DOCSLIB.ORG

Geochronology of the Indian Precambrian *

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Geochronology of the Indian Precambrian * Ceol. Sac. Malaysia, Bulletin 6, July 1973; pp. 213-226. Geochronology of the Indian Precambrian * M.S. BALASUNDARAMI AND M.N. BALASUBRAHMANYAN1 Abstract: Precambrian geochronology of India is now known with greater precision because of the dating of samples carefully se lected, in respect of geological consideration and set up, from several areas in the pas t decade. Vestiges of older nuclei dating more than 3000 m.y. have been identified in southern, eastern and western India. The Charnockite-Khonda­ lite supergroup (c.2900-2600 m.y.) is now considered to be older than the Dharwar super­ group; the Eastern Ghats (sensu stricto) rocks are now considered belonging to the Charnoc­ kite-Khondalite supergroup proper but with impress of events at 1650 m.y. and 1400 m.y. at about the same time as events in Cuddapah Basin, Nellore Schist Belt and Amgaon group. The Aravalli, Bailadila, Bengpal and Iron Ore groups are correlated wi th the Dharwar and range in age from c.2500-<:.2000 m.y. The Delhi supergroup appears to be coeval with the lavas of the Gwalior 'series'. Vindhyan sedimentation which started at c.1400 m.y. continued into Cambrian (?) un­ like the Cuddapah supergroup where sedimentation ended by about 1300 m.y. The success­ ively younger dates for the mobile belts from south to north, with respect to the southern nucleus, indicates a migration of geosynclines in the same direction. The Satpura 'group' despite valid e.vidences for its abolition as a supergroup appears to indicate the reactivation of the Narmada-Son lineament at 950/ 1000 m.y. in part or eastern India. The manifestation of carbonatite and anorogenic granites dating 725 m.y. in southern India, high-level granites in western India, dating 730 m.y., Mylliem granite at 765 m.y. in eastern India and carbona­ tite in Rajasthan at 960 m.y. appear to be rel ated to reactivation of lineaments in these areas at these dates. The overprint of minera I ages at c.500 m.y. along the east coast is also suggest­ ive of activity of lineaments but further studies are necessary to confirm this view. INTRODUCTION Dates on I~ss than a score of minerals were available when Arthur Holmes (1955, p. 81) presented the first account of the geochronology of the Precambrian tectonic cycles in the Indian Shield. At present, nearly six hundred dates are available re­ presenting a much wider spectrum of the Indian Shield: (Aswathanarayana, 1956; 1959 ; 1962 and 1964; Sarkar et al., 1964 ; 1967 and 1969; Venkatasubramanian er al. , 1968 and 1971 ; Crawford I 969a, 1969b and 1970 ; Crawford and Compston, 1970). A review of the stratigraphy and geochronology by Sarkar (1968) has been supplemented by a review by Chaterji et al., (/971). Even fission track methods have been applied for pegmatite minerals (Mehta el al. , 1968 and 1970). At present many institutions in India, including the Geological Survey of India, have commissioned mass spectro­ meters and a wealth of data will be flowing from these institutions in the years to come. PRECAMBRIAN DATES General Fig. I depicts the histograms of isotopic ages of the Indian Precambrian Shield. Even though it will be hazardous to interpret the average of dates or the histograms (Cahen and Snelling, 1966, p. 16), it is now fairly well established that peaks of histo­ grams do reflect orogenies (Clifford, 1968 , p. 302). An attempt is made here to focus attention on the dates of major tectonic events and also elucidate the concordance or discordance between different methods of dating in the same group of rocks. * Published by kind permission of the Director General, Geological Survey of India. 1 Geological Survey ofTndia, Calcutta. 