Interlayered Eclogites, Blueschists and Epidote Amphibolites from NE Oman: a Record of Protolith Compositional Control and Limited Fluid Infiltration

El‐Shazly, A. K.; Worthing, M. A.; Liou, J. G.

doi:10.1093/petroj/38.11.1461

Cited by 31 publications

(18 citation statements)

References 53 publications

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“…At Pointe des Chats (Chat) in zone II, metre-scale boudins of blueschist occur in a greenschist matrix. Similar coexisting blueschists and greenschists are observed in other high-pressure terrains (Brown and Bradshaw 1979;Seidel et al 1981;Oberhänsli 1986;Schliestedt and Matthews 1987;Bröcker 1990;El Shazly et al 1997;Cartwright and Barnicoat 1999). In general, one could distinguish among ªprimaryº greenschists of specific bulk composition which were affected by a greenschist-facies metamorphism only, and ªsecondaryº greenschists which were formed from blueschists during the greenschist-facies stage after a high-pressure metamorphism.…”

Section: Bulk-rock Geochemistrysupporting

confidence: 63%

“…Altherr et al 1979;Matthews and Schliestedt 1984;Owen 1989;Okrusch and Bröcker 1990;Oh et al 1991;Bröcker et al 1993;Seck et al 1996;El-Shazly et al 1997). This interlayering has been attributed to (a) differences in P±T conditions of equilibration in the layers and tectonic juxtaposition (Reinsch 1979;Ridley 1984), (b) different protolith compositions (Dungan et al 1983;El Shazly et al 1997) or (c) different retrograde overprinting as a result of variable fluid infiltration (Triboulet 1979;Bröcker 1990). It has been demonstrated that transformation of blueschist-facies mineral assemblages to greenschist and amphibolitefacies assemblages by volatization reactions can be triggered by channelized infiltration of external fluids during the uplift of the rocks (Schliestedt and Matthews 1987;Barrientos and Selverstone 1993).…”

Section: Introductionmentioning

confidence: 99%

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Two-stage prograde and retrograde Variscan metamorphism of glaucophane-eclogites, blueschists and greenschists from Ile de Groix (Brittany, France)

Schulz

Triboulet

Audren

et al. 2001

International Journal of Earth Sciences

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Two-stage prograde and retrograde Variscan metamorphism of glaucophane-eclogites, blueschists and greenschists from Ile de Groix (Brittany, France) Abstract On Ile de Groix, Variscan metamorphic former tholeiitic and alkaline basalts occur as glaucophane-eclogites, blueschists and greenschists in isolated lenses and layers within metapelites. Whole-rock d 18 O SMOW values of the metabasites show limited variations (10.4±12.0½) and no systematic differences among rock types and metamorphic grades. This provides no argument for large-scale blueschist-to-greenschist transformation driven by infiltration of externally derived fluids. Metamorphic mineralogical changes should have been triggered by internal fluids. Element variations in interlayered blue-and greenschists can be attributed to magmatic fractionation. Assemblages with garnet, clinopyroxene and glaucophane of a high-pressure/low-temperature (HP±LT) metamorphism M1, and NaCa-amphiboles (barroisite, magnesiohornblende, actinolite) of a medium-pressure/medium-temperature metamorphism M2 crystallized during deformation D1. Detailed core-rim zonation profiles display increasing and then decreasing Al IV in glaucophane of M1. NaCa-amphiboles of M2, mantling glaucophane and crystallized in porphyroblasts, show first increasing, then decreasing, Al IV and Al VI . Empirically calibrated thermobarometers allowed P±T path reconstructions. In glaucophane-eclogites of a metamorphic zone I, a prograde evolution to M1 peak conditions at 400±500 C/10±12 kbar was followed by a retrograde P±T path within the glaucophane stability field. The subsequent M2 evolution was again prograde up to >600 C at 8 kbar and then retrograde. Similarly, in metamorphic zones II and III, prograde and retrograde paths of M1 and M2 at lower maximal temperatures and pressures exist. The almost complete metamorphic cycle during M2 signalizes that the HP±LT rocks escaped from an early erosion by a moderate second burial event and explains the longlasting slow uplift with low average cooling rates.Keywords P±T paths´High-pressure metamorphismÁ mphibole mineral chemistry´Amphibole thermobarometry´Oxygen isotopes´Uplift´South Armorican Domain´Variscan orogeny B. Schulz ( ) )

