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Ring, U., Glodny, J., Hansman, R., Scharf, A., Mattern, F., Callegari, I., . . . Hong, Y. (2024). The Samail subduction zone dilemma: Geochronology of high-pressure rocks from the Saih Hatat window, Oman, reveals juxtaposition of two subduction zones with contrasting thermal histories. Earth-Science Reviews, 250, Article ID 104711.
Open this publication in new window or tab >>The Samail subduction zone dilemma: Geochronology of high-pressure rocks from the Saih Hatat window, Oman, reveals juxtaposition of two subduction zones with contrasting thermal histories
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2024 (English)In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 250, article id 104711Article, review/survey (Refereed) Published
Abstract [en]

The Samail Ophiolite in the Oman Mountains formed at a Cretaceous subduction zone that was part of a wider Neo-Tethys plate-boundary system. The original configuration and evolution of this plate-boundary system is hidden in a structurally and metamorphically complex nappe stack below the Samail Ophiolite. Previous work provided evidence for high-temperature metamorphism high in the nappe pile (in the metamorphic sole of the Samail Ophiolite), and high-pressure metamorphism in the deepest part of the nappe pile (Saih Hatat window), possibly reflecting a downward younging, progressive accretion history at the Samail subduction zone. However, there is evidence that the two subduction-related metamorphic events are disparate, but temporally overlapping during the mid-Cretaceous. We present the first geochronologic dataset across the entire high-pressure nappe stack below the Samail Ophiolite, and the shear zones between the high-pressure nappes. Our 22 new Rb-Sr multimineral isochron ages from the Saih Hatat window, along with independent new field mapping and kinematic reconstructions, constrain the timing and geometry of tectonometamorphic events. Our work indicates the existence of a highpressure metamorphic event in the nappes below the ophiolite that was synchronous with the hightemperature conditions in the metamorphic sole. We argue that the thermal conditions of these synchronous metamorphic events can only be explained through the existence of two Cretaceous subduction zones/segments that underwent distinctly different thermal histories during subduction infancy. We infer that these two subduction zones initially formed at two perpendicular subduction segments at the Arabian margin and subsequently rotated relative to each other and, as a consequence, their records became juxtaposed: (1) The hightemperature metamorphic sole and the Samail Ophiolite both formed above the structurally higher, outboard, 'hot' and rotating Samail subduction zone and, (2) the high-pressure nappes developed within the structurally lower, inboard, 'cold' Ruwi subduction zone. We conclude that the formation and evolution of both subduction zones were likely controlled by the density structure of the mafic-rock-rich Arabian rifted margin and outermost Arabian Platform, and the subsequent arrival of the buoyant, largely mafic-rock-free, full-thickness Arabian lithosphere, which eventually halted subduction at the southern margin of Neo-Tethys.

Keywords
Subduction-zone processes, High-pressure metamorphism, Rb-Sr geochronology, Exhumation, Oman
National Category
Physical Geography
Identifiers
urn:nbn:se:su:diva-229008 (URN)10.1016/j.earscirev.2024.104711 (DOI)001199076100001 ()
Available from: 2024-05-07 Created: 2024-05-07 Last updated: 2024-05-07Bibliographically approved
Villa, I. M., Glodny, J., Peillod, A., Skelton, A. & Ring, U. (2023). Petrochronology of polygenetic white micas (Naxos, Greece). Journal of Metamorphic Geology, 41(3), 401-423
Open this publication in new window or tab >>Petrochronology of polygenetic white micas (Naxos, Greece)
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2023 (English)In: Journal of Metamorphic Geology, ISSN 0263-4929, E-ISSN 1525-1314, Vol. 41, no 3, p. 401-423Article in journal (Refereed) Published
Abstract [en]