214 M. S. BALASUNDARAM AND M. N. BALASUBRAHMANYAN 30 Ii d. K - Ardatu 20 10 " ~ IT1 20 C . Rb- Sr dates 0 C IT1 b. U -Th/Pb, Common Pb. Pb'£' dofes Z () -< o. All Dotes 500 1000 1500 2000 2500 3000 3500 ISGTOPIC AGE IN MILLION YEARS M .N .8olclubrohmonya n G. S . I . Fig. 1. Indian Precambrian Dates (Histograms) Histograms a, b, c and d of Fig. 1 represent respectively the dates available i) by all the methods ii) by U-Th/Pb method, lead alpha method and common lead method and iii) by Rb/Sr methods pertaining to single whole rock analysis with initial ratio at 0.7 and mineral dates and iv) K/Ar method on whole rock basic igneous rocks and mineral dates. The histogram 'a' represents major events at 500 m.y., 950-1000 m.y., 1500- 1600 m.y., 2100 m.y., 2600 m.y. , 3100-3200 m.y. and 3500 m.y. matched by U­ Th/Pb date peaks at 1000 m.y., 1600 m.y., 2600 m.y. and 3500 m.y. The lack of other dates is possibly due to lack of datable material only. The peaks of Rb/Sr dates are at 500 m.y., 800 m.y.-900 m.y., 1500 m.y., 2100 m.y., and 2600 m.y.-2700 m.y. However Rb-Sr whole rock isochrons (Fig. 2) are concordant to the peaks of U-Th/Pb at 1000 m.y. , 1700 m.y., 2000 m.y. and 2600 m.y. , indicating that these pertain to major pluto­ nic activity. The KjAr dates with peaks at 500 m.y., 900 m.y., 1500-1600 m.y., 2100 m.y., 2300 m.y. , 2500 m:y., and 3200 m.y;, based as they are mainly on mineral dates, lend to reflect the metamorphic and uplift dates in general. GEOCHRONOLOGY OF THE INDIAN PRECAMBRIAN 215 - '- - ,-; --"~-l fl,. 2 THE INDIAN ~CA"BAIAH (S~~~) 't . .. ' ~. j' ... , .. _ ... ... u::::iJJiJ .... ~ ....... ............... I)M ••• " ... 0: ..,,. ••• ~ ' ,"" =G8 .:;::..;.!. ';':....~.: ..:: ;:-; '."., ..,., • • gQ · .......... .... ·1·. .. .... ·_ ... .. ··00 .. , CJI!IJ t ... " . .... , " ... .... .. ... .... ... \e . .. , ,"110 .. , ~ s ....,.'I •••~ . s " ••.•. G4 .... ' . ' •• I . U . .. t ' ••• ,."oo .. , . ,/ ~ oo,~ . ..... " ... U IClO .. , o:J ..... ~ .. •. _ .... _ ... ,." ..... 1lO . .. '_' I" " . 2 ~ ClO .. , ~ :::.:::~::2:::~ '::: ., .'.: ~" , .I., ~ " ... ,... ~ ......., . Fig. 2. The Tndi an Preca mbrian (Shield) Relating these peaks to the regions where they are pertinent (Fi g. 2), it is obse rved that: (i) a 500 m.y. event is seen only in southern, east coast and Shillong plateau areas and it indicates a biotite rejuvenation date due to ( ?) reactivation of basement fractures. (ii) a 950-1000 m.y. event in eastern India, in what has been described as areas showing a 'Satpura trend' pari passu with magmatism in northwest Tndi a. This event is perhaps similar to the 500 ill.y. event. (iii) a 1600- 1700 m.y. event related to the development ofCuddapah Basin with effusion of lavas, Nellore Schist Belt with emplacement of pegmatites, east coast with a metamorphic/uplift event and in northeast India with emplace­ ment of granitic bodies. (iv) a 2100 m.y. event related to the retrogression of granulite facies rocks to amphibolite facies in southern India and migmatisatioll of the associated paragneisses. 216 M. S. BALASUNDARAM AND M. N. BALASUBRAHMANYAN (v) a 2600 m.y. plutonic event of crystallisation of charnockites under granulite facies conditions in the region pari passu with regional migmatisation result­ ing in the evolution of Peninsular Gneisses of Mysore-Hyderabad region. and (vi) a 3000 m.y.-3100 m.y. plateau and a peak at 3500 m.y. revealing nuclei in southern India, eastern India and western India. The periodicity of the events is similar to those in other continents, particularly similar to the geochronology of Africa (Clifford, 1968, p. 303) except for the event at 1400 m.y. which is recorded insignificantly in India. Classification into supergroujJs Fig. 3 details the stratigraphy and geochronology of the different supergroups in the Indian Precambrian. The approximate time range in the tectonic and post tectonic evolution of these are also detailed together with histograms of dates pertinent to the supergroups shown. The Dharwar