the dharwar craton, southern india, and its late archaean

The Dharwar craton, southern India, and its Late Archaean plate tectonic sett ing: current interpretat ions and

controvers ies

BRIAN CHADWICK*, V N VASUDEV @ and G V HEGDEt

* Earth Resources Centre, University, Exeter EX~ 4QE, UK 120/~5(A) III Block, Thyagarajanagar, Bangalore 560 028, India

t Department of Mines and Geology, Government of Karnataka, Bangalore 560 027, India

In spite of detailed geological investigations of the Dharwar craton since the 1890s, its principal lithological units, structure and chronology remain contentious. Important new work on lithostratigraphy, basin development, structure, geochemistry and geochronology has led to wide-ranging speculation on the Late Archaean plate tectonic setting. Much of the speculation is based on uniformitarian models which contrast with a recent proposal that the evolution of the craton was controlled by gravity-driven processes with no crustal shortening.

1. T h e D h a r w a r c r a t o n

The Late Archaean Dharwar craton (figure 1), in the sense of Ramakrishnan (1993), is an important part of the collage of Archaean and Proterozoic terrains in Peninsular India. Areas east and south of the craton are characterized by structures, metamorphism and igneous bodies related to the Pan-African assembly of Gondwana, but the interior of the craton largely escaped significant Pan-African overprinting. The northern margin of the craton is concealed by Proterozoic sedimentary rocks and the Deccan lavas, whereas the east is overlain by the Meso-Neoproter- ozoic Cuddapah basin. Late Archaean metamorphism in much of the western part of the craton varies from LT greenschist to amphibolite facies in contrast with HT greenschist to amphibolite facies in the eastern part which is related to the emplacement of voluminous granite. Effects and possible causes of Late Archaean granulite facies metamorphism in the extreme south of the craton have been reviewed by Hansen et al (1995), among others. This contribution comprises a brief review of recent findings in the Dharwar craton north of the terrain affected by Archaean granulite facies metamorphism.

The craton can be subdivided into two principal parts (figure 1) which are separated by a steep belt of mylonites, c l - l . 5 k m wide, trending approximately N-S or NW-SE (Chadwick et al 1989). The belt of mylonites has been interpreted as a thrust by many workers on the grounds of a relatively shallow, easterly dipping reflector identified by Kaila et al (1979), but there is no obvious curvature along the length of its outcrop to suggest that the steep mylonites are part of a listric structure. Shallow and steeply plunging linear fabrics in the mylonites (Chadwick et al 1989) are ambiguous in terms of the principal displacement direction within the belt.

2. W e s t e r n part o f t h e c r a t o n

2.1 Peninsular Gneiss and the Sargur Group

West of the mylonite belt the craton is characterized by Late Archaean volcanic and sedimentary rocks (Dharwar Supergroup; Swami Nath et al 1976) that were deposited in the period c2900-2600 Ma (Taylor et a11984; Nutman et a11996; Kumar et a11996) on a sialic basement of orthogneisses and granodiorites

Keywords. Dharwar craton; Late Archaean; plate tectonics; Dharwar batholith.

Proc. Indian Acad. Sci. (Earth Planet. Sci.), 106, No. 4, December 1997, pp. 249-258 �9 Printed in India 249

250 Brian Chadwick et al

Figure 1. Simplified geological map of the Late Archaean Dharwar craton (ornamented) in southern Peninsular India: DS: Dharwar Supergroup; PG: Peninsular Gneiss (basement to the Dharwar Supergroup); H: Holenarsipur schist belt, > c.3000 Ma; m: steep belt of mylonites (see text); black: Late Archaean volcano-sedimentary schist belts in the eastern part of the craton (Hu: Hutti; K: Kolar; R: Ramagiri; S: Sandur); DB: Dharwar batholith; g: Late Archaean granulite facies metamorphism; KA: Kibbanahalli Arm (see text). Blank areas are mostly Proterozoic and younger rocks, including CB: Cuddapah basin; PSZ: Proterozoic shear zones; PAT: terrain dominated by Pan-African phenomena. B: Bangalore; C: Chitradurga; Ma: Madras; My: Mysore; T: Trivandrum.

which are known collectively as the Peninsular Gneiss. Many workers have included the younger Archaean plutonic rocks in the eastern part of the craton as part of the Peninsular Gneiss following W F Smeeth who coined the term nearly a century ago. Because of the confusions that have arisen with its application to rocks with a wide range of ages (see Naha et al 1993; Srinivasan and Naha 1996, for recent examples), Radhakrishna and Vaidyanadhan (1994) proposed that the term be abandoned. They suggested that the term Older Gneiss Complex be used for gneisses older than 3000 Ma, and Younger Gneiss Complex for those c2600 Ma. Because the younger gneisses are a high- strain component of the Dharwar batholith which is discussed later, we recommend that the term Penin- sular Gneiss be retained, but restricted to gneisses older than c2900 Ma.

The basement orthogneisses and low-strain plutonic rocks in the western part of the craton have ages in the range c2900-3300Ma (Beckinsale et al 1980;

Taylor et al 1984; Bhaskar Rao et al 1991; Naha et al 1993; Peucat et a11993). Whereas much of the Penin- sular Gneiss is part of a tonalite-trondhjemite- granodiorite suite whose precursors had short periods of crustal residence (Bhaskar Rao ct al 1983; Monrad 1983; Stroh et al 1983; Jayaram et al 1983; among others), its tectonic evolution prior to c2900Ma is poorly understood.

The gneisses include tracts of older volcanic and sedimentary rocks and stratiform gabbro-anorthosite complexes (Sargur Group; Swami Nath et al 1976). SHRIMP and single grain evaporation ages of zircon (Nutman et a11992; Ramakrishnan et a11994; Peucat et al 1995) show that the Sargur Group has an age of c2960-3300 Ma, and it includes detrital zircon grains as old as 3580 Ma. It is likely that the Sargur Group includes a number of different tracts of supracrustal rocks of different ages. The Sargur Group includes banded iron formations, fuchsite quartzites of detrital origin (Chadwick et al 1986; Argast 1995), metape- lites, basaltic amphibolites, metaperidotites and stratiform gabbro-anorthosites: the depositional, volcanic and tectonic setting remains unclear.

