Extensional tectonics in the Gorringe Bank rocks, Eastern Atlantic ocean: evidence of an oceanic ultra-slow mantellic accreting centre

The Gorringe Bank corresponds to an upper mantle peridotite ridge enclosing a 500-m thick/ 50-km long laccolith-like body of gabbro, locally cut and p oorly covered by tholeiitic rocks. Strain and kinematic analysis of orienta ted gabbros and peridotites sampled during the GORRINGE diving cruise (1996 ) provides new kinematic constraints on extensional high-temperature deform ation recorded at deep levels during stretching, near an accreting centre a xis of a mantle-dominant oceanic lithosphere. It is argued that the Gorring e Bank lithosphere formed at an oceanic ultra-slow, N010 degrees-020 degree s-trending accreting centre, mostly by passive tectonic denudation of the m antle, without any synchronous large magmatism. This peculiar lithosphere m ay be representative of the Iberia oceanic domain located between the conti nent and the J anomaly ridge, which likely marks the beginning of true spre ading at an oceanic spreading ridge.