ANALYTICAL METHODS AND RESULTS

Transcription

1 ANALYTICAL METHODS AND RESULTS 4.1 Analytical Methods Geochemical analysis involves many steps from powdering of rock samples to dissolutions and finally analysis. 5 to 10 kg of fresh samples were collected from the rock quarries to represent different phases of granitoid rocks. Based on field and petrographic studies, 16 samples were selected for geochemical and geochronological studies and crushed manually using a hardened steel mortar and to a size of less than 2 mm. By coning and quartering method 150 g of < 2 mm crushed sample is aliquoted and is ground to 84 to 88 μm size using an agate ball mill. 50 g of this is again powdered to 70 to 74 μm manually using an agate mortar. The remaining portion of the samples after the coning and quartering method were sieved to different size fractions. Mineral fractions for geochronological studies are separated using bromoform and isodynamic separation methods as described in Chapter Sample dissolution One of the preliminary steps in geochemical analysis is to dissolve the rock sample in to solution either by fusion or acid dissolution techniques. In fusion method rock powder is mixed with a flux such as lithium metaborate (LiBO 2 ) or sodium peroxide (Na 2 O 2 ) and fused at a high temperature of 1050º C in a graphite or nickel crucible in a muffle furnace. In acid digestion method the sample powder is reacted with acids like HF, HCl and HNO 3 in an inert Teflon vessel. Lithium metaborate (LiBO 2 ) fusion Precislely weighed, 0.2 g of < 74 μm (-200 mesh size ) size rock powder is mixed with excess lithium metaborate (1:4 ratio) powder in a graphite crucible and fused for 20 to 30 minutes at 1050 C inside a muffle furnace. After the ignition, the melt is poured directly into a beaker containing about 30 ml of 2N nitric acid which is being agitated on a magnetic stirrer. The solution is made up to 100 ml (dilution factor is 500X) and used for major and trace element analysis. 40

2 B Solution B solution was also prepared to replicate and to compare the major and trace element data obtained using LiBO 2 fused samples. About 0.5 g of 74 μm size rock powder is taken in a 50 ml cleaned Teflon beaker and 10 ml HF, 5 ml HNO 3 and 1 ml HCl are added to this. It is capped and heated for about 12 hours on a hot plate at a temperature of about 120º C for closed digestion. And then lid is removed and the solution evaporated. This step is done to remove silica and the fluorides of different elements formed which are seen white in color. In the next step, 5 ml HF and 10 ml HNO 3 are added and evaporated to incipient dryness. HNO 3 is added to break the fluorides formed. Finally 15 ml concentrated HNO 3 is added and evaporated completely and 30 ml of 2 N HCl is added to dissolve the dried residue in the Teflon beaker and heated gently to get a clear solution. The solution is then made up to 100 ml with dilution factor of 200 and this is used for trace element analysis. 5 ml of the above solution is again made up to 100 ml (4000 times diluted) for major element analysis. Major and trace element analyses were performed using an ICP-AES (Jobin Yuvan Ultima 2) in the Department of Earth Sciences, Pondicherry University. A Solution A solution is prepared to analyze the silica weight percentage 0.05 gm of mesh rock powder is fused with excess amount of NaOH flux in a nickel crucible using a Meker burner for about 15 to 20 minutes. The melt is swirled repeatedly to mix well with flux which yields a homogeneous mixture. The crucible is allowed to cool and after attaining the room temperature approximately 20 ml of triple distilled water is added and the crucible is covered with lid and left overnight. After this the contents of the crucible are transferred to a 500 ml beaker containing 250 ml of very low normal HCl (~ 0.1 N HCl). During transferring the contents from the crucible care is taken so that the solution should fall directly to the low normality acid without touching the wall of the beaker when glass beaker is used. If the solution is cloudy it is heated till the solution is clear and allowed to cool down to the room temperature. The solution is transferred to a one liter volumetric flask and triple distilled water is added to make up to volume. The solution is mixed thoroughly by shaking and 41

