Fluid entrapment and reequilibration during subduction and exhumation: A case study from the high-grade Nestos shear zone, Central Rhodope, Greece

Kurt Krenn, Christoph Bauer, Alexander Proyer, Evripidis Mposkos, Georg Hoinkes

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

A fluid inclusion study on metamorphic minerals of successive growth stages was performed oil highly deformed paragneisses from the Nestos Shear Zone at Xanthi (Central Rhodope), in which microdiamonds provide unequivocal evidence for ultrahigh-pressure (UHP) metamorphism. The correlation of fluid inclusion density isochores and fluid inclusion reequilibration textures with geothermobarometric data and the relative chronology of micro- and macro-scale deformation stages allow a better understanding of both the fluid and metamorphic evolution along the P-T-d path. Textural evidence for subduction towards the NE is recorded by the orientation of intragranular NE-oriented fluid inclusion planes and the presence of single, annular fluid inclusion decrepitation textures. These textures occur within quartz "foam" structures enclosed in an earlier generation of garnets with prolate geometries and rarely within recrystallized matrix quartz, and reequilibrated both in composition and density (luring later stages of exhumation. No fluid inclusions pertaining to the postulated ultrahigh-pressure stage for microdiamond-bearing garnet-kyanite-gneisses have yet been found. The prolate shape of garnets developed during the earliest stages of exhumation that is recorded structurally by (L >> S) tectonites, which subsequently accommodated progressive ductile SW shearing and folding up to shallow crustal levels. The majority of matrix kyanite and a later generation of garnet were formed during SW-directed shear under plane-strain conditions. Fluid inclusions entrapped in quartz during this stage of deformation underwent density loss and transformed to almost pure CO(2) inclusions by preferential loss of H(2)O. Those inclusions armoured within garnet retained their primary 3-phase H(2)O-CO(2) compositions. Reequilibration of fluid inclusions in quartz aggregates is most likely the result of recrystallization along with stress-induced, preferential H(2)O leakage along dislocations and planar lattice defects which results in the predominance of CO(2) inclusions with supercritical densities. Carbonic fluid inclusions from adjacent kyanite-corundum-bearing pegmatoids and, the presence of shear-plane-parallel fluid inclusion planes within late quartz boudin structures consisting of pure CO(2)-fluid inclusions with negative crystal shapes, bear witness of the latest stage of deformation by NE-directed extensional shear. This study shows that the textures of early fluid inclusions that formed already during the prograde metamorphic path can be preserved and used to derive information about the kinematics of subduction that is difficult to obtain from other sources. The textures of early inclusions, together with later generations of unaltered primary and secondary inclusions in metamorphic index minerals that can be linked to specific deformation stages and even P-T conditions, are a welcome supplement for the reconstruction of a rather detailed P-T-cl path. (C) 2007 Elsevier B.V. All rights reserved.
Original languageEnglish
Pages (from-to)33-53
Number of pages21
JournalLithos
Volume104
Issue number1-4
DOIs
Publication statusPublished - 2008

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exhumation
fluid inclusion
shear zone
subduction
Fluids
fluid
Quartz
garnet
Garnets
texture
quartz
kyanite
Carbon Monoxide
Textures
Bearings (structural)
Phosmet
Rhodopes
ultrahigh pressure metamorphism
Minerals
matrix

