Emplacement of the Aya Variscan granitic pluton (Basque Pyrenees) in a dextral transcurrent regime inferred from a combined magneto-structural and gravimetric study

Abstract

Magmatic structure, three-dimensional shape and emplacement mode of the Aya pluton, Variscan Pyrenees, have been studied by combining magneto-structural and gravimetric studies. The Aya pluton displays a fabric, acquired using the anisotropy of magnetic susceptibility technique, comparable to that of several other plutons in the Pyrenees, with shallow-plunging lineations and steep foliations trending E-W and NE-SW, forming an S pattern in map view. Gravity modelling was used to determine the probable root of the pluton, directly below the most basic (gabbro-dioritic) facies. This has a funnel shape, with an E-W-trending elliptical horizontal section and a maximum depth of 3.5 km. These different data demonstrate that this pluton was synorogenically emplaced during the main D2 Variscan tectonic phase, in a dextral transcurrent regime.

Structural and magnetic fabric study of the Marimanha granite (Axial Zone of the Pyrenees)

“…This kind of geometry has been invoked for other Pyrenean granites emplaced in the low-grade upper crust from gravity studies (Olivier et al 1999). Other authors (Gleizes et al 2001) infer from structural observations, granite bodies with their length/height ratio [ 1 that also point to laccolite geometries.…”

“…However, some authors have claimed for the coeval development of this magmatism with metamorphism and the main Variscan deformation (e.g., Carreras and Druguet 1994;Leblanc et al 1996;Evans et al 1998). In this sense, the AMS studies developed in these granites have provided evidences about their emplacement under a transpressive regime, which has been related to the D2 Variscan deformation phase (Leblanc et al 1996;Evans et al 1998;Gleizes et al 1998aGleizes et al , b, 2001Gleizes et al , 2006Olivier et al 1999;Román-Berdiel et al 2004Auréjac et al 2004). U-Pb ages published in the last decade for the Pyrenean granites indicate that Variscan plutonism in the Pyrenees is essentially Late Carboniferous in age (Romer and Soler 1995;Paquette et al 1997;Roberts et al 2000;Gleizes et al 2006).…”

“…Many structural studies about the Variscan granites bodies in the Axial Zone of the Pyrenees have been carried out in the last decade (Leblanc et al 1996;Evans et al 1998;Gleizes et al 1998aGleizes et al , b, 2001Gleizes et al , 2006Olivier et al 1999;Román-Berdiel et al 2004Auréjac et al 2004). These studies have demonstrated and corroborated that the tectonic regime during granite emplacement is a dextral transpression, and their emplacement is produced in relation with the main Variscan phase in the Pyrenees (the so-called D2) (Zwart 1986).…”

Structure of volcano plumbing systems: A review of multi-parametric effects

“…Several examples, mainly based on field data, indicate that melt upwelling in the deeper parts of plumbing systems was channelled along transcurrent zones (Mitjavila et al, 1997;Olivier et al, 1999;Rossetti et al, 2000;Rosenberg, 2004;Weinberg et al, 2004;Marcotte et al, 2005). This is mainly related to two facts:…”

Volcanism in Reverse and Strike-Slip Fault Settings

“…The focus of this review is convergent margins and intra-plate volcanism; it does not address the relationship between compressional tectonics and plutonism, which has been the focus of a great deal of recent studies (e.g. Olivier et al, 1999;Rosenberg, 2004;Weinberg et al, 2004, and references therein), nor does it address the relationship between strike-slip tectonics and volcanism in ocean ridge or other divergent margin settings.…”