Chilka Lake Research Articles

Temperature Change Scenarios over the Chilika Lagoon of India during 1901-2100

Temperature change scenarios over the Chilika Lagoon of India for 200 years (1901-2100) were quantified by the observational data sets of the Climate Research Units (CRU) of UK as well as 39 numbers of simulations from the Couple Model Inter-comparison Project Phase 5 (CMIP5) through Mann Kendall trends analysis. Long-term trend during 1901-2005 over Chilka Lake indicates the highest warming in the pre-monsoon season (1.79°C) and lowest warming (1.09°C) was shown in both the winter and post-monsoon seasons while opposite warming trends i.e., the lowest warming was observed in pre-monsoon season and highest warming was shown in the winter season for recent four decades (1969-2009) data. The performance of the CMIP5 was evaluated over a target point of Chilika Lake. Twelve numbers of models were considered as a group of performing GCMs on the basis of their ability to simulate the long-term trends as well as the mean seasonal correlation with observation. Quantile mapping technique is used for adjusting the bias for the selected GCMs. Improvement in the multi-model ensemble (MME) of bias corrected better performing models compared to MME of 39 was judged with the help of Taylor plot as well as using four different conventional statistical indices viz. correlation (r), index of agreement (d index), Nash-Sutcliffe efficiency (NSE) and root mean square error (RMSE). All the ensemble members commonly available in the four Representative Concentrations Pathways (RCPs) from the better performing selected models show a temperature change of 0.27-3.61°C, 0.38-3.98°C, 0.28-3.72°C, 0.33-3.41°C and 0.22-2.50°C in annual, winter, pre-monsoon, monsoon and post-monsoon seasons respectively at the end of 21st century over Chilika Lagoon.

Evolution of the Chilka Lake granulite complex, northern Eastern Ghats Belt, India: First evidence of ~ 780 Ma decompression of the deep crust and its implication on the India–Antarctica correlation

High-grade para- and orthogneissic rocks near the Chilka Lake granulite complex, northern part of the Eastern Ghats Belt show complex structural and petrological history. Based on field and petrographic characters, five (M1–M5) metamorphic events could be identified. The earliest metamorphic event (M1) produced amphibolite grade mineral assemblage which produced the peak granulite (M2) assemblages at 900–950°C, 8.5–9.0kbar. The third metamorphic event caused decompression of the deeper crust up to 700–800°C, 6.0–6.5kbar. This was followed by cooling (M4) and subsequent thermal overprinting (M5). Fluid-composition during M3 was dominated by high-density CO2 and changed to low-density mixed CO2–H2O during the M3. Zircon U–Pb SHRIMP data suggest 781±9Ma age for M3 event. Texturally constrained monazite U–Th–Pb EPMA data, on the other hand, yield a group age of 988±23Ma from grain interior, which can signifies the age of M2 event. Few spots with younger dates in the range of 550–500Ma are also noted. This interpretation changes the existing tectonothermal history of northern Eastern Ghats Belt. Our data show that the two adjacent crustal domains of the Eastern Ghats Belt show distinctly contrasting Neoproterozoic histories. While the central Domain 2 evolved through early anticlockwise P–T path culminating in ultrahigh temperature, the northern Domain 3 evolved through a clockwise P–T path. It appears that the Domain 3 was contiguous to East Antarctica and became part of the Eastern Ghats Belt during the assembly of Gondwana. The ca. 780Ma decompression event in the northern Eastern Ghats Belt opens up new possibilities for interpreting the breakup of Rodinia.