Naxos in the Greek Cyclades preserves a type example of polymetamorphism. The southern and northern parts of the island record different Tertiary P–T histories between Eocene and Miocene times, including a blueschist facies event, one or more amphibolite/greenschist facies overprint(s) and contact metamorphism. Age attributions for these events are inconsistent in the literature. Here, we propose a new approach that combines electron probe microanalyzer (EPMA) characterization of the white mica (WM) with 39Ar-40Ar–Rb-Sr multichronometry. Textural–petrographic–compositional observations reveal that the polygenetic WM consists of five different generations: pre-Eocene relicts, paragonite, high-Si phengite, low-Si phengite and muscovite. EPMA mapping of four WM samples, previously analysed by Rb-Sr, reveals major element compositions heterogeneous down to the μm scale. Each WM consists of chemically distinct generations, documenting submicron-scale retrogression of high-pressure (HP) phengite grains to muscovite. Four WM samples from a N-S traverse across the island were analysed by 39Ar-40Ar stepheating, comparing coarse and fine sieve size fractions to obtain overdetermined K-Ar systematics. Fine sieve fractions are richer in Cl than coarse ones. Linear arrays in Cl/K-age isotope correlation diagrams show two predominant WM generations (one Cl-poor at ca. 38 Ma and one Cl-rich at <20 Ma). A lower-grade sample from southern Naxos was less pervasively recrystallized, provides older ages and preserves at least three WM generations, including a relict WM with a pre-Palaeocene K-Ar age, consistent with the high Ar retentivity of WM in the absence of complete recrystallization. The age of the Cl-poor end-member WM approximates the age of the HP event, 38 Ma. Ar inheritance in Cretaceous mica relicts is heterogeneous at the single-grain scale. Comparing the degassing rates of the WM fractions rules out ‘multidomain’ diffusion. As no sample is monomineralic, the degassing rate of each polygenetic mica is instead controlled by the mass balanced sum of the unrelated rate constants of its constituent minerals. Given the commonness of zoned and composite micas, the approach detailed here is potentially useful for reconstructing polyphase metamorphic histories worldwide. 

Keywords
39Ar-40Ar–Rb-Sr multichronometry, Cycladic Blueschist Unit, geochronology, petrochronology, white mica
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-213843 (URN)10.1111/jmg.12700 (DOI)000902408500001 ()2-s2.0-85145315457 (Scopus ID)
Available from: 2023-01-18 Created: 2023-01-18 Last updated: 2023-04-24Bibliographically approved
Ring, U., Glodny, J., Scharf, A. & Hansman, R. (2023). Some Like It Cold: The “Conundrum of Samail” Revisited. Tectonics, 42(1), Article ID e2022TC007531.
Open this publication in new window or tab >>Some Like It Cold: The “Conundrum of Samail” Revisited
2023 (English)In: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194, Vol. 42, no 1, article id e2022TC007531Article in journal (Refereed) Published
Abstract [en]

Most tectonic models consider that the “Samail subduction zone” was the only subduction zone at the mid-Cretaceous convergent Arabian margin. We report four new Rb-Sr multimineral isochron ages from high-pressure (HP) rocks and a major shear zone of the uppermost Ruwi-Yiti Unit of the Saih Hatat window in the Oman Mountains of NE Arabia. These ages demand a reassessment of the intraoceanic suprasubduction-zone evolution that formed the Samail Ophiolite and its metamorphic sole in the Samail subduction zone. Our new ages constrain waning HP metamorphism of the Ruwi subunit at ∼99-96 Ma and associated deformation in the Yenkit shear zone between ∼104 and 93 Ma. Our ages for late stages of deformation and HP metamorphism (thermal gradients of ∼8–10°C km−1) overlap with published ages of ∼105-102 Ma for Samail-subduction-zone prograde-to-peak metamorphism (thermal gradients of ∼20–25°C km−1), subsequent decompressional partial melting of the metamorphic sole and suprasubduction-zone crystallization of the Samail Ophiolite (thermal gradients of ∼30°C km−1) between ∼100 and 93 Ma. Thermal considerations demand that two subduction zones existed at the mid-Cretaceous Arabian margin. High-pressure metamorphism of the Ruwi-Yiti rocks occurred in a mature, thermally equilibrated “Ruwi subduction zone” that formed at ∼110 Ma. Initiation of the infant, thermally unequilibrated and, thus, immature, outboard intraoceanic Samail subduction zone occurred at ∼105 Ma. The Samail Ophiolite and its metamorphic sole were then thrust over the exhuming Ruwi-Yiti HP rocks and onto the Arabian margin after ∼92 Ma, while the bulk of the Saih Hatat HP rocks below the Ruwi-Yiti Unit started to be underthrust in the Ruwi subduction zone.

