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

constrained 3d modeling of the mesoproterozoic benagerie volcanics australia abstract the benagerie volcanics form part of a hotspot track that affected large sections of eastern australia during the mesoproterozoic understanding the location and controls on eruption centres of the benagerie volcanics and coeval plutons is difficult because they do not outcrop and are known only from limited drillhole data we have applied various combinations of forward and inversion modeling of magnetic and gravity to well constrained petrophysics and drillholes areas to characterize the 3d geometry and extent of the volcanic province and its crustal architecture thereby adding to a better understanding of the emplacement mechanisms involved we interpret the sw limit of the benagerie shear zone corridor to be a major terrane boundary separating relatively magnetic crust to the sw from crust with low magnetic susceptibility to the ne 2d and 3d models show a pronounced thickening of felsic material coincident with the shear zone that may be interpreted as a plutonic root thereby corroborating interpretations that this shear zone acted as a structural conduit for the ascent and emplacement of magma

a retreating fan delta system in the neoproterozoic chattisgarh rift basin central india major controls on its evolution a thick wedge of immature siliciclastics characterizes the basal part of the basin fill succession in the eastern part of the neoproterozoic chattisgarh basin it comprises a mosaic of mass flow deposited conglomerate and pebbly sandstone coarse grained sandy braided stream deposits wave lag pebble sheets high energy wave dominated foreshore and upper shoreface facies and wave and tide dominated lower shoreface facies the succession is characterized by strong lateral and vertical facies variation the facies associations and stacking pattern point to the development of an alluvial fan to fan delta complex with outbuilding of delta lobes onto a high energy shallow marine shelf via a high gradient narrow delta plain the delta front deposits of coarse grained sand interfinger and grade into prodelta mud in the seaward direction the dominance of coarse grained sandy detritus with a high content of fresh feldspar grains points to mechanical weathering of granites and gneisses of the cratonic basement and a semiarid climate the sediment caliber and the climate exerted a major control on the facies and on processes of sediment transfer from the fan to the shelf a critical balance between progradation aggradation and retrogradation controlled the evolution of delta successions within an overall transgressive regime related to the extension of a cratonic rift basin repeated fault controlled uplift of the source followed by subsidence and transgression generated multiple fining upward cycles and a retreating fan delta system the marked variations in thickness of the delta succession and the stacking pattern in different measured profiles reflect the overriding tectonic controls on delta evolution the accumulated fault displacement in active sectors created higher accommodation and thicker delta sequences intermittent uplift of fault blocks exposed fresh bedrock to mechanical weathering generated a large amount of detritus and resulted in forced regressions repeatedly disrupting the fining upward pattern the controls of source rock lithology or climate were of secondary importance to tectonic effects retreating fan deltas are rarely reported and may be a stratigraphic response of marine connected rift basins at the early stage of extension the delta stratigraphy is analogous to the submarine fan stratigraphy in the case where basin shales act as hydrocarbon sources the fan deltas are potential hydrocarbon reservoirs the coarse grained lobes can be excellent reservoirs with the enclosing prodelta muds acting as seals to vertical migration of hydrocarbon the coarse grained deposits of the delta plain and proximal delta front occurring as laterally coalesced large sand bodies blanketed by transgressive prodelta mud might also form good reservoirs

aeromagnetic patterns of half graben and basin inversion implications for sediment hosted massive sulfide pb zn ag exploration the inverted extensional basins of the palaeoproterozoic north australian craton are amongst the most metallogenically endowed on earth for sediment hosted massive sulphide shms pb zn ag deposits faults that evolved during the evolution of these basins are an important exploration vector as they have behaved as conduits for mineralizing fluids controlled facies architecture and impacted on hydrothermal convection cells we attempt to map out ancient normal faults using integrated structural and aeromagnetic analysis to identify faults that are either buried beneath younger cover or have been inverted during later orogenic events this technique can be used for targeting potential conduits for mineralising fluids during shms pb zn ag exploration as well as a tool to map the architecture of extensional basins we have constructed simplified cross sections of half graben and inverted half graben and have forward modelled their magnetic response the aeromagnetic signature of a pre inverted half graben shows that the tilt block is characterised by a shallow magnetic gradient related to the shallowing of the magnetic marker beneath the half graben normal offset of the marker unit across a normal fault is characterised by a steeper magnetic gradient as the depth to the marker horizon increases simplified cross sections of isolated growth anticlines and the hanging wall buttressing show that the general shape of the magnetic profiles are maintained until the half graben has been completely inverted and the magnetic marker horizon displays reverse offset along the reactivated normal fault

