G.W.A.R. Fernando

The Valaichchenai Lagoon, located in Batticaloa District, is surrounded by several different industries such as fishing harbor, paper mill, rice mills, and shrimp farms. Hence, it acts as a sink for pollutants. However, there is no study on the pollution of the lagoon and there should be an extensive study in this regard to adopt any measures to free the lagoon from further pollution. In this regard, the present study had been undertaken with the aim of identifying the potential industrial effluents by studying the spatiotemporal variation of some surface water chemical parameters of selected points of Valaichchenai lagoon. The present study analyzed some physiochemical parameters (such as pH, Nitrates, Nitrites, Phosphates, Dissolved Oxygen, Turbidity, Salinity and Electrical Conductivity) of the water in selected study sites of the Lagoon. The Significant differences were tested by one-way ANOVA at 5% probability level. According to the results, nitrate (p=0.00) and nitrite (p=0.003) showed significant difference among locations. High levels of nitrates and nitrites were observed in paper mill discharging area. Further, contribution to total nitrogen was also higher than the level of acceptance (1 mg/L) in all the locations of lagoon. Phosphates did not show significant difference (p=0.06) among the locations but comparatively higher level was observed at fishing harbor. Contribution to total phosphorous was also higher than the level of acceptance in all places. Dissolved Oxygen did not shows significant difference (p=0.078) among locations but it fluctuated very much and sometimes it was as low as 3.00 mg/L in some points. pH also did not shows significant difference (p=0.875) among locations but in paper mill discharging area sometimes pH level reached 4.5, which is detrimental to aquatic organisms. There was significant difference in turbidity (p=0.00) among locations and high level of turbidity was observed at paper mill discharging area. Salinity and Electrical Conductivity also showed significant difference (p=0.00) among locations. High level of Electrical conductivity was observed at fishing harbor and very low salinity was observed at paper mill discharging area. According to the above findings, it is obvious that paper mill discharges high level of pollutants into the lagoon. The paper mill now is in reduced operation unlike its early days, and it discharges effluents irregularly. However, the fishing harbor and rice mill discharges the wastes continuously. Therefore, fishing harbor and rice mills are another potential polluting industries.

The Rakwana mountain range, which is located in the margin of the northern side of Sinharaja, a UNESCO world heritage site, is an area having rich biodiversity. The recent excavations of the alluvial deposits in Sabaragamuwa basin associated with northern side of Sinharaja area revealed that the existance of caves in the vicinity of Pannila mountain. The cave formation is seen within the rocks of crystalline limestons (marble),which is popularly known as 'Pannila Hunugala' is of 550 m in length and 350 cm height at its entrance of which 60 cm filled with water, where special cave characteristics are visible. Stalagmite and stalactites of 2.5 m height at the core of the cave was believed to be formed after re-crystallization of pre-existing crystalline limestones-the basement rock-in the Highland Complex of Sri Lanka belongs to the Precambrian age. Speleothem dimensions were used to measure the volume of stalagmite and stalagtites. The action of chemical weathering of crystalline limestone followed by limy solutions makes it secondary features like stalagmite and stalactite.It is postulated from the Geological map of Sri Lanka that the same crystalline limestones bed is extended to the Rakwana

