Publication Date:
2016-09-14
Description:
The basement of the Vera and Huercal Overa basins (southeastem Betics) is fonned by
rocks ofthe Alboran Crustal Domain; a terrain which collided with the South-Iberian and Maghrebian
continentalmargins in the Lower Miocene, resulting in the fonnation of the Gibraltar Are mountain
chain. The Alpuja1Tide complex which occupies an intermediate structural position within the Alboran
Domain, above the Nevado-Filabride and below the Malaguide complexes, includes at least three
tectonic units in the southeastern Betics. From bottom to top in the slTuctural sequence, these units
are Almagro, Almanzora and Variegato. The metapelitic rocks of these units show significative
differences in their tectonic fabrics and in their P-T metamorphic paths. The lower Almagro unit
underwent low-P/low-T metamorphism (300 oc and 3-4 kbar) and its metapelites are slates with no
differentiated metamorphic fabric, which show two sets of spaced axial-plane cleavages. The
intennediate Almanzora unit has two differentiated metamorphic fabrics. The oldest foliation (S,)
preserved in quartz-rich domains of a crenulation cleavage (S ce) grew during high-P/low-T
metamorphism (between 300 °C/12 kbar and 350 oC/6 kbar). The Scc cleavage deyeloped after an
isobaric heating to 475 oc at 5 kbar and registers an initial isothennal decompression to 475 oc at 3
kbar followed by cooling to 300 oc at 2 kbar. A brittle spaced cleavage axial plane to N-vergent
asymmetric folM cuts the S ce fabtic.
At the top ofthe Alpujarride tectonic pile the Variegato unit, includes up to tlu·ee imbrications formed
from top to bottom by gamet schists, fine"grained schists and Triassic carbonates. The main Scc foliation
in the gamet schists grew during a nearly isothennal decompression between 500 oc at 8 kbar and 525 oc at 2 kbar. In the Variegato dark schists, the spaced crenulation cleavage associated to Nvergent
folds is defined by muscovite and chlorite lepidoblasts and is overprinted by the growth of
andalousite porphyroblasts. This assemblage equilibrated at 450-460 oc at 2 kbar.
The Variegato fine-grained schists include a high-P/low-T Mg-carpholite-bearing assemblage, within
pre-Scc quartz veins equilibrated at 8-10 kbar and approximately 400 °C. Furthermore, a chlorite +
phengite + quartz assemblage defining the se relic foliation in lenticular domains of the scc cleavage
shows local equilibria at 11 to 9 kbar at 400 °C.
The superposition ofthese units was related with N-directed compressional brittle-ductile shear zones
and associated N-vergent asymmetric folds, which were active at a late stage of the metamorphic
evolution after coaxial ductile flattening of the Variegato and Almanzora units. The thrust pile that
resulted from this late compressional event was later thinned by two consecutive brittle extensional
systems with northward and southwestward tectonic transport. Final! y, these metamorphic rocks were
exhumed to the surface in the core of E-W oriented anticlinal ridges, which developed during the
Upper Neogene and the Quaternary. Folding and strike-slip faulting of the Miocene Alboran basin
produced the present basin and range morphology of the southeastern Betics, which is characterised
by the formation of isolated sedimentary basins in the synclines.
Type:
Article
,
NonPeerReviewed
Format:
text
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