Examinando por Autor "Pedrera, Antonio"

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Inhomogeneous rift inversion and the evolution of the Pyrenees
(Earth-Science Reviews, 2023-10) Pedrera, Antonio; García-Senz, Jesús; Pueyo, Emilio L.; López-Mir, Berta; Silva-Casal, Roi; Díaz-Alvarado, Juan
The kinematic evolution of the Pyrenees was largely controlled by structural and thermal heterogeneities inherited from a precursor rift system, resulting in complex along-strike variations in structural style and amount of shortening that remain a matter of debate. Based on a comprehensive compilation of published geological and geophysical data, this paper presents four newly-built sequentially restored cross-sections that make it possible to quantify the cumulative deformation along the Pyrenees and to assess the factors behind inhomogeneous lith ospheric shortening. In map-view, the cumulative shortening estimates are further constrained by regional vertical-axis rotations inferred from an extensive paleomagnetic dataset. Total shortening estimates reach maximum values of 125-122 km in the Central Pyrenees (Lannemezan and ECORS cross-sections, respectively) and diminish sideways, becoming 102 km in the Andorra cross-section, to the east, and 94 km in the Oloron ´ cross-section, to the west. To explain this shortening gradient, a new tectonic model with three key stages is proposed. (1) The onset of convergence took place during the Late Cretaceous, with the squeezing of a shallow asthenosphere and the extrusion of thinned crust pieces along the rift axis. (2) The dominant mechanism of deformation transitioned from squeezing to indentation during most of the Eocene, with the northern rift margin (European crust), including the thick exhumed lithospheric mantle, indenting into the weaker southern rifted margin (Iberian crust). The resulting bivergent orogenic wedge was heavily influenced by the lateral variability of the southern rifted margin geometry, with a long necking taper that narrows westward. (3) Crustal under thrusting, mostly operating in Priabonian-Aquitanian times, advanced steadily in the four studied cross-sections, with the strain gradually localizing into a single frontal basement thrust, which promoted incipient subduction. Frictional variations were greatly enhanced by thickness changes of the basal Upper Triassic salt unit, which favored a greater basement-cover decoupling in the Central Pyrenees, and explain the large-scale 20◦ clockwise vertical-axis rotations documented in the South-Western Pyrenees.
Seismic evidence for ductile necking of the mid-lower crust beneath the Columbrets Basin (Western Mediterranean)
(Terra Nova, 2023-10) Ramos, Adrià; Pedrera, Antonio; García-Senz, Jesús; López-Mir, Berta; Salas, Ramon
The Columbrets Basin is the largest Mesozoic rift basin of the Valencia Trough in the Western Mediterranean. The analysis of a seismic- reflection survey makes it possi-ble to reconstruct the tectonic fabric underlying the sedimentary basin, including the structure of the top of the lower crust and the Moho. It is proposed that the ductile deformation of the mid- lower crust was the main mechanism controlling the basin geometry, with the radial flow of mid- lower crust coeval with the reactivation of two large- offset SW-dipping normal faults, inherited from the precursor Permian–Triassic rifting. Mid- lower crustal necking occurred below the major depocenters, immedi-ately before hyperextension. Our results provide new insight into the formation of circular-shaped basins and the evolution of depth-dependent extensional processes during rifting.
Tectono-metamorphic interaction of upper mantle peridotites and lower crustal units during continental rifting in the western Betic Cordillera
(Elsevier, 2024-08) Díaz-Alvarado, Juan; González-Menéndez, Luis; Hidas, Károli; Azor, Antonio; Pedrera, Antonio
Recent geological mapping conducted in the Ronda Peridotites (Betic Cordillera, S Spain) has revealed a systematic field correlation between lower crustal metamorphic units and different tectono-metamorphic domains of the ultramafic massif. Mylonitic and highly tectonized Spl ± Grt peridotites (i.e., Grt-Spl mylonite and Spl tectonite domains), which are considered to be derived from a thick continental lithosphere, are in contact with garnet-bearing gneisses (i.e., kinzigites) of the Jubrique unit along a narrow but continuous mylonitic shear zone. Phase equilibrium calculations indicate that the metamorphic rocks of the Jubrique unit are consistent with an initial continental setting characterized by normal crustal thicknesses, which underwent two melting events. The first melting occurred at 0.9–1.0 GPa / 770–800 °C and resulted in 13 %melt, while the second one took place at shallower crustal conditions (0.4–0.5 GPa and 710–765 °C) and led to more restricted melt production (2–3 %melt). In contrast, the Spl ± Pl peridotites (Pl-tectonite domain), which are stable only at shallowest mantle levels within a highly extended continental lithosphere, are consistently found exposed in contact with heterogeneous granites and migmatites of the Guadaiza unit. According to new thermodynamic modeling, the Guadaiza metamorphic rocks record a single melting event characterized by a theoretical melt production of 6 to 11 % at the base of a very thin continental crust (ca. 0.3 GPa and 675–710 °C). This process was likely facilitated by influx of external water, necessary to generate high melt fractions observed in the diatexites. The systematic correlation observed between crustal metamorphic units, consistently overlaying the mantle rocks, and specific ultramafic domains of the Ronda massif, suggests that their juxtaposition primarily resulted from the severe extension of the continental lithosphere. U-Pb radiometric dating of zircons from gneisses, migmatites, and heterogeneous granites in the middle crustal rocks of the Guadaiza unit indicates that extensional processes, crustal anatexis, and melt stagnation occurred at around 280 Ma. Comparison of these new radiometric ages with previous results from the Jubrique unit suggests that a Permian high-temperature / low- to medium-pressure event uniformly affected the crustal units over the Ronda Peridotites. This event coincided with the formation of characteristic ultramafic mineral assemblages within the Ronda massif and provides evidence for the interaction between upper mantle rocks and lower- to mid-crustal metamorphic rocks during this period
Translation, collision and vertical-axis rotation in the Organyà and Montsec minibasins (South-Central Pyrenees, Spain)
(Wiley, 2024-01-31) García-Senz, Jesús; Lopez-Mir, Berta; Robador, Alejandro; Dinarè-Turell, Jaume; Pedrera, Antonio
This paper presents a sequentially restored cross-section of the Organyà and Montsec minibasins based on geological mapping, new field observations and available borehole data. The main objective was to describe the geometry and evolution of both basins in terms of salt tectonics and minibasin mobility. To this end, a comprehensive palaeomagnetic database has been used to constrain vertical-axis rotations potentially related to minibasin translation and pivoting. The Organyà minibasin constitutes an asymmetric depocentre formed during the Upper Jurassic-Lower Cretaceous by translation above a southerly inclined salt layer. Salt evacuation and minibasin touchdown induced salt accumulation on the northern side of the basin that culminated in the development of the major Santa Fe unconformity during the late Albian—early Cenomanian. Indicative of salt quiescence is the following isopachous Cenomanian to lower Santonian sequence Salt tectonics resumed during the late Santonian—Palaeocene, with the Montsec minibasin downbuilding coinciding with the onset of Pyrenean convergence. Changes of the base-salt topography reflects regional-scale geodynamic processes. The acceleration of crustal thinning in the North Pyrenean zone during the late Albian-early Cenomanian favoured uplift in the Axial Zone, increasing slope and triggering salt mobilization in the Southern Pyrenees. Likewise, the onset of contraction renewed the downslope gliding of the Organyà and Montsec minbasins, and supports the idea that the early stages of basin inversion were governed by gravity tectonics. The kinematic reconstruction suggests that the more that 30° counterclockwise vertical axis rotation records pivoting during the suprasalt translation of the Organyà minibasin rather than solely the Iberian microplate rotation.