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Korostelev F.,CNRS Paris Institute of Earth Sciences | Leroy S.,CNRS Paris Institute of Earth Sciences | Keir D.,UK National Oceanography Center | Weemstra C.,Technical University of Delft | And 8 more authors.
Terra Nova | Year: 2016

Non-volcanic continental passive margins have traditionally been considered to be tectonically and magmatically inactive once continental breakup has occurred and seafloor spreading has commenced. We use ambient-noise tomography to constrain Rayleigh-wave phase-velocity maps beneath the eastern Gulf of Aden (eastern Yemen and southern Oman). In the crust, we image low velocities beneath the Jiza-Qamar (Yemen) and Ashawq-Salalah (Oman) basins, likely caused by the presence of partial melt associated with magmatic plumbing systems beneath the rifted margin. Our results provide strong evidence that magma intrusion persists after breakup, modifying the composition and thermal structure of the continental margin. The coincidence between zones of crustal intrusion and steep gradients in lithospheric thinning, as well as with transform faults, suggests that magmatism post-breakup may be driven by small-scale convection and enhanced by edge-driven flow at the juxtaposition of lithosphere of varying thickness and thermal age. © 2016 John Wiley & Sons Ltd.

Korostelev F.,CNRS Paris Institute of Earth Sciences | Leroy S.,CNRS Paris Institute of Earth Sciences | Keir D.,UK National Oceanography Center | Ahmed A.,CNRS Paris Institute of Earth Sciences | And 7 more authors.
Geosphere | Year: 2015

We image the lithospheric and upper asthenospheric structure beneath the central and eastern parts of the northern Gulf of Aden rifted passive continental margin with 59 broadband stations to evaluate the role of transform fault zones on the evolution of magma-poor continental margins. We used teleseismic tomography to compute a relative P wave velocity model in eastern Yemen and southern Oman down to 400 km depth. Our model shows low-velocity anomalies located in the vicinities of five major fracture zones and regions of recent volcanism. These low-velocity anomalies are likely caused by localized asthenospheric upwelling and partial melting, caused by small-scale convection promoted by gradients in the lithosphere-asthenosphere boundary topography near the fracture zones. In addition, low velocities underlie regions of elevated topography between major sedimentary basins. We suggest that locally buoyant mantle creates uplift and dynamic topography on the rift margin that affects the course of seasonal rivers and the sedimentation at the mouth of those rivers. Our new P wave velocity model suggests that the dynamic topography and recent volcanism in the central and eastern Gulf of Aden could be due to small-scale convection at the edge of the Arabian plate and/or in the vicinity of fracture zones. © 2015 Geological Society of America.

Pik R.,University of Lorraine | Bellahsen N.,CNRS Paris Institute of Earth Sciences | Leroy S.,CNRS Paris Institute of Earth Sciences | Denele Y.,CNRS Paris Institute of Earth Sciences | And 5 more authors.
Tectonophysics | Year: 2013

In the Gulf of Aden, different types of fracture zones (F.Z.) have been defined and potential links with continental transfer zones have been proposed (Bellahsen et al., 2013-this volume-a). In this study, we investigate the denudation history of the south-eastern continental margin of the Gulf of Aden on the Socotra Island, in order to highlight the interplay of normal and transfer/transform tectonic structures in the course of rift evolution. Samples belong from two distinct East and West domains of the Socotra Island separated by the continental Hadibo Transfer Zone (HTZ). Tectonic denudation started during the Priabonian-Rupelian along low-angle normal faults and removed part of the overlying sedimentary formations allowing basement exhumation toward the surface (~. 1.1-1.5. km of exhumation). Forward t-T modelling of the data requires a slightly earlier date for initiation of rifting in the E-Socotra domain (~. 38. ±. 2. Ma), compared to the W-Socotra domain (~. 32. ±. 2. Ma), which suggests that the HTZ was already active at that time. A second major event of basement cooling and exhumation (additional. ~. 0.7-1. km), starting at about ~. 20. ±. 2. Ma, has only been recorded on the E-Socotra domain. This second denudation phase significantly post-dates local rifting period but appears synchronous with Ocean Continent Transition formation (OCT: 20-17.6. Ma). This late syn-OCT uplift is maximum close to the HTZ, in the wedge of footwall delimited by this transfer system and the steep north-dipping normal faults that accommodated the vertical motion. This particular pattern of uplift and denudation during the OCT reorganisation suggests that the late uplift of the margin can be strongly differential from a segment to another, depending on the amplitude of thinning experienced by each of the adjoining segments. © 2013 Elsevier B.V.

Bellahsen N.,CNRS Paris Institute of Earth Sciences | Leroy S.,CNRS Paris Institute of Earth Sciences | Autin J.,University of Strasbourg | Razin P.,Bordeaux Montaigne University | And 5 more authors.
Tectonophysics | Year: 2013

Transfer zones are ubiquitous features in continental rifts and margins, as are transform faults in oceanic lithosphere. Here, we present a structural study of the Hadibo Transfer Zone (HTZ), located in Socotra Island (Yemen) in the southeastern Gulf of Aden. There, we interpret this continental transfer fault zone to represent a reactivated pre-existing structure. Its trend is oblique to the direction of divergence and it has been active from the early up to the latest stages of rifting. One of the main oceanic fracture zones (FZ), the Hadibo-Sharbithat FZ, is aligned with and appears to be an extension of the HTZ and is probably genetically linked to it. Comparing this setting with observations from other Afro-Arabian rifts as well as with passive margins worldwide, it appears that many continental transfer zones are reactivated pre-existing structures, oblique to divergence. We therefore establish a classification system for oceanic FZ based upon their relationship with syn-rift structures. Type 1 FZ form at syn-rift structures and are late syn-rift to early syn-OCT. Type 2 FZ form during the OCT formation and Type 3 FZ form within the oceanic domain, after the oceanic spreading onset. The latter are controlled by far-field forces, magmatic processes, spreading rates, and oceanic crust rheology. © 2013 Elsevier B.V.

Civiero C.,Imperial College London | Hammond J.O.S.,Imperial College London | Goes S.,Imperial College London | Fishwick S.,University of Leicester | And 11 more authors.
Geochemistry, Geophysics, Geosystems | Year: 2015

Mantle plumes and consequent plate extension have been invoked as the likely cause of East African Rift volcanism. However, the nature of mantle upwelling is debated, with proposed configurations ranging from a single broad plume connected to the large low-shear-velocity province beneath Southern Africa, the so-called African Superplume, to multiple lower-mantle sources along the rift. We present a new P-wave travel-time tomography model below the northern East-African, Red Sea, and Gulf of Aden rifts and surrounding areas. Data are from stations that span an area from Madagascar to Saudi Arabia. The aperture of the integrated data set allows us to image structures of ∼100 km length-scale down to depths of 700-800 km beneath the study region. Our images provide evidence of two clusters of low-velocity structures consisting of features with diameter of 100-200 km that extend through the transition zone, the first beneath Afar and a second just west of the Main Ethiopian Rift, a region with off-rift volcanism. Considering seismic sensitivity to temperature, we interpret these features as upwellings with excess temperatures of 100±50 K. The scale of the upwellings is smaller than expected for lower mantle plume sources. This, together with the change in pattern of the low-velocity anomalies across the base of the transition zone, suggests that ponding or flow of deep-plume material below the transition zone may be spawning these upper mantle upwellings. © 2015. The Authors.

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