Geodynamic significance of the Santorini Detachment System (Cyclades, Greece)

Abstract

We present field and geochronologic evidence for a Miocene top-to-SSE detachment system on Santorini, which exhumed the Cycladic Blueschist Unit (CBU) below a package of low-grade Upper Triassic marbles that contain well-preserved Megalodon fossils forming a syncline with metaflysch in the core. White mica bundles from the mylonitic foliation in the CBU yield 40 Ar/ 39 Ar dates of 25-19 Ma and zircon (U-Th)/He dates are 11-8 Ma. A weakly foliated granitic intrusion that crosscuts the CBU is 8.5 Ma based on zircon U-Pb geochronology. Detrital white mica from the metaflysch yields Jurassic to early Palaeogene single grain 40 Ar/ 39 Ar dates, with a dominant Palaeocene signature. Zircon (U-Th)/He dating similarly reveals dispersed ages between 36 and 15 Ma suggesting Miocene metamorphic temperatures were insufficient (<200°C) to completely reset all of the zircon cooling ages. The low-grade rocks of the hangingwall above the newly discovered Miocene low-angle Santorini Detachment System most likely belong to the Pelagonian zone with a Triassic carbonate platform discordantly transgressed by an Eocene flysch deposit.

40 Ar/ 39 Ar thermochronology in the Ios basement terrane resolves the tectonic significance of the South Cyclades Shear Zone

“…Position of the West and North Cycladic detachment system shown schematically, modified from various authors. Variation in lineation trends is in excess of what can be shown at the scale illustrated, with trends as based on our own work and including the following authors: Augier et al (2015), ), Gautier et al (1993, Grasemann et al (2012), Jolivet et al (2004bJolivet et al ( , 2013, Rosenbaum & Ring (2007), Schneider et al (2011Schneider et al ( , 2018, Vandenberg & Lister (1996), Walcott & White (1998. Many shear zones that record Early Oligocene ages are also overprinted in Miocene time.…”

Tectono‐magmatic and Stratigraphic Evolution of the Cycladic Basement, Ios Island, Greece

“…The Upper Unit dominantly consists of Mesozoic to early Cenozoic ophiolite and metabasite rocks in the north‐central Cyclades (e.g., Andros, Anafi, Naxos, Paros, and Tinos) that exhibit evidence for Cretaceous (70‐100 Ma) greenschist‐amphibolite metamorphism, as well as nonmetamorphosed Permian to Cretaceous sedimentary rocks, MP‐HT metamorphic rocks, and Late Cretaceous granitoids (Bargnesi et al, ; Bolhar et al, ; Bröcker, ; Huet et al, ; Katzir et al, ; Martha et al, ; Patzak et al, ; Reinecke et al, ; Soukis & Papanikolaou, ). The Upper Unit includes Miocene supradetachment sedimentary basins exposed mainly on Anafi, Mykonos, Naxos, and Paros (Beaudoin et al, ; Böger, ; Lecomte et al, ; Reinecke et al, ; Soukis & Papanikolaou, ) and is separated from the underlying CBU by large‐scale Miocene detachment systems (Bargnesi et al, ; Brichau et al, , ; Grasemann et al, ; Jolivet et al, ; Laurent et al, ; Schneider et al, ; Soukis & Stockli, ).…”

“…However, ages for HP‐LT metamorphism in the Cyclades range from ~53 Ma to as young as ~30 Ma on Evia and Sifnos islands (Ring et al, ; Ring et al, ; Wijbrans et al, ) and tend to overlap in time with the greenschist‐facies overprint throughout the Cyclades (Kumerics et al, ; Peillod et al, ; Ring et al, ). These MCCs succeeded in unroofing middle‐crustal blocks by generally N or NE (North Cyclades, with late‐stage NW) or SE dipping (West Cyclades, Santorini/Thira) detachment faults (Brun et al, ; Grasemann et al, ; Jolivet et al, ; Schneider et al, ). The Ios Detachment Fault (Forster & Lister, ; Forster & Lister, ; Lister et al, ) or South Cycladic Shear Zone (SCSZ; Thomson et al, ; Vandenberg & Lister, ) was proposed as the detachment system responsible for the exhumation of Ios and Sikinos in the southern Cyclades.…”

“…The Attic-Cycladic Complex consists of two distinct tectono-metamorphic units that are characterized by fundamentally different tectono-metamorphic histories: (1) the Cycladic subduction complex, composed of the CB and the CBU, that underwent HP-LT metamorphism in the Paleogene, and (2) the Upper Unit which structurally overlies the CBU and formed the upper-plate of the late Mesozoic-early Cenozoic subduction zone (Avigad & Garfunkel, 1991;Dürr et al, 1978;Jolivet & Brun, 2010;Ring et al, 2010 Bolhar et al, 2017;Bröcker, 1990;Huet et al, 2015;Katzir et al, 1996;Martha et al, 2016;Patzak et al, 1994;Reinecke et al, 1982;Soukis & Papanikolaou, 2004). The Upper Unit includes Miocene supradetachment sedimentary basins exposed mainly on Anafi, Mykonos, Naxos, and Paros Böger, 1983;Lecomte et al, 2010;Reinecke et al, 1982;Soukis & Papanikolaou, 2004) and is separated from the underlying CBU by large-scale Miocene detachment systems (Bargnesi et al, 2013;Brichau et al, 2006Brichau et al, , 2007Grasemann et al, 2012;Laurent et al, 2015;Schneider et al, 2018;.…”

Zircon U‐Pb Chronostratigraphy and Provenance of the Cycladic Blueschist Unit and the Nature of the Contact With the Cycladic Basement on Sikinos and Ios Islands, Greece

“…Exhumation took place in two stages, the Eocene synsubduction stage and Oligo‐Miocene back‐arc extension with the exhumation of MCCs along low‐angle normal faults (e.g., Jolivet & Brun, ; Laurent et al, ; Ring et al, ). Four main detachment fault systems with divergent kinematics exhumed a series of MCCs in the Cyclades: the North Cycladic Detachment System, the Paros‐Naxos extensional fault system, the West Cycladic Detachment System, and the Santorini Detachment System (Beaudoin et al, ; Brichau et al, ; Gautier & Brun, ; Grasemann et al, ; Iglseder et al, ; Jolivet & Brun, ; Kumerics et al, ; Lister et al, ; Ring et al, ; Royden, ; Schneider et al, , Soukis & Stockli, ; Urai et al, ). The Attic‐Cycladic Complex comprises three tectono‐metamorphic units: the CB, the CBU, and the Pelagonian Upper Unit.…”