Formation of arcuate orogenic belts in the western Mediterranean region
The Alpine orogen in the western Mediterranean region, consisting of the Rif-Betic belt and the Apennine-Calabrian-Maghrebide belt, is a classic example of an arcuate orogen. It contains fragments of Cretaceous to Oligocene high-pressure/low-temperature (HP/LT) rocks, which were exhumed and dispersed during post-Oligocene extensional deformation and are presently exposed in the soles of metamorphic core complexes. In this paper, we illustrate that the arcuate shape of the orogenic belt was attained during extensional destruction of the earlier HP/LT belt, driven by subduction rollback in a direction oblique or orthogonal to the direction of convergence. Since the Oligocene, sub-duction of M…
The Western Alps from the Jurassic to Oligocene: spatio-temporal constraints and evolutionary reconstructions
Abstract Despite extensive research in the last 150 years, the regional tectonic reconstruction of the Western Alps has remained controversial. The curved orogenic belt consists of several ribbon-like continental terranes (Sesia/Austroalpine, Internal Crystalline Massifs, Brianconnais), which are separated by two or more ophiolitic sutures (Piemonte, Valais, Antrona?, Lanzo/Canavese?). High-pressure (HP) metamorphism of each terrane occurred during distinct orogenic episodes: at ∼65 Ma in the Sesia/Austroalpine, at ∼45 Ma in the Piemonte zone and at ∼35 Ma in the Internal Crystalline Massifs. It is suggested that these events reflect individual accretionary episodes, which together with kin…
Phylogenetic analysis informed by geological history supports multiple, sequential invasions of the Mediterranean Basin by the angiosperm family Araceae
Despite the remarkable species richness of the Mediterranean flora and its well-known geological history, few studies have investigated its temporal and spatial origins. Most importantly, the relative contribution of geological processes and long-distance dispersal to the composition of contemporary Mediterranean biotas remains largely unknown. We used phylogenetic analyses of sequences from six chloroplast DNA markers, Bayesian dating methods, and ancestral area reconstructions, in combination with paleogeographic, paleoclimatic, and ecological evidence, to elucidate the time frame and biogeographic events associated with the diversification of Araceae in the Mediterranean Basin. We focuse…
Tectonometamorphic evolution of high-pressure rocks from the island of Amorgos (Central Aegean, Greece)
Structural and metamorphic data from the island of Amorgos (central Aegean Sea) show evidence for the existence of two distinct high-pressure units, the Metabasite Unit and the Basal Conglomerate Unit. These are exposed at the base of a thick marble sequence and overlying flysch deposits. The Metabasite Unit is characterized by a mineral assemblage of blue amphibole, garnet and clinopyroxene, indicating P – T conditions of 500–600 °C and >13 kbar. It is juxtaposed below carpholite-bearing metaconglomerates and quartz-rich micaschists of the Basal Conglomerate Unit, for which metamorphic conditions of 300–450 °C and 10–14 kbar are estimated. The contact between the two units is interpreted a…
Subduction of the Nazca Ridge and the Inca Plateau: Insights into the formation of ore deposits in Peru
A large number of ore deposits that formed in the Peruvian Andes during the Miocene (15-5 Ma) are related to the subduction of the Nazea plate beneath the South American plate. Here we show that the spatial and temporal distribution of these deposits correspond with the arrival of relatively buoyant topographic anomalies, namely the Nazca Ridge in central Peru and the now-consumed Inca Plateau in northern Peru, at the subduction zone. Plate reconstruction shows a rapid metallogenic response to the arrival of the topographic anomalies at the subduction trench. This is indicated by clusters of ore deposits situated within the proximity of the laterally migrating zones of ridge subduction. It …
Continental extension: From core complexes to rigid block faulting
Extension of overthickened continental crust is commonly characterized by an early core complex stage of extension followed by a later stage of crustal-scale rigid block faulting. These two stages are clearly recognized during the extensional destruction of the Alpine orogen in northeast Corsica, where rigid block faulting overprinting core complex formation eventually led to crustal separation and the formation of a new oceanic backarc basin (the Ligurian Sea). Here we investigate the geodynamic evolution of continental extension by using a novel, fully coupled thermomechanical numerical model of the continental crust. We consider that the dynamic evolution is governed by fault weakening, …
The effect of energy feedbacks on continental strength
The classical strength profile of continents is derived from a quasi-static view of their rheological response to stress--one that does not consider dynamic interactions between brittle and ductile layers. Such interactions result in complexities of failure in the brittle-ductile transition and the need to couple energy to understand strain localization. Here we investigate continental deformation by solving the fully coupled energy, momentum and continuum equations. We show that this approach produces unexpected feedback processes, leading to a significantly weaker dynamic strength evolution. In our model, stress localization focused on the brittle-ductile transition leads to the spontaneo…