structural anatomy of the kushtagi schist belt dharwar craton south india an example of archaean transpression abstract the nw se trending kushtagi schist belt in the eastern dharwar craton records the tectonic consequences of a transpression regime it was formed due to late archaean oblique convergence in the dharwar craton this relatively unknown schist belt is characterized by two major episodes of deformation the dominant d 1 deformation forming tight to isoclinal non cylindrical folds and a regional axial planar schistosity is a consequence of transpression the transpression related sinistral shear regime is followed by development of a conjugate set of f 2 folds and s 2 cleavages that are superimposed on the d 1 structures the maximum shortening direction associated with the f 2 folds is nw se which suggests longitudinal compression subsequent to transpression riedel shear fractures were developed in the sinistral shear regime and dolerite dykes were emplaced along the conjugate riedel shear fractures intrusive granite bodies within and outside the schist belt were emplaced in the late phase of d 1 transpression

space weathered rims found on the surfaces of the itokawa dust particles on the basis of observations using cs corrected stem we identified three types of surface modification probably formed by space weathering on the surfaces of itokawa particles they are 1 redeposition rims 2 3 nm 2 composite rims 30 60 nm and 3 composite vesicular rims 60 80 nm these rims are characterized by a combination of three zones zone i occupies the outermost part of the surface modification which contains elements that are not included in the unchanged substrate minerals suggesting that this zone is composed of sputter deposits and or impact vapor deposits originating from the surrounding minerals redeposition rims are composed only of zone i and directly attaches to the unchanged minerals zone iii zone i of composite and composite vesicular rims often contains nanophase fe mg s the composite rims and the composite vesicular rims have a two layered structure a combination of zone i and zone ii below which zone iii exists zone ii is the partially amorphized zone zone ii of ferromagnesian silicates contains abundant nanophase fe radiation induced segregation and in situ reduction are the most plausible mechanisms to form nanophase fe in zone ii their lattice fringes indicate that they contain metallic iron which probably causes the reddening of the reflectance spectra of itokawa zone ii of the composite vesicular rims contains vesicles the vesicles in zone ii were probably formed by segregation of solar wind he implanted in this zone the textures strongly suggest that solar wind irradiation damage and implantation are the major causes of surface modification and space weathering on itokawa

strain patterns decollement and incipient sagducted greenstone terrains in the archaean dharwar craton south india the archaean dharwar craton is characterized by two greenstone successions the 3 ga sargur group and the 3 0 2 5 ga dharwar supergroup examples of both successions are described from the region of jayachamarajapura where they are also distinguished by different tectonic patterns the younger greenstones have undergone only minor deformation and are only slightly metamorphosed and so provide a good case study of the relative behavior of greenstones in relation to their granite gneiss country rocks a detailed structural analysis indicates two strain fields associated with two deformational episodes d1 and d2 the d1 episode produced dome and basin structures and affected merely the older greenstones and the gneisses the mapped strain field is compatible with the hypothesis that it is associated with the development of diapiric type gravitational instabilities the d2 episode affects only the younger greenstone belt which has the overall geometry of a complex syncline it is discordant over a complex of gneisses and older greenstones that was deformed during the d1 episode the base of the discordant cover sequence is tectonized and constitutes a decollement surface kinematic criteria at this surface have opposite sense and converge towards the belt axis these structural features are interpreted in terms of progressive deformation compatible with the incipient development of a sagducting trough these results are consistent with those obtained from other parts of the craton where the tectonic evolution appears to reflect mainly relative vertical displacements facilitated by the reheating of continental crust during two major archaean tectonometamorphic episodes copyright 1996 elsevier science ltd

2 61 ga potassic granites and crustal reworking in the western dharwar craton southern india tectonic geochronologic and geochemical constraints abstract we present combined field structural data and spot image analysis petrographic data u pb zircon ages nd isotopes and whole rock geochemical data for the late archaean granite plutons from arsikere banavara ab suite and chitradurga jampalnaikankote hosdurga cjh suite in the western dharwar craton wdc ab plutons are syn kinematic with respect to the development of dome and basin patterns resulting from partial crustal diapiric overturn d1 whilst cjh suite plutons show deformation patterns resulting from the superimposition of large scale regional strike slip shearing d2 onto d1 syn emplacement fabrics sims u pb zircon ages of 2614 10 ma for the chitradurga pluton cjh and of 2617 3 ma for the arsikere pluton ab define the minimum age of the d1 strain pattern the cjh and ab suites are mainly high k granites whose origin is to be sought in partial melting of an old 3 0 ga depleted lower crust of intermediate composition the cjh and ab suites correspond mainly to the ca1 and ca2 types of archaean calc alkaline granites and some facies to the transitional ttg their heterogeneous chemical compositions indicate involvement of various sources and also significantly different depths of partial melting to produce these granites these results allow documenting regional partial reworking of the wdc 2615 ma ago requiring an ht event to have taken place before 2 61 ga and thus different from the 2 55 to 2 51 ga granulite facies metamorphic episode associated to regional scale strike slip shearing d2 that affected the entire craton partial reworking of the older lower crust at 2 61 ga and associated deformation would result from heat advection and or crustal thickening that may relate to voluminous mafic greenstone volcanism and moderate shortening at that time

predictive uncertainty of peak outflow relations for landslides dam breach risk assessment development considering the failure of landslide dams often requires the estimation of peak outflow through the breach the empirical equations based on data from case studies tend to be the first direct approach this paper conducted an uncertainty analysis when these empirical relations were utilized to predict the peak outflow of a breached landslide dam the results suggest that the relations derived from manmade dams or embankments typically overestimate the peak outflow about 1 5 to 3 4 of an order of magnitude and the relations derived from the database of landslide dams have much smaller mean prediction errors and also exhibit broad uncertainty bands application of the uncertainly analysis was illustrated by the tangjiashan landslide dammed lake formed during 2008 wenchuan earthquake in addition the predicted results from eq 1 deduced herein were considered to be the reliable estimate of peak outflow through the breach of landslide dam

draining the tangjiashan barrier lake this paper documents the emergency breaching of an approximately 110 m high landslide dam that was created at tangjiashan during the 2008 wenchuan earthquake of china s southwest sichuan province as an emergency measure a 13 m deep channel was excavated to reduce the volume and head of the released water during the dam breaching and to create a controlled flood that was intended to prevent catastrophic consequence for 1 2 million people downstream from detailed monitoring and survey works carried out during and after the dam break it was found that 1 the breaching initiated at a pool water level of 742 1 m with an estimated flow velocity of 2 4 m s and virtually terminated at a pool water level of 720 3 m with an estimated velocity of 2 5 m s which can be regarded as the incipient velocity that initiated erosions for the soils at this particular site 2 a controlled flood released 167 106 m3 reservoir water with a peak flow rate of 6 500 m3 s during which a maximum velocity of about 5 0 m s

secondary submicrometer impact cratering on the surface of asteroid 25143 itokawa abstract particle ra qd02 0265 returned by the hayabusa spacecraft from near earth asteroid 25143 itokawa displayed a unique abundance of submicrometer sized 500 nm impact craters which are rarely observed among the hayabusa samples the particle consists of intensely twinned diopside that was subjected to a large scale shock event before exposure to the space environment on the surface of 25143 itokawa intense sub micrometer scale impact cratering may suggest a long surface exposure and hence a long residence time of regolith material on the surface of small asteroids bearing implications for the dynamical evolution of these bodies however our combined fe sem and fib tem study shows that the degree of solar wind induced space weathering and the accumulation of solar flare tracks are not exceptionally different from other hayabusa particles with surface exposure ages estimated to be less than 1 ka a 500 nm wide crater on the surface of ra qd02 0265 exhibits microstructural damage to a depth of 400 nm below its floor and contains residues of fe ni metal excluding a formation by space craft exhausts or curatorial handling the geometrical clustering among the 15 craters is unlikely random and we conclude that the craters have formed through the impacts of secondary projectiles at least partially fe ni metal created in a nearby micro impact event besides structural damage by the solar wind and deposition of impact generated melts and vapors secondary impact cratering on the submicrometer scale is another potential mechanism to modify the spectral properties of individual regolith grains the lack of extensively exposed regolith grains supports a dynamic regolith on the surface of 25143 itokawa

evolution of archaean crust in the dharwar craton the nd isotope record abstract a synthesis of the available nd isotope data from the dharwar craton puts important constrains on antiquity of crust extent of basement terranes and events marking juvenile crustal addition and crustal recycling the craton is divided into two blocks namely eastern dharwar craton edc and western dharwar craton wdc nd model ages trace crust extraction as far as 3 5 ga back in both the blocks although rock record of such antiquity is yet to be found in the craton in wdc 3 35 3 0 ga is the most significant period of juvenile crustal addition as well as crustal recycling significantly depleted mantle 1 5 to 6 4 existed below the wdc as early as 3 35 ga which was probably refertilized in a later event from the resultant chondritic to slightly enriched mantle 0 3 to 0 4 juvenile mafic crust was added to the wdc during 2 9 2 6 ga a widespread crustal recycling event at 2 6 ga marks the last major event in this block in edc 3 3 3 0 ga granitoids occur as vestiges and show nd model ages higher than crystallizations ages suggesting recycling of palaeoarchaean crust during 2 7 2 5 ga extensive juvenile magmatism took place in edc from variably depleted mantle 1 4 to 5 6 which is later than the global 2 7 ga peak of crustal growth attendant crustal recycling destroyed most of the earlier crust distribution of nd model ages suggests in contrast to general believe that palaeoarchaean crust was not only abundant in the wdc but also widespread in an area extending from the wdc edc boundary to further 60 150 km east up to the hungund ramagiri kolar hrk belt this belt appears to be a major crustal boundary along which terranes of different nd isotope signatures were amalgamated during the late neoarchaean by horizontal accretion major neoarchaean crustal recycling events documented in the dharwar craton are missing from nd isotope record of the eastern block eb of the north china craton this fact does not support correlation between the two cratons as suggested by some authors

late archaean terrane accretion in the godthab region southern west greenland tectono stratigraphic terranes fault bounded blocks of the earth s crust characterized by a geological history distinct from that of adjacent terranes1 are now widely recognized in phanerozoic and proterozoic orogenic belts and their present configurations are thought to result from plate tectonic processes similar to those in operation today2 4 there has been much debate about whether such processes operated in archaean times5 6 here we present new data from the archaean high grade gneiss complex of the godthab now nuuk region of southern west greenland which show that discrete tectonic units recognized in the south of the region7 can be more widely identified at least four terranes are recognized each of which evolved separately until their juxtaposition in the late archaean this suggests that at least some archaean high grade gneiss complexes may resemble more recent orogenic belts formed by plate tectonic processes

experimental investigation on the longitudinal evolution of landslide dam breaching and outburst floods abstract accurate prediction of the evolution of a landslide dam that is breached due to overtopping failure is necessary to estimate the outflow hydrograph and the resulting inundation in this study physical flume tests on the breaching of landslide dams were conducted a wide grain size distribution with unconsolidated dam material was used dam breaching was initiated by cutting a notch across the crest of the dam adjacent to the side wall of the flume this allowed water to escape from the dam while a steady inflow of water was continuously supplied upstream the effects of upstream inflow on the timescales and magnitudes of the peak discharges and the time to inflection point were also investigated experimental results reveal that the whole hydrodynamic process of dam breaching can be divided into three stages defined by clear inflection points and peak discharge a new longitudinal evolution model is proposed this model captures the initial increase of the soil erosion rate of landslide dam and its subsequent decrease along the longitudinal direction in addition a linear relationship between the soil erosion rate and shear stress of water flow was observed and this is similar to that observed in large scale natural landslide dams furthermore soil erosion resistances of landslide dam against water flow above are observed to increase with the concentration of entrained sediments along the flow direction