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Section: Bulk-rock Geochemistrysupporting

confidence: 63%

Section: Introductionmentioning

confidence: 99%

Two-stage prograde and retrograde Variscan metamorphism of glaucophane-eclogites, blueschists and greenschists from Ile de Groix (Brittany, France)

Schulz

Triboulet

Audren

et al. 2001

International Journal of Earth Sciences

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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: 58%

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

Okay

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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“…In zone B, garnet-glaucophane schists are interlayered with glaucophane-epidote schists, clinopyroxene-rich granofelses and epidote amphibolites. Zone C is defined by the appearance of eclogites that are interlayered with garnet blueschists, clinopyroxene-rich granofelses and epidote-amphibolites (El-Shazly et al, 1997). Peak conditions for this zone are estimated at 550-580 uC and 12-15 kbar (El-Shazly et al, 1997;El-Shazly, 2001), although Wendt et al (1993) and favoured much higher pressures of 20 kbar for these rocks.…”

Section: Geological Settingmentioning

confidence: 99%

Formation and exhumation of blueschists and eclogites from NE Oman: new perspectives from Rb–Sr and ⁴⁰Ar/³⁹Ar dating

El‐Shazly¹,

Bröcker²,

Hacker³

et al. 2001

Journal Metamorphic Geology

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Seven eclogite facies samples from lithologically different units which structurally underlie the Semail ophiolite were dated by the 40Ar/39Ar and Rb–Sr methods. Despite extensive efforts, phengite dated by the 40Ar/39Ar method yielded saddle, hump or irregularly shaped spectra with uninterpretable isochrons. The total gas ages for the phengite ranged from 136 to 85 Ma. Clinopyroxene–phengite, epidote–phengite and whole‐rock–phengite Rb–Sr isochrons for the same samples yielded ages of 78 ± 2 Ma. We therefore conclude that the eclogite facies rocks cooled through 500 °C at c. 78 ± 2 Ma, and that the 40Ar/39Ar dates can only constrain maximum ages due to the occurrence of excess Ar inhomogeneously distributed in different sites. Our new results lead us to conclude that high‐pressure metamorphism of the Oman margin took place in the Late Cretaceous, contemporaneous with ophiolite emplacement. Previously published structural and petrological data lead us to suggest that this metamorphism resulted from intracontinental subduction and crustal thickening along a NE‐dipping zone. Choking of this subduction zone followed by ductile thinning of a crustal mass wedged between deeply subducted continental material and overthrust shelf and slope units facilitated the exhumation of the eclogite facies rocks from depths of c. 50 km to 10–15 km within c. 10 Ma, and led to their juxtaposition against overlying lower grade rocks. Final exhumation of all high‐pressure rocks was driven primarily by erosion and assisted by normal faulting in the upper plate.

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Interlayered Eclogites, Blueschists and Epidote Amphibolites from NE Oman: a Record of Protolith Compositional Control and Limited Fluid Infiltration

Cited by 31 publications

References 53 publications

Two-stage prograde and retrograde Variscan metamorphism of glaucophane-eclogites, blueschists and greenschists from Ile de Groix (Brittany, France)

Two-stage prograde and retrograde Variscan metamorphism of glaucophane-eclogites, blueschists and greenschists from Ile de Groix (Brittany, France)

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

Formation and exhumation of blueschists and eclogites from NE Oman: new perspectives from Rb–Sr and ⁴⁰Ar/³⁹Ar dating

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Interlayered Eclogites, Blueschists and Epidote Amphibolites from NE Oman: a Record of Protolith Compositional Control and Limited Fluid Infiltration

Cited by 31 publications

References 53 publications

Two-stage prograde and retrograde Variscan metamorphism of glaucophane-eclogites, blueschists and greenschists from Ile de Groix (Brittany, France)

Two-stage prograde and retrograde Variscan metamorphism of glaucophane-eclogites, blueschists and greenschists from Ile de Groix (Brittany, France)

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

Formation and exhumation of blueschists and eclogites from NE Oman: new perspectives from Rb–Sr and 40Ar/39Ar dating

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Formation and exhumation of blueschists and eclogites from NE Oman: new perspectives from Rb–Sr and ⁴⁰Ar/³⁹Ar dating