Magneto-Mineralogy Characterization and Analysis of Magnetic Fabrics of the High Grade Rocks from Chilka Lake Area, Eastern Ghats Belt, India

Magneto-Mineralogy Characterization and Analysis of Magnetic Fabrics of the High Grade Rocks from Chilka Lake Area, Eastern Ghats Belt, India

WSB-DA: Water Surface Boundary Detection Algorithm Using Landsat 8 OLI Data

The satellite remote sensing technique provides a comprehensive output, which helps to assess the wetland condition and regional-to-global hydrological cycle. Several algorithms facilitate the delineation of water surface boundary, but these are computationally difficult and vulnerable to unrealistic representation of the inland wetlands. The objective of this study is to develop a semiautomated, generic, parameter-free, and multispectral water surface boundary-detection algorithm (WSB-DA) to delineate the free water surface boundary of wetlands. The uniqueness of WSB-DA is that, it is a combination of five different methods: 1) standard water indices (e.g., ${\text {AWE}}{\text{I}_{{\rm nsh}}}$ , MNDWI, and ${\text {NDW}}{\text{I}_{{6} - {3}}}$ ); 2) the tasseled cap transformation; 3) hue saturation value (HSV) color transformation; 4) high-pass filtering; and 5) vector analysis. Furthermore, this algorithm uses “ultra-blue” rather than “normal blue” band of the Landsat 8 OLI image. The final output of the WSB-DA is verified using detailed GPS survey points and real time photographic evidences of Sambhar Lake. Additionally, the proposed algorithm provides appropriate results for other wetland test sites, i.e., Great Salt Lake, Chilka Lake, and parts of Sundarban Delta. The WSB-DA allows extraction of water surface boundary in a simple way, which is currently nonexistent for extremely shallow wetlands. Moreover, the WSB-DA is a reasonable proxy for the establishment of free water surface boundary detection, which allows for avoiding extensive ground survey.

Recent Foraminifera from the Chilka Lake, Orissa, East Coast of India

Chilka Lake is a brackish marine lagoon in the Orissa State, India. The Lake is divided into the Outer Channel, the Northern Sector, the Central Sector and the Southern Sector for the present study. A total of eighty eight species of foraminifera have been identified from the Chilka Lake. Asterorotalia inflata, A. Trispinosa, Cibicides lobatulus, Nonion grateloupi, Pararotalia nipponica, Ammobaculites exiguous, Miliammina fusca, M. fusca var., Quinqueloculina seminulum, Ammonia beccarii, A. Tepida, Elphidium craticulatum and Nonion deprssulus are abundant occurecne. Although the endemic species tolerate wide fluctuations in ecological variables, their reproduction is active under conditions of salinity from 30.0‰ to 40.0‰ and temperature from 27 0 to 32 0 C. Faunal sequences obtains from Outer Channel to the inner lake and from Northern Sector through Central Sector to Southern Sector, Miliammina fusca dominating in the Outer Channel and Quinqueloculina seminulum, the Central and Southern Sectors.

Crustal structure and nature of emplacement of the 85°E Ridge in the Mahanadi offshore based on constrained potential field modeling: Implications for intraplate plume emplaced volcanism

An integrated interpretation of multi-channel seismic reflection, gravity and magnetic datasets belonging to northern most part of the 85°E Ridge in the Mahanadi offshore is carried out to study the crustal structure and mode of its emplacement. The basement structure map of the ridge reveals that it is 130–150km wide and is composed of an eastern high which appears as a continuous, broad and smooth topographyand the western high characterized by several steep isolated highs. The seismic velocities reported for the first time over the ridge indicate several sedimentary sequences ranging in velocities between 1.6 and 4.0km/s above the acoustic basement top. The salient aspects of the sedimentary velocities are; a low velocity layer (2.6–3.2km/s) within the Cretaceous sequence in the intervening depressions encompassing the flank region, and a regionally widespread higher velocity layer (3.5–3.8km/s) belonging to the Eocene–Oligocene section overlying the ridge. A layer having a velocity of 4.2–4.7km/s probably made of volcanoclastic rocks is observed immediately below the acoustic basement. The sediment isopach maps presented here for three major horizons are used to compute the 3-D sediment gravity effect to obtain a crustal Bouguer anomaly map of the region. Detailed analysis of the gravity and magnetic anomaly maps clearly demonstrates the continuity of ridge up to the Mahanadi coast at Chilka Lake. Seismically constrained gravity and magnetic models indicate that the ridge is composed of volcanic material that was emplaced on continental crust in the shelf-slope areas and over the oceanic crust in the deep offshore areas. The modeled crustal structure below the ridge further indicates volcanic emplacement of the ridge on a relatively younger lithosphere. We propose two alternative models for the emplacement of the ridge.

