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Papers by Ricardo Arenas

J Afr Earth Sci, 1995

In the Moroccan Hercynian belt, the Rehamna massif has been affected by an important extensional ... more In the Moroccan Hercynian belt, the Rehamna massif has been affected by an important extensional tectonism, developed inmediately after a compressive regime with associated Barrovian metamorphism up to the lower-T part of the amphibolite facies. Three main detachments were developed during the extensional regime (Kef El Mouneb, El Broumi and western Ouled Zednes), which caused an important thinning and can be considered to be the origin of the extreme condensation outlined by the metamorphic zones. The extensional movements were oriented from southwest to northeast in the lower parts of the massif, whereas in the upper parts a main sense of movement from northwest to southeast can be detected.

Tectonophysics, 2015

The existence of a large allochthonous nappe pile emplaced onto the hinterland of the Iberian Mas... more The existence of a large allochthonous nappe pile emplaced onto the hinterland of the Iberian Massif and covering most of the basement of NW and SW Iberia proposed by Díez Fernández and Arenas has been called into question on the basis of structural, geophysical, and regional data from SW Iberia. The discussion provided here is based on a revision of the fundamentals of the Variscan geology of NW Iberia and on a more detailed presentation of the geology of SW Iberia. Our counterarguments reveal the reasoning of Simancas et al. against the verisimilitude of the large allochthonous pile as inconclusive, incomplete, or erroneous in some cases. Therefore we maintain that our structural correlation and its implications remain fully valid for the case of the Iberian Massif.

Two Paleozoic ophiolites of different age mark the Variscan suture in the Cabo Ortegal Complex (n... more Two Paleozoic ophiolites of different age mark the Variscan suture in the Cabo Ortegal Complex (northwestern Iberian Massif). The Moeche and Purrido alloch-thonous ophiolites are structurally located between an exotic terrane of continen-tal affi nity (basal units), below, and another terrane with arc affi nity (upper units), above. The mafi c rocks of the Moeche unit are greenschist with a composition typical of tholeiitic basalt. Their rare earth element (REE) concentrations range from 12 to 31 times the chondritic abundances, with almost fl at chondrite-normalized REE patterns ([La N /Yb N ] avg = 0.83), and they have no signifi cant Eu anomalies. According to their contents in some immobile trace elements, the geochemical composition of these metabasalts seems to be transitional between normal mid-ocean-ridge basalt (N-MORB) and island-arc tholeiites. Their abundances in the most immobile trace elements with the highest discriminating power (Th, Nb, Ce, Zr, Ti, and Y), normal-iz...

Tectonophysics, 2015

Correlation of three high-P and low to intermediate-T belts from NW and SW Iberia allows recognit... more Correlation of three high-P and low to intermediate-T belts from NW and SW Iberia allows recognition of a single terrane affected by Late Devonian continental subduction during the Variscan orogeny. This terrane is located in the lower part of the allochthonous complexes of NW Iberia, and in a lower position in most of the Ossa Morena Zone that, therefore, emerges as another allochthonous complex of Iberia. The Ossa Morena Complex together with the allochthonous complexes of NW Iberia form a huge rootless nappe that was transported towards the Variscan foreland during final assembly of Pangea.

Special Paper 364: Variscan-Appalachian dynamics: The building of the late Paleozoic basement, 2002

... Paper 364 2002 Prograde development of corona textures in metagabbros of the Sobrado unit (Or... more ... Paper 364 2002 Prograde development of corona textures in metagabbros of the Sobrado unit (Ordenes Complex, northwestern Iberian Massif) Ricardo Arenas Departamento de Petrologfa v Geoquimica, Universidad Complutense, 28040 Madrid, Spain Jose R. Martinez ...

Special Paper 423: The Evolution of the Rheic Ocean: From Avalonian-Cadomian Active Margin to Alleghenian-Variscan Collision, 2007

The Journal of Geology, 2012

Tectonophysics, 2013

ABSTRACT 40Ar/39Ar dating of white mica in metapelites, thermobarometric calculations and new str... more ABSTRACT 40Ar/39Ar dating of white mica in metapelites, thermobarometric calculations and new structural and geological mapping have been carried out in the Somosierra region (Iberian Central System, ICS) to investigate the Variscan thickening–exhumation processes and the evolution of the paleo-thermal structure in a key region of the Central Iberian Zone. The rocks underwent an intermediate P/T event (M1) during a D1 stage of crustal thickening initiated between 354 and 347 Ma. This event was probably related to a first S to SE-directed emplacement of the NW Iberian allochthon, and during the initial development of a mid-crustal subhorizontal shear zone accommodating the ductile flow of thermally weakened crust parallel to the main orogenic trend. Syn-convergent extension of the upper levels occurred by 335–327 Ma, when tectonic unroofing led to D2 domal uplift of the orogenic roots and to recrystallization of rocks under intermediate to low P/T conditions (M2). Individualized gneiss domes developed along the orogenic trend, whereas some post-M2 thrusts dated at c. 319 Ma reflect lateral flow related to limited gravitational spreading of the domes. Younger upright to SW verging folding of the ICS dome during D3 progressive renewal of contractive deformation took place after 316 Ma. Final D4 gravitational collapse occurred under low P/T conditions (M3) at c. 300 Ma, accompanied by the intrusion of large volumes of anatectic granitoids.