Collaborative Research: Developing New Models of Oceanic Magmatism and Source Heterogeneity Using the 8 degree 20' N Seamounts as Windows into the Sub-Ridge Mantle

合作研究：利用北纬 8 度 20 英尺海山作为进入亚脊地幔的窗口，开发大洋岩浆作用和源异质性的新模型

• 批准号: 2001331
• 负责人: Virginia Dorsey Wanless
• 金额: $ 16.21万
• 依托单位: Boise State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-05-01 至 2025-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2001331&HistoricalAwards=false
• 关键词: Collaborative; Research; Developing; New; Models

Eruptions of lava form submarine volcanoes, known as seamounts, near mid-ocean ridge spreading centers. These lavas can provide important information about what Earth’s uppermost (~ 120 miles) mantle is composed of and how it melts to form the majority of Earth’s crust. At present no studies have examined long chains of seamounts adjacent to mid-ocean ridges to address these fundamental questions. In this study, we plan to analyze over 400 well located lava samples from the 8°20'N seamount chain. The chain was previously sampled and mapped in 2016 and 2018 using the submersible Alvin and autonomous vehicle Sentry. The geochemical, mineralogical, and age data to be obtained under this project will allow us to determine the origin of the magmas that feed the seamounts and nearby ridge. The data will also tell us how those magmas evolve to form oceanic lavas, and how the volcanism is related to regional tectonic processes. The study will promote advances in the field of geochemistry, marine geology, and geodynamics. This project will provide significant mentorship and training for students at a variety of levels. It will fully or partially support three graduate students at Florida and Boise State and will provide training for several undergraduates in geochemical techniques and interpretation, and support senior research projects. The project will also support education and diversity by funding two female scientists, one a first-generation college graduate, toward obtaining their PhDs in geochemistry. Both principal investigators are heavily involved in outreach and education at the K-12 levels in Florida and Idaho.Sparse sampling and geochemical analyses of seamounts scattered throughout the northeastern Pacific suggest the sub-ridge mantle associated with the East Pacific Rise (EPR) has far greater compositional variability then is preserved in lavas erupted on-axis. While the relative homogeneity of axial lavas has resulted in intriguing generalizations about magma differentiation and mixing processes at mid-ocean ridges (MOR), seamount studies have had a significant impact on our understanding of the source compositions for oceanic basalts, the scales of mantle heterogeneity, and mantle melting systematics at MOR. However, many of these studies have focused on dredged lavas from individual seamounts with very few combining in situ sampling and high-resolution mapping from a single chain oriented perpendicular to the ridge axis. To fill this gap in knowledge about the sub-ridge mantle, two research cruises in 2016 and 2018 investigated the 8°20’N seamount chain that extends ~200km west of the EPR. The 8°20’N seamount chain was unexplored and virtually unsampled before our highly successful OASIS cruises. Geophysical, observational, and preliminary geochemical data from this nearly continuous chain of volcanoes led us to unexpected discoveries about their construction and revealed extreme compositional variability in the near MOR mantle that was previously only surmised from regional seamount studies in the northeast Pacific. The location, orientation, and preliminary data from the 8°20'N seamount chain make it an ideal a natural laboratory to investigate source heterogeneity and melting systematics in the near-ridge mantle. We propose to study the petrologic processes and mantle sources feeding MOR and near-axis volcanoes though comprehensive geochemical analyses of lavas and melt inclusions from the 8°20’N seamounts. Site-specific sampling using HOV Alvin and extensive, fine-scale mapping with AUV Sentry along the seamount chain, coupled with our previous comprehensive investigations of the 8°- 10°N EPR provide an exceptional opportunity to constrain geodynamic and geochemical models of mantle melting near MOR and determine the extent and length scales of mantle heterogeneity. We propose to collect a wide spectrum of petrologic and geochemical data including Sr, Nd, Pb, and Os isotopes, melt inclusion compositions, volatile contents, and 40Ar/39Ar age dates of lavas from the extensive collection of samples we have from the 8°20’N seamount chain. These results will be combined with numerical models to produce a petrologic model of mantle melting and magmatic processes in the near-ridge mantle. This extensive off-axis seamount chain provides a rare opportunity to probe the compositions of the mantle near MOR and to understand how magmas are spatially and temporally distributed in the shallow mantle and crust. Results from this research have implications for the generation of the majority of Earth’s crust.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

