PRESENTED BY PRAMODA G

GEOLOGY

Presentation on

GEOLOGICAL MAPPING, PETROGRAPHIC STUDY and FIELD RELATION OF KARIGHATTA SCHIST BELT, DHARWAR CRATION, SOUTH

INDIA.

CONTENTS:

• Introduction• literature review• Methodology • Petrographic studies • Results and Conclusion• Reference

INTRODUCTION:Karighatta is one of the oldest rocky in south India, which could be considered very much for geological studies. These rocks come under granite – green stone belt. The rock types are meta-volcanic which were deposited in the ocean and later metamorphosed. The Karighatta has housed variety of rocks both igneous & metamorphic.

The study of the Granite-Greenstone belts has attracted the attention of many Geologists as it offers an excellent opportunity to understand the Crust forming process during the early period of the Earth’s history. The Dharwar Craton in Southern India exposes crustal segments in which geological activity can be traced continuously throughout the Pre-Cambrian.

Location 11°30' North and 18°30' North latitudes 74° East and 78°30' East longitude.

Geology of Karnataka is a fascinating subject. Oldest rocks exposed in Gorur area, Hassan district, Karnataka date back to about 3300 million years. The Precambrian craton of Karnataka is made up of western and eastern segments. The Precambrian of Karnataka have been divided into older Sargur supracrustals (about 3300 to 3000 million year old) and younger Dharwar supracrustals(about 3000 to 2600 million year old. The Dharwar supracrustals Supergroup has been further divided into older Bababudan Group(ca.3000 to 2700 million years) and younger Chitradurga Group(ca.2700 to 2500 million years). The schist belts of the Eastern craton, like Kolar,Hutti,Sandur etc., appear to be approximately equivalent to the Chitradurga Group.

GEOLOGY OF KARNATKA

GEOLOGY OF DHARWAR CRATON

The Dharwar or Karnataka Craton in South India presents a natural cross-section of late-Archaean continental nuclei lying between longitude 72°45´–80° andlatitudes 11°–19°.

Dharwar Craton is one of the best studied terrains of Peninsular India and is renowned for its Greenstone Schist Belt, Grey-Gneisses, Charnokites, and younger Granites . The Craton is divided into two tectonic blocks after Swaminath et. al. (1976), viz. the Western Block renamed respectively as the Western Dharwar Craton (WDC), and Eastern Dharwar Craton (EDC) are separated by Chittradurga Shear Zone which is situated at the Eastern margin of Chittradurga Schist Belt, not far from the Western margin of Closepet –Granite.

GEOLOGY OF DHARWAR CRATON

The contact between WDC and EDC is not sharp, and there is a Transition Zone between Chittradurga Shear Zone and Closepet Granite. The Grey-Gneiss complex covering the entire Craton was formerly known is Peninsular Gneiss in the view of its critical differences in age, composition and mutual relation with associated Supracrustal Rocks and Geographic distribution in separate Tectonic Blocks. Dominantly, Granitic terrain of EDC is Called Dharwar Batholiths (>2500m.a.) after Chadwick et al. (2000). According to Ramakrishnan and Swaminath (1981), Dharwar Craton has been divided into two.

1. Eastern Dharwar Craton (EDC)

2. Western Dharwar Craton (WDC)

EASTERN DHARWAR CRATON (EDC)

The EDC is bounded to the north by the Deccan Traps and the Bastar Craton, to the east by the Eastern Ghats Mobile Belt, and to the south by the Southern Granulite Terrain (Balakrishnan et al., 1999). The Craton is composed of the Dharwar Batholith (dominantly granitic), greenstone belts, intrusive volcanic, and middle Proterozoic to more recent sedimentary basins (Ramakrishnan and Vaidyanadhan, 2008).

Geological Map of Eastern Dharwar Craton (Modified from Naqvi and Rogers, 1987)

EASTERN DHARWAR CRATON (EDC)

The Western Dharwar Craton (WDC) is located in southwest India and is bound to the east by the Eastern Dharwar Craton (EDC), to the west by the Arabian Sea, and to the south by a transition into the so-called “Southern Granulite Terraine”. The remaining boundary to the north is buried under younger sediments and the Cretaceous Deccan Traps. The division between the Western and Eastern Dharwar Cratons is based on the nature and abundance of greenstones, as well as the age of surrounding basement and degree of regional metamorphism (Rollinson et al., 1981).

