Fluorine-Rich Clinohumite from Ambasamudram Marbles, Southern India: Mineralogical and Preliminary FTIR Spectroscopic Characterization

Mineralogical Magazine, August 1998, Vol. 62(4), pp. 509-519

Fluorine-rich clinohumite from Ambasamudram marbles, Southern India: mineralogical and preliminary FTIR spectroscopic characterization

M. SATISH-KUMARAND NAOYUK/NIIMI Department of Geosciences, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka-558-8585, Japan

ABSTRACT

Humite group minerals occur in the marbles of granulite grade at Ambasamudram, southern India. Detailed mineralogical and mineral chemical characterization indicate the mineral is a flourine-rich titanian-poor variety of clinohumite. Average MTi/Si values of 2.22 with typical XRD pattern indicate the mineral to be clinohumite. Petrological constraints on the clinohumite formation shows a high temperature (>700~ and low aco2 during its formation. The fluorine content of these clinohumites is the highest reported in any environment, with F/(F+OH) ratio reaching a value of 0.70. The high fluorine content reflect the high P-T condition of formation. The OH content of the clinohumites is around 0.59 mole fraction. Preliminary FT1R spectra of the clinohumites show eight sharp absorption peaks between wave numbers 3700 and 3400 cm -j and a broad absorption band with a peak at 3840 cm -1. The sharp peaks are due to OH in the clinohumite. The high fluorine content of the Ambasamudram clinohumites possibly resulted from the isochemical reactions involving (OH-F) silicates such as amphiboles or phlogopites. The internal fluid buffering is also supported by the stable isotope as well as the petrological studies of the marble assemblages.

KEYWOROS: fluorine, clinohumite, mineralogy, FTIR, India, humite.

Introduction clinohumite and titanium rich variety is commonly described as titanoclinohumite. THE humite-group consists of four minerals, Contrasting views have been proposed as to the norbergite, chondrodite, humite and clinohumite. possibility of clinohumites acting as H20 The group is defined by the general formula reservoirs in the upper mantle (Aoki et al., 1976; Trommsdorff and Evans, 1980). nMg2SiO4.Mgl_xTix(OH,F)2_2xO2~ Humite-group minerals were reported from the where n = 1 for norbergite, n = 2 for chondrodite, marbles of southern Indian granulite facies n = 3 for humite and n = 4 for clinohumite. The regional metamorphic terrain by Krishnanath minerals of the humite-group have a limited (1981). In this study we present results of paragenesis and occurrence. Metamorphosed and mineralogical and mineral chemical features of metasomatised limestones and dolomites adjacent clinohumite. Preliminary FTIR spectroscopic to acid plutonic rocks have humite minerals characterization of clinohumite is also presented. typically poor in titanium and rich in fluorine Based on the evidences presented here, we (Fujino and Takeuchi, 1978). Contrary to this, the evaluate the possible source and movement of humite-group minerals in rocks of ultrabasic volatiles in marble of the present study area. compositions, including carbonatites and kimber- lites (McGetchin et al., 1970; Aoki et al., 1976) Regional geological situation and serpentinites (Trommsdorff and Evans, 1980) are enriched in titanium and generally contain less The Kerala Khondalite Belt which forms the fluorine. Ti usually substitutes for Mg in southern part of the granulite facies segment of

