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

mesoproterozoic emplacement and enriched mantle derivation of the racherla alkali syenite palaeo mesoproterozoic cuddapah basin southern india insights from in situ sr nd isotopic analysis on apatite we report an in situ sm nd isochron age of 1326 73 ma determined by la mc icp ms laser ablation multiple collector inductively coupled plasma mass spectrometry on crystalline apatite grains from the racherla alkali syenite occurring in the palaeo mesoproterozoic cuddapah basin southern india the obtained mesoproterozoic age necessitates the racherla syenite to be an intrusive into the sedimentary rocks of the cuddapah basin contrary to some previous suggestion that it represents an inlier of the basement pluton age of the dated syenite within its error limits is also coeval with that of the nearby chelima lamproite 1354 52 ma and other syenite complexes c 1352 ma located elsewhere within the eastern ghats mobile belt southern india thereby implying a common geotectonic control in all of their generation incompatible trace element signatures high la nb zr nb and la yb 87 sr 86 sr 0 70432 10 and the lower nd isotopic ratio end t 8 9 of the apatite suggest derivation of the racherla syenite parent magma from an enriched mantle source our findings provide compelling evidence for the existence of ancient c 2 6 ga metasomatized lithospheric mantle at the archaean palaeoproterozoic boundary beneath the cuddapah basin this enriched mantle appears to have had played a dominant role in the generation of co spatial and coeval lamproites within and around the cuddapah basin and a plethora of alkaline and sub alkaline syenites within the eastern ghats mobile belt implications of our study in the context of indo antarctic collisional tectonics are also explored

inverted metamorphism in the intracontinental ductile shear zone during himalayan collision tectonics collision tectonics in the himalaya ca 50 ma remobilized the proterozoic basement and its cover of the indian plate into the higher himalayan crystalline belt this belt displays an inverted metamorphism progressing from a garnet to a sillimanite k feldspar zone toward higher topographic and structural levels because previously hypothesized mechanisms are not sufficient to explain inverted metamorphism we propose that ductile shear displacements along ubiquitous closely spaced s c shear planes may have caused metamorphic inversion across a 15 20 km thick southwest vergent higher himalayan shear zone

structural geological and metamorphic significance of the kaapvaal craton limpopo belt contact abstract the hout river shear zone forms the terrane boundary between the granite greenstone terrane of the kaapvaal craton cratonic terrane and the high grade granulite terrane high grade gneiss province of the limpopo belt this structure is superimposed onto a thin skinned northward verging thrust system which exercises a significant control on the distribution of the ene wsw trending greenstone belts the hout river shear zone however dips steeply to the north and flattens out toward the south this structure was responsible for the emplacement of hot granulites against and over the cooler granite greenstone terrane and strongly influenced the metamorphic evolution of the area the shear zone acted as a conduit for infiltrating co2 rich h2o bearing fluids into still hot crust producing a retrograde isograd and associated zone of rehydration in the granulitic hanging wall of the structure retrogressed granulites in the hanging wall are characterized by fine grained kyanite as part of the retrograde assemblages while the greenstones in the footwall are characterized by coarse grained prograde kyanite the terrane boundary appears to be in thermal equlibrium with the lithologies in both the footwall and hanging wall so that tectonically mixed prograde greenstones and retrogressed granulites in and adjacent to the shear zone are apparently at a similar metamorphic grade the granulites appear to have had a hot iron effect on the cooler footwall rocks over which they have been displaced

two dimensional modeling of the p t t paths of regional metamorphism in simple overthrust terrains quantitative modeling of metamorphic p t t paths in thrust belts has so far been limited to one dimensional simplification we have developed a two dimensional time dependent finite element procedure capable of tracing and updating fault and strata boundaries during faulting for modeling thermal evolution of overthrust terrains we show that the two dimensionality of an overthrust and the speed and duration of thrusting have significant effects on the p t t paths of rocks in orogenic belts the results suggest that petrological studies of p t paths of rocks from different lateral positions in an orogenic belt along with two dimensional modeling procedure can put strong constraints on models of regional tectonic processes

