Timing and modes of granite magmatism in the core of the Alboran Domain, Rif chain, northern Morocco: Implications for the Alpine evolution of the western Mediterranean

Abstract

The Betic‐Rif orogen forms the western termination of the Alpine orogenic system in the Mediterranean region. The precise timing, structural evolution, and distribution of high‐grade metamorphic units (Alpine versus pre‐Alpine) in the inner zones of the orogen (Alboran Domain) remain controversial issues. In this paper we report occurrence of distinct generations of peraluminous granitic bodies intruded within Beni Bousera peridotites and their amphibolite‐to‐granulite facies envelope, in the core of the Alboran Domain of the Rif chain (northern Morocco). These granitic bodies are central to the reconstruction of the high‐grade evolution of the Alboran Domain because they provide first‐order structural markers to assess the P‐T‐t deformation history of the high‐grade terranes. Here we document the petrography and structural relationships with the host rocks and constrain the timing of granite emplacement using laser ablation–inductively coupled plasma–mass spectrometry U‐Pb zircon and/or monazite dating, complemented by 40Ar/39Ar dating. The results indicate that granite emplacement occurred in two major episodes of anatectic magmatism, during the Hercynian (circa 300 Ma) and Alpine (circa 22 Ma) periods, respectively. These data (1) provide conclusive evidence for an important phase of Hercynian magmatism and high‐grade metamorphism in the Alboran Domain and (2) permit a revaluation of the significance of the high‐grade early Miocene event documented in the Alboran Domain in terms of a late stage, thermal pulse that reworked a polymetamorphic (Hercynian and Alpine) nappe pile. These results provide new constraints for construction of a feasible tectonometamorphic model for the Alpine evolution of the western Mediterranean.

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

“…Fernandez et al, 2016;Mahdjoub et al, 1997;Montel et al, 2000;Peucat and Bossière, 1981;Saadallah and Caby, 1996;Sánchez-Gómez et al, 1999;Zeck, 1999). However, it is mainly characterized by the signature of the Alpine events, ranging from HP-LT for the earliest events (Bruguier et al, 2017;Caby et al, 2014;Mahdjoub et al, 1997) to HT-LP for the most recent ones during Early to Middle Miocene (Fernandez et al, 2016;Michard et al, 2006;Platt et al, 2013;Rossetti et al, 2010 with references therein). The Edough massif presents a peculiar case.…”

“…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).…”

“…11). The Oligocene-Early Miocene event either fossilized or reworked in extension many of the former compressional structures (among others, see for the Pyrenees: Fillon and van der Beek, 2012; Vergés and García-Senz, 2001; for the Catalan Range: Roca, 1994; for the Baleares: Etheve et al, 2016;Roca, 1994; for AlKaPeCa: Aïte and Gélard, 1997;Arab et al, 2016;Caby et al, 2001;Comas et al, 1999;Heymes et al, 2008Heymes et al, , 2010Rossetti et al, 2004Rossetti et al, , 2010Saadallah and Caby, 1996; for the Atlas belt: Bracène and Frizon de Lamotte, 2002;Ghandriche, 1991;Khomsi et al, 2016;Muratet, 1991;Torbi and Gélard, 1994). …”

The composition of nanogranitoids in migmatites overlying the Ronda peridotites (Betic Cordillera, S Spain): the anatectic history of a polymetamorphic basement

“…Zeck et al 1989;Platt et al 2013). Conversely, schist, migmatites and mylonitic gneisses are preCarboniferous and represent a polymetamorphic basement affected by at least the Variscan and Alpine orogenies (Montel et al 2000;Whitehouse and Platt 2003;Rossetti et al 2010;Massonne 2014). Rocks from all levels in the crustal section seem to record nearly isothermal decompression paths, from 1.4-1.2 kbar to 0.6-0.4 GPa at 750-850 ºC in the case of the mylonitic gneisses located at the contact with the Ronda peridotites (Torres-Roldán 1981;Argles et al 1999;Platt et al 2003;Barich et al 2014).…”

Late Palaeozoic to Triassic formations unconformably deposited over the Ronda peridotites (Betic Cordilleras): Evidence for their Variscan time of crustal emplacement

“…Chalouan et al (2008) discussed the possible ages of the exhumation of the peridotites without presenting a clear conclusion. Rossetti et al (2010) reported the occurrence of distinct generations of peraluminous granitic bodies intruded within Beni Bousera peridotites and the overlying crustal rocks during the Variscan (~300 Ma) and the Alpine (~22 Ma) periods, respectively. Finally, Ruiz Cruz et al (2011 and , 2103 argued in favour of a pre-Mesozoic emplacement of the peridotites in the Jubrique and Ceuta zones, using petrological criteria and recent zircon dating.…”