proterozoic accretionary tectonics in the east kimberley region australia abstract the east kimberley region contains well preserved tectonic structure dating back to the earth s most significant stage of continental growth the assembly of the nuna supercontinent an integrated geological geophysical investigation of this region has been conducted and reveals insight into its tectonic evolution including potential influence of significant crustal scale structures in the development of regional architecture the emplacement of magma and the relationship of these structures to large scale deformation some newly interpreted features include a north trending structure and three north west trending structures that segment the north east trending orogen the central segment of the orogen is a zone of higher metamorphic grade and is host to a distinct gravity high this gravity high can be explained by excess mass in the mid crust this anomaly is consistent with either a large mafic ultramafic intrusion or a high density crustal fragment possible tectonic models to explain the geophysical and metamorphic anomalies involve in the latter case the accretion of a crustal fragment to the kimberley craton prior to the 1865 1850 ma hooper orogeny or in the former case intrusion of voluminous mafic magmas into the middle crust whether by igneous or structural means we consider the development of this anomalous region to be a result of along strike variations in subduction dynamics these were perhaps driven by variations in slab geometry accommodated by the orogen normal structures we identify the orogen normal structures are interpreted to be crustal scale faults along which significant vertical displacement occurred when a crustal fragment collided with kimberley craton and exhumed high grade metamorphic rocks to the surface

iridium enrichment in volcanic dust from blue ice fields antarctica and possible relevance to the k t boundary event abstract blue ice fields in antarctica well known as stranding zones of antarctic meteorites contain ice that is several tens to hundreds of thousand years old which records numerous events that have taken place since its formation among the most important structures on the ice fields are dust bands which are mostly of volcanic origin and consist of small volcanic glass shards and lithic fragments petrographic and chemical studies of a number of dust bands during earlier investigations have shown that significant ash layers are deposited at distances of up to several thousand kilometers from the source volcanoes samples of dust layers taken in the lewis cliff beardmore glacier area in antarctica analyzed in the course of this work for major and trace elements were identified as consisting of volcanic ash probably originating from the pleiades melbourne volcanic province northern victoria land some of these dust samples were found to contain iridium in concentrations of up to 7 5 ppb a positive correlation between ir and se as well as enrichments in as sb and other volcanogenic elements has been observed the dust samples investigated here have very small grain size consistent with the distance from the source volcanoes the small grain size of the dust suggests that the ir enrichment is a surface effect and was probably caused by condensation from a vapor phase this is the first time that significant ir enrichments have been found in volcanic dust which demonstrates that ir and possibly also other platinum group metals may be present in some volcanic ash deposits although this has been doubted by the proponents of the pure impact theory for the k t boundary event the results of this study suggest that the ir in the k t boundary clays is not necessarily of cosmic origin but alternatively may have originated from mantle reservoirs that were tapped during extensive volcanic eruptions which may been triggered by impact events

evidence for a battle mountain eureka crustal fault zone north central nevada and its relation to neoproterozoic early paleozoic continental breakup 1 combined evidence from gravity radiogenic isotope and magnetotelluric mt data indicates a crustal fault zone that coincides with the northwest trending battle mountain eureka bme mineral trend in north central nevada usa the bme crustal fault zone likely originated during neoproterozoic early paleozoic rifting of the continent and had a large influence on subsequent tectonic events such as emplacement of allochthons and episodic deformation magmatism and mineralization throughout the phanerozoic mt models show the fault zone is about 10 km wide 130 km long and extends from 1 to 5 km below the surface to deep crustal levels isotope data and gravity models imply the fault zone separates crust of fundamentally different character geophysical evidence for such a long lived structure likely inherited from continental breakup defies conventional wisdom that structures this old have been destroyed by cenozoic extensional processes moreover the coincidence with the alignment of mineral deposits supports the assertion by many economic geologists that these alignments are indicators of buried regional structures