Sri Lanka is a crucial Gondwana fragment mostly composed of granulitic rocks in the Highland Complex surrounded by rocks with granulite to amphibolite grade in the Vijayan and Wanni Complex that were structurally juxtaposed during Pan-African orogeny. Fluids associated with granulite-facies metamorphism are thought to have controlled various lower crustal processes such as dehydration/hydration reactions, partial melting, and high-temperature metasomatism. Chemical disequilibrium in the hybrid contact zone between a near peak post-tectonic ultramafic enclave and siliceous granulitic gneiss at Rupaha within the Highland Complex produced metasomatic reaction zones under the presence of melt. Different reaction zones observed in the contact zone show the mineral assemblages phlogopite + spinel + sapphirine (zone A), spinel + sapphirine + corundum (zone B), corundum (~30%) + biotite + plagioclase zone (zone C) and plagioclase + biotite + corundum (~5%) zone (zone D). Chemical potential diagrams and mass balance reveal that the addition of Mg from ultramafic rocks and removal of Si from siliceous granulitic gneiss gave rise to residual enrichment of Al in the metasomatized mineral assemblages. We propose that contact metasomatism between the two units, promoted by melt influx, caused steady state diffusional transport across the profile. Corundum growth was promoted by the strong residual Al enrichment and Si depletion in reaction zone whereas sapphirine may have been formed under high Mg activity near the ultramafic rocks. Modelling also indicated that metasomatic alteration occurred at ca. 850°C at 9 kbar, which is consistent with post-peak metamorphic conditions reached during the initial stage of exhumation in the lower crust and with temperature calculations based on conventional geothermometry.

The serpentinite blocks of Indikolapelessa, located along an identified litho-tectonic boundary between the Highland Complex (HC) and the Vijayan Complex (VC) of Sri Lanka, have undergone extensive lateralization with metal enrichment. Characteristic serpentinite vegetation with some endemic species was recognized in the soils and supergene deposits develop on serpentinite lithology. This type of geological and ecological relationship forms vegetation covers on serpentinite lithologies which are sharply demarcated from the surrounding metamorphic terrains. The aforesaid "geo-ecological phenomenon" can be used as a tool for geo-vegetation mapping in ultramafic terrains to trace the geological boundaries in landscapes where rock outcrops are virtually absent. We successfully applied the concept of geo-vegetation mapping in order to demarcate the boundary of underlain serpentinite rocks from surrounding non-serpentinite metamorphic rocks (e.g. granitic gneiss). The hypothesis was supported by the geochemical variations of soils/supergene deposits found at serpentinite and non-serpentinite sites, especially immobile elements and some trace elements. Based on whole rock chemistry and soil chemical data obtained, we suggest that the Indikolapelessa serpentinite outcrop, together with the other four serpentinite outcrops, is more likely to represent the Mg-rich mantle fragments at the time of overthrusting of the two crustal blocks of HC and VC during the Pan-African event.

Concordant ultramafic rocks are exposed in lower crustal granulites in Sri Lanka. The ultramafic rocks at Rupaha, Sri Lanka were emplaced early and subjected to deformation and granulite facies metamorphism at 850 o C at 9 kbar during the Pan-African tectono-thermal episode. The results thermometry of ultramafic rocks is consistent with geothermobarometric results obtained from the surrounding granulites. Fluid circulating in the deep crust resulted in the formation of phlogopite blackwalls. Structures, textures and the mineralogy of the blackwall suggest that the Kmetasomatism took place contemporaneous to the granulite facies metamorphism. The metasomatic reactions were started by infiltration of K 2 O and SiO 2 along the lithological contacts between ultramafic rocks and surrounding gneisses and diffusion of these elements between two wall rocks. Carbonation and hydration had occurred on these blackwall rocks at the upper level of the crust up on cooling together with surrounding rocks as evidenced by textures of a partial retrogression to tremolite and dolomite, which formed through introduction of CaO and CO 2. The stability of tremolite + dolomite at 730-640 o C and 9 kbar condition records a 0.40 ≥ X CO2 ≥ 0.15 for the fluid phase.

