Research
Metamorphic Evolution of Charnockites Across the Inferred Highland-Wanni Boundary in Northeastern Sri Lanka
Authors:
W. M. R. Jayathilake ,
University of Peradeniya, LK
About W. M. R.
Department of Geology
P. L. Dharmapriya,
University of Peradeniya, LK
About P. L.
Department of Geology
R. Kleinschrodt,
University of Cologne, DE
About R.
Institute for Geology and Mineralogy
B. Spiering
University of Bonn, DE
About B.
Steinmann Institutfür Geologie
Abstract
Charnockites are hypersthene-bearing granitoids that form a minor but important component of the Earth’s lower crust. Charnockite is a common lithology in the Highland Complex (HC) and Wanni Complex (WC) of Sri Lanka. These two Complexes are considered lithotectonic units having two different protolith histories. The northeastern part of the HC and WC is poorly explored compared to the central, southern, and southwestern parts of the two Complexes. In this study for the first time, we have attempted to study the metamorphic evolution of charnockites across the northeastern part of the inferred boundary between the HC and WC studying equilibrium mineral assemblages utilizing conventional and trace element geothermometers. In the WC side, hedenbergite-ferrosilite assemblage in a charnockite can be considered as the preserved relict assemblages of the rock’s igneous protolith. Orthopyroxene of the majority of charnockites in both HC and WC is apparently formed during the prograde dehydration of hornblende and biotite. Mineral assemblages and reaction textures of all the charnockites provide evidence for a clockwise pressure-temperature path during late prograde to retrograde evolution. The studied charnockites were metamorphosed from hornblende-granulites to pyroxene-granulite facies conditions with a minimum temperature of around 750- 800 °C. A period of the near-isobaric cooling (IBC) stage after peak metamorphism has been suggested for both HC and WC charnockites. We confirm that there is no evidence for contrasting metamorphic evolution of charnockites across the inferred HC-WC boundary.
How to Cite:
Jayathilake, W.M.R., Dharmapriya, P.L., Kleinschrodt, R. and Spiering, B., 2022. Metamorphic Evolution of Charnockites Across the Inferred Highland-Wanni Boundary in Northeastern Sri Lanka. Journal of the Geological Society of Sri Lanka, 23(1), pp.34–54. DOI: http://doi.org/10.4038/jgssl.v23i1.65
Published on
05 Dec 2022.
Peer Reviewed
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