mid archaean evolution of the eastern indian craton geochemical and isotopic evidence from the bonai pluton abstract the archaean eastern indian craton consists of several granitoid batholiths intruding greenstone like sequences the bonai pluton one such body in the central sector of the craton consists of a dominant porphyritic and a subordinate equigranular variety ranging in composition from trondhjemite to granite xenoliths of massive trondhjemite migmatite and quartzite occur in both phases the granitoid xenoliths represent remnants of a sialic crust and are the oldest recognizable element in the bonai pluton these are high al 2 o 3 trondhjemites with a highly fractionated rare earth element ree pattern a pb pb isochron age of 3369 57 ma has been obtained from a few spatially related xenoliths the porphyritic and equigranular granitoids show similar petrographic characteristics and most of the samples show a calc alkaline trondhjemitic association a few granite samples however belong to a normal calc alkaline association the trondhjemitic samples are of the low al 2 o 3 type with fractionated light ree lree flat heavy ree hree and a marked negative eu anomaly granites of the calc alkaline association have an identical ree pattern pb isotopic data for all samples together yield a pb pb isochron age of 3163 126 ma the ree characteristics of the two trondhjemite suites can be generated by partial melting of a mafic source with variable residual phases at different depths on the other hand the normal calc alkaline granite may be generated by partial melting of trondhjemite similar in composition to that represented by the 3369 ma xenoliths isotopic ages and the chemical nature of the bonai pluton are similar to those identified in the adjacent singhbhum granite complex it is suggested that the entire eastern indian craton has a common mid archaean history the earliest sialic crust formed at 3400 ma and was followed by trondhjemitic addition at 3300 ma during this phase restricted reworking of the older sialic crust produced calc alkaline granites

a modified placer origin for refractory gold mineralization within the archean radioactive quartz pebble conglomerates from the eastern part of the singhbhum craton india

lithospheric thinning in the eastern indian craton evidence for lithospheric delamination below the archean singhbhum craton abstract we herein present shear velocity structure extending down to 300 km depth below the archean singhbhum odisha craton soc and proterozoic chotanagpur granitic gneissic terrain cggt which has been obtained through the inversion modeling of p receiver functions we use three component broadband recordings of 200 teleseismic earthquakes 30 90 from a 15 station seismic network that has been operational in the eastern indian shield since february 2013 we obtain the thinnest crust of 35 km overlying a thin lithosphere of 78 km below the region near south singhbhum shear zone which could be attributed to the 1 6 ga plume activity associated with dalma volcanic however the thickest crust of 47 km overlying a thin lithosphere of 81 km is noticed below the region near the singhbhum granite of 3 6 ga this thinning of lithosphere could be attributed to the delamination of lithospheric root due to the himalayan orogeny with a shortening rate of 2 cm year this delamination model in soc gets further support from the densification of the lower crust which could result from repeated episodes of basaltic underplating associated with episodes related to dalma 1 6 ga and rajmahal 117 ma volcanisms this led to relatively more mafic heterogeneous and deformed crustal structure in soc as well as egmb with an average crustal vs of 4 0 km s in comparison to that in cggt with an average crustal vs of 3 9 km s as seen through our modeling results the thickest lithosphere of 100 km is observed in the southwestern soc as well as northeastern cggt we also notice that a sharp and flat moho in cggt which could be attributed to thermal reactivation and large volume melting of the mafic cratonic crust during the late archean subduction process and associated volcanism episodes this model gets further support from the estimated 169 km thick lower vs zone in the upper mantle below cggt our modeling results also support a northward subduction of archean soc under the proterozoic cggt during 1 0 1 6 ga as earlier proposed by the geological age data from the region

pressure temperature deformation history for a part of the mesoproterozoic fold belt in north singhbhum eastern india abstract the supracrustal rocks in the easternmost part of the proterozoic fold belt of north singhbhum eastern india are folded into a series of large upright folds with variable plunges the regional schistosity is axial planar to the folds the folds were produced by a second phase of deformation d2 and were preceded by d1 deformation which gave rise to isoclinal folds mapped outside the study area and the locally preserved bedding parallel schistosity a shearing deformation during d2 was responsible for the sheath like geometry of a major fold the axial planes were curved by d3 warping the first metamorphic episode m1 of low pressure type produced andalusite porphyroblasts prior to or in the early stage of d1 deformation the main metamorphism m2 responsible for the formation of chloritoid kyanite garnet and staurolite porphyroblasts was late to post d2 in occurrence the staurolite isograd separates two zonal assemblages recorded in the high alumina and the low alumina pelitic schists geothermobarometric calculations indicate the peak metamorphic temperature to be 550 c at 5 5 kb fluid composition in the rocks before and during m2 metamorphism was buffered and fluid influx if any was not extensive enough to overcome the buffering capacity of the rocks from m1 to m2 the p t path is found to have a clockwise trajectory that is consistent with a tectonic model involving initial asthenospheric upwelling and rifting followed by compressional deformation leading to loading and heating

dating the oldest terrestrial rocks fact and fiction abstract this paper is a review of well documented geochronological and related isotopic evidence for the age and total crustal residence time of the oldest known terrestrial rocks mainly using rb 1bsr sm 1bnd and u 1bpb decay schemes the oldest known stable sialic crust of true continental character predominantly composed of calc alkaline orthogneisses was produced during major mantle differentiation some 3 7 3 5 ga ago and is represented on several continents enclaves of older supracrustal rocks as well as a major remnant of a volcano sedimentary sequence of greenstone belt affinity dated at 3 8 ga are preserved within the surrounding gneisses in southern west greenland recent ionmicroprobe evidence for 4 1 ga old detrital zircon grains in a younger early archaean metasedimentary sequence in western australia is also discussed several cases are reviewed where claims for early archaean 3 4 ga dates are believed to be erroneous and to result from oversimplistic and incorrect interpretation of isotopic data some of the geological and geochemical mechanisms which have given rise to claims for spuriously old sm 1bnd u 1bpb and pb pb dates are critically discussed to supplement published data we present several new sets of whole rock sm 1bnd and pb pb isotopic data from west greenland labrador zimbabwe and eastern india relevant to the overall topic of this review

proterozoic sedimentation and volcanism in the singhbhum crustal province india and their implications abstract the proterozoic volcano sedimentary succession comprising successively younger dhanjori chaibasa dhalbhum dalma and chandil formations of the singhbhum crustal province india records sedimentation and volcanism in a rapidly changing tectonic scenario cooling of the vast volume of archaean singhbhum granite possibly induced an isostatic readjustment the associated tensional regime and deep seated fractures controlled the formation of the proterozoic singhbhum basin the dhanjori formation unconformably overlies the singhbhum granite and is entirely terrestrial dominantly fluvial at the base the conglomerate deposits coarse grained sandstone and shale represent the distal fringe of an alluvial fan complex the rest of the formation including the volcaniclastic rocks consists almost entirely of fining upward fluvial cycles the base of the dhanjori formation is a sequence boundary and the formation itself represents a lowstand systems tract the dhanjori volcano sedimentary succession displays evidence of having passed through passive as well as active phases of continental rifting with an increasingly important influence of volcanism on the sedimentation through time the chaibasa formation sharply overlies the dhanjori formation and a transgressive lag demarcates their contact the basal part of the chaibasa formation immediately overlying the transgressive lag deposit represents a transgressive systems tract while offshore shales that sharply overlie the shallow marine sandstones up section represent marine flooding surfaces the shallow marine subtidal sandstones bear an excellent record of sandwave migration and provide a rare opportunity to unlock the late palaeoproterozoic lunar orbital periodicities unlike the chaibasa the overlying dhalbhum formation is entirely terrestrial fluvial aeolian indicating that the chaibasa dhalbhum contact is a sequence boundary the dalmas overlying the dhalbhum formation represents concordant lava outpourings without any break in sedimentation these lavas are genetically related to mantle plume upwelling in an intracontinental rift setting the volcano sedimentary package lying north of the dalma volcanic belt chandil formation is of mesoproterozoic age the entire late palaeoproterozoic volcano sedimentary package displays post depositional compressional deformation and greenschist to amphibolite facies metamorphism dated at ca 1600 ma forming the so called north singhbhum fold belt the volcano sedimentary package lying south of the dalma volcanic belt was pushed further south towards the singhbhum granite batholith complex as a result of uplift related to the dalma plume the singhbhum granite batholith acted as a rigid body this gave rise to a compressional stress regime that induced shearing thrusting at ca 1600 ma along the singhbhum shear zone the dalma plume magmatism was possibly part of a 1600 ma global tectono thermal event

