Extreme Crustal Metamorphism during a Neoproterozoic Event in Sri Lanka: A Study of Dry Mafic Granulites
K. Sajeev of Yonsei University, Korea
The Journal of Geology, volume 115 (2007), pages 563–582
Grains of the peak metamorphic assemblage, garnet-clinopyroxene-quartz, are commonly separated and embayed by late orthopyroxene-plagioclase symplectites; however, in some domains, rare grain-to-grain associations of the peak assemblages are still preserved.
Thermodynamic modeling in the CaO-Na2O-K2O-FeO-MgO-Al2O3-SiO2 system indicates peak metamorphic conditions of 12.5 kbar at 925°C. The temperature estimates using garnet and clinopyroxene core compositions are in the range 844°
982°C, in agreement with the thermodynamic modeling.
In conclusion, the textural, geochemical, and thermodynamic modeling and
thermobarometric data indicate a multistage decompression after HP-UHT
metamorphism. U-Pb zircon (laser ablationinductively coupled plasma mass
spectrometry) ages represent the timing of the peak metamorphism at
ca. 580 Ma. A Sm-Nd internal isochron from mineral phases (garnet,
clinopyroxene, orthopyroxene, and felsic fraction) and from a whole rock
yields an age of534±12
Our results from the central Highland Complex of Sri Lanka provide important
constraints on the Neoproterozoic orogeny associated with the assembly of Gondwana.
K. Sajeev of Yonsei University, Korea
The Journal of Geology, volume 115 (2007), pages 563–582
Garnet-clinopyroxene-quartz granulites of the central Highland Complex of Sri Lanka preserve textural and compositional features indicative of high-pressure, ultrahigh-temperature (HP-UHT) crustal metamorphism and multistage retrogression.
Grains of the peak metamorphic assemblage, garnet-clinopyroxene-quartz, are commonly separated and embayed by late orthopyroxene-plagioclase symplectites; however, in some domains, rare grain-to-grain associations of the peak assemblages are still preserved.
Thermodynamic modeling in the CaO-Na2O-K2O-FeO-MgO-Al2O3-SiO2 system indicates peak metamorphic conditions of 12.5 kbar at 925°C. The temperature estimates using garnet and clinopyroxene core compositions are in the range 844°
982°C, in agreement with the thermodynamic modeling.In conclusion, the textural, geochemical, and thermodynamic modeling and
thermobarometric data indicate a multistage decompression after HP-UHT
metamorphism. U-Pb zircon (laser ablation
inductively coupled plasma massspectrometry) ages represent the timing of the peak metamorphism at
ca. 580 Ma. A Sm-Nd internal isochron from mineral phases (garnet,
clinopyroxene, orthopyroxene, and felsic fraction) and from a whole rock
yields an age of
Our results from the central Highland Complex of Sri Lanka provide important
constraints on the Neoproterozoic orogeny associated with the assembly of Gondwana.
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