paleoproterozoic granitoids in the basement of bangladesh a piece of the indian shield or an exotic fragment of the gondwana jigsaw abstract we present the first precise age for precambrian basement rocks in bangladesh these lie within the dinajpur block located between the indian craton to the southwest and the shillong massif to the east there are no surface outcrops and the rocks were intersected by drill holes they consist of a suite of tonalitic and granodioritic rocks variously deformed to granitic gneiss and intruded by younger monzogranite a tonalite obtained at a depth of 227 48 m in drill hole bh 2 at maddhapara in northwestern bangladesh records a shrimp zircon 207pb 206pb magmatic age of 1722 6 ma paleoproterozoic rocks with similar magmatic ages are unknown in the adjacent indian blocks of the chotanagpur plateau indian craton or shillong massif this lack of comparable ages may be due to the paucity of precise radiometric ages from the indian terrains or more likely because there are real age differences with the buried rocks at maddhapara representing a separate and discrete microcontinental fragment the dinajpur block that was trapped by the northward migration of india during gondwana dispersal

early archean crust in bastar craton central india a geochemical and isotopic study abstract high a12o3 trondhjemitic gneisses occur in enclaves within granites at markampara in the bastar craton central india these gneisses exhibit a highly fractionated rare earth element ree pattern frsol la yb n 60 83 and may have been produced by partial melting of an amphibolitic protolith a zircon u pb age of 3509 14 7 ma dates primary crystallization of the trondhjemites a granite surrounding the gneissic enclaves yields a zircon u pb age of 2480 3ma rb sr wholerock data for the trondhjemitic gneisses are somewhat disturbed and indicate initial 87 sr 86 sr ratios of 0 7016 pb isotopic data are poorly correlated and suggest a three stage evolution with an early period of high u pb growth 9 5 10 5 after emplacement at 3 5 ga followed by isotopic disturbance and u depletion at 2 5 ga during widespread magmatism and metamorphism loss of rb and other mobile elements may also have occurred at this time

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

reservoir assessment using non invasive geophysical techniques this paper describes the use of three geophysical techniques to detect potential seepage that could jeopardise the integrity of reservoir embankments could induce partial or total collapse and pose a risk to the population nearby a fast scanning geophysical technique using two dipole electromagnetic em profile apparatus gem2 provided the first step to detect the weakest points on the selected dams in order to proceed to a more detailed analysis and visualisation of the soil erosion fissuring or piping using electrical resistivity tomography ert finally self potential surveys were carried out to relate to the em and ert anomalies that could be pathways for seepage and changes of the water displacement inside the embankment the three geophysical techniques used were evaluated in one case study of reservoir in a location relevant to flooding issues in czech republic a risk approach based on the geophysical results was undertaken for the reservoir embankment the three techniques together were compared for the same problematic section and confirmed seepage by showing similar results conclusions were also drawn on the efficiency of using these three techniques as a package to give a comprehensive non invasive assessment to be used as common practice by local authorities and environment agencies whereby remedial action could be recommended to protect assets and civilians

using resistivity measurements for dam safety evaluation at enemossen tailings dam in southern sweden internal erosion is a major reason for embankment dam failures resistivity measurements is an essentially non destructive technique which may have the possibility of detecting internal erosion processes and anomalous seepage at an early stage before the safety of the dam is at stake this paper presents results from part of a dam safety investigation conducted at the enemossen tailings dam in southern sweden longitudinal resistivity sections 2d measurements along the dam crest provided an overview of the whole dam and served to detect anomalous zones in selected areas additional cross sectional 2d surveys gave detailed information about the geo electrical situations in the embankments this information is valuable for similar investigations as information about resistivity in embankment construction material is scarce known problem areas were associated with low resistivities even though the resistivity measurements alone did not provide enough information to confidently come to a decision about the status of the dams

crossline resistivity tomography for the delineation of anomalous seepage pathways in an embankment dam crossline resistivity tomography was developed to find out anomalous seepage pathways in an embankment dam by applying crossline tomography to the investigation of embankment dams leakage pathways can be effectively located because the crossline tomogram presents resistivity distribution in the horizontal plane of an embankment dam to test the effectiveness of crossline tomography we applied it to data from an experiment designed to delineate anomalous seepage pathways in the embankment dam the method yields relatively accurate geoelectric structure of the dam when applied to synthetic data in the crossline resistivity tomogram abrupt discontinuities of a low resistivity band corresponding to the core of the dam can be interpreted as leakage pathways application to real data obtained from an embankment dam in korea yields the result which accurately depicts two anomalous seepage pathways the identified pathways were consistent with low resistivity zones in the dipole dipole resistivity section obtained on the crest of the dam one pathway was confirmed by visual inspection of the dam and afterward by trenching

precambrian mafic dyke swarms in the singhbhum craton eastern india and their links with dyke swarms of the eastern dharwar craton southern india discussion

