Four types of relationships between rainfall and paddy production in Sri Lanka

Due to the absence of marked thermal differences in Sri Lanka, the paddy-climate relationship has been confined to rainfall alone in this study. Increase in total paddy production is highly attributed by the increase in paddy lands rather than yields, particularly in the drier parts, called Dry Zone. The effective rainfall period for the two principal cropping seasons in Sri Lanka, Maha and Yala, were determined according to the crop calendar of the Districts. The deviation values from the trend lines of 20 years (1961–1980) observations in sown, harvest and yield were well correlated with the deviations from the mean rainfall. The effects of rainfall on paddy production are well pronounced in the Dry Zone during the Maha season and in the Wet Zone during the Yala season. From the statictical analyses, four types of relationship, were observed: (1) Type I is the positive relationship, (2) Type II is the negative relationship, (3) Type III is the no realtionship and (4) Type IV a complex one which has a positive relationship below certain critical rainfall value and no or negative relationship above the critical rainfall value. The combination of Types I and IV shows the areas which need irrigation facilities with proper water management while the combination of the Types II and III indicates the areas which are prone to frequent floods and waterloggings.     

Monsoon and land use in Sri Lanka

Agricultural land use in Sri Lanka roughly shows a division of the island in two major parts, according to the climatic division into thr Wet and Dry Zones. Therefore, it is the ultimate, most important question for agricultural land use in Sri Lanka whether the seasonal occurrence of a distinct dry season, which is characteristic of the Dry Zone, is also the most delimiting factor for land use or not. It seems true, in fact, that the long SW monsoonal dry season in the Dry zone is the major fact for a large-scale division of Sri Lanka according to the crops under cultivation and the cropping systems. Paddy (rice) and tea are the leading crops in the Dry as well as Wet Zone. They are at the same time the crops with the greatest economic importance for the island: tea for the international market, rice for the national market. Thus, the main attention is drawn on specific climatic effects, in a large- and meso-(local-)scale, upon tea and paddy and their agroclimatic potential of cultivation. Besides this, also some effects of the monsoon climate of Sri Lanka upon animal husbandry, forestry and pests have been studied briefly, added finally by an outlook on the correlation between the monsoon climate and fishery even, as manifested in the phenomenon of migrating fishermen.     

Arrested charnockite formation in southern India and Sri Lanka

Arrested prograde charnockite formation in quartzofeldspathic gneisses is widespread in the high-grade terrains of southern India and Sri Lanka. Two major kinds of orthopyroxene-producing reactions are recognized. Breakdown of calcic amphibole by reaction with biotite and quartz in tonalitic/granitic gray gneiss produced the regional orthopyroxene isograd, manifest in charnockitic mottling and veining of mixed-facies exposures, as at Kabbal, Karnataka, and in the Kurunegala District of the Sri Lanka Central Highlands. Chemical and modal analyses of carefully chosen immediately-adjacent amphibole gneiss and charnockite pairs show that the orthopyroxene is produced by an open system reaction involving slight losses of CaO, MgO and FeO and gains of SiO₂ and Na₂O. Rb and Y are depleted in the charnockite. Another kind of charnockitization is found in paragneisses throughout the southern high-grade area, and involves the reaction of biotite and quartz±garnet to produce orthopyroxene and K-feldspar. Although charnockite formation along shears and other deformation zones at such localities as Ponmudi, Kerala is highly reminiscent of Kabbal, close pair analyses are not as suggestive of open-system behavior. This type of charnockite formation is found in granulite facies areas where no prograde amphibole-bearing gneisses exist and connotes a higher-grade reaction than that of the orthopyroxene isograd. Metamorphic conditions of both Kabbaltype and Ponmudi-type localities were 700°–800° C and 5–6 kbar. Lower P(H₂O) in the Ponmudi-type metamorphism was probably the definitive factor.CO₂-rich fluid inclusions in quartz from the Kabbaltype localities support the concept that this type of charnockite formation was driven by influx of CO₂ from some deep-seated source. The open-system behavior and high oxidation states of the metamorphism are in accord with the CO₂-streaming hypothesis. CO₂-rich inclusions in graphitebearing charnockites of the Ponmudi type, however, commonly have low densities and compositions not predictable by vapor-mineral equilibrium calculations. These inclusions may have suffered post-metamorphic H₂ leakage or some systematic contamination.Neither the close-pair analyses nor the fluid inclusions strongly suggest an influx of CO₂ drove charnockite formation of the Ponmudi type. The possibility remains that orthopyroxene and CO₂-rich fluids were produced by reaction of biotite with graphite without intervention of fluids of external origin. Further evidence, such as oxygen isotopes, is necessary to test the CO₂-streaming hypothesis for the Ponmudi-type localities.     

