Proceedings of the National conference on Advances in Lasers and Spectroscopy (ALS-2012) 01-03 November,

2012, pp.123-130, ISM Dhanbad, India

Paper Code. No. TP-xx

TP-xx-1

QUANTITATIVE ANALYSIS OF FLUID INCLUSION STUDY

VIS-À-VIS MANTLE EVOLUTION USING LASER RAMAN

SPECTROSCOPIC (LRS) TECHNIQUE.

Javid Ahmad Dar and R.K.Dubey

Department of Applied Geology, Indian School of Mines, Dhanbad 826 004, (Jharkhand) India.

E-mail:-javidgeor@gmail.com and rkdubey1085@hotmail.com

Abstract

The Laser Raman Spectroscopy (LRS) in geological perspective works on the basis of inelastic

scattering of monochromatic light from a laser in visible, near-infrared, and near

ultraviolet ranges through the fluid inclusions of various chronological orders. By measuring the

peak positions relative to the incident light it is possible to measure the energy of the normal

modes of vibration and identify the symmetry and chemical structure of the examined molecules

as per symmetry and selection rules. The present study incorporates the use of LRS technique for

the study of different kinds of inclusions present in the various minerals. The inclusions reveals

the spectral shifts (Raman shift) from an excited laser waves, which has resulted from the

molecular vibrations of chemical bonds in the different immiscible phases (meltfluid, fluid-fluid,

fluid-gas).

The identification of these fluid phases based on the peaks of spectrum and quantified values of

their relative intensities obtained from Raman microprobes was utilised to define the

dissimilarity of scattering patterns as the function of temperature, pressure, fluid composition and

their phases of formation. The various scattering patterns analysed for different kinds of

inclusions present in minerals reveals the higher stretch of materials (Olivine) and compression

decompression phenomena enhancement towards the shallow depth of the mantle and lower

crust. Besides, these the pattern delineated in pyroxene suggest the higher concentration of

metallic component at higher temperatures and pressures conditions. Hence, the mantle of the

Earth appears to be comprised of different layers of specific temperatures, pressures and

viscosities.

Introduction

The fluid inclusions are the principle components that can be used to analyse different types and

phases of minerals. Fluid inclusions are the small amounts of relict fluids trapped in the minerals

that provide the evidence regarding the active participation of fluids in geological processes.

They provide an estimate of fluid trapping temperatures and pressures and fluid densities. In the

Proceedings of the National conference on Advances in Lasers and Spectroscopy (ALS-2012) 01-03 November,

2012, pp.123-130, ISM Dhanbad, India

Paper Code. No. TP-xx

TP-xx-2

process of cooling and crystallization of magma, one or several events of the exsolution separate

immiscible fluid phases. The processes of magmatic immiscibility (meltfluid, fluid-fluid, fluid-

gas) are well recorded in minerals in the form of fluid inclusions [1].These also provides the

evidences hypersaline fluid phase evolutions from the heterogeneous melt containing variable

proportions of fluids [1,2]. Moreover, the immiscible phase separation during cooling and

crystallization of the magma is an inherently fugitive phenomenon which provides the remaining

evidence of such processes. In addition, the information allied to these fluid inclusions at

variable temperature (T), pressure (P) and composition (C) is a useful tool in mineral exploration

due to proper understanding of the ore forming fluids and petrogenetic history of late

hydrothermal fluids. The application of Laser Raman Spectroscopy (LRS) offers the exciting

opportunity to interrogate rocks in their natural geological context due to the ability of the

method to collect the information related to constituents, textures and morphological features of

mineral/rocks [3, 4]. Besides, this technique is found to be useful for extra-terrestrial exploration

programmes such as in situ exploration on Mars, Venus, and the Moon,

In view of wide applicability and relevance of the LRS method the present study is attempted to

analyse the number of minerals based on the different fluid inclusions categorization. For the

purpose, the various databases (fingerprints) obtained from LRS were used to identify the

different minerals.

Methodology

The LRS technique scrutinizes the roughly polished surfaces in which most of the spectra is

taken by using an objective with a low numerical aperture (20´, NA = 0.4, long working

distance) by using an automated scanning procedure. The diameter of the laser beam ranged

from ~1 to ~5 mm depending on the precision of the focus, which varies along the traverses. The

spectral quality for mineral identification is essentially the same on the rough surface as on the

polished surface [5]. The schematic set up of LRS is shown in the Fig.1. The setup works on the

basis of inelastic scattering of monochromatic light from a laser in the visible, near-infrared, and

or near ultraviolet range through the minerals and fluid inclusions of various chronological

orders (Fig.2). The LRS observes the spectral shifts (Raman shift) from an excitation laser

wavelength caused by the molecular vibrations of chemical bonds in a material.

Proceedings of the National conference on Advances in Lasers and Spectroscopy (ALS-2012) 01-03 November,

2012, pp.123-130, ISM Dhanbad, India

Paper Code. No. TP-xx

TP-xx-3

Fig.1. Schematic representation of Laser Raman Spectrometer for the study of

various inclusions.