Excellent outcrops in Matale Sri Lanka provide unique insight into the emplacement and evolution history of hydrothermal and pegmatitic rocks in the central highlands of Sri Lanka. Field, structural, petrological, thermo-barometric studies in the metamorphic basement rocks in the central highlands and related hydrothermal deposits are presented in this study. Detailed petrographic and mineralogical data reveal peak metamorphic conditions for the crustal unit in the study area as 854 ± 44˚C at 10.83 ± 0.86 kbar. Hydrothermal veins consisting of quartz and mica are closely related to cross-cutting pegmatites, which significantly postdate the peak metamorphic conditions of the crustal unit. Field relations indicate that the veins originated as ductile-brittle fractures have subsequently sealed by pegmatites and hydrothermal crystallization. Geological, textural and mineralogical data suggest that most enriched hydrothermal veins have evolved from a fractionated granitic melt progressively enriched in H 2 O, F, etc. Quartz, K-feldspar, mica, tourmaline, fluorite and topaz bear evidence of multistage crystallization that alternated with episodes of resorption. It was suggested that the level of emplacement of pegmatites of the Matale District was middle crust, near the crustal scale brittle-ductile transition zone at a temperature of about 600˚C. For this crustal level and temperature range, it is considered very unlikely that intruding pegmatitic melts followed pre-existing cracks. As such the emplacement temperatures of the pegmatites could be well below the peak metamorphic estimates in the mafic granulites. The metamorphic P-T strategy and position of formation of hydrothermal deposits and pegmatites is summarized in the modified P-T-t-D diagrams.

Stream sediment geochemistry is extensively used in mineral exploration and environmental studies. However, quantitative assessments of the effectiveness of stream sediment geochemistry for describing upstream lithologies are rare, especially in high-grade metamorphic terrains. This study statistically evaluates whether stream sediment geochemistry can aid in recognizing variations in upstream geology in several high-grade metamorphic lithotectonic units having different metamorphic and tectonic histories, including the Highland Complex, Vijayan Complex, Wanni Complex, and Kadugannawa Complex of Sri Lanka. For this study, concentrations of 21 elements were measured in 2080 stream sediment samples collected from the Walawe River, Maha Oya, Gala Oya basins located on above lithotectonic units and Uma Oya, Belihul Oya, Badulu Oya basins situated adjacent to each other on the Highland Complex. These rivers flow across dry, intermediate and wet zones of Sri Lanka, with river courses having both slope (> 20°) and flat (< 20°) areas. Elemental concentrations, averaged over each river basin, show patterns of enrichment and depletion which may relate to localized mineralization conditions, local lithological changes, anthropogenic activities and environmental factors such as local variations in climate and morphology among river basins. Comparison of element concentrations in sediments from the four different lithotectonic units shows that enrichmentdepletion patterns can be partly related to rock geochemistry of the associated lithotectonic unit. However, climate and basin morphology also seem to play an important role. Results of Kruskal-Wallis H tests show that both major and trace element levels in sediments from the four different lithotectonic units, as well as from adjacent Uma Oya, Badulu Oya and Belihul Oya basins, are significantly different. Discriminant function analysis appropriately classifies sediments into the four different lithotectonic units with an accuracy of 91.9%. This method also classifies sediments into river basins which share common lithology being situated adjacent to each other in the same lithotectonic unit with an accuracy of 89.5%. This strongly suggests that stream sediment geochemistry is capable of describing the upstream regional scale as well as local scale lithological changes at a great accuracy in complex high-grade metamorphic terrains. In both cases use of channel slope and basin climatic zone as additional variables does not significantly increase overall or individual accuracy in classification.

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The growth of gem quality metamorphic minerals is most likely in fluid rich systems, where growth rate exceed the rate of nucleation. This condition typically occurs when crystallizing is close to equilibrium. This communication discusses metasomatic growth of corundum crystals at the boundary between ultramafic and acidic granulites. The phase petrology of the formation of corundum at the Rupaha deposit is presented Corundum forms due to desilification of the acidic granulite during peak granulite facies.