3 allowed to be undisturbed for at least 5 hours for a better homogenization. 100 ml of this solution is used for analysis using the ICP-AES REE analysis Pre-concentration of Rare earth elements (REEs) are essential for their precise analysis using ICP - AES. About 0.5 g of 74 μm size (-200 mesh) sample is fused for minutes with 1.25 gm of Na 2 O 2 and 1 gm of NaOH in a 25 ml nickel crucible with lid using a Meker burner. When the crucibles are completely cooled 3/4 th volume of crucible is filled with deionized water (Elix ) and kept overnight. The fused cake dissolved in Elix water is then transferred from the nickel crucible to 500 ml glass beaker. The remaining sample from the nickel crucible is recovered using Teflon rod and repeated wash with 6 N HCl. The collected solution is dried until viscous silica gel (H 4 SiO 4 ) is formed which is then filtered and the precipitate is repeatedly washed with 6 N HCl. The solution is again dried completely at 100ºC. About drops of phenol red indicator is added along with 30 ml of 1 N HCl in order to turn the colour of the solution into orange. At next stage ammonia solution (1:1) is added till the color of the solution is changed from orange to pink. REE and trivalent ions are precipitated from the solution as a group which is brown in color. After centrifuging, the clear pink solution is decanted by leaving the precipitate in. This precipitate is dissolved in 1 N HNO 3 and passed through HNO 3 and HCl cation exchange columns in order to separate REE as a group. Both HNO 3 and HCl Columns are filled with Bio-Rad AG50-WX8 (50 to 100 mesh) cation-exchange resin. The sample solution is passed through HCL columns followed by low polar HNO 3 column. These columns are specially calibrated to remove elements like Ca, Mg, Fe etc. in low normality (1.7 N) acids and REEs are collected only in higher normality(6 N) acids Isotope analysis Rb-Sr and Sm-Nd separation Precisely weighed 0.1 g of sample was fused with 0.4 g of LiBO 2 inside a muffle furnace in graphite crucibles at 1050 C for about 20 minutes. Fused sample melt in the graphite crucibles was carefully transferred into a pre-weighed 125 ml 42

4 wide mouth bottle using about 30 ml of 3N HNO 3 Solution was thoroughly stirred using a Teflon coated magnetic stirrer rod. Total weight of the solution with bottle is precisely measured. The solution is then split into two aliquots. One of the aliquots was used for the determination of the Isotopic Composition (IC) of Sr and Nd while the other was used for the determination of Rb, Sr, Sm and Nd concentrations through Isotope Dilution technique (ID). Both the solutions were dried in different PTFE/PFE beakers. For sample digestion about 1 to 2 ml of HF, 1 ml HNO 3 and a few drops of HCl were added to the sample containing beaker and left on the hot plate at 110 C for overnight with the lid tightly closed. The digested solution was then dried and about 1 ml of HNO 3 was added three times and dried to remove any traces of HF. The IC and the ID fractions were passed through Bio-Rad AG50-WX8 cationexchange resin filled HCl columns. Rb and Sr were collected with 2N HCl and REE as a group was collected with 6 N HCl. Rubidium and Sr fractions separated were purified further by passing through a set of secondary Bio-Rad (PP) columns that were also filled with Bio-Rad AG50-WX8 cation-exchange resin and calibrated for the above mentioned elements. The collected Rb and Sr solutions were dried. The REE eluted as a group from HCl column was dried and dissolved in 300 µl of 0.18 N HCl. The IC and ID REE fractions were passed through different HDEHP columns. Neodymium was collected with 0.3 N HCl and Sm were collected with 0.4 N HCl. Loading of Sr for mass spectrometry was done using the following procedure. 1 µl of Tantalum oxide (TaO) activator was loaded on a pre-warmed rhenium (Re) single filament and dried at 0.5 A current. Rb was dissolved in 1 to 2 µl of 1N HCl and loaded on top of TaO on the filament and dried at 0.5 A current. 1 µl of Tantalum oxide (TaO) activator was again loaded on top of the sample making a sandwich of sample between layers of TaO. The filament was then heated to dull red colour for about 10 seconds and loaded on the turret of the Thermal Ionization Mass Spectrometer (Make: Thermo Finnigan, Model: TRITON) for analysis. Sr was dissolved in 1 µl of 1N HNO 3 and loaded between two layers of TaO on a rhenium filament and dried at 0.5 A current. The filament was then heated to dull red colour for about 20 seconds and loaded on the turret of the TIMS for analysis. 43

