deformation of the proterozoic successions in the pranhita godavari basin south india a regional perspective abstract a number of proterozoic intracratonic basins namely cuddapah pranhita godavari pg abujhmar indravati ampani chattisgarh and khariar basins occur to the immediate west of the eastern ghats granulite belt eggb in india of these the pg basin hosts an axial outcrop of late paleozoic mesozoic gondwana rocks flanked on either side by proterozoic sedimentary successions among the latter the somanpalli group in the eastern part and the penganga and yellandlapad groups in the western part show contractional folds imbricate thrusts and cleavage these deformed rock groups and the pakhal group in the western belt include shallow to deep marine sedimentary successions stratigraphic relations indicate that the major episode of deformation in the pg basin occurred prior to deposition of the unconformably overlying sullavai group the latter is a neoproterozic undeformed fluvial sequence with some aeolian intercalation deformed successions also occur in other proterozoic basins of the south indian craton notably those in the nallamalai fold belt nfb along the eastern part of the cuddapah basin the major fold fault structures in the arcuate nfb vary in trend from nnw sse in the southern part to ne sw in the northern part at least one phase of folding and thrusting predates the 1000 ma old event in the eggb deformation associated with the grenville and later pan african tectonic mobility has imprints on the neoproterozic kurnool group in the palnad sub basin northern nfb the major structural trend in the pg basin is nw se except for the yellandlapad area in the southern part where late superposed folds trend e w the deformation along the eastern margin of the chattisgarh basin its southern extension in khariar ampani and indravati basins may also be related with the main grenville deformation in the eggb a regional mesoproterozic episode of basin closure and inversion is thus evident from the proterozoic cratonic successions west of the eastern ghats this occurred prior to a regional development of neoproterozoic successions at these sites

petrology geochemistry and geochronology of the chilka lake igneous complex orissa state india abstract the chilka lake igneous complex of orissa the largest known anortosite massif of the indian shield occurs in a catazonal environment of high grade metamorphics of the eastern ghats precambrian orogenic province the syntectonic massif consists of the anorthositic balugaon dome leuconoritic rambha lobe and quartz mangeritic kallikota cover a completely gradational suite comprising anorthosite leuconorite norite minor jotunite the anorthositic suite constitutes most of the complex the subordinate of suite of acid rocks spatially associated with this is of a broad quartz mangeritic lithology with minor granitic rocks the acidic suite geochemical evolution of the complex in the sequence anorthosite leuconorite norite jotunite acidic rocks shows moderate iron enrichment in the noritic jotunitic stage and is marked by an overall decrease in al 2 o 3 cao mgo ni co sr ba k rb and increase in sio 2 k 2 o v ni k ba and rb sr such progressive variation in geochemical parameters appears i essentially gradual and frequently overlapping in rock members of the intergradational anorthositic suite and ii rather abrupt across transition zones between the anorthositic suite and the acidic suite due to near absence of intervening intermediate lithologies rb sr whole rock isochron studies indicate that the complex was emplaced ca 1400 ma ago the initial 87 sr 68 sr 0 70661 implies limited hybridisation of the parent magma prior to emplacement a critical appraisal of all the available evidence suggests that i the anorthositic suite of rocks form a perfectly consanguinous and comagmatic assemblage and ii the spatially associated acidic suite emerged through a convergence of magmatic and metasomatic processes the latter brought about by contact anatexis of the host rocks the complex as well as the host metamorphics are intruded by an atectonic suite of noritic dykes emplaced ca 850 ma ago

