lithospheric uplift in eastern gondwana evidence for a long lived mantle plume system recent work has demonstrated that modern drainage systems on rifted continental margins may be the product of ancient lithospheric doming in areas of flood basalt magmatism this uplift is thought to reflect the existence of widespread mafic underplating and excess melt generation at rift zones here i show that uplift due to the initiation of a thermal anomaly plume head in the asthenosphere may be evidenced by the formation of discrete rift structures and persistent paleodrainage sediment dispersal patterns for up to 150 m y prior to the commencement of igneous activity and final continental breakup volcanism thus occurs as a comparatively late stage geochemical response to the long term residence of hot plume material beneath continental mantle lithosphere

archean paleoproterozoic transition the indian perspective abstract india has perhaps the richest paleoarchean to paleoproterozoic crustal components on earth miller et al 2018 notwithstanding this much of the indian subcontinent remains unexplored compared to other ancient cratons in north america australia brazil and africa there are five archean cratonic nuclei in india the aravalli bundelkhand singhbhum bastar and the dharwar with well preserved proterozoic supracrustal sequences this paper critically reviews the paleoarchean to paleoproterozoic supracrustal record of the indian subcontinent with special emphasis on the archean paleoproterozoic transition which is generally placed at 2 5 ga based on the emplacement age of the great dyke of zimbabwe in general the archean paleoproterozoic transition in indian cratonic blocks is associated with high continental freeboard condition unlike north america south africa and western australia the indian cratonic blocks except bastar are devoid of paleoproterozoic glacial diamictite mazumder et al 2015 however similar to the pongola supergroup of south africa there are evidences of neoarchean glaciation in dharwar ojakangas et al 2014 in contrast to the global scenario of extensive development of bif across the archean paleoproterozoic transition the indian paleoproterozoic successions are devoid of banded iron formation bif except the 1 85 ga old bif in bundelkhand in contrast the majority of the indian bifs are of paleoarchean or neoarchean age thus the geodynamic and supracrustal data collected from five indian archean cratonic blocks do not correspond uniquely and precisely to a global change in tectonic style onset of neoarchean global magmatism and rifting or lithostratigraphic and environmental changes suggested across the archean paleoproterozoic transition van kranendonk et al 2012 therefore a revision and redefinition of the archean proterozoic boundary is outstanding this article is part of a special issue entitled archean earth processes edited by rajat mazumder and patrick eriksson

effects of strength properties of discontinuities on the unstable lower slope in the chiu fen erh shan landslide taiwan abstract the chiu fen erh shan landslide was a huge dip slope avalanche triggered by the devastating chi chi earthquake in central taiwan in 1999 anomalous geomorphic precursors such as ground subsidence and thrust which are signs of slope instability were subsequently observed on the lower slope of the chiu fen erh shan landslide in november 2002 post failure behavior and affected area of the lower part of the landslide must be investigated to provide adequate countermeasures this study presents the results of the post failure behavior simulation of the lower slope of the chiu fen erh shan landslide using discontinuous deformation analysis dda the simulation results show that the surface rocks in the sliding mass move faster and further than the rocks at great depth the angle of internal friction is found to have a great influence on the failure process than does the cohesion the sliding rocks are accumulated in the depression in front of the toe of the landslide except under the conditions of very low internal friction the depression performs as a buffer zone when the lower slope fails

effects of near fault seismic loadings on run out of large scale landslide a case study this study presents the run out analysis of the daguangbao landslides subjected to near fault multi direction earthquake forces using discontinuous deformation analysis dda the daguangbao landslide is the largest landslide induced by the 2008 wenchuan earthquake in order to investigate the effects of near fault seismic force on landslide run out kinematic behavior of sliding mass is simulated by a dynamic discrete numerical analysis method called dda in this simulation based on the shape of failure surface and the feature of slope geology the whole slope is divided into three parts base block upper sliding mass and lower sliding mass then two sliding masses are divided into the smaller discrete deformable blocks based on pre existing discontinuities size effect of the huge landslide is also considered baseline corrected real horizontal and vertical ground motions are taken as volume force acting to the base block the results show that seismic force has a significant influence on the landslide progression sliding distance and shape of post failure results of the horizontal and vertical situation are in good agreement with those obtained from post earthquake field investigation remote sensing image and description from the survivors

precambrian mafic dyke swarms in the singhbhum craton eastern india and their links with dyke swarms of the eastern dharwar craton southern india discussion

pressure temperature deformation history for a part of the mesoproterozoic fold belt in north singhbhum eastern india abstract the supracrustal rocks in the easternmost part of the proterozoic fold belt of north singhbhum eastern india are folded into a series of large upright folds with variable plunges the regional schistosity is axial planar to the folds the folds were produced by a second phase of deformation d2 and were preceded by d1 deformation which gave rise to isoclinal folds mapped outside the study area and the locally preserved bedding parallel schistosity a shearing deformation during d2 was responsible for the sheath like geometry of a major fold the axial planes were curved by d3 warping the first metamorphic episode m1 of low pressure type produced andalusite porphyroblasts prior to or in the early stage of d1 deformation the main metamorphism m2 responsible for the formation of chloritoid kyanite garnet and staurolite porphyroblasts was late to post d2 in occurrence the staurolite isograd separates two zonal assemblages recorded in the high alumina and the low alumina pelitic schists geothermobarometric calculations indicate the peak metamorphic temperature to be 550 c at 5 5 kb fluid composition in the rocks before and during m2 metamorphism was buffered and fluid influx if any was not extensive enough to overcome the buffering capacity of the rocks from m1 to m2 the p t path is found to have a clockwise trajectory that is consistent with a tectonic model involving initial asthenospheric upwelling and rifting followed by compressional deformation leading to loading and heating

carbonate platform development in a paleoproterozoic extensional basin vempalle formation cuddapah basin india abstract sedimentological investigation of the late paleoproterozoic orosirian vempalle formation of the cuddapah basin dharwar craton india reveals three facies association that range from supratidal to deep subtidal sedimentary rocks of this succession are dominated by heterolithic carbonate mudstone intraformational carbonate conglomerate and a variety of columnar domal and stratiform microbialite facies deposition occurred in an extensional regime during development of a low gradient ramp where the distribution of microbialite facies is distinctly depth partitioned a gradual increase in synoptic relief of columnar stromatolites through the section and the upward transition from stratiform to columnar microbialites record a prolonged marine transgression with little or no influx of terrigenous detritus siliciclastic influx along the northeastern side of the shelf reflects the redistribution of topographic highs concomitant with large scale volcanic activity redistribution of topographic highs eventually led to progradation of peritidal facies and shutting down of the carbonate factory earthquake induced ground shaking and voluminous volcanism experienced by this platform point to the reactivation of a deep seated mantle plume that resulted in thermal doming of the dharwar crust prior to the onset of cuddapah deposition isotopic and elemental chemistry of a selection of vempalle formation carbonate rocks record elevated mn2 and fe2 concentrations and depleted carbon isotope values in inner ramp lagoonal facies relative to more open marine stromatolitic facies patterns of isotopic and elemental variation suggest the presence of geochemically distinct water masses either within the water column or within substrate pore fluids that resulted from a combination of globally low marine oxygenation and restricted oceanographic circulation in inner ramp environments these data suggest that even in the aftermath of early paleoproterozoic oxygenation that ocean chemistry was heterogeneous and strongly affected by local basin conditions