Keywords
subduction zone, high-pressure rocks, high-temperature rocks, geochronology, Saih Hatat window, Oman
National Category
Geology
Identifiers
urn:nbn:se:su:diva-229517 (URN)10.1029/2022TC007531 (DOI)000998826400001 ()2-s2.0-85147094801 (Scopus ID)
Available from: 2024-05-27 Created: 2024-05-27 Last updated: 2024-05-27Bibliographically approved
Craddock, J. P., Ring, U. & Pfiffner, O. A. (2022). Deformation of the European Plate (58-0 Ma): Evidence from Calcite Twinning Strains. Geosciences, 12(6), Article ID 254.
Open this publication in new window or tab >>Deformation of the European Plate (58-0 Ma): Evidence from Calcite Twinning Strains
2022 (English)In: Geosciences, E-ISSN 2076-3263, Vol. 12, no 6, article id 254Article in journal (Refereed) Published
Abstract [en]

We present a data set of calcite twinning strain results (n = 209 samples; 9919 measured calcite twins) from the internal Alpine nappes northwestward across the Alps and Alpine foreland to the older extensional margin along the Atlantic coast in Ireland. Along the coast of Northern Ireland, Cretaceous chalks and Tertiary basalts are cross-cut by calcite veins and offset by calcite-filled normal and strike-slip faults. Both Irish sample suites (n = 16 with four U-Pb vein calcite ages between 70–42 Ma) record a sub-horizontal SW-NE shortening strain with vertical extension and no strain overprint. This sub-horizontal shortening is parallel to the margin of the opening of the Atlantic Ocean (~58 Ma), and this penetrative fabric is only observed ~100 km inboard of the margin to the southeast. The younger, collisional Alpine orogen (~40 Ma) imparted a stress–strain regime dominated by SE-NW sub-horizontal shortening ~1200 km northwest from the Alps preserved in Mesozoic limestones and calcite veins (n = 32) in France, Germany and Britain. This layer-parallel shortening strain (−3.4%, 5% negative expected values) is preserved across the foreland in the plane of Alpine thrust shortening (SE-NW) along with numerous outcrop-scale contractional structures (i.e., folds, thrust faults). Calcite veins were observed in the Alpine foreland in numerous orientations and include both a SE-NW layer-parallel shortening fabric (n = 11) and a sub-vertical NE-SW vein-parallel shortening fabric (n = 4). Alpine foreland strains are compared with twinning strains from the frontal Jura Mountains (n = 9; layer-parallel shortening), the Molasse basin (n = 26; layer-parallel and layer-normal shortening), Pre-Alp nappes (n = 39; layer-parallel and layer-normal shortening), Helvetic and Penninic nappes (Penninic klippe; n = 46; layer-parallel and layer-normal shortening plus four striated U-Pb calcite vein ages ~24 Ma) and calcsilicates from the internal Tauern window (n = 4; layer-normal shortening). We provide a chronology of the stress–strain history of the European plate from 58 Ma through the Alpine orogen.

Keywords
calcite strains, structural geology, thrust belt evolution
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-212180 (URN)10.3390/geosciences12060254 (DOI)000816626000001 ()2-s2.0-85132864712 (Scopus ID)
Available from: 2022-12-02 Created: 2022-12-02 Last updated: 2022-12-02Bibliographically approved
Ring, U., Fassoulas, C., Uysal, I. T., Bolhar, R., Tong, K. & Todd, A. (2022). Nappe Imbrication Within the Phyllite-Quartzite Unit of West Crete: Implications for Sustained High-Pressure Metamorphism in the Hellenide Subduction Orogen, Greece. Tectonics, 41(11), Article ID e2022TC007430.
Open this publication in new window or tab >>Nappe Imbrication Within the Phyllite-Quartzite Unit of West Crete: Implications for Sustained High-Pressure Metamorphism in the Hellenide Subduction Orogen, Greece
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2022 (English)In: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194, Vol. 41, no 11, article id e2022TC007430Article in journal (Refereed) Published
Abstract [en]

We report four K-Ar fault-gouge and eight U-Pb calcite ages from the high-pressure Phyllite-Quartzite Unit (PQ) and the overlying, strongly thinned non-high-pressure Tripolitza and Pindos units of western Crete, Greece. We relate consistent 26–21 Ma fault-gouge ages to a discrete top-to-the-S, brittle-ductile, contractional shear zone (Intra-PQ Thrust) that formed during high-pressure conditions within the Phyllite-Quartzite Unit. The Intra-PQ Thrust separates the Phyllite-Quartzite Unit into an upper and a lower unit and is associated with gypsum deposits and high finite strain. Below the Intra-PQ Thrust, U-Pb calcite ages between about 16 and 13 Ma are also associated with top-to-the-S kinematic indicators and, in part, developed during aragonite stability. The brittle-ductile contact zone to the overlying Tripolitza and Pindos units yielded U-Pb calcite ages of 13 to 12 Ma. Our data imply that the upper Phyllite-Quartzite Unit underwent high-pressure metamorphism at the commonly envisaged time of 24–21 Ma. However, the lower Phyllite-Quartzite Unit started to be underthrust at 26–21 Ma and was high-pressure metamorphosed at 16–13 Ma, as suggested by the U-Pb calcite ages of aragonite-bearing samples and published zircon fission track ages. We discuss a tectonic model of successive underthrusting, high-pressure metamorphism and subsequent exhumation of both Phyllite-Quartzite units in extrusion wedges until 12–11 Ma, after which Crete underwent crustal extension. Our work suggests that there might be more than one Cretan Detachment. It also has implications for sustained underthrusting and exhumation of continental crust in subduction zones.