5 Nd and Sm were dissolved separately in 1 µl of 1N HNO 3 and were loaded on pre-warmed rhenium (Re) double filaments. No TaO activator is used for Nd and Sm loading. The sample was dried at 0.5 A current. The filament was then heated to dull red color for about 20 seconds and was loaded in the turret of the TIMS for analysis. Pb-Pb separation About 0.1 gm of sample powder is weighed into a PTFE/Savillex beaker. About 1 to 2 ml of HF + 1 ml HNO3 +a few drops of HCl were added to the sample beaker and left on the hot plate at 120 ºc overnight with closed lids for digestion. The acid was then dried and about 1 ml of HNO 3 was added three times and dried to remove any traces of HF present. For the digestion of 10 to 20 mg of sphenes and 50 to 60 mg of K-feldspar proportionate amount of acids were used. K- feldspar is analyzed to find out the isotopic composition of common Pb in each sample. Pure K- feldspars were picked manually using binocular stereo microscope. To avoid contamination due to presence of any possible tiny inclusion at the rim of K-feldspar the hndpicked grains were cleaned by HF leaching method. Selected K-feldspar grains are kept in a Savillex beaker and 0.1 normal HF is added. Closed beaker is shaken well for a few minutes and HF is immediately removed by continuous washing with few ml of Milli-Q to another Savillex beaker. Both the digested sample-residue and leachate were processed separately for separation of Pb. About 0.8 ml of 1 ml quartz columns is filled with 100 to 200 mesh Bio-Rad AG1 X8 anion-exchange resin. Columns are regenerated by passing about 3 resin bed volume (2.4 ml) of 6 N HCl followed by rinsing with 3 resin bed volume of Milli Q. After equilibrating with 1 N HBr, sample dissolved in same normality HBr is loaded on to the column. Columns were calibrated to collect Pb in a particular amount of 6N HCl. Collected Pb solution after column separation is dried and picked in 3 N HCl. Same columns after regeneration process are further used to purify the collected Pb. Pb dissolved in 3 N HCl is again loaded in to the respective columns and Pb is collected in 6 N HCl. Resin used for a sample is discarded after each use. Collected Pb solution is dried on a hot plate. For mass spectrometric analysis, the separated element is loaded on rhenium filament. Pb sample dissolved in 2 to 3 μl of 6 N HCl is loaded on rhenium filament which was pre- loaded with 2 μl Silica Gel- 44

6 suspension and H 3 PO 4 acid and dried at 0.5 A. For the present study all the isotope analysis were carried out using the thermal ionization mass spectrometer (Thermo- Finnigan, model Triton) at the National Facility for Isotope Geosciences at Pondicherry University. 4.2 Analysis Major, trace element and REE analysis were carried out using ICP-AES (Jobin Yuvan Ultima 2) at the department of Earth Sciences, Pondichery University. About five numbers of different rock standards and blank were digested in the same way as samples were digested. These rock standards were used to calibrate the ICP-AES to reduce the procedural blank. Different rock standards were repeated many times during the course of analysis to check the precision of the data. The precision of the major element data is about 3%. For the trace elements the precision is better than 5%. International standards SRM 987 and La-Jolla and AMES (internal standard) were loaded with each set of samples during the course of Sr and Nd isotope analysis to check the precision and accuracy. Repeated analysis of SRM 987 yielded a mean value of 87 Sr/ 86 Sr ratio of with an external precision of (1 ) and a mean value of 143 Nd/ 144 ratio of with an external precision of (1 ) for AMES. La -Jolla yielded a mean value of with an external precision of (1 ). Blanks were prepared using same normality and same amount of acids in a similar fashion as the samples were digested.same conditions. The acids HF (supra pure), HCl, HNO 3 and HBr (for Pb-Pb column chemistry) were again double distilled before use. Repeated analysis gave procedural blank values of 0.7 ng for Rb, 0.4 ng for Sr, 68 pg for Nd, ng for Sm and 200 pg for Pb. For Pb-Pb isotopic analysis, measurement of high 206 Pb / 204 Pb ratios were done by using secondary electron multiplier (SEM) for ion counting system of TIMS. About 15 repeat analysis of NBS 981 yielded a mean value of 206 Pb/ 204 Pb = Pb/ 204 Pb= and 208 / 204 Pb= Correction for Pb mass fractionation was done by multiplying the difference between the mean value of repeated standard analysis and true standard value. Major, trace element and REE analysis results are given in table 4.1. Rb-Sr 45