Neoproterozoic massif-type anorthosites and related magmatic suites from the Eastern Ghats Belt, India: Implications for slab window magmatism at the terminal stage of collisional orogeny

The Jugsaipatna massif-type anorthosite complex (JAC) in the Eastern Ghats Belt of India comprises anorthosite–leuconorite–norite in the central part and gabbros, gabbronorites and porphyritic granites in the periphery. In this study, we report laser ablation ICP-MS zircon U–Pb data and REE geochemistry from the anorthosites, gabbros and porphyritic granites from the JAC. The zircon data yield weighted mean 207Pb/206Pb ages of 918±33Ma (MSWD=2.2) for the anorthosite and 931±38Ma (MSWD=2.2) and 928±35Ma (MSWD=0.99) for two leuconorites. The gabbros bordering the anorthosite body yield weighted mean 207Pb/206Pb ages of 984±10Ma (MSWD=0.41) and 969±12Ma (MSWD=1.5). Zircons from the associated porphyritic granites define two concordant age groups: an older group with 207Pb/206Pb weighted mean age of 996±11Ma (MSWD=2.1) and a younger group with an age of 964±29Ma (MSWD=2.1). Zircons from another granite sample yield an age of 957±17Ma (MSWD=1.1), identical to the Neoproterozoic age data obtained from the zircons in the anorthosites and gabbros of the JAC. The zircons from anorthosites show moderate REE contents, prominent HREE enrichment and a conspicuous positive Eu anomaly. The zircons from the granites show high REE contents, prominent HREE enrichment and a conspicuous positive Eu anomaly, suggesting a common melt source. The ages reported in study correlate well with similar ages of 983±2.5Ma for the anorthosites from Chilka Lake complex and the ca. 930Ma for Bolangir anorthosite in the Eastern Ghats Belt. The early Neoproterozoic ages reported from the magmatic suite in this study remarkably coincide with the timing of ultrahigh-temperature metamorphism reported from various localities in the Eastern Ghats Belt in recent studies. The coeval nature of mantle-derived magmatism and ultrahigh-temperature metamorphism in a collisional orogen following a prolonged subduction-accretion history along the eastern periphery of the Indian lithosphere suggests asthenospheric upwelling, probably through a slab-window mechanism. We correlate the geodynamic setting to post-collisional slab-break off at the terminal stages of the orogeny.

Genetic Diversity of Asian Sea Bass, Lates calcarifer (Bloch) Populations in India Revealed by Randomly Amplified Polymorphic DNA

The genetic diversity of five feral populations of Asian Sea bass, Lates calcarifer collected from five isolated locations in India viz., Paradeep, Chilka lake, Kakinada, Chennai and Mumbai was studied using randomly amplified polymorphic DNA. Out of 20 primers screened, 5 decamer random primers amplified a total of 373 DNA bands of which 137 bands were polymorphic. The Kakinada population showed the highest polymorphism (65.71 %) whereas the Chennai population showed the lowest (48.28 %). The inter-population genetic similarity (GS) values estimated for the five populations were checked by one-way ANOVA and found to be significantly different at P < 0.01. The highest inter-population GS was found between Paradeep and Chilka (0.909) and lowest was between Kakinada and Chennai (0.800). Genetic distance tree developed by Unweighted Pair Group Method with Arithmetic Mean cluster analysis depicted that the Sea Bass of Paradeep, Chilka and Kakinada belong to one cluster while Chennai and Mumbai populations make different cluster. Overall, Randomly Amplified Polymorphic DNA technique could be used for genetic differentiation of diverse populations of Sea bass to provide information on their population genetic structure.

