Southernmost Patagonia: The Connection Between Magmatism, Subduction Zone, Slab Window and Sub-continental Mantle Lithosphere

地幔的体积约占地球的82%，质量约占地球的68%，因此，它影响着地球表面的构造板块运动、地震和火山活动。通过研究玄武岩熔岩(地幔的部分熔体)来了解地幔的组成和性质的一个基本步骤是确定地球内部挥发物(氢、碳、氟、氯、硫)的平衡和分布。挥发物影响地幔熔融、岩浆结晶、岩浆迁移和火山喷发，其丰度和空间分布对地幔流动和温度模型具有重要的制约作用。此外，挥发物是地球大气和海洋的关键成分，因此，限制挥发物在地球内部和表面之间的循环对于理解我们星球的长期演化至关重要，因为它们从根本上影响板块构造、气候和宜居性。该项目将资助一名非裔美国女研究生、一名印度研究科学家和一名布朗大学的西班牙裔教授。它促进了与来自美国、阿根廷和智利三个不同国家的九个机构的地球化学家的合作，并将加强布朗大学、俄勒冈州立大学和伍兹霍尔海洋研究所的研究和教育基础设施。结果的交流将通过以下方式进行：1)同行评议的期刊、在会议上的演讲和受邀的大学演讲，2)当地小学和高中课堂的动手科学学习活动，以及3)通过公开讲座向一般观众宣传。关于巴塔哥尼亚南部岩浆活动的起源提出了各种假说，从俯冲的纳斯卡和南极板块去挥发过程中地幔楔子的通量熔融，到从板岩窗口上升的碳酸和含水软流圈的绝热减压熔融，到富挥发分交代的次大陆岩石圈地幔的熔融。所有提出的假设都提到了挥发物的作用。令人惊讶的是，关于该地区玄武岩和地幔包体挥发性含量的数据并不存在。考虑到挥发物的重要性，这是地球化学数据中的一个明显遗漏。这项研究的重点将是研究与巴塔哥尼亚南部地震台阵共处的地球化学特征良好的始新世近期玄武岩和相关的地幔捕虏体的挥发分含量和显微结构的区域和时间变化。该地区的熔岩及其包体代表了从缺乏稳定岩浆室的地区局部开采的较小熔体体积，经历的混合和分异相对较少，提供了确定地幔来源的成分、岩性和挥发分含量的最佳机会。将这些地球化学和微结构数据整合到以前资助的地震实验中，将能够更好地约束巴塔哥尼亚南部地幔的温度、成分、粘度和密度结构。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Earth's mantle represents approximately 82% by volume and 68% by mass of the Earth, and therefore, it influences the movement of tectonic plates, earthquakes and volcanism on the surface. A fundamental step to understand the composition and nature of the Earth's mantle from the study of basaltic lavas (partial melts of the mantle) is to establish the budget and distribution of volatiles (hydrogen, carbon, fluorine, chlorine, sulfur) in the Earth's interior. Volatiles influence mantle melting, magma crystallization, magma migration and volcanic eruption, and their abundances and spatial distribution provide important constraints on models of mantle flow and temperature. Moreover, volatiles are key constituents of the Earth's atmosphere and oceans and, thus, constraining the cycling of volatiles between the Earth's interior and surface is of fundamental importance to understand the long-term evolution of our planet, as they fundamentally affect plate tectonics, climate, and habitability. The project will support an African-American female graduate student, an Indian research scientist and a Hispanic Professor at Brown University. It promotes the collaboration with geochemists from nine institutions from three different countries: USA, Argentina and Chile, and will enhance the infrastructure for research and education at Brown University, Oregon State University and Woods Hole Oceanographic Institution. Communication of results will occur through: 1) peer-reviewed journals, presentations at conferences and invited university lectures, 2) hands-on science learning activities for local elementary and high school classes, and 3) outreach to the general audience through public lectures.Diverse hypotheses have been proposed for the origin of the magmatism in southern Patagonia, from flux melting of the mantle wedge during devolatilization of the subducted Nazca and Antarctic plate, to adiabatic decompression melting of a carbonated and hydrous asthenosphere upwelling through the slab window, to melting of a volatile-rich metasomatized subcontinental lithospheric mantle. All proposed hypotheses invoke the role of volatiles. Surprisingly, data on the volatile contents of basalts and mantle xenoliths from this region are non-existent. This is a glaring omission from the geochemical data given the importance of volatiles. The focus of this study will be to examine the regional and temporal variations in volatile contents and microstructure of geochemically well-characterized Eocene-recent basalts and associated mantle xenoliths co-located with the seismic array from southern Patagonia. The lavas and their xenoliths in this region represent smaller melt volumes tapped locally from areas lacking steady-state magma chambers, experience relatively less mixing and differentiation, and offer the best opportunity to determine the composition, lithology and volatile contents of the mantle sources. The integration of these geochemical and microstructural data to a previously funded seismic experiment will enable better constraints on the temperature, composition, viscosity and density structure of the mantle beneath southern Patagonia.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.