Metamorphic evolution of high-pressure and ultrahigh-temperature granulites from the Highland Complex, Sri Lanka

• Published in: Journal of Asian earth sciences Vol. 28; no. 1; pp. 20 - 37
• Main Authors: Osanai, Yasuhito, Sajeev, Krishnan, Owada, Masaaki, Kehelpannala, K.V.Wilbert, Prame, W.K.Bernard, Nakano, Nobuhiko, Jayatileke, Sarath
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.10.2006
• Subjects: Clockwise P–T path; High-pressure mafic granulite; Highland Complex; Sri Lanka; UHT-pelitic granulites; Highland Complex; Clockwise P–T path; Sri Lanka; High-pressure mafic granulite; UHT-pelitic granulites
• ISSN: 1367-9120; 1878-5786
• DOI: 10.1016/j.jseaes.2004.09.013

Sapphirine+quartz-bearing pelitic granulites, garnet–clinopyroxene–quartz-bearing mafic granulites and quartzo-feldspathic granulites with corundum–garnet–quartz constitute rare but important members of the Highland Complex in Sri Lanka. Peak metamorphic conditions from the Highland Complex generally have been considered to be up to ∼850–900 °C and ∼8 10 kbar. However, this study on the above mentioned rocks indicates that ultrahigh-temperature and high-pressure conditions (>1100 °C and ∼12 kbar) were attained during peak conditions. A metamorphic evolution of the ultrahigh-temperature metamorphic rocks was determined from careful analyses of shifts in divariant assemblages and reaction textures. This shows a clockwise P–T path from more high-pressure conditions (∼1000 °C and ∼17 kbar; stage 0 as part of the prograde metamorphic path) to lower-pressure and -temperature conditions (∼950 °C and ∼9 kbar; stage 4 as part of the retrograde path) through the peak metamorphic conditions (stage 1). Widespread lower pressure and temperature granulite-facies metamorphic rocks surround the ultrahigh-temperature granulites and are interpreted to have formed by the strong effect of the retrograde metamorphism and deformation. The widely reported Pan-African metamorphic ages derived from similar granulite-facies metamorphic rocks in the Gondwana fragments (Highland Complex in Sri Lanka, Lützow-Holm Complex in east Antarctica, etc.) may also be the result of retrograde metamorphism of ultrahigh-temperature metamorphic rocks. There remains a possibility that this early ultrahigh-temperature/high-pressure granulite-facies metamorphism in the Highland Complex, as well as that in the Lützow-Holm Complex, might pre-date Pan-African metamorphism.