Petrotectonic framework of granulites from northern part of Chilka Lake area, Eastern Ghats Belt, India: Compressional vis-à-vis transpressional tectonics

Granulite-facies rocks occurring north-east of the Chilka Lake anothosite (Balugan Massif) show a complex metamorphic and deformation history. The M1–D1 stage is identified only through microscopic study by the presence of S1 internal foliation shown by the M1 assemblage sillimanite–quartz–plagioclase–biotite within garnet porphyroblasts of the aluminous granulites and this fabric is obliterated in outcrop to map-scale by subsequent deformations. S2 fabric was developed at peak metamorphic condition (M2–D2) and is shown by gneissic banding present in all lithological units. S3 fabric was developed due to D3 deformation and it is tectonically transposed parallel to S2 regionally except at the hinge zone of the F3 folds. The transposed S2/S3 fabric is the regional characteristic structure of the area. The D4 event produced open upright F4 folds, but was weak enough to develop any penetrative foliation in the rocks except few spaced cleavages that developed in the quartzite/garnet–sillimanite gneiss. Petrological data suggest that the M4–D4 stage actually witnessed reactivation of the lower crust by late distinct tectonothermal event. Presence of transposed S2/S3 fabric within the anorthosite arguably suggests that the pluton was emplaced before or during the M3–D3 event. Field-based large-scale structural analyses and microfabric analyses of the granulites reveal that this terrain has been evolved through superposed folding events with two broadly perpendicular compression directions without any conclusive evidence for transpressional tectonics as argued by earlier workers. Tectonothermal history of these granulites spanning in Neoproterozoic time period is dominated by compressional tectonics with associated metamorphism at deep crust.

Distribution and succession of aquatic macrophytes in Chilka Lake - India

Chilka is the largest brackish water lake in Asia and also the second largest lake in the world. It is situated between 19°28' and 19°54' North latitude and 85°05' and 85° 38' East longitude. A mix of estuarine, marine and freshwater ecosystem is observed here and the lagoon has a long history of sustainable fishing. In September 2000 as a part of its management endeavour, the local authority had opened a new mouth at Satpada to facilitate efficient tidal mixing between the lake and the sea. Prior to this (1996 to 1997) salinity in the lake was low, which favoured intense growth of (invasive) macrophytic vegetation (e.g. Potamogeton, Halophila, Gracilaria, Ruppia etc.) and the effect is the greatest in the northern most part of the lake with intense (freshwater) weeds mainly Eichornia, Hydrilla, Chara, etc. Aquatic macrophytes are important in the functioning of the water body. They offer food and shelter for many organisms and promote habitat diversity. The paper seeks to isolate and describe weedy and non weedy zones inside the lake using grid sampling by Gramin® GPS. Key words: Chilka Lake, macrophyte, weeded and nonweeded, global positioning system (GPS), salinity

Additions to the genus Phycomenes Bruce, 2008 (Crustacea: Decapoda: Pontoniinae)

The genus Phycomenes was recently described by Bruce (2008)) for a small sea-grass inhabiting shrimp, Phycomenes zostericola Bruce, 2008, from south-east Queensland, Australia. The close similarity of this species to Periclimenes indicus (Kemp 1915) was noted. Subsequently specimens of Kemp’s species from the type locality, Chilka Lake, Orissa, India, were examined and the most characteristic features of the genus Phycomenes were found to be present, i.e., a transverse triangular median process on the fourth thoracic sternite and the greatly reduced size of the second pereiopods in comparison with other Periclimenes species, with a very well developed ocular ocellus. Periclimenes indicus is therefore transferred to the genus Phycomenes Bruce. Periclimenes cobourgi Bruce &amp; Coombes, 1995 has also been noted as closely similar to Periclimenes indicus, showing the same major features and should also be considered as congeneric with Phycomenes zostericola. Similarly, examination of specimens of Periclimenes sulcatus Ďuriš, Horká, &amp; Marin, 2008, and P. siankaanensis Martínez-Mayén, &amp; Román-Contreras, 2006, kindly donated by Dr Zdenek Ďuriš and Dr Mario Martinez-Mayén to the Queensland Museum, Brisbane, show the same features and should be similarly placed in the genus Phycomenes. Martínez-Mayén and Román-Contreras (2006) considered P. siankaanensis to be a member of the “iridescens” species complex, including also P. iridescens Lebour, 1949, P. platalea Holthuis, 1951, P. antipathophilus Holthuis &amp; Eibl-Eibesfeldt, 1964, P. patae Heard &amp; Spotte, 1991, and P. mclellandi Heard &amp; Spotte, 1997. Periclimenes platalea has recently been removed from this complex and placed in the genus Rapipontonia Marin by Marin (2007). No examples of these species have been examined but it seems likely that some may possibly be better placed in Phycomenes. Some of these taxa have been reported as associates of coelenterate hosts rather than from sea-grass habitat, but such a coelenterate association has also been reported in the case of the holotype specimen of P. cobourgi found on a gorgonian host. The specimens of P. indicus were kindly donated by the Zoological Survey of India, Calcutta (ZSI). The specimens examined are deposited in the collections of the Northern Territory Museum, Darwin (NTM) and Queensland Museum, Brisbane (QM).

