Ultrahigh-temperature metamorphism (1150°C, 12 kbar) and multistage evolution of Mg-, Al-rich granulites from the central Highland Complex, Sri Lanka

K. Sajeev, Yasuhito Osanai

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Abstract

Mg- and Al-rich granulites of the central Highland Complex, Sri Lanka preserve a range of reaction textures indicative of a multistage P-T history following an ultrahigh-temperature metamorphic peak. The granulites contain a near-peak assemblage of sapphirine-garnet orthopyroxene-sillimanite-quartz K-feldspar, which was later overprinted by intergrowth, symplectite and corona textures involving orthopyroxene, sapphirine, cordierite and spinel. Biotite-rims, kornerupine and orthopyroxene-rims on biotite are considered to be late assemblages. Thermobarometric calculations yield an estimated P-T of at least 1100°C and 12 kbar for the near-peak metamorphism. Isopleths of Al2O3 in orthopyroxene are consistent with a peak temperature above 1150°C. The P-T path consists of four segments. Initial isobaric cooling after peak metamorphism (Segment A), which produced the garnet sapphirine-quartz assemblage, was followed by near-isothermal decompression at ultrahigh temperature (Segment B), which produced the multiphase symplectites. Further isobaric cooling (Segment C) resulted in the formation of biotite and kornerupine, and late isothermal decompression (Segment D) formed orthopyroxene rims on biotite. This evolution can be correlated with similar P-T paths elsewhere, but there are not yet sufficient geochronological and structural data available from the Highland Complex to allow the tectonic implications to be fully assessed.

Original languageEnglish
Pages (from-to)1821-1844
Number of pages24
JournalJournal of Petrology
Volume45
Issue number9
DOIs
Publication statusPublished - Sep 1 2004

Fingerprint

Sri Lanka
ultrahigh temperature metamorphism
highlands
orthopyroxene
biotite
sapphirine
kornerupine
Quartz
rims
Garnets
pressure reduction
decompression
Textures
garnets
Cooling
garnet
metamorphism
textures
Temperature
quartz

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

Cite this

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abstract = "Mg- and Al-rich granulites of the central Highland Complex, Sri Lanka preserve a range of reaction textures indicative of a multistage P-T history following an ultrahigh-temperature metamorphic peak. The granulites contain a near-peak assemblage of sapphirine-garnet orthopyroxene-sillimanite-quartz K-feldspar, which was later overprinted by intergrowth, symplectite and corona textures involving orthopyroxene, sapphirine, cordierite and spinel. Biotite-rims, kornerupine and orthopyroxene-rims on biotite are considered to be late assemblages. Thermobarometric calculations yield an estimated P-T of at least 1100°C and 12 kbar for the near-peak metamorphism. Isopleths of Al2O3 in orthopyroxene are consistent with a peak temperature above 1150°C. The P-T path consists of four segments. Initial isobaric cooling after peak metamorphism (Segment A), which produced the garnet sapphirine-quartz assemblage, was followed by near-isothermal decompression at ultrahigh temperature (Segment B), which produced the multiphase symplectites. Further isobaric cooling (Segment C) resulted in the formation of biotite and kornerupine, and late isothermal decompression (Segment D) formed orthopyroxene rims on biotite. This evolution can be correlated with similar P-T paths elsewhere, but there are not yet sufficient geochronological and structural data available from the Highland Complex to allow the tectonic implications to be fully assessed.",
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N2 - Mg- and Al-rich granulites of the central Highland Complex, Sri Lanka preserve a range of reaction textures indicative of a multistage P-T history following an ultrahigh-temperature metamorphic peak. The granulites contain a near-peak assemblage of sapphirine-garnet orthopyroxene-sillimanite-quartz K-feldspar, which was later overprinted by intergrowth, symplectite and corona textures involving orthopyroxene, sapphirine, cordierite and spinel. Biotite-rims, kornerupine and orthopyroxene-rims on biotite are considered to be late assemblages. Thermobarometric calculations yield an estimated P-T of at least 1100°C and 12 kbar for the near-peak metamorphism. Isopleths of Al2O3 in orthopyroxene are consistent with a peak temperature above 1150°C. The P-T path consists of four segments. Initial isobaric cooling after peak metamorphism (Segment A), which produced the garnet sapphirine-quartz assemblage, was followed by near-isothermal decompression at ultrahigh temperature (Segment B), which produced the multiphase symplectites. Further isobaric cooling (Segment C) resulted in the formation of biotite and kornerupine, and late isothermal decompression (Segment D) formed orthopyroxene rims on biotite. This evolution can be correlated with similar P-T paths elsewhere, but there are not yet sufficient geochronological and structural data available from the Highland Complex to allow the tectonic implications to be fully assessed.

AB - Mg- and Al-rich granulites of the central Highland Complex, Sri Lanka preserve a range of reaction textures indicative of a multistage P-T history following an ultrahigh-temperature metamorphic peak. The granulites contain a near-peak assemblage of sapphirine-garnet orthopyroxene-sillimanite-quartz K-feldspar, which was later overprinted by intergrowth, symplectite and corona textures involving orthopyroxene, sapphirine, cordierite and spinel. Biotite-rims, kornerupine and orthopyroxene-rims on biotite are considered to be late assemblages. Thermobarometric calculations yield an estimated P-T of at least 1100°C and 12 kbar for the near-peak metamorphism. Isopleths of Al2O3 in orthopyroxene are consistent with a peak temperature above 1150°C. The P-T path consists of four segments. Initial isobaric cooling after peak metamorphism (Segment A), which produced the garnet sapphirine-quartz assemblage, was followed by near-isothermal decompression at ultrahigh temperature (Segment B), which produced the multiphase symplectites. Further isobaric cooling (Segment C) resulted in the formation of biotite and kornerupine, and late isothermal decompression (Segment D) formed orthopyroxene rims on biotite. This evolution can be correlated with similar P-T paths elsewhere, but there are not yet sufficient geochronological and structural data available from the Highland Complex to allow the tectonic implications to be fully assessed.

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