Zircon U-Pb and geochemical signatures in high-pressure, low-temperature metamorphic rocks as recorders of subduction zone processes, Sikinos and Ios islands, Greece

Poulaki, Eirini M.; Stöckli, Daniel F.; Flansburg, Megan E.; Gevedon, Michelle; Stockli, Lisa D.; Barnes, Jaime D.; Soukis, Konstantinos; Kitajima, Kouki; Valley, John W.

doi:10.1016/j.chemgeo.2021.120447

Cited by 20 publications

(31 citation statements)

References 147 publications

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“…Zircon U-Pb ages are robust records of igneous crystallization, but as metamorphic ages they can be difficult to place in pro-or retrograde context (Liu et al, 2006;Poulaki et al, 2021;Tomaschek et al, 2003;Yakymchuk et al, 2017). We include U-Pb ages from Tomaschek et al (2003) for comparison with other ages, but we do not rely on them for island-scale interpretations.…”

Section: Synthesis Of Previously Published Metamorphic Geochronologymentioning

confidence: 99%

Subduction, Underplating, and Return Flow Recorded in the Cycladic Blueschist Unit Exposed on Syros, Greece

et al. 2022

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Exhumed high‐pressure/low‐temperature (HP/LT) metamorphic rocks provide insights into deep (∼20–70 km) subduction interface dynamics. On Syros Island (Cyclades, Greece), the Cycladic Blueschist Unit preserves blueschist‐to‐eclogite facies oceanic‐ and continental‐affinity rocks that record the structural and thermal evolution linked to Eocene subduction. Despite decades of research, the metamorphic and deformation history (P‐T‐D) and timing of subduction and exhumation are matters of ongoing discussion. We suggest that Syros comprises three coherent tectonic slices and that each slice underwent subduction, underplating, and syn‐subduction return flow along similar P‐T trajectories, but at progressively younger times. Subduction and exhumation are distinguished by lineations and ductile fold axis orientations, and are kinematically consistent with previous studies that document top‐to‐the‐S‐SW shear (prograde‐to‐peak subduction), top‐to‐the‐NE shear (blueschist facies exhumation), and then E‐W coaxial stretching (greenschist facies exhumation). Amphibole zonations record cooling during decompression, indicating return flow above a cold slab. Multi‐mineral Rb‐Sr isochrons and compiled metamorphic geochronology show that the three slices record distinct stages of peak subduction (53–52, ∼50, and 45 Ma) that young with structural depth. Retrograde blueschist and greenschist facies fabrics span ∼50–40 and ∼43–20 Ma, respectively, and also young with structural depth. Synthesized data sets support a revised tectonic framework for Syros, involving subduction of structurally distinct coherent slices and simultaneous return flow of previously accreted tectonic slices in the subduction channel shear zone. Distributed, ductile, dominantly coaxial return flow in an Eocene‐Oligocene subduction channel proceeded at rates of ∼1.5–5 mm/yr and accommodated ∼80% of the total exhumation of this HP/LT complex.

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Section: Synthesis Of Previously Published Metamorphic Geochronologymentioning

confidence: 99%

Subduction, Underplating, and Return Flow Recorded in the Cycladic Blueschist Unit Exposed on Syros, Greece

et al. 2022

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“…In two samples, ZHe ages from single aliquots are anomalously younger than AHe aliquots from the same sample, likely due to enriched‐U metamorphic zircon overgrowths (e.g. Bargnesi et al, 2013; Bargnesi, Stockli, Hourigan, & Hager, 2016; Hourigan, Reiners, & Brandon, 2005) observed in zircon U–Pb data from these same samples (Flansburg et al, 2019; Poulaki et al, 2019, 2021).…”

Section: (U‐th)/he Thermochronology and Time–temperature Modellingmentioning

confidence: 91%

“…The CB‐CBU contact has been regionally correlated with the Trans‐Cycladic Thrust (Grasemann et al, 2018) on Sikinos (Ring & Glodny, 2021) and Ios (Glodny & Ring, 2022). Another hypothesis suggests a parautochthonous nature of the CBU, and evidence for Oligocene static fluid alteration along the CB‐CBU contact argues against large‐magnitude displacement <20 Ma (Poulaki et al, 2019, 2021). These scenarios support minor extensional displacement along the CB‐CBU contact during the formation of the Ios‐Sikinos MCC.…”