4d velocity of strombolian eruptions and man made explosions derived from multiple doppler radar instruments abstract we used a novel system of three continuous wave doppler radars to successfully record the directivity of i strombolian explosions from the active lava lake of erebus volcano antarctica ii eruptions at stromboli volcano italy and iii a man made explosion in a quarry erebus volcano contains a convecting phonolite lava lake presumably connected to a magma chamber at depth it is one of the few open vent volcanoes that allow a direct observation of source processes during explosions its lava lake is the source of frequent violent strombolian explosions caused by large gas bubbles bursting at the lake surface the exact mechanism of these bubble bursts is unclear as is the mechanism of the creation of the infrasound signal accompanying the explosions we use the doppler radar data to calculate the directivity of strombolian eruptions at erebus this allows us to derive information about the expected type of infrasound source pattern i e the role of a dipole in addition to the monopole signature and the physical structure of the volcano we recorded 10 large explosions simultaneously with three radars enabling us to calculate time series of 3d directivity vectors i e effectively 4d which describe the direction of preferred expansion of the gas bubble during an explosion such directivity information allows a comparison to dipole infrasound radiation patterns recorded during similar explosions only a few weeks later video observations of explosions support our interpretation of the measurements we conclude that at erebus the directivity of explosions is mainly controlled by random processes since the geometry of the uppermost conduit is assumed to have a large effect on the directivity of explosions the results suggest a largely symmetrical uppermost conduit with a vertical axis of symmetry for infrasound recordings a significant dipole signature can be expected in addition to the predominant monopole signature

tectonothermal evolution of the gneiss complex at salur in the eastern ghats grnaulite belt of india textural relations thermobarometry and petrogenetic grid considerations in the syn tectonic granitoid massif and the enveloping metasedimentary gneisses at salur are consistent with a counter clockwise p t t path for the rocks the low p high t prograde sector is documented by the pre to syn d1 cordierite orthopyroxene garnet spinel bearing metatexite leucosomes in metapelites heating and loading of the rocks syn to post d1 resulted in the formation of garnet orthopyroxene cordierite bearing diatexites and decomposition of cordierite in metatexite leucosomes to orthopyroxene sillimanite biotite quartz symplectites near peak temperature 850 c at 8 0 kbar was reached syn to post d2 post peak cooling resulted in the stabilization of coronal grossular and anorthite calcite symplectites at the expense of scapolite wollastonite calcite assemblages in calc silicate gneisses and the resetting of cation exchange temperatures at 700 750 c near isothermal decompression at c 700 750 c is manifested by the decomposition of garnet porphyroblasts in the granitoid gneisses to plagioclase orthopyroxene ilmenite biotite two phase coronas and restabilization of cordierite at garnet margins in metapelites subsequent low p near isobaric cooling led to the overprinting of granulite facies assemblages by muscovite calcite assemblages and further resetting of cation exchange thermometers to lower temperatures c 600 c the tectonothermal evolution of the salur gneiss complex vis a vis the eastern ghats belt is therefore consistent with high degrees of lower crustal melting followed by prograde heating of the cover rocks due to magma invasion synchronous with crustal compression and finally thermal relaxation over a protracted period punctuated by tectonic erosional denudation of the thickened crust