distribution pattern of earthquake induced landslides triggered by the 12 may 2008 wenchuan earthquake abstract this paper presents the preliminary results of an extensive study of the mapping the distribution of landslides triggered by the wenchuan earthquake in sichuan province china on 12 may 2008 an extensive landslide interpretation was carried out using a large set of optical high resolution satellite images e g aster alos cartosat 1 spot 5 and ikonos as well as air photos for both the pre and post earthquake situation landslide scarps were mapped as points using multi temporal visual image interpretation taking into account shape tone texture pattern elevation and ridge and valley orientation nearly 60 000 individual landslide scarps were mapped the landslide distribution map was compared with the inventory map that was prepared directly after the earthquake which contains about 11 000 individual landslide points through the calculation of normalized landslide isopleths maps remarkable differences were observed as the earlier inventory mapping did not consider the pre earthquake situation and did not consider all individual landslides as part of the landslide inventory landslides were identified that had blocked the drainage and had formed landslide dams the landslide distribution was compared with a number of aspects such as the seismic parameters distance to epicenter distance to fault rupture co seismic fault geometry and co seismic slip distribution and geology the most remarkable correlation found was with the co seismic slip distribution and the fault geometry landslide distribution in the section of the fault that had mainly a thrust component with low angle fault plane was found to be much higher than the sections that had steeper fault angles and a major strike slip component

diapirism bulk homogeneous shortening and transcurrent shearing in the archaean dharwar craton the holenarsipur area southern india abstract qualitative strain data are spatially integrated in order to define archaean foliation trajectories and variations in strain intensity and ellipsoid type in the holenarsipur area dharwar craton southern india the study provides constraints on the bulk geometry the progressive deformation and the kinematic history of this region of archaean continental crust two major structural events have shaped the study area i a regional diapiric event contemporaneous with a magmatic event and ii a later sinistral transcurrent ductile shear event which has locally reoriented both foliations and stretching lineations the entire holenarsipur supracrustal belt underwent a common tectono metamorphic history that included two metamorphic events each event corresponds temporally to a distinct strain field the first a regional amphibolite facies event was contemporaneous with the main tectonic event and probably with the intrusion of halekote trondhjemites the second occurred under greenschist facies conditions and was restricted to a late transcurrent shear zone at the eastern boundary of the greenstone belt the strain pattern prior to transcurrent shearing cannot be explained by a thrusting event unless all trace of this event had been erased by the diapirism we interpret all structures older than the transcurrent shearing to be the direct result of vertical movements linked to body forces augmented by minor horizontal crustal shortening

differentiation of late archean crust in the eastern dharwar craton krishnagiri salem area south india the late archean crust south of krishnagiri tamil nadu consists of tonalitic trondhjemitic granodioritic ttg gneisses with mafic and sedimentary enclaves formed between 2 7 and 2 5 ga and metamorphosed at amphibolite facies in the north to granulite facies in the south close to 2 5 ga migmatization occurred at all grades and numerous small granite bodies were emplaced near the amphibolite to granulite facies horizon this nearly syn accretion meta morphism affected the entire crust and left a chemically differentiated section later exposed by uplift and erosion detailed chemical and petrographic study of 60 samples across a 90 km traverse provides evidence for an essentially unbroken crustal cross section paleopressures range from 4 kbar corresponding to 12 14 km paleodepth in the north to 8 kbar corresponding to 24 28 km paleodepth to the south corresponding paleotemperatures vary between 650 and 800 c across the section mineralogic grade monitors particularly increasing tio 2 con

visible ir and raman microspectroscopic investigation of three itokawa particles collected by hayabusa mineralogy and degree of space weathering based on nondestructive analyses hayabusa returned samples offer a unique perspective for understanding the link between asteroids and cosmomaterials available in the laboratory and provide insights on the early stages of surface space weathering this study characterizes the mineralogy and the extent of space weathering of the three itokawa particles ra qd02 0163 ra qd02 0174 and ra qd02 0213 provided by jaxa to our consortium we report here a series of results based on nondestructive analyses through visible near infrared reflectance and raman spectroscopy results were obtained on the raw particles both in their original containers and deposited on diamond windows identification of the minerals characterization of their elemental compositions and measurements of their relative abundances were led through raman spectroscopy in punctual and automatic mode reflectance spectra in the visible and near ir wavelengths constrain the mineralogy of the grains and allow direct comparison with the surface of itokawa the spectra reflect the extent of space weathering experienced by the three particles particle ra qd02 0163 consists of a heterogeneous mixture of minerals olivine fo76 dominates an assemblage with both ca rich en50 wo50 and ca poor en85 pyroxenes the elemental compositions of the silicates are consistent with those previously reported for distinct hayabusa particles particles ra qd 0174 and ra qd02 0213 are solely composed of olivine whose chemical composition is similar to that observed in ra qd02 0163 it has been previously shown that the s type asteroid 25143 itokawa is a breccia of poorly equilibrated ll4 and highly equilibrated ll5 and ll6 materials the three particles studied here can be related to the least metamorphosed lithology ll4 based on the high forsterite content of the olivine neither carbonaceous matter nor hydrated minerals were detected through raman on the three allocated particles the nir vis reflectance incidence 45 light collection at e 0 spectra of the three particles in particular the 1 m band are consistent with the presence of both olivine and pyroxene detected via raman the spectra of particles ra qd02 0163 and ra qd02 0213 are also fully compatible with the ground based observations of asteroid 25143 itokawa in terms of both spectral features and slope by contrast particle ra qd02 0174 has a similar 1 m band depth but higher redder spectral slope than the surface of itokawa this probably reveals a variable extent of space weathering among the regolith particles ra qd02 0174 may contain a higher amount of nanophase metallic iron and nanophase fes such phases are products by space weathering induced by solar wind previously detected on other itokawa particles

evolution of fabric in chitradurga granite south india a study based on microstructure anisotropy of magnetic susceptibility ams and vorticity analysis abstract in this paper the fabric in massive granite 2 6 ga from the chitradurga region western dharwar craton south india is analyzed using microstructure anisotropy of magnetic susceptibility ams study and kinematic vorticity analysis the microstructural investigation on the granite shows a progressive textural overprint from magmatic through high t to low t solid state deformation textures the mean magnetic foliation in the rocks of the region is dominantly nw se striking which have developed during regional d1 d2 deformation on account of ne sw shortening the plunge of the magnetic lineation varies from nw to vertical to se and interpreted to be a consequence of regional d3 deformation on account of nw se to e w shortening the vorticity analysis from magnetic fabric in the region reveals that the nw se oriented fabric formed under pure shear condition during d1 d2 regional deformation however some parts of the region particularly close to the adjacent chitradurga shear zone show that the magnetic fabrics are oblique to the foliation as well as shear zone orientation and inferred to be controlled by simple shearing during d3 regional deformation the shape preferred orientation spo analysis from oriented thin sections suggest that the shape of the recrystallized quartz grains define the magnetic fabric in chitradurga granite and the degree of the spo reduces away from the chitradurga shear zone it is interpreted that the change in magnetic fabrics in some parts of the granite in the region are dominantly controlled by the late stage sinistral shearing which occurred during the development of chitradurga shear zone

strain patterns in archaean dome and basin structures the dharwar craton karnataka south india abstract models simulating the role of gravity in the earth s crust are the main source of criteria used for the field identification of diapirs after a short review of the distribution of finite strain in experimental diapir models we describe an example where differential erosion of a tilted craton has provided 3d geometrical information on patterns in a diapiric system at various depths from greenschist to granulitic facies conditions within the archaean continental crust of the dharwar craton south india diapirs and anti diapirs sagducted greenstones are observed at different levels structures and strain are consistent with all the field identification criteria inferred from experimental simulation but some peculiar structural features are also observed which are not predicted by the models these features such as strain trajectory triple junctions result from i the progressive deformation of diapiric domes or sagducted basins ii interferences between diapiric structures body forces and iii the superimposition of diapiric strain fields on regional horizontal shortening boundary forces

the formation and breaching of a short lived landslide dam at hsiaolin village taiwan part ii simulation of debris flow with landslide dam breach abstract typhoon morakot 2009 caused serious damage in southern taiwan due to intensive rainfall with long duration the issue of greatest concern arising from the disasters brought about by this extreme event was the burying of the entire village of hsiaolin by a massive debris flow and landslide based on seismological and near surface magnetic data this tragic scenario arose due to a combination of events a massive landslide the formation of a landslide dam and the consequent debris flow when this dam was breached the objective of this part of the study is to investigate the spatial and temporal characteristics of the debris flow induced by the landslide breach the us national weather service breach model and the federal emergency management agency approved flo 2d model are integrated to facilitate the investigation of this catastrophe a series of simulations including a 2d rainfall runoff simulation over the cishan river basin landslide dam breach routing and 2d debris flow simulation around the hsiaolin village were conducted hydraulic calculations were performed to determine the equivalent top elevation of the landslide dam based on inflows computed from the 2d rainfall runoff simulation in association with the digital terrain model dtm and upstream constraint of the backwater inundation areas the hydrograph of the upstream inflow which induced overtopping failure was provided by a 2d rainfall runoff simulation using the flo 2d model calibrated by comparison with the downstream discharge record the longevity of the landslide dam was less than 1 h and it took only about 8 minutes to completely breach the peak discharge rate of this massive landslide dam breach was 70 649 m3 s the dam break hydrograph was then used for upstream inflow to drive the flo 2d debris flow simulation the average sediment concentration by volume was 0 362 the simulated deposited sediment depth showed a reasonable match to the differences of dtms before and after the disaster