Sri Lanka - India Intraplate Tectonics - Precambrian to Present

The tectonic history of Sri Lanka - India can be traced from the Precambrian to the present. On the basis of the geological record, plate tectonic processes have operated for example, the Highland Group of Sri Lanka may have represented a Precambrian plate tectonic suture. Tectonic models of these Precambrian events may be presented by spreading, collision, subduction, shearing or in situ jostling. The recent tectonic history of Sri Lanka and India relates to the evolution of the Indian Ocean since at least the Cretaceous. Although Sri Lanka is considered to be a part of the larger Indo - Australian plate, it may have had a local independent history as a block within the larger crustal unit of India. There is evidence that the separation of Sri Lanka from India was in part controlled by Precambrian structures and a history of translational, rotational and vertical adjustments to the Indian Ocean developmental plate tectonic stresses still operating.     

Co-existing cordierite-almandine-a key to the metamorphic history of Sri Lanka

A co-existing cordierite—almandine assemblage is described from the pelitic metasedimentary rocks of the Precambrian granulite-facies terrain of Sri Lanka. The chemical control on this assemblage is demonstrated, as has been observed in granulite-facies terrains elsewhere. The previous view of a low-pressure origin of cordierite in pelitic rocks, and the subdivision of the central granulite-facies belt of Sri Lanka based thereon, is hence doubtful.     

Cross-twinning in a natural spinel from Sri Lanka

A modified cross-twinning growth mechanism is put forward to explain the anomalous morphology of a spinel multiple-twin from Sri Lanka, flattened crosswise the twin planes. Cross-twinning in spinel was found also in other specimens from Pegu (Myanmar), and the results were published in a previous paper. This particular type of twinning is derived from the combination of cyclic twinning with lamellar twinning, so that these samples may be thought of as partial fivelings (cubic cyclic {111} twins with five components sharing a common <110> pseudo-fivefold axis). In the present paper, the sample from Sri Lanka has been suitably cut with the aim of focusing the study on the cross-twinning region. The transformation matrices that link the orientation states of each couple of twin components have been determined by means of White Beam Synchrotron Radiation Topography. They showed that the specimen is made up of four twin components (A, B, C and D), with three twin planes: and They also showed that the cross-twinned individuals (B and D) actually are not twinned to each other, and that a simple crystallographic relationship holds between them. X-ray diffraction topography by conventional source allowed to image the crossing-region and to determine that the cross-twinned individuals are in contact through a semi-coherent boundary, with twinning dislocations contributing to relieve the coherency strains. Electron probe microanalyses with wave dispersive spectroscopy showed that the chemical composition is almost homogeneous, at least within the spatial resolution limit of this technique. The similar growth features observed in the spinel sample from Sri Lanka and in those from Myanmar are interpreted as growth marks, indicators of a similar origin: in both cases they are found in impure dolomitic marbles. In particular, the specimen from Sri Lanka results from the interaction of thermal and metasomatic effects due to contact metamorphism. An unusual stepped morphology of the face close to the twin boundary, possibly due to corrosion and re-growth processes acted preferentially at a re-entrant corner by metasomatic fluids, is interpreted as indicator of a metasomatic event that succeeded to the crystal growth, the latter occurred by thermal effect.

