topographical changes revealed by high resolution airborne lidar data the 1999 tsaoling landslide induced by the chi chi earthquake abstract the 1999 chi chi earthquake triggered the catastrophic tsaoling landslide in central taiwan we mapped the landslide area and estimated the landslide volume using a high resolution digital elevation model from airborne lidar light detection and ranging aerial photographs and topographic maps the comparison between scar and deposit volumes about 0 126 km3 and 0 150 km3 respectively suggests a coseismic volume increase of 19 due to decompaction during landsliding in july 2003 the scar and deposit volumes were about 0 125 km3 and 0 110 km3 respectively these estimates suggest that 4 years after the event the volume of landslide debris removed by river erosion was nearly 0 040 km3 these determinations are confirmed by direct comparison between the most accurate topographic models of the post landslide period indicating a very high erosion rate at the local scale 0 01 km3 year for the deposit area of the landslide such a large value highlights the importance of landslide processes for erosion and long term denudation in the taiwan mountain belt

fold patterns and multilayer rheology of the lurestan province zagros simply folded belt iran abstract anticlines of the lurestan province in the zagros fold thrust belt have been studied by integrating field based analysis with the use of high resolution satellite images and data available from the literature the distribution of folds in the southeastern lurestan province expressed in terms of axial length and wavelength distribution shows a direct link with the characteristics of the sedimentary multilayer in which the folds developed within the carbonate deposits of the late cretaceous bangestan group the transition from pelagic to neritic facies determines a threefold increase in anticline spacing and promotes the development of thrust structures in the forelimb of anticlines the oligocene miocene shahbazan asmari unit folds harmonically with the bangestan group except in the areas where the palaeogene deposits interposed between the two units exceed 1300 m of thickness in these areas the shahbazan asmari carbonates display short wavelength folds indicating a complete decoupling from the underlying folds of the bangestan group it is suggested that this decoupling occurs because the summed thickness of the incompetent units separating the two carbonate units exceeds the extension of the zone of effective contact strain of the bangestan group folds

characterisation and engineering properties of tectonically undisturbed but lithologically varied sedimentary rock masses tectonically undisturbed sedimentary rocks deposited in a quiescent shallow marine environment often include a sequence of strata that may present significant lithological variety at the scale of an engineering structure such rock masses exhibit engineering properties that are significantly different from tectonically disturbed rock masses of similar composition for example molasse consists of a series of tectonically undisturbed sediments of sandstones conglomerates siltstones and marls produced by the erosion of mountain ranges after the final phase of an orogeny they behave quite differently from flysch which has the same composition but which was tectonically disturbed during the orogeny the molasses behave as continuous rock masses when they are confined at depth and the bedding planes do not appear as clearly defined discontinuity surfaces close to the surface the layering of the formations is discernible and only then similarities may exist with the structure of some types of flysch therefore extreme care is necessary in the use of geotechnical classification systems for the selection of design parameters in order to avoid penalizing the rock mass unnecessarily a discussion on the use of the geological strength index gsi for the characterisation of such rock masses is presented two gsi charts are proposed for estimating the mechanical properties of these masses one mainly for tunnels and the second for surface excavations an example is given to illustrate the process of tunnel design in molassic rocks

rock magnetism and palaeomagnetism of the oddanchatram anorthosite tamil nadu south india rock magnetic and palaeomagnetic data are reported on the proterozoic massif type anorthosite body from oddanchatram on the northern slopes of the kodaikanal palani ranges tamil nadu alternating field demagnetization treatment indicated a very stable direction of magnetization progressive heating revealed a remanence that became unblocked at 580degreesc the demagnetization analysis yields a characteristic component with a mean direction d m 97 3degrees im 28 8degrees k 51 alpha 95 7 2degrees and n 9 sites in addition to this characteristic component specimens from a few sites show the presence of a low coercivity component with a mean palaeomagnetic direction of d 36 7degrees i 29 4degrees k 63 alpha 95 4 4degrees and n 18 the isothermal remanent magnetization acquisition curves indicate magnetite as the main carrier of the stable remanence the direction of the characteristic component corresponds to a pole position at 9 7degreesn 1 7degreese d p 4 4 d m 7 9 the location of this pole is comparable to palaeomagnetic poles reported for the period of 1100 1000 ma for a range of formations from the indian shield the pole for the secondary component 45degreess 23degreese fits well with poles for 550 ma associated with the pan african thermal event that extensively caused granulite grade metamorphism in the southern granulite terrain despite the high temperature 700degreesc that prevailed during the pan african event the remanence magnetization of 1100 1000 ma is preserved in the oddanchatram anorthosite it is inferred that the northern boundary of the terrain affected by the dominant 550 ma granulitic metamorphism lies close to the southern margin of the oddanchatram anorthosite body thus oddanchatram anorthosite escaped the high temperatures metamorphism the weak secondary magnetization found in a few specimens is attributed to hydrothermal activity associated with the intrusion of pink granites immediately south of the oddanchatram anorthosite body a mid proterozoic magnetization age of the oddanchatram anorthosite supports the view that this body was emplaced remobilized during the eastern ghat orogeny similar to1000 ma and this body can be seen as a western extension of the string of massif type anorthosites in the eastern ghat mobile belt

the impact of cover rock rheology on the style of folding in the zagros fold thrust belt abstract the present day morphology of the zagros fold thrust belt is dominated by magnificent exposures of nw se trending folds these folds differ in their size and geometry and these differences are related mainly to the rheological profile of the cover rock the cover rock succession of the zagros consists of a sequence of competent and incompetent units which vary both along and across the belt field based study combined with the use of satellite images reveals that the thickness and facies distribution of the cover rock succession has a significant impact on the style of deformation during the shortening linked to the current convergence of the arabian and iranian plates the incompetent units act as detachment horizons which localise thrusting and which act as decollement above which detachment folds form in addition where these incompetent units are thick e g 1 km they allow the deformation above and below them to become completely decoupled enabling disharmonic folding to occur as a result the folds above and below the incompetent units in the central part of the zagros folded belt have significantly different geometries and wavelengths as the zagros folds host the majority of the hydrocarbon reserves in iran and iraq an understanding of the processes that influence their geometry and spatial organization at different levels in the cover rock is crucial for the future exploration in the region

stratigraphy and geochemistry of the balwan limestone vindhyan supergroup india evidence for the bitter springs δ13c anomaly abstract the vindhyan supergroup of india deposited in an intracratonic basin is one of the important proterozoic marine successions of the world that contains some of the most controversial precambrian fossil discoveries despite their importance the chronology of the host strata and global correlation of the events that occurred within the basin remain equivocal here we present results of a detailed geological geochemical and isotopic sr c o study of the balwan limestone the youngest carbonate formation of the supergroup exposed only in the western sector of the basin our results suggest that the vindhyan basin had become a structurally controlled marginal sea towards the end of its existence and that the limestone was deposited in a subtidal environment that had strong depositional currents we find evidence for a strong storm event or a tsunami during its deposition near primary 87sr 86sr of 0 70676 at the top and 207pb 206pb age of 866 90 ma gopalan et al 2013 of this 120 m thick formation suggest its deposition during late tonian 13c stratigraphy reveals the presence of the globally synchronous bitter springs anomaly 12 shift in the formation the first such report from india

kinematic evidence for downdip movement on the mormon peak detachment province to the west and the little extended colorado plateau to the east the most enigmatic feature of the range the mormon peak detachment wernicke 1981 is a sharp locally planar surface that cuts nearly all other structures dips on average 20 away from the center of the range and generally places younger mostly limestone paleozoic strata from the hanging wall of the mormon thrust on top of older mostly dolostone paleozoic strata from the footwall of the same thrust gsa data repository fig dr1 1

kimberlite exploration at serra da canastra province brazil kimberlite and lamproite pipes are the only economically significant source rocks forming primary diamond deposits brazil the world s seventh largest diamond producer has all of its production from alluvial deposits the quest for a primary deposit has continued over several decades with very few positive results to that end airborne magnetic data from the serra da canastra diamondiferous province was used to identify kimberlite signatures serra da canastra is located in the central portion of the brazilian province in a low magnetic latitude region the main tectonic feature of the area is a northwest southeast major crustal fracture zone that extends for more than 3000 km within the territory the interpretation strategy was based on joint analysis of analytic signal and euler deconvolution a selected kimberlite target should typically have a roughly circular analytic signal anomaly coincident with a depth 0 200 m and structural n 2 constrained euler solution the proposed approach led to rec

