Petrography study


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Petrography study

  1. 1. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 115 Petrographic Study around Vallanadu Area, Tuticorin District, Tamilnadu, India a Manimaran D, a Besheliya J, a Manimaran G a Department of Geology, V.O.Chidambaram College, Thoothukudi-628008, Tamilnadu, India Vallanadu area of southern Granulite terrain forms an Achankovil shear zone. Charnockites, khondalites, cordierite gneisses, calc-silicate rocks and grey and pink granite are the main lithotypes. The study highlights petrography, modal based geochemistry, shears and joints of the area. Two sets of conjugate shear system are observed. Ductile natured NW-SE dextral shear conjugating with NE-SW sinistral subordinate shear and brittle-ductile natured NW-SE to WNW-ESE achankovilsinstral shear conjugating with N-S dextral subordinate shear are identified. Granites of the area are of syntectonic origin. Vallanadu area of Achankovil shear zone suffered by initial ductile deformation followed by brittle-ductile deformation during the uplift and collision tectonics of Neoproterozoic to Cambrian time. KEYWORDS: Vallanadu, Petrography, Joints, Modal analysis, Achankovil shear zone, Southern Granulite. INTRODUCTION The Vallanadu area is a high grade metamorphic terrain of almandine amphibolite to granulite facies and forms a part of Achankovil shear zone. The area is essentially comprised of different lithotypes i.e., quartzites, calc-silicate rocks, khondalites, composite gneisses, cordierite gneiesses, charnockites, greygranites and pink granites and veins of pyroxene granulites and amphibolites (Manimaran 2012; Manimaran and Manimaran 2013). Achankovil shear zone (ASZ) is well studied in Kerala region while in Tamilnadu region detailed study are yet to going on (Santosh, 1984, Srikandappa etal 1985; Chacko etal 1987; Santosh and Drury 1988; Ramakrishnan, 1993; Manimaran and Roy Chacko, 1996; Rajesh etal 2001; Ravindrakumar and Subash Sugumaran, 2003; Cenki and Kriegsman, 2005; Guru Rajesh and Chetty, 2006; Manimaran 2009; Manimaran and Manimaran 2013). Recently collisional suture natured tectonics status was established for ASZ through geophysical deep electrical studies by Dhanujaya Naidu etal 2011; and from seismic reflectivity studies on southern granulite terrain by Rajendra Prasad etal. 2007. The texture and mineral Content of the rocks of the area are well studied to establish Petrography and petrogenesis of the vallanadu area. Thin section and megascopic studies of the rocks and Modal content of the rocks are studied. The modal analysis of six important rocks of the study area have been studied and their chemical constituents (average) of the rocks were derived from modal analysis and C.I.P.W. norms and Niggli values were calculated, and variation diagrams and chemical discriminate plots were constructed so as to establish the petrochemical characteristics and relationships of the various lithounits of the study area (Fig.1) were delineated. Abstract
  2. 2. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 116 LITHOLOGY AND FIELD RELATIONSHIPS ROCKS OF KERALA KHONDALITE BELT Khondalites of vallanadu area of Kerala Khondalite Belt (KKB) are represented by pelitic, Semipelitic, psammitic and calcareous members. The distribution of various lithotypes of the area is shown in Fig.1a. QUARTZITES The psammitic members of KKB are represented by the quartzites and are mostly granular and massive in appearance. They occurs bands and veins in both gneisses and charnockites of the area. South of Vallanadu isoclinally folded quartzite occur within the host of garnetiferous biotite sillmanite gneiss. Intercalation of small bands and veins of calc-granulites are noticed admist quartzites. Quartzite exposures are occurring at Vallanadu, east of Seydunganallur, south of Rajagopalapuram and Rajavallipuram. The general trend of the quartzites is NNW-SSE to NW-SE with variable dips. A quartzite band at north of Vallanadu occur at the junction among granites, charnockites, cordierite gneiss and garnetiferous biotite sillimanite gneiss. CALC-SILICATE ROCKS (CALC-SILICATES) The calcareous members are represented by calc-granulites, calc-gneisses, limestones and dolomitic limestones. Linear ellipsoidal band of calc-silicates occur at palamadai, east of Rajavallipuram and Maruvathalai, east of sivalaperi. Limestone is essentially composed of calcite with minor minerals of sphene, spinel and graphite. The calc-granulites and calc-gneisses are manily represented by calcite-wollastonite, diopside and quartz –wolanstonite – calcite – grossularite and Clinopyroxenes mineral assemblages. At places scapolite and chondrodite are also noticed in the field. GARNETIFEROUS BIOTITE SILLIMANITE GNEISSES AND GARNET BIOTITE GNEISSES The pelitic and semipelitic members of KKB are represented by graphite bearing garnetiferous biotite sillimanite gneisses and Garnet biotite gneisses respectively. The foliations are entirely due to the presence of alternating layers of quartz and feldspars rich, biotite rich, sillimanite rich zones. Biotite rich layers is from 1cm to 10 cm; Quartzofeld spathic rich layer is from 1cm to 50cm; sillimanite layer 2cm to 16cm thick are noted in the field. Imperceptible gradation between garnetiferous biotite sillimanite gneiss and garnet biotite gneiss and at places biotite-poor leptinitic variety (acid khondalite), Garnet sillimanite gneiss (white and yellow) is also occur. At places, bands veins and patches of incipient charnockites are noticed in garnet biotite genisses. CORDIERITE GNEISSES Cordierite gneisses are exposed at paraikulam, vasavappapuram, Rajagopalapuram, Papayankulam, Ganagaigondan (Railway station), Maruvathalai and Anavaradanallur.The bluish violet, pearly sheen cordierite formed as idioblastic clots and crystals. Cordierite formed as rich layers and biotite is associated with cordierite rich layer 1cm to 6cm thick cordierite rich layers are foliated alternately with quartzofeldspathic layer and depletion of garnet content in cordierite rich layer is common. Cordierite gneisses developed in the host of garnetiferous gneisses and charnockites are observed. Band and veins of basic granulites and grey and pink granites are also observed within the country rocks of cordierite gneisses. Cordierite gneisses are showing sinistral shearing plans along NW-SE direction, which are parallel to Achankovil shear zone.