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

crustal structure and domain tectonics of the dharwar craton india insight from new gravity data abstract the precambrian dharwar craton of peninsular india comprises three distinct crustal domains namely the western dharwar craton wdc the eastern dharwar craton edc and the eastern ghats mobile belt egmb the domain boundaries are demarcated by bipolar positive and negative gravity anomalies measured along a 600 km long udipi kavali seismic line the two and half dimensional modelling of the gravity anomalies well constrained by available seismic depth sections identified the two contact zones one occurs between the wdc relatively low density and the edc intermediate density to the east of the chitradurga schist belt and the second occurs between the edc and the egmb high density to the east of cuddapah basin as west verging thrust faults the three layer crustal structure is up to 41 km thick beneath the wdc thinning to 37 km beneath the west coast under the edc the depth of the moho varies from 38 km towards the west to 40 km beneath the cuddapah basin and decreases to a depth of 35 km beneath the egmb a high density steeply inclined ridge like body is modelled between 5 and 20 km depth beneath the closepet granite and a similar body is modelled under the egmb it is suggested that the three domains of the dharwar craton were brought and welded together at the suture zones in the period from late archaean to late proterozoic through collisional tectonics the apparent offsets in the moho depth may be the imprint of the relative domain movement that probably was initiated by the convergent plate motion the steeply inclined ridge like high density bodies are interpreted as stacked lower crustal blocks from the convergent tectonic setting the cuddapah basin with a 10 km thick shelf marine sedimentary sequence is interpreted as a peripheral foreland basin abutting the egmb a lopolith of likely mafic composition is modelled at 10 km depth and is interpreted as a product of juvenile magmatism beneath the edc

engineering risk mitigation measures for the landslide dams induced by the 2008 wenchuan earthquake abstract more than 257 sizable landslide dams were induced by the 2008 wenchuan earthquake which required timely risk mitigation measures this paper aims to summarize the engineering measures taken to mitigate the landslide dam risks provide a method for optimal design of spillways to minimize the risks and quantitatively evaluate practical options for spillway design with a physically based dam breach model the engineering measures taken to mitigate the risks of 37 highly hazardous landslide dams induced by the wenchuan earthquake are summarized an optimization method is proposed and applied to the spillway design for the tangjiashan landslide dam which is the largest one caused by the wenchuan earthquake it is found that the peak outflow rate could be reduced from the recorded 6500 m3 s to 2900 m3 s using the optimal design a spillway with a shallow and broad cross section is suitable for low erodibility dams while a spillway with a deep and narrow cross section is suitable for high erodibility dams a spillway with a large longitudinal gradient is beneficial for high erodibility dams with large dam widths and gentle downstream dam slopes a spillway close to one bank can reduce the peak outflow rate if the bank is erosion resistant

ion microprobe u pb age determinations on zircon from the late archean granulite facies transition zone of southern india abstract the southern dharwar craton of karnataka and tamil nadu states in south india exposes a depth profile of late archean crust amphibolite facies felsic to intermediate peninsular gneiss of protolith ages 3 4 2 9 ga with subordinate infolded supracrustal relics and the large closepet granite body give way southward to granulite facies orthopyroxene bearing gneisses over a transition zone about 40 km wide with mineralogic pressure indicators increasing from about 4 kbar corresponding to about 15 km paleodepth to about 7 kbar corresponding to near 25 km paleodepth previous whole rock and zircon geochronology have established that amphibolite facies metamorphism migmatization and granite intrusion took place in the latest archean at 2 53 2 51 ga however some workers have considered the foliated granulites as products of an earlier metamorphism distinct from the terminal archean events this work presents whole rock geochemical studies coupled with ion microprobe 207pb 206pb ages and th u

analyzing successive landslide dam formation by different triggering mechanisms the case of the tangjiawan landslide sichuan china abstract the catastrophic tangjiawan landslide triggered by the 2008 wenchuan earthquake blocked the duba river impounding one of the most dangerous coseismic barrier lakes in beichuan china the lake was drained by an artificial spillway within one month after the earthquake to minimize the potential dam breach flooding risk however on september 5 2016 this landslide was reactivated and dammed the river again creating a 20 m high dam at the same location and resulting in the formation of a barrier lake with a volume of 0 6 million m3 the day after the event we carried out a field investigation of the landslide and obtained a high resolution image and dem using uav the satellite images from 2005 2008 2010 and 2015 were also collected to analyze the evolution of the landslide together with multi temporal dems the geometry and volumes of the displaced mass and the landslide dams and barrier lakes were calculated using image interpretation and 3d spatial analysis with gis this landslide is of great scientific interest as it presents a good example of multiple reactivation of a pre historical giant landslide under different triggering conditions a reactivation of an older landslide during the wenchuan earthquake and a second reactivation during a rainfall event several years later meanwhile from the hazard assessment and prevention perspective it is also representative as it dammed the river twice in 2008 and 2016 posing threats to both upstream and downstream areas we infer that the successive landslides in this region could be caused by the strong tectonic activities including earthquakes and high average uplifting rate the results of landslide volume analysis using multi temporal dems contribute to the landslide mechanism analysis and suggest that the landslide volume estimation is effected by the landslide type landslide rupture surface location and resolution of dem we also compare the performance of different empirical models of landslide stability and dam breach flood parameters and discuss their application during the quick assessment of the potential hazard of the landslide dams generally the successive landslide dams at the tangjiawan site are caused by the successive landslide reactivations on an anti dip slope controlled by strong tectonic activity and river erosion involve with a mass of loose materials of previous landslide deposition and possess high flood risk to the downstream area the experience gained in this work can be used to assist the hazard assessment and the planning of the emergency measures for similar landslide dams in the future

sinking of the dharwar basin south india implications for archaean tectonics abstract archaean tectonic regimes can be constrained by structural analysis of greenstone belts and adjacent granite gneiss masses the late archaean bababudan greenstone belt dharwar craton south india contains a low grade volcanosedimentary basin sequence the dharwar supergroup which unconformably overlies a previously eroded basement made up mainly of granite and gneiss fabric trajectories kinematic indicators and superimposed deformation patterns show that greenstones have undergone a radial converging downward flow with respect to underlying basement rocks as well as strike slip shearing this is attributed to the progressive sagduction gravity sinking of the greenstone belt into its basement along a decollement horizon and to late transcurrent shearing we propose a deformation model for the bababudan belt that may explain common features of many greenstone belts such as decollements and superimposed upright fold patterns which are attributed to the progressive sinking of the supracrustals into their basement the results of our study and other field investigations in the crust of the dharwar craton as well as structural evidence from other cratons zimbabwe and pilbara raise the possibility that a unique continental tectonic regime existed during the archaean controlled by the emplacement of dense volcanic traps mantle underplating and thermal blanketing of the continental crust this tectonic regime differs from that observed within the modern lithosphere as it is characterized by the pervasive development of gravity i e rayleigh taylor instabilities between the volcanic traps and the rest of the continental crust it allowed heat and material transfer through the crust and has to be seen as an efficient recycling mechanism for the young continental crust during periods of mantle underplating the diapiric phenomenon is independent of the boundary forces acting at the limits of the protocontinents and is associated in time and space with large scale accretion events of the continental crust perhaps in hot spot environments

layered internal structure and breaching risk assessment of the higashi takezawa landslide dam in niigata japan the internal structure and geotechnical properties of landslide dams have rarely been examined in detail although they largely control the longevity and potential failure mechanisms of the dams during the 2004 mid niigata prefecture earthquake thousands of landslides were triggered and many landslide dams were formed in the imo river basin among these landslides dams the biggest one that occurred in the higashi takezawa district threatened both the upstream and downstream areas emergency and eventual permanent countermeasures were successfully performed to mitigate the hazards presented by the dam the preserved landslide dam provides a good field study area for improving understanding of the formation and stability of similar features to characterize its internal structure and to provide more reliable information for stability analysis we used a multiple channel surface wave technique and microtremor array measurements to survey the dam s s wave velocity v s profile our results show that the integrated use of these methods is an effective approach for determining the s wave velocity structure of landslide dams irrespective of the mountainous environment in which they typically occur the v s profile suggests that the displaced landslide materials had been little disturbed during movement although movement was rapid and over a long distance we also discuss herein the landsliding mechanism and assess the breaching risk of the landslide dam due to overtopping c 2016 elsevier b v all rights reserved

regolith migration and sorting on asteroid itokawa high resolution images of the surface of asteroid itokawa from the hayabusa mission reveal it to be covered with unconsolidated millimeter sized and larger gravels locations and morphologic characteristics of this gravel indicate that itokawa has experienced considerable vibrations which have triggered global scale granular processes in its dry vacuum microgravity environment these processes likely include granular convection landslide like granular migrations and particle sorting resulting in the segregation of the fine gravels into areas of potential lows granular processes become major resurfacing processes because of itokawa s small size implying that they can occur on other small asteroids should those have regolith

structural fabric of the southern indian shield as defined by gravity trends abstract southern indian shield represents a mosaic comprised of several smaller structural domains separated by discrete shear zones here we present a horizontal bouguer gravity gradient map of the indian shield south of 14 n to define a continental mosaic of gravity trends domains akin to structural domains the gravity gradient image is based on 7862 newly collected observations merged with 6359 old gravity data this combined dataset delineates structural boundaries of the five gravity domains related to the eastern dharwar craton the eastern ghats mobile belt the extended eastern ghats mobile belt the southern granulite terrain and the western dharwar craton other belts of significant gravity gradients are found associated with the eastern and the western coasts the loci of closepet granite and kolar schist belts do not manifest themselves as boundary zones between two distinct gravity domains of the eastern dharwar craton lack of a gravity gradient across karur oddanchatram kodaikanal and karur kambam painavu trichur shear zones may be attributed to a lack of gravity measurements caused by difficulties in collecting data in topographically difficult terrain the subdued gravity gradient across the palghat cauvery shear zone and a weak gradient across the achankovil shear zone indicates a lithological and or morphological boundary rather than a terrane boundary alternatively structural domains encompassing palghat cauvery and achankovil shear zones may have been in a neighbouring position during the gondwana assembly when pan african thermal perturbation reactivated the structures and reworked partly or totally obliterating earlier crustal fabric

geology geochemistry and tectonic setting of archaean greywackes from karnataka nucleus india more than 80 of the area covered by the chitradurga and shimoga schist belts 3 0 2 6 ga of karnataka nucleus india is made up of greywackes feldspathic lithic and quartzose greywackes are deposited respectively along the western northern and the eastern margin of the chitradurga schist belt greywackes of the shimoga schist belt show a large compositional scatter between feldspathic and lithic types compositional differences indicate variable provenance for the different localities tonalite trondhjemite gneisses ttg mafic ultramafic schists basic intermediate acid volcanic rocks sedimentary rocks like banded iron formation quartzites and cherts and k granites in minor quantity were exposed in the source area volcanic debris was also contributed from contemporaneous volcanism in the basin greywackes in this region are invariably interbedded with fine grained biotite rich phyllites and schists marked compositional differences are observed between the greywackes and the interbedded phyllites the greywackes have k2o na2o 1 whereas phyllites show large variation in k2o na2o ratios ranging from 1 5 to 15 0 high cr ni content of the greywackes and phyllites of the chitradurga belt are indicative of an important contribution from ultramafic rocks light ree enrichment and negative eu anomalies are particularly pronounced in the mudpacks of the greywackes represented by phyllite the ree and other chemical data such as la th ti zr and k2 mgo ratios indicate that these greywackes were supplied from a juvenile continental nucleus and were laid down on a simatic and converging active continental margin an archaean miniplate model with low angle subduction and sedimentary basins of moderate size is proposed to explain the geochemical and tectonic features of the schist belts

breaching parameters for earth and rockfill dams dam risk analysis is at the heart of dam failure prevention and mitigation in order to assess dam risk it is essential to conduct a quantitative analysis of the process of a dam breach which can be described by such parameters as breach geometry breaching duration and peak outflow rate the main objective of this paper is to develop robust empirical formulas with physical meaning for predicting dam breaching parameters based on past dam failure data a database of 182 earth and rockfill dam failure cases has been compiled among these cases nearly one half are for large dams higher than 15 m a multiparameter nonlinear regression model is recommended to develop empirical relationships between five breaching parameters breach depth breach top width average breach width peak outflow rate and failure time and five selected dam and reservoir control variables dam height reservoir shape coefficient dam type failure mode and dam erodibility the relative importance of each control variable is evaluated the dam erodibility is found to be the most important factor influencing all five breaching parameters the reservoir shape coefficient and the failure mode also play an important role in the prediction models two case studies are presented to show the application of the empirical models developed in this paper

