Solving the mystery of Bermuda: Implications for intraplate magmatism

百慕大岛位于大西洋最大的非中洋脊火山平台之一，距离美国东海岸不远。 这个平台的起源，组成它的熔岩的来源和成分，以及导致其形成的熔融机制仍然未知。这项研究将分析目前存放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年代钻过百慕大地台的，从未进行过分析。这项研究将探索关于平台来源和起源的各种假设，它也可能对火山灾害工作和大气二氧化碳浓度产生影响。 关于百慕大地台的起源，有各种各样的理论。一种是它是由地幔柱形成的，地幔柱是一种来自地幔深处的高温、长寿、静止的岩浆射流，将熔岩喷到海底，类似于夏威夷、冰岛和加拉帕戈斯群岛的形成过程。 另一种假设是，该平台是由岩浆上涌形成的，因为地幔中的对流碰撞到北美大陆的根部并翻转，导致持续的熔融和火山活动，形成了百慕大平台。这项研究的重点是了解百慕大火山活动的来源以及世界各地具有相同特征的其他类似海底火山地点。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，因为百慕大钻芯中的一些样本似乎来自强烈碳酸化的地幔来源。该研究的更广泛影响包括支持来自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，并为他们提供了在最先进的分析技术方面的丰富研究经验。该项目的成果将被纳入大学课程，此外还将通过弗吉尼亚理工大学的地球科学博物馆用于公共宣传活动和教师专业发展研讨会。该项目还将促进与一名瑞士科学家的国际合作，并将拯救一个重要的岩心，将其转移到美国的岩心储存库，在那里进行管理，并向公众和希望研究百慕大火山平台的其他科学家提供样本。地幔柱模型已被普遍接受为板内火山作用的合理机制。然而，并不是所有被认为是热点的地方都有地震和地球化学特征来支持一个根深蒂固的地幔柱。小尺度对流（例如，边缘驱动对流，剪切驱动对流）已被提出作为地幔柱模型的替代方案，特别是用于描述百慕大隆起。这个火山平台靠近大陆，但远离洋中脊，使其成为测试板内岩浆生成替代模型的理想地点。迄今为止，没有地球化学，挥发性，或岩石学数据已公布的百慕大，这是至关重要的数据，以阐明熔融机制和岩浆过程。1972年，百慕大深钻岩心被收集起来，然后被遗忘。初步的地球化学结果表明，一些百慕大火山单位来自碳酸盐源，表明存在一个深碳储层连接到一个高度放射性地幔端员。这项研究将解决地幔地球化学和动力学的基本问题，如：（1）地幔柱和小规模对流形成的岩浆如何在地球化学和岩石学上相互区别;（2）百慕大火山岩的地幔源成分;以及（3）深部碳酸盐地幔储集层与硅欠饱和岩浆的生成之间的联系，因此，板内岩浆活动在全球碳循环中的作用。地球化学分析表明岩浆源的温度、熔融包裹体的挥发性成分及其形成深度，对熔岩及其放射性同位素成分进行全套主要和微量元素地球化学分析，将用于确定百慕大火山岩的起源和来源，并评价各种拟议假设的有效性。

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.