1998 The Mineralogical Society M. SATISH-KUMAR AND N. NIIMI

southern India is a vast metasupracrustal terrain. for a peak of 750_+ 50~ and 5 + 1 kbar (Chacko This belt is bounded to the north by the et al., 1987; Santosh et al., 1993). Achankovil Shear Zone and to the south by the The Achankovil metasediments (cf. Bartlett, Nagercoil massif charnockites (Fig. 1A). A recent 1995) comprise a narrow belt of young (c. classification of this region identifies the south of 1.3-1.4 Ga) sediments metamorphosed to gran- the Achankovil shear zone as the Trivandrum ulite grade. The main lithologies in this zone are block (formerly the Kerala Khondalite Belt), cordierite-bearing assemblages, calc-silicates and which consists of the Achankovil metasediments marbles. The cordierite-bearing assemblages (cf. south of the shear zone (having younger Nd Santosh, 1987) occur as elongate patches in this model ages of about 1.3-1.4 Ga), the Kerala zone and exhibit reaction histories indicative of Khondalite Belt (with older Nd model ages partial replacement of a higher pressure garnet- between 3.0 and 2.0 Ga) and the Nagercoil bearing assemblage by lower pressure one, a massif (possibly of igneous origin) in the feature that is also well supported by fluid extreme south (Bartlett et al., 1995; Bartlett, inclusion studies (Santosh, 1987). A well 1995; Brandon and Meen, 1995; Harris et al., defined Sm-Nd isochron age of 539_+20 Ma 1996). The marble horizon in which clinohumite from the cordierite assemblages has been reported occurs forms part of the Achankovil metasedi- (Santosh et al., 1992). This zone is also ment zone. characterized by diopside-rich calc-silicate bands The Kerala Khondalite Belt predominantly (Satish-Kumar et aL, 1996). Further towards the consists of metapelitic lithologies which include eastern extension of the Achankovil shear zone, garnet + biotite + graphite gneisses, garnet + calcite-rich marble and metapelitic gneisses sillimanite + graphite -+ cordierite gneisses and predominate (cf. Satish-Kumar et al., 1996) othopyroxene-bearing anhydrous granulites. An extensive band of marbles and associated Subordinate lithologies include mafic granulites, calc-silicate rocks occurs in the northeastern part quartzites and calc-silicates. These lithologies of Ambasamudram in southern Tamil Nadu have been metamorphosed to upper amphibolite (Fig. 1B). This band can be traced for about 10 and to granulite facies conditions. Estimates of km along strike and varies in thickness from 25 m metamorphic P-T conditions reported account to 300 m. It is structurally concordant with the

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FIc. 1. A. Regional geological setup of southern Indian Granulite terrain. B. Generalised geological map of Ambasamudram area showing the marble horizon of the present study (after Satish-Kumar et al., 1997a).

Sl0 F-RICH CLINOHUMITE

adjacent lithologies, striking parallel to the graphite; (ii) calcite + clinopyroxene + scapolite + NW-SE trending Achankovil shear. Within the wollastonite _ grossular __+ titanite ___ quartz + marble horizon, the calcite-rich marbles show graphite; (iii) calcite + clinohumite + chondrodite great variations in grain size from coarse grained + spinel + phlogopite + clinopyroxene +__ titanite (>5 mm) to fine grained (<1 mm). The marble + graphite; (iv) calcite + forsterite + spinel -+- band is intercalated with quartzite bands of dolomite ___ diopside; (v) calcite + K-feldspar + varying thickness and is often graphite bearing. phlogopite + quartz + graphite; (vi)calcite + A humite + chondrodite + spinel + magnesian graphite. calcite assemblage has been reported in a marble The equilibrium mineral assemblage in marble from this locality (Krishnanath, 1981; Satish- layers might have resulted in prograde reactions Kumar et al., 1996; Pradeepkumar et al., 1996; from an impure dolomitic limestone. Prograde Rosen et al., 1996). mineral reactions in the calcite-rich marble can be modeled in the system K20-CaO--MgO-A1203- SiO2-H20-COz (KCMAS). The T-Xco2 reaction Petrological features grid in this system was constructed (Fig. 2) using Calcite-rich marbles dominate the lithologies THERMOCALC (Powell and Holland, 1988) within the marble horizon at Ambasamudram. with the internally consistent data set of Holland Different layers paralleling the regional trend of and Powell (1990). A confining fluid pressure of the band have varying mineral assemblages. The 6 kbar was assumed for the peak metamorphic marble is chiefly composed of more than half the assemblages. End-member mineral activities were mode of calcite/magnesian calcite and the used for the solid solution series in the variations in mineralogy are controlled by the computation of the grid. Mg-rich phases. The characteristic mineral One of the main problems in deducing the P-T assemblages include (i) calcite + scapolite + conditions of the metacarbonates is the lack of phlogopite + K-feldspar + titanite + quartz _ appropriate mineral geothermobarometric pairs.

I I l I

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500 I I I I 0 0.2 0.4 0.6 0.8 Xco 2 FIG. 2. Isobaric T-Xco2 grid constructed for marble assemblages in the system K20~aO-MgO-AI203-SiO2-H20- CO2 (KCMAS) at 6 kbar. Mineral abbreviations are Cc - calcite; Chu - clinohumite; Dol - dolomite; Di - diopside; Fo - forsterite; Ksp - K-feldspar; Phl - phlogopite; Qtz - quartz; Sp - spinel; Sph -sphene; Tr - tremolite.