sandstone chert and laminated chert black shale couplets cretaceous uhangri formation southwest korea depositional events in alkaline lake environments abstract the cretaceous uhangri formation southwest korea is a lacustrine sequence surrounded by acidic volcanic terrain and comprises sandstone chert and laminated chert black shale couplets in the upper part in both cases the uhangri chert is composed mainly of sio 2 74 81 al 2 o 3 10 12 and k 2 o 6 7 its impure nature is largely due to the presence of feldspar grains and clays within a microcrystalline quartz matrix the uhangri chert is characterized by common soft sediment deformation in situ brecciation slumping and no organic traces which collectively indicate its inorganic origin the sandstone chert couplets are alternations of massive graded crudely stratified rippled or ripple cross laminated sandstone layers and generally homogeneous chert layers the laminated chert black shale couplets consist of alternating light and dark coloured laminae of chert and overlying black shale these couplets were most likely deposited by episodic riverine inflows into a silica rich alkaline lake the freshwater input could trigger direct inorganic silica precipitation through an abrupt decrease in lake water ph the sandstone chert couplets would be deposited by high density underflows whereas the laminated chert black shale couplets by fine sediment dominant overflows

sm nd isotopic and geochemical study of the archean tonalite amphibolite association from the eastern indian craton we report the results of a sm nd isotopic major element and rare earth element ree study of the older metamorphic group omg tonalite amphibolite association of the eastern indian craton the older metamorphic tonalite gneisses omtg have been previously dated to be 3 8 ga using sm nd isotope systematies and 3 2 3 4 ga by rb sr and pb pb dating the results of this study indicate that the protoliths of the omg amphibolites are 3 3 ga isochron age 3 30 0 06 ga nd 0 9 0 7 and therefore the omtg which intrude into the associated amphibolites cannot be any older than 3 3 ga the amphibolites display light ree enrichment ce yb n 2 2 6 7 la 30 100 x chondrite and nearly flat heavy ree patterns tb lu n 1 2 1 9 the basaltic parents of the amphibolites were probably generated by the partial melting of a spinel lherzolite mantle strong linear relationships between the amphibolites and tonalites in 147sm 144nd 143nd 144nd space isochron age 3 29 0 04 ga nd 0 8 0 8 imply that they are genetically related the tonalites display fractionated ree patterns la 100 300 x chondrite with moderate heavy ree depletions tb lu n 1 9 3 4 the isotopic major element and ree data are consistent with the derivation of the omtg from partial melting of omg amphibolites or equivalent rocks at amphibolegarnet stabilization depths an initial nd t value of 0 9 0 7 for the amphibolites indicates the presence of a slightly depleted mantle source at 3 3 ga with 147sm 144nd between 0 20 and 0 22 it is suggested that the growth of continental crust in the eastern indian craton occurred in response to magmatic underplating in a plume setting

geochronological constraints on evolution of singhbhum mobile belt and associated basic volcanics of eastern indian shield abstract the singhbhum mobile belt smb of the eastern indian shield represents a roughly east west trending arcuate belt of folded supracrustals overlying the granite greenstone basement of the singhbhum orissa craton along its northern eastern and western margins and is bounded by the chotanagpur gneissic complex to further north the radiometric ages of the basement singhbhum and equivalent granites and the intrusive anorogenic mayurbhanj granite pluton constrain the time of evolution of this mobile belt between 3 12 and 3 09 ga hence the smb supracrustals also known as singhbhum group is late mesoarchaean in age and not proterozoic as thought earlier the evolution of the smb was followed by emplacement of some major basic igneous rocks within or adjacent to the supracrustals these include simlipal volcanics at 3 09 ga on the smb mayurbhanj gabbro along with mayurbhanj granite at 3 09 ga along the marginal part of the craton near the smb and the dalma volcanics on the smb along with the dhanjori volcanics adjacent to smb at 2 80 ga the 2 80 ga old basic volcanics is also associated with emplacement of some small granite plutons occurring along the marginal part of the craton one of them the tamperkola granite intrudes the smb the 3 09 ga onward igneous activities along the marginal part of singhbhum orissa craton took place essentially under anorogenic tectonic setting before being affected by a major metamorphism at 2 50 ga which is recorded on the dalma volcanics and on some small granite pluton occurs along the marginal part of the craton the jagannathpur and stratigraphically equivalent malangtoli volcanics occurring within the singhbhum orissa craton at the west were erupted at 2 25 ga the boundary between the smb supracrustals and the singhbhum orissa craton is demarked by a prominent shear zone known as the singhbhum shear zone which shows multiple reactivation the oldest being at 3 09 ga followed by subsequent reactivation during palaeo and mesoproterozoic periods at 2 2 1 8 1 6 1 5 1 4 and 1 0 ga respectively the singhbhum group and the adjacent chotanagpur gneissic complex appear to have evolved from a near shore syn rift and a distal post rift stable shelf sedimentary assemblages respectively which were deposited without any stratigraphic break in a marine basin existed in the present north of the singhbhum orissa craton both of these assemblages were deformed and metamorphosed together during proterozoic at 2 5 to 2 3 ga 1 6 ga and 1 0 ga

mesoarchaean palaeoproterozoic stratigraphic record of the singhbhum crustal province eastern india a synthesis the mesoarchaean palaeoproterozoic stratigraphic record of the singhbhum crustal province eastern india implies sedimentation and volcanism in a changing tectonic scenario and thus assumes immense geological significance although efforts have been made by many researchers in the past several decades to summarize various geological aspects of the singhbhum crustal province a critical synthesis of various stratigraphic issues was long overdue the present contribution is an updated critical synthesis of the mesoarchaean palaeoproterozoic stratigraphic record of the singhbhum crustal province we have pointed out the problematic stratigraphic issues of the singhbhum crustal province that deserve careful scrutiny in order to gain better insights into the mode of stratigraphic sequence building

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

coalescing microstructure and fabric transitions with ams data in deformed limestone implications on deformation kinematics abstract the microstructures of the heterogeneously deformed limestones of the kolhan group singhbhum craton sc eastern india are investigated to study deformation mechanism grain size and shape preferred orientation spo development the texture of the deformed rocks is analyzed by electron back scattered diffraction ebsd in order to determine crystallographic preferred orientation cpo development in calcite grains the c axis pattern in protomylonite and mylonite define girdle patterns developed perpendicular to local shear planes showing monoclinic symmetry the latter is interpreted in terms of a top to south shear which is consistent with the observed microstructural and fabric data from the deformed rocks the anisotropy of magnetic susceptibility ams studies are performed on 22 heterogeneously strained limestone specimens to document strain variation within the kolhan rocks the field fabric spo data measured from calcite and mica grains cal and mi and calcite cpo data are compared with observed variation in ams fabric intensity pj across the kolhan basin integration of these data sets help to establish presence of large internal thrust planes within the kolhan basin which form a part of the regional foreland vergent thrust system developed along the northern margin of the sc

evolution of mayurbhanj granite pluton eastern singhbhum india a case study of petrogenesis of an a type granite in bimodal association abstract the a type mayurbhanj granite pluton 3 09 ga occurring along the eastern margin of the singhbhum orissa craton eastern india represents the final phase of acid plutonism in this crustal block of archean age the granite shows a bimodal association with a voluminous gabbroid body exposed mainly along its western margin and is associated with the singhbhum shear zone the granite pluton is composed mainly of a coarse ferrohastingsite biotite granite phase with an early fine grained granophyric microgranitic phase and a late biotite aplogranitic phase petrogenetic models of partial melting fractional crystallisation and magma mixing have been advocated for the evolution of this pluton new data combined with earlier information suggest that two igneous processes were responsible for the evolution of the mayurbhanj granite pluton partial melting of the singhbhum granite followed by limited amount of mixing of acid and basic magmas in an anorogenic extensional setting the necessary heat for partial melting was provided by the voluminous basaltic magma now represented by the gabbroid body emplaced at a shallow crustal level and showing a bimodal association with the mayurbhanj granite pluton the singhbhum shear zone provided a possible channel way for the emplacement of the basic magma during crustal extension it is concluded that all three phases of the mayurbhanj granite pluton were derived from the same parent magma generated by batch partial melting of the singhbhum granite at relatively high temperatures 980 c and low pressures 4 to