alluvial fan to storm dominated shelf transition in the mesoproterozoic singhora group chattisgarh supergroup central india abstract mesoproterozoic siliciclastic strata at the basal part of the singhora group central india provide an example of a pre vegetation alluvial fan and braid delta depositional system detailed process based facies and paleoenvironmental analysis have led to the identification of 15 facies types grouped under four different facies associations which record paleoenvironmental settings ranging between continental alluvial fan and distal marine shelf two formations investigated are the rehtikhol formation formed in a conglomeratic or coarse arenaceous alluvial fan braid plain and delta setting and the overlying saraipalli formation which preserved the sedimentation record of a storm infested inner to distal shelf setting the preponderance of granular and sandy sediment gravity flow products with subordinate rock fall deposits within the alluvial fan system together with a pervasive west northwesterly paleocurrent is suggestive of a gently sloping beveled source area in the east southeast distal to the inferred fan a braid plain system developed with the decrease in the depositional slope streams within the braid plain had widths up to several hundred meters the braid plain system at the margin of the marine basin developed a delta with the deposition of wave reworked fluvial dominated sediments the crest trends of wave generated bedforms within the inferred delta sediments depict the northeast southwest shoreline interpreted for the singhora sea the prodeltaic basinal part of the singhora braid delta was storm infested the inner shelf acted as a zone of throughput with high velocity storm flows eroding deep narrow scours gutter casts and is interpreted as a zone of bypass operation of geostrophic currents on the singhora shelf has been inferred from the directional relationship of gutters with the inferred orientation of the shoreline a proximal distal relationship has been established within the shelf products based on the relative dominance of erosional and depositional features the singhora alluvial fan and braid delta facies are arranged in a fining upward sequence denudation of the source area increasing bathymetry with relative rise in sea level or a combination of both is inferred both extrabasinal and intrabasinal forcings possibly contributed to the deepening upward trend

basal tuffs and contemporaneity of the chattisgarh and khariar basins based on new dates and geochemistry abstracttime bracketing of thousands of meters thick unmetamorphosed fossil free sedimentary successions is a long standing challenge in indian proterozoic stratigraphy limited geochronologic ages from either the basal or the upper part of the successions prevent workers from constraining the precise age interval for individual basin fill leaving aside the issue of correlatability between different basin sequences this article deals with silicic tuff units from the basal part of two areally separated proterozoic sedimentary successions of central india the singhora group of the chattisgarh supergroup and the khariar group the singhora tuff is enriched in large ion lithophile rb ba th etc elements and light rare earth elements and in a discrimination diagram falls within the volcanic arc granite field u th pb electron probe microanalyzer geochronology of monazite and zircon grains from the singhora tuff revealed several age data clusters namely 2500 2100 1800 1500 and 1000 ma in c

multi scale analysis of proterozoic shear zones an integrated structural and geophysical study abstract structural mapping of poorly exposed shear zone outcrops is integrated with the analysis of aeromagnetic and bouguer gravity data to develop a multi scale kinematic and relative overprinting chronology for the palaeoproterozoic tallacootra shear zone australia d 2 mylonitic fabrics at outcrop record kimban aged ca 1730 1690 ma n s shortening and correlate with sz 1 movements overprinting d 3 sinistral shear zones record the partitioning of near ideal simple shear and initiated riedel to regional scale sz 2 strike slip on the tallacootra shear zone sz 2 previously undocumented ne sw extension led to the emplacement of aplite dykes into the shear zone and can be correlated to the ca 1595 1575 ma hiltaba magmatic event d 4 dextral transpression during the ca 1470 1450 ma coorabie orogeny reactivated the tallacootra shear zone sz 2 r4 exhuming lower crust of the northwestern fowler domain within a positive flower structure this latest shear zone movement is related to a system of west dipping shear zones that penetrate the crust and sole into a lithospheric detachment indicating wholesale crustal shortening these methods demonstrate the value of integrating multi scale structural analyses for the study of shear zones with limited exposure