Laser Mirror

Interference

Polarization rotator

Mineral Sample

Collecting lens

Polaroid

Spherical Mirror

Double Grating Spectrometer

CCD

Detector

Focusing lens Amplifier

PC

Ray

leig

h

scat

teri

ng

Sto

kes

scat

teri

ng

An

ti-S

tokes

scat

teri

ng

Ground

state

Virtual Energy

level

Ener

gy

V0

V1 V1

V0

V1

V0

Fig.2. Principle of Laser Raman inelastic scattering and change of energy states.

Proceedings of the National conference on Advances in Lasers and Spectroscopy (ALS-2012) 01-03 November,

2012, pp.123-130, ISM Dhanbad, India

Paper Code. No. TP-xx

TP-xx-4

Spectral Variations and Fluid Inclusions

The Raman spectra for the different mineral inclusions like silicates, oxides, hydroxides,

carbonates etc., with associated liquid and gaseous phases shows the sharp and mostly non-

overlapping spectra in the particular range. These different spectral patterns occur in relation to

their different structures (monomers, chains, layers, frameworks) and different crystal structures

(e.g., monoclinic versus orthorhombic crystal systems) Fig.3.

The various peaks for other groups are easily distinguishable from those of the silicates, which

are important for identifying sedimentary minerals (e.g., carbonates, sulphates, clays). Some

peak frequencies within a given oxy-anion group depend on cation proportions (e.g., Fe2+

and

Mg2+

in olivine, and Fe2+

, Mg2+

, and Ca2+

in carbonates and pyroxenes [6]. Therefore, on the

basis of LRS technique the examination of dominant minerals inclusions showing different

spectra is studied below.

(C-C) Sulphates Carbonates (C-H)

Oxides

Hydroxides

Silicates (C-C)

(C=O)

H20 O-H

Laser Raman Spectra of various inclusions

Fig.3. Characteristic Laser Raman Spectra of various inclusions.

Proceedings of the National conference on Advances in Lasers and Spectroscopy (ALS-2012) 01-03 November,

2012, pp.123-130, ISM Dhanbad, India

Paper Code. No. TP-xx

TP-xx-5

Pyroxene

The Raman spectral pattern of pyroxene in various inclusions shows the three spectral regions:

(1) near 1000 cm-1, (2) near 670 cm-1, and (3) 400 to 200 cm-1. The frequencies of these Raman

peaks in these regions shift systematically with Mg/Fe content of the pyroxenes. The Spectra

shows the different patterns for the three structural types orthorhombic, monoclinic and triclinic

pyroxenes [7, 8].

Olivine

Raman spectroscopy is highly sensitive to olivine, which does not give the specific pattern in the

various minerals and rock samples [7, 9]. The two major peaks observed (815 cm-1and 847 cm-

1) belong to the SiO4-streching mode are visible. The observation for the fayalite shows a change

in the intensity of these bands, which might be the result from iron in olivine where the magnetic

interactions can take place.

500

1000

200 400 600 800 1000 1200 1400

335

67

8

10

06

660

Raman Shift (cm-1

)

Ram

an I

nte

nsi

ty (

arb

.un

its)

700

1400

200 400 600 800 1000 1200

287

57

6

81

5

84

7

94

6

SiO2 stretch

Raman Shift (cm-1

)

Ram

an I

nte

nsi

ty (

arb

.un

its)

Proceedings of the National conference on Advances in Lasers and Spectroscopy (ALS-2012) 01-03 November,

2012, pp.123-130, ISM Dhanbad, India

Paper Code. No. TP-xx

TP-xx-6

Magnetite

The spectrum of Magnetite shows the broad pattern with only one major peak near 670 cm-1

and in the 387 cm-1 region.

Pyrrhotite

Pyrrhotite has more than one structural form therefore the examined Raman spectral patterns

gave different positions. The Raman spectra have a main broad band centered near 430 cm-1,

which is similar to the spectrum of magnetic pyrrhotite [7, 8].

Tremolite (amphibole)

Tremolite presents the only one large shift at 548 cm-1, which belongs to the Al–O deformation

mode. The very small shift only in vacuum at the 674 cm-1 band fits to the symmetrical Si–O–Si

and Si–O vibrations [8, 9].

500

1000

200 400 600 800 1000 1200 1400

67

0

38

7

Raman Shift (cm-1

)

Ram

an I

nte

nsi

ty (

arb

.un

its)

500

1000

200 400 600 800 1000 1200 1400

430

Raman Shift (cm-1

)

Ram

an I

nte

nsi

ty (

arb.u

nit

s)

Proceedings of the National conference on Advances in Lasers and Spectroscopy (ALS-2012) 01-03 November,

2012, pp.123-130, ISM Dhanbad, India

Paper Code. No. TP-xx

TP-xx-7

Plagioclase Feldspar

Feldspar is generally associated with the aluminosilicate magmas and the resulting minerals. The

feldspar shows the large shifts in the region of 200 cm-1 to 600 cm-1 with dominant peak in

309cm-1 and 503 cm-1 [9, 8].

