Geochemical Evolution of the East African Rift System: Constraints from He, Pb, Nd and Sr Isotopes and 40Ar-39Ar Geochronology

东非裂谷系统的地球化学演化：来自 He、Pb、Nd 和 Sr 同位素和 40Ar-39Ar 地质年代学的约束

• 批准号: 9614508
• 负责人: David Graham
• 金额: $ 11万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-01-01 至 1998-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9614508&HistoricalAwards=false
• 关键词: Geochemical; Evolution; East; African; Rift

9614508 Graham The long term goal of this study is to provide the geochemical framework to help detail the timing and the nature of the interactions between the mantle plume, the convecting upper mantle and the subcontinental lithospheric mantle during the evolution of the East African Rift. The preliminary data has shown marked geochemical differences between various provinces on the western branch of the Rift. These differences can be related to the timing of ancient metasomatic events and to the development of isotopically-discrete domains within the subcontinental lithosphere. Whether these isotopic systematics are a general feature of the western branch of the rift remains to be demonstrated. Continuation of this line of study will be done by analysing He and radiogenic isotope compositions for classic suites of the Toro-Ankole and Virunga provinces and by dating lavas from the South Kivu province where the largest variations in radiogenic signatures have been observed. High 3He/4He ratios are known to be present in volcanic rocks of the Afar region and the northern parts of the main Ethiopian Rift and they are interpreted to reflect the influence of a mantle plume. A second goal of this study is to track the effects of this plume signature in pre-rift and post-rift magmas of the southern Ethiopian Rift.

9614508 Graham本研究的长期目标是提供地球化学框架，以帮助详细说明东非裂谷演化期间地幔柱、对流上地幔和次大陆岩石圈地幔之间相互作用的时间和性质。初步数据表明，裂谷西部分支各省之间存在明显的地球化学差异。 这些差异可能与古交代事件的发生时间和次大陆岩石圈内同位素离散域的发展有关。 这些同位素系统学是否是裂谷西部分支的一般特征还有待证明。将继续进行这一系列的研究，分析托罗-安科勒和维龙加两省经典岩套的He和放射成因同位素组成，并对南基伍省的熔岩进行年代测定，因为在那里观察到的放射成因特征变化最大。 已知阿法尔地区和埃塞俄比亚裂谷北方火山岩中存在高的3 He/4 He比值，并将其解释为反映地幔柱的影响。 本研究的第二个目标是跟踪这种羽签名的影响，在前裂谷和后裂谷岩浆的南部埃塞俄比亚裂谷。