preface archaean geology of the eastern goldfields of western australia regional overview abstract the eastern goldfields region forms part of the yilgarn craton which after the superior province of canada is one of the largest fragments of archaean granite greenstone terrain exposed at the surface of the earth this craton has much in common with the more intensely studied superior province but there are also significant differences between these two cratons both cratons were assembled from numerous smaller crustal fragments in a relatively brief period during the late archaean the superior province was assembled between 2725 and 2695 ma card 1990 and the yilgarn craton was assembled between c 2670 and 2650 ma myers 1993 both cratons contain fragments of older continental crust and volcanic arcs that formed just prior to collision and cratonisation the superior province contains extensive belts of metasedimentary rocks interpreted as accretionary prisms card 1990 whereas metasedimentary rocks form only a minor component of the yilgarn craton and most appear to postdate accretion both cratons contain significant concentrations of gold and support thriving gold mining industries the most prominent difference between the cratons lies in the nature of the granitoid rocks the superior province is dominated by tonalite and granodiorite whereas the yilgarn craton largely consists of granite this applies to granitoid rocks of all ages in each craton granite studies form a major part of this special volume of precambrian research

2 61 ga potassic granites and crustal reworking in the western dharwar craton southern india tectonic geochronologic and geochemical constraints abstract we present combined field structural data and spot image analysis petrographic data u pb zircon ages nd isotopes and whole rock geochemical data for the late archaean granite plutons from arsikere banavara ab suite and chitradurga jampalnaikankote hosdurga cjh suite in the western dharwar craton wdc ab plutons are syn kinematic with respect to the development of dome and basin patterns resulting from partial crustal diapiric overturn d1 whilst cjh suite plutons show deformation patterns resulting from the superimposition of large scale regional strike slip shearing d2 onto d1 syn emplacement fabrics sims u pb zircon ages of 2614 10 ma for the chitradurga pluton cjh and of 2617 3 ma for the arsikere pluton ab define the minimum age of the d1 strain pattern the cjh and ab suites are mainly high k granites whose origin is to be sought in partial melting of an old 3 0 ga depleted lower crust of intermediate composition the cjh and ab suites correspond mainly to the ca1 and ca2 types of archaean calc alkaline granites and some facies to the transitional ttg their heterogeneous chemical compositions indicate involvement of various sources and also significantly different depths of partial melting to produce these granites these results allow documenting regional partial reworking of the wdc 2615 ma ago requiring an ht event to have taken place before 2 61 ga and thus different from the 2 55 to 2 51 ga granulite facies metamorphic episode associated to regional scale strike slip shearing d2 that affected the entire craton partial reworking of the older lower crust at 2 61 ga and associated deformation would result from heat advection and or crustal thickening that may relate to voluminous mafic greenstone volcanism and moderate shortening at that time

neoarchean crustal growth by accretionary processes evidence from combined zircon titanite u pb isotope studies on granitoid rocks around the hutti greenstone belt eastern dharwar craton india abstract the neoarchean hutti greenstone belt hosts mesothermal gold deposits and is surrounded by granitoid rocks on all sides combined u pb dating of zircon and titanite from the granitoid rocks constrains their emplacement history and subsequent geologic evolution the golapalli and yelagatti granodiorites occurring to the north of the hutti greenstone belt were emplaced at 2569 17 ma the yelagatti granodiorite yielded a younger titanite age of 2530 6 ma which indicates that it was affected by a post crystallization thermal event that exceeded the titanite closure temperature the western granodiorites from kardikal have identical titanite and zircon ages of 2557 6 ma and 2559 19 ma respectively the eastern kavital granodiorites yielded titanite ages of 2547 6 ma and 2544 24 ma which are identical to the published u pb zircon shrimp ages these ages imply that the granitoid rocks surrounding the hutti greenstone belt were formed as discrete batholiths within a short span of ca 40 ma between 2570 ma and 2530 ma ago they were juxtaposed by horizontal tectonic forces against the supracrustal rocks that had formed in oceanic settings at the end of the archean the first phase of gold mineralization coincided with the last phase of granodiorite intrusion in the hutti area a metamorphic overprint occurred at ca 2300 ma ago that reset the rb sr isotope system in biotites and possibly caused hydrothermal activity and enrichment of au in the ore lodes the eastern dharwar craton consists of quartz monzodiorite granodiorite granite suites of rocks that are younger than the greenstone belts that are older than 2650 ma reported from earlier studies the granitoid magmatism took place between 2650 and 2510 ma ago indicating accretionary growth of the eastern dharwar craton

nature of charnockite and closepet granite in the dharwar craton implications for the architecture of the archean crust abstract the architecture of the archean crust is crucial in understanding the geodynamics of cratonization the dharwar craton in the indian peninsula is well known for its continuous change of metamorphic grades from granulite facies in the south to amphibolite facies in the middle and greenschist facies in the north here the genetic relationship of different units is re analyzed to decipher the crustal architecture of the craton the major lithologic unit the granitoids can be subdivided into ttg charnockite closepet granite and anatectic granites migmatites the charnockite near salem has two types of occurrence one is massive garnet free and plutonic crystallized at 2560 ma and the other is gneissic garnet bearing and incipient metamorphosed at 2490 ma both types are compositionally close to tonalite granodiorite and generally show positive eu anomalies a large proportion of zircons of both types show positive hft values varying from 3 to 9 indicating a relatively juvenile parent 2900 ma crust at medium pressure in the middle crustal level with significant mantle contribution the genetic relationship of different units the spatial age difference of greenstone belts and the spatial variation of metamorphic grade in the dharwar craton suggest a trinity of archean crustal architecture sandwich structure with 2700 2500 ma dominated uppercrust 3400 2900 ma dominated middle crust and 2560 to 2500 ma anatectic lower crust this sandwich structure possibly indicates vertical growth of the crust in the archean the whole craton was tilted at 2500 ma with the southern end uplifted the most by an intra cratonic process and then it was shaped by later orogenic events resulting in the formation of the dominantly n s trending structures in the basement

the mechanics of frontal imbrication a first order analysis the detachment and imbrication of thrust slices at the front of a thrust wedge is one of the principle modes by which such wedges grow collapse of the frontal ramp under longitudinal compressional stress cannot explain the regular formation of new slices of finite length unless there are regularly spaced heterogeneities in the footwall layer or the underlying basement surface advance of the thrust wedge over the frontal ramp however increases both the vertical load on the ramp and the traction on the upper flat this will in general produce a peak deviatoric stress in the footwall layer below the leading edge of the thrust wedge failure will occur at this point when the thrust wedge has advanced a distance l such that the deviatoric stress in the footwall layer exceeds its strength l is a function of a rock density b ramp angle c the resistances to motion on the basal detachment the ramp and the upper flat and d the strength and thickness of the footwall layer these mechanical parameters can therefore control the formation of new thrust slices of regular length in the absence of footwall heterogeneities

timing of gold mineralization in the hutti gold deposit dharwar craton south india the hutti orogenic gold deposit in the eastern dharwar craton of south india is located in a cuspate greenstone belt which is tectonically juxtaposed against tonalite trondhjemite granodiorite ttg basement on its western margin the host rocks to gold mineralization are mafic and felsic volcanic rocks metamorphosed to the amphibolite facies mineralization is confined to nine broadly parallel quartz reefs within north south to north northwest south southeast trending shear zones that dip approximately 70 w six of these 2 to 10 m thick boudinaged veins have been mined to a depth of over 810 m free gold occurs in the veins and alteration haloes and is spatially and temporally associated with quartz and disseminated pyrite and arsenopyrite which in turn are closely associated with hydrothermal monazite and xenotime in the biotite plagioclase wall rock alteration around veins gold is considered to have been deposited during d 2 to d 3 deformation broadly coincident with the emplacement of syntectonic granitoids the history of volcanism granitic magmatism and gold mineralization is defined by u pb geochronology of magmatic zircons and hydrothermal monazite and xenotime the felsic volcanic host rocks have a u pb zircon age of 2587 7 ma about 40 m y older than the age of gold mineralization at 2547 10 ma determined from hydrothermal monazite the syntectonic kavital granitoid has a u pb zircon age of 2545 7 ma which overlaps with the timing of gold deposition and is consistent with structural interpretations the ramagiri and kolar gold deposits elsewhere in the dharwar craton are considered to have a similar structural timing and the hutti geochronology suggests that gold mineralization occurred throughout the dharwar craton some 80 to 120 m y later than the major peak of late archean world class orogenic gold mineralization in most other archean cratons

shrimp zircon and titanite u pb ages lu hf isotope signatures and geochemical constraints for 2 56 ga granitic magmatism in western dharwar craton southern india evidence for short lived neoarchean episodic crustal growth abstract shrimp u pb zircon and titanite age data for granites adjacent to the gadag greenstone belt ggb in the western dharwar craton wdc india establish the occurrence of voluminous 2 56 ga granitic magmatism and indicate the development and evolution of the ggb over a time span of 70 m y these new data show that the ggb has an evolutionary history distinct from the chitradurga greenstone belt cgb to the south which was previously considered to be linked to that of the ggb based on the continuity of lithological associations whole rock geochemical data indicate granites marginal to the ggb are potassic were derived from intracrustal melting of an arc crust without the involvement of mantle and demonstrates the prevalence of horizontal tectonics in the evolution of dharwar craton lu hf zircon studies indicate that these rocks were derived from a heterogeneous arc crust with distinct crustal histories on either side of the ggb the voluminous 2 56 ga granitic magmatism surrounding the ggb in the wdc in addition to the known 2 61 and 2 56 2 52 ga felsic magmatism supports a number of short lived episodic crustal growth events within the dharwar craton during the neoarchean over a period of 100 m y short lived episodic crustal growth during the archean typically within the time scale of few million years marks the distinction with long lived modern style subduction processes these variations are often attributed to hotter archean mantle and prevailing geodynamic regime

evolution of archaean crust in the dharwar craton the nd isotope record abstract a synthesis of the available nd isotope data from the dharwar craton puts important constrains on antiquity of crust extent of basement terranes and events marking juvenile crustal addition and crustal recycling the craton is divided into two blocks namely eastern dharwar craton edc and western dharwar craton wdc nd model ages trace crust extraction as far as 3 5 ga back in both the blocks although rock record of such antiquity is yet to be found in the craton in wdc 3 35 3 0 ga is the most significant period of juvenile crustal addition as well as crustal recycling significantly depleted mantle 1 5 to 6 4 existed below the wdc as early as 3 35 ga which was probably refertilized in a later event from the resultant chondritic to slightly enriched mantle 0 3 to 0 4 juvenile mafic crust was added to the wdc during 2 9 2 6 ga a widespread crustal recycling event at 2 6 ga marks the last major event in this block in edc 3 3 3 0 ga granitoids occur as vestiges and show nd model ages higher than crystallizations ages suggesting recycling of palaeoarchaean crust during 2 7 2 5 ga extensive juvenile magmatism took place in edc from variably depleted mantle 1 4 to 5 6 which is later than the global 2 7 ga peak of crustal growth attendant crustal recycling destroyed most of the earlier crust distribution of nd model ages suggests in contrast to general believe that palaeoarchaean crust was not only abundant in the wdc but also widespread in an area extending from the wdc edc boundary to further 60 150 km east up to the hungund ramagiri kolar hrk belt this belt appears to be a major crustal boundary along which terranes of different nd isotope signatures were amalgamated during the late neoarchaean by horizontal accretion major neoarchaean crustal recycling events documented in the dharwar craton are missing from nd isotope record of the eastern block eb of the north china craton this fact does not support correlation between the two cratons as suggested by some authors