proterozoic to mesozoic east gondwana the juxtaposition of india sri lanka and antarctica jurassic and cambro ordovician paleomagnetic pole positions deduced from rocks of sri lanka and antarctica generally conform when sri lanka is juxtaposed with the coast of lutzow holm bay east antarctica in a manner similar to a current gondwana reassembly the highland and southwest groups mostly proterozoic of sri lanka are correlated with the ongul and skallen groups of east antarctica on the basis of similar lithology structural characteristics structural trend tectonothermal history ranging from early proterozoic to mesozoic and the pressure temperature time path of the main metamorphism some neighboring lithotectonic units are also comparable between the two areas fracture lineament systems of sri lanka and antarctica formed after the latest silurian and during or before the jurassic conform in this reconstruction an improved fit of the 2000 m isobaths of india sri lanka antarctica and continuation of the latest archaean mobile belt from enderby land to peninsular india is obtained by fitting sri lanka into lutzow holm bay and enderby land into the embayment in the east coast of peninsular india this juxtaposition of peninsular india to east antarctica involves about 80 km northward movement and about 30 clock wise rotation of sri lanka relative to india the reassembly thus obtained accords well with data supporting the idea that east gondwana existed from the earliest proterozoic to middle mesozoic although some disruption collision events of limited scale are considered possible

late proterozoic charnockites in orissa india a u pb and rb sr isotopic study charnockite formation in the angul district of orissa took place between 1088 26 17 ma the u pb zircon upper intercept crystallization age of a leptynite neosome and 957 8 4 956 pm 4 ma the u pb zircon monazite upper intercept and u pb monazite crystallization ages of a granite confirmation of the proterozoic age of the charnockites is given by 1 a u pb zircon upper intercept 1159 h 59 30 ma age and a rb sr whole rock 1080 pm 65 ma age for an augen gneiss which pre dates the leptynite and 2 u pb monazite ages of 973 pm 5 964 pm 4 and 953 pm 4 ma for a gray quartzofeldspathic gneiss the augen gneiss and the leptynite respectively these late proterozoic dates are interpreted as representing ages recorded during charnockitization the ca 950 980 ma charnockite and granite forming events are related to the evolution of mantle derived co 2 bearing basic magma emplaced into the deeper levels of an extensional tectonic transcurrent fault regime the ca 1100 1150

diversity patterns of early jurassic brachiopod assemblages from the westernmost tethys eastern subbetic abstract a detailed faunal succession based upon 6400 brachiopods from the early jurassic in the eastern external subbetic palaeogeographical domain betic range spain is characterized and analyzed this study allows recognition of five assemblages with original biostratigraphical data in sediments where biostratigraphical markers were very scarce it also enables a sound diversity dynamics pattern to be established among the brachiopod assemblages recorded this pattern shows progressive diversification from the sinemurian to the late pliensbachian although with significant episodes during the sinemurian pliensbachian transition the first initial pulses of the disintegration of the south iberian palaeomargin played an important role in the brachiopod assemblages as a notable faunal renewal event is detected assemblage 1 to assemblage 2 maximum biodiversity and abundance were reached in the pliensbachian toarcian transition due to the partial contemporaneity of assemblages 2 and 3 and the settlement of taxa from nearby palaeogeographical basins a decrease related to the early toarcian anoxic event etoae global effect is suggested after which a slight recovery began with colonization by opportunistic taxa soaresirhynchia bouchardi but pre etoae diversity and abundance were subsequently never again reached a palaeogeographical analysis has been carried out to compare taxonomic diversity dynamics in the eastern subbetic with other representative tethyan basins this study also enables palaeobiogeographical affinities to be established for the eastern subbetic domain showing mediterranean palaeobioprovince influences until the late pliensbachian early toarcian a period when replacement occurred that shows faunal unification free connection between the sub boreal and mediterranean provinces may be inferred from the late pliensbachian early toarcian onwards

ramgundam sandstone a middle proterozoic shoal bar sequence abstract much of the abundant precambrian sedimentary record of india appears to have been deposited in shallow coastal environments one example of this the ramgundam sandstone is a moderately thick 120 m unit composed of lens shaped bodies of arkosic sandstone and interbedded sandstone and shale outcrops are mostly limited to small quarry pits but sufficient exposures are present to show major bedding characteristics principal components are wave built bars and interbar fillings the bars 1 to 5 m thick and tens of meters wide contain laterally accreting sets of trough cross bedded sandstone interbar deposits are composed of horizontal to subhorizontal beds of ripple laminated sandstones and interlaminated shales siltstone and sandstone containing wavy lenticular and flaser laminae shallow water subaerial exposure and probable tidal fluctuations are recorded on the bar surfaces by flat topped ripples and interference ripples water recession marks and desiccation cracks