supergroup is shown separately from that of the Charnockite-Khondalite supergroup; the Eastern Ghats formations belong to the Charnockite-Khondalite group, but certain dates have attributes of the adjoining Cuddapah supergroup also and hence shown alongside for comparison of dates. Earlier views that the Charnockites represent metamorphosed Dharwar and that they belong to two periods (Pichamuthu, 1962) and they intrude the Dharwar (Rama Rao, 1936) are now questionable hypotheses. Evidences have been presented by Narayanas­ wami (1963) , Iyengar and Banerji (1971) and Balasundaram and Balasubrahmanyan (1971) that the Charnockite-Khondalite supergroup forms a craton to the Dharwar. On the basis of isotopic age data, the east coast Eastern Ghats rocks have been thought to be of a younger age (Crawford, 1969b), in relation to their southern equivalents. The status of the Nellore Schist Belt, which is now included in the Dharwar super­ group, will be subjected to review perhaps on more modern geological data and isotopic age, as suggested by Crawford (1968). The data for central India groups ofKhairagarh, Sausar, Sakoli, Amgaon and as those of the Singhbhum region are tentative and will have to await Rb/Sr studies as the present data rely on K /Ar dates only. The events in the Aravalli and Delhi supergroups together appear to span the time range from 3000 m.y. to 700 m.y. and future work will throw much light on the detailed correlation of the region. Thus Fig. 3 is partly based on existing data as such and partly on reinter­ pretation of such data by the authors, well supported by other workers, as already referred to. Charnockite-Khondalite Supergroup In lithology, regional structure and metamorphism, the rock formations in the Charnockite Province of Fermor (1936) are similar. The province comprises the eastern coastal tract of Eastern Ghats group of Andhra Pradesh and Orissa and the southern extensions in Tamil Nadu and Kerala proper.
Load more

Recommended publications
  • Sedimentational, Structural and Migmatitic History of the Archaean Dharwar Tectonic Province, Southern India
    Proc. Indian Acad. Sci. (Earth Planet. Sci.), Vol. 100, No. 4, December 1991, pp. 413-433. Printed in India. Sedimentational, structural and migmatitic history of the Archaean Dharwar tectonic province, southern India K NAHA 1, R SRINIVASAN 2 and S JAYARAMa 1Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302, India 2National Geophysical Research Institute, Hyderabad 500007, India aDepartment of Mines and Geology, Karnataka State, Lai Bagh Road, Bangalore,560027, India MS received 27 July 1991 Abstract. The earliest decipherable record of the Dharwar tectonic province is left in the 3-3 Ga old gneissic pebbles in some conglomerates of the Dharwar Group, in addition to the 3"3-3-4Ga old gneisses in some areas. A sialic crust as the basement for Dharwar sedimentation is also indicated by the presence of quartz schists and quartzites throughout the Dharwar succession. Clean quartzites and orthoquartzite-carbonate association in the lower part of the Dharwar sequence point to relatively stable platform and shelf conditions. This is succeeded by sedimentation in a rapidly subsiding trough as indicated by the turbidite-volcanic rock association. Although conglomerates in some places point to an erosional surface at the contact between the gneisses and the Dharwar supracrustai rocks, extensive remobilization of the basement during the deformation of the cover rocks has largely blurred this interface. This has also resulted in accordant style and sequence of structures in the basement and cover rocks in a major part of the Dharwar tectonic province. Isoclinal folds with attendant axial planar schistosity, coaxial open folds, followed in turn by non-coaxial upright folds on axial planes striking nearly N-S, are decipherable both in the "basement" gneisses and the schistose cover rocks.