archean turbidite hosted orogenic gold mineralization in the gadag greenstone belt western dharwar craton peninsular india abstract turbidite hosted orogenic gold mineralization in the archean gadag greenstone belt of the western dharwar craton forms a major auriferous zone central auriferous zone extending over a strike length of about 12 km in the gadag duplex the turbidite sequence comprises thick inter bedded medium to coarse grained lithic graywacke and thin laminated layers of fine grained carbonaceous phyllite gold bearing quartz veins impregnate preferentially along the en echelon shear planes fractures and schistosity planes auriferous quartz veins are enveloped by the altered wall rocks mineralogy of the auriferous zone is dominated by gangue minerals like quartz ankerite chlorite sericite and carbonaceous matter with subordinate plagioclase monazite and xenotime are the important accessory minerals arsenopyrite and pyrite are the major sulfide minerals but pyrrhotite chalcopyrite sphalerite galena and scheelite are also present gold in native state occurs within quartz silicates and arsenopyrite notable distinctions in mineral assemblage texture and in chemical compositions of altered wall rocks compared to the precursor host rock in the study area implies that the metasomatism and wall rock alterations are the results of pervasive infiltration and intense interaction between hydrothermal fluids and the surrounding host rocks over a prolonged period sulfides carbonates carbonaceous matter k2o mgo cao cr ni cu pb zn as and higher values of gold 0 98 4 72 ppm are added into the altered wall rocks immediately enveloping the auriferous quartz vein bodies the chondrite normalized ree pattern of altered wall rocks exhibits enriched lree lan ybn av 9 54 with prominent negative eu anomaly the observed variation in geochemical characteristics and mineral assemblages in the alteration zones indicates differential response of the host rock and intensity of alteration depending on the composition of host rocks and hydrothermal fluids the auriferous hydrothermal fluids were of low salinity 2 0 to 6 6 wt nacl dominated by co2 h2o about 30 mol co2 with moderate densities 0 7 to 1 04 g cm3 and gold deposition occurred over a wide temperature range between 175 c and 325 c gold deposition was influenced by fluid mixing phase separation and redox reactions mixing between co2 h2o fluids and more reduced fluids which evolved during fluid reaction with adjacent carbonaceous wall rocks was the key factor causing gold deposition the formation of the gadag duplex deformation folds and reverse strike slip faults discontinuities was caused by the compression associated with subduction related tectonic processes during the initial period of intrusive magmatism 2 555 6 ma regional metamorphism occurred in the entire greenstone belt while during later period hydrothermal fluids responsible for gold mineralization probably were derived from metamorphic processes as well as from intrusive granites such fluids channeled through the thrust in host turbidite sequence carrying dissolved gold associated metals and sulfur ultimately were precipitated in a reducing environment in the splays to the thrust in the gadag duplex at about 2 522 6 ma resulting in retrograde alteration assemblages

archaean gold mineralization synchronous with late cratonization of the western dharwar craton india 2 52 ga u pb ages of hydrothermal monazite and xenotime in gold deposits new zircon u pb ages for a felsic volcanic rock 2 588 10 ma and an intrusive granite 2 555 6 ma in the gadag greenstone belt in the western dharwar craton southern india are similar to dates for equivalent rocks in the eastern dharwar craton and indicates docking of the two cratons prior to this time the zircons in the intrusive granite are strongly overprinted and coexisting titanites yielded two different age populations the dominant group gives an age of 2 566 7 ma interpreted as the emplacement age whereas the minor group gives an age of 2 516 10 ma reflecting a hydrothermal overprint in situ u pb dating of monazite and xenotime in gold reefs of the gadag 2 522 6 ma and ajjanahalli 2 520 9 ma gold deposits reveal a previously undated episode of gold mineralization at 2 52 ga substantially younger than the 2 55 ga hutti deposit in the eastern dharwar craton the new dates confirm that both the younger greenstone belts and lode gold mineralization in the dharwar craton are about 100 120 my younger than in other well dated archaean cratons although gold mineralization across the craton postdates most of the magmatic activity and metamorphism at upper crustal levels widespread thermal reworking of the lower middle crust involving partial melting metamorphism and lower crustal granitoid intrusion occurred concurrently with gold mineralization it is likely that the large scale hydrothermal fluid flow that produced widespread gold deposition was also part of this tectono thermal event during the final stages of cratonization of the dharwar craton in southern india

100 ma timing paradox of archean gold abitibi greenstone belt canada new evidence from u pb and pb pb evaporation ages of hydrothermal zircons abundant hydrothermal zircon occurs within quartz tourma line veins at four gold deposits in the val d or district of the archean abitibi greenstone belt canada host rocks to the gold bearing veins are characterized by pronounced metasomatic enrichment of zr hf y and rare earth elements hydrothermal zircons contain inclusions of quartz tourmaline scheelite pyrite and gold in hydrothermal zircons and quartz primary low salinity h2 co2 fluid inclusions coexist with co2 rich inclusions indicating co2 unmixing and gold precipitation at 260 to 380 c and 2 kbar the zircons have 207pb 206pb evaporation ages of 2683 20 to 2703 4 ma close to a concordant u pb age of 2693 2 ma both commensurate with previous shrimp ages for the zircons the same vein systems have u pb ages on rutile and titanite sm nd dates on scheelite and 40ar 39ar ages on muscovite that scatter between 2630 to 2579 ma these ages gave rise to a late gold model in the archean superior province vein gold deposits are related in space and time to terrane boundary structures which mark the diachronous accretion of allochthonous tectonostratigraphic terranes from south to north from 2720 to 2680 ma consequently the vein zircon ages of 2690 to 2680 ma at val d or represent the primary mineralizing event consistent with its late kinematic timing throughout the superior province and with late archean supercontinent assembly globally whereas the young scattered ages record the time of secondary fluid events associated with reactivation of the structures resetting some isotopic systems below their conventional blocking temperature

diapirism bulk homogeneous shortening and transcurrent shearing in the archaean dharwar craton the holenarsipur area southern india abstract qualitative strain data are spatially integrated in order to define archaean foliation trajectories and variations in strain intensity and ellipsoid type in the holenarsipur area dharwar craton southern india the study provides constraints on the bulk geometry the progressive deformation and the kinematic history of this region of archaean continental crust two major structural events have shaped the study area i a regional diapiric event contemporaneous with a magmatic event and ii a later sinistral transcurrent ductile shear event which has locally reoriented both foliations and stretching lineations the entire holenarsipur supracrustal belt underwent a common tectono metamorphic history that included two metamorphic events each event corresponds temporally to a distinct strain field the first a regional amphibolite facies event was contemporaneous with the main tectonic event and probably with the intrusion of halekote trondhjemites the second occurred under greenschist facies conditions and was restricted to a late transcurrent shear zone at the eastern boundary of the greenstone belt the strain pattern prior to transcurrent shearing cannot be explained by a thrusting event unless all trace of this event had been erased by the diapirism we interpret all structures older than the transcurrent shearing to be the direct result of vertical movements linked to body forces augmented by minor horizontal crustal shortening

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

lead isotopic compositions of the western dharwar craton southern india evidence for distinct middle archean terranes in a late archean craton abstract lead and sr isotopic compositions of whole rocks and feldspar separates from several fielddefined suites of rocks from the western dharwar craton of southern india elucidate a complex history of the area the evolution of the craton earlier than 3 0 ga is difficult to determine because of thermal and metasomatic overprinting at 3 0 ga many whole rocks were completely reset then but feldspar separates preserve some of the earlier history apparently a series of terranes evolved from the mantle over the period 3 4 to 3 0 ga to form the western dharwar craton in each case metamorphism and anatexis of older terranes accompanied extraction of juvenile material from the mantle the oldest gneisses 3 4 ga had radiogenic pb and sr isotopic compositions when they formed and were derived from older crustal protoliths that were plausibly accreted to the crust at or even before 3 8 ga the old gneisses were greatly depleted in rb probably at 3 4 ga when the protoliths of younger magmatic rocks may have separated from the mantle younger gneisses apparently formed from these mafic intermediate protoliths in the age range of 3 2 to 3 0ga the 3 0 ga event in the central part of the craton was accompanied by intrusion of small diapiric trondhjemites formed by melting of older crust and penecontemporaneous metasomatism of country rocks by hydrous fluids carrying u and other lithophilic elements the resultant deep crust was greatly depleted in heat producing elements and the craton has been inactive since 3 0 ga except for production of minor granites from depleted source regions at 2 5 2 6 ga the lack of activity at 2 5 ga contrasts strongly with extensive magmatism and metamorphism in surrounding areas that had not undergone depletion at 3 0 ga lower crustal depletion also has caused present day reduced heat flow to be very low

geochemistry and petrogenesis of amphibolites kolar schist belt south india evidence for komatiitic magma derived by low percentages of melting of the mantle the kolar schist belt of the dharwar craton of south india is an archean greenstone belt dominated by metavolcanic rocks the mafic metavolcanic rocks occur as komatiitic and tholeiitic amphibolites the komatiitic amphibolites occur along the margins of the n s trending synformal belt they are much less abundant than the tholeiitic amphibolites and have 14 to 21 3 wt per cent mgo the komatiitic amphibolites from the west central part of the belt have two distinctive ree patterns 1 those enriched in the middle to light ree but depleted in ce relative to nd and 2 those with patterns that are convex up i e depleted in both light and heavy ree although more depleted in the light ree associated tholeiites have light ree depleted to flat ree patterns komatiitic and tholeiitic amphibolites from the eastern part of the belt have enriched light ree patterns the tholeiitic amphibolites from the kolar schist belt are similar to the th i and th ii types of archean tholeiites of condie 1981 the komatiitic amphibolites are similar to komatiites and komatiitic basalts of barberton mountainland but have higher feo and tio 2 abundances and lower yb gd ratios the petrogenetic interpretations for these rocks are based primarily on a modification of the mgo feo diagram of hanson langmuir 1978 and modelling of zr ni and ree all of the rocks have undergone some fractionation while the modelling does not give accurate temperatures pressures compositions and extents of melting of the mantle sources for the various amphibolites it does present an approach which can be used for estimating these parameters for example the komatiitic amphibolites appear to be derived from melts generated by 10 to 25 per cent melting of the mantle over a range of depths and temperatures greater than 80 km and 1575 c the variation in the p t conditions of magma generation is possibly due to adiabatic melting in mantle diapirs with a range of feo mgo ratios if the tholeiitic amphibolites are derived from similar mantle sources it is not clear that they are their parent melts may have been generated by similar extents of melting but at depths of less than 80 km the komatiitic amphibolites from the west central part of the belt were generated from light ree depleted mantle whereas those from the eastern part of the belt appear to have been generated from light ree enriched mantle the sources for the komatiitic amphibolites in both areas were significantly enriched in feo relative to pyrolite thus a light ree depleted and a light ree enriched source appear to have provided mafic volcanics with similar major element chemistry to this belt during its evolution

accretionary history of the archean barberton greenstone belt 3 55 3 22 ga southern africa the 3 55 3 22 ga barberton greenstone belt south africa and swaziland and surrounding coeval plutons can be divided into four tectono stratigraphic blocks that become younger toward the northwest each block formed through early mafic to ultramafic volcanism onverwacht group probably in oceanic extensional island or plateau settings volcanism was followed by magmatic quiescence and deposition of fine grained sediments possibly in an intraplate setting late evolution involved underplating of the mafic crust by tonalitic intrusions along a subduction related magmatic arc yielding a thickened buoyant protocontinental block the growth of larger continental domains occurred both through magmatic accretion as new protocontinental blocks developed along the margins of older blocks and when previously separate blocks were amalgamated through tectonic accretion evolution of the barberton belt may reflect an early archean plate tectonic cycle that characterized a world with few or no large stabilized blocks of sialic crust

alluvial architecture paleohydrology and provenance tracking from the neoproterozoic banganapalle formation kurnool group india an example of continental sedimentation before land plants abstract an integrated study involving facies association analysis architectural element analysis paleohydrology and detrital zircon geochronology allowed detail insight of sedimentology and paleogeography of neoproterozoic banganapalle formation bf kurnool group detailed process based facies and paleoenvironmental analysis have led to the identification of fourteen facies types grouped under four different facies associations which record paleoenvironmental settings ranging between mid alluvial fan to distal fluvial plain whereas mass flows hyperconcentrated flows streamlets and sheet floods dominate the depositional process on the bf fan middle to distal surface streams of varied geometry viz braided and ephemeral meandering occupied the proximal and distal bf alluvial plain our study supports the emerging view that even without the buffering effect of land plants channels developed sinuous planform in pre vegetation time subject to low gradient and discharge of alluvial plain and adequate supply of fine detritus from occurrence of boulder gravelly mass flows boundary pebbly streamlet thalweg and pebbly granular sheet flood deposits in the alluvial fan thick silty muddy stable flood plain deposits in the distal alluvial plain and unequivocal southward paleocurrent irrespective of facies association it is inferred that the bf alluvial basin received mixed sediment from long term beveled source in the north and northwest from two u pb detrital zircon geochronology age clusters viz paleo to mesoarchean 3410 ma 3075 ma and neoarchean to late paleoproterozoic 2750 ma 2500 ma provenance for the bf is tracked in the north and northwest of the kurnool basin i e the ttg suite of the peninsular gneiss and volcanics hosted greenstone belts in the central and western dharwar craton a mixing of sediments from two different provenances is inferred a consistent low water discharge with marginal downstream increase is suggested for the bf alluvial system from paleohydraulic analysis except for some occasional spurts of high discharge in mid fan at times of intense rainfall in the hinterland