Deformation of the Sargur Group in the Hole- narsipur belt (figure 1) took place in three distinct periods (Chadwick et a11978). Bouhallier et al (1993) argued that the structure of this belt was controlled by diapiric emplacement of the adjacent components of the Peninsular Gneiss in amphibolite facies conditions and subsequent sinistral transcurrent shearing in greenschist facies conditions. The diapiric emplacement appears to have taken place prior to c2900 Ma, whereas the sinistral shearing appears to be Late Archaean. Chardon et al (1996) extended the diapiric model to structures in the Peninsular Gneiss and Sargur rocks which underlie the Dharwar Supergroup in the Kibbanahalli Arm (figure 1) west of the Chitra- durga schist belt. They noted that orthogneisses are generally located in domes, whereas Sargur supracrustal rocks are mainly found in intervening basins. This distribution contrasts with the common intersheeting of the gneisses and Sargur rocks elsewhere in the western part of the craton, the intersheeting having been due principally to intrusion of the supracrustal rocks by precursors of the gneisses. The intersheeted relationship suggests that a significant sub-horizontal regime of plutonic intrusion and deformation characterized much of the Peninsular Gneiss before the generation of upright structures like those described by Bouhallier et al (1993) and Chardon et al (1996).

2.2 Dha~war Supergroup

Although the unconformable relationship between the Dharwar Supergroup and its basement of Peninsular Gneiss is disputed by some workers (Naha et al 1993; Srinivasan and Naha 1996), the field evidence south of

The Dharwar craton in southern India 251

Bababudan, north of Sigegudda, west of the Chitra- durga belt and on the west and east of the Kibbanahalli Arm points overwhelmingly to an unconformable relationship which shows that deposition of the Dharwar Supergroup did not begin until cooling, uplift and peneplanation of the basement had taken place after c3000Ma (Swami Nath et al 1976). The age of the Dharwar Supergroup is constrained to the period c2900-2600 Ma on the grounds of the age of its basement, intrusion of the Chitradurga Granite (2605 • 18 Ma; Taylor et a11984) and a Pb/Pb metamorphic recrystallization age of 2639 • 32 Ma of limestones from various parts of the Dharwar stratigraphy (Russell et al 1996). SHRIMP zircon age data from acid volcanic rocks at a relatively high stratigraphic level indicate melt crystallization at 2614• (Nutman et al 1996), whereas well constrained arrays of Sm-Nd data interpreted as isochrons by Kumar et al (1996) show that some of the oldest basic volcanic rocks in the supergroup are 2911 • old and other volcanic suites low in the stratigraphic sequence are 2848 i 70Ma and 2747 • 15Ma old. Isotopic whole rock ages of 2565 + 28Ma (Pb/Pb; Taylor et a11984) and 2520 • 62 Ma (Rb-Sr; Bhaskar Rao et al 1992) for volcanic rocks high in the stratigraphy and other younger ages for rocks elsewhere in the stratigraphy (2240 • 50 Ma, Bhaskar Rao et al 1992; 2439• Srinivasan et al 1992; 2480 • 31 Ma, Naha et al 1993) appear to be effects of unspecified metamorphic disturbance.

Facies distributions and well-preserved primary depositional and volcanic structures in the Dharwar Supergroup in the central part of the western half of the craton show that it was deposited in mixed-mode basins whose evolution was probably controlled by transpression (Chadwick et al 1989, 1992). Future detailed stratigraphic studies combined with precise isotopic dating are likely to reveal that the supergroup formed in a series of independent basins.

Chadwick et al (1992) proposed that the Dharwar Supergroup accumulated in three stages. The first was characterized by crustal extension which led to prolific eruption of basalts, emplacement of sub-volcanic gabbros, and deposition of shallow marine sands, carbonaceous muds, volcaniclastic sediments and banded iron formations (with major economic deposits of iron in the Kudremukh area). Koma~iites are a very minor component in the Dharwar Supergroup compared with supracrustal belts of similar age in other continents. The basal quartz-pebble conglomerate at the unconformity with the Peninsular Gneiss basement has been interpreted as fluvial by Srinivasan and Ojakangas (1986) and Farreddudin et al (1988), but shallow marine by Chadwick et al (1985a). The presence of an unambiguous sialic basement to the Dharwar Supergroup is inconsistent with proposals by Naqvi et al (1988), among others, that parts of the supergroup had a simatic basement.

The second stage of basin development saw the accumulation of alluvial and shallow marine fans, debris flows, quartz arenites, greywackes and local stromatolitic limestones, with sporadic basic and acid volcanism. The coarse polymict conglomerates in the alluvial fans and debris flows include not only crowded clasts of Dharwar metabasalt, gabbro, banded iron formation and quartzite, but also orthogneisses which show that areas of basement were elevated and eroded during basin development. The final stage was marked by deposition of a widespread, but relatively thin, banded iron formation which was followed by thick fine-grained greywackes with intercalations of chert and volcanic rocks. The mixed-mode basin development and volcanic facies (Bhaskar Rao and Drury 1982; Drury 1983) suggest an incipient back-arc or an active continental margin, with similarities in the Mesozoic-Cenozoic setting of New Zealand and the western United States (Chadwick et al 1992).

Interpretation of the Late Archaean structure of the Dharwar Supergroup and its sialic base~nent is controversial (Mukhopadhyay 1986). Naqvi (1973) and Naha and Chatterjee (1982) took the view that banded iron formations host early, large-scale isoclinal folds that are refolded by younger structures. Drury and Holt (1980) and Drury et al (1984) took a wider view in the sense that they believed that the Dharwar Supergroup is characterized by early E-W recumbent folds and thrusts propagated from the south which were refolded by movements in wide N-S or NW-SE shear zones. However, their claims of large-scale recumbent folds" are not supported by stratigraphic data. In contrast, Chadwick et al (1981a, 1985b, 1988, 1989, 1992) interpreted the Dharwar schist belts in terms of one principal phase of deformation with superimposed younger folds related to transcurrent sinistral displacements. Moreover, Mukhopadhyay and Ghosh (1983); Mukhopadhyay and Baral (1985) and Naha et al (1995) believed that the principal structures are the result of two distinct periods of deformation which gave rise to broadly parallel upright folds or refolded recumbent folds.

i a h a et al (1986) and Naha et al (1990) made a more controversial claim that the ductile migmatitic structures in the Peninsular Gneiss of the basement were contemporaneous with folds in the Dharwar Supergroup: they referred to this relationship as a "unity of structures". However, their view is at variance with the fact that the low-grade Dharwar Supergroup rests unconformably on folds that were generated during high-grade migmatitic events in the orthogneisses of its basement. They argued that the basement was extensively remobilized during deformation of the Dharwar Supergroup and the unconformities were 'blurred' (Naha et al 1991). The alleged blurring is inconsistent with the sharp unconformities mapped by Chadwick et al (1981b, 1985a);


Viswanatha et al (1982) and Venkata Dasu et al (1991). The problem at the heart of the concept of unity of structures is compounded by the fact that, following W F Smeeth, the definition of Peninsular Gneiss used by Naha et al (1990), and more recently by Srinivasan and Naha (1996), embraces orthogneisses (> c2900 Ma) which are basement to the Dharwar Supergroup in the western part of the craton and others which are high-strain components of the youn- get Dharwar batholith (< c2750Ma) that comprises the eastern part of the craton (Chadwick et al 1996).