a reassessment of the archean mesoproterozoic tectonic development of the southeastern chhattisgarh basin central india through detailed aeromagnetic analysis abstract we constrained the geological framework over polydeformed paleoproterozoic sonakhan greenstone belt and addressed the tectonic evolution of singhora basin in the fringes of bastar craton central india by utilizing aeromagnetic data interpretation 2 5d forward modelling and 3d magnetic susceptibility inversions the sonakhan greenstone belt exposes volcano sedimentary sequences of the sonakhan group within nnw sse to nw se trending linear belts surrounded by granite gneisses which are unconformably overlain by sedimentary rocks of chhattisgarh basin the orientations of aeromagnetic anomalies are coincident with geological trends and appear to correlate with lithology and geologic structure regional magnetic anomalies and lineaments reveal both nnw sse and ne sw trends prominent e w trending linear high amplitude magnetic anomalies are interpreted as the trans chhattisgarh aeromagnetic lineament tcal nw se trending aeromagnetic signatures related to sonakhan greenstone belt extends below the singhora sedimentary rocks and forms the basement in the west the analysis suggests that tcal is a block fault with northern block down thrown and affected the basement rocks comprising the sonakhan greenstone belt and samblapur granitoids the episode of faulting represented by the tcal is pre singhora sedimentation and played a vital role in basin evolution the basement configuration image generated by estimates of depth to magnetic basement suggests a complex pattern of nne ssw to ne sw trending depressions separated by a linear n s trending basement ridge it is inferred from the 3d magnetic susceptibility inversion that the thickness of sediments is more towards the eastern basin margin and the n s ridge is a manifestation of post sedimentary faulting results of 2 5d modelling of a wnw ese profile across the singhora basin combined with results from 3d inversion suggest suggests the basin subsidence was controlled by ne sw trending regional faults in an active system the basin geometry evolved by e w block faulting overprinted by ne sw trending pre to syn depositional normal faults generating ne sw depression which are affected by n s trend post sedimentary faulting though the present work relates the basin evolution with the initiation of rift basin it warrants further work to establish the deformation within the basin pertaining to the proximal thrust and uplift along the craton fringe

architecture of proterozoic shear zones in the christie domain western gawler craton australia geophysical appraisal of a poorly exposed orogenic terrane abstract large scale mesoproterozoic crustal shear zones are partially exposed from beneath cover sequences in the christie domain of the northwestern gawler craton southern australia these structures are associated with gravity and magnetic anomalies that allow them to be mapped under cover and their three dimensional geometry and kinematics to be evaluated gravity and magnetic forward modelling indicate that these shear zones form an imbricate oblique thrust stack with combined top to the southeast left lateral transport the longest shear zones in the stack penetrate the crust to at least 15 km depth and dip to the northwest at 70 their inferred sense of motion are consistent with kinematic indicators from sparse outcrops from northwest to southeast the stack includes crustal slices bound by the karari fault zone tallacootra and blowout shear zones colona and coorabie fault zones and the muckanippie shear zone these structures separate discrete tectonometamorphic packages within the previously undifferentiated christie gneiss of the archean mulgathing complex and imply several generations of transport of material from the lower and middle crust three dimensional inversion of gravity data indicates that the muckanippie shear zone a shallowly rooted second order splay of the coorabie fault zone has an antithetic dip to the southeast and is part of a positive flower structure cross cutting relationships coupled with recent reconnaissance geochronology suggest that the western gawler craton part of the mawson continent was under a long lasting oblique slip deformational regime after ca 1590 ma this tectonic reworking is correlated with episodic pervasive metamorphism and deformation recorded elsewhere in the gawler craton between ca 1550 and 1450 coorabie orogeny pointing to a complex history of stabilization in proterozoic rodinia the tallacootra colona and coorabie structures are all cut at a high angle to their strikes by mesozoic rift faults of the southern rift system and may form piercing points in reconstructions of gondwana and earlier rodinia configurations

the discovery and initial characterization of allan hills 81005 the first lunar meteorite antarctic meteorite alha81005 discovered in the allan hills region of victoria land is a polymict anorthositic breccia which differs from other meteorites in mineralogical and chemical composition but is strikingly similar to lunar highlands soil breccias the petrologic character and several independent lines of evidence identify alha81005 as a meteorite from the moon two small clasts of probable mare basalt occur among the highlands lithologies in thin section 81005 22 this lunar specimen which shows relatively minor shock effects has generated new ideas on the types of planetary samples we may find on the earth and has added fresh excitement to the antarctic meteorite program