late archaean 2550 2520 ma juvenile magmatism in the eastern dharwar craton southern india constraints from geochronology nd sr isotopes and whole rock geochemistry the results of field geochronologic geochemical and isotopic studies are presented for the granitoids that occur east of the closepet batholith up to the kolar schist belt ksb field data such as common foliation strong shear deformation occasionally leading to mylonitization together with petrographic data including reduction in grain size with corroded borders show characteristics of the syn kinematic emplacement of the granitoids single zircon evaporation ages define a minimum age of 3127 ma for the tonalitic trondhjemitic granodioritic ttg basement and 2552 2534 ma plateau ages for the emplacement of the granitoids which slightly predate 20 30 ma the emplacement of the 2518 ma closepet batholith major and trace element data together with isotopic data suggest at least four magmatic suites from closepet batholith to the east which have independent magmatic evolution histories the observed data are compatible with magma mixing for the closepet batholith melting of ttg and assimilation fractional crystallization processes for bangalore granites either melting of heterogeneous source or different degree of melting of the same source for the granitoids of hoskote kolar and fractional crystallization for the western margin of the ksb isotopic nd sr and geochemical data lree and lil elements suggest highly enriched mantle and ancient ttg crust for the closepet batholith enriched mantle and ttg crust for the bangalore granites c a chondritic mantle source for the granitoids of hoskote kolar and the quartz monzonites of the western margin of the ksb and slightly depleted mantle for granodiorites of the eastern margin of the ksb we interpret all these geochronologic geochemical and isotopic characteristics of granitoids from the closepet batholith to the east up to the ksb in terms of a plume model the centre of the plume would be an enriched hot spot in the mantle that lies below the present exposure level of the closepet batholith melting of such an enriched mantle hot spot produces high temperature magmas closepet that penetrate overlying ancient crust where they strongly interact and induce partial melting of the surrounding crust these magmas cool very slowly as the hot spot maintains high temperatures for a long time thus they appear younger 2518 ma on the contrary to the east the plume induces melting of c a chondritic or slightly depleted mantle that produces relatively colder and less enriched magmas which show less or no interactions with the surrounding crust and cool rapidly and appear slightly older 2552 2534 ma this plume model can also account for late archaean geodynamic evolution including juvenile magmatism heat source for reworking inverse diapirism and granulite metamorphism in the dharwar craton

archean wrench fault tectonics and structural evolution of the blake river group abitibi belt quebec structural analysis of the blake river group volcanic rocks in the rouyn noranda region shows the formations to be distributed largely in z shapes resulting from the interference of two early fold systems oriented west northwest east southeast and east west respectively the first of these two fold systems is probably related to the shortening associated with left lateral movement along the two major fractures in the region namely the porcupine destor and larder lake cadillac faults the second system appears to be the result of north south compression perpendicular to the two major fractures the two major faults the first system of early folding the normal and reverse faults and the minor dextral and sinistral strike slip faults that have been observed in the blake river group rocks can all be integrated into one tectonic system that of wrench fault tectonics the orientations of the principal structures recognized in the abitibi belt major shear zones folding and faulting suggest that the d

the formation and breach of a short lived landslide dam at hsiaolin village taiwan part i post event reconstruction of dam geometry abstract in this paper technologies from multiple disciplines are used to reconstruct the shape of the hsiaolin landslide dam a short lived landslide dam sld that was triggered by typhoon morakot here the formation failure mode and breaching process of this sld are investigated the results indicate that the overtopping time and the debris budget constrained the dam geometry the inferred volume of the hsiaolin landslide dam 15 4 million m3 is much smaller than the actual landslide volume 25 2 million m3 even considering the rock mass dilation and debris entrainment meanwhile a 46 error could be induced if an over simplified equation a function of the dam height length and width is used to calculate the dam volume the saddle of the dam crest which is where overtopping occurred could be used as a reference to measure the dam height and length accordingly the determined dam dimensions of height 44 m length 370 m and width 1500 m are suggested to be the representative geometrical indices that influenced the stability of the hsiaolin landslide dam the flow rate of the dammed river another variable relevant to dam stability was determined from a run off simulation it is suggested that instead of the peak flow before the dam formation the flow rate during the blockage period 2974 m3 s should be used as the training data for building a statistical model for stability predictions finally the low hydraulic gradient at the toe of the dam s surface and the high safety factor of the dam slope indicate that the piping and slope instability were irrelevant to the failure of the hsiaolin short lived landslide dam it is postulated that overtopping about one hour after the blockage dominated the failure process of this heavy rainfall induced landslide dam

new constraints on the early formation of the western dharwar craton india from igneous zircon u pb and lu hf isotopes abstract the western dharwar craton wdc is an archean crustal segment for which the earliest stages of development have remained poorly constrained because the oldest identified lithologies are chronologically indistinguishable despite vastly different compositions and origins i e 3352 110 ma sargur group komatiites and 3342 6 ma hassan gorur ttg gneiss indication for older crust come from ancient detrital zircons 3450 3610 ma although their genetic link to the wdc is purely conjectural in order to bring new understanding to early development of the wdc we studied orthogneisses around the holenarsipur schist belt hsb for their petrography major oxide concentrations zircon u pb geochronology and lu hf isotope systematics our results reveal that the wdc igneous record contains crust older than 3350 ma in the form of a 3410 8 3 6 ma granitic gneiss and inherited zircons with ages ranging from 3295 18 to 3607 16 ma that were found within a 3178 10 ma trondhjemitic gneiss and a biotite rich enclave found within it the presence of muscovite and the peraluminous signature of the granitic gneiss in spite of mildly depleted hf isotopic signature ehf 2 2 0 6 at 3410 8 ma suggest that this sample formed by reworking of a felsic precursor with short crustal residence time possibly marking the beginning of wdc formation the oldest inherited zircons display variable ehf ranging from 10 4 at 3414 ma to 2 3 at 3607 ma that did not seem to have influenced the hf isotopic composition of granitoids of the wdc that formed between 3200 and 3410 ma except perhaps in the sargur area we suggest that the wdc formed remote from continental crust until a crustal block containing 3410 ma zircons was accreted to it 3200 my ago this event resulted in the stabilization of the wdc which is marked by diapiric granitoids to which the 3178 ma trondhjemitic gneiss belongs after 3200 ma the crustal block together with granitoids formed between 3410 and 3200 ma buffered the hf isotopic signature of newly formed granitoids hence indicating that by then the wdc already was a stable continental segment

the tectonic evolution of the abitibi greenstone belt of canada based on structural geochemical sedimentological and geochronological studies we have formulated a model for the evolution of the late archaean abitibi greenstone belt of the superior province of canada the southern volcanic zone svz of the belt is dominated by komatiitic to tholeiitic volcanic plateaux and large bimodal mafic felsic volcanic centres these volcanic rocks were erupted between approximately 2710 ma and 2700 ma in a series of rift basins formed as a result of wrench fault tectonics the svz superimposes an older volcanic terrane which is characterized in the northern volcanic zone nvz of the abitibi belt and is approximately 2720 ma or older the nvz comprises basaltic to andesitic and dacitic subaqueous massive volcanics which are cored by comagmatic sill complexes and layered mafic anorthositic plutonic complexes these volcanics are overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 2 ma the tectonic model envisages the svz to have formed in a series of rift basins which dissected an earlier formed volcanic arc the nvz analogous rift environments have been postulated for the hokuroko basin of japan the taupo volcanic zone of new zealand and the sumatra and nicaragua arcs the difference between rift related submergent volcanism in the svz and emergent volcanism in the nvz resulted in the contrasting metallogenic styles the former being characterized by syngenetic massive sulphide deposits whilst the latter was dominated by epigenetic porphyry type cu au deposits

geologic evolution of the late archean abitibi greenstone belt of canada the southern volcanic zone svz of the late archean abitibi belt of the superior province of canada is dominated by komatiitic to tholeiitic volcanic plateaus and large bimodal mafic felsic volcanic centers these volcanic rocks were erupted between about 2717 and 2700 ma in a series of rift basins that formed as a result of wrench fault tectonics they overlie and juxtapose a volcano plutonic assemblage characterized in the northern abitibi belt the age of the assemblage is about 2720 ma or older and it comprises basaltic to andesitic and dacitic subaqueous massive volcanics cored by comagmatic sills and layered anorthositic complexes and overlain by felsic pyroclastic rocks that were comagmatic with the emplacement of tonalitic plutons at 2717 2 ma a tectonic model is proposed in which the svz formed in a series of rift basins that dissected an earlier formed volcanic arc comparisons are made with rift environments that have been postulated for phanerozoic areas such as the hokuroko basin of japan the taupo volcanic zone of new zealand and the sumatra and nicaragua arcs

the stratigraphy and structure of the chitradurga region an illustration of cover basement interaction in the late archaean evolution of the karnataka craton southern india abstract the succession in the late archaean supracrustal belts in the chitradurga region begins with basal quartz pebble conglomerates and quartzites which were deposited on a basement of tonalitic granitic gneisses ca 3000 ma containing tracts and enclaves of older supracrustal rocks the basal beds are overlain by basic metalavas and amphibolites interbedded with cross bedded quartzites and siliceous phyllites this series passes up into siliceous phyllites locally containing a large lenticular mass of polymict conglomerate talya conglomerate overlain by banded iron formations and siliceous phyllites including sporadic chert pebble conglomerates greater subsidence in part of the basin accommodated greater thicknesses of basic volcanic and acid pyroclastic rocks the latter being more abundant at higher levels with progressive deepening of the whole basin fine grained graded greywackes and local polymict conglomerates aimangala conglomerate were deposited the turbidite sequence forms the youngest sedimentary rocks exposed estimated total stratigraphic thickness is at least 10 km in deeper parts of the basin deformation led to a series of upright anticlines and synclines and related ls fabrics with extreme variations in plunge of the coaxial fold axes and l fabrics within axial surfaces which maintain a steep orientation low grade metamorphism outlasted the deformation sedimentation and volcanism in the chitradurga supracrustal belt is linked to variable subsidence of the basement foundation probably as a result of rifting the structural evolution of the belt followed as a direct continuation of events that controlled the depositional and volcanic history variable displacement of the basement during these late archaean events in the karnataka craton took place on shear zones and related fractures that acted as channels for water and co 2 as indicated by vein minerals and alteration products uplift of basement segments and their distension by granitic diapirs led to deformation of the supracrustal cover made ductile by its high water content

compositions and sources of metasediments in the upper dharwar supergroup south india texturally mature quartz rich sandstones texturally mature mafic rich sandstones and texturally immature graywackes are abundant in the late archean chitradurga group of the dharwar craton in south india when compared to graywackes of paleozoic age from northeastern north america the chitradurga graywackes have slightly higher average concentrations of na and ferromagnesian elements indicating the existence of a more tonalitic and mafic rich provenance during the late archean in karnataka the regional tonalitic gneiss peninsular gneiss is the predominant source of these sediments although mafic ultramafic volcanic debris from unidentified sources is also important neither intermediate nor felsic volcanics nor an extensive metasedimentary terrane were prominent in the provenance although the composition of the craton was dominantly sialic the presence of abundant ferromagnesian debris in some of the texturally mature sandstones that probably formed in shallow water intracratonic or platform

metamorphism of cordierite gneisses from the bangalore region of the indian archean abstract mineral compositions from cordierite bearing metasedimentary enclaves adjacent to the closepet granite in the bangalore region of the south indian craton indicate peak metamorphism in the range 4 5 5 0 kb 690 730 c p h 2 o is found to decrease towards the south and those assemblages which lie south of the charnockite line are formed under conditions of p h 2 o total 250 km north bangalore andalusite bearing assemblages from the northern margin of the closepet granite indicate peak metamorphic conditions in the range 2 6 3 8 kb 520 620 c the inferred piezotacrmic array is strongly convex towards the temperature axis and may represent a transient geotherm in the upper crust related to the emplacement of the closepet granite or to volatile activity along the margins of the granite