late syn rift sequence architecture and sedimentary evolution of a continental rift basin a case study from fulongquan depression of the songliao basin northeast china abstract as an important stage in continental rift basin evolution late syn rift stage is characterized by the combination of broad crustal subsidence and episodic pulses of extension sequence architecture and sedimentary filling process during this period present a certain particularity due to distinctive tectonic subsidence and variable influencing factors this paper analyzes sequence stratigraphy and sedimentary facies development and their evolution in the fulongquan depression a continental rift basin of the songliao basin and discusses the determinants influencing the sequence architecture and depositional systems evolution during late syn rift stage a major transition in the depositional systems from predominantly lacustrine and correlated depositional systems to fluvial floodplain settings was recorded in the evolution of basin fill this gradual and slow peneplanation is the final response to the decrease of differential subsidence the spatial and temporal variability of sedimentary evolution are mainly associated with specific growth history of the major boundary faults sequence stratigraphic units recognized in the fulongquan depression are likely corresponded to different episodic pulses of extension respectively each sequence can be further divided into a lowstand systems tract lst transgressive systems tract tst and highstand systems tract hst maximum differential subsidence and water deepening mainly occur in the lst the expanded tst and hst of each sequence tend to be developed in a broader thermal subsidence regime the depositional systems transition and detrital provenance changes usually occur in the hst throughout the late syn rift stage in addition to major changes of provenance systems tectonic movement is likely to be the main factor in controlling the variations of sediment supply with the decrease of tectonic activity the impact of climate changes and lake level fluctuations on basin filling tends to be increased

deformation pattern in the kurnool and nallarnalai groups in the northeastern part palnad area of the cuddapah basin south india and its implication on rodinia gondwana tectonics abstract the proterozoic basins of india adjoining the eastern ghats granulite belt eggb in eastern and southern india contain both mesproterozoic and neoproterozoic successions the intracratonic set up and contractional deformation fo the neoproterozoc successions in the paland sub basin in the northeastern part of cuddapah basin and similar crustal shortening in contemporaneous successions lying west of the eggb and nellore schist belt nsb are considered in relation to the proposed geodynamic evolution of the the rodinia and gondwana supercontinents tectonic shortening in the palnad sub basin northeast cuddapah partitioned into top to westnorthwest thrust shear flexural folds and cleavage development under overall e w contraction suggests foreland style continental shortening within an intracratonic set up a thrust sheet containing the nallamalai rocks and overlying the kurnool rocks in the northeastern part of palnad sub basin exhibits early tight to isoclinal folds and slaty phylllitic cleavage which can be correlated with early mesoproterozoic deformation structures in the nothern nallamalai fold belt nfb nne ssw trending folds and cleavage affect the kurnool group and overprint earlier structures in the thrust sheet thrusting of the nallamalai rocks and the later structures may have been related to convergence of the eastern ghats terrane and the east dharwar bastar craton during early neoproterozoic greenvillian and or later rejuvenation related to pan african amalgamation of east and west gondwana