new dynamic procedure for back calculating the shear strength parameters of large landslides abstract case histories of the tsaoling landslide and the chiu fen erh shan landslide both located in taiwan are used in this study to validate the procedure proposed for the dynamic back calculation of the shear strength parameters of the sliding surfaces of large landslides this new procedure uses the newmark sliding model while simultaneously considering the critical displacement concept the premise of the new procedure is that in a stable slope back calculation tends to underestimate the shear strength however as the intensity of earthquake shaking increases and the slope approaches failure the back calculated shear strength will approach to the true value based on this concept the new procedure method is developed and validated with the two well documented case histories the shear strength parameters back calculated using the proposed method agree well with those reported in the literature the new dynamic back calculation procedure is especially suitable in the situation where groundwater monitoring data are unavailable thus the new method is complementary to the traditional groundwater based limiting equilibrium back calculation approach

discussion on new aspects of deformed cross strata in fluvial sandstones examples from neoproterozoic formations in northern norway by s l roe and m hermansen

proterozoic sedimentation and volcanism in the singhbhum crustal province india and their implications abstract the proterozoic volcano sedimentary succession comprising successively younger dhanjori chaibasa dhalbhum dalma and chandil formations of the singhbhum crustal province india records sedimentation and volcanism in a rapidly changing tectonic scenario cooling of the vast volume of archaean singhbhum granite possibly induced an isostatic readjustment the associated tensional regime and deep seated fractures controlled the formation of the proterozoic singhbhum basin the dhanjori formation unconformably overlies the singhbhum granite and is entirely terrestrial dominantly fluvial at the base the conglomerate deposits coarse grained sandstone and shale represent the distal fringe of an alluvial fan complex the rest of the formation including the volcaniclastic rocks consists almost entirely of fining upward fluvial cycles the base of the dhanjori formation is a sequence boundary and the formation itself represents a lowstand systems tract the dhanjori volcano sedimentary succession displays evidence of having passed through passive as well as active phases of continental rifting with an increasingly important influence of volcanism on the sedimentation through time the chaibasa formation sharply overlies the dhanjori formation and a transgressive lag demarcates their contact the basal part of the chaibasa formation immediately overlying the transgressive lag deposit represents a transgressive systems tract while offshore shales that sharply overlie the shallow marine sandstones up section represent marine flooding surfaces the shallow marine subtidal sandstones bear an excellent record of sandwave migration and provide a rare opportunity to unlock the late palaeoproterozoic lunar orbital periodicities unlike the chaibasa the overlying dhalbhum formation is entirely terrestrial fluvial aeolian indicating that the chaibasa dhalbhum contact is a sequence boundary the dalmas overlying the dhalbhum formation represents concordant lava outpourings without any break in sedimentation these lavas are genetically related to mantle plume upwelling in an intracontinental rift setting the volcano sedimentary package lying north of the dalma volcanic belt chandil formation is of mesoproterozoic age the entire late palaeoproterozoic volcano sedimentary package displays post depositional compressional deformation and greenschist to amphibolite facies metamorphism dated at ca 1600 ma forming the so called north singhbhum fold belt the volcano sedimentary package lying south of the dalma volcanic belt was pushed further south towards the singhbhum granite batholith complex as a result of uplift related to the dalma plume the singhbhum granite batholith acted as a rigid body this gave rise to a compressional stress regime that induced shearing thrusting at ca 1600 ma along the singhbhum shear zone the dalma plume magmatism was possibly part of a 1600 ma global tectono thermal event

initiation movement and run out of the giant tsaoling landslide what can we learn from a simple rigid block model and a velocity displacement dependent friction law abstract tsaoling landslide is the largest and best documented landslide among several large landslides induced by the 1999 taiwan chi chi earthquake pliocene sedimentary rocks of about 125 mm 3 in volume slid along very flat bedding planes dipping by 14 with an average speed of 35 40 m s for about 1650 m before hitting the bank of the chinshui river during the landslide detailed analysis of dtms before and after the earthquake using a gis software leads to an accurate determination of the locations of the centroids of landslide mass revealing the horizontal and vertical displacements of the 2524 m and 524 m respectively those displacements and landslide mass give an apparent friction coefficient of 0 21 and the release of the potential energy of 1 6 10 15 j we conducted rotary shear high velocity friction experiments on fault gouge from bedding parallel faults under semi wet conditions and at 3 mpa normal stress corresponding to the overburden pressure of the landslide mass we also compiled reported data on the frictional properties on shale powders and fault gouge from the landslide site under both dry and wet conditions and proposed a velocity displacement dependent friction law that can describe most experimental data newmark analysis of landslide motion with six scenarios for different landslide materials and conditions assuming a simple rigid block sliding and using measured frictional parameters revealed that the landslide did not occur with dry frictional properties and that the landslide occurred at 38 39 s with accumulated displacements of 0 62 m 1 09 m and reached at the river bank at 82 87 s after the generation of chi chi earthquake at its epicenter those timings are consistent with high frequency signals at 32 40 s and at 76 s recorded at a nearby seismic station and with a survivor s witness that the landslide initiated 10 s after he felt strong ground motion possible s wave arrival at 25 2 s slip weakening is essential in initiating the landslide and low friction coefficient 0 08 0 1 allowed high speed of the landslide possible the landslide was caused by a few peaks of northeast oriented strong accelerations of the ground motion frictional work during the sliding of the landslide mass was estimated to be of about 23 of potential energy and the rest of the released energy is likely to have been consumed during the stopping phase of the landslide after hitting the river bank in complex processes such as fragmentation heat dissipation and spreading of the landslide deposits

landslide reconstruction using seismic signal characteristics and numerical simulations case study of the 2017 6 24 xinmo landslide abstract landslide modeling based on seismic signal characteristics is an effective method to study landslide evolution the scientific challenge lies in how to systematically characterize and reconstruct the entire landslide evolution process using the recorded seismic data we selected the 2017 6 24 xinmo landslide as a case study empirical mode decomposition emd is used to analyze the seismic signals from 14 seismic stations near the landslide area numerical simulations using two dimensional discrete element methods dem are performed to simulate landslide dynamics using the calculated kinetic energy profile after analyzing the short time fourier transform stft and fast fourier transform fft characteristics of the signal the landslide process is reconstructed and compared with the dem simulation the landslide process is observed to consist of a stationary stage slipping stage transition stage entrainment transportation stage and a deposition stage this is the first study that uses seismic signals to identify a transition stage which is a feature that is difficult to constrain from field survey and analysis alone landslide development and movement in the transition stage are discussed considering the sedimentology of the study area this study provides improved theoretical guidance for the reconstruction and characterization of landslide processes by seismic signals

mesoarchaean palaeoproterozoic stratigraphic record of the singhbhum crustal province eastern india a synthesis the mesoarchaean palaeoproterozoic stratigraphic record of the singhbhum crustal province eastern india implies sedimentation and volcanism in a changing tectonic scenario and thus assumes immense geological significance although efforts have been made by many researchers in the past several decades to summarize various geological aspects of the singhbhum crustal province a critical synthesis of various stratigraphic issues was long overdue the present contribution is an updated critical synthesis of the mesoarchaean palaeoproterozoic stratigraphic record of the singhbhum crustal province we have pointed out the problematic stratigraphic issues of the singhbhum crustal province that deserve careful scrutiny in order to gain better insights into the mode of stratigraphic sequence building

pin stripe lamination a distinctive feature of modern and ancient eolian sediments abstract pin stripe laminations are a distinctive feature of modern and ancient eolian sediments in sets of eolian ripple or translatent strata they represent deposition of silt and very fine sand in the troughs of the advancing wind ripples in sets of avalanche strata they probably result from the downward settling of fine sand and silt within the moving avalanche to the interface of moving and unmoving sands wind tunnel experiments suggest that pin stripe laminations can also form in grainfall deposits the textural segregation associated with deposition of the fine layers in most cases leads to early cementation along and near the finest sand and silt comprising the pin stripe lamination the pin stripe effect seen in outcrops is usually due to resistance to weathering along such cemented zones the cementation of the pin stripe laminations can occur early in the history of diagenesis and thus may provide clues to the post depositional history of the rock pin stripe laminations in many instances represent the sequestering of the small population of ultrafine sediment present in most eolian depositional systems they may prove useful in the recognition of ancient eolian sediments

