomena. The proposed work will involve significant international collaboration with Icelandic scientists, as has our previous work in the area. The project will support a graduate student who will work on the survey data as a primary part of his/her thesis. As in our previous cruise we plan to mentor several undergraduate students at sea through the NSF-funded Marine Advanced Technology Education (MATE) Internship program and thus further NSF education and human resource development goals. Results will be integrated into classroom teaching by the P.I.s, and thus disseminated to a fairly wide audience including many underrepresented minority groups in Hawaii, enhancing scientific infrastructure. We think that improved understanding of this obviously important plate boundary reorganization will form an invaluable tool for further research and teaching, and we will make these data sets available on a project website. We think a movie of Reykjanes Ridge evolution projected onto a sphere could ultimately be a valuable teaching aid and museum display.

目前在冰岛南部，正在对北大西洋海底扩张几何形状进行大规模的重组。以前的正交脊/转换阶梯几何形状典型的缓慢扩展的脊系统正在逐步改变到目前的不分段的倾斜扩展几何形状的雷克雅内斯脊转换故障被相继消除。这种重组目前被解释为一种热现象，与脉冲的温暖地幔扩张远离冰岛羽造成的下轴地幔流变学从脆性到韧性的渐进变化，使转换断层不能再维持。这一解释几乎被普遍认为是正确的，并用于推断有关地球深部岩石圈地球动力学的重要结论，这些结论也几乎被普遍认为是正确的。PI将进行为期一个月的海洋地球物理考察，收集多波束磁力重力数据，这些数据将为冰岛羽流（或任何形式的地幔对流或异质性创造冰岛）如何导致冰岛南部大西洋中脊的重组提供根本不同的热构造假说之间的决定性测试。这项测试的一个重要结果将是，建模者要么相信他们的热雷克雅未克海岭重组模型提供了关于地球行为的准确信息，要么他们可以自信地开始模拟正确的机制。这一项目的另一个好处是，将首次绘制Bight转换断层/断裂带复合体的精确地图，已知该复合体是北大西洋中层水环流穿过雷克雅内斯海脊边界向西流动的重要通道，是控制全球气候变化的重要手段。教育和人力资源解决这一大规模板块边界重组的起源具有重要意义，超越了测试一个长期的冰岛地幔柱地球动力学的基本假设。热羽流脉冲被解释为导致区域隆起/下沉事件，这些事件调节洋流并影响整个北大西洋的气候和沉积模式。拟议中的研究将探讨替代构造解释的机制和时间顺序消除转换断层在这方面，从而推断这些现象之间的联系的影响。拟议的工作将涉及与冰岛科学家的重大国际合作，正如我们以前在该领域的工作一样。该项目将支持研究生谁将工作的调查数据作为他/她的论文的主要部分。正如我们之前的巡航一样，我们计划通过NSF资助的海洋先进技术教育（MATE）实习计划在海上指导几名本科生，从而进一步实现NSF的教育和人力资源开发目标。研究结果将被PI纳入课堂教学，从而传播给相当广泛的受众，包括夏威夷许多代表性不足的少数群体，加强科学基础设施。我们认为，对这一明显重要的板块边界重组的进一步理解将为进一步的研究和教学提供宝贵的工具，我们将在项目网站上提供这些数据集。我们认为，一部放映在球体上的雷克雅未克山脊演变的电影最终可能成为一个有价值的教具和博物馆展示。