Infiltration vs. thermal overprinting of epidote blueschists, Ile de Groix, France

Barrientos, Ximena; Selverstone, Jane

doi:10.1130/0091-7613(1993)021<0069:ivtooe>2.3.co;2

Cited by 33 publications

(28 citation statements)

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“…(5)) requires H 2 O-rich fluids for its completion (Miyashiro and Banno, 1958;Brown, 1974;Maruyama et al, 1986). The close field association of epidote -blueschists and epidote-amphibolites is probably due to irregular influx of H 2 O-rich fluids, as has been shown in several other blueschist -greenschist terrains (e.g., Schliested and Matthews, 1987;Bröcker, 1990;Barrientos and Selverstone, 1993;El-Shazly et al, 1997).…”

Section: P -T Evolution Of the Eclogite Blueschist And Epidote-amphimentioning

confidence: 57%

Triassic blueschists and eclogites from northwest Turkey: vestiges of the Paleo-Tethyan subduction

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Monod

Monié

2002

Lithos

152

100

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Triassic eclogite and blueschist facies rocks occur as a thrust sheet, 25-km long and over 2-km thick, in an Eocene fold-andthrust belt in northwest Turkey along the İzmir -Ankara suture. The thrust sheet consists mainly of metabasites with minor marble, phyllite and metachert, and rare lenses of serpentinite. The common blueschist facies mineral assemblage in the metabasites is sodic amphibole + epidote + albite + chlorite + phengite F garnet. Sodic amphibole commonly shows replacement by barroisite, and there is continuous petrographic transition from blueschist -metabasites to barroisite-bearing epidoteamphibolites. Eclogite with the mineral assemblage of garnet + sodic pyroxene + sodic -calcic amphibole + epidote is found only in one locality. P -T conditions of the epidote -blueschist facies metamorphism are estimated as 450 F 50 jC and 11 F 2 kbar. The blueschist formation was followed by a decrease in pressure and increase in temperature, leading to the development of barroisite-bearing epidote -amphibolites. Phengite, sodic amphibole and barroisite Ar/Ar ages from three metabasic rocks range between 215 and 205 Ma, and indicate Late Triassic high-pressure metamorphism. The Triassic blueschists in northwest Turkey constitute part of a much larger allochthonous tectonic unit of Triassic mafic volcanic rocks. They probably represent the upper layers of a Triassic oceanic plateau, which was accreted to the Laurasian margin during the latest Triassic. The close spatial association of the Triassic and Cretaceous blueschists along the İzmir -Ankara suture suggests that the suture represents a long-lived plate boundary of Late Palaeozoic to early Tertiary age. D

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Section: P -T Evolution Of the Eclogite Blueschist And Epidote-amphimentioning

confidence: 57%

Triassic blueschists and eclogites from northwest Turkey: vestiges of the Paleo-Tethyan subduction

Okay

Monod

Monié

2002

Lithos

152

100

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“…Bröcker (1990) and Barrientos and Selverstone (1993) suggested that the 635 retrograde blueschist-to-greenschist transformation is catalyzed by the availability of 636 synmetamorphic fluid as the rocks pass through the greenschist facies by a selective 637 infiltration overprinting process. All of the Pichilemu rocks show evidence for retrograde 638 infiltration, but the effects were different in individual layers.…”

Section: Pre-metamorphic Variability Versus Metamorphic Overprinting 608mentioning

confidence: 99%

Retrograde metasomatic effects on phase assemblages in an interlayered blueschist–greenschist sequence (Coastal Cordillera, Chile)

Halama

Konrad‐Schmolke

2015

Lithos

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“…Based on mineral assemblages developed in the mafic rocks exposed on ile de Groix, two metamorphic stages generally are recognized: M1 blueschist facies metamorphism (450-550 "C, 10-18 kbar - Barrientos, 1992;Barrientos & Selverstone, 1993) followed by an M2 greenschist facies overprint (400-550 "C, 4-9 kbar -Barrientos, 1992). The age of blueschist facies metamorphism and the subsequent cooling history of this unit provides a constraint on possible tectonic models for the entire Variscan belt.…”

Section: Blueschist Belt Metamorphismmentioning

confidence: 99%

Rapid Variscan exhumation and the role of magma in core complex formation: southern Brittany metamorphic belt, France

Brown

Dallmeyer

1996

Journal Metamorphic Geology

114

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The high-grade migmatitic core to the southern Brittany metamorphic belt has mineralogical and textural features that suggest high-temperature decompression. The chronology of this decompression and subsequent cooling history have been constrained with 40Ar/39Ar ages determined for multigrain concentrates of hornblende and muscovite prepared from amphibolite and late-orogenic granite sheets within the migmatitic core, and from amphibolite of the structurally overlying unit. Three hornblende concentrates yield plateau isotope correlation ages of c. 303-298 Ma. Two muscovite concentrates record well-defined plateau ages of c. 306-305 Ma. These ages are geologically significant and date the last cooling through temperatures required for intracrystalline retention of radiogenic argon. The concordancy of the hornblende and muscovite ages suggest rapid post-metamorphic cooling. Extant geochronology and the new 40Ar/3'Ar data suggest a minimum time-integrated average cooling rate between c. 725 "C and c. 125 "C of c. 14+4"C Ma-', although below 600 'C the data permit an infinitely fast rate of cooling. Mineral assemblages and reaction textures in diatexite migmatites suggest c. 4 kbar decompression at 800-750 "C. This must have pre-dated the rapid cooling. Emplacement of two-mica granites into the metamorphic belt occurred between 345 and 300 Ma. The youngest plutons were emplaced synkinematically along shallow-dipping normal faults interpreted to be reactivated Eo-Variscan thrusts. A penetrative, west-plunging stretching lineation developed in these granites suggests that extension was orogen-parallel. Extension was probably related to regional uplift and gravitational collapse of thermally weakened crust during constrictional (escape) tectonics in this narrow part of the Variscan orogen. This followed slab breakor during the terminal stages of convergence between Gondwana and Laurasia; detachment may have been consequent upon a change in kinematics leading to dextral displacement within the orogen. Dextral ductile strike-slip displacement was concentrated in granites emplaced synkinematically along the South Armorican Shear Zone. Rapid cooling is interpreted to have resulted from tectonic unroofing with emplacement of granite along decollement surfaces. The high-grade migmatitic core of the southern Brittany metamorphic belt represents a type of metamorphic core complex formed during orogen-parallel extensional unroofing and regional-scale ductile flow.

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Infiltration vs. thermal overprinting of epidote blueschists, Ile de Groix, France

Cited by 33 publications

References 0 publications

Triassic blueschists and eclogites from northwest Turkey: vestiges of the Paleo-Tethyan subduction

Triassic blueschists and eclogites from northwest Turkey: vestiges of the Paleo-Tethyan subduction

Retrograde metasomatic effects on phase assemblages in an interlayered blueschist–greenschist sequence (Coastal Cordillera, Chile)

Rapid Variscan exhumation and the role of magma in core complex formation: southern Brittany metamorphic belt, France

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