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

late paleo mesoproterozoic plate margin deformation in the southern gawler craton insights from structural and aeromagnetic analysis abstract the integration of structural analysis of outcrop and aeromagnetic interpretation has revealed a complex tectonic evolution for the southern gawler craton that reflects the regional tectonic signal during the late paleo to early mesoproterozoic results suggest that exposures at yarlbrinda hill comprise the margin of a highly deformed st peter suite pluton emplaced within the southwestern gawler craton at ca 1611 ma d 1 at outcrop records east to northeast directed ductile thrusting regionally this deformation overprints north south trending dextral yarlbrinda shear zone fabrics within ca 1622 ma st peter suite granite and ca 1690 1670 ma tunkillia suite granite progressive east to northeast directed thrust movements led to exhumation of the deformed ca 1611 ma granite d 2 deformation is recorded by the brittle reactivation of first generation mylonitic fabrics accompanied by cataclasis alteration and pseudotachylite development d 3 records a switch to northwest southeast shortening which led to the folding and tear faulting of the d 1 2 shear zone a switch to extension and subsequent rotations of the principle stress axes led to hiltaba suite granite emplacement and contemporaneous faulting under east west extension during d 4 and west northwest east southeast extension during d 5 deformation of ca 1622 ma st peter suite granite is consistent with movement on the yarlbrinda shear zone and requires the st peter suite to have been emplaced into or adjacent to the ca 1690 1670 ma tunkillia suite prior to shear zone activity and on the overriding plate during subduction d 1 d 3 deformation is constrained by the emplacement of ca 1580 ma hiltaba suite granite and correlates with the wartakan orogeny in the southeastern gawler craton and the olarian orogeny in the curnamona province a 52 disparity between the shortening directions in these respective areas suggests different degrees of mesoproterozoic rotation which likely aided the formation of an intervening basin province the remnants of which are presently preserved in the mount painter inlier the record of convergent deformation is geochronologically constrained to a 30 myr period and places this region of the central gawler craton near a late paleoproterozoic convergent plate margin prior to a period of transient extension beginning at ca 1580 ma the continental scale signal of tectonic events can be recognized at the outcrop scale highlighting the importance of detailed outcrop studies in sparsely exposed areas

evolution of the mount woods inlier northern gawler craton southern australia an integrated structural and aeromagnetic analysis structural mapping integrated with interpretation and forward modelling of aeromagnetic data form complimentary and powerful tools for regional structural analysis because both techniques focus on architecture and overprinting relationships this approach is used to constrain the geometry and evolution of the sparsely exposed mount woods inlier in the northern gawler craton the mount woods inlier records a history of poly phase deformation high temperature metamorphism and syn and post orogenic magmatism between ca 1736 and 1584 ma the earliest deformation involved isoclinal folding and the development of bedding parallel and axial planar gneissic foliation s1 this was accompanied by high temperature upper amphibolite to granulite facies metamorphism at ca 1736 ma during subsequent north south shortening d2 open to isoclinal south southeast oriented f2 folds developed as the palaeoproterozoic successions of the inlier were thrust over the archaean nuclei of the gawler craton the syn d2 engenina adamellite was emplaced at ca 1692 ma the post d2 history involved shear zone development and localised folding exhumation of metamorphic rocks and deposition of clastic sediments prior to the emplacement of the ca 1584 ma granite balta suite the mount woods inlier is interpreted as the northern continuation of the kimban orogen

multi scale integrated structural and aeromagnetic analysis to guide tectonic models an example from the eastern musgrave province central australia abstract in many polydeformed precambrian provinces the understanding of their tectonic history is limited by insufficient exposure which leads to difficulty in developing links between local and regional architecture and results in poorly constrained models of their regional scale architecture high resolution aeromagnetic data allows interpretation and modelling at a scale comparable to structural mapping and by integrating these methods these links can be developed with high confidence as an example we integrate structural mapping aeromagnetic data interpretation and 3d magnetic inversions in a multi scale structural analysis of the polydeformed eastern musgrave province in central australia deformation during the ca 1200 ma musgravian orogeny is characterised by an originally northeast trending structural grain defined by shear zones and tight to isoclinal folds at all scales 3d magnetic inversion models of syn to post musgravian granites indicate that this structural grain is predominantly west dipping this architecture suggests that a northeast oriented fold and thrust belt developed as a result of northwest southeast compression in central australia during the musgravian orogeny the next deformation event is characterised by an array of originally east southeast trending shear zones that truncate and offset the musgravian structural grain with apparent dextral displacements of up to 1 km these shear zones are commonly co located with mafic and granitic dykes suggesting a dilational origin and they are interpreted to have initiated under northeast southwest extension during the ca 1080 ma giles event the architecture of these two mesoproterozoic events was later extensively overprinted by two deformation events during the pan african aged ca 550 ma petermann orogeny the first is characterised by the widespread reactivation of mesoproterozoic structures resulting in a network of shear zones of variable orientation and the second is characterised by the development of crustal scale transpressional shear zones motion on which has caused the rotation of lithospheric blocks and the reorientation of prior structural trends by up to 90 collectively the architecture of these two events suggests broadly north south crustal shortening in central australia as an intraplate response to gondwana assembly this example demonstrates that the integration of structural geology with aeromagnetic interpretation and modelling can be used to develop high confidence links between local and regional structures these links permit the derivation of better constrained models of major tectonic events particularly in regions where outcrop is poor and the structural architecture is complex