Section: Geology Of the Cycladesmentioning

confidence: 99%

Coeval Miocene exhumation of the Cycladic Blueschist Unit and the Cycladic Basement in the southern Cyclades, Ios and Sikinos, Greece

et al. 2022

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Miocene extension in the back arc of the retreating Hellenic subduction zone resulted in metamorphic core complex formation and exhumation of the Cycladic HP‐LT rocks. The extension was accommodated by bivergent detachment systems, generally occupying the interface between the Cycladic Blueschist Unit (CBU) and overlying Pelagonian units. However, the nature and kinematic history of the contact between the CBU and underlying Cycladic Basement (CB) in the southern Cyclades remains debated due to the presence of both top‐to‐the‐N and top‐to‐the‐S kinematics and ambiguities dating the final exhumation stages. Zircon and apatite (U‐Th)/He data and thermal modelling for the CB and CBU on Ios and Sikinos show that both units were likely exhumed as a coherent footwall block in response to rapid slip along the bivergent Miocene Santorini and Naxos‐Paros detachment systems.

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“…The contact between CB/CBU has been variably considered as either an extensional detachment fault, ductile shear zone [78][79][80][81], or thrust [58]. While undoubtedly tectonically overprinted in a number of places, recent detrital zircon U-Pb studies have documented a deformed depositional CBU-CB contact with the CBU resting unconformably on the CB and representing continuous sedimentation from the late Permian to late Cretaceous [15,23,25,82,83]. This suggests a parautochthonous nature for the contact between CB and CBU that is also supported by the similarity of DZ signatures of the basal CBU, closely resembling the underlying CB [15,83].…”

Section: Geological Settingmentioning

confidence: 99%

“…While undoubtedly tectonically overprinted in a number of places, recent detrital zircon U-Pb studies have documented a deformed depositional CBU-CB contact with the CBU resting unconformably on the CB and representing continuous sedimentation from the late Permian to late Cretaceous [15,23,25,82,83]. This suggests a parautochthonous nature for the contact between CB and CBU that is also supported by the similarity of DZ signatures of the basal CBU, closely resembling the underlying CB [15,83]. The DZ signatures of the CB and CBU metasedimentary units throughout the Cyclades revealed a Gondwanan provenance [20] that remained relatively unchanged until the CBU rocks approached the trench of the subduction zone, as indicated by significant late-stage input from the Internal Hellenides [14,15,25].…”

Section: Geological Settingmentioning

confidence: 99%

Structural Study and Detrital Zircon Provenance Analysis of the Cycladic Blueschist Unit Rocks from Iraklia Island: From the Paleozoic Basement Unroofing to the Cenozoic Exhumation

et al. 2022

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Detailed mapping and structural observations on the Cycladic Blueschist Unit (CBU) on Iraklia Island integrated with detrital zircon (DZ) U-Pb ages elucidate the Mesozoic pre-subduction and the Cenozoic orogenic evolution. Iraklia tectonostratigraphy includes a heterogeneous Lower Schist Fm., juxtaposed against a Marble Fm. and an overlying Upper Schist Fm. The contact is an extensional ductile-to-brittle-ductile, top-to-N shear zone, kinematically associated with the Oligo-Miocene exhumation. The DZ spectra of the Lower Schist have Gondwanan/peri-Gondwanan provenance signatures and point to Late Triassic Maximum Depositional Ages (MDAs). A quartz-rich schist lens yielded Precambrian DZ ages exclusively and is interpreted as part of the pre-Variscan metasedimentary Cycladic Basement, equivalent to schists of the Ios Island core. The Upper Schist represents a distinctly different stratigraphic package with late Cretaceous MDAs and dominance of Late Paleozoic DZ ages, suggestive of a more internal Pelagonian source. The contrast in the DZ U-Pb record between Lower and Upper Schist likely reflects the difference between a Paleotethyan and Neotethyan geodynamic imprint. The Triassic DZ input from eroded volcanic material is related to the final Paleotethys closure and Pindos/CBU rift basin opening, while late Cretaceous metamorphic/magmatic zircons and ~48–56 Ma zircon rims constrain the onset of Neotethyan convergence and high-pressure subduction metamorphism.

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Zircon U-Pb and geochemical signatures in high-pressure, low-temperature metamorphic rocks as recorders of subduction zone processes, Sikinos and Ios islands, Greece

Cited by 20 publications

References 147 publications

Subduction, Underplating, and Return Flow Recorded in the Cycladic Blueschist Unit Exposed on Syros, Greece

Subduction, Underplating, and Return Flow Recorded in the Cycladic Blueschist Unit Exposed on Syros, Greece

Coeval Miocene exhumation of the Cycladic Blueschist Unit and the Cycladic Basement in the southern Cyclades, Ios and Sikinos, Greece

Structural Study and Detrital Zircon Provenance Analysis of the Cycladic Blueschist Unit Rocks from Iraklia Island: From the Paleozoic Basement Unroofing to the Cenozoic Exhumation

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