511 M. SATISH-KUMAR AND N. NIIMI

Only an approximation of the conditions can be mounted on glass plates and used for mineral deduced from the assemblages. Since the mineral chemical analyses. Care was taken to analyse the assemblages are controlled by the fluid composi- exact point at which FTIR spectra were taken. tions in the P-T space, one way is to approach EPMA analysis were done using JEOL JXA 8600 the given assemblages through the T-Xc% space. housed at Kochi University, Japan. The analyses As mentioned above, the grid was constructed were done with an accelerating voltage of 15 kV, with end-member compositions for the marble a beam diameter of 2-3 ~tm and a beam current assemblages (Fig. 2). The assemblage forsterite + of 18 mA. Both natural and synthetic standards diopside + K-feldspar + phlogopite + calcite + were used, and oxide ZAF correction was dolomite is stable at the invariant point marked I performed throughout. Quantitative analyses of in the grid. This indicates that the fluid fluorine were obtained using a JEOL JXA 8800 at composition was nearly equal to unit Xco2 and the National Institute of Polar Research in Tokyo. the temperature conditions to be around 700~ The analytical conditions were 15 kV acceler- On the other hand, stability of humite-bearing ating voltage, 15 mA beam current and a assemblages in other layers indicate that the fluid minimum beam diameter (~1 I~m). Bence and conditions should be nearly equal to unit XH2o. As Albee (1968) correction was used. can be seen below, the stable isotopes of calcites coexisting with humite do not show any imprint of infiltration of water-rich fluids to buffer the Results and discussion system, and hence it can be assumed that the fluid The Ambasamudram clinohumite occurs as composition in this assemblage was also intern- granular crystals set in a matrix of coarse calcite ally buffered. Again, the local occurrence of exhibiting a granoblastic texture (Fig. 3). It shows grossular-bearing assemblage indicates a fluid- honey-yellow to orange-yellow colour and absent or low-fluid activity. The grossular-bearing displays a light yellow to colourless pleochroism assemblages formed during cooling from higher in thin section. No optical discontinuity was temperatures. Taken altogether, it can be observed. concluded that the prograde metamorphism of An XRD pattern of the pure mineral separate is the marble band occurred with layer by layer shown in Fig. 4. Twenty four peaks corre- internally controlled fluid compositions. Satish- sponding exactly with the standard of clinohumite Kumar et al. (1997a) reported the carbon isotope were observed. The typical absence of the peak at thermometric results which yields temperatures in 8.4 ~ which is prominent for humite and the the range of about 720~ presence of peaks at 20 ~ amd 17.6 ~ which should be absent for chondrodite, confirms that the present sample consists only of clinohumite, Analytical techniques although other members of the group have been The present study concentrated on the miner- reported (Krishnanath, 1981; Pradeepkumar et al., alogical, chemical and spectroscopic characteriza- 1996; Rosen et al., 1996). tion of clinohumite. A marble sample containing pure humite group minerals was crushed and sieved to a fraction between 0.5 to 1 ram. Pure crystals were separated trader a binocular micro- scope, powdered and analysed at room temperature using a R1GAKU XRD with analytical condition of 30 kV and 10 mA. Doubly polished sections (~300 ~tm) were prepared from the same hand specimen. Micro FTIR measurements were carried out using a SHIMADZU FTIR-4200 spectrometer. The spectrometer is an interference type which is based on the principle of the Michelson interferometer. Analyses were carried out at room temperature with an unpolarised incident beam. The analysis targets were carefully FIG. 3. Photomicrograph of clinohumite set in a selected in order to avoid microcracks or granoblastic texture with calcite. Width of the photo- inclusions. The same polished wafers were later graph is 3 mm.

512 F-RICH CLINOHUMITE

II111 2~ 30 ~ 40 ~ 50 ~ 20

FIG. 4. X-ray diffractogram of clinohumite.

