Chapter 2

Methodology

The methodolog) adopted for this stud1 includes field ~ o r k and sample collec;ion,

cia) mineral studies. major and trace eiernent geochemical studies and Rb-Sr and Sm-

Nd isotope studies. Claj mineral studies iniolve separation of c i a minerals from

bulk samples. some preliminaq studies on their qualitative determination using

Fourier Transform lnfra Red (FTIR) Spectroscop) and qlialitative and semi

quantitative studies using X-raq Diffractmeter. Major and trace element geochemical

studies involve preparation of solutions from finel) crushed (-200 ASTM mesh) bulk

samples following standard dissolution procedures and their analqses using

inductively Coupled Piasma - Atomic Emission Spectrometer (ICP-AES). Isotope

studies involve dissolution of samples for Rb-Sr and Sm-Nd isotope analysis. element

separation based on ion-exchange chromatography and determination of isotopic

abundances using Thermal Ionization Mass Spectrometer (TIMS).

2.1 Field study and sample collection

Extensive field work was carried out in and around Mangalore. Chikmagalur

and Banasandra in Karnataka to locate in situ weathering profiles and to collect

representative samples for various analyses. Samples were collected from well

developed weathering profiles found along road and canal cuttings and in quarries. In

each profile, different zones were identified based on their degree of weathering. The

physical parameters that were considered for determining the degree of weathering

were colour, grain size, compactness, rock structure and texture. The zone comprising

the top 5-15 cm was not sampled to avoid any surface contamination. In each zone,

the outer most part was scraped off before sample collection to reduce the effect of

any external leached material. In all profiles, samples were uniformly named with

alphabets (A, B, C etc.) starting with A for the least weathered or sample at the

bottom of each profile.

2.1.1 Weathering Profiles around Mangalore

The Mangalore area has undergone intense lateritization and a number of

quarries take out these laterites for construction work. Thick sections of laterites were

exposed along these quarry walls but the bed rock was not exposed as they limit the

q u a q i n g up ro the iateriie part. hirhough ?he g u a p uails nere moderate!:, deep

(more than 7 m) no ph>sicai variation in \teathering intensily could be seen in the

field for dill'erent parts of the section. Hence, in order to get samples representing

different stages of \beathering, sampling \bas done from adjacenr areas that shorved

variation in weathering intensib.

Samples were coiiected from different sites around three locations in

Mangalore (Figure 2.1). The first location was Mangaiore airport in Bajpe (N 12"

57.419' E 74" 53.485'), second was near Kaikamba (N 12" 52.98' E 74" 52.416') the

third was near Fisheries College (N 12" 5 1.42' E 74" 5 1.96').

0 Peninsular Gneiss I" Laterite I 0 CharnockitelGranulite / Coastal Sediments

/ Sample Location I

Figure 2.1 Simplified geological map of Mangalore area showing sample locations. Samples were collected from different sites around three locations in Mangalore (modified from Geological map of Karnataka state, Geological Survey of India, 1981).

Profiles MI . XI:! and 3.1 \+ere colieceed from three sites near Bajpe

(Mangalore Airpoc). The parrern of &eathering appeared similar in these three

profiies in field. Profiie MvII nas coliected from a laterite quarry (Figure 2.2) close to

the Mangalore airport. This location i+as at a higher elevation compared to all other

profiles studied From the Mangalore area. The quarq face was about 7 m deep where

samples were collected. The sample M I A was cojlected from the bottom most part

which appeared verj light coioured, soft and nodular. Sample MIB was coilected

from 2 m depth from the surface. This part was more reddish in colour and appeared

more compact.

Figure 2.2 Profile MI in a laterite quany near Mangalore airport. The quarry wall is more than 7 m deep. MIA and MlB represent bottom and top samples collected according to the physical variation observed in the field. The MlB was collected from about 2 m depth from the top which is not covered in the photograph.

Profile kl? \+as coiieeted on top of a small hiilock (Figure 3.3. The eltent of

&eathering appeared lo be less compared to the M I profile in fieid. Vv'eak gneissic

foliation \\as visible En some pasts of the profile and quartz has large11 escaped

alterarion. Even some mica could be seen \+hi& appeared to be muscovite. Samples

M2A and M2B were collected from the less altered and more altered zones of the

profile based on :he physical variation in weathering intensity as appeared in the field.

Figure 2.3 Weathering profile M2 collected near Mangalore airport. M2A and M2B represent less weathered and more weathered samples from this profile.

Profile M4 was near Konchadi village in a quany half kilometer south east of

the Kavur-Mangalore road (Figure 2.4). The lateritized area was showing some type

of zoning. There was an organic-rich top layer followed by a horizon showing

leaching of clays. The bottom part largely consisted of pinkish coloured material

which could be a coating formed by the leaching of Fe- and Mg- bearing minerals.