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

anomalous crustal and lithospheric mantle structure of southern part of the vindhyan basin and its geodynamic implications abstract tectonically active vindhyan intracratonic basin situated in central india forms one of the largest proterozoic sedimentary basins of the world possibility of hydrocarbon occurrences in thick sediments of the southern part of this basin has led to surge in geological and geophysical investigations by various agencies an attempt to synthesize such multiparametric data in an integrated manner has provided a new understanding to the prevailing crustal configuration thermal regime and nature of its geodynamic evolution apparently this region has been subjected to sustained uplift erosion and magmatism followed by crustal extension rifting and subsidence due to episodic thermal interaction of the crust with the hot underlying mantle almost 5 6 km thick sedimentation took place in the deep faulted jabera basin either directly over the bijawar mahakoshal group of mafic rocks or high velocity high density exhumed middle part of the crust detailed gravity observations indicate further extension of the basin probably beyond nsl rift in the south a high heat flow of about 78 mw m2 has also been estimated for this basin which is characterized by extremely high moho temperatures exceeding 1000 c and mantle heat flow 56 mw m2 besides a very thin lithospheric lid of only about 50 km many areas of this terrain are thickly underplated by infused magmas and from some segments granitic gneissic upper crust has either been completely eroded or now only a thin veneer of such rocks exists due to sustained exhumation of deep seated rocks a 5 8 km thick retrogressed metasomatized zone with significantly reduced velocities has also been identified around mid to lower crustal transition

a comparison of pyroclastic flow and debris avalanche mobility many pyroclastic flows have runout distances longer than expected from basic frictional arguments in these cases the ratio of the height descended h and the runout l are as small as 0 2 a feature which has been attributed to fluidization however significant fluidization by gases is now considered unlikely during emplacement of debris avalanches where h l and volume are inversely related we determine whether pyroclastic flows are more mobile than debris avalanches of the same volume and if different emplacement mechanisms are needed to describe their runout h l and volume data were compiled for 34 nonvolcanic and 40 volcanic debris avalanche deposits as well as 15 pyroclastic flow deposits systematic differences in the volume versus h l plots were explored by statistical analysis results show an inverse relationship between h l and volume for both nonvolcanic and volcanic debris avalanche deposits as expected and also for pyroclastic flow deposits regression lines for plots of pyroclastic flow and volcanic debris avalanche data are statistically indistinguishable and the non volcanic debris avalanche line is parallel to the other two we argue that the nonvolcanic and volcanic debris avalanche differences are due to material properties rather than emplacement mechanisms therefore since pyroclastic flows and volcanic debris avalanches have indistinguishable h l versus volume it is unlikely that pyroclastic flows have a significantly different primary emplacement mechanism based on the data in hand we conclude that it is unnecessary to invoke gas fluidization to explain the mobility of the types of pyroclastic flows examined or the excess runout of large volume debris avalanches

seismic imaging across the eastern ghats belt cuddapah basin collisional zone southern indian shield and possible geodynamic implications abstract the evolutionary nature of the area encompassing cuddapah basin nellore schist belt and the ongole domain of eastern ghats belt south india which contains paleo neoproterozoic imprints of thick sedimentation intense magmatism subduction accretion and possible collision between eastern dharwar craton and east antarctica is still being debated an attempt has been made here to decipher the deep crustal structure and tectonics of this region by reprocessing deep seismic sounding data acquired earlier through the modeling of first arrival refraction and wide angle reflection travel times the derived crustal seismic velocity structure reveals that the intracratonic proterozoic cuddapah basin containing only 4 km thick sediment is bounded by two major faults the moho reaching fault detected on its eastern boundary demarcates cuddapah basin from the nellore schist belt although a deep normal fault is mapped within the nallamalai fold belt but no thrusting signatures are apparent almost all the crustal layers beneath nellore schist belt and the ongole domain of eastern ghats belt show distinct eastward dipping trend conforming to an upthrusted feature suggesting possible presence of a collisional suture besides the areas lying east of cuddapah basin appear to be an accreted orogenic terrain beneath which lower crust has upwarped substantially the entire stretch of the studied region is underplated by unprecedently thick 20 km high velocity 7 0 7 4 km s magma layer above the moho indicating strong crust mantle thermal perturbation and massive subcrustal erosion further an expression of a deep seated mantle thermal anomaly has also been found below the parnapalle region of the sw cuddapah basin beneath which deeper crustal layers have exhumed

comment on new ar ar ages of southern indian kimberlites and a lamproite and their geochemical evolution by osborne et al precambrian res 189 2011 91 103 abstract osborne et al 2011 precambrian res 189 91 103 report new 40 ar 39 ar age results for two kimberlites muligiripalle pipe 5 and tummatapalle pipe 13 and one lamproite pochampalle from the archaean dharwar craton in southern india previous studies indicate that kimberlites and related rocks are highly susceptible to extraneous argon contamination leading to anomalously old ages although reliable 40 ar 39 ar ages can be obtained from step heating analyses of groundmass phlogopite grains osborne et al 2011 carried out single step 40 ar 39 ar fusion analyses on phlogopite phenocrysts and xenocrysts this approach is not favoured because it does not allow identification of argon loss gain effects thus complicating data interpretation and reducing confidence in the reliability of the reported ages in particular it is suggested that the pochampalle lamproite was emplaced osborne et al 2011 it is recommended that 40 ar 39 ar geochronology of kimberlite and lamproites include step heating analyses of matrix phlogopite grains with anomalous or contentious results verified using other dating methods

earthquake induced chains of geologic hazards patterns mechanisms and impacts large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking most moderate and large magnitude earthquakes trigger landslides ranging from small failures in the soil cover to massive devastating rock avalanches some landslides dam rivers and impound lakes which can collapse days to centuries later and flood mountain valleys for hundreds of kilometers downstream landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows cracks and fractures can form and widen on mountain crests and flanks promoting increased frequency of landslides that lasts for decades more gradual impacts involve the flushing of excess debris downstream by rivers which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency settlements ecosystems and infrastructure ultimately earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales two recent events have attracted intense research into earthquake induced landslides and their consequences the magnitude m 7 6 chi chi taiwan earthquake of 1999 and the m 7 9 wenchuan china earthquake of 2008 using data and insights from these and several other earthquakes we analyze how such events initiate processes that change mountain landscapes highlight research gaps and suggest pathways toward a more complete understanding of the seismic effects on the earth s surface

bedding plane slip in initial stages of fault related folding abstract frictional slip along bedding planes contributes to fault related folding of layered rocks we use numerical experiments to investigate the deformation of frictional bedding planes near dipping faults under layerparallel contraction and extension within the numerical experiments contraction boundary conditions produce asymmetric anticlines and extension produces asymmetric synclines the fold shape may be used to infer dip of the underlying fault in situations where the fault may not be observable additionally sense of slip along bedding planes may indicate proximity to the fault tip under uniform remote tectonic strain fault slip induces deformation in both the hangingwall and the footwall at depths as shallow as 1 km there is no significant difference between fold amplitudes in the hangingwall and the footwall this result is contrary to many kinematic models currently in use kinematic models of fault related folds commonly include the development of flat ramp and flat ramp flat fault geometries which may be attributed to initial ramp thrusting and later flat development our mechanical models show that fault flats may be produced from fault ramps due to slip along frictional bedding planes near the thrust fault tips our numerical experiments also evaluate joint initiation joints perpendicular to bedding are promoted in extensional environments we compare the results of the mechanical model to kinematic models of fault propagation folds and conclude that mechanical models offer important insights to better understand the folding process

contrasting high and intermediate pressures of metamorphism in the archaean sargur schists of southern india the archaean karnataka craton of southern india contains eastern and western crustal blocks separated by a major thurst in which sargur schists occur as lenses within tonalitic peninsular gneisses the schist complex comprises pelites quartzitic psammites carbonates and calc silicates iron formations and basic rocks and thus provides many mineral assemblages ideal for the calculation of pt conditions with their gneisses the sargur rocks are unconformably overlain by the dharwar greenstone belts and are generally thought to be older than 3 000 my

catastrophic emplacement of the heart mountain block slide wyoming and montana usa the mechanism that allowed many tens of km of movement of the enormous block slide floored by the rootless heart mountain detachment fault in nw wyoming has long been a puzzle carbonat rich microbreccia that is widespread along the fault and in dikes in the upper plate contains accreted grains indistinguishable from those observed as fallout from volcanic eruption clouds accretionary lapilli and impact ejecta clouds and in intrusive diatremes in these settings and also in industrial processing accreted grains form when particles in a turbulent gaseous suspension containing limited water adhere to a nucleating grain or to each other elongate grains in thick microbreccia have strong but diverse shap preferred orientations unlike those reported from other fault rocks but instead suggestive of turbulent flow and the microbreccia contains layering and other features of sedimentary character that appear to record deposition from suspension rather than frictional processes along a fault we suggest that frictional heating led to dissociation of carbonate rock along the fault producing supercritical co 2 as the suspending medium high co 2 pressure drastically reduced friction along the fault and allowed continuation of catastrophic movement probably initiated by a volcanic or phreatomagmatic explosion resulting in very large displacement on a low dipping surface earlier slower sliding may have occurred but final emplacement was rapid minutes and spectacular

