A new geological map of the Island of Syros (Aegean Sea, Greece): Implications for lithostratigraphy and structural history of the Cycladic Blueschist Unit

Keiter, Mark; Ballhaus, Chris; Tomaschek, Frank

doi:10.1130/2011.2481

Cited by 37 publications

(121 citation statements)

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“…Then, final exhumation stages of the CBU towards the surface were accommodated by post‐metamorphic brittle deformation through low‐angle and steeply dipping normal faults (e.g. Jolivet & Patriat, ; Jolivet et al., ; Keiter et al., ; Mehl, Jolivet, & Lacombe, ; Philippon et al., ; Ring, Thomson, & Bröcker, ; Ring et al., ).…”

Section: Discussionmentioning

confidence: 99%

“…Eclogite parageneses are therefore recognized within all three subunits (Laurent et al., ), implying that despite their entirely different degrees of retrogression, these three subunits have undergone similar HP–LT metamorphic and peak P–T conditions (Trotet, Vidal, et al., ). Finally, structurally positioned above the CBU (Keiter et al., , ; Soukis & Stockli, ; Trotet, Jolivet, et al., ), the Vari Unit is formed by a greenschist mylonitic unit overlain by the orthogneiss of Vari intruding amphibolite facies metabasite. High‐ P imprinting is not recognized and apparently lacking as in other outcrops of Pelagonian rocks (Laurent et al., ; Soukis & Stockli, ).…”

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%

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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: Discussionmentioning

confidence: 99%

Section: Geological Contextmentioning

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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“…On Samos, an additional composite system of granitic and granodioritic dykes is observed along the western coast (Mezger and Okrusch, 1985). Keiter et al (2011) also suggest the possible existence of a Miocene granitoid below the southwestern part of Syros island, which would explain the hydrothermal alteration and silicification observed in the field. The petrology of the I-type intrusions evolves from monzonites in the east (i.e.…”

Section: Petrology and Chemistry Of Cycladic Intrusions The Main Gramentioning

confidence: 72%

The geological signature of a slab tear below the Aegean

et al. 2015

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Mediterranean Highlights-Rotation of Hellenides is coeval with granite migration -Migration of granitoids signs a slab tear in the Cyclades -HT domes and a left-lateral gradient of extension also sign the tear AbstractIn this paper we explore the geology of the Aegean region in the Miocene to identify the geological signature of a first-order slab tear observed in all tomographic models. From 15 to 8 Ma, the tear is associated, spatially and timely, with a fast clockwise rotation of the External Hellenides, alkaline volcanism, high-temperature metamorphic domes with a predominance of north-dipping detachments, south-westward migration of granitoids intrusions. These features suggest a warmer geodynamic environment during the rotation and the impact of a hot mantle flow associated with the tear. The ~8 Ma duration between the first hightemperature metamorphic domes in the centre of the archipelago and the beginning of the fast rotation may correspond to the time needed for the slab to bend, stretch and finally tear.

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“…The Cycladic blueschist unit (Figures a and c), arguably one of the best exposed fossil subduction complexes in the world [e.g., Le Pichon and Angelier , ; Gautier et al ., ; Gautier and Brun , ; Ring and Layer , ; Ring et al ., ; Jolivet et al ., ; Roche et al ., ], has one of its most extensive occurrences on Syros Island, Greece [e.g., Keiter et al ., ]. Former oceanic crust of probable Cretaceous age [ Keiter et al ., ] was subducted within the Mesohellenic subduction system on a pressure‐dominated prograde pressure‐temperature path (PT path; Figure b) and rapidly exhumed thereafter. The Cycladic blueschist unit comprises a wide range of blueschists and eclogites with variable fabrics and compositions.…”

Section: Geological Setting Syros Islandmentioning

confidence: 99%

Textures of eclogites and blueschists from Syros island, Greece: Inferences for elastic anisotropy of subducted oceanic crust

Keppler¹,

Behrmann

2017

JGR Solid Earth

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Many blueschists and eclogites are inferred to have formed from oceanic basalts in subducted slabs. Knowledge of their elastic behavior is essential for reconstructing the internal structure of subduction zones. The Cycladic blueschist unit, exposed on Syros Island (Greece), contains rocks belonging to an exhumed Tertiary subduction complex. They were possibly part of a subduction channel, a shear zone above the subducting slab in which exhumation is possible during subduction. Intense plastic deformation, forming crystallographic preferred orientations (CPO), accompanied blueschist and eclogite metamorphism. CPO of the constituent minerals in the collected samples was determined by time‐of‐flight neutron diffraction. Two samples are foliated fine‐grained blueschists with strong CPO, rich in glaucophane, zoisite, and phengite. Two coarser‐grained eclogite samples rich in omphacite and clinozoisite, or glaucophane, have weaker CPO. Vp and Vs anisotropies were computed from the orientation distribution function and single‐crystal elastic constants. All samples show velocity maxima parallel to the mineral lineation, and minima normal to the foliation, providing important constraints on orientations of seismic anisotropy in subduction channels. Vp anisotropies are up to 3 times higher (6.5–12%) in the blueschists than in the eclogites (3–4%), pointing to a potentially important lithological control of elastic anisotropy in subducted oceanic crust.

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A new geological map of the Island of Syros (Aegean Sea, Greece): Implications for lithostratigraphy and structural history of the Cycladic Blueschist Unit

Cited by 37 publications

References 0 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

The geological signature of a slab tear below the Aegean

Textures of eclogites and blueschists from Syros island, Greece: Inferences for elastic anisotropy of subducted oceanic crust

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