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

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

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

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

high precision 207pb206pb zircon geochronology using a small ion microprobe abstract a small geometry ion microprobe cameca ims 4f has been successfully used for the routine measurement of 207 pb 206 pb ratios in individual zircons with a spatial resolution of 20 m in spite of the lower sensitivity of the small ion microprobe resulting from operating at high mass resolution m m 4600 in order to resolve isobaric molecular interferences we can discern archean components whose ages differ by 50 ma a single measurement requires 90 min of data acquisition thus a comprehensive study of a zircon population can be accomplished in a few days three sets of precambrian zircons analyzed earlier by other techniques yielded ages which are within 2 of their true values as our first unknown we analyzed zircons from a sample of orthogneiss collected from the aravalli craton of northwestern india for this sample we obtained a minimum age of 3281 3 ma 1 which we believe closely approximates the time of crystallization of the gneiss s igneous protolith

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

gravity field over singhbhum its relationship to geology and tectonic history abstract the gravity field over singhbhum and adjoining areas lying between latitude 21 to 23 15 n and longitude 84 to 87 30 e has been analysed the region has a very complex precambrian history dating as far back as 3200 m y and extending up to 850 m y during which time it experienced a number of orogenic cycles the activity has left an imprint on the gravity field which is marked by prominent gravity highs and lows the highs are invariably surrounding the singhbhum granite batholith whereas the lows are conspicuous over the granites and their margins the regional gravity field has been removed using a 4th order polynomial surface the residual anomalies over prominent highs and lows have been interpreted using two dimensional and three dimensional models for underlying rock formations it is inferred that the gravity highs are generally related to synclinal structures filled with sedimentary or metasedimentary formations and volcanics such as the iron ore group the singhbhum group dhanjori and simlipal basins the gravity lows can be attributed to a considerable thickness of granites of varying density which could have been formed during different metamorphic orogenic cycles by melting of a preexisting sialic crust

stabilization of the aravalli craton of northwestern india at 2 5 ga an ion microprobe zircon study abstract in order to establish the stabilization age of the aravalli craton of northwestern india we have used an ion microprobe to measure 207 pb 206 pb ages of zircons from six samples collected from the southern aravalli mountains our analyses gave precise results for four granitoids whose minimum crystallization ages ranged between 2562 6 and 2440 8 ma 1 a single sample of gneiss gave an age of 2502 4 ma which is unexpectedly younger than an age of 3281 ma which we previously obtained from another gneissic sample we interpret the 2502 ma age as the time of emplacement of the sample s igneous protolith suggesting that the mewar gneiss contains multiple metamorphic components of differing ages based on our data we conclude that the southern segment of the aravalli craton had broadly stabilized by 2 5 ga this stabilized landmass formed the basement on which the younger aravalli supergroup was unconformably deposited this study represents the first application of a small geometry ion microprobe for routine geochronology

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

early proterozoic metallogeny tectonics and geochronology of the singhbhum cuu belt eastern india abstract the singhbhum thrust belt hosts three types of mineralisation sulphides of copper and other metals uranium oxides and apatite magnetite regional geological investigations reveal that the thrust belt and the mineralisations evolved through several distinct geological episodes 1 the oldest is the deposition of the protoliths of the older metamorphic group their subsequent deformation and metamorphism and the post kinematic intrusion of the singhbhum granite the older metamorphic orogeny 3 15 3 0 ga the chotanagpur gneiss to the north is also thought to have originally belonged to this period 2 the chotanagpur gneiss and the singhbhum granite together formed an extensive sialic basement of the archaean period which subsequently underwent extension producing a continental basin filled with platform sediments of the iron ore group and deep sea basins on sialic basements filled with flysch like sediments of the singhbhum group this was accompanied by extensive mafic volcanism the dalma volcanics the dhanjori volcanics and the dolerite dyke the sulphide ores were formed as strata bound layers associated with the volcanism of the dhanjori volcanics uranium minerals and phosphates were deposited as sediments or related to later felsic plutonic activity volcanism sedimentation and mineralisation were controlled by rift fractures forming the basins these were later subjected to deformation and metamorphism of the singhbhum orogeny 2 05 2 0 ga the rift fractures developed into thrust belts felsic magmatic activity took place hydrothermal activity along the thrust belt modified the mineralised belt 3 a later thermal event 1 6 ga was imprinted on the rocks of the thrust belt

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

electrical resistivity response due to variation in embankment shape and reservoir levels the safety of the center core type of fill dam structure was assessed by examining the effects of the distortion of electrical response verified in terms of two dimensional 2d apparent resistivity and its inverted sections from three dimensional 3d modeling for the embankment the distortion effect is due to 2d interpretation of the 3d structure of the embankment from the analysis it was found that water level was correctly described by the resistivity section around the middle part rather than each side at the end of the embankment this is due to the 3d terrain effect when the material of the embankment is assumed to be horizontally uniform in addition when the slope of the outer rock fill section is set as uniform the resistivity section is more similar for sharper center core slopes on the other hand when the rock fill slope is steep the resistivity section shows the water level at a lower position than the real one and the 3d distortion effect at the end of the embankment is enhanced