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Krenn, Kurt ; Bauer, Christoph ; Proyer, Alexander ; Mposkos, Evripidis ; Hoinkes, Georg. / Fluid entrapment and reequilibration during subduction and exhumation: A case study from the high-grade Nestos shear zone, Central Rhodope, Greece. In: Lithos. 2008 ; Vol. 104, No. 1-4. pp. 33-53.
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abstract = "A fluid inclusion study on metamorphic minerals of successive growth stages was performed oil highly deformed paragneisses from the Nestos Shear Zone at Xanthi (Central Rhodope), in which microdiamonds provide unequivocal evidence for ultrahigh-pressure (UHP) metamorphism. The correlation of fluid inclusion density isochores and fluid inclusion reequilibration textures with geothermobarometric data and the relative chronology of micro- and macro-scale deformation stages allow a better understanding of both the fluid and metamorphic evolution along the P-T-d path. Textural evidence for subduction towards the NE is recorded by the orientation of intragranular NE-oriented fluid inclusion planes and the presence of single, annular fluid inclusion decrepitation textures. These textures occur within quartz {"}foam{"} structures enclosed in an earlier generation of garnets with prolate geometries and rarely within recrystallized matrix quartz, and reequilibrated both in composition and density (luring later stages of exhumation. No fluid inclusions pertaining to the postulated ultrahigh-pressure stage for microdiamond-bearing garnet-kyanite-gneisses have yet been found. The prolate shape of garnets developed during the earliest stages of exhumation that is recorded structurally by (L >> S) tectonites, which subsequently accommodated progressive ductile SW shearing and folding up to shallow crustal levels. The majority of matrix kyanite and a later generation of garnet were formed during SW-directed shear under plane-strain conditions. Fluid inclusions entrapped in quartz during this stage of deformation underwent density loss and transformed to almost pure CO(2) inclusions by preferential loss of H(2)O. Those inclusions armoured within garnet retained their primary 3-phase H(2)O-CO(2) compositions. Reequilibration of fluid inclusions in quartz aggregates is most likely the result of recrystallization along with stress-induced, preferential H(2)O leakage along dislocations and planar lattice defects which results in the predominance of CO(2) inclusions with supercritical densities. Carbonic fluid inclusions from adjacent kyanite-corundum-bearing pegmatoids and, the presence of shear-plane-parallel fluid inclusion planes within late quartz boudin structures consisting of pure CO(2)-fluid inclusions with negative crystal shapes, bear witness of the latest stage of deformation by NE-directed extensional shear. This study shows that the textures of early fluid inclusions that formed already during the prograde metamorphic path can be preserved and used to derive information about the kinematics of subduction that is difficult to obtain from other sources. The textures of early inclusions, together with later generations of unaltered primary and secondary inclusions in metamorphic index minerals that can be linked to specific deformation stages and even P-T conditions, are a welcome supplement for the reconstruction of a rather detailed P-T-cl path. (C) 2007 Elsevier B.V. All rights reserved.",
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Fluid entrapment and reequilibration during subduction and exhumation: A case study from the high-grade Nestos shear zone, Central Rhodope, Greece. / Krenn, Kurt; Bauer, Christoph; Proyer, Alexander; Mposkos, Evripidis; Hoinkes, Georg.

In: Lithos, Vol. 104, No. 1-4, 2008, p. 33-53.

Research output: Contribution to journalArticle

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T1 - Fluid entrapment and reequilibration during subduction and exhumation: A case study from the high-grade Nestos shear zone, Central Rhodope, Greece