Locational specificities of fertility transition in Sri Lanka

Sri Lanka has one of the lowest fertility rates among poor countries of the world. The fertility decline which began in the 1950s has held steady during the last four decades, despite low levels of economic development. Widespread use of contraception is the primary cause of the fertility decline. However, there is no one single homogenous body of people that can be characterized as a ‘modern’ contracepting population through which new methods of family planning have spatially diffused. There is evidence that the overall fertility decline began even before the establishment of the modern family planning program in Sri Lanka. Our analysis showed four broad regional regimes of fertility transition with considerable social and place-to-place differences in method-specific rates of contraception among them. Non-modern ‘traditional techniques’ of contraception which are widely used are an important part of fertility regulation. Sterilization is the most common method of modern contraception in all regions. Less than a tenth of the protected couples use methods such as the pill and the IUD; moreover, these methods are often discontinued after initial use. Traditional methods are an important part of the contraceptive mix in Sri Lanka, and it would be inadvisable to discourage the use of such practices. This revised version was published online in August 2006 with corrections to the Cover Date.     

The relationship between soil geochemistry and die back of montane forests in Sri Lanka: a case study

Tropical montane forests of Sri Lanka form a unique ecosystem with more than 50% of endemic plant species. It has been noted that trees, belonging to different size and age classes of these forest, have been dying due to a yet unknown factor. This phenomenon was first observed in the Horton Plains National Park, which is a high plateau, composed of tropical montane forests. Later dying of forests were observed at several areas including Hakgala montane forest. Physical parameters trace nutrients as well as toxic element concentrations in soils, were studied in order to identify the possible geochemical factors behind the forest die back. Systematic soil sampling was carried out covering the entire Horton Plains National Park and random samples were collected from Hakgala montane forest. Samples were analyzed for available Fe, Mn, Zn, Cu, Ni, Cd, Al and Pb using standard colorimetric and atomic absorption spectrometric procedures. Physical parameters such as pH, moisture content, and conductivity of the samples were also measured. Among extractable micro-nutrients Cu and Zn, and Ni show no deficiency or excess levels. However, the recorded available high concentrations of Fe, Mn and Al can be toxic to certain montane plant species. Acidic moist soil of the area may enhance the toxic effects of these elements. Possible source of these elements should be the underground lithology of the area. According to the results obtained, there is a relationship between forest die back and high Pb concentrations. The same phenomenon was also observed in the Hakgala forest. The distribution pattern of Pb in the Horton Plains coincides well with the die back distribution pattern. The observed Pb values at Horton Plains and Hakgala are almost similar to values observed at Pannipitiya and Dombagaskanda locations, which are located close to main roads carrying heavy traffic. It is quite possible therefore, that Pb toxicity may be a significant factor behind the forest die back even though other factors should not be completely ruled out at this juncture. Strong monsoon winds, bringing Pb from the polluted southwestern part of the country, can be the most possible source of soil Pb. Further studies however are indeed necessary to confirm the conclusion.     

Weathering of phosphatic marble to exploitable apatite deposit,Sri Lanka

Weathering of a granulite-amphibolite facies phosphatic marble from Eppwala, Sri Lanka is described. During the weathering process, apatite is concentrated to an exploitable grade. Primary metamorphic phosphates in the marble from Sri Lanka are hydroxyapatite, as indicated by EPMA and XRD. Weathered phosphates and weathered crystalline products are composd of carbonate fluorapatite, crandellite, wardite, fluellite, kaolinite, goethite and gibbsite. DTA, SIM, SIMS and SAM show the presence of amorphous materials, such as oxides of Fe, Al, Si, Al + Si, and S, on the surface of weathered phosphate. Using SEM, TEM, EDX and electron diffraction techniques, the presence of these amorphous and crystalline materials with several transitions have been clearly identified in weathered phosphate. Secondary crystalline phosphate, consisting of P, Ca and Fe, has partially developed on the surface of the primary phosphate. Recrystallization of phosphate occurred during weathering and calcite dissolution, with nucleation and precipitation of secondary phosphates. The lattice images of hydroxyapatite are gradually increased from 8.3 to 9.1Åbasal spacings during weathering.     

