Geodynamic Evolution of the East African Superplume: Insights From Volcanism in the Western Turkana Basin
Geodynamic Evolution of the East African Superplume: Insights From Volcanism in the Western Turkana Basin
复制标题
DOI：
10.1029/2023jb026755
复制
发表时间：
2023-09
期刊：
影响因子：
--
通讯作者：
Yue Cai;Sara Mana;Stephen E. Cox;Catherine C. Beck;C. Feibel;Jean Hanley;Tanzhuo Liu;L. Bolge;Sidney R. Hemming;Steven L. Goldstein
中科院分区：
文献类型：
--
作者：
Yue Cai;Sara Mana;Stephen E. Cox;Catherine C. Beck;C. Feibel;Jean Hanley;Tanzhuo Liu;L. Bolge;Sidney R. Hemming;Steven L. Goldstein
人们一致认为，沿着东非裂谷系（EARS）的火山活动与地幔柱活动有关。然而，由于我们对当地岩石圈地幔的了解有限，地幔柱的动力学很难受到岩浆化学的约束。图尔卡纳盆地是研究与地幔柱有关的火山活动的最佳地点之一，因为那里的岩石圈地幔异常薄。Turkana西部火山岩的新的Ar-Ar年代学和地球化学数据表明，始新世火山岩具有相对较低的206 Pb/204 Pb（3.78）。它们相对较高的Ba/Rb（35-78）比值表明来自浅岩石圈地幔的贡献。渐新世-中新世图尔卡纳火山岩具有HIMU-和EMI-型富集地幔特征，总体Ba/Rb比值较低，这与地幔柱物质的部分熔融一致。上新世和更年轻的图尔卡纳火山岩具有低的Ba/Rb和Sr-Nd-Pb同位素比值，类似于具有高的3 He/4 He比值的埃塞俄比亚火山岩。这种时间上的变化可以与层状地幔柱模型相协调，在该模型中，外层的古老再循环洋壳和沉积物覆盖在更原始的下地幔物质上。在埃塞俄比亚之下，地幔柱的外层要么消失，要么被约1000年时较厚的岩石圈地幔分层刺穿。30 Ma，这一事件将促进羽状流内部的快速上涌，并引发埃塞俄比亚洪水火山作用。EARS南部的羽流外层可能更厚，这可以解释具有原始惰性气体特征的年轻HIMU和EMI型火山岩的发生。
There is a consensus that volcanism along the East African Rift System (EARS) is related to plume activities. However, because of our limited knowledge of the local lithospheric mantle, the dynamics of the plume are poorly constrained by magma chemistry. The Turkana Basin is one of the best places to study plume‐related volcanism because the lithospheric mantle there is unusually thin. New Ar‐Ar geochronology and geochemical data on lavas from western Turkana show that Eocene volcanics have relatively low 206Pb/204Pb (3.78). Their relatively high Ba/Rb (35–78) ratios suggest contributions from the shallow lithospheric mantle. Oligo‐Miocene Turkana volcanics have HIMU‐ and EMI‐ type enriched mantle signatures with overall lower Ba/Rb ratios, which is consistent with partial melting of plume material. Pliocene and younger Turkana volcanics have low Ba/Rb and Sr‐Nd‐Pb isotope ratios that resemble those of Ethiopian volcanics with elevated 3He/4He ratios. This temporal variation can be reconciled with a layered plume model where an outer layer of ancient recycled oceanic crust and sediment overlies more primitive lower mantle material. Beneath Ethiopia, the outer layer of the plume is either missing or punctured by the delamination of the thicker overlying lithospheric mantle at ca. 30 Ma, an event that would have facilitated the rapid upwelling of the inner portion of the plume and triggered the Ethiopian flood volcanism. The outer layer of the plume may be thicker in the southern EARS, which could explain the occurrence of young HIMU‐ and EMI‐type volcanics with primordial noble gas signatures.