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

proterozoic platform sequences of peninsular india implications towards basin evolution and supercontinent assembly abstract a group of less disturbed and unmetamorphosed proterozoic platformal sediment package lying over deformed and metamorphosed archean to paleoproterozoic basement in several parts of peninsular india is informally termed as purana basins in indian stratigraphy the trend shift in the understanding of these basin fills in last two decades often supported by international collaborations has made significant advancements in respect to unconformity and sequence development relationship with accretion and break up of the supercontinents initiation and evolution of the basins in different tectonic set ups nature of sediment provenance paleoclimate and paleo weathering patterns and basin water chemistry geophysical backups encompassing the basins occasionally extending up to the craton and adjacent mobile belts helped in refining the understanding on the basement structure and tectonic forcings the present paper is an attempt towards the collation of the database generated in last two decades in order to present the status of current understanding on different purana basins with regard to interactions of physical chemical and biological parameters of the proterozoic earth

structural pattern and kinematic framework of deformation in the southern nallamalai fold fault belt cuddapah district andhra pradesh southern india abstract an association of westerly verging asymmetric folds easterly dipping cleavages and contractional faults control the pattern and intensity of structures at different scales in the southern nallamalai fold fault belt cuddapah district of andhra pradesh southern india variation in structural geometry is manifested across the section by the occurrence of relatively low amplitude folds sometimes only a monocline and by the near absence of contractional faults in the wsw but tight to isoclinal folds with frequent fold fault interactions through the central areas towards ene the relationships of structural elements in terms of orientation style sense of movement and general vergence indicate their development under a progressive contractional deformation the structures are interpreted to result from a combination of bulk inhomogeneous shortening across the belt and a top to west variable simple shear localized developments of crenulation cleavage rotation of cleavage in the shorter limbs of some mesoscale asymmetric folds and general variation of structural elements in morphology and associations across the belt indicate partitioning of deformation and a varying degree of non coaxiality in discrete domains of the bulk deformation

archean proterozoic evolution of indian charnockites isotopic and geochemical evidence from granulites of the eastern ghats belt pyroxene granulites and charnockites are associated with metasedimentary khondalite garnet sillimanite gneiss and migmatites in the eastern ghats mobile belt various stages of in situ granulitization similar to those observed in southern india and sri lanka are present geochemically the granulite suite around visakhapatnam is bimodal with acid and mafic variants there is an increase in the concentration and fractionation of the rare earth elements ree from pyroxene granulites to charnockites and six sm nd models ages t dm range from 2 86 to 2 35 ga with 2 1 ga for a younger granite the charnockites a pyroxene granulite and granite define a pb pb isochron age of 1176 pm 201 ma u pb ages of zircons and monazites from a charnockite near phulbani orissa yield near concordant data with ages of 985 pm 5 ma and 965 pm 7 ma respectively the new isotopic data and the available ages from the northeastern part of the eastern ghats in orissa suggest a major charnockite formati

proterozoic events in the eastern ghats granulite belt india evidence from rb sr sm nd systematics and shrimp dating metamorphic and protolith ages of five rock types mafic granulite orthopyroxene granulite leptynite sillimanite granite and metapelite from rayagada in the north central part of the eastern ghats granulite belt eggb india were determined from rb sr and sm nd whole rock and mineral isochrons in combination with shrimp u pb zircon data most of the whole rock isochron ages in both sm nd and rb sr systems point to either 1450 or 1000 ma and the mineral isochron ages are 1000 800 and 550 ma shrimp u pb zircon ages of 940 ma were obtained from metapelite which are in close agreement with the sm nd and rb sr isochron ages from all these data four age clusters 1450 1000 800 and 550 ma have been noted the 1450 ma ages are interpreted to represent igneous protolith formation of mafic granulite and leptynite the 1000 ma age cluster is regarded as the intrusion ages of sillimanite granite and charnockite and associated granulite facies metamorphism two other age clusters 800 a

