Re-routing of submarine channels by Plio-Quaternary extensional tectonics along the Tanzania margin and implications for an offshore branch of the East African Rift System,Basin Research

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Re-routing of submarine channels by Plio-Quaternary extensional tectonics along the Tanzania margin and implications for an offshore branch of the East African Rift System
Basin Research ( IF 2.8 ) Pub Date : 2024-06-14 , DOI: 10.1111/bre.12878
Marina Dottore Stagna ₁ , Vittorio Maselli _{1,

2} , David J. Reynolds ₁ , Djordje Grujic ₁ , David Iacopini ₃ , Pamela Reynolds ₁ , Sugandha Tewari ₄ , Arjan van Vliet ₅

Affiliation

The distribution and timing of Neogene extensional structures along the offshore Tanzania margin and their influence on submarine sediment dispersal pathways remain poorly constrained. This knowledge gap limits understanding of the propagation of the East African Rift System (EARS) in the western Indian Ocean. In this study, we use 2D and 3D seismic reflection data to explore a portion of the upper slope region offshore the Rufiji River delta which led to the discovery of a new extensional structure. Horizon maps and seismic sections extracted from the 3D volume reveal that the slope was intersected by W-E-oriented turbidite channels during the Cenozoic until the early Pliocene (5.3 Ma). Since then, the opening of this graben, whose timing is also constrained by stratigraphic horizon flattening, has led to a southward reorientation of these channels, a pattern that persists today, as evidenced by the flow direction of the channels at the modern seafloor. 2D seismic profiles reaching depths of 10 s two-way travel time (TWT) indicate that the formation of this graben is not related to the reactivation of Mesozoic structures. In detail, seismic data show that the acoustic basement is intersected by extensional faults, likely related to the Jurassic rift tectonics, which is reactivated during the middle Cretaceous forming a gentle monocline. The lack of deformation in the post-Cretaceous suggests a period of tectonic quiescence which persists until the establishment of a new extensional regime responsible for the graben's opening, indicating a decoupling between Mesozoic and Neogene tectonics. Considering the similarity in kinematics, orientation and timing between the graben and other structures along the margin, onshore and offshore, we interpret this graben to be generated by a later tectonic phase of the EARS. These new results may indicate that tectonic stresses associated with the EARS migrated from the Tanzania craton, where the oldest rift structures are dated to ca. 25 Ma, to the western Indian Ocean, where the tectonic activity started during the middle-late Miocene to Pliocene.

中文翻译：

沿坦桑尼亚边缘的普里奥-第四纪伸展构造对海底通道的改道及其对东非裂谷系统近海分支的影响

坦桑尼亚近海边缘新近纪伸展构造的分布和时间及其对海底沉积物扩散路径的影响仍然很少受到限制。这种知识差距限制了对西印度洋东非裂谷系统（EARS）传播的理解。在这项研究中，我们使用 2D 和 3D 地震反射数据来探索鲁菲吉河三角洲近海的上斜坡区域的一部分，从而发现了一个新的伸展结构。从 3D 体积中提取的层位图和地震剖面表明，在新生代至上新世早期（5.3Ma）期间，斜坡被东西向的浊积岩通道相交。从那时起，这个地堑的开放，其时间也受到地层地平线平坦化的限制，导致这些河道向南重新定位，这种模式一直持续到今天，现代海底河道的流动方向就证明了这一点。深度达到 10 秒双向走时 (TWT) 的二维地震剖面表明，该地堑的形成与中生代构造的重新激活无关。具体而言，地震数据显示声学基底被伸展断层贯穿，可能与侏罗纪裂谷构造有关，该构造在白垩纪中期重新激活，形成平缓的单斜。白垩纪后缺乏变形表明构造静止期一直持续到导致地堑张开的新伸展机制建立为止，这表明中生代和新近纪构造之间的脱钩。考虑到地堑与沿边缘、陆上和近海的其他结构在运动学、方向和时间上的相似性，我们解释该地堑是由 EARS 的后期构造阶段生成的。这些新结果可能表明，与 EARS 相关的构造应力从坦桑尼亚克拉通迁移而来，那里最古老的裂谷结构可追溯到约 1977 年。 25Ma，到西印度洋，构造活动开始于中新世中晚期至上新世。

更新日期：2024-06-16

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