strain patterns in archaean dome and basin structures the dharwar craton karnataka south india abstract models simulating the role of gravity in the earth s crust are the main source of criteria used for the field identification of diapirs after a short review of the distribution of finite strain in experimental diapir models we describe an example where differential erosion of a tilted craton has provided 3d geometrical information on patterns in a diapiric system at various depths from greenschist to granulitic facies conditions within the archaean continental crust of the dharwar craton south india diapirs and anti diapirs sagducted greenstones are observed at different levels structures and strain are consistent with all the field identification criteria inferred from experimental simulation but some peculiar structural features are also observed which are not predicted by the models these features such as strain trajectory triple junctions result from i the progressive deformation of diapiric domes or sagducted basins ii interferences between diapiric structures body forces and iii the superimposition of diapiric strain fields on regional horizontal shortening boundary forces

correlations between the eastern block of the north china craton and the south indian block of the indian shield an archaean to palaeoproterozoic link abstract recent tectonometamorphic data reveal that the north china craton formed by amalgamation of an eastern block eb and a western block wb along the trans north china orogen tnco and the indian shield formed by amalgamation of the south indian block sib and the north indian block nib along the central indian tectonic zone citz the eb of the north china craton and the sib of the indian shield share many similar magmatic and sedimentary features the early archaean supracrustal sequences in both the eb and sib consist of 3 6 3 4 ga fuchsite quartzites pelitic gneisses calc silicates marbles banded magnetic quartzites and amphibolites called the caozhuang group in the eb and the older metamorphic group omg in the sib the middle archaean assemblages in both the blocks can be divided into an early 3 4 3 3 ga phase represented by the chentaigou supracrustal rocks and orthogneisses in the eb and the holenarsipur supracrustal rocks and the gorur orthogneisses in the sib and a late 3 1 2 9 ga phase represented by the qianan supracrustal rocks and the yangyashan orthogneiss in the eb and the sargur group and the peninsular gneiss in sib the late archaean taishan group and its equivalents in the eb are stratigraphically similar to the dharwar supergroup in the sib moreover both the eb and sib are characterised by near contemporaneity of late archaean granitoid intrusive and metamorphic events in addition dome and basin structures are dominant in both the eb and sib and anticlockwise p t paths charaterise the metamorphic evolution of the late archaean granulites in the two blocks the palaeoproterozoic sedimentary volcanic rocks in both blocks comprise lower clastic rich middle volcanic rich and upper clastic carbonate sequences the strong resemblance of the archaean to palaeoproterozoic magmatic and sedimentary records suggests that it is possible that the eb and sib are dispersed remnants of what was once a single continent a possible fit is proposed for the reconstruction of the eb and sib where the northern margin of the eb is placed adjacent to the western margin of the sib with the tnco and wb representing the continuations respectively of the citz and nib this fit suggests that the eb sib and the wb nib represent two discrete continental blocks that joined along the tnco citz orogen during a palaeoproterozoic collisional event fragmentation of the eb and sib may have occurred at the beginning of the mesoproterozoic and by 1 4 ga the eb and sib may have separated into two different continental blocks as evidenced by striking differences in the mesoproterozoic sedimentary successions and associated bimodal volcanics in the two blocks

u pb sphene dating of metamorphism the importance of sphene growth in the contact aureole of the red mountain pluton laramie mountains wyoming the relative importance of thermal diffusion versus new growth or recrystallization on u pb isotopic data from sphene is assessed through a study of amphibolites and granite gneisses within the contact aureole of the red mountain pluton laramie anorthosite complex wyoming samples were collected along a traverse approximately perpendicular to the margin of the intrusion over a distance of 0 13 to 2 65 km from the contact the 207pb 206pb ages of sphene from amphibolite samples range between 1 43 ga the intrusive age of the red mountain pluton to 1 78 ga the age of regional metamorphism the 207pb 206pb ages of sphene in rocks metamorphosed above 700 c are within error of the intrusive age of the pluton and appear to have resulted from diffusional resetting of preexisting sphene and the metamorphic growth of additional sphene at 1 43 ga at greater distance from the contact the 207pb 206pb ages range from 1 45 to 1 72 ga this 300 million year spread in ages is interpreted to result from two periods of sphene growth one produced during regional metamorphism at 1 78 ga and another generation of newly grown or recrystallized sphene that formed during contact metamorphism at 1 43 ga these two age populations may be identified on the basis of petrographic textures the morphologies and color differences of grain separates as well as by the u pb systematics in rocks metamorphosed to temperatures less than 700 c sphene growth was the dominant process controlling the response of the u pb isotope system to contact metamorphism sphene grew well outside the zone of obvious contact metamorphism the u pb sphene ages were reset by diffusion only at high temperatures supporting the experimentally determined closure temperature estimates for the u pb system in sphene of around 650 c cherniak 1993 this study demonstrates that u pb ages of sphene can be used to date metamorphism not only in areas with a simple geologic history such as igneous intrusion or single metamorphic or deformational events but also to date multiple events so long as different generations of sphene can be identified and separated

pb sr and nd isotope systematics of metavolcanic rocks of the hutti greenstone belt eastern dharwar craton constraints on age duration of volcanism and evolution of mantle sources during late archean abstract the hutti greenstone belt hosting major gold mines is made up of tholeiitic basalts felsic volcanic rocks and sediments metamorphosed to amphibolite facies and surrounded by granitoid rocks predominantly of granodiorite in composition the granitoid rocks show intrusive contact relationship at places along the eastern and northern margins of the belt while such relationships could not be observed along the western margin as it is covered by soil the tholeiitic basalts have flat to moderately lree enriched chondrite normalized ree patterns and show depletion in nb relative to morb the hutti metabasalts define a collinear array in the rb sr isotope evolution diagram with a slope corresponding to an age of 2706 130 ma the higher uncertainty is due to scatter caused by mobility of rb and sr during metamorphism and low temperature hydrothermal alteration in the 206 pb 204 pb vs 207 pb 204 pb diagram the metabasalts define a collinear array corresponding to an age of 2637 150 ma with significant scatter indicating that pb was also mobilized by the post crystallization alteration processes the sm nd isotope system in the hutti metabasalts has been least disturbed giving an isochron age of 2662 81 ma which is suggested as the age of formation of their precursors combined with the published u pb shrimp ages on zircons from the felsic volcanic rocks it is inferred that the hutti greenstone belt formed over a period of 86 ma the major greenstone belts of the eastern dharwar craton have evolved coevally at ca 2700 ma ago and are older than the surrounding granitoid rocks the metabasalts have e nd values of 1 4 to 3 0 and e sr values of 23 4 to 2 0 and plot close to the mantle array they were derived from long term lree depleted mantle source the felsic volcanic rocks have e nd values of 1 3 and 1 4 and e sr values of 30 6 and 89 3 respectively their magmas were derived from older continental crustal sources

archean banded iron formations of india abstract archean banded iron formations bifs are important lithologies for understanding the early earth processes greenstone belts in the four archean cratonic nucleii of peninsular india namely singhbhum bastar dharwar and bundelkhand host bif units that can be important candidates for case studies the bifs in these greenstone successions represent both algoma and superior type associations the oldest record comes from the paleoarchean southern eastern and western iron group of the singhbhum craton and the sargur supracrustals of the dharwar craton mesoarchean and neoarchean greenstone belts in the dharwar and bundelkhand cratons record a number of cycles of bif deposition in a spectrum of depositional settings from manganiferous arenite carbonate shelf associations to deep water volcanics and graywacke associations the bifs from the neoarchean bailadila group in the bastar craton were deposited in siliciclastic shelf association compositional variations in major trace and ree patterns have been evaluated from published data high grade iron ores are mainly mined from the bifs and locally mn ores occur in association as well microbial carbonates associated with some of the paleoarchean as well as neoarchean iron manganese formations suggest early life activities the lithological association of the archean iron formations have been explained in terms of both active margin and passive margin depositional settings bifs in association with manganiferous formations as old as paleoarchean time provide an opportunity to probe into the redox stratification of oceanic hydrosphere and in turn the oxygenation of early atmosphere

formation of archean 3600 2500 ma continental crust in the dharwar craton southern india abstract the generation preservation and destruction of continental crust on earth is of wide interest in understanding the formation of continents cratons and supercontinents as well as related mineral deposits in this contribution we integrate the available field petrographic geochronologic elemental nd hf pb isotope data for greenstones ttg gneisses sanukitoids and anatectic granites from the dharwar craton southern india this review allows us to evaluate the accretionary processes of juvenile crust mechanisms of continental growth and secular evolution of geodynamic processes through the 3600 2500 ma window hence providing important insights into building of continents in the early earth the dharwar craton formed by assembly of micro blocks with independent thermal records and accretionary histories the craton can be divided into three crustal blocks western central and eastern separated by major shear zones the western block contains some of the oldest basement rocks with two generations of volcano sedimentary greenstone sequences and discrete potassic plutons whereas the central block consist of older migmatitic ttgs abundant younger transitional ttgs remnants of ancient high grade supracrustal rocks linear volcanic dominated greenstone belts voluminous calc alkaline granitoids of sanukitoid affinity and anatectic granites in contrast the eastern block comprises younger transitional ttgs abundant diatexites thin volcanic sedimentary greenstone belts and calc alkaline plutons published geochronologic data show five major periods of felsic crust formation at ca 3450 3300 ma 3230 3150 ma 3000 2960 ma 2700 2600 ma and 2560 2520 ma which are sub contemporaneous with the episodes of greenstone volcanism u pb ages of inherited zircons in ttgs as well as detrital zircons together with nd pb hf isotope data reveal continental records of 3800 3600 ma the u pb zircon data suggest at least four major reworking events during ca 3200 ma 3000 ma 2620 2600 ma and 2530 2500 ma corresponding to lower crustal melting and spatially linked high grade metamorphic events the ttgs are sub divided into the older 3450 3000 ma ttgs and the younger 2700 2600 ma transitional ttgs the older ttgs can be further sub divided into low al and high al groups elemental and isotopic data suggest that the low al type formed by melting of oceanic island arc crust within plagioclase stability field in contrast the elemental and isotopic features for the high al group suggest derivation of their magmatic precursor by melting of oceanic arc crust at deeper levels 55 65 km with variable garnet and ilmenite in residue the transitional ttgs likely formed by melting of composite sources involving both enriched oceanic arc crust and sub arc mantle with minor contamination of ancient crustal components the geochemical and isotopic compositions of granitoids with sanukitoid affinity suggest derivation from enriched mantle reservoirs finally anatectic granites were produced by reworking of crustal sources with different histories in the light of the data reviewed in this contribution we propose the following scenario for the tectonic evolution of the dharwar craton during 3450 3000 ma ttgs sources oceanic arc crust formed by melting of down going slabs and subsequent melting of such newly formed crust at different depths resulted in ttg magmas on the contrary by 2700 ma the depth of slab melting increased melting of slab at greater depth alongside the detritus results in enriched melts partly modified the overlying mantle wedge subsequent melting of such newly formed enriched oceanic arc crust and surrounding arc mantle generated the magmatic precursor to transitional ttgs finally at ca 2600 2560 ma eventual breakoff of down going slab caused mantle upwelling which induced low degree 10 15 melting of overlying enriched mantle at different depths thereby generating the sanukitoid magmas which upon emplacement into the crust caused high temperature metamorphism reworking and final cratonization the crustal accretion patterns in the dharwar craton share similarities with those in other archean cratons such as the bundelkhand craton in central india pilbara yilgarn craton in western australia southern africa swaziland and limpopo belt north china craton tanzania craton antongil craton ne madagascar