Precambrian structure and chronology in the Highland Series of Sri Lanka

Field studies in the Kandy district and elsewhere in the Highland Series demonstrate that these granulite facies rocks have been repeatedly deformed. The major folds (D3) postdate one and possibly two phases of isoclinal folding (D1 and D2) during which the main L-S fabric was formed. The main metamorphic peak probably occurred during these early phases, around 2200 Ma ago. The D3 episode appears to have predated the formation of the Vijayan gneisses at 1200 Ma. Hornblende-bearing gneisses mainly restricted to synformal basins are regarded as the result of local partial melting and mobilization during D3.     

Tidal choking and bed friction in Negombo Lagoon,Sri Lanka

We have studied bed friction and water exchange in a small, almost enclosed, shallow lagoon in Sri Lanka, where both tides and freshwater supply are important for the circulation. Because of the narrow entrance, the lagoon is strongly choked for semidiurnal tidal forcing (the choking coefficient is 0.25). A set of tide gauges positioned on each side of the entrance channel was used to calculate bed friction. Measurements made over three short periods having different freshwater supply to the lagoon indicate an average friction (drag) coefficient C_D=0.0041±0.0002 (using a quadratic friction law). A comparison between observed and calculated velocities in the channel for a variety of velocities, indicates that the quadratic friction law is a good tool for parameterization. High freshwater supply increases the lagoonal sea level substantially and decreases the residence time.     

Geochemistry and genesis of granitoid rocks from Southern Sri Lanka

Summary Pyroxene granulites of intermediate to felsic composition comprise a major part of the Precambrian terrain exposed in southern Sri Lanka. Chemical characteristics and field relations reveal that there are two closely associated groups of granitoids both occurring as discrete layers or deformed bodies. Granitic-adamellitic rocks are more common and can be distinguished from tonalitic-trondhjemitic rocks. Granitoids of these two groups and minor metabasalt and metadiorite/meta-andesite have been subjected to high-grade metamorphism and were mapped as charnockite or charnockitic rocks. Rocks of granitic composition are mostly meta-aluminous and, in the AFM diagram, fall in the tholeiitic field. These rocks are mainly A-type granites characterized by high K₂O/Na₂O, FeO/MgO and high Zr, Nb and LREE contents, most belonging to the relatively Ce- and Y-enriched A₂-type. Tonalitic rocks are meta-aluminous to per-aluminous and display a calc-alkaline trend. These rocks are classified as I-type, although some of them have very low K₂O and REE contents.Tonalites and granites are not products of a consanguineous fractionation process. In spite of their close field association, they appear to be polygenetic. The parent magmas of the A-type granites seem to have been differentiated melts derived from felsic continental crust. They were emplaced into normal or attenuated continental crust in a non-Compressive (extensional or trans-tensional) tectonic regime. Tonalites most probably represent volcanic arc granitoids emplaced in a compressive tectonic setting. Present intercalation of these polygenetic granitoids, generated in different tectonic environments, is a result of the complex tectonic activity which prevailed before or during Pali-African (550–610 Ma) granulite facies metamorphism.

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Geochemie und Genese von Granitoiden aus dem süchen Sri Lanka

