
L. R. K. PereraUniversity of Peradeniya | UOP · Department of Geology
L. R. K. Perera
Master of Philosophy
Modelling isotopic dating systems on computer and application of Isochron Translation to explore early earth evolution.
About
44
Publications
60,292
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
379
Citations
Introduction
With help from computers, I am trying to bridge the gap between isotopic records of rocks & minerals and their geological interpretation. Isochron Translation is a process I was able to unearth from the isotopic records of metamorphic rocks that was hidden for eight decades & unexplored, but critical for a better understanding of their isotopic evolution. Using the process, I have developed a geological criterion to identify an isochron. I am exploring the process in zircon of metamorphic rocks.
Additional affiliations
March 2017 - February 2023
September 1980 - February 2023
Publications
Publications (44)
The International Union of Geo-Scientists (IUGS) Sub-Commission on Precambrian Stratigraphy recommended isotopic age as a tool for correlation among Precambrian terrains. Such terrains often have had complex histories of evolution, and variable significances attached to isotopic ages allow pseudo-correlations and anti-correlations between them. Any...
A charnockitic gneiss and a charnockitic to amphibolite-facies gneiss transition zone in the Kadugannawa Complex show isochron relationships indicating centimetre-and metre-scale isotopic homogenization in both Sm-Nd and Rb-Sr systems. Nine 2-cm thick slabs and five 7-cm cube samples of the charnockitic gneiss give a Sm-Nd whole-rock isochron age o...
Dumortierite, a rare aluminum-rich borosilicate, occurs in sillimanite-bearing granitic to pegmatitic veins in a pelitic gneiss at Veheragala quarry North of Habarana, Sri Lanka. The veins (thickness ∼1 to 4cm) containing the mineral occur both parallel and oblique to the foliation of the host gneiss. The Dumortierite is bluish–violet in hand-speci...
Isochron is an equal-age line for measured present-day parent and daughter isotopic ratios of co-genetic minerals and rocks plotted on an isochron diagram. Isochrons provide ages and initial isotopic ratios of the samples useful to understand their geological evolution. However, the statistical criterion used to declare an isochron cannot guarantee...
Most of natural topaz is colorless; thus, methods of color enhancement are widely used for coloring this mineral. Currently, blue color is obtained by cobalt diffusion due to drawbacks in existing coloration methods. In this study, optimum conditions suitable for Cobalt diffusion in Sri Lankan colorless topaz were investigated and coloration mechan...
Crust formation is inferred from Nd-model ages of orthogneisses and crystallization ages of protolith zircons. During crustal residence Sm-Nd system of whole-rocks and U-Pb system of zircons may have been modified during repeated isotopic resetting associated with metamorphism and deformation. In the Kadugannawa Complex (KC), four adjacent granulit...
Felsite inclusions (FIs) in granulite garnets from continental collision orogens are supercooled felsic melt inclusions. Not only do these represent non-equilibrium textures , such as dendritic and spherulitic crystals of quartz and other minerals, but the porphyritic texture is that of hypabyssal and volcanic rocks. This paper presents representat...
This paper describes the outcome of a comprehensive study carried out to analyse the seismic hazards affecting Sri Lanka. The main seismic threat is from oceanic earthquakes originating at failed Mannar rift zone and Comorin ridge off the west to south west coast with some secondary influence from South Indian crustal earthquakes. The analyses were...
This paper describes a study carried out to analyse the historical records of earthquakes in the vicinity of Sri Lanka. The records indicate that the 1615 earthquake was the most significant earthquake that affected Sri Lanka. By analysing over 300 records of earthquakes around Sri Lanka, it was found that Mannar rift zone and Comorin ridge is the...
U-Pb dating of zircon is widely used in exploring the earth and planetary objects since the mineral is capable of memorizing past events after several cycles of geological evolution. Advances in analytical capabilities have allowed geoscientists to find the ages of different components that were added to and modified in a composite zircon since it...
Throughout last eight decades of application of the isochron method of dating to metamorphic rocks, there had not been any criteria to scrutinize whether a best-fit line (BFL) with a Mean Square of Weighted Deviates (MSWD) ≈ 1 for a set of present-day parent and daughter isotopic ratios is truly an isochron. Thus, an attempt was made to develop suc...
PETROGRAPHY OF ROCKS OF KAHATAGAHA- KOLONGAHA GRAPHITE MINE, WANNI COMPLEX, SRI LANKA
N. H. M. C. Nawarathna* and L. R. K. Perera
Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka
*Corresponding Author Email: maheshnawarathna544@gmail.com
ABSTRACT
Present study is a field and petrographic analysis of lithologies of the Kahat...
TONIGALA GRANITE IS NOT POST-TECTONIC
M.L.G.N.T. Jayatilaka* and L.R.K. Perera
Department of Geology, Faculty of Science, University of Peradeniya, Peradeniya *Corresponding Author Email: nayana92uop@gmail.com
ABSTRACT
A Km wide and ~13 Km long sheet-like body trending ENE and concordant with the lithologies of the northwestern Wanni Complex o...
P-T- t EVOLUTION OF PELITIC AND MAFIC ROCKS AROUND DELPITIYA, IN THE HIGHLAND COMPLEX, SRI LANKA
R.M.D.M. Ratnayake* and L.R.K. Perera
Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka
*Corresponding Author Email: dilanrath@gmail.com
ABSTRACT
Delpitiya area East of Gampola in the central Highland Complex has received attenti...