mesoarchean convergent margin processes and crustal evolution petrologic geochemical and zircon u pb and lu hf data from the mercara suture zone southern india abstract the mercara shear zone is sandwiched between the western dharwar craton and the coorg block in the southern granulite terrain of india and is marked by steep gravity gradients interpreted to suggest the presence of underplated high density material in the lower crust here we present geological petrological and geochemical data together with zircon u pb ages and lu hf isotopes from a suite of metaigneous ttg related gneisses charnockite metagabbro mafic granulite and metasedimentary quartz mica schist khondalite garnet biotite gneiss kyanite sillimanite bearing metapelite rocks from this zone geochemical data on the magmatic suite suggests formation through subduction related arc magmatism whereas the metasediments represent volcano sedimentary trench sequences phase equilibrium modeling of mafic granulites from the mercara shear zone suggests p t range of 10 12 kbar at 700 c to 900 c the zircon data yield weighted mean 207pb 206pb ages of 3229 80 ma for metagabbro 3168 25 ma for the charnockite and 3181 20 ma for the mafic granulite ages ranging from 3248 28 ma to 3506 26 ma were obtained from zircons in the kyanite sillimanite bearing metapelite 3335 44 ma from khondalite 3135 14 ma from garnet biotite gneiss 3145 17 ma to 3292 57 ma from quartz mica schist and 3153 15 ma to 3252 36 from ttg gneiss the tightly defined ages of 3 1 to 3 2 ga from igneous zircons in the magmatic suite suggest prominent mesoarchean convergent margin magmatism the timing of high grade metamorphism as constrained from metamorphic overgrowths in zircons is ca 3 0 ga which might mark the collisional event between the western dharwar craton and the coorg block hf isotope features suggest magma derivation mostly from juvenile sources and the lu hf model ages indicate that the crust building might have also involved partial recycling of basement rocks as old as ca 3 8 ga our study defines the mercara shear zone as a terrane boundary and possible mesoarchean suture along which the coorg block was accreted to the western dharwar craton the accretion of these continental fragments might have coincided with the birth of the oldest supercontinent ur

removing the heavy mineral effect to obtain a new pb isotopic value for the upper crust 1 based on the concept that sedimentary processes average large areas of exposed crust sediment data have been widely used to estimate the average pb isotopic composition of the upper continental crust however the possible effects of mineral sorting processes on sediment pb isotopes have never been fully investigated here we report pb isotopic compositions of himalayan river sediments as well as those of several grain size fractions and mineral separates we demonstrate that pb isotopes of both bed loads and suspended loads are biased toward more radiogenic values than their source rocks due to a heavy mineral effect caused by mineral sorting during fluvial transport on continents the sparse zircons monazites and allanites present in all samples 1 wt including suspended loads generate a pb isotopic variability as large as that observed in the earth s mantle after correction of this effect we propose an average value for the composition of the upper himalayan crust together with a new pb isotopic value for the earth s upper continental crust we conclude that mineralogical effects must be evaluated carefully before using pb isotopes of sediments as provenance and anthropogenic tracers

neoarchean microblock amalgamation in southern india evidence from the nallamalai suture zone abstract a collage of crustal blocks ranging in age from mesoarchean to neoarchean accreted to the southern margin of the dharwar craton in peninsular india preserve distinct evolutionary history but share a common metamorphic record during archean proterozoic transition here we investigate the tectonic boundary between two of these microblocks the shevaroy block to the west and the madras block to east termed as the nallamalai suture zone nlsz we present integrated field petrological geochemical and zircon u pb and lu hf data from a suite of meta igneous and metasedimentary units along the nlsz and its flanks zircon grains from the meta monzogranite hornblende biotite gneiss amphibolite granodiorite diorite charnockite bif banded iron formation and bmq from this area show magmatic emplacement ages clustering around 2 50 to 2 56 ga except for the meta monzogranite showing ages up to 3 2 ga correlating with long lived convergent margin magmatism through multiple slab melting episodes all the rocks show tightly constrained early paleoproterozoic ca 2 46 2 48 ga metamorphic ages including the metamorphic zircon in the bifs marking the timing of collision of the two continental blocks with consumption of the intervening oceanic lithosphere the ehf t values of magmatic zircon grains from the different rock types range from 4 1 to 5 7 and together with t dm c hf model ages of 2672 3247 ma a dominantly juvenile crust growth is indicated which initiated around 3 3 ga and continued to 2 7 ga followed by crustal reworking in a continental arc towards the end of neoarchean the geochemical data suggest that tholeiitic to calc alkaline parental melts for the mafic intermediate felsic suite were generated by low degree partial melting of a peridotitic mantle wedge metasomatized by subduction derived fluids and sediments and continuous slab melting ensued by intracrustal fractional crystallization of melts with reworking of older continental crust the bif and bmq samples display positive eu anomalies negative to negligible ce anomalies and superchondritic y ho ratios suggesting their formation in an oceanic realm proximal to an active continental margin setting the magmatic and tectonic attributes are consistent with eastward oceanic subduction and ocean closure along the nlsz which is defined here as the trace of a suture welding the shevaroy and madras blocks we envisage that multiple subduction and amalgamation of several microblocks occurred in the dharwar craton and its southern domains amalgamating several microblocks during the archean paleoproterozoic transition

u pb investigations on zircons from pre variscan gneisses i a study from the schwarzwald west germany abstract field observations in the schwarzwald indicate that pre variscan rocks were formed by the following events 1 1 intrusion of granitic to granodioritic magma into sediments 2 2 a sequence of two anatectic events with an intervening regional metamorphism and development of a gneissic schistosity the absolute chronology of these older gneisses and migmatites has not yet been satisfactorily resolved we collected several samples of a coarse grained homogeneous orthogneiss of granodioritic composition and one sample of a metasedimentary source rock related to this orthogneiss body in the einetwald forest north of steinach kinzig valley the metasedimentary rock corresponds to the biotitepoor paragneisses in the schwarzwald the zircons in the latter sample are detrital and only very small specimens 45 m are euhedral the zircons from the orthogneiss samples are euhedral some are zoned and some have dark inclusions analyses of the three coarser fractions of the paragneiss form a linear array on a concordia diagram with upper and lower intercepts of about 2000 myr and 524 20 myr respectively the 2000 myr value is interpreted as the average age of the sedimentary source rocks for this material the 524 myr intercept defines an event responsible for most of the lead loss in the zircons as well as new zircon growth analyses of the zircons from the orthogneiss samples do not show a linear array on the concordia diagram because of inclusions of older inherited zircons stepwise leaching of two zircon fractions shows newly grown u rich zircon rims around old cores a 207 pb 206 pb age of 517 15 myr was found for the first dissolution steps about 50 of the zircons dissolved in subsequent steps with progressive dissolution of the residue 207 pb 206 pb age increased to 950 myr the u pb zircon data for the paragneiss and the orthogneiss establish an age of 520 15 myr for the magma intrusion

bimodal magmatism in the eastern dharwar craton southern india implications for neoarchean crustal evolution abstract archean cratons provide windows to the crustal evolution history in the early earth the dharwar craton is one of the major cratonic blocks in peninsular india and is composed of several ancient microcontinents where multiple continental growth and recycling occurred from 3 8 to 2 5 ga here we investigate a suite of magmatic rocks including granitoids mafic magmatic enclaves ultramafic inclusions and synplutonic mafic dyke from the western margin of the eastern dharwar craton which provide insights on bimodal magmatism in a subduction related arc setting and crustal growth during neoarchean field evidence and geochemical features suggest mixing and mingling of mafic and felsic magmas geochemical features including incompatible and high field strength element features of the enclaves indicate heterogeneous sources involving dominantly enriched mantle reservoirs with minor depleted mantle whereas the host granitoids display depleted to enriched source we present zircon u pb age data from the various rock types and the combined results display unimodal distribution with a single peak of 207pb 206pb age at 2531 ma n 159 suggesting a major neoarchean bimodal magmatic pulse the zircon u pb ages of the mafic enclaves indicate either similar ages or slightly younger ages as compared to their host granitoids implying that enclaves represent late stage injections into crystallizing host granitoid magmas the trace and rare earth element data on zircon from these rocks are consistent with magmatic crystallization zircons from most of the rocks in our study display uniformly positive ehf t 0 3 8 6 suggesting depleted mantle juvenile source for the neoarchean arc building and formation of new crust some of the mafic magmatic and ultramafic enclaves as well as the mafic dyke and charnockite display mixed positive and negative ehf t values 7 0 to 3 8 implying mixed depleted mantle and reworked crustal components of neoarchean to mesoarchean age most of the hf depleted mantle model ages tdm 2520 3115 ma and crustal residence ages tdmc 2507 ma to 3452 ma fall within the region bounding chur and depleted mantle lines suggesting that the dominant magma source involved juvenile depleted mantle components thus latest neoarchean marks a major phase of continent building in the eastern dharwar craton and the results presented in our study suggest that bimodal magmatism in a subduction related setting identical to those in modern convergent margins contributed to crustal growth

neoarchean magmatism in shimoga greenstone belt india evidence for subduction accretion processes in the evolution of the western dharwar stratigraphy abstract new geochemical and geochronological data are presented for a suite of metavolcanic rocks from shimoga greenstone belt to understand their petrogenesis and to constrain the timing of final mafic magmatic activity in western dharwar craton we report an sm nd isochron age of 2638 66 ma for metabasaltic and metaandesitic rocks of the stratigraphically uppermost medur formation of dharwar supergroup exposed in the belt which is the youngest age obtained yet for neoarchean mafic magmatism in western dharwar craton the emplacement of the basalt andesite dacite rhyolite suite of rocks took place in a magmatic arc culminating in the deposition of vast greywacke argillites in a continental margin type setting the magmatic precursors of the metavolcanic rocks were generated by partial melting of depleted mantle by slab derived fluids with variable input from the subducting slab assimilation fractional crystallization processes may also have contributed to the magmas to a significant extent the younger mafic lithologies of the dharwar stratigraphy represent accretionary orogens and the date obtained in this study points towards the final stages for the assembly of western dharwar craton by subduction processes during neoarchean the thickness and extent of the greywacke argillite suite in sgb could be attributed to the protracted deposition during amalgamation of western dharwar craton with a northern archean continental crust that might underlie deccan volcanic rocks

a 2 5 ga porphyry cu mo au deposit at malanjkhand central india implications for late archean continental assembly abstract eight re os ages from six molybdenite samples representative of the cu mo au mineralization at the giant malanjkhand deposit in madhya pradesh were obtained using id ntims these data provide a clear late archean early paleoproterozoic age for this deposit and by implication for its calc alkaline granitoid host among other diverse models the origin of malanjkhand has been debated as orogenic lode style associated with development of a quartz reef in a shear zone or as porphyry style associated with a pink granitoid intrusion that is conspicuously present in the vicinity of the brittle ductile deformed quartz reef previous models included middle proterozoic ages for the cu mo au mineralization based on poorly constrained rb sr and k ar data direct dating of molybdenite shows that stringer mineralization in the quartz reef and disseminated and vein mineralization in the granite were contemporaneous at 2490 8 ma 2489 5 1 4 ma based on regression without uncertainty in the 187re decay constant mswd 0 5 n 5 additional molybdenite from the quartz reef dated at 2475 and 2450 ma represents at least two pulses of reworking that we suggest configured the elongate and arcuate quartz reef into its present position we suggest that the quartz reef is a high silica stockwork cap embedded in its primary potassic alteration halo and subsequently tilted so that it lies convex to the east with deeper levels exposed to the north petrographic evidence coupled with high re concentrations for molybdenites 400 650 ppm support this scenario and suggest that malanjkhand is a subduction related stockwork porphyry style cu mo au deposit involving mantle malanjkhand geology shares little affinity with three surrounding and tectonically juxtaposed terranes we suggest that the malanjkhand cu mo au deposit and the surrounding batholith containing multiple cu mo au prospects may be the vestiges of a microplate captured along the north margin of the nearly amalgamated southern indian craton at 2 5 ga as the southern craton began to converge with the northern indian craton or other protocontinents now embedded or consumed within the central indian tectonic zone citz this scenario could imply an early paleoproterozoic age for the earliest development of the citz at least in the region of the central indian shear suture cis whose marked ene trend imprints the northwestern part of the malanjkhand batholith and the cu mo au deposit based on a compilation of 2 5 ga events in both the southern and northern indian cratons we suggest that some units in the citz linked an extensive and continuous late archean early paleoproterozoic orogenic belt that may extend to the moyar bavali bhavani attur palghat and cauvery shear zones in southern india and include inboard units of the eastern ghats and the aravalli delhi orogenic belts robust geochronology that can be tied to the early history within these orogenic belts is scarce and extensive reworking during grenvillian and pan african time creates a pervasive overprint at some localities this late archean early paleoproterozoic belt preserves sutures within a coalesced late archean continent that included east antarctica napier and vestfold hills complexes at 2 5 ga