Recent work by Chadwick et al (1989, 1992) has revealed that the deformation in the Dharwar Super- group can be explained in terms of NE-SW crustal shortening which led to ductile folding and localized thrusting verging SW. In contrast, the gneissic base- meat deformed in a less pervasive way in myriad shear zones and narrow zones of mylonite. These shear zones and belts of mylonite are not parts of post- Dharwar lineaments as claimed by Srinivasan and Naha (1996). The NE-SW shortening was accompa- nied and outlasted by sinistral displacements on N-S and NW-SE wrench faults. The common occurrence of carbonate in the basement shear zones suggests C Q - rich fluids played a prominent role in the deformation. Emplacement of the Chitradurga Granite (c2600 Ma; Taylor et al 1984) into the Dharwar Supergroup and its basement gneisses appears to have taken place during a late stage of the deformation in the west of the craton. Two other bosses of comparable Late Archaean granite intrude the basement gneisses further south (Rogers 1988).

An alternative view of the structure of the western part of the Dharwar craton has emerged from the interpretation of the Kibbanahalli Arm (figure 1) by Chardon et al (1996). They reported that the basal rocks in the complex synclinal structure of the Kibbanahalli Arm constitute a dScollement with kine- matic indicators indicating convergence of slip direc- tions towards the syncline axis. They proposed that this convergence could only be explained by sagduction (after Goodwin and Smith 1980), i.e. an effect of vertical movements consequent on gravitational instability driven by deep-seated thermal variations. Chardon and his co-workers maintained that vertical movements related to gravitational instability were predominant in the development of the Dharwar craton and they rejected uniformitarian models based on crustal shortening and orogenic collapse. There are, however, difficulties with a non-uniformitarian explanation for the relative elevation of the numerous segments of basement in the western part of the craton, for example in the tract of the Dharwar Supergroup between Bababudan and Ranibennur (Chadwick et al 1992). We favour a uniformitarian mechanism, namely, elevation of basement segments as a consequence of NE-SW shortening and transpression related to strike-slip movements in the plethora

of steep, N-S shear zones which ramify through the western part of the craton (see, for example, Chadwick ct al figure 3, 1988; Bouhallier et al figure 9, 1993).

3. E a s t e r n p a r t o f t h e c r a t o n ( D h a r w a r b a t h o l i t h )

East of the steep belt of mylonites the Dharwar craton is distinctly different. It is dominated by voluminous granites, granodiorites and their high-strain gneissic equivalents, c2750-2550 Ma (Balakrishnan ct al 1990; Friend and Nutman 1991; Krogstad et al 1991, 1995; Peucat et al 1989, 1993; Subba Rao et al 1992; Zacharaiah et a11995; Nutman et a11996). They host a series of linear and irregular schist belts with sedimentary and volcanic rocks that have many lithological aspects in common with the Dharwar Supergroup in the west. Limited isotopic ages indicate that volcanism took place in the period c2750-2650 Ma (Balakrishnan ct al 1990; Zacharaiah et. al 1995; Nutman et al 1996). P b / P b data show that metamorphic recrystallization of the limestones in the Sandur schist belt took place 2475 + 65 Ma ago: the #1 value of 8.50 contrasts with that of 7.79 of the limestones in western Karnataka (Russell et al 1996). The difference in the timing of the metamorphic crystallization in western and eastern Karnataka suggests that regional heating related to granite emplacement in the east of the craton outlasted metamorphic effects in the west. The difference in #1 values suggests a more evolved sdu~ce for lead in the east of the craton compared with the west, but the nature of the sources is enigmatic.

Whereas there are lithological and chronological similarities between the Late Archaean volcanic and sedimentary rocks in the western and eastern parts of the craton, no precise correlations have been made so far. Moreover, there are no reports to date of extensive areas of orthogneisses as old as the c2900-3300Ma Peninsular Gneiss basement which underlies the Dharwar Supergroup in the west.

3.1 Late Archaean schist belts

Critical new work by Matin and Mukhopadhyay (1987) and Mukhopadhyay and Matin (1993) in the Sandur schist belt, a major tract with the largest stratigraphic sequence of Late Archaean volcanic and sedimentary rocks in the eastern part of the craton, raised serious questions about previous interpreta- tions of the stratigraphy and structure. Subsequently, Chadwick et al (1996) showed that its lithostratigraphy youngs consistently from SW to NE and is c35 km thick. They attributed this thickness to thrust stacking, although thrusts are not well exposed and have been inferred mostly from gross regional relationships.


Claims by Manikyamba and Naqvi (1996) that the western part of the Sandur schist belt has been overridden by its eastern part are not substantiated by their field data. Geochemical and isotopic age data from amphibolites in the Ramagiri schist belt (Zacharaiah et al 1995, 1996) suggest that thrust thickening may have occurred in other schist belts in the east of the craton. Large-scale, steeply plunging, upright, synclinal sheath folds with deep cusps between steep wedges or elongate domes of granite are also an important component of the structure of the Sandur schist belt (Chadwick et a11996). Parts of these folds were excised during the NE-SW thrusting. Our unpublished field data also suggest that the Hutti schist belt north of Sandur has a steep cuspate structure.

The irregular outcrop patterns of the Sandur and Hutti belts contrast with most of the other belts, including Kushtagi, Ramagiri, Kadiri and Kolar, which have a linear N-S outcrop with steep dips and widths of only a few kms. Recognition of the lithostratigraphy in these linear belts is difficult because of poor exposure, intense deformation and lack of unambiguous way up criteria. The Hutti, Ramagiri and Kolar belts host economic deposits of gold in steep shear zones.

