Tectonic evolution of the Careon ophiolite (northwest Spain). A remnant ofoceanic lithosphere in the Variscan belt

Analysis of the Careon Unit in the Ordenes Complex (northwest Iberian Massi f) has supplied relevant data concerning the existence of a Paleozoic ocean ic lithosphere, probably related to the Rheic realm, and the early subducti on-related events that were obscured along much of the Variscan belt by sub sequent collision tectonics. The ophiolite consists of serpentinized harzbu rgite and dunite in the lower section and a crustal section made up of coar se-grained and pegmatitic gabbros. An Early Devonian zircon age (395 +/- 2 Ma, U-Pb) was obtained in a leucocratic gabbro. The whole section was intru ded by numerous diabasic gabbro dikes. Convergence processes took place sho rtly afterward, giving rise to a mantle-rooted synthetic thrust system, wit h some coeval igneous activity. Garnet amphibolite, developed in metamorphi c soles, was found discontinuously attached to the thrust fault. The soles graded downward to epidote-amphibolite facies metabasite and were partially retrogressed to greenschist facies conditions. Thermobarometric estimation s carried out at a metamorphic sole (T approximate to 650 degrees C; P appr oximate to 11.5 kbar) suggested that imbrications developed in a subduction setting, and regional geology places this subduction in the context of an early Variscan accretionary wedge. Subduction and imbrication of oceanic li thosphere was followed by underthrusting of the Gondwana continental margin .