mineral chemistry and stable isotope constraints on the magmatism hydrothermal alteration and related pge base metal sulphide mineralisation of the mesoarchaean baula nuasahi complex india the baula nuasahi complex on the southern flank of the singhbhum archaean nucleus in north eastern india exposes a series of mesoarchaean igneous suites these are 1 a gabbro anorthosite unit which is petrographically homogeneous although mineral chemistry data hint at a subtle eastward differentiation 2 a peridotite unit with three chromitite layers together with 3 a pyroxenite unit which display cumulate textures modal layering and for the peridotite unit differentiation trends in both mineralogy and mineral chemistry and 4 the bangur gabbro 3 1 ga which defines an oblong intrusion crosscutting the older igneous suites in the southern part of the complex with a curvilinear nw trending apophysis 2 km long and up to 40 m wide magmatic breccia comprising ultramafic and chromitite wall rock clasts in a gabbro matrix is exposed at the contact of the main bangur gabbro body and also forms the entire bangur gabbro apophysis concentrations of platinum group minerals pgms are found where the breccia contains abundant chromitite clasts and two types of platinum group element pge mineralisation are recognised type 1 pt 1 1 14 2 pd 0 1 2 1 ppm with an average pt pd 8 9 is a contact type mineralisation which occurs in the breccia at the contact between the bangur intrusion and its ultramafic host the pgms pt alloys isoferroplatinum and sulphides braggite malanite are enclosed by pyroxene and plagioclase reflecting a magmatic origin significant wall rock assimilation by the magma giving rise to the bangur gabbro is indicated by changes in pyroxene composition and by the presence of relicts of chromite from the host now altered to secondary ferritchromite in the contact zone type 2 pge mineralisation pt 0 3 1 6 pd 1 8 6 0 ppm with pt pd 0 5 3 0 is restricted to the breccia apophysis of the bangur gabbro where it occurs in the breccia matrix associated with an intense hydrothermal alteration which does not exist in the contact zone pgms pge arsenides tellurides bismuthides and antimonides and where present base metal sulphides bmss form intergrowths with hydrous silicates reflecting a hydrothermal origin oxygen isotope geothermometry documents the main stages of hydrothermal alteration within a decreasing temperature range between 700 1 000 and 500 600 c and oxygen hydrogen and sulphur isotopes show that the hydrothermal fluids were derived from the magma rather than an external source pervasive hydrothermal alteration in the breccia apophysis likely represents upward channelling of late magmatic fluids along a narrow near vertical subplanar conduit which led away from the main magma chamber we suggest that type 2 mineralisation was produced by late magmatic hydrothermal remobilisation and reconcentration of type 1 pge mineralisation and that the composition of the hydrothermal fluids controlled whether bmss were enriched along with the pgms

the genesis of archaean chromitites from the nuasahi and sukinda massifs in the singhbhum craton india abstract the chromitite deposits of the nuasahi and sukinda massifs are part of layered ultramafic bodies which occur within archaean low grade metamorphic rocks of the iron ore group iog in the singhbhum craton of the indian shield the chromitite seams are interlayered with dunite and associated with orthopyroxenite detailed electron microprobe study reveals very high mg numbers 0 66 0 82 and cr numbers 0 75 0 87 for chromite in massive chromitite from the seams high fo content fo 92 95 for olivine in dunite and high en content en 89 94 for orthopyroxene in orthopyroxenite our study suggests that the original igneous compositions for these minerals are preserved in the respective monomineralic rocks and can be used to evaluate the primary magmatic petrogenesis of the rocks the primitive compositions of the minerals in monomineralic rocks suggest high degree of partial melting of the source mantle during the mesoarchaean the parental magma from which the massive chromitites crystallized was of siliceous high mg basaltic or boninitic compositions similar to the compositions of spatially associated chromite bearing siliceous high mg basalts of the iron ore group the parental magma may have generated due to the interaction of a depleted mantle with a fluid enriched melt possibly derived in response to the dehydration of a subducting slab monomineralic chromitite layers formed either in response to mixing of magmas or due to the suppression of silicate mineral crystallization in response to elevated h 2 o concentrations in the parent magmas the parental magmas that produced chromitites may have intruded into the volcano sedimentary greenstone belts of a supra subduction zone setting

group velocity dispersion characteristics and one dimensional regional shear velocity structure of the eastern indian craton abstract in the past three years a semi permanent network of fifteen 3 component broadband seismographs has become operational in the eastern indian shield region occupying the archean 2 5 3 6 ga singhbhum odisha craton soc and the proterozoic 1 0 2 5 ga chotanagpur granitic gneissic terrane cggt the reliable and accurate broadband data for the recent 2015 nepal earthquake sequence from 10 broadband stations of this network enabled us to estimate the group velocity dispersion characteristics and one dimensional regional shear velocity structure of the region first we measure fundamental mode rayleigh and love wave group velocity dispersion curves in the period range of 7 70 s and then invert these curves to estimate the crustal and upper mantle structure below the eastern indian craton eic we observe that group velocities of rayleigh and love waves in soc are relatively high in comparison to those of cggt this could be attributed to a relatively mafic rich crust mantle structure in soc resulting from two episodes of magmatism associated with the 1 6 ga dalma and 117 ma rajmahal volcanisms the best model for the eic from the present study is found to be a two layered crust with a 14 km thick upper crust uc of average shear velocity vs of 3 0 km s and a 26 km thick lower crust lc of average vs of 3 6 km s the present study detects a sharp drop in vs 2 to 3 at 120 260 km depths underlying the eic representing the probable seismic lithosphere asthenosphere boundary lab at 120 km depth such sharp fall in vs below the lab indicates a partially molten layer further a geothermal gradient extrapolated from the surface heat flow shows that such a gradient would intercept the wet basalt solidus at 88 103 km depths suggesting a 88 103 km thick thermal lithosphere below the eic this could also signal the presence of small amounts of partial melts thus this 2 3 drop in vs could be attributed to the presence of partial melts in the upper mantle related to the earlier volcanic episodes viz back arc volcanism associated with the archean proterozoic subduction 1 6 ga dalma volcanism and 117 ma rajmahal volcanism the main result of our modeling provides evidences for the absence of keel or thick lithosphere below the eic

source levels of shallow explosive charges experimental measurements are reported in this article for the source levels of 0 82 kg signals underwater sound sus charges detonated at nominal depths of 18 3 91 and 183 m the data were recorded in the farfield using a high resolution digital data acquisition system that provided good reproduction of both the high and low frequency components of the signal from the explosion the results are presented in 1 3 octave bands from 5 630 hz and represent the mean values of samples of at least 30 charges for each depth group the standard deviations were within 1 db for most frequency bands analysis of the distribution of explosion depths indicated that the average detonation depths were consistently deeper than the nominal depths this result was attributed to the effect of the relatively cold water temperatures at the experimental site in addition to the measured source levels estimates for 0 82 kg sus charges at 244 m were scaled from the experimental data using a method suggested by hughes r hu

discovery of a neoproterozoic basin in the prydz belt in east antarctica and its implications for gondwana assembly and ultrahigh temperature metamorphism abstract detrital zircon u pb age data from ultrahigh temperature metasedimentary rocks 950 c and 10 12 kbar in the rauer group and a granulite grade metasedimentary rock 850 c and 7 8 kbar in the bolingen islands in prydz bay east antarctica indicate the existence of a neoproterozoic ediacaran cover sequence that was deposited on basement ranging in age between approximately 2800 ma and 940 ma the neoproterozoic succession has a maximum depositional age of approximately 600 ma with derivation from igneous and metamorphic sources of archaean palaeoproterozoic and neoproterozoic age the minimum depositional age is constrained to be approximately 575 ma based on existing th u pb monazite metamorphic ages from the uht metasedimentary rocks the identification of late neoproterozoic protoliths to the uht granulites in the rauer group demonstrate that ultrahigh temperature metamorphism in prydz bay must be ediacaran to cambrian in age the timing of basin development ca 600 575 ma is coincident with the amalgamation of eastern gondwana the palaeogeography of the prydz bay region during the amalgamation of gondwana is uncertain but in our proposed reconstruction we suggest that inherited zircons were derived from indo antarctic crust ocean closure is inferred to have occurred along a suture zone to the southeast of prydz bay and the prince charles mountains our palaeogeographic model invites further work on the possibility of a shared history between india and a large portion of east antarctica prior to the final amalgamation of eastern gondwana during the ediacaran cambrian

geochemistry of banded iron formation of orissa india major and trace element analyses of representative samples of various types of banded iron formation and its various minerals associated sediments iron ores and volcanic tuff from different localities of orissa india are presented in this paper the orissa banded iron formation is classified as precambrian banded iron formation and is similar to the oxide facies iron formation of lake superior type the orissa iron formation consists only of iron oxide and silica with total absence of iron silicate sulfide and carbonate minerals and is devoid of terrigenous material the trace element content suggests the source of the underlying quartzite to be a continental igneous rock mass while the interbedded tuff are of undoubted volcanic origin the overlying iron formation were chemically precipitated as oxidate sediments in which the principal iron mineral magnetite was formed at low temperature in a shallow marine environment from the overwhelming similarity of major and trace element contents of all the samples from the different localities it is postulated that these detached outcrops originated in the same continous basin

