Tectonic pattern of the Azores spreading centre and triple junction

Searle, R. C.

doi:10.1016/0012-821x(80)90221-6

Cited by 234 publications

(148 citation statements)

References 31 publications

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“…Searle 1980;Patriat & Courtillot 1984). Non-stationary location and jumps of the branches, together with transient transform faults characterize triple junctions and their instability over time.…”

Section: Introductionmentioning

confidence: 99%

Current deformation in Central Afar and triple junction kinematics deduced from GPS and InSAR measurements

Doubre¹,

Déprez²,

Masson³

et al. 2016

Geophys. J. Int.

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S U M M A R YKinematics of divergent boundaries and Rift-Rift-Rift junctions are classically studied using long-term geodetic observations. Since significant magma-related displacements are expected, short-term deformation provides important constraints on the crustal mechanisms involved both in active rifting and in transfer of extensional deformation between spreading axes. Using InSAR and GPS data, we analyse the surface deformation in the whole Central Afar region in detail, focusing on both the extensional deformation across the Quaternary magmato-tectonic rift segments, and on the zones of deformation transfer between active segments and spreading axes. The largest deformation occurs across the two recently activated Asal-Ghoubbet (AG) and Manda Hararo-Dabbahu (MH-D) magmato-tectonic segments with very high strain rates, whereas the other Quaternary active segments do not concentrate any large strain, suggesting that these rifts are either sealed during interdyking periods or not mature enough to remain a plate boundary. Outside of these segments, the GPS horizontal velocity field shows a regular gradient following a clockwise rotation of the displacements from the Southeast to the East of Afar, with respect to Nubia. Very few shallow creeping structures can be identified as well in the InSAR data. However, using these data together with the strain rate tensor and the rotations rates deduced from GPS baselines, the present-day strain field over Central Afar is consistent with the main tectonic structures, and therefore with the long-term deformation. We investigate the current kinematics of the triple junction included in our GPS data set by building simple block models. The deformation in Central Afar can be described by adding a central microblock evolving separately from the three surrounding plates. In this model, the northern block boundary corresponds to a deep EW-trending trans-tensional dislocation, locked from the surface to 10-13 km and joining at depth the active spreading axes of the Red Sea and the Aden Ridge, from AG to MH-D rift segments. Over the long-term, this plate configuration could explain the presence of the en-échelon magmatic basins and subrifts. However, the transient behaviour of the spreading axes implies that the deformation in Central Afar evolves depending on the availability of magma supply within the well-established segments.

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Section: Introductionmentioning

confidence: 99%

Current deformation in Central Afar and triple junction kinematics deduced from GPS and InSAR measurements

Doubre¹,

Déprez²,

Masson³

et al. 2016

Geophys. J. Int.

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“…This difference in density suggests that the uppermost mantle below 43øN-50øN is about 150øC cooler than that beneath the Azores. Such a difference in mantle temperature is also suggested by the variation in crustal thickness, from normal oceanic thickness around 45øN [Fowler, 1978;Fowler and Keen, 1979] to 8-10 km under the Azores Platform [Searle, 1976[Searle, , 1980. Thus it seems that basalts of hot spot character are, close to 45øN, being melted from mantle nearly as cold as beneath normal mid-ocean ridges.…”

Section: Thickening the Crust Is Not Possible Under The 45øn Area Sincementioning

confidence: 83%

“…This file contains the present-day plate boundaries for the North Atlantic, identified using data from more than one of bathymetric charts, satellite altimeter profiles, magnetic anomalies and earthquake epicenters [Searle, 1980 Seafloor ages were obtained from the digital age grid (6 arcmin) of the ocean floor [Muller et al, 1997], which is also available from the NGDC. This is based on a global plate reconstruction and identification of magnetic anomalies and fracture zones.…”

Section: Data Setmentioning

confidence: 99%

Anomalous mantle at 45°N Mid‐Atlantic Ridge?

Mello¹,

Cann²,

Fowler³

1999

J. Geophys. Res.

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Abstract. The Mid-Atlantic Ridge at 45øN has a ridge crest depth close to normal for slow spreading ridges and a crustal thickness of 6 km. However, the free-air gravity over the region is higher than expected for such axial depths, and erupted basalts are enriched in incompatible trace elements and radiogenic isotopes, which could be taken to indicate the presence of a mantle plume beneath the spreading axis. But the ridge is at normal depths and the crust is of normal thickness. We model free-air gravity across and parallel to the strike of the ridge. A density structure derived from a cooling model provides a good fit for gravity across the ridge axis. A gravity model along the ridge axis indicates that most of the gravity signal over the Azores and Reykjanes Ridge is related to thicker crust, while the gravity signal over 45øN can be modeled by a density anomaly, which extends along the spreading axis from about 43øN to 50øN and from zero age to 35 m.y. Such a mass excess can be explained by an increase in the garnet content of the mantle within the stability field of garnet peridotite. The enriched basalts occur in the same region as the mass anomaly. We interpret them as originating from cool hotspot mantle. This anomalous mantle may derive from a hotspot that existed at the North America-Africa-Eurasia triple junction when it was at 45øN between 59 and 26 m.y. The King's Trough Complex is the remnant of that hotspot. We consider that this cool hotspot mantle still underlies the spreading axis and contributes to crustal construction.

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“…From this longitude a complex bathymetry is observed where it is difficult to identify a comprehensible alignment, since it is fulfilled by large submarine mountains and abyssal plains. Along this fracture, various NS similar fractions are recognized with profiles containing significant recent scarps, Searle (1980). Besides, Gloria Fault is a right lateral transform fault, Buforn et al (1988a) that seems to be presently inactive (Fig.…”

Section: The Central Regionmentioning

confidence: 91%

Seismo-electromagnetic phenomena in the western part of the Eurasia-Nubia plate boundary

Silva

Bezzeghoud

Rocha

et al. 2011

Nat. Hazards Earth Syst. Sci.

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Abstract. This paper presents a work that aims to monitor seismo-electromagnetic phenomena in the Western Part of the Eurasia-Nubia Plate Boundary. This region has a significant tectonic activity combined with relatively low electromagnetic noise levels, rendering high quality seismoelectromagnetic measurements possible. An overview of the seismicity of this region is presented and the research plan is discussed accordingly.

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Tectonic pattern of the Azores spreading centre and triple junction

Cited by 234 publications

References 31 publications

Current deformation in Central Afar and triple junction kinematics deduced from GPS and InSAR measurements

Current deformation in Central Afar and triple junction kinematics deduced from GPS and InSAR measurements

Anomalous mantle at 45°N Mid‐Atlantic Ridge?

Seismo-electromagnetic phenomena in the western part of the Eurasia-Nubia plate boundary

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