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

archean paleoproterozoic transition the indian perspective abstract india has perhaps the richest paleoarchean to paleoproterozoic crustal components on earth miller et al 2018 notwithstanding this much of the indian subcontinent remains unexplored compared to other ancient cratons in north america australia brazil and africa there are five archean cratonic nuclei in india the aravalli bundelkhand singhbhum bastar and the dharwar with well preserved proterozoic supracrustal sequences this paper critically reviews the paleoarchean to paleoproterozoic supracrustal record of the indian subcontinent with special emphasis on the archean paleoproterozoic transition which is generally placed at 2 5 ga based on the emplacement age of the great dyke of zimbabwe in general the archean paleoproterozoic transition in indian cratonic blocks is associated with high continental freeboard condition unlike north america south africa and western australia the indian cratonic blocks except bastar are devoid of paleoproterozoic glacial diamictite mazumder et al 2015 however similar to the pongola supergroup of south africa there are evidences of neoarchean glaciation in dharwar ojakangas et al 2014 in contrast to the global scenario of extensive development of bif across the archean paleoproterozoic transition the indian paleoproterozoic successions are devoid of banded iron formation bif except the 1 85 ga old bif in bundelkhand in contrast the majority of the indian bifs are of paleoarchean or neoarchean age thus the geodynamic and supracrustal data collected from five indian archean cratonic blocks do not correspond uniquely and precisely to a global change in tectonic style onset of neoarchean global magmatism and rifting or lithostratigraphic and environmental changes suggested across the archean paleoproterozoic transition van kranendonk et al 2012 therefore a revision and redefinition of the archean proterozoic boundary is outstanding this article is part of a special issue entitled archean earth processes edited by rajat mazumder and patrick eriksson

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

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

progressive development of structures in a ductile shear zone in the singhbhum shear zone of eastern india successive generations of folds grew in response to a progressive ductile shearing during this deformation a mylonitic foliation was initiated and was repeatedly transposed the majority of fold hinges were formed in an arcuate manner at low angles to the y axis in an e w trending subhorizontal position and major segments of the fold hinges were then rotated towards the down dip northerly plunging x axis the striping and intersection lineations were rotated in the same manner the down dip mylonitic lineation is a composite structure represented by rotated early lineations and newly superimposed stretching lineations the consistent asymmetry of the folds the angular relations between c and s surfaces and the evidence of two dimensional boudinage indicate that the deformation was non coaxial but with a flattening type of strain with 1 2 the degree of non coaxiality varied both in space and time from the progressive development of mesoscopic structures it is concluded that the 2 3 km wide belt of ductile shear gave rise to successive anastomosing shear zones of mesoscopic scale when a new set of shear lenses was superimposed on already sheared rocks the preexisting foliation generally lay at a low angle to the lenses no new folds developed where the acute angle was sympathetic to the sense of shear displacements where the acute angle was counter to the sense of shear the pre existing foliation lying in the instantaneous shortening field was deformed into a set of asymmetric folds

a quantitative study of ionospheric density gradients at midlatitudes the subauroral ionosphere at the magnetic latitudes which characterize the northeastern united states is subject to severe f region ionospheric density structuring due to the space weather effects of magnetospheric disturbance electric fields communications and navigation systems relying on transionospheric propagation must be able to compensate for the effects of the sharp changes 10x in total electron content tec associated with the ionospheric trough and storm time disturbance effects at midlatitudes the millstone hill incoherent scatter radar database has been used to investigate the spatial extent and temporal evolution of tec and density altitude latitude structure at middle and subauroral latitudes as a function of solar cycle local time and level of geomagnetic activity more than 11 000 radar elevation scans covering 20 of latitude and altitudes between 150 and 750 km have been used to identify the characteristics of the density gradient near the equatorward edge of the ionospheric trough in a variety of circumstances spanning 20 years and two solar cycles pronounced density gradients can be identified in 35 of the millstone hill scans and we present a statistical characterization of average magnitude and location for these steepest tec gradients in some cases especially near noon the equatorward edge of the trough lies poleward of our observational field of view and gradients associated with phenomena other than the trough contribute to our statistics on most days the trough appears in the radar scans between 1600 and 2000 magnetic local time mlt larger tec gradients occur at solar maximum and when the background tec is higher the steepest gradients occur in an environment of high tec at solar maximum and adjacent to regions of storm enhanced density sed when the processes which generate the trough are strongest high kp high gradient values occur in the sunlit sector with maximum values of tec gradient 10 tec deg latitude with 1 tec unit 10 16 el m 2 found in the postnoon ionosphere mean solar maximum tec gradient at 1600 mlt is 3 4 tec deg for kp 100 over new england and tec gradients of 50 tec deg

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

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

long duration penetration of the interplanetary electric field to the low latitude ionosphere during the main phase of magnetic storms 1 it is well known that the interplanetary electric field can penetrate to the low latitude ionosphere it is generally believed that the penetration of electric fields can last only for 30 min because of the shielding effect in the ring current in this paper we present the observations of the dayside ionospheric electric field enhancements at middle and low latitudes in association with reorientations of the interplanetary magnetic field imf in six cases the eastward electric field in the dayside equatorial ionosphere measured by the jicamarca incoherent scatter radar was enhanced for 2 3 hours after the imf turned southward and remained continuously southward in one case the eastward electric field in the dayside midlatitude ionosphere measured by the millstone hill incoherent scatter radar was continuously enhanced for 10 hours during southward imf since millstone hill is close to the equatorward boundary of the auroral zone during magnetic storms the penetration electric field there may be different from that at the equatorial ionosphere the most striking feature of the measurements is that the enhancements of the ionospheric electric field can last for many hours without significant decay the electric field enhancements in the middle and low latitude ionosphere are closely related to magnetic activity and occur during the main phase of magnetic storms the observations show that the interplanetary electric field can continuously penetrate to the low latitude ionosphere without shielding for many hours as long as the strengthening of the magnetic activity is going on under storm conditions