  3. 3. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 117 CHARNOCKITES The massive charnockite exposures are exposed at Timmarajapuram and KTC Nagar, southeast of sivalaperi; Gangaigondan, Maruvathalai, singattakurichi and NE of Vallanadu area. It dark green glistening rock having hypersthene as a essential mineral occuras dark green porphyroblastic crystals. Bands, veins and lenses of basic granulites, grey and pink granites are common in charnockites. At places near pegmatite intrusions, the breaking of the charnockite leads to rertograde gneisses evolved from charrockites are also encountered in the field. Relic patches of garnet biotite gneisses in charnockite, at contact abrupt warpping of the gneissic foliation at the boundary of charnockite suggest that the charnockites of the area is subsequent to khondalites and the pelitic genises of the area were transformed into charnockites. BASIC GRANULITES The basic granulites are essentially consists of orthopyroxenes (hypersthene) and clinopyroxenes (Diopside and Augite), hence the name two-pyroxene granulites. They occur and associated with all types of rocks of the area and usually as small veins and lenses in the country rocks of khondalites, quartzites, cordierite gneisses and charnockites. GRANITES The Granites and pegmatites are of in two colours-gray and pink. A large grey granite band of 1km breadth and 10km length intruded the major isoclinal fold of vallanadu is traced in the field. The other bands of granite are occur at west of Vallanadu and east of Sivalaperi at Maruvathalai. The composite gneisses are having veins and bands of grey as well as pink granites. Since granites intruded all lithotypes it is the youngest rocks of the area. COMPOSITE GNEISSES It is a special kind of rock yielding black soil of the area due to its high Mg and Ca contents. It is mainly represented by graphite bearing garnetiferous biotite gneisses showing multi intercalations of veins and bands of calc-silicate rocks, incipient charnockites, basic granulites, granites and pegmatites. calc-silicate rocks and basic granulites are also play vital role in the genesis of black (cotton) soil due to their Ca and Mg bearing minerals. At places, composite gneisses were intruded by lit-par-lit Injection of grey granites and grey pegmatites and bands of charnockites and basic granulites were retrograded into regressive gnesisses. The overall multi kind network lithology status of the rock assigns the name composite gneisses. PETROGRAPHY AND MICROTECTONIC FEATURES QUARTZITES Quartzite shows granular texture and Varieties include white, Milky, Rosy and Smoky. In general quartzites are feldspathic, ferruginous (haematite and Ilmenite) bearing quartzite running like a linear band. At vallanadu, quartzites occur in the core of a isoclinal plunging major fold. The modal content of the quartzite is as follows: Quartz 93.2; graphite 2.5; Biotite 1; Ilmenite 1; apatite 0.25 and plagioclase 2. Microphotograph (Fig.4.1) shows fluid inclusions bearings (H2O + CO2) quartz grains of a quartzite. CALC-GRANULITE They are dark green coloured with white sacchoroidal grains of calcite and quartz. The following mineral assemblages are traced from thin sections.
