Interactions of plutons and detachments, comparison of Aegean and Tyrrhenian granitoids

Abstract

Abstract. Back-arc extension superimposed on mountain belts leads to distributed normal faults and shear zones, interacting with magma emplacement in the crust. The composition of granitic magmas emplaced at this stage often involves a component of crustal melting. The Miocene Aegean granitoids were emplaced in metamorphic core complexes (MCC) below crustal-scale low-angle extensional shear zones and normal faults. Intrusion in such contexts interacts with extension and shear along detachments, from the hot magmatic flow within the pluton root zone to the colder ductile and brittle deformation along the detachment. A comparison of the Aegean plutons with the Elba Island MCC in the back-arc region of the Apennines subduction shows that these processes are characteristic of pluton-detachment interactions in general and we discuss a conceptual emplacement scenario, tested by numerical models. Mafic injections within the partially molten lower crust above the hot asthenosphere trigger the ascent within the core of the MCC of felsic magmas, controlled by the strain localization on persistent crustal scale shear zones at the top that guide the ascent until the brittle ductile transition is reached during exhumation. Once the system definitely enters the brittle regime, the detachment and the upper crust are intruded while new detachments migrate upward and in the direction of shearing. Numerical models reproduce the geometry and the kinematic evolution deduced from field observations.

Reply on CC2

“…The case of the Tuscan Archipelago is partly similar with the geothermal fields of Larderello and Monte Amiata developed above recent shallow plutons in a context of asymmetric extension with top-to-the east low-angle shear zones (Jolivet et al, 1998;Brogi et al, 2003;Rochira et al, 2018). The Monte Capanne and Porto Azzuro plutons on Elba are associated with hydrothermal activities and mineralization (Maineri et al, 2003;Rossetti and Tecce, 2008;Liotta et al, 2015) that make them good exhumed analogues of active geothermal fields, a situation that is found also in the Cyclades with the mineralizations observed on Mykonos or Serifos in the Cyclades (Salemink, 1985;St. Seymour et al, 2009;Menant et al, 2013;Tombros et al, 2015;Ducoux et al, 2016).…”

“…The eastern part of the island shows granitic dykes emanating from the buried younger Porto Azzuro pluton intruding the Calamiti schists complex (Complex I, figure 6) (Daniel and Jolivet, 1995;Maineri et al, 2003;Musumeci and Vaselli, 2012). Here too, evidence for topto-the east shearing at the time of intrusion have been described (Daniel and Jolivet, 1995) (figure 7).…”

“…Arrows show stretching lineations and sense of shear and black bars on the Tinos and Serifos plutons shows the direction of the magnetic lineation. (Grasemann and Petrakakis, 2007;Berger et al, 2013;Scheffer et al, 2016), the plutons crop out in the core of MCCs exhumed by north-dipping detachments, such as the North Cycladic Detachment System (NCDS) (Gautier and Brun, 1994b, a; or the Naxos-Paros Fault System (NPFS) (Urai et al, 1990;Gautier et al, 1993;Vanderhaeghe, 2004;Bargnesi et al, 2013;Cao et al, 2017). The detachments upper plate is made of the Upper Cycladic Nappe, a remnant of the Pelagonian domain, made of greenschists-facies metabasites or serpentinite with, in a few cases, early to late Miocene sediments deposited during extension (Angelier et al, 1978;Sanchez-Gomez et al, 2002;Kuhlemann et al, 2004;Menant et al, 2013).…”

“…(Grasemann and Petrakakis, 2007;Berger et al, 2013;Scheffer et al, 2016), the plutons crop out in the core of MCCs exhumed by north-dipping detachments, such as the North Cycladic Detachment System (NCDS) (Gautier and Brun, 1994b, a; or the Naxos-Paros Fault System (NPFS) (Urai et al, 1990;Gautier et al, 1993;Vanderhaeghe, 2004;Bargnesi et al, 2013;Cao et al, 2017). The detachments upper plate is made of the Upper Cycladic Nappe, a remnant of the Pelagonian domain, made of greenschists-facies metabasites or serpentinite with, in a few cases, early to late Miocene sediments deposited during extension (Angelier et al, 1978;Sanchez-Gomez et al, 2002;Kuhlemann et al, 2004;Menant et al, 2013). The MCCs are made of various units of the Cycladic Blueschists, more or less retrograded in the greenschist-facies, or the Cycladic basement, showing HT-LP metamorphic facies and even anatectic conditions on several islands, such as Naxos, Paros, Mykonos or Ikaria (Buick and Holland, 1989;Urai et al, 1990;Buick, 1991;Keay et al, 2001;Duchêne et al, 2006;Seward et al, 2009;Kruckenberg et al, 2011;Beaudoin et al, 2015;Laurent et al, 2015;Rabillard et al, 2015;.…”

“…The Monte Capanne and Porto Azzuro plutons on Elba are associated with hydrothermal activities and mineralization (Maineri et al, 2003;Rossetti and Tecce, 2008;Liotta et al, 2015) that make them good exhumed analogues of active geothermal fields, a situation that is found also in the Cyclades with the mineralizations observed on Mykonos or Serifos in the Cyclades (Salemink, 1985;St. Seymour et al, 2009;Menant et al, 2013;Tombros et al, 2015;Ducoux et al, 2016). Pourhiet designed the modeling procedure and ran the numerical experiments.…”