Genesis of Harrat Basalts in Western Saudi Arabia

该项目旨在了解喷出大陆地壳的大量玄武岩熔岩场的形成，在那里它们为陆地和水生生物提供重要的营养物质，以及供人类使用的地热和矿产资源。这项研究之所以在沙特阿拉伯西部进行，是因为地壳本身的热和物质结构是玄武岩火山活动的屏障，而研究区域的火山活动长达3000万年。这项工作使用玄武岩熔岩的地球化学作为透镜，通过它来探索最下层地壳的长期演化，即大陆的“底层”，不能直接观察到。该研究项目将确定该地区的板块构造过程是如何影响地壳厚度和完整性的，可能会使大陆大幅变薄和变弱，从而促进火山活动。这项工作是与沙特阿拉伯的同事合作进行的，沙特阿拉伯对石油和天然气资源以外的经济组合多样化感兴趣。该项目的资金支持一名博士候选人和几名来自地球科学背景的本科生；与一名当地教师合作，帮助建立一个中学学习单元，并举办一个以沙特熔岩田的艺术、文化、宗教和生态意义为重点的博物馆展览。这项工作将创造关于地球长期演变的新知识，帮助我们为可持续和多样化的未来做好准备。大陆玄武岩是地球上最常见的陆上火山特征，但在厚厚的大陆地壳下融化是很难实现的。地球化学和地质年代学数据，结合地球物理证据，将用于确定地幔熔化的机制以及地幔源域的矿物学、同位素和热气压参数，这些参数有助于两个长期存在的阿拉伯西部哈拉（Uwayrid和Ash Shaam）的碱性基性火山活动。地球化学和同位素调查将记录一个复杂构造区域的源域演化和地幔熔融机制，并将测试两个阿拉伯盆地中重新恢复的基性碱性火山作用是否来自岩石圈滴岩浆作用。这一过程的地球化学证据主要集中在记录单个小体积富含挥发物的熔体批，来自辉长岩源的贡献，熔融深度和温度增加的小尺度时间趋势，以及深度和地幔熔融程度之间的正相关关系。该研究将通过对来自Harrats Uwayrid和Ash Shaam的熔岩以及熔岩和捕虏体中的单个晶体进行强有力的主要和微量元素分析来寻找这一证据。高精度的40Ar/39Ar定年将建立岩浆化学的时间趋势，而熔岩和捕虏体的Sr-Nd-Pb-Hf-He同位素研究将建立物源特征。该研究探索了来自阿法尔地幔柱、周围上地幔和交代岩石圈的贡献，并记录了这些贡献在整个阿拉伯板块的时空变化。这些发现对地幔柱物质的运输、交代岩石圈地幔重力不稳定带的发育以及死海断层和红海北部的演化具有重要意义。该奖项反映了美国国家科学基金会的法定使命，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。

This project seeks to understand the formation of large-volume basalt lava fields that erupt onto continental crust, where they provide important nutrients for terrestrial and aquatic life as well as geothermal and mineral resources for human use. The research is pursued in Western Saudi Arabia because the thermal and material structure of the crust itself is a barrier to basalt volcanism, and yet the study areas have been volcanically active for up to 30 million years. The work uses the geochemistry of basalt lavas as a lens through which to explore the long-term evolution of the lowermost crust, i.e., the “underlayer” of the continent that cannot be observed directly. The research project will determine how plate tectonic processes acting in the region have affected crustal thickness and integrity, potentially thinning and weakening the continent substantially and thereby encouraging volcanic activity. The work is conducted in partnership with Saudi colleagues who are interested in diversifying their economic portfolio beyond petroleum and natural gas resources. Funds from this project support a doctoral candidate and several undergraduate students from backgrounds that are underrepresented in the geosciences; help develop a middle-school learning unit in cooperation with a local teacher and a museum display focused on the artistic, cultural, religious and ecological significance of the Saudi lava fields. This work will create new knowledge about the long-term evolution of our planet that helps us prepare for a sustainable and diverse future. Continental basalts are the most common subaerial volcanic features on Earth but melting beneath thick continental crust is difficult to achieve. Geochemical and geochronologic data, integrated with geophysical evidence, will be used to determine the mechanism(s) of mantle melting and the mineralogic, isotopic and thermo-barometric parameters of mantle source domains that contribute to alkaline mafic volcanism in two long-lived western Arabian Harrats (Uwayrid and Ash Shaam). The geochemical and isotopic investigation will document evolution of source domains and mantle melting mechanisms in a region of complex tectonics and will test whether rejuvenated mafic alkaline volcanism in two Arabian harrats results from lithospheric drip magmatism. Geochemical evidence for this process has focused on documenting individual small-volume volatile-rich melt batches, contributions from a pyroxenitic source, small-scale temporal trends of increasing melting depth and temperature, and a positive correlation between depth and degree of mantle melting. The research will pursue this evidence through robust major and trace element analysis of lavas and individual crystals in lavas and xenoliths from Harrats Uwayrid and Ash Shaam. High precision 40Ar/39Ar dating will establish temporal trends in magma chemistry, and Sr-Nd-Pb-Hf-He isotopic study of lavas and xenoliths will establish source characteristics. The research explores contributions from the Afar plume, ambient upper mantle and metasomatized lithosphere, and documents spatial and temporal variations to these contributions across the Arabian plate. The findings have implications for transport of plume material, for the development of gravitationally unstable zones in metasomatized lithospheric mantle, and for evolution of the Dead Sea Fault and northern Red Sea.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.