The Bazar ophiolite
The Bazar unit consists of serpentinized ultrabasic and basic metaigneous rocks (gabbros and minor pegmatoid gabbros). The unit represents an N-MORB oceanic lithosphere, probably formed in Late Cambrian times (Sánchez Martínez, 2009). Tectonometamorphic evolution includes: 1) a low/intermediate – pressure granulite-facies episode, which are preserved in boudins within metabasites, (~7 kbar/ ~700ºC; Díaz García, 1990; Sánchez Martínez et al., 2009), and 2) a general retrogression under amphibolite and greenschist facies conditions.
An imbricate structure is recognized, with several slices repeating the basic and ultrabasic association (Díaz García, 1990). Imbrications are limited by faults, in which kinematic criteria are scarce. Those reported in the literature and confirmed in this work suggest a top to the E and NE sense of shear. The main imbrication is located on top of the Bazar unit, and is called the Carballo-Bazar slice. The slice consists of 3500-4000 m of metabasites (amphibolites and flasergabbros) with a foliation developed under HT amphibolite facies conditions (Díaz García, 1990; Sánchez Martínez et al., 2009).
Besides the internal structure of the Bazar ophiolite, the nature of the upper and lower boundaries is controversial. Both limits were soon recognized as tectonic contacts (e.g. Warnaars, 1967; Díaz García, 1990). The lower boundary separates the Bazar ophiolite and the Basal units (Díaz García, 1990) and has been interpreted alternatively as an extensional or thrust fault (Gómez Barreiro, 2007b). It has been demonstrated recently that this contact represents a reactivated shear zone, where several extensional detachments overlap previous thrust faults during the gravitational collapse of the Variscan pile (Gómez Barreiro et al. 2010b; Díez Fernández et al. 2012).
The nature of the upper boundary is unclear. It separates the ophiolite from the base of the IP Upper units above: the Monte Castelo unit (Abati et al., 1999). Different lines of evidence suggest a complex evolution of the tectonic contact. For example, the absence of HP-HT Upper units between the Monte Castelo and Bazar units might be due to a subtractive accident, in the form of an extensional or out-of-sequence low angle shear zone. (Martínez Catalán et al., 2002). However documented kinematic criteria to date are very rare and limited to one observation at the N-S branch of the contact, with an eastward sense of shearing (Díaz García, 1990). New observations along NW-SE branch of the contact are presented below, in order to shed light on the structural evolution of this contact.