DOI: 10.5176/2251-3353_GEOS14.35
Authors: T.B.N.S. Madugalla, H.M.T.G.A. Pitawala and D.G.G.P. Karunaratne
Abstract: The calcite rich carbonate rocks (CRR) with in the granulite facies metamorphic rocks of Balangoda, Sri Lanka reflect uncommon calcite deposits. The present study investigates the mineralogical and geochemical characteristics of the CRR to constraints the petrogenesis of them. The CRR formations appear to be hosted in the dolomitic marbles of Highland Complex (HC) near to the tectonic boundary between Vijayan Complex (VC) and HC. The host dolomitic marbles consist of dolomite and forsterite bearing high grade assemblages while rarely they contain calcite and phlogopite rich assemblages with dolomite ex-solution lamellae. CRR occur as patchy or layer wise large scale formations with coarse grained multi-colored mega-crystals of calcite. Within these CRR, large xenoliths having compositions similar to that of adjacent charnockitic rocks can be identified and they show sharp contacts with CRR. The major and minor elemental compositions of carbonate phase of each carbonate rocks are distinct. The Ca content is highest in calcite crystals of CRR while the Mg content is lowest. Contrary to that, the lowest Ca and highest Mg contents are noted for carbonate phase of dolomitic marble. Calcitic marble reflect intermediate Ca and Mg contents. The Sr and K concentrations are lowest in dolomitic marbles and are comparable to those of other dolomitic marbles of the country. However, the contents of these elements are highest in calcitic marble and values are much higher than that of the other calcitic marbles. Although, the Sr and Mn content of CRR are higher than those of calcites in marble, the values are lower than that of the calcite in carbonatites. The different colored calcite formations reflect systematic variability of Fe and Mn compositions, indicating the chemical heterogeneity prevailed during the origin of CRR. Field settings, mode of occurrence and Sr and K geochemistry of the CRR indicate that CRR have been formed due to the postdated fluid activity suffered by dolomitic marble. The existing dolomitic marble may have partially melted to form CRR under such fluid conditions. However, the low concentrations of Mg still ambiguous and therefore further studies are needed to be carried out to understand the genesis of CRR.
Keywords: calcite rich carbonate rocks; Balangoda; dolomitic marble; calcite
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