Diffusion modeling of zoning profiles in garnet rims from mafic granulites is used to estimate cooling rates in the Proterozoic basement of Sri Lanka, which represents a small, but important fragment of the Gondwana super-continent. Metamorphic peak temperatures and pressures, estimated with two-pyroxene thermometry and garnet-clinopyroxene-plagioclase-quartz (GADS) barometry, yield 875 AE 20 C and 9.0 AE 0.1 kbar. These peak metamorphic conditions are slightly higher than results obtained by garnet-biotite Fe-Mg exchange thermometry of 820 AE 20 C. Reset flat zoning profiles were observed in most garnets. Only narrow garnet rims touching biotite exhibit retrograde zoning in terms of Fe and Mg exchange. The garnet zoning observed requires a slow cooling history. Equilibrium was achieved along grain boundaries during or close to peak metamorphism. During subsequent cooling to lower temperatures, only local exchange between garnet and biotite occurred. A cooling rate of 1-5 C=Ma is estimated. The estimated temperature-time history from garnet profiles is in good agreement with the cooling history inferred from mineral radiogenic ages in the literature.

Grossular-wollastonite-scapolite calc-silicate granulites from Maligawila in the Buttala klippe, which form part of the overthrusted rocks of the Highland Complex of Sri Lanka, preserve a number of spectacular coronas and replacement textures that could be effectively used to infer their P-T-fluid history. These textures include coronas of garnet, garnet-quartz, and garnet-quartz-calcite at the grain boundaries of wollastonite, scapolite, and calcite as well as calcite-plagioclase and calcitequartz symplectites or finer grains after scapolite and wollastonite respectively. Other textures include a double rind of coronal scapolite and coronal garnet between matrix garnet and calcite. The reactions that produced these coronas and replacement textures, except those involving clinopyroxene, are modelled in the CaO-Al 2 O 3-SiO 2-CO 2 system using the reduced activities. Calculated examples of T-X CO2 and P-X CO2 projections indicate that the peak metamorphic temperature of about 900-875°C at a pressure of 9 kbar and the peak metamorphic fluid composition is constrained to be low in X CO2 (0.1 < X CO2 < 0.30). Interpretation of the textural features on the basis of the partial grids revealed that the calc-silicate granulites underwent high-temperature isobaric cooling, from about 900-875°C to a temperature below 675°C, following the peak metamorphism. The late-stage cooling was accompanied by an influx of hydrous fluids. The calc-silicate granulites provide evidence for high-temperature isobaric cooling in the meta-sediments of the Highland Complex, earlier considered by some workers to be confined exclusively to the meta-igneous rocks. The coronal scapolite may have formed under open-system metasomatism.

Sri Lanka is a crucial Gondwana fragment mostly composed of granulitic rocks in the Highland Complex surrounded by rocks with granulite to amphibolite grade in the Vijayan and Wanni Complex that were structurally juxtaposed during Pan-African orogeny. Fluids associated with granulite-facies metamorphism are thought to have controlled various lower crustal processes such as dehydration/hydration reactions, partial melting, and high-temperature metasomatism. Chemical disequilibrium in the hybrid contact zone between a near peak post-tectonic ultramafic enclave and siliceous granulitic gneiss at Rupaha within the Highland Complex produced metasomatic reaction zones under the presence of melt. Different reaction zones observed in the contact zone show the mineral assemblages phlogopite + spinel + sapphirine (zone A), spinel + sapphirine + corundum (zone B), corundum (~30%) + biotite + plagioclase zone (zone C) and plagioclase + biotite + corundum (~5%) zone (zone D). Chemical potential diagrams and mass balance reveal that the addition of Mg from ultramafic rocks and removal of Si from siliceous granulitic gneiss gave rise to residual enrichment of Al in the metasomatized mineral assemblages. We propose that contact metasomatism between the two units, promoted by melt influx, caused steady state diffusional transport across the profile. Corundum growth was promoted by the strong residual Al enrichment and Si depletion in reaction zone whereas sapphirine may have been formed under high Mg activity near the ultramafic rocks. Modelling also indicated that metasomatic alteration occurred at ca. 850°C at 9 kbar, which is consistent with post-peak metamorphic conditions reached during the initial stage of exhumation in the lower crust and with temperature calculations based on conventional geothermometry.