Granite intrusion in a metamorphic core complex: The example of the Mykonos laccolith (Cyclades, Greece)

Abstract

The Aegean domain is a well-suited place to study the formation of metamorphic core complex (MCC) and to investigate the role of syn-tectonic granites on their development. In the northern Cyclades, the Mykonos-Delos-Rhenia MCC is characterized by the intrusion of a kilometer-scale Late Miocene pluton of I-type granitoids within a migmatitic gneiss dome. New combined AMS (anisotropy of magnetic susceptibility) and microstructural studies on the Mykonos granitoids together with recently published thermochronological data allow us to use the granitoids as strain markers.The Mykonos granitoids form a laccolith-like intrusion with a N70°E long axis. The laccolith is strongly asymmetric with an outlying root zone to the SW and a major body mainly developed to the NE. The laccolith construction is due to successive pulses of more or less differentiated magma that intruded the Cycladic Blueschist Unit. The attitude of stretching markers suggests an important (about 60°) vertical-axis local rotation phenomenon in the cycladic upper crust during the exhumation of the Mykonos MCC. Structural data suggest a four-stage evolution of the Mykonos MCC: (i) a first stage characterized by flat shearing toward the N-NE and by the formation of a domal structure in migmatitic paragneisses with multi-scale generation of folds with axes either perpendicular or parallel to the regional stretching, as a result of the interplay between regional N20°E-directed extension and EW shortening; (ii) a second stage marked by the emplacement of the Mykonos laccolith at 13.5 ± 0.3 Ma at the top of the migmatitic paragneisses; (iii) the third stage corresponding to the development of protomylonitic foliations and lineations in the whole laccolith in high to medium temperature conditions; and (iv) the late stage marked by an acceleration of the exhumation of the Mykonos MCC. This exhumation was accommodated by important rotations of upper crustal blocks. During the end of the exhumation processes, around 10 Ma, deformation localized at the top of the laccolith in semi-ductile conditions and then in brittle conditions in the major detachment plane.Our study shows that the Cycladic plutonism event had no role on the initiation of the MCC. However, the geometry of the Mykonos intrusion supports that the magmas are "sucked" into the direction of regional extension and that the intrusion of magmas has caused an acceleration of the last stages of the MCC development. This acceleration was marked by a very fast exhumation of the laccolith after its emplacement.

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

“…Oligocene-early Miocene [Black et al, 2013] and in the Menderes massif and the Cyclades in the Miocene (figure 5) [Faure and Bonneau, 1988;Altherr and Siebel, 2002;Piper, 2006, 2007;Iglseder et al, 2009;Denèle et al, 2011;Laurent et al, 2015;. Migmatites associated with S-type granites have also been described in the cores of these metamorphic domes [Jansen and Schuiling, 1976;Lister et al, 1984;Okay and Satır, 2000b;Vanderhaeghe, 2004;Bozkurt et al, 2010;Kruckenberg et al, 2011;Laurent et al, 2015;Beaudoin et al, 2015].…”

“…Migmatites associated with S-type granites have also been described in the cores of these metamorphic domes [Jansen and Schuiling, 1976;Lister et al, 1984;Okay and Satır, 2000b;Vanderhaeghe, 2004;Bozkurt et al, 2010;Kruckenberg et al, 2011;Laurent et al, 2015;Beaudoin et al, 2015]. These intrusions are exposed in the footwall of major detachments where they show strong foliation with extensional kinematic indicators as well as cataclastic zones at the contact with the detachments [Faure and Bonneau, 1988;Gessner et al, 2001a;Iglseder et al, 2009;Denèle et al, 2011;Rabillard et al, 2015]. They were emplaced first in the northeastern Menderes massif with the Egrigöz and Koyunoba plutons both dated at ~21 Ma (UPb crystallization ages on zircon) in the footwall of the Simav detachment [Ring and Collins, 2005].…”

“…At the same time, numerous syn-tectonic intrusive bodies were emplaced in the footwalls of detachment systems in the central Menderes massif and the Cyclades [Faure and Bonneau, 1988;Gessner et al, 2001a;Iglseder et al, 2009;Lecomte et al, 2010;Denèle et al, 2011;Laurent et al, 2015;Rabillard et al, 2015].…”

“…This high-K magmatism often developed during the exhumation of MCCs (figures 9 and 10). In this context, detachment systems control the exhumation and cooling of syn-tectonic intrusions that show a pervasive co-magmatic to ductilebrittle deformation controlled by the regional extensional stress regime [Faure and Bonneau, 1988;Dinter and Royden, 1993;Gessner et al, 2001a;Denèle et al, 2011;Laurent et al, 2015;Rabillard et al, 2015]. With ongoing extension, the respective proportions of crustal and mantle source…”

Metamorphic Core Complex dynamics and structural development: Field evidences from the Liaodong Peninsula (China, East Asia)

“…Besides, AMS is a versatile method for analysing both qualitatively and quantitatively the magmatic and solid-state fabric of granitic rocks (e.g. Hrouda, 1982;Rochette et al, 1992;Borradaile and Henry, 1997;Bouchez, 1997;Talbot et al, 2004;Charles et al, 2009;Joly et al, 2009;Denèle et al, 2011). 708 cores from 78 sample sites have been studied for the Early Cretaceous anatectic granitoids emplaced into the Gudaoling MCC and 403 cores from 50 sample sites have been studied for the two granitic facies of the Early Cretaceous Yinmawanshan pluton (Tables 1 and 2).…”