207pb 206pb zircon ages and the evolution of the singhbhum craton eastern india an ion microprobe study1this paper is dedicated to prof a k saha one of the senior co authors who passed away after submission of the paper 1 abstract we used an ion microprobe to measure 207 pb 206 pb ages of single zircons from four key lithologies from the singhbhum craton of eastern india detrital zircons from the oldest recognized sedimentary sequence of the craton the older metamorphic group yielded 3 5 3 6 ga ages indicating that crustal formation had already been initiated by 3 6 ga in this region this data also established an older limit of 3 5 ga for the age of sediment deposition the first appearance of extensive continental crust in the singhbhum region marked by the emplacement of the older metamorphic tonalite gneisses is dated at 3 44 ga our data from both of these units reveal that a 3 2 ga event induced overgrowths within each of these pre existing zircon populations we determine an age of 3328 7 ma for the singhbhum granite phase ii the most widespread of this granite s three phases the emplacement of the two phases of the mayurbhanj granite marking the youngest major episode of acid plutonism in this craton took place in rapid succession at 3 1 ga marking the broad scale stabilization of this terrain

characterization of organic matter and its implications for pyrite hosted refractory gold mineralization along the south purulia shear zone eastern india abstract refractory gold bearing sulphide mineralization is spatially associated with the carbonaceous matter rich meta sedimentary rocks of the proterozoic south purulia shear zone spsz the carbon rich layers occurring as black continuous laminae are the metamorphosed derivatives of carbonaceous matter which were originally present in the sedimentary rocks and bear the characteristics of initial sedimentary environment of the refractory gold bearing formations of spsz the carbonaceous laminae aligned along the bedding foliation planes got remobilized into the sulfide bearing quartz carbonate veins during the metamorphic and deformational events the typical disordered bands as well as graphitic band in the raman spectra indicate that the carbonaceous matter is partially graphitized from the precursor carbon rich layers the light and homogeneous carbon isotopic values 13c 26 7 to 28 2 of the graphitized carbon suggests its origin due to the evolution from an organic precursor the 13c values fall within the range typical for organic carbon deposited during the paleo to meso proterozoic period the organic matter is considered to have played an essential role in buffering the oxygen fugacity of the initial sedimentary basin the dissolved sulfate ions in seawater were reduced resulting in sulfidation and adsorption of au in sedimentary pyrites to form refractory gold later during the deformational stages the hydrothermal fluids interacted with the graphitized matter which provided suitable redox conditions for the precipitation of auriferous sulfides such as pyrite pyrrhotite chalcopyrite and arsenopyrite within the quartz carbonate veins

superposed deformation fabrics in the precambrian metabasic rocks of the iron ore group singhbhum craton eastern india evidences from anisotropy of magnetic susceptibility studies abstract anisotropy of magnetic susceptibility ams data have been utilized to build up the multiple deformation sequences and strain variation from an apparently undeformed metabasic lava sequence of the basal part of the paleo mesoarchean greenstone succession of the iron ore group rocks in the western iron ore basin singhbhum craton eastern india the basal lava crops out bordering the regional horseshoe shaped outcrop the horseshoe synclinorium structure of the overlying bif rocks ams data of 892 cylindrical specimens drilled from 83 samples collected from different structural domains within the synclinorium structure are presented in the analysis ams orientation data have been analyzed in the light of superposed fold type 1 interference fabrics developed within bif as a result of successive deformation episodes d1 and d2 it is found that the lava samples ubiquitously present two consistent magnetic fabrics homogeneous over smaller sub areas which have been successfully correlated with the d1 and d2 deformation fabrics from the bif rocks moreover a regional scale variation in intensity and nature of strain is noticed from the ams data which have been utilized to decipher folding mechanism as well as the changing deformation pattern during successive folding events

invisible gold occurrence within the quartz reef pyrite of babaikundi area north singhbhum fold and thrust belt eastern indian shield evidence from petrographic sem and epma studies abstract the mesoproterozoic metasedimentary rocks of chandil formation belong to the northern part of singhbhum crustal province eastern india the chandil formation lies within the north singhbhum fold and thrust belt and is demarcated at its southern margin by the dalma volcano sedimentary belt tamar porapahar shear zone tpsz separates the chandil formation from the meso neoproterozoic chhotanagpur granite gneissic complex cggc at its northern boundary the area is characterized by quartz mica sericite schist quartzite amphibolites and carbonaceous phyllites and is ubiquitously traversed by mineralized quartz reefs veins the field relationships and the petrographic characteristics of the lithounits of chandil formation indicate evidence of multi phase deformations exhibited by the presence of s c fabric s1 s2 planes of schistosity alternate layers of coarse and thin quartz veins the gold mineralization in the study area occurs along the east west oriented babaikundi birgaon axis which has been established as a sheared fractured contact running parallel to the tamar porapahar shear zone lying to the north gravity magnetic resistivity and induced polarization ip survey across the babaikundi birgaon axis indicates the presence of sheared fractured contact and sulfide mineralization the gold mineralization within the area is confined to the quartz reef along the contact of mica schist and ambhibolites ore minerals observed in the area are chalcopyrite pyrite pyrrhotite arsenopyrite and sphalerite the majority of the sulfide mineralization is associated with the ferruginous quartz veins gold occurs in two distinct forms as lodes nuggets and as invisible gold within the pyrite mineralization field observations reflected and transmitted light microscopic study sem analysis and electron probe micro analyzer epma were used to give a brief account of the mineral chemistry and presence of different forms of gold including the first report of invisible gold within north singhbhum fold and thrust belt the occurrence of gold in the crystal lattice of the pyrite may be attributed to the substitution and replacement of fe ion within the pyrite aided by the hydrothermal activity

authigenic precipitation of ferric oxyhydroxides and greenalite in archean oceans abstract the initial mineral phases of banded iron formations bifs were mostly altered during diagenesis and metamorphism the initial iron mineral whether it was hydrous ferric oxides hfo or hydrous ferrous silicates hfs is a matter of debate each of those being the primary iron mineral offers us considering completely different biogeochemical conditions of archean oceans some archean greenstone bifs of badampahar 3 2 ga singhbhum craton and nuvvuagittuq 3 8 ga northern quebec consist alternating grunerite magnetite and quartz rich authigenic sedimentary bands the minerals appear to be co crystallized during metamorphism and show evidence of being originated from different precursor minerals e g magnetite from hfo and grunerite from hfs the process of such episodic hfo and hfs precipitations apparently related to two different fe si cycles in the archean oceans is not understood yet in situ trace element geochemistry of the minerals proves their authigenic origin and shows some characteristic geochemical differences e g grunerite having higher contents of hydrothermally sourced trace elements whereas magnetite being rich in elements involved in marine biogenic cycles the origin of mineralogically different e g quartz grunerite and magnetite rich bands of the studied bifs is explained with a model of hfs rich precipitation during episodic hydothermalism subsequent hfo rich precipitation by microbial oxidation and silica rich precipitation during no hydrothermal activity or non depositional period of iron minerals