Monazite chronology, metamorphism–anatexis and tectonic relevance of the mid-Neoproterozoic Eastern Indian Tectonic Zone

A highly tectonized zone (Eastern Indian Tectonic Zone, EITZ) of N- to NNE-trending non-cylindrical asymmetric folds, associated sinistral shears, and shear-related granitoids, traceable for >150 km along its strike, has been identified in eastern India. The EITZ near-orthogonally truncates the older metamorphic fabrics in the eastern fringes of the Chotanagpur Gneissic Complex (CGC), the North Singhbhum Mobile Belt (NSMB), and the Singhbhum Craton, three incongruently evolved crustal domains last metamorphosed at 0.95 Ga, 1.3 Ga and 2.1 Ga, respectively, before tectonism along the EITZ. Neoproterozoic monazite overgrowth at 872–838 Ma on older monazite in EITZ-hosted CGC gneiss and NSMB mica schist, and new monazite crystallization at 876–784 Ma in syn-EITZ granitoids in CGC constrain the timing of tectonism in the EITZ. Shearing occurred at greenschist to lower amphibolite facies conditions in NSMB and Singhbhum Craton. In CGC, prograde metamorphism and anatexis associated with the EITZ occurred in the presence of 5.9 mole% H 2O at peak P– T of 11.3 kb and 800 °C, followed by an isothermal pressure increase to 12.7 kb and retrogression to 9 kb and 730 °C. These P– T conditions are different from the Mesoproterozoic and Grenvillian P– T conditions deduced for the CGC in earlier studies. The Neoproterozoic deformation, metamorphism, and anatexis in the EITZ are coeval with the 0.9–0.7 Ga deformation and anatexis in the Chilka Lake area of the Eastern Ghats Belt, ∼280 km south-southeast along strike of the EITZ, and felsic magmatism/metamorphism in the Rayner Complex of East Antarctica. The regionally extensive 0.87–0.78 Ga sinistral shearing and anatexis in the EITZ is probably related to a distinct period of southward movement of India after its ∼1 Ga collision with East Antarctica during Rodinia assembly. Therefore, rifting related to Rodinia break-up between India and East Antarctica may not have started until 0.78 Ga.

Palynological records of mangrove degradation around Chilka Lake, Orissa, India

The pear shaped Chilka Lake lying along the eastern coast of Orissa State, is one of the ecological and socioeconomical important wetlands of India. This open lagoon is identified as a nationally important and internationally renowned ecosystem, which harbours a range of marine, brackish and fresh water biodiversity. Palynological syntheses based on the results of investigated mid-late Holocene profiles (Balugaon, Rambha, Nalabana, Dangmal, Solari, Chandrapur, Geokhala, Bhowania) are compared with the upper part of core CHI-9 encompassing period of 13,000 years. It has been observed from the pollen record that tropical dense mangrove forest thriving luxuriantly during early Holocene has decreased considerably with the passage of time.&#x0D; The present mangrove ecosystem, though more restricted, is fairly stable with maintenance of conserved mangrove forests in protected prograding bays in Mahanadi delta and in estuaries kept open by adequate river flow. However, siltation, eutrophication and industrial development are major threatening factors affecting the sensitivity of lake resulting in shrinkage and total disappearance of surrounding vegetation. It has been indicated that certain metals, such as Co, Cr, Cu, Ni, V, Zn As, Pb, Cd are responsible for the environmental stress of the ecosystem which are continuously incorporated by the use of fertilizers and pesticides in agriculture. There should be an appeal and educational effort to stop the destruction and fragmentation of mangroves. The planned eco-friendly rehabilitation of mangroves, along with harmonious urban development and industrialization is required in order to restore the past glory of Chilka Lake.

