Collaborative Research: Non-peridotite Melting in Plume-influenced Extensional Environments: Lithological Heterogeneity of the African Superplume and African Lithosphere

智力优势。 本项目旨在确定源岩岩性（例如，地幔熔融的橄榄岩，辉石岩），促成了渐新世埃塞俄比亚大陆溢流玄武岩火山活动，先于东非裂谷的发展。地幔熔体的渗入通过弱化和聚焦应变在岩石圈减薄的启动和演化中起着重要作用。因此，了解组成，特别是矿物学，地幔熔体的来源是至关重要的，以限制参加熔体生成的条件。非橄榄岩岩性，如上涌柱中的辉石岩或岩石圈地幔内的交代体，是潜在的肥沃的地幔源，能够产生大量的岩浆。相反，典型的橄榄岩岩性在这些条件下可能不会产生显著的熔体（即，地幔减压程度较小或地幔位温较低）。此外，研究区下地幔的特点是显着的地震衰减，这已被归因于热地幔物质的非洲超级地幔柱上涌的存在。 该研究旨在探讨岩石圈与地幔柱作为原始岩浆源的相对贡献。 具体而言，地幔源岩性（即橄榄岩与辉石岩）将通过地球化学表征的保存完好的2000米厚的部分洪水玄武岩从埃塞俄比亚高原西部，以前从未被研究过。丰富的岩石圈地幔熔体生成的可能贡献将通过一个不寻常的硅不饱和岩石喷发在中新世盾状火山，初步数据意味着从古非洲岩石圈地幔岩浆衍生的平行研究进行评估。分析计划将涉及测量主要和选定的微量元素，Sr-Nd-Pb-Hf同位素和橄榄石中的微量元素，并将在新的Ar/Ar地质年代学和古地磁研究建立的时间框架内进行解释，旨在限制这些矿床的时间，持续时间和喷发率。这些数据将为玄武岩生成过程提供新的见解。更广泛的影响。 从这个项目产生的数据将提供第一个岩石学的见解，起源的岩石学推导的成分组成部分的非洲超级羽，并将直接相关的正在进行的地球物理项目正在该地区进行。该项目将支持Tyrone Rooney（博士，2006年），并通过与阿迪斯大学研究人员的互动促进国际合作。该项目代表了五个美国机构（Rooney-MSU，Herzberg-Rutgers，Kappleman/Holt-UT Austin，Spell-UNLV和Konter-UTEP）的科学家之间的新合作，所有这些机构都将为分析测量，解释和建模做出贡献。该项目利用并扩展了密歇根州立大学（激光烧蚀ICP-MS）、罗格斯大学（电子微探针）、UT奥斯汀（古地磁实验室）、UNLV（稀有气体MS）和UTEP（MC-ICPMS）的最先进分析设施的应用。该项目还将支持对一名博士的指导。来自密歇根州立大学的学生通过在埃塞俄比亚的五个美国机构和研究人员的广泛合作互动。

Intellectual Merit. This project seeks to determine the source lithology (e.g., peridotite, pyroxenite) of mantle melts that contributed to Oligocene Ethiopian continental flood basalt volcanism that preceded development of the East African Rift. Infiltration of mantle melts can play a central role in the initiation and evolution of lithospheric thinning by weakening and focusing strain. Thus, understanding the composition, and in particular the mineralogy, of the sources of mantle melts is critical to constrain the conditions attending melt generation. Non-peridotite lithologies such as pyroxenite in an upwelling plume or metasomes within the lithospheric mantle are potentially fertile mantle sources capable of producing significant volumes of magmas. In contrast typical peridotite lithologies may not produce significant melt under these conditions (i.e., smaller degrees of mantle decompression, or lower values of mantle potential temperature). Moreover, mantle underlying the study area is characterized by significant seismic attenuation, which has been attributed to the presence of an African superplume upwelling of hot mantle material. The proposed study aims to investigate the relative contributions of lithospheric vs. plume-like mantle as primary magma sources. Specifically, mantle source lithologies (i.e. peridotite versus pyroxenite) will be evaluated via geochemical characterization of a well-preserved 2000 m thick section of flood basalts from the western Ethiopian Plateau that has never before been studied. The possible contribution of enriched lithospheric mantle to melt generation will be assessed through a parallel study of unusual Si-undersaturated rocks erupted in a Miocene shield volcano, for which preliminary data imply magma derivation from ancient African lithospheric mantle. The analytical program will involve measurement of major and selected trace elements, Sr-Nd-Pb-Hf isotopes, and minor elements in olivine, and will be interpreted within a temporal framework to be established by new Ar/Ar geochronology and paleomagnetic studies designed to constrain the timing, duration, and eruptive rates of these deposits. Together these data will provide new insights into processes of basalt generation. Broader Impacts. The data resulting from this project will offer the first petrologic insights into the origin of the geophysically-deduced compositional component of the African superplume and will be directly relevant to ongoing geophysical projects ongoing in the region. This project will support the early career research of Tyrone Rooney (Ph.D., 2006), and fosters international collaboration through interactions with researchers at Addis Ababa University. The project represents a new collaboration between scientists at five US institutions (Rooney-MSU, Herzberg-Rutgers, Kappleman/Holt-UT Austin, Spell-UNLV, and Konter-UTEP), all of whom will contribute to the analytical measurements, interpretations, and modeling. The project utilizes and extends the applications of state-of-the-art analytical facilities at Michigan State University (laser ablation ICP-MS), Rutgers University (electron microprobe), UT Austin (paleomagnetic lab), UNLV (Noble gas MS), and UTEP (MC-ICPMS). The project also will support mentoring of a Ph.D. student from MSU through the wide range of collaborative interactions at the five US institutions and researchers in Ethiopia.