  4. 4. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 118 i) Calcite – Wollastonite – quartz – diopside and ii) Calcite – Wollastonite – scapolite – diopside. Graphite, ilmenite and sphene are occurring as minor minerals. Scapolite occurs as prismatic crystals with cleavages intersecting at 90o and 45o and it show second order interference color and straight extinction. GARNET BIOTITE GNEISSES The gneissic textured garnet biotite gneisses show mineral assemblage of plagioclase (An 25 – 35 oligoclase and andesine composition) + Orthoclase +quartz + garnet + biotite + Graphite ± sillimanite ± cordierite. The biotite flakes define the foliation and planar fabrics of the rocks. Garnet occurs as irregular and idioblastic grains. Biotite occurs as irregular plates and laths and is strongly pleochroic from dark brown to light brown. At places, they are perthitic in nature. The average modal content of garnet biotite gneiss is as follows quartz 34.18; orthoclase 5.29; plagioclase 19.01; microcline 3.85; garnet 12.03; biotite 12.76; perthite 7.22; Magnetite 3.61 and apatite 2.05. CORDIERITE GNEISSES The well foliated cordierite gneisses shows alternating foliations of Cordierite rich, biotite rich and quartzofeldspathic are common. Cordierite rich zones are generally depleted in garnet. The modal content of Cordierite gneiss of Maruvathalai is Quartz 7; Orthoclase 5; Plagioclase (An 25) 5.25; Perthite 1; biotite 4; Cordierite 29; Magnetite 14; Apatite 14; Ilmenite 2 and Hypersthene 30. The photomicrograph (fig.2) shows large porphyroblastic, twinned Cordierite associated with minerals of biotite, hypersthene, orthoclase, quartz, sillimanite, plagioclase and ilmenite crystals. The above equilibric minerals assemblages suggest the following equation. Biotite + sillimanite +Quartz = Cordierite + Spinal + Orthoclase + ilmenite The above assemblage is noticed in cordierite gneisses associated with garnet biotite sillimanite gneisses. Hypersthene showing ‘S’ pattern alignment and in contact with quartz and cordierite and garnet inclusions suggest the following decompression reaction. Garnet + Quartz = Hypersthene and Cordierite The above assemblages are traced in the cordierite gneisses associated with Charnockite and garnet biotite gneisses. Cordierite gneiss at Ariyakulam under thin section (fig.3) shows sinistrally deformed and displaced biotite flakes. Near shear the quartz grains are also seen. The above features suggest the genesis of Cordierite gneisses are related to the Sinistral shearing of Achankovil shear event. The cordierite gneiss at Paraikulam shows (fig.4) relic of garnet in neomineralized biotite. Two generation of biotite is common. A sinistrally deformed cordierite gneiss at Ariyakulam depicts (fig.5) sinistrally deformed biotite plate. The adjoining sheared garnet show retrogression and garnet is converted into green colored chlorites along the shear planes. The material migrations of quartz along the shear planes are also seen. Fig.6 reveals mineralized and shear localized quartz micro rods along the shear planes. A sinistrally sheared biotite is on the right side also visible (location: Ariyakulam). A major cordierite grain at Ariyakulam shows (fig.7) stretched (interference color of dark grey) orthoclase feldspar and the pattern of stretching suggest a dextral shearing and the photo micrograph (fig.8) also shows a stretched orthoclase displaying ‘Z’ vergence also
  5. 5. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 119 pointed out a micro dextral shearing of cordierite gneiss suggest that the area was also suffered through conjugate shearing. CHARNOCKITE Charnockite shows both granulitic as well as gnessic texture. Massive and incipient Charnockites are also common in the area. Incipient Charnockite are in the host of Cordierite biotite gneisses, Cordierite gneisses and in composite gneisses. Whereas the massive charnockites are exposed at KTC Nagar, Timmarajapuram, Sivalaperi and north of vallanadu. The modal content of massive charnockite of KTC nagar , Quartz 20.39; Orthoclase 4.65; Plagioclase 4.47; perthite 65.18; apatite 2.25; ilmenite 0.17; Hypersthene 2.50 and zircon 0.39. The modal content of incipient charnockite of pallamadai is as follows: Quartz 13.48; orthoclase 17.13; plagioclase (An 50); Biotite 16.04; garnet 19.10; Magnetite 3.65; apatite 1.68; Hypersthene 7.58 and chlorite 1.12. At places, in the field observation the incipient charnockite shows discernible megascopic garnet and quartz yielding corditerite and hypersthene equilibric assemblages are also noticed from gneisses with intimately associated incipient charnockite quarries(Paraikulam quarry). Garnet + Quartz = Cordierite + hypersthene The photomicrograph of Akkanaikkanpatti(fig.9 ) shows a gnessic charnockite showing stretched quartz, hypersthene and biotite and feldspars. The retrograded and non- retrograded original hypersthene of charnockite is discernible. From the field it is known that the location is intruded by pink granite. COMPOSITE GNEISS The composite gneiss essentially composed of Khondalites intruded by many veins and bands of grey pegmatites and pink pegmatites, sills and dykes (now bands of pyroxene granulites) of basic sills. A composite gneiss (fig.10) showing garnet, biotite, quartz, feldspar and apatite. The altered composite gneiss (fig.11) at Keelapuvani shows Fluorite, biotite and kaolinized feldspars. The composite gneiss at Lakshmipuram (fig.12) shows sinistrally sheared biotite and quartz ribbons suggest the existence of Achankovil shear zone upto Lakshmipuram. GRANITES Megascopically Granites of Vallanadu are classified into two