geochemistry of adakites from neoarchaean active continental margin of shimoga schist belt western dharwar craton india implications for the genesis of ttg abstract adakites are identified for the first time from a neoarchaean active continental margin acm preserved in the eastern part of the shimoga schist belt near ranibennur western dharwar craton india these adakites consists mainly of quartz plagioclase and minor amphiboles and are interlayered with the turbidites they exhibit typical adakitic low y 8 35 14 70 ppm and yb 0 85 1 47 ppm may be classified as high sio2 and low mg ni and cr type adakites other constituents such as na2o k2o nb zr lree and hree and their ratios such as na2o k2o zr sm nb la la yb n gd yb n and th u also closely resemble with the high silica adakites hsa of martin et al martin h smithies r h rapp r moyen j f champion d 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 24 sr y values are moderate generally lower than the high sr low silica cenozoic adakites but within the range of archaean adakites the negative nb ta and ti anomalies characteristic of cenozoic adakites are found in ranibennur adakites also zr zr and hf hf ratios are also similar to hsa these adakites further depict compositional similarities with meso and neoarchaean tonalite trondhjemite granodiorites ttgs such types of adakites have been experimentally generated by the partial melting of hydrous basalts that are similar to adakitic glass veins low mgo cao cr and ni found in peridotite xenoliths of kamchatka arc xiong x l xia b xu j f niu h c xiao w s 2006 na depletion in modern adakites via melt rock reaction within the sub arc mantle chem geol 229 273 292 since archaean had higher geothermal regime subduction of the basaltic slab was most probably shallow and significant mantle wedge was not available to react with adakitic melt hence archaean adakites in general and particularly from ranibennur are relatively depleted in the peridotiitic mantle wedge components their identification from an archaean acm and their compositional similarities with the paleo meso archaean ttgs suggest the possibility of identical origin i e the melting of a shallow hydrous basaltic slab this mechanism during archaean was widespread and rapid resulted in faster continental crustal growth during the early history of the earth identification of archaean adakites in association with island arc turbidites from a greenstone belt sequence supports the rapid subduction mechanism for the crustal growth that coincides with 2 7 ga peak episode of almost all geological processes

stability analysis of landslide dams under surge action based on large scale flume experiments abstract in recent years large magnitude earthquakes have caused the formation of a large number of landslide dams the rising water level in the landslide lakes may induce a large number of landslides in the lake areas when landslides rush into a lake area large scale surges may be produced and would then strongly impact on the dam stability and cause a breaching process to understand the erosion failure modes of dam bodies caused by surges and the variation in the pore water pressure in the dam body large scale wave flume tests were carried out in this study six groups of comparative tests were carried out to study the two main influencing factors namely the upstream water level and the wave height it was found that 1 when subjected to surge waves the landslide dam stability is determined by the difference h between the effective water level the sum of the water level and the overlapping wave height and the effective dam height the dam height after lowering due to local sliding 2 when h 0 the dam is overtopped and breached by the next waves 3 during dam breach by overtopping with surge waves the erosion in the breach initiation phase is much faster than by overtopping without surge waves but the difference in the breaching development phase is not very significant and 4 the pore water pressure close to the upstream slope is much more sensitive to the action of the surge waves than deeper inside the dam body

paleostress field reconstruction in the western dharwar craton south india evidence from brittle faults and associated structures of younger granites abstract we present new fault slip data to decipher the tectonic stress regime in younger granites 2 61 ga of western dharwar craton wdc south india the study is based on paleostress reconstruction of the terrain using fault slip data from the small scale oblique slip normal faults of chitradurga granite paleostress analysis using right dihedron and rotational optimization methods reveal that these faults have developed under nne ssw directed extension similar results are also obtained when left lateral and right lateral oblique slip normal faults are treated as separate entities it is envisaged that all faults in chitradurga granite have developed under a single tectonic event and are considered to be extensional shear fractures we interpret that the oblique slip normal faults in granite oriented along nnw sse to n s p shear nw se r shear ne sw r shear and wnw ese t are defined as the respective shear components of the regional riedel shear system it developed due to sinistral movement along the chitradurga shear zone csz during late d3 deformation at shallow crustal level the fault planes act as primary or secondary shear planes depending on their proximity to the csz and kinematically fit well with regional far field compression the present study addresses the formation of oblique slip normal faults in the chitradurga granite and its implication in reconstructing the paleostress field in the precambrian south indian shield

prediction of the overtopping induced breach process of the landslide dam abstract timely prediction of a landslide dam breach is particularly important for assessments of expected disaster consequences and to plan emergency responses however due to the complex composition and specific geotechnical properties of the landslide dam material such a prediction is challenging in this study geological survey results and landslide dam breach mechanisms were used to develop a numerical model for overtopping induced landslide dam breaches considering variation of soil erodibility with depth the model included a hydrodynamic process module a soil erosion module and a breach evolution module moreover a time step iteration algorithm was adopted to simulate the soil and water coupling process during dam breach a comparison of calculated and measured breach hydrographs variations of dammed lake water level breach sizes as well as two other typical models were used to validate the rationality of the numerical model by considering the baige landslide breach case of november 3 2018 with detailed measured data parameter sensitivity analysis showed that the soil erodibility coefficient exerted an important influence on the breach process while soil critical shear stress had a relatively small influence which remained within 15 for output parameters when it was multiplied by 0 5 1 0 and 2 0 furthermore spillway excavation was found to significantly reduce the peak breach flow if the dammed lake has a large storage capacity thus identifying it as an effective measure for disaster mitigation

precambrian continental crust of india and its evolution the indian precambrian continental crust exhibits a variety of geological features fashioned at different times by different geotectonic processes the bulk of this crust was formed prior to 2600 m y ago and remobilized at least twice between 2600 2000 m y ago early proterozoic mobile belt epmb and 2000 1500 m y ago middle proterozoic mobile belt mpmb three early precambrian nucleii karnataka kn jeypore bastar jbn and singhbhum sn appear to have survived in the craton and are characterized by low grade supracrustals and tonalitic trondhjemite gneisses formed 3800 2600 m y ago the epmb event involved sedimentation amphibolite granulite facies metamorphism and co 2 k metasomatism and produced amphibolite facies rocks and k granites in the north and charnockite and other granulite facies rocks in the south gold sporadically distributed in the supracrustal rocks of the craton was remobilized during the epmb event k granites form a garland around the central dharwar craton sugg

modeling lateral enlargement in dam breaches using slope stability analysis based on circular slip mode abstract evaluation of breach flood of landslide or artificial dams is usually performed by combining the hydraulic modeling of the breach flow and geotechnical analysis of the breach channel stability this paper is a continuation of the previous work which mainly focused on the hydraulic aspects of a dam breach flood efforts have been made to improve the related slope stability analysis approach that traditionally adopts a simple wedge failure mode the improvements includes a vertical cut at the slope toe due to soil erosion an approach to determine the critical slip surface the effective and total stress methods dealing with different dam materials and a procedure to model the stepped failures of the breach bank due to continuous toe cutting using vba programming an excel spreadsheet entitled dbs iwhr has been developed to perform the stability analysis this spreadsheet has been incorporated into another spreadsheet entitled db iwhr for the calculation of the flood hydrograph the developed model has been tested by back analysis of the yigong landslide dam breached at the tibetan plateau in china in 2000 with a flood peak of 94 013 m 3 s the calculated results of the final breach base level and the peak discharge are in good agreement with the field data further the results are shown to be insensitive to the variations in the geotechnical parameters used in the model

the structural anatomy of the sandur schist belt a greenstone belt in the dharwar craton of south india abstract two belts of metasedimentary rocks occurring at the eastern and western flanks and a central terrane of metavolcanic rocks make up the late archaean sandur schist belt in the dharwar craton of south india contrary to the traditional interpretations the regional structure of the belt is not a synclinorium the earliest episode of deformation produced major and minor isoclinal folds in the banded iron formation bif their axial planes are parallel to the regional attitude of bedding d 2 folds have a consistent sinistral sense of vergence throughout the schist belt and they refold the d 1 folds the d 2 axial planes make small angles with regional bedding there was a strong component of layer parallel simple shear during d 2 deformation the styles of d 1 and d 2 folds show a general similarity the fold axes have variable plunge though in general it is moderate to steep the variability of the geometry of minor folds is ascribed to progressive development of folds and the rotation of their axes and axial planes during non coaxial deformation simple shear it is likely that the d 1 and d 2 structures were not products of entirely unrelated episodes of deformation and they might have formed at the early and late stages of a progressive deformation history a noteworthy feature is that the deformation is mostly concentrated in the two metasedimentary belts and the internal strain is low in the central metavolcanic unit this is probably due to concentration of layer parallel simple shear in the metasedimentary rocks both flattening and simple shear played major roles in the development of the structural pattern and the deformation regime may be compared to one of transpression

modeling gradual dam breaches a simulation model of the gradual failure of an earth dam has been formulated developed and tested with real life data a significant feature of the model is its ability to account for the growth of the breach and the eventual draining of the reservoir concepts of water and sediment routing are used in conjunction with a channel geometry descriptor to arrive at a self contained mathematical model of the breach enlargement and the ensuing flood wave unsteady flow elements of the simulation are an implicit numerical solution of the complete saint venant equations coupled with a sequential sediment routing technique this approach provides an increased rational basis for determining outflow hydrographs from postulated earth dam breaches

the archean craton of southern india metamorphic evolution and p t conditions the archaean craton of southern india is characterized by a highly complicated and not yet fully understood geological history comprizing several cycles of sedimentation and volcanism deformation and metamorphism in the span between about 3400 and 2500 m y the large scale regional variation in metamorphic grade observed today is essentially related to a metamorphic event at about 2600 m y ago which affected an older migmatite gneiss greenstone terrain 2900 3400 m y

analysis of gradual earth dam failure analytical models are developed for the simulation of earthdam breach erosion using a reservoir water mass depletion equation broad crested weir hydraulics and a breach erosion relation solutions are derived for rectangular triangular and trapezoidal shaped breaches breach erosion is assumed to be either a linear or quadratic function of the outflow mean water velocity historical data are used to test the models a sensitivity analysis is performed to determine the importance of the various parameters involved

population characteristics of submicrometer sized craters on regolith particles from asteroid itokawa abstract we investigated impact crater structures on regolith particles from asteroid itokawa using scanning electron microscopy we observed the surfaces of 51 itokawa particles ranging from 15 m to 240 m in size craters with average diameters ranging from 10 nm to 2 8 m were identified on 13 itokawa particles larger than 80 m we examined the abundance spatial distribution and morphology of approximately 900 craters on six itokawa particles craters with sizes in excess of 200 nm are widely dispersed with spatial densities from 2 6 m2 to 4 5 m2 a fraction of the craters was locally concentrated with a density of 0 1 m2 the fractal dimension of the cumulative crater diameters ranges from 1 3 to 2 3 craters of several tens of nanometers in diameter exhibit pit and surrounding rim structures craters of more than 100 nm in diameter commonly have melted residue at their bottom these morphologies are similar to those of submicrometer sized craters on lunar regolith we estimated the impactor flux on itokawa regolith forming craters assuming that the craters were accumulated during direct exposure to the space environment for 102 to 104 yr the range of impactor flux onto itokawa particles is estimated to be at least one order of magnitude higher than the interplanetary dust flux and comparable to the secondary impact flux on the moon this indicates that secondary ejecta impacts are probably the dominant cratering process in the submicrometer range on itokawa regolith particles as well as on the lunar surface we demonstrate that secondary submicrometer craters can be produced anywhere in centimeter to meter sized depressions on itokawa s surface through primary interplanetary dust impacts if the surface unevenness on centimeter to meter scales is a significant factor determining the abundance of submicrometer secondary cratering the secondary impact flux could be independent of the overall shapes or sizes of celestial bodies and the secondary impact flux could have similar values on itokawa and the moon

