Geochronology of clasts in allochthonous Miocene sedimentary sequences on Mykonos and Paros Islands: implications for back-arc extension in the Aegean Sea

Abstract

In the Cyclades, low-angle normal faults juxtaposed Miocene sedimentary rock units lying over Alpine blueschist- and greenschist-facies metamorphic rocks and Miocene granites. The sedimentary units in the hanging wall were deposited in fault-bounded basins while their footwalls progressively emerged through the ductile and brittle crust.The sedimentation in the basins evolved from marine turbidites in the Early Miocene to shallow/continental conglomerates during the Late Miocene. The transition from marine to fan delta sedimentation was coeval with widespread magmatism and possibly reflects true crustal uplift. It is inferred that the sequence is no younger than 8 Ma.K–Ar and 40Ar/39Ar geochronology, petrology and petrography of the clasts deposited on the hanging wall provide proof of progressive exhumation of the footwall and reveal the nature of the overburden that covered the Cycladic blueschist belt during Alpine orogeny in the Tertiary. Abundant metamorphic clasts yielding mica cooling ages between 80 and 100 Ma occur throughout the sedimentary section and probably pertain to a vast Pelagonian-type rock mass that covered the internal Hellenides from the Olympos to the central Cyclades. In addition, volcanic clasts dated at 10 Ma reveal the existence of a hitherto unknown volcanic province of that age in the central Aegean. Miocene crustal extension and exhumation of granitic plutons is recorded in the detrital sequence in a concentration of 10 Ma granitic clasts restricted to the top of the conglomerate sequence. A group of metamorphic clasts that yielded ages of 13–16 Ma possibly represents exhumation of mid crustal levels. Clasts similar to the currently-exposed Cycladic Blueschist Unit, such as 40 Ma old blueschists, eclogites and marble, were not found, thus indicating the very late exposure of these footwall rocks.

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

“…The lack of clasts belonging to the Cycladic Blueschists unit indicates late exposure of this unit in the late Miocene [Sánchez-Gómez et al, 2002].…”

“…in Tinos) [Katzir et al, 1996]. In Mykonos, Ikaria and Naxos, syn-tectonic sedimentary basins were also deposited in the hanging wall of these detachments during the Miocene [Photiades, 2002;Sánchez-Gómez et al, 2002;Lecomte et al, 2010;Laurent 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]. 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]. Further east, the exhumation of the Menderes massif was accommodated in the north by the top-to-the N Simav detachment recording at least ~50 km of displacement [Işik and Tekeli, 2001;Bozkurt et al, 2011] and in the south by a top-to-the S shearing just below the overlying Lycian nappes (figures 10 and 11) [Bozkurt and Satır, 2000;Gessner et al, 2001a;.…”

“…Surface exposure of the metamorphic rocks then occurred in the late Miocene (figure 11) [Sánchez-Gómez et al, 2002]. Further east, displacement along the Simav detachment continued until ~8 Ma [Bozkurt et al, 2011] and was contemporaneous with the exhumation of the central part of the Menderes massif below the top-to-the NE Alaşehir and the top-to-the S Büyük detachments, which occurred up to the end of the Miocene (figures 10 and 11) [Hetzel et al, 1995a[Hetzel et al, , 1995b; M A N U S C R I P T…”

Rifting and shallow-dipping detachments, clues from the Corinth Rift and the Aegean

“…The lower branch is ductile and it separates an upper plate made of greenschist metabasites from a granite dated from the Late Miocene (Sanchez-Gomez et al, 2002;Brichau et al, 2008). The granite intrudes the upper plate and a ductile deformation localised along the contact.…”