Some part of the profile appeared as if developed on a felsic rock whereas some other

pon-ricns appeared like developed w e r more rnafic parent rock. Mafic inclusions nere

seen ~ r h i c h shoued distinct foliations defined b j micaceous minerals. T ~ s c sarnples

\+ere col!ected from here. V3A from the comparatively iess ueathered zor~c and M3B

from more weathered zone.

Figure 2.4 Weathering profile M4 collected near the village Konchadi in Mangalore. M4A and M4B represent comparatively less weathered and more weathered samples as appeared in field from this profile.

Profiles M j and MS were collected from two locations around Kaikamba

village. Profile M5 was in a small quarry near Kaikamba village on Mangalore -

Bangalore Highway (Figure 2.5). Unaltered bed rock of feisic granulite was visible in

this area but not exactly under the weathered zone. The total width of the profile at the

sampling site was about 4 m. At a depth of 2.9 m from top a quartz vein was present

which shows the in sztu nature of the weathered rock. Some mafic enclaves were also

seen here. Samples of bed rock (M5A) and weathered rock (M5B) were collected

from here. One weathered sample (MSB) and a relatively fresh sample (MSA) were

collected in a railway cutting in an adjacent location representing weathering of a

felsic granulite.

Figure 2.5 Profile M.5 near Kaikamba in Mangalore. Sample M j B was collected from this profile. A fresh rock sample M5A of felsic granulite was also collected adjacent to this profile in this location.

Secondary iaterites (allochthonus laterites) are reported from the low lying

areas in these regions (Widdowson and Gunnel 2001). Three samples of secondary

laterites were collected from location MI0 near the Fisheries College (Figure 2.6) to

compare their mineralogical characteristics with the primary laterites.

Figure 2.6 Secondary laterites near fisheries college, Mangalore. Three samples were collected from this location for clay mineralogical studies.

2.1.2 Wruf1zeriragproflIe.s r~round Chihrnagalur

Deep profi!es are scarce\> seen in this area. Profiles found here are generallj -2

m deep or less. The sarnpiing location (N i3°15'48" E 75'51'20") is show2 in a

simplified geological map of Chikmagalur area in Figure 2.7. Samples were collected

from an in siizc ueathering profile (Figure 2.8) formed over Chikmagalur graniie.

/ Peninsular Gneiss Granite

Metabasalt Quartzite

0 ~hyll i te Sample Location

Figure 2.7 Simplified geological map showing sample location (CM2) near Chikmagalur (modified from Geological map of Karnataka state, Geological Survey of India, 198 1).

Figure 2.8 Weathering profile developed over Chikrnagalur granite. The least altered sample CM2A was collected adjacent to this profile (- 3 m away). The arrow mark represents the 'stone line' consisting of silica and iron rich nodules.

At a depth of 1 m from the surface, a zone of partly altered rocks of -40 cm

width (CM2 B) was seen overlain by a more weathered horizon of variable thickness

(CM2 C) (25 cm at the sampling point). A "stone line'' of about 14 cm width consisting

of iron and silica rich nodules was found developed over the zone above this (CM2 D)

and the zone above this was part of the top soil (Figure 2.8). Altered boulders of parent

rock were found scattered within the bottom most part of the weathering profile. As

fresh rock was not exposed in the sampling point, a saprock was collected (CM2 A)

adjacent to the profile. The top 20 cm, which was part of the topsoil, was not sampled.

Around Banasandra some good profiles \\ere developed and exposed along the

ne.1~1) dug irrigarion canals. Samples bere col!ected from in sitw vreathering profiles

developed over various rock types in four locations around Banasandra. The sampling

locations are marked in geological map of Banasandra area (Figure 2.9)

76730' 76745' E

Peninsular Gneiss ( Granite

0 Metabasalt 0 Amphibolite

~hyl l i te 0 Ukramafic Rocks

Greywacke Sample Location

Figure 2.9 Simplified geological map of Part of the Chitradurga schist belt showing sample locations around Banasandra (modified from Geological map of Karnataka state, Geological Survey of India, 1981). Bana 13 and Bana 14 are locations of weathering profiles developed over metabasalts, Bana 15 is the location of profile over granodiorite gneiss and Bana 16 is the location of profile over metagreywacke.

.A \+ell-dekeioped tieathering profile formed oker metamorphosed Lasalts

(Bana 13) !%as found in a canal cutting in Banasandra village ;h 13"15'42". E 76O

39'37") (Figure 2.i0).

Figure 2.10 Weathering profile developed over metabasalts near Banasandra (Bana 13). Four samples 13A, 13B, 13C and 13D were collected from this location. 13A represents the bottom most sample.

The unaltered parent rock was not visible and the bottom most part was in the

saprolite stage. The sample collected from this part at a depth of 7 m was black with

yellow stains. Another sample was colleted from a depth of about 4.5 m and this

appeared to be more weathered. Two more samples one at 2.3 m and another at 1.5 m

were colleted from this profile. The samples were named as 13 A, B, C and D from

bottom to top.