geochronological constraints on evolution of singhbhum mobile belt and associated basic volcanics of eastern indian shield abstract the singhbhum mobile belt smb of the eastern indian shield represents a roughly east west trending arcuate belt of folded supracrustals overlying the granite greenstone basement of the singhbhum orissa craton along its northern eastern and western margins and is bounded by the chotanagpur gneissic complex to further north the radiometric ages of the basement singhbhum and equivalent granites and the intrusive anorogenic mayurbhanj granite pluton constrain the time of evolution of this mobile belt between 3 12 and 3 09 ga hence the smb supracrustals also known as singhbhum group is late mesoarchaean in age and not proterozoic as thought earlier the evolution of the smb was followed by emplacement of some major basic igneous rocks within or adjacent to the supracrustals these include simlipal volcanics at 3 09 ga on the smb mayurbhanj gabbro along with mayurbhanj granite at 3 09 ga along the marginal part of the craton near the smb and the dalma volcanics on the smb along with the dhanjori volcanics adjacent to smb at 2 80 ga the 2 80 ga old basic volcanics is also associated with emplacement of some small granite plutons occurring along the marginal part of the craton one of them the tamperkola granite intrudes the smb the 3 09 ga onward igneous activities along the marginal part of singhbhum orissa craton took place essentially under anorogenic tectonic setting before being affected by a major metamorphism at 2 50 ga which is recorded on the dalma volcanics and on some small granite pluton occurs along the marginal part of the craton the jagannathpur and stratigraphically equivalent malangtoli volcanics occurring within the singhbhum orissa craton at the west were erupted at 2 25 ga the boundary between the smb supracrustals and the singhbhum orissa craton is demarked by a prominent shear zone known as the singhbhum shear zone which shows multiple reactivation the oldest being at 3 09 ga followed by subsequent reactivation during palaeo and mesoproterozoic periods at 2 2 1 8 1 6 1 5 1 4 and 1 0 ga respectively the singhbhum group and the adjacent chotanagpur gneissic complex appear to have evolved from a near shore syn rift and a distal post rift stable shelf sedimentary assemblages respectively which were deposited without any stratigraphic break in a marine basin existed in the present north of the singhbhum orissa craton both of these assemblages were deformed and metamorphosed together during proterozoic at 2 5 to 2 3 ga 1 6 ga and 1 0 ga

topographic effects on the seismic response of steep slopes a frequency domain parametric study using generalized consistent transmitting boundaries has been performed to evaluate the significance of topographic effects on the seismic response of steep slopes the results show that the peak amplification of motion at the crest of a slope occurs at a normalized frequency h 0 2 where h is the slope height and is the wavelength of the motion the importance of the natural site frequency is illustrated by the analysis of a stepped layer over a half space it was found that the natural frequency of the region behind the crest can dominate the response relative to the topographic effect for the conditions studied moreover the effect of topography can be handled separately from the amplification due to the natural frequency of the deposit behind the crest of the slope this concept of separating the amplification caused by topography from that caused by the natural frequency is advantageous to the development of a simplified method to estimate topographic effects

soft sediment deformation structures in the earth s oldest seismites abstract the chaibasa formation in eastern india which was deposited between 2100 and 1600 million years ago shows deformations that must have formed when the sediments were not yet consolidated some of these deformation structures have never been described before here they are described depicted and their origin is analysed we show that they must be the result of shocks which can only be explained satisfactorily as triggered by earthquakes the layers containing these deformation structures are termed seismites they are among the earliest records of earthquakes known in the earth s history

archean banded iron formations of india abstract archean banded iron formations bifs are important lithologies for understanding the early earth processes greenstone belts in the four archean cratonic nucleii of peninsular india namely singhbhum bastar dharwar and bundelkhand host bif units that can be important candidates for case studies the bifs in these greenstone successions represent both algoma and superior type associations the oldest record comes from the paleoarchean southern eastern and western iron group of the singhbhum craton and the sargur supracrustals of the dharwar craton mesoarchean and neoarchean greenstone belts in the dharwar and bundelkhand cratons record a number of cycles of bif deposition in a spectrum of depositional settings from manganiferous arenite carbonate shelf associations to deep water volcanics and graywacke associations the bifs from the neoarchean bailadila group in the bastar craton were deposited in siliciclastic shelf association compositional variations in major trace and ree patterns have been evaluated from published data high grade iron ores are mainly mined from the bifs and locally mn ores occur in association as well microbial carbonates associated with some of the paleoarchean as well as neoarchean iron manganese formations suggest early life activities the lithological association of the archean iron formations have been explained in terms of both active margin and passive margin depositional settings bifs in association with manganiferous formations as old as paleoarchean time provide an opportunity to probe into the redox stratification of oceanic hydrosphere and in turn the oxygenation of early atmosphere

seismically induced rock slope failures resulting from topographic amplification of strong ground motions the case of pacoima canyon california abstract the 1994 northridge earthquake mw 6 7 triggered extensive rock slope failures in pacoima canyon immediately north of los angeles california pacoima canyon is a narrow and steep canyon incised in gneissic and granitic rocks peak accelerations of nearly 1 6 g were recorded at a ridge that forms the left abutment of pacoima dam peak accelerations at the bottom of the canyon were less than 0 5 g suggesting the occurrence of topographic amplification topographic effects have been previously suggested to explain similarly high ground motions at the site during the 1971 mw 6 7 san fernando earthquake furthermore high landslide concentrations observed in the area have been attributed to unusually strong ground motions rather than higher susceptibility to sliding compared with nearby zones we conducted field investigations and slope stability back analyses to confirm the impact of topographic amplification on the triggering of landslides during the 1994 earthquake our results suggest that the observed extensive rock sliding and falling would have not been possible under unamplified seismic conditions which would have generated a significantly lower number of areas affected by landslides in contrast modelling slope stability using amplified ground shaking predicts slope failure distributions matching what occurred in 1994 this observation confirms a significant role for topographic amplification on the triggering of landslides at the site and emphasises the need to select carefully the inputs for seismic slope stability analyses

207pb 206pb zircon ages and the evolution of the singhbhum craton eastern india an ion microprobe study1this paper is dedicated to prof a k saha one of the senior co authors who passed away after submission of the paper 1 abstract we used an ion microprobe to measure 207 pb 206 pb ages of single zircons from four key lithologies from the singhbhum craton of eastern india detrital zircons from the oldest recognized sedimentary sequence of the craton the older metamorphic group yielded 3 5 3 6 ga ages indicating that crustal formation had already been initiated by 3 6 ga in this region this data also established an older limit of 3 5 ga for the age of sediment deposition the first appearance of extensive continental crust in the singhbhum region marked by the emplacement of the older metamorphic tonalite gneisses is dated at 3 44 ga our data from both of these units reveal that a 3 2 ga event induced overgrowths within each of these pre existing zircon populations we determine an age of 3328 7 ma for the singhbhum granite phase ii the most widespread of this granite s three phases the emplacement of the two phases of the mayurbhanj granite marking the youngest major episode of acid plutonism in this craton took place in rapid succession at 3 1 ga marking the broad scale stabilization of this terrain