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 abstract the succession in the late archaean supracrustal belts in the chitradurga region begins with basal quartz pebble conglomerates and quartzites which were deposited on a basement of tonalitic granitic gneisses ca 3000 ma containing tracts and enclaves of older supracrustal rocks the basal beds are overlain by basic metalavas and amphibolites interbedded with cross bedded quartzites and siliceous phyllites this series passes up into siliceous phyllites locally containing a large lenticular mass of polymict conglomerate talya conglomerate overlain by banded iron formations and siliceous phyllites including sporadic chert pebble conglomerates greater subsidence in part of the basin accommodated greater thicknesses of basic volcanic and acid pyroclastic rocks the latter being more abundant at higher levels with progressive deepening of the whole basin fine grained graded greywackes and local polymict conglomerates aimangala conglomerate were deposited the turbidite sequence forms the youngest sedimentary rocks exposed estimated total stratigraphic thickness is at least 10 km in deeper parts of the basin deformation led to a series of upright anticlines and synclines and related ls fabrics with extreme variations in plunge of the coaxial fold axes and l fabrics within axial surfaces which maintain a steep orientation low grade metamorphism outlasted the deformation sedimentation and volcanism in the chitradurga supracrustal belt is linked to variable subsidence of the basement foundation probably as a result of rifting the structural evolution of the belt followed as a direct continuation of events that controlled the depositional and volcanic history variable displacement of the basement during these late archaean events in the karnataka craton took place on shear zones and related fractures that acted as channels for water and co 2 as indicated by vein minerals and alteration products uplift of basement segments and their distension by granitic diapirs led to deformation of the supracrustal cover made ductile by its high water content

pb and nd isotope constraints on the origin of high mg and tholeiitic amphibolites kolar schist belt south india the late archean north south trending kolar schist belt in south india 4 km wide by 80 km long is thought to be a suture between two gneiss terranes krogstad et al 1989 within this volcanics dominated belt are recognized both tholeiitic and high mg komatiitic and picritic amphibolites which make up some 70 and 5 respectively of the exposed outcrops a massive tholeiitic amphibolite separates the belt into western and eastern parts a pb pb whole rock age of 2732 155 ma on samples from a single outcrop of massive tholeiite is a minimum age for this rock samples of this rock have nd values at 2700 ma that range between 3 8 and 6 8 1 initial 238u 204pb of 7 5 and k1 initial 232th 238u of about 4 two different types of high mg amphibolites are recognized from the western part of the belt a picritic or p type and a komatiitic or k type the p type have highly variable ce al ratios all greater than chondritic nd yb ratios greater than chondritic nd at 2700 ma of 1 5 to 8 and pb isotope compositions variable in 207pb 204pb with 1 of about 8 0 and k1 of about 4 the trace element data suggest that the light ree enrichment is a character of the mantle source and is not due to residual garnet the k type amphibolites have near chondritic ce al and nd yb ratios nd at 2700 ma of 1 5 to 8 and 1 of about 8 and k1 of about 4 although the p type is light ree enriched compared to the k type both types have similar ce nd ratios as well as initial pb and nd isotopes if the 2696 136 ma age for the sm nd isochron which includes both types of high mg amphibolite has any significance it dates the time of light ree enrichment of the mantle source for the p type komatiitic amphibolites the high mg amphibolites in the eastern part of the belt are light ree enriched have pb isotopic compositions that are variable in 207pb 204pb with a 1 about 8 5 and nd at 2700 ma of 1 8 to 4 5 hydrothermal fluids associated with metamorphism and shearing prior to about 2400 ma ago were responsible for the introduction of gold quartz carbonate veins into the kolar schist belt the pb isotope composition of galena in these veins suggests that these fluids may have also introduced extraneous pb from adjacent older granitoid gneisses into the amphibolites which could be responsible for the variability in the 207pb 204pb ratios of the samples this extraneous pb probably is not responsible for the distinct pb isotope character of each type of amphibolite

archean granite greenstone tectonics at kolar south india interplay of diapirism and bulk inhomogeneous contraction during juvenile magmatic accretion 1 the structural study of the kolar greenstone belt and surrounding granite gneiss terrains combined with u pb dating reveals that the middle and lower crustal tectonoplutonic pattern of the eastern dharwar craton developed during a major magmatic accretion event between 2550 and 2530 ma the granite greenstone pattern resulted from the interference of gravity driven sagging of the greenstones i e diapirism e w bulk inhomogeneous shortening combined with horizontal n s stretching and syntectonic juvenile pluton emplacement bulk inhomogeneous contraction is accommodated by the synchronous development of a pervasive n s trending vertical foliation shallow stretching lineation and conjugate strike slip shear zone pattern within and outside the greenstone belt resulting in regional horizontal pure shear deformation the plutons around the greenstone belt record regional contraction by developing one set of strike slip c s fabrics of the shear zone pattern the development of the granite greenstone pattern was coeval and compatible with deformation during juvenile magmatic accretion melting and granulite metamorphism in the lower crust the kolar example points to a specific crustal rheology that allowed sagduction of the greenstones and regional distributed bulk inhomogeneous strain due to mechanical homogeneity and low viscosity provided by large scale melting during the accretion event this example further suggests specific boundary conditions to the craton that allowed e w inhomogeneous shortening to be accommodated by n s stretching and spreading of the crust without significant tectonic thickening such tectonoplutonic pattern is specific to the archean and may develop as a consequence of mantle plume activity in intracontinental settings

archean sedimentation on dharwar craton india and its implications abstract the dharwar craton is the largest archean cratonic nuclei of india and is made up of western and eastern blocks separated by the 2 5 ga closepet granite batholith the western dharwar craton consists mostly of 3 3 3 0 ga ttg the peninsular gneissic complex older mesoarchean greenstone sargur type and younger neorchean greenstone the dharwar supergroup comprising of lower bababudan and upper chitradurga groups in contrast the eastern dharwar craton is mostly made of granitoid gneisses and felsic volcanics with some neorchean supracrustal enclaves sandur ramgiri kolar kadri schist belts recently it has been suggested that the dharwar cratonic block is formed by assembly of western central and eastern micro blocks separated by shear zones jayananda et al 2018 the greenstone successions are present in all three dharwar micro blocks however the proportion of greenstones is much higher and the quality of preservation is much better in the western micro block the mesoarchean sargur group hosts barite deposit and consists of fuchsite quartzites carbonates metapelites banded iron formations and metamorphosed basalts and komatiites researchers have postulated a platformal orthoquartzite carbonate pelite association for the sargur group some researchers examined the barite deposits of the sargur group and inferred a subaerial volcanism during the sargur sedimentation the neoarchean bababudan group comprises largely terrestrial to shallow marine sedimentary successions glacial deposits bif volcanic and volcaniclastics rocks in contrast the overlying chitradurga group comprises conglomerates greywackes phyllites carbonates bifs cherts shales associated with a variety of volcanic rocks ranging from pillowed basalts to rhyolites and indicates relatively deep water sedimentation in a subsiding basin in an active continental margin setting stromatolites are abundant in the chitradurga group as also in other neoarchean supracrustal successions of the dharwar craton in this review we have critically synthesized published sedimentological data from both older as well as younger greenstone successions of the dharwar craton and have presented the archean sedimentation history of the dharwar craton we have highlighted the research gaps that researchers may find helpful

u pb and hf isotope records in detrital and magmatic zircon from eastern and western dharwar craton southern india evidence for coeval archaean crustal evolution abstract u pb and lu hf isotopic records in detrital and magmatic zircons from the eastern and the western dharwar craton edc and wdc suggest presence of 3 4 ga crustal components in both the blocks magmatic zircon from the western block has ages ranging between 3 1 and 3 2 ga while those from the eastern block show a bi modal age distribution with records of 3 0 3 2 ga protolith components as well as 2 7 and 2 5 ga metamorphic overgrowths detrital and magmatic zircons from granitoid conglomerate clasts of the western dharwar block show initial hf values consistent with models for the early archaean mantle suggesting their juvenile character lower hf values in younger as well as detrital zircons from eastern dharwar block reflect importance of reworking of 3 2 ga crust the combined u pb and hf isotope study strengthens suggestions for contemporaneous crust formation processes in both the western and eastern parts of the dharwar craton

the geologic setting mineralogy geochemistry and genesis of gold deposits of the archean kolar schist belt india the kolar schist belt one of the auriferous archean schist belts in the dharwar craton includes two types of gold deposits 1 a stratiform sulfide type associated with amphibolites and banded ferruginous quartzite and 2 a gold quartz carbonate vein type associated with light rare earth element lree enriched komatiitic and tholeiitic amphibolites on the eastern part of the belt many lodes of the former are banded and show deformation similar to that of their host rocks the latter type consists of veins localized within shear zones both types have only a few inches of altered border rock characterized dominantly by biotite with minor diopside and garnet the sulfide lodes contain 5 to 30 vol percent sulfides which include dominantly pyrrhotite and arsenopyrite the lodes also contain variable amounts of magnetite and ilmenite no systematic variation in ore minerals is discernible among the lodes of the entire belt however in the kolar gold fields area a set of four parallel sulfide lodes exhibit certain textural and mineralogical zoning ore minerals show metamorphic equilibrium textures and the temperature of final equilibration of sulfides is 500 degrees c or higher sulfide lodes have low but variable abundances of base metals no correlation among total sulfide contents sulfide minerals and abundances of base metals and gold is observed nor is there any geochemical coherence between gold and arsenopyrite in the several lodes studied major oxides particularly al 2 o 3 tio 2 and k 2 o also show a large variation the ree abundances of the sulfide lodes vary widely but their patterns are similar with enrichment in both light ree and heavy ree normalized eu shows strong to negligible enrichment the ree patterns are similar to those of the banded ferruginous quartzite or iron formation samples with high ree abundances also have high base metals al 2 o 3 tio 2 and k 2 o abundances and low arsenopyrite contents based on these observations and limited nd and o isotope data it is suggested that the sulfide lodes were originally auriferous complex interflow sediments formed from submarine hydrothermal exhalations seawater and detrital sediments the vein type mineralization has only trace amounts of sulfides with galena as the dominant phase narayanaswami et al 1960 the veins consist dominantly of quartz with minor amounts of calcite and alkali feldspar and trace amounts of scheelite and tourmaline the gold content of the veins is generally 10 ppm the veins are also unusually enriched in cr and ni these observations and the fluid inclusion studies on vein quartz santosh 1986 suggest the presence of co 2 bearing ore fluids one sample of the ore vein has a strongly fractionated light ree enriched pattern with an epsilon nd value of 2 8 at 2 600 ma galena from the ore samples have pb isotope ratios reported by venkatasubramanian et al 1977 and chernyshev et al 1980 that are similar to those of the 2 600 ma intrusive granodioritic gneisses present on the west side of the schist belt krogstad et al 1989 the delta 18 o of vein quartz is 11 6 or 0 7 per mil golding 1982 these geochemical data suggest that the gold quartz veins were formed dominantly from magmatic fluids derived from the crystallization of granitic rocks a contribution from metamorphic fluids is also conceivable as indicated by the abundance of ni and cr in the veins

precambrian continental crust of india and its evolution the indian precambrian continental crust exhibits a variety of geological features fashioned at different times by different geotectonic processes the bulk of this crust was formed prior to 2600 m y ago and remobilized at least twice between 2600 2000 m y ago early proterozoic mobile belt epmb and 2000 1500 m y ago middle proterozoic mobile belt mpmb three early precambrian nucleii karnataka kn jeypore bastar jbn and singhbhum sn appear to have survived in the craton and are characterized by low grade supracrustals and tonalitic trondhjemite gneisses formed 3800 2600 m y ago the epmb event involved sedimentation amphibolite granulite facies metamorphism and co 2 k metasomatism and produced amphibolite facies rocks and k granites in the north and charnockite and other granulite facies rocks in the south gold sporadically distributed in the supracrustal rocks of the craton was remobilized during the epmb event k granites form a garland around the central dharwar craton sugg

