Genesis of Harrat Basalts in Western Saudi Arabia

这个项目试图了解大量玄武岩熔岩田的形成，这些熔岩田喷发到大陆地壳上，为陆地和水生生物提供重要的营养物质，并为人类提供地热和矿产资源。这项研究是在沙特阿拉伯西部进行的，因为地壳的热和物质结构本身是玄武岩火山活动的障碍，但研究地区的火山活动长达3000万年。这项工作使用玄武岩熔岩的地球化学作为透镜，通过它来探索最下面地壳的长期演化，即无法直接观察到的大陆的“下层”。该研究项目将确定该地区的板块构造过程如何影响地壳厚度和完整性，有可能使该大陆显著变薄和变弱，从而鼓励火山活动。这项工作是与沙特的同事合作进行的，这些同事对实现石油和天然气资源以外的经济组合多元化感兴趣。该项目的资金支持一名博士生和几名本科生，这些学生的背景在地球科学中的代表性不足；帮助与一名当地教师合作建立一个中学学习单元和一个博物馆展览，重点展示沙特熔岩场的艺术、文化、宗教和生态意义。这项工作将创造关于我们星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准备。大陆玄武岩是地球上最常见的空中火山特征，但在厚厚的大陆地壳下很难融化。将利用地球化学和地质年代学数据，结合地球物理证据，确定地幔熔融机制(S)，以及促成两个长寿的阿拉伯西部哈拉特(Uway Rid和Ash Shaam)碱性镁铁质火山活动的地幔源域的矿物学、同位素和热气压参数。地球化学和同位素研究将记录复杂构造地区的源区和地幔熔融机制的演化，并将检验两个阿拉伯哈拉特地区重新焕发活力的镁铁质碱性火山活动是否源于岩石圈滴状岩浆作用。这一过程的地球化学证据侧重于记录单个小体积富挥发分熔体批次、辉石岩源的贡献、熔融深度和温度增加的小规模时间趋势以及地幔熔融深度和程度之间的正相关关系。这项研究将通过对哈拉特、乌韦里德和阿什·沙姆的熔岩和包体中的熔岩和单个晶体进行强有力的主元素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，而熔岩和包体的Sr-ND-Pb-Hf-He同位素研究将建立源区特征。这项研究探索了阿法尔地柱、周围上地幔和交代岩石圈的贡献，并记录了阿拉伯板块这些贡献的时空变化。这些发现对羽流物质的运输、交代岩石圈地幔中重力不稳定带的发展以及死海断层和红海北部的演化都有影响。这一裁决反映了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。

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.