WESTERN DHARWAR CRATON (WDC)

Geological map of the Western Dharwar Cratons (after Naqvi and Rogers, 1987; Ramakrishnan and Vaidyanadhan, 2008).

WDC EDCSCHIST BELT LARGE WITH VOLCANICS, SUBORDINATE SEDIMENTS.

NARROW, WITH GREENSTONE BELTS. PILLOW BASALTS.

BASEMENT IS PENINSULAR GNEISS. UNCONFORMITY MARKED BY QPC.(<3000MY)

DHARWAR BATHOLITH INTRUSIVE ON ALL SIDES .(2500-2700 MY)

OLDER SEQUENCE (SARGUR GROUP)AS NARROW BELTS AND ENCLAVES, ABUNDANT IN THE SOUTH.

OLDER SEQUENCE(WARANGAL GROUP) MOSTLY AS ENCLAVES IN THE NORTH.

INTER MEDIATE PRESSURE METAMORPHISM.

LOW PRESSURE METAMORPHISM.

Comparison between WDC and EDC

Karighatta Schist belt is the southernmost part of Chittradurga Schist Belt characterized by Peninsular Gneiss, Quartzites (± Fuchsite), Garnet-Biotite-Schist, Amphibolites, BIF, Pyroxenite, Pegmatite, etc. These rocks are intruded by Dykes like Diorite Porphyry and surrounded by Gneisses belonging to Peninsular Gneisses Complex. The Relict Sedimentary Structures like bedding, lamination, current bedding, or less cross bedding can be noticed in the Metasediments.

KARIGHATTA SCHIST BELT

AIM AND SCOPE OF PRESENT STUDY The aims of the investigations are:

* To prepare geological map of Karighatta Schist Belt of the scale 1:500 and to bring out field relationships of the various rock types.

* To record petrography features of different rock types, their textures and mineral assemblages. The geology and tectonic activity of the area.

* To Elements of geological map. Basics of construction of geological maps and cross-sections.

* Obtaining and marking samples and describing and measuring where they came from in an outcrop;

* Measuring and recording orientation (i.e., altitude) of strata or other planar features;

GEOLOGICAL MAPPING

Field mapping can be physically and mentally challenging. Hundreds of questions arise, dictating that hundreds of decisions must be made during the course of a single day. Where should I go? What unit is this? Why does this? bed abruptly end? Thus, field mapping is the ultimate application of the scientific method – a good field mapper is constantly testing predictions about the next outcrop and evaluating multiple hypotheses about the structure. In the midst of this mental workout, it is important to maintain your focus and purpose by remembering the goals of your project or research. Try to maintain a good sense of humor and enjoy the day. After all, didn’t most of us decide to go into geology because we like being outdoors and we like thinking about the Earth?

GEOLOICAL MAPPING

PLANNING OF FIELD WORK Each mapping/structural field project in geology requires the following deliverables (i.e., products to be turned in), typically at a designated time/place on the evening of the last day of the project: Geologic map – lightly colored and burnished Structural cross-section(s) – lightly colored and burnished Key or explanation that describes all rock units and

explains structural symbols, etc. Written report, usually based on a set of questions posed

at the onset of the project; some reports may require accompanying stereonets

Field notebook

LOCATION FIELD DATA A geological map is prepared by locating many points, lines and data on a base map. Points on a map by a number of methods, the most suitable for which must be chosen depending on the base map, the map itself has to be oriented with reference to “North” direction.

Data can be plotted directly by inspection when the configuration of surface features makes it possible to identify them positively on the map. Examples of such points are distinctive turns or interaction in steams, roads of rid characteristic topography, etc.

LOCATION BY OBSERVATION AND A BEARING LINE Data along liner features, such as bridges, roads, or steams can often be located by taking a bearing from a point that can be identified exactly on the map, then plotting the back bearing from that point to intersect the linear feature on which the observation stands.

LOCATING BY INTERSECTION OF BEARING LINES

When the features that can be identified on the base map are too distant for facing bearing to two such features from the required point is read and the back bearing lines are plotted. The intersection point of the bearing lines will indicate the location of the required point on the base map. They include angle between the bearing lines should not be very acute or obtuse.

