A three‐dimensional electromagnetic model of the southern Kenya Rift: Departure from two dimensionality as a possible consequence of a rotating stress field

Simpson, Fiona

doi:10.1029/2000jb900106

Cited by 45 publications

(42 citation statements)

References 35 publications

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“…However, crustal anisotropy was only found in Namibia and South Africa (Weckmann et al, , 2011 . More often, electrical anisotropy is associated with the upper mantle (Simpson, 2000;Häuserer and Junge, 2011). Nevertheless, electrical anisotropy could be more generally associated with continental collision and breakup, in particular if anisotropy is a possible candidate for the weakness of mobile belts.…”

Section: Discussionmentioning

confidence: 99%

“…Simpson, 2000;Hamilton et al, 2006;Weckmann et al, 2011Weckmann et al, , 2003bHäuserer and Junge, 2011). However, crustal anisotropy was only found in Namibia and South Africa (Weckmann et al, , 2011 .…”

Section: Discussionmentioning

confidence: 99%

“…The model is divided into three depth regions: (1) the near-surface expression of the conductive sedimentary infill of the north-south striking rift, with the western half of the graben being more conductive than the eastern half, (2) an upper mantle being more conductive west of the rift, and (3) dominant and deeply penetrating, northwest-southeast striking conductive lineaments, which are required to dissect both flanks of the rift as well as the rift itself. Simpson (2000) interpreted these structures as being related to the suture zone between the Mozambique Mobile Belt and the Nyanza Cratonic Segment and to the rifting process itself. Since the Quaternary, rotation of the stress field resulted in reactivation of the existing, northwestsoutheast trending faults.…”

Section: Breaking a Continent -Case Studiesmentioning

confidence: 99%

“…For longer periods (∼ 1000 s) they exhibit deep conductivity features with an oblique strike direction to the rift. Some years later, Simpson (2000) interpreted the data set and in particular the induction vectors using a 3D forward model (Figure 8a)). The model is divided into three depth regions: (1) the near-surface expression of the conductive sedimentary infill of the north-south striking rift, with the western half of the graben being more conductive than the eastern half, (2) an upper mantle being more conductive west of the rift, and (3) dominant and deeply penetrating, northwest-southeast striking conductive lineaments, which are required to dissect both flanks of the rift as well as the rift itself.…”

Section: Breaking a Continent -Case Studiesmentioning

confidence: 99%

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Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

Weckmann

2011

Surv Geophys

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The African continent inherits a long history of continental accretion and breakup. The stage of "making" a continent goes back to the Archean, when the first continental masses formed cratons which mostly remained stable ever since. Subsequent collision of weaker continental masses was followed by several extension and compression episodes that resulted in the formation of supercontinents. After the assemblage of Gondwana, a period of predominantly "breaking" , i.e. the breakup of supercontinents, took over. The modern day African continent exhibits different types of margins; continental rifting occurs side by side with recent collision. Since the late 1960's Magnetotelluric (MT) experiments have played an important role in studies of the electrical conductivity structure of Africa. The early results significantly shaped the MT community's understanding of continental scale conductivity belts and basic characteristics of cratons and mobile belts on both crustal and lithospheric mantle scale for some decades. Modern MT studies in Africa have generally supported earlier results with high resistivities observed on cratons and low resistivities observed across mobile belts. Advances in instrumentation, data processing and interpretation resulted in higher resolution images of the lithosphere which in consequence induce an improved understanding of tectonic processes and geological prerequisites for the occurrence of natural resources. The high electrical conductivity of mobile belts and their relation to reactivated fault and detachment zones were often interpreted to characterize mobile belts as tectonic weak zones, which can accommodate stress and constitute zones along which continents can break. Recent breaking of the African continent can be studied on land across the East African rift; however, the lack of amphibian MT experiments across today's margins does not allow for good resolution of remnants of continental break-up processes. Naturally, the regions and the focus of the MT studies in Africa are diverse, but they all contribute to the story of making and breaking a continent.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Breaking a Continent -Case Studiesmentioning

confidence: 99%

Section: Breaking a Continent -Case Studiesmentioning

confidence: 99%

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Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