geological causes and geomorphological precursors of the tsaoling landslide triggered by the 1999 chi chi earthquake taiwan the tsaoling landslide one of the largest landslide areas in taiwan has been affected by catastrophic events triggered by rain or earthquakes six times since 1862 these landslides including that caused by the 1999 earthquake have essentially not been reactivated old slides but were sequential new ones that developed upslope retrogressively the landslide area is underlain by pliocene sandstone and shale to form a dip slope with a bedding plane dipping uniformly at 14 the slip surface of the 1999 landslide was smooth and planar parallel to the bedding plane with a slightly stepped profile it formed within thinly alternated beds of fine sandstone and shale with ripple lamination or in a shale bed the shale is weathered by slaking and probably by sulfuric acid which is inferred to be one of the major causes of the intermittent retrogressive development of the landslides the weathering was likely accelerated by the removal of overlying beds during earlier landslides in 1941 and 1942 the top margin of the 1999 landslide in plan view coincided with a v shaped scarplet which can be clearly recognized on aerial photographs taken before the landslide this geomorphological feature indicates that this landslide had already moved slightly before its 1999 occurrence providing precursory evidences

sedimentation pattern and tectonic evolution of the proterozoic singhbhum basin in the eastern indian shield abstract the proterozoic singhbhum basin psb located on the flank of an archaean platform ca 3400 ma is a distinct lithotectonic unit of the singhbhum crustal province of the eastern indian shield the present contribution traces the evolution of this basin filled by volcanics dominated submarine supracrustals and sedimentary formations the proterozoic singhbhum basin has been identified to be a marginal basin evolved in a back arc setting an axial volcanic belt manifesting mor like basaltic eruptions divided the basin into two domains with parallel but distinct sedimentation patterns an asymmetry in sedimentation pattern and source polarity are documented in litho as semblages and ree distribution patterns of cover rocks in the basinal domain flanking the southern platform prevailing tectonics strongly controlled the mechanism of sedimentation which coupled with the volcanic history of the basin indicates its riftogenic character progressive lithospheric stretching successively produced picritic volcanics and mor type basalts along the axial zone of the basin being related to a stretching factor of 2 continental margin rifting ultimately resulted in an oceanic transition as supported also by available geophysical data the evolution of the proterozoic singhbhum basin in its broad perspective was controlled by subduction related processes

the 2 7 2 0 ga volcano sedimentary record of africa india and australia evidence for global and local changes in sea level and continental freeboard abstract the 2 7 2 0 ga volcano sedimentary records of the african indian and australian cratons indicate two broadly defined periods of extensive drowning of the emergent continental areas concomitant with lowered freeboard carbonate banded iron formation bif platforms characterised the first such event at ca 2 6 2 4 ga africa and australia to 2 7 ga india these earlier globally enhanced sea levels are ascribed to increased mid ocean ridge activity possibly related to breakup of a postulated late archaean southern supercontinent alternatively a transition from global scale catastrophic mantle overturn events to the onset of plate tectonics may have occurred in the late archaean nelson 1998 earth planet sci lett 158 109 119 both explanations of increased mid ocean ridge activity are compatible with significant early to middle archaean crustal growth armstrong 1981 phil trans r soc london a 301 443 472 with the emergent high freeboard cratons being subjected to aggressive weathering and erosion enhanced continental crustal growth near the archaean proterozoic boundary mclennan and taylor 1982 j geol 90 347 361 related to the development of significant island arc complexes would have resulted in common lowered freeboard enhanced sea level conditions at the passive margins of the southern cratons the diachronous nature of these earlier transgressions in the various cratons may reflect the effect of local tectonic movements and or the thermal state of the cratons from ca 2 4 2 2 ga cratons that make up the present day continents of india africa and australia had relatively high continental freeboard and lowered sea levels glacigenic deposits are preserved on the kaapvaal africa singhbhum india and pilbara australia cratons the second broadly defined drowning event at ca 2 15 ga was probably due to post glacial climatic amelioration freeboard was reduced by the combination of eustatic rise and the reestablishment of aggressive weathering as warmer palaeoclimates returned in india carbonates were more prominent than the siliciclastic sediments including prominent black shales seen in africa and australia

geochemical and sm nd isotopic characteristics of the late archaean palaeoproterozoic dhanjori and chaibasa metasedimentary rocks singhbhum craton e india implications for provenance and contemporary basin tectonics abstract in significant contrast to other cratonic blocks of india the singhbhum cratonic successions record continuous depositional record from the palaeoarchaean to mesoproterozoic although the sedimentary facies characteristics and mode of stratigraphic sequence building of the dhanjori and chaibasa formations are well known sedimentary geochemistry provenance and tectonic milieu of deposition of these two formations are hitherto unknown the current manuscript presents geochemical and sm nd isotopic data from the dhanjori and chaibasa formations for the first time and combine previous sedimentological data with the goal to expand the framework for understanding the depositional and tectonic setting of these two formations the sm nd isotopic data for the chaibasa clastics is unambiguous with respect to provenance average nd t 2 2 ga 0 8 1 0 and average nd model age tdm 2 51 0 08 ga with average 147 sm 144 nd ratios 0 1114 0 0041 for phyllites and quartzites indicate an extremely homogeneous source signature consistent with a late archaean juvenile crustal provenance possibly a dominantly upper crustal provenance the sm nd isotopic data from the older dhanjori formation also indicate broadly similar provenance as comparable lithologies in the younger chaibasa formation our sm nd isotopic data is entirely consistent with the previous sedimentological data and confirms a terrestrial rift dominated tectonic setting for the dhanjori formation proximal sources poorly mixed provenance and a marginal marine to offshore setting for the more homogeneous nd isotopic signature of the chaibasa formation distal sources well mixed provenance

evaluation of factors controlling earthquake induced landslides caused by chi chi earthquake and comparison with the northridge and loma prieta events over 10 000 landslides were triggered by the september 21 1999 chi chi earthquake a large number of these landslides have been mapped from spot images and a smaller number were described in a detailed field investigation geographic information systems gis was used to conduct a spatial characterization of the slope failures including distribution of type size slope angle bedrock geology ground motion and distance from earthquake source the most abundant landslides were shallow disaggregated rock and soil slides landslides occurred primarily in tertiary sedimentary rocks which are well known for their susceptibility to landsliding in many parts of the world landslide concentration values diminish beyond epicentral distances of 40 and 70 km from the epicenter and the surface projection of the fault plane respectively ground motion was found to be the most significant factor in triggering the shallow landslides in the chi chi earthquake overall 74 of all slope failures occurred in regions with vertical ground motions greater than 0 2g and 81 of all slope failures occurred in the region with mean horizontal peak ground accelerations pga greater than 0 15g these factors were used to compare landslides generated by the chi chi earthquake to the landslides triggered by the 1989 loma prieta earthquake and the 1994 northridge earthquake the major difference in distribution of landslides between the chi chi earthquake and the two california earthquakes was the distribution of slope angles in the chi chi earthquake 90 of the failures occurred on slopes steeper than 45 while more than 80 of failures occurred on slopes less than 50 in california apparently reflecting much steeper and tectonically more active geologic setting in taiwan

massive sandstone facies in the hawkesbury sandstone a triassic fluvial deposit near sydney australia abstract massive sandstone is a common facies in the hawkesbury sandstone a triassic formation attributed to deposition by a large braided river the massive sandstone occurs as sheets and in elongate depressions trending perpendicular to the paleoslope as indicated by the unidirectional mean orientation of abundant cross strata some of the depressions filled with massive sandstone also contain angular mudstone intraclasts up to several meters in length massive sandstone is also associated with deformed cross strata formed by progressive loss of lamination during mass movement down foreset slopes foreset failure is attributed to liquefaction due to falling water level or to collapse of adjacent mud banks the latter mechanism resulted in rapid loading of bedform foresets and introduce large mudclasts into the massive sand sand and mudclasts accumulated in transverse scours at the foot of the foreset slopes but also travelled along the scours or spilled out to form massive sheet sands the abundance of massive sandstone in the hawkesbury sandstone is attributed to deposition in a large river in which flood stage bedforms were probably up to 15 m high because of the size of the bedforms large volumes of liquefied sand were generated when foreset slopes failed