Zusammenfassung Pyroxengranulite intermediärer bis saurer Zusammensetzung bilden einen Hauptbe standteil des präkambrischen Terrains im südlichen Sri Lanka. Chemische Untersuchungen und Feldbeziehungen ermöglichen die Unterscheidung von zwei räumlich eng assoziierten Gruppen von Granitoiden, die beide lagenförmig oder in Form deformierter Körper auftreten. Granitisch-adamellitische Gesteine sind häufiger und sind von tonalitisch-tronhjemitischen Gesteinen zu unterscheiden. Diese Granitoide und untergeordnet vorkommende Metabasalte und Metadiorite/Metaandesite wurden von hochgradiger Metamorphose erfaßt und als Charnockite bzw. charnokitische Gesteine kartiert. Gesteine granitischer Zusammensetzung sind meist metaluminös und fallen im AFM Diagramm ins Feld der Tholeiite. Es sind A-Typ Granite des an Ce und Y angereicherten A2-Subtyps mit hohem K₂O/Na₂O, FeO/MgO und hohen Gehalten an Zr, Nb und LREE. Tonalitische Gesteine sind met-bis peraluminös und folgen einem kalk-alkalischen Trend. Sie werden als I-Typ Granite klassifiziert, obwohl einige Proben sehr niedrige K₂O und REE Gehalte aufweisen. Die Tonalite und Granite sind nicht die Produkte eines cogenetischen Fraktionie rungsprozesses und sind, trotz ihrer räumlichen Assoziation, polygenetischen Ursprungs. Die Ausgangsmagmen der A-Typ Granite scheinen differentierte Schmelzen saurer krustaler Herkunft zu sein, die in normal dicker oder verdünnter Kruste in einem nicht kompressionellen tektonischen Regime (ex- oder transtensional) intrudierten. Die Tonalite sind wahrscheinlich in einem Kompressionsregime enstandene Granitoide eines Vulkanbogens. Das heutige Nebeneinander dieser polygnetischen, in unterschiedlichen geotektonischen Bereichen gebildeten, Granitoide ist das Ergebnis komplexer tektonischer Aktivität vor oder während der panafrikanischen (550–610 Ma) granulitfaziellen Metamorphose.

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With 11 Figures     

Thermal and baric evolution of garnet granulites from Sri Lanka

Abstract Garnet granulites from Sri Lanka preserve textural and chemical evidence for prograde equilibration at temperatures of at least 700–750°C and pressures in the vicinity of 6–8 kbar. Associated strain patterns suggest prograde metamorphism occurred during and immediately following an episode of crustal thickening, with the prograde P–T conditions probably reflecting a combination of the conductive and advective transport of heat at the mid-levels of tectonically thickened crust. The occurrence of prograde wollastonite provides evidence for internally buffered fluid compositions, or fluid absent conditions, during peak metamorphism and precludes pervasive advection of a CO₂-rich fluid. The advective heat component is therefore likely to have been provided by the transport of silicate melt. Intricate symplectitic textures record partial re-equilibration of the garnet granulites to lower pressures (˜ 4–6 kbar) at high temperatures (600–750°C), and testify either to the erosional denudation of the overthick crust prior to significant cooling (i.e. quasi-isothermal decompression) or to a subsequent static heating possibly of early Palaeozoic age (Pan-African). The metamorphic history of the Sri Lankan granulites is compared with high grade terrains in the neighbouring fragments of Gondwana, with the emphasis on similarities with Proterozoic granulites of the East Antarctic craton.     

Modes of occurrence and provenance of Gemstones of Sri Lanka

The island of Sri Lanka is underlain primarily by Precambrian metamorphic rocks belonging to the Amphibole, Cordierite and Pyroxene facies. Gemstones occur mainly in the Cordierite and Pyroxene facies terrains of the Southwestern and Highland Groups of rocks. Gem mining is carried out on hill tops, river valleys and beds and gemstones are found associated with eluvial, residual and alluvial sediments. The dominant gemstones mined are blue sapphires, rubies and beryl. The sources of gem type minerals are determined to be garnetiferous gneisses, cordierite gneisses, marbles and pegmatites.

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Résumé L'île de Sri Lanka est formée presque entièrement des roches métamorphiques de l'âge precambrien. Celles-ci appartiennent aux faciès granulitiques à cordierite et à pyroxène. Les pierres précieuses se trouvent dans les terrains caractérisés par ces faciès que l'on classe dans les groupes dits Highland et Southwestern. L'exploitation des pierres précieuses se fait aux sommets des collines ainsi que dans les vallées ou dans les lits des rivières et une bonne partie de pierres ainsi exploitées sont des saphirs bleus, rubis et de béryls. Les minéraux qui sont à l'origine des pierres précieuses proviennent des gneiss à grenat ou à cordierite, des marbres ou des pegmatites.

