New insights from seismic tomography on the complex geodynamic evolution of two adjacent domains: Gulf of Cadiz and Alboran Sea

Abstract

In this study, we present a three‐dimensional P wave upper‐mantle tomography model of the southwest Iberian margin and Alboran Sea based on teleseismic arrival times recorded by Iberian and Moroccan land stations and by a seafloor network deployed for 1 year in the Gulf of Cadiz area during the European Commission Integrated observations from NEAR shore sourcES of Tsunamis: towards an early warning system (EC NEAREST) project. The three‐dimensional model was computed down to 600 km depth. The tomographic images exhibit significant velocity contrasts, as large as 3%, confirming the complex evolution of this plate boundary region. Prominent high‐velocity anomalies are found beneath Betics‐Alboran Sea, off‐shore southwest Portugal, and north Portugal, at sublithospheric depths. The transition zones between high‐ and low‐velocity anomalies in southwest and south Iberia are associated to the contact of oceanic and continental lithosphere. The fast structure below the Alboran Sea‐Granada area depicts an L‐shaped body steeply dipping from the uppermost mantle to the transition zone where it becomes less curved. This anomaly is consistent with the results of previous tomographic investigations and recent geophysical data such as stress distribution, GPS measurements of plate motion, and anisotropy patterns. In the Atlantic domain, under the Horseshoe Abyssal Plain, the main feature is a high‐velocity zone found at uppermost mantle depths. This feature appears laterally separated from the positive anomaly recovered in the Alboran domain by the interposition of low‐velocity zones which characterize the lithosphere beneath the southwest Iberian peninsula margin, suggesting that there is no continuity between the high‐velocity anomalies of the two domains west and east of the Gibraltar Strait.

The upper-mantle transition zone beneath the Ibero-Maghrebian region as seen by teleseismic Pds phases

“…On the other hand, the 660 is, on average, deeper to the east and shallower to the west of the region. In this area, the tomographic images from Monna et al (2013) show a negative P-wave velocity anomaly extending to the upper-mantle transition zone (from sub-lithospheric depths down to the bottom of the model at about 660 km depth), interpreted as hot mantle.…”

“…Tomography studies reveal a positive P-wave velocity anomaly beneath the Alboran Sea extending from the base of the crust across the entire upper mantle (e.g., Bezada and Humphreys, 2012;Faccenna et al, 2004;Monna et al, 2013;Piromallo and Morelli, 2003;Spakman, 1990;Spakman and Wortel, 2004;Villaseñor et al, 2003;Wortel and Spakman, 2000). This anomaly has an arcuate shape, but loses its geometry or resolution as the transition zone (TZ) is approached, at about 400 km depth.…”

“…Nevertheless, there is still room for the different interpretations. Additionally, recent tomographic images have revealed a negative P-wave velocity anomaly beneath the Gulf of Cadiz and south Portugal (Monna et al, 2013) extending to the upper-mantle transition zone, which might be related to high mantle temperatures and to the origin of the sublithospheric magma source responsible for the anorogenic magmatism in the Mediterranean.…”

Subduction and volcanism in the Iberia–North Africa collision zone from tomographic images of the upper mantle

“…This feature has been identified by many authors (Blanco and Spakman, 1993;Calvert et al, 2000;Piromallo and Morelli, 2003;Spakman and Wortel, 2004) and has also been the subject of recent studies, some using a similar dataset to this one (Bezada et al, 2014;Bezada et al, 2013;Bonnin et al, 2014;Monna et al, 2013).…”

Ambient Noise Recorded by a Dense Broadband Seismic Deployment in Western Iberia

“…Current knowledge of the crustal structure under Portugal relies mainly on seismic wide-angle surveys dating back to the 1980s (Victor et al, 1980;Hirn et al, 1982;Díaz et al, 1993). In spite of recent work (Villaseñor et al, 2007;Salah et al, 2011;Monna et al, 2013;Silveira et al, 2013;Palomeras et al, 2014), the lateral extension and interrelation between shallow and deep lithospheric structures have yet to be fully characterized. The impact of tectonic convergence on the structure of the Iberian lithosphere is still unclear, especially to the west, beneath Portugal (e.g., Borges et al, 2001;Cloetingh et al, 2002).…”