The microprobe analytical results of MT,/Si Ambasamudram clinohumite are given in Table 1. From the EPMA results, cations were Gaspar (1992) introduced a new mineralogical calculated on the basis of 18 (O). Several points criteria to identify the humite group minerals were analysed to find out any compositional using the ratio of total octahedral cations variations within and between the grains. There is including Ti to the Si. This (MTi/Si, MTi = only minor compositional variation between Mg+Fe+Mn+Ti+Ca) is found to be 3.0, 2.5, 2.33 grains of clinohumite. TiO2 content is very low and 2.25 respectively for the minerals with n from (<0.49 wt.%) and with low FeO content. Only 1 to 4. The Ambasamudram samples gave an negligible quantities of other cations are present average MTi/Si value of 2.27 (ranging from 2.21 in the clinohumite. These general characters to 2.38). The range of the values show a bimodal indicates the Ambasamudram clinohumites as distribution (Fig. 5). This suggests the possibility titanium free fluorine rich type, which is typical of an intergrowth of humite with clinohumite. But for marbles. neither petrographic observatons nor XRD pattern points to such an intergrowth. It is possible that very thin lamellae which could not be identified OH content by normal optical observation might be present. The OH content of the clinohumites were calculated from the mineral chemical analysis Fluorine content using the method given by Jones et aL (1969). OH is calculated using the relation (OH) = 2 - 2Ti The humite group minerals in contact with - F. The calculations show that Ambasamudram regionally metamorphosed impure dolomitic clinohumite contain OH from 0.51 to 0.61 in mole limestone are generally titanian-poor and fraction, with an average of OH content of 0.58. fluorine-rich. The fluorine content of

513 M. SATISH-KUMAR AND N. NIIMI

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514 F-RICH CLINOHUMITE

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0 2.08 2.12 2.16 2.20 2.24 2.28 2.32 2.36 2.40 MTi/Si value

Fio. 5. Histogram representing the MTi/Si values of different analysis of clinohumite grains. Total 24 analyses of 8 clinohumite grains gave results indicative of clinohumite as the prominent phase.

Ambasamudram clinohumites varies from 4.20 to hand, the F/(F+OH) values of clinohumite in 4.43 wt.% with an average of 4.3 wt.% and are basic rocks are very low. listed in Table 1. The F/(F+OH) values of the It would be expected that fluorine contents clinohmnites range from 0.692 to 0.741, with an correlate inversely with titanium according to the average of 0.709 (Table 1). This value is higher substitution (Mg,Fe) + 2(OH,F) = Ti + 2(0) than that previously reported for clinohumites. (Evans and Trommsdorff, 1983; Dymek et al., Rice (1980) demonstrated that the increase in 1988). The substitution is thought to have the stoichiometric amount of (OH, F) in the humite effect of stabilizing the structure under high-grade series from clinohumite to norbergite is accom- P-T condition. Fujino and Takenouchi (1978) panied by an increase in the mole fraction of determined hydrogen atom positions and inferred fluorine F/(F+OH). The most fluorine-rich natural that strong repulsion in the Mg(O,OH) layers clinohumite reported contains 63 mole% F. The would occur. This results in a replacement of OH F/(F+OH) values for the clinohumite previously by fluorine or by oxygen to stabilize the structure. reported in different geological environments Therefore, we can consider that the very high were calculated. These clinohumites occur in F/(F+OH) values of the Ambasamudram clinohu- carbonatites (Gaspar, 1992), metamorphosed mite reflect the condition under which they were impure dolomitic limestone recrystallized near formed. In this case, the clinohumite of 5 kbar pressure (Rice, 1980), serpentinite (Dymek Ambasamudram occurs in the Achankovil meta- et al., 1988), dolomitic marbles of the upper sediments (cf. Bartlett, 1995) metamorphosed to amphibolite-facies (Hiroi and Kojima, 1988), granulite grade. Estimates of metamorphic P-T garnet ortho-pyroxenite (Okay, 1994), in lime- conditions reported account for a peak of stone (Sahama, 1953), marble (Muthuswami, 750+50~ and 5-t-1 kbar (Chacko et al., 1987; 1958) and in vein in ultramafic alkaline complex Santosh et at., t993). Rice (t980) has reported (Nielsen and Johnsen, 1978). Fig. 6 shows the that clinohumite+calcite stability increases with F/(F+OH) values where almost all clinohumite in higher fluorine content and decreasing pressure. calcitic and dolomitic rocks (open symbols) The Ambasamudram clinohumites are fluorine- reported are between 0.3 to 0.6 in spite of rich, which agrees well with the calculated variation of titanium contents. On the other stability.

515 M. SATISH-KUMARAND N. NIIMI

o Gaspar C 0.8 v Gaspar R n Rice Sahama I o Hiroi&Kojima Okay Nielsen&Johnsen 0.6 V Dymek + this study -t- P A o o O D o + .D A 0 0 I1 OAr 0 0 0.4 v V vA II 0 OOA V

0.2

0 0.2 0.4 0.6 0.8 1

FI~. 6. F/(F+OH) vs titanium plot for clinohumites in carbonatites (Gaspar, 1992), in reaction rock (carbonatite with magnetite pyroxenite; Gaspar, 1992), in dolomitic limestone (Rice, 1980), in serpentinite (Dymek et al., 1988), in dolomitic marble (Hiroi and Kojima, 1988), in garnet pyroxenite (Okay, 1994), in plateau basalt (Nielsen and Jolmsen, 1978), in limestone (Sahama, 1953) and in marbles (this study).

Spectroscopic characterization of volatile tion bands are observed at 3693, 3675, 3647, phase 3572, 3563, 3534, 3410 and 3394 cm -1, Although Absorption in the 3800-3000 cm -1 wave number the sharp narrow bands in three major bands infrared region is typical of the O-H stretching change in intensity relatively, their peak positions vibration, its presence is the first indication that a are fixed for all samples analysed. If no cracks or mineral contains hydrogen (Aines and Rossman, fluid inclusions or grain boundaries were included 1984). FTIR spectroscopy is a useful tool to study in the measured area, then these absorption bands the hydrous components in minerals. Humite can be attributed to the OH which is incorporated group minerals contain hydrous components of in brucite layers in the clinohumite. Moreover, a OH in their structure. Eight crystals were analysed weak broad peak at 3840 cm -l is also observed. for Micro-FTIR spectrum and a typical spectrum In general, the absorption band due to molecular of clinohumite is shown in Fig. 7. Eight water is broad and ranges from 3700 to absorption bands are observed with the major 2800 cm -1 centered at 3400 cm -1, which is a three showing sharp narrow bands. symmetric absorption band. Surficial hydrogen Distinguishable relatively narrow sharp absorp- species like silanol groups give rise to a relatively

516 F-RICH CLINOHUMITE

1.5 room temperature spectrum

0 0 C (g 1.0, ,.Q t._ 0 m

0.5-

I ' I ' i l i I 4000 3500 3000 wavenumber (cm -1) FI~. 7. Room temperature infrared spectrum of the Ambasamudram clinohumite in the 3 pm infrared region. Vertical axis shows absorbance. Sample thickness is about 0.3 mm.

sharp absorption band in the same region. Kerrick, 1976). Pradeepkumar et al. (1996), However, the broad band observed is not due to based on the geochemical studies of mineral and both these cases because of its shape and peak rock samples of Ambasamudram marbles, wave-ntunber. Further detailed spectroscopic suggested an extraneous origin for the fluids, analysis is necessary to characterise this. which they attributed to the granitic gneiss, which expelled aqueous fluorinated fluids. Our views contradict this. The EPMA results show that Origin of fluorine-rich clinohumite, clinohumite in Ambasamudram marbles is metasomatic or metamorphic? fluorine rich. Rice (1980) stated that it is possible The origin of fluorine-rich clinohumites can be that all marbles which contain fluorine-rich attributed to one of the two processes, viz. a clinohumite have not resulted from metasomatic metasomatic process resulting from the extemal introduction of fluorine and that concentration of influx of fluorinated fluids or to internal buffering fluorine can result from strong 'partitioning' of during metamorphism. The former is normally the fluorine into hydrous minerals. The primary case in the contact aureoles, where granitic and evidence is from the stable isotopes of calcite in granodioritic intrusions inject fluids into the association with the clinohumite. The 813C and impure limestones causing the formation of 8180 of calcite are +2%0 and +21%o respectively fluorine-rich clinohumites (e.g. Moore and (Satish Kumar et al., 1997a). If the marbles were