    [Show full text]
  • Streaming of Saline Fluids Through Archean Crust
    Lithos 346–347 (2019) 105157 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos Streaming of saline fluids through Archean crust: Another view of charnockite-granite relations in southern India Robert C. Newton a,⁎, Leonid Ya. Aranovich b, Jacques L.R. Touret c a Dept. of Earth, Planetary and Spaces, University of California at Los Angeles, Los Angeles, CA 90095, USA b Inst. of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Science, Moscow RU-119017, Russia c 121 rue de la Réunion, F-75020 Paris, France article info abstract Article history: The complementary roles of granites and rocks of the granulite facies have long been a key issue in models of the Received 27 June 2019 evolution of the continental crust. “Dehydration melting”,orfluid-absent melting of a lower crust containing H2O Received in revised form 25 July 2019 only in the small amounts present in biotite and amphibole, has raised problems of excessively high tempera- Accepted 26 July 2019 tures and restricted amounts of granite production, factors seemingly incapable of explaining voluminous bodies Available online 29 July 2019 of granite like the Archean Closepet Granite of South India. The existence of incipient granulite-facies metamor- phism (charnockite formation) and closely associated migmatization (melting) in 2.5 Ga-old gneisses in a quarry Keywords: fl Charnockite exposure in southern India and elsewhere, with structural, chemical and mineral-inclusion evidence of uid ac- Granite tion, has encouraged a wetter approach, in consideration of aqueous fluids for rock melting which maintain suf- Saline fluids ficiently low H2O activity for granulite-facies metamorphism.
    [Show full text]
  • SOME PROBLEMS PERTAINING to Tile PENINSULAR GNEISSIC COMPLEX Just As in Human Affairs Where the So-Called 'Eternal Triangle'
    JOURNAL OF THE GEOLOGICAL SOCIETY OF INDIA Vol. 17, No. I, 1976, p. I (a 16 SOME PROBLEMS PERTAINING TO TIlE PENINSULAR GNEISSIC COMPLEX C. S. PICHAMUTHU V~~"'\~~'i'l\,G~~\~%\~'Il\~~d~\'j ~\ ~n~\'Il, v,'IlTl%'Il\t>1~ Abstract Since the terrns Peninsular gneiss and Dharwar schist have recently been used by some writers without reference to the original meaning ascribed to them by the geologists who first coined those terms, attention is drawn here to their exact scope and significat1ce. In Karnataka, 'Peninsular gneiss' comprised all granites and gneisses except those of Closepet, Chitaldr1Jg, Hosdurga, Arsikere, Banavar, and Saulanga ; and 'Dharwar schist' included all the crystalline schists (metavo!canics and metasediments) as opposed to the felsic gneisses. peninsular gneiss was considered to be intrusive into the Dharwars­ No early geologist in India was entirely of the opinion that the Dharwars were youvger than the gneisses. The Bababudan Syncline contains the oldest Dharwar sequence composed of mafic and ultramafic volcanics and intrusives (some of komatiitic affinity) intercalated with iron formations. Limestones are entirely absent. The actual base of the Dharwars has nowhere been definitely proved. Vertical shafts more than 3l<m deep in the Kolar Gold Fields have not touched the bottom. 'fhe fact that in some places the schists are seen' resting on gneiss' does not mean that t)ley constitute the lowest Dharwars. A general progressive metamorphism in the schist belts in southern Karnataka can be noticed frol11 north to south, culminating in high grade granulite facies rocks. There is no field evidence which lends support to the presumption that the chamockites are overthrust on the Dharwars.
