Constraints on the Mantle Wavespeed and Discontinuity Structure below the Turkana Depression, East Africa: Insights into Topographic Development and Ethiopian Flood Basalt Volcanism
Constraints on the Mantle Wavespeed and Discontinuity Structure below the Turkana Depression, East Africa: Insights into Topographic Development and Ethiopian Flood Basalt Volcanism
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东非图尔卡纳凹陷下方地幔波速和不连续结构的约束：地形发育和埃塞俄比亚溢流玄武岩火山作用的见解
DOI：
10.1002/essoar.10508941.2
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Boyce A
中科院分区：
文献类型：
--
作者：
Boyce A
图尔卡纳凹陷低洼的地形将东非的埃塞俄比亚高原和肯尼亚高原分隔开来。由于缺乏对上地幔结构和动力学的约束，解释其地形的机制一直存在争议。了解图尔卡纳下方地幔在埃塞俄比亚和东非南部主要裂谷之间的裂谷演化和埃塞俄比亚洪水玄武岩火山爆发中的作用的努力也因数据有限而受到阻碍。在这里，最近在图尔卡纳和邻国乌干达部署的地震台网使我们能够开发一种新的绝对P波速度层析模型(AFRP21)来成像图尔卡纳凹陷下方的地幔结构。此外，我们使用P-to-S接收函数来绘制地幔过渡带的不连续结构图。在浅地幔中，广泛分布的慢波速度分布在埃塞俄比亚主要裂谷的下方。在南部，慢波速度出现在东非裂谷下方的焦点区域，但在图尔卡纳凹陷北部，这些慢波速度被一条狭窄的东西向快速波速度带横切。在MTZ上部深度，慢波速度在东非裂谷下方大致连续，但在MTZ底部开始分离为两个明显的异常。虽然接收函数显示东非新生代裂谷相关岩浆活动下方的MTZ广泛变薄，但图尔卡纳凹陷下方存在最薄的过渡带。图尔卡纳凹陷下方缓慢的波速和变薄的MTZ表明有热的上升流物质，因此其低洼性质不是由于缺乏潜在的动力支撑。相反，与成像的浅层快波速带有关的中新生代东西向裂谷作用可能更好地解释了这种凹陷的地形。此外，埃塞俄比亚洪水玄武岩火山活动的主喷发期可能与非洲板块在图尔卡纳异常变薄的MTZ上方的位置有关(约30 Ma)。
The subdued topography of the Turkana Depression separates the elevated Ethiopian and Kenyan Plateaus in East Africa. Mechanisms to explain its topography are debated because constraints on upper mantle structure and dynamics are lacking. Attempts to understand the role of the mantle below Turkana in the evolution of rifting between the Main Ethiopian and Southern East African rifts and the onset of Ethiopian Flood Basalt volcanism are also hindered by limited data availability. Here, recently deployed seismic networks in Turkana and neighboring Uganda enable us to develop a new absolute P-wavespeed tomographic model (AFRP21) to image mantle structure below the Turkana depression. Additionally, we use P-to-s receiver functions to map the mantle transition zone (MTZ) discontinuity structure. In the shallow mantle, broadly distributed slow wavespeeds reside below the Main Ethiopian rift. To the south, slow wavespeeds occur in a focused zone below the East African rift, but beneath the northern Turkana depression these are cross-cut by a narrow E-W band of fast wavespeeds. At upper MTZ depths slow wavespeeds are broadly continuous below the East African rift but begin to separate into two distinct anomalies at the base of the MTZ. While receiver functions reveal a broadly thinned MTZ below Cenozoic rift-related magmatism in East Africa, the thinnest transition zone exists below the Turkana Depression. Slow wavespeeds and a thinned MTZ below the Turkana Depression indicate hot upwelling material, thus its low-lying nature is not due to the lack of underlying dynamic support. Instead, the depressed topography may be better explained by Mesozoic-Cenozoic E-W rifting associated with the imaged shallow fast wavespeed band. Furthermore, the main eruptive phase of Ethiopian Flood basalt volcanism may be associated with the African plate’s position over the anomalously thinned MTZ in Turkana at ~30Ma.
从相对远震走时到绝对远震走时：绝对到达时间恢复方法（AARM）
影响因子：
3
作者：
A. Boyce;I. Bastow;S. Rondenay;R. Hilst
通讯作者：
R. Hilst