Lithospheric structure of the Gorringe Bank: Insights into its origin and tectonic evolution

Abstract

[1] The Gorringe Bank is a 5000 m high seamount near the Atlantic coast of Iberia characterized by a 9 m high geoid anomaly and a ∼120 mGal Bouguer anomaly relative to the surrounding abyssal plains. It has been linked to a NW directed thrust carrying exhumed upper mantle rocks and transitional crust on top of flexeddown Eurasian oceanic crust along the Tagus Abyssal Plain. However, estimations of crustal shortening have yielded dissimilar results, and the deep structure of the ridge remains highly unknown. We present a restored cross section and a new model of the lithospheric structure based on gravity, geoid, elevation, and the presence of serpentinized peridotites. At least 20 km of shortening took place along a flat-ramp-flat thrust fault, and the density structure of the lithosphere is consistent with mantle serpentinization varying from 70% at the surface to 20% at 14 km depth and 0% at 40 km. The topographic relief and gravity anomalies are explained by assuming a flexural isostatic model with an elastic thickness T e of ∼30 km. The evolution of the Gorringe Bank since the Late Jurassic is interpreted in relation to Eurasia-Africa-North America plate motion in four stages: (1) transtension between Newfoundland-Iberia and Africa, which generated small oceanic basins and mantle exhumation; (2) opening of the North Atlantic and seafloor spreading at the NW side of the exhumed Gorringe, which produced gabbro intrusions and serpentinization; (3) a quiescent tectonic period dominated by subsidence and sediment accumulation; and (4) a transpressional plate boundary between Eurasia and Africa with NW directed subcrustal thrusting and generation of the present Gorringe relief. Citation: Jiménez-Munt, I., M. Fernàndez, J. Vergés, J. C. Afonso, D. Garcia-Castellanos, and J. Fullea (2010), Lithospheric structure of the Gorringe Bank: Insights into its origin and tectonic evolution, Tectonics, 29, TC5019,

Owen Ridge deep-water submarine landslides: implications for tsunami hazard along the Oman coast

“…For instance, in the Atlantic Ocean, the Gorringe Bank rock avalanche (Zitellini et al, 2009), which is 60-80 km 3 in volume and 26-30 kyr old, could have generated a potentially destructive tsunami on densely populated Portuguese, Spanish (Lo lacono et al, 2012) and Moroccan coastlines. In contrast with the numerous large landslides observed along the Owen Ridge, the Gorringe Bank rock avalanche is the only large landslide (> 1 km 3 ) observed along the Gorringe Bank since its Miocene uplift (Jiménez-Munt et al, 2010), which is conspicuous with regards to the high frequency of large magnitude earthquakes (M w > 6) in the area (Baptista and Miranda, 2009). This contrasts with slope failures on the nearby Portuguese margin that produced turbiditic deposits whose estimated ages correlate well with the most important historic earthquakes and tsunamis (Gràcia et al, 2010).…”

From the North-Iberian Margin to the Alboran Basin: A lithosphere geo-transect across the Iberian Plate

“…Using a Te that is consistent with the tectonothermal age of the lithosphere (Watts, 2001) allows reducing the misfit below uncertainty and then the regional isostasy can explain the topographic profile and the misfit of the local isostatic model. See Jiménez-Munt et al (2010) for details about flexural calculation.…”

The Tell-Rif orogenic system (Morocco, Algeria, Tunisia) and the structural heritage of the southern Tethys margin

“…Thus, this basin filled with flyschs outcropping in the Ketama unit simply appears as an appendix belonging to the Flyschs Basin itself. It is worth noting that a similar timing is also recognized for mantle exhumation along the south Iberian margin in the Gorringe Bank area (Girardeau et al, 1998;Jiménez-Munt et al, 2010).…”