Solving the mystery of Bermuda: Implications for intraplate magmatism

百慕大岛坐落在大西洋中最大的非洋中脊火山平台之一上，离美国东海岸不远。这个台地的起源，构成它的熔岩的来源和成分，以及导致它形成的融化机制仍然未知。这项研究将分析目前储存在加拿大达尔豪斯大学的岩心的火山和侵入火成岩的地球化学，该岩心是在20世纪70年代从百慕大平台钻出来的，从未被分析过。这项研究将探索关于平台来源和起源的各种假设，它也可能对火山危险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，人们提出了各种各样的理论。一种说法是，它是由地幔柱形成的，地幔柱是一种来自地幔深处的热的、长期存在的、静止的岩浆射流，它将熔岩喷发到海底，类似于夏威夷、冰岛和加拉帕戈斯群岛的形成过程。另一种假说认为，百慕大地台是由地幔中的对流碰撞北美大陆根部时岩浆上涌而形成的，并被掀翻，导致持续的融化和火山活动，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和世界上其他类似的海底火山活动的来源，这些火山活动具有相同的特征。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化的地幔源。该研究的更广泛影响包括支持来自科学领域代表性不足的少数群体的早期职业科学家，他们在吸引和指导本科生和研究生方面有着良好的记录，并为他们提供了最先进的分析技术的全面研究经验。除了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外，该项目的成果将被纳入大学水平的课程。该项目还将促进与瑞士科学家的国际合作，并将通过将一个重要的岩心转移到美国的一个岩心储存库来拯救它，在那里它将被管理，样品将向公众和其他希望研究该岩心的科学家开放百慕大火山台地。地幔柱模型被普遍认为是板块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深根地幔柱。小尺度对流（如边缘驱动对流、剪切驱动对流）已被提出作为地幔柱模式的替代，特别是用于描述百慕大膨胀。这个火山台地靠近大陆，但远离洋中脊，这使它成为测试板内岩浆生成替代模型的理想地点。迄今为止，没有发表百慕大的地球化学、挥发性或岩石学数据；这是阐明熔融机制和岩浆过程的关键数据。1972年，百慕大深钻岩心被收集起来，然后被遗忘了。该岩心样品的初步地球化学结果表明，一些百慕大火山单元来自碳酸化源，表明存在与高放射性成因的地幔端元相关的深层碳储层。本研究将解决地幔地球化学和动力学的基本问题，如：(1)地幔柱和小尺度对流衍生岩浆在地球化学和岩石学上的差异；(2)百慕达火山岩地幔源组成；(3)深部碳酸化地幔储层与硅质欠饱和岩浆的产生之间的联系，以及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，熔体包裹体的挥发性成分及其形成深度，以及熔岩及其放射性成因同位素组成的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.