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OKAYAMA University Science Reports, Vol. 9, No. 1, 1 8, (2002)

Geology of high- to ultrahigh-temperature from central Madurai block, southern India; with emphasis on the evolution of Grt-Opx-Crd

K. Sajeev* and Y. Osanai** *Graduate school ofNatural science and Technology, Okayama University, Tsushima Naka 3- J-J, Okayama, Japan. **Department ofEarth sciences, Faculty ofEducation, Okayama University, Tsushima Naka 3-J-J, Okayama, Japan.

The of Ganguvarpatti area situated at the central Madurai block of southern India consisting of various high-grade metamorphic types. This contribution briefly describes the geology, field occurrences and petrography of metamorphic rocks from Ganguvarpatti area. Ganguvarpatti is known for its occurrence of sapphirine-bearing UHT granulites while the surrounding granulites are less studied. So in this contribution we have discussed the -temperature stability and evolution of granulites surrounding UHT granulites. The pressure-temperature estimation of -orthopyroxene­ cordierite granulite resulted a near peak temperature condition of >950° C at a pressure between 9-10 kbar. These results are in good agreement with the stability field in the KFMASH .

Keywords: Madurai block, southern India, UHT-granulites, P-T estimation, multi-stage evolution

I. Introduction stability of Grt-Crd-Opx granulites from the adjacent areas of UHT granulites Southern India comprises of several granulite terranes separated by various deep crustal shear zones 11. Geology and petrographical characteristics of (Fig. 1) (Drury and Holt, 1980). Towards the south of Ganguvarpatti area Palghat-Cauvery shear zone, the Madurai block is the largest as well as least studied granulite terrane. Recent The present study area is about ca. 20 km2 around reports form this terrane record extreme temperature Ganguvarpatti, within 10°5'- 10°15' N longitudes and crustal (ultrahigh-temperatures (UHT» 77°35'-77°47' E latitudes (Fig. 2). The -based (e.g. Brown and Raith, 1996; Raith et aI., 1997; Satish­ classification is not easy in high-grade metamorphic rocks Kumar, 2000; Sajeev et aI., 2001). The occurrences of so that we adopted assemblage-based classification even sapphirine-bearing granulites are only reported from the though the pelitic-semipelitic , mafic granulites, central part of the Madurai block. This rock type has calc-silicate gneisses and igneous rocks are considered as significant importance because of their nature of different categories. The pelitic gneisses inter-layered with preserving a wide range of reaction textures, which trace mafic granulites and minor amount of calc-silicates are their multi-stage metamorphic evolution. Sapphirine­ seen parallel to the (opx-, Hbl-bearing bearing granulites have been reported only from a few granitic rock). Layered gneisses are mainly garnet- localities in southern India: at Ganguvarpatti (Grew, 1982; inter-layered with boudins and disrupted bands of Mohan et aI., 1986; Hensen, 1988; Sajeev et aI., 2001), mafic granulites. Thin layers and patches of garnet­ Panrimalai (Grew, 1984) and Perumalmalai of Palni hills -cordierite gneisses are also present within the (Sivasubramanian et aI., 1991; Brown and Raith, 1996; layered gneisses. Sillimanite-bearing rocks are relatively Raith et aI., 1997) (See, Fig. 1 for location distribution). fine grained while the grain size of garnet Among these, ultrahigh-temperature metamorphic increases compared to other garnet-bearing granulites. conditions have been reported only from Palni hills by Partial rim of cordierite and biotite around garnet Brown and Raith (1996) and Raith et al. (1997) and from can be identified from many fresh Ganguvarpatti by Sajeev et al. (2001) with P-T conditions exposures from the mapped area. Sillimanite-rich garnet­ ranging up to ca. 1000° C and ca. 10 kbar. Satish-Kumar sillimanite gneiss is exposed as patches within the (2000) reported ultrahigh-temperature metamorphism of garnet-sillimanite-cordierite- gneiss. The layered from Kannisseri in the Madurai block using -poor, orthopyroxene-bearing granulites are exposed - isotope thermometry. only in one location. Calc-silicaties are seen as lenses and In this contribution we will deal with the geology and disrupted intercalation present within the gneisses. Based petrographical significance of the area surrounding the on the assemblages pelitic to semipelitic gniesses sapphirine occurrence of Ganguvarpatti and we will also are classified into seven types while mafic granulites into made an attempt to calibrate the pressure-temperature three and calc-silicates into two types. 2 K. Sajeev and Y. Osanai