dda validation of the mobility of earthquake induced landslides abstract this paper studies the run out of earthquake induced landslides there are more than 20 mechanical models to explain long run out of rapid landslides including some earthquake induced landslides however notably few of them considered the effect of seismic loading on the run out of landslides in a previous study we have proposed a model which is called the multiplex acceleration model mam to interpret the long run out mechanism and a shaking table test has been performed to verify the mam because the previous mam is a conceptual model and only a single stone has been examined under sine waves by the shaking table test the mam needs to be extended and further verified in this paper the mam was extended by introducing the movement change that was induced by the so called trampoline effect of earthquake loading and the latest practical numerical simulation program discontinuous deformation analysis dda was used to verify the mobility of earthquake induced landslides after a conceptual landslide model was used to verify the effect of seismic loading on the mobility the donghekou landslide which was a typical long run out landslide that was induced by the 2008 wenchuan earthquake was analyzed the results show that the seismic loading could be one of the factors that could eventually help increase the run out of landslides

archean sedimentation on dharwar craton india and its implications abstract the dharwar craton is the largest archean cratonic nuclei of india and is made up of western and eastern blocks separated by the 2 5 ga closepet granite batholith the western dharwar craton consists mostly of 3 3 3 0 ga ttg the peninsular gneissic complex older mesoarchean greenstone sargur type and younger neorchean greenstone the dharwar supergroup comprising of lower bababudan and upper chitradurga groups in contrast the eastern dharwar craton is mostly made of granitoid gneisses and felsic volcanics with some neorchean supracrustal enclaves sandur ramgiri kolar kadri schist belts recently it has been suggested that the dharwar cratonic block is formed by assembly of western central and eastern micro blocks separated by shear zones jayananda et al 2018 the greenstone successions are present in all three dharwar micro blocks however the proportion of greenstones is much higher and the quality of preservation is much better in the western micro block the mesoarchean sargur group hosts barite deposit and consists of fuchsite quartzites carbonates metapelites banded iron formations and metamorphosed basalts and komatiites researchers have postulated a platformal orthoquartzite carbonate pelite association for the sargur group some researchers examined the barite deposits of the sargur group and inferred a subaerial volcanism during the sargur sedimentation the neoarchean bababudan group comprises largely terrestrial to shallow marine sedimentary successions glacial deposits bif volcanic and volcaniclastics rocks in contrast the overlying chitradurga group comprises conglomerates greywackes phyllites carbonates bifs cherts shales associated with a variety of volcanic rocks ranging from pillowed basalts to rhyolites and indicates relatively deep water sedimentation in a subsiding basin in an active continental margin setting stromatolites are abundant in the chitradurga group as also in other neoarchean supracrustal successions of the dharwar craton in this review we have critically synthesized published sedimentological data from both older as well as younger greenstone successions of the dharwar craton and have presented the archean sedimentation history of the dharwar craton we have highlighted the research gaps that researchers may find helpful

sedimentology of the paleoproterozoic kungarra formation turee creek group western australia a conformable record of the transition from early to modern earth abstract this paper presents the first detailed sedimentological analysis of the paleoproterozoic kungarra formation the lowermost of three formations comprising the turee creek group in western australia which was deposited across the rise in atmospheric oxygen the great oxidation event or goe and the transition from early to modern earth the data show that the kungarra formation has a gradational conformable lower contact with underlying banded iron formation of the hamersley group and predominantly comprises an upward shallowing succession from deepwater shales and siltstones through rippled fine grained sandstones and stromatolitic carbonates to tidal flat deposits that immediately underlie coastal fluvial deposits of the overlying koolbye formation at the base of the kungarra formation is a gradual transition from alternating units of magnetic green shale and thin units of banded iron formation that pass upsection to units of non magnetic shale and ferruginous chert and grey chert reflecting a gradual loss of iron from the world s oceans accompanying the rise of atmospheric oxygen a falling stage systems tract is recognised above this transition in the hardey syncline area capped by stromatolitic carbonates and a period of exposure marked by an erosional unconformity and carbonate beachrock two glacio eustatic cycles are recognised within the middle to upper parts of the kungarra formation each of which is marked by the rapid onset of falling systems tracts and characterised by falling systems tracts during and following diamictite deposition stratigraphic data are used to infer a depobasin filled by a sediment wedge prograding from southeast to northwest in contrast to previous models of a north northeastward deepening foreland basin the lack of seismites or internal unconformities within the formation precludes a foredeep setting rather deposition is interpreted as having occurred within an intracratonic basin with detritus sourced from erosion of uplifted bedrock to the southeast

geological and geomorphological precursors of the chiu fen erh shan landslide triggered by the chi chi earthquake in central taiwan abstract special features were correlated to the geological causes of the chiu fen erh shan landslide a gigantic rockslide on a dip slope induced by the chi chi earthquake ml 7 3 in central taiwan in 1999 an aerial photo interpretation and the succeeding geological mapping of the failure were employed in this study a linear depression a steep step and a low drainage density in the landslide area were detected from the aerial photos taken in 1998 the gravitational creep was believed to result in the features of the linear depression and the low drainage density the steep step represented a buckling feature found in the field the landslide area is composed of stratified sandstone and shale with dip angles ranging 20 36 the slip surface developed along a pre existing bedding fault that resulted from flexural slip folding before the chi chi earthquake the rock on the upslope side buckled and was retained by a thick bedded sandstone downslope the earthquake shock seriously damaged the sandstone support and led to the catastrophic landslide this type of landslide is likely to occur on the moderately dipping slope of stratified rocks that were previously deformed by flexural slip folding

an experimental study to characterize the initiation of the seismic induced tsaoling rock avalanche abstract the tsaoling rock avalanche which had a sliding volume of 120 million m3 and a maximum thickness of 170 m was triggered by the chi chi earthquake in 1999 however the initiation mechanism has not been well understood because different friction models have been proposed to describe the triggering process using the newmark sliding model and numerical simulations in this study a new dynamic ring shear test with a maximum normal stress higher than 3400 kpa is applied as an alternative approach to investigate the initiation of the seismic induced rock avalanche along the wet sliding surface at the interface of the cholan sandstone and consolidated remold shale experimental results verify that the seismic stresses at the wet sliding surface touch the failure surface and generate significant cumulative shear displacements additionally the shear surface should have non linear failure criteria rather than the well known linear mohr coulomb failure criteria with a constant friction angle furthermore the initiation time of the tsaoling rock avalanche obtained from the dynamic ring shear test is strongly correlated with the available seismic signal interpretations and the interviews of witnesses who travelled with the sliding mass this is the first experiment clarifying the co seismic behavior of the sliding surface and the initiation of the tsaoling landslide during the chi chi earthquake additionally from the development of the ring shear test the integrations of high normal stress the wet sandstone shale interface and the dynamic test with seismic loadings greatly extend the use of ring shear tests to rock avalanches

marine to fluvial transition proterozoic upper rewa sandstone maihar india abstract the proterozoic upper rewa sandstone in central india is generally interpreted as entirely marine a detailed study in maihar madhya pradesh however reveals upward transition from marine to fluvial through a mixed facies association also bearing eolian imprints facies associations differ in stratal geometry and arrangement palaeocurrent direction and pattern as well as in grain size and sorting the fine grained marine association is dominated by tidal sheet deposits with characteristic rhythmic changes in thickness and style of cross stratification and their packages as well as local evidence of current reversals subordinate beach deposits are also present the major palaeocurrent direction is highly consistent and westward the coarse grained often granule rich sandstones of the fluvial association are embodied by four facies correlatable with flow stages and relative bed shear these braided stream deposits are preserved in vertical stacks of tabular sandbodies in response mainly to basin subsidence the palaeocurrent pattern is unimodal and northwestward but its dispersion covers 180 the rocks are poorly sorted and at places incorporate sand clasts although they are virtually mud free and mineralogically mature as in two other associations the medium to fine grained sandstones at the intermediate interval between the marine and fluvial associations are of distinct lensoid geometry they incorporate representatives from the previous two associations as well as translatent strata interdune erg deposits and possibly aeolian cross strata consequently the palaeocurrent pattern is polymodal with a spread over 270 an overall coarsening up trend in the fluvial part and thinning up trend in the tidal part imply progradation in spite of evidence of basin subsidence a high rate of sediment discharge from a perennial river system in a humid climate is suggested

