Structure and kinematics of Upper Cenozoic extensional detachment on Naxos and Paros (Cyclades Islands, Greece)

Abstract

This paper presents a study of the ductile and brittle deformation on Naxos and Paros islands (Cyclades, Greece). Previous maps and studies of the two islands have shown that a major low‐angle fault zone separates surface rocks above the contact from an initially deep‐seated unit below, showing a metamorphic evolution from high to low pressures. Structural analysis, as well as available stratigraphical, metamorphic, and geochronological data taken together demonstrate that this fault zone is a major normal‐sense detachment zone dipping to the north. Rapid denudation of footwall rocks subsequent to high temperature metamorphism, at an estimated rate of 1.8–9.5 mm/yr, attests for tectonic unroofing during regional‐scale top‐to‐the north ductile shearing. The change from ductile to brittle behavior of the footwall rocks together with a progressive localization of high strain intensity deformations just below the hangingwall is explained by the progressive cooling of the uprisen footwall of the detachment. Mio‐Pliocene clastic sediments in the hangingwall represent the infilling of half grabens opened in between major normal faults that are synthetic to the underlying ductile shear zone. These sediments are as old as (Aquitanian‐25 Ma), or younger than the earliest recognized evidence of ductile extension in the footwall. This provides a minimum age for the onset of extension in the Cyclades, which appears significantly older than maximum ages reported up to now (13–5 Ma). Structural data strongly suggest that the detachment fault was initially rather low dipping (≈35°). An evolutionary model is proposed, in which migmatite domes in the footwall correspond to the uprise of the lower ductile crust between two separating upper crustal blocks, during a process of asymmetric boudinage of the crust. This detachment model applies to a previously thickened continental lithosphere, which then suffers thermal relaxation and weakening, allowing extensional deformation to reach a climax during and subsequent to high temperature metamorphism. In the Cyclades, crustal‐scale extension started after Early Cenozoic thrusting, while the crust was still thick, or less likely, before late underthrusting below the present surface.

Exhumation with a twist: Paleomagnetic constraints on the evolution of the Menderes metamorphic core complex, western Turkey

“…Vertical axis block rotations in the west Aegean region (50°since ∼15 Ma [van Hinsbergen et al, 2005b]) are well established, but have been shown to postdate most of the back-arc extension history , illustrating that the block rotation history of the Aegean is perhaps partly accommodated by, but not directly caused (if at all) by, back-arc extension. Moreover, most of the rotating region lies to the northwest of the Cycladic and south Aegean crystalline complexes where much of the Aegean extension was accommodated [Gautier et al, 1993;Fassoulas et al, 1994;Gautier and Brun, 1994;Jolivet et al, 1994bJolivet et al, , 1996Ring et al, 2003b;Jolivet and Brun, 2010]. Although relations between rotation and exhumation in the Rhodope core complex have been postulated [Brun and Sokoutis, 2007;van Hinsbergen et al, 2008a], the region that could have experienced major extension-related rotations in the west lies offshore central or southwestern Greece (Figure 1).…”

Kinematic reconstructions and magmatic evolution illuminating crustal and mantle dynamics of the eastern Mediterranean region since the late Cretaceous

“…5-8.5 kbar, 500-700°C) and associated migmatites also developed in the central Cyclades, such as in the Naxos, Paros, Mykonos and Ikaria islands [Jansen and Schuiling, 1976;Lister et al, 1984;Urai et al, 1990;Keay et al, 2001;Vanderhaeghe, 2004;Duchêne et al, 2006;Kruckenberg et al, 2011;Beaudoin et al, 2015;Laurent et al, 2015]. Exhumation of these rocks as MCCs was accommodated during the Oligocene-Miocene by several ductile-brittle detachment systems (figures 4 and 6) comprising the top-to-the NE North Cycladic Detachment System (NCDS) [Faure et al, 1991;Lee and Lister, 1992;Gautier and Brun, 1994;Mehl et al, 2005Mehl et al, , 2007Brichau et al, 2007Brichau et al, , 2008Jolivet et al, 2010a], the top-to-the N Naxos/Paros Extensional Fault System (NPEFS) [Urai et al, 1990;Gautier et al, 1993;Brichau et al, 2006;Seward et al, 2009;Bargnesi et al, 2013] and the top-to-the SW West Cycladic Detachment System (WCDS) [Grasemann and Petrakakis, 2007;Brichau et al, 2010;Iglseder et al, 2011;Grasemann et al, 2012]. The minimum offset of these extensional structures is estimated at 60-100 km for the NCDS [Jolivet et al, 2004a;Brichau et al, 2008] and ~50 km for the NPEFS (figure 3) [Brichau et al, 2006].…”

“…Further south, Oligocene-early Miocene exhumation of MCCs mainly in greenschist-facies conditions occurred in the Cyclades and the Menderes massif [Altherr et al, 1982;Lister et al, 1984;Gautier and Brun, 1994;Jolivet et al, 1994;Bozkurt and Oberhänsli, 2001;Vanderhaeghe and Teyssier, 2001;Ring et al, , 2010Catlos and Çemen, 2005;Jolivet & Brun, 2010], associated with additional HT-MP metamorphism affecting the northern Menderes massif and the central Cyclades in the Oligocene and early Miocene, respectively (figures 8n-r and 11) [Jansen and Schuiling, 1976;Lister et al, 1984;Gautier et al, 1993;Keay et al, 2001;Catlos and Çemen, 2005;Duchêne et al, 2006;Bozkurt et al, 2010;Beaudoin et al, 2015]. In the Cyclades, the NCDS accommodated this exhumation since the Oligocene (figures 9 and 11) [Faure et al, 1991;Lee and Lister, 1992;Brichau et al, 2007Brichau et al, , 2008Jolivet et al, 2010a] while the NPEFS and the WCDS became active in the early Miocene [Urai et al, 1990;Gautier et al, 1993;Vanderhaeghe, 2004;Brichau et al, 2006;Seward et al, 2009;Iglseder et al, 2011;Grasemann et al, 2012].…”

“…In the Cyclades, the NCDS accommodated this exhumation since the Oligocene (figures 9 and 11) [Faure et al, 1991;Lee and Lister, 1992;Brichau et al, 2007Brichau et al, , 2008Jolivet et al, 2010a] while the NPEFS and the WCDS became active in the early Miocene [Urai et al, 1990;Gautier et al, 1993;Vanderhaeghe, 2004;Brichau et al, 2006;Seward et al, 2009;Iglseder et al, 2011;Grasemann et al, 2012]. Syntectonic sediments started to be deposited in the hanging wall of these extensional structures [Photiades, 2002;Sánchez-Gómez et al, 2002;Kuhlemann et al, 2004;Lecomte et al, 2010;Laurent et al, 2015].…”

“…In the Cyclades, for example, three large-scale structures with wellconstrained kinematics and timing have been considered: the NCDS cropping out in the Tinos, Mykonos and Ikaria islands [Lee and Lister, 1992;Gautier and Brun, 1994;Mehl et al, 2005;Brichau et al, 2007;Jolivet et al, 2010a;Lecomte et al, 2010], the NPEFS cropping out in the Naxos and Paros islands [Lister et al, 1984;Urai et al, 1990;Gautier et al, 1993;Seward et al, 2009;Bargnesi et al, 2013] and the WCDS cropping out in the Serifos island (figures 3 and 6) [Grasemann and Petrakakis, 2007;Brichau et al, 2010;Iglseder et al, 2011; A C C E P T E D M A N U S C R I P T…”