phosphorus distribution and fractionation during weathering of amphibolites and gneisses in different climatic setups of the kaveri river catchment india abstract phosphorus distribution and fractionation during weathering of rocks are seminal to its availability to the life system here the p fractionation pattern is reported in weathering profiles of two different rock types i e amphibolites and granitic gneisses subjected to semi arid and humid climatic conditions in the catchment of the kaveri river southern india known for its fertile flood plain and delta weathering profiles developed on the two rock types were analysed for evaluating the intensity of chemical weathering using major ion geochemistry and for accompanying p fractionation the chemical index of alteration cia and the mineralogy of different zones of the weathering profiles show that profiles under humid climatic conditions are more weathered than those under semi arid conditions it was also found that p present dominantly as the apatite inorganic p aip fraction in the bedrocks was converted into non apatite inorganic p naip and organic p op both of which increase with progressive weathering the two major rock types show a very similar pattern of p fractionation during weathering which is similar to those observed in soil chronosequences however the transfer of p from aip to op and naip is near total in both rock types under humid conditions of weathering under semi arid conditions a part of aip was also available in the most weathered zone thus the lithology of the bedrock has little and climate a dominant control on p fractionation during rock weathering it was also observed that there is a net loss of total p during the weathering associated fractionation that could be attributed to the incorporation into biologically available forms and their subsequent removal to the fertile floodplains and delta in an undisturbed riverscape

inherited pb components in magmatic titanite and their consequence for the interpretation of upb ages abstract the occurrence of inherited radiogenic pb components in 35 ma old magmatic titanite is reported here for the first time the about 810 ma age of the inherited components is identical to that contained in zircon from the same amphibole bearing syenite sample in both minerals the precambrian components were not totally reset during magmatic new growth at 35 ma this age pattern substantiates that the u pb chronometer in titanite is resistant to temperatures in excess of 712 c as is already known for zircon and monazite in consequence u pb ages from crystalline titanites have to be interpreted as the age of mineral formation or re crystallization rather than the time of u pb system closure during cooling of the rock

subduction related tectonic evolution of the neoarchean eastern dharwar craton southern india new geochemical and isotopic constraints the neoarchean eastern dharwar craton edc is distinct from the mesoarchean western dharwar craton wdc in many aspects of its geology the important distinguishing features of the edc are the predominance of younger granitoids abundance of gold mineralization and the exposure at lower crustal depths no consensus exists on evolutionary models for edc mutually exclusive plume and subduction derived tectonic models have been proposed geochemical and radiogenic isotopic studies on the granitoids and volcanic rocks of three greenstone belts along a cross section in the northern part of edc are presented herein the evolved nd isotopic signatures radiogenic pb isotopic ratios and arc like geochemical signatures are suggestive of a subduction regime and the involvement of recycled older crust in the derivation of these rocks the proposed petrogenetic mechanism involves multi stage processes in a supra subduction regime involving slab dehydration formation of hydrous basaltic melts and re melting and interaction with sub arc basaltic crust at low pressures where amphibole plagioclase is the dominant residual phase there is a notable systematic decrease in the extent of older crustal involvement from west to east in the edc this is in concurrence with the younging of dharwar craton from west to east and eastward subduction the proposed petrogenetic model can efficiently explain the variations in older crustal involvement which is very common in other archean cratons c 2012 elsevier b v all rights reserved

u pb ages for zircon and titanite from the ramagiri area southern india evidence for accretionary origin of the eastern dharwar craton during the late archean abstract the north south trending ramagiri schist belt is trident shaped with three prongs separating three granitic terranes whereas the western and eastern prongs contain metatholeiites and banded ferruginous quartzite the central prong includes felsic metavolcanics and volcanogenic metasediments the u pb zircon age for the pyroclastics in the central prong of the ramagiri schist belt is documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 2707 pm 18 end document ma considered as the time of emplacement of the felsic volcan

crustal velocity structure of the neoarchean convergence zone between the eastern and western blocks of dharwar craton india from seismic wide angle studies abstract the dharwar craton in the southern part of the indian shield comprises two distinct blocks viz the meso neoarchean western and the predominantly neoarchean eastern blocks which are popularly referred to as western dharwar craton wdc and eastern dharwar craton edc the boundary between the wdc and edc is marked by a prominent shear zone the chitradurga eastern margin shear zone csz several studies suggested neoarchean convergence between the edc and wdc although there is diversity of opinion on the tectonic process we present here the results of a new seismic refraction wide angle reflection experiment along a 200 km long profile across the wdc and edc encompassing the csz to elucidate the crustal velocity structure of the convergence zone travel time inversion and amplitude modeling of the seismic data delineate a five layered crustal velocity model for the dharwar craton with a 42 km minimum thick crust in the wdc grading to a distinctly thinner crust up to 38 km in the edc the transect is also characterized by a high velocity 7 0 7 1 km s 1 mafic lower crustal layer but with distinctly variable thickness 10 km in wdc and 8 km in edc the transition from thick to thinner crust coincides with the csz the thick crust with a high velocity basal layer is atypical of archean cratons but more akin to proterozoic terrains the crustal velocity structure across the edc wdc boundary zone is consistent with the neoarchean plate convergence model that invoke tectonic scenarios such as accretion of a hot orogen the edc and or westward subduction of the latter beneath the wdc spatial variation in the high velocity lower crustal layer across the craton is ascribed to post accretional mafic magmatism and underplating mainly during the paleoproterozoic and phanerozoic

geochemical and nd isotope constraints on petrogenesis of granitoids from nw part of the eastern dharwar craton possible implications for late archaean crustal accretion abstract geochemical and nd isotope data on granitoids of the nw part of the late archaean eastern dharwar craton are presented to elucidate their petrogenesis and role in crust formation the granitoids are divided into three suites viz trondhjemite granodiorite gneisses biotite monzogranites and porphyritic biotite granodiorites the gneisses are pre to syn kinematic with respect to deformation in the adjacent hungund kushtagi schist belt which show variable sio2 and al2o3 enriched lree and depleted hree with slightly negative to no eu anomalies they display unusual chemistry in having higher feo t k2o ba cr and ni compared to the typical archaean tonalite trondhjemite granodiorite ttg the biotite monzogranites are mostly syn to late kinematic and exhibit evolved calc alkaline compositions with high sio2 k2o lile and lree depleted to undepleted hree and strongly negative to no eu anomalies the porphyritic granodiorites show syn to late kinematic calc alkaline sanukitoid like character with a wide range of sio2 higher tio2 p2o5 sr ba cr and ni and lower rb they however uniquely display higher k2o ree and th than typical sanukitoids the trondhjemite granodiorite gneisses are interpreted as product of melting of a subducted basaltic slab followed by slight contamination from the overlying metasomatized mantle wedge subsequent melting of the extremely metasomatized mantle wedge resulted in formation of the parental magma of the porphyritic granodiorites intrusion of the latter triggered melting of the ttg crust accreted earlier and generated the evolved monzogranites the monzogranites occurring east of the hungund kushtagi schist belt show higher end but lower tdm ages than those occurring to the west indicating that terranes with different histories were juxtaposed by lateral accretion

a plausible model for evolution of schist belts and granite plutons of dharwar craton india and madagascar during 3 0 2 5 ga insight from gravity modeling constrained in part from seismic studies abstract gravity modeling of an e w profile across dharwar craton india and madagascar integrated with the results of deep seismic sounding dss across the dharwar craton suggest a thick crust of 40 42 km under the eastern part of eastern dharwar craton edc the western dharwar craton wdc and the central part of the madagascar towards east of these blocks the crustal thickness is reduced to 36 38 km along the eastern ghat fold belt egfb shear zone between the edc and the wdc and the east coast of madagascar respectively these zones of thin crust are also characterized by high density lower crustal rocks associated with thrusts the seismic section across dharwar craton shows domal shaped reflectors in the lower crust and upper mantle under the wdc which may be related to asthenopheric upwelling during an extension phase the occurrences of large schist belts with volcano sedimentary sequences of marine origin of late archean period 3 0 2 7 ga as rift basins in the wdc and madagascar also suggest an extensional phase in this region during that period it is followed by a convergence between the wdc and the edc giving rise to collision related shear and thrust zones between the wdc and the edc associated with high density lower crustal rocks the seismic section shows upwarped reflectors in the upper crust which may be related to this convergence eastward dipping reflectors under wdc and edc and west verging thrusts suggest convergence from the west to the east which resulted in easterly subduction giving rise to subduction related k granite plutons of the edc of 2 6 2 5 ga in this regard the closepet granite in the edc which extends almost parallel to the shear zone between the wdc and edc and shows an i type calk alkaline composition may represent relict of an island arc and the linear schist belts with bimodal volcanics of the edc east of it might have developed as back arc rift basins subsequent collision between india and antarctica along the egfb during middle proterozoic indicated by eastward dipping reflectors in the crust and the upper mantle and west verging thrust gave rise to contemporary high grade rocks of the egfb 1 6 1 0 ga and associated mafic and felsic intrusives of this belt the part of adjoining cuddapah basin contemporary to the egfb towards the west consisting of marine shelf type of sediments which are highly disturbed and thickest at its contact with the egfb may represent a peripheral foreland basin gravity modeling provides thickest crust of 42 km in the southern part of the wdc and does not support sharp increase in crustal thickness of 50 60 km with high velocity upper mantle as suggested from receiver function analysis it may represent some foreign material of high density trapped in this section such as part of oceanic crust during convergence and subduction that is referred to above it is supported from eastward dipping reflectors in lower crust and upper mantle in adjoining region

age of younger tonalitic magmatism and granulitic metamorphism in the south indian transition zone krishnagiri area comparison with older peninsular gneisses from the gorur hassan area abstract a major episode of continental crust formation associated with granulite facies metamorphism occurred at 2 55 2 51 ga and was related to accretional processes of juvenile crust dating of tonalitic trondhjemitic granitic gneisses and charnockites from the krishnagiri area of south india indicates that magmatic protoliths are 2550 2530 5 ma as shown by both u pb and 207pb 206pb single zircon methods monazite ages indicate high temperatures of cooling corresponding to conditions close to granulite facies metamorphism at 2510 10 ma these data provide precise time constraints and sr nd isotopes confirm the existence of late tonalitic granodioritic juvenile gneisses at 2550 ma pb single zircon ages from the older peninsular gneisses gorur hassan area are in agreement with some previous sr ages and range between 3200 20 and 3328 10 ma these gneisses were derived from a 3 3 3 5 ga mantle source as indicated from nd isotopes they did not participate significantly in the genesis of the 2 55 ga juvenile magmas all these data together with previous work suggest that the 2 51 ga granulite facies metamorphism occurred near the contact of the ancient peninsular gneisses and the 2 55 2 52 ga juvenile tonalitic trondhjemitic terranes during synaccretional processes subduction mantle plume rb sr biotite ages between 2060 and 2340 ma indicate late cooling probably related to the dextral major east west shearing which displaced the 2 5 ga juvenile terranes toward the west

weathering of gneissic rocks in the upper reaches of cauvery river south india implications to neotectonics of the region in the upper reaches of the cauvery catchment area in southern india the archean peninsular gneisses exhibit a greater degree of weathering in the field relative to the massive charnockites and granites although the gneisses have been physically broken down along foliation planes fractures and compositional discontinuities secondary mineral such as chlorite smectite kaolinite and fe oxyhydroxide formation is insignificant consequently there is little chemical change even up to the stage of saprolite development only in the regolith there is some loss of ca na sr ba mg and sio2 other elements such as fe mn al cr ni and ree all show enrichment relative to tio2 in areas which have developed profiles by in situ weathering the chondrite normalized ree patterns however show little change excepting a slight flattening of the patterns because of greater hree mobility during weathering clay minerals also have flattened ree patterns because of relative hree enrichment the depletion and the enrichment of different elements appear to be related to mild leaching of primary mafic minerals by meteoric water rather than by mineral breakdown this and the extent of variation in chemical index of alteration values suggest that that the gneisses have suffered only incipient chemical weathering for the extent of physical weathering undergone by them it is likely that this contrasting weathering extents of these 2500 ma rocks is due to their exposure to surface geological processes only recently because of ongoing periodic uplift and physical erosion of this region