517 M. SATISH-KUMAR AND N. NIIMI

infiltrated by aqueous fluorinated fluids from Bartlett, J.M. (1995) Crustal evolution of the high-grade extraneous granitic sources, then the oxygen terrain of South India. Unpub. Ph.D. thesis, Open isotopes should preserve the isotopic signatures. Univ., U.K., 230 pp. The present values correspond with the primary Bartlett, J.M., Harris, N.B.W and Hawksworth, C.J. Proterozoic sedimentary carbonate values. Also, (1995) New isotope constraints on the crustal Satish-Kumar et al. (1997b) suggested, from evolution of South India and Pan-African granulite detailed petrological and stable isotopic studies, metamorphism. In: India and Antarctica during the during the prograde and peak metamorphic Precambrian (M. Yoshida and M. Santosh, eds.), conditions, that fluid compositions of the Geol. Soc. India. Mem., 34, 391-7. Ambasamudram marbles were internally Bence, A.E. and Albee, A.L. (1968) Empirical controlled. In addition, both the marbles and the correlation factors for electron microanalysis of silicates and oxides. J. Geol. 76, 382-403. granitic gneisses have been affected by regional Brandon, A.D. and Moon, J.K. (1995) Nd isotopic metamorphism during which the formation of evidence for the position of southernmost Indian clinohumites occurred, and there is lack of terranes within East Gondwana. Precam. Res., 70, synmetamorphic granitic activity. This also 269-80. suggests an internal fluid buffering rather than Chacko, T., Ravindrakumar, G.R. and Newton, R.C. an external fluid influx. Calcite-rich marbles are (1987) Metamorphic P-T conditions of the Kerala usually impermeable to fluids, except for fracture- (southern India) Khondalite Belt, A granulite facies controlled fluid infiltration (Holness and Graham, supracrustal terrain. J. Geol., 95, 343-8. 1991). The clinohumite-bearing assemblages at Dymek, R.F., Boak, J.L. and Brothers, S.C. (1988) Ambasamudram are calcite-rich and hence Titanian chondrodite- and titanian clinohumite- supports our view that they were not affected by bearing metadunite from the 3800 Ma Isua the external influx. supracrustal belt, West Greenland: Chemistry, The origin of fluorine in the Ambasamudram Petrology, and Origin. Amer. MineraL, 73, 547-58. clinohumites can be attributed to the isochemical Evans, B.W. and Trommsdorf, V. (1983) Fluorine reactions involving (OH-F) silicates such as hydroxyl titanian clinohumite in Alpine recrystal- amphiboles or phlogopite, which are abundant in lized garnet peridotite: Compositional controls and the marble. Rice (1980) attributed to the petrological significance. Amer. J. Sci., 283A, partitioning of fluorine into hydrous silicates 355 -69. relative to HzO-CO2 fluids. We, in our case, Fujino, K. and Takeuchi, Y. (1978) Crystal chemistry of also attribute the source for the high concentration titanian chondrodite and titanian clinohumite of high of fluorine in clinohumite to this internal pressure origin. Amer. MineraL, 63, 535-43. buffering mechanism of fluorine concentration. Gasper, J.C. (1992) Titanian clinohumite in the carbonatites of the Jacupiranga Complex, Brazil: Mineral chemistry and comparison with titanian Acknowledgements clinohumite from other environments. Amer. The authors are grateful to Dr Yoichi Motoyoshi MineraL, 77, 168-78. for the electron microprobe analysis of Harris, N.B.W., Bartlett, J.M. and Santosh, M. (1996) Neodymium isotope constraints on the tectonic Clinohumite at NIPR Tokyo. NN thanks Prof. evolution of East Gondwana. J. Southeast Asian Aikawa and Dr Shinoda for advice and assistance. Earth Sci., 14, 119-25. MS-K acknowledges Monbusho for financial Hiroi, Y. and Kojima, H. (1988) Petrology of dolomitic support. Prof. M. Yoshida and Dr M. Santosh marbles from Kasumi rock, Prince Olav coast, East are gratefully acknowledged for their suggestions. Antarctica. Proc. NIPR Symp. Antarct. Geosci., 2, 96-109. References Holland, T.J.B. and Powell, R. (1990) An enlarged and updated internally consistent thermodynamic dataset Aines, R.D. and Rossman, G.R. (1984) Water in with uncertainties and correlations: the system KzO- N20-CaO-MgO-MnO-FeO-FezO3-AIzO3-TiOz- minerals? a peak in the infrared. J. Geophys. Res. SiO2~-H2-O2. J. Metam. Geol., 8, 89-124. 89, 4059-71. Holness, M.B. and Graham, C.M., (1991) Equilibrium Aoki, K. Fujino, K. and Akaogi, M. (1976) dihedral angles in the system HzO~COz-NaC1- Titanochondrodite and titanoclinohumite derived calcite, and implications for fluid flow during from the upper mantle in the Buell Park kimberlite, metamorphism. Contrib. Mineral Petrol., 108, Arizona, USA. Contrib. Miner. PetroL, 56, 243-53. 368-83.