\+'eathered inerabasairs twre also exposed dong a stream ccsing adjacent to

the location of profile Bana E 3 /N i 3" i 9'20" E 76°32'35"). Samples of ieasd altered

metabasalts sere colIected from here. Samples of kighij weathered rock aere also

collected for clay mineral anallsis (samples 13 C, D).

Seven samples here coEIected from weathering profile exposed in an

abandoned pit occurring 10 km east of Nittur on the southern side of Pumkur-

Shimoga road (N f 3'1 9'35" E 76'50'44") (Figure 2.1 1).

Figure 2.11 Weathering profile developed over granodiorite gneiss in Banasandra (Bana 15). Sampling points are marked as A, B: C etc. The arrow mark indicates the quartzo-feldspathic vein running through the profile.

The parent rock was not exposed but from the field observations and

geological map it was inferred to be granodiorite gneiss (Banal5). Total depth of the

profile was 3.5 m and in the topmost part within the soil layer there was a thin stone

line. The profile had a light yellow color layer below the stone line and plant roots

were seen up to this layer. Further below this layer, the profile turns to dark brown in

coior and a quaflzo-fcldspa~hic irin of \ac ing thichness \$as seer running through

this zone. The bottom most iqe r kxas having purpie and qe?io\s colour and quartz

grains uere prominenrij seen t+ithin this zone. Samples collected from this profile

Mere named as 15 A. B. G. D. E, F and C from bottom ?o the top.

A deep canal section of about i4 m depth was found developed over

metagreyw acke near Banasandra (N i 3" 2 1.25 1' E 76" 47.506') (Figure 2.1 2).

Figure 2.12 Weathering profile developed over metagreywacke in a deep canal cutting in Banasandra. There is no gradual up profile variation in weathering intensity. 13 samples were collected from this profile. The top portion consists of some laterites which are not part of this profile.

The fresh rock was not exposed at the bottom most portion of this profile,

however the original rock structure, particularly schistosity and foliarion planes were

preserved in some zones of the profile. The rock was clearly layered and weathered

feldspars and mafic minerals were visible in hand specimens. The profile did not

show any gradual up profile increase in weathering intensity, but some zones

appeared to be more weathered compared to the adjacent zones. Shiny white portions

of feldspar altering to cia) c o ~ l d be seen in inore nearhered lajess. Pan]! \%eathered

micas ioujd also be seen in some pohtions. The top portion consEated of some

secondar? la'rrrites. tthicl? do not appear to ha\e been deriked from or part of this

profile. Although the process of neathering had affected the rocks to more than 15 m

depth, the extent of chemical $\eathering seemed ro be jess as ekidenced by presence

of primarq minerals in tarious stages of alteration. Samples coliected from this profile

were named as 16 A to l6M from bottom to top.

2.2 Clay mineralogical studies

Cla) minerals are part of phyllosilicares and the> commonly have a particie

size of < 2 pm. X-ray Diffractometrq (XRD) is the most nideij used method for clay

mineral characterization. Since this facility was not available \\hen this stud) was

initiated, an attempt has done to use Fourier Transform Infra Red (FTIR)

Spectroscopy. which is less used in clay mineral studies compared to XRD for

characterization of clay mineral assemblage. But as the XRD facility was established

later, this was extensively used for the present study.

2.2.1 Separation of clay mineralsfrom bulk samples

For analyzing clay minerals, first they need to be separated from other rock

forming minerals in the bulk samples. As clay minerals have an average grain size of

< 2 pm they can be separated out from other minerals which are usually of larger

grain size based on their differential settling speed in a column of water due to

gravity. The separation procedure adopted for this study was based on method

described by Hardy and Tucker (1988).

Samples were mildly crushed, taking care not to grind them which will reduce

the size of the coarse grained non-clay minerals to the ciay-size range, to make the

large pieces in to smaller ones. Before suspending in settling columns, the samples

were mixed with distilled water and kept in ultrasonic bath for 30 minutes (Gipson

1963) to disaggregate the particles. If the sample contains significant amounts of

organic matter, the X-ray diffraction peaks will be broad and the background will be

increased. Hence, to remove the organic matter dilute hydrogen peroxide solution was

used. The samples were washed thoroughly with distilled water after this treatment.

A$er tnis. rhe sanpirs uere tier sieled to remoic: ?Be particiss caarscr thar: 63 pni

and defloecu;atec! b! rhe addition of sodium hexametaphosphaie solution 11 0 VO).

Afier the aboie treatments ihe sanpies were transferred to 1000 mi g!ass

c>!inders used as settling coiumni for separation of claq sized particles uslng Stoies'

Lau .iihich can he expressed as

where g is the acceieration due to grayit), a is the sphere radius. dl is the

densily of the particles. d? is the density of seltiing medium (usually water) and IJ. its

viscosit).. Table 2.1 gives the standard time of withdraual for different particle sizes

at different temperatures. The liquid-suspension in the top 5 cm of the column was

siphoned out after appropriate time which contains the clay fraction.