magnetic fabric and emplacement of the post collisional pomovaara granite complex in northern fennoscandia abstract the proterozoic pomovaara granite complex in northern finland comprises three separate highly magnetic granite stocks they are discordant apparently unfoliated and according to isotope data a significant archaean component characterizes the source of these granites the three stocks are aligned in an array parallel to major trans crustal faults as interpreted from both aeromagnetic and gravity data their younger age of 1 8 ga compared to the main tectonic events at 1 9 ga in northern fennoscandia indicates their post collisional nature with respect to these events the anisotropy of magnetic susceptibility ams was studied together with magnetic gravity and geological data in order to assess the emplacement mechanisms of the pomovaara granite complex and the possible tectonic control of fault systems on the ascent and emplacement of granitic magma the orientation of magnetic fabrics within the granite stocks indicates that the direction of the original magma upwelling was from the sw parallel to the major fault zones that controlled at the crustal scale the ascent of granite magmas the predominant nw se orientations of the minimum magnetic axes of the magnetic ellipsoid and the elongate shapes of the stocks indicate compression normal to the deep fault trend during the crystallization of the granite magma

depositional history of the chhattisgarh basin central india constraints from new shrimp zircon ages a reply abstract the indian shield includes the singhbhum bastar and east and west dharwar cratons proterozoic sedimentary basins formed on these cratons have preserved rocks with a range of degrees of metamorphism and deformation in the chhattisgarh basin within the bastar craton the ca 2200 2500 m thick chhattisgarh supergroup has been preserved in nearly pristine condition previous work has shown that the sukhda tuff located about 2200 m from the base of the section was formed ca 1007 ma new u pb shrimp age determinations show that the singhora tuff located about 100 m above the base of the basin is not older than ma thus most of the chhattisgarh supergroup was deposited between 1400 and 1000 ma age data for detrital zircons from sandstones show that regardless of their stratigraphic position there is a unimodal age peak near 2500 ma the typical age of adjacent granitic and rhyolitic basement rocks indicating that these constituted the principal provenance of the sediments in the chhattisg

comparing 1800 1600 ma accretionary and basin processes in australia and laurentia possible geographic connections in columbia abstract we focus on potential pinning points on the southern and eastern margins of australia and the southern and western margins of laurentia and interpret a convergent plate boundary along the southern margin of the proto australian continent during the palaeo to mesoproterozoic 1800 1600 ma specific geological events within the southern australian margin can be correlated with events preserved along the medicine bow yavapai mazatzal belt in southwestern laurentia these belts were characterised by southward continental growth with varying degrees of crustal reworking and accretion of juvenile material in australia crustal reworking appears to have been the dominant process from 1800 to 1670 ma with more juvenile material accreted at 1620 ma in contrast the southern laurentian terranes were dominated by accretion of juvenile material from 1800 to 1620 ma although reworked continental crust was also accreted to the margin in the interior of both continents basins developed with comparable histories from 1800 to 1670 ma thereafter the evolution of the interior basins diverged with sag phase processes dominant in northern australia and a protracted depositional hiatus in laurentia the geologic evolution is consistent with palaeomagnetic data and provides further evidence for geographic links between eastern australia and western laurentia from 1800 to 1600 ma