smnd pbpb and rbsr geochronology and petrogenesis of the mafic dyke swarm of mahbubnagar south india implications for paleoproterozoic crustal evolution of the eastern dharwar craton abstract the sm nd rb sr and pb pb isotopic systematics of whole rock and separated mineral fractions from four tholeiitic mafic dykes of the mahbubnagar swarm have been investigated this dyke swarm intrudes the granitic basement of the cuddapah basin in the eastern dharwar craton edc the sm nd data on whole rock samples of four gabbros and one dolerite and 15 mineral fractions yielded a linear array with an isochron age of 2173 64 ma and an initial nd value of 0 4 0 3 the sm nd data of a metapyroxenite and its three mineral fractions plot parallel to this array yielding an isochron age of 2189 123 ma with a negative initial nd value of 1 8 1 4 rb sr and pb pb internal isochron ages of three gabbros and a pb pb internal isochron age of a metapyroxenite dyke range between 2031 and 2284 ma and within the limits of experimental error broadly conform to the sm nd isochron age by contrast rb sr internal isochron ages of three other samples range between 1474 and 1952 ma and one sample yields a pb pb internal isochron age of 3446 ma showing the effects of partial isotopic resetting possibly due to hydrothermal alteration these data suggest that mafic dykes of the mahbubnagar swarm were emplaced at c 2170 ma marking an episode of the crustal extension and fracturing which ultimately resulted in the formation of the cuddapah basin different petrological and geochemical variants of mafic dykes seen in the area most probably represent generation and or crystallization of the progressively evolved batches of magma during a relatively short time interval the initial nd values calculated at 2170 ma range from 0 6 to 2 0 and can be explained as reflecting contamination of depleted mantle derived magma by crustal rocks of edc the initial 87 sr 86 sr ratios 0 7027 0 7064 and model 1 values 8 3 8 5 of apparently undisturbed samples are also consistent with this suggestion

structural framework of the zagros fold thrust belt iran abstract data gleaned from the literature on the zagros have been compiled and used in conjunction with new interpretations to provide a better picture of the structures sedimentation history and deformation of this hydrocarbon rich mountain belt the belt parallel mountain front the n s trending kazerun izeh and e w trending bala rud fault zones are defined as the master structural elements of the belt these fault zones divide the zagros basin into zones with different stratigraphic successions and different rheological profiles this resulted in different structural styles developing along the belt during the subsequent collision the kazerun and izeh fault zones acted as the depositional system transition zone between the lurestan and fars regions in jurassic cretaceous time and partly controlled the distribution of the kazhdumi formation one of the major source rocks by the end of the cretaceous the nw se trending mountain front fault divided the present folded belt of the zagros into a major foreland basin to the southwest and a piggyback basin to the northeast activity along other major transfer fault zones including the izeh kazerun and bala rud fault zones occurred at this time and controlled the sedimentation and subsidence of the dezful embayment the main target region for hydrocarbon exploration these fault zones controlled the thickness of the asmari formation one of the main reservoirs and also the considerable thickness and facies changes of the gachsaran formation the major seal to the asmari formation the present morphology of the mountain belt is interpreted as being mainly related to the pinning of the mountain front fault to the northwest of the dezful embayment and to the north of the strait of hormuz

evironmental change in southwestern iran the holocene ostracod fauna of lake mirabad ostracod faunal data are presented from a sediment core taken from extant iranian lake mirabad ostracod faunal successions indicate relatively high concentrations of mainly nektonic taxa between c 9265 and 6505 cal 14c yr bp followed by lower concentrations of mainly benthic forms after 6505 cal bp these results suggest that lake levels were low during the early holocene and that water levels rose during mid holocene times notably after c 4048 cal 14c yr bp these findings confirm and consolidate palaeoclimatic inferences based on previously published pollen diagrams from the region but indicate an apparent timelag between the early to mid holocene forest advance and increased lake levels this may be explained by changes in precipitation evaporation ratios the increase in winter precipitation was sufficient to allow the expansion of arboreal vegetation but summer evaporation remained high this also gives support to the idea that the delayed readvance of forests in eastern turkey and western

predictability of long runout landslide motion implications from granular flow mechanics quality of landslide motion prediction is directly linked to the understanding of the basic flow mechanisms although it is known that landslides are granular mass flows and granular flow mechanics is an established area of research hypotheses on landslide motion are still based on simple geometrical relations and heuristic assumptions new insights into the development of flow properties of high speed high concentration granular flows are given by results of discrete particle simulations rapid granular flows are self organizing dynamic systems that are forced to develop a plastic body rheology this behaviour must be described by a coefficient of internal friction cm that refers to the center of mass of a flow coefficients of rapid granular flows of inelastic and rough particles which are typical for common rock materials do not vary significantly around cm 0 45 that is definitively smaller than the friction coefficient of soil creep 0 6 the motion of the center of mass is superimposed by the spreading of the granular mass that is controlled by the same plastic body rheology this combined motion is a scale invariant self similar process that depends only on the drop height of a landslide and its volume this allows specification of implications that must be given special attention in the development of future models for landslide prediction

role of hydrothermal activity in uranium mineralisation in palnad sub basin cuddapah basin india abstract unconformity related uranium mineralisation occurs in banganapalle formation of palnad sub basin cuddapah basin several evidences of hydrothermal activity exist in both basement granite and the cover sediments in koppunuru and rallavagu tanda r v tanda uranium prospects of palnad sub basin profuse development of fracture filled veins consisting of epidote quartz chlorite quartz and quartz is observed at various depths above and below unconformity fluid rock interaction during the formation of these veins has resulted in the alteration of feldspars and mafic minerals of granite and arkosic quartzite into a mineral assemblage consisting of various proportion of illite chlorite muscovite and pyrite with the intensity of alterations being highest near to the unconformity pyrite is often associated with illite dominant alteration zone we infer that circulation of basinal brine through basement granite and cover sediments was responsible for mobilising uranium from granite and its precipitation at favourable locations in cover sediments increase in ph of ore fluid due to illitisation and chloritisation of wallrock together with availability of carbonaceous matter and pyrite as reductant have controlled the localisation of uranium mineralisation in banganapalle formation

evolution of the west andean escarpment at 18 s n chile during the last 25 ma uplift erosion and collapse through time abstract the geological record of the western andean escarpment warp reveals episodes of uplift erosion volcanism and sedimentation the lithological sequence at 18 s comprises a thick pile of azapa conglomerates 25 19 ma an overlying series of widespread rhyodacitic oxaya ignimbrites up to 900 m thick ca 19 ma which are in turn covered by a series of mafic andesite shield volcanoes between 19 and 12 ma the surface of the oxaya ignimbrites evolved into a large monocline on the western slope of the andes a giant antithetically rotated block oxaya block 80 km 20 km formed on this slope at about 10 12 ma and resulted in an easterly dip and a reversed drainage on the block s surface morphology topography and stratigraphic observations argue for a gravitational cause of this rotation a secondary gravitational collapse 50 km3 extending 25 km to the west occurred on the steep western front of the oxaya block alluvial and fluvial sediments 11 2 7 ma accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall indicating further shortening between 8 and 6 ma flatlying upper miocene sediments

pb pb age of earliest megascopic eukaryotic alga bearing rohtas formation vindhyan supergroup india implications for precambrian atmospheric oxygen evolution abstract though considered to be the earliest known well preserved megascopic body fossil of an eukaryotic alga grypania spiralis has not yet been dated directly and reliably in any of its four known locations in the world we report a pb pb isochron age of 1599 48 ma for the grypania bearing rohtas formation of the vindhyan supergroup central india besides being about 500 myears older than the previously inferred age for this formation this pb pb age together with close age constraints on the same fossil bearing horizons in jixian china and montana usa indicates that grypania bloomed on a global scale between 1 6 and 1 5 ga being an obligate aerobe the appearance of a much older grypania within one of the principal bif deposits near michigan usa has been linked to a significant jump in atmospheric oxygen between 2200 and 1900 ma inferred from geochemical evidence the long gap of 400 myears between the older and younger grypania occurrences could be due to reduction of atmospheric oxygen below the grypania survival threshold as a result of extensive bifs between about 1950 and 1850 ma

without power landslide inventories in the face of climate change projected scenarios of climate change involve general predictions about the likely changes to the magnitude and frequency of landslides particularly as a consequence of altered precipitation and temperature regimes whether such landslide response to contemporary or past climate change may be captured in differing scaling statistics of landslide size distributions and the erosion rates derived thereof remains debated we test this notion with simple monte carlo and bootstrap simulations of statistical models commonly used to characterize empirical landslide size distributions our results show that significant changes to total volumes contained in such inventories may be masked by statistically indistinguishable scaling parameters critically depending on among others the size of the largest of landslides recorded conversely comparable model parameter values may obscure significant i e more than twofold changes to landslide occurrence and thus inferred rates of hillslope denudation and sediment delivery to drainage networks a time series of some of earth s largest mass movements reveals clustering near and partly before the last glacial interglacial transition and a distinct step over from white noise to temporal clustering around this period however elucidating whether this is a distinct signal of first order climate change impact on slope stability or simply coincides with a transition from short term statistical noise to long term steady state conditions remains an important research challenge copyright 2011 john wiley sons ltd

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

deformation pattern in the kurnool and nallarnalai groups in the northeastern part palnad area of the cuddapah basin south india and its implication on rodinia gondwana tectonics abstract the proterozoic basins of india adjoining the eastern ghats granulite belt eggb in eastern and southern india contain both mesproterozoic and neoproterozoic successions the intracratonic set up and contractional deformation fo the neoproterozoc successions in the paland sub basin in the northeastern part of cuddapah basin and similar crustal shortening in contemporaneous successions lying west of the eggb and nellore schist belt nsb are considered in relation to the proposed geodynamic evolution of the the rodinia and gondwana supercontinents tectonic shortening in the palnad sub basin northeast cuddapah partitioned into top to westnorthwest thrust shear flexural folds and cleavage development under overall e w contraction suggests foreland style continental shortening within an intracratonic set up a thrust sheet containing the nallamalai rocks and overlying the kurnool rocks in the northeastern part of palnad sub basin exhibits early tight to isoclinal folds and slaty phylllitic cleavage which can be correlated with early mesoproterozoic deformation structures in the nothern nallamalai fold belt nfb nne ssw trending folds and cleavage affect the kurnool group and overprint earlier structures in the thrust sheet thrusting of the nallamalai rocks and the later structures may have been related to convergence of the eastern ghats terrane and the east dharwar bastar craton during early neoproterozoic greenvillian and or later rejuvenation related to pan african amalgamation of east and west gondwana

