He-Ne-Ar-N2-CO2 Isotope Characterization of the East Africa Rift System

东非裂谷系统 He-Ne-Ar-N2-CO2 同位素表征

• 批准号: 1019489
• 负责人: David Hilton
• 金额: $ 26.6万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1019489&HistoricalAwards=false
• 关键词: He; Ne; Ar; N2; CO2

This project is to undertake a comprehensive study of the East African Rift System (EARS) concentrating on the analyses of the major (CO2) and trace volatile (He-Ne-Ar-N2) characteristics of geological samples from all three branches of current rifting and volcanism in eastern Africa. These are: the Main Ethiopian Rift, including the Afar Depression, and the Kenyan and Western rifts. The aim of the study is to utilize the isotopic and relative abundance systematics of the volatiles to define the nature of the underlying mantle (one or two deep-seated mantle plumes) and to understand its interaction with the overlying continental lithosphere throughout eastern Africa. The research plan involves analyzing geothermal fluids, mantle xenoliths, phyric lavas and tephras to gain an unprecedented overview of the volatile characteristics of this active region which incorporates continental rifting, dynamic uplift and formation of nascent oceanic crust. Through an integrated approach combining analyses of the light noble gases (He-Ne-Ar) and other volatiles (N2 and CO2), the team will determine if the postulated mantle plume supporting the Ethiopian Dome is the sole deep-seated anomaly beneath the EARS or whether a second plume is responsible for uplift of the Kenyan Dome. In this respect, they will test if the high 3He/4He provinces of the Main Ethiopian Rift and Afar Depression have unique volatile isotopic characteristics that can be defined and exploited to map the spatial extent of the deep-seated Ethiopian plume influence. Additionally, the hypothesis that provinces of the Kenyan and Western rifts, i.e., south of the Turkana Depression, also have unique volatile isotopic characteristics that can be defined will form the basis of testing the involvement of subcontinental mantle lithosphere (SCLM) and/or a second plume in the petrogenesis of magmas from the Kenyan Dome. All targeted volatiles - either alone (e.g., 3He/4He) or in combination with other volatiles (e.g., CO2/3He) possess characteristics that make them sensitive tracers of deep mantle provenance that allows distinction between magmatic sources that are derived from the lithosphere and which are shallow. Taken together, this study will provide the essential volatile database that addresses key questions that test the relationship between the continent-wide African superswell and magma source characteristics throughout different regions of the EARS.

该项目将对东非裂谷系统进行全面研究，重点是分析东非现今裂谷和火山活动所有三个分支的地质样品的主要（CO2）和微量挥发物（He-Ne-Ar-N2）特征。它们是：埃塞俄比亚主裂谷，包括阿法尔洼地，肯尼亚和西部裂谷。这项研究的目的是利用挥发物的同位素和相对丰度系统学来确定下伏地幔（一个或两个深埋地幔柱）的性质，并了解其与整个非洲东部上覆大陆岩石圈的相互作用。该研究计划涉及分析地热流体、地幔捕虏体、斑状熔岩和火山岩，以前所未有地概述这个活动区域的挥发性特征，其中包括大陆裂谷、动态隆升和新生洋壳的形成。 通过综合分析轻惰性气体（He-Ne-Ar）和其他挥发物（N2和CO2），研究小组将确定假设的支持埃塞俄比亚穹丘的地幔柱是否是EARS下方唯一的深层次异常，或者第二个地幔柱是否是肯尼亚穹丘隆起的原因。在这方面，他们将测试埃塞俄比亚主裂谷和阿法尔凹陷的高3 He/4 He省份是否具有独特的挥发性同位素特征，这些特征可以被定义和利用，以绘制深层埃塞俄比亚羽流影响的空间范围。此外，假设肯尼亚和西部裂谷的省份，即，Turkana凹陷南部，也有独特的挥发性同位素特征，可以定义将形成测试的基础上，参与次大陆地幔岩石圈（SCLM）和/或第二羽岩浆的岩石成因从肯尼亚圆顶。所有目标挥发物-单独（例如，3 He/4 He）或与其它挥发物（例如，CO2/3 He）具有的特点，使他们成为深地幔源区的敏感示踪剂，允许来自岩石圈和浅源岩浆源之间的区别。总之，这项研究将提供必要的挥发性数据库，解决关键问题，测试整个大陆的非洲超井和岩浆源特性之间的关系，在整个EARS的不同地区。