progressive deformation structures associated with ductile thrusts in the moine nappe sutherland n scotland in the deeper parts of mountain belts polyphase structural sequences observed at outcrop scale can arise due either to overprinting of regionally distinct deformation phases e g reworking changes in orogenic boundary conditions or to localized controls that bring about transient changes in the patterns of ductile flow these are unlikely to be mutually exclusive processes and examples from scotland demonstrate that once regionally separate events are delimited using radiometric evidence it is possible to isolate complex deformation sequences arising due to local controls in the western moine nappe of sutherland the dominant structures were formed during caledonian ductile thrusting towards the wnw whilst earlier precambrian phases are relatively minor in importance two groups of caledonian folds and fabrics are recognized in many exposures main phase d2 structures which are broadly contemporaneous with ductile thrust fabrics and later secondary phase f3 folds the latter can be divided into two geometric groups sheath fold types which formed initially as wnw overturned buckles subsequently modified by ductile shearing and asymmetric types which are commonly open folds apparently formed with axes close or sub parallel to the thrust transport direction secondary structures show a close spatial association with high strain zones along ductile thrusts and can be shown to have formed during the later stages of thrusting in certain critical exposures i propose that they may form due to strain perturbations resulting from variations in the relative rates of ductile flow within the mylonites where differential shearing occurs due to flow normal perturbations wrench related asymmetric fold types may form in contrast secondary sheath fold structures may result from localized compression phases caused by flow parallel perturbations local flow perturbation models may be appropriate in situations where the distribution of later structures is apparently related to spatial variations in strain intensity and or there is a strong geometric and kinematic similarity between sets of folds and fabrics if such features are not observed a regional polyphase sequence is more likely and it is therefore necessary to obtain radiometric dates or some other independent source of data to demonstrate a time separation

structural evolution across the eastern ghats mobile belt bastar craton boundary india hot over cold thrusting in an ancient collision zone along the western margin of the eastern ghats mobile belt egmb ultrahigh temperature granulites are thrust westward over hornblende granites and sedimentary rocks of the bastar craton multiply deformed migmatitic gneisses and porphyritic charnockite of the egmb unit preserve thrust related shear fabrics s3m in the cratonic foreland undeformed granites show a progressive decrease in grain size and increase in penetrative foliation to the east evolving into orthogneiss near the mylonitized contact zone with charnockite foreland fabrics with a consistent top to the west shear sense are conformable with s3m in charnockite and correlate with s3b in polydeformed orthogneisses of cratonic windows s3b in the windows parallels s3m in overlying egmb migmatitic gneisses while s3m accompanied granulite metamorphism in the egmb s3b temperature estimates vary from t 700 c in the windows to t 550 c in the west decreasing temperature and later fabric formation in the west are explained by an evolving thermal profile in the cold craton which is caused by thrusting against hot lower crustal egmb rocks based on lithologic structural and metamorphic variations across the contact and resemblances between the egmb and rayner complex the craton mobile belt boundary is considered a result of indo antarctic collision leading to the formation of an ancient supercontinent

contrasting pressure temperature deformation history across a vestigial craton mobile belt boundary the western margin of the eastern ghats belt at deobhog india at deobhog migmatitic gneisses and granulites of the eastern ghats belt are juxtaposed against a cratonic ensemble of banded augen gneiss amphibolite and calcsilicate gneiss intruded by late hornblende granite and dolerite in the migmatitic gneiss unit early isoclinal folds syn d1m and d2m are reoriented along n s trending and e dipping shear planes s3m with s1m s3m intersection lineations having steep to moderate plunges the near peak p t condition was syn d3m 900 c 9 5 kbar as inferred from syn d3m grt opx bearing leucosomes in mafic granulites and from thermobarometry on grt corona opx cpx pl qtz assemblages the p t values are consistent with the occurrence of opx spr crd assemblages in spatially associated high mg al pelites a subsequent period of cooling followed by isothermal decompression 800 850 c c 7 kbar is documented by the formation of coronal garnet and its decomposition to opx pl symplectites in mafic granulites hydrous fluid infiltration accompanying the retrograde changes is manifested in biotite replacing opx in some lithologies the cratonic banded gneiss granite unit also documents two phases of isoclinal folding d1b d2b with the l2b lineation girdle different from the lineation spread in the migmatitic gneiss unit calcsilicate gneiss hbl pl cpx scap cal and amphibolite hbl pl grt cpx within banded gneisses record syn d2b peak metamorphic conditions c 700 c 6 5 kbar followed by cooling to c 500 c manifested in the stabilization of coronal clinozoisite epidote the d3b shear deformation post dates granite and dolerite intrusions and is characterized by top to the west movement along n s trending e dipping shear planes deformation mechanisms of quartz and feldspar in granites and banded gneisses and amphibole plagioclase thermometry within shear bands in dolerites document an inverted syn d3b thermal gradient with temperature increasing from 350 to 550 c in the west to 700 c near the contact with the migmatitic gneiss unit the thermal gradient is reflected in the stabilization of chlorite after hornblende in s3b shears to the west and post d2b neosome segregation along d3b folds and shears to the east the contrasting lithologies early structures and peak metamorphic conditions in the two units indicate unconnected pre d3p t deformation histories the shared d3 deformation in the two units the syn d3 inverted thermal gradient preserved in the footwall cratonic rocks and the complementary cooling and hydration of the hanging wall granulites across the contact are attributed to westward thrusting of hot eastern ghats granulites on cool cratonic crust it is suggested that the eastern ghats migmatitic gneiss unit is not a reworked part of the craton but a para autochthonous allochthonous unit emplaced on and amalgamated to the craton

