Solving the mystery of Bermuda: Implications for intraplate magmatism

百慕大岛位于大西洋最大的非大洋中脊火山平台之一，距离美国东海岸不远。这个地台的起源，组成它的熔岩的来源和组成，以及导致它形成的熔融机制仍然未知。这项研究将分析目前储存在加拿大达尔豪西大学的一个钻芯的火山岩和侵入火成岩的地球化学，该钻芯是在20世纪70年代通过百慕大平台钻探的，从未进行过分析。这项研究将探索关于地台来源和来源的各种假说，它还可能对火山灾害工作和大气二氧化碳浓度产生影响。对于百慕大地台的起源，人们提出了各种不同的理论。其一是它是由地幔羽流形成的，地幔羽流是一种来自地幔深处的高温、长期、静止的岩浆喷流，将熔岩喷发到海底，类似于夏威夷、冰岛和加拉帕戈斯群岛的形成。另一种假设是，地台是由于地幔中的对流撞击北美大陆的根部并倾覆，导致持续的熔融和火山作用而形成的，形成了百慕大地台。这项研究的重点是了解百慕大火山活动的来源和世界各地具有百慕大火山活动特征的其他类似海底火山遗址。这项工作还将为这种火山活动在全球碳循环中的作用提供新的线索，因为百慕大钻探岩芯中的一些样本似乎来自强烈碳化的地幔来源。这项研究的更广泛影响包括支持在科学界代表性不足的少数群体的早期职业科学家，他们在参与和指导本科生和研究生方面有着良好的记录，并为他们提供最先进的分析技术方面的全面研究经验。该项目的成果除了用于公共宣传活动和通过弗吉尼亚理工大学地球科学博物馆举办的教师专业发展讲习班外，还将被纳入大学课程。该项目还将促进与一名瑞士科学家的国际合作，并将通过将其转移到美国岩芯储存库来拯救一个重要的钻芯，在那里将对其进行管理，并向公众和其他希望研究百慕大火山平台的科学家开放样本。地幔热柱模型被普遍认为是板内火山活动背后的一种可信的机制。然而，并不是所有被认为是热点的地点都有地震和地球化学特征来支持根深蒂固的地幔热柱。小尺度对流(如边缘驱动对流、剪切驱动对流)已被提出作为地幔热柱模型的替代模型，特别是用来描述百慕大隆起。这个火山平台靠近一个大陆，但远离大洋中脊，这使得它成为测试板内岩浆生成的替代模型的理想地点。到目前为止，还没有关于百慕大的地球化学、挥发分或岩石学数据；这是阐明熔融机制和岩浆过程的关键数据。1972年，百慕大深部钻芯被收集起来，然后被遗忘。该岩心样品的初步地球化学结果表明，百慕大火山单元中的一些单元来自碳酸盐来源，这表明存在与高放射性地幔端员有关的深层碳储。这项研究将解决地幔地球化学和动力学的基本问题，例如：(1)地幔热柱和小规模对流产生的岩浆在地球化学和岩石学上有何不同；(2)百慕大火山的地幔来源组成；(3)深部碳酸盐地幔储层与二氧化硅不饱和岩浆的产生之间的联系，从而板内岩浆活动在全球碳循环中的作用。将使用指示岩浆来源温度、熔体包裹体挥发成分及其形成深度的地球化学分析，以及对熔岩及其放射性同位素组成的全套常量元素和微量元素地球化学分析，以确定百慕大火山岩的起源和来源，并评估各种提出的假设的有效性。

The island of Bermuda, which sits on one of the largest non-mid-ocean ridge volcanic platforms in the Atlantic Ocean, is not far from the East Coast of the United States. The origin of this platform, the source and composition of the lavas that make it up, and the melting mechanisms that caused its formation are still unknown. This research will analyze the geochemistry of the volcanic and intrusive igneous rocks of a drill core, presently stored at Dalhousie University in Canada, that was drilled through the Bermuda platform back in the 1970's and never analyzed. The research will explore various hypotheses as to the platform's source and origin And it may also have implications for volcanic hazard work and atmospheric CO2 concentrations. Various theories have been proposed for the origin of the Bermuda platform. One is that it was formed by a mantle plume, which is a hot, long-lived, stationary jet of magma that comes from deep in the mantle and erupts lava onto the seafloor, similar to how Hawaii, Iceland, and the Galapagos islands formed. Another hypothesis is that the platform was formed by the upwelling of magma as convection in the mantle bumped up against the roots of the North American continent and overturned, causing sustained melting and volcanism that formed the Bermuda Platform. This research is focused on understanding the source of the Bermuda volcanic activity and other similar seafloor volcanic sites around the world that share its characteristics. The work will also provide new clues as to the role this kind of volcanic activity has in the global carbon cycle because some of the samples in the Bermuda drill core appear to have come from a strongly carbonated mantle source. Broader impacts of the research include support of early career scientist from a minority group under-represented in the sciences who has a strong track record of engaging and mentoring both undergraduate and graduate students and providing them with full-bodied research experiences in state-of-the-art analytical techniques. Results of the project will be incorporated into college level courses in addition to being used for public outreach activities and teacher professional development workshops through the Geosciences Museum at Virginia Tech. The project will also foster international collaboration with a Swiss scientist and will rescue an important drill core by moving it to a US core repository where it will be curated and samples will be made accessible to the public and to other scientists wishing to study the Bermuda volcanic platform. The mantle plume model has generally been accepted as a plausible mechanism behind intraplate volcanism. However, not all locations that are considered hotspots have the seismic and geochemical signatures to support a deep-rooted mantle plume. Small-scale convection (e.g., edge-driven convection, shear-driven convection) has been proposed as an alternative to the mantle plume model, especially to describe the Bermuda swell. This volcanic platform is near a continent, but away from mid-ocean ridges, making it an ideal location to test alternative models for intraplate magma generation. To date, no geochemical, volatile, or petrological data have been published for Bermuda; and this is crucial data to elucidate melting mechanisms and magmatic processes. In 1972, the Bermuda Deep Drill Core was collected and then forgotten. Preliminary geochemical results of samples from this core suggest that some of the Bermuda volcanic units are derived from a carbonated source, indicating the presence of a deep carbon reservoir linked to a highly radiogenic mantle end-member. This research will address fundamental questions of mantle geochemistry and dynamics, such as: (1) how mantle plume and small-scale convection-derived magmas differ from one another geochemically and petrologically; (2) the mantle source composition of Bermuda volcanics; and (3) what the link is between a deep carbonated mantle reservoir and the generation of silica under-saturated magmas and, thus, the role of intraplate magmatism in the global carbon cycle. Geochemical analyses that indicate the temperature of the magma source, the volatile composition of melt inclusions and depth of their formation, and the full suite of major and trace element geochemical analyses of the lavas and their radiogenic isotope compositions will be used to determine the origin and source of the Bermuda volcanics and evaluate the validity of the various proposed hypotheses.