types, namely grey granites and pink granites. The Vallanadu grey granite forms as an axial plane intrusion of the major Vallanadu quartzite isoclinal Fold (Fig.1). It is also seen at east of Vasavappapuram and at Maruvathalai. Mode of occurrence of Granites is of two types 1. Linear band and 2. Foliation guided granite veins. Intrusions of pink granite veins are observed in charnockites, all gneisses and also grey granites. The grey granite band of Vallanadu shows the modal contents – quartz 49.5; orthoclase 23.89, plagioclase 15.27, Biotite 6.18, Magnetite 1.28, Apatite 1.66, chlorite 1.07, zircon 0.37 and sphene 0.78. A grey granite vein associated with incipient charnockites in cordierite gneisses shows the following mineral assemblages – quartz 56.59, orthoclase 7.96, plagioclase 2.74, perthtie 28.57, apatite 0.27, chlorite 0.58 and Fluorite 3.29. The pink granite of Akkanaiyakkanpatti shows the modal content of quartz 38.81, orthoclase 23.43, plagioclase 8.46, perthite 17.39, zircon 0.72, apatite 3.88, chlorite 1.30, fluorite 3.95, magnetite 0.99, Ilmenite 0.27, biotite 0.27 and sphene 0.61. Fig.13 the pink
  6. 6. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 120 granite shows oriented apatite grains in quartz and feldspar. The pink granite clearly shows (fig.14) the mineralization of newly forming quartz grain along the mineral borders of perthite, quartz and feldspar suggest insitu melting due to shearing of mineral grains. The pink granite (fig.15) shows fluorite, magnetite, apatite and quartz. Fluorite partly isotropic and partly optically showing anomalous interference colors. Crystals of fluorite are ubiquitous in Akkanaiyakkanpatti pink granites exposures. The perthite of the pink granite shows sheared rods of perthite and left stepping of newly formed lense shaped sodic plagioclase from the sheared rods of sodic plagioclase suggest that the rock experienced a sinistral shearing (fig.16). KANKAR The composite gneisses of Puliyampatti reveal conjugate microshear fractures in quartz and feldspar (fig.17) and they were converted into kankar formations. The fig.18 shows concretionary kankar formation around a pore space developed in composite gneiss due to meteoritic water perculations. Also the fig.19 exhibits a filamentous kankar formed along the gneissic foliations of composite gneisses country rock. Black soil invariably originated from composite gneisses of the area. At Kilpuvani the composite gneiss shows (fig.20) the development of calcrite formation due to alteration of plagioclase feldspar. Kaolinised orthoclase and chloritised biotite are also visible. The lithotypes of the study area are well displaying microshear features viz. shear fractures, sinistral and dextral shearing and conjugate shearing. The dominantsinistral shear pattern suggests that the area belongs to part of Achankovil shear zone and boundary of the shear zone should be located beyond North to the present study area. PETROCHEMISTRY MINERALS The modal percentage of various minerals of the selected rocks types around vallanadu are presented in the table 1. Examination of the table reveals that the most of the rocks of the area have modal quartz more than 10% (acid type). Cordierite gneisses were formed from shearing and decompression reactions of khondalitic gneisses and charnockites. There is a general reduction in the modal abundance of biotite in massif charnockite than the associated cordierite gneisses while in the incipient charnockites modes of biotite are almost higher in the particular sample due to intrusion of grey granites and retrogression of incipient charnockites. The depletion of garnet in Cordierite gneisses and Charnockites are pointing out decompression and shear related origin from the earlier Khondalitic gneisses. The modal quartz of granites are varies from 38 to 16% suggest they are derived from salic enriched source. GEOCHEMISTRY Mineral Modal based major oxides of the selected six rocks of the vallanadu area are tabulated in the tables (table 1-8). The estimated Niggli values are given in table 9. The variation diagram plotted for sio2 versus oxides figures 21, 22 and 23 shows weak linear relationship for the rocks of the Vallanadu area suggest they are mostly derived from a Para type-sedimentary provenance, suggest that they are Metasedimentary with some igneous component. The plots (Fig.24) versus Na2O K2O the rock types of Vallanadu area fall in Granite-Adamellite fields Where as the Cao versus K2O plot (fig.25) fall in the field of Tonalite- Granite field suggest the para-provenance source for these rocks were highly silicic source i.e. proterozoic in age. The K2O-Na2O-Cao plots (fig.26) fall in the fields of
  7. 7. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 121 Granite to Tonalite also pointing the same sialic source for the lithotypes. The Niggli variation diagram (Fig.27) constructed for the major oxides versus SiO2 suggest pacific suite for these rocks. The SiO2 versus Na2O+K2O (Fig.28) fall in the field of calcic. The calcic and pacific suite nature of the rocks reflects that the sediments were partially produced from Archaean-terrain also i.e. North of Palaght-Cauvery shear zone (or) Archaean terrain of SriLanka and Madagascar during the late proterozoic time which were formed as contiguous land during the formation of Gondwana Land. TECTONIC STUDIES FOLIATION The gneisses of khondalites are usually well foliated and their foliation is essentially parallel to the bedding. The foliation planes are two to three millimeter apart in the fine grained types and in the layers of garnet rich and cordierite rich zones it is 