Crustal and upper-mantle structure beneath the western Atlas Mountains in SW Morocco derived from receiver functions

Spieker, Kathrin; Thomas, Christine; Harnafi, M.; Moudnib, Lahcen El

doi:10.1093/gji/ggu216

Cited by 31 publications

(19 citation statements)

References 52 publications

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“…The crustal thickness was found to decrease to 20 km in the offshore. A crustal thickness of 36 km close to the profile MI-01 increasing towards the Atlas Belt to up to 45 km were calculated from receiver function using teleseismic earthquakes (Spieker et al, 2014). Towards the south the crustal thickness decreases to 27 km at the Souss Basin.…”

Section: Continental Domain : Structure Of the Unthinned Crust/width mentioning

confidence: 94%

“…Figure 15: Magnetic anomaly of the DAKHLA cruise study region with bathymetric contours from satellite altimetry overlain (Maus et al, 2009;Sandwell and Smith, 1997) Weigel et al, 1982).White broken line marks the extent of the deformation front of the accretionary wedge. (White et al, 1992) and grey line velocities of thinned continental crust (Christensen and Mooney, 1995) Spieker et al (2014) and blue line wide-angle seismic profiles from Markris et al (1985). WACMA is marked by orange and red outlines and Tafelney plateau by grey outlines.…”

Section: Acknowledgementsmentioning

confidence: 99%

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Crustal structure variations along the NW-African continental margin: A comparison of new and existing models from wide-angle and reflection seismic data

et al. 2016

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Deep seismic data represent a key to understand the geometry and mechanism of continental rifting. The passive continental margin of NW-Africa is one of the oldest on earth, formed during the Upper Triassic-Lower Liassic rifting of the central Atlantic Ocean over 200 Ma. We present new and existing wide-angle and reflection seismic data from four study regions along the margin located in the south offshore DAKHLA, on the central continental margin offshore Safi, in the northern Moroccan salt basin, and in the Gulf of Cadiz. Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. Volcanic activity seems to be mostly confined to the region next to the Canary Islands, and is thus not related to the initial opening of the ocean, which was associated to only weak volcanism. Comparison with the conjugate margin off Nova Scotia shows comparable continental crustal structures, but 2-3 km thinner oceanic crust on the American side than on the African margin. Highlights ► This compilation deep seismic data from the NW African margin reveals variations of the crustal thickness and structure along the margin. ► The continent-ocean transition zone is broader in the North and narrowing in the South ► Continental crust thins from 37 km to only 28 from North to South ► Comparison to the conjugate NE American margin gives insight into early stages of continental breakup and accretion of early oceanic crust.

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Section: Continental Domain : Structure Of the Unthinned Crust/width mentioning

confidence: 94%

Section: Acknowledgementsmentioning

confidence: 99%

Crustal structure variations along the NW-African continental margin: A comparison of new and existing models from wide-angle and reflection seismic data

et al. 2016

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“…Waveforms sampling the lowermost mantle beneath the Atlantic Ocean come from 21 three‐component seismic stations of a temporary array deployed in Morocco in the period 2010–2013 (Spieker et al, ). We use 30 earthquakes with foci located along the Cocos and Nazca plate subduction zones, beneath Central and North America, respectively (Figure a).…”

Section: Data and Observationsmentioning

confidence: 99%

Discriminating Between Causes of D″ Anisotropy Using Reflections and Splitting Measurements for a Single Path

2019

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Knowledge of deep mantle deformation is based on seismic anisotropy: the variation of seismic wave speed and polarization with direction. Measuring this directional dependency requires azimuthal seismic coverage at D″ depth-the bottom few hundred kilometers of the mantle-which is often a limit in retrieving the style of anisotropy. Shear wave splitting is the standard technique for probing mantle anisotropy, and recently, reflections from the D″ region have been used to infer azimuthal anisotropy. Here we combine observations and modeling of D″ reflections with shear wave splitting along a given raypath direction in order to constrain mineralogy and dynamics of the lower mantle. From our modeling, a clear distinction between different anisotropic media is possible by using both types of observations together but only one directional path. We focus on the lowermost mantle beneath the central Atlantic Ocean by using South-Central American earthquakes recorded in Morocco. We find complex azimuthal and distance variation for both polarities of D″ reflections and shear wave splitting parameters, which rules out a simple style of anisotropy-such as vertical transverse isotropy-for the region. Our preferred model consists of a phase transition from a randomly oriented bridgmanite to lattice-preferred orientation fabric in postperovskite, developed in a tilted plane sheared along a roughly SW-NE deformation direction.

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“…Z‐Z′ denotes location of profile shown in Figure . Data from Figure a are Cooper and Miller (), Jessell et al (), Mancilla and Diaz (2012); Miller and Becker (), and Spieker et al () and Figure b are sourced from Tokam et al () and Gallacher and Bastow ().…”

Section: Overviewmentioning

confidence: 99%

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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Crustal and upper-mantle structure beneath the western Atlas Mountains in SW Morocco derived from receiver functions

Cited by 31 publications

References 52 publications

Crustal structure variations along the NW-African continental margin: A comparison of new and existing models from wide-angle and reflection seismic data

Crustal structure variations along the NW-African continental margin: A comparison of new and existing models from wide-angle and reflection seismic data

Discriminating Between Causes of D″ Anisotropy Using Reflections and Splitting Measurements for a Single Path

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

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