Table 2.1 Pipette withdrawal times calculated from Stokes' Law for spherical particles (SG = 2.65) in a settling column of water at different temperatures.

Temperature (in OC) Diameter

Finer Withdrawal Elapsed time for withdrawal of sample in hours (h), minutes than Depth (cm) (min) and seconds (s) (PN 20° 21° 22O 23O 24O 2S0

62.5 20 20s 20s 20s 20s 20s 20s

44.2 20 lmin 54s lmin 51s lmin 49s lmin 46s lmin 44s lmin 41s

Restir Restir Restir Restir Restir Restir

31.2 10 1 rnin 54s 1 min 51s 1 min 49s 1 min 46s 1 min 44s 1 min 41s

22.1 10 3 rnin 48s 3 min 42s 3 min 37s 3 min 32s 3 min 27s 3 min 22s

15.6 10 7 min 36s 7 min 25s 7 min 15s 7 min 5s 6 min 55s 6 min 45s

7.8 10 30min 26s 29min 41s 28 min 59s 28min 18s 27 min 39s 27 min 1s

3.9 5 60 min 51s 59 min 3s 57 min 58s 56min 36s 55 min 18s 54 min 2s

1.95 5 4h 3 min 3h 58 min 3h 52 min 3h 46 min 3h 41 min 3h36 min

0.98 5 16hi4 min ljh5O min l5h28 min 15h 6 min 14h 5 min 14h25 min

0.49 5 64h 54 min 63h20 min 6lh50 min 60h 3 min 48h59 min 57h38 rnin

For FTIR analysis the sample fraction withdrawn as explained above was

centrifuged to get the clay concentrate and dried in room temperature to get the clay

fraction in powder form. For XRD analysis the sample fraction withdrawn as

explained above was processed further using the procedure given in section 2.2.2

2.2.2 Prepurution rgfclay mineral samp!esfor X-ray Dvfrucfolajetty

.&her separating c l a ~ fraction fron: the buik sediments. saine chemical

pretreatmerits are necessan for cla) mineral identification using X-ra\ DiEractometer

(SRD). Cia) minerals can absorb anions and cations and hold them in an

exchangeable state otsing to their particular crqstal structure. In X-ray Diffraction

method, the characteristic basal spacing of the claq mineral is used extensively for

their identification (Broitn and Brindle 1980). The (001) spacing of oriented clay

depends on the type of cations in the interlayer region. In nature. clays and soils are

saturated xith various types of cations including ha-, ~a'-. VIg2-. K-. Hence, if they

are made mono-ionic, their identification bill be easier. For this purpose, different

aliquots of clays were saturated with Ca and K before their XRD identification. The

principle of ion saturation is that when the clay minerals are treated with a 1 M

chloride solution of the cation of choice. an exchange reaction \+ill take place,

replacing cation A? adsorbed on the claq mineral. with cation B from the solution

containing excess B cations. The ion saturation was achieved using the following

procedure of Brown and Brindley (1980).

Sufficient amount of sample in suspension was taken in centrifuge tube. To

that about 3 rnl of IN solution of required ion chloride was added and mixed

thoroughly using a cyclo-mixer. The solution was centrifuged and the supernatant

solution decanted carefully. This was repeated four times. After this the sample was

washed with distilled water followed by 50% alcohol washing and 100 % alcohol

washing (two times). Before each washing the sample was mixed using cyclo-mixer.

After the alcohol washing step -1 mi of distilled water was added to the centrihge

tube mixed thoroughly and a smear slide was prepared for XRD analysis.

The Ca- and K- saturated samples were first scanned at room temperature.

Another diffractogram of the Ca-saturated slides were obtained after subjecting them

to glycolation by placing the slides in a desiccator that contained approximately 0.25

litre of ethylene glycol and kept in an oven at 60°C for about 4 hours. The K-saturated

slides were scanned after heating to 1 10°C (overnight), 300°C (4-5 hours) and 550°C

(for 4-5 hours).

2.2.3 Preparation i?fclay mitzerad samples$~r Fourier Tmnsfi)rm I~gra Wed (FTIR,

Sperbrriscopy

The cia) fraction form :hin plates ithen dr) Hence. these \+ere siighrlj

crushed in order to get them in ponder Fam. Pregrounding is necessar) to avoid

interference from particles ~ i t h s i ~ e s greater than 9 pm. The coarser particles m i l l

cause scattering of incident !R radiation and the distortion and broadening of

absorption bands. Grinding uas done using an agaie mortar and pestle. Sample

po\~ders of clay )<ere dispersed in KBr pressed discs and the spectra were taken.