Most of the schist belts include greywaekes (with economic deposits of manganese in the Sandur belt), polymiet conglomerates (with clasts of banded ferru- ginous chert, metabasalt and granite: some of the boulders of granite in the conglomerates in the Kolar belt are up to 1.5 m in size), banded iron formations (with major economic deposits of iron in the Sandur belt), and rare orthoquartzites (Sandur, Hutti and Ramagiri belts) and stromatolitic limestones (Sandur belt): the orthoquartzites and limestones indicate shallow marine conditions. The sedimentary rocks are interbedded with locally voluminous pillow- s t ructured metabasal ts , gabbros and ultramafic schists. Acid volcanic rocks are widespread but volumetrically subordinate. Acid volcanic rocks, polymiet conglomerates and sheets of mylonitized granite in the Kolar belt were described together as the Champion Gneiss by early workers: this unfortu- nate misnomer was applied by Smeeth (1915) to many other parts of the Late Archaean volcanic and sedimentary rocks of the Dharwar craton. The volcano- sedimentary association in the Sandur schist belt accumulated in mainly shallow marine environments in a setting comparable with that of mixed-mode basins, i.e., with variable intra- and extra-basinal uplift and subsidence (Chadwick et al 1996). The chemical composition of the volcanic rocks is consistent with an intra-are setting (Hanuma Prasad et al 1997). We proposed that the other schist belts are also relics of other intra-arc basins (Chadwick et al 1996), a view supported by Krogstad et al (1995) with their new interpretation of an arc setting for the volcanic rocks of the Kolar belt in contrast with their previous

opinion that the belt comprised two distinct oceanic suites (Krogstad et al 1989).

3.2 The Dharwar batholith

The voluminous plutonic rocks which surround and intrude the schist belts in the eastern part of the craton are dominated by granites s.s., granodiorites, monzonites and diorites of the calc-alkaline suite. Most were emplaced as steep wedges or elongate domes trending N-S or NW-SE: one of the larger plutons of granodiorite is up to 20 km wide and at least 100 km long. In addition to late swarms of pale pink granite dykes trending NW-SE that cut plutons of granite s.l. and granodiorite, we have found that mafic dykes of the appinite suite (in the sense of Pitcher 1993) are also locally abundant. Many of the appinite dykes are podded or folded, but their mixed melt compositions and discordances with magmatic and tectonic fabrics in their host rocks are clearly evident.

Similar orientations of tectonic fabrics in the schist belts and the magmatic and tectonic fabrics in the plutonic rocks indicate that many were emplaced syntectonically, but some granites are post-tectonic, e.g. the Joga granite in the north of the Sandur schist belt (Chadwick et al 1996). Steep, magmatic planar fabrics and relatively shallow mineral lineations and elongation of mafic enclaves are parallel to C fabrics (Cisaillement, after Berth~ et al 1979) and mineral lineations in persistent N-S or NW-SE belts of mylonites within the plutonie rocks: S - C fabrics and feldspar a-textures indicate predominantly sinistral displacements. These relationships are in accordance with progressive emplacement of steep wedges of plutonic rocks during regional sinistral transpression. The generally steep, sheet or wedge form of the plutonic rocks contrasts sharply with the predomi- nance of shallow reflectors in the seismic profile recorded by Kaila et al (1979), but the reason for the contrast is unclear.

The scale, distribution and composition of the plethora of Late Archaean plutonic rocks in the eastern part of the Dharwar craton led Chadwick et al (1996) to propose that they be described as the Dharwar batholith (figure 1). The batholith has a western transition zone dominated by anatectic granites (e2500Ma; Friend and Nutman 1991) that were derived from Peninsular Gneiss, c2900 Ma. The transition zone passes eastwards into mainly juvenile granites and granodiorites (Krogstad et a11991, 1995; Peucat et al 1989, 1993; Bhaskar Rao et al 1992). Accretion of the batholith took place as a series of anatectic and juvenile additions in the form of steep wedges and sheets, but much of the chronology of pluton emplacement is unclear. Detailed field and isotopic age studies are necessary to resolve the outstanding issues of the accretion chronology.


3.3 The Closepet Granite - A misnomer

Many maps of the Dharwar craton show a narrow linear belt of granites called the Closepet Granite which is alleged to form the boundary between the western and eastern halves. The term was introduced by W F Smeeth early in this century (see Smeeth 1915), but it has never been defined unambiguously. The Closepet Granite is a misnomer because it contains a wide range of plutonic rocks, including anatectic and juvenile components and their high- strain equivalents. Its boundaries on many maps, especially in its alleged northern part, do not coincide with those between different polyphase varieties of granites. On the grounds of these inconsistencies, we have recommended that the term be abandoned (Chadwick et al 1996). We are not in favour of the term Closepet batholith (Allen et al 1986; Jayananda et al 1995) because it is ill-defined and the plutonic rocks in the linear belt do not warrant special distinction from the myriad other components of the Dharwar batholith.

4. Late Archaean plate tectonic set t ing of the Dharwar craton

Various plate tectonic models have been proposed for the craton. Among the earliest was the thickening model of Drury et al (1984) which involved northerly subduction and stacking of swathes of supracrustal rocks and basement slices verging to the south in the high-grade area in the south of the craton. Con- temporaneous effects in the north of the craton were believed to include N-verging nappes and backthrusts. Later NS shear zones were interpreted as effects of irregularities in the accreting slices. Although this thickening model explains the granulite facies metamorphism in the south of the craton, it is inconsistent not only with the regional structure, but also the site of batholith accretion in the east of the craton.

Krogstad et al (1989) also linked the high-grade metamorphism in the southeast of the craton with collision of continental lithospheric plates and shearing along a suture zone marked by the Kolar schist belt which was believed to include intervening oceanic material on the grounds of the geochemistry of the amphibolites. Krogstad et al (1995) presented addi- tional isotopic and geochemical data to substantiate their claim that the Kolar schist belt includes a N-S suture. Their latest view is that the suture separates gneisses generated c2630-2550 Ma ago in a continental magmatic arc to the west from gneisses that formed c2530 Ma ago in an evolved island arc to the east.

