Timing and nature of formation of the Ios metamorphic core complex, southern Cyclades, Greece

Abstract

We apply low-temperature thermochronology, Rb/Sr geochronology, petrological data, and structural mapping to constrain the timing and kinematics of the Ios metamorphic core complex. Top-to-north extension in the lower plate Headland Shear Zone was active at 18-19 Ma under metamorphic conditions of 475-610 8C and 0.65-1.1 GPa. The South Cyclades Shear Zone/Ios Detachment Fault (SCSZ/IDF) system shows top-to-south extensional shear active at c. 19 Ma at 380-550 8C, with local top-to-north bands. Extensional shear above the SCSZ/IDF is dominantly top-to-south to top-to-SW. PT estimates from an eclogite boudin constrain Eocene high-pressure metamorphism to 430-560 8C and 1.21 + 0.42 GPa to 0.66 + 0.37 GPa. Similar low-temperature thermochronometric ages across Ios demonstrate that ductile extensional movement ceased by c. 15 Ma. Exhumation to shallow crustal levels took place between c. 15 and 9 Ma at cooling rates of up to 120 8C Ma 21 with a slow down to ,20 8C Ma 21 between 12 and 9 Ma, most likely accommodated by extensional slip at rates of c. 3 km Ma 21 along the top-to-SW Coastal Fault System. We propose a model of bivergent extension for exhumation of the Ios core complex between 19 and 9 Ma, with Ios forming a secondary antithetic top-to-south to top-to-SW extensional fault system to a more dominant top-to-north Naxos/Paros detachment system.

Normal faulting on Sifnos and the South Cycladic Detachment System, Aegean Sea, Greece

“…Because the top-tothe-south structures of the Sifnos Detachment largely formed in the brittle crust, the onset of deformation on the Sifnos Detachment probably did not commence long before the oldest ZFT ages of c. 13 Ma. Such an inference is corroborated by detailed work on other detachments in the Aegean Sea region, which showed that these detachments are rather short-lived structures that operated over c. 5-10 Ma (Gessner et al 2001;Ring et al , 2007bBrichau et al 2006Brichau et al , 2007Brichau et al , 2008Brichau et al , 2010Thomson & Ring 2006;Thomson et al 2009). …”

“…1). Research over the last two decades has demonstrated the importance of Miocene low-angle extensional detachments in the formation of the Cyclades horst (Lister et al 1984;Avigad & Garfunkel 1989;Buick 1991;Brichau et al 2006;Thomson et al 2009;Jolivet & Brun 2010;. The detachments are top-to-the-north displacing at the northern end of the Cyclades (Evia, Andros, Tinos, Mykonos, Ikaria, Samos) (Avigad & Garfunkel 1991;Lee & Lister 1992;Kumerics et al 2005;Brichau et al 2007Brichau et al , 2008Mehl et al 2005 referred to a large part of these extensional faults as the North Cycladic Detachment System.…”

“…The detachments are top-to-the-north displacing at the northern end of the Cyclades (Evia, Andros, Tinos, Mykonos, Ikaria, Samos) (Avigad & Garfunkel 1991;Lee & Lister 1992;Kumerics et al 2005;Brichau et al 2007Brichau et al , 2008Mehl et al 2005 referred to a large part of these extensional faults as the North Cycladic Detachment System. In the central Cyclades (Syros, Paros, Naxos, Amorgos, North Ios) the extensional detachments are also top-to-the-north directed (John & Howard 1995;Ring et al , 2009Rosenbaum et al 2007;Seward et al 2009;Thomson et al 2009; Fig. 1).…”

“…In recent years the importance of top-to-the-south displacing detachments at the southern end of the Cyclades horst (South Ios, Sikinos, Serifos, Kithnos) and their role in the opening of the Sea of Crete have become better known (Vandenberg & Lister 1996;Ring et al 2001a;Lenauer et al 2008;Huet et al 2009; Thomson et al 2009;Brichau et al 2010). The earliest of these top-to-the-south extensional faults is the Ios Detachment, with movement at c. 19-18 Ma ).…”

Fast cooling following a Late Triassic metamorphic and magmatic pulse: implications for the tectonic evolution of the Korean collision belt

“…Metamorphic core complexes have been documented in areas marked by crustal extension interpreted as the result of gravitational collapse of a previously thickened crust (Brun, 1999;Buck, 1991;Corti et al, 2003;Jolivet et al, 2013). Their occurrence has been discussed for the North American Cordillera (e.g., Cubley et al, 2013a,b;Dallmeyer et al, 1986;Dokka et al, 1986;Kruckenberg et al, 2008;Norlander et al, 2002;Rey et al, 2009;Vanderhaeghe et al, 2003;Whitney et al, 2013), the eastern Mediterranean (Cyclades, western Turkey-Aegean) (Thomson et al, 2009;Dilek and Altunkaynak, 2009;Le Pourhiet et al, 2012;Jolivet et al, 2013), the Variscan Orogen of Europe (Augier et al, 2015;Brown and Dallmeyer, 1996;Ledru et al, 2001), and the central part of eastern Asia (Charles et al, 2012; Daoudene et al, 2013). Results of thermo-mechanical modeling of the evolution of many metamorphic core complexes show very rapid cooling after near-isothermal decompression under peak temperature conditions (e.g., Le Pourhiet et al, 2012;Rey et al, 2009).…”