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

geological and morphological study of the daguangbao landslide triggered by the ms 8 0 wenchuan earthquake china abstract landslides are one of the most significant geomorphic processes in mountainous regions recently a gigantic landslide daguangbao dgb landslide with a volume of 1 2 109 m3 was triggered by the ms 8 0 wenchuan earthquake china and has attracted widespread attention this landslide 28 38 16 93 e 104 06 02 35 n is located 85 km north northeast nne of the epicenter and on the hanging wall side 4 km away from the surface rupture zone of the earthquake our long term 2008 present study which includes topographic interpretation and geological and geomorphological investigations allows us to define the geological model of the dgb landslide and estimate the initiation and traveling mechanisms the topography was studied by using high resolution digital elevation models arial images and abundant photos at different scales are used to performed geomorphological analysis the geology in the landslide area was studied by exploratory trenches a tunnel and terrestrial laser scanning tls the results show that the mass movement destabilized a folded slope along a deep seated average depth of 400 m bedding fault developed in the dolomite of the sinian formation the morphology of the landslide main scarp is characterized by steep 55 75 and high up to 730 m release surfaces resulting from the linkage of three joint sets an excess pore water pressure dependent loss of shear strength at the basal layer during the earthquake is assumed to have favored landslide initiation an internal shear running subparallel to the stratification surface is confirmed to have dominated the longitudinal mobility of the landslide and driven landslide mass thrusting to a height of 500 m on the slopes on the other side of the valley the dgb landslide as a transient destabilization and morphogenesis event has largely contributed to erosion in the study area

geometry kinematics and fracture pattern of the bangestan anticline zagros sw iran thrust related anticlines in the zagros simply folded belt provide excellent exposed analogue structures for fractured reservoirs located in the more external sectors of the belt in these structures it is possible to study the fracture network attributes and understand their relationships to the folding process thus gathering fundamental information for fracture modelling in reservoirs in this work we analyse the mesoscopic deformation pattern of the nw se trending bangestan anticline sw zagros iran and discuss its relationship to the kinematic evolution of the hosting structure the deformation pattern mostly includes extensional structures and pressure solution cleavages striking parallel to the fold axial trend i e longitudinal transversal extensional structures and n s and e w striking extensional structures oriented oblique to the fold axis with the aid of deep wells and a transversal reflection seismic profile we constructed a balanced cross section of the anticline and propose a kinematic evolution pathway constrained by the mesoscopic deformation pattern longitudinal and transversal deformation structures developed before and or in the very early stages of fold growth during this stage the bangestan anticline grew as a set of unconnected decollement anticlines involving the cambrian to pliocenic sedimentary cover in a later stage inherited basement faults were reactivated with a right lateral strike slip component and the previously developed anticlines propagated laterally up to their complete linkage and thrust breakthrough this produced the right lateral strike slip reactivation of longitudinal joints and the development of n s and e w striking extensional structures which were also frequently reworked as strike slip faults

structures of the zagros fold thrust belt in iran the zagros fold thrust belt in iran forms the external part of the zagros active orogenic wedge it includes a sequence of heterogeneous latest neoproterozoic phanerozoic sedimentary cover strata 7 to 12 km thick and composed of alternating incompetent and competent layers overlying precambrian crystalline basement with a complex pre zagros structural fabric balancing structures of the cover statigraphic units in the zagros fold thrust belt requires in sequence and out of sequence involvement of the precambrian basement in the deformation six detailed balanced and retrodeformable cross sections which are constructed based on geological and geophysical data across various sectors of the belt show fault bend and fault propagation folds interpreted to have formed by slip on their subjacent thrusts out of sequence basement rooted thrusts as the interpretations in the constructed cross sections suggest have breached the cover basement interface and using incompetent cover strata for propagation cut across the cover structures and have created associated new folds superimposed upon the pre existing structures this style of deformation which has resulted in structural complexity of the belt characterizes a 200 to 300 km wide zone of distributed partly synchronous deformation with along strike and across strike variations it also implies that the zagros fold thrust belt as the external part of the orogenic wedge is still in its subcritical condition with internal deformation to achieve a critical taper in creating structural complexity in addition to out of sequence thrusting mechanically weak layers evaporites and mudstones of the cover strata have played a significant role by providing several detachment horizons shortening estimates across the belt are variable based on the constructed cross sections and their restorations minimum shortening estimates range from 16 percent to 30 percent in different sectors of the belt

imprints of a proterozoic tectonothermal anomaly below the 1 1 ga kimberlitic province of southwest cuddapah basin dharwar craton southern india summary a detailed 2 d modelling of the seismic structure and other geological and geophysical signatures across the cuddapah basin of the southern indian shield suggests upwarping of highvelocity and high density layers which are observed close to the surface below the southwestern part of the basin this anomalous feature is constrained by i a strong gravity high anomaly of about 55 mgal ii a 100 km wide high conductivity anomaly resistivity 100 m extending from surface to a minimum depth of 50 km in the mantle lithosphere and iii large scale massive intrusive activity these features are interpreted to be an expression of a thermal anomaly which may have acted like a plume during the proterozoic and could well correspond to a 1 1 ga kimberlitic activity below this region the thin granitic gneissic crust is underlain by well differentiated high velocity layers possibly due to underplating and densification of much of the crust by extruded magma

lithospheric electrical imaging of the deccan trap covered region of western india 1 we present here the results of magnetotelluric mt studies carried out along a 330 km long ne sw trending traverse from daulatabad at the northeastern end to koyna on the southwestern end across the deccan volcanic province dvp in western india the 2 d mt modeling results obtained along this traverse together with those from other mt traverses in this area are examined and integrated with the results from deep seismic sounding 3 d teleseismic tomography and heat flow studies the deep geoelectric section as deduced from mt models point out to a two layered lithospheric mantle structures with an upper very high resistive layer several thousands of ohm m and a bottom relatively conductive one a few tens of ohm m to a few hundred ohm m the lithospheric electrical structure is inferred to be linked to compositional changes associated with a depleted lithospheric upper mantle in the dharwar craton an impressive feature that the study has brought out is the presence of a well defined lithospheric upper mantle conductor in the depth range of 80 120 km limited to the middle segment of the mt traverse from sangole to partur over the dvp the electrical characterization of the region including the presence of upper mantle conductor shows close similarities with that of other similar cratonic regions like the slave and superior cratons in northwestern canada

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

detrital mineral age radiogenic isotopic stratigraphy and tectonic significance of the cuddapah basin india abstract the cuddapah basin is one of a series of proterozoic basins that overlie the cratons of india that due to limited geochronological and provenance constraints have remained subject to speculation as to their time of deposition sediment source locations and tectonic geodynamic significance here we present 21 new stratigraphically constrained u pb detrital zircon samples from all the main depositional units within the cuddapah basin these data are supported by hf isotopic data from 12 of these samples that also encompass the stratigraphic range and detrital muscovite 40ar 39ar data from a sample of the srisailam formation taken together the data demonstrate that the papaghni and lower chitravati groups were sourced from the dharwar craton in what is interpreted to be a rift basin that evolved into a passive margin the nallamalai group is here constrained to be deposited between 1659 22 ma and 1590 ma it was sourced from the coeval krishna orogen to the east and was deposited in its foreland basin nallamalai group detrital zircon u pb and hf isotope values directly overlap with similar data from the ongole domain metasedimentary rocks depositional age constraints on the srisailam formation are permissive with it being coeval with the nallamalai group and it was possibly deposited within the same basin the kurnool group saw a return to dharwar craton derived provenance and is constrained to being neoproterozoic it may represent deposition in a long wavelength basin forelandward of the tonian eastern ghats orogeny detrital zircons from the gandikota formation which is traditionally considered a part of the chitravati group constrain it to being deposited after 1181 29 ma more than 700 ma after the lower chitravati group it is possible that the gandikota formation is correlative with the kurnool group the new data suggest that the nallamalai group correlates temporally and tectonically with the somanpalli group of the pranhita godavari valley basin which is tightly constrained to being deposited at 1620 ma these syn orogenic foreland basin deposits firmly link the se india proterozoic basins to their orogenic hinterland with their discovery filling a missing link in the tectonic development of the region