    [Show full text]
  • Subsurface Topography of Supra Crustals of Dharwar Craton Through Inversion of Regional Bouguer Gravity
    Available online a t www.pelagiaresearchlibrary.com Pelagia Research Library Advances in Applied Science Research, 2016, 7(5): 54-89 ISSN: 0976-8610 CODEN (USA): AASRFC Subsurface topography of Supra crustals of Dharwar Craton through inversion of Regional Bouguer Gravity Bhagya K. and Ramadass G. Center of Exploration Geophysics, Osmania University, Hyderabad _____________________________________________________________________________________________ ABSTRACT Regional gravity data have been analyzed to estimate the supra crustal thickness in parts of Dharwar Craton (73°30' E to 78° 30' E and latitude 12° N to 17°N). The depositions of supra crustal four deep seated faults and several other lineaments were delineated from qualitative analysis of Bouguer gravity. The supracrustal (Charnokite, Younger granites, Closepet granite, Sargur belt, Chitradurga schist belt, Bababudan group , Deccan Basalt, Bhima sediments, and western part of Cuddapah Sediments) as well as deep crustal (Peninsular gneiss, Upper crustal and deeper crust layer ( up to Moho) structural configuration in the Dharwar craton were obtained via the inversion of modeling of eleven east-west traverses ( T1 to T 11) digitized from the Bouguer gravity contour map. The sub-surface configuration of each of these supra crustal layers were obtained by digitizing the corresponding crustal structure and presented as 3D contour map reveal structural complexity with plunging synclines, anticlines and refolded along E-W trending warps. The peninsular gneissic layer is very uneven in geometry varying in thickness from 6.9 to 11 km, upper crustal layer varies between 18.2 to 24.55 km and deep crustal layer 34 km to 40 km . Key words: Crustal configuration, supracrustal, anticlines, synclines, up warps, plunging _____________________________________________________________________________________________ INTRODUCTION Earlier geophysical studies in the Dharwar craton include gravity [67]; [19]; [21]; [28]; Magsat [30].
    [Show full text]
  • Tectonic Framework for Precambrian Sedimentary Basins in India
    1 1 The Archean and Proterozoic History of Peninsular India: Tectonic 2 Framework for Precambrian Sedimentary Basins in India 3 4 Joseph G. Meert1 and Manoj K. Pandit2 5 1Department of Geological Sciences, 241 Williamson Hall, University of Florida, Gainesville, FL 32611 USA 6 2Department of Geology, University of Rajasthan, Jaipur 302004, Rajasthan, India 7 2 8 Abstract 9 The Precambrian geologic history of peninsular India covers nearly 3.0 billion years of time. The Peninsula 10 is an assembly of five different cratonic nuclei known as the Aravall-Bundelkhand, Eastern Dharwar, Western 11 Dharwar, Bastar and Singhbhum cratons along with the Southern Granulite Province. Final amalgamation of these 12 elements occurred either by the end of the Archaean (2.5 Ga) or the end of the Paleoproterozoic (~1.6 Ga). Each of 13 these nuclei contains one or more sedimentary basins (or metasedimentary basins) of Proterozoic age. This paper 14 provides an overview of each of the cratons and a brief description of the Precambrian sedimentary basins in India 15 that form the focus of the remainder of this book. In our view, it appears that basin formation and subsequent clo- 16 sure can be grossly constrained to three separate intervals that are related to the assembly and disaggregation of the 17 supercontinents Columbia, Rodinia and Gondwana. The oldest Purana-I basins developed during the 2.5-1.6 Ga in- 18 terval, Purana-II basins formed during the 1.6-1.0 Ga interval and the Purana-III basins formed during the 19 Neoproterozoic-Cambrian interval. 20 21 Introduction 22 Peninsular India represents an amalgam of ancient cratonic nuclei that formed and 23 stabilized during Archaean to Paleoproterozoic (3.8-1.6 Ga).