2.2.4 Fourier Transform lnfra Red (FTIR) Spectroscopy

A few selected samples of claq fractions aere studied using ABB BOMEM

MB 104 Fourier transform infrared (FTIR) spectrometer in the Department of

Chemistry, Pondicherry University. The spectral range of the instrument uas from

400 to 4000 cm-'. Pure samples of kaolinite and smectite obtained from Dr. Kailasa

Pandarinath of Ocean Science and Technology Cell, Mangalore Universio Itere also

analyzed to study the spectra of individual clay minerals. To provide adequate

characterization of a clay mineral by IR spectroscopy, the spectrum should be

recorded over the range 4000 to 250 cm-' and if possible to 200 cm-' (Russell and

Fraser 1994). But the instrument used for this study could record only up to 400 cm-'

and also the spectra below 600 cm-I was not very good.

2.2.5 XRD analysis of clay minerals

Before the XRD facility was established in the Department of Earth Sciences,

Pondicherry University. some preliminary XRD analyses were carried out in the

School of Environmental Sciences. Jawaharlal Nehru University, New Delhi usins the

dried clay powders. Later, a few samples of clay slides prepared by the procedure

described above were analyzed in the National Bureau of Soil Survey and Land Use

Planning (NBSS&LUP), Nagpur. Subsequently all the samples were analyzed using

the newly established PAnalytical XPertProTM X-ray Diffractometer (XRD) equipped

with a copper target, operating at 40 kV and 25 mA in the Department of Earth

Sciences, Pondicherry University. All the XRD charts shown in Chapter 3 are from

this analysis. XRD patterns of oriented clay slides were recorded using a step size of

0.02" 28 and a scan speed of 0.6" 20 / min and scanned from 2 to 30' 20. For each

sa:nple the fc,i;ntbip.g slz scans \!ere made: ( i 1 Ca-satur3te.d r l i h->d;~r;l?,~d 3; room

temperature i 3 ) afier gl!co,at:cn and after hearir,~ io (4) 1 1OSC, 15) 2OO"C and t6)

i i ( ) "C. - v

Cia> minerals iserr: identified foiio~in; the methods of Bro~xn and Brindle)

(1980). A semi quantitarihs estimation of cia). minera!~ &as done from peak area

using the fomu!a

9'o cia) mineral = 100 \i [I ; ,., 1 Z 1 n3 Ili-d,J in hat sample

U here I = peak area of the clay minerals used For samples nhere smectites here

present. the gl~colated panerns were ilsed fbs semi-quantification. For samples

viithout smectites, Ca-saturated patterns v.ithout glycolation were used. The peaks

used for semi quantification are: 17 A - smectites. 7 4 - kaolinite-smectite and

kaolinite. lob, - clay mica. 4.8 a - gibbsite, 1.18 A - goethite.

2.3 Major and trace element geochemical studies

2.3.1 Preparation of sample powder for digestion

Bulk samples collected from different weathering profiles were crushed using

a steel mortar and pestle to approximatelq -80 ASTM mesh size. About 150 g of

sample from this was taken by coning and quartering and crushed further using a ball

mill. About 30 g of sample powder taken through coning and quartering from the ball

mill crushed portion was further crushed to -200 mesh size using an agate mortar and

pestle and stored in plastic containers for geochemical analysis.

2.3.2 Sample digestion procedures for major and trace element analysis

For the determination of major and trace elements, excluding silica, zirconium

and rare earth elements (REE). "B solution" after Shapiro and Brannock (1962) was

prepared as per the procedure described below: 0.5 g of each sample was taken in a

~e f lon@ crucible. 10 ml of HF, 5 m1 of HNO; and 2.5 ml of HC104 were added to the

crucible and digested overnight at 120°C with the lid on. After digestion the crucible

contents were evaporated to dryness. 5 ml of HF, 10 ml of HN03 and 1 ml of HC104

were then added to the crucible and evaporated to complete dryness. 10 mi of HN03

was added to the crucible and dried to remove traces of fluorides followed by the

addition of 10 ml 6N HC1 and drying. The dried crucible contents were dissolved in

dilute HCI and made up to 100 ml volume using distilled water. This formed 200

tirnri dilurea 5oliition F,?r the anai>>is of tract elemen:&. For major element anai>sis

this soiution aias further diluted to 300ii times.

Silica and zirconium \%ere determined from solutions prepared b~ lirhium

meta'sorale fusion me~hod. For this 0.2 g of each sample a a s fused ~ i t h 0.8 g of

LiBO? in graphite crucibles zt 1050°C in a muffle furnace for 15-30 minutes. Afiier

ignition. the melt \%as poured direct15 into a beaker containing IM nitric acid to

shatter the molten bead in to srnaii fragments that \+i l l dissolve rapid]!. For better

dissolution. magnetic stirring bars \%ere placed inside the beaker and stirring

commenced before the sample bas poured in. After complete dissolution of the bead.

the solutior,s were transferred to 100 mi ~olumetric flasks for making up the volume.

This formed 500 times diluted solution ahich &as used for the anaiqsis of zirconium

and a further dilution of 2500 times \%as used for silica anal~sis.