1cm to 1m apart. Abrupt warpping of gneissic foliation at the sharp contact of charnockite and also the continuity of same gneissic pattern (foliation) in charnockite of diffuse contact zones are encounter in the field. At places, grey granites and pink granites show faint foliation due to the orientation of tiny crystals of biotite. The general strike of foliation displayed by the rocks of the area is mostly from NW to SE and the amount of dip varies from 15° to 85° towards South West. At hinges of khondalite folds show foliation striking either N-S with easterly dip or E-W with northerly dip. LINEATION The observed linear elements are usually the mineral lineations and axes of the megascopic folds. In the gneissic of Khondalites, spangles of biotite, needles of sillimanite and in charnockites, the oriented laths of feldspars and hypersthenes are developed as mineral lineations. The mineral lineation of sub-horizontal plunging and vertical lineations are also observed in the field. Based on the pattern of fold axes, the study area is divided into four different structural domains for tectonic analysis (Fig.29). FOLD PATTERNS The well-banded gneissic pattern of the area display both major and megascopic folds and crenulations. Intra-folial isoclinals folds of gneissic bonding are common, although their hinges do not define a simple systematic orientation and probably reflect near plastic deformation. The folded quartzite veins are of tight and open types and the strike of the axial planes of the fold varies from N-S to NE-SW. The quartzite hillock of Vallanadu shows a northwesterly moderate plunging, isoclinals overturned anticline fold (Fig.1). The area is a part of Achankovil sinistral shear zones. Apart from NW-SE sinisterly shears the gneisses of the area exhibits conjugate shear bands systems of an earlier NW-SE dextral conjugating with NE-SW sinistral followed by overprinting of NW-SE sinisterly conjugating with N-S dextral shears. JOINTS The area is mainly traversed by strike joints running parallel to NW-SE and dipping steeply towards SW and are well developed in all litho units expect in granites. Steep N-S joints dipping east and NE-SW joints dipping NW are the other master joints observed in the field. For tectonic analysis the study area is divided into four blocks based on the mineral lineation and fold axes observed i.e. Block I Vallanadu, Block II RajaGopalapuram, blockIII Rajavallipuram and block IV Akkanayakkanpati. For each block the observed joint readings like strike and pole to the attitude of the joints are plotted in the equal area
  8. 8. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 122 contour plots and rose diagrams as Fig.30 a, b; Fig.31 a, b; Fig. 32 a, b and Fig.33 a, b respectively. The above plots reveal in all blocks joints are radiating almost in all direction and are dipping steep to moderate nature and six sets of joints are delineated from the area and are given in order of prominence. • NW-WNW to SE-ENE dipping SW with steep to moderate dips. • NW-WNW to SE-ENE dipping steep NE. • NE-SW dipping moderate to steep NW. • NE-SW dipping SE. • N-S to NNW-SSE group dips easterly. • E-W to ENE-WSW group dips steeply north. Apart from the above master joint systems minor joints and gush joints of different orientations are observed at places, from various litho units of different blocks. The megascopic interpretation of Achankovil shear zone in satellite imagery displays en-echelon pattern of lineament with right overstepping arrangement, which can be interpreted as an evidence of the latest Sinistral transpersonal deformation [Guru Rajesh and Chetty,2006). Manimaran, (2009) identified three-dimensional finite stain pattern from gneissic rocks of Tenkasi-Ambassamudram region and suggest Transpressive nature of Achankovil shear zone during the late Neoproterozoic to Cambrian time. CONCLUSION Based on the field and petrography evidence delineated from Vallanadu area rock types the geological history is established. As a part of Kerala Khondanlite Belt, the Vallanadu region commences with the depositions of varied sediments of regional metamorphism due to the Lit-par –Lit emplacement of granite material derived from sialic crustal source which is now represented by Khondalitic group of rocks. Subsequently, the basic sills were intruded the knondalitic rocks which are now represented by basic granulites seen in all litho types of the area. During Achankoil sinistral shearing CO2 rich fluids were migrated from deep crustal source and syntectonic cordierite gneisses, incipient charnockites were formed. Last phase of syntectonic event of granite intrusions into the earlier country rocks and regressive Changes were brought about in the earlier rocks. Joints/fractures of the area were originated from shears and extension tectonic origin. Tectonically the Vallanadu region was experienced a series of sub-horizontal compression of N-S and NE-SW, directions during its earlier ductile regime and the area was subjected to a later ENE-WSWhorizontal compression during the event of uplift and brittle deformation. Acknowledgement The authors are thankful to Shri.A.P.C.V.Chockalingam, Secretary, Dr.C.Veerabahu, Principal and II M.Sc. Geology students (2009-2010), V.O.Chidambaram College, Tuticorin. REFERENCES Cenki, B and Kriegsman, L.M (2005) Tectonics of the Neoproterozoic Southern Granulite Terrain, South India. Precambrian Res. V.138, p 37-56. Chacko, T. Ravindrakumar, G.R and Newton, R.C (1987) Metamorphic P.T conditions of the Kerala (South India) Khondalite belt, a granulite facies Supra crustal terrane Jour, Geol V.95, pp. 343-358.