enhanced resolution of geological structures from magnetic data an example from the abitibi greenstone belt of northern ontario structural information about that portion of the economically important destor porcupine deformation zone and its associated faults which lie buried under many metres of clay belt sediments in the region north of matheson ontario must rely principally on interpretation of geophysical data in this area the archean greenstones of the abitibi are crosscut by at least three generations of strongly magnetic diabase dykes the predominant dyke set the matachewan trend north south orthogonal to structures in the greenstones directional horizontal derivative analysis of the total magnetic field which has a much sharper angular cutoff than that provided by standard fourier based filters provides a method for separating the magnetic contributions from these two sources this analysis revealed the existence of a previously unidentified fault the winslow fault located to the north of and parallel to the economically significant pipestone fault we also define a second new fault the carr fault that is

deformation pattern of the nw terrane boundary of the eastern ghats mobile belt india a tectonic model and correlation with antarctica abstract thrusts interspersed with lateral ramp and wrench structures mark the join between proterozoic eastern ghats mobile belt and archaean cratons of the eastern india the join referred to as terrane boundary shear zone exhibits an arcuate geometry at the nw margin of the eastern ghats where the mobile belt shows the presence of northwesterly verging nappes based on this the area has been described to represent the salient part of a fold thrust belt juxtaposition of the granulites over the low grade craton is largely attributed to thrusting along the terrane boundary shear zone as the folds are disoriented and the granulites are retrograded along the thrusts the terrane boundary shear zone is interpreted to be a retrograde shear zone the shear zone hosts a number of synkinematic alkali intrusive rocks that constrain the age of thrusting to 1 4 ga in the correlative framework of gondwanaland the terrane boundary shear zone is very likely to be contiguous with the rayner napier boundary of antarctica

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

regressive depositional architecture on a mesoproterozoic siliciclastic ramp sequence stratigraphic and nd isotopic evidences from bhalukona formation singhora group chhattisgarh supergroup central india abstract a paleo environmental and sequence stratigraphic study of the mesoproterozoic bhalukona formation singhora group central india provides new interpretations applicable to understanding sedimentation and stratigraphic architecture in the proterozoic siliciclastic ramp settings under falling and lowstand sea level conditions beside delineation of two diachronous surfaces process based facies analysis identified fourteen facies types that are grouped under five different facies associations paleo environments range among continental fluvial beach foreshore upper shoreface lower shoreface and wave dominated delta front from the paleocurrent measurement within the fluvial channel sandstones and measurement of crest line orientations of wave generated swash bedforms it is inferred that the bhalukona sea had nne ssw shoreline trajectory and the south easterly flowing river system carried sediment on the shoreline from a source in the west northwest such inference though in clear discordance with the earlier proposed south southeastern sediment source for the singhora basin finds support in the shift in e nd t t 1 42 ga values from 3 5 3 3 to 9 3 2 2 indicating change in sediment provenance at the early bhalukona sedimentation history sediments in the bhalukona formation derived from more evolved or older continental crustal sources in comparison to those of the underlying saraipalli formation a tectonic forcing behind the shift in sediment provenance and fall in relative sea level is inferred that established the forced regressive and lowstand shoreline in the singhora basin during the bhalukona time abrupt basin ward shift of facies tract and incision on shelf is exhibited by the occurrence of poorly sorted coarse granular bhalukona fluvial system carrying rip up mud clasts directly above the argillaceous highstand saraipalli shelf with 10 m incision and is inferred as the signal for forced regression and development of type i sequence boundary in low gradient proterozoic ramp settings without shelf slope break we interpret that the bhalukona fluvial system incised the coastal prism developed on the saraipalli highstand coastline the low gradient of the ramp however prompted long distance 15 km regression represented by the offlapped and detached delta front lobe away from the shoreline the slow steady rise in sea level onset of lowstand and establishment of a wave dominated coastline caused reworking of fluvial sediments in the basinal part within the wave base and resulted development of ravinement deposit basin ward the surface grades into correlative conformity with aggradational and weak retrogradational stacking the beach foreshore upper and lower shoreface in order of superposition record the lowstand depositional history the basin scale transgression is witnessed with formation of transgressive surface of erosion tse and establishment of the chuipalli shelf system dominantly beyond storm wave base taking into consideration 23 m preserved shoreface succession 1 m per year eustatic rise consistent with present day rate and average rate of shoreface retreat 0 5 m per year 11 5 km retreat for the bhalukona shoreline is estimated in its lowstand history