    [Show full text]
  • Government of India Ministry of Mines Lok Sabha Unstarred Question No. 858 to Be Answered on 07.02.2019 Geological Survey Of
    GOVERNMENT OF INDIA MINISTRY OF MINES LOK SABHA UNSTARRED QUESTION NO. 858 TO BE ANSWERED ON 07.02.2019 GEOLOGICAL SURVEY OF INDIA 858. DR. SHASHI THAROOR: Will the Minister of MINES be pleased to state: (a) whether the Geological Survey of India (GSI) has a comprehensive repository of geological structures in the country; (b) if so, the details thereof; (c) if not, whether the Government proposes to create such a repository and if so, the details thereof; (d) whether GSI has a policy for geological conservation, to protect unusual rock types, landforms that preserve records of natural events of the past, significant fossil localities, stratigraphic sections, areas where significant advances in geology have been made, and deposits of particular minerals; and (e) if so, the details thereof and if not, whether the Government proposes to create such a policy and if so, the details thereof? ANSWER THE MINISTER OF STATE FOR MINES AND COAL (SHRI HARIBHAI PARTHIBHAI CHAUDHARY) (a) to (e): Geological Survey of India (GSI) has identified many sites of unique geological importance and exceptional geomorphic expression/ landscapes. It has designated 32 various such types of naturally preserved geological structures/ monuments as geo-heritage sites/ national geological monuments across the country for protection and maintenance. The details of these sites are as follows: S. Geological heritage site / S. Geological heritage site / No National geological monument No National geological monument ANDHRA PRADESH MAHARASHTRA 1. Volcanogenic bedded Barytes, 22. Lonar Lake, Buldana Dist. Mangampeta, Cuddapah District (Dist.). 2. Eparchaean Unconformity, Chittor Dist. CHATTISGARH 3. Natural Geological Arch, Tirumala Hills, 23.
    [Show full text]
  • Incipient Charnockites from Southern India: the Role of Brines
    Geoscience Frontiers xxx (xxxx) xxx HOSTED BY Contents lists available at ScienceDirect China University of Geosciences (Beijing) Geoscience Frontiers journal homepage: www.elsevier.com/locate/gsf Research Paper Incipient charnockites from southern India: The role of brines Jacques L.R. Touret a,*, Robert C. Newton b, Michel Cuney c a 121 Rue de la Réunion, F-75020, Paris, France b Department of Earth, Planetary and Space Sciences, UCLA, Los Angeles, CA, USA c Université de Lorraine, CNRS-CREGU, GeoRessources BP70239, F-54506, Vandoeuvre-les-Nancy Cedex, France article info abstract Article history: Southern India and Sri-Lanka are the places where “incipient charnockites”, i.e. the local transformation Received 13 December 2018 of amphibolite-facies gneisses into orthopyroxene-bearing, igneous looking charnockites, have been Received in revised form discovered in the early sixties. The fact that some incipient charnockites occur along a network of brittle 7 March 2019 fractures, together with CO remnants preserved in mineral inclusions, had called for the role of fluids Accepted 9 March 2019 2 during charnockite alteration. The present work presents new observations on fluid inclusions and Available online xxx Handling Editor: M. Santosh microtextures of incipient charnockites from type localities in southern India. In addition to CO2-rich fluid inclusions in quartz and feldspar, all of the occurrences have disrupted remnants of concentrated Keywords: aqueous alkali chloride solutions. CO2 inclusions are more abundant in paragneiss (Kerala) than in fi Incipient charnockite orthogneiss (Karnataka/Tamil Nadu). The nding of disrupted brine inclusions in the Kabbal charnockite High-grade crustal metamorphism is a key link between closely associated massive charnockites and Closepet Granite, both of which also CO2 share the brine remnants.