characteristics of the landslide dams induced by the 2008 wenchuan earthquake and dynamic behavior analysis using large scale shaking table tests abstract the ms 8 0 wenchuan earthquake triggered at least 257 landslide dams more than 300 aftershocks with the magnitudes higher than ms 4 0 occurred after the formation of these landslide dams which might largely influence the structure and soil properties of these dams this paper aims to comprehensively investigate the characteristics of the landslide dams induced by the 2008 wenchuan earthquake and study the dynamic behaviors of the landslide dams under aftershocks using large scale shake table tests first the characteristics of the landslide dams including the distribution geometric parameters stability and longevity mitigation measures and the influence of the aftershocks are proposed then two groups of shaking table tests to simulate the dynamic behaviors of two types of landslide dams under aftershocks are illustrated one with quartz sand contained 10 kaolin dam i and the other with quartz sands all dam ii finally the results of the tests including the acceleration distribution dam deformation and dam breaching process are discussed through this study it is found that the landslide dams caused by high magnitude earthquakes have distinctive characteristics which may largely influence the stability breach process and risks of these dams in the model tests the accelerations are generally higher on the surface of the dams either on the crest or on the both upstream and downstream slopes the dam i was prone to settlement and cracking the aftershocks may not directly trigger the failures of landslide dams but accelerate the overtopping failures by lowering the dam crest with settlement and cracking

rbsr ages of late archean metavolcanics and granites dharwar craton south india and evidence for early proterozoic thermotectonic event s comment

a large landslide triggered by the 2008 wenchuan m8 0 earthquake in donghekou area phenomena and mechanisms abstract during the 2008 wenchuan earthquake more than 60 000 landslides were triggered resulting in about 20 000 casualties among these landslides a catastrophic one occurred in donghekou area of qingchuan county donghekou landslide had a volume of about 1 107 m3 traveled fast for approximately 2 km killing about 780 people the source area consisted of unstable sedimentary strata and the runout path was made of colluvial deposits during the earthquake the colluvial deposits started to move first before the arrival of the displaced landslide debris from the main source area we performed undrained cyclic ring shear tests on samples taken from the runout path and concluded that liquefaction of the runout path material enhanced the mobility of the debris material a fumarole was identified on the upper part of the runout path 6 months later we analyzed the gas and water venting out and concluded that the fumarole was not the result of fault movement it resulted instead from the weathering of slate from the source area the long travel landslide materials blocked two rivers forming two landslide dams that breached with the occurrence of overtopping to better understand the internal structure of the landslide deposits and then provide evidence for a rational plan of countermeasures to stabilize the landslide dams we measured the shear wave velocity of the landslide deposits by a surface wave technique called multichannel analysis of surface waves masw the results revealed that the landslide dams consisted of loosely deposited debris suggesting that the landslide dams were mechanically weak and prone to erosion by overtopping

facies distributions and structure of a dharwar volcanosedimentary basin evidence for late archaean transpression in southern india the bababudan nallur basin c 60 km 125 km is part of a series of late archaean basins accommodating volcanic and sedimentary rocks of the dharwar supergroup within the low grade terrain of the province of karnataka initial development of the bababudan nallur basin was characterized by rapid subsidence with eruption of mainly basaltic lavas breaks in eruption were marked in some instances by thin but persistent deposits of shallow marine quartz sands and muds subsidence in the south continued with accumulation of banded ferruginous cherts and muds whilst uplift of the volcanic pile took place in the north this uplift promoted erosion of the volcanic cover and its basement gneisses and granodiorites with deposition of alluvial and shallow marine fans and debris flows adjacent to the uplifted blocks the fans passed laterally into intertidal and offshore quartz sands greywackes and muds with interbedded dolomitic limestones accumulation of rhyolites banded ferruginous cherts and greywackes took place further north the structure of the basin is dominated by mainly upright folds and faults with the trend of the folds broadly parallel to the boundaries of exposed blocks of basement the basement deformed cataclastically on myriad fractures in contrast with the ductile behaviour of the cover many cover basement contacts are faults with mylonites although unconformities are preserved especially in the south the facies distributions and structure of bababudan nallur and other dharwar belts have characteristics in common with mixed mode basins developed as a consequence of strike or oblique slip on long lived fault zones these relations suggest that transcurrent plate interactions comparable with those of the phanerozoic were significant in the late archaean evolution of southern india

thermal fatigue as the origin of regolith on small asteroids space missions1 2 and thermal infrared observations3 have shown that small asteroids kilometre sized or smaller are covered by a layer of centimetre sized or smaller particles which constitute the regolith regolith generation has traditionally been attributed to the fall back of impact ejecta and by the break up of boulders by micrometeoroid impact4 5 laboratory experiments6 and impact models4 however show that crater ejecta velocities are typically greater than several tens of centimetres per second which corresponds to the gravitational escape velocity of kilometre sized asteroids therefore impact debris cannot be the main source of regolith on small asteroids4 here we report that thermal fatigue7 8 9 a mechanism of rock weathering and fragmentation with no subsequent ejection is the dominant process governing regolith generation on small asteroids we find that thermal fragmentation induced by the diurnal temperature variations breaks up rocks larger than a few centimetres more quickly than do micrometeoroid impacts because thermal fragmentation is independent of asteroid size this process can also contribute to regolith production on larger asteroids production of fresh regolith originating in thermal fatigue fragmentation may be an important process for the rejuvenation of the surfaces of near earth asteroids and may explain the observed lack of low perihelion carbonaceous near earth asteroids10

early archean foredeep sedimentation related to crustal shortening a reinterpretation of the barberton sequence southern africa abstract the upper dominantly terrigenous sedimentary successions of the early archean barberton sequence kaapvaal province record an evolution similar to that of phanerozoic foredeeps and may represent the oldest known foredeep sequence rather than a passive continental margin sequence as previously proposed pre foredeep ocean crust the 3 5 ga old onverwacht group consists of bimodal volcanics with intercalated shallow water sediments gravity modeling and boundary shear zones indicate that deformed onverwacht crust was obducted northward onto sialic continental crust immediately before during or after burial by the synorogenic terrigenous clastic fill foredeep basin deepening due to crustal loading from the south is recorded by basinal iron formation chert and mudstone of the basal fig tree group which accumulated paraconformably on the onverwacht overlying sediments of the fig tree group consist of 2 km of submarine fan greywackes and mudstones shoaling of the basin is indicated by the transition to the overlying braided alluvial and shallow marine sediments of the ca 3 3 ga old moodies group 3 km thick changing ree patterns and relative abundances of ni cr sr th and ur in the sediments of the fig tree and moodies groups indicate a significant ultramafic mafic volcanic component diluted upward in the stratigraphic sequence by an increasing granitic contribution a similar trend is reflected in sandstone petrography in which the ratio of extrusive to intrusive rock fragments decreases upwards in the fig tree group whereas the moodies group sediments are enriched in quartz and potassium feldspar a persistent chert component in both units suggests that the tectonic setting of the basin is analogous to that of phanerozoic recycled orogens the distribution of facies in the fig tree and moodies groups and paleocurrent petrographic and geochemical data indicate progressive unroofing of a southerly source terrane consisting of the onverwacht volcanics and intercalated sediments and the 3 5 3 2 ga old ancient gneiss complex agc in addition older components of the fig tree group were recycled into overlying stratigraphie units the agc consists of mantle derived 3 5 ga old bimodal metavolcanics and metasediments a tonalite gneiss batholith metabasite dikes and meta anorthosites its structures record progressive northwestward uplift beginning around 3 4 ga ago intense homogeneous ductile strains were overprinted by northwest verging major folds rotated by large scale northwestward simple shear followed by imbricate faulting and pseudotachylite formation by 3 3 ga ago the fig tree and moodies groups had also shortened with similar kinematics to those of the agc by partly syndepositional folding and volume loss during the formation of transecting cleavage further folding and slide formation followed during subsolidus diapiric rise of the initially tabular kaap valley tonalite by 3 2 ga and emplacement of trondhjemite plutons from 3 3 to 3 0 ga ago

evolution of lakes created by landslide dams and the role of dam erosion a case study of the jiajun landslide on the dadu river china abstract during the late pleistocene strong erosional riverine environments led to the widespread occurrence of landslides along the river valleys in southwestern china such landslides along the middle reaches of the dadu river often caused large scale dammed lakes in this study the typical large scale jiajun landslide and its associated dammed lake were investigated the relatively complete sedimentary sequence of the lake was examined and multi depositional characteristics were found analysis of the history of the dammed lake revealed the relationship between its formation and the river valley erosion the evolution of the dammed lake was reconstructed based on changes of the sedimentary environments we concluded that the lake experienced two stages of high lake level stable lacustrine sedimentation during this period a two stage large scale dam breach and retention periods lasting more than 100 years the relationship between the formation of the ancient barrier lake and the river valley erosion in the middle reaches of the dadu river is indicative of the erosive and depositional environments the evolution of the ancient dammed river landslide valley had considerable effect on valley erosion and the sedimentary environment of the dadu river

stratigraphic and sedimentological evidence bearing on structural repetition in early archean rocks of the barberton greenstone belt south africa abstract the 3 5 3 3 ga old swaziland supergroup in the barberton greenstone belt south africa includes a lower predominantly volcanic unit the onverwacht group and an upper largely sedimentary section the fig tree and moodies groups although viljoen and viljoen concluded that the onverwacht group exceeds 15 km in stratigraphic thicknesses more recent workers have suggested that it represents a much thinner section of rocks repeated by folding and faulting our mapping indicates that the upper half of the group includes at least 8 km of unrepeated stratigraphic section inferences of structural repetition have arisen in part because a major shear zone is present in the upper half of the onverwacht group on the west limb of the onverwacht anticline shearing and the overturning of large blocks of the igneous sequence have combined with the later intrusion of felsic magma to produce a generally stratiform highly complex zone of deformation up to 2 km wide the displacement across the zone is unknown but the presence of unfaulted sections of this part of the stratigraphic sequence indicates that the gross stratigraphic arrangement of units within the group has not been significantly altered structures previously mapped as major fold hinges within the upper part of the onverwacht group can be shown to have formed by local deformation and reflect neither large scale folding nor structural repetition of the rocks several kilometers higher in the section rocks of the uppermost onverwacht and fig tree groups are stacked and repeated in a series of thrust nappes individual nappes extend for up to 15 km along strike and include as much as 900 m of allochthonous volcanic and sedimentary rocks they were apparently emplaced by faulting or gravity sliding at or near the earth s surface their formation involved the movement of sheets made largely up of sedimentary rocks along shear surfaces within underlying much weaker serpentinized ultramafic komatiites locally the sheets were deformed to form fold nappes the lower limbs of the fold nappes commonly show extreme attenuation and brittle deformation whereas the upper limbs are largely intact the thrust faults are the loci of small hypabyssal igneous bodies that appear to be co magmatic with a suite of upper fig tree volcanic rocks this style of faulting has not affected rocks of the overlying moodies group although estimates of the timing of deformation are as yet imprecise these features suggest that it occurred during a late fig tree phase of tectonism and volcanism