Newton (1990) suggested that the original Kolar basin had an E-W strike before it was involved in N-S plate convergence analogous to the model of Drury et al (1984). Newton concluded that south to north

subduction beneath the Dharwar craton gave rise to Andean margin and island arc magmatism. Like Newton (1990), Srinivasan and Naha (1993) took the view that the trend of the original basins of the Dharwar Supergroup in the western part of the craton was E-W. This orientation led them to speculate that a Late Archaean volcanic arc which was related to southerly subduction is buried beneath the Deccan basalts. They believed that its associated intra-arc and back-arc basins are represented by the Dharwar Supergroup south of the Deccan basalts. This model is consistent with the geochemistry of the metabasalts (Bhaskar Rao and Drury 1982; Drury 1983), but it is inconsistent with the SW vergence of folds in the supergroup (Chadwick et al 1991) and the site of Dharwar batholith accretion in the east of the eraton.

Chadwick et al (1996) proposed that the two-fold division of the Dharwar craton into the western part comprising the basins of the Dharwar Supergroup and their sialic basement and the eastern part comprising the Dharwar batholith and its Late Archaean schist belts is consistent with a convergent plate ~etting. The western part represents a continental margin (foreland) with marginal or back-arc basins represented by the Dharwar Supergroup, whereas the eastern part represents a batholith and intra-arc basins (the schist belts) which accreted against the continental margin. The subduction direction is unclear. The limited evidence of thrust thickening from NE to SW in the Sandur schist belt (Chadwick et al 1996) and the SW vergenee of structures in the Dharwar Supergroup north of Honnali (Chadwick et al 1991) suggest that subduction was' broadly from west to east. On the other hand, the back-arc or continental margin setting of the Dharwar Supergroup suggested by the geochemistry of its volcanic rocks (Bhaskar Rao and Naqvi 1978; Anantha Iyer and Vasudev 1979; Drury 1983), and the spatial setting of anatectic granites in the foreland (Chitradurga granite; Taylor et al 1988) and the western part of the Dharwar batholith (Friend and Nutman 1991) favour east to west subduction. The ambiguity in the subduetion direction is complicated by transcurrent sinistral displacements in the foreland and the batholith which indicate an oblique component to the convergent system.

Published isotopic age data from the schist belts and widely separated parts of the Dharwar batholith suggest that granite emplacement took place in the period c2750-2550Ma, whereas volcanic rocks were erupted in the period c2750-2650 Ma. Although the age data are scanty, they suggest that accretion of the Dharwar batholith and its intra-arc basins took place for at least c150 Ma. The prolonged thermal activity may have been the consequence of basalt underplating that was associated with either a mantle plume or ridge subduction like that described, for example, by Haeussler et al (1995). This thermal setting is in accord with Jayananda et al (1995) who attributed


the Late Archaean granulite facies metamorphism in the southern part of the craton to thickened crust and higher heat flow, perhaps related to a mantle plume. Basalt underplating related to a mantle plume or subducted ridge is also in accord with the chemical composition of volcanic rocks from the Sandur schist belt reported by Hanuma Prasad et al (1997).

Choukroune et al (1995) took an extreme view of the influence of mantle plumes in the tectonic evolution of the Dharwar craton in particular, and the Archaean in general. Their argument was based on the predomi- nance of vertical structures affecting large volumes of crust and the alleged absence of evidence of major thrusting in Archaean cratons. In well-exposed high- grade Archaean terrains such as southern West Greenland, for example, there is abundant evidence of thrusts and fold nappes older than the widespread upright structures (Chadwick and Nutman 1979; Nutman et al 1989; Chadwick 1990). Whereas parts of the Peninsular Gneiss basement to the Dharwar Supergroup in the western part of the Dharwar craton may appear to be dominated by diapiric structures of the type described by Bouhallier et al (1993), Choukroune et al (1995) and Chardon et al (1996), earlier structures like those in the comparable high- grade gneiss terrain of Greenland may be present in the areas of flat-lying Peninsular Gneiss in western Karnataka, but they have not been identified because of poor exposure.

Chardon et al (1996) have extended the non- uniformitarian view of deformation in the Dharwar craton at c3000 Ma to its Late Archaean tectonism. They argued that the schist belts were deformed as a consequence of sagduction (after Goodwin and Smith 1980) which was caused by gravitational instability. Chardon and his colleagues maintained that gravity- driven vertical movements were predominant and there was no contribution from tangential tectonics to crustal thickening in the Dharwar craton. This claim is at odds with the SW verging folds in the Dharwar Supergroup north of the Honnali dome (Chadwick et a11991), thrust thickening in the Sandur schist belt (Chadwick et al 1996), and the gross structure of the Dharwar craton which has aspects closely similar to those of younger convergent plate settings, namely, a continental foreland and a calc-alkaline batholith with intra-arc basins. Recourse to a non-uniformitarian model for the tectonic evolution of the Dharwar craton by Chardon et al (1996) also contrasts strongly with the wide acceptance of uniformitarian plate tectonic regimes for comparable Archaean terrains elsewhere, for example, the Superior and Slave Provinces in Canada, the Yilgarn and Pilbara Blocks in Australia, and the Barberton Mountain Land in South Africa (see general review by Windley 1995). The debate on uniformitarian and non-uniformitarian models for the evolution of the Dharwar craton is set to continue against the background of a continuing

need for further detailed work on lithostratigraphy, basin analysis, structure (including seismic profiles), geochemistry and geochronology.

Acknowledgements

Professor K Naha ventured into the Archaean geology of southern India in the 1980s, relatively late in his career. He will be remembered primarily for his claim, with his principal co-worker, R. Srinivasan, that all of the rocks in the Dharwar craton had experienced the same chronology of Archaean deformation which was manifested in what he called "uni ty of structures". This claim was highly contentious although it had a positive outcome in the sense that it prompted a closer examination of the data. We remember Prof. Naha with affection as a good friend and a stimulating scientific colleague.

We gratefully acknowledge the logistical support of the Department of Mines and Geology, Government of Karnataka, Bangalore, and grants from the Royal Society, London, and the University of Exeter, UK.

