Lateral variations of pressure-temperature evolution in non-cylindrical orogens and 3-D subduction dynamics: the Betic-Rif Cordillera example

Abstract

<p>Orogens closely linked to 3-D subduction dynamics are frequently non-cylindrical and the Mediterranean region is a perfect natural laboratory to observe several of them, as well as their interactions. Through the succession of extension, subduction and sometimes collision events, the kinematic reconstructions of such orogens can be difficult and the subject of active debates. The internal zones are often non-consensual, especially when their long-term Pressure-Temperature-time-deformation (P-T-t-d) evolutions are studied. This complexity is mostly due to pre-orogenic inheritance or complex interactions between the subducting lithosphere, the overriding plate and the asthenosphere. All these elements are described and documented in Mediterranean orogens, i.e., a complex shape of the Eurasian and African margins in pre-orogenic times and a complex slab retreat and tearing dynamics. Their 3-D geometry results in strongly arcuate belts, such as the Betic-Rif Cordillera, located in the westernmost part of the Mediterranean region.</p><p>Focused on the Internal Zones of the Betic-Rif Cordillera and based on recent findings (Orogen Project framework), a synthesis of the tectono-metamorphic evolution shows the relations in space and time between tectonic and P-T evolutions. The reinterpretation of the contact between peridotite massifs and Mesozoic sediments as an extensional detachment leads to a discussion of the geodynamic setting and timing of mantle exhumation. Based on new <sup>40</sup>Ar/<sup>39</sup>Ar ages in the Alpujárride Complex (metamorphic formations of the Betic Internal Zones) and a discussion of published ages in the Nevado-Filabride Complex (metamorphic formations of the Betic Internal Zones), we conclude that the age of the HP-LT metamorphism is Eocene in all the Internal Zones. A first-order observation is the contrast between the well-preserved Eocene HP-LT blueschists-facies rocks of the Eastern Alpujárride-Sebtide Complex and the younger HT-LP conditions reaching partial melting recorded in the Western Alpujárride. We propose a model where the large longitudinal variations in the P-T evolution are mainly due to (i) differences in the timing of subduction and exhumation, (ii) the nature of the subducting lithosphere and (iii) a major change in subduction dynamics at ~20 Ma associated with a slab-tearing event.</p>

Timing of Alpine Orogeny and Postorogenic Extension in the Alboran Domain, Inner Rif Chain, Morocco

“…Considering this uncertainty, these closure temperatures are slightly below or similar to the peak metamorphic temperature of ∼300°C during the D 1 /M 1 event and could indicate that the ages of 37‐34 Ma represent the end of D 1 /M 1 (re)crystallization processes and the beginning of exhumation of Tizgarine unit. These ages are consistent with the 40 Ar/ 39 Ar phengite age of 38 Ma recently reported for HP/LT rocks of the Alpujarride units in the Betic Cordilleras (Bessière et al., 2021).…”

“…The late Eocene (∼37‐34 Ma) ages in the TZ unit of the Upper Sebtides provide the first absolute time constraint for development of the Alpine D 1 /M 1 orogenic fabric in the Alboran Domain of the Rif. This scenario is in line and supports the Eocene timing already proposed for the Betic counterpart (Augier et al., 2005; Bessière et al., 2021; Li & Massonne, 2018; Massonne, 2014; Platt et al., 2005). Significantly, the late Eocene timing for the Alpine D 1 /M 1 event is also compatible with the tectonostratigraphic reconstruction of the Ghomaride‐Malaguide complex, where the same time period for the Alpine orogenic event has been proposed (Chalouan et al., 2008; Lonergan, 1993; Serrano et al., 2006).…”

“…In the Betics, Eocene ages (ca. 50‐40 Ma) have been proposed based on white mica 40 Ar/ 39 Ar geochronology on both the Alpujarrides (Bessière et al., 2021; Platt et al., 2005) and Nevado‐Filabrides (Augier et al., 2005), recently confirmed by electron microprobe dating of monazite from both the Alpujarride (Massonne, 2014) and Nevado‐Filabride (Li & Massonne, 2018) complexes. Nonetheless, U‐Pb zircon (López Sánchez‐Vizcaíno et al., 2001), Lu‐Hf garnet (Platt et al., 2006) and Rb/Sr multimineral isochron (Kirchner et al., 2016) geochronological data indicate a Miocene age (18‐14 Ma) for continental subduction in the Nevado‐Filabrides Complex.…”

“…Consequently, there are large uncertainties in the tectonic reconstructions used to frame the geodynamic environment responsible for orogeny and crustal thickening in the region. This is clearly evident in the Western Mediterranean (Figure 1), where a widespread early Miocene thermal event is documented across the metamorphic hinterland of the Betic‐Rif orogen (the so‐called Alboran Domain; see Bessière et al., 2021 for a recent review) and debate continues in relation to the Alpine tectonometamorphic evolution of the Alboran Domain, with regard to: (a) the geodynamic scenario during consumption of the Neotethys ocean and formation of the Apennine‐Maghrebian‐Betic orogen, with models involving either double or single subduction scenarios (see e.g., Bessière et al., 2021; Carminati et al., 2012; Daudet et al., 2020; Faccenna et al., 2004; Handy et al., 2010; Lacombe & Jolivet, 2005; Leprêtre et al., 2018; Malusà et al., 2015; Molli & Malavieille, 2011; Pedrera et al., 2020; Platt et al., 2006; Romagny et al., 2020; Rosenbaum et al., 2002; van Hinsbergen et al., 2020; Vergés & Fernàndez, 2012; Williams & Platt, 2018); (b) the age of crustal thickening and thinning, including the role of structural inheritance (e.g., Acosta‐Vigil et al., 2014; Augier et al., 2005; Gueydan et al., 2015; Homonnay et al., 2018; Li & Massonne, 2018; Massonne, 2014; Michard et al., 1997; Montel et al., 2000; Platt & Vissers, 1989; Platt & Whitehouse, 1999; Platt et al., 1998, 2005, 2006; Rossetti et al., 2010, 2020; Ruiz Cruz & Sanz De Galdeano, 2013; Sánchez‐Navas et al., 2014, 2017; Sánchez‐Rodríguez & Gebauer et al., 2000; Zeck & Whitehouse, 2002; Zeck & Williams, 2001); (c) the metamorphic conditions prevailing during late‐orogenic extension (e.g., Azañón et al., 1998; Michard et al., 2006; Platt et al., 1998, …”

“…Most of the Alpine geochronological and thermochronological data available for the Alboran Domain cluster, irrespective of the method, in the early Miocene (24‐18 Ma time interval; see reviews in: Acosta‐Vigil et al., 2014; Bessière et al., 2021; Gómez‐Pugnaire et al., 2019; Homonnay et al., 2018; Michard et al., 2006; Platt et al., 2013; Rossetti et al., 2010, 2020; van Hinsbergen et al., 2020; Vergés & Fernàndez, 2012; Williams & Platt, 2018), obscuring the early orogenic tectonometamorphic fabrics. Consequently, the timing of the Alpine crustal thickening phase (D 1 deformation and M 1 metamorphism, D 1 /M 1 event) and the associated HP/LT subduction‐zone metamorphism in the Western Mediterranean is still largely debated.…”