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

3 56ga tonalite in the central part of the bastar craton india oldest indian date abstract the lack of information regarding early achaean rocks from the indian peninsula is mainly due to the absence of high quality u pb zircon ages a tonalite sample from the ttg gneiss supracrustal association from the central part of the bastar craton in central india is dated at 3 56 ga this is the oldest protolith age so far recorded from india these ttg gneisses have enclaves of metasedimentary and metavolcanic rocks that may provide important information on the first billion year history of the indian craton this new date for tonalite from the bastar craton is the first precise u pb zircon age from india s first u pb geochronology laboratory located at the geological survey of india which hopefully will remedy the paucity of good geochronological data for older rocks of the indian peninsula

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

genesis of metasomatic gold mineralization in the pahardiha rungikocha gold deposit eastern india constraints from trace element signatures in chromite cored magnetite and bulk rock geochemistry abstract the pahardiha rungikocha gold deposit is located south of the dalma volcano sedimentary belt within the north singhbhum mobile belt nsmb in the eastern part of india the rocks of this area have undergone three phases of deformation viz d1 d2 d3 while the d1 and d2 events signify progressive regional metamorphism the d3 stage was a consequence of continued n s compression resulting in e w trending displacement fractures this d3 deformation event was responsible for the mobilization of auriferous fluids within the host quartz chlorite schist and subsequent gold precipitation here gold occurs as native grains either within the cracks or along grain boundaries of euhedral pyrite detailed mineral paragenesis reveals that euhedral pyrite associated with gold is coeval with abundant chromite cored magnetite the chromite cored magnetite shows a complex paragenetic history i e an initial chromite alteration event followed by epitaxial growth of magnetite rims on the chromite cores as revealed by la icp ms trace element data and epma x ray compositional maps the paragenetic stages of the chromite cored magnetite is synchronous with the successive deformation events of the host rock the final phase of deformation is responsible for the formation of the chromite cored magnetite rims which is coeval with the gold mineralizing event these magnetite rims formed as a result of metasomatism brought about by the interaction of hydrothermal fluids with the wall rock the chromite cored magnetite trace element signatures resemble the high temperature ca fe alteration and high temperature k fe alteration facies reported from various iocg and ioa type deposits there is a distinct enrichment of mafic elements such as ni cr v mg v cu within magnetite rims a similar pattern of enrichment in mafic elements is also seen in the bulk rock geochemical data major element discrimination diagrams reveal that the chlorite schists evolved from a mixed provenance of felsic and mafic ultramafic rocks consequently the d3 induced metasomatism most likely resulted in preferential stripping of the mafic elements which is well reflected in the analyzed magnetite rims thus we propound that the bulk rock chemical composition of the host chlorite schist had a first order control on the chemistry of the chromite cored magnetite coeval with the gold mineralizing event given the fact that there are no causative igneous intrusions underlying the host chlorite schists we infer that the gold mineralizing fluids were intrabasinal in nature and were mobilized due to reactivation of pre existing faults and fractures during the d3 deformation event

life on land in the proterozoic evidence from the torridonian rocks of northwest scotland the stoer group and diabaig formation of the torridonian succession in northwest scotland are late mesoproterozoic to early neoproterozoic ca 1200 1000 ma features preserved on the top surfaces of fine to medium grained sandstone beds in a number of stratigraphically and geographically separated localities are attributable to microbially induced sedimentary structures these include wrinkle structures remnants of apparent microbial crusts and indications of original cohesiveness and pliancy in sand sized sediment the surfaces on which the microbial structures formed were exposed subaerially abundant deep desiccation cracks and locally pedogenic structures in alluvial interfluve and lacustrine margin settings and many of the structures developed in areas well away from the perennially wetted regions adjacent to shorelines and fluvial channels thus these features indicate that earth9s biosphere had adapted to and colonized land surfaces many hundreds of millions of years before the dawn of the phanerozoic

an overview of the palaeoproterozoic geology of peninsular india and key stratigraphic and tectonic issues abstract the archaean proterozoic rock successions in india have the potential to enrich the global database on precambrian stratigraphic development and to offer valuable clues to global tectonic reconstructions built over four distinct archaean cratonic nuclei the major palaeoproterozoic supracrustal belts cover sequences include the dhanjori group the singhbhum group including the dalma volcanics and the chandil formation in eastern india the cuddapah supergroup and the adjoining nellore schist belt bordering the eastern dharwar craton the aravalli supergroup in the aravalli delhi fold belt in nw india the lower vindhyan semri group and the mahakosal sausar betul belts close to the central indian tectonic zone citz and possibly the dongargarh supergroup in bastar a major erosional unconformity separates the archaean tonalite trondjhemite gneiss basement in these cratons from the overlying volcano sedimentary successions an overview of palaeoproterozoic stratigraphic development in these cratonic blocks is presented to bring out the salient features for global comparison and to highlight issues requiring further attention multiple metamorphic magmatic and deformation events are recorded in the fold belts at the join of the cratons or their margins inviting application of the plate tectonic paradigm however a comprehensive tectonic model for the amalgamation of the indian archaean nuclei is yet to emerge and is crucial for our understanding of palaeoproterozoic supercontinent development

amplification of seismic accelerations at slope crests earthquake accelerations can cause many problems in sloping ground one such problem is that accelerations are greatly amplified at the crest of slopes this topographic amplification can lead to a

precambrian continental freeboard and geological evolution a time perspective abstract continental crustal growth rates crustal volumes thicknesses and continental freeboard are considered to be intimately related however none are easy to quantify least of all in the precambrian additionally crustal volumes thicknesses and isostasy are related to changing mantle heat and the concomitant variation in thickness of ocean crust another set of variables would be the interaction of plate tectonics and the onset of plate tectonics a contentious issue in itself and mantle plumes superplumes further complication is provided by the ranges of freeboard elevations and eustatic sea level changes overlapping in scale and sharing common genetic causes the constant freeboard model suggests that the net results of the interaction of this complex set of variables has been that continental elevation relative to sea level has remained essentially similar on a global average basis over much of geological time assuming an essentially constant ocean volume since c 3 8 ga application of this model to the precambrian geological record suggests that sigmoidal crustal growth rate models are probably the most reliable a conundrum of the constant freeboard model would be that freeboard would tend to become lowered towards mean sea level for any specific craton over time this freeboard equilibrium would be interrupted for a particular craton by active geodynamic processes resulting from the interplay of plate tectonics and mantle thermal instabilities in this paper we test the validity of this thesis of alternating approximate freeboard equilibrium and active geodynamics by examining the volcano sedimentary record of a number of cratons kaapvaal singhbhum and pilbara for the singhbhum craton and bearing in mind its poor chronological data base freeboard equilibrium appears to have prevailed until c 2 1 ga but for kaapvaal and pilbara until c 1 8 ga the geodynamic processes largely outweighed the tendency towards equilibrium except for c 200 my from c 2 6 to 2 4 ga when global sea level appears to have remained high and transgression was the norm we thus tentatively add the plate tectonic cycle and mantle thermal processes to the already complex association of concepts controlling continental freeboard over time

