The regional ultrahigh–temperature (UHT) metamorphism of the Highland Complex, Sri Lanka is well established and has an important role in our understanding of the tectonic history of the Gondwana supercontinent. U–Pb zircon dating of sapphirine–bearing Mg–Al granulites yielded two major metamorphic age populations at approximately 620–590 and 563–525 Ma with no evidence of older zircon cores. Pelitic granulite samples with a Grt–Sil–Spl–Crd assemblage have similar metamorphic ages with concordant data clusters at ~ 602, 563, and 526 Ma and inherited zircon cores aged from 2040 to 1600 Ma. The pelitic granulites also underwent two stages of metamorphism (565–520 and 622–580 Ma). Some of these pelitic granulite samples have inherited zircon cores ranging from 3060 to 760 Ma. Zircons in mafic granulite samples have age ranges of 566–533 and 620–578 Ma. A calc–silicate granulite sample also has similar age populations at 591, 541, and 524 Ma. Combining these new results with previously published ages from Sri Lanka and formerly adjacent continental fragments of Gondwana, we propose that the terranes in southern Madagascar (south of Ranotsara Shear Zone), Northern and Southern Madurai and the Trivandrum Blocks of southern India, the Highland Complex of Sri Lanka, and the Skallen Group in the Lützow–Holm Complex of East Antarctica represent a unique metamorphic belt that regionally experienced the Ediacaran–Cambrian UHT event during the amalgamation of the Gondwana supercontinent.
The ultrahigh–temperature (UHT) regional metamorphism of Sri Lanka has a significant role in understanding the tectonics and formation of the Gondwana supercontinent. Sri Lanka is specifically important because of its central position in Gondwana, located between southern India, Madagascar and eastern Antarctica. In particular, the Highland Complex has been the focus of several previous studies because of the prominence of metasedimentary rocks that experienced UHT metamorphism. The central Highland Complex of Sri Lanka consists of Spr–bearing Mg–Al rich granulites intercalated with other pelitic, mafic granulites and calc–silicates, which preserve several textural evidences for UHT metamorphism. The calculated peak metamorphic conditions for the Mg–Al rich granulite yielded a temperature range from 910 to 1005 °C at 1.0 GPa, and the pressure varies between 0.9 to 1.2 GPa. The estimated metamorphic P–T conditions and evolution path is in good agreement with previous studies and also to that of similar rock–types from southern Madagascar, southern India and East Antarctica.
The Kontum Massif is situated in the southern part of Trans Vietnam Orogenic Belt (TVOB), central Vietnam, and contains various types of magmatic and metamorphic rocks, the latter including both ultrahigh–pressure and ultrahigh–temperature units. While geochronological data indicate the existence of two main tectonothermal events at 480–420 Ma and 270–240 Ma, the most intense metamorphic and magmatic activity occurred between the Late Permian and Early Triassic due to continental collision between the South China and Indochina cratons. In this study, U–Pb LA–ICP–MS geochronological analyses of zircon obtained from two samples of metagabbro and one sample of charnockite from the massif yielded a magmatic age range of 260–250 Ma for all three samples and an inherited age of ~ 1400 Ma for the charnockite. These magmatic ages overlap with those documented for peak metamorphism in the Kontum Massif. When combined with Nd isotopic data for granitic rocks and pelitic gneisses from the region, these data suggest that the massif may have been derived from reworked continental crust. Geochemical characteristics of metagabbros from the massif reveal that the parental basaltic magma can be correlated with the Song Da igneous suite situated in the northern part of the TVOB, and was assimilated by crustal materials. The Song Da igneous suite is a member of the Emeishan large igneous province and resulted from Late Permian mantle plume activity. We conclude that the plume–related magma intruded into the deeper part of Kontum Massif and induced ultrahigh–temperature metamorphism of the lower crust by acting as a heat source.