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

2 5d resistivity modeling of embankment dams to assess influence from geometry and material properties repeated resistivity measurement is a potentially powerful method for monitoring development of internal erosion and anomalous seepage in earth embankment dams this study is part of a project to improve current longterm monitoring routines and data interpretation and increasing the understanding when interpreting existing data this is accomplished by modeling various occurrences typical of embankment structures using properties from two rockfill embankment dams with central till cores in the north of sweden the study evaluates the influence from 3d effects created by specific dam geometry and effects of water level fluctuations in the reservoir moreover a comparison between different layout locations is carried out and detectability of internal erosion scenarios is estimated through modeling of simulated damage situations software was especially developed to model apparent resistivity for geometries and material distributions for embankment dams the model shows that the 3d effect from the embankment geometry is clearly significant when measuring along dam crests for dams constructed with a conductive core of fine grained soil and high resistive rockfill the effect becomes greatly enhanced also water level fluctuations have a clear effect on apparent resistivities only small differences were found between the investigated arrays a layout along the top of the crest is optimal for monitoring on existing dams where intrusive investigations are normally avoided because it is important to pass the current through the conductive core which is often the main target of investigation the investigation technique has proven beneficial for improving monitoring routines and increasing the understanding of results from the ongoing monitoring programs although the technique and software are developed for dam modeling it could be used for estimation of 3d influence on any elongated structure with a 2d cross section

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

chemical and boron isotope compositions of tourmaline from the jaduguda u cu fe deposit singhbhum shear zone india implications for the sources and evolution of mineralizing fluids abstract the proterozoic jaduguda u cu fe deposit in the singhbhum shear zone eastern india hosts the oldest and most productive uranium mine in india the polymetallic ores in jaduguda are hosted in altered sheared and metamorphosed volcano sedimentary rocks and this complexity has lead to a confusion in ore genetic models for the deposit a characteristic of the mineralization is the presence of abundant tourmaline locally exceeding 50 vol which is spatially associated with u and cu mineralization in all rock types and its chemical and b isotopic variations provide important constraints on fluid source s and ore deposit affinity we examined tourmaline from the u cu ore zone and adjacent footwall and hanging wall meta sedimentary rocks tourmaline grew in three different stages pre kinematic tourmaline 1 represented by fractured and porphyroblastic grains is ubiquitous in the wall rocks and the u cu zone syn kinematic tourmaline 2 and post kinematic tourmaline 3 are found exclusively in the u cu zone where intense shear deformation has focussed fluid flow alteration and metamorphism all tourmalines belong to the alkalic group and most are dravitic systematic contrasts in major element compositions between tourmaline 1 and tourmaline 2 are attributed to the influence of high fluid rock ratios in the u cu ore zone tourmaline from the jaduguda deposit exhibits a wide overall range of 11b values from 6 8 to 17 2 positive values of tourmaline 1 are irrespective of host rock and ore association u or u cu and range between 2 3 to 17 2 n 44 the calculated 11b values of fluid in equilibrium with this tourmaline for mineralization temperatures of 300 450 c range from 4 to 20 the 11b values of syn kinematic tourmaline 2 are much lower than tourmaline 1 between 6 8 and 4 n 7 and the corresponding fluid 11b values are 4 8 6 the high values of 11b for tourmaline 1 and early fluid suggest a marine evaporite or basinal brine was the source of boron and this fits with abundant mineralogical and geochemical evidence for highly saline fluids during mineralization we propose that the isotopically lighter fluid associated with tourmaline 2 and related syn kinematic mineralization mobilization was derived from the metamorphic volcano sedimentary rocks at high fluid rock ratios in and around the shear zone post kinematic tourmaline 3 is compositionally and isotopically 11b 4 to 11 1 n 5 similar to tourmaline 1 in the same samples suggesting it formed by local recrystallization of the early tourmaline or from a renewed influx of saline fluids similar to those which formed the pre kinematic mineralization integrating the results of this tourmaline study with the geological and geochemical characteristics of the jaduguda u cu fe mineralization suggests that it is best regarded as a variant of the fe oxide cu u ree or iocg class of deposits

imaging regional geology and au sulphide mineralization over dhanjori greenstone belt implications from 3 d inversion of audio magnetotelluric data and petrophysical characterization abstract the 2 1 ga old paleoproterozoic dhanjori group of rocks covers 800 sq km area within the singhbhum crustal province of eastern india and is composed of siliciclastic metasedimentary sequence interlayered with mafic to ultramafic rocks the meta volcanosedimentary sequence is deformed and is of low grade greenschist metamorphic facies the gold occurrences within the study area are confined to the sulphide hosted mafic ultramafic volcanic rocks and also in the basal quartz pebble conglomerates qpc within the dhanjori formation gold mineralization within the mafic ultramafic meta volcanics formations occurs within the quartz carbonate vein i e lode gold and as detrital gold within the qpc 0 5 7 ppm of phuljhari formations regional audio magnetotelluric amt measurements across the geological domains of dhanjori group and iron ore group iog were carried out in the frequency range of 10 khz 10 hz this work discusses the conductivity model from 3 d inversion along with geology and petrophysical properties in mapping the regional geological features associated sulphide mineralization and influence of texture grain and bulk properties on mineralization dimensionality and strike analysis of the amt data indicate complex conductivity structures 3 d inversion of off diagonal component of impedance was performed for obtaining an optimum value of uniform half space initial resistivity and error floor for off diagonal component of impedance data these were used to perform 3 d inversion of full impedance to produce a conductivity model of the study area the conductivity model delineated major geological boundaries and the sulphide bearing mineralized zone a major conductor is observed which extends to a depth of 250 m within meta volcanics on comparison with the available borehole adjacent to this it is confirmed that the conductor corresponds to sulphide mineralization the resistivity low at a depth of 150 m coincides with metabasalts pyrite present which extends to 159 m with arsenopyrite another mineralized zone is observed at the boundary of iron ore group volcanics and proterozoic gabbro anorthosite ultramafics pgau it starts appearing from a depth of 400 m and can be seen which extends to a depth of 800 m it is worth mentioning that there lies kundarkocha gold mine in the same geological domain in addition near surface conductor to a maximum depth of 50 m is observed all along the amt profile the sediments and fluids could account for this conducting feature this is in agreement with available electrical resistivity tomography section the borehole within dhanjori volcanics also detected sulphide mineralization for 50 m thus it can be inferred that the near surface conductor indicates the presence of gold in association with other sulphide minerals the petrophysical studies helped to estimate the concentration of minerals within the rocks high density and low susceptibilities in the area is an indicative of low grade metamorphism and low level of serpentenization combined density and susceptibility scatter diagram and component proportion phase diagram suggests 20 vol 78 vol and 2 vol of haematite sulphides barren rocks and magnetite respectively the high value of chargeability and negligible value of susceptibility indicates the presence of disseminated sulphides rather than haematites and or massive sulphides in the rocks ternary plot suggest that the mineralization is controlled by texture and grain properties petrophysical analysis suggests that the lithotypes of the study area are similar to those of greenstone terrain in the abitibi subprovince integrating inverted section geology and petrophysical properties has a substantial impact on the study area in terms of predicting the mineralization prospect and at the same time substantially reduces the drilling cost thus the study provides a new orientation and advancement to the exploration strategy for deeper deposits

archean granitoids at the contact of eastern ghat granulite belt and singhbhum orissa craton in bhuban rengali sector orissa india abstract the small granite plutons occurring at the contact of the singhbhum orissa iron ore craton ioc to the north and the eastern ghat granulite belt eggb to the south in eastern indian shield are characterised by the presence of enclaves of the granulites of eggb and the greenschist facies rocks of ioc these granites also bear the imprints of later cataclastic deformation which is present at the contact of the ioc and the eggb in situ pb pb zircon dating of these granites gives minimum age of their formation 2 80 ga a whole rock three point rb sr isochron age of this rock is found to be 2 90 ga therefore the true age of formation of these granites will be around 2 90 2 80 ga these granitic rocks also contain xenocrystic zircon components of 3 50 ga and show a later metasomatic or metamorphic effect 2 48 ga obtained from the analyses on overgrowths developed on 2 80 ga old zircon cores the presence of granulitic enclaves within these contact zone granite indicates that the granulite facies metamorphism of the eggb is 2 80 ga or still older in age the cataclastic deformations observed at the contact zone of the two adjacent cratons is definitely younger than 2 80 ga and possibly related to 2 48 ga event observed from the overgrowths as 2 80 ga granite plutons of small dimensions are also observed at the western margin of the ioc it can be concluded that a geologic event occurred 2 80 ga over the ioc when small granite bodies evolved at the marginal part of this craton after its stabilisation at 3 09 ga

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

3 56ga tonalite in the central part of the bastar craton india oldest indian date abstract the lack of information regarding early achaean rocks from the indian peninsula is mainly due to the absence of high quality u pb zircon ages a tonalite sample from the ttg gneiss supracrustal association from the central part of the bastar craton in central india is dated at 3 56 ga this is the oldest protolith age so far recorded from india these ttg gneisses have enclaves of metasedimentary and metavolcanic rocks that may provide important information on the first billion year history of the indian craton this new date for tonalite from the bastar craton is the first precise u pb zircon age from india s first u pb geochronology laboratory located at the geological survey of india which hopefully will remedy the paucity of good geochronological data for older rocks of the indian peninsula

ion microprobe 207pb 206pb ages of zircons from the bundelkhand massif northern india implications for crustal evolution of the bundelkhand aravalli protocontinent abstract 207pb 206pb ages of zircon from gneissic rocks and granitoids representing all major lithological units of the bundelkhand massif northern india have been determined using an ion microprobe the presence of early archaean granitic crust in this region is established from these ages ages for the kuraicha and the mahoba gneisses and associated metabasic enclaves suggest the oldest partial and metamorphic melting event in this region occurred at 3 3 ga the presence of younger gneisses with ages of 2 7 and 2 5 ga suggests the existence of multiple protolith age components within the massif three major granitoid suites hornblende biotite leuco granitoids were emplaced at 2 5 ga within a time span of a few tens of millions of years felsic volcanism also occurred around this time an age of 2 49 ga for the youngest phase of leucogranitoid marks the time of overall stabilization of this massif the geochronological history of the bundelkhand massif appears to be remarkably similar to that of the basement complex of the aravalli delhi orogenic belt another prominent archaean crustal block to the west of this massif geochemical features of the different rock types in these two regions are also very similar we propose that these two apparently discrete blocks evolved as a single crustal unit with stabilization taking place at 2 5 ga

combined analysis of electrical resistivity and geotechnical spt blow counts for the safety assessment of fill dam electrical resistivity survey and the geotechnical spt blow counts n value method were simultaneously analyzed to investigate the stability of a center core type earth fill dam against the seepage phenomenon the coupling of these heterogeneous field methods provided a chance to understand the status of underground material by comparing the geophysical and geotechnical view the analysis shows that the zones with low resistivity value generally have low n value which means low stiffness however some zones with a high resistivity pattern are not accompanied by an increase of its n value and are even showing a lower n value these results imply that one should be careful to directly correlate resistivity value with the real status of the core material of a fill dam and a highly resistive zone may be in poor status due to the effect of increase of resistivity value as a result of the piping condition additional laboratory tests show that there is a deficiency of fine soil particles believed as the clay at the troubled region which means an increase in resistivity value therefore multiple explorations should be planned to reduce the uncertainty in application of geophysical methods to dam safety evaluation in order to compensate the resistivity information of core material

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

suspended sediment movement in the estuary of the ganges brahmaputra meghna river system abstract topographical flow volume and suspended sediment concentration ssc measurements are presented in the large area of a turbidity maximum in the estuary of the ganges brahmaputra meghna river system in bangladesh the zone of turbidity maximum is indicated by the satellite imagery taken during the low river discharge period topographical and flow volume measurements the aspect ratio and the flow ratio indicate that the system is divided into flood and ebb dominated channels suspended sediment movement in the estuary appears to be associated with the horizontal stratification of flow and with the residual movement induced by the asymmetry of the tidal wave the flow ratio at different sections indicates that net import of suspended sediment takes place through flood channels while the net export occurs through ebb channels despite this difference in the direction of net movement of sediments measurements show that the ssc both in the flood channel and in the ebb channel is dependent on the tidal range the spring tidal ssc is about twice that of the neap tide and locations with higher tidal range show higher magnitudes of ssc the response of sediments to the varying energy environment of tidal range and tidal current however is not instantaneous the ssc shows a time lag in its variation with the varying energy condition the amplification and asymmetry of the tidal wave in the flood channels and the slack water asymmetry measured in a flood dominant location indicate that a possible landward residual transport of suspended sediment due to this factor is more pronounced through flood channels

assessing preferential seepage and monitoring mortar injection through an earthen dam settled over a gypsiferous substrate using combined geophysical methods abstract for several decades the sant llorenc de montgai reservoir has experienced different problems that could affect the safety of the engineering structure for this reason several corrective actions have been taken over the years here we present a study involving complementary geophysical methods including electrical resistivity tomography seismic refraction tomography and frequency domain electromagnetic surveys the analysis of the inverted electrical resistivity tomography cross sections combined with the seismic refraction results and land subsidence monitoring data show the likely mechanism of abnormal seepage the areas where mortar injections were applied as a corrective measure are also clearly delineated in addition the evolution of the state of the embankment has been established from two successive electrical resistivity tomography surveys in the last two decades the results show areas where corrective mortar injections have been effective while in other areas new abnormal seepage has been detected the lithological heterogeneity of the bedrock especially the dissolution of gypsum rich rocks induced subsidence effects and caused abnormal seepage in different areas along the embankment our results indicate how corrective solutions can be optimized to reduce the cost of corrective engineering interventions

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

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

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

suspended sediment distribution and residual transport in the coastal ocean off the ganges brahmaputra river mouth abstract an examination of suspended sediment dispersal in the coastal ocean off the ganges brahmaputra river system using shipboard and satellite data reveal distinct patterns of sediment distribution and sediment motion which help explain the dynamics of the world s largest sediment dispersal system during the low discharge period suspended sediment concentration distribution is mainly a function of tidal energy and the sediments are primarily transported as a suspension population satellite and sea bed data indicate that transport of river sediments is largely restricted to an area landward of about the 20 isobath during the low discharge period a simplistic estimate of residual transport and its separation into tidal and non tidal components indicate that non tidal transport contributes about 47 of the total transport and has transport directions mostly southwestward during the northeast monsoon the tidal residual transport which contributes about 53 of the total transport however does not show any particular direction for most of the stations although some landward stations show shoreward transport although few water column measurements were made during the high discharge period data from this and previous studies suggest that the dominant transport direction is to the southwest for most of the year

kinematic analysis using ams data from a deformed granitoid abstract this study highlights the usefulness of anisotropy of magnetic susceptibility data from a deformed granitoid in deciphering its kinematic evolution vis a vis shear zone data are presented from the chakradharpur granitoid ckpg that lies to the north of the northerly dipping ene wsw striking singhbhum shear zone ssz eastern india whilst the foliation recorded in the field in some parts of the granitoid is parallel to the ssz the magnetic foliation is n54 e 90 mean orientation it is suggested that the magnetic fabric provides a window into an evolutionary stage prior to the final shearing thrusting event the evidence of which is preserved on the mesoscopic scale it is envisaged that during the initial stages of deformation there was simple shear along the evolving ssz that resulted in sinistral strike slip movement the vorticity axis at this stage was steeply plunging and sense of rotation was anticlockwise space was generated in a direction n25 e perpendicular to maximum instantaneous stretching axis into which ckpg emplaced synchronously with regional deformation and evolving ssz with continued deformation there was thrusting along the ssz the vorticity axis flipped to a sub horizontal orientation thus leading to the development of down dip stretching lineations and sheath folds within the ssz however at the same time the vorticity axis responsible for fabric evolution within the syntectonically crystallizing cooling ckpg was steeply plunging with clockwise rotation the magnetic foliation mean orientation n54 e 90 developed during the final stage of syntectonic crystallization however deformation in the region and thrusting along the ssz continued even after the ckpg had fully crystallized and solidified which led to the development of the ene wsw striking mesoscopic foliation that is parallel with the ssz we propose that the angle between the magnetic foliation and the ssz foliation recorded in the field enables to decipher the kinematic vorticity number of flow responsible for fabric evolution of the ckpg it is concluded that transpression was an important mechanism and during regional deformation whilst the ssz developed structures by dominantly simple shear the ckpg underwent dominantly pure shear

chronological correlations between the pilbara and kaapvaal cratons abstract the early geological development of the pilbara and kaapvaal cratons has many features in common attempts have been made to correlate geologically similar features of the two cratons and it has been postulated that they originated as contiguous components of a single continent vaalbara during this time the early geological histories of the pilbara and kaapvaal cratons are here compared in detail and the evidence that they were initially contiguous is assessed these comparisons indicate significant differences in the chronologies of magmatic events within the granite greenstone crusts of the pilbara and kaapvaal cratons in addition igneous correlatives emplaced during ca 2985 and 2782 ma magmatic events on the kaapvaal craton have not been identified on the pilbara craton and a well defined 2760 ma magmatic event manifest as widespread emplacement of granitic rocks into the pilbara granite greenstone basement and eruption of flood basalts of the lower part of the fortescue group is absent from the kaapvaal craton furthermore similarities in first and second order transgression regression cycles within the sedimentary supracrustal sequences may be attributable to global sea level fluctuations and thus may be irrevelant to the question of former contiguity however similarities in some aspects of the geological development of the pilbara and kaapvaal cratons imply that there were periods extending for between 60 and 200 ma of the archaean era during which the style of crust formation intensity of volcanism and subaerial erosion and magnitude of sea level fluctuations may have varied on a global scale such similarities include the overall duration of formation of the granite greenstone crusts from ca 3650 to 3100 ma the onset of craton wide erosion in the interval ca 3125 to 3000 ma the major episodes of flood basaltic volcanism between 2760 and 2680 ma the predominance of chemical carbonate and banded iron formation sedimentation between ca 2630 and 2440 ma and the transition to widespread clastic sedimentation within the interval 2440 to 2200 ma

the nature of mesoproterozoic central indian tectonic zone with exhumed and reworked older granulites abstract the ese wnw trending central indian tectonic zone citz divides the indian subcontinent into southern and northern crustal provinces its narrow northern belt consists of closed early proterozoic mahakoshal rift zone which is presently confined between two moho reaching faults that characterize the son narmada sona lineament the mesoproterozoic sausar mobile belt smb the chhotanagpur granite gneiss complex cggc and the gneissic complex of northeast india represent the wider southern belt the mahakoshal rift belt has a thick pile of mafic ultramafic rocks and possibly oceanic components the basin closed due to a south directed subduction creating a magmatic arc that was sutured to its southern boundary during 1 8 1 7 ga a south dipping ductile shear zone known as the son narmada south fault affects both its supracrustals and intrusive granitoids the son narmada south fault generally delimits the northern boundary of the gondwana basins whereas the son narmada north fault delineates the northern boundary of the mahakoshal mobile belt and the southern boundary of the meso neoproterozoic vindhyan basin the smb representing the southern belt of the citz in the central sector comprises strongly folded and metamorphosed non volcanic and mn rich sausar sediments intermixed with reworked basement gneisses migmatites and granulites representing the pre sausar assemblage the sausar orogeny closed during terminal mesoproterozoic ca 1 0 ga on the other hand metamorphism in the basement gneiss migmatites and northern and southern granulite belts pre dates the sausar orogeny the earliest structure of the smb truncates and rotates the n s oriented structures of the southward located sakoli and the dongargarh belts of neoarchaean palaeoproterozoic age the northern granulite belt of the smb and the cggc and the high grade supracrustals from the sonapahar area in ne india all indicate very high p t conditions during 1 7 1 5 ga peak metamorphism which was followed by decompressional cooling the setting resembles continental collision which was followed by tectonic exhumation and denudation on the other hand the southern granulite belt from the smb documents a late archaean 2 6 ga event and a later 1 4 ga event the dalma volcanic belt located close to the southern tectonized boundary of the cggc belt and possibly the assemblage of copious mafic enclaves within the ca 550 ma granite plutons from ne india represent back arc like setting during 1 6 1 5 ga the setting is caused due to the southward subduction of the north indian block beneath the southern block leading to continental collision the metasedimentary belt located further to the south of the dalma volcanic belt and flanking the archaean singbhum craton to the north on the other hand is palaeoproterozoic in age but has been metamorphosed during ca 1 6 ga because of the northern collision related orogeny reworking and incorporation of basement gneisses and granulites from the mid crust level to the younger sausar cover sediments denote renewed spell of thrust tectonics that remobilized the collision zone rocks of the earlier orogeny the tectonic transport was from the north to the south with north dipping thrusts thus there was a reversal in the direction of convergence from the preceding orogeny the sausar orogeny closed during ca 1 0 ga it caused anatectic event producing granitoid plutons migmatites and charnockites in the cggc belt and migmatites in the gneissic complex in ne india

the paleogene record of himalayan erosion bengal basin bangladesh a knowledge of himalayan erosion history is critical to understanding crustal deformation processes and the proposed link between the orogen s erosion and changes in both global climate and ocean geochemistry the most commonly quoted age of india asia collision is 50 ma yet the record of paleogene himalayan erosion is scant either absent or of low age resolution we apply biostratigraphic petrographic geochemical isotopic and seismic techniques to paleogene rocks of the bengal basin bangladesh of previously disputed age and provenance our data show that the first major input of sands into the basin in the 1 km thick deltaic barail formation occurred at 38 ma our biostratigraphic and isotopic mineral ages date the barail formation as spanning late eocene to early miocene and the provenance data are consistent with its derivation from the himalaya but inconsistent with indian cratonic or burman margin sources detrital mineral lag times show that exhumation of the orogen was rapid by 38 ma the identification of sediments shed from the rapidly exhuming southern flanks of the eastern central himalaya at 38 ma provides a well dated accessible sediment record 17 myr older than the previously described 21 ma sediments in the foreland basin in nepal discovery of himalayan detritus in the bengal basin from 38 ma 1 resolves the puzzling discrepancy between the lack of erosional evidence for paleogene crustal thickening that is recorded in the hinterland 2 invalidates those previously proposed evidences of diachronous collision which were based on the tenet that himalayan derived sediments were deposited earlier in the west than the east 3 enables models of himalayan exhumation e g by mid crustal channel flow to be revised to reflect vigorous erosion and rapid exhumation by 38 ma and 4 provides evidence that rapid erosion in the himalaya was coincident with the marked rise in marine 87sr 86sr values since 40 ma whether 38 ma represents the actual initial onset of vigorous erosion from the southern flanks of the east central himalaya or whether older material was deposited elsewhere remains an open question

precambrian mafic dyke swarms in the singhbhum craton eastern india and their links with dyke swarms of the eastern dharwar craton southern india abstract based on trend cross cutting relationships and u pb dating precambrian mafic dykes in the singhbhum craton earlier collectively identified as newer dolerite swarm have been separated into seven distinct swarms which are thought to be the plumbing systems for large igneous provinces lips these singhbhum swarms range in age from 2 80 ga to 1 76 ga and include the 2 80 ga ne sw trending keshargaria swarm 2 75 2 76 ga nne ssw to ne sw trending ghatgaon swarm the 2 26 ga ne sw to ene wsw trending kaptipada swarm based on a new u pb id tims age 2256 6 ma the 1 77 ga wnw ese trending pipilia swarm the early paleoproterozoic e w to ene wsw trending keonjhar swarm the middle paleoproterozoic nw se to nnw sse trending bhagamunda swarm and the late paleoproterozoic n s to nne ssw trending barigaon swarm two of the singhbhum swarms the 2 26 ga kaptipada and 1 77 ga pipilia are closely matched with the 2 26 2 25 ga ippaguda dhiburahalli and 1 79 ga pebbair swarms respectively of the eastern dharwar craton the correlations suggest that the singhbhum and dharwar cratons were close enough at these times to share two reconstructed lips a 2 26 2 25 ga kaptipada ippaguda dhiburahalli lip and a 1 79 1 77 ga pipilia pebbair lip and if so both swarms must be present in the intervening bastar craton candidates are proposed also the 2 76 2 75 ga ghatgaon swarm of the singhbhum craton can be provisionally correlated with 2 7 ga keshkal swarm of the bastar craton the 2 26 2 25 ga kaptipada ippaguda dhiburahalli lip of the singhbhum bastar dharwar reconstruction has age matches in the vestfold hills of antarctica 2 24 ga dykes the kaapvaal craton the 2 25 2 23 ga hekpoort lavas and perhaps the zimbabwe craton 2 26 ga chimbadzi troctolite intrusions the 1 76 1 79 ga pipilia pebbair lip of the singhbhum bastar dharwar reconstruction has age matches in the north china australian shield amazonian rio de plata and sarmatia cratons the relevance of these matches for reconstructions will require future testing using paleomagnetic studies while there are 2 7 2 8 ga lip type greenstone belts in many crustal blocks there are no precise matches with the 2 76 2 75 ga ghatgaon swarm of the singhbhum craton however the 2 80 ga keshargaria swarm can be potentially linked with units in the pilbara and yilgarn cratons

reversing buoyancy in turbidity currents developing a hypothesis for flow transformation and for deposit facies and architecture a turbidity current that contains fresher or otherwise less dense water than its surroundings may initially be denser than the ambient and propagate as a bottom hugging flow but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient seawater it is proposed that this reversal in buoyancy may be a significant mechanism controlling the structure and facies of turbiditic deposits buoyancy reversal followed by lofting may directly affect the relative distribution of fine and coarse material in the deposit while buoyancy reversal itself may mediate the transformation between dilute and highly concentrated suspension flows particularly in distal regions and thus lead to the formation of complex turbiditic beds in particular the generation of distal co genetic debrites may be expected similar transformations occur within dilute pyroclastic density currents where a mobile basal concentrated flow termed a surge derived pyroclastic flow develops through rapid sedimentation from the suspended load of the overlying surge the physical mechanisms involved in these processes are discussed leading to the proposal of some associated facies models these are compared with field data from the northern apennines with some striking similarities being noted as well as some differences on the basis of this discussion some directions are suggested for future experimental and modelling work on the topic