     

Application of Rb-Sr ratios to gem exploration in the granulite belt of Sri Lanka

The geochemical distribution of rubidium and strontium in the central granulite belt of Sri Lanka, where many of the gem deposits are found, was studied. The Rb-Sr ratios, particularly in the stream sediments, were found to be useful in delineating gem-bearing areas from the non gem-bearing or low potential areas. Among the main gem minerals that are mined at present are corundum, spinel, zircon and tourmaline. It was observed that higher Rb-Sr ratios correspond to high gem potential and, even within areas of good potential, barren areas could be delineated using these ratios. During pegmatite formation, Rb is enriched, and there is a marked depletion of Sr yielding a high Rb-Sr ratio. Pegmatites, granites and other magmatic bodies are associated with gem formation under granulite facies conditions and, when used in conjunction with geology, structure, and mineralogy, the Rb-Sr ratio could be used effectively to delineate target areas for further exploration.     

Factors controlling fluoride contents of groundwater in north-central and northwestern Sri Lanka

Chemical characterization has been made of groundwater bodies at 294 locations in four village districts in north-central and northwestern Sri Lanka, with special focus on fluorine contamination. High fluoride contents in groundwater are becoming a major problem in the dry zone of Sri Lanka, and dental fluorosis and renal failures are widespread. Field measurements of temperature, pH, and electrical conductivity were made during sampling. Chemical analyses of the water samples were later made using atomic absorption spectroscopy, spectrophotometry, and titration. Fluoride concentrations in the study area vary from 0.01 to 4.34 mg/l, and depend on pH and the concentrations of Na, Ca, and HCO₃ ⁻. Basement rocks including hornblende biotite gneiss, biotite gneiss, and granitic gneiss seem to have contributed to the anomalous concentrations of fluoride in the groundwater. Longer residence time in aquifers within fractured crystalline bedrocks may enhance fluoride levels in the groundwater in these areas. In addition, elevated fluoride concentrations in shallow groundwater in intensive agricultural areas appear to be related to the leaching of fluoride from soils due to successive irrigation.     

Secondary phosphate mineralization in a karstic environment in Central Sri Lanka

At Eppawala in central Sri Lanka secondary phosphate mineralization is intimately associated with laminated fabrics within depressions (sinkholes and smaller cavities) formed in the thick weathering profiles of a hilly terrain underlain by a Precambrian apatite-bearing formation. The lowermost levels of the profile show extensive zones of leaching where derived apatite crystals occur within fine-grained, laminated stromatolite sequences. The stromatolitic groundmass, which diagenetically formed by percolating oxygenated phosphate and carbonate-rich groundwaters, is impregnated by the phosphate minerals francolite and collophane. Scanning electron microscopy (SEM) reveals that fine filaments, characteristic of microorganisms, are associated with the secondary phosphate mineralization. Continuous degradation and fragmentation of the stromatolitic mat has produced pellets, peloids, and intraclasts all enriched in secondary apatite. Degrading recrystallization around the edges of the primary apatite crystals has developed coated grains. The widespread occurrence of phosphate-enriched allochems in stromatolitic groundmasses is a unique development of a modern phosphorite in a karstic environment.     

Weathering of Monuments at Jethawanaramaya Complex in North-Central,Sri Lanka

Abstract: Sri Lanka has the richest archaeological sites in Asia. Jethawanarama Complex, one of the valuable sites in the country, is suffering from deterioration due to weathering. Monuments were built mainly from stones (granitic gneiss and marble) and clay bricks. The present study aimed to categorize weathering forms and interpret the recently-developing weathering processes. The growing of lichens on surfaces and the development of saline conditions are the major threats on the survival of monuments other than the typical weathering processes of tropical climates Morinite (NaCa2Al2[PO4)]2[F,OH]5·2H2O) is identified as a weathering product of monuments and is generated from lichens.