a regularized wiener hopf filter for inverting models with magnetic susceptibility abstract for a magnetic target the spatial magnetic signal can be expressed as a convolutional integral over green s function of an assumed model with susceptibility as its parameter a filter can be used to obtain the susceptibility by minimizing the mismatch between observed and the computed magnetic anomalies in this perspective we report the development of an advanced digital filter which is efficient and can be used to map rock susceptibility from the acquired magnetic data to design the new filter we modified the space domain standard wiener hopf filter by imposing two different constraints i the filter energy constraint and ii normalization of the filter coefficients these constraints make it capable to characterize source bodies from their produced magnetic anomalies we assume that the magnetic data are produced by induced magnetization only and interpretation can be as good as the subsurface model our technique is less sensitive to the data noise which makes it efficient in enhancing the interpretation model the modified filter demonstrates its applicability over the synthetic data with additive white gaussian noise in order to check the efficacy and adaptivity of this tool in a more realistic perspective it is also tested on the real magnetic data acquired over a kimberlitic district adjoining to the western margin of the cuddapah basin in india to identify the source bodies from the anomalies our result shows that the modified wiener hopf filter with the constraint for the magnetic data is more stable and efficient than the standard wiener hopf filter

the gigantic seymareh saidmarreh rock avalanche zagros fold thrust belt iran the seymareh rock avalanche first described by j v harrison and n l falcon in the 1930s is the largest known subaerial non volcanic landslide on earth the volume of its debris 44 gm 3 is approximately equal to that of the largest known subaerial landslide of any kind the 100 ka collapse of mount shasta volcano 45 gm 3 and approaches those of gigantic landslides on mars using satellite imagery srtm 3 data and detailed field investigations we gain a new understanding of the gigantic rock avalanche the initial failure 38 gm 3 involving a dip slope consisting of a relatively weak interbedded limestone mudrock sequence capped by resistant asmari limestone had an average thickness of 410 m along a 15 5 km width of the kabir kuh anticline the rockslide transformed into a rock avalanche that travelled 19 0 km with a fahrboschung the angle between the highest point of the pre landslide source area topography and the distal limit of the debris of only 3 6 initial failure involved complex planar sliding dictated by four structural elements 1 bedding parallel shears and 2 across bedding break throughs combined to produce a low angle 11 overall sliding surface that 3 broke out through the asmari carapace at the toe of the failed slope while 4 tectonically weakened bedding normal joints provided lateral release surfaces nine discrete bedding parallel basal sliding surfaces divided the detached mass into nine stacked plates the upper plate 23 gm 3 included 20 7 gm 3 of asmari limestone analysis of accelerator mass spectrometry radiocarbon dates from this study and by others indicates that the rock avalanche occurred between c 8710 and 9800 14 c years bp supplementary material a summary of the tectonics stratigraphy and physiography of the zagros fold thrust belt together with a description of surficial gravity collapse structures in the region harrison falcon 1934 1936 is available at www geolsoc org uk sup18612

sedimentology of rock avalanche deposits case study and review abstract detailed sedimentological studies concerning different facies types and the factors influencing their development such as lithology topography substrates etc were carried out at the carbonate tschirgant rockslide rock avalanche deposit in the eastern alps of austria several depositional facies and sub facies have been identified at this and other sites by many researchers these facies are found throughout the debris regardless of depth or travel distance and result from highly heterogeneous stress distributions in time and space during emplacement one of the most important recent observations in terms of emplacement dynamics is that shear is not confined to the base but is distributed throughout the debris except the coarse carapace due to the preservation of source stratigraphy in these non turbulent mass movements any horizontal facies or grain size variations need to be regarded in context since they strongly depend on source stratigraphy and hence the spatial distribution of lithologies i e geological units of different mechanical properties for example some lithologies do not form a boulder carapace due to absence of large in situ blocks in the source rock mass however at tschirgant slight facies maturation with distance within the same lithology is observed i e clast fragmentation progresses to create the distinct facies characteristic grain size distribution only after some distance travelled these details are revealed through facies based sampling and analysis studies based on bulk sampling in some cases observed progressively reduced grain sizes with distance and depth which might be a function of added variations within different facies sampled together in this paper the wealth of observations on rockslide and rock avalanche sedimentology of the past decades is combined with a detailed case study of a lithologically relatively simple deposit to outline global and site specific depositional structures and facies with the aim to summarize review and refine the current state of knowledge on rock avalanche and rockslide emplacement processes

insights into rock avalanche emplacement processes from detailed morpho lithological studies of the tschirgant deposit tyrol austria large rapid rockslope failures generate deposits with complex morphologies due to a number of causal and influencing factors to investigate these we conducted a detailed case study at the carbonate tschirgant deposit tyrol austria it preserved evidence of simultaneous rock sliding very large coherent hummocks and rock avalanche spreading smaller more scattered hummocks and ridges motion indicators such as longitudinal ridges furthermore pinpoint the transition between linear sliding and radial spreading the lithological distribution in the tschirgant deposit shows that it retained source stratigraphy despite being split into two accumulation lobes by a high bedrock ridge furthermore lithology had a very strong control on the final deposit morphology in that the different lithologic units form individual deposit surfaces river erosion has created fortuitous outcrops that reveal the basal rock avalanche contact the underlying valley fill sediments substrates have been intricately involved in shaping the rock avalanche morphology and where entrained highlight internal rock avalanche deformation features this study shows that intrinsic dynamic properties of granular media e g tendency for longitudinal alignments emplacement mode lithology and source predisposition runout path topography and substrates form the quintet of causal factors that shape rock avalanche morphology copyright 2015 john wiley sons ltd

the neoproterozoic cratonic successions of peninsular india abstract the peninsular india hosts extensive record of mesoproterozoic and neoproterozoic successions in several mobile belts and cratonic basins the successions provide excellent opportunities for chronostratigraphic classification in tune with the chronometric classification adopted by iugs for inter regional correlation on a global scale major tectono thermal events at 1000 950 ma in the mobile belts correlatable with the grenville orogeny may be considered as the datum for meso neoproterozoic classification in india principles of chronostratigraphic classification however can not be applied yet to the cratonic successions of india because of inadequate radiometric data paucity of biostratigraphic studies and lack of regionally correlatable stratigraphic or palaeoclimatic datum the kimberlite magmatism which affected the peninsular india on a continental scale at about 1100 ma holds the key to the identification of neoproterozoic successions of the cratonic basins thus the stratigraphically confined diamond bearing conglomerates and or the tuffs associated with kimberlites may be considered as the datum to define the base of the neoproterozoic fixed at about 1000 ma accordingly the rewa and bhander groups in the vindhyan basin the kurnool group in the cuddapah basin the jagdalpur formation in the indravati basin and the sullavai group in the pranhita godavari basin are taken to represent the neoproterozoic successions in the peninsular india the chattisgarh group in the central india the lower part of the marwar supergroup in western rajasthan the badami group in the kaladgi basin and the bhima group are the other possible neoproterozoics in the peninsula the closing phase of the mesoproterozoic in all these basins are characterised by stable shelf lithologic associations attesting to high crustal stability the neoproterozoic basins by contrast mark a new phase of rifting and extension and the basin fills exhibit signatures of initial instability which evolved with time into a more stable platformal condition a major episode of sea level rise has been recorded in most of the basins the riftogenic origin and evolution of the basins are comparable with the history of neoproterozoic basins of australia though there is no unequivocal record of glaciation in the indian formations

magnetic mapping of majhgawan diamond pipe of central india magnetic response over kimberlite lamproite pipes can be used to map their horizontal and vertical cross sections a published ground magnetic vertical intensity contour map is used to map the majhgawan kimberlite pipe near panna in central india using barnett s 1976 method we obtained a reasonable match between the computed and observed fields with three separate bodies the model suggests a possible later intrusion into the main pipe geological studies using drill hole data imply a nearly concentric vertical lithological zoning within the pipe and thus support the hypothesis of multiple intrusions indicated by magnetic data the multiple intrusion hypothesis is of interest to exploration because specific intrusions within one composite pipe may differ markedly in the incidence of diamonds the higher incidence of diamonds reported in the central part of the majhgawan pipe as compared to the outer part also supports the possibility of a later intrusion into the main pipe

c o sr and pb isotope systematics of carbonate sequences of the vindhyan supergroup india age diagenesis correlations and implications for global events abstract the vindhyan supergroup of central india records a substantial portion of proterozoic time and contains some of the most disputed precambrian cambrian fossil discoveries despite the significance of these fossil finds many issues including reliable geochronology remained unresolved similarly the geochemical aspects of the sedimentary sequences and their implications to the evolution of proterozoic oceans have been studied only at a reconnaissance level here we report the results of the pb pb dating for the rohtasgarh limestone from the lower vindhyan supergroup giving an age of 1601 130 ma an estimate that is in accord with the recent u pb zircon dating of the lower vindhyan supergroup by rasmussen et al geology 30 2002 103 and ray et al geology 30 2002 131 sr isotope stratigraphy of carbonates from the upper vindhyan supergroup suggests a mid neoproterozoic 750 650 ma age for these formations this in turn argues for a long hiatus between the deposition of the lower and upper vindhyan supergroups our results conflict with the reports of cambrian age small shelly fossils and ediacaran fossils from the upper vindhyan rocks at the same time they suggest that the alleged trace fossils in the lower vindhyan rocks must be of paleoproterozoic age the most common 18 o values for calcitic components from limestone formations of the supergroup range from 10 to 7 similar to paleo neoproterozoic carbonates worldwide the modes of 13 c in the lower and upper vindhyan supergroups are 0 2 and 3 2 respectively again consistent with the worldwide dataset the secular patterns of carbon isotope trends do not support the earlier assumptions that the carbonate sequences at the southern margin correlate with those at the western or northern margins of the vindhyan basin c and sr isotope data provide new calibration points for the seawater evolutionary curves particularly for the paleoproterozoic for strontium isotopes the data from the lower vindhyan supergroup suggest that seawater departed probably less rapidly from mantle values than was previously believed

lake sediments deposited on the flims rockslide mass the key to date the largest mass movement of the alps long piston cores taken from the subsurface of two mountain lakes of the eastern swiss alps recovered sediments which overlie the flims rockslide deposits these sediments provide new information on the chronology of the largest known alpine rockslide and can be used to reconstruct the post landslide environmental evolution the oldest 14 c date of the lake sediments yields a minimum age of the rockslide at 9660 9430 cal yr bp in addition the dating of a wood fragment contained in the rockslide deposits directly below the lake sediments shows a maximum age of 9480 9120 cal yr bp the overlap of the maximum and minimum ages 9480 9430 cal yr bp approximates the age of the flims rockslide this early holocene range coincides with a period of higher frequency of large mass movements observed in the alps which could be related to climatic changes