  9. 9. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 123 Dhanunjaya Naidu, G., Manoj, C., Patro, P.K., Sreejesh V. Sreedhar and Harinarayana, T. (2011) Deep electrical signatures across the Achankovil Shear Zone, Southern Granulite Terrain inferred from Magneto tellurics. Gondwana Res. V.20, p.405-426. Guru Rajesh, K. and Chetty, T.R.K. (2006) Structure and tectonics of the Achankovil Shear Zone, Southern India, Gondwana research, v.10, pp 86-98. Manimaran, D (2012) Groundwater Geochmistry Study Using GIS in and Around Vallanadu Hills, Tamilnadu, India , Research journal recent sciences V.1(7), p 52- 58. Manimaran, D and Manimaran, G (2013) Arsenic contamination of groundwater in Vallanadu region of Ttuticorin district, Tamilnadu, India, Online international interdisciplinary research journal, v.III, p230-242. Manimaran, G. (2009) Three-dimensional finite Strain Pattern from Achankovil Transpression Zone, South India. Outreach v.2 pp. 70-75. Manimaran, G. and Roy Chacko, P.T. (1996). Shear lineaments and tectonic setting of Massive and incipient charnockites of Tambraparni shear zone southern India. In: Ram Mohan, V. (Ed). International symposium on charnockite and graulite facies rocks, Aug. 1996. Abstract, Univ. of Madras, Madras, India, pp.12- 13. Rajendra Prasad, B., Kesava Rao., Mall, D.M., Koteswara Rao, P., Raju, S., Reddy, M.S., Rao, G.P.S., Sridhar, V. Prasad, A.S.S.R.S., (2007) Tectonic implication of seismic reflectivity pattern observed over the Precambrian southern Granulite Terrain, India. Precambrian Res. V.153, p.86-98. Rajesh, V.J., Arima, M. and Santosh, M., 2001. Geology of the Achankovil Shear zone, southern India Gondwana Research 4, 744-745. Ramakrishnan, M. (1993). Tectonic evolution of the granulite terrain of Southern India. In: Radhakrishna, P.B. (Ed.), Continental crust of South India, Jou, Geol. Soc. India Memoir No.25, pp.35-44. Ravindrakumar.G.R. and Subbash sugumaran(2003). Petrology and Geochemistry of gneiss, charnockite and charno-enderbite of palghat Region, southern India. In: Ramakrishnan,M.(Ed.), Teckoincs of southern Granulite Terrain, Memoir 50. Geol.Soc. of India pp. 409-434. Santosh, M. and Drury, S.A. (1988). Alkali granites with Pan-African affinities from Kerala, South India. Jou. Geol. V.96. pp.616-626. Santosh, M. (1984) Fluid inclusions petrography of Charnockites form the granulite facies terrain of Kerala, South India. N. Jb. Mineral, Mh., H-8, 337-348. Srikantappa, C., Raith, M. and Spiering, B. (1985). Progressive charnockitisation of leptynite-Khondalite suite in Southern Kerala, India. Evidence for formation of Charnockite through decrease in the fluid pressure. Jr. Geol, Soc. India. V.96. pp.1-10.