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

soft sediment deformation structures in the earth s oldest seismites abstract the chaibasa formation in eastern india which was deposited between 2100 and 1600 million years ago shows deformations that must have formed when the sediments were not yet consolidated some of these deformation structures have never been described before here they are described depicted and their origin is analysed we show that they must be the result of shocks which can only be explained satisfactorily as triggered by earthquakes the layers containing these deformation structures are termed seismites they are among the earliest records of earthquakes known in the earth s history

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

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

dayside midlatitude ionospheric response to storm time electric fields a case study for 7 september 2002 1 with the storm of 7 8 september 2002 as a study case we demonstrate that an ionospheric model driven by a suitable storm time convection electric field can reproduce the f region dayside density enhancements associated with the ionospheric storm positive phase the ionospheric model in this case is the utah state university time dependent ionospheric model tdim the electric field model is the university of michigan s hot electron and ion drift integrator heidi extensive ground truth is available throughout the study period from two independent sources ground based vertical tec and ionosonde stations our simulation results are in good agreement with these observations we address the question of what is the source of the high density plasma that is seen during the positive storm phase and show that in this case a magnetospheric electric field with an eastward component that penetrates to midlatitudes increases local production on the dayside to a degree that is sufficient to account for the storm time density increases that have been observed

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

sedimentation pattern and tectonic evolution of the proterozoic singhbhum basin in the eastern indian shield abstract the proterozoic singhbhum basin psb located on the flank of an archaean platform ca 3400 ma is a distinct lithotectonic unit of the singhbhum crustal province of the eastern indian shield the present contribution traces the evolution of this basin filled by volcanics dominated submarine supracrustals and sedimentary formations the proterozoic singhbhum basin has been identified to be a marginal basin evolved in a back arc setting an axial volcanic belt manifesting mor like basaltic eruptions divided the basin into two domains with parallel but distinct sedimentation patterns an asymmetry in sedimentation pattern and source polarity are documented in litho as semblages and ree distribution patterns of cover rocks in the basinal domain flanking the southern platform prevailing tectonics strongly controlled the mechanism of sedimentation which coupled with the volcanic history of the basin indicates its riftogenic character progressive lithospheric stretching successively produced picritic volcanics and mor type basalts along the axial zone of the basin being related to a stretching factor of 2 continental margin rifting ultimately resulted in an oceanic transition as supported also by available geophysical data the evolution of the proterozoic singhbhum basin in its broad perspective was controlled by subduction related processes

ionosphere disturbances observed throughout southeast asia of the superstorm of 20 22 november 2003 1 ionospheric disturbances in the southeast asian region during the super magnetic storm of 20 22 november 2003 were investigated through an ionosonde chain and a gps network assisted by the space borne instruments at early stage of the storm in the postsunset sector large enhancements in the critical frequency of f2 layer and total electron content were observed at northern crest region of the equatorial ionization anomaly eia which might be produced by both the storm meridional wind superimposed with traveling atmospheric disturbances and prompt penetration electric field ppe during the main phase of the storm when interplanetary magnetic field started a 12 h southward turning equatorial ionosphere was elevated to a very high level which should be most probably caused by a long duration ppe event meanwhile at mid low latitudes ionosphere witnessed an initial simultaneous decrease then followed by drastic increases which is very different from the past observations in this region reddy and nishida 1992 combined analysis of the data from the ionosonde and other space based measurement shows that for the present case the penetration efficiency of the interplanetary electric field ief to the equatorial ionosphere was larger at night than in the daytime which agrees with the results of fejer et al 2007 showing the ratios of ppe and ief changes were highly variable with the local time during the recovery phase eia was severely inhibited owing to a wind convergence and possibly because of the westward disturbance dynamo electric field

the 2 7 2 0 ga volcano sedimentary record of africa india and australia evidence for global and local changes in sea level and continental freeboard abstract the 2 7 2 0 ga volcano sedimentary records of the african indian and australian cratons indicate two broadly defined periods of extensive drowning of the emergent continental areas concomitant with lowered freeboard carbonate banded iron formation bif platforms characterised the first such event at ca 2 6 2 4 ga africa and australia to 2 7 ga india these earlier globally enhanced sea levels are ascribed to increased mid ocean ridge activity possibly related to breakup of a postulated late archaean southern supercontinent alternatively a transition from global scale catastrophic mantle overturn events to the onset of plate tectonics may have occurred in the late archaean nelson 1998 earth planet sci lett 158 109 119 both explanations of increased mid ocean ridge activity are compatible with significant early to middle archaean crustal growth armstrong 1981 phil trans r soc london a 301 443 472 with the emergent high freeboard cratons being subjected to aggressive weathering and erosion enhanced continental crustal growth near the archaean proterozoic boundary mclennan and taylor 1982 j geol 90 347 361 related to the development of significant island arc complexes would have resulted in common lowered freeboard enhanced sea level conditions at the passive margins of the southern cratons the diachronous nature of these earlier transgressions in the various cratons may reflect the effect of local tectonic movements and or the thermal state of the cratons from ca 2 4 2 2 ga cratons that make up the present day continents of india africa and australia had relatively high continental freeboard and lowered sea levels glacigenic deposits are preserved on the kaapvaal africa singhbhum india and pilbara australia cratons the second broadly defined drowning event at ca 2 15 ga was probably due to post glacial climatic amelioration freeboard was reduced by the combination of eustatic rise and the reestablishment of aggressive weathering as warmer palaeoclimates returned in india carbonates were more prominent than the siliciclastic sediments including prominent black shales seen in africa and australia