2.3.3 Sample digestion and pse-concentration procedure for Rare Earth Element

unalysis

The REE analysis involved their separation and pre-concentration as a group

by cation-exchange chromatography. AG 50W- X8 of 100-200 mesh size cation-

exchange resin was used in a two column procedure involving HNO- and HC1 3

columns. For digestion, 0.5 g of each sample was fused with a mixture of 1 g NaOH

and 1.25 g Na202 in nickel crucibles at 800°C for 15 minutes using a Mecker burner.

After fusion, the crucibles were allowed to cool and filled up to 3/4Ih volume with

distilled water and left overnight to permit the melt to disintegrate. The crucibles were

then scrapped with ~eflon' rods and the contents were transferred to 500 ml glass

beakers by washing repeatedly with 6 N HC1. The solutions were kept on hot plate for

evaporation till silica gel forms. The silica gel was filtered off b> washing with 6 N

HC1 and the solutions were again dried completely. The dried residues were picked up

in 30 ml of 1 N HC1 and transferred to centrifuge bottles. Around 11 drops of Phenol

red indicator was added to all bottles and the colour of the solution became orange.

1:l Ammonia solution was then added to all the bottles till the colour changed from

orange to pink and a brown coloured precipitate was seen. The solution was then

centrifuged and the precipitate was separated by decanting the supernatant solution.

The precipitate was dissolved in 6 N HCl and transferred to ~e f lon@ beakers for

drying. The dried residue was picked up in 30 ml of 1 N mO: for loading to the

SINO- coiumn. The solution iaas loaded to !he coiurnri afirr equilibrating \t i th N

HhCd:. .After the loaded solution \{as passed throuzh the column. 51) rn! of 1.74 N

HNQ3 \+as passed and the coliected so!ution nas discarded. Then 180 mi of 6% WN03

\\as passed and collected in TeilonQeakers. This solution was dried and re-dissolved

in 30 mi of 1 N HCl and loaded in MCi column after equiiibrating the column with 10

mi 1 X MCI. After the loaded solution was passed through. 70 mi 1.74 N HCI was

passed through the coiumn and the collected solution was discarded. Then the REEs

were eluted i b i r h 330 ml of 6 N HC1. The collected solution is dried and dissolved in

l0ml of 1 N WSOj for analysis by ICP-AES.

2.3.4 Elemental analysis using ICP-AES

Elemental analjses aere carried out in the Department of Earth Sciences,

Pondicherq Universitj using an Inductively Coupled Piasma Atomic Emission

Spectrometer (ICP-AES) (Jobin Yvon bltima 2). The soiueion B prepared as

described in section 2.3.2 were analyzed for the determination of major elements and

trace elements, such as, Ba, Cr, Ni. Sr. Y, Zr, Th, Co and Zn. Silica and Zirconium

were determined from lithiun: metaborate fused soiutions. Rock standards AMH and

DGH supplied by the Wadia Institute of Himalayan Geology. Dehradun (Saini et al.

1998) and internal rock standards 86-69, 21-6 and VM-9 that were calibrated using

the USGS rock standards BHVO-I. RGM-1 and BCR-2 were used for calibration of

ICP-AES for major and trace element analysis (Krogstad et ul. 1995; Rajamani et a1

1985). For determination of thorium. calibration of ICP-AES was done using

elemental standards. Rare Earth Elements were determined on pre-concentrated

solutions after calibrating the ICP-AES with the standards AMH. DGH, 86-69 and

90-57. REE values of the internal rock standards were previously determined using

isotope dilution technique at Stony Brook, New York, USA (Krogstad et ul. 1995)

and these values were used for calibrating ICP-AES for REE analysis. The accuracy

of the analysis was checked by analysing the standards AMH and DGH as unknowns.

The precision of the major, trace and REE analyses were checked by replicate

analysis of samples. The estimated reproducibility expressed as percentage of amount

present for the major elements was < 3% for Si, A1 Ti, Fe and Mn, < 7% for Mg and

Ca and 10% for Na and K. The reproducibility for the trace elements was < 5%.

2.3.5 Drf~rmi~intio~z (fLo.s$ OM IgilitiC)n (LO4

Sampies usre kept ic a hot air oten at l i09C oien~igh: ro reitlake ;he

moisture in rhe samples. About 1.8 g of sample raken in a silica crricible b i t R lid i+as

kept inside a muffle furnace at 1090°C for 2 hours. Then it mas alloned to cool to

room temperalure inside a desiccator to aioid absorption of moisture and i$eighed

again. LO1 !$as then calculated using the foilobi ing formula:

LOI (wight %) = 100 X ((n2-n;) in>-n,))

Where. n~ is the \\eight of empb cmcible. n: is the total weight of crucible and

sample before keeping inside furnace and n; is the total \\eight of crucible and sample

after hearing to 1 OOO°C.