forced folds and fractures this volume is concerned with defining the major similarities and difference between forced folds and buckle folds in order that these differences can be used to recognize the type of folding and therefore the expected fracture pattern present in regions of poor exposure or where the geologist has to rely on seismic images an understanding of the differences between the two fold types their 3d geometry spatial organization fracture patterns etc provides an invaluable tool for earth scientists concerned with assessing the possible role of folds and their associated fracture patterns in controlling fluid migration and concentration within the crust the papers presented here are grouped into 4 sections contributions in the first section describe the use of numerical analyses to investigate the formation of fractures in forced folds including compaction folds and the section contains a description of large scale compaction folding in which the associated fracturing has given rise to the development of large sandstone dykes the papers in the second section deal with the formation of forced folds as a result of normal faulting in various geological environments including along a classical graben margin and around a resurgent caldera the third section contains papers relating to forced folding in compressional and strike slip regimes the final section considers the temporal and spatial relationships between forced folds and buckle folds the formation of crustal scale folds and a method of determining the distribution of strain on any folded surface a key parameter controlling the distribution of fractures

microstructures in feldspars from a major crustal thrust zone the grenville front ontario canada abstract samples collected across the nw grenville front in ontario canada have been used to document the change in feldspar microstructures produced during shearing under metamorphic conditions that range from upper amphibolite to lower greenschist grade the differential displacement across this 5 km thick section of the grenville front tectonic zone is at least 10 km at upper to mid amphibolite conditions both plagioclase and potassium feldspars behave plastically grainsize reduction occurs through grain boundary migration and or subgrain rotation and produces a core and mantle structure at middle to lower amphibolite grade grain size reduction is accomplished through grain boundary migration at lower amphibolite to upper greenschist grade grain size reduction occurs by the nucleation and growth of new grains with a different composition the abundance of intracrystalline deformation at this grade is inversely proportional to the amount of fine grained matrix in ultramylonite with a high matrix to porphyroclast ratio few intracrystalline strain features occur other than ubiquitous undulatory extinction myrmekite is well developed on the high stress boundaries in k feldspar at upper to mid greenshist conditions feldspars deform mainly by slip on synthetic shear fractures deformation twins undulatory extinction deformation bands and kink bands occur in plagioclase and perthite flames and myrmekite occur principally on high stress boundaries in k feldspar grain size reduction in feldspar is accomplished through cataclasis at middle to lower greenschist facies deformation in feldspars is dominated by antithetic fractures the transition from the dominance of synthetic to antithetic fractures is gradational below lower greenschist grade rocks deform by pervasive cataclasis of all minerals