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

dynamic disintegration processes accompanying transport of the holocene flims sturzstrom swiss alps abstract a sturzstrom is a large scale landslide that evolves during transport into a rapid granular flow rock avalanche by a dynamic disintegration process numerous theoretical hypotheses have been proposed to explain the excessive mobility of these catastrophic mass movements but the role of disintegration processes remains poorly understood exceptional outcrop conditions at the giant 12 km3 flims sturzstrom swiss alps permit the analysis of disintegration processes that result from shearing during transport in confined zones of the rock mass shearing is concentrated along preferred surfaces originating as bedding planes which evolve into shear band layers differential velocities of slabs separated by these shear layers induce oblique fractures in the slabs by accommodation contacts between grains are maintained in the shear layers in unconfined zones near the top and the lateral margins shearing generates dilatancy the rock mass is affected by anisotropic dispersion without mixing and disintegrated material is preferentially produced to the top due to inflation the rock slide then evolves to a granular flow the consequence of these processes is the formation of two distinct depositional facies in the sturzstrom the structured facies exhibits a stratified aspect close to the base reflecting confined slab on slab shearing motion towards the top and distally it evolves into a chaotic facies with some isolated pockets of the structured facies reduction of confining forces on the moving sturzstrom allows transformation of the structured facies into the chaotic facies this characteristic transition observable in many sturzstrom deposits seems to be necessary for the rock avalanche process to occur and offers insights into the long runout characteristics of these catastrophic mass movements

green lake landslide and other giant and very large postglacial landslides in fiordland new zealand abstract green lake landslide is an ancient giant rock slide in gneiss and granodiorite located in the deeply glaciated fiordland region of new zealand the landslide covers an area of 45 km 2 and has a volume of about 27 km 3 it is believed to be new zealand s largest landslide and possibly the largest landslide of its type on earth it is one of 39 known very large 10 6 10 7 m 3 and giant 10 8 m 3 postglacial landslides in fiordland discussed in the paper green lake landslide resulted in the collapse of a 9 km segment of the southern hunter mountains slide debris moved up to 2 5 km laterally and 700 m vertically and formed a landslide dam about 800 m high impounding a lake about 11 km long that was eventually infilled with sediments geomorphic evidence supported by radiocarbon dating indicates that green lake landslide probably occurred 12 000 13 000 years ago near the end of the last otira glaciation the landslide is described and its geomorphic significance age failure mechanism cause and relevance in the region are discussed in relation to other large landslides and recent earthquake induced landslides in fiordland the slope failure occurred on a low angle fault zone undercut by glacial erosion and was probably triggered by strong shaking mm ix x associated with a large m 7 5 8 earthquake on the alpine fault c 80 km to the northwest geology was a major factor that controlled the style and size of green lake landslide and in that respect it is significantly different from most other gigantic landslides future large earthquakes on the alpine fault in fiordland are likely to trigger more very large and giant landslides across the region causing ground damage and devastation on a scale that has not occurred during the last 160 years with potentially disastrous effects on towns tourist centres roads and infrastructure the probability of such an event occurring within the next 50 years may be as high as 45

seepage problems in the right abutment of the shahid abbaspour dam southern iran abstract in this study seepage phenomena through the right abutment of shahid abbaspour dam are investigated the shahid abbaspour dam is a 200 m high arch dam which regulates the waters of the karun river serves power generation and flood control and irrigation needs the dam site lies in the zagros mountains of southern iran this region presents continuous series of mainly of karstic limestone marl shale and gypsum ranging in age from jurassic to pliocene the region has subsequently been folded and faulted seepage from the shahid abbaspour reservoir occurs mainly through the karstic limestone the basic foundation treatment of the dam consisted of consolidation grouting a high pressure grout curtain and a drainage curtain moreover a 144 m high and 30 m wide concrete cutoff wall was built to prevent reservoir seepage through a clay filled fracture zone in the right abutment the grout curtain penetrates the principal vuggy zone only beneath the central portion of the dam and below the cutoff wall in the right abutment fan curtains were constructed to reduce drainage flows but the seepage problem could not be solved in order to determine the seepage direction and karstification pattern hydrogeological studies have been carried out additional investigation boreholes have been drilled to monitor fluctuations in groundwater level besides these water chemistry dye tracer pinhole and xrf tests have been carried out as a result of these studies seepage paths have been identified in the karstic limestone in the right abutment of the dam

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

paleomagnetism of ca 2 3 ga mafic dyke swarms in the northeastern southern granulite terrain india constraints on the position and extent of dharwar craton in the paleoproterozoic abstract the pole positions reported for the mafic dykes occurring in the northeastern southern granulite terrain and easterly trending dykes of dharwar craton are alike while their ages differ by ca 700 ma confounding tectonic reconstruction to resolve the discordance and to constrain the position of the indian continent in the proterozoic paleomagnetic and geochronological studies have been carried out on the mafic dyke swam in the northeastern southern granulite terrain two distinct pole positions are obtained one from the group of tiruvannamalai dykes as 27 7 s 231 5 e dp dm 12 14 with corresponding mean declination dm and inclination im as 125 and 73 8 95 22 7 6 respectively and second from the east coast dykes as 2 32 s 188 2 e dp dm 5 8 with corresponding mean dm and im as 88 9 and 33 8 95 48 7 1 respectively the remanent efficiency of magnetization values between 0 01 and 0 08 suggest that the dykes have been cooled through curie temperature of magnetite which is the carrier of magnetization the baked contact test confirms that the characteristic remanent magnetization is the primary magnetization the sm nd mineral whole rock isochron from one of the tiruvannamalai dykes yielded an age of 2318 60 ma mswd 1 9 this age is the time of intrusion of the tiruvannamalai dykes and is similar within errors to the age of dykes in the dharwar craton thus the contiguity of dharwar craton with the northern block of southern granulite terrain as early as 2 3 ga ago is established the pole position thus obtained corresponds to a high latitudinal position of dharwar craton during early paleoproterozoic

palaeoproterozoic indian shield in the global continental assembly evidence from the palaeomagnetism of mafic dyke swarms abstract palaeomagnetic study of palaeoproterozoic mafic dykes in the basement along the margins of the cuddapah basin the largest precambrian sedimentary basin in south india is presented in detail for a general discussion of palaeoproterozoic igneous activity in india the results are compared with all earlier published data on mafic dykes in india and are integrated with recently published high precision u pb baddeleyite ages to provide a comprehensive account of palaeoproterozoic igneous activity in india the analysis consolidates palaeomagnetic poles for six age divisions between 2 45 and 1 85 ga with robust statistical criteria our best estimates of overall mean poles from 241 dykes are situated at 1 17 7 n 106 0 e a95 9 0 7n 24 at c 2 45 ga 2 7 1 n 57 2 e a95 4 5 n 69 at c 2 37 ga 3 41 6 s 5 5 e a95 5 1 n 34 at c 2 22 ga 4 4 7 n 343 0 e a95 4 4 n 31 at 2 18 ga 5 49 2 n 332 9 e a95 4 8 n 24 at 1 99 1 89 ga and 6 73 7 n 282 6 e a95 2 9 n 39 at 1 86 ga the data permit us to construct an apparent polar wander path for the indian shield for an 600 ma interval of the palaeoproterozoic eon 2 45 1 85 ga testing and evaluation of continental reconstructions for this interval which are mostly based on geological correlations reveal many inconsistencies between 2 45 and 2 37 ga the indian shield was situated at higher latitudes similar to the yilgarn craton of australia it was subsequently located near the equator at 2 22 2 18 1 99 and 1 86 ga thus an india australia connection is supported during these times but a proposed australia kaapvaal link in zimvaalbara and a dharwar india slave connection in sclavia or a superior zimbabwe india connection in superia are inconsistent with indian data in addition the close palaeomagnetic comparison between the palaeoproterozoic dykes of dharwar bastar bundelkhand cratons in india indicates an age of 2 45 ga for orogenic activity along the central indian tectonic zone hence matching this zone with the 2 0 1 8 ga trans north china orogenic belt or positioning north china adjacent to india or juxtaposition of the indian shield along the western margin of laurentia in the columbia reconstructions is not supported the indian data appear to be in accord with the essential features of the refined protopangaea model and the original ur configuration finally the results are interpreted in terms of four dyke emplacement events in the age range 2 45 2 18 ga linked to short lived 5 10 ma lips developed over mantle plumes the dykes of 1 99 1 89 ga age probably relate to continued long lived igneous activity while the 1 86 ga dykes are relatively fewer in number and may represent waning stage of a large igneous event related to a major mantle plume