Weckmann

2011

Surv Geophys

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“…In Africa, rift valleys have received particular attention [3][4][5][6][7][8]. Anomalous crustal conductors are sometimes related to seismic activity.…”

Section: Introductionmentioning

confidence: 99%

Electrical structure of the tectonically active Kalabsha Fault, Aswan, Egypt

Mekkawi

Schnegg

Arafa-Hamed

et al. 2005

Earth and Planetary Science Letters

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In this work, we use the magnetotelluric (MT) method to detect geoelectrical conductivity anomalies in the Earth's crust and link them to local seismic activity. This application affords the unusual opportunity to study the percolation of water from a lake into a fault system and its effect on the induced seismicity. MT measurements were carried out in the period range 0.0046-420 s at nine sites along a 15 km-long North-South profile crossing the Kalabsha Fault, on the western bank of Lake Aswan. Data were analysed by 2D simultaneous inversion of both polarisations. The resulting model is compared with the local seismicity map and reveals the conductive signature of the fault, as well as geological and tectonic stresses prevailing in the Aswan area. Our MT investigations show the following features:The measured MT strike aligns with the seismic epicentre axis corresponding to the Kalabsha Fault. While crossing the Fault, enhanced conductivity is found down to depths of 5 km on a 1-2 km profile segment. At mid-crustal depths (20 km), a very high conductive body is found to coincide with the main seismic cluster in the Aswan area.These observations indicate that seismic activity and high electrical conductivity are related. The link between them is the presence of crustal fluids which are presumably the cause of the high conductivity observed. Their presence is also required to trigger the observed seismicity. In addition, we explain the lower conductivity of the local upper crust in terms of stress-modulated rock porosity. We believe that these results are of general significance, as they could explain the mid-crustal seismicity of tectonically active zones.

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Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes

et al. 2017

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The Cenozoic East African rift (EAR), Cameroon Volcanic Line (CVL), and Atlas Mountains formed on the slow‐moving African continent, which last experienced orogeny during the Pan‐African. We synthesize primarily geophysical data to evaluate the role of magmatism in shaping Africa's crust. In young magmatic rift zones, melt and volatiles migrate from the asthenosphere to gas‐rich magma reservoirs at the Moho, altering crustal composition and reducing strength. Within the southernmost Eastern rift, the crust comprises ~20% new magmatic material ponded in the lower crust and intruded as sills and dikes at shallower depths. In the Main Ethiopian Rift, intrusions comprise 30% of the crust below axial zones of dike‐dominated extension. In the incipient rupture zones of the Afar rift, magma intrusions fed from crustal magma chambers beneath segment centers create new columns of mafic crust, as along slow‐spreading ridges. Our comparisons suggest that transitional crust, including seaward dipping sequences, is created as progressively smaller screens of continental crust are heated and weakened by magma intrusion into 15–20 km thick crust. In the 30 Ma Recent CVL, which lacks a hot spot age progression, extensional forces are small, inhibiting the creation and rise of magma into the crust. In the Atlas orogen, localized magmatism follows the strike of the Atlas Mountains from the Canary Islands hot spot toward the Alboran Sea. CVL and Atlas magmatism has had minimal impact on crustal structure. Our syntheses show that magma and volatiles are migrating from the asthenosphere through the plates, modifying rheology, and contributing significantly to global carbon and water fluxes.

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A three‐dimensional electromagnetic model of the southern Kenya Rift: Departure from two dimensionality as a possible consequence of a rotating stress field

Cited by 45 publications

References 35 publications

Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

Electrical structure of the tectonically active Kalabsha Fault, Aswan, Egypt

Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes

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