new tectonic divisions of the grenville province southeast canadian shield on the basis of geological geophysical and geochronological data the grenville province has been divided into three first order longitudinal belts the parautochthonous belt pb allochthonous polycyclic belt apb and allochthonous monocyclic belt amb these are set apart by three first order tectonic boundaries the grenville front gf allochthon boundary thrust abt and monocyclic belt boundary zone mbbz the belts are subdivided into terranes based on internal lithological character the gf separates the archean to proterozoic foreland northwest of the orogen from reworked equivalents to the southeast continuous at the scale of the orogen its main characteristic is that of a crustal scale contraction fault the pb although less clearly identified along the length of the orogen in most places represents upgraded and tectonically reworked rocks of the adjacent foreland the boundary between the pb and the apb to the southeast the abt is most clearly delineated in the eastern half of the province it is the locus of major crustal delamination along which high grade mostly middle proterozoic polycyclic terranes were tectonically transported northwest toward and onto the pb the amb comprises two separate areas underlain by the wakeham supergroup and what is currently known as the grenville supergroup respectively its basal contact the mbbz is a decollement zone of variable kinematic significance between older polycyclic rocks and tectonically overlying monocyclic rocks this first order zonation implies a tectonic polarity to the grenville province superimposed on which are second order features evident from contrasting tectonic styles and radiometric ages these characteristics are consistent with a diachronous or oblique collisional model for the grenville orogen

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

numerical modelling of the thermal history of the nw himalayas kullu valley india abstract this paper demonstrates two dimensional time dependent finite difference modelling of himalayan metamorphism illustrated by the kullu s lahul area himachal pradesh after the collision between india and asia and the over thrusting of the higher himalayas over the lesser himalayas it is shown that a one dimensional model with crustal thickening by a single thrust cannot satisfy the observations present in the section along the kullu valley a two dimensional solution demonstrates that during thrust sheet emplacement at geologically realistic strain rates of several centimetres a year a temperature inversion does not occur in contrast to the inversion assumed by the one dimensional instantaneous thrust models therefore the variability of two other model parameters were explicitly considered i there is a significant conductivity contrast between the different types of rocks as conductivity layers function as a barrier to the transport of heat the conductivity limit should be variable for different regions in the grid ii rocks in the higher himalayas record a phase of metamorphism that preceded the movements on the main central thrust this observation together with the knowledge that rocks with different radiogenic heat production and conductivity are not uniformly distributed in the crust emphasizes that there were considerable horizontal temperature variations across the whole region for that reason the initial temperature profile too has to be adapted for a realistic model

response of wave dominated and mixed energy barriers to storms wave dominated and mixed energy barriers are extremely dynamic landforms responding to processes operating over a spectrum of time scales ranging from daily to monthly fluctuations related to storm and post storm conditions to century to millennium scale evolution driven by relative sea level change two types of storms are of particular relevance warm core tropical and cold core extratropical cyclones both are responsible for generating very large waves highly energetic surf zone dynamics and sediment transport elevated inshore water levels and extensive morphological responses all cyclones are affected by climate change which governs their frequency intensity and tracks barrier storm response is primarily governed by maximum storm runup and barrier morphology as conceptualised in abby sallenger s storm impact scale model sallenger 2000 this model defines four storm impact regimes and includes erosive as well as accretionary responses on the erosion side the swash regime drives bar and berm flattening the collision regime is marked by dune scarping and beach lowe the overwash regime leads to dune scouring and channel incision and the inundation regime may result in barrier destruction on the deposition side storm berms and beach ridges may form and accrete in the swash and collision regimes localised vertical beach and barrier accretion are associated with the collision and overwash regimes and washover deposition takes place in the overwash and inundation regimes site specific factors play a key role in moderating the morphological response and include storm characteristics type duration and track longshore sediment supply upwelling downwelling currents coastal setting and inner shelf topography the response of a barrier to a tropical or extratropical cyclone can however not be considered in isolation and has to be appreciated in a longer temporal context involving morphological preconditioning due to antecedent wave and water level conditions additionally a simple process response approach of the cause and effect type is inappropriate and a more complex conceptual framework involving thresholds feedbacks resilience and vulnerability will need to be adopted a useful way to visualise and conceptualise more complex storm behaviours and the longer term vulnerability of barriers is the resilience trajectory which maps out the changes in barrier geometry elevation and width over various time scales from weeks to years or even longer and under varying forcing conditions including changes in storminess and sea level rise an increased understanding of barrier response to storms and sequences of storms is required to better quantify long term barrier response to climate change high resolution and comprehensive decadal records of barrier response to storms are a prerequisite to achieve this ambition linking site specific coastal settings hydrodynamic drivers and morphological responses and allowing the recognition of recovery and impact dominated phases the enhanced insights in barrier response to extreme events must then be incorporated into improved coastal response models to help predict the impacts of future climate change on wave dominated and mixed energy barriers around the world 2013 elsevier b v