precambrian tectonics and crustal evolution in south india about 3 4 ga ago voluminous calc alkaline magmas represented by the granitoid gneisses of southern india were emplaced into a now poorly preserved non continental crust unstable ensialic basins initiated at about 3 0 ga were filled with volcanic and sedimentary rocks up to about 2 6 ga this basement cover sequence was deformed at the close of the archaean first by northward accretion and thickening of several crustal slabs formerly separated by prisms of stable shelf sediments structures produced by this episode were refolded and dislocated by large n s strike slip shear belts to impart intense steep planar fabrics to large volumes of the crust fluids rich in co possibly derived from sedimentary material driven beneath the crustal slabs by the thickening mechanism purged the deep crust of h o to form granulites upward migration of hot h o rich fluids encouraged partial melting at intermediate crustal levels these late archaean tectonic and thermal events began soon after the close of basin f

precambrian continental strain and shear zone patterns south indian case 1 this study addresses the tectonic and mechanical significance of crustal scale strain and shear zone patterns in the south indian precambrian lithosphere it is based on a tectonic map of the dharwar craton derived from landsat imagery existing documentation and our own field observations we document the contrasted responses of the two main parts of the craton to late archean 2 56 2 51 ga shortening the old 3 ga lithosphere of the western dharwar craton stabilized at 2 61 ga underwent moderate shortening and strain localization along spaced shear zones the eastern dharwar craton rejuvenated by late archean juvenile magmatic accretion responded to shortening by flowing laterally against the western dharwar craton shortening operated without significant thickening because of the high buoyancy of the juvenile crust and the very low strength of its mantle lithosphere the late archean crustal scale shear zone network did not accommodate large displacements and only contributed to smoothing out of strain heterogeneities during the latest stages of flow the shear zone pattern only reflects the symmetry of the regional finite strain field of a wide hot orogen it does not result from terrain amalgamation but accompanies crustal flow and does not compare with those of modern active margins which accommodate unidirectional transpression our analysis further suggests that the shear zones bounding the craton did not record large horizontal displacements during final assembly of gondwana but rather transverse shortening and vertical extrusion

petrography chemistry and isotopic ages of peninsular gneiss dharwar acid volcanic rocks and the chitradurga granite with special reference to the late archean evolution of the karnataka craton southern india abstract new petrographic major and trace element and isotopic age data are presented for four suites of rocks from the low to medium grade part of the south indian archaean craton in central karnataka two suites are from the peninsular gneiss basement to the late archaean dharwar supergroup the third is a suite of dharwar potassic rhyolites and the fourth is from the chitradurga granite which has intrusive contacts with the dharwar supergroup the chikmagalur granite granodiorite which with its host gneisses forms part of the basement peninsular gneiss to the dharwar supergroup in the bababudan basin yields rb sr and pb pb whole rock isochron dates of 3080 110 ma and 3175 45 ma respectively an initial 87 sr 86 sr ratio of 0 7013 0 0009 and a 1 value 238 u 204 pb of 7 98 host tonalitic gneisses to the chikmagalur granite give an rb sr whole rock isochron date of 3060 160 ma with an initial 87 sr 86 sr ratio of 0 7015 0 0004 and a pb pb whole rock isochron date of 3190 100 ma with a model 1 value of 8 00 a suite of granites and granodioritic tonalitic gneisses chitradurga granitic rocks and gneisses forming part of the peninsular gneiss basement to the dharwar supergroup west of the chitradurga belt yields rb sr and pb pb whole rock isochron dates of 2970 100 ma and 3028 28 ma respectively with an initial 87 sr 86 sr ratio of 0 7035 0 0013 and a model 1 value of 7 62 the suite of dharwar acid volcanic rocks from north of honnali defines a poorly fitted 207 pb 206 pb linear array mswd 15 8 which gives an apparent age of 2565 28 ma and a model 1 value of 7 46 the poor fit of this isochron shows that a closed system was not maintained a conclusion supported by high k abundances which are attributed to a syn or post magmatic ion exchange process the chitradurga granite which intrudes the older rocks of the dharwar supergroup in the chitradurga belt yields a well fitted pb pb whole rock isochron date of 2605 18 ma with a model 1 value of 7 68 the u pb relations in these suites from karnataka are in marked contrast with the commonly severe u depletion and consequently unradiogenic pb isotopic compositions observed in deeply eroded high grade archaean gneiss terranes such as those bordering the north atlantic this contrast indicates that the cratonic rocks in central karnataka represent a relatively high level in the original archaean continental crust

model for predicting floods due to earthen dam breaching i formulation and evaluation this paper proposes a dam breach model which predicts in a simple but physically based manner not only the peak discharge but the whole outflow hydrograph and breach development the following aspects are taken into account the geometry of the embankment the shape of the reservoir the hydraulic characteristics of the flow through the breach and its erosive capacity and the shape of the breach the model needs only one calibration parameter and can be easily applied to real cases the application of the model with a single value of the calibration parameter produced excellent results in the simulation of 12 historic earthfill dam failures with a discharge range covering three orders of magnitude

the dharwar craton southern india interpreted as the result of late archaean oblique convergence abstract the dharwar craton comprises two distinct parts separated by a steep n s sinistral shear zone in the western part a pre 2900 ma complex of orthogneisses granodiorites and narrow tracts of supracrustal rocks sargur group forms the basement to volcanic and sedimentary basins of the dharwar supergroup ca 2800 2550 ma late archaean deformation is characterised by ne sw crustal shortening and steep n s sinistral shear zones the eastern part is underlain by parallel steep n s or nw se linear belts of calc alkaline anatectic and juvenile granites and granodiorites dharwar batholith ca 2750 2510 ma with intervening volcanic and sedimentary schist belts ca 2800 2550 ma the plutonic belts are 15 25 km wide up to 150 km long and bounded by steep nw se high strain zones up to 2 km wide with sinistral shear sense except one which is dextral magmatic state fabrics and structures in the plutonic rocks are parallel to solid state sinistral shear fabrics in the high strain zones but diffuse magmatic banding is commonly oblique to these zones and coincides with the plane of instantaneous shortening in sinistral shear magmatic state structures swarms of vertical nw se dykes of granite and the vertical wedge shape of the linear belts are consistent with emplacement of the batholith during sinistral shear when magma pressure exceeded regional horizontal compressive stress upright folds and schistosity steep reverse faults and effects of regional ht lp metamorphism show that deformation was partitioned into ne sw shortening in the schist belts during emplacement of the plutonic belts in the sinistral shear regime the western part of the craton is interpreted as the foreland to an accretionary arc represented by the batholith and schist belts intra arc basins in the east ne sw shortening and sinistral transcurrent displacements in the foreland and arc are consistent with arc normal and arc parallel displacements during oblique convergence analogous to mesozoic cenozoic convergent settings

scale amplification of natural debris flows caused by cascading landslide dam failures debris flows are typically caused by natural terrain landslides triggered by intense rainfalls if an incoming mountain torrent collapses a series of landslide dams large debris flows can form in a very short period moreover the torrent can amplify the scale of the debris flow in the flow direction the catastrophic debris flows that occurred in zhouqu china on 8 august 2010 were caused by intense rainfall and the upstream cascading failure of landslide dams along the gullies in the wake of the incident a field study was conducted to better understand the process of cascading landslide dam failures and the formation of debris flows this paper looks at the geomorphic properties of the debris flow gullies estimates the peak flow discharges at different locations using three different methods and analyzes the key modes i e different landslide dam types and their combinations of cascading landslide dam failures and their effect on the scale amplification of debris flows the results show that five key modes in luojiayu gully and two modes in sanyanyu gully accounted for the scale amplification of downstream debris flows in the zhouqu event this study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream as a complex cascade of geomorphic events failure of landslide dams and erosion of the sloping bed can scale to become catastrophic discharges neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in a high cost

the rubble pile asteroid itokawa as observed by hayabusa during the interval from september through early december 2005 the hayabusa spacecraft was in close proximity to near earth asteroid 25143 itokawa and a variety of data were taken on its shape mass and surface topography as well as its mineralogic and elemental abundances the asteroid9s orthogonal axes are 535 294 and 209 meters the mass is 3 51 1010 kilograms and the estimated bulk density is 1 9 0 13 grams per cubic centimeter the correspondence between the smooth areas on the surface muses sea and sagamihara and the gravitationally low regions suggests mass movement and an effective resurfacing process by impact jolting itokawa is considered to be a rubble pile body because of its low bulk density high porosity boulder rich appearance and shape the existence of very large boulders and pillars suggests an early collisional breakup of a preexisting parent asteroid followed by a re agglomeration into a rubble pile object

structural pattern in the dharwar craton high grade and low grade supracrustal belts sargur and dharwar set in a matrix of gneisses dotted with granitic plutons of different ages make up the dharwar craton the overall structural pattern is one of subparallel linear belts and stringers whose regional trend changes from nw se in the northern part to n s in the south both the high grade and low grade belts show three principal episodes of folding however the correlation between the deformation episodes in the sargur and the dharwar rocks is controversial and the structural relations between them are not unequivocally established parallelism of the first phase structures in the sargur and the dharwar rocks can be interpreted either as synchronous development or rotation of the earlier sargur structures into parallelism with the younger dharwar structures during later deformation the extension of the supracrustal belts is parallel to the f 2 axial traces of the second deformation granite diapirism and basement uplift further modified

influence of textural properties on the failure mode and process of landslide dams abstract the failure of a landslide dam is a sudden geo hazard which can significantly threatens the lives and property of local residents in this study 11 experiments were designed to reproduce the failure process of landslide dams with different grain size distributions and hydrodynamic conditions in order to fully consider the influence of seepage on the stability of landslide dams with different textural properties the inflow discharge was small in these tests by analyzing the experimental data we found that the textural properties plays a key role in the failure modes and process of landslide dams the eleven tests produced five different results the landslide dam in experiment 1 and 8 remained stable the landslide dam in experiment 2 partially failed in experiments 3 6 the dams failed due to overtopping and erosion while in experiment 7 the dam failed due to overtopping and soil collapse in experiment 9 11 the dams failed due to piping overtopping and erosion in addition the evolution of the outflow discharge and density also varied for the different textural properties of the dam materials based on the experimental results the landslide dam materials were classified as coarse matrix controlled medium particle controlled fine matrix controlled and balanced composition the failure modes and process as well as the evolution characteristics of the outflow discharge and flow density were all summarized providing a scientific reference for disaster prevention and mitigation research of landslide dams

the nature of the crust in southern india implications for precambrian crustal evolution 1 we present crustal thickness and poisson s ratio determinations from receiver function analyzes at 32 sites on the archaean and proterozoic terrains of south india the crustal thickness in the late archaean 2 5 ga eastern dharwar craton varies from 34 39 km similar crustal thickness is observed beneath the deccan volcanic province and the cuddapah basin the most unexpected result is the anomalous present day crustal thickness of 42 51 km beneath the mid archaean 3 4 3 0 ga segment of the western dharwar craton since the amphibolite grade metamorphic mineral assemblages 5 7 kbar paleopressures in this part of western dharwar craton equilibrated at the depths of 15 20 km our observations suggest the existence of an exceptionally thick 57 70 km crust 3 0 ga ago beneath the exhumed granulite terrain in southernmost india the crustal thickness varies between 42 60 km the poisson s ratio ranges between 0 24 0 28 beneath the precambrian terrains indicating the presence of intermediate rock type in the lower crust these observations of thickened crust suggest significant crustal shortening in south india during the archaean