a multi stage pressure temperature record in the chilka lake granulites the epitome of the metamorphic evolution of eastern ghats india metapelitic and charnockitic granulites exposed around chilka lake in the northern sector of the eastern ghats india preserve a multi stage p t record a high t decompression from above 10 kbar to 8 kbar around 1100 c has been determined from mg rich metapelites xmg 0 60 with quartz cordierite orthopyroxene sillimanite and cordierite orthopyroxene sapphirine spinel assemblages between this and a second decompression to 6 0 kbar isobaric cooling from 830 to 670 c at 8 kbar is evident these changes are registered by the rim compositions of orthopyroxene and garnet in charnockites and metapelites with an orthopyroxene quartz garnet plagioclase cordierite assemblage and are further supported by the garnet quartz orthopyroxene cordierite and biotite producing reactions in sapphirine bearing metapelites another indication of isobaric cooling from 800 to 650 c at 6 0 kbar is evident from rim compositions of orthopyroxene and garnet in patchy charnockites two sets of p t values are obtained from metapelites with a quartz plagioclase garnet sillimanite cordierite assemblage garnet and plagioclase cores yield 6 2 kbar 700 c and the rims 5 kbar 650 c suggesting a third decompression the earliest deformation f1 structures are preserved in the larger charnockite bodies and the metapelites which retain the high p t record the effects of post crystalline f2 deformation are observed in garnet megacrysts formed during or prior to f1 in some metapelites fold styles indicate a compressional regime during f1 and an extensional regime during f2 these lines of evidence and two phases of cooling at different pressures point to a discontinuity after the first cooling and imply reworking two segments of the present p t path replicate parts of the p t paths suggested for four other granulite terranes in the eastern ghats and the sense of all the paths is the same this plus the signature of three phases of deformation identified in the eastern ghats suggests that the chilka lake granulites could epitomize the metamorphic evolution of the eastern ghats

shrimp u pb zircon provenance of the sullavai group of pranhita godavari basin and bairenkonda quartzite of cuddapah basin with implications for the southern indian proterozoic tectonic architecture abstract proterozoic basins in cratonic india referred to as purana basins cover about 20 of the archean basement of the subcontinent although the stratigraphy of most of these basins has been well established it is only recently that radiometric age constraints have been obtained for some of the sedimentary sequences this study provides new data for two of the purana basins in southern india using shrimp u pb analysis of detrital zircons for the pranhita godavari basin an age limit of 709 ma is provided for the age of deposition of the sullavai group this prolongs the duration of proterozoic sedimentation to approximately one billion years ca 1700 709 ma and establishes the venkatpur sandstones of sullavai group as the youngest purana basin succession identified in india so far a major zircon provenance age peak at about 1000 ma and zircon ages between 800 and 750 ma are correlated with major tectonothermal events in the eastern ghats mobile belt egmb and intrusion of granites and associated pegmatites at that time the main provenance area of the venkatpur sandstones is interpreted to be the egmb with subordinate supply of sediments from the eastern dharwar craton it is suggested that portions of the egmb must have been an integral part of peninsular india at the time of deposition of these sediments for the cuddapah basin new u pb detrital zircon age constraints are provided for the nallamalai group sediments bairenkonda quartzites within the nallamalai fold belt the youngest population of which yielded an age of ca 1550 ma this age is similar to the emplacement age of the vinukonda granite 1589 4 4 ma in the nellore schist belt this suggests that the nellore schist belt was a source region for the bairenkonda quartzites and that deposition continued until at least 1550 ma a high precision archean age ca 3366 ma for a detrital zircon grain indicates the presence of paleoarchean components within the sediment source region provided that paleoarchean rocks are as yet unknown from the largely juvenile neoarchean eastern dharwar craton there exists a possibility that the nallamalai group was sourced from the ongole domain of the egmb

stratigraphic and structural development of the precambrian cuddapah basin s e india abstract the present work recognizes a subdivision of the cuddapah basin into 3 separate main units of deposition some of the earlier correlations proved to be untenable for practical reasons king s widely used stratigraphy is retained where possible in a revised form we recognise the cuddapah group 2000 1490 1450 ma nallamalai group 1490 1450 1090 870 ma and the kurnool group 1090 870 500 ma on the basis of surface geology mapping and photo interpretation we discern 5 tectonic zones the boundaries of these zones coincide with deep crustal faults encountered in a deep seismic sounding survey three phases of tectonic activity are 1 1 crustal movements resulting in broad folds affecting the cuddaph rocks exposed in the western area followed by 2 2 folding of the nallamalai rocks east of the rudravaram line and 3 3 later folding and metamorphism in the eastern tectonic zones structural sections allow an interpretation of an eastward continuation of the cuddapah basin rocks into the highly metamorphosed series underlying the eastern ghats complex a colour geological map and sections are included

