High-pressure/low-temperature metamorphism of basalts in Lavrion (Greece): implications for the preservation of peak metamorphic assemblages in blueschists and greenschists

Ioannis Baziotis, Alexander Proyer, Evripidis Mposkos

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21 Citations (Scopus)

Abstract

The Upper Tectonic Unit of the Lavrion area is part of the Attic-Cycladic blueschist belt and was affected by high-pressure, low-temperature metamorphism. Blueschists and greenschists occur in the same outcrop and are believed to have experienced the same pressure-temperature (P-T) history which has been quantified using geothermobarometry and pseudosections for specific bulk-rock compositions. Calculated P-T conditions indicate minimum pressure of similar to 0.9 GPa and temperature of similar to 370 degrees C for the peak of metamorphism. The prograde and retrograde paths followed a very similar low geothermal gradient (10-12 degrees C/km) with cooling during decompression. Pseudosections show that both blueschists and greenschists can exist stably at the metamorphic peak, the dominant amphibole being a function of bulk composition: the blueschists, on average, have lower Mg# than the greenschists, which results in a larger P-T stability field of blue amphibole. A pseudosection analysis of the dehydration behaviour indicates that blueschists and some greenschists can preserve their peak assemblages (no dehydration along the retrograde path), whereas greenschist assemblages, in general, are rather prone to undergo dehydration and hence re-equilibration to lower P-T conditions during exhumation.
Original languageEnglish
Pages (from-to)133-148
Number of pages16
JournalEuropean Journal of Mineralogy
Volume21
Issue number1
DOIs
Publication statusPublished - 2009

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blueschist
greenschist
metamorphism
basalt
dehydration
Amphibole Asbestos
Dehydration
temperature
amphibole
Temperature
geothermal gradient
decompression
exhumation
Tectonics
low pressure
Chemical analysis
outcrop
cooling
Rocks
tectonics

Cite this

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title = "High-pressure/low-temperature metamorphism of basalts in Lavrion (Greece): implications for the preservation of peak metamorphic assemblages in blueschists and greenschists",
abstract = "The Upper Tectonic Unit of the Lavrion area is part of the Attic-Cycladic blueschist belt and was affected by high-pressure, low-temperature metamorphism. Blueschists and greenschists occur in the same outcrop and are believed to have experienced the same pressure-temperature (P-T) history which has been quantified using geothermobarometry and pseudosections for specific bulk-rock compositions. Calculated P-T conditions indicate minimum pressure of similar to 0.9 GPa and temperature of similar to 370 degrees C for the peak of metamorphism. The prograde and retrograde paths followed a very similar low geothermal gradient (10-12 degrees C/km) with cooling during decompression. Pseudosections show that both blueschists and greenschists can exist stably at the metamorphic peak, the dominant amphibole being a function of bulk composition: the blueschists, on average, have lower Mg# than the greenschists, which results in a larger P-T stability field of blue amphibole. A pseudosection analysis of the dehydration behaviour indicates that blueschists and some greenschists can preserve their peak assemblages (no dehydration along the retrograde path), whereas greenschist assemblages, in general, are rather prone to undergo dehydration and hence re-equilibration to lower P-T conditions during exhumation.",
author = "Ioannis Baziotis and Alexander Proyer and Evripidis Mposkos",
year = "2009",
doi = "10.1127/0935-1221/2008/0020-1853",
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pages = "133--148",
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issn = "0935-1221",
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AU - Baziotis, Ioannis

AU - Proyer, Alexander

AU - Mposkos, Evripidis

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N2 - The Upper Tectonic Unit of the Lavrion area is part of the Attic-Cycladic blueschist belt and was affected by high-pressure, low-temperature metamorphism. Blueschists and greenschists occur in the same outcrop and are believed to have experienced the same pressure-temperature (P-T) history which has been quantified using geothermobarometry and pseudosections for specific bulk-rock compositions. Calculated P-T conditions indicate minimum pressure of similar to 0.9 GPa and temperature of similar to 370 degrees C for the peak of metamorphism. The prograde and retrograde paths followed a very similar low geothermal gradient (10-12 degrees C/km) with cooling during decompression. Pseudosections show that both blueschists and greenschists can exist stably at the metamorphic peak, the dominant amphibole being a function of bulk composition: the blueschists, on average, have lower Mg# than the greenschists, which results in a larger P-T stability field of blue amphibole. A pseudosection analysis of the dehydration behaviour indicates that blueschists and some greenschists can preserve their peak assemblages (no dehydration along the retrograde path), whereas greenschist assemblages, in general, are rather prone to undergo dehydration and hence re-equilibration to lower P-T conditions during exhumation.

AB - The Upper Tectonic Unit of the Lavrion area is part of the Attic-Cycladic blueschist belt and was affected by high-pressure, low-temperature metamorphism. Blueschists and greenschists occur in the same outcrop and are believed to have experienced the same pressure-temperature (P-T) history which has been quantified using geothermobarometry and pseudosections for specific bulk-rock compositions. Calculated P-T conditions indicate minimum pressure of similar to 0.9 GPa and temperature of similar to 370 degrees C for the peak of metamorphism. The prograde and retrograde paths followed a very similar low geothermal gradient (10-12 degrees C/km) with cooling during decompression. Pseudosections show that both blueschists and greenschists can exist stably at the metamorphic peak, the dominant amphibole being a function of bulk composition: the blueschists, on average, have lower Mg# than the greenschists, which results in a larger P-T stability field of blue amphibole. A pseudosection analysis of the dehydration behaviour indicates that blueschists and some greenschists can preserve their peak assemblages (no dehydration along the retrograde path), whereas greenschist assemblages, in general, are rather prone to undergo dehydration and hence re-equilibration to lower P-T conditions during exhumation.

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DO - 10.1127/0935-1221/2008/0020-1853

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