neoarchean tectonothermal imprints in the rengali province eastern india and their implication on the growth of singhbhum craton evidence from zircon u pb shrimp data a detailed zircon u pb shrimp geochronological study of the amphibolite to granulite grade rocks of the rengali province of eastern india records the growth history of the southern margin of the singhbhum craton pelitic and mafic granulites from the gneissic belt exhibit contrasting styles of metamorphism zircon of the pelitic granulites from the eastern segment yields c 3528 3064 ma detrital ages charnockitic gneiss from the eastern segment has protolith age of 3058 15 ma while that from the central segment has protolith age of 2861 30 ma the latter rock records high grade metamorphism at 2818 15 ma hornblende gneiss from the central sector has a protolith age of 2828 9 ma deformed leucogranite in the central and undeformed granitoid in the eastern segment were emplaced at 2807 13 and 2809 13 ma respectively the protolith of felsic gneiss from the central sector was emplaced at 2776 24 ma most of the zircon samples contain overgrowths of c 2500 ma inferred to be the age of reworking of the gneissic belt our data suggest that the rengali province evolved as an orogenic belt in the neoarchean time c 2800 2500 ma during southward growth of the singhbhum craton these tectonothermal imprints at the margin of the singhbhum craton are possibly related to its inclusion within the supercontinent ur

reappraisal of the structure of the western iron ore group singhbhum craton eastern india implications for the exploration of bif hosted iron ore deposits abstract the middle to late archean iron ore group rocks occurring along the western margin the western iron ore basin of the singhbhum granite massif in the singhbhum craton were deformed during iron ore orogeny and are disposed in a horseshoe shaped synclinal structure in the eastern part of the indian shield the western iron ore basin hosts almost all the major high grade iron ore deposits of eastern india contrary to the established view present analysis emphasizes that the horseshoe fold in reality is a synclinorium consisting of a syncline anticline fold pair which were later cross folded along an east west axis structural analysis in the eastern anticline of the horseshoe synclinorium suggests that the bif hosting the high grade iron ore bodies are disposed in three linear nne ssw trending belts each showing an open synclinal geometry later cross folding produced development of widespread dome and basin pattern at the sub horizontal hinge zones of these synclinal fold belts the major iron ore deposits in the eastern anticline at the present level of erosion are preferentially localized within shallow elongated basinal structures only the axis of the adjoining western syncline was similarly uplifted as partial culminations where cross folded against e w anticlinal axes but here the bif iron ore bodies are preferentially localized within elongated domal structures in contrast to the basinal sites in the adjacent eastern anticline such an inference based on structural analysis could probably be utilized as a potential tool for all future explorations reserve estimation and recovery of the iron ore deposits in the terrain

possible juvenile palaeoarchaean ttg magmatism in eastern india and its constraints for the evolution of the singhbhum craton high precision shrimp u pb zircon dating yields a late palaeoarchaean age 3290 8 6 ma for a large unmetamorphosed weakly peraluminous ttg body the keonjhargarh bhaunra pluton in the singhbhum craton of eastern india one inherited subhedral zircon grain gave a concordant age of 3495 9 5 3 ma and nd isotope characteristics show a juvenile trend with end t 0 and t dm 3395 3453 ma the data support a model of typical archaean crustal evolution until late palaeoarchaean times for the singhbhum craton which is in contrast to the more southerly bastar craton where palaeoarchaean non ttg granites have been identified these data demonstrate the diachronous development of continental crustal blocks now forming the basement of the eastern and central peninsular of india

constraints of mineralogical characterization of gold ore implication for genesis controls and evolution of gold from kundarkocha gold deposit eastern india abstract gold mineralization in kundarkocha gold deposit occurs in the eastern indian craton that is hosted by sheared quartz carbonate sulfide veins emplaced within the graphitic schist carbonaceous phyllite and talc chlorite serpentine schist belongs to gorumahisani badampahar schist belt of iron ore group gold mineralization exhibits both lithological and structural controls in the study area albeit the stratigraphic control is more ubiquitously observed detailed mineralogical characterization coupled with electron probe microanalysis of the sulfide phases reveal the occurrences of gold in three distinct forms i as lattice bound form within sulfides especially enriched in arsenopyrite loellingite pyrite pyrrhotite and chalcopyrite in decreasing order of abundance ii as micro inclusions or nano scale gold inclusions within pyrite and arsenopyrite especially along the growth zones and micro fractures as substrates and iii as free milling nugget gold grains either along the grain boundaries of sulfides or within the host rocks three generations of pyrite py i py ii and py iii and arsenopyrite asp i asp ii asp iii have been identified based on textural morphological characteristics and mineral chemistry the lattice bound gold content in pyrite and arsenopyrite varies from 600 to 2700 ppm and 900 to 3600 ppm respectively and increase in concentration of such refractory gold is seen in the order of chalcopyrite pyrrhotite pyrite loellingite arsenopyrite the evolutionary stages of different forms of gold include remobilization of the lattice bound grains in pyrite and arsenopyrite py i and asp i and re concentration along the zoned pyrite and arsenopyrite py ii and asp ii and ultimately as native gold nuggets surrounding the sulfides as well as within the main mineralized zone lattice bound gold distribution could have resulted due to metamorphic devolatilization reactions which are further aided by the influx of hydrothermal fluids these reactions along with additional input of hydrothermal fluid paved the way for expulsion of lattice bound gold from sulfides to concentrate as nuggets main lode within shear fractures channelizing the fluid flow thermometry results of the arsenopyrite pyrite pyrrhotite assemblage yielded a temperature range from 375 to 390 c which is the ideal condition for gold precipitation native silver gersdorffite and arsenian ullmannite are being reported for the first time from this deposit indicating the complexity and wide variety of mineral phases associated with gold implying magmatic hydrothermal input of the source fluid

mesoarchaean crustal history of the eastern indian craton smnd and upb isotopic evidence abstract a variety of xenoliths representing high al trondhjemites and supracrustal lithologies occur within mesoarchaean granitoid rocks of the eastern indian craton a trondhjemitic xenolith from the bonai pluton yields a u pb age of 3380 6 4 ma for magmatic zircon and a minimum age of 3448 ma for xenocrystic zircon grains this sample also shows an nd value of 4 2 and t dm of 3 9 ga whereas four other xenoliths yield nd values ranging from 0 3 to 1 8 and t dm of 3 54 to 3 37 which are consistent with published data from the region and suggest a derivation from protoliths with relatively short lived crustal residence times

shear wave splitting in eastern indian shield detection of a pan african suture separating archean and meso proterozoic terrains abstract based on fast axes orientation and delay time t measurements at fifteen broadband stations the archean eastern indian craton eic is classified into three main tectonic zones viz singhbhum odisha craton soc 82 8 and t 1 5 0 2 s chotanagpur granitic gneissic terrain cggt 63 9 and t 1 4 0 3 s and eastern ghats mobile belt egmb 70 10 and t 1 3 0 2 s the results in the archean province of eic depict a moderate to large delay times 1 0 1 9 s with azimuths that reveals an upper mantle anisotropy with a mean orientation of 74 5 5 6 sub parallel to the e w trending structural grain of the archean craton evidencing frozen lithospheric anisotropy the direction of anisotropy n39 e in northern meso proterozoic cggt is found to be consistent with the direction of current absolute plate motion of indian plate regional variation of observed orientation of fast axes near the flanking paleo and late archean orogenic belts is attributed to the tectonic control rather than current plate motion nevertheless estimated large mean delay times 1 41 0 27 s do also suggest a contribution from the anisotropy associated with asthenospheric mantle flow most interestingly our study detects a transition zone coinciding with the location of damodar graben separating south late archean and north meso proterozoic cggt across which the fast axes orientation changes from e w 71 to ne 39 which could be evidencing the signatures of the eastward extension of pan african 550 500 ma suture as also observed in antarctica

uraniferous paleoplacers of the mesoarchean mahagiri quartzite singhbhum craton india depositional controls nature and source of 3 0 ga detrital uraninites abstract the quartz pebble conglomerate qpc hosted detrital uranium mineralization is unique in character in terms of their restricted distribution before 2 2 ga atmosphere during pre great oxidation event pre goe such qpc paleoplacer deposits over the world are good targets for moderate to high tonnage and low grade uranium deposits and more importantly for their gold content the mahagiri quartzite dated c 3 02 ga for their youngest detrital zircon population is developed unconformably over the mesoarchean singhbhum granite 3 44 ga to 3 1 ga the mahagiri quartzite includes a conglomerate pebbly sandstone dominated subaerial alluvial fan to coastal braided plain sequence in the lower parts and shallow marine mature quartz arenite in the upper parts the alluvial fan braided plain deposits in the lower parts host a number of pyritiferous and uraniferous conglomerate and pebbly sandstone beds the uraninite grains are rounded to subrounded in outline suggesting mechanical transport and detrital origin together with detrital pyrite and uraninite constitute the example of 3 0 ga paleoplacer closely comparable to the witwatersrand au u deposits epma and sem eds studies suggest that the uraninite grains are rich in th 4 wt s and ree y chemical formula calculations from epma analyses suggest uraninite grains belong to two populations with different oxidation states as revealed from y ree and cation u4 u6 apfu ratios the u contents of the detrital uraninite grains from mahagiri are significantly lower than that of the ideal stoichiometric composition of uo2 this is mainly due to higher amount of heterovalent cationic substitution by th ree y pb and ca in mahagiri qpc uraninite structures and partial alteration and metamictization of uraninites alteration due to metamictization resulted in elevated concentration of si al p and ca in more altered and metamict uraninite grains the ree pattern is typically flat with comparable lree hree concentration the high th content flat ree pattern suggests that the uraninitere presents high temperature phases 350 c and are magmatic in origin the mahagiri detrital uraninite grains suggest existence of highly felsic and k rich richer than ttg granodiorite granite monzogranite suites ggm of rocks older than 3 1 ga in the singhbhum craton

a review of hadean to neoarchean crust generation in the singhbhum craton india and possible connection with pilbara craton australia the geochronological perspective abstract the precambrian singhbhum craton sc of the eastern india holds a prolonged record of sporadic crust generation and evolution starting from as ancient as the hadean till late archean like every craton episodic nature of crust generation in the sc has been indicated by several workers based on numerous stratigraphic and geochronological evidence long before however it is only in the past decade that a growing zircon u pb hf database has resolved its evolution in detail such as the timing of juvenile crust versus reworking events integration of over a thousand geochronological data n 1558 from hadean 4 ga till the end of archean 2 5 ga exhibits multiple prominent crustal growth peaks during c 3320 ma 3300 ma and 2780 ma combined with moderate peaks at c 3460 ma 3380 ma and 2820 ma integral crust modelling of hf isotopezircon indicates major juvenile crust addition during the periods c 3760 3640 ma 3620 3440 ma while prominent age frequency peak at c 2780 ma defined by u thbaddeyelite ages of regional mafic ultramafic dyke swarm provides a direct proxy of large scale juvenile crust generation the interplay between the growth of new crust and reworking of older crust combined with multiphase deformation and metamorphic events till the end of archean constructed the critical juxtaposition of diverse crustal components of this important craton constraining crust generation and deformation events from an updated geochronological database of this craton reveal remarkable similarity in crustal growth pattern with the archean pilbara craton australia moreover paleomagnetic studies of the neoarchean mafic dyke swarms of both the cratons indicate similar paleo positions therefore compiled field geochronological paleomagnetic parameters invoke the possibility that the archean singhbhum and pilbara cratons might have been connected and shared similar crustal history at least till the neoarchean era

a vertic paleosol at the archean proterozoic contact from the singhbhum orissa craton eastern india abstract we report on an inferred paleoproterozoic soil horizon from the singhbhum orissa craton near keonjhargarh orissa eastern india which preserves vertic vertisol like features the 2 10 m thick white shale consists of quartz muscovite pyrophyllite interpreted as a paleosol overlies 3 32 ga granite and is covered by pre 2 0 ga sandstones kolhan group deposited in marginal marine environments the paleosol passes downwards through a partly altered granite saprolith zone to fresh granite abundant pedogenic slickensides ped structures gilgai topography reddish stain on ped surfaces and sepic plasmic microfabric in the paleosol were probably related to shrink and swell processes driven by marked seasonal precipitation in a well drained landscape an observed decrease of alkali elements and an increase of silica alumina and cia values from granite to paleosol together with relatively constant ti al ratios suggest in situ weathering of granite protolith however a paleo vertisol necessitates a mafic parent rock either directly igneous or reworked through alluvium the c 2 25 ga malangtoli jagannathpur basaltic rocks are relatively widespread and close to the inferred paleosol occurrences and provide a logical solution geochemistry of the highly depleted paleosol in contrast particularly when applying the isochon method strongly supports a granitic parent the apparent conundrum can possibly be solved through repeated alluvial reworking of both granitic and mafic detritus and accumulation of weathered material with varying proportions of these two components yet enough smectitic clays 30 to form a paleo vertisol this pre 2 0 ga weathering event in the singhbhum craton is consistent with a global scenario of paleoproterozoic weathering which followed an extended global glaciation and thus has the potential to contribute to understanding of pre 2 0 ga amalgamation of regional and global cratonic blocks

chemical environments of deposition of ancient iron and manganese rich sediments and cherts despite detailed classification criteria to distinguish between marine and freshwater environments of deposition in fine grained non clastic sedimentary rocks are scanty data on recent lacustrine and marine chemical precipitates reveal that these two environments can be distinguished in terms of their composition in the cao mgo na2o k2o system provided carbonates and detrital components associated with them are trivial lacustrine ferromanganese precipitates display low na2o and k2o but a high cao cao mgo ratio 0 70 similar to the world average river water in contrast diagenetically mature marine ferromanganese precipitates and nodules show a lower 0 60 cao cao mgo ratio in general and variable na2o and k2o recent pelagic cherts reveal an average cao cao mgo ratio comparable to that of ocean water whereas those affiliated to ocean floor hydrothermal activity span a wide range of composition in cao mgo na2o k2o space and mostly avoid the lacustrine field extension of the observed relations to the ancient archean bifs and cherts from 1 isua supracrustals greenland 2 yilgarn block australia 3 montana usa and proterozoic bifs from 4 hamersley basin australia 5 labrador trough canada 6 biwabik iron formations usa and the late proterozoic 7 upper tindhir group iron formation alaska and many others reveal a marine signature corroborating the inferences based on ree and isotope studies however chemical data on a number of deposits including the late proterozoic bifs mn deposits and cherts from the damara orogen africa bifs from rapitan formation northwest territories canada and several proterozoic mn deposits and cherts from india suggest a freshwater chemical environment of deposition the concurrence in the results obtained from studies on iron and or manganese deposits and coexisting cherts from several archean proterozoic and phanerozoic basins suggests that the chemistry of the more abundant siliceous sedimentary rocks can provide an additional tool for palaeogeographic reconstruction

magmatic and metamorphic history of paleoarchean tonalite trondhjemite granodiorite ttg suite from the singhbhum craton eastern india texturally controlled dating of zircon from paleoarchean tonalite trondhjemite granodiorites of the older metamorphic tonalitic gneisses and the singhbhum granite batholith phases i ii and iii from the singhbhum craton in eastern india reveals a polycyclic evolution of the archean crust the granitoid suites were emplaced in two pulses at 3 45 3 44 ga and 3 35 3 32 ga tonalites and trondhjemites of the older metamorphic tonalitic gneisses were emplaced at ca 3 45 3 44 ga together with phase iii of the singhbhum granite pluton while granites belonging to the older metamorphic tonalitic gneisses were emplaced at ca 3 35 3 32 together with phase i and phase ii of the singhbhum granite pluton both crustal units underwent an early phase of relatively high grade metamorphism at 3 30 3 28 ga followed by extensive fluid induced alteration during low grade metamorphism at 3 19 3 12 ga and 3 02 2 96 ga the two units have also been marginally affected at ca 2 52 ga and 1 06 ga by major metamorphic events in the north singhbhum mobile belt and the singhbhum shear zone at the northern margin of the craton the zircon grains in granites have inherited cores with ages of ca 3 61 ga and 3 46 3 41 ga and with well developed oscillatory growth zonation which suggests the granitic magmas were derived by partial melting of an igneous precursor or sedimentary rocks derived from an igneous source the emplacement of the expansive granitoids belonging to the older metamorphic tonalitic gneisses and the singhbhum granite was synchronous with the amphibolite facies metamorphism ca 3 32 ga of older meta igneous and metasedimentary rocks belonging to the older metamorphic group major felsic crust formation in the craton occurred in a narrow time interval between 3 46 and 3 32 ma with minor contributions of material as old as 3 6 ga the complex polycyclic evolution of the paleoarchean crust in the singhbhum craton can account for the wide range of often disparate ages obtained using whole rock isochron dating techniques with some of the isochron dates being geologically meaningful while others representing mixing lines or disturbance of the isotopic systems during metamorphism

palaeoproterozoic sedimentation on the singhbhum craton global context and comparison with kaapvaal the singhbhum craton has a limited palaeoproterozoic supracrustal record which suggests a three part history comprising a long period of high freeboard and palaeosol formation on granitoids subsequent rift related mafic ultramafic volcanism and subordinate sedimentation c 2 25 2 1 ga dhanjori and jagannathpur basin fills possibly also simlipal malangtoli and ongarbira basin fills which overlapped locally with mafic soil formation and a major regression at around2 0 ga followinga longhiatus theapproximately 1 6 gadhalbhum dalmasuccession was laid down probably under continental conditions this rather truncated record stands in con trast to the chronologically and geographically much more widespread supracrustal basin fills of the kaapvaal craton and there appears to be an overall poor comparison between these two early precambrian crustal blocks however on kaapvaal three analogous events are identified widespread approximately 2 2 ga mafic volcanism followed by a well developed palaeosol and a major transgression prior to 2 05 ga the three shared events between the two cratons are com patible with the postulate of a global approximate 2 45 2 2 ga shutdown of magmatic and tec tonic geodynamics with the origin of the triumvirate directly reflecting its resumption again after about 2 2 ga we recognize here that a large diversity of views on singhbhum s geodynamic history exists predicated on a lack of precise geochronology and commonly poor outcrops and the current hypotheses are presented with these factors in mind

mineral chemistry and geothermometry of chlorites in relation to physico chemical conditions of uranium mineralization in the central part of the singhbhum shear zone eastern india abstract the singhbhum shear zone ssz in eastern india is one of the major uranium repositories of the country some of the important uranium deposits viz bagjata jaduguda bhatin narwapahar and banadungri singridungri are juxtaposed in the central part of ssz the uranium mineralization in central ssz is mainly hosted by tourmaline apatite magnetite bearing sericite quartz chlorite schist with uraninite being the main radioactive mineral phase a close spatial relationship exists between uraniferous minerals and chlorite occurrences in central ssz three different types of chlorite assemblages were recognized and their relationship with uranium mineralization was studied in detail to unravel the physico chemical conditions for precipitation of uranium vis a vis chlorite geothermometry and constrains on the chlorite chemistry detailed petrographic studies and mineral chemical studies of the host rocks indicate three distinct chlorite type viz 1 metamorphic chlorite forming a typical metamorphic assemblage with quartz muscovite sericite biotite and k feldspar 2 hydrothermal alteration product of biotite and 3 hydrothermal vein chlorite the three chlorite types were characterized based on 1 the range of xfe and aliv 2 correlation between si apfu and xfe and 3 compositional diagram between xfe vs aliv based on the mineral chemistry and thermometry of chlorite 3 the co genetic uranium mineralization has been suggested to be precipitated from a hydrothermal fluid rich in fe mg and ti in a reducing environment within a temperature window of about 312 c 355 c a fluid mixing model for the remobilization and reconstitution of this hydrothermal uranium mineralization vis a vis chlorite occurrence is postulated and its geothermometry suggest an epithermal mineralization in the study area a comparative study of chlorites from four important uranium provinces of the world i e jabiluka of australia rozna of czech republic beaverlodge of canada and central ssz of india reveals a similarity in the mineral chemistry of the chlorites associated with uranium mineralization thus textural study of chlorites corroborated with their mineral chemistry and geothermometry is a useful reconnoitre tool for uranium exploration

40ar 39ar incremental heating study of mineral separates from the early archean east indian craton implications for the thermal history of a section of the singbhum granite batholithic complex 40ar 39ar incremental heating studies on mineral separates from three sets of rocks in the singbhum craton in eastern india have helped unravel the thermochronometric history of the terrane and explain an earlier discrepancy between sm nd 3800 ma and rb sr 3100 ma whole rock ages for the older metamorphic tonalitic gneiss omtg high precision plateau ages for hornblende separates from the older metamorphic group of rocks omg suggest that this unit is older than 3300 ma and that enclaves of both the omtg and omg within the batholithic complex cooled to 500 c at 3300 15 ma following engulfment in magma forming the singbhum granite sg results from a biotite separate from the omtg imply that slow cooling continued to a temperature of 300 c at 3160 ma study of a feldspar separate from the singbhum granite suggests final cooling uplift through the 150 c isotherm 660 ma ago we suggest that an earlier rb sr whole rock age of 3130 85 ma on the omtg did not yield the crystallisation a

generation and evolution of palaeoarchaean continental crust in the central part of the singhbhum craton eastern india abstract palaeoarchaean granitoids are exposed over wide area in the singhbhum craton whose origin and role in crustal evolution are not well constrained this study presents whole rock and mineral chemical data coupled with zircon u pb dating and hf isotope results on such granitoids from the central part of the craton to understand their petrogenesis tectonic setting and role in continental crustal evolution the first phase of granitoid magmatism in this area is represented by a 3 47 ga na rich gneissic tonalite belonging to the archaean ttg tonalite trondhjemite granodiorite suite this rock is characterized by high hree heavy rare earth elements negative eu anomaly low sr y ratio and positive zircon hf isotope signature ehft 2 1 to 4 8 it is interpreted to be formed by shallow melting of a juvenile mafic source at 3 35 ga a silicic ferroan porphyritic biotite granite formed it shows variable k na low y and high sr y moderately fractionated hree and positive zircon ehft 1 8 to 4 0 and is explained as a product of high temperature melting of a heterogeneous juvenile source consisting of tonalites and mafic rocks at lower crustal depth the final phase of granitoid magmatism is marked by a 3 30 ga non porphyritic ferroan silica rich biotite granite geochemical characteristics like moderately high k moderately fractionated hree low ca and sr y and zircon ehft 0 8 to 3 7 suggest that the granite was formed by high pressure melting of a tonalite dominated source with short crustal residence all the three granitoid phases display low mg ni and cr contents and magnesium number mg precluding direct involvement of mantle in their origin rather crustal reworking caused by episodic plume related mafic ultramafic magma underplating and intraplating in an oceanic plateau setting is suggested as the possible mechanism for formation of the granitoids successive crustal reworking events involved progressively greater amount of previously formed felsic crust generating more evolved k rich granitoids it appears to be a globally important process which led to effective crustal differentiation and maturing of the cratons during palaeoarchaean

the archaean nucleus of singhbhum the present state of knowledge abstract the supracrustal rocks of the older metamorphic group omg consisting of metasediments and ortho amphibolite constitute the oldest unit in the archaean nucleus of singhbhum however there are indications that still older 3 4 3 8 ga crust of both sialic and mafic composition existed in this region the omg ortho amphibolites were formed by partial melting of mantle with near chondritic composition ca 3 3 ga ago probably as a result of plume activity shortly afterwards partial melting of the underplated mafic material produced a tonalitic melt older metamorphic tonalitic gneiss omtg which intruded the omg supracrustals and the entire suite was deformed and metamorphosed to upper amphibolite facies subsequent to this melting of the omg ortho amphibolites and the lower crustal material of probable andesitic composition produced melts varying in composition from tonalite to granite and these intruded in different phases to produce plutons of singhbhum granite bonai granite and kaptipada granite which together form volumetrically the major part of the archaean nucleus the older omg and omtg occur as enclaves within these younger granitoids the time difference between the emplacements of the omtg and the early phases of younger granitic intrusion was of the order of 100 200 ma thus serial additions of juvenile material led to the formation of a stable microcontinent by 3 2 ga thermally triggered stretching in this microcontinent produced basins peripheral to the present day singhbhum granite pluton and in these basins the younger supracrustal rocks of the iron ore group iog consisting of bif associated argillaceous and subordinate arenaceous rocks and mafic lavas were laid down there is inadequate field or geochronological evidence to resolve the issue of whether the different iron ore basins were coeval or not meagre geochronological data suggest that some of the bifs are older than ca 3 1 ga post iog activity is confined to the intrusion of mafic dyke swarms and formation of intracratonic basins the ages of both being uncertain