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

ejection landslides triggered by the 2008 wenchuan earthquake and movement modelling using aerodynamic theory and artificial disintegration collision technique many ejection landslides in the 2008 wenchuan earthquake exhibited unusually dramatic behaviour in which a huge sliding mass was launched into the air and supported for a long distance because of the aerodynamic effect in this paper the formation conditions and movement characteristics of ejection landslides are analysed the flight behaviour of the centroid of the ejection mass is studied by numerical solution with and without the aerodynamic effect the impact and movement processes of the sliding mass are simulated by incorporating an advanced discretisation approach into discontinuous deformation analysis dda simulation results of the dayanke rock avalanche induced by the 2008 wenchuan earthquake show that the aerodynamic effect significantly affects its flight behaviour before collision simultaneously the colluvium on the slope surface remarkably reduces its traveling speed and runout moreover the initial angle between the velocity of the detached ejection mass and the horizontal direction strongly affects the flight distance and final deposition pattern of the avalanche

neoarchean paleoproterozoic stratigraphy of the dhanjori basin singhbhum craton eastern india and recording of a few u pb zircon dates from its basal part abstract the stratigraphy of the dhanjori basin placed at the northeastern margin of the paleo mesoarchean singhbhum craton has been revised a mainly quartz pebble conglomerate qpc and volcani clastics bearing unit at the base of the dhanjori basin and intruded by the mayurbhanj granite has been named phuljhari formation the dhanjori volcani sedimentary sequence with quartzite polymictic conglomerate at its base disconformably overlies the phuljhari formation and non conformaby over the mayurbhanj granite the dhanjori group is inferred to broadly range in age from 2 6 2 1 ga detrital zircons from qpc belonging to the phuljhari formation have yielded oldest chemical ages of 3 09 3 04 ga thus fixing the upper age limit of the formation the 3 09 ga old zircons recovered earlier from the mayurbhanj granite which is intrusive into the relatively younger phuljhari fm therefore appears to be xenocrystic in nature a fine grained variety of the mayubhanj granite close to its intrusive contact with the phuljhari fm was sampled during the present study it has recorded strong impress of acid magmatic event around 1 0 0 8 ga by its lower intercept and an upper intercept age of 2 8 ga the latter might record the inherited age of protolith to the mayurbhanj granite and correspond to widespread granite magmatic activity affecting the margin of the singhbhum craton signature of 1 0 0 08 ga old thermal perturbation also affected lower parts of the dhanjori basin and the singhbhum shear zone detrital au u bearing qpc in the phuljhari formation represent neoarchean sedimentation at the margin of the peneplained craton the dhanjhori group comprising mafic ultramafic volcanics and siliciclastics was hosted in rift induced intracratonic basin around neoarchean palaeoproterozoic threshold

tidal rhythmites in offshore shale a case study from the palaeoproterozoic chaibasa shale eastern india and implications abstract tidal rhythmites have been documented from modern continental shelves and distal offshore settings in significant contrast to their modern counterparts sedimentological studies of ancient tidal rhythmites formed in distal offshore settings and quantification of tidal rhythms encoded therein are however scarce this paper presents sedimentological analysis of vertically accreted tidal rhythmites from the palaeoproterozoic chaibasa shale facies in india and quantification of their tidal rhythms the facies characteristics of the chaibasa shale coupled with harmonic analysis of the laminae thicknesses of the sandstone inter layers corroborate a distal shelf palaeogeography for the generation of the vertically accreted tidal rhythmites the latter are the distal counterparts of laterally accreted tidal bundle deposits well preserved within the shallow marine chaibasa sandstones the number of lunar days in a synodic month 23 estimated from the chaibasa shale facies is however considerably lower than that estimated from the chaibasa sandstone facies 32 suggesting that the tidal record encoded from the chaibasa shale facies is incomplete

petrogenesis and geochronology of the arkasani granophyre and felsic dalma volcanic rocks implications for the evolution of the proterozoic north singhbhum mobile belt east india the north singhbhum mobile belt nsmb is a 200 km long curved proterozoic fold thrust belt that skirts the northern margin of the archean singhbhum craton of ne india the singhbhum shear zone ssz developed between the dhanjori and chaibasa formations near the southern margin of the nsmb and represents an important cu u p metallotect a shrimp u pb zircon date of 1861 6 ma obtained for the syn to post kinematic arkasani granophyre that has intruded the ssz provides a minimum age for the prolonged tectonic activity and mineralization along the ssz and for the time of closure of the chaibasa and dhanjori sub basins the dalma volcanic belt a submarine rift related bimodal mafic felsic volcanic suite forms the spine of the nsmb a shrimp u pb zircon igneous crystallization date of 1631 6 ma was obtained for an unfoliated felsic volcanic rock from the base of the dalma volcanic sequence these new findings suggest that the different sub basins in the nsmb evolved diachronously under contrasting tectonic environments and were juxtaposed during a later orogenic movement

simulation of tsaoling landslide taiwan based on saint venant equations over general topography the 1999 chi chi earthquake triggered the catastrophic tsaoling landslide in taiwan the geomorphological change measured from the data of the 1989 and 2000 aerial photos reveals that the scar and deposit volumes are about 0 126 km3 and 0 15 km3 respectively the debris material ran over a distance of 1 6 km with 500 m descent in elevation in this paper we use the continuum model of hydraulic flow shaltop2d based on the equations of bouchut and westdickenberg to simulate numerically the landslide dynamics when the mass is moving the flow is assumed hydrostatic with a basal coulomb friction the best fit is obtained using the basal friction angle equal to 6 the only parameter of the simulation uniformly applied in the calculation domain the landslide front reaches the chinshui river valley the foothill of the slope within only about 25 s after initiation and the motion settles in about 113 s the maximum speed is estimated 75 m s the spreading of the deposit agrees well with the field measurement

analysis of the chiufengershan landslide triggered by the 1999 chi chi earthquake in taiwan abstract a disastrous earthquake rocked taiwan on september 21 1999 with magnitude m l 7 3 and an epicenter near the small town of chi chi in central taiwan the chi chi earthquake triggered landslide on the dip slope at the chiufengershan in this study a review of the topography and geology of this area was followed by field investigations laboratory testing was applied to understand the geomaterial composing the slope then based on a series of limit equilibrium analyses the failure mechanism of this landslide and the risk of the residual slope were studied according to the stability analyses the pre quake slope is quite stable with factor of safety of 1 77 dry to 1 35 full groundwater level explaining why there is no written record of a landslide here for the past 100 years in contrast a back analysis shows that the chi chi earthquake induced dynamic loading is far more than the dip slope can sustain due in part to the short distance to the epicenter a monte carlo type probability analysis suggests that the residual slope is more dangerous than the pre quake slope and needs more attention

sedimentation history of the palaeoproterozoic dhanjori formation singhbhum eastern india abstract the palaeoproterozoic dhanjori formation eastern india is a terrestrial dominantly fluvial volcano sedimentary succession basal conglomerate coarse grained sandstone and shale rests directly on the granite basement and represents the distal fringe of an alluvial fan complex sieve sheet flood mass flow and alluvial channel and overbank deposits comprise the fan segment the rest of the formation is entirely constituted by fining upward fluvial cycles an event of basin tilting and volcanic eruption intervened and resulted a second phase of dhanjori sedimentation although the general fluvial depositional framework remained unaltered the two members of the dhanjori formation display different paleocurrent trends related to fluvial response to basin tilting in the lower member spatial variability in paleocurrent directions occurs as a consequence of fan development unlike the first phase the second phase of fluvial deposition incorporates profuse volcanics and accompanying volcaniclastic deposits these volcanic and volcaniclastic rocks might have locally blocked the river courses resulting in short lived lacustrine deposition composition of the volcanics varies upward from ultramafic to mafic the dhanjori volcanism took place in an intracontinental rift setting as is evident from the interbedded terrestrial deposits interbedded volcanic and volcaniclastic rocks in different stratigraphic levels suggest episodic volcanic eruption a semiarid paleoclimate is proposed and is consistent with development of an alluvial fan comprised of coarse clastic deposits

