Deformation within the Cycladic subduction–exhumation channel: new insights from the enigmatic Makrotantalo nappe (Andros, Aegean)

Gerogiannis, Nikolaos; Xypolias, P.; Chatzaras, Vasileios; Aravadinou, E.; Papapavlou, Konstantinos

doi:10.1007/s00531-019-01680-3

Cited by 23 publications

(62 citation statements)

References 119 publications

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“…Upright open folds (F 3 ), with their axes trending parallel to the NE‐SW shear direction developed during exhumation and were probably related to constriction within the extruding channel, owing to along‐strike variations in channel thickness. These features have also been documented across the CBU (Gerogiannis et al, 2019; Xypolias & Alsop, 2014). If there were no variation in along‐strike exhumation rates, narrower zones within the channel would produce a component of convergent flow orthogonal to the main transport direction (e.g., Lévy & Jaupart, 2011; Mancktelow & Pavlis, 1994) toward unrestricted zones.…”

Section: Discussionmentioning

confidence: 71%

The Cycladic Blueschist Unit on Tinos, Greece: Cold NE Subduction and SW Directed Extrusion of the Cycladic Continental Margin Under the Tsiknias Ophiolite

et al. 2020

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High pressure-low temperature (HP-LT) metamorphic rocks structurally beneath the Tsiknias Ophiolite make up the interior of Tinos Island, Greece, but their relationship with the overlying ophiolite is poorly understood. Here, new field observations are integrated with petrological modeling of eclogite and blueschists to provide new insight into their tectonothermal evolution. Pseudomorphed lawsonite-, garnet-, and glaucophane-bearing schists exposed at the highest structural levels of Tinos (Kionnia and Pyrgos Subunits) reached~22-26 kbar and 490-520°C under water-saturated conditions, whereas pseudomorphed lawsonite-and aegirine-omphacite bearing eclogite reached~20-23 kbar and 530-570°C. These rocks are separated from rocks at deeper structural levels (Sostis Subunit) by a top-to-SW thrust. The Sostis Subunit records P-T conditions of~18.5 kbar and 480-510°C and is overprinted by pervasive top-toNE shearing that developed during exhumation from (M 1) blueschist to (M 2) greenschist facies conditions of~7.3 ± 0.7 kbar and 536 ± 16°C. These P-T-D relationships suggest that the Cycladic Blueschist Unit represents a discrete series of tectonometamorphic subunits that each experienced different tectonic and thermal histories. These subunits were buried to variable depths and sequentially extruded toward the SW from a NE dipping subduction zone. The difference in age and P-T conditions between the HP-LT rocks and the overlying metamorphic sole of the Tsiknias Ophiolite suggests that this NE dipping subduction zone was active between circa 74 and 46 Ma and cooled at a minimum rate of 1.2-1.5°C/km/Myr prior to continent-continent collision between Eurasia and Adria/Cyclades. Plain Language Summary High pressure-low temperature metamorphic rocks make up the interior of Tinos Island, Greece and underlie an ancient piece of oceanic crust and mantle (Tsiknias Ophiolite). The rocks that make up Tinos were once mudstones and limestones deposited on the NE margin of the Cycladic-Adriatic continent and were deeply buried in a subduction zone. In this work, we investigate the structures and mineralogy of the Tinos high-pressure rocks and find they were buried to variable depths (80-60 km) and reached temperatures of 500-550°C. These packages of rock were then emplaced against each other during their return journey toward the surface after subduction ended. We document evidence for circa 25 Myr (ca. 74 and 46 Ma) of subduction prior to continent-continent collision (between Eurasia and Adria/Cyclades) on Tinos and that this records the closure of an ancient ocean to the NE of the Cyclades.

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Section: Discussionmentioning

confidence: 71%

The Cycladic Blueschist Unit on Tinos, Greece: Cold NE Subduction and SW Directed Extrusion of the Cycladic Continental Margin Under the Tsiknias Ophiolite

et al. 2020

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“…Recently, some petrological evidence on a former high‐ P event (Huyskens & Bröcker, ) dated at 116 Ma (Cretaceous) by Ar–Ar dating of white micas (Huet, Labrousse, Monie, Malvoisin, & Jolivet, ) has been documented from the Makrotantalon unit. Because Cretaceous high‐ P metamorphism has been unknown from the CBU in the central Aegean islands, there is still a continuing debate on the Makrotantalon unit and whether it belongs to the Pelagonian Zone (Huet et al, ) or to the CBU (Gerogiannis, Xypolias, Chatzaras, Aravadinou, & Papapavlou, ; Huyskens & Bröcker, ). The Permian sections rest on both the CB and the Mesozoic series of the CBU with a tectonic contact defined as a low‐angle normal fault (Bulle et al, ; Gautier, Brun, & Jolivet, ; Huyskens & Bröcker, ; Philippon et al, ; Ring, Glodny, Will, & Thomson, ).…”

Section: Discussionmentioning

confidence: 99%

P–T–tevolution of the Cycladic Blueschist Unit in Western Anatolia/Turkey: Geodynamic implications for the Aegean region