evolution of the continental crust in the proterozoic eastern ghats belt india and new constraints for rodinia reconstruction implications from sm nd rb sr and pb pb isotopes abstract for this study nd sr and pb isotope compositions were analyzed for ortho and paragneisses from the eastern ghats belt of india in order to determine its crust formation and crustal evolution this belt represents a proterozoic orogen that extends along the east coast of peninsular india and forms part of the mobile belts in east gondwana and rodinia the eastern ghats belt was affected by mesoproterozoic granulite facies metamorphism in the western segment western charnockite zone and a grenvillian regional scale high grade event in the central and eastern segments western khondalite zone charnockite migmatite zone and eastern khondalite zone as well as a local pan african overprint the results of the isotope studies are used for the large scale reconstruction of the indo antarctic part of the rodinia supercontinent based on nd model ages and pb isotope ratios from leached feldspars four crustal domains can be distinguished in the eastern ghats belt these domains can in part be correlated with the lithological division of the belt 1 the western charnockite zone south of the godavari graben is characterized by nd model ages between 2 3 and 2 5 ga for orthogneisses and 2 6 and 2 8 ga for metasediments domain 1 the pb isotopes are primitive indicating reworking of dominantly archean and mixing with minor proterozoic material 2 north of godavari graben nd model ages for orthogneisses are significantly higher with values ranging from 3 2 to 3 9 ga the pb isotopes are strongly retarded 3 the north eastern parts of the charnockite migmatite zone and western khondalite zone form a distinct and almost homogeneous crustal domain domain 3 with nd model ages between 1 8 and 2 2 ga 4 between the isotopically homogeneous terranes stretches a broad transition zone domain 2 enclosing parts of the western khondalite zone charnockite migmatite zone and eastern khondalite zone the nd model ages for metasediments 2 1 2 5 ga are younger than paragneiss ages of the adjoining western charnockite zone the nd model ages for orthogneisses 1 8 3 2 ga display a large spread which is consistent with the pb isotope signatures that indicate mixing of archean with proterozoic material the border zone between domain 3 and the archean eastern indian craton forms a second transition zone domain 4 characterized by metasediments with nd model ages between 2 2 and 2 8 ga and orthogneisses with model ages around 3 2 ga reworking of archean crustal material is most intense along the border zones of the belt and juvenile material is more dominant away from the orogenic front this scenario is indicative of an active continental margin setting for the two proterozoic episodes of orogenesis in the eastern ghats belt a correlation of domain 3 with the rayner complex and the prydz bay region antarctica for the early crustal evolution is supported by the similarity of the isotope signatures the napier complex is very different to the eastern ghats belt and an early joint evolution of these terranes is ruled out on the basis of the pb pb and sm nd systematics

