Many continental rifts are subjected to volcanism in tandem with rifting, which has raised a long-standing debate about whether magmatism is the cause or the consequence of plate fragmentation. To re-evaluate this chicken-and-egg question, we took advantage of five decades of research on the East African Rift System (EARS), the largest active continental rift on Earth, to explore the spatial and temporal relationship between rifting and magmatism. By comparing the co-occurrence of tectonics and volcanism since the Eocene with the present-day seismicity, we delimit the EARS as a ~ 5000 km-wide zone of volcano-tectonics made of four branches affecting not only East Africa but also the Mozambique channel and Madagascar. We then developed a quality filtering procedure of published radiometric ages in order to build two independent, robust, and comprehensive age compilations for magmatism and rifting over this extended EARS. Our thorough quality-checked selection of ages reveals that the EARS presents two distinct regimes of volcanism. Since the Upper Eocene, the rift system was affected by (1) pulses of volcanism in 500–1000 km-wide areas, and (2) a discontinuous but remarkably simultaneous volcanic activity, scattered along the four branches of the EARS since 25–27 Ma. Combining this spatio-temporal evolution of volcanism with a critical review of the timing of rifting, we show that the tectonics of the EARS evolves through time from trap-scale to plate-scale rifting. Until the Middle Miocene, extension structures first developed following flood basalt events and plateau uplifts. Then, volcanism resumed synchronously all over the EARS at ca. 12–12.5 Ma, followed by a general extensional deformation. This evolution, which cannot be explained by the sole action of a plume or of tectonics, is therefore interpreted in an intermediate way in which the EARS results from (1) extensive stresses acting on the African lithosphere in the long-lived context of the Gondwana breakup and (2) an overall complex mantle upwelling dynamics arising from the African Large Low Shear Velocity Province (LLSVP). We propose that extension stresses affecting the African lithosphere also modulate the melting of mantle anomalies and/or the collection of magma through the Pan-African belts. This influence explains the synchronous occurrence of many magmatic and tectonic events in the EARS and at the boundaries of the Nubia and Somali plates. Finally, our results suggest that the source of extension stresses affecting the African plate probably evolved from a dominant far-field origin to prevailing variations of gravitational potential energy (GPE) and a diverging basal shear of the Nubia and Somali lithosphere. This change would stem from an increase of the mantle flux in the Middle Miocene, yielding a change in the EARS’ dynamics from trap-scale to plate scale rifting.

许多大陆裂谷伴随着裂谷作用受到火山作用的影响，这引发了关于岩浆作用是板块破碎的原因还是结果的长期争论。为了重新评估这个先有鸡还是先有蛋的问题，我们利用对地球上最大的活跃大陆裂谷东非裂谷系统 (EARS) 的 5 年研究来探索裂谷与岩浆活动之间的时空关系。通过比较始新世以来构造和火山活动的同时发生与今天的地震活动，我们将 EARS 划定为一个约 5000 公里宽的火山构造带，由四个分支组成，不仅影响东非，而且影响莫桑比克海峡和马达加斯加。然后，我们开发了一个已发布辐射年龄的质量过滤程序，以构建两个独立的、稳健的、以及在这个扩展的EARS上的岩浆作用和裂谷的综合年龄汇编。我们对年龄进行全面质量检查的选择表明，EARS 呈现出两种不同的火山活动状态。自上始新世以来，裂谷系统受到 (1) 500-1000 公里范围内火山活动脉冲的影响，以及 (2) 自 25-27 年以来沿 EARS 的四个分支散布的不连续但显着同时的火山活动嘛。将火山活动的这种时空演化与对裂谷时间的批判性回顾相结合，我们表明 EARS 的构造随着时间的推移从圈闭尺度演变为板块尺度裂谷。直到中中新世，在洪水玄武岩事件和高原隆起之后，首先发展了伸展构造。然后，火山活动在大约 EARS 各处同步恢复。12–12.5 毫安，其次是一般的拉伸变形。这种演化，不能用羽流或构造的唯一作用来解释，因此以一种中间方式解释，其中 EARS 是由（1）在冈瓦纳大陆的长寿背景下作用于非洲岩石圈的广泛应力造成的分裂和（2）非洲大低剪切速度省（LLSVP）产生的整体复杂的地幔上涌动力学。我们提出影响非洲岩石圈的伸展应力也调节地幔异常的融化和/或通过泛非带的岩浆收集。这种影响解释了 EARS 以及努比亚和索马里板块边界处许多岩浆和构造事件的同步发生。最后，我们的研究结果表明，影响非洲板块的伸展应力的来源可能从主要的远场起源演变为重力势能（GPE）的主要变化以及努比亚和索马里岩石圈的发散基底剪切。这种变化将源于中中新世地幔通量的增加，导致EARS的动力学从圈闭尺度到板块尺度裂谷的变化。