stratigraphic architecture of the proterozoic succession in the eastern chattisgarth basin india tectonic implications abstract the basin fill succession of the proterozoic eastern chattisgarth basin comprises a sandstone shale conglomerate dominated shallow marine assemblage and an assemblage of limestone shale pyroclastics deposited in off shelf slope base of slope environments the proximal and distal lithologic assemblages developed as lateral equivalents and show signatures of sea level fluctuations amenable to chronostratigraphic correlation the stratigraphic architecture of the proximal assemblage is characterized by cyclic deposition on different scales the largest order cyclicity is represented by alternating sandstone sequences and mudstone dominated sequences of the order of several tens of metres the smallest order cyclicity is represented by metre scale units punctuated aggradation cycles pac bounded by isochronous surfaces the lowermost large scale sandstone sequence the lohardih sandstone unconformably overlies the highly deformed rocks of the gneissic basement complex the sequence was deposited as alluvial fan fan delta complexes controlled by basin margin faulting the upper two sandstones the daihan sandstone and the kansapathar sandstone represent two different phases of major sand accumulation in fan or river deltas their rapid emplacement over muddy shelf deposits along erosional surfaces signaled abrupt sea level fall and basinward migration of facies belts generation and accumulation of very large volumes of sand and their rapid influx into the basin accompanied by major changes in depositional motif and in the circulation system in the basin collectively indicate that larger order sand depositing cycles were caused by tectonic uplift of the cratonic basement the smallest order cycles the pacs on the other hand may be attributed to glacioeustacy though tectonic control cannot be ruled out the sand deficient mud dominated large scale sequences are attributed to major transgression during periods of relative tectonic quiescence and subsidence of the cratonic hinterland episodic tectonic uplift and derivation of sands from similar quartzo feldspathic sources suggest repeated rifting of the cratonic basement and expansion of the rift into a major marine basin

forced regressive wedges on a neoproterozoic siliciclastic shelf chandarpur group central india abstract outcrop based sequence analysis across the transition from the chaporadih to the kansapathar formation of chandarpur group chattisgarh supergroup central india resolved a long standing uncertainty on occurrence of depositional discontinuity through undoubted identification of a forced regressive wedge and associated intraformational unconformity process based facies analysis identified eleven different facies types that are grouped into five different facies associations paleoenvironments range from shelf shoreface foreshore and beach tide influenced estuary and delta bounded between the surface of marine erosion at its base and subaerial unconformity marked by paleosol development at its top the coarse grained wedges of shoreface sandstone is interpreted as forced regressive in origin the basinward downstepping of two such regressive wedges bears evidence for lowering of wavebase in connection with relative fall in sea level the valley created during the falling sea level was filled by sediments in lowstand transgressive and highstand depositional motif the aggradational to weakly progradational bedsets of foreshore beach sediments record the history of early slow rise in base level with steepening in the rate of relative sea level rise the coastline transformed from wave dominated to tide dominated wide variability in the balance between sediment supply and accommodation is recorded in the facies types and stacking motif of transgressive estuarine sections at different studied locations the highstand tidal delta is a supply driven normal regressive product at stable or marginally rising base level

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

topographic phase recovery from stacked ers interferometry and a low resolution digital elevation model a hybrid approach to topographic recovery from ers interferometry is developed and assessed tropospheric ionospheric artifacts imprecise orbital information and layover are key issues in recovering topography and surface deformation from repeat pass interferometry previously we developed a phase gradient approach to stacking interferograms to reduce these errors and also to reduce the short wavelength phase noise see sandwell and price 1998 and appendix a here the method is extended to use a low resolution digital elevation model to constrain long wavelength phase errors and an iteration scheme to minimize errors in the computation of phase gradient we demonstrate the topographic phase recovery on 16 m postings using 25 ers synthetic aperture radar images from an area of southern california containing 2700 m of relief on the basis of a comparison with 81 gps monuments the ers derived topography has a typical absolute accuracy of better than 10 m except in areas of layover the resulting topographic phase enables accurate two pass real time interferometry even in mountainous areas where traditional phase unwrapping schemes fail as an example we form a topography free 127 m perpendicular baseline interferogram spanning 7 5 years fringes from two major earthquakes and aseismic slip on the san andreas fault are clearly isolated