timing of atmospheric precipitation in the zagros mountains inferred from a multi proxy record from lake mirabad iran abstract a sediment core 7 2 m long from lake mirabad iran was examined for loss on ignition mineralogy oxygen isotopic composition of authigenic calcite and trace element composition of ostracodes to complement earlier pollen and ostracode assemblage studies pollen ostracode inferred lake level and high sr ca ratios indicate that the early holocene 10000 to 6500 cal yr bp was drier than the late holocene low 18 o values during this interval are interpreted as resulting from winter dominated precipitation characteristic of a mediterranean climate increasing 18 o values after 6500 cal yr bp signal a gradual increase in spring rains which are present today a severe 600 yr drought occurred at ca 5500 cal yr bp shortly after the transition from pistachio almond to oak forest during the late holocene two milder droughts occurred at about 1500 and 500 cal yr bp within the resolution of the record no drought is evident during the collapse of the akkadian empire 4200 3900 cal yr bp rather a decrease in 18 o values to early holocene levels may indicate the return to a mediterranean precipitation regime

giant landslides topography and erosion abstract distributions of slope angles in tectonically active mountain belts point to the development of threshold conditions where hillslopes attain a critical inclination or height at which they fail readily because of limitations in material strength it has been proposed that hillslopes adjust to rapid uplift and bedrock incision through an increase in the rate of relief limiting landsliding rather than gradual slope steepening here we test this concept by investigating the relationship between mean local relief h which we take to be a proxy of long term erosion rates e and the occurrence of over 300 of the largest v 10 8 m 3 terrestrial landslides on earth we find that nearly two thirds of these giant landslides have occurred in the steepest 5 of the earth s land surface where relief is close to its proposed upper strength limit they are primarily located in deeply incised valleys along fault bounded fringes of active mountain belts and in volcanic arcs this distribution coincides with areas of high long term erosion rates 4 mm yr 1 confirming that giant landslides contribute to rapid denudation of mountains most of the eroded volume is concentrated in the smallest but steepest parts of mountain belts and volcanic arcs first order estimates of minimum erosion rates accomplished by the largest landslides are 0 01 mm yr 1 these rates are between 1 and 10 of the late pleistocene to holocene mean erosion rates in a given area importantly the landslide erosion rates show a nonlinear increase with mean local relief suggesting that the contribution of giant landslides in total and per event increases significantly with increasing overall erosion rates however giant landslides also occur in areas of lower than average relief h 300 700 m irrespective of whether threshold hillslopes have developed or not factors contributing to these failures include soft rocks extensive low angle discontinuities high rates of fluvial bedrock incision and tectonically driven deformation and slope loading

the 2000 yigong landslide tibetan plateau rockslide dammed lake and outburst flood review remote sensing analysis and process modelling abstract in april 2000 a large scale rock avalanche dammed the yigong zangpo river forming an extensive rockslide dammed lake the impoundment lasted for 62 days before a catastrophic breaching caused a massive outburst flood in the yarlung zangpo tibet and the dihang rivers india that travelled downstream to the main floodplain of the brahmaputra in northeastern india in response to discrepancies in the published literature on the event we present a review and re evaluation of the characteristics of the rock avalanche and associated landslide dammed lake we use digital topographical data srtm 3 and dynamic landslide modelling dan w and dan3d to determine the salient characteristics of the damming landslide and to characterise its behaviour our analysis indicates that the volume of the damming rockslide was ca 115 mm3 including 91 mm3 from the initial rockslope failure bulked during disaggregation to 109 mm3 and 6 mm3 from entrainment during its 10 1 km travel down zhamulong gully the debris travelled with an average velocity of 15 18 m s and resulted in a landslide dam on the yigong river with a minimum height of about 55 m using landsat 7 imagery obtained before during and after impoundment in conjunction with an srtm 3 dem we reproduced the filling of the lake we determine that the landslide dam formed an extensive reservoir with an impounded volume of 2 015 gm3 and a maximum possible lake level of 2264 m asl rounded to 2265 m asl our figures differ from those previously published but are believed to be well constrained verifiable estimates of the volumes of the 2000 yigong events the outburst occurred after an attempt by army personnel to manually dig a spillway over the landslide debris and resulted in the entire volume of the lake draining in about 12 h the outburst flood travelled over 500 km south into india with a recorded rise in river level of 5 5 m at the pasighat gauging station 462 km downstream in terms of historical outburst volumes from rockslide dammed lakes the volume of the 2000 yigong event is only exceeded by that of the 1841 outburst flood from the indus river rockslide dammed lake northern pakistan

mineralogy of the tk1 and tk4 kimberlites in the timmasamudram cluster wajrakarur kimberlite field india implications for lamproite magmatism in a field of kimberlites and ultramafic lamprophyres abstract a mineralogical study of the hypabyssal facies late cretaceous macrocrystic pulse of tk1 intrusion and the mesoproterozoic aphanitic pulse of tk4 intrusion in the wajrakarur kimberlite field of southern india shows that the rocks contain macrocrysts of forsteritic olivine phenocrysts and microphenocrysts of al na poor diopside and phlogopite set in a groundmass mainly of al na poor diopside and phlogopite other groundmass minerals are spinel perovskite and fluorapatite in tk1 and spinel titanite chlorite calcite and gittinsite in tk4 k richterite and perovskite occur only as inclusions in phlogopite and titanite respectively in tk4 late stage deuteric phases include pyrite and barite in tk1 and strontianite chalcopyrite galena and pentlandite in tk4 diopside microphenocrysts in tk4 exhibit oscillatory zoning with characteristics of diffusion controlled magmatic growth tk1 spinels show magmatic trend 2 that evolves from magnesiochromite and culminates in titaniferous magnetite whereas tk4 spinels are less evolved with magnesiochromite composition only tk1 phlogopites show a simple compositional trend that is typical of lamproite micas while four distinct growth zones are observed in tk4 phlogopites with the following compositional characteristics zone i high cr 2 o 3 and tio 2 and low bao zone ii low cr 2 o 3 zone iii low tio 2 and high bao zone iv low bao forsterite contents and trace element concentrations reveal two xenocrystic core populations and one magmatic rim population for tk1 olivines mineralogically both tk1 and tk4 are classified as diopside phlogopite lamproites rather than archetypal kimberlites the two lamproites are considered to have formed from the same parent magma but crystallised under distinct oxygen fugacity conditions with elevated content of fe 3 in phlogopite spinel and perovskite tk1 appears to have crystallised in a relatively high oxygen fugacity environment multiple growth generations of phlogopite spinel and fluorapatite in tk4 indicate a complex evolutionary history of the magma close spatial and temporal associations of mesoproterozoic kimberlites and lamproites in southern india can possibly be explained by a unifying model which accounts for the generation of diverse magmas from a range of geochemical resevoirs in a continental rift setting

rbsr ages of proterozoic kimberlites of india evidence for contemporaneous emplacement abstract rb sr analyses of leached phlogopite macrocrysts from kimberlite pipes 1 2 5 and 7 in south india give concordant ages of 1091 20 1092 15 1093 20 and 1091 10 ma respectively indicating contemporaneous emplacement of these pipes the present results are in contradiction with earlier measurements groundmass mineral assemblages with low rb sr ratios give a tight set of initial sr ratios at 0 7029 2 0 7019 2 0 7029 2 and 0 7030 4 suggesting derivation of the primary kimberlite magma from a relatively uniform and depleted mantle source a similar age and initial sr isotopic ratio of one sample of the majhgawan lamproite from central india imply that the proterozoic kimberlite lamproite activities in india though widely separated in space were nearly contemporaneous

plate margin paleostress variations and intracontinental deformations in the evolution of the cuddapah basin through proterozoic abstract the sedimentary basins are often influenced by adjoining mobile belts as is the case of the proterozoic cuddapah basin in southern india lying in proximity of the eastern ghats granulite belt egb and the southern granulite terrain sgt two major faults gani kalva and kona faults in the western part of the cuddapah basin have been examined in this work to comment on the changes in paleostress conditions affecting the basin evolution punctuated by several stages of extensional and compressional regimes in the time interval 1 9 0 5 ga the tensor solutions were obtained for the mesoscale faults and fault striae using the improved right dihedron method followed by the rotational optimization method tensor delvaux and sperner 2003 combining the paleostress field reconstruction and other structural stratigraphic attributes we propose a possible scenario of punctuated evolution of the cuddapah basin and its inversion the stress regimes are tentatively correlated with multiple stages of basin opening and deformation of basin in fill representing the pre grenvillian through the pan african orogeny the paleostress conditions derived from various stratigraphic horizons provide an opportunity to comment on the changes in tectonic stresses including several stages of extensional and compressive regimes in the cuddapah basin the tensor solutions were obtained for the mesoscale faults and fault striae in the neighborhood of above two fault lines using the improved right dihedron method followed by the rotational optimization method tensor delvaux and sperner 2003 the most prominent stress states recorded around the two fault lines can be classified into those affecting 1 the paleoproterozoic lower cuddapah successions 2 the younger kurnool group and 3 both the groups integrating the stress states of the fault slip analysis obtained from different unconformity bounded rock groups of lower cuddapah and other geologic data we suggest extensional to transtensive pure strike slip regime to be active during the first phase of basin opening and c 1 89 ga mafic igneous activity late compressional to transpressive pure strike slip regimes are well recorded from the younger kurnool group representing late neoproterozoic deformations the tensor solutions from different unconformity bound stratigraphic horizons constrain different states of deformation we relate the extensional to transtensive pure strike slip regimes from lower cuddapah successions to the ongoing basin opening events and the associated palaeoproterozoic igneous activities the late neoproterozoic to early paleozoic compressional to transpressive strike slip regime present the possible effects of compressional activities happening around the cratonic margin the present analysis lends further support to the idea that estimation of paleostress states from fault slip data even in regions of relatively weak deformation in continental interior are important while assessing influence of plate margin stresses on the continental interior