whole rock pbpb isotopic ages of late archaean limestones karnataka india application of the pbpb isotopic dating technique to metamorphosed limestones from late archaean low and high temperature greenschist amphibolite facies terrains in karnataka southern india has revealed distinct differences in the evolution of each terrain and in their model 1 values the western low temperature terrain is characterised by tracts of late archaean volcanic and sedimentary rocks dharwar supergroup their basement of orthogneisses and granodiorites 3400 2900 ma and enclaves of older supracrustal rocks intrusions of late archaean granite 2600 ma occur sporadically in the low temperature terrain in contrast the eastern high temperature terrain is dominated by late archaean polyphase syn and post tectonic granites 2500 ma which intruded tracts of supracrustal rocks that are similar to the dharwar supergroup in the low temperature terrain the low and high temperature terrains are separated by a n to nnw trending steep belt of mylonites which is over 400 km in length the pbpb data show that metamorphic recrystallisation of the limestones in the low temperature terrain took place 2639 32 ma ago whereas limestones in the high temperature terrain recrystallised 2475 65 ma ago this finding is consistent with previously published ages of late archaean granites in the low and high temperature terrains limestones from the low temperature terrain have a 1 value of 7 79 whereas those from the high temperature terrain have a 1 value of 8 50 these values suggest that the u and pb that was incorporated in the limestones of the low temperature terrain came from a less evolved source than the u and pb in the limestones in the high temperature terrain and indicate a further contrast between these two divisions of the archaean craton in karnataka the nature of the sources is enigmatic but they may reflect differences in composition of the lithospheric plates that were involved in the dharwar collision system data from the high temperature terrain indicate disequilibrium between the measured pb isotopic ratios of carbonate and residue components of the limestones pb isotopic compositions of hci insoluble residues are consistently more radiogenic than those of associated carbonate minerals and they define a younger rotated palaeoisochron that has no age significance this is the first documentation of carbonate residue disequilibrium on the scale of a single hand specimen it highlights the need for a thorough evaluation of pb isotope systematics and the potential effects of acid leaching for multi component limestones

oxygen three isotope ratios of silicate particles returned from asteroid itokawa by the hayabusa spacecraft a strong link with equilibrated ll chondrites abstract oxygen three isotope ratios of four mineral phases olivine low ca and high ca pyroxene and plagioclase in seven silicate particles from asteroid itokawa were measured to investigate oxygen isotope systematics of asteroidal materials in order to obtain highly precise and accurate oxygen isotope ratios 0 3 in 18 o we used a new indium mounting method that minimizes potential instrumental mass fractionation due to surface topography the oxygen isotope data of the seven itokawa particles are distributed above the terrestrial fractionation line with indistinguishable o 17 o 17 0 52 o 18 values of 1 34 0 36 2sd n 22 which is similar to those of itokawa particles analyzed by yurimoto et al 2011 and nakamura et al 2012 however 18 o values of the seven itokawa particles are tightly clustered 3 9 to 5 9 vsmow compared to previous analyses of the itokawa particles 1 4 to 8 8 the average 17 o values and 2sd of the two equilibrated ordinary chondrites eocs which were analyzed for comparison are 1 31 0 49 for st severin ll6 and 0 83 0 64 for guarena h6 the 17 o values of the seven itokawa particles are similar to those of st severin the average bulk 18 o value of the seven itokawa particles is estimated as 4 8 which is within the 18 o range of bulk ll5 and ll6 chondrites it is suggested that itokawa particles are similar to those of equilibrated ll chondrites which strengthens a link between asteroid itokawa and equilibrated ll chondrites that fell to earth the seven itokawa particles and two eocs have 18 o values of high ca pyroxene that are lower than those of olivine indicating that oxygen isotopes between the two mineral phases are not in equilibrium apparent oxygen isotope equilibrium temperatures estimated from a pair of low ca pyroxene and olivine are excessively higher than those from a pair of plagioclase and high ca pyroxene 800 c and peak metamorphic temperatures oxygen isotopes in olivine and low ca pyroxene do not represent equilibrium on the other hand oxygen isotope ratios in high ca pyroxene and plagioclase were mass dependently fractionated accompanied by recrystallization and possibly by diffusion during thermal metamorphism values of 18 o in high ca pyroxene were lowered by exchange which may have resulted in the reverse 18 o fractionation between olivine and high ca pyroxene

cascading breaching of the tangjiashan landslide dam and two smaller downstream landslide dams abstract the 2008 mw 7 9 wenchuan earthquake triggered at least 257 landslide dams most of which formed in series along rivers the failure of an upstream dam could cause the failure of dams downstream one after another the cascading dam breaching may result in a sharp increase in the flood and more serious damage downstream this paper aims to simulate the cascading breaching of landslide dams with a case study of the tangjiashan landslide dam and two smaller dams downstream a modified daba model is applied for this purpose in which the water soil interactions are simulated with erosion and shallow water flow theory this paper first introduces the methodology of the cascading dam breach simulation emphasizing modifications to the daba model then the cascading breaching of the tangjiashan landslide dam and two smaller downstream dams is simulated using the modified daba model finally the influences of several key factors e g dam height dam width dam erodibility on cascading dam breaching are analyzed to identify the critical conditions of overlapping effect in breaching floods the modified daba model is shown to be a reliable tool for simulating the cascading dam breaching the flood from the tangjiashan dam was not significantly amplified by the breaching of the two small dams downstream because the two smaller dams breached before the tangjiashan dam some parameters such as dam crest width and initiation water level may not influence the peak outflow rate and breach size of a single dam obviously but may influence the cascading breaching of several dams significantly through the amplification effect the cascading breaching of several dams is likely to generate multi peak floods a critical condition for the overlapping effects of cascading dam breaching is that large and increasing inflow erodes the dam breach downstream in the development phase if cascade breaching of several landslide dams is inevitable one principle to mitigate the risks is to lower the breach flood of the largest dam with engineering measures if significant overlapping effect is predicted engineering measures may also be taken to breach the smaller dams before the breaching of the large dam upstream or delay the breach of those downstream dams by reinforcement measures

barrier lake bursting and flood routing in the yarlung tsangpo grand canyon in october 2018 abstract ice soil mixture landslide dams formed frequently in the tibetan plateau in response to global warming which pose great threats to both upstream and downstream areas due to inundation and lake bursting on 17 october 2018 a large landslide induced by an ice avalanche at the sedongpu basin of the yarlung tsangpo blocked the main course of the river near gyalha the barrier lake level rose quickly and the dam was overtopped naturally at 13 30 on 19 october 2018 generating a dam breaching flood with a peak flow rate of 32 000 m3 s this paper presents a comprehensive study of the disaster chain of landslide barrier lake dam breaching river flooding in the yarlung tsangpo grand canyon detailed geological and hydrological characteristics of the study region rapid prediction of the dam breaching hydrograph using an erosion based numerical model and analysis of the flood routing in a 460 km canyon reach along the yarlung tsangpo the simulated peak discharge at the dam site is over 30 000 m3 s and the corresponding dam breaching and flood routing hydrographs agree well with the observations two additional scenarios with larger inflow rates are also considered results show that with a larger inflow into the barrier lake the erosion of the dam body becomes more rapid when the inflow rate is increased by six times the peak dam breaching discharge can be doubled the study serves as basis to manage the flood risks due to landslide dam bursting on the yarlung tsangpo or similar rivers

nanomorphology of itokawa regolith particles application to space weathering processes affecting the itokawa asteroid abstract the morphological properties of 26 regolith particles from asteroid itokawa were observed using scanning electron microscopes in combination with an investigation of their three dimensional shapes obtained through x ray microtomography surface observations of a cross section of the ll5 chondrite and of crystals of olivine and pyroxene were also performed for comparison some itokawa particles have surfaces corresponding to walls of microdruses in the ll chondrite where concentric polygonal steps develop and euhedral or subhedral grains exist these formed through vapor growth owing to thermal annealing which might have been caused by thermal metamorphism or shock induced heating in itokawa s parent body most of the itokawa particles have more or less fractured surfaces indicating that they were formed by disaggregation probably caused by impacts itokawa particles with angular and rounded edges observed in computed tomography images are associated with surfaces exhibiting clear and faint structures respectively these surfaces can be interpreted by invoking different degrees of abrasion after regolith formation a possible mechanism for the abrasion process is grain migration caused by impact driven seismic waves space weathered rims with blisters are distributed heterogeneously across the itokawa regolith particles this heterogeneous distribution can be explained by particle motion and fracturing combined with solar wind irradiation of the particle surfaces the regolith activity including grain motion fracturing and abrasion might effectively act as refreshing process of itokawa particles against space weathered rim formation the space weathering processes affecting itokawa would have developed simultaneously with space weathered rim formation and regolith particle refreshment

tectonostratigraphy of the late archean dharwar supergroup dharwar craton india defining a tectonic history from spatially linked but temporally distinct intracontinental and arc related basins abstract the dharwar supergroup comprises the unconformity bound bababudan and chitradurga groups the bababudan group which is best preserved in the western dharwar craton records a divergent margin comprising a basalt dominant intracontinental rift sequence a shale bif drift sequence and a sandstone shale thermal subsidence sequence the rift stage evolved from 2765 ma to 2720 ma whereas the succession was folded uplifted and eroded during development of a convergent continental margin from 2680 ma ocean opening was to the east or southeast the chitradurga group records a two stage back arc basin behind an east facing continental arc stage i evolved between 2609 ma and 2582 ma and stage ii between 2582 ma and 2540 ma the two stages are separated by a subaerial unconformity stage i comprises siliciclastic fluvial shallow marine and deep marine sedimentary rocks and bimodal volcanic rocks stage i is best preserved in the western dharwar craton but there are equivalents in the eastern dharwar craton stage ii in the western dharwar craton comprises deep marine turbidites of siliciclastic and volcaniclastic provenance and basaltic and felsic volcanic rocks volcanic stage ii sequences in the eastern dharwar craton define an arc adjacent position tectonically driven cyclic uplift and erosion were responsible for the mismatch between preserved stratigraphic thickness and time particularly for stage ii sequences a remnant of a

sedimentology of quartz pebble conglomerates and quartzites of the archean bababudan group dharwar craton south india evidence for early crustal stability the 3200 to 3000 ma bababudan group locally as thick as 1800 m consists of a variety of rocks indicating deposition on a stable platform u and au bearing pyritiferous quartz pebble conglomerate a few meters thick overlies a regolith at the basal unconformity with a gneissic basement the bulk of the column consists of mafic volcanics including subaerial flows lahars and sills ultramafic and felsic rocks iron formation and pelites are minor lithologies in most of the sequence but iron formation forms a major unit at the top of the group quartzite units intercalated with the volcanics are generally less than 40 m thick and make up 25 to 50 of the column they are mineralogically mature and texturally submature recrystallization generally obscures original textures but units that were originally clayey quartz arenites have survived total recrystallization rounded zircons dominate the nonopaque detrital heavy mineral suite verifying a history of extensive abrasion paleocurrent patterns bas