Strain localization in a fossilized subduction channel: Insights from the Cycladic Blueschist Unit (Syros, Greece)

Laurent, Valentin; Jolivet, Laurent; Roche, Vincent; Augier, Romain; Scaillet, Stéphane; Cardello, Giovanni Luca

doi:10.1016/j.tecto.2016.01.036

Cited by 62 publications

(165 citation statements)

References 83 publications

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“…In this archipelago, the CBU, belonging to the Pindos oceanic domain (Bonneau, ; Bonneau & Kienast, ), reached peak‐pressure conditions during the formation of the Hellenides at 53–48 Ma (Figure ; Lagos et al., ; Laurent et al., ; Lister & Forster, ; Tomaschek et al., ; Uunk, Brouwer, ter Voorde, & Wijbrans, ). This HP–LT metamorphic unit was exhumed during the Eocene within the subduction channel between a top‐to‐the south thrust at the base and top‐to‐the east/northeast syn‐orogenic detachment at the top, the Vari Detachment (Figure ; Augier, Jolivet, Gadenne, Lahfid, & Driussi, ; Brun & Faccenna, ; Huet, Labrousse, & Jolivet, ; Jolivet, Faccenna, Goffé, Burov, & Agard, ; Laurent et al., ; Ring et al., , ). In the Cyclades, regional‐scale detachments such as the North Cycladic Detachment System (NCDS), the Naxos‐Paros Detachment or the West Cycladic Detachment System (WCDS) have accommodated back‐arc extension (Figure ; Grasemann, Schneider, Stöckli, & Iglseder, ; Jolivet et al., ).…”

Section: Geological Contextmentioning

confidence: 99%

“…Consequently, this island has been the focus of petrological, structural and geochronological studies aimed at constraining the tectonometamorphic evolution of the CBU subduction complex (e.g. Cliff, Bond, Butler, & Dixon, ; Keiter, Ballhaus, & Tomaschek, ; Keiter, Piepjohn, Ballhaus, Lagos, & Bode, ; Lagos et al., ; Laurent et al., , ; Lister & Forster, ; Philippon, Brun, & Gueydan, ; Schumacher, Brady, Cheney, & Tonnsen, ; Soukis & Stockli, ; Tomaschek, Kennedy, Villa, Lagos, & Ballhaus, ; Trotet, Jolivet, & Vidal, ; Trotet, Vidal, & Jolivet, ). However, after a decade of investigations, the tectonometamorphic evolution of the CBU of Syros is still actively debated, as attested by the different shapes of P–T paths proposed in the literature from burial to exhumation (Figure ).…”

Section: Introductionmentioning

confidence: 99%

“…This study presents an extensive petrological data set that is used to refine the P–T trajectory of several subunits of the CBU on Syros previously reported in Laurent et al. (). As discussed above, detailed petrological observations are required to support the results of P–T modelling which have serious implication for tectonic scenarios.…”

Section: Introductionmentioning

confidence: 99%

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Exhumation of eclogite and blueschist (Cyclades, Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling

Laurent

Lanari

Naïr

et al. 2018

Journal Metamorphic Geology

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High‐P rocks such as eclogite and blueschist are metamorphic markers of palaeo‐subduction zones, and their formation at high‐P and low‐T (HP–LT) conditions is relatively well understood since it has been the focus of numerous petrological investigations in the past 40 years. The tectonic mechanisms controlling their exhumation back to the surface are, however, diverse, complex and still actively debated. Although the Cycladic Blueschist Unit (CBU, Greece) is among the best worldwide examples for the preservation of eclogite and blueschist, the proposed P–T evolution followed by this unit within the Hellenic subduction zone is quite different from one study to another, hindering the comprehension of exhumation processes. In this study, we present an extensive petrological data set that permits refinement of the shape of the P–T trajectory for different subunits of the CBU on Syros. High‐resolution quantitative compositional mapping has been applied to support the thermobarometric investigations, which involve semi‐empirical thermobarometry, garnet equilibrium modelling and P–T isochemical phase diagrams. The thermodynamic models highlight the powerful use of reactive bulk compositions approximated from local bulk compositions. The results are also combined with Raman spectrometry of carbonaceous material (RSCM) to retrieve the metamorphic peak temperature distribution at the scale of the island. A major result of this study is the good agreement between all the independent thermobarometric methods, permitting reconstruction of the prograde and retrograde P–T trajectories. Garnet compositional zoning was used to retrieve prograde, peak and retrograde growth stages in line with the results of the P–T isochemical phase diagrams, RSCM temperature and peak‐pressure crystallization of the garnet–omphacite–phengite assemblage. Our results are consistent with previous thermobarometric estimates from other occurrences of CBU rocks (Tinos, Andros), suggesting a multistage exhumation process with (1) early syn‐orogenic exhumation within the subduction channel, (2) isobaric heating at mid‐crustal depths (~10–12 kbar) following thermal re‐equilibration of the lithosphere from a cold syn‐orogenic regime in the subduction zone to a warmer post‐orogenic regime in the back‐arc domain and (3) exhumation and cooling related to a post‐orogenic phase of extension following slab retreat. Expanding to the general aspects of subduction zones, we suggest that such metamorphic evolution of HP–LT units should be regarded as a characteristic feature of exhumation driven by slab rollback.

