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The geochemistry and Sr-Nd-Pb isotopic ratios of high 3He/4He Afar and MER basalts indicate a significant role of the African Superplume in EARS magmatism
Lithos ( IF 3.5 ) Pub Date : 2020-12-01 , DOI: 10.1016/j.lithos.2020.105791
Paterno R. Castillo , Xijun Liu , Paolo Scarsi

Abstract Basaltic rocks from the Afar Depression and Main Ethiopian Rift at the northern end of the East African Rift System with 3He/4He from 6 to 17 times the atmospheric value (3He/4HeAir or RA) define two geographically and, to a lesser extent, geochemically distinct groups. These groups are inconsistent with the commonly held view that there is a distinct Afar mantle plume at the northern end of the rift system, and that the plume influence systematically decreases away from its center in Lake Abhe. The high (>9 RA) 3He/4He Afar and Ethiopian rift basaltic suites possess a common, high 3He/4He component. The ca. 30 Ma very high titanium transitional basalts and picrites from the Ethiopian-Yemeni plateau with the highest 3He/4He (ca. 20 RA) closely represent the common component. Combined with their OIB-like compositional features, the high 3He/4He basalts indicate a metasomatized or anomalous upper mantle sensu lato and African Superplume source. Similar to the mantle source of ocean island basalts, the superplume is heterogeneous as it consists of various enriched end-components with low 3He/4He (≤8 RA) and the common, depleted ‘focus zone’ component with high 3He/4He (>9 RA). Northern rift magmas are mainly pseudo-binary mixtures between the anomalous upper mantle and currently upwelling plumes from the superplume.

中文翻译:

高 3He/4He Afar 玄武岩和 MER 玄武岩的地球化学和 Sr-Nd-Pb 同位素比表明非洲超级羽流在 EARS 岩浆活动中的重要作用

摘要 来自东非裂谷系北端的阿法尔凹陷和埃塞俄比亚主裂谷的玄武岩,其 3He/4He 是大气值的 6 到 17 倍(3He/4HeAir 或 RA)在地理上定义了两个,在较小程度上,地球化学上不同的群体。这些群体与普遍持有的观点不一致,即在裂谷系统的北端有一个明显的阿法尔地幔柱,并且柱状结构的影响从阿比湖的中心逐渐减少。高 (>9 RA) 3He/4He Afar 和埃塞俄比亚裂谷玄武岩套件具有共同的高 3He/4He 成分。约。来自埃塞俄比亚-也门高原的 30 Ma 超高钛过渡玄武岩和苦橄榄岩具有最高的 3He/4He(约 20 RA),紧密代表了共同成分。结合它们类似 OIB 的成分特征,高 3He/4He 玄武岩表明存在交代或异常的上地幔感觉和非洲超羽源。类似于海岛玄武岩的地幔源,超级羽流是不均匀的,因为它由各种富集的低 3He/4He (≤8 RA) 的末端成分和具有高 3He/4He (> 9 RA)。北部裂谷的岩浆主要是异常上地幔和当前来自超羽流的上涌羽流之间的伪二元混合物。
更新日期:2020-12-01
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