Cauvery and Mannar basins produced by a failed continental rift are floored by ~ 10 km
thick faulted blocks of gneisses and sedimentary successions the latter laid down on the
faulted gneissic basement since the Cretaceous period. During exploratory drilling for oil
in the above basins, frozen basaltic lava flows have been encountered that are inte...
The Highland-Vijayan boundary of Sri Lanka is an important geological contact zone which should be critically assessed to suggest its possible origin and evolution. Many researchers interpret it as a thrust contact between the two complexes. Since this boundary is passing through the area around Bibile in southeastern Sri Lanka, a petrological stud...
In Sri Lanka, very few petrologic studies have been carried-out on metamorphosed carbonate rocks. Most of the studies have concentrated on calc-silicate rocks in the HC. This could be due to limited variation in mineralogical assemblages of marble, and their relative ease of recrystallization during prograde and retrograde metamorphic changes elimi...
The augen gneiss occurrence around Minneriya in close proximity to the Highland Complex-Vijayan Complex boundary is one of the most significant geological features that require a critical assessment of its origin. With limited information available on its geological evolution, most researchers believe that the augen gneiss is the trace of a shear z...
Isochron rotation within an isochron diagram is envisaged during isotopic resetting since the inception of the isochron method of dating more than seven decades ago. But Rb-Sr and Sm-Nd data of incompletely reset whole-rock and mineral samples suggest isochron translation during isotopic resetting. Thus, isotopic resetting in whole-rock and mineral...
Computer simulation of Pb-Pb isochron translation is useful to understand concordance and discordance in U-Pb isotopic systems in zircon and monazite like minerals showing both open and closed system behaviour. Simulations revealed that concordance, and normal and reverse discordance are mutually complementary features originating during both close...
A Pb-Pb isochron translates parallel to itself during isotopic resetting unlike the Rb-Sr and Sm-Nd isochrons translating across themselves. Despite this difference, isochron translation in Pb-Pb whole-rock systems also produces daughter isotopic gradients at the culmination of isochron translation reflecting the field relationship of lithological...
Nd-model ages of Sri Lankan high-grade gneisses show a continuum from 1.0-3.2 Ga and a bimodal distribution with peaks at 1.6 Ga and 2.6 Ga. The older model age peak is shown by the granulites of the Highland Complex, and the younger peak is shared by the amphibolite-facies Wanni, Vijayan and Kadugannawa Complexes. A similar relationship is shown b...
Internal textures and U–Pb ages of zircons in garnet–biotite gneiss of the Southwestern Highland Complex (SWHC), Sri Lanka, were studied to clarify the repeated thermal events in the study area. The zircons from garnet–biotite gneiss consist of the detrital cores and overgrowths with two to five growth stages. The detrital zircon cores are rounded...
Present study of mineral assemblages and reaction textures of calc-silicate rocks in the southern Highland Complex of Sri Lanka around Galle area and Middeniya - Embilipitiya area has placed important constraints on the P-T-t path and fluid evolution. The studied samples can be divided into three main groups based on the mineralogy. Group I - wolla...
In late 1980s, U-Pb zircon ages of metasediments were combined with Nd-model ages of high-grade gneisses to suggest that the Sri Lankan Precambrian consists of four lithotectonic units which evolved independently from one another. The amalgamation of the units during a period of tectonism around 600-550 Ma is believed to have led to multiple deform...
In late 1980s, U-Pb zircon ages of metasediments were combined with Nd-model ages of high-grade gneisses to suggest that the Sri Lankan Precambrian consists of four lithotectonic units which evolved independently from one another. The amalgamation of the units during a period of tectonism around 600-550 Ma is believed to have led to multiple deform...
P-T-t PATH OF THE SOUTHWESTERN HIGHLAND COMPLEX AROUND BALANGODA, SRI LANKA
G.G.M.S. Wickramasinghe and L.R.K. Perera*
Department of Geology, Faculty of Science, University of Peradeniya, Sri Lanka *keerthip@pdn.ac.lk
Mineral reaction textures in calc-silicate gneisses and siliceous dolomitic marbles are important to understand the P-T-t path of...
Field relations, petrography, and geochemistry of the augen gneiss at Minneriya suggest that its protolith is an igneous intrusion. The augen gneiss cross cuts the host granitic gneiss and invades it as tongue-like offshoots at the contacts and contains occasional xenoliths. The augen gneiss is characterized by very coarse-grained augens of megacry...
Citrine (yellow), amethyst (violet), water-clear quartz (colourless) and green quartz available in Sri Lanka were subjected to γ-ray and neutron-beam irradiation to understand colour enhancement in gem-quality quartz. Faceted (cut and polished) stones and thin-sections prepared from above quartz varieties showing distinct colour differences were us...
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 condi...
Field data of the arrested charnockite (orthopyroxene-bearing quartzo-feldspathic rock in broad sense) formation are the striking evidence for CO2 flushing and resultant subsolidus dehydration reactions or partial melting. Such a local phenomenon is however, distinct from the preceding regional granulite metamorphism, because it took place under mu...
The high-grade gneisses of Sri Lanka display spectacular in-situ granulitization phenomena similar to those observed in southern India and of current interest for evolutionary models of the lower continental crust. The absolute ages of these rocks are poorly constrained and so, using the SHRIMP ion microprobe, the authors have analyzed small spots...
A co-existing cordierite-alamandine 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,...
Pink granites are common throughout the Precambrian metasedimentary terrain of
Sri Lanka and play a significant role in reconstructing the geologic evolution of this
country. Essentially microcline-bearing rocks, they form conformable layers with the
associated metasedimentary rocks and are always interlayered and associated with rocks
possessing a...
Questions
Questions (9)