petrography chemistry and isotopic ages of peninsular gneiss dharwar acid volcanic rocks and the chitradurga granite with special reference to the late archean evolution of the karnataka craton southern india abstract new petrographic major and trace element and isotopic age data are presented for four suites of rocks from the low to medium grade part of the south indian archaean craton in central karnataka two suites are from the peninsular gneiss basement to the late archaean dharwar supergroup the third is a suite of dharwar potassic rhyolites and the fourth is from the chitradurga granite which has intrusive contacts with the dharwar supergroup the chikmagalur granite granodiorite which with its host gneisses forms part of the basement peninsular gneiss to the dharwar supergroup in the bababudan basin yields rb sr and pb pb whole rock isochron dates of 3080 110 ma and 3175 45 ma respectively an initial 87 sr 86 sr ratio of 0 7013 0 0009 and a 1 value 238 u 204 pb of 7 98 host tonalitic gneisses to the chikmagalur granite give an rb sr whole rock isochron date of 3060 160 ma with an initial 87 sr 86 sr ratio of 0 7015 0 0004 and a pb pb whole rock isochron date of 3190 100 ma with a model 1 value of 8 00 a suite of granites and granodioritic tonalitic gneisses chitradurga granitic rocks and gneisses forming part of the peninsular gneiss basement to the dharwar supergroup west of the chitradurga belt yields rb sr and pb pb whole rock isochron dates of 2970 100 ma and 3028 28 ma respectively with an initial 87 sr 86 sr ratio of 0 7035 0 0013 and a model 1 value of 7 62 the suite of dharwar acid volcanic rocks from north of honnali defines a poorly fitted 207 pb 206 pb linear array mswd 15 8 which gives an apparent age of 2565 28 ma and a model 1 value of 7 46 the poor fit of this isochron shows that a closed system was not maintained a conclusion supported by high k abundances which are attributed to a syn or post magmatic ion exchange process the chitradurga granite which intrudes the older rocks of the dharwar supergroup in the chitradurga belt yields a well fitted pb pb whole rock isochron date of 2605 18 ma with a model 1 value of 7 68 the u pb relations in these suites from karnataka are in marked contrast with the commonly severe u depletion and consequently unradiogenic pb isotopic compositions observed in deeply eroded high grade archaean gneiss terranes such as those bordering the north atlantic this contrast indicates that the cratonic rocks in central karnataka represent a relatively high level in the original archaean continental crust

plate tectonics 2 5 billion years ago evidence at kolar south india the archean kolar schist belt south india is a suture zone where two gneiss terranes and at least two amphibolite terranes with distinct histories were accrted amphibolites from the eastern and western sides of the schist belt have distinct incompatible element and isotopic characteristics sugesting that their volcanic protoliths were derived from dint mantle sources the amphibolite and gneiss terranes were juxtaposed by horizontal compression and shearing between 2530 and 2420 million years ago ma along a zone marked by the kolar schist belt this history of accretion of discrete crustal terranes resembles those of phanerozoic convergent margins and thus suggests that plate tectonics operated on earth by 2500 ma

geochemistry and petrogenesis of granitoids around the kolar schist belt south india constraints for the evolution of the crust in the kolar area the peninsular gneiss surrounding the n s trending kolar schist belt in the dharwar craton includes several components of granitic rocks that range in composition from tonalite to granite on the west the different phases are referred to as the dod the dosa and the banded gneiss and the patna granite the gneisses on the east are dominantly of one type and are referred to as the kambha gneiss the champion gneiss occurring within the eastern part of the belt is compositionally similar to the plutonic dod gneiss and probably represents a near surface intrusion late aplites are present on both sides of the belt the banded gneiss was formed by partial melting of tonalitic rocks and the aplites were formed by the action of aqueous fluids during amphibolite grade metamorphism excepting these two rocks all other granitoids seem to have been formed from silica oversaturated parent magmas derived from lile enriched mantle sources by fractionation processes including liquid immiscibility and fractional cry

a 3 1 billion year old marble and the 87sr 86sr of late archean seawater a marble band in the 2 75 gyr old ramagiri schist belt in the dharwar craton of south india gave a pb pb age of 3 075 0 095 gyr the geochemical data including high sr and low ba and mn indicate seawater origin for the parent rock and that there was insignificant geochemical exchange between the marble and the surrounding rocks the calculated initial nd isotopic composition and 1 indicate an older continental crustal source for the nd and pb the initial 87sr 86sr of the marble is 0 70128 which is higher than the calculated mantle value at 3 ga although pre 3 gyr old marine carbonate rocks are thought to be buffered by mantle sr the ramagiri marble contains evolved crustal sr despite this the marble has the lowest measured 87sr 86sr among carbonates and represents one of the least radiogenic periods in seawater sr isotope composition

postcrystallization disturbance in the neodymium and lead isotope systems of metabasalts from the ramagiri schist belt southern india archean metabasaltic rocks from three separate blocks that constitute the north south trending ramagiri schist belt of the eastern dharwar craton have large variations in nd2750 even samples of the same rock type from one outcrop that are less than 50 cm apart from each other show a range of up to 5 5 nd2750 units the trends of the fields defined by the three suites in smnd vs nd2750 space intersect at smnd 0 1 to 0 2 and nd2750 8 to 12 suggesting that these rocks have lost lrees and have interacted with and exchanged at least nd with a common extraneous phase the isotopic composition of this phase suggest derivation of its neodymium from sources which had a long term history of lree enrichment this phase may have derived its isotopic composition from older continental crust one of the unaltered dikes cutting the three blocks in the belt and the surrounding gneisses gives a 147sm144nd 143nd144nd age of 2454 100 ma a minimum for the time of block assembly and alteration of rees including nd while a set of samples from the central block lie along an isochron with a pb pb age of 2746 64 ma the samples from the eastern and western blocks show large uncorrelated variations in 207pb204pb with 206pb204pb residues after acid leaching of sample powders have lead isotope ratios that are distinct for samples from each of the block and are compatible with their derivation from archean mantle the lead isotope composition of the acid leaches suggest disturbance of the metabasalts by an isotopically extraneous phase that had variable and high 207pb204pb and 208pb204pb ratios for a given 206ph204pb relative to expected archean mantle values both lead and neodymium isotope disturbances are best explained as a result of alteration of these rocks by an extraneous phase which had derived its isotopic composition from ca 3 5 ga continental crust

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 orthogneisses adjacent to the kolar schist belt were emplaced as tonalitic to granodioritic magmas between 2630 and 2530 ma an orthogneiss unit east of the kolar schist belt apparently was a homogeneous granodioritic intrusion at about 2532 ma cooling to the blocking temperature of the u pb system in sphene by 2521 2517 ma gneisses on the west side of the kolar schist belt were emplaced as at least three separate intrusions dated at 2631 2610 and 2552 ma evidence from an older basement into which these rocks were intruded comes from inherited zircons with an age of 2800 ma rocks with zircons of the appropriate age to be part of this basement occur as tectonic fragments and inclusions in the area gneisses west of the kolar schist belt were last cooled through the blocking temperature of the u pb system in sphene at about 2552 ma synchronous with the last major intrusive event late felsic dikes and plutons apparently postdate deformation and yield sphene pb pb ages of 2480 ma a sample of muscov

mineral thermobarometry and fluid inclusion studies on the closepet granite eastern dharwar craton south india implications to emplacement and evolution of late stage fluid the closepet granite cpg a spectacularly exposed magmatic body along with other intrusive bodies to the east of it typifies the late archean granitic activity in the eastern dharwar craton edc south india in the present study the p t fo2 conditions of emplacement and physico chemical environment of the associated magmatic hydrothermal regime of cpg have been retrieved on the basis of mineral chemical and fluid inclusion studies amphibole plagioclase ti in amphibole and ti in biotite geothermometers along with al in amphibole geobarometer have been used to reconstruct the emplacement temperature and pressure conditions in the majority of the pluton estimated temperatures of emplacement of cpg vary from to 740 to 540 c a variation of pressure from 4 8 to 4 1 kilo bars corresponding to this temperature range was obtained while there is a faint south to north negative gradient in temperature the variation of pressure does not seem to follow this trend and indicates more or less same crustal level of emplacement for the body between ramanagaram kalyandurga segment extending for about 230 km mineral chemistry of biotite indicates crystallization of cpg under high oxygen fugacity conditions mostly above qfm buffer with no clear spatial variation in the fugacity of halogen species in the late stage magmatic fluid it may be surmised that barring the southernmost part of cpg there is no perceptible variation in the physicochemical environment of emplacement fluid inclusion studies in the granitic matrix quartz and pegmatite vein quartz show dominance of h2o and h2o co2 fluids respectively in them the difference in the fluid characteristics is interpreted in terms of the initial loss of co2 rich fluid from granitic magma and aqueous rich nature during the later stages of crystallization of quartz the exsolved co2 rich fluid was responsible in formation of the later quartz and pegmatitic veins at different crustal levels and also possibly was responsible in co2 induced metamorphism charnockitization preserved in the kabbaldurga area in the southernmost part the fluid characteristics in the vast tract of cpg revealed from mineral chemical and fluid inclusion studies make a case for its involvement in gold mineralization in the schist belts in edc

the lower crust of the dharwar craton southern india patchwork of archean granulitic domains u pb geochronological major and trace element and isotope geochemical data identify crustal domains of contrasted petrological origins and histories in the lower crust of the dharwar craton all affected by granulite facies metamorphism and deformation in the neoarchean four lower crustal domains have been identified and investigated across the neoarchean amphibolite to granulite facies transition zone 1 in the southern part of the western dharwar craton wdc high grade metamorphism affects rocks formed before 3 0 ga high grade metamorphism is recorded at ca 2 51 ga followed by possible complex cooling and resetting until 2 2 ga 2 the br hills mm hills domain represents the lower crust of the central dharwar province cdp which is here defined as a transitional crust between the old 3 ga wdc and the eastern dharwar province edp not older than 2 7 ga this granulitic domain contains the oldest rocks of the dharwar craton with ttg suites formed at ca 3 4 ga and ca 2 6 ga suites of probable crustal recycling origin both suites are involved in 2513 5ma granulite facies metamorphism 3 the nilgiri granulitic domain is tectonically juxtaposed with the deepest level of the wdc as a consequence of neoarchean dextral slip along the moyar shear zone the massif consists of rocks of orogenic affinities formed between 2 70 and 2 56 ga and overprinted by granulite facies metamorphism at 2518 10 ma 4 the krishnagiri domain exposes the deepest levels of the eastern dharwar craton it is composed of ttg and calc alkaline igneous protoliths formed between 2 55 and 2 53 ga migmatization in the upper part of the domain took place at 2507 6ma and granulite facies overprint in the deepest parts of the domain is constrained at 2516 5 ma the krishnagiri domain was magmatically accreted to the lower crust of both the cdp and edp by interaction with mafic magmatism inducing reworking of the 2 7 2 6 ga or older overlying crust the nilgiri granulites share several temporal and petrological properties with the madras granulites that make the easternmost outcrop of the dharwar craton we tentatively suggest that the nilgiri and madras granulites evolved as parts of a common madras domain in the lower crust of the edp before activation of the moyar shear zone in this sense the nilgiri massif may be considered as an allochtonous unit in a context of neoarchean ultra hot orogeny in south india

