Tectonostratigraphic subdivision and petrological characterisation of the deepest complexes of the Betic zone: a review

Abstract

The Veleta and Mulhacen Complexes, previously considered together as the Nevado-Filabride Complex, constitute the deepest units of the Betic Cordilleras. The Veleta Complex (VC) is mainly formed of several thousand metres of graphite-bearing micaschists and crops out as a series of tectonic windows below the Mulhacen Complex (MC). This latter complex comprises a pile of thrust nappes of crustal origin, composed of a Palaeozoic basement and Mesozoic cover series, between which a Jurassic-Cretaceous ophiolitic nappe is tectonically intercalated. The Alpine metamorphism developed in eclogite facies followed by Ab-Ep amphibolite facies in the MC, and in Ab-Ep amphibolite facies followed by greenschist facies in the VC. Pre-Alpine metamorphism in high gradient amphibolite facies is locally well preserved in some basement levels of the MC. In contrast, only scarce relics of pre-Alpine metamorphism, in greenchists facies, have been preserved in the VC. Within the MC nappes of crustal origin there appear metagranitic rocks, which were generated during two stages of late Hercynian magmatic activity: one of syncollisional acidic magmatism and the other of postcollisional intraplate acidic-to-intermediate volcanism. The ophiolitic nappe is composed of basic, ultramafic and sedimentary rocks affected by ocean-floor and orogenic metamorphism. The basic rocks partly retain their original E-MORB geochemical character. The ultramafic rocks are serpentinites and secondary harzburgites containing partly rodingitized basaltic dykes. The Soportujar Formation of the MC is made up of continental and evaporitic metasediments and meta-andesitic rocks that originated during an intraorogenic relaxation period between the eo-Alpine and meso-Alpine metamorphic events.

The Betic Ophiolites and the Mesozoic Evolution of the Western Tethys

“…The range of ages corresponding to the different metamorphic events shown in Figure 4 can be seen in [13] and in Table 1 of this paper, and summarized as follows:…”

“…Figure 1 shows the location of the most significant betic ophiolitic outcrops from which most of the petrological, geochemical and geochronological data mentioned in this study have been obtained. These ophiolites are exclusively located in the Mulhacén Complex (MC), in the central and eastern area of the Betic Cordillera, and are never found in the underlying Veleta Complex (VC) [13,16,23,37,38]. This suggests that these two complexes pertained to different palaeogeographic domains before and during the Jurassic-Cretaceous period, when the ophiolites originated from exhumation of an oceanic floor [8,10,15,[17][18][19]39,40].…”

“…The BOA outcrops, deriving from the betic oceanic floor [8,13,19], allow the reconstruction of the pristine oceanic lithostratigraphy represented in Figure 2, which has been tectonically superimposed on the crustal rocks of its adjoining western continental margin, currently forming the Caldera crustal unit of the MC, and were overthrusted by the rocks deriving from its eastern continental margin, now forming the Sabinas crustal unit (Figure 2). Each of these crustal units consists of rocks deriving from a Paleozoic basement with abundant granitic and rhyolitic orthogneisses, covered by Triassic sediments [13,16,37,38,41,42] and, together with the Jurassic-Cretaceous Ophiolite Unit, constitute the MC.…”

“…Each of these crustal units consists of rocks deriving from a Paleozoic basement with abundant granitic and rhyolitic orthogneisses, covered by Triassic sediments [13,16,37,38,41,42] and, together with the Jurassic-Cretaceous Ophiolite Unit, constitute the MC. Figure 2 also shows, in its legend, the main lithologic differences existing between the Caldera and the Sabinas units, as well as the more notable differences characterizing the currently underlying VC by respect to the overlying MC, and their different tectonic units [13,23].…”

“…This criticism on the oceanic nature of the BOA has been largely bypassed by recent papers which coupled radiometric dating to new petrological and geochemical studies (such as those in [13][14][15][16][17][18][19][20][21][22][23], among others), certainly ascribing the provenance of some BOA outcrops to a MORB-type tectonic setting, or to an Ocean-Continent-Setting (OCT). This hypothesis conforms to the interpretations proposed for ophiolite sequences of the Alps and Apennines as shown in [24][25][26][27][28][29][30][31].…”