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Section: Geological Contextmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Exhumation of eclogite and blueschist (Cyclades, Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling

Laurent

Lanari

Naïr

et al. 2018

Journal Metamorphic Geology

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“…() and Laurent et al . () which link (dashed line in Fig. ), the east–west‐trending Serpentinite Belt that crosses the northern part of Syros, with a north–south‐oriented discontinuity that places the northern tip of Syros (Diapori) stratigraphically below the Serpentinite Belt.…”

Section: Discussionmentioning

confidence: 99%

“…(), Soukis & Stockli (), Laurent et al . () and others interpret this unit as an upper tectonic sheet, carried onto high‐ P rocks by a regionally extensive, low‐angle extensional detachment fault.…”

Section: Geology Of Syrosmentioning

confidence: 99%

Geochronological challenges posed by continuously developing tectonometamorphic systems: insights from Rb–Sr mica ages from the Cycladic Blueschist Belt, Syros (Greece)

Cliff

Bond

Butler

et al. 2016

Journal Metamorphic Geology

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Is metamorphism and its causative tectonics best viewed as a series of punctuated events or as a continuum? This question is addressed through examination of the timing of exhumation of the Cycladic Blueschist Belt (CBB). The cause of scatter beyond analytical error in Rb-Sr geochronology was investigated using a suite of 39 phengite samples. Rb-Sr ages have been measured on phengite microsamples drilled from specific microstructures in thin sections of calcschists and metabasites from the CBB on Syros. The majority are from samples that have well-preserved blueschist facies mineral assemblages with limited greenschist facies overprint. The peak metamorphic temperatures involved are below the closure temperature for white mica so that crystallization ages are expected to be preserved. This is supported by the coexistence of different ages in microstructures of different relative age; in one sample phengite from the dominant extensional blueschist facies fabric preserves an age of 35 Ma while post-tectonic mica, millimetres away, has an age of 26 Ma. The results suggest that micro-sampling techniques linked to detailed microstructural analysis are critical to understanding the timing and duration of deformation in tectonometamorphic systems. North of the Serpentinite Belt in northern Syros, phengite Rb-Sr ages are generally between 53 and 46 Ma, comparable to previous dates from this area. South of the Serpentinite Belt phengite in blueschist facies assemblages associated with extensional fabrics linked to exhumation have ages that range from 42 Ma down to c. 30 Ma indicating that extensional deformation while still under blueschist facies conditions continued until 30 Ma. No age measurements on samples with unambiguous evidence of deformation under greenschist facies conditions were made; two rocks with greenschist facies assemblages gave phengite ages that overlap with the younger blueschist samples, suggesting blueschist facies phengite is preserved in these rocks. Two samples yielded ages below 27 Ma; one is from a post-tectonic microstructure, the other from a greenschist in which the fabric developed during earlier blueschist facies conditions. These ages are consistent with previous evidence of greenschist facies conditions from c. 25 Ma onwards. The data are consistent with a model of deformation that is continuous on a regional scale.

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

Gerogiannis

Xypolias

Chatzaras

et al. 2019

Int J Earth Sci (Geol Rundsch)

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Strain localization in a fossilized subduction channel: Insights from the Cycladic Blueschist Unit (Syros, Greece)

Cited by 62 publications

References 83 publications

Exhumation of eclogite and blueschist (Cyclades, Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling

Exhumation of eclogite and blueschist (Cyclades, Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling

Geochronological challenges posed by continuously developing tectonometamorphic systems: insights from Rb–Sr mica ages from the Cycladic Blueschist Belt, Syros (Greece)

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

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