late archaean crust mantle interactions geochemistry of lree enriched mantle derived magmas example of the closepet batholith southern india the closepet batholith in south india is generally considered as a typical crustal granite emplaced 2 5 ga ago and derived through partial melting of the surrounding peninsular gneisses 3 3 to 3 0 ga in the field it appears as a composite batholith made up of at least two groups of intrusions a an early sio2 poor group clinopyroxene quartz monzonite and porphyritic phyritic monzogranite is located in the central part of the batholith these rocks display a narrow range in both initial 87sr 86sr 0 7017 0 7035 and nd 0 9to 4 1 b a later sio2 rich group equigranular grey and pink granites is located along the interface between the sio2 poor group and the peninsular gneisses they progressively grade into migmatised peninsular gneisses thus indicating their anatectic derivation their isotopic characteristics vary over a wide range 87sr 86sr ratios 0 7028 0 7336 and nd values from 2 7 to 8 3 at 2 52 ga field and geochronological evidence shows that the two groups are broadly contemporaneous 2 518 2 513 ga and mechanically mixed this observation is supported by the chemical data that display well defined mixing trends in the sr vs nd and elemental variation diagrams the continuous chemical variation of the two magmatic bodies is interpreted in terms of interaction and mixing of two unrelated end members derived from different source regions enriched peridotitic mantle and peninsular gneisses it is proposed that the intrusion of mantle derived magmas into mid crustal levels occurred along a transcurrent shear zone these magmas supplied additional heat and fluids that initiated anatexis of the surrounding crust during this event large scale mixing occurred between mantle and crustal melts thus generating the composite closepet batholith the mantle derived magmatism is clearly associated with granulite facies metamorphism 2 51 0 01 ga ago both are interpreted as resulting from a major crustal accretion event possibly related to mantle plume activity

geochemistry of two stratigraphically related ultramafic komatiite layers from the neoarchean sigegudda greenstone terrane western dharwar craton india evidence for compositional diversity in archean mantle plumes abstract two compositionally different ultramafic units are present in the neoarchean sigegudda greenstone terrane western dharwar craton india these ultramafic units occur in the same volcano sedimentary sequence and are separated by a fault bounded volcanic arc association because of deformation and amphibolite facies metamorphism the primary igneous textures have been extensively modified in both ultramafic units given their spatial and temporal association with sedimentary and volcanic rocks and high mgo contents 12 29 wt these ultramafic rocks are interpreted as metamorphosed komatiites and komatiitic basalts field relationships and rock types indicate that the lower section of the sigegudda volcano sedimentary sequence was deposited in a peri cratonic continental rift setting the lower ultramafic unit is characterized by 12 4 29 6 wt mgo mg 76 91 and 526 1150 ppm ni the upper ultramafic unit is overall more magnesian and compositionally restricted mgo 21 6 25 9 wt mg 86 89 and ni 610 1000 ppm the lower unit features a combination of relatively elevated tio 2 0 40 0 90 wt al 2 o 3 tio 2 the chondritic ratio of 21 and gd yb n ratios 1 these are ti enriched komatiites reported for the first time from greenstone belts in the dharwar craton the upper unit is compositionally comparable to al undepleted komatiites and characterized by al 2 o 3 tio 2 21 lree depletion coupled with near flat chondrite normalized hree patterns geochemical data indicate that the sigegudda komatiites and komatiitic basalts were variably contaminated by either continental crust or sub continental lithospheric mantle or both the geochemical differences between the two units are explained by variable depths and degrees of partial melting the ti enriched lower unit appears to have been formed through lower degrees of partial melting at depths 90 km whereas the al undepleted upper unit was generated by higher degrees of partial melting at depths 90 km field relationships and geochemical characteristics of the sigegudda komatiites can be explained by a geodynamic model in which the stratigraphically lower ti enriched komatiites were erupted from a mantle plume onto a rifting continental margin whereas the stratigraphically upper al undepleted komatiites originated from a younger mantle plume and erupted onto a volcanic arc sequence that accreted to the rifted continental margin

3 35ga komatiite volcanism in the western dharwar craton southern india constraints from nd isotopes and whole rock geochemistry abstract we present field petrographic sm nd whole rock isochron and whole rock geochemical data for komatiites from sargur group greenstone belts of the western dharwar craton field evidence such as pillow structure indicates their eruption in a marine environment petrographic data reveal that the igneous mineralogy has been altered during post magmatic hydrothermal alteration processes corresponding to greenschist to lower amphibolite facies conditions with rarely preserved primary olivine and orthopyroxene a 16 point sm nd whole rock isochron gives an age of 3352 110 ma for the timing of eruption of komatiite lavas about 60 of the studied komatiite samples show al depletion whilst the remaining are al undepleted the al depleted komatiites are characterised by high cao al2o3 ratios 1 01 1 34 and low al2o3 tio2 5 16 whereas al undepleted komatiites show lower cao al2o3 ratios 0 59 0 99 and higher al2o3 tio2 17 26 trace element distribution patterns of komatiites suggest that most of the primary geochemical and nd isotopic compositions are preserved with only minor influence of post magmatic alteration processes and negligible crustal contamination the chemical characteristics of al depleted komatiites such as high gd yb n together with lower hree y zr and hf imply their derivation from deeper upper mantle with garnet majorite involvement whereas lower gd yb n slightly higher hree y zr and hf suggest derivation from shallower upper mantle without garnet involvement the observed chemical characteristics cao al2o3 al2o3 tio2 mgo ni cr nb zr y hf ree indicate derivation of the komatiite magmas from different depths in a plume setting whereas sub contemporaneous felsic volcanism and ttg accretion can be attributed to an arc setting in order to explain the spatial association of komatiite volcanism with contemporaneous mafic felsic volcanism and ttg accretion we propose a combined plume arc setting nd isotope data of the studied komatiites indicate depleted mantle reservoirs which may have evolved by early 4 53 ga global differentiation of the silicate earth as suggested by boyet and carlson boyet m carlson r w 2005 142nd evidence for early 4 53 ga global differentiation of silicate earth science 309 577 581 or extraction of continental crust during the early archaean

dissecting through the metallogenic potentials of precambrian granitoids case studies from the bastar and eastern dharwar cratons india

40ar 39ar age constraints on timing of a late hydrothermal event in the hutti greenstone belt karnataka india abstract obtaining constraints on the timing of orogenic gold mineralization hosted in shear zones in greenstone belts is often difficult because of the lack of easily datable minerals and problems of overprinting of earlier events of mineralization by later hydrothermal events in the orogenic hutti gold deposit the u pb shrimp date obtained from a monazite grain within arsenopyrite that gave an age of 2547 10 ma is generally accepted as the age of early hydrothermal mineralization nevertheless other work has indicated that hydrothermal mineralization may have occurred in later episodes as well this study reports new 40ar 39ar ages for hydrothermal biotite amphibolite and hornblende in granites that occur along the northern and southeastern boundary of the greenstone belt the 40ar 39ar ages of biotite samples are inferred to be the result of re setting of the ages of alteration biotite by the last phase of hydrothermal activity in this area at 2332 ma the study indicates that the effects of the thermal event are more significant in areas of greater hydrothermal access such as within the hutti shear zone this late hydrothermal alteration event may be related to the d3 deformational event of roy 1991 the results of the present work are important because it demonstrates a significant hydrothermal event much after the major 2 58 2 52 ga accretionary event and accompanying ttg and felsic magmatism in the eastern dharwar craton

geochronological constraints on meso and neoarchean regional metamorphism and magmatism in the dharwar craton southern india this contribution addresses the time framework of the regional metamorphism in the three crustal provinces making the archean dharwar craton we present results of texturally controlled in situ epma chemical dating of monazites chemical dating of monazite separates as well as sm nd garnet whole rock isochrons and shrimp u pb zircon ages for pelites amphibolites and granitoids over target areas typical of the various crustal levels of the provinces the western dharwar craton has undergone a major thermal pulse at 2 52 ga followed by slow cooling to ca 2 4 ga and recorded earlier thermal events around 3 0 ga and 3 1 ga the central dharwar craton records a major high grade thermal imprint at ca 2 55 2 51 ga followed by cooling up to 2 45 ga and earlier thermal events at ca 2 62 and 3 20 ga in the eastern dharwar craton the widespread thermal pulse between 2 55 and 2 52 ga is best recorded from 2 52 ga on the entire craton ultimately and contemporaneously undergoes the main event of regional ht lp metamorphism the contrasted thermal records of the three provinces reflect their accretion age s and their degree of involvement in a wide latest archean hot orogen which sets the capacity of these lithospheric segments to be impact by deformation and mantle fluxes the tectonic setting of latest archean hot orogeny is compatible with active plate margin processes having interacted with mantle instabilities i e plumes the tectonic setting of pre 2 5 ga thermal pulses is difficult to assess but considering their systematic links with documented magmatic pulses they may have been generated in contexts comparable that of latest archean hot orogeny where lateral constrictional flow of hot orogenic crust achieves gravity driven flow 3d mass redistribution of viscous lower crust submitted to convergence

neoarchean greenstone volcanism and continental growth dharwar craton southern india constraints from sims u pb zircon geochronology and nd isotopes abstract we present sims u pb zircon ages and nd isotope data for the felsic volcanic rocks from seven neoarchean greenstone belts of the eastern dharwar craton edc and from the chitradurga greenstone belt in the western dharwar craton wdc zircon ages show bimodal age distribution of felsic volcanism the ca 2 70 2 65 ga felsic volcanic event is contemporaneous with 2 7 ga mafic greenstone volcanism and emplacement of juvenile tonalitic to granodioritic crust while 2 58 2 54 ga felsic volcanics are coeval and spatially and probably genetically in some cases linked to the major episode calc alkaline magmatic accretion in the edc the chitradurga and veligallu greenstone belts host felsic volcanics of the first generation the latter showing inheritance at ca 2 95 ga four of the five greenstone belts hosting the second generation of felsic volcanics chitradurga kolar kadiri hutti show crustal inheritance at ca 2 6 2 7 2 9 3 0 3 1 and 3 3 ga ndt indicate derivation of the felsic volcanics from juvenile sources or short lived crustal sources with minor influence of older crust the new and existing data are consistent with two stage growth of the dharwar craton in the neoarchean first stage accretion led to the growth of a 2 7 2 6 ga juvenile crustal province of mafic volcanics and felsic plutons along the eastern margin of the wdc second stage accretion 2 58 2 52 ga led to the emplacement of ttg and calc alkaline plutons and felsic volcanics throughout the eastern dharwar craton an active margin context could apply for the two stage accretion scenario considering a west dipping subducting slab beneath the craton in the framework of long lived ultra hot accretionary orogen but the great width of influence of magmatic accretion and or reworking particularly during the second stage would suggest large scale mantle flow reorganization that would have generated large plume s

tectonostratigraphy of the late archean dharwar supergroup dharwar craton india defining a tectonic history from spatially linked but temporally distinct intracontinental and arc related basins abstract the dharwar supergroup comprises the unconformity bound bababudan and chitradurga groups the bababudan group which is best preserved in the western dharwar craton records a divergent margin comprising a basalt dominant intracontinental rift sequence a shale bif drift sequence and a sandstone shale thermal subsidence sequence the rift stage evolved from 2765 ma to 2720 ma whereas the succession was folded uplifted and eroded during development of a convergent continental margin from 2680 ma ocean opening was to the east or southeast the chitradurga group records a two stage back arc basin behind an east facing continental arc stage i evolved between 2609 ma and 2582 ma and stage ii between 2582 ma and 2540 ma the two stages are separated by a subaerial unconformity stage i comprises siliciclastic fluvial shallow marine and deep marine sedimentary rocks and bimodal volcanic rocks stage i is best preserved in the western dharwar craton but there are equivalents in the eastern dharwar craton stage ii in the western dharwar craton comprises deep marine turbidites of siliciclastic and volcaniclastic provenance and basaltic and felsic volcanic rocks volcanic stage ii sequences in the eastern dharwar craton define an arc adjacent position tectonically driven cyclic uplift and erosion were responsible for the mismatch between preserved stratigraphic thickness and time particularly for stage ii sequences a remnant of a

u pb geochronology of the grenville orogen of ontario and new york constraints on ancient crustal tectonics based on lithological structural and geophysi cal characteristics the proterozoic grenville orogen of southern ontario and new york has been divided into domains that are separated from each other by ductile shear zones in order to constrain the timing of meta morphism u pb ages were determined on metamorphic and igneous sphenes from marbles calc silicate gneisses amphibolites granitoids skarns and pegmatites in addi tion u pb ages were obtained for monazites from meta pelites and for a rutile from an amphibolite these mineral ages constrain the timing of mineral growth the duration of metamorphism and the cooling history of the different domains that make up the southern part of the exposed grenville orogen based on the ages from metamorphic minerals regional and contact metamorphism occurred in the following intervals central granulite terrane