  10. 10. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 124 Table 1: Mineral Modal Percentage of Various rocks around Vallanadu TABLE 2: PINK GRANITE – MODAL ANALYSIS Minerals Volume Specific Gravity Weight Weight Percentage Approximate Weight Quartz 38.81 2.65 102.28 37.99 38 Orthoclase 23.43 2.55 59.74 22.19 22 Plagioclase 8.46 2.65 22.41 8.32 8 Perthite 17.39 2.56 44.51 16.53 17 Zircon 0.72 4.6 3.31 1.22 1 Apatite 3.88 3.20 12.41 4.61 5 Chlorite 1.30 2.6 3.38 1.25 1 Fluoride 3.95 3.0 11.85 4.40 4 Magnetite 0.99 5.20 5.14 1.90 2 Ilmenite 0.27 4.5 1.21 0.45 1 Biotite 0.27 3.10 0.83 0.31 0 Sphene 0.61 3.45 2.10 0.78 1 269.17 99.95 100 Minerals Pink granite Cordierite gneiss Charnockite Cordierite gneiss Composite gneiss Garnetiferous Biotite gneiss Calcite - - - - - 47.84 Quartz 38.81 30.35 56.85 18.41 33.33 10.79 Orthoclase 23.43 17.24 9.22 12.44 34.35 9.72 Plagioclase 8.46 17.48 18.94 10.64 18.26 9.04 Perthite 17.39 - - - 5.71 - Zircon 0.72 - 0.29 - 1.45 - Apatite 3.88 1.09 2.97 2.304 3.48 1.58 Chlorite 1.30 0.30 - - - - Fluoride 3.95 - - - - - Magnetite 0.99 0.04 2.68 - 0.24 2.46 Ilmenite 0.27 - 0.83 1.72 2.55 - Biotite 0.27 8.49 0.07 13.98 0.26 3.49 Sphene 0.61 - - - - - Garnet - 4.32 - 15.22 - - Sillimanite - 0.12 - 1.21 - - Cordierite - 20.63 - 25.51 - - Monazite - - 0.08 - - - Hypersthene - - 8.22 - - - Albite - - - - 0.31 - Enstaite - - - - - 1.15 Limestone - - - - - 0.86 Kaolin - - - - - 13.05 Total 100 100 100 100 100 100
  11. 11. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 125 TABLE 3: CORDIERITE GNEISS – MODAL ANALYSIS Mineral Volume % Specific gravity Weight Weight % Approximate Weight % Quartz 30.35 2.65 80.42 29.15 29 Orthoclase 17.24 2.55 43.96 15.93 16 Plagioclase 17.48 2.65 46.32 16.79 17 Cordierite 20.63 2.65 54.66 19.81 20 Garnet 4.32 4.30 18.57 6.73 7 Biotite 8.49 3.10 26.32 9.54 10 Apatite 1.09 3.20 3.48 1.26 1 Chlorite 0.30 2.60 0.78 0.28 0 Sillimanite 0.12 3.23 0.38 0.13 0 Magnetite 0.04 5.20 0.20 0.07 0 275.87 99.69 100 TABLE 4: CHARNOCKITE - MAJOR ANALYSIS Minerals Volume % Specific Gravity Weight Weight % Approximate Weight % Quartz 56.85 2.65 150.65 53.22 53 Orthoclase 9.22 2.55 23.51 8.31 8 Plagioclase 18.94 2.65 50.19 17.73 18 Hypersthene 8.22 3.6 29.59 10.45 11 IImenite 0.83 4.5 3.73 1.32 1 Magnetite 2.68 5.20 13.93 4.92 5 Apatite 2.97 3.20 9.50 3.36 3 Monozite 0.08 5.4 0.43 0.15 0 Biotite 0.07 3.10 0.22 0.06 0 Zircon 0.29 4.6 1.33 0.47 1 283.08 99.99 100 TABLE 5: CORDIERIDE GNEISS - MODAL ANALYSIS Minerals Volume Specific Gravity Weight Weight % Approximate Weight % Quartz 18.41 2.65 48.79 16.09 16 Orthoclase 12.44 2.55 31.72 10.46 11 Plagioclase 10.64 2.56 27.24 8.98 9 Garnet 15.22 4.30 65.45 21.58 22 Apatite 2.30 3.20 7.37 2.43 2 Biotite 13.98 3.10 43.34 14.30 14 Cordieride 25.51 2.65 67.60 22.30 22 Sillmanite 1.21 3.23 3.91 1.29 1 Ilmenite 1.72 4.5 7.74 2.55 3 303.16 99.98 100
  12. 12. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 126 TABLE 6: COMPOSITE GNEISS – MODAL ANALYSIS Minerals Volume % Specific Gravity Weight Weight % Approximate Weight % Quartz 33.33 2.65 88.32 32.58 33 Orthoclase 34.35 2.55 87.59 32.32 32 Plagioclase 18.26 2.65 48.38 17.85 18 Apatite 3.48 3.20 11.13 4.11 4 Magnetite 0.24 5.20 1.24 0.45 1 Perthite 5.71 2.56 14.61 5.39 5 Ilmenite 2.55 4.5 11.47 4.23 4 Biotite 0.26 3.10 0.81 0.29 0 Albite 0.31 2.63 0.802 0.29 0 Zircon 1.45 4.6 6.67 2.46 3 271.02 99.97 100 TABLE 7: GARNET BIOTITE GNEISS – MAJOR ANALYSIS Minerals Volume % Specific Gravity Weight Weight % Approximate Weight % Quartz 10.79 2.65 28.59 10.38 10 Orthoclase 9.72 2.55 24.79 9.00 9 Plagioclase 