Excursion Guide to the Field Trip on Seriphos, Syros, and Naxos

Dixon, John; Feenstra, Anne; Jansen, J. Ben H.; Kreulen, Rob; Ridley, John; Salemink, J.; Schuiling, R. D.

doi:10.1007/978-94-009-4013-0_18

Cited by 9 publications

(25 citation statements)

References 13 publications

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“…The best preserved tracts of eclogites and blueschists are found on Syros, within the Ermoupolis Unit (Dixon 1976;Dixon et al 1987;Okrusch & Br6cker 1990). Peak conditions are generally estimated to lie in the upper pressure limits of the epidote-blueschist stability field, at about 20 kbar and 500 ~ (e.g.…”

Section: The Geology Of Syrosmentioning

confidence: 97%

“…2) on the northern tip of the island has been described as the best area for the preservation of HP mineral assemblages (Ridley 1982;Dixon et al 1987;Keiter et al 2004). There are three mappable metasedimentary units: (1) marble containing thin layers of dolomite, but mainly grey and cream calcite; (2) conglomerate containing deformed clasts of calcite, quartz and metabasite;…”

Section: I a P O R Imentioning

confidence: 99%

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Co-axial horizontal stretching within extending orogens: the exhumation of HP rocks on Syros (Cyclades) revisited

Bond

Butler

Dixon

2007

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Although the role of extensional tectonics in the exhumation of high-pressure metamorphic terranes is widely established, the kinematics of such deformation remains ambiguous. This paper outlines new field data from the Attic-Cycladic blueschist belt that suggest that distributed ductile strain plays a significant role in the extension and that, consequently, the role of major detachment faults may have been over-emphasized in previous studies. The high-pressure blueschist terrane (Ermoupolis Unit) of Syros shows abundant evidence of subhorizontal extension, manifest as layer boudinage and ductile thinning without the development of significant internal detachments. The deformation approximates to pure shear stretching that was heterogeneously distributed in space and time. Minor zones of asymmetric shear are interpreted not as through-going extensional shear zones but as structures that maintain compatibility between zones of differential stretching. The progression of deformation is charted through the systematic development of increasingly lower-pressure metamorphic assemblages. However, most of the decompression (potentially from 20 kbar to 6 kbar) occurred within the blueschist stability field, as the rocks were actively extending. Heterogeneous retrogression and concomitant deformation are believed to relate to the local chemistry and availability of hydrous fluids.The relative importance of broadly distributed, approximately pure shear deformation and strongly localized, approximately simple shear through the crust is a recurrent debate in continental tectonics. Mike Coward was at the vanguard of early attempts to explain highdeformation zones in the continental crust, chiefly in terms of simple shear, through his work on basement structures in Africa and NW Scotland. As focus shifted to basin dynamics in the 1980s, debates polarized between homogeneous rifting (sometimes called 'pure shear'; McKenzie 1978) and whole lithospheric shear zone models (e.g. Wernicke 1985). Common ground was found through the development of 'depth-dependent' stretching models (see Roberts & Yielding 1992, for review), including the heterogenous rifting model of Coward (1986). Yet the whole lithosphere shear models have retained much influence, especially in tectonic scenarios for the exhumation of high-pressure metamorphic rocks. Drawing on models from the Basin-and-Range Province that inspired Wernicke's (1985) lithospheric models, Lister et al. (1984) proposed that blueschists of the Attic-Cycladic belt in the Aegean had been exhumed in the footwall to major low-angle, crustal-scale normal faults. This model has since seen widespread use, not only in the Aegean but also in other parts of the Mediterranean (e.g. Jolivet et al. 1998) and further afield. With these continuing studies it is pertinent to examine the structural geology of these settings carefully.To what degree are the high-pressure (HP) rocks in the footwalls to large faults merely passive passengers back to upper crustal conditions, or do they contain significan...

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Section: The Geology Of Syrosmentioning

confidence: 97%

Section: I a P O R Imentioning

confidence: 99%

Co-axial horizontal stretching within extending orogens: the exhumation of HP rocks on Syros (Cyclades) revisited

Bond

Butler

Dixon

2007

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“…Ridley, 1982). The Ermoupolis Unit was metamorphosed to eclogite-blueschist facies (Dixon, 1976;Dixon et al, 1987;Okrusch & Br€ ocker, 1990). Peak metamorphic conditions are generally estimated to lie in the epidote-blueschist/ eclogite stability field, at~20 kbar and 500-550°C (e.g.…”

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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“…This work focuses on the Cycladic Blueschist Unit of Greece (CBU), but the issues which obscure its structural history are common to HP‐LT terranes worldwide. Within the CBU, primary depositional features have been erased from metasediments by deformation, recrystallization, and metamorphism¸ although mafic blueschists and eclogites may locally retain primary igneous textures [ Dürr et al, ; Dixon et al, ; Seck et al, ]. Fossils, as a means of constraining depositional age, are a rarity, although notable exceptions exist, such as on Andros Island [ Papanikolaou, ], Attica [ Marinos and Petraschek, ], Naxos [ Négris and Meunier, ], Tinos [ Melidonis, ], and Samos Island [ Papanikolaou, ].…”

Section: Introductionmentioning

confidence: 99%

The provenance and internal structure of the Cycladic Blueschist Unit revealed by detrital zircon geochronology, Western Cyclades, Greece

2017

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This study presents detrital zircon U‐Pb analyses of 23 samples of the Cycladic Blueschist Unit (CBU) from Kea, Kythnos, and Serifos islands, as well as the Lavrion Peninsula of SE Attica. The maximum depositional ages (MDA) and age distributions of detrital zircon U‐Pb dates are used to correlate metasediments between the islands considered herein and infer their provenance. Two distinct detrital zircon U‐Pb age distributions are found in CBU metasediments: “Proterozoic,” comprised of >40% Neoproterozoic zircons with Triassic‐Early Jurassic maximum depositional ages and “Paleozoic,” containing >30% Paleozoic zircons and yielding Late Jurassic‐Cretaceous MDAs. Proterozoic affinity metasediments are rift margin deposits derived from the northern Gondwanan margin. Paleozoic metasediments are flysch sediments most probably sourced from the Internal Hellenides. This metamorphosed flysch forms a distinct marker horizon found in a similar structural position in Lavrion, Kythnos, and Serifos. Based on lithologic correlation, sediment provenance, and MDA estimates, the CBU of Kythnos is correlative to the Lavrion Schists of Attica. On the islands of Serifos and Kythnos and within the Lavrion Schists only young‐on‐old relationships exist between rocks based on MDA estimates.

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Excursion Guide to the Field Trip on Seriphos, Syros, and Naxos

Cited by 9 publications

References 13 publications

Co-axial horizontal stretching within extending orogens: the exhumation of HP rocks on Syros (Cyclades) revisited

Co-axial horizontal stretching within extending orogens: the exhumation of HP rocks on Syros (Cyclades) revisited

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

The provenance and internal structure of the Cycladic Blueschist Unit revealed by detrital zircon geochronology, Western Cyclades, Greece

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