2.1 Rb-Sr and Sm-Nd Isotope studies

2.4.1 Separation of Wferent grain size fractionsfor isotope studies

Rb-Sr and SM-Nd isotope studies were carried out on different grain size

fractions in the silt and clay range from the selected weathering profile samples. The

grain size fractions used were 63-20 pm, 20-6 pm, 2-0.6 pm. 0.6-0.2 prn and < 0.2

pm. The coarser fractions were separated from the bulk samples by suspension

method and the finer fractions by centrifugation method. Disaggregating reagents like

sodium hexametaphosphate were not added to avoid external contamination during

sample preparation. The times and depths of withdrawals for particles were calculated

using the following formula as per Folk (1971).

T,,, = Depth in cm. 2.1

1500*A*d2 (mm)

In which T is the time in minutes: d2 is the square of the particle diameter in

mm: and A is a constant which depends upon viscosity of the water (a function of

temperature), the force of gravitation, and the density of the particles whose value was

taken from Table No.2.2.

Table 2.2 b l u e s of 4 in eqilation 2.6 for saricxs particle densities and temFcratures (Fcib i9'1;.

- --- - - -- --- --- -- - - Clays Amphibole

Temperature "C Quartz DernsiQ 3.00 gicc DensiQ?; 3.35 glcc

Densi3 2.55 gicc

16 3.23 3.92. 3.60

20 3.57 4.33 5.08

24 3 93 4.76 5.60

28 4.30 5.21 6.2 1

32 4.68 5.57 6.60

Bulk samples were first wet sieved to get rid of grain size fraction more than

63 pm. The < 63 pm fraction &as transferred to 1000 m! cylinder. mixed well and

allowed to stand still for the appropriate time calculated for withdrawal of < 63 pm

fraction. This fraction was withdrawn first and transferred to another 1000 rnl

cylinder. Afier withdrawing sufficient fraction to fill the cylinder, the second cylinder

was shaken well and allowed to stand still for the withdrawal of < 20 pm size

fraction. The < 20 pm fraction was withdrawn repeatedly and suspended in a third

cylinder till almost all the particles less than that size were removed. The second

cylinder thus contained the grain size fraction 63-20 pm. From the third cylinder

containing < 20 pm, < 6 pm fraction was separated in the same way leaving the third

cylinder with the fraction 20-6 pm. Similarly < 2 pm Fraction was withdrawn from

the < 6 pm fraction and this fraction was further split in to three fractions using

centrifugation method.

The < 2 pm fraction was split again in to three fractions viz. 2-0.6 pm, 0.6-0.2

pm and < 0.2 pm using centrifugation method. The time and speed of centrifuging

was determined by the following formula of Hathaway (1956).

where, T is total time in seconds (s), t, is time of acceleration (s), t d is time of

deceleration (s), q is viscosity of the medium (poises), R1 is initial distance from

rotational axis (cm), RZ is final distance from rotational axis (cm), r is particle radius

Llalem33e sehz pasuads!p uollnlos Jagell jo lunoure ayL .s!sLlouo a1 loj pasn

aq 01 uorpey aqlol pappe seM (100~ pueuv) uo!lnIos la3e.u adolos! paxp pawq!Ie3

i(lsno!,\a~d 'asobnd s!q$ JOJ -sluaurala jo suo!paua3uo3 ayl jo uo!leu!uualap ayl .IOJ

pasn s! amix!ur ayljo uop!sodwo3 3!dolos! ayl put? (.IS %a) S~IL aql8u!sn pamseaur

JO (qa 3.a) paxg laqqa s! luaurala leqljo uo!1!soduro3 s!dolos~ ayL 'u~ouq Klas!3ald

an uognlos ~a3s.u aql u~ uoy~!soduro~ 3!dolos! sl! pue pau!urla$ap aq 01 luaurala

adolos! jo mnoure u~ouy e jo uo!l:ppe saizlo,\u! s!s,i[eue uo!ml!p ado~os~

.(a~> uo!ml!p adolos! /Cq suo!ltqua3uo3 p,q pue US '.IS 'qx 30 uo!leu!uuaiap ayl JOJ pasn

sehi laylo aql sealay,hn p~ pue IS~O (31) UO!I!SO~UIO~ 3!do~os! aqljo uo!yeu!uualap aql

JOJ pasn SBM SUO!I~~JJ ayljo aug .suo!pey ow o~u! ~yds pue 13~ alnl!p u! paAloss!p

alaM s$ua$uo3 layeaq aqt uayL .iClala1duro3 payp pue Sam!! o,u pappe uayl sehz 13~

pa$e.iwaouo:, jo [ur I lnoqv .Ziu!hp pue sarug aaq CONH jo 1" I inoqe 8u!ppe Lq

8u!sn $no paiues seu s!sipeue s!dolos! p~-rus pue IS-qa JOJ uoysaS!p aldures

yon adolosi loj way$ Su!sn

a~ojaq papp pue 8uiSnj!~lua3 iq pai~~lirasrmos ala%\ suojlseq az!s aifr ~lv .spuo3as