LOCATION The area selected for present study is situated North of Mysore City Karighatta( 12°25'05''N and 76°43'17''E, Toposheet - 57D/11) is a hill situated a few kilometer’s outside the ‘island’ town of Srirangapatna, on SH NO.17, Mysore-Bangalore Road, representing a narrow linear schist belts around Karighatta, termed as Karighatta Schist Belt.

Our base Map for geological field work of Karighatta

Traverse pattern

FIELD SETTINGAND

PETROGRAPHY

Basic Job Description:Study composition, structure, and history of the earth's crust; examine rocks, minerals, and fossil remains to identify and determine the sequence of processes affecting the development of the earth; apply knowledge of chemistry, physics, biology, and mathematics to explain these phenomena and to help locate mineral and petroleum deposits and underground water resources; prepare geologic reports and maps; and interpret research data to recommend further action for study.

 

FIELD DESCRIPTION AND PETROGRAPHY

PetrographyPetrography is a branch of petrology that focuses on detailed descriptions of rocks. The mineral content and the textural relationships within the rock are described in detail. The classification of rocks is based on the information acquired during the petrographic analysis. Petrographic descriptions start with the field notes at the outcrop and include macroscopic description of hand specimens. However, the most important tool for the petrographer is the petrographic microscope. The detailed analysis of minerals by optical mineralogy in thin section and the micro-texture and structure are critical to understanding the origin of the rock. Electron microprobe analysis of individual grains as well as whole rock chemical analysis by atomic absorption or X-ray fluorescence are used in a modern petrographic lab. Individual mineral grains from a rock sample may also be analyzed by X-ray diffraction when optical means are insufficient.

PENINSULAR GNEISS GPS Coordinates Latitude - 12°25'25''

Longitude - 76°41'47'' Elevation – 2232 ft

In thin section, the Peninsualar Gneisses exhibits Gneissosity which are alternate layers of Sialic and Mafic rich bands are observed and the thickness of the bands are variable. Sialic rich bands consist of feldspar and quartz, whereas mafic parts are made up of Biotite and Hornblende.

Under microscopic thin section

Peninsular Gneiss having trend of N400E Elevation:662mts

Peninsular Gneisses occupy in the low land area in Karighatta schist belt. They are medium to course grained rocks that exhibits gneissic fabric which consists of alternate layers of light and dark bands of minerals. They are well foliated along the strike direction ranging from N-S to N40˚E and an amount of dip varies from 80˚ to almost sub vertical. Pegmatite or Quartz feldspathic veins are found parallel to the banding. Furthermost amphibolites and some pure white quartz are also found. There are some pegmatite veins which occurred between amphibolites and peninsular gneiss. The minerals which are found in Peninsular Gneiss are quartz, plagioclase, K-feldspar, biotite etc.

Peninsular Gneiss exposed in Kaveri River.

Quartzites:GPS Coordinates Latitude - 12°25'29'' Longitude - 76°43'10'' Elevation – 2482 ft

Under microscopic thin section

Quartzite (from German: Quarzit) is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in various shades of pink and red due to varying amounts of iron oxide (Fe2O3). Other colors, such as yellow, green, blue and orange, are due to other mineral impurities.

Fuchsite Quartzite having strike N500Ewith dip of 550 towards west Elevation:762mts

AMPHIBOLITEGPS Coordinates Latitude - 12°25'30''

Longitude - 76°a43'19''

Elevation – 2475 ft

Medium to fine grained containing Hornblende, Garnet, plagioclase, etc. The general strike direction of Amphibolites is N-S to N600E dipping with an amount of 400W to almost sub-vertical. Amphibolites are traversed by white massive quartz veins and loose garnets are found. The width of the amphibolites ranges from 0.5 to 2m. There is a contact between amphibolites and pegmatite vein

Amphibolite Direction of trending N650E Elevation:760mts

In thin section, Plagioclase + Hornblende + opaque are seen. Hornblende grains are prismatic and cleavages not distinct, It shows inclined extinction with high order interference colour. The pleochroic colours ranges from yellowish green to green. Few grains consist of inclusions of plagioclase. No alteration observed. Plagioclase is colourless without cleavage and untwined. It is tabular showing inclined extinction. Some of the Plagioclase grains exhibit characteristic multiple twinning. In some of the sections, the granulation of individual grains is noticed.