    [Show full text]
  • Precambrian Geology of India
    This content is prepared from various sources and has used the study material from various books, internet articles etc. The teacher doesn’t claim any right over the content, it’s originality and any copyright. It is given only to the students of PG course in Geology to study as a part of their curriculum. Precambrian Geology of India Generalized tectonic map of Indian subcontinent: Precambrian Cratons, Mobile Belts and Lineaments. AFB = Aravalli Fold Belt, DFB = Delhi Fold Belt, EGMB = Eastern Ghats Mobile Belt, SMB = Satpura Mobile Belt, NSL = Narmada-Son Lineament, CIS = Central Indian Suture and BPMP = Bhavani–Palghat Mobile Belt. Proterozoic Rifts and Basins include IB = Indravati Basin, ChB = Chhattisgarh Basin, GB = Godavari Basin; MR = Mahandi Rift; CuB = Cuddapah Basin, VB = Vindhyan Basin. CG = Closepet Granite (modified from Rao and Reddy, 2002). Each craton has undergone progressive stabilization of the block, suffered post-stabilization intrusive events like mafic dyke swarms and development of Proterozoic sedimentary basins within the cratons. Mafic dyke swarms are indicators of crustal extension and can represent supercontinent assembly and/or dispersal, subduction, large igneous province emplacement, and crust/mantle interaction. Typically a craton begins with a few hundred million years of accumulation of gneisses and greenstone belts and then becomes stable within a few tens of millions of years. Stabilization is demonstrated by the closure of whole-rock isotopic systems, intrusion of undeformed plutons, and deposition of platform sediments on the newly created basement. After formation, cratons move about the earth but are not subjected to pervasive compressional deformation. Dharwar Craton •The Dharwar Craton is split into Eastern and Western Cratons, with major differences in lithology and ages of rock units.
    [Show full text]
  • Geology of the Western Dharwar Craton
    IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) e-ISSN : 2278-1684, p-ISSN : 2320–334X PP 22-26 www.iosrjournals.org Geology of the Western Dharwar Craton Ms Poornima Bongale1, Mr Ambareesh Kshirsagar2 1(Department of Civil Engineering, Imperial College of Engineering and Research/ Savitribai Phule Pune University, India) 2(Department of Civil Engineering, Rajarshi Shahu College of Engineering/ Savitribai Phule Pune University, India) Abstract : The Peninsular Gneissic complex is one the most ancient stable part of the Peninsular shield. It forms the basement for the younger Dharwar Supergroup which unconformably overlies them. Rocks that make up the Supergroup are one of the oldest rocks of the earth. The PGC has been rejuvenated so many times that it now appears to be younger than the overlying craton. The Supergroup has been divided into the Eastern Dharwar craton and the Western Dharwar craton. This paper deals with interpretation of the geochemical and petrographical data gathered from the samples collected around Dharwad city area. Keywords – Archaeans, Dharwar craton, Geochemistry,Greenstones, Greywackes. I. Introduction Petrography and geochemistry of clastic metasedimentary rocks of the Archaean supracrustal belts have provided reliable clues regarding the nature of the upper continental crustal rocks, exposed for weathering, thereby providing information on physical conditions of exogenic processes, geodynamic settings and crustal evolution. In many instances, the provenance regions get destroyed but their record
    [Show full text]
  • Green Campus Initiatives
    ROCK GARDEN Nature always mesmerises human by its beauty, complexity and the mechanism it works. At our Dr.N.S.A.M. FGC we have piece of nature’s wonder erupted Rock Hill piece – A nature’s Rock gift . As per many geological survey studies and also Geographical Survey of India opined, Bangalore city is sitting on a large Rock eruption happened billions of years ago (2.5 to 3.4 billion years). Based on the tectonics, Indian subcontinent is mainly divided into Peninsular, Extra peninsular and Indo-Gangetic alluvium. Peninsular India is tectonically shield or stable area, consisting of cratons and sedimentary basins. Peninsular India is dominated by Archaean group of rocks. Peninsular Gneissic Complex forms the basement for all formation. Peninsular Gneiss is metamorphic rock. That is, it is rock which has been subjected to heat and pressure, causing profound physical andchemical changes. It is, of course, spread over the area surrounding our city, too. Peninsular Gneiss is a term coined to high light the older gneissic complex of the metamorphics found all over the Indian Peninsula. This term was first fashioned by W.F.Smeeth of the Mysore Geological Department in 1916 based on the first scientific study of this rock exposure. The Geological Survey of India identified one of the best exposures of this rock mass, protruding high above the ground as a hillock, dated 2.5 to 3.4 billion years, in the Bengaluru city in India at the famous Lalbagh gardens and declared it as a National Geological Monument to propagate the knowledge of the rock formation among the public, since Lalbagh is frequented by visitors from all over the world.
