¿Existió un basamento Mesoproterozoico en NW África? Geocronología U-Pb de la ofiolita de tipo back-arc de Vila de Cruces

Laburpena

The NW Iberian Massif shows a variety of ophiolites formed at two different stages in Cambrian and Devonian times (c. 500 Ma and c. 400 Ma, respectively). These ophiolites provide information about the complex Paleozoic evolution of the NW African margin of Gondwana. New U-Pb geochronology data of the Vila de Cruces Ophiolite obtained in zircons from orthogneisses (3 samples) and related gabbros (1 sample), provided ages (LA-ICP-MS) in the range 506-491 Ma. Moreover, two different gabbro samples contain a scattered population of zircons with an average age of c. 1150 Ma, which probably represent xenolitic material included in the gabbroic magma during its ascent and emplacement in the Gondwanan margin. Taking into account the architecture of the Vila de Cruces Ophiolite and its geochemical composition characteristic of a supra-subduction zone setting, this ophiolite must be considered a section of oceanic or transitional lithosphere formed in a back-arc basin opened in the peri-Gondwanan realm. Moreover, the presence of inherited Mesoproterozoic zircons, also described in another Devonian ophiolite from the NW Iberian Massif, suggests the existence of a Mesoproterozoic basement in the NW African margin of Gondwana during Paleozoic times. The current location and extent of such unexposed basement is unknown.