age of the baula pge mineralization orissa india and its implications concerning the singhbhum archaean nucleus abstract two types of platinum group element pge mineralization are identified in the mafic facies of the baula complex intruding the gabbro anorthosite unit of the singhbhum archaean nucleus the first pt dominated is magmatic the pgm are included in the magmatic silicates of a gabbro norite intrusion the bangur gabbro cutting the complex s ultramafic facies and are found preferentially where the gabbro incorporates clasts of dunite and chromitite near the gabbro ultramafics contact the second pd dominated is hydrothermal the pgm are associated with hydrous silicates located in the gabbro matrix of a magmatic breccia in which the blocks are from the baula ultramafic facies the originating fluids for the second type of mineralization were exsolved from the magma and concentrated pge and volatile elements we see no evidence of remobilization or external fluid contamination a structural study has demonstrated that a the breccia was provoked by the intrusion of the upper part of the bangur gabbro and b the breccia matrix corresponds to the bangur gabbro consequently both types of pge mineralization are associated with the same magmatic event a zircon age of 3122 5 ma has been obtained for the main bangur gabbro intrusion and similar ages 3123 7 and 3119 6 ma have been obtained on the pge mineralized gabbro matrix of the breccia this supports the hypothesis of a genetic link between the bangur gabbro with its pt dominated pge and the breccia with its pd dominated pge giving a mean weighted age of 3121 3 ma for the mineralization sm nd data on eight gabbro samples of the baula complex yielded a similar age of 3205 280 ma the dating of these events places them close to the broad scale stabilization of the singhbhum archaean nucleus estimated at 3 1 ga and defines one of the oldest pge mineralizing events ever recorded the bangur gabbro shows many affinities with the gabbro anorthosite unit of the singhbhum archaean nucleus in terms of age of emplacement and isotopic composition it may be therefore that the bangur gabbro actually forms part of the gabbro anorthosite unit and that a fundamental control of its two types of pge mineralization is the presence of ultramafic clasts

the structural and geochemical evolution of the singhbhum granite batholithic complex india abstract the singhbhum granite batholithic complex of eastern india is composed mainly of a the older metamorphic group tonalite trondhjemite gneiss omtg 3800 ma old whch intruded synkinematically into the enveloping older metamorphic group omg 3800 ma old and b the singhbhum granite sbg consisting of three distinct but closely related phases of at least twelve separate magmatic units of granodiorite granite 2950 ma old and a number of patches of granitised omg orthoamphibolites geochemical studies including ree and lil elements suggest that a the omg orthoamphibolites were derived either by re melting of a k poor basalt lkt or of mantle peridotite with high concentration of lil elements b the omg tonalite was derived by partial melting of amphibolite and c the singhbhum granite magmas appear to have formed in two distinct modes i partial melting of amphibolite for the magmas of phases i and ii and ii partial melting of a siliceous garnet bearing granulite for magmas of the phase iii units

sedimentation history of the paleoproterozoic singhbhum group of rocks eastern india and its implications abstract this paper reviews the sedimentological geochemical and stratigraphic characteristics of the paleoproterozoic chaibasa and dhalbhum formations the singhbhum group of eastern india and presents a comparative study with other paleoproterozoic lithostratigraphic units of india both the formations are entirely siliciclastic and deformed and metamorphosed generally at greenschist to upper amphibolite facies the older chaibasa formation consists of sandstone shale and sandstone shale interbanded heterolithic facies it conformably overlies the late archean paleoproterozoic dhanjori formation of terrestrial alluvial fan fluvial origin the lower chaibasa member formed in a marine setting the shale and heterolithic facies formed in a continental shelf setting below and above the storm wave base respectively the sandstone facies formed in a subtidal setting during sea level fall in contrast the upper chaibasa member formed in a shallow marine setting both the shale and heterolithic facies formed above the storm wave base in significant contrast the overlying dhalbhum formation is dominated by finer clastics with much lower proportion of sandstones the base of the terrestrial dhalbhum formation is a sequence boundary unconformity sedimentary facies analysis clearly shows two broad facies association of terrestrial origin fluvial and aeolian the aeolian facies association overlies the fluvial facies association the dhalbhum sandstones show typical ree pattern of quartz dilution with lower concentrations compared to the mudstones the dhalbhum finer clastics mimic typical ree patterns resembling abundances in the continental crust rare earth element plots display a good match with post archean australian shales paas including similar concentrations steep negative slope for lrees negative eu anomaly and nearly flat hrees the singhbhum paleoproterozoic succession is devoid of both chemical sediments and paleoproterozoic glacial deposits in contrast to neighboring cratons

teleseismic receiver functions modeling of the eastern indian craton abstract we estimate receiver functions rfs through the time domain deconvolution using three component broadband data of 100 teleseismic events 30 90 from 15 seismographs in the eastern indian craton estimated radial rfs show a positive phase at 4 6 5 8 s delay time corresponding to the crustal thicknesses of 37 46 km through the differential evolution de waveform inversion modeling of radial receiver functions we delineate the crustal structure at 15 broadband stations on an average the archean singhbhum odisha craton soc is characterized by a thick crust of 43 3 km in comparison to a relatively thin crust of 41 1 km underlying the proterozoic chotanagpur granite gneissic terrain cggt while a thin crust of 38 1 km characterizes the younger eastern ghats mobile belt egmb the main results of our modeling reveal a 46 km thick archean crust underlying the singhbhum granite sg of 3 6 ga which is characterized by a 3 km crustal thickening probably resulted from the archean subduction process our modeling also detects a 2 3 km crustal thinning with the thinnest crust of 37 km below the region near south singhbhum shear zone which could be attributed to the 1 6 ga plume activity associated with dalma volcanic our modeling also led to the delineation of a crustal thinning of 2 3 km underlying the region in egmb which was influenced by a much younger 117 ma rajmahal magmatism associated with the gondwana break up episode however our study could not detect any age dependent variation of crustal thicknesses in the eastern indian craton the main result of our modeling suggests a two phase crustal evolution process for the soc viz older e w crustal thickening due to e w plate compression and later crustal thinning episodes associated with the dalma volcanism in the north and the rajmahal volcanism in the south

geochemical and sm nd isotopic characteristics of the late archaean palaeoproterozoic dhanjori and chaibasa metasedimentary rocks singhbhum craton e india implications for provenance and contemporary basin tectonics abstract in significant contrast to other cratonic blocks of india the singhbhum cratonic successions record continuous depositional record from the palaeoarchaean to mesoproterozoic although the sedimentary facies characteristics and mode of stratigraphic sequence building of the dhanjori and chaibasa formations are well known sedimentary geochemistry provenance and tectonic milieu of deposition of these two formations are hitherto unknown the current manuscript presents geochemical and sm nd isotopic data from the dhanjori and chaibasa formations for the first time and combine previous sedimentological data with the goal to expand the framework for understanding the depositional and tectonic setting of these two formations the sm nd isotopic data for the chaibasa clastics is unambiguous with respect to provenance average nd t 2 2 ga 0 8 1 0 and average nd model age tdm 2 51 0 08 ga with average 147 sm 144 nd ratios 0 1114 0 0041 for phyllites and quartzites indicate an extremely homogeneous source signature consistent with a late archaean juvenile crustal provenance possibly a dominantly upper crustal provenance the sm nd isotopic data from the older dhanjori formation also indicate broadly similar provenance as comparable lithologies in the younger chaibasa formation our sm nd isotopic data is entirely consistent with the previous sedimentological data and confirms a terrestrial rift dominated tectonic setting for the dhanjori formation proximal sources poorly mixed provenance and a marginal marine to offshore setting for the more homogeneous nd isotopic signature of the chaibasa formation distal sources well mixed provenance

eastern indian 3800 million year old crust and early mantle differentiation samarium neodymium data for nine granitic and tonalite gneisses occurring as remnants within the singhbhum granite batholith in eastern india define an isochron of age 3775 89 x 10 6 years with an initial 143 nd 144 nd ratio of 0 50798 0 00007 this age contrasts with the rubidium strontium age of 3200 x 10 6 years for the same suite of rocks on the basis of the new samarium neodynium data field data and petrologic data a scheme of evolution is proposed for the archean crust in eastern india the isotopic data provide evidence that parts of the earth s mantle were already differentiated with respect to the chondritic samarium neodymium ratio 3800 x l0 6 years ago