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

合作研究：受地幔柱影响的伸展环境中的非橄榄岩熔融：非洲超地幔柱和非洲岩石圈的岩性非均质性

• 批准号: 1219647
• 负责人: Tyrone Rooney
• 金额: $ 25.53万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-15 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1219647&HistoricalAwards=false
• 关键词: Collaborative; Research; Non; peridotite; Melting

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.

智力优点。 该项目旨在确定地幔熔体的来源岩性（例如橄榄岩、辉石岩），这些熔体促成了东非裂谷发育之前的渐新世埃塞俄比亚大陆洪水玄武岩火山活动。地幔熔体的渗透可以通过减弱和集中应变而在岩石圈减薄的引发和演化中发挥核心作用。因此，了解地幔熔体来源的组成，特别是矿物学对于限制熔体生成的条件至关重要。非橄榄岩岩性，例如上升流羽流中的辉石岩或岩石圈地幔内的变体，是能够产生大量岩浆的潜在肥沃地幔源。相比之下，典型的橄榄岩岩性在这些条件下可能不会产生显着的熔化（即地幔减压程度较小，或地幔潜在温度值较低）。此外，研究区域下方的地幔具有显着的地震衰减特征，这归因于热地幔物质的非洲超地幔柱上涌的存在。 拟议的研究旨在调查岩石圈与羽状地幔作为主要岩浆源的相对贡献。 具体而言，将通过对埃塞俄比亚高原西部保存完好的 2000 米厚的溢流玄武岩部分进行地球化学表征来评估地幔源岩性（即橄榄岩与辉石岩），而此前从未对其进行过研究。丰富的岩石圈地幔对熔融生成的可能贡献将通过对中新世盾状火山中喷发的不寻常硅不饱和岩石的平行研究进行评估，初步数据表明岩浆源自古代非洲岩石圈地幔。该分析计划将涉及橄榄石中主要和选定的微量元素、Sr-Nd-Pb-Hf 同位素和微量元素的测量，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，该框架旨在限制这些沉积物的时间、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。 该项目产生的数据将为非洲超地幔柱地球物理推导的成分成分的起源提供第一个岩石学见解，并将与该地区正在进行的地球物理项目直接相关。该项目将支持 Tyrone Rooney（博士，2006 年）的早期职业研究，并通过与亚的斯亚贝巴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）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。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 Austin（古磁实验室）、UNLV（稀有气体MS）、和 UTEP (MC-ICPMS)。该项目还将支持博士生的指导。密歇根州立大学的学生通过与埃塞俄比亚的五个美国机构和研究人员的广泛合作互动。