Gypsum (hydrous sulfate)

The strongest Raman shift of gypsum is visible in the translational modes H2O-Ca at 316 cm-1.

Minor shifts are visible for the stretching vibration mode of water at the characteristic band of

941 cm-1 and at the symmetric bending of the SO4-tetrahedra at 594 cm-1 [7, 10 ].

210

230

300 500 700 900 1100 1300 1500 6

74

220

13

40

310

54

8

Si-O-Si, Si-O

Al-O

Raman Shift (cm-1

)

Ram

an I

nte

nsi

ty (

arb

.un

its)

900

1800

200 400 600 800 1000 1200 1400

430

503

390

197

280

559

1096

Raman Shift (cm-1

)

Ram

an I

nte

nsi

ty (

arb.u

nit

s)

Proceedings of the National conference on Advances in Lasers and Spectroscopy (ALS-2012) 01-03 November,

2012, pp.123-130, ISM Dhanbad, India

Paper Code. No. TP-xx

TP-xx-8

Anhydrite (sulfate)

The spectra of anhydrite present the strongest shift at the weakest band at 234 cm-1, which

belongs to the vibrational mode of Ca-O bonding. Further shifts are visible at 675 cm-1 (due to

sulfate tetrahedra) [7, 11].

Calcite and Quartz

The main peak position in the calcite shows in the range of 200 cm-1 to 400 cm-1 and the quartz

in the 1000 cm-1 to 1200 cm-1 due to Si-O2 stretch modes [11].

The studied CO2 and H2O inclusions also signify the sharp peak spectra due to presence of OH

stretching modes. The broader H2O bands result from hydration of less specific sites [12, 13, 11,

14].

200 300 400 500 600 700 800

23

4

31

6

59

4

675

Gypsum

Anhydrite

H2O-Ca

Bending of SO4-tetrahedra

Ca-O

Raman Shift (cm-1

)

Ram

an I

nte

nsi

ty (

arb

.un

its)

500

1000

200 400 600 800 1000 1200 1400

670

38

7

SiO2 Stretch

Calcite

Quartz

Raman Shift (cm-1

)

Ram

an I

nte

nsi

ty (

arb.u

nit

s)

Proceedings of the National conference on Advances in Lasers and Spectroscopy (ALS-2012) 01-03 November,

2012, pp.123-130, ISM Dhanbad, India

Paper Code. No. TP-xx

TP-xx-9

Fluid Inclusions and Mantle Evolution

Fluid inclusions entrapped in various minerals provide the direct information of the mantle

processes. They are important for the understanding the nature of the mantle and the varieties of

processes such as metasomatism, partial melting, fuid/melt percolation melt and fluid inclusions

in minerals as a sample for the study of the nature and evolution of the mantle fluids. The

enrichment of the clinopyroxenes in Al2O3, TiO2, Na2O, and Zr, and the presence of fluid

inclusions in the xenoliths provide strong evidence for fluid-related cryptic metasomatism of the

minerals/rocks [15]. The presence of magnesite and quartz in various inclusions are the products

of a post entrapment carbonation reaction, whereby the reactants are the CO2-richfluid and the

host orthopyroxenes. The lack of water, observed in several fluid inclusions shows the evidences

for dry conditions in upper mantle sources. However, due to the rapid rate of diffusion of water-

derived species in olivine the low hydrogen concentration within fluid inclusions in olivine is not

indicative of low water content in the mantle [16].

The study of the above mentioned inclusions with the use of LRS technique also provides an

estimate of the pressure of trapping. If the temperature of trapping is known, then the pressure of

trapping is given by the intersection of the fluid inclusion isochore (line that represent the range

of P-T conditions over which a fluid of that density was trapped) with the isotherm, [17]. In

upper mantle xenoliths the co-genetic relationship between fluid and melt inclusions allows to

constrain the P-T trapping conditions. Therefore, the homogenization temperature of the melt

inclusions is genetically related to the fluid inclusions and is considered as being close to the

trapping temperature. This assumption and the estimated density at the time of trapping allow an

estimation of the pressure prevailing at the time of trapping.

Conclusion

The study concludes the importance of Raman spectra for identification of minerals and history

of their formations in the interior of the Earth. It suggest the different layers of mantle with

defined set of temperatures, pressures and fluids responsible for the different surface and

subsurface geological activities with the subsequent mineral genesis. The study also reveals the

information related to existence of metastable phases during the crystallization of the melt.

Acknowledgement

The authors thankfully acknowledge the financial assistance provided by the University Grants

Commission under the CSIR-UGC (NET-JRF) and Research Project Scheme to carry out this

work. Further, the authors are also thankful to Prof.D.C.Panigrahi (Director) Indian School of

Mines, Dhanbad-826 004, India for their inspirations and administrative supports.

Proceedings of the National conference on Advances in Lasers and Spectroscopy (ALS-2012) 01-03 November,

2012, pp.123-130, ISM Dhanbad, India

Paper Code. No. TP-xx

TP-xx-10

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