response of the topside ionosphere to recurrent geomagnetic activity received 15 june 2010 revised 4 september 2010 accepted 24 september 2010 published 21 december 2010 1 in the present study we investigate the solar activity local time and latitudinal dependence of the topside ionosphere response to recurrent geomagnetic activity using 8 years 1998 2005 of data on total ion density ni retrieved from defense meteorological satellites program observations at about 840 km altitude it is the first attempt to explore the presence of oscillations in the topside ionosphere in response to recurrent geomagnetic activity results indicate that striking periodic oscillations around 9 days in ni are present during the latter part of the declining phase of solar cycle 23 the percentage of the magnitude of 9 day oscillations relative to background values in ni at 2130 lt tends to be 5 10 larger than at three other local times 0930 0510 and 1710 lt moreover latitudinal profiles of bandpass filtered 9 day perturbations in ni show multiple peaks as a function of local time and day of the year which is distinctly different from previous results at or around the f2 layer peak there are in phase correlations between kp and the ni responses in the winter hemisphere and at middle and low latitudes and approximately anti phase at high latitude in the summer hemisphere additionally the 9 day oscillations in ion temperature are is mainly restricted to high latitudes the combined effects of neutral winds e b drift auroral ionization precipitation and migration of subauroral trough region are possible candidates to explain the latitudinal profiles of the 9 day variations in ni

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

longitudinal variations in the equatorial vertical drift in the topside ionosphere 1 the vertical ion drift is important for understanding and modeling the electrodynamics at low latitudes measurements from the ion drift meter on the defense meteorological satellite program dmsp f15 are used to examine longitudinal variations in the vertical ion drift at the dip equator in the topside ionosphere local time was restricted to 0930 and the data were organized by month for 2001 and 2002 two features were found contributing to the longitudinal variations in the electrodynamics meridional winds contribute to the equatorial vertical ion drift at the 830 km magnetic apex due to their dynamo action at the foot points of the magnetic field lines in the f region at magnetic latitudes near 15 electric fields producing a downward perturbation drift at 0930 are produced by hemispheric differences in the dynamo current due primarily to the different orientation of the magnetic meridian relative to the terminator this produces the seasonally dependent variation as a function of longitude that is observed a wavenumber 4 longitudinal variation also appears to be present throughout the year but is more influential during equinox conditions this variation also shows a seasonal cycle shifting east during northern summer and west during northern winter further analysis would be required to isolate the characteristics of a wavenumber 4 driver from the wavenumber 4 component of the fourier series used here to fit the data

dynamically recrystallised quartz c axis fabrics in greenschist facies quartzites singhbhum shear zone and its footwall eastern india influence of high fluid activity abstract oriented specimens of quartz tectonites from the singhbhum shear zone ssz an important tectonic element in the precambrian eastern indian shield and its footwall have been analysed for c axis fabrics of dynamically recrystallised quartz grains in individual specimens the fabric pattern is either an asymmetric type i cross girdle or an asymmetric kinked single girdle irrespective of whether the fabric is from the ssz or its footwall the asymmetry of the fabric confirms a southward thrust movement of the northern block on a northerly dipping shear zone the measured fabrics are characterised by a concentration near the y axis of the finite strain ellipsoid with an equally or subordinately developed concentration near the z axis although some earlier works suggest the y concentration of the quartz c axis fabric as due to the influence of higher temperature obtained in amphibolite facies the occurrence of a similar concentration in the quartz c axis fabric from quartz tectonites of the ssz and its footwall interpreted to have formed under greenschist facies condition is explained by formation of the fabric under high fluid activity during deformation

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

variations in the low and middle latitude topside ion concentration observed by dmsp during superstorm events 1 observations of the topside ion number density by the dmsp satellites on the dayside near 0930 lt and near dusk describe a characteristic evolution during the course of three superstorm events in november 2001 november 2003 and november 2004 density enhancements at middle latitudes and at the equator may be identified as separate features that may appear together but can evolve independently these characteristics are consistent with the action of both upward outward e b drifts and equatorward neutral winds and it is suggested that both f region drivers are required to reproduce the observed behavior on these occasions upward excursions of the e b drift at the equator may be short lived compared to the satellite orbit period of about 100 min but may also exist for longer periods under the influence of penetration fields and modified dynamo fields upward drifts at middle latitudes may be induced by meridional winds and by the high latitude convection pattern as it expands to latitudes as low as 40 degrees magnetic

precambrian continental freeboard and geological evolution a time perspective abstract continental crustal growth rates crustal volumes thicknesses and continental freeboard are considered to be intimately related however none are easy to quantify least of all in the precambrian additionally crustal volumes thicknesses and isostasy are related to changing mantle heat and the concomitant variation in thickness of ocean crust another set of variables would be the interaction of plate tectonics and the onset of plate tectonics a contentious issue in itself and mantle plumes superplumes further complication is provided by the ranges of freeboard elevations and eustatic sea level changes overlapping in scale and sharing common genetic causes the constant freeboard model suggests that the net results of the interaction of this complex set of variables has been that continental elevation relative to sea level has remained essentially similar on a global average basis over much of geological time assuming an essentially constant ocean volume since c 3 8 ga application of this model to the precambrian geological record suggests that sigmoidal crustal growth rate models are probably the most reliable a conundrum of the constant freeboard model would be that freeboard would tend to become lowered towards mean sea level for any specific craton over time this freeboard equilibrium would be interrupted for a particular craton by active geodynamic processes resulting from the interplay of plate tectonics and mantle thermal instabilities in this paper we test the validity of this thesis of alternating approximate freeboard equilibrium and active geodynamics by examining the volcano sedimentary record of a number of cratons kaapvaal singhbhum and pilbara for the singhbhum craton and bearing in mind its poor chronological data base freeboard equilibrium appears to have prevailed until c 2 1 ga but for kaapvaal and pilbara until c 1 8 ga the geodynamic processes largely outweighed the tendency towards equilibrium except for c 200 my from c 2 6 to 2 4 ga when global sea level appears to have remained high and transgression was the norm we thus tentatively add the plate tectonic cycle and mantle thermal processes to the already complex association of concepts controlling continental freeboard over time

equatorial plasma fountain and its effects over three locations evidence for an additional layer the f 3 layer the equatorial plasma fountain and equatorial anomaly in the ionospheres over jicamarca 77 w trivandrum 77 e and fortaleza 38 w are presented using the sheffield university plasmasphere ionosphere model under magnetically quiet equinoctial conditions at high solar activity the daytime plasma fountain and its effects in the regions outside the fountain lead to the formation of an additional layer the f3 layer at latitudes within about plus or minus 10 of the magnetic equator in each ionosphere the maximum plasma concentration of the f3 layer which occurs at about 550 km altitude becomes greater than that of the f2 layer for a short period of time before noon when the vertical e b drift is large within the f3 layer the plasma temperature decreases by as much as 100 k the ionograms recorded at fortaleza on january 15 1995 provide observational evidence for the development and decay of an f3 layer before noon the neutral wind which causes large north south asymmetries in the plasma fountain in each ionosphere during both daytime and nighttime becomes least effective during the prereversal strengthening of the upward drift during this time the plasma fountain is symmetrical with respect to the magnetic equator and rises to over 1200 km altitude at the equator with accompanying plasma density depletions in the bottomside of the underlying f region the north south asymmetries of the equatorial plasma fountain and equatorial anomaly are more strongly dependent upon the displacement of the geomagnetic and geographic equators jicamarca and trivandrum than on the magnetic declination angle fortaleza

neoarchean paleoproterozoic stratigraphy of the dhanjori basin singhbhum craton eastern india and recording of a few u pb zircon dates from its basal part abstract the stratigraphy of the dhanjori basin placed at the northeastern margin of the paleo mesoarchean singhbhum craton has been revised a mainly quartz pebble conglomerate qpc and volcani clastics bearing unit at the base of the dhanjori basin and intruded by the mayurbhanj granite has been named phuljhari formation the dhanjori volcani sedimentary sequence with quartzite polymictic conglomerate at its base disconformably overlies the phuljhari formation and non conformaby over the mayurbhanj granite the dhanjori group is inferred to broadly range in age from 2 6 2 1 ga detrital zircons from qpc belonging to the phuljhari formation have yielded oldest chemical ages of 3 09 3 04 ga thus fixing the upper age limit of the formation the 3 09 ga old zircons recovered earlier from the mayurbhanj granite which is intrusive into the relatively younger phuljhari fm therefore appears to be xenocrystic in nature a fine grained variety of the mayubhanj granite close to its intrusive contact with the phuljhari fm was sampled during the present study it has recorded strong impress of acid magmatic event around 1 0 0 8 ga by its lower intercept and an upper intercept age of 2 8 ga the latter might record the inherited age of protolith to the mayurbhanj granite and correspond to widespread granite magmatic activity affecting the margin of the singhbhum craton signature of 1 0 0 08 ga old thermal perturbation also affected lower parts of the dhanjori basin and the singhbhum shear zone detrital au u bearing qpc in the phuljhari formation represent neoarchean sedimentation at the margin of the peneplained craton the dhanjhori group comprising mafic ultramafic volcanics and siliciclastics was hosted in rift induced intracratonic basin around neoarchean palaeoproterozoic threshold

depositional mechanisms as revealed from grain size measures of the palaeoproterozoic kolhan siliciclastics keonjhar district orissa india abstract the depositional mechanisms of the palaeoproterozoic kolhan siliciclastics have been examined using grain size analytical approaches grain size distributions of different lithofacies reveal a somewhat diversified paralic depositional environment including nearshore beach macrotidal estuary and inland dunes these inferences arise from different ways of analysing grain size data such as cumulative curves bivariant plots linear and multigroup discriminant functions and sediment trend matrix analyses sediment trend matrix analysis of various lithofacies taken together appears to be most effective for synthesizing the relationship between facies and sub environments taking into account the regional and local variations of lithofacies distribution and primary sedimentary structures grain size distributions and sediment transport paths as revealed from the above statistical parameters suggest overall hydraulic control of the grain size distribution of the kolhan siliciclastics in a fluvio beach shallow marine depositional setup

the source of the steep plasma density gradient in middle latitudes during the 11 12 april 2001 storm 1 a steep plasma density gradient has been observed in the middle latitude f region during large geomagnetic storms this phenomenon can be understood as a special form of the middle latitude ionization trough hereafter trough but its causal linkage has not yet been clarified we investigate the association of the steep density gradient and the trough by comparing their morphologies and occurrence locations using the satellite and ground observation data during the 11 12 april 2001 storm steep density gradients are detected in the dusk sector at the equatorward edges of the aurora by the defense meteorological satellite program dmsp f13 spacecraft the locations of the steep density gradients coincide with the locations of the ionospheric footprints of the plasmapause identified by the imager for magnetopause to aurora global exploration satellite these observations demonstrate that the steep density gradient is created at the typical location of the trough however the steep density gradient is not produced by the formation of an intense trough during the storm the temporal evolution of the total electron content maps shows that the steep density gradient observed at dusk by dmsp is associated with the plasma density enhancement in the dayside and its corotation into the dusk sector the severe plasma density enhancement in middle latitudes in combination with the trough and presumably the plasma depletion in high latitudes by the neutral composition change produces the steep density gradient in the subauroral region during the storm

implication of mafic magmatism in an intracontinental rift setting a case study from the paleoproterozoic dhanjori formation singhbhum crustal province india abstract we present major trace rare earth element and selected high field strength element ratios nb th zr nb nb y and zr y of the paleoproterozoic dhanjori volcanic and volcaniclastic rocks of the singhbhum crustal province eastern india the geochemical characteristics of the upper dhanjori volcanic rocks indicate that these are basaltic komatiites our geochemical data in combination with the sedimentological and stratigraphic characteristics of the interbanded metasedimentary rocks clearly indicate an intracontinental rift setting for dhanjori volcanism and sedimentation

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 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

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

implications of lunar orbital periodicity from the chaibasa tidal rhythmite india of late paleoproterozoic age harmonic analysis of the sandstone foreset laminae thickness series from the chaibasa tidal rhythmite india clearly shows that a normal semidiurnal tidal system with synodic month of 32 lunar days was in effect during the late paleoproterozoic 2100 1600 ma the minimum number of solar days in a lunar sidereal month was 31 published quantitative tidal rhythmite data of others in combination with data derived from the chaibasa tidal rhythmite indicate long term stability of the lunar orbit and progressive increase in the earth moon distance during the proterozoic

sedimentation history of the palaeoproterozoic dhanjori formation singhbhum eastern india abstract the palaeoproterozoic dhanjori formation eastern india is a terrestrial dominantly fluvial volcano sedimentary succession basal conglomerate coarse grained sandstone and shale rests directly on the granite basement and represents the distal fringe of an alluvial fan complex sieve sheet flood mass flow and alluvial channel and overbank deposits comprise the fan segment the rest of the formation is entirely constituted by fining upward fluvial cycles an event of basin tilting and volcanic eruption intervened and resulted a second phase of dhanjori sedimentation although the general fluvial depositional framework remained unaltered the two members of the dhanjori formation display different paleocurrent trends related to fluvial response to basin tilting in the lower member spatial variability in paleocurrent directions occurs as a consequence of fan development unlike the first phase the second phase of fluvial deposition incorporates profuse volcanics and accompanying volcaniclastic deposits these volcanic and volcaniclastic rocks might have locally blocked the river courses resulting in short lived lacustrine deposition composition of the volcanics varies upward from ultramafic to mafic the dhanjori volcanism took place in an intracontinental rift setting as is evident from the interbedded terrestrial deposits interbedded volcanic and volcaniclastic rocks in different stratigraphic levels suggest episodic volcanic eruption a semiarid paleoclimate is proposed and is consistent with development of an alluvial fan comprised of coarse clastic deposits

correlations between the eastern block of the north china craton and the south indian block of the indian shield an archaean to palaeoproterozoic link zhao et al 2003 have made an attempt to test and extend the hypothesis of kroner et al 1998 that the north china craton and the southern india might have constituted part of a major active plate margin at the archaean proterozoic boundary through correlation between archaean and proterozoic rocks of north china craton and the south indian block sib and i welcome their effort i am presently working on the palaeoproterozoic volcano sedimentary successions of the singhbhum crustal province of the sib as part of my ongoing research assignment and would like to make two comments

seismites in a proterozoic tidal succession singhbhum bihar india abstract early proterozoic metasediments of the chaibasa formation galudih ghatsila dhalbhumgarh region singhbhum bihar india comprise a number of cyclic fining upward prograding successions of tidalites the tidalites show indications for earthquakes in the form of synsedimentary deformation features apart from the structures due to high energy wave action deformed cross bedding convolute laminations synsedimentary faults graben like structures sandstone dykes pseudonodules and slump folds record the seismic activity a gradual decline in the frequency of seismites and tsunami related depositional features in combination with an upward increase in thickness of the tidal cycles are attributed to gradual diminishing of tectonic activity within the basin

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

geochemical and petrological evidence for subduction accretion processes in the archean eastern indian craton the composition of sandstones often provides key evidence about the tectonic weathering and transport processes operating on the surface at the time of deposition petrologic and geochemical analyses of little metamorphosed middle late archean sandstones from the eastern indian craton show that the sedimentary rocks were derived from dominantly 3 3 ga old amphibolites of the older metamorphic group omg and tonalites of the older metamorphic tonalite gneisses omtg the two oldest lithologic units of this craton chondrite normalized rare earth element ree patterns of the sandstones show a light ree enriched signature with la sm n varying from 5 2 to 6 7 with no eu anomaly while the heavy rees display flat patterns with gd lu n values of 0 9 1 6 primitive mantle normalized incompatible and compatible trace element plots of these sandstones demonstrate an overall similarity with global proterozoic archean sandstones including strong nb ta negative anomalies in an fsm nd vs ond 0 diagram the sandstones plot precisely between the regional amphibolites and tonalites we infer from the ree abundances and the fsm nd vs ond 0 plot that the sandstones represent a bimodal mechanical mixture of omg and omtg the low ce pb ratios of these rocks of 1 4 indicate a variably pb enriched archean crust and that the ce pb ratio acquired the continental crustal signature distinctly different from those of the bulk silicate earth and mantle values at least as early as mid archean strong nb ta depletion relative to the primitive mantle suggests the sandstones were derived from subduction related magmatic arc sources this latter suggestion is strongly supported by the low nb ta and high zr sm ratios of these sandstones identical to archean tonalite trondhjemites that require based on recent trace element partitioning results their protoliths to have formed by subduction melting of lowmagnesium amphibolites or metamorphosed hydrous basalts 1 2 the average nd model ages of the sandstones are greater than the sm nd crystallization ages of the omg and omtg at v3 3 ga the geochemical data presented here can be collectively interpreted to suggest the presence of subduction accretion processes operational in the midarchean eastern indian craton because the omg and omtg the source rocks of the sandstones formed in a subduction related arc setting the basement rocks upon which this arc was constructed must have been older this observation and the depleted mantle nd model ages tdm of the sandstones ranging from 3 6 to 4 0 ga strongly indicate the presence of continental crust in this eastern indian craton older than 3 3 ga and possibly as old as

tidal sandwaves and related storm deposits in the transgressive protoproterozoic chaibasa formation india abstract despite deformation and metamorphism the 2 3 ga fine grained siliciclastic chaibasa formation of eastern india locally retains an excellent record of sandwave migration under the influence of tides and storms within a precursor sandstone facies in a largely subtidal setting and provides a rare opportunity to detect tidal periodicities in the finer facies locally preserved minor features provide glimpses of the depositional mechanisms and settings the silt dominated precursor heterolithic silt mud facies contain numerous slides and slumps and was formed on a relatively steep slope between the fairweather and storm wave bases the shale facies formed in a deeper setting beneath the wave base earthquakes occasionally have interrupted normal sedimentation and massflow products are present in all the facies but with increasing frequency within the finer facies the sandstone facies units which were emplaced during repeated lowstands were first subjected to progradation and subsequently drowned in an overall transgression trend

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

evolution of the proterozoic rift margin sediments north singhbhum mobile belt jharkhand orissa india abstract the proterozoic north singhbhum mobile belt nsmb a proterozoic rift basin registered a complex interplay of tectonism and sedimentation the siliciclastic sedimentary succession developed along the southern margin of the nsmb offers a deep insight into the changing pattern of sedimentation in response to crustal dynamism along a rift margin stratigraphic sedimentologic structural and tectonic studies of the proterozoic sedimentary succession bisrampur formation indicate deposition in a series of half grabens developed successively along the margin of the rift basin under the influence of lithospheric stretching analyses of the sedimentary facies attributes and the architecture of the studied sedimentary succession and paleocurrent patterns indicate filling of the half grabens by archean basement derived siliciclastic sediments in an alluvial fan fan delta environment the structural elements developed in these sediments and neighboring rock units suggest that deformation and final collapse of the half graben basins took place during a terminal orogeny on the basis of an integrated analysis of the dataset generated in the present study and the database available in published work a comprehensive evolutionary model of the north singhbhum mobile belt is reconstructed

2 8 ga old anorogenic granite acid volcanics association from western margin of the singhbhum orissa craton eastern india abstract the tamperkola granite acid volcanics association occurring at the western margin of the archaean singhbhum orissa iron ore craton soc eastern india is intrusive into the darjing group which represents a sequence of mobile belt metasediments in this part of the soc the darjing group rests unconformably on the bonai granite 3 2 ga old absence of any deformational imprints of the country rock metasediments on the tamperkola granite acid volcanics together with its undeformed and unmetamorphosed nature its alkali feldspar dominant mineralogy and its high sio 2 and na 2 o k 2 o and low mgo and cao contents suggest that this granite acid volcanics association is anorogenic in nature two representative samples one each from the granite and the acid volcanics have been dated by in situ 207 pb 206 pb zircon dating method using a small ion microprobe minimum age of crystallisation of the acid volcanics is found to be 2 8 ga strong peak in the 207 pb 206 pb frequency diagram and equality of the observed and expected errors in radiogenic 207 pb 206 pb ratios suggest that this age probably represents the true age of formation of the volcanics the age data place the deposition and metamorphism of the mobile belt metasediments of the darjing group in between 3 2 and 2 8 ga occurrence of 2 9 2 8 ga old small granitoid plutons alkali feldspar granite to syenogranite in composition is also known from the southern margin of the soc therefore it appears that around 2 9 2 8 ga small alkali granite bodies formed at the marginal part of this cratonic block after its stabilisation at 3 1 ga

storm time plasma transport at middle and high latitudes associated with the large scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions solar produced f region plasma is transported to and through the noontime cleft from a source region at middle and low latitudes in the afternoon sector as a result of the offset between the geomagnetic and geographic poles the afternoon sector region of strong sunward convection is shifted to increasingly lower geographic latitude throughout the interval between 12 ut and 24 ut a snowplow effect occurs in which the convection cell continually encounters fresh corotating ionospheric plasma along its equatorward edge producing a latitudinally narrow region of storm enhanced plasma density sed and increased total electron content which is advected toward higher latitudes in the noon sector the millstone hill incoherent scatter radar regularly observes sed as a spatially continuous large scale feature spanning local times between noon and midnight and at latitudes between the polar cap and its mid or low latitude source region for local times away from noon the latitude of most probable sed occurrence moves equatorward by 6 for an increase of 2 in the kp index during strong disturbances the topside sed is observed to be convecting sunward at 750 m s 1 with a flux of 1014 m 2 s 1 this feature accounts for the pronounced enhancement of ionospheric density near dusk at middle latitudes observed during the early stages of magnetic storms called the dusk effect and constitutes a source for the enhanced f region plasma observed in the polar cap during disturbed conditions

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

the paleoproterozoic supracrustal kolhan group in singhbhum craton india and the indo african supercontinent abstract the 2 0 ga supracrustal kolhan group to the south of chaibasa in singhbhum craton eastern india is a shale dominated succession deposited in continental rift setting it begins with thin plane and cross bedded red and purple sandstones consisting of ferric oxide rich quartz arenite with beds lenses of conglomerates deposited in shallow ephemeral braided streams the thick and extensive shale deposited in lacustrine environment overlies the sandstone the shale succession consisting of thin and even bedded shale and silty shale contains lenticular bodies of finely laminated thin bedded limestones and manganese rich interval towards the basal part it lacks subaerial exposure and tidal features and at places exhibits small wave ripples on bed surfaces petrography geochemistry and cia values of kolhan siliciclastics suggest passive margin tectonic setting an intensely weathered low relief provenance dominantly composed of granitoid rocks and a warm and humid palaeoclimate based on similarities in age lithology petrography depositional environment and type of mineralization the kolhan group in singhbhum craton is correlated with manganese bearing wyllies poort formation of the soutpansberg group northeast kaapvaal craton south africa this correlation suggests the two cratonic blocks may formerly have been juxtaposed and represents the sundered fragments of an archean craton

evaluation of the tectonic setting of precambrian dalma volcanic belt eastern india using major and trace element characters geochemical characterisation of dalma basalt the upper member of a volcanic belt occupying the spine of a precambrian basin has been used to elucidate the eruptive environment dalma basalt in general is high magnesian in character as well as depleted in incompatible elements the major and trace element distributions are strongly indicative of ocean ridge magmatism with a feeble impression of arc volcanism such a transitional tectonic environment corroborated by the overall geologic setting of the volcanic belt is strongly indicative of a marginal basin situation during proterozoic time in this part of the indian shield

geochemistry and tectonic significance of the ongarbira metavolcanic rocks singhbhum district india abstract the volcanic sedimentary sequence of ongarbira occurs to the south of the singhbhum shear zone and rests uncomformably on a basement topographic low between the chakradharpur granite and the singhbhum granite structural analysis reveals that the ongarbira synform and other adjoining structures are kilometre scale first generation folds on e w striking axial planes these structures are in marked contrast with the corresponding kilometre scale first generation folds typical of the iron ore group synclinorium towards the south of the ongarbira belt the ongarbira metavolcanic rocks exhibit a limited range of tholeitic basalt compositions the basalts are grouped according to their mg and the details of their ree patterns groups i and ii are relatively unevolved and very similar to lree and lil depleted ocean ridge tholeiites the most evolved group iii with lree enrichment is most similar to lil enriched ocean floor basalts but may be contaminated with crustal materials in general the ongarbira volcanics evolve upward stratigraphically petrogenetic major element modelling of the ongarbira basalts suggests that the primary melt was generated by batch melting 30 of lherzolite at pressures of at least 1 5 gpa sequential fractionation of ol o1 cpx pl and cpx pl followed comparison of incompatible and compatible element distributions indicates a very similar batch m melting fractional crystallization sequence for ongarbira groups i and ii basalts group iii basalts may have been derived from a batch melt initially more enriched in incompatible elements trace element discrimination of the ongarbira basalts suggests that they were generated in an extensional environment primordial mantle normalized element distributions indicate that the basalts are similar to continental rift basalts but with oceanic affinities the chemical data along with the associated sediments indicate that the ongarbira basalts were probably emplaced in a mature continental rift although a back arc origin cannot be completely disregarded it is concluded that the ongarbira volcanics were emplaced as part of the same rifting event that resulted in outpourings of the proterozoic dalma and dhanjori volcanics implying that the ongarbira suite is proterozoic and not part of the archaean iron ore group the structural geometry of the ongarbira rocks is more conformable to that of the singhbhum mobile belt than to the iron ore group synclinorium in the singhbhum craton it is likely that the southern limit of the singhbhum mobile belt is defined by the interface of its e w structures with the nne structures of the iron ore group rocks thus the singhbhum shear zone does not mark the interface between the archaean singhbhum craton and the proterozoic singhbhum mobile belt in the eastern indian shield

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

ionospheric signatures of plasmaspheric tails 1 we make direct comparisons between gps maps of total electron content tec over the north american continent millstone hill radar observations of storm enhanced density and low and high altitude satellite measurements of the perturbation of the outer plasmasphere during the march 31 2001 geomagnetic storm we find that storm enhanced density sed and plumes of greatly elevated tec are associated with the erosion of the outer plasmasphere by strong sub auroral polarization electric fields the sed tec plumes identified at low altitude map closely onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by euv imaging from the image spacecraft characteristics of the sed tec plumes tails for the march 31 2001 event are tec 100 tecu f region sunward velocity 1000 m s sunward flux 5 1024 ions s 1 total transport to dayside magnetopause merging region 3 hr event 5 1028 ions