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

migration of deformation fronts during progressive deformation evidence from detailed structural studies in the pennsylvania anthracite region u s a abstract detailed study of selected outcrops in the pennsylvania anthracite region has resulted in identification of five at least partly continuous stages of alleghanian progressive deformation these structural stages are in sequence a layer parallel shortening and top to the foreland layer parallel shear b a second episode of layer parallel shortening c flexural slip and flexural flow folding d fold modification and late thrust faulting and e late veining and fracturing at each outcrop an average shortening direction was determined for each observed structural stage the mean regional shortening direction for each structural stage was calculated and maps showing the spatial distribution of the shortening directions for each stage were constructed the mean regional shortening directions for the five structural stages successively rotated 25 30 clockwise during the evolution of the fold and thrust belt shortening directions for structural stages b and c over the region show a systematic clockwise change in orientation from hinterland to foreland indicating that these structural stages of progressive deformation were time transgressive on a regional scale

analysis and interpretation of composite foliations in areas of progressive deformation abstract in areas of progressive deformation where successive structures develop during a relatively continuous deformation within a geologically short time period traditional chronological notations of structural elements e g s 1 s 2 etc can give erroneous impressions of how large rock masses evolve in time and space we demonstrate from field examples that successive structures can develop which a are comparable in morphology and orientation but of different ages b are different in morphology but of comparable age and c show rapid morphological changes over short distances under such conditions correct identification of the relative age of structures is often difficult to impossible we consider the concepts of a composite foliation and of transposition cycles as vehicles to objectively evaluate the significance of different sets of structures in the evolution of larger rock masses we suggest that 1 structural elements be labeled using morphological notation adding numerical subscripts only when independent evidence is available 2 geologists more fully acknowledge and integrate the concept of deformation partitioning into their models and 3 when analyzing areas of multiple deformation more emphasis is placed on the relationship between domains of differing complexity integration of these three perspectives in the analysis will lead to a more realistic basis upon which to model the structural evolution of large rock masses

polyphase deformation in the western mount isa inlier australia episodic or continuous deformation abstract the polyphase deformation history of the mount novit ranges western mount isa inlier australia involved the development of four generations of n s to nw plunging folds development of which alternated with movement on n s striking faults shear zones with west over east displacement the spatial relationships between successive structures and the distinct similarities in the kinematics style and asymmetry are all consistent with continuous deformation during e w to ne sw shortening additional support for this hypothesis is based on the development of the three major fold generations and the intervening faults and shear zones during low p high t metamorphism although the duration of this metamorphic event cannot be constrained recent studies have linked low p metamorphism to heat advection by migrating melts thermal modelling indicates that such metamorphic events will be short lived in comparison to those associated with thermal relaxation of over thickened crust low p metamorphism is unlikely to persist through two or more separate tectonic events therefore syn metamorphic polyphase deformation in the mount novit ranges apparently formed during a single continuous tectonic episode this structural history differs from both the regional scheme and that of previous workers in this area the main differences are i no evidence was found for early thrust faulting prior to n s folding ii there are four generations of n s to nw se folds as opposed to two and iii this study favors a single consistent tectonic regime in contrast to the interpretation of three discrete isolated tectonic events

unraveling sedimentary provenance and tectonothermal history of high temperature metapelites using zircon and monazite chemistry a case study from the eastern ghats belt india abstract the geochemical behavior of detrital zircon and monazite during granulite facies anatexis in metapelites from the eastern ghats belt egb india is explored using u pb geochronology hf isotopes and trace elements in a metapelite from the ongole domain detrital zircon reequilibrated by coupled dissolution reprecipitation and diffusion reaction during ultrahigh temperature metamorphism at 1 63 ga the event completely reset the u pb systems but hf isotopes and trace elements were only partially reequilibrated overgrowths on the altered cores date migmatization at 1 61 ga monazite yields metamorphic ages similar to those of zircon in metapelites from the eastern ghats province egp detrital zircon grains give 2 44 1 40 ga ages and metamorphic ones 1 2 0 5 ga ages metamorphic components include detrital grains reequilibrated by coupled dissolution reprecipitation in the presence of anatectic melt and newly crystallized overgrowths and grains in reequilibrated domains the u pb system wa