proterozoic evolution of eastern dharwar and bastar cratons india an overview of the intracratonic basins craton margins and mobile belts abstract based on critical analysis of stratigraphic succesions in the proterozoic intracratonic basins geochronological data and possible connections or disconnections with adjacent fold belts and craton margin mobile belts an overview of the proterozoic evolution of the eastern dharwar and bastar cratons in india is presented the chattisgarh and cuddapah basins in these cratons with archean nuclei host sedimentary successions ranging in age from the paleoproterozoic to the ediacaran period and representing several silicilastic and carbonate cycles the proterozoic successions of the pranhita godavari valley pgv basin along the dharwar bastar join record multiple rifting since late neoarchean suturing of the two cratons we postulate a first order stratigraphic correlation across the cratons and their join and discuss how major sea level fluctuations coupled with regional tectonic events shaped the development of unconformity bound successions adjoining fold belts and the mobile belts with supposed global tectonic connections the oldest paleoproterozoic intracratonic sedimentation is preserved in the cuddapah and pgv basins while sedimentation in the bastar craton is largely mesoproterozoic the fluviodeltaic to shallow marine neoproterozoic sedimentation followed emplacement of end mesoproterozoic kimberlites and lamproites indicating thermal rejuvenation of the indian continental crust the allochthonus nallamalai fold belt in eastern cuddapah basin and the early mesoproterozoic fold belt in pgv basin point to craton margin crustal convergences which punctuated the paleoproterozoic sedimentation widespread development of carbonate bearing sequences in the mesoproterozoic to neoproterozoic successions point to peneplanation of the cratons and stable platformal sedimentation the neoproterozoic sedimentation was terminated following the docking of the eastern ghats belt to the eastern margin of the dharwar bastar ensemble and possible final tectonic hiccups in the central indian tectonic zone bordering the bastar craton the available data and their analysis rule out any foreland basin type connection between the eastern ghats belt and cratonic sedimentation in bastar and eastern dharwar

geochronology and tectonic evolution of karimnagar and bhopalpatnam granulite belts central india abstract the karimnagar granulite belt kgb and the bhopalpatnam granulite belt bgb occur along both flanks of the pranhita godavari pg rift basin we present a state of the art overview on the geochronological and tectonic aspects of these belts and surrounding geologic domains and report new age data on zircon monazite and uraninite recovered from granulite facies assemblages from kgb and bgb based on electron microprobe analyses epma zircons from kgb charnockites show core ages of up to 3 1 ga mantled by rims of 2 6 ga zircons from bgb have 1 9 ga cores mantled by 1 7 ga rims zircons with core ages of 1 6 to 1 7 ga in bgb rocks suggest new growth at this time monazites and uranitite from kgb show clear peaks with well defined ages in the narrow range between 2 42 0 08 ga and 2 47 0 03 ga rims of monazite show mean age of 2 21 0 08 ga monazites from bgb define sharp linear trend in pbo vs tho2 diagram delineating a clear isochron with age of 1 59 0 03 ga age data from kgb and bgb presented in this report negate current models linking these terrains to godavari granulite belt and considering them as single and contemporaneous entity the mid archaean to early palaeoproterozoic signature recognized from kgb is totally missing in bgb on the other hand kgb rocks do not record any evidence for major mesoproterozoic thermal regime the two granulite belts shouldering the pg rift basin have therefore evolved in different times under distinct p t conditions and thermal regimes our results have important implications in evaluating models of supercontinent assemblies particularly the older assemblies of ur columbia and rodinia while tectonothermal events in kgb broadly match with those of east dharwar we propose that bgb represents a 1 6 ga collisional mobile belt between the bastar and the dharwar cratons the 1 6 ga collisional mobile belt at the southern margin of the bastar craton was superposed by rift activity along the pg basin at 1 5 ga this sequence of events goes against the existence of a 3 0 ga old contiguous assembly of ur but closely matches with the history of accretion and break up of the columbia further parts of the pg basin located away from the influence of the eastern ghats mobile belt neither recorded any grenville ages 1 0 ga corresponding to the rodinia accretion nor late pan african ages ca 550 ma relating to the gondwana amalgamation indicating that the region did not witness any of these younger tectonic events