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

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

evidence for a neoarchean lip in the singhbhum craton eastern india implications to vaalbara supercontinent abstract we report eight new pb pb baddeleyite ages and paleomagnetic results on a series of hitherto unknown neoarchean nne ssw trending mafic dyke swarms intruding the paleoarchean basement rocks in the singhbhum craton eastern india being the most dominant dyke swarms in the region they occur over the entire singhbhum craton with an areal distribution extending to about 30 000 km 2 of the eight dyke samples analysed across the entire dyke swarm six were emplaced at 2762 4 2 0 ma weighted mean of 6 dyke ages two with similar strike directions yielded older and younger ages of 2800 2 0 7 ma and 2752 0 0 9 ma respectively the older 2800 2 0 7 ma dyke event appears to be coeval with several other magmatic events reported earlier from the singhbhum craton emplacement of dacite tuffs within the malaigiri basin on the southern margin of the craton the budhapal and rengali granite from the south western and southern parts of the craton along with the temperkola granite activity and associated acid volcanics in the western part of the craton and perhaps the mayurbhanj granite fine grained phase are also contemporaneous suggesting a fairly wide spread thermal event in the region at this time well defined craton wide magmatic events contemporaneous to the 2762 4 2 0 ma singhbhum dyke activity have been reported from the pilbara the younger 2752 0 0 9 ma age dyke event occurring in the singhbhum is also know from the eastern pilbara an older event at 2783 1 2 ma gaborone kanye plantation porphyry derdepoort modipe episode was identified in the kaapvaal craton comparison of paleomagnetic data obtained on the singhbhum neoarchean dyke swarms with the pilbara and kaapvaal data show all these continents were located at steep latitudes and could have been proximal to each other during this time if pilbara and kaapvaal formed supercraton vaalbara during the neoarchean time we propose singhbhum with similar archean geology could also have had its ancestry in the same supercraton

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

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

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

correcting the distortion of apparent resistivity pseudosection produced by 3d effect of the embankment geometry two dimensional electrical resistivity tomography data acquired on the crest of the embankment are distorted by the 3d effect of the embankment geometry reservoir water level and abutment the distortion affects seriously the final solution of the 2d inverse problem by comparing the apparent resistivity pseudosections from a 3d and 2d electrical resistivity model of the embankment the distortion degrees of the apparent resistivity pseudosections along the axis on the crest were estimated for the cases of reservoir and which does not contain water the obtained results indicate that the distortion degree acquired in the case of a reservoir that contains water was much less than that in the case of the reservoir that does not contain water in the case of reservoir that contains water the apparent resistivity pseudosections of the p p and ed ed arrays had the largest distortion degree and of d d w s and p d arrays had the smallest distortion degree in the case of the reservoir that does not contain water the apparent resistivity pseudosection of p p array had the smallest distortion among all arrays through modeling investigation a correction process to reduce the distortion of the apparent resistivity pseudosection was proposed the correction process was tested in the embankment model and two field works were carried out in the to lich river in hanoi and khuan cat embankment in lang son province vietnam it is possible to bring the distortion of the apparent resistivity pseudosection down to 2 8 13 9 depending on the type of electrode arrays and the type of reservoirs containing or does not contain water the distortion correction of the apparent resistivity pseudosection is strongly recommended before doing the 2d inverse interpretation

discussion of management of fluid mud in estuaries bays and lakes i present state of understanding on character and behavior by w h mcanally c friedrichs d hamilton e hayter p shrestha h rodriguez a sheremet and a teeter

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

detection of seepage paths in earth dams using self potential and electrical resistivity methods abstract earth and rockfill dams are designed to operate under steady state seepage anomalous seepage may be a threat to the integrity of the structure in spite of advances made in the fields of geotechnical engineering it is not possible to have 100 leak proof structure any excessive and unplanned seepage may lead to the failure of the dam especially in unconsolidated or fractured terrains geophysical methods play an important role in mapping seepage paths and monitoring the changes of the seepage with time enabling to plan technically and economically worthwhile remedial measures in the present paper utilisation of electrical methods for delineation of seepage zones at two of the four saddle dams of the som kamla amba project rajasthan state india which is founded on heterogeneous rock mass is discussed electrical resistivity method was used to delineate zones favourable for seepage whereas self potential sp method was used to delineate the seepage paths sp measurements have shown negative anomaly of the order of 10 20 mv in amplitude indicating low seepage coinciding with the seepage measurements made by the project authorities

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

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

electrical resistivity imaging and dye tracer test for the estimation of water leakage paths from reservoir of akdegirmen dam in afyonkarahisar turkey the seepage occurrence from the reservoir on the right bank of the akdegirmen dam located in afyonkarahisar province in the turkey has been investigated when the reservoir began to fill with water a large amount of water seepage occurred at the dam the seepage developed at the base of the spillway and the right downstream slope of the dam the various attempts have been made to reduce the seepage using grouting although the additional grouting operations was reduced the seepage at the base of the spillway there has not been a reduction in seepage at the water outlet location at the downstream slope electrical resistivity measurements along the eight lines with the dipole dipole array and dye tracer tests were performed in order to identify the seepage locations the interpretation of electrical resistivity data showed the distribution of strata and the seepage zone along the right downstream of the dam groundwater flow rates calculated from dye tests indicated that there is an excessive seepage south eastwardly on the downstream slope of the dam integrated interpretation of resistivity data and dye tests indicate that the seepage paths are in the direction from nw to e and se

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