7 and Sm-Nd isotope analysis of whole rock and mineral separates are given in table 4.2 and 4.3 respectively. Pb-Pb isotope analysis results are given in table 4.4. Table 4.1 Major, trace and REE data of granitoid rocks around the ag area of the Chitradurga greenstone belt. Major elements are in wt% and trace and Rare Earth Elements are in ppm. 004/ G28 009/1 SiO TiO Al2O FeO(Total) MnO MgO CaO Na 2 O K 2 O P 2 O Total: Ba Sr Rb Cr Ni Y Zr La Ce Nd Sm Eu Gd Dy Er Yb Lu (La/Sm) N (Sm/Yb) N (La/Yb) N Eu/Eu*

8 G SiO TiO Al 2 O FeO (Total) MnO MgO CaO Na 2 O K 2 O P 2 O Total: G19 Ba Sr Rb Cr Ni Y Zr La Ce Nd Sm Eu Gd Dy Er Yb Lu (La/Sm) N (Sm/Yb) N (La/Yb) N Eu/Eu* NA 47

9 Table 4.2 Rb Sr isotopic data for granitoid rocks around the ag area of the Chitradurga greenstone belt. An uncertainty of 1% (1 Sigma) was assigned for the calculation of 87 Rb/ 86 Sr are expressed as Standard Error. The ε Sr values are calculated for an 2600 Ma and also for its sphene Pb-Pb age which is given in chapter 6. r refers to replicate. N. A. is not analysed. Sample Rb (ppm) Sr (ppm) 87Rb/86S r 48 87Sr/87S r Error (± 1 sigma) ε 2600 S Lakkundi domain 004/ ± ± r ± ± r ± ± r ± G ± Harpanahalli domain 009/ ± ± r ± ± r N.A 96.5 N.A ± N.A N.A Mineral separates 009/1 Gt ± /1 Bt ± /1 Plag ± /1 Kfelds ± Kfelds ± Muscovite ± Bt ± Hbl ± Srimant Gudda domain ± ± ± ± ± ± r ε t Sr r ± r ± r ± G ± Rhyolite and Quartz conglomerate 021_Rhy ± G 19_QC ± Standards K ±

10 BCR ±

11 Table 4.3 Sm Nd isotopic data for granitoid rocks around the ag area of the Chitradurga greenstone belt. An uncertainty of 1% (1 Sigma) was assigned for the 147 Sm/ 144 Nd. The ε Nd values are calculated for a 2600 Ma and also for its sphene Pb-Pb age which is given in chapter 6. r refers to replicate. Sample Sm (ppm) Nd (ppm) 147 Sm/ 144 Nd 143 Nd/ 144 Error (1 Nd ) T CHUR T DM fsm/nd ε 2600 Nd ε t Nd Eastern side: Lakkundi domain 004/ ± ± r ± ± r ± ± r ± G ± SW Side: Harpanahalli domain 009/ ± ± r ± ± r ± Mineral separates 009/1 Gt ± /1 Bt ± /1 Pl ± /1 Kf ± Kf ± Msc ± Bt ± Hbl ± Western side: Srimant Gudda domain ± ± ± ± ± ± r ± r ± r ± G ± Rhyolite and Quartz conglomerate 021_Rhy ± G 19_QC ± Standards K ± BCR ±

12 Table 4.4 Pb-Pb isotope data on the granitoid rocks around the ag area of the Chitradurga greenstone belt. wr = whole rock. sample 206 Pb/ 204 Pb 207 Pb/ 204 Pb 208 Pb/ 204 Pb Lakkundi domain wr 004/1_wr _wr _wr _wr G28_wr Harpanahalli domain wr 009/1_wr _wr _wr Srimant Gudda domain wr 012_wr _wr _wr G15_wr _wr _wr Rhyolite and Qtz Conglomerate 021_wr G19_wr Lakkundi domain K-felds 004/1_K-Feld /1_K- Feld_L _K-Feld _K-Feld_L _K-Feld _K-Feld_L _K-Felds G28_K-Felds Harpanahalli domain K-felds 009/1_K-Felds _K-Feld Srimant Gudda domain K-felds 012_K-Felds _K-Felds _K-Felds Z_017_K-Felds

13 Lakkundi domain sphenes 004/1_Sph _Sph G28_Sph G28_Sph _Sph Srimant Gudda domain sphenes 012_Sph _Sph _Sph _Sph _Gt _Gt Table 4.5 Pb-Pb isotope data of 15 analyses of standard NBS_981 is given. Fractionation factor is calculated using the mean value of this analysis. Serial No. Sample No 206 Pb/ 204 Pb 207 Pb/ 204 Pb 208 Pb/ 204 Pb 1 NBS_ NBS_ NBS_ NBS_ NBS_ NBS_ NBS_ NBS_ NBS_ NBS_ NBS_ NBS_ NBS_ NBS_ NBS_ Mean value of 15 analysis True value of NBS_ Fractionation factor

14 4.3 Results Classification One of the simple and widely used classification schemes of plutonic rocks is given by Streckeisen (1976). The abundances of major elements are reconstituted in terms of CIPW normative mineralogy. The amount of quartz, alkali feldspar and plagioclase feldspars are normalized to 100 and are plotted in QAP (Quartz, Alkali Feldspar and Plagioclase) ternary diagram to assign a name for the rock. All the samples of granitoid rocks around the Chitradurga greenstone belt plot in granite and granodiorite fields and most of the granitoid rocks from the Lakkundi domain fall on the discrimination line between the granite and granodiorite fields (Fig. 4.1). However, samples from northwestern and southeastern parts of the domain plot in the granite and granodiorite fields respectively. All granitoid rocks of Harpanahalli domain plot in granite field. The samples from Srimant Gudda domain, except those from southwest, are recognized as granodiorites. Overall these granites and granodiorites have a range of silica content that varies from to and Al 2 O 3 abundance varies from 12.9 to Most of the granitoid rock samples are rich in Na 2 O compared to K 2 O. However the granite samples from Harpanahalli and the Lakkundi domain, as well as, rhyolite sample from the greenstone belt are exceptions to this with K 2 O/Na 2 O ratios > 1. 53

15 Qtz Lakkundi Harpanahalli Srimantgudda Rhyolite G GAD004/1 GD GAD016 GAD017 T GAD007 QM QMD QD K-felds (Ab+An) Figure. 4.1 Quartz-K-feldspar Plagioclase normative plot of granitoids in and around gadag schist belt. The fields shown are based on modal mineralogy of Granitoids by Streckeisen (1976). G, GD, T, QD, QMD, and QM refer to granite, granodiorite, tonalite, quartz-diorite, quartz-monzodiorite, and quartz-monzonite respectively. Trace element concentrations of Ba, Rb, La, Ce, Sr, Nd, Sm, Zr, Ti, Y, Yb are normalized to the composition of chondritic meteorites and plotted from left to right in the order of increasing compatibility during small extents of partial melting of the mantle is given in Fig All granitoid rocks are enriched in these incompatible trace elements compared to the chondritic values. The granitoid rocks from the Lakkundi domain show three different trace element patterns. The granite sample ( 004/1) is enriched in all the above mentioned elements except Ba and Sr with a high Y content with moderate Cr and Ni abundance. This sample shows highest Rb abundance of 295 ppm among various samples from this domain. Granodiorite ( 007) exposed in the southeastern part of the Lakkundi domain is comparatively more abundant in Ba and Sr but depleted in all other elements compared to other samples. This granodiorite shows a high Cr and Ni abundance of 295 ppm and 119 ppm respectively with a low Y content of 1.8 and is less abundant in Rb with a value of 82. (Cr+Ni)/Y ratio of 004/1 is 1.96 and 007 is 225 and other samples have 54

16 ratios 20. (Ba+Sr)/Rb ratios of the same samples also vary proportionately with ratios of 0.86, and 6 respectively Lakkundi domain 004/ G Harpanahalli domain 009/ Rock/Chondrite 10 1 Rock/Chondrite Ba Rb La Ce Sr Nd Sm Zr Ti Y Yb 0.1 Ba Rb La Ce Sr Nd Sm Zr Ti Y Yb 1000 Srimant gudda domain 700 Inside Greenstone Belt G 19 Rock/Chondrite Gaad 014 G Rock/Chondrite Ba Rb La Ce Sr Nd Sm Zr Ti Y Yb Ba Rb La Ce Sr Nd Sm Zr Ti Y Yb Figure 4.2 Chondrite normalized trace element patterns of different granitoid rocks that outcrop around the northern part of Chitradurga greenstone belt. 021 and G 19 are rhyolite and quartz conglomerate respectively. Samples of granites from Harpanahalli domain show more or less similar trace element abundances. However one granite sample ( 011) has slightly lower Ba and Sr abundances and is more enriched in Y and Yb than other samples. All these granites have similar Ni and Cr abundances. To the west of the schist belt in and around Mulgund area granodiorite shows similar trace element concentrations. Barium content ranges from 446 ppm to 512 ppm, Sr content ranges from 253 ppm to 282 ppm and Rb abundance is from 107 ppm to 149 ppm. Ni and Y abundance are 53 ppm and 11 ppm respectively. Cr concentration of the samples varies from 117 ppm to 147 ppm. However granite samples near Belhatti area are considerably different than this. Comparing to Mulgund granitoids 016 near Belhatti area has lower abundance of Ba and Sr 55

17 (131 ppm) with a higher Y value. 017 shows very low Ba and Sr content (22 ppm and 11 ppm respectively) and is enriched in Rb (275 ppm). This granitoid has a very high Y abundance of 187 ppm. However, Ni and Cr values are similar to that of Mulgund granitoids. The ratio of (Cr+Ni)/Y of this sample is lowest as 1.0 compared to other samples. In general, all the granodiorite samples of Srimant Gudda domain show similar trace element concentrations compared to the granites which have lower abundances of Ba and Sr but much higher Y value Rare earth elements (REE) Chondrite-normalized REE patterns of granitoid rocks from the various domains have resemblance to Archean granodiorites and granites reported from other cratons. All the granodiorite samples are enriched in light REE compared to chondrites (Fig. 4.3). The granodiorite samples from the Lakkundi domain show similar steeply fractionated REE patterns with no prominent Eu anomaly. One of the Granodiorite samples has lower REE abundance than others and shows small positive Eu anomaly. The granite sample from this domain shows less fractionated REE pattern and is enriched in heavy REE with a significant negative Eu anomaly. Among the granites of the Harpanahalli domain, all the samples show a distinct negative Eu anomaly. These samples have a moderately fractionated REE pattern. However one granite sample ( 011) is HREE enriched with a strong negative Eu anomaly. The granodiorites of the Srimant Gudda domain show steeply fractionated more or less similar chondrite normalized REE patterns with small negative Eu anomaly. However the granites ( 016 and 017) are enriched in HREE with significant negative Eu anomaly. Interestingly these two samples contain garnet. Rhyolite sample found in the greenstone belt shows less fractionated chondrite normalized REE pattern with a prominent negative Eu anomaly. Quartz conglomerate sample has very low abundances of REEs and is less fractionated. 56

18 Lakkundi domain GAD004/1 GAD G28 GAD Harpanahalli domain GAD009/1 010 GAD011 Rock/Chondrite 10 1 Rock/Chondrite La Ce Nd Sm Eu Gd Dy Er Yb Lu 1 La Ce Nd Sm Eu Gd Dy Er Yb Lu 1000 Srimantgudda domain GAD012 GAD013 GAD014 GAD016 GAD017 G Inside Greenstone Belt GAD021 G Rock/Chondrite 10 Rock/Chondrite 10 1 La Ce Nd Sm Eu Gd Dy Er Yb Lu 1 La Ce Nd Sm Eu Gd Dy Er Yb Lu Figure 4.3. Chondrite normalized REE patterns of different granitoid rocks that outcrop around the northern part of Chitradurga greenstone belt. GAD021 and G19 are rhyolite and quartz conglomerate respectively Isotope analysis Results of the Rb-Sr, Sm-Nd and Pb-Pb isotopic studies are also consistent with the characteristics of major trace and REE data. Most of the samples were reanalyzed for checking its precision. These results are compiled in Tables 4.2, and 4.5. Among the granitoid rocks from Lakkundi domain occurring to east of the greenstone belt, 004/1 has considerably high 87 Sr / 86 Sr ratio of and high 87 Rb / 86 Sr ratio of The same sample shows higher 147 Sm / 144 Nd ratio of compared to the other samples. -007, located much southeast shows considerably lower 87 Sr / 86 Sr ratio of and 87 Rb / 86 Sr ratio of and 147 Sm / 144 Nd ratio of All other granitoids present in this domain have ratios in between them. ε t Nd & ε t Sr values are calculated for time t = 2600 Ma. The granite sample of Lakkundi has considerably high 87 Sr / 86 Sr and 87 Rb / 86 Sr as well as ε 2600 Sr ratios. ε t Nd & ε t Sr signatures (-6.1 and 2203 respectively) of this sample show a definite 57

19 crustal source characteristics with higher T DM age of 3.5 Ga. Granodiorite sample from this domain shows considerably lower 87 Sr / 86 Sr, 87 Rb / 86 Sr and 147 Sm / 144 Nd ratios with ε t Sr values of with T DM age of 3.26 Ga. Other samples from the eastern side around Lakkundi area has a slight range of ε t Nd varies from to 0.14 and ε t Sr values range between to Granite sample 004/1 shows higher whole rock 206 Pb/ 204 Pb ratio of and 207 Pb/ 204 Pb ratio of On the other hand granodiorite sample 007 from the southeastern part of this domain shows lower values of 206 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios like and respectively. Other samples of this domain have whole rock 206 Pb/ 204 Pb ratios ranges from to Granites of Harpanahalli domain have 87 Sr / 86 Sr ratios that range between and with comparatively high 87 Rb / 86 Sr ratios. ε t Sr values are between to 513. These granitoid rocks exhibit comparatively higher initial Sr ratios with T DM ages between Ga and ε t Nd (t= 2600 Ma) values ranging between -1.8 to These granites have similar whole rock 206 Pb/ 204 Pb ratios ranges from to Granodiorites of Srimant Gudda domain have comparatively similar isotopic composition and is different from the granites present further south in the same domain. Granodiorites have 87 Sr / 86 Sr ratios ranging from to and 87 Rb / 86 Sr ratios are ranging from with ε t Sr values varying from 17.4 to These granodiorites show T DM age of 2.8 Ga. One of granite samples has comparatively old T DM age of 3.0 Ga. with ε t Nd and ε t Sr characteristics of an upper mantle or mafic source. The other granite sample ( 017 at Belhatti) with younger model age has negative ε t Nd and higher positive ε t Sr value shows signatures of a definite upper crustal source. This sample has whole rock 206 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios of and respectively. Granodiorite samples of the northwestern part of this domain have similar whole rock 206 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios range from to and to Rhyolite and Quartz conglomerate show T DM model ages at 3 and 3.3 Ga, respectively. 58