9.04 2.65 23.96 8.70 9 Biotite 3.49 3.10 10.82 3.93 4 Calcite 47.84 2.71 129.65 47.07 47 Magnetite 2.46 5.20 12.79 4.64 5 Apatite 1.58 3.20 5.06 1.84 2 Enstatite 1.15 3.21 3.69 1.34 1 Limestone 0.86 2.32 1.99 0.72 1 Kaolin 13.05 2.61 34.06 12.37 12 275.4 99.94 100 TABLE 8: Major constituents of various rocks of Vallandadu area Oxide s Pink granit e Cordierit e gneiss Charnockit e CORDIERIT E GNEISS COMPOSIT E GNEISS garnitiferro us biotite gneiss SiO2 73.84 70.88 76.78 59.04 75.02 24.64 Al2O3 6.45 11.61 4.38 13.12 0.8 15.4 Fe2O3 1.0 - 2.5 - 0.5 2.5 FeO 1.5 2.62 5.75 7.28 2.5 3.08 MgO 0.4 5.91 2.75 9.18 - 0.79 CaO 7.08 3.48 4.5 4.52 5.25 26.63 Na2O 1.56 1.06 1.13 0.56 1.44 0.56 K2O 3.81 2.71 1.0 2.38 4.31 1.42 P2O5 1.25 0.25 0.75 0.5 1.0 0.5 F2 2.0 - - - - - H2O 0.32 1.42 - 2.0 - 0.58 CO2 - - - - - 24
  13. 13. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 127 TiO2 0.83 - 0.5 1.5 2.0 - TABLE 9: NIGGLI VALUES FOR VARIOUS ROCK TYPES OXIDES Si al fm alk C Pink granite 413.09 21.14 14.42 22.15 42.28 Cordierite gneiss 290.88 28.07 45.32 11.33 15.27 Charnockite 384.38 12.91 54.35 8.70 24.02 Cordierite gneiss 171.13 22.43 57.56 5.91 14.08 Composite gneiss 443.26 27.65 14.53 24.46 33.33 Garnet biotite gneiss 55.09 20.24 12.73 3.21 63.80 Figure 1
  14. 14. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 128 Figure 1a Figure 2 Figure 3 Figure 4 Figure 5 Figure 6
  15. 15. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 129 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12
  16. 16. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 130 Figure 13 Figure 14 Figure 25 Figure 36 Figure 17 Figure 48
  17. 17. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 131 Figure 59 Figure 20 Figure 21
  18. 18. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 132 Figure 22 Figure 23
  19. 19. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 133 Figure 24 Figure 25 Figure 26
  20. 20. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 134 Figure 27 Figure 28 Figure 29
  21. 21. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 135 Fig.30 (a) (b) Fig.31 (a) (b) Fig. 32 (a) (b) Fig.33 (a) (b) . CAPTIONS Fig.1 Study area Fig.1a Lithotypes Fig.2 Cordierite Fig.3 Biotite flakes Fig.4 Garnet Fig.5 Sinisterly deformed biotite flakes Fig.6 Four generation of quartz in cordierite gneiss Fig.7 Altered hypersthenes, perthite, quartz and potash feldspar. Fig.8 Altered hypersthenes under crossed nicols. Fig.9 Charnockite. Fig.10 Charnockite under crossed nicols. Fig.11 Granite-feldspathic material through shear planes. Fig.12 Grey granite-graphite within the feldspar-sinistral shearing. Fig.13 Pink granite Fig.14 Pink granite with shearing of mineral grains. Fig. 15 Pink granite with fluorite Fig.16 Rod perthite with sinistral shearing Fig.17 Composite gneiss Fig.18 Concretionary kankar Fig.19 Filamentous kankar Fig.20 Calcrite formation Fig.21 Variation diagram Fig.22 Variation diagram
  22. 22. Online International Interdisciplinary Research Journal, {Bi-Monthly}, ISSN2249-9598, Volume-IV, Issue-I, Jan-Feb 2014 w w w . o i i r j . o r g I S S N 2 2 4 9 - 9 5 9 8 Page 136 Fig.23 Variation diagram Fig.24 Variation diagram Fig.25 Variation diagram Fig.26 Variation diagram Fig.27 Variation diagram Fig.28 Variation diagram Fig.29 Four Tectonic domains based on fold axes Fig.30 Joints (a) - Equal area contour plot and (b) - Rose diagram Fig.31 Joints (a) - Equal area contour plot and (b) - Rose diagram Fig.32 Joints (a) - Equal area contour plot and (b) - Rose diagram Fig.33 Joints (a) - Equal area contour plot and (b) - Rose diagram