Spatio-temporal distribution of zooplankton in Chilka lake- A Ramsar site on the Indian east coast.

The spatio-temporal variation in zooplankton species composition, population density and relative abundance in Chilka lake studied during pre-monsoon (May), monsoon (August) and post-monsoon (October) showed conspicuous fluctuations. The average population density varied between 218 and 1296 org. m -3 ; while the biomass values ranged from 1.72- 3.30 g m -3 . Copepods, chaetognaths, cladocerans, mysids, lucifers, euphausids, siphonophores and sergestids have emerged as dominant groups. Copepods alone contributed nearly 70% of total density. The distribution of zooplankton found to be significantly influenced by salinity variations. Role of other physico-chemical parameters and food supply could also be taken as important factors influencing the sector wise distribution of zooplankton in the lake system.

Geochronology of the 983‐Ma Chilka Lake Anorthosite, Eastern Ghats Belt, India: Implications for Pre‐Gondwana Tectonics

Abstract U‐Pb zircon dating indicates that the Balugaon Anorthosite Massif of the Chilka Lake Domain, Eastern Ghats Belt, India, crystallized at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $983.0\pm 2.5$ \end{document} Ma, ∼200 m.yr. earlier than previously inferred from ferrodiorite that intruded the massif. An integration of the new date with published structural data indicates that the anorthosite intruded a crust that was deformed twice before the intrusion. Furthermore, U‐Th‐Pb chemical dating of monazite cores ( \docume...

Influence of net ecosystem metabolism in transferring riverine organic carbon to atmospheric CO2 in a tropical coastal lagoon (Chilka Lake, India)

Studies on biogeochemical cycling of carbon in the Chilka Lake, Asia’s largest brackish lagoon on the east coast of India, revealed, for the first time, strong seasonal and spatial variability associated with salinity distribution. The lake was studied twice during May 2005 (premonsoon) and August 2005 (monsoon). It exchanges waters with the sea (Bay of Bengal) and several rivers open into the lake. The lake showed contrasting levels of dissolved inorganic carbon (DIC) and organic carbon (DOC) in different seasons; DIC was higher by ∼22% and DOC was lower by ∼36% in premonsoon than in monsoon due to seasonal variations in their supply from rivers and in situ production/mineralisation. The DIC/DOC ratios in the lake during monsoon were influenced by physical mixing of end member water masses and by intense respiration of organic carbon. A strong relationship between excess DIC and apparent oxygen utilisation showed significant control of biological processes over CO2 production in the lake. Surface partial pressure of CO2 (pCO2), calculated using pH–DIC couple according to Cai and Wang (Limnol and Oceanogr 43:657–668, 1998), exhibited discernable gradients during monsoon through northern (1,033–6,522 μatm), central (391–2,573 μatm) and southern (102–718 μatm) lake. The distribution pattern of pCO2 in the lake seems to be governed by pCO2 levels in rivers and their discharge rates, which were several folds higher during monsoon than premonsoon. The net CO2 efflux, based on gas transfer velocity parameterisation of Borges et al. (Limnol and Oceanogr 49(5):1630–1641, 2004), from entire lake during monsoon (141 mmolC m−2 d−1 equivalent to 2.64 GgC d−1 at basin scale) was higher by 44 times than during premonsoon (9.8 mmolC m−2 d−1 ≈ 0.06 GgC d−1). 15% of CO2 efflux from lake in monsoon was contributed by its supply from rivers and the rest was contributed by in situ heterotrophic activity. Based on oxygen and total carbon mass balance, net ecosystem production (NEP) of lake (−308 mmolC m−2 d−1 ≈ −3.77 GgC d−1) was found to be almost in consistent with the total riverine organic carbon trapped in the lake (229 mmolC m−2 d−1 ≈ 2.80 GgC d−1) suggesting that the strong heterotrophy in the lake is mainly responsible for elevated fluxes of CO2 during monsoon. Further, the pelagic net community production represented 92% of NEP and benthic compartment plays only a minor role. This suggests that Chilka lake is an important region in biological transformation of organic carbon to inorganic carbon and its export to the atmosphere.