    [Show full text]
  • The Nature of the Basement in the Archaean Dharwar Craton of Southern India and the Age of the Peninsular Gneiss
    Proc. Indian Acad. Sci. (Earth Planet. Sci.), Vol. 102, No. 4, December 1993, pp. 547-565. © Printed in India. The nature of the basement in the Archaean Dharwar craton of southern India and the age of the Peninsular Gneiss K NAHA*, R SRINIVASAN 2, K GOPALAN 2, G V C PANTULU 2, M V SUBBA RAO 2, A B VREVSKY 3 and YE S BOGOMOLOV a 1Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721302, India 2National Geophysical Research Institute, Uppal Road, Hyderabad 500007, India 3Institute of Precambrian Geology and Geochronology, Makarova emb. 2, St. Petersberg 199034, Russia MS received 14 July 1993 Abstract. The Archaean Peninsular Gneiss of southern India is considered by a number of workers to be the basement upon which the Dharwar supracrnstai rocks were deposited. However, the Peninsular Gneiss in its present state is a composite gneiss formed by syn- kinematic migmatization during successive episodes of folding (DhFI, DhFI, and DhF2) that affected the Dharwar supracrustal rocks. An even earlier phase of migniatization and deformation (DhF,) is evident from relict fabrics in small enclaves of gneissic tonalites and amphibolites within the Peninsular Gneiss. We consider these enclaves to represent the original basement for the Dharwar supracrustal rocks. Tonalitic pebbles in conglomerates of the Dharwar Supergroup confirm the inferenoe that the supracrustal rocks were deposited on a gneissic basement. Whole rock Rb-Sr ages of gneisses showing only the DhF1 structures fall in the range of 310(O3200 Ma. Where the later deformation (DhF 2) has been associated with considerable recrystallization, the Rb-Sr ages are between 2500 Ma and 2700 Ma.
    [Show full text]
  • There Is a Need to Develop and Conserve
    e-Journal Earth Science India: www.earthscienceindia.info Popular Issue, July, 2008 "There is a need to develop and conserve them as museum of natural sculptures more vigorously by providing geotourism guide books, maps, multimedia kits and integrated geotourism packages in coordination with State Governments." Nature has sculptured many eye-catching features by geological processes. India has been bestowed with a large number of such magnificent geological sites spread throughout its length and breadth and spanning over the entire length of the geological time scale. These sites attract not only the earth scientists but also the common man. These natural exquisite land sculptures have become nature lover's delight and are gaining importance as tourist spots and promoting geotourism. Promotion of these geosites, several of which have been declared as National Geological Monuments in India by Geological Survey of India (GSI),have potential to attract tourists. There is a need to develop and conserve them as museum of natural sculptures more vigorously by providing geotourism guide books, maps,multimedia kits and integrated geotourism packages in coordination with State Governments. In addition to these monuments, there are several other important and picturesque geological features and sites which need preservation and protection from human developmental activities. Several state government departments and GSI have been taking a leading role in preserving and protecting such sites of rich scientific values by declaring them as geological monuments and preserving them within its resources. GSI, during its 150th anniversary celebrations in 2001 has published a Special Volume on National Geological Monuments which gives detail account of locations, geology, palaeontology and stratigraphy of all the monuments supported by pictorial illustrations.
    [Show full text]