Exhumation, doming and slab retreat in the Betic Cordillera (SE Spain):in situ⁴⁰Ar/³⁹Ar ages andP–T–d–tpaths for the Nevado‐Filabride complex

Abstract

The combination of metamorphic petrology tools and in situ laser 40 Ar/ 39 Ar dating on phengite (linking time of growth, compositions and P-T conditions) enables us to identify a detailed P-T-d-t path for the still debated tectonometamorphic evolution of the Nevado-Filabride complex and infer new geodynamic-scale constraints. Our data show an isothermal decompression (at 550°C) from 20 kbar for the Be´dar-Macael unit and 14 kbar for the Calar Alto unit down to c. 3-4 kbar for both units at 2.8 mm year )1 . At 22-18 Ma, this first part of the exhumation is followed by a final exhumation at 0.6 mm year )1 along a high-temperature low-pressure (HTLP) gradient of c. 60°C km )1 . The age of the peak of pressure is not precisely known but it is shown that it is around 30 Ma and possibly older, which is at variance with recent models suggesting a younger age for high-pressure (HP) metamorphism. Most of the exhumation is related to late-orogenic extension from c. 30 to 22-18 Ma. Thus the formation of the main ductile extensional shear zone, the Filabres Shear Zone (FSZ), occurred at 22-18 Ma and is clearly associated with a top-to-the-west shear sense once the FSZ is well localized. The transition from ductile to brittle then occurred at c. 14 Ma. The final exhumation, accommodated by brittle deformation, occurred from c. 14 to 9 Ma and was accompanied, from 12 to 8 Ma, by the formation of nearby extensional basins. The duration of the extensional process is c. 20 Myr which argues in favour of a progressive slab retreat from c. 30 to 9 Ma. The change in the shape of the P-T path at 22-18 Ma together with strain localization along the main top-to-the-west shear zone suggests that this date corresponds to a change in the direction of slab retreat from southwards to westwards.

From ductile to brittle, late- to post-orogenic evolution of the Betic Cordillera: Structural insights from the northeastern Internal zones

“…On the other hand, the recognition of low-angle extensional shear zones able to exhume deep-seated metamorphic rocks sometimes equilibrated in eclogitic conditions rather suggests a late-orogenic collapse [Platt and Vissers, 1989;García-Dueñas et al, 1992;Jabaloy et al, 1993;Vissers et al, 1995;Martínez-Martínez et al, 2002Augier et al, 2005b;Agard et al, 2011] active as recently as the Late-Miocene [Monié et al, 1994;Johnson et al, 1997;Augier et al, 2005c;Platt et al, 2005;Vázquez et al, 2011]. In parallel, extensional structures, with variable kinematics have also been described in the onshore basins [e.g.…”

“…While the Malaguide complexe is usually devoid of alpine metamorphic imprint, the Alpujárride and the NevadoFilábride complexes both contain HP relics related to subduction and crustal thickening phases [e.g. Goffé et al, 1989;Gómez-Pugnaire and Fernández-Soler, 1987;Azañón and Crespo-Blanc, 2000;Puga et al, 2002;Augier et al, 2005a;2005c]. The Alpujárride metamorphic complex is indeed characterized by the widespread occurrence of Fe-Mg-carpholite, kyanite, Mg-rich chloritoid or aragonite [Goffé et al, 1989;Azañón and Goffé., 1997;Azañón et al, 1998] yielding locally peak-conditions of the order of 10-12 kbar for 450-500 o C [Azañón and Crespo-Blanc, 2000].…”

“…Martínez-Martínez et al, 2004]. Metamorphic domes currently correspond to structural culminations [Vissers et al, 1995;Martínez-Martínez and Azañón, 1997] of three metamorphic complexes, from bottom to top the Nevado-Filábride, Alpujárride and Malaguide complexes, separated from each other by crustal-scale extensional shear zones [Platt, 1986;García-Dueñas et al, 1992;Lonergan and Platt, 1995;Platt et al, 2005;Augier et al, 2005c]. While the Malaguide complexe is usually devoid of alpine metamorphic imprint, the Alpujárride and the NevadoFilábride complexes both contain HP relics related to subduction and crustal thickening phases [e.g.…”

The Tell-Rif orogenic system (Morocco, Algeria, Tunisia) and the structural heritage of the southern Tethys margin

“…They revealed large-scale extension associated with HT metamorphism (among others Fernandez et al, 2016;Negro et al, 2006;Platt and Whitehouse, 1999) and formation of crustal scale detachements (Augier et al, 2005;Caby et al, 2001;Crespo-Blanc et al, 1994;Jabaloy et al, 1993;Platt et al, 2005) producing deep unroofing during the Late OligoceneEarly Miocene, within the AlKaPeCa domain (Bruguier et al, 2009;Michard et al, 2006;Monié et al, 1992;Monié et al, 1994;Platt et al, 2003). This Miocene signal shows diachronous stages between the "AlKa" and "PeCa" domains, being older for the Peloritani and Calabria than for Alboran and the Kabylie basement (Michard et al, 2006;Platt et al, 2013 for the Betics-Rif-Tell data; Heymes et al, 2010;Rossetti et al, 2004Rossetti et al, , 2010 for the Peloritani-Calabria data).…”

Deformation history of the eclogite‐ and jadeitite‐bearing mélange from North Motagua Fault Zone, Guatemala: insights in the processes of a fossil subduction channel

“…It can be calculated with a Monte Carlo technique (Lieberman and Petrakakis 1991;Vidal and Parra 2000), which lead to the estimation of the maximum permissible scatter (sP max and sT max ) of any P-T estimate. The estimated sP max and sT max values for assemblages including chlorite and phengite are 0.08 GPa and 258C, respectively (Vidal and Parra 2000;Trotet et al 2001a;Parra et al 2002b;Augier et al 2005;Rimmelé et al 2005).…”