Petrology across a calcareous rock–anorthosite interface from the Chilka Lake Complex, Orissa: Implications for Neo-Proterozoic crustal evolution of the northern Eastern Ghats Belt

Mineral assemblages, reaction textures and consideration of deduced mineral reactions in appropriate petrogenetic grids in calc-silicate rocks occurring at the contact of the 0.79 Ga Chilka Lake anorthosite pluton, northeastern part of the Eastern Ghats Belt, India, reveal UHT-metamorphism ( T > 1000 °C) at mid-crustal depths (corresponding to 7 ± 1 kbar). This 0.79 Ga thermal metamorphism completely erased imprints of an earlier (0.96 Ga) granulite facies metamorphism in the calc-silicate rocks. The anorthosite and UHT contact metamorphic rocks were overprinted by amphibolite–granulite facies tectonothermal re-working at 0.69–0.66 Ga. Both the anorthosite-induced UHT metamorphism and the high-grade Pan-African re-working are unique for the Eastern Ghats Belt. These new observations provide clues regarding integration and disintegration of Rodinia and Indo-Antarctic correlation in the Precambrian.

U–Th–Pb monazite geochronometry of the Eastern Ghats Belt, India: Timing and spatial disposition of poly-metamorphism

The Eastern Ghats Belt of peninsular India exposes the deeply eroded high-grade parts of a composite orogenic belt that, including the Rayner Complex in Antarctica, once formed an important crustal component of Proterozoic East Gondwana. Recent work established four major crustal units separated by tectonic boundaries: the Late Archaean Jeypore and Rengali Provinces (northwest and north), the Late Palaeoproterozoic Ongole Domain (southwest) and the Meso-Neoproterozoic Eastern Ghats Province (east). To identify the timing and regional distribution of tectonothermal events within the composite belt, monazites in 66 pelitic and felsic granulite samples from 26 localities were studied with the electron microprobe chemical dating technique. In most cases the monazites are polygenetic with rock- and grain-scale chemical and chronological heterogeneities that document growth during episodes of partial melting and significant modifications through strain- and fluid-induced recrystallisation and replacement. In the Ongole Domain, monazite apparent age populations show that the fabric-defining high- to ultrahigh-grade metamorphism occurred between 1650 and 1590 Ma, after the emplacement of basic and felsic plutonic complexes into the supracrustal granulites at ca. 1.7 Ga. The monazites do not record pre-intrusion tectonothermal events, but give evidence of later imprints of ductile to brittle deformation accompanied by hydration between 1450 and 1350 Ma that are correlated with Mesoproterozoic crustal extension, rifting and alkaline plutonism along the eastern cratonic margin. The Ongole Domain was not involved in Grenvillian crustal reworking, and Pan-African tectonism (∼520 Ma) was focused in shear zones, especially at tectonic boundaries. In the Eastern Ghats Province, monazite apparent age populations in the time span between 1260 and 500 Ma witness a prolonged and polyphase tectono-metamorphic evolution during Mesoproterozoic and Neoproterozoic–Early Phanerozoic times. Apparent ages of high-Y monazite grains armoured in garnet of khondalites and high-MgAl granulites bracket the timing of early ultra-high temperature metamorphism between 1250 and 1100 Ma. Dominant and comparable apparent age populations of matrix monazites in metapelitic and felsic granulites indicate that the fabric-defining granulite facies metamorphism and anatexis of the entire terrane occurred between 980 and 940 Ma, synchronous with the intrusion of voluminous megacrystic granitoid plutons. The easternmost Chilka Lake domain experienced renewed pervasive deformation and high-grade metamorphism and melting at ca. 800 Ma coeval with emplacement of massif-type anorthosite, and further high-grade reworking during Neoproterozoic tectonism (680–650 Ma). Apparent ages of 530–470 Ma recorded in matrix monazites of strongly sheared mylonitic granulites indicate that the internal segmentation and structural configuration of the Eastern Ghats Belt and its cratonic forelands occurred during late Neoproterozoic–Early Phanerozoic times through W- to NW-directed intracratonic deformation focussed on major shear zones and terrane boundaries, when the Grenvillian Eastern Ghats Province–Rayner Complex terrane collided with India.

