Stretched Thin: Oligocene Extrusion and Ductile Thinning of the Basal Unit Along the Evia Shear Zone, NW Cyclades, Greece

Ducharme, Taylor; Schneider, David; Grasemann, Bernhard; Klonowska, Iwona

doi:10.1029/2022tc007561

Cited by 9 publications

(2 citation statements)

References 129 publications

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“…Together, this package of meta‐carbonates and Eocene meta‐flysch is characteristic of the Basal Unit, which is understood to be the metamorphosed equivalent of the Gavrovo‐Tripolitza (Godfriaux, 1968; Papanikolaou, 2021). This package is overlain by HP‐LT blueschist‐facies rocks at Olympos‐Ossa, Almyropotamos (Evvia), and various locations in the Cyclades (e.g., Samos) (Ducharme et al., 2022; Papanikolaou, 2021; Schermer et al., 1990; Shaked et al., 2000).…”

Section: Geological Settingmentioning

confidence: 99%

Zircon and Apatite U‐Pb Constraints on the Tectonic Affinity and Metamorphic History of the Blueschist‐Facies Ambelakia Unit, Mt. Ossa, Greece

2023

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The geologic record of Hellenic subduction in the exhumed Attic-Cycladic Crystalline Complex (ACCC) has profoundly impacted our understanding of subduction zone processes, including coherent underplating, rheologic, and petrologic behaviors at depth, and slab dynamics of rollback and break-off (Brun & Faccenna, 2008;Jolivet et al., 2003). The Mesozoic tectonic evolution of the eastern Mediterranean is dominated by African-Eurasian convergence and Neotethys closure, involving convergence, subduction, and collision of various oceanic basins, attenuated continental crusts, and microcontinents (

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Section: Geological Settingmentioning

confidence: 99%

Zircon and Apatite U‐Pb Constraints on the Tectonic Affinity and Metamorphic History of the Blueschist‐Facies Ambelakia Unit, Mt. Ossa, Greece

2023

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“…A nappe that has been subducted and experienced high‐pressure (HP) metamorphism can be exhumed to a shallower crustal level through a series of different processes (Guillot et al, 2009; Platt, 1993 and reference therein). One of these processes is wedge extrusion, which is thought to operate during exhumation of the Cycladic Blueschist Unit (CBU), Greece (Figure 1 – Aravadinou & Xypolias, 2017; Ducharme et al, 2022; Ernst et al, 1997; Gessner et al, 2001; Ring, Will, et al, 2007, Ring, Glodny, et al, 2007; Ring & Glodny, 2010 and references therein). A wedge extrusion may show internal deformation, which can cause the development of thrusts or thrust splays causing thickening of the lower parts of the wedge during exhumation.…”

Section: Introductionmentioning

confidence: 99%

Disruption of a high‐pressure unit during exhumation: Example of the Cycladic Blueschist unit (Thera, Ios and Naxos islands, Greece)

Peillod,

Patten,

Drüppel

et al. 2023

Journal Metamorphic Geology

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Reconstructing the original geometry of a high‐pressure tectonic unit is challenging but important to understand the mechanisms of mountain building. While a single nappe is subducted and exhumed, nappe‐internal thrusts may disrupt it into several subunits. The Middle‐CBU nappe of the Cycladic Blueschist Unit (Hellenide subduction orogen, Greece) shows evidence of such disruption along a Trans‐Cycladic‐Thrust (TCT), however, the timing of this thrusting is unknown. Here, we report multi‐petrological and geochronological data from the Middle‐CBU nappe from the Thera and Ios islands (Greece). Using Zr‐in‐rutile thermometry coupled with quartz‐in‐garnet elastic barometry, average P–T and phase equilibrium thermodynamic modelling, we show that garnet growth in Ios occurred during prograde metamorphism at 6.7 ± 1.4 kbar to 13.0 ± 1.6 kbar and 326 ± 20°C to 506 ± 13°C (2σ uncertainty) followed by early exhumation to 10.1 ± 0.6 kbar and 484 ± 14°C and a greenschist facies overprint at 5.7 ± 1.2 kbar and 416 ± 14°C. For Thera, we constrain peak HP conditions of 7.6 ± 1.8 kbar and 331 ± 18°C, followed by exhumation and equilibration at ~2 kbar and ~275°C using average P–T and phase equilibrium thermodynamic modelling. For Ios, Uranium‐Pb garnet geochronology provides ages of 55.7 ± 5.0 Ma (2σ uncertainties) for prograde and 40.1 ± 1.4 Ma for peak HP metamorphism. Combining our new P–T–t data from Thera and Ios islands with existing data from Naxos island, we conclude that the studied nappe segments represent remnants of a former coherent nappe. The P–T–t data define an Eocene subduction rate of 2.1 ± 1.0 km/Ma, which is distinctly slower than the current subduction rate of 40–45 km/Ma. After subduction, the exhumation of the Middle‐CBU nappe occurred during the Oligocene at different rates for different localities. The Middle‐CBU nappe of Naxos was exhumed at a rate of ~6 km/Ma, contrasting with the exhumation rate of ~3 km/Ma calculated for Ios. This result suggests that the Middle‐CBU nappe of Naxos rocks was thrust on the Ios one during the Oligocene. Using P–T–t data and assuming realistic subduction angles during the Eocene and the Oligocene, we present a 2D structural reconstruction of the Middle‐CBU nappe of these islands. This reconstruction helps to understand the mechanisms of subduction of a continental margin and its disruption during exhumation.

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Syn-exhumation metasomatic glaucophane-phengite-quartz veins formed at moderate pressures: exploring the control of fO2 and bulk composition on nominally HP metamorphic assemblages

Ducharme,

Schneider,

Grasemann

et al. 2024

Contrib Mineral Petrol

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Stretched Thin: Oligocene Extrusion and Ductile Thinning of the Basal Unit Along the Evia Shear Zone, NW Cyclades, Greece

Abstract: Exhumation of high-pressure, low-temperature (HP-LT) metamorphic rocks may be accomplished by a number of complementary or independent tectonic phenomena (e.g.,

Cited by 9 publications

References 129 publications

Zircon and Apatite U‐Pb Constraints on the Tectonic Affinity and Metamorphic History of the Blueschist‐Facies Ambelakia Unit, Mt. Ossa, Greece

Zircon and Apatite U‐Pb Constraints on the Tectonic Affinity and Metamorphic History of the Blueschist‐Facies Ambelakia Unit, Mt. Ossa, Greece

Disruption of a high‐pressure unit during exhumation: Example of the Cycladic Blueschist unit (Thera, Ios and Naxos islands, Greece)

Syn-exhumation metasomatic glaucophane-phengite-quartz veins formed at moderate pressures: exploring the control of fO2 and bulk composition on nominally HP metamorphic assemblages

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