Çetinkaplan

Candan

Oberhänsli

et al. 2020

Journal Metamorphic Geology

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Eclogite and blueschist facies rocks occurring as a tectonic unit between the underlying Menderes Massif (MM) and the overlying Afyon Zone/Lycian Nappes and the Bornova Flysch Zone in western Anatolia represent the eastward continuation of the Cycladic Blueschist Unit (CBU) in Turkey. This high-P unit is attributed to the closure of the Pindos Ocean and consists of (a) a Triassic to Upper Cretaceous coherent series derived from passive continental margin sediments and (b) the tectonically overlying Upper Cretaceous Selçuk mélange with eclogite blocks embedded in a pelitic epidote-blueschist matrix. The coherent series has experienced epidote-blueschist facies metamorphism (490 ± 25°C/11.5 ± 1.5 kbar; 38 km depth). 40 Ar/ 39 Ar white mica and 206 Pb/ 238 U monazite dating of quartz metaconglomerate from coherent series yielded middle Eocene ages of 44 ± 0.3 and 40.1 ± 3.1 Ma for epidote-blueschist facies metamorphism, respectively. The epidote-blueschist facies metamorphism of the matrix of the Selçuk mélange culminates at 520 ± 15°C/13 ± 1.5 kbar, 43 km depth, and is dated at 57.5 ± 0.3-54.5 ± 0.1 Ma ( 40 Ar/ 39 Ar phengite). Eclogite facies metamorphism of the blocks (570 ± 30°C/18 ± 2 kbar, 60 km depth) is early Eocene and dated at 56.2 ± 1.5 Ma by 206 Pb/ 238 U zircon. Eclogites experienced a nearly isothermal retrogression (490 ± 40°C/~6 to 7 kbar) during their incorporation into the Selçuk mélange. The retrograde overprints of the coherent series (410 ± 15°C/7 ± 1.5 kbar from Dilek Peninsula and 485 ± 33°C/~6 to 7 kbar from Selçuk-Tire area) and the Selçuk mélange (510 ± 15°C/6 ± 1 kbar) are dated at 35.8 ± 0.5-34.3 ± 0.1 Ma by 40 Ar/ 39 Ar white mica and 31.6 ± 6.6 Ma by 206 Pb/ 238 U allanite dating methods, respectively. Regional geological constrains reveal that the contact between the MM and the CBU originally formed a lithosphere-scale transform fault zone. 40 Ar/ 39 Ar white mica age from the contact indicates that the CBU and the MM were tectonically juxtaposed under greenschist facies conditions during late Eocene, 35.1 ± 0.3 Ma. K E Y W O R D S Cycladic Blueschist Unit, eclogite, Menderes Massif, Pindos Ocean, Selçuk mélange 380 | ÇETINKAPLAN ET AL. | 381 ÇETINKAPLAN ET AL. Note: (1) Quartz metaconglomerate; (2) blueschist metabasite; (3) eclogite; (4) omphacite epidotite; (5) omphacite metagabbro; (6) blueschist metabasite; (7) garnet-phengite schist; (8) garnet-biotite schist.

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“…A ca. 40–30 Ma Eocene‐Oligocene metamorphic event linked to synorogenic exhumation driven by ductile extrusion has been identified by white mica 40 Ar/ 39 Ar and Rb‐Sr dating (Gerogiannis et al, 2019; Huet et al, 2009; Jolivet et al, 2010; Ring et al, 2007; Scheffer et al, 2016; Schneider et al, 2011). Deeper levels of the CBU are suggested to have continued experiencing high‐pressure metamorphism until 30 Ma (Huet et al, 2014; Lister & Forster, 2016; Wijbrans et al, 1990) even as the higher structural levels were partially exhumed and undergoing contemporaneous greenschist facies metamorphism (Ring et al, 2010).…”

Section: Geological Settingmentioning

confidence: 99%

Lateral Termination of a Cycladic‐Style Detachment System (Hymittos, Greece)

et al. 2020

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The bedrock of Hymittos, Attic peninsula, Greece, exposes a pair of low-angle crustal-scale ductile-then-brittle detachment faults. The uppermost detachment fault separates sub-greenschist facies phyllite and marble of a Pelagonian Zone hanging wall, from greenschist facies metasedimentary schist, calc-schist, and marble correlated to the Cycladic Blueschist Unit. A second, structurally lower detachment fault subdivides the metamorphic rocks of the Cycladic blueschist unit footwall into middle and lower units. There is a marked step in metamorphic grade between the sub-greenschist facies uppermost package, and the middle-to-upper greenschist facies middle and lower packages. A suite of new white mica 40 Ar/ 39 Ar and zircon (U-Th)/He dates indicates accommodation of deformation along these faults occurred from the late Oligocene to the late Miocene with both faults active during the middle Miocene. The structures have clear top-S/SSW kinematics determined from flanking folds, sigmoids, shear bands, stair-stepping of strain shadows on porphyroclasts, and SCC' fabrics. The ductile-to-brittle deformation of the structures, morphology of the massif, and the increase in metamorphic grade suggest these low-angle structures are part of a major, crustal-scale extensional complex, located at the northwest end of the West Cycladic Detachment System, that accommodated Miocene bivergent exhumation of Attic-Cycladic metamorphic core complexes in the central Aegean. Taken together, the above data suggest that multiple coeval detachment branches may form in areas with high strain gradients to accommodate the mechanically necessary termination of Cycladic-style detachment systems.

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Deformation within the Cycladic subduction–exhumation channel: new insights from the enigmatic Makrotantalo nappe (Andros, Aegean)

Cited by 23 publications

References 119 publications

The Cycladic Blueschist Unit on Tinos, Greece: Cold NE Subduction and SW Directed Extrusion of the Cycladic Continental Margin Under the Tsiknias Ophiolite

The Cycladic Blueschist Unit on Tinos, Greece: Cold NE Subduction and SW Directed Extrusion of the Cycladic Continental Margin Under the Tsiknias Ophiolite

P–T–tevolution of the Cycladic Blueschist Unit in Western Anatolia/Turkey: Geodynamic implications for the Aegean region

Lateral Termination of a Cycladic‐Style Detachment System (Hymittos, Greece)

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