Origin and evolution of FeAl-granulite in the thermal aureole of the Chilka Lake anorthosite, Eastern Ghats Province, India

The Chilka Lake anorthosite (792 ± 2 Ma) in the northeastern part of the Eastern Ghats Province provides an excellent example of deep-crustal diapiric emplacement and ultra-high temperature (UHT) contact metamorphism. Within a narrow contact zone, supracrustal granulates were heated to temperatures in excess of 1000°C, causing renewed partial anatexis and melt segregation under dynamic conditions, with hybridization of the marginal leuconorite. The thermal history of the innermost aureole is well manifested by reaction textures in a FeAl-granulite occurring at the immediate contact SE of Balugaon. The tightly folded rock shows a finely banded structure. Typically, spinel+ilmenite layers are separated from quartz+garnet 1 ± perthite layers by successive coronitic layers of sillimanite and garnet 2 . The sillimanite fabric indicates synkinematic development of the corona. The reaction texture, mineral and bulk chemical characteristics, and geothermobarometric modelling suggest the following thermal evolution: (1) near-isobaric heating of a banded metapelitic granulite (khondalite: grt 1 +sil+qtz+kfsp) to c . 1100°C (7–8 kbar). Coeval with partial melting and extraction of the felsic melt, the divariant reaction (FeMg)grt+2sil → 3(FeMg)spl+6qtz is crossed at c . 1050°C, leading to the formation of a restitic FeAl-granulite made up of alternating spl+ilm and qtz+grt 1 layers. The segregated felsic melt causes hybridization of the adjacent leuconorite. (2) Subsequent near-isobaric cooling of the FeAl-granulite (spl+qtz+ilm+grt 1 ) from c . 1100°C to the stable geotherm. Reversal of the divariant reaction [3(FeMg)spl+6qtz → (FeMg)grt+2sil] produces the multi-layered coronitic texture. During this stage, coronal garnet forms also in the closely associated ferrodiorite via the reaction opx+pl → grt+qtz. The P-T data indicate that the Chilka Lake anorthosite intruded thickened crust at a depth of c . 28 km.

Aspects of the Biodiversity of Brackish Water Foraminifera

Foraminiferal fauna of the Chilka lake situated between 19° 25′ and 19° 54′N and 85° 6′ and 85° 38′E in Orissa state on the east coast of India during different seasons was studied using Pielou's, Simpson's, Margalef's, Shannon–Wiener's, and Heip's evenness indices of diversity. Mean diversity levels were low during the postmonsoon period (November) when there is heavy rainfall followed by the diluting effects of the river systems of the area; however, levels were high during the premonsoon season (March and May) due to prevalence of marine conditions in the lake. Furthermore, the evaluation of different sectors in the study area showed somewhat poor diversity within the lagoon and rich diversity in the outer channel, the fauna of which was similar to the nearshore foraminiferids of Bay of Bengal. The spatial pattern of species diversity was predictable and was related to environmental features of the areas in the lake. Regarding the spatial community structure, outer channel showed highly stable environment due to its proximity to the sea whereas northern sector showed highly fluctuating environment being away from the oceanic region and highly affected by variations in the salinity. Seasonal comparison showed postmonsoon season as the most consistent period, whereas early premonsoon was the least consistent period. Bray-Curtis group linkage cluster analysis showed that none of the clusters of foraminiferal species present during post-monsoon occurred during pre-monsoon. In contrast to this observation, approximately 30% of the species were always clustered together during early premonsoon and late premonsoon, indicating the possibility of succession of species during November. An interesting observation was that a species replacement takes place in the case of foraminiferal fauna over a seasonal cycle. This finding could be an indication of the seasonality of this community through species succession.