Initial Cenozoic magmatic activity in East Africa: new geochemical constraints on magma distribution within the Eocene continental flood basalt province
Initial Cenozoic magmatic activity in East Africa: new geochemical constraints on magma distribution within the Eocene continental flood basalt province
复制标题
DOI：
10.1144/sp518-2020-262
复制
发表时间：
2021-08
期刊：
影响因子：
--
通讯作者：
R. Steiner;T. Rooney;G. Girard;N. Rogers;C. Ebinger;L. Peterson;R. Phillips
中科院分区：
文献类型：
--
作者：
R. Steiner;T. Rooney;G. Girard;N. Rogers;C. Ebinger;L. Peterson;R. Phillips
非洲大低剪切速度区物质与非洲岩石圈的初始相互作用表现为始新世大陆大火成岩区（LIP），集中在埃塞俄比亚南部和肯尼亚北方。在这里，我们提出了一个地理上分布良好的地球化学数据集，包括始新世大陆LIP的溢流玄武岩熔岩，以将区域火山地层细化为三个不同的岩浆单元：（1）高碱性小体积Akobo玄武岩（49.4- 46.6Ma），代表岩石圈-地幔交代体熔融的溢流玄武岩火山作用的初始阶段;（2）原始的、空间局限的Amaro玄武岩（45.2- 39.8Ma），代表了上涌热化学异常熔融的溢流玄武岩火山作用的早期主相;空间上广泛的Gamo-Makonnen岩浆单元（38-28 Ma），代表了在岩石圈内经历了重大加工的溢流玄武岩火山作用的成熟主阶段，均匀的组合物。这些主相岩浆超过10万年的集中侵入，使非洲岩石圈在随后的岩石圈拉伸事件中的应变局部化。应力集中到该大陆LIP所占据的区域可能有助于与东非裂谷相关的埃塞俄比亚西南部的初始延伸。
Abstract The initial interaction between material rising from the African Large Low Shear Velocity Province and the African lithosphere manifests as the Eocene continental large igneous province (LIP), centred on southern Ethiopia and northern Kenya. Here we present a geographically well-distributed geochemical dataset comprising flood basalt lavas of the Eocene continental LIP to refine the regional volcano-stratigraphy into three distinct magmatic units: (1) the highly alkaline small-volume Akobo Basalt (49.4–46.6 Ma), representing the initial phase of flood basalt volcanism derived from the melting of lithospheric–mantle metasomes; (2) the primitive and spatially restricted Amaro Basalt (45.2–39.8 Ma), representing the early main phase of flood basalt volcanism derived from the melting of the upwelling thermochemical anomaly; and (3) the spatially extensive Gamo–Makonnen magmatic unit (38–28 Ma), representing the mature main phase of flood basalt volcanism that has undergone significant processing within the lithosphere and resulted in relatively homogeneous compositions. The focused intrusion of these main phase magmas over 10 myr preconditioned the African lithosphere for the localization of strain during subsequent episodes of lithospheric stretching. The focusing of strain into the region occupied by this continental LIP may have contributed to the initial extension in SW Ethiopia that is associated with the East African Rift.