Seismic evidence of exhumed mantle rock basement at the Gorringe Bank and the adjacent Horseshoe and Tagus abyssal plains (SW Iberia)

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doi: 10.1016/j.epsl.2013.01.021
Author(s): Sallarès, Valentí; Martínez-Loriente, Sara; Prada, Manel; Gràcia, Eulàlia; Ranero, César; Gutscher, Marc-André; Bartolome, Rafael; Gailler, Audrey; Dañobeitia, Juan José; Zitellini, Nevio
Author Affiliation(s): Primary:
Unidad de Tecnologia Marina, Barcelona, Spain
Other:
Institució Catalana de Recerca i Estudis Avançats, Spain
Université de Brest, France
Comissariat d'Energie Atomique, France
Istituto di Scienze Marine, Italy
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, Vol.365, p.120-131. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Supplemental information/data is available in the online version of this article. 73 refs.; illus., incl. sects., geol. sketch map
Summary: The Gorringe Bank is a gigantic seamount that separates the Horseshoe and Tagus abyssal plains offshore SW Iberia, in a zone that hosts the convergent boundary between the Africa and Eurasia plates. Although the region has been the focus of numerous investigations since the early 1970s, the lack of appropriate geophysical data makes the nature of the basement, and thus the origin of the structures, still debated. In this work, we present combined P-wave seismic velocity and gravity models along a transect that crosses the Gorringe Bank from the Tagus to the Horseshoe abyssal plains. The P-wave velocity structure of the basement is similar in the Tagus and Horseshoe plains. It shows a 2.5-3.0 km-thick top layer with a velocity gradient twice stronger than oceanic Layer 2 and an abrupt change to an underlying layer with a five-fold weaker gradient. Velocity and density is lower beneath the Gorringe Bank probably due to enhanced fracturing, that have led to rock disaggregation in the sediment-starved northern flank. In contrast to previous velocity models of this region, there is no evidence of a sharp crust-mantle boundary in any of the record sections. The modelling results indicate that the sediment overlays directly serpentinite rock, exhumed from the mantle with a degree of serpentinization decreasing from a maximum of 70-80% under the top of Gorringe Bank to less than 5% at a depth of ∼20 km. We propose that the three domains were originally part of a single serpentine rock band, of nature and possibly origin similar to the Iberia Abyssal Plain ocean-continent transition, which was probably generated during the earliest phase of the North Atlantic opening that followed continental crust breakup (Early Cretaceous). During the Miocene, the NW-SE trending Eurasia-Africa convergence resulted in thrusting of the southeastern segment of the exhumed serpentinite band over the northwestern one, forming the Gorringe Bank. The local deformation associated to plate convergence and uplift could have promoted pervasive rock fracturing of the overriding plate, leading eventually to rock disaggregation in the northern flank of the GB, which could be now a potential source of rock avalanches and tsunamis. Abstract Copyright (2013) Elsevier, B.V.
Year of Publication: 2013
Research Program: DSDP Deep Sea Drilling Project
Key Words: 18 Geophysics, Solid-Earth; Abyssal plains; Atlantic Ocean; Basement; DSDP Site 120; DSDP Site 135; Deep Sea Drilling Project; Density; Exhumation; Free-air anomalies; Geophysical methods; Geophysical profiles; Geophysical surveys; Gorringe Bank; Gravity anomalies; Horseshoe abyssal plain; Igneous rocks; Leg 13; Leg 14; Mantle; Metaigneous rocks; Metamorphic rocks; Metasomatic rocks; Metasomatism; North Atlantic; Ocean floors; Peridotites; Plate boundaries; Plutonic rocks; Seamounts; Seismic methods; Seismic profiles; Seismotectonics; Serpentinite; Serpentinization; Surveys; Tagus abyssal plain; Tectonics; Ultramafics; Uplifts; Velocity structure; Wide-angle methods
Coordinates: N353000 N373000 W0100000 W0130000
Record ID: 2013047652
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands