gravity anomalies and the indian lithosphere review and analysis of existing gravity data abstract the upper part of the lithosphere has been actively involved in various exogenic and endogenic processes which have left their imprint on the gravity field on the indian peninsula and the himalaya analysis of the gravity field over the dharwar craton shows that the greenstone belts of this craton have been formed as a result of development of deep fractures in the earth s crust during archaean times precambrian mountain ranges such as the aravallies vindhyans satpura and eastern ghats are located peripheral to archaean cratons most of these mountain belts are characterized by gravity highs suggesting that the underlying crust is of higher than normal density these mountain ranges with the exception of the eastern ghats do not appear to be locally compensated regional compensation seems to prevail over all these areas eastern ghats ranges are also underlain by a crust of higher than normal density relative to the dharwar and bastar cratons and exist with a sharp contact with the cratons in the west isostatic compensation in the eastern ghats appears to have been achieved by thickening of the underlying crust the himalaya has attained a fairly high degree of isostatic compensation

proterozoic coastal sabkha halite pans an example from the pranhita godavari valley south india abstract extensive occurrences of pseudomorphs and casts of halite in association with wave formed shallow water structures and evidence of emergence in quartzarenites at the base of the middle proterozoic pakhal group c 1276 20 ma in south india point to the development of sabkha environments in arid to semi arid elimatic conditions periodic inundation of the sabkha during storm and subsequent desiccation led to displacive growth of the halite and its dissolution within the sediment just below the surface the brine pools within the sabkha seem to have developed in fault controlled topographic depressions formed at the embryonic stage of an intra continental rift ocean or graben system

stratigraphy and palaeogeography of the godavari supergroup in the south central pranhita godavari valley south india abstract the proterozoic succession of the pranhita godavari valley pg valley defined as the godavari supergroup occurs in two nw se trending belts flanking the margins of the valley the supergroup comprises several unconformity bound sequences of group status and exhibits strong regional variations in the distribution of different groups deposited in widely variable conditions ranging from fan alluvial setting to deep water slope base of slope and basinal environments the lithologic assemblages indicate that the basin experienced multiple rifting and tectonic environment varied from an unstable rift setting to a stable shelf regime the godavari supergroup with a complex history of stratigraphic evolution is still plagued by multiple problems of classification and correlation that have long been the major impediments to basin analysis in the present paper the attributes of the genetically linked stratal packages the unconformities separating them and their correlation in the south central part of the valley have been critically evaluated to address the problems of regional stratigraphy the godavari supergroup is bounded by two inter regional unconformities separating it from the underlying crystalline cratonic basement and from the overlying gondwana sedimentary rocks of late paleozoic mesozoic age the supergroup in turn is subdivided into four major sequences by three regional unconformities in the south central part of the valley comparison of stratigraphic profiles at different points indicates that the thickness of the unconformity bound sequences or of individual formations and also the number of formations increases from the central part of the valley towards the southeast the stratigraphic relationships collectively suggest that the basin deepened and opened in a southeasterly direction the basin in its southeastern part appears to have been much wider than the present day outcrop width and to have been continuous with other adjoining proterozoic basins the central part of the basin was a relatively stable and positive area compared to the southern part where the basin floor repeatedly moved across the base level to the order of several hundred meters the amplitude of movements indicates tectonically controlled subsidence and uplift

diapycnal mixing in western boundary currents in a previous study pelegri and csanady 1991 we found upward entrainment and two way exchange between the upper thermocline and surface layers of the gulf stream here we use isopycnic coordinates to analyze the mechanism of diapycnal shear induced mixing in western boundary currents a hydrographic section across the gulf stream off the mid atlantic bight is used for a case study it shows that the upper thermocline layers of the gulf stream are characterized by relatively small 16 m averaged gradient richardson numbers ri analysis of the jacobian j z p with z the depth and p the potential density total vorticity and potential vorticity fields shows that this region has low jacobian values associated with high values of potential vorticity as required theoretically for the case of dominant diapycnal mixing the density tendency wp dp dt is calculated from the vertical gradient of the reynolds density flux the latter parameterized as density eddy diffusivity divided by the jacobian we use munk and anderson s 1948 expression for the eddy diffusivity coefficient modified to conform to data of ueda et al 1981 maintaining a ri 3 2 dependence for large ri from this we obtain an explicit expression for wp in terms of the ri and j distributions the distributions of wp its diapycnal gradient wp p and the diapycnal velocity wd jwp are then calculated regions of high diapycnal convergence large negative wp p values coincide with the location of anomalously low jacobians in agreement with the idea that diapycnal mixing is the consequence of anomalies produced during frontogenesis in some phase of the meanders we suggest that this process taking place intermittently in space and time is responsible for two way exchange in western boundary currents

genesis of copper lead mineralization in the regionally zoned agnigundala sulfide belt cuddapah basin andhra pradesh india shallow marine sandstone shale carbonate sedimentary rocks of the paleoproterozoic northern cuddapah basin host copper nallakonda deposit copper lead dhukonda deposit and lead mineralization bandalamottu deposit which together constitute the agnigundala sulfide belt the cu sulfide mineralization in sandstone is both stratabound and disseminated and pb sulfide mineralization occurs as stratabound fracture filling veins and or replacement veins within dolomite systematic mineralogical and sulfur carbon and oxygen isotope studies of the three deposits indicate a common ore fluid that deposited copper at nallakonda copper lead at dhukonda and lead at bandalamottu under progressive cooling during migration through sediments the ore fluid was of low temperature 200 c and oxidized thermochemical reduction of basinal water sulfate produced sulfide for ore deposition it is envisaged that basal red bed and evaporite bearing rift related continental to shallow marine sediments might have acted as the source for the metals rift related faults developed during sedimentation in the basin might have punctured the ore fluid pool in the lower sedimentary succession and also acted as conduits for their upward migration the ore bearing horizons have participated in deformations during basin inversion without any recognizable remobilization

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

seismic imaging of the proterozoic cuddapah basin south india and regional geodynamics abstract cuddapah basin has been believed to be one of the largest intra cratonic proterozoic sedimentary basins of india situated in the eastern part of the dharwar craton of the south indian shield which is magmatically infested and contain thick column of sediments its overall sedimentary thickness as well as the nature of crustal evolution has remained enigmatic based on deep seismic sounding and other geological studies in the past it was perceived that this basin may contain as much as 10 12 km thick sediments the results of our present analysis derived up to a depth of 12 km reveals five layered upper crust associated with velocities i 4 50 km s ii 5 20 5 30 km s iii 5 50 5 80 km s iv 5 85 6 00 km s and v 6 40 km s out of which second and third layers correspond to upper and lower cuddapah sediments the results suggest the presence of only 4 0 km thick sediments in the deepest part of the basin below the nallamalai fold belt which has its implications in the developmental history of the basin a thermal driving force was invoked by earlier workers to account for estimated 10 12 km thick sediments however the present estimate of only 4 km basement depth in the cuddapah basin shows that the role of the thermal driving force may be marginal particularly in the deeper eastern cuddapah as isostatic subsidence due to sedimentary accumulation alone is enough to explain the basin depth further a basement sag of about 10 km would have logically needed lateral extension of the order of several hundreds of kilometers however as our present estimate of the sediment thickness gets reduced from earlier 10 km to only 4 km the size of the basin 44 500 km 2 would be in conformity with isostatic subsidence due to sedimentary accumulation hypothesis the structural features derived from present analysis like maximum depth observed near the thrust suture on the basin margin from where it decreases away from it its association of shallow marine sediments the arcuate shape of the basin along with its areal dimension resembles foreland basin between continent continent collisions

a two dimensional diabatic isopycnal model simulating the coastal upwelling front abstract a two dimensional diabatic isopycnal model is designed to study coastal upwelling the diabatic effect is represented by vertical mixing of the density field vertical eddy coefficients are determined by either a richardson number dependent formula or a diagnostic second order moment closur turbulence model some idealized coastal upwelling cases are studied the results show that in a frontal zone not only the density and velocity but also the mixing intensity develop strong spatial variability by using the turbulence model sharp boundaries exist between the fully turbulent and quiescent regions the thermal wind relation is greatly affected by turbulent mixing besides the effect of vertical diffusion of longshore momentum as suggested by one dimensional models vertical diffusion of density at a different rate horizontally has a strong effect on the thermal wind balance localized turbulent mixing will change the horizontal density gradient of its surrounding areas as a result strong upw

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

lithospheric mantle deformation beneath the indian cratons abstract the nature of deformation of the deep continental roots beneath the archean early proterozoic terrains opens the question whether these ancient terrains have had stable roots since the precambrian or whether recent plate motions have deformed them in view of this we make an attempt to study the thermal structure beneath the cratonic regions of the indian shield which vary in lithospheric thickness from 65 km in the singhbhum craton to 148 km in the archean dharwars the average depth of 104 km to the top of the underlying asthenosphere is consistent with other termination methods and is in fact less than half the 200 400 km depth found in other stable areas of the earth similarly the average reduced heat flow of about 35 mw m2 and moho temperature of about 550 c range 400 730 c for the indian cratons are also much higher than their counterparts elsewhere our study indicates a large scale deformation of the cratonic mantle lithosphere beneath the indian shield since the mesoproterozoic c

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

palaeomagnetism of mesoproterozoic limestone and shale successions of some purana basins in southern india the purana basins were long considered neoproterozoic basins until geochronology and palaeomagnestism showed parts of the chattisgarth and lower vindhyan basins to be a billion years older historically the successions in the chattisgarth basin are correlated with similar successions in the pranhita godavari and indravati basins in india differentiating between early late mesoproterozoic rocks and those spanning the mesoproterozoic neoproterozoic boundary is possible by comparing magnetic declination and inclination palaeomagnetism is therefore a very useful correlation tool here we report a new stenian aged palaeopole 50 1 n 67 4 e radius of cone of 95 confidence a 95 12 4 precision k 30 1 from carbonate and shale successions of the pranhita godavari and chattisgarth basins the c magnetization in addition an early diagenetic remagnetization component a was identified no primary or early diagenetic magnetizations were identified from the indravati basin here as well as in stratigraphically higher parts of the other two successions widespread younger magnetic overprints were identified b and b magnetic components our c palaeopole is constrained by palaeomagnetic stability field tests is different from known 1 4 ga and 1 0 ga indian palaeopoles but similar to a 1 19 ga palaeopole penganga group pranhita godavari basin deposition was probably initiated at around 1 2 ga a similar palaeomagnetic signature confirms its correlation with the raipur group chattisgarth basin of which the deposition spans most of the stenian period c 1 2 1 0 ga sedimentation in these groups began significantly later than c 1 4 and c 1 6 ga as suggested by ages reported from below the raipur and penganga groups respectively

the inner shelf response to wind driven upwelling and downwelling abstract a two dimensional numerical model is used to study the response to upwelling and downwelling favorable winds on a shelf with a strong pycnocline during upwelling or downwelling the pycnocline intersects the surface or bottom forming a front that moves offshore the characteristics of the front and of the inner shelf inshore of the front are quite different for upwelling and downwelling for a constant wind stress the upwelling front moves offshore at roughly a constant rate while the offshore displacement of the downwelling front scales as t because the thickness of the bottom layer increases as the front moves offshore the geostrophic alongshelf transport in the front is larger during downwelling than upwelling for the same wind stress magnitude because the geostrophic shear is near the bottom in downwelling as opposed to near the surface in upwelling during upwelling weak stratification is maintained over the inner shelf by the onshore flux of denser near bottom water this weak stratif

proterozoic felsic volcanism in the pranhita godavari valley india its implication on the origin of the basin abstract the proterozoic sedimentary rocks in the pranhita godavari valley pg valley south india were deposited in diverse environments ranging from continental shallow shelf to deep basin and occur as several unconformity bound sequences the sedimentary rocks also include felsic pyroclastics in different formations and at different stratigraphic levels repeated occurrences of intrabasinal pyroclastic rocks of similar composition suggest that the detritus might have been erupted from a common chamber which was activated at different times throughout the basin filling episode it is postulated that the mature proterozoic crust of indian craton acted as a heat lens resulting in extensive partial melting at the lower crustal levels localized stretching and rifting of the craton leading to the formation of the intracratonic basin the sedimentological attributes also support extensional setting and the hypothesis may be extended for several meso neoproterozoic cratonic basins in the indian shield the mechanism operated over the time span of 1 6 0 7 ga and overlaps with the age of development of an extensive granite rhyolite province in north america the process of accumulation of heat at the lower crustal levels generating a heat lens is typical of the stationary phase of supercontinental cycles and the origin of the cratonic basins the origin of the pg valley basin may be related to the fragmentation of a supercontinent of which the indian craton was a part

new constraints from zircon monazite and uraninite dating on the commencement of sedimentation in the cuddapah basin india the cuddapah basin in southern india consisting of the palnad srisailam kurnool and papaghni sub basins contains unmetamorphosed and undeformed sediments deposited during a long span of time in the proterozoic in the absence of robust age constraints there is considerable confusion regarding the relative timing of sedimentation in these sub basins in this study u pb isotopic dating of zircon and u th pb total dating of monazite and uraninite from the gritty quartzite that supposedly belongs to the formation banganapalle quartzite have been used to constrain the beginning of sedimentation in the palnad sub basin magmatic and detrital zircons recording an age of 2 53 ga indicate that the sediments were derived from the granitic basement or similar sources and were deposited after 2 53 ga hydrothermally altered zircons both in the basement and the cover provide concordant ages of 2 32 and 2 12 ga and date two major hydrothermal events thus the gritty quartzite must have been deposited sometime between 2 53 and 2 12 ga and represents the earliest sediments in the cuddapah basin monazite and uraninite give a wide spectrum of ages between 2 5 ga and 150 ma which indicates several pulses of hydrothermal activity over a considerable time span both in the basement granite and the overlying quartzite the new age constraints suggest that the gritty quartzite may be stratigraphically equivalent to the gulcheru quartzite that is the oldest unit in the cuddapah basin and that a sedimentary erosional hiatus exists above it

proterozoic rifting in the pranhita godavari valley implication on india antarctica linkage abstract the pranhita godavari pg valley a major lineament within the south indian cratonic province that preserves sediment dominated deposits spanning from mesoproterozoic to mesozoic appears to be a key element in supercontinent reconstruction the sedimentary basins of the valley include a thick succession of early mesoproterozoic to late neoproterozoic rocks the godavari supergroup which is unconformably overlain by the late palaeozoic mesozoic gondwana sequence the godavari supergroup is internally punctuated by several regional and interregional unconformities into a number of unconformity bound sequences having group level and subgroup level status the lithostratigraphic attributes of the succession indicate multiple events of fault controlled sedimentation marked by transgression and regression as well as uneven rates of uplift and subsidence of the basin floor in an extensional tectonic regime the amplitude of translation of the unconformity surfaces across the base level attests to collective role of tectonic movement and sea level changes in building the stratigraphic framework of the valley the stratigraphic framework and depositional systems such as fan and fan deltas together with local outburst of felsic volcanism further indicate repeated rifting of the craton geochronologic data indicate that the rift basin started to open in early mesoproterozoic concomitantly with the breakup of the mesoproterozoic supercontinent during which the india and east gondwana fragments were separated the spatial variation in the declivity of the unconformity surfaces and the trend of thickness variation of the unconformity bound sequences point that the basin deepened and opened towards southeast to join an ocean that developed between the south indian craton and east antarctica the contractional deformation structures preserved in several lithounits were produced under ne sw directed regional compression during late neoproterozoic basin inversion

the purana basins of southern cratonic province of india a case for mesoproterozoic fossil rifts abstract since its cratonization in the palaeoproterozoic southern peninsular india witnessed the development of a number of large intracratonic sedimentary basins traditionally referred to as purana basins spanning in age from late palaeoproterozoic through neoproterozoic the localization of these intracratonic basins namely pranhita godavari pg chattisgarh and cuddapah basins is apparently controlled by pre existing sutures and or weak zones the pg basin and the cuddapah basin host unconformity bound thick sediment dominated successions attesting to several cycles of fluvial shallow marine to shelf slope basin sedimentation deposition was punctuated by block uplifts resulting in local hiatuses and or volcanic upheavals leading to intercalation of thin but persistent basaltic flows and acid tuffs and ignimbrites basin margin deep faults apparently played a role in the facies distribution in these basins based on these features we propose that these basins initiated as continental rifts which however never opened up into a full fledged ocean basin but links with open seaway are evident from frequent occurrence of deposits representing tidal and storm influence particularly in upper part of the chattisgarh succession spatial distribution of facies and sediment thickness in the cuddapah and pg basins suggest that an open seaway existed to the east of the south indian cratonic province during the mesoproterozoic while similar criteria point to the existence of an open seaway north of the chattisgarh basin development history including nature of inversion suggest that the southern cratonic province of india existed as a single large continental mass since the mesoproterozoic in spite of episodes of supercontinent build up and fragmentation involving india and east gondwana during the proterozoic