fracture patterns in the zagros simply folded belt fars iran constraints on early collisional tectonic history and role of basement faults pre early folding fracture patterns were recognized in several anticlines from three structural domains in the simply folded belt of the fars arc these fracture sets were characterized in terms of opening mode and relative chronology and used to reconstruct the main compressional trends related to the early zagros collisional history the palaeostress reconstructions based on these fracture sets were further refined by combination with newly collected or already available fault slip and calcite twin data as an alternative to previous models of rigid block rotations or regional stress rotation we propose that the complex pattern of pre folding fractures and the contrasting palaeostress orientations through time in the different domains investigated are related to the presence of basement faults with n s and wnw trends above which basement and cover were variably coupled during stress build up and early deformation of the arabian margin beyond regional implications this study draws attention to the need to carefully consider pre existing fractures possibly unrelated to folding to build more realistic conceptual fold fracture models

geochemistry of mesoproterozoic sedimentary rocks of upper vindhyan group southeastern rajasthan and implications for weathering history composition and tectonic setting of continental crust in the northern part of indian shield abstract the upper vindhyan succession of southeastern rajasthan is divisible into kaimur rewa and bhander groups the major and trace element including rare earth elements data of the upper vindhyan shales and sandstones are investigated to determine the weathering history composition and tectonic setting of mesoproterozoic continental crust cia chemical index of alteration values a cn k plot a al2o3 cn cao na2o k k2o and depletion in u na2o cao sr and ba suggest that the source area experienced moderate to high degree of chemical weathering under warm and humid conditions provenance modeling indicates that the kaimur sandstones are best modeled with a mixture having 40 granitic gneiss 20 tonalite trondhjemite granodiorite ttg 20 mafic enclaves and 20 berach granite of the banded gneissic complex bgc a mixture of 60 granitic gneiss 20 mafic enclaves and 20 berach granite of the bgc can model the rewa and bhander groups it is suggested that the upper vindhyan sedimentation commenced at the time of delhi sausar orogeny at about 1100 1000 ma the orogenic movements uplifted the parts of old continental crust in the bgc terrain creating positive areas which exposed older crustal blocks containing ttg as important component the debris of kaimur sandstone probably derived from these uplifted blocks as indicated by palaeocurrent data the rewa and bhander formations were derived from bundelkhand granitic gneiss complex bggc occurring to the north of the basin and or the chotanagpur granitic gneiss complex cggc of eastern indian shield the derivation of lower and upper groups of vindhyan succession from different source terrains of identical composition suggests that at the time of vindhyan sedimentation the bgc of rajasthan the bggc of central india and the cggc of eastern india had similar lithological composition this implies that well before the origin of the vindhyan basin these discrete terrains evolved as a single unit that existed as a mesoarchaean nucleus in the northern part of the indian shield

gigantic paleolandslide associated with active faulting along the bogd fault gobi altay mongolia on the basis of analyses of satellite imagery aerial photographs and field observations we describe the occurrence of one of the largest paleolandslides 50 km3 ever recognized in an intracontinental domain the slide occurred along the active bogd fault in the gobi altay mountain range in mongolia morphological and structural analyses of the relationships between the landslide and the area affected by active tectonics suggest that this gigantic mass movement was associated with surface faulting during a strong earthquake

mo ni and organic carbon isotope signatures of the mid late mesoproterozoic oxygenation abstract this study performed a redox sensitive trace element rste and organic carbon isotope investigation on the shallow section of 1 2 ga bijaigarh shale kaimur group vindhyan supergroup the results demonstrate that unlike the coeval deeper section in which mo and ni concentrations are several folds higher compared to the upper continental crust ucc the shallow section contains mo and ni equivalent to the upper continental crust ucc this spatially heterogeneous burial of mo and ni is very similar to the modern stratified basins i e black sea and cariaco basin where ni and mo composition of the sediments underlying a shallow oxic water column is comparable to the ucc however the deeper sediments underlying the anoxic euxinic contains several folds higher mo and ni compared to the ucc bulk precipitation of mo in a hydrosphere is mainly controlled by sulphide present in the anoxic euxinic layers of the water column on the other hand ni precipitation is generally controlled by oxygenic primary productivity though the shallow section of the bijaigarh shale is depleted in ni a significant correlation between ni and toc is still relevant and indicates an oxygen rich surface water layer for the respective palaeohydrosphere furthermore 13c org values between 32 0 and 30 4 from the shallow section suggests that the organic carbon exported into the sediments during the bijaigarh shale deposition was primarily derived from oxygenic photosynthesis in the concurrent surface water layers

evaluating failure mechanisms of dip slope using a multiscale investigation and discrete element modelling abstract this study proposed an in depth multiscale analysis procedure to identify the dip slope area and assess dip slope stability and influencing area the proposed analysis procedure comprised five stages 1 identifying the potential area of a dip slope 2 analyzing the possible failure types of the dip slope 3 evaluating slope activity 4 analyzing dip slope stability under the influence of possible triggering factors and 5 assessment of the deformation and deposition area to validate the proposed procedure the chaochouhu region of taiwan was analyzed as a dip slope case in stages 1 to 3 the scale of the utilized map and the precision of associated data were evaluated to identify the potential area of a dip slope the possible failure types and the activity of each slope unit in stages 4 and 5 the processes of deformation and sliding in a high activity slope unit were simulated using the discrete element method the numerical model was first verified using in situ monitoring data obtained from inclinometers subsequently the model was used to predict the slope behavior under conditions of wetting deterioration of geomaterial the multiscale analysis revealed comprehensive information regarding the dip slope the application of the proposed approach would be useful to civil engineers for evaluating dip slope stability as well as to relevant authorities for planning hazard mitigation strategies

depositional history of the upper vindhyan succession central india time constraints from pb pb isochron ages of its carbonate components abstract age of the upper sedimentary units rewa and bhander groups of the largest proterozoic vindhyan basin in central india has so far been considered to be close to 650 ma late neoproterozoic based on collective proxy dates in the absence of direct isotopic dates a drastic upward revision of this age by more than 300 ma has very recently been proposed from the similarity of the paleomagnetic directions in these units with those of the 1070 ma old majhgawan kimberlite intrusion into their basal parts and the presence of detrital zircons not younger than 1020 ma we report now pb pb isochron ages of 908 72 ma 866 180 ma and 1073 210 ma for the three distinct carbonate horizons bhander balwan and lakheri limestones respectively as independent and direct evidence on the age of the upper vindhyan succession the consistency of the three ages close to 900 ma provides a strong support for the proposed shift on the timing and duration of sedimentation in the upper vindhyan sequence

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

carbon oxygen and strontium isotope geochemistry of proterozoic carbonate rocks of the vindhyan basin central india abstract carbon oxygen and strontium isotope compositions of carbonate rocks of the proterozoic vindhyan supergroup central india suggest that they can be correlated with the isotope evolution curves of marine carbonates during the latter proterozoic the carbonate rocks of the lower vindhyan supergroup from eastern son valley and central vindhyan sections show 13c values of 0 v pdb and those from rajasthan section are enriched up to 2 8 in contrast the carbonate rocks of the upper vindhyan succession record both positive and negative shifts in 13c compositions in the central vindhyan section the carbonates exhibit positive 13c values up to 5 7 and those from rajasthan show negative values down to 5 2 the 18o values of most of the carbonate rocks from the vindhyan supergroup show a narrow range between 10 and 5 v pdb and are similar to the best preserved 18o compositions of the proterozoic carbonate rocks in the central vindhyan and eastern son valley sections carbonates from the lower vindhyan exhibit best preserved 87sr 86sr compositions of 0 7059 6 which are lower compared to those from rajasthan 0 7068 4 the carbonates with positive 13c values from upper vindhyan are characterized by lower 87sr 86sr values 0 7068 2 than those with negative 13c values 0 7082 6 a comparison of c and sr isotope data of carbonate rocks of the vindhyan supergroup with isotope evolution curves of the latter proterozoic along with available geochronological data suggest that the lower vindhyan sediments were deposited during the mesoproterozoic eon and those from the upper vindhyan represent a neoproterozoic interval of deposition