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Jones, N.W., Ribbe, P.H. and Gibbs, G.V. (1969) Crystal dite marbles in the Kerala Khondalite Belt, southern chemistry of humite minerals. Amer. Mineral., 54, India. In: Proceedings of the UNESCO-IUGS-IGCP- 391-411. 368 International fieM workshop on the continental Krishnanath, R. (1981) Coexisting humite-chondrodite- crust of southern India, Gondwana Research Group spinel magnesium calcite assemblage from the calc- Misc. Pub. 4, (M. Santosh and M. Yoshida, eds.) silicate rocks of Ambasamudram, Tamil Nadu, India. Field Science Publishers, Osaka. 115 p. J. Geol. Soc. India, 22, 235-42. Sahama, Th. G. (1953) Minerology of the humite group. McGetehin, T.R., Silver, L.T. and Chodos, A.A. (1970) Ann. Accad. Sci. Fennicae, III. Geol. Geogr., 31, Titanoelinohumite: A possible mineralogical site for 1-50. water in the upper mantle. J. Geophy. Res., 75(2), Santosh, M. (1987) Cordierite gneisses of Southern 255 -9. Kerala, India: petrology, fluid inclusions and Moore, J.N. and Kerriek, D.M. (1976) Equilibria in implications for crustal uplift history. Contrib. siliceous dolomites of the Alta aureole, Utah. Amer. Mineral. Petrol., 96, 343-56. J. Sei., 276, 502-24. Santosh, M., Kagami, H., Yoshida, M. and Nanda- Muthuswami, T.N. (1958) Clinohumite, Sauser series, Kumar, V. (1992) Pan-African eharnockite forma- Bhandara District, India. Proc. Indian Acad. Sci., 48 tion in East Gondwana: geochronologic (Sm-Nd and A, 9-28. Rb-Sr) and petrogenetic constraints. Bull. Ind. Geol. Nielsen, T.F.D. and Johnsen, O. (1978) Titaniferous Assoc., 25, 1-10. clinohumite from Gardiner Plateau complex, East Santosh, M., Jackson, D.H. and Harris, N.B.W. (1993) Greenland. Mineral. Mag., 42, 99-101. The significance of channel and fluid inclusion CO2 Okay, AT (1994) Sapphirine and Ti-clinohumite in in cordierite: Evidence from carbon isotopes. J. ultra-high-pressure garnet-pyroxenite and eelogite Petrol., 34, 233-58. from Dabie Shan, China. Contrib. Mineral. Petrol., Satish-Kumar, M., Santosh, M. Harley, S.L. and 116, 145-55. Yoshida, M. (1996) Calc-silicate assemblages from Powell, R. and Holland, T.J.B. (1988) An internally the Kerala Khondalite Belt, southern India: consistent dataset with uncertainties and correla- Implications for pressure-temperature-fluid histories. tions: 3. Applications to geobarometry, worked J. Southeast Asian Earth Sci., 14, 245-63. examples and a computer program. J. Metam. Satish-Kumar, M. Santosh, M. and Wada, H. (1997a) Geol., 9, 173-204. Carbon isotope thermometry in marbles of Pradeepkumar, A.P., Krishnanath, R. and Rosen, K. Ambasamudram, Kerala Khondalite Belt, southern (1996) Humite marbles of the Kerala Khondalite India. J. Geol. Soc. India, 49, 523-32. Belt in the Pan-African Zone of South India. In: Satish-Kumar, M., Wada, H., Santosh, M. and Yoshida, Proceedings of the UNESCO-IUGS-IGCP-368 M. (1997b) Petrologic and microscale stable isotopic International field workshop on the continental crust evidence for peak metamorphic internal fluid of southern India, Gondwana Research Group Misc. buffering and late stage fluid infiltration in Pub. 4, Field Science Publishers, Osaka. (M. Ambasamudram marbles, southern India. (sub- Santosh and M. Yoshida, eds.) pp 53-54. mitted). Rice, J.M. (1980) Phase equilibria involving humite Trommsdorff, V. and Evans, B.W. (1980) Titanian minerals in impure dolomitic limestones, Part I. hydroxyl-clinohumite: Formation and breakdown in Calculated stability of clinohumite. Contrib. antigorite rocks (Malenco, Italy). Contrib. Mineral. Mineral. Petrol., 71, 219-35. Petrol., 72, 229-42. Rosen, K. Pradeepkumar, A.P., Raith M. and Krishnanath, R. (1996) Reaction textures and P-T [Manuscript received 9 July 1997: fluid evolution of clinohumite, humite and chondro- revised 11 December 1997]

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