source and seal coupling mechanism for shale gas enrichment in upper ordovician wufeng formation lower silurian longmaxi formation in sichuan basin and its periphery abstract in recent years theoretical geologic research has made important progress in shale gas exploration and development and new discoveries such as the jiaoshiba weiyuan and changning shale gas fields provide geological cases to define key controls on shale gas accumulation in wufeng formation longmaxi formation marine shale strata a mechanism coupling source and seal development for shale gas enrichment is proposed in this study based on detailed research results of isochronous stratigraphic distribution of source rock and seals and source seal dynamic evolution great thickness wide distribution and high total organic carbon content toc of sources are key controls on the shale gas content and storage capacity in organic matter hosted pores micro cracks and bedding fissures is intensively developed the wufeng formation and the lower part of the first member of the longmaxi formation wf2 lm4 graptolitic zone are favorable sources that feature a slow deposition rate well graptolitic zone favorable organic organism type and high toc the organic matter type is benefit to the development of organic matter pores because the planktonic algae tends to generate and expulse large amounts of hydrocarbon and form many organic matter pores both high biogenic quartz and high toc ensure development of abundant organic matter hosted pores and result in a three dimensional network of interconnected organic matter pores that allows shale gas storage and flow the seal can be divided into direct and indirect seals the direct seal refers to the middle and upper parts of the first member of the longmaxi formation lm5 and higher graptolitic zone that are characterized by low toc and low porosity the indirect seal refers to the regionally distributed lower middle triassic gypsum layer s and mudstone that maintain regional geopressure systems the shale gas fields of jiaoshiba fushun yongchuan and changning have high geopressure coefficient factors 1 5 2 0 and 1 5 respectively in the absence of the lower middle triassic gypsum layer s and mudstone regional seals the high pressure system was destroyed and resulted in low normal geopressure shale gas reservoirs for instance the pengshui and zhaotong wells the static match and dynamic match of source and seal constrain the location of shale gas reservoirs and the degree of shale gas enrichment the model of a mechanism coupling source and seal for shale gas enrichment provides new ideas and methods for the assessment of shale gas this model promotes the evaluation of shale gas from the static parameters approach to the source and seal dynamic approach in the sichuan basin and its peripheral areas the promising areas for shale gas accumulation are those with favorable sources in the wf2 lm4 graptolitic zone and the presence of the lower middle triassic gypsum layer s and mudstone regional seal

proterozoic glauconitic peloids from south india their origin and significance glauconitic minerals as peloids are widespread in the arkosic and subarkosic sandstones of the three proterozoic units of the pranhita godavari valley south india these minerals grew at the expense of detrital feldspars on a scale so far unknown and the process offers a viable alternative model for origin of the glauconitic peloids particularly in the proterozoic and some unfossiliferous phanerozoic rocks as well conversion in situ is testified inter alia by the presence of feldspar relics within the peloids replacement of the peloids by all other authigenic phases and evidence of their compaction and high precement porosity of the host sandstones point to preburial authigenesis of these minerals near the depositional surface glauconitization was entirely inorganic and the morphology of the peloids is dictated by that of the precursor grains occurrence in rapidly deposited sediments under semiarid to arid conditions with extensive development of current and wave features suggests formation under conditions of warm open circulation with high sediment influx and therefore modifies existing ideas about the physical constraints on glauconitization

the near surface dynamics of coastal upwelling abstract an attempt is made to examine some observational and theoretical aspects of upper ocean dynamics in regions of strong coastal upwelling upper ocean is roughly defined as about the upper 10 30 m of the water column for most systems first the basic surface ekman and mixed layers are discussed including some of the modifications due to upwelling next coastal upwelling fronts and their associated circulation are treated finally areas of strongly three dimensional upwelling are classified and discussed horizontal advection of heat and momentum appear to be generally important for the near surface dynamics of coastal upwelling and these phenomena make realistic theoretical treatments especially difficult