influence of micaceous impurity on dynamically recrystallized quartz c axis fabric in l s tectonites from the singhbhum shear zone and its footwall eastern india when temperature and strain rate remain constant the quartz c axis fabric in deformed pure quartz aggregates is largely dependent on deformation kinematics asymmetry of the fabric e g in type i asymmetric crossed girdle pattern in natural quartz tectonites simulated fabric or experimentally deformed quartz aggregates is generally related to sense of vorticity for a non coaxial flow natural quartz tectonites however often contain micaceous impurities measurement on a sample of 59 quartz tectonites with mesoscopic l s fabric and representing low ttm deformation under non coaxial flow from the singhbhum shear zone and dhanjori quartzites eastern india provides the basic data to quantitatively assess the influence of mica on i asymmetry of quartx c axis fabric and ii degree of crystallographic preferred orientation i e fabric intensity taking c axes of dynamically recrystallized quartz grains as a fabric element a fabric intensity parameter is defined as the ratio of the greatest eigenvalue to the least eigenvalue of the orientation tensor matrix corresponding to c axis orientations in each measured specimen the modal percent of mica in the sample varies from 2 to 35 that of recrystallized quartz grains as opposed to relict clasts from 45 to 98 the asymmetry of the fabrics in the above sample measured either as the am statistic or as the angle between the central segment of the fabric skeleton and direction of mineral elongation lineation is independent of mica content correlation regression analysis of the variables and demonstrate a negative correlation between micaceous impurity and the fabric intensity parameter the regression equation is of the form 0 13 1 11 0 617

petrochemistry of the lavas from proterozoic dalma volcanic belt singhbhum eastern india the dalma volcanic belt of the singhbhum precambrian terrain in eastern india is developed along the median zone of a linear basin flanked by archaean cratonic basement to the south the lavas in a low grade metamorphic environment preserve a strong compositional bimodality with highly magnesian picritic volcanics developed at the base and low k basalt flows above constituting the bulk of the lava pile the ultrabasic lavas have low concentrations of immobile incompatible elements ratios of which are probably controlled by the source character dalma mafic flows are closely comparable in geochemical character to modern day mid oceanic ridge basalts morb with a dominance of light ree depleted basalts and ferrobasalts however in terms of certain element ratios th ta deviation from morb characteristics toward island arc tholeiites is apparent in this respect the dalma basalts appear to have a modified morb composition and the closest chemical analogy may be basalts from back arc basins i e a supra subduction zone environment the bimodality of ultrabasic and mafic lavas is reminiscent of archaean komatiitic provinces the geochemical signature of the dalma lavas and the geological framework of the terrain strongly point to a marginal basin domain developed in this crustal segment during the proterozoic

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

dating the oldest greenstone in india a 3 51 ga precise u pb shrimp zircon age for dacitic lava of the southern iron ore group singhbhum craton abstract this article reports a precise 3506 8 2 3 ma u pb shrimp zircon age for dacitic lava in a well preserved low grade metamorphic and low strained greenstone belt succession of the southern iron ore group singhbhum craton india this age makes the succession the oldest known greenstone belt succession in india and one of the oldest low strain greenstone successions in the world after the 3 51 ga coonterunah group of the pilbara craton western australia and the moderately deformed 3 54 ga theespruit formation of the barberton greenstone belt kaapvaal craton south africa the geochemical composition of the dacitic lava and related volcanic rocks suggests that they formed in a volcanic arc setting the succession also contains a major 120 m thick oxide facies banded iron formation that distinguishes it from the slightly older successions of the pilbara and kaapvaal cratons this banded iron formation may well be one of the oldest and most well preserved and together with associated volcanics

mapping of coda wave attenuation and its frequency dependency over eastern indian shield the study area comprises two tectonic blocks namely the chotanagpur microplate and the singhbhum microplate waveform data of 112 local earthquakes of magnitude mw 2 5 were considered for the present analysis coda q qc for each event at eight different central frequencies 1 14 hz and four different coda windows was estimated using back projection algorithm the average q0 qc at 1 hz and exponent values were regionalized by projecting each value in selected square grid of dimension 0 1 0 1 back projection algorithm was used for inversion of qc and the final values were computed after ten iterations when the residual error was reduced to acceptable level inversion was stabilized by a nine point spatial smoothening gaussian filter to compute the qc values for each frequency and subsequently combined values of q0 and were also computed the final power law equation of the coda wave attenuation for the concerned region was found to be qc 336 38 16 50 f 0 83 0 036 q0 varies from 180 to 255 270 to 360 297 to 386 and 340 to 420 and vary from 0 9 to 1 02 0 79 to 0 89 0 79 to 0 88 and 0 79 to 0 86 for 30 35 40 and 45 s coda windows increase in q0 and decrease in values with increase of coda window length shows the depth dependency of seismic wave attenuation at 1 hz frequency the central part surrounding the receiver lying at the junction of the chotanagpur and the singhbhum tectonic provinces documents lower q0 and higher values and presumably caused by more heterogeneities present in the area the higher concentration of lower magnitude earthquakes in this area support this observation the mapping values of attenuation can be utilized for hazard assessment of the area

depositional history of diamictites from the late paleoproterozoic dalma formation e india abstract the paleoproterozoic dalma formation situated on the singhbhum craton in eastern india consists almost entirely of mafic to ultramafic rocks that were deposited by effusive volcanic activity and as pyroclastic deposits the main focus of the present study however is on diamictites consisting like both other rock types exclusively of chlorite and actinolitic hornblende that are intercalated with these volcanic rocks these diamictites are interpreted as mass flow deposits the textures and mineralogical composition of the diamictites suggests a volcanic origin of the material most probably they are reworked pyroclastic deposits with the same mineralogy as the dalma lavas on this basis it is concluded that the diamictites represent the deposits of one or more volcanic mudflows they must have formed of material that had already travelled over a considerable distance in the form of grain by grain transport as indicated by the presence of both rounded and distinctly broken clasts and by the relatively small size of the clasts both the grain by grain and the mass transport must have occurred following pathways that were covered all over with volcanic material of mafic composition this transport must have taken place under terrestrial conditions as no marine or lacustrine clasts or matrix is included the results of the study suggest that the diamictites within the dalma formation cannot be seen as a possible equivalent of paleoproterozoic glacigenic sediments such as known from australia and south africa

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

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex