G.W.A.R. Fernando

Open University of Sri Lanka

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Christoph Hauzenberger

University of Graz

Daniela Gallhofer

University of Graz

C.B. Dissanayake

University of Peradeniya

Lukas P. Baumgartner

University of Lausanne

Joseph E. Andrew

University of Kansas

T. H. N. G. Amaraweera

Uva Wellassa University

Marcel Masten

University of Graz

P.N. Ranasinghe

Woods Hole Oceanographic Institution

Andreas Möller

University of Kansas

Nikolaus Lechner

University of Graz

Cooperative Institutions

University of Peradeniya

University of Graz

National Institute of Fundamental Studies

Sabaragamuwa University of Sri Lanka

Johannes Gutenberg University Mainz

University of Western Australia

University of Jaffna

State Key Laboratory of Continental Dynamics

Northwest University

Centre National de la Recherche Scientifique

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Pegmatites Derived from Fractionation of a Melt: An Example from Pegmatites in the Owala-Kaikawala Area, Matale, Sri Lanka

Journal of the Geological Society of India (2008)

H.M.T.G.A. Pitawala T. H. N. G. Amaraweera G.W.A.R. Fernando Christoph Hauzenberger

Pegmatite

Anatexis

Fractional crystallization (geology)

Fluorite

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Citations (7)

Petrology and geochronology of cordierite bearing assemblages from the Wanni Complex – Sri Lanka

Nikolaus Lechner Christoph Hauzenberger Marcel Masten Dominik Sorger G.W.A.R. Fernando

Based on differences in metamorphic grade and isotope model ages, the basement rocks of Sri Lanka can be subdivided from NW to SE into the Wanni Complex (WC), the Highland Complex (HC) and the Vijayan Complex (VC) (Milisenda et al. 1994). The UHT conditions of the HC were studied extensively and are well constrained whereas data from the WC and VC are less abundant. Only few recent petrological and geochemical work has been done especially along the WC&#8211;HC boundary which is still ill-defined (Kitano et al. 2018; Wanniarachchi & Akasaka 2016). Due to the common occurrence of migmatites, pyroxene bearing gneisses, and cordierite bearing metapelites/paragneisses, the WC clearly experienced granulite facies metamorphism. However, PT conditions are lower compared to the HC. In this study, U-Th-Pb monazite dating combined with a petrological study including phase equilibria modelling and thermobarometry was conducted focusing on cordierite bearing migmatic biotite gneisses located at the WC&#8211;HC boundary in the West of Sri Lanka. The HC underwent UHT metamorphism at 580-570Ma (Sajeev et al. 2010), the main metamorphic phase of the VC is dated with 580Ma. (Kr&#246;ner et al., 2013). With U-Th-Pb monazite ages of around 530 Ma, the cordierite bearing assemblages from the WC are significantly younger (Wanniarachchi & Akasaka 2016). The predominantly felsic but also mafic peraluminous migmatic ortho- and paragneisses comprising the mineral assemblage cordierite + garnet + biotite + plagioclase + k-feldspar + quartz + ilmenite + magnetite + spinel + sillimanite &#177; orthopyroxene and contain monazite (+ zircon &#177; xenotime) as garnet inclusions (Group1) and in the matrix (Group2). Group1 monazite ages cluster around 575&#177;5 Ma and 561&#177;5 Ma whereas ages of Group 2 cluster at 550&#177;3 and 527&#177;3. Based on ages and textural occurrence of monazite we suggest that two thermal events at ca. 550-575 Ma and ca. 530-550 Ma are recorded in this rock type indicating a complex evolution during the late stage of the Pan-African orogeny. PT conditions range from 700&#8211;900&#176;C and from 5&#8211;8 kbar with a decreasing north-south gradient. Further geochronological investigations are needed to relate either to the older or the younger overprint to the main metamorphic phase of the WC.Kitano, I., Osanai, Y., Nakano, N., Adachi, T., & Fitzsimons, I. C. W. (2018). Journal of Asian Earth Sciences, 156, 122&#8211;144.Kr&#246;ner, A., Rojas-Agramonte, Y., Kehelpannala, K. V. W., Zack, T., Hegner, E., Geng, H. Y., &#8230; Barth, M. (2013). Precambrian Research, 234, 288&#8211;321.&#160;Milisenda, C. C., Liewa, T. C., Hofmanna, A. W., & K&#246;hler, H. (1994). Precambrian Research, 66(1&#8211;4), 95&#8211;110.Sajeev, K., Williams, I. S., & Osanai, Y. (2010). Geology, 38(11), 971&#8211;974.Wanniarachchi, D. N. S., & Akasaka, M. (2016). Journal of Mineralogical and Petrological Sciences, 111(5), 351&#8211;362.

Cordierite

Geochronology

Migmatite

10.5194/egusphere-egu2020-9956

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ORIGIN OF THE SILICA SAND DEPOSITS IN WESTERN SRI LANKA WITH SPECIAL EMPHASIS TO THE EKALA DEPOSIT

Kosala Somapala G.W.A.R. Fernando

Among the sources for the quartz (silica) which are found in Sri Lanka, including vein quartz, quartz sand and quartzite, more attention is paid on quartz (silica) sand because silica sand is the major raw material used in manufacturing glass owing to its specific features being fine graded, white in colour and high purity making its commercially viable. Few commercially extracted silica sand deposits are known to occur in western Sri Lanka at Nattandiya, Marawila, Madampe, which extend towards south of Colombo as sporadically distributed deposits. The deposit intercalated with the marshy and lagoonal deposits, which has considerably acidic peaty soils and underlies the Precambrian metamorphic rocks. Relatively undisturbed deposit of silica sand has been recognized at Ekala, the territory of the Sri Lanka Air Force premises, which appeared to be of aeolian origin, has been unconfirmed until the present study (Fig.1). The objectives of the study were to (i) establish procedures for interpreting the provenance of silica sand deposits located at the west coast referring to the undisturbed deposit at Ekala and (ii) to study the effect of peaty layers to change the colour of silica sands from usual brown to white colour. Here we present mineralogical, sedimentological and geochemical evidence to prove the origin of silica sand deposits in the west of Sri Lanka.

Sri lanka

Dissolved silica

Granulometry

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Citations (1)

A Scientific approach to locate new gem deposits of high-grade metamorphic terrains with special reference to Sri Lanka

G.W.A.R. Fernando

Sri lanka

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Citations (2)

Two contrasting mineralized belts in the Matale district:some field evidencies

G.W.A.R. Fernando T.H.N.G. Amaraweera A. H. M. T. G. A. Pitawala

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Medical geology of endemic goiter in Kalutara, Sri Lanka; distribution and possible causes

Environmental Geochemistry and Health (2017)

G.W.A.R. Fernando P. L. C. L. Liyanage Anushka Upamali Rajapaksha Meththika Vithanage

Iodised salt

10.1007/s10653-017-9985-7

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Emplacement and Evolution History of Pegmatites and Hydrothermal Deposits, Matale District, Sri Lanka

International Journal of Geosciences (2011)

G.W.A.R. Fernando H.M.T.G.A. Pitawala T. H. N. G. Amaraweera

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 ± 44oC at 10.83 ± 0.86 kbar. Hydrothermal veins consisting of quartz and mica are closely related to cross-cutting pegmatites, which significantly post-date 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 H2O, 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 600oC. 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.

Pegmatite

Tourmaline

10.4236/ijg.2011.23037

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Citations (12)

Occurrences of two new types of gem deposits in the Okkampitiya gem field, Sri Lanka

Journal of gemmology/The journal of gemmology (2000)

V. Mathavan S. T. Kalubandara G.W.A.R. Fernando

Sri lanka

10.15506/jog.2000.27.2.65

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Characterization of zircon megacrysts from an atypical occurrence of carbonatite at Kawisigamuwa, Sri Lanka

Daniela Gallhofer Etienne Skrzypek Christoph Hauzenberger Andreas Möller Joseph E. Andrew

Zircon megacrysts are unusually large crystals (> 5 mm) that are commonly associated with mantle-derived kimberlites, carbonatites, alkali basalts and syenitic pegmatites (e.g., Hoskin and Schaltegger 2003). Such zircons form during relatively short timespans and therefore, are often used as reference material for U-Pb geochronology. Here, we determine the geochemical and isotopic (U-Pb, Hf, O) characteristics of a little-known occurrence of zircon megacrysts at Kawisigamuwa, Sri Lanka.The dark brown megacrysts are euhedral, commonly elongate crystals with double pyramidal terminations and have faintly corroded crystal surfaces. The zircons consist of oscillatory zoned and nearly featureless cathodoluminescence-bright patches, some of which appear to follow sealed cracks. All zircon domains show a low to moderate FWHM of the ν3 (SiO4) Raman band (2.5 to 7.3 cm-1), have a low to moderate radiation damage (total α-dose mainly <0.5 x 1018 events/g) and therefore are intermediate to well crystalline. Contents of most trace element (U, Th, REE, P) are elevated in the oscillatory zoned domains, while Hf content is elevated in the CL-bright domains and seems to be grain-dependant. The oscillatory zoned domains yielded a TIMS weighted mean 206Pb/238U age of 532.39 ± 0.66 Ma (2sd). The206Pb/238U dates within the CL-bright domains are partially reset by a single event of recrystallisation at ~518 Ma. The mean Hafnium isotopic compositions of the tested grains show a narrow range of 176Hf/177Hf from 0.281969 to 0.282003. Oxygen isotopes determined on two oscillatory zoned zircon megacrysts are homogeneous (mean δ18O of 12.1 and 12.2).    While some of the trace and major element characteristics (Th/U, Zr/Hf, Hf content) of the Kawisigamuwa megacrysts resemble those of carbonatite zircons, their hafnium and oxygen isotope ratios are clearly different from mantle values. The isotopic values indicate that a significant amount of a crustal component must be involved in the formation of the zircons. Recently, several studies have found evidence for melting of carbonate rocks under high grade metamorphic conditions in Sri Lanka (e.g., Wang et al. 2021). It might be feasible that zircons grow from interaction of crustal derived carbonate melts and silicate melts or wall rocks under high grade metamorphic conditions.Hoskin P.W.O. and Schaltegger U. (2003). The Composition of Zircon and Igneous and Metamorphic Petrogenesis. Reviews in Mineralogy and Geochemistry, 53 (1), 27–62.Wang J., Su B.-X., Chen C., Ferrero S., Malaviarachchi S.P.K., Sakyi P.A., Yang Y.-H. and Dharmapriya P.L. (2021). Crustal derivation of the ca. 475-Ma Eppawala carbonatites in Sri Lanka. Journal of Petrology, 62 (11), 1-18.

Carbonatite

Geochronology

Phlogopite

Baddeleyite

Pegmatite

10.5194/egusphere-egu23-12969

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Geo-vegetation mapping and soil geochemical characteristics of the Indikolapelessa serpentinite outcrop, southern Sri Lanka

Journal of Earth Science (2014)

Tilak Hewawasam G.W.A.R. Fernando Danushka Priyashantha

Outcrop