Ch'M

N•

o Study area z UHT Sapphirine-granulitl." locality 1, * • UHT localily DAnorthosite o Gneisscs DChamockilcs [i] Moyar shear zone o,,50 Km mBhavani shear zone mPalghal-Cauvcry shear wne ~AchankoviJshear zone agarcoil block o Phanerozoic soil cover

Fig. I. Tcctonic classification of southern India after Drury and HoIt (1980). Inset shows the geographic position of India.

The trends almost parallel to all gneisses of arrangements of biotite ill the matrix are interpreted to be the study area. The general foliation varies from N 75 °E_ form during the retrograde during later stage. Rare S 75 °W to E·W with a southward dip of 58° to 75° in the occurrence of komerupine is identified in a gamet-, major part of the field quartz-. sillimanite-absent and spinel-, sapphirine-, cordierite-present domains locally. A. Orrhopyroxene-!>'jffimanite-qllartz granulite B. Gamer-biOiire-sitIima"ire-!>pillel-cordierite gne is!>'es Thin layers of sapphirine-bearing orthopyroxene­ sillimanile-quartz granulite, orthopyroxene-spinel This rock type exposed in the central part of the study granulite and two granulites are identified from area. These exposures are partly migmatised and in many a small exposure in a pit al Ganguvarpatti village (Fig. exposures initial foliation was disbursed by the partial 3a). The field exposure of orthopyroxene-sillimanite­ melting processes. Distinct melanosomes as well as quartz granulite is relatively weathered so that direct leucosomes can be identified even in meter scale from the is not well exposed. Garners in sapphirine-bearing small quarry near road junction (Fig. 3b, c). orthopyroxene-sillimanite-quartz granulites are large Petrographic studies on this rock type reveals the major porphyroblasts. which is rimed by various symplectites, mineral assemblages are Grt-Bt-Sil-Spl-Crd-Qtz-Kfs±P1. can be identified from the hand specimen. On the northern Sillimanite. quartz. biotite and minor opaque are border of the exposure it is of a ridge followed present as major inclusion phases in garnet by a thin layer of biOlite gneiss. porphyroblasts. Cordierite-sillimanite-spinel assemblage Petrography and evolution of these granulites are is present as partial rim around garnet porphyroblasts (Fig, explained in Sajeev et aJ. (2001) and Sajeev et al. 4b). The direct coexistence of spinel and quartz is not (submitted). The Mg- and AI-rich silica under-saturated present in any of our studied samples. In some samples granulites from Ganguvarpani, preserves an assemblage of very thin rim of cordierite separates the grain boundary of orthopyroxene-sillimanite-garnet ± quartz ± K-, is spinel and quartz. From the textural relations spinel­ considered to be fonned at near peak condition of cordierite-quartz assemblage is considered to be the near­ ultrahigh-temperature metamorphism (1050" C and 1I peak assemblage present in this rock type. kbar). Porphyroblasts of cordierite and sapphirine are present in few samples, which is also considered to be a C. Garner-orrhopyro:cene-cordierite-biotjre gneiss near peak assemblage. These assemblages were strongly overprinted by symplectite, coronas and later aggregates At the central part of the studied area garnet­ of sapphirine, spine!. cordierite and orthopyroxene during orthopyroxene-cordierite-biotite gneiss is exposed as thin the metamorphic evolution (Fig. 4a). Coarse and scattered layers and is associated with garnet-biotite-sillimanite- Geology of high to ultrahigh temperature granulites, Madurai block, Southern India 3

!\.omb,,", India

0rdnil~ Q"",V.iu: Ri,",", ami "m~, b"dk.,. M3!ic [)~kc =::.; ("alc·silicates (in·Op, ~n"iss I.a)cn.-.J 01" ~r.lnuli'e III III \;nciss Gn.IlI.S'l.("n1 tlnciss l.a~ e",d """is< ~~" Ch"rn"dilc

