The Gibraltar subduction: A decade of new geophysical data.

Gutscher, M.-A., Dominguez, S., Westbrook, G.K., Le Roy, P., Rosas, F., Duarte, J.C., Terrinha, P., Miranda, J.M., Graindorge, D., Gailler, A., Sallares, V. and Bartolome, R. (2012) The Gibraltar subduction: A decade of new geophysical data. Tectonophysics, 574-575 . pp. 72-91. DOI 10.1016/j.tecto.2012.08.038.

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The Gibraltar arc, spans a complex portion of the Africa-Eurasia plate boundary marked by slow oblique convergence and intermediate and deep focus seismicity. The seemingly contradictory observations of a young extensional marine basin surrounded by an arcuate fold-and-thrust belt, have led to competing geodynamic models (delamination and subduction). Geophysical data acquired in the past decade provide a test for these models and support a narrow east-dipping, subduction zone. Seismic refraction studies indicate oceanic crust below the western Gulf of Cadiz. Tomography of the upper mantle reveals a steep, east-dipping high P-wave velocity body, beneath Gibraltar. The anisotropic mantle fabric from SKS splitting shows arc-parallel "fast directions", consistent with toroidal flow around a narrow, westward retreating subducting slab. The accompanying WSW advance of the Rif-Betic mountain belt has constructed a thick pile of deformed sediments, an accretionary wedge, characterized by west-vergent thrust anticlines. Bathymetric swath-mapping images an asymmetric embayment at the deformation front where a 2 km high basement ridge has collided. Subduction has slowed significantly since 5 Ma, but deformation of recent sediments and abundant mud volcanoes suggest ongoing activity in the accretionary wedge. Three possible origins for this deformation are discussed; gravitational spreading, overall NW-SE convergence between Africa and Iberia and finally a WSW tectonic push from slow, but ongoing roll-back subduction. In the absence of arc volcanism and shallow dipping thrust type earthquakes, evidence in favor of present-day subduction can only be indirect and remains the object of debate. Continued activity of the subduction offers a possible explanation for great (M>8.5) earthquakes known to affect the area, like the famous 1755 Great Lisbon earthquake. Recent GPS studies show SW motion of stations in N Morocco at velocities of 3-6 mm/yr indicating the presence of an independent block, a "Rif-Betic-Alboran" microplate, situated between Iberia and Africa

Document Type: Article
Keywords: Iberia; Roll-back subduction; Tethys oceanic lithosphere; Accretionary wedge; Active deformation; Earthquakes
Refereed: Yes
Publisher: Elsevier
Projects: FLOWS
Date Deposited: 27 Jan 2015 13:00
Last Modified: 27 Jan 2015 13:00

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