Under microscopic thin section

DIORITE PORPHYRY:

GPS Coordinates Latitude - 12°25'53'' Longitude - 76°43'17'' Elevation – 2502 ft

Diorite porphyry exhibits 3 sets of color’s from dark grey, pale pink to chocolate brown colour. The phenocryst often due to the alteration of feldspar grains with the release of Iron Oxide and the groundmass is of pink colour. The general strike direction is N450E with an amount of dip of almost vertical.

Diorites Extended 310mts longDirection of extension N450E Elevation:769mts

In thin section, there is a porphyritic texture where two modes of mineralogy are observed. It consists of bigger grains forming phenocrysts and smaller fine grains forming ground mass. It consists of plagioclase Feldspar Hornblende + Opaque. Plagioclase Feldspar is tabular, colourless, indistinct, non-pleochroic. It shows inclined extinction with multiple twinning and low order interference colour. It is found as phenocrysts showing alteration to Sericite along the grain boundaries and cleavage plains. Some of the Feldspar grains are traversed by irregular fractures. Hronblende is green in colour, prismatic and shows inclined extinction. It shows high order interference colour and pleochroic colour varies from green to yellowish green. Cleavages are not distinct. Opaque’s are dark colour, isotropic and grains are present as

accessorie

Under microscopic thin section

Garnets: GPS Coordinates

Latitude - 12°25'39'' Longitude - 76°43'14'' Elevation – 2492 ft.We have found good crystals of garnets

on the next stage after the Amphibolite. The Garnets what we have found in Karighatta area varies from 1-5cm in diameter. These Garnets are showing Dodecahedral crystals. The colors of the Garnets are dark pink. It is hardly scratched by pen knife, Diaphaneity opaque, luster dull. Garnets generally have indistinct cleavage planes, uneven fracture. Garnets can be used as Gem minerals.

Under microscopic thin section

Garnetiferrous Mica SchistDirection of trending N27ᴼWElevation:778-785mts

Current beddings:

Just after the Diorite extension, we saw current beddingshaving thin lamination.

Pegmatite + Quartz Vein ………. Quartz + Plagioclase + K-Feldspar

Mica Schist ………….………… Garnet + Biotite + Plagioclas + Muscovite +

Sericite + Quartz

Diorite Porphyry ….………… Plagioclase + Hornblende+ Orthoclase+CPx

Amphibolite……………………Hornblende + Plagioclase + CPx + Garnet

Fuchsite Quartzite ………………… Quartz + Silliminite +

Fuchsite

Peninsular Gneiss ………………….. Quartz + mica + Biotite +

Hornblende

LITHOSTRATIGRAPHIC SUCCESSION

Karighatta Succession1.Banded peninsular gneiss(Age 2.8 B.Y)

2.Larger boulder Quartzites

3.Huge Fuchsite quartzite(Joined and Huge )

4.Diorite Porphyry

5.Amphibolite

6.Garnet Biotite Schist

CONCLUSIONThe Dharwar Craton in Southern India is composed of extensive linear Granite-Greenstone Belts called as the Gneissic-Granulite belt occupy large area of the craton.

The study area Karighatta Schist Belt consist of Banded Peninsular gneiss which are look like large boulder, Fuchsite quartzite if joined trending N55E.

After the formation of Fuchsite quartzite Diorite Porphyry it indicates later volcanic activity, this followed by Amphibolite later Garnet Biotite Schist.

In the study are micaceous enclaves also seen and Shielding also visible.

In lower regions Feldspar is alternated into epidote.

Ripple marks and Cross bedding also seen in hill lock region this indicates that paleoclimate condition is marine.

The occurrence of Garnet in many of the rock type indicates “Prograde Metamorphism”. The entire area was subjected to Upper Amphibolites to Lower Granulites Facies of Metamorphism and the sediments are now found as Quartzites trending NE.

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• Swami Nath.j. & Ramachandra,M.(1981),Mem.Geol.surv.India, vol.112,p. 175-181.

• Janardhan,A.S.,Ramachandra,H.M. & Ravindra, K.G.R.(1379), J.Geol.soc.India,p.20,61-72.

• Wadia.D.N.(2004)``Geology of India”,Tata Mc Graw Hill,p.89-112.• Compton, R.R., 1962, Manual of Field Geology: New York, John Wiley and

Sons, 378 p.• Chamberlain, T.C., 1890, The method of multiple working hypotheses:

Science, v. 15, p. 92-97. Reprinted in Science, v. 148, p. 754-759 (1965).

REFERENCE

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