2 .1 Km

Fig. 2. Geological map of the study area. The inset shows the location with in the southern India. A-A' in the figure represents the position of cross section as shown bellow. The layered gneiss as well as layered Opx granulite represents very fine layered granulilcslgneiss. which is described in the text. spinel-cordierite gneisses (Fig. 3b, c). Garnet is rarely garnet porphyroblasls. The portion is dominated by present in this orthopyroxene-rich rock type. Other than K-feldspar, quartz and minor . garnet. biotite, quailz and can be well identified under the naked eye. This rock type are also migmatised F. Gamet-biotite gneiss along with the associated gneisses in many of the exposure. From the petrographic observations cordierite is Gamet-biotite gneiss is dominated in the layered also identified which fomls partial rim around resorbed gneiss (fig. 3f). Normally garnet-biotite gneiss is seen in and orthopyroxene porphyroblasts (Fig. 4<:). This association with two pyroxene granulite and garnet­ association could be used as one of the mosl reliable pair sillimanite ± cordierite gneiss. In almost all cases of the thermobarometric analysis. exposures of garnet-biotite gneiss is seen as fine grained rocks but an exposure near Ghat road. garnet-biotite D. Biotite gneiss gneiss is seen as very course grained. In this exposure large porphyroblasts of garnel is rimmed by aggregates of Biotite gneiss is exposed as thin layers at the nonhern biotite. Felsic minerals are almost absent in this layer. In boundary, in the central pail of the mapped area. Biotite some samples from the south of Valliyur have similar gneiss is granitic in composition, which exposed as thin assemblages to that of other areas but have minor layers. The contact of biotite gneiss with layered gneisses inclusions of spinel within the garnet (fig 4e). In this rock in the north and biotite gneisses in the south are well type there is no quartz is present in association with spineI exposed. Most of the exposures are well-foliated (Fig. 3d) as inclusions in garnet. bUI in some locations the foliation is completely disturbed by the migmatic processes (Fig. 3e). The major mineral G. Quartzite assemblage is gamel-biotite-plagioclase-K-feldspar-quartz (F;g.4d) The are nonnally pure and always forming ridges due to its high resistance to (Fig. 3g). E. Gamet-sillimanite ± cordierite gneiss Quanzite is mainly exposed in the central part associated with biotite gneiss or with layered gneisses. Thin layers and patches of gamet-sillimanite gneiss with minor cordierite are exposed at some locations in the H. Garnet two pyroxelle granulite eastern part of the study area. The foliation of garnet­ sillimanite gneiss is always seen parallel to the associated Garnet-bearing two pyroxene granulite is exposed in only garnet-biotite gneiess. In some locations. large amount of one location at the eastern part of the study area. In this sillimanite with minor cordierite forms partial rim around exposure, they form boudins within the gamet-biotite 4 K. Sajeev and Y. Osanai

-. Ch:ml,:.:I.,ll' qu.m}j

Fig. 3. Field occurrences of Ganguvarpatti area. a) Exposure of Spr-bcaring Opx-Sil-QIZ granulite associated with two pyroxcnc granulite. b) An outcrop of layered gncisscs exposed al the centml pan of the study area. c) A close view of layered gneiss where Gn­ Opx.Crd granulite samples were collected. d) Well foliated III gneiss exposure. c) SI gneiss exposure in which foliation is disturbed by migmatic processes. f) Exposure of a contact between On-SI gneiss and chamockite. g) Field exposure of quartzite h) Field occurrences of calc-silicate gneiss in which both Ort-bearing and -absenllypes intercalated. i) A chamockitc quarry at the northern part of the study area.

gneiss. Fine grains of garnet can be identified from the assemblages through hand specimen because the rock hand specimen. seems to be homogenous. In thin sections only spinel and orthopyroxene is present and shows perfect granular I. Two pyroxene granulite texture (Fig. 4g). Inclusion of orthopyroxene in spinel as well as spinel in orthopyroxene is the only inclusion Two pyroxene granulites are exposed in the northern texture preserved in this granulite. part of the study area. which are associated with sapphirine~bearing orthopyroxene-sillimanite-quartz K. Garnet-bearing calc-siJiclltes granulite and onhopyroxene-spinel granulite. No garnet can be identified from any of the thin sections of this rock Gamet~bearing calc~silicate exposed at the west­ type. Minor amount of opaque minerals is also present in central part of the mapped area (Fig. 3h). The mineral this rock type apan from orthopyroxene. clinopyroxene. assemblages consist of garnet (). . quam. plagioclase and minor biotite (Fig. 4f) . . . calcite. plagiocJase and quartz. Major notable textural features are the formation J. Orthopyroxene-spine! granulite of garnet rims. sacapolile-quartz symplectite and garnet­ quartz symplectite (Fig. 4h). The textural evolution is not Orthopyroxelle-spinel granulite is exposed only at well determined from these localities till now as the Ganguvarpatti. in association with two pyroxene granulite garnet~bearing symplectite have not been identified from and sapphirine-bearing orthopyroxene-sillimanite-quartz any other calc-silicate localities from southern India. granulite. It is very difficult 10 identify the mineral Geology of high to ullrahigh temperature granulites. Madurai block. Southern India 5

Fig. 4. Photomicrographs of various rock types from Ganguvarpaui area. a) Spr-Opx-Crd±PI symplcctitc. a vcry common rctrograde texturc from Ganguvarpatli. b)l>anial rim of Crd-Sil-Spl around resorbcd garnet. c) Gn-Opx-Crd granulitc. Note the line rim of cordicritc in betwccn Gn and Opx porphyroblast. d) Photomicrograph of 8t gnciss. c) Spl inclusions in Grt porphyroblast in Gn-Bt gnciss. n Photomicrograph of two pyroxcnc granulitc which associated with sapphrine-bearing Opx-Sil-Qtz granulitc from Ganguvarpani. g) Spl-Opx granulitc from Ganguvarpaui. h) Gn-Scp symplcctite in gamct-bering calc-silicatc i) Scp-Qtz symplcctitc in garnet-absent calc-silicate. Thc scale bar rcprcsents I mm.

Hornblend- and biotite-bearing granites are exposed in the southern part of the study area as small hillocks. The Calc·silicates are inter layered with garnet-bearing association with charnockites are exposed in some part of calc-silicates which are present as lenses and disrupted the exposure. intercalation within the gamct-biotite-sillimanite­ cordierite gneiss. Mineral assemblages are similar to Ill. Pressure-Temperature estimation garnet-bearing calc-silicate except the presence of garnet. Scapolite-quartz symplectite is one of the dominant The different closure temperatures in exchange textures in this rock type (Fig. 4i). thennometers and net transfer reactions barometers have limitations on the reliability of conventional M. thennobaromctry to calculate the thermal peak of high­ and ultrahigh-temperature rocks (e.g. Raith et al.. The study area is dominated by massive charnockite 1997.Fitzsimons and Harley. 1994; Frost and Chacko. (orthopyroxene ± bearing granitic rock) (Fig. 1989). The pressure-temperature estimation had been 3i) in the northern and southern part block. Some carried out by using garnct-onhopyroxcne pairs from exposurcs show weak foliation while the textures have not garnct-orthopyroxene-cordierite-biotite gneiss. The XM1 show any metamorphic features. IMgI(Mg+Fe)1 composition of garnet core varies from

0.324 - 0.342. The orthopyroxene has a XM1 that varies

N. Granite from 0.510-0.592. Cordierite preserves a XM1 of 0.715­ 0.794. P1agioclase associated with gamet and 6 K. Sajl.'ev and Y. Osanai

Ganguly (1988) provides the highest reliable limit of 13 1056, 1032 and lOll" C. The calibration of Bhattacharya 12 et al. (1991) yields an intermediate value of 1018,977 and 937" C for each reference pressure respectively. 11 D A reasonable convergence from the above •'D • 10 ~ .. thermobarometers would be around 950-1025" C at 8-10

D 9 kbar. The result of pressure temperature calibration is ", shown in Fig. 5. '", 8 ,.. •, .' ~ 7 .. ::-:. IV. Metamorphic evolution 6 " The application of petrogenetic grids in realising the , .' stability field in turn to understand the pressure­ be 1001 4 temperature conditions and is consider a powerful 900 1000 1100 in metamorphic geology to understand the evolution. The TCmOCfalun: (Q Cl evolution of UHT granulites from Ganguvarpatti is well explained by Sajeev et at. (2001) and Sajeev et al. Fig. S. Pressure-lcmperalUre estimation of gamct-onhopyroxene­ (submitted). In the present study we will consider the cordieritc granulite using gamct-orthopyroxene-plagioclase evolution of gamet-orthopyroxene-cordierite-biotite pairs. See text for description. Open squire represents barometer gnei sses and garnet-biotite-si II imani te-spi nel-cordieri le of Bhattacharya cl al. (1991), filled for Harley and gneisses. We will also discuss the possible relation of Green (1982), filled squire for HaTley (I 984b) and open diamond these surrounding granulites with that of UHT granulites. for Wood (1974). For geothennometers open circle represent HaTley (1984a) Open triangle pointing down represent The metamorphic history of most of the mineral thermometer of Lee and Ganguly (1988) while filled triangle for assemblages and their chemical relationships can be Bhauacharya Cl aJ. (1991). Open triangle represents Sen and graphically represented using KzO-FeO-MgO-Alz0 3-SiOz­ Bhattacharya (1984) and star for Lal (1993). Hp (KFMASH) petrogenetic grid. To avoid the unnecessary complexity in the reaction negligible factors

orthopyroxene show reverse zoning with a X...n content of like Ca, Na and Ti are not considered. Minor Ti content 0.562·0.600. may enter into the structure of biotile and the On considering the Kp-FeO-MgO-AIP3-SiOrH20 remaining will be accumulated in . while Ca and (KFMASH) petrogenctic grid (discussed bellow) a Na in plagioclase are not considered. reference temperature between 900" C to 1050" C is The KFMASH petrogenetic grid developed in this suitable for the mineral assemblage. where orthopyroxene study is based on the calculations of Hensen and Harley and garnet is stable. Reference pressure is also detennined (1990) and Spear et al. (1999) considering quartz in on Ihe similar basis with a pressure which is bellow the excess (Fig. 6). The cordierite-absent invariant point (hear orthopyroxene-sillimanite-quartz stability field (11 kbar) after represented as ]Crdl for absent phases at invariant and above the univariant reaction which produce spinel. points). IOpxl. IMsl are fixed based on the data sets of cordierite and quartz (about 5 kbar) where the peak Bermen (1988). The ISpll invariant point is fixed which is assemblage is stable in the petrogenetic grid. The pressure based on the experiments of Carirington and Harley estimation corresponding to the initial mineral (1995) with reference to the new work on high­ assemblages was made using garnet--orthopyroxene temperature assemblages on KFMASH by Mac Dade and barometer (Wood. 1974: Harley and Green. 1982; Harley, Harley (2000). Carirington and Harley (1995) fix the jSpl1 I984b). At a reference temperature of 1050" C. the invariant at a temperature of 900" C at 8.8 kbar. calibrations by Wood (1974) yield a pressure of 13.7 kbar, From the textural features garnet-biotite-sillimanite­ while at 950" C, 9.7 kbar and at 900" C resulted 8.0 kbar. spinel-cordierite gneisses preserve inclusions of biotite. The barometer suggested by Harley and Green (1982) sitlimanite and quartz in garnet and cordierite is the results pressure values of 11.1, 7.6 and 6.1 kbar for prograde assemblage preserved. In garnet-orthopyroxene­ temperature of 1050. 950 and 900" C. respectively. cordierite-biotite gneisses cordierite forms partial rim in Method of Harley (1984b) yielded a slightly lower between garnet and orthopyroxene is considered to be the pressure values with respect to other barometers. near peak assemblage and later decompression results Barometry following the method of Bhattacharya et al. spinel-cordierite assemblage. (1991) yielded pressure values of 9.3, 8.7, 8.2 kbar respectively for the same reference explained V. Discussion and Conclusion above. Peak temperatures were estimated using From the petrogenetic grid the rock exhibit a normal garnet--orthopyroxene pairs for the different data sets. The evolution profile. The peak temperature estimated using reference pressures 11 kbar, 8 kbar and 5 kbar. which are geolhermobarometer (900-1000" C) is in good agreement described in the same order for all calibrations bellow. with the results from petrogenelic grids (Fig. 6). The The experimental themlOmeter of Harley (1984a) yield a divariant assemblages in each field is described using temperature of 929.909 and 889" C. while that of Lee and SiOz-Alz0 3-(FeO+MgO) diagram in fig. 6. Sajeev et al. Geology of high to ultrahigh temperature granuliles. Madurai block. Southern India 7

"

HI

, Fig. 6. KFMASH petrogenetic grid modified from Spcar Cl al. (1999). The , description of the grid construction is given in the lext. Tie-lines in tri-plots indicate the univariant reactions and , the grey rectangle represents the "00 calculated P-T field

(2001) and Sajeev et al. (submitted) suggest a multi-stage terrane to other continental fragments white it is a metamorphic evolution for the sapphirine-bearing stepahead in understanding the evolution of high­ granulites of Ganguvarpatti. So it is apparent that the same temperature granulites surrounding the UHT granulites. terrane preserves a different evolution history for the surrounding rock types. Acknowledgements Isotope geochronological data are sparse from Madurai block and any evaluation of the timing of the various The fieldwork was partly supported from the project events would be arbitrary. Few available isotope ages led by M. Yoshida. First author is thankful to K. P. indicate Paleoproterozoic emplacement of intrusive Shabeer for his comments on this manuscript. This work enderbites (charnockites) in the Kodaikkanal region, is supported by the Grand-in-Aid for Scientific Research adjacent to Ganguvarpatti (Bartlett et al., 1995. Jayananda from Ministry of Education, Science, Sports and Culture, et al., 1995). Sm-Nd and U-Pb dating of garnet, monazite Japan to Y. Osanai, No. 14340150. This work is a and metamorphic overgrowths from Kodaikkanal contribution to IGCP 368 and 440. granulites yielded Pan-African cooling ages (Bartlett et al., 1995, Jayananda et al., 1995). It is thus apparent that Reference the terrane evidenced multiple metamorphic episodes. While the resent studies form the adjacent metamorphic Banlett, J.M., Harris, N.B.W., Hawkesworth, C,J. and terrane of Sri Lanka. Osanai et a!. (1996) and Sajeev and Santosh, M. (1995) New isotope constraints on the Osanai (2002) reported older ages for the UHT granulites crustal evolution of south India and Pan-African from Highland complex. In this view the sapphirine­ metamorphism. In: Yoshida, M. and Santosh, M. (eds) bearing granulites from the Madurai block could also be India and during . Mem. Geo!. older and hence it is acceptable to have a different Soc. India, 34, 391-397. evolution history. Even though the above possibility exists Berman, R.G. (1988) Internally consistent thermodynamic it is not possible to explain a clear tectonic model for this data for minerals in the system Na20-K20-CaO-MgO­ terranes because of the absence of isotopic data from the FeO-Fe20rAI203-SiOrTi02-H20-C02' J. PetroL, 29. sapphirine-bearing granulites and from the surrounding 445-522. granulites. Apart from , petrologic work is Bhattacharya, A., Krishnakumar, K.R., Raith, M. and Sen, also insufficient from Madurai block. Many of the work S.K. (1991) An improved set of a-X parameters for Fe­ have been concentrated on the sapphirine-granulite (e.g. Mg-Ca garnets and refinements of the orthopyroxene­ Grew, 1982; Mohan et al., 1986; Hensen. 1988 ; Grew, garnet thermometer and orthopyroxene-garnet­ 1984 Sivasubramanian et al., 1991; Brown and Raith, plagioclase-quartz barometer. J. Petrol., 32, 629-656. 1996; Raith et al., 1997), while the surrounding granulites Brown. M. and Raith, M. (1996) First evidence of have been studied by few workers (e.g. Harris el al., ultrahigh-temperature decompression from the 1994; Sajeev et al., 2000). So the present contribution is granulite province of southern India. J. Geol. Soc. not sufficient enough to correlate this large granulite London, 153,819-822. 8 K. Sajeev and Y. Osanai

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