AU - Krenn, Kurt

AU - Bauer, Christoph

AU - Proyer, Alexander

AU - Mposkos, Evripidis

AU - Hoinkes, Georg

PY - 2008

Y1 - 2008

N2 - A fluid inclusion study on metamorphic minerals of successive growth stages was performed oil highly deformed paragneisses from the Nestos Shear Zone at Xanthi (Central Rhodope), in which microdiamonds provide unequivocal evidence for ultrahigh-pressure (UHP) metamorphism. The correlation of fluid inclusion density isochores and fluid inclusion reequilibration textures with geothermobarometric data and the relative chronology of micro- and macro-scale deformation stages allow a better understanding of both the fluid and metamorphic evolution along the P-T-d path. Textural evidence for subduction towards the NE is recorded by the orientation of intragranular NE-oriented fluid inclusion planes and the presence of single, annular fluid inclusion decrepitation textures. These textures occur within quartz "foam" structures enclosed in an earlier generation of garnets with prolate geometries and rarely within recrystallized matrix quartz, and reequilibrated both in composition and density (luring later stages of exhumation. No fluid inclusions pertaining to the postulated ultrahigh-pressure stage for microdiamond-bearing garnet-kyanite-gneisses have yet been found. The prolate shape of garnets developed during the earliest stages of exhumation that is recorded structurally by (L >> S) tectonites, which subsequently accommodated progressive ductile SW shearing and folding up to shallow crustal levels. The majority of matrix kyanite and a later generation of garnet were formed during SW-directed shear under plane-strain conditions. Fluid inclusions entrapped in quartz during this stage of deformation underwent density loss and transformed to almost pure CO(2) inclusions by preferential loss of H(2)O. Those inclusions armoured within garnet retained their primary 3-phase H(2)O-CO(2) compositions. Reequilibration of fluid inclusions in quartz aggregates is most likely the result of recrystallization along with stress-induced, preferential H(2)O leakage along dislocations and planar lattice defects which results in the predominance of CO(2) inclusions with supercritical densities. Carbonic fluid inclusions from adjacent kyanite-corundum-bearing pegmatoids and, the presence of shear-plane-parallel fluid inclusion planes within late quartz boudin structures consisting of pure CO(2)-fluid inclusions with negative crystal shapes, bear witness of the latest stage of deformation by NE-directed extensional shear. This study shows that the textures of early fluid inclusions that formed already during the prograde metamorphic path can be preserved and used to derive information about the kinematics of subduction that is difficult to obtain from other sources. The textures of early inclusions, together with later generations of unaltered primary and secondary inclusions in metamorphic index minerals that can be linked to specific deformation stages and even P-T conditions, are a welcome supplement for the reconstruction of a rather detailed P-T-cl path. (C) 2007 Elsevier B.V. All rights reserved.

AB - A fluid inclusion study on metamorphic minerals of successive growth stages was performed oil highly deformed paragneisses from the Nestos Shear Zone at Xanthi (Central Rhodope), in which microdiamonds provide unequivocal evidence for ultrahigh-pressure (UHP) metamorphism. The correlation of fluid inclusion density isochores and fluid inclusion reequilibration textures with geothermobarometric data and the relative chronology of micro- and macro-scale deformation stages allow a better understanding of both the fluid and metamorphic evolution along the P-T-d path. Textural evidence for subduction towards the NE is recorded by the orientation of intragranular NE-oriented fluid inclusion planes and the presence of single, annular fluid inclusion decrepitation textures. These textures occur within quartz "foam" structures enclosed in an earlier generation of garnets with prolate geometries and rarely within recrystallized matrix quartz, and reequilibrated both in composition and density (luring later stages of exhumation. No fluid inclusions pertaining to the postulated ultrahigh-pressure stage for microdiamond-bearing garnet-kyanite-gneisses have yet been found. The prolate shape of garnets developed during the earliest stages of exhumation that is recorded structurally by (L >> S) tectonites, which subsequently accommodated progressive ductile SW shearing and folding up to shallow crustal levels. The majority of matrix kyanite and a later generation of garnet were formed during SW-directed shear under plane-strain conditions. Fluid inclusions entrapped in quartz during this stage of deformation underwent density loss and transformed to almost pure CO(2) inclusions by preferential loss of H(2)O. Those inclusions armoured within garnet retained their primary 3-phase H(2)O-CO(2) compositions. Reequilibration of fluid inclusions in quartz aggregates is most likely the result of recrystallization along with stress-induced, preferential H(2)O leakage along dislocations and planar lattice defects which results in the predominance of CO(2) inclusions with supercritical densities. Carbonic fluid inclusions from adjacent kyanite-corundum-bearing pegmatoids and, the presence of shear-plane-parallel fluid inclusion planes within late quartz boudin structures consisting of pure CO(2)-fluid inclusions with negative crystal shapes, bear witness of the latest stage of deformation by NE-directed extensional shear. This study shows that the textures of early fluid inclusions that formed already during the prograde metamorphic path can be preserved and used to derive information about the kinematics of subduction that is difficult to obtain from other sources. The textures of early inclusions, together with later generations of unaltered primary and secondary inclusions in metamorphic index minerals that can be linked to specific deformation stages and even P-T conditions, are a welcome supplement for the reconstruction of a rather detailed P-T-cl path. (C) 2007 Elsevier B.V. All rights reserved.

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DO - 10.1016/j.lithos.2007.11.005

M3 - Article

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SP - 33

EP - 53

JO - Lithos

JF - Lithos

SN - 0024-4937

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