Keywords
high-pressure metamorphism, structural analysis, geochronology, subduction zone processes, Crete, Greece
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-212579 (URN)10.1029/2022TC007430 (DOI)000928053800007 ()2-s2.0-85142869531 (Scopus ID)
Available from: 2022-12-16 Created: 2022-12-16 Last updated: 2023-04-11Bibliographically approved
Scharf, A., Mattern, F., Bolhar, R., Callegari, I., Mattern, P. & Ring, U. (2022). Oligocene/Early Miocene E/W-Shortening in the Oman Mountains Related to Oblique Arabia-India Convergence. Tectonics, 41(12), Article ID e2022TC007271.
Open this publication in new window or tab >>Oligocene/Early Miocene E/W-Shortening in the Oman Mountains Related to Oblique Arabia-India Convergence
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2022 (English)In: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194, Vol. 41, no 12, article id e2022TC007271Article in journal (Refereed) Published
Abstract [en]

Field survey, literature review, geological map interpretation, GPlates reconstruction and LA-ICP-MS U-Pb dating of synkinematic calcite demonstrate that ∼E/W-shortening in eastern Oman was significant and related to oblique convergence of Arabia and India from 32.5 to 20 Ma. Approximately N/S-striking contractional structures, WNW to NNW-striking sinistral faults and ∼E/W-striking normal faults characterize a ∼250 km × ∼50 km wrench corridor in the eastern Oman Mountains (Hajar Wrench Corridor, HWC). Numerous faults/folds indicate that deformation of the HWC is widely distributed but concentrated along WNW to NNW-striking major faults at the SW margin of the Saih Hatat Dome, forming the Hajar Shear Zone, which reactivated basement faults. GPlates reconstructions reveal that N-drifting India rotated 8° counter-clockwise with respect to fixed Arabia from 32.5 to 20 Ma, leading to a minimum of 100 km E/W convergence between both plates. This convergence created the sinistral HWC with a displacement of a few to several tens of kilometers. Independently from the GPlates time constraints, two U-Pb ages of synkinematic calcites, crystallized along faults during HWC movement, yield compatible ages of 30.08 ± 0.47 and 22.31 ± 2.15 Ma (2 standard error). E/W-shortening also affected the northern Oman Mountains, creating the ∼N/S-striking Hagab Thrust in the Musandam Peninsula and the Jabal Hafit Anticline.

National Category
Other Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-215312 (URN)10.1029/2022TC007271 (DOI)000924523700001 ()2-s2.0-85145193886 (Scopus ID)
Available from: 2023-03-06 Created: 2023-03-06 Last updated: 2024-05-28Bibliographically approved
Scharf, A., Bailey, C. M., Bolhar, R., Mattern, F. & Ring, U. (2022). Post-obduction listwaenite genesis in the Oman Mountains inferred from structural analysis and U-Pb carbonate dating. Earth and Planetary Science Letters, 595, Article ID 117756.
Open this publication in new window or tab >>Post-obduction listwaenite genesis in the Oman Mountains inferred from structural analysis and U-Pb carbonate dating
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2022 (English)In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 595, article id 117756Article in journal (Refereed) Published
Abstract [en]

