Vertical-axis rotations accommodated along the Mid-Cycladic lineament on Paros Island in the extensional heart of the Aegean orocline (Greece)

Abstract

The Aegean-west Anatolian orocline formed due to Neogene opposite rotations of its western and eastern limbs during opening of the Aegean back-arc basin. Stretching lineations in exhumed metamorphic complexes in this basin mimic the regional vertical-axis rotation patterns and suggest that the oppositely rotating domains are sharply bounded along a Mid-Cycladic lineament, the tectonic nature of which is enigmatic. Some have proposed this lineament to be an extensional fault accommodating orogen-parallel extension, while others have considered it to be a transform fault. The island of Paros hosts the only exposure of the E-to NE-trending lineations characterizing the NW Cyclades and the N-trending lineations of the SE Cyclades. Here, we show new paleomagnetic results from isotropic, ca. 16 Ma granitoids that intruded both domains and demonstrate that the trend difference resulted from post-16 Ma ~90° clockwise and 10° counterclockwise rotation of the NW and SE blocks, respectively. We interpret the semiductile to brittle, low-angle, SE-dipping Elitas shear zone that accommodated this rotation difference to reflect the Mid-Cycladic lineament. We conclude a two-stage exhumation history for Paros that is consistent with regional Aegean reconstructions. Between ca. 23 and 16 Ma, the metamorphic rocks of Paros were exhumed from amphibolite-facies to greenschist-facies conditions along a top-to-theN detachment. The Elitas shear zone then started to exhume the northwestern, clockwiserotating domain from below the southeastern, counterclockwise rotating domain since 16 Ma. From this, we infer that the Mid-Cycladic lineament is an extensional shear zone, consistent with geometric predictions that Aegean oroclinal bending was accommodated by orogennormal and orogen-parallel extension.

Multiphase boudinage: a case study of amphibolites in marble in the Naxos migmatite core

“…Jolivet et al, 2013;Philippon et al, 2011), or normal faulting in an overall extensional regime (Gautier et al, 1999;Hinsbergen and Schmid, 2012) including vertical axis rotations in the footwall (Malandri et al, 2017). Field evi-dence is controversial, as there seems that there is neither support for a major detachment (Brun et al, 2016;Jolivet et al, 2015;Philippon et al, 2014) nor is strike-slip faulting observed on Paros, where the Mid-Cycladic Lineament might be exposed (Malandri et al, 2017;Walcott and White, 1998a). Additional complexity is added due to interaction of slab roll-back with westward migration of the Anatolian Plate since ∼ 11 Ma Ring et al, 2010).…”

“…Combining field data with microstructural analysis we link the different boudin generations to rheology and metamorphic conditions. Furthermore, since the amphibolites are older than the pegmatites, they record a longer deformation history and provide insights into the tectonic evolution of the Aegean, specifically the nature of east-west shortening of the domain, recognized by several authors (Urai et al, 1990;Ring and Layer, 2003;Hinsbergen and Schmid, 2012;Menant et al, 2013;Malandri et al, 2017) .…”

Multiphase Boudinage: a case study of Amphibolites in Marble in the Naxos Migmatite core

“…Combining field data with microstructural analysis we link the different phases of deformation to metamorphic conditions on the retrograde path. In addition to insights into the rheological and deformational evolution of the lower metamorphic levels of the Aegean metamorphic core complex, this study may help to constrain the nature of East-West shortening of the domain, recognized by several authors (Urai et al, 5 1990;Ring and Layer, 2003;Jolivet and Brun, 2010;Hinsbergen and Schmid, 2012;Menant et al, 2013;Malandri et al, 2017) .…”

“…Jolivet et al, 2013;Philippon et al, 2011), or normal faulting in an overall extensional regime (Gautier et al, Solid Earth Discuss., https://doi.org /10.5194/se-2017- Hinsbergen and Schmid, 2012) including vertical axis rotations in the footwall (Malandri et al, 2017). Field evidence is controversial, as there seems neither support for a major detachment (Brun et al, 2016;Jolivet et al, 2015;Philippon et al, 2014), nor is strike-slip faulting observed on Paros, where the Mid Cycladic Lineament might be exposed (Malandri et al, 2017;Walcott and White, 1998a). Additional complexity is added due to interaction of slab roll-back with westward migration of the Anatolian Plate since ~11 Ma (Jolivet et al, 2013;Ring et al, 2010).…”

“…Earlier E-W shortening in the Aegean may be explained by the proto-North Anatolian Fault, as witnessed by ductile shearing in Turkey, that might have been linked to activity along the Mid Cycladic Lineament (Philippon et al, 2014 and references therein). Alternatively, E-W shortening may be partly independent of the North Anatolian Fault and related to crustal attenuation and viscoplastic deformation during upward flow and partial melting 10 of the crust and mantle in an overall extensional regime (Kruckenberg et al, 2010Malandri et al, 2017). This scenario does not exclude late-stage shortening related to movement of the North Anatolian Fault, but most strain is accommodated earlier, locally constrained to the thermal domes.…”