radioactivity heat flow and rifting of the indian continental crust the relationship between heat flow q and heat production a in india is quite different for the northern and southern parts of the peninsula in the north locations in a variety of tectonic settings including gondwana rifts show a linear relationship between q and a with a common reduced heat flow q about 40 mwm 2 in southern india the heat production of surface rocks is greater than is expected for the measured heat flow relative to other continental shields g is high in northern india and about average in the south apparently the indian crust evolved with a content of radioactive elements higher than in most shields and the southern part of the peninsula has undergone regional depletion in the lower crust and possibly upper mantle this depletion may coincide with a regional granulite event about 2 500 m y ago the high heat flow and heat production in northern india may explain several unique characteristics of the indian peninsula one feature is the continued reactivation of rif

a new correlation of sapphirine granulites in the indo antarctic metamorphic terrain late proterozoic dates from the eastern ghats province of india abstract uranium lead and thorium lead ages were obtained from perrierite and zircons in two samples from the eastern ghats province of south india a sapphirine bearing granulite from anakapalle and a charnockite from visakhapatnam the isotopic data are concordant or close to concordant at 1 ga which is interpreted to be the age of granulite facies metamorphism and charnockite plutonism in the vicinity of anakapalle and visakhapatnam and provides the first report of a late proterozoic granulite facies event in the eastern ghats province in reassemblies of gondwanaland based on dutoit s original proposal the eastern ghats province is juxtaposed against a high grade terrain in east antarctica affected by a granulite facies event and charnockitic plutonic activity 800 1100 ma ago the ages reported here suggest that a portion of the eastern ghats province represents an extension of the late proterozoic terrain from antarctica into india the radiometric results on the anakapalle rocks are the first evidence in south india for sapphirine formation during the late proterozoic other south indian sapphirine localities appear to be archaean in age a review of sapphirine localities in the indo antarctic metamorphic terrain indicates that sapphirine developed under a range of pressure temperature conditions during the archaean and proterozoic evidence for a systematic change in peak metamorphic conditions with time is obscured by these regional variations characterization of the entire pressure temperature path in addition to estimates for the peak conditions is needed to distinguish the archaean and proterozoic metamorphic regimes

deformation pattern and evolution of the structures in the penganga group the pranhita godavari valley india probable effects of grenvillian movement on a mesoproterozoic basin abstract recent studies reveal imprints of tectonic deformation in the mesoproterozoic rocks of the pranhita godavari p g valley india outcrop scale structures that record a progressive sequence of deformation can thus be used to clarify the kinematic evolution of the penganga group a mesoproterozoic succession in the northern and central parts along the sw marginal proterozoic belt of the pg valley overprinting relationships among the structures in the northern part indicate three distinct structural stages 1 layer parallel shortening 2 thrusting and folding in combination and 3 extensional joint and fracture opening the former two stages are explained in the framework of a progressive deformation model the extensional structures were produced during exhumation similar structures are also developed in the central part of the sw belt of the pg valley though the two areas slightly differ in the overall pattern of deformation the geometry of the progressive deformation structures from both regions of the belt suggests that they were produced under a regime of ne sw ene wsw directed regional compression the deformation in the proterozoic basin is possibly related to the grenvillian orogeny recorded in the eastern ghats mobile belt and may represent a small scale meso neoproterozoic convergence event