Listwaenite, a distinctive rock formed by carbonation of peridotite, is important for understanding carbon fluxes and storage in the deep Earth. In northern Oman, this lithology occurs near/at the base of the Semail Ophiolite and has been proposed to have formed in the mantle wedge during Late Cretaceous obduction and ophiolite emplacement. Listwaenite occurs as tabular sheets associated with post-obductional extensional faults. Specifically, listwaenite formed in (1) extensional duplexes bound by shallowly-dipping normal faults, (2) moderately- to steeply-dipping extensional faults, and (3) layers that overlie rocks of the metamorphic sole and unmetamorphosed platform carbonates. Two dolomite veins cutting listwaenite yield near-identical LA-ICP-MS U-Pb ages of 60.3 ± 15.4 and 55.1 ± 4.7 Ma (2 standard error). Thus, listwaenite formed prior to or is coeval with the ∼60-55 Ma veins. One carbonate listwaenite sample yields a LA-ICP-MS U-Pb age of 64.31 ± 6.28 Ma. Further six listwaenite samples yield imprecise ages of ∼33-3 Ma. Thus, listwaenite is interpreted to have formed during at least two post-obductional deformational events in the Oman Mountains. Hydrothermal circulation of carbon-rich fluids along upper crustal extensional faults facilitated listwaenite formation. Our results indicate that listwaenite formed during post-obductional extension, challenging models of listwaenite genesis in the mantle wedge during obduction.

Keywords
extension, subduction, doming, carbonated and silicified ultramafics, CO2 sink
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-211565 (URN)10.1016/j.epsl.2022.117756 (DOI)000877976300001 ()2-s2.0-85136296549 (Scopus ID)
Available from: 2022-11-25 Created: 2022-11-25 Last updated: 2022-11-28Bibliographically approved
Glodny, J. & Ring, U. (2022). The Cycladic Blueschist Unit of the Hellenic subduction orogen: Protracted high-pressure metamorphism, decompression and reimbrication of a diachronous nappe stack. Earth-Science Reviews, 224, Article ID 103883.
Open this publication in new window or tab >>The Cycladic Blueschist Unit of the Hellenic subduction orogen: Protracted high-pressure metamorphism, decompression and reimbrication of a diachronous nappe stack
2022 (English)In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 224, article id 103883Article in journal (Refereed) Published
Abstract [en]

We discuss the assembly and tectonochronology of the Cycladic Blueschist Unit (CBU) in the central Aegean Sea region, Greece, as a composite, subduction-related, high-pressure (blueschist to eclogite facies) stack of nappes. Our work is based on a review of geochronologic data from the Cycladic islands of Tinos, Syros and Sifnos. In addition, we present a large set of 34 new, internally consistent Rb-Sr multimineral isochron age data from these islands that can be linked to distinct metamorphic stages and episodes of ductile deformation. The reviewed and new ages provide remarkably similar results indicating that the age data and their interpretation is robust. We find that three distinct, significantly diachronous, CBU high-pressure nappes were sequentially accreted between ~55 and ~30 Ma, with a fourth ~24-22 Ma old high-pressure belt, the Basal Unit, below the CBU. Each CBU nappe was exhumed soon after its high-pressure imprint and experienced greenschist-facies overprinting with partial metamorphic reworking ~10 Ma after high-pressure accretion. At the time the structurally higher high-pressure nappe was exhumed, an underlying nappe was accreted and metamorphosed at high-pressure conditions. Our work suggests that the high-pressure nappes were considerably exhumed as rather coherent units during sustained lithospheric shortening in a subduction channel by return flow. The early Oligocene underthrusting of the External Hellenides to the south of the Cyclades, and tectonically below the CBU, is interpreted to have reduced the taper of the Hellenic subduction wedge, which caused significant shortening across the Cyclades region and an important phase of out-of-sequence thrusting that emplaced the non-high-pressure upper units above the CBU. Our analysis shows that this shortening event also caused significant reimbrication within the CBU along the recently discovered Trans Cycladic Thrust.

Keywords
Geochronology, High-pressure rocks, Continental subduction, Accretion, Exhumation, Cycladic Blueschist Unit, Aegean Sea region
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-204548 (URN)10.1016/j.earscirev.2021.103883 (DOI)000778934800001 ()2-s2.0-85120953444 (Scopus ID)
Available from: 2022-05-10 Created: 2022-05-10 Last updated: 2022-05-10Bibliographically approved
Peillod, A., Majka, J., Ring, U., Drüppel, K., Patten, C., Karlsson, A., . . . Tehler, E. (2021). Differences in decompression of a high-pressure unit: A case study from the Cycladic Blueschist Unit on Naxos Island, Greece. Lithos, 386–387, Article ID 106043.
Open this publication in new window or tab >>Differences in decompression of a high-pressure unit: A case study from the Cycladic Blueschist Unit on Naxos Island, Greece
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2021 (English)In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 386–387, article id 106043Article in journal (Refereed) Published
Abstract [en]