8s pug alnu!ru $z loj ~dtf 000t. :e Su!8nj!.iluas iq pajnas alati wri z.0 wyl ~asleos

sapzled pue spuosas 55 pue salnup 01 loj g<h;d;ti 000~ ~e Su!Snj!iluas iq pquas aJaM

wn' 9.0 ueyl las.1~03 sal~y~d .spuo~as cg ptie alnuy i ~oj p,dx 000~ le Su!8r,j!.i~uas

iq painas a.zay\ rud ueql daveos sa~s!vt?d -suo~!e~nnle:, azoqo aql uo pasea

xCms 31 ojpaut ayljo il!suap

Sl 'd ~E'E" i &I?@) aj?:1.~ed atj? JO <>!map S! d -(xs \ai: il!~oja~ reln5ue si \ -(uI~)

The 1C' and the 1D frzctions \+ere passed through 3 ml quartz columns filled

t i l t h Bio-Rad 4G50-\h X8 cation-exchange resin (200-400 mesh) calibrated for the

eler~lents Rb. Sr, Ca. Fe. Mg. .4l and REE (Anand 2007). Rb and Sr were collected

i t~t l? 2 U HCI and REE as a group )+as co!lected with 6 h HCl. Rb and Sr fractions

thus separated nere purified further by passing through a set of secondary Bio-Rad

(PP) 2 mi columns that uere also filled with Bio-Rad AG50-WX8 cation-exchange

resin (200-400 mesh) and calibrated for the above mentioned elements. Rb and Sr

tiere collected from this column with 2 N HCI and were dried.

Sm and Nd here separated from the REE solutions eluted as a group from HC1

columns using HDEHP @-ethyl hevyl hydrogen phosphate) columns (procedure

modified from Richard et a1 (1976) and Gioia and Pimentel (2000)). The REE

fraction collected from HCI column was dried and dissolved In 200 pl of 0.18 N HC1

for loading on the column. The LC and ID REE fractions were passed through

different HDEHP columns. Nd was collected with 0.3 N HCI and Sm was collected

aith 0.4 N HCI. A drop of -0.5 M H~POI was added to the collected Nd and Sm cuts

and dried to ensure visibility while loading onto the Re filament.

2.4.3 Muss Spectrometry

Loading of Rb and Sr for mass spectrometry was done using the TaO

activator. One p1 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 pl

of 1N HC1 and loaded on top of TaO on the filament and dried at 0.5 A current. 1 p1

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 TIMS for analysis. Sr was

dissolved in 1 pI of IN HNO:, and loaded between hvo 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.

Nd and Sm were dissolved separately in 1 p1 of 1 N HNO3 and were loaded on

pre-warmed rhenium (Re) double filaments for mass spectrometry. A double filament

assembly includes two filaments of which one is used as sample evaporation filament

and the other is used as ionization filament. The sample was dried at 0.5 A current.

The filament was then heated to dull red colour for about 20 seconds until all the

H3P04 evaporated and were loaded in the turret of the TIMS for analysis.

During :he course of this stud) Sr iso:ope standard SRZl 987 and h d isotope

stcndard, La Jolla and A~nes Rere run rrpeatedl). instrumental mass fractionation

during tne deterininslion of Sr and Zd isotopic compositions in standards and sampies

iras corrected bq internall norrnaiizing the measured ratios bq the ratios S 6 ~ r / s 8 ~ r =

0. : 194 for Sr and ""hdl'"~d = 0.72 ! 878 for t'd using exponential fractionation law.

The mean raiue obtained on 40 analqses of SWM 987 for Sr is 0.710244 i: 5. The

mean baEue obtained on 35 analqses of La .ioEla for Nd is 0.51 1848 i 4 and 25

anailsis of Ames for Nd is 0.52 1969 = 3. Procedurai blanks mere < 0.2 ng for Rb, < 3

ng for Sr, < 0.2 ng for Sm and < 0.3 ng for Nd. Sample to blank ratios were greater

than 100 for Sr and 600 for Nd and thus the effect of blank on Sr and Nd isotope

analqsis is considered negligible.

The isotopic mass fractionation in the mass spectrometer can not be corrected

using an internal normalization ratio for the isotope dilution anallses as the isotopic

compositions are altered due to the addition of isotopic tracer. Therefore. suitable

fractionation correction factors were determined for Rb. Sr, Sm and Nd from repeated

analyses of isotope standards, such as. SRM987 for Sr, La Jolla and Ames Nd

standards for Nd. calibrating solution prepared from Johnson Matthey Rb metal for

Rb and SPEX CertiPrep Sm elemental standard solution for Sm. The fractionation

correction factor was calculated from the formula of the form.

where, F is the fractionation factor; m - measured ratio; t - true ratio as determined

from standard runs; AM - mass difference between the two isotopes considered. The

fractionation factor was applied to the measured isotopic ratios (ID) of standards and

samples and corrected for the isotopic mass fractionation.