intense non coaxial shear and the development of mega scale sheath folds in the arunta block central australia abstract the strangways orogenic belt of 1800 ma granulites in the central arunta block was completely reworked at granulite facies grades during the middle proterozoic 1400 1500 ma the bulk strain regime of the initial episodes of this reworking is presented ductile reworking involved non coaxial deformation on a regional scale and produced map scale sheath folds high bulk shear strains are inferred on microscopic and macroscopic scales and the spatial variation in bulk shear strain throughout the region is discussed the high bulk shear strains were accommodated by east over west ductile ramping and fold repetition resulting in easterly inclined structures crustal shortening and crustal over thickening

superposed deformation and inherited structures in an ancient dilational step over zone post mortem of the rengali province india abstract in the eastern indian shield a dextral strike slip system juxtaposed the archaean singhbhum province against the proterozoic eastern ghats belt at 490 470 ma two wnw ese trending strands of the strike slip system enclose a multiply deformed d1 to d3 intervening domain called the rengali province with d3 representing dextral shearing in a granulite lens within the province an early fabric sgr was deformed by an amphibolite facies d1 d2 deformation continuum in the late archaean time forming cylindrical folds in the surrounding quartzofeldspathic gneisses quartzites and mica schists of the province superimposition of syn d3 shortening on d1 d2 folds generated complex non cylindrical geometries the granulites escaped d3 strain microstructures in the province bounding shear zones confirm that d3 deformation was associated with mylonitization dynamic recrystallization and greenschist facies metamorphism in the quartzites syn d3 folds can be correlated with rotation of d1 d2 structures through the shortening zone of bounding dextral shears since the province bounding shears form a step over zone the structural complexity within the rengali province arises from superposition of syn d3 shortening structures on initially asympathetically oriented inherited cylindrical d1 d2 folds hydrous fluid channeling causing greenschist facies metamorphism and quartz vein emplacement accompanied d3 as the step over zone was dilational in nature

ultra high temperature metamorphism of metapelitic granulites from kondapalle eastern ghats belt implications for the indo antarctic correlation a suite of quartz and corundum bearing metapelitic granulites intruded by layered gabbronorite pyroxenite anorthosite at kondapalle eastern ghats belt preserves a multitude of reaction textures involving oxide and silicate minerals that attest to several prograde and retrograde reactions in the quartz bearing associations the reactions are a biotite sillimanite quartz garnet liquid b garnet sillimanite spinel magnetite quartz c fe2tio4 o2 ferrian ilmenite magnetite d reversal of reaction b e fe2o3 rich ilmenite plagioclase quartz fe2o3 poor ilmenite garnet o2 reactions in the corundum bearing associations are f spinel biotite sillimanite garnet liquid g biotite sillimanite garnet ti rich spinel corundum liquid h biotite sillimanite garnet corundum liquid i fe2tio4 feal2o4 o2 ferrian ilmenite fe3o4 al2o3 in ilmenite j garnet corundum spinel sillimanite to examine the paragenetic evolution of the metapelitic granulites a petrogenetic grid for the kfmash system at high temperatures and pressures involving quartz and corundum was constructed the sequence of inferred reactions documents an anticlockwise heating cooling path reintegrated compositions of spinel with 10 mol fe2tio4 and feldspars indicate ultra high temperature uht of metamorphism 1000 c comparable with the liquidus temperature of the enclosing magmatic rocks crystallization pressures inferred for the magmatic rocks and the pressure constraints imposed by the petrogenetic grid on the metapelite assemblages indicate that the emplacement of the igneous suite and the accompanying uht metamorphism occurred in the lower crust 8 kbar reported u pb cooling ages of monazite and allanite from a late pegmatite suggest the uht metamorphism to be older than 1600 ma the deduced p t history and the absence of grenvillian high grade metamorphism in the study area provide important constraints on the configuration of east gondwana in particular on the continuation of the napier rayner terrane boundary into the eastern ghats belt