The Aracena metamorphic belt, in the southwest Iberian Massif, is characterized by the presence of MORB-derived amphibolites and continental rocks deformed and metamorphosed during the Hercynian orogeny. Geochemical relationships of these amphibolites indicate the existence of a multiple fractionation process from a set of parental magmas, implying the existence of a multi-chamber system beneath the ridge where the basalt protolith was extruded. Neodymium isotopic ratios are typical of MORB, and oxygen isotopes indicate that these amphibolites have been derived from the uppermost part of the oceanic crust Thermal evolution, revealed from the study of chemical variations in the amphibole chemistry, is interpreted as resulting from subduction in a low-pressure regime in which the thermal structure of the continental hanging-wall played an important role. This continental wall was previously heated by subduction of a slab window resulting from migration of a triple junction along the continental edge during plate convergence. Three petrologic arguments support this tectonic model These are: (1) the low-pressure inverted metamorphic gradient of amphibolites of the oceanic domain; (2) the high-temperaturelow-pressure metamorphism of the continental hanging wall; (3) the early intrusion of boninites into the continental domain.

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The El Salvador Fault Zone (ESFZ) is part of the Central American Volcanic Arc and accommodates the oblique separation movement between the forearc sliver and the Chortis block (Caribbean Plate). In this work, a triclinic transtension model was applied to geological (fault-slip inversion, shape of volcanic calderas), seismic (focal mechanisms) and geodetic (GPS displacements) data to evaluate the characteristics of the last stages of the kinematic evolution of the arc. The El Salvador Fault Zone constitutes a large band of transtensional deformation whose direction varies between N90°E and N110°E. Its dip is about 70° S because it comes from the reactivation of a previous extensional stage. A protocol consisting of three successive steps was followed to compare the predictions of the model with the natural data. The results show a simple shear direction plunging between 20° and 50° W (triclinic flow) and a kinematic vorticity number that is mostly higher than 0.81 (simple-shearing-dominated flow). The direction of shortening of the coaxial component would be located according to the dip of the deformation band. It was concluded that this type of analytical model could be very useful in the kinematic study of active volcanic arcs, even though only information on small deformation increments is available.

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