sediment distribution and transport across the continental shelf and slope under idealized wind forcing abstract resuspension transport and deposition of sediments over the continental shelf and slope are complex processes and there is still a need to understand the underlying spatial and temporal dynamical scales as a step towards this goal a two dimensional slice model zero gradients in the alongshore direction based on the primitive flow equations and a range of sediment classes has been developed the circulation is forced from rest by upwelling or downwelling winds which are spatially uniform results are presented for a range of wind speeds and sediment settling speeds upwelling flows carry fine sediments low settling speeds far offshore within the surface ekman layer and significant deposition eventually occurs beyond the shelf break however coarser sediments quickly settle out of the deeper onshore component of the circulation which can lead to accumulation of bottom sediments within the coastal zone downwelling flows are more effective at transporting coarse sediments off the shelf however strong vertical mixing at the shelf break ensures that some material is also carried into the surface ekman layer and returned onshore the concentrations and settling fluxes of coarse sediments decrease offshore and increase with depth under both upwelling and downwelling conditions consistent with trends observed in sediment trap data however finer sediments decrease with depth upwelling or reach a maximum around the depth of the shelf break downwelling it is shown that under uniform wind conditions suspended sediment concentrations and settling fluxes decay offshore over a length scale of order s f ws where s is the wind stress the water density f the coriolis parameter and ws is the sediment settling velocity this scaling applies to both upwelling and downwelling conditions provided offshore transport is dominated by wind driven advection rather than horizontal diffusion

structural trends in the cuddapah basin from deep seismic soundings dss and their tectonic implications abstract structural trends in the upper proterozoic cuddapah basin at the basement level and at the moho level have been discussed based on deep seismic sounding dss studies results of dss studies along the alampur koniki profile profile 2 of fig 1 crossing the northern part of the cuddapah basin have been discussed in detail these results combined with the results of the kavali paranpalle section of the kavali udipi dss profile profile 1 of fig 1 kaila et al 1979 crossing the basin on its southern flank along with geological data and earthquake epicentral locations are used to explain the structural trends of the area it has been shown that the cuddapah basin was first created in its western part by downfaulting of the crustal block between faults 7 and 14 towards the west and fault 6 in the east fig 1 subsequently the eastern part was downfaulted against fault 6 before the commencement of upper cuddapah sedimentation further downfaulting towards the north along fault 5 created the srisailam block minor scale downfaulting between faults 7 and 13 in the west and fault 6 in the east and fault 8 in the north gave rise to the kurnool sub basin at a later stage similar downfaulting east of fault 9 and north of fault 5 gave rise to the palnad sub basin both these sub basins received kurnool sediments after the close of kurnool sedimentation the blocks between faults 4 and 6 along profile ii and between 11 and 6 along profile i were uplifted at the basement level thus giving rise to the nallamalai hills and iswarakuppam dome fig 1 the low angle thrust fault 3 on the eastern margin of the cuddapah basin might be a post cuddapah phenomenon the low angle thrust fault 2 probably occurred in the post dharwar period faults 1 17 and 10 near the east coast of india seem to be comparatively younger probably of mesozoic time along which the coastal block is downfaulted giving rise to the sedimentary basins

the dharwar craton and the assembly of peninsular india peninsular india can be separated into five discrete crustal areas the bhandara singhbhum and aravalli bundelkhand cratons the eastern ghats and a block in southern india containing the dharwar craton and adjoining granulite terrain these areas are separated by four major joins eastern ghats front godavari rift mahanadi rift sukinda thrust and narmada son lineament and associated thrusts all joins except the godavari rift are former orogenic belts where thrusts juxtapose rocks of different metamorphic grade these thrusts and the absence of clear correlation of suites among different cratons suggest that the indian shield formed by accretion of separate continental fragments epicontinental late archean early pro terozoic sediments throughout india however may indicate that the joins are intracontinental formed within a coherent block the term dravidian shield is used for the southernmost of the five crustal blocks including all of india south of the deccan basalts and godavari rift

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

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