References

Allen P, Condie K C and Bowling G P 1986 Geochemical characteristics and possible origins in the southern Closepet batholith, South India; J. Geol. 94 283-299

Anantha Iyer G V and Vasudev V N 1979 Geochemistry of Archaean meta-volcanic rocks of Kolar and Hutti Gold Fields, Karnatak.a, ~ndia; J. Geol. Soc. India 20 419-432

Argast S 1995 Detrital Origin of Fuchsite-bearing Quartzites in the western Dharwar craton, Karnataka, India; J. Geol. Soc. India 45 559-575

Balakrishnan S, Hanson G N and Rajamani V 1990 Pb and Nd isotope constraints on the origin of high Mg and tholeiitic amphibolites, Kolar Schist Belt, South India; Contrib. Mineral. Petrol. 107 279-292

Beckinsale R D, Drury S A and Holt R W 1980 3,360 Myr old gneisses from the south Indian craton; Nature (London) 283 469-470

Berth@ D, Choukroune P and Jegouzo P 1979 Orthogneiss, mylonite and non-coaxial deformation of granites: The example of the South Armorican shear zone; J. Struet. Geol. 1 31-42

Bhaskar Rao Y J, Beck W, Rama Murthy V, Nirmal Charan S and Naqvi S M 1983 Geology, geochemistry and age of metamorphism of Archaean grey gneisses around Channar- ayapatna, Hassan District, Karnataka, South India; In Precambrian of South India; (eds) S M Naqvi and J J W Rogers Geol. Soc. India Memoir 4 309-328

Bhaskar Rao Y J and Drury S A 1982 Incompatible trace element geochemistry of Archaean metavolcanic rocks from the Bababr..dan Volcanic-Sedimentary Belt, Karnataka; J. Geol. Soc. India 23 1-12

Bhaskar Rao Y J, Naha K, Srinivasan R and Gopalan K 1991 Geology, geochemistry and geochronology of the Archaean Peninsular Gneiss around Gorur, Hassan District, Karna- taka, India; Proc. Indian Acad. Sci. (Earth Planet. Sci.) 100 399-412

Bhaskar Rao Y J and Naqvi S M 1978 Geology and geochemistry of metavolcanics and associated rock types


from the Bababudan schist belt: A late Archaean/early Proterozoic volcano-sedimentary pile from India; In Arch- aean geochemistry (eds) B F Windley and S M Naqvi (Amsterdam: Elsevier) 325-341

Bhaskar Rao Y J, Sivaram T V, Pantulu G V C, Gopalan K and Naqvi S M 1992 Rb-Sr ages of Late Archaean metavolcanics and granites, Dharwar craton, South India, and evidence for Early Proterozoic thermotectonic(s); Precarnb. Res. 59 145-170

Bouhallier H, Choukroune P and Ball~vre M 1993 Diaprism, bulk homogeneous shortening, and transcurrent shearing in the Archaean Dharwar craton: The Holenarsipur area, southern India; Precamb. Res. 63 43-58

Chadwick B 1990 The stratigraphy of a sheet of supracrustal rocks within high-grade orthogneisses and its bearing on Late Archaean structure in southern West Greenland; J. Geol. Soc. London 147 639-652

Chadwick B and Nutman A P 1979 Archaean structural evolution in the northwest of the Buksefjorden region, southern West Greenland; Precamb. Res. 9 199-226

Chadwick B, Ramakrishnan M, Vasudev V N and Viswanatha M N 1989 Facies distributions and structure of a Dharwar volcano-sedimentary basin: Evidence for late Archaean transpression in southern India?; J. Geol. Soc. London 146 825-834

Chadwick B, Ramakrishnan M and Viswanatha M N 1981a The stratigraphy and structure of the Chitradurga region: An illustration of cover-basement interaction in the Late Archaean evolution of the Karnataka craton, southern India; Precamb. Res. 16 31-54

Chadwick B, Ramakrishnan M and Viswanatha M N 198tb Structural and metamorphic relations between Sargur and Dharwar supracrustal Rocks and Peninsular Gneiss in central Karnataka; J. Geol. Soc. India 22 557-569

Chadwick B, Ramakrishnan M and Viswanatha M N 1985a Bababudan - A Late Archaean intracratonic volcano- sedimentary basin, Karnataka, Southern India. Part I: Stratigraphy and Basin Development; J. Geol. Soc. India 26 769-801

Chadwick B, Ramakrishnan M and Viswanatha M N 1985b Bababudan - A Late Archaean intracratonic volcano- sedimentary basin, Karnataka, Southern India. Part II: Structure; J. Geol. Soc. India 26 802-821

Chadwick B, Ramakrishnan M and Viswanatha M N 1986 Detrital Chromite and Zircon in Archaean Sargur metasedimentary Rocks, Karnataka; Geol. Surv. India Spl. Publ. 12 87-96

Chadwick B, Ramakrishnan M, Viswanatha M N and Srinivasa Murthy V 1978 Structural studies in the Archaean Sargur and Dharwar supracrustal rocks of the Karnataka craton; J. Geol. Soc. India 19 531-549

Chadwick B, Vasudev V N and Ahmed N 1996 The Sandur Schist belt and its adjacent plutonic rocks: Implications for Late Archaean crustal evolution in Karnataka; J. Geol. Soc. India 47 37-57

Chadwick B, Vasudev V N and Jayaram S 1988 Stratigra- phy and structure of Late Archaean volcanic and sedimentary rocks and their basement in a part of the Shimoga Basin, East of Bhadravathi, Karnataka; Y. Geol. Soc. India 32 1-19

Chadwick B, Vasudev V N, Krishna Rao B and Hegde G V 1991 The stratigraphy and structure of the Dharwar supergroup adjacent to the Honnali Dome: Implications for Late Archaean basin development and regional structure in the western part of Karnataka; J. Geol. Soc. India 38 457-484

Chadwick B, Vasudev V N, Krishna Rao B and Hegde G V 1992 The Dharwar supergroup: Basin development and implications for Late Archaean tectonic setting in western Karnataka, southern India; In The Archaean: Terrains,

Processes and Metallogeny (eds) J E Glover and S Ho University of Western Australia, Publ. 22 3-15

Chardon D, Choukroune P and Jayananda M 1996 Strain patterns, d~collement and incipient sagducted greenstone terrains in the Archaean Dharwar craton (south India); J. Struct. Geol. 18 991-1004

Choukroune P, Bouhallier H and Arndt N T 1995 Soft lithosphere during periods of Archaean crustal growth or crustal reworking; In Early Precamb~ian Processes (eds) M P Coward and A C Ries Geol. Soc. London Spl. Publ. 95 67-86

Drury S A 1983 The petrogenesis and setting of Archaean metavolcanics from Karnataka Stat~, South India; Geoehirn. Cosmochim. Acta 47 317-329

Drury S A, Harris N B W, Holt R W, Reeves-Smith G J and Wightman R T 1984 Precambrian tectonics and crustal evolution in south India; J Geol. 92 3-20

Drury S A and Holt R W 1980 The tectonic framework of the south India craton: A reconnaissance involving LANDSAT imagery; Tectonophysics 65 111-115

Far reddudin Janardhan A S and Basavalingu B 1988 Sedimentotogy, Mineralogy and Geochemistry of the Kala- sapura Conglomerate; Geol. Soc. India Memoir" 9 65-82

Friend C R L and Nutman A P 1991 SHRIMP U-Pb Geochro- nology of the Closepet Granite and Peninsular Gneiss, Karnataka, south India; J. Geol. Soc. India 38 357-368

Goodwin A M and Smith I E M 1980 Chemical discontinuities in Archaean metavolcanic terrains and the de)elopment of the Archaean crust; Precarnb. Res. 10 301-311

Haeussler P J, Bradley D, Goldfarb R, Snee L and Taylor C 1995 Link between ridge subduction and gold mineralization in southern Alaska; Geology 23 995-998

Hansen E C, Newton R C, Janardhan A S and Lindenberg S 1995 Differentiation of Late Archaean Crust in the Eastern Dharwar Craton, Krishnagiri Salem Area, south India; J. Geol. 103 629-651

Hanuma Prasad M, Krishna Rao B, Vasudev V N, Srinivasan R and Balaram V 1997 Geochemistry of Archaean Bimodal Volcanic Rocks of the Sandur Supracrustal Belt, Dharwar Craton, southern India; J. Geol. Soc. India 47 307-322

Jayananda M, Martin H, Peucat J-J and Mahabaleshwar B 1995 Late Archaean crust-mantle interactions: Geochemis- try of LREE-enriched mantle derived magmas. Example of the Closepet batholith, south India; Contrib. Mineral. Petrol. 119 314-329

Jayaram S, Venkatasubramanian V S and Radhakrishna B P 1983 Geochronology and trace element distribution in some tonalitic and granitic gneisses of the Dharwar craton; In Precarnbrian of South India (eds) S M Naqvi and J J W Rogers Geol. Soc. India Memoir 4 377-388

Kaila K L, Roy Chowdury K, Reddy P R, Krishna V G, Narain H, Subbotin S I, Sollogub V B, Chekunov A V, Kharetchko G E, Lazerenko M A and Ilchenko T V 1979 Crustal structure along Kavali-Udipi profile in the Indian peninsular shield from deep seismic sounding; J. Geol. Soc. India 20 307-333

Krogstad E J, Hanson G N and Rajamani V 1991 U-Pb Ages of Zircon and Sphene for Two Gneiss Terranes Adjacent to the Kolar Schist Belt, South India: Evidence for Separate Crustal Evolution Histories; J. Geol. 99 801-816

Krogstad E J, Hanson G N and Rajamani V 1995 Sources of continental magmatism adjacent to the late Archaean Kolar Suture Zone, south India: Distinct isotopic and elemental signatures of two Late Archaean magmatie series; Contrib. Mineral. Petrol. 122 159-173

Krogstad E J, Balakrishnan S, Mukhopadhyay D K, Rajamani V and Hanson G N 1989 Plate tectonics 2.5 Billion Years Ago: Evidence at Kolar, south India; Science 243 1337-1340

Kumar A, Bhaskar Rao Y J, Sivaraman T V and Gopalan K 1996 Sm-Nd ages of Archaean metavolcanics of the Dharwar craton, South India; Precarnb. Res. 80 206-215

The D h a r w a r cra ton in s o u t h e r n India 257

Manikyamba C and Naqvi S M 1996 Evidence of Archaean crustal shortening from deformed pillow lavas: An example from Sandur greenstone belt, Dharwar craton; Curr. Sci. 71 476-479

Matin A and Mukhopadhyay D 1987 Structural Interpretation of the North Western Termination of the Sandur schist belt; Indian J. Earth Sci. 14 214-216

Monrad J R 1983 Evolution of sialic terranes in the vicinity of the Holenarsipur belt, Hassan District, Karnataka, India; In Precambrian of South India (eds) S M Naqvi and J J W Rogers Geol. Soc. India Memoir 4 343-364

Mukhopadhyay D 1986 Structural Pattern in the Dharwar Craton; J. Geol. 94 167-186

Mukhopadhyay D and Baral M C 1985 Structural geometry of the Dharwar rocks near Chitradurga; J. Geol. Soc. India 26 547-566

Mukhopadhyay D and Ghosh D 1983 Superposed deformation in the Dharwar rocks of the southern part of the Chitradurga schist belt near Dodguni, Karnataka; Geol. Soc. India Memoir 4 275-292

Mukhopadhyay D and Matin A 1993 The structural anatomy of the Sandur schist belt - a greenstone belt in the Dharwar craton of south India; J. Struct. Geol. 15 309-322

Naha K and Chatterjee A K 1982 Axial plane folding in the Bababudan hill ranges of Karnataka; Indian J. Earth Sci. 9 37-43

Naha K, Mukhopadhyay D, Dastidar S and Mukhopadhyay R P 1995 Basement-cover relations between a granite gneiss body and its metasedimentary envelope: A structural study from the Early Precambrian Dharwar tectonic province, southern India; Precamb. Res. 72 283-299

Naha K, Srinivasan R, Gopalan K, Pantulu G V C, Subba Rao M V, Vrevsky A B and Bogomolov Y E S 1993 The nature of the basement in the Archaean Dharwar craton of southern India and the age of the Peninsular Gneiss; Proc. Indian Aead. Sci. (Earth Planet. Sci.) 102 547-565

Naha K, Srinivasan R and Jayaram S 1990 Structural evolution of the Peninsular Gneiss - an early Precambrian migmat i t i c complex from south India; Geologische Rundschau 79 99-109

Naha K, Srinivasan R and Jayaram S 1991 Sedimentational, structural and migmatitic history of the Archaean tectonic province, southern India; Proc. Indian Aead. Sci. (Earth Planet. Sei.) 100 413-433

Naha K, Srinivasan R and Naqvi S M 1986 Structural unity in the early Preeambrian Dharwar tectonic province, Penin- sular India; Q. J. Geol. Mineralog. Metallurg. Soc. India 58 219-243

Naqvi S M 1973 Geological structure and aeromagnetic anomalies in the central part of the Chitaldrug schist belt, Mysore, India; Bull. Geol. Soc. America 84 1721-1732

Naqvi S M, Sawkar R H, Subba Rao D V, Govil P K and Gnaneshwar Rao T 1988 Geology, geochemistry and tectonic setting of Archaean greywackes from Karnataka nucleus, India; Precamb. Res. 39 193-216

Newton R C 1990 The Late Archaean high-grade terrain of south India and the deep structure of the Dharwar eraton; In Exposed cross-sections of the continental crust (eds) M H Salisbury and D M Fountain, Kluwer Academic Publishers 305-326

Nutman A P, Chadwick B, Krishna Rao B and Vasudev V N 1996 SHRIMP U/Pb Zircon ages of acid volcanic rocks in the Chitradurga and Sandur Groups, and granites adjacent to the Sandur Schist Belt, Karnataka; J. Geol. Soc. India 47 153-164

Nutman A P, Chadwick B, Ramakrishnan M and Viswanatha M N 1992 SHRIMP U-Pb ages of detrital zircons in Sargur supracrustal rocks in western Karnataka, southern India; J. Geol. Soc. India 39 367-374

Nutman A P, Friend C R L, Baadsgaard H and McGregor V R 1989 Evolution and Assembly of Archaean Gneiss Terranes in the Godths Region, Southern West Greenland: Structural, Metamorphic, and Isotopic Evidence; Tectonics 8 573-590

Peucat J J, Bouhallier H, Fanning C M and Jayananda M 1995 Age of the Holenarsipur Greenstone Belt, Relationships with the Surrounding Gneisses (Karnataka, south India); J. Geol. 103 701-710

Peueat J J, Mahabaleshwar B and Jayananda M 1993 Age of younger tonalitic magmatism and granulitic metamorphism in the South India transition zone (Krishnagiri area): Comparison with older Peninsular gneisses from the Gorur- Hassan area; J. Metamorphic Geol. 11 879-888

Peucat J J, Vidal P, Bernard-Griffiths J and Condie K 1989 Sr, Nd and Pb isotopic systematics in the Archaean low- to high- grade transition zone of southern India: Syn-aceretion vs. post-accretion granulites; J. Geol. 97 537-550

Pitcher W S 1993 The nature and origin of granite; (London: Blackie) 321 pp

Radhakrishna B P and Vaidyanadhan R 1994 Geology of Karnataka; Geol. Soc. India Bangalore 298 pp

Ramakrishnan M 1993 Tectonic evolution of the granulite terrains of southern India; In Continental crust of South India (ed.) B P Radhakrishna, Geol. Soc. India Memoir 25 35-44

Ramakrishnan M, Venkata Dasu S P and Kroner A 1994 Middle Archaean age of Sargur Group by single grain zircon dating and geochemical evidence for the elastic origin of metaquartzite from J C Pura Greenstone belt, Karnataka; J. Geol. Soc. India 44 605-616

Rogers J J W 1988 The Arsikere Granite of southern India: Magmatism and metamorphism in a previously depleted crust; Chem. Geol. 67 155-163

Russell J, Chadwick B, Krishna Rao B and Vasudev V N 1996 Whole-rock P b / P b isotopic ages of Late Archaean limestones, Karnataka, India; Precamb. Res. 78 261-272

Smeeth W F 1915 Geological map of Mysore; Department of Mines and Geology, Mysore

Srinivasan R and Naha K 1993 Archaean sedimentation in the Dharwar craton, southern India; Proc. Natl. Acad. Sci. India 63(A) 1-13

Srinivasan R and Naha K 1996 Apropos of the Sargur Group in the early Precambrian Dharwar tectonic province, southern India; In Recent Researches in Geology (ed.) A K Saha 16 43-48

Srinivasan R and Ojakangas R W 1986 Sedimentology of quartz-pebble conglomerates and quartzites of the Archaean Bababudan Group, Dharwar craton, south India: Evidence for early crustal stability; J. Geol. 94 199-214

Srinivasan R, Subba Rao D V, Pantulu G V C, Sivaraman T V, Balaram V and Gopalan G 1992 Negative Europium anomalies and reset Rb-Sr ages of Archaean detrital metasedimentary rocks of the low-grade supracrustal belts of the Dharwar craton, south india; In The Archaean: Terrains, processes and metallogeny (eds) J E Glover and S E Ho, University of Western Australia Publication 22 295-304

Stroh P T, Monrad J R, Fullager P D, Naqvi S M, Hussain S M and Rogers J J W 1983 3000m.y.-Old Halekote Trondhje- mite; A record of stabilization of the Dharwar Craton; In Precambrian of South India (eds) S M Naqvi and J J W Rogers Geol. Soc. India Memoir 4 365-376

Subba Rao M V, Divakara Rao V, Govil P K, Balaram V and Pantulu G V C 1992 Geochemical and Sr-isotope signatures in the 2.6 by Lepakshi granite, Anantapur district: Implica- tions for its origin and evolution; Indian Min. 46 289-302

Swami Nath J, Ramakrishnan M and Viswanatha M N 1976 Dharwar stratigraphie model and Karnataka eraton evolution; Geol. Surv. India Records 107 149-175

258 B r i a n Chadwick et al

Taylor P N, Chadwick B, Moorbath S, Ramakrishnan M and Viswanatha M N 1984 Petrography, chemistry and isotopic ages of Peninsular Gneiss, Dharwar acid volcanic rocks and the Chitradurga granite with special reference to the late Archaean evolution of the Karnataka craton; Precamb. Res. 2 3 349-375

Taylor P N, Chadwick B, Friend C R L, Moorbath S, Ramakrishnan M and Viswanatha M N 1988 New Age Data on the Geological Evolution of Southern India; J. Geol. Soc. India 31 155-157

Venkata Dasu S P, Ramakrishnan M and Mahabaleshwar B 1991 Sargur-Dharwar relationship around the komatiite-rich Jayachamarajapura greenstone belt in Karnataka; J. Geol. Soc. India 38 577-592

Viswanatha M N, Ramakrishnan M and Swami Nath J 1982 Angular unconformity between Sargur and Dharwar supra- erustals in Sigegudda, Karnataka craton, south India; Y. Geol. Soc. India 23 85-89

Windley B F 1995 The evolving continents (3rd edition) (Chichester: John Wiley) 526 pp

Zacharaiah J K, Hanson G N and Rajamani V 1995 Postcrystallization disturbance in the neodymium and lead isotope systems of metabasalts from the Ramagiri schist belt, southern India; Geoehim. Cosmochim. Acta 59 3189-3203

Zacharaiah J K, Mohanta M K and Rajamani V 1996 Accre- tionary Evolution of the Ramagiri Schist Belt, Eastern Dharwar Craton; J. Geol. Soc. India 47 279-291

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