Determining the tectonic evolution and thermal structure of a tectonic unit that experiences a subduction-related pressure temperature (P-T) loop is challenging. Within a single unit, P-T conditions can vary from top to bottom which can only be revealed by detailed petrological work. We present micropetrological data from the middle section of the Cycladic Blueschist Unit (CBU) in Naxos, Greece, which indicates a different P-T loop than that for the top of the sequence. Using Zr-in-rutile and Ti-in-biotite thermometry coupled with quartz-in-garnet elastic barometry and phase equilibrium thermodynamic modeling, we identify a prograde path from 15.4 +/- 0.8 kbar to 19.9 = 0.6 kbar and from 496 +/- 16 degrees C to 572 +/- 7 degrees C (2a uncertainty), equilibration during decompression at 8.3 +/- 15 kbar and 519 +/- 12 degrees C followed by near-isobaric heating to 92 +/- 0.8 kbar and 550 +/- 10 degrees C (or even 584 +/- 19 degrees C), and a final greenschist-facies equilibration stage at 3.8 +/- 0.3 kbar and 520 +/- 4 degrees C. We compare these P-T estimates with published data from the top and also the bottom of the CBU section and find that the bottom half of the CBU on Naxos records higher peak high-pressure (HP) of about 4 kbar than the top of the unit, defining the thickness of the CBU section on Naxos to about 15 km in the Eocene. We determine that crustal thickening of up to similar to 15% occurs in the upper half of the CBU section during exhumation of the HP rocks in an extrusion wedge in a convergence setting. At about 30 Ma, the bottom half of the CBU was finally thrust onto the radiogenic Cycladic basement. Subsequently this bottom half of the CBU section underwent isobaric heating of 9-96 degrees C between c. 32-28 and 23-21 Ma. Isobaric heating occurred below the upper CBU section that thickened during decompression and commenced when HP metamorphism in the Cyclades ended. This suggests that thermal relaxation following tectonic accretion in the Cyclades controlled heating of the evolving Cycladic orogen during a tectonically quiescent period before lithospheric extension commenced by 23-20.5 Ma.

Keywords
Hellenide orogen, Cycladic Blueschist Unit, High-pressure metamorphism, Exhumation, Isobaric heating, Zr-in-rutile, Quartz-in-garnet (QuiG), Thermodynamic modeling
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-193053 (URN)10.1016/j.lithos.2021.106043 (DOI)000632736400002 ()
Available from: 2021-05-09 Created: 2021-05-09 Last updated: 2022-02-25Bibliographically approved
Ring, U. & Glodny, J. (2021). Geometry and Kinematics of Bivergent Extension in the Southern Cycladic Archipelago: Constraining an Extensional Hinge Zone on Sikinos Island, Aegean Sea, Greece. Tectonics, 40(6), Article ID e2020TC006641.
Open this publication in new window or tab >>Geometry and Kinematics of Bivergent Extension in the Southern Cycladic Archipelago: Constraining an Extensional Hinge Zone on Sikinos Island, Aegean Sea, Greece
2021 (English)In: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194, Vol. 40, no 6, article id e2020TC006641Article in journal (Refereed) Published
Abstract [en]

We report the results of a field study on Sikinos Island in the Aegean extensional province of Greece and propose a hinge zone controlling incipient bivergent extension in the southern Cyclades. A first deformation event led to top-S thrusting of the Cycladic Blueschist Unit (CBU) onto the Cycladic basement in the Oligocene. The mean kinematic vorticity number (Wm) during this event is between 0.56 and 0.63 in the CBU, and 0.72 to 0.84 in the basement, indicating general-shear deformation with about equal components of pure and simple shear. The strain geometry was close to plane strain. Subsequent lower-greenschist-facies extensional shearing was also by general-shear deformation; however, the pure-shear component was distinctly greater (Wm = 0.3–0.41). The degree of subvertical pure-shear flattening increases structurally upward and explains alternating top-N and top-S shear senses over large parts of the island. Along with an increased coaxial deformation component, the strain geometry became oblate. Published quantitative data from nearby Ios Island are similar and both data sets define an extensional hinge zone between top-N extensional deformation across large parts of the central and northern Cyclades and top-S extensional deformation at the southern and western fringe of the archipelago. This extensional hinge zone is an important large-scale structure forming early in the history of lithospheric extension due to southward retreat of the Hellenic slab.

Keywords
Aegean Sea, Cycladic blueschist unit, extensional deformation, Greece, kinematic vorticity, strain analysis
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-196782 (URN)10.1029/2020TC006641 (DOI)000665973300007 ()
Available from: 2021-09-29 Created: 2021-09-29 Last updated: 2022-02-25Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-3347-9284

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