熔岩喷发形成海底火山，称为海山，靠近洋中脊扩张中心。这些熔岩可以提供有关地球最上层（约120英里）地幔组成的重要信息，以及它如何融化形成大部分地壳。目前，还没有任何研究对大洋中脊附近的海山长链进行研究，以解决这些基本问题。在这项研究中，我们计划分析来自8° 20 'N海山链的400多个位置良好的熔岩样品。该链条此前曾在2016年和2018年使用潜水器Alvin和自动驾驶车辆Sentry进行采样和绘制。在这个项目下获得的地球化学、矿物学和年龄数据将使我们能够确定供给海山和附近海脊的岩浆的来源。这些数据还将告诉我们这些岩浆是如何演变成海洋熔岩的，以及火山活动如何与区域构造过程相关。 这项研究将促进地球化学、海洋地质学和地球动力学领域的进展。该项目将为各级学生提供重要的指导和培训。 它将全部或部分支持佛罗里达和博伊西州的三名研究生，并将为几名本科生提供地球化学技术和解释方面的培训，并支持高级研究项目。该项目还将通过资助两名女科学家（其中一名是第一代大学毕业生）获得地球化学博士学位来支持教育和多样性。两个主要的调查人员都积极参与在佛罗里达和爱达荷州的K-12水平的推广和教育。稀疏的采样和分布在整个东北太平洋海山的地球化学分析表明，与东太平洋海隆（EPR）的次洋脊地幔有更大的成分变化，然后保存在轴上喷发的熔岩。轴向熔岩的相对均一性导致了大洋中脊（莫尔）岩浆分异和混合过程的有趣概括，海山研究对我们理解大洋玄武岩的源成分、地幔不均一性的尺度和莫尔的地幔熔融系统学产生了重大影响。然而，其中许多研究都侧重于个别海山的疏浚熔岩，很少结合现场取样和垂直于海脊轴的单链高分辨率绘图。 为了填补这一关于次洋脊地幔的知识空白，2016年和2018年的两次研究巡航调查了EPR以西约200公里的8° 20 'N海山链。 在我们非常成功的绿洲巡航之前，8° 20 'N海山链未经勘探，几乎没有取样。地球物理，观测和初步的地球化学数据，从这个几乎连续的火山链，使我们意外的发现他们的建设，并揭示了极端的成分变化，在近莫尔地幔，这是以前只推测从区域海山研究在东北太平洋。8° 20 'N海山链的位置、方向和初步数据使其成为研究近洋脊地幔源区异质性和熔融系统学的理想天然实验室。通过对8° 20 'N海山熔岩和熔融包裹体的综合地球化学分析，探讨了莫尔火山和近轴火山的岩石学过程和地幔来源。使用HOV Alvin进行的特定地点取样和使用AUV Sentry沿着海山链进行的广泛、精细比例尺制图，加上我们先前对8°- 10°N EPR的全面调查，为限制莫尔附近地幔熔融的地球动力学和地球化学模型并确定地幔不均匀性的范围和长度尺度提供了一个难得的机会。我们建议从我们从8° 20 'N海山链收集的大量样品中收集广泛的岩石学和地球化学数据，包括Sr，Nd，Pb和Os同位素，熔体包裹体成分，挥发分含量和熔岩的40 Ar/39 Ar年龄。这些结果将与数值模型相结合，以产生一个岩石学模型的地幔熔融和岩浆过程中的近脊地幔。这一广泛的离轴海山链为探测莫尔附近地幔的成分和了解岩浆在浅部地幔和地壳中的时空分布提供了难得的机会。这项研究的结果对大多数地壳的生成有影响。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。