controls on spatial and temporal distribution of precambrian eolianites abstract inversely graded stratification generated by the migration of wind ripples and adhesion structures permit unequivocal identification of precambrian eolianites these criteria in combination with scale of cross beds angle of inclination of foresets geometry of depositional units and associated non eolian facies are used to discriminate between precambrian dune draa dune plinth sand sheet and interdune deposits that formed in inland and coastal settings based on an analysis of published literature fundamental conclusions can be drawn on the spatial and temporal distribution of precambrian eolianites the oldest reported eolianites are from the ca 2 1 ga deweras group in zimbabwe and hurwitz group in canada and numerous examples of eolianites are reported from the 1 8 ga and younger rock record lack of archean and early paleoproterozoic eolianites and their widespread development after 1 8 ga are examined with respect to absence of vegetation crustal growth and tectonic setting relative sea level fluctuations unfavorable atmospheric and or climatic change and non recognition the lack of pre 2 2 ga eolianites may be related to reworking by braided rivers combing across non vegetated floodplains reworking of coastal eolianites during transgression or their non recognition in the early precambrian record the temporal concentration of eolianites at 1 8 ga may best be related to the early stages of breakup and the assembly phases of supercontinents

single zircon evaporation ages constraining the growth of the archaean aravalli craton northwestern indian shield single grain 207 pb 206 pb zircon ages were determined for granitoids and gneisses which constitute the archaean basement rocks of the aravalli craton of rajasthan northwestern indian shield the protolith ages for two gneisses collected from east of udaipur are 3230 ma and 2887 ma respectively the granitoids display an intrusive relationship with the gneisses and yielded ages ranging between 2666 ma and 2620 ma these ages provide the basis for a geochronological model of evolution of the oldest basement of the aravalli craton

seismites in a proterozoic tidal succession singhbhum bihar india abstract early proterozoic metasediments of the chaibasa formation galudih ghatsila dhalbhumgarh region singhbhum bihar india comprise a number of cyclic fining upward prograding successions of tidalites the tidalites show indications for earthquakes in the form of synsedimentary deformation features apart from the structures due to high energy wave action deformed cross bedding convolute laminations synsedimentary faults graben like structures sandstone dykes pseudonodules and slump folds record the seismic activity a gradual decline in the frequency of seismites and tsunami related depositional features in combination with an upward increase in thickness of the tidal cycles are attributed to gradual diminishing of tectonic activity within the basin

magmatic and metamorphic history of paleoarchean tonalite trondhjemite granodiorite ttg suite from the singhbhum craton eastern india texturally controlled dating of zircon from paleoarchean tonalite trondhjemite granodiorites of the older metamorphic tonalitic gneisses and the singhbhum granite batholith phases i ii and iii from the singhbhum craton in eastern india reveals a polycyclic evolution of the archean crust the granitoid suites were emplaced in two pulses at 3 45 3 44 ga and 3 35 3 32 ga tonalites and trondhjemites of the older metamorphic tonalitic gneisses were emplaced at ca 3 45 3 44 ga together with phase iii of the singhbhum granite pluton while granites belonging to the older metamorphic tonalitic gneisses were emplaced at ca 3 35 3 32 together with phase i and phase ii of the singhbhum granite pluton both crustal units underwent an early phase of relatively high grade metamorphism at 3 30 3 28 ga followed by extensive fluid induced alteration during low grade metamorphism at 3 19 3 12 ga and 3 02 2 96 ga the two units have also been marginally affected at ca 2 52 ga and 1 06 ga by major metamorphic events in the north singhbhum mobile belt and the singhbhum shear zone at the northern margin of the craton the zircon grains in granites have inherited cores with ages of ca 3 61 ga and 3 46 3 41 ga and with well developed oscillatory growth zonation which suggests the granitic magmas were derived by partial melting of an igneous precursor or sedimentary rocks derived from an igneous source the emplacement of the expansive granitoids belonging to the older metamorphic tonalitic gneisses and the singhbhum granite was synchronous with the amphibolite facies metamorphism ca 3 32 ga of older meta igneous and metasedimentary rocks belonging to the older metamorphic group major felsic crust formation in the craton occurred in a narrow time interval between 3 46 and 3 32 ma with minor contributions of material as old as 3 6 ga the complex polycyclic evolution of the paleoarchean crust in the singhbhum craton can account for the wide range of often disparate ages obtained using whole rock isochron dating techniques with some of the isochron dates being geologically meaningful while others representing mixing lines or disturbance of the isotopic systems during metamorphism

effects of seismic anisotropy and geological characteristics on the kinematics of the neighboring jiufengershan and hungtsaiping landslides during chi chi earthquake abstract the chi chi earthquake mw 7 6 of september 21 1999 triggered many landslides in central taiwan two of these landslides hungtsaiping htp and jiufengershan jfes were situated as close as 2 km from each other but had significant differences in their kinematics jfes landslide was a catastrophic rockslide avalanche and the htp landslide was relatively slow moving the authors conducted a study to explore the reasons for such differences factors such as the characteristics of strong ground motion sliding direction of landslide and friction angle of the sliding surface were considered in the study an analysis of 12 strong motion records collected in the study area showed that the distribution of horizontal pseudostatic coefficients earthquake energy ratio and permanent sliding block displacements newmark displacement were anisotropic with their predominant direction mostly in the e w ese wnw trending this direction is perpendicular to the axis of the main geological structures of the studied area the computed newmark displacement in the sliding direction of the jfes landslide is larger 44 than that of the htp landslide with sliding surface inclination of 21 and friction angle of 28 we can conclude that the seismic anisotropy and the corresponding sliding direction are important contributing factors to the kinematics of studied landslides the back calculated friction angle of the sliding surface that corresponds to a critical newmark displacement for the jfes landslide is about 3 5 higher than that of htp landslide the material colluvium on the sliding surface in htp should be less velocity dependent than that of the jfes landslide rock according to the back calculations the importance of seismic anisotropy sliding direction and mechanical properties of sliding surface on the kinematics of deep seated landslides is demonstrated

depositional setting and implications of paleoproterozoic glaciomarine sedimentation in the hamersley province western australia a combination of facies analysis and the identification of dropstones as well as striated and faceted clasts in diamictites and associated sedimentary rocks from the hamersley province confirms earlier suggestions of their glacial origin ten lithofacies comprising two diamictite four sandstone and four fine grained facies have been identified and arranged into three glaciomarine facies associations massive diamictite interbedded with laminated siltstone in the southern part of the province is interpreted to have been deposited peripheral to the margin of rapidly melting tidewater glaciers emanating from more extensive ice cover in highlands to the south distal diamictites sandstones and laminated siltstones preserved north of the hardey syncline were deposited from sediment gravity flows sediment plumes and rain out from rare icebergs background marine sedimentation consisted of banded iron formation and siltstone using these glacial deposits as an event marker it can be shown that 2000 m of turbidites and shallow marine sedimentary rocks in the turee creek group on the southern margin of the hamersley province are lateral facies equivalents of as much as 400 m of banded iron formation and mudrock to the north this correlation demonstrates the markedly asymmetric nature of subsidence in the mcgrath trough which has previously been interpreted as a foreland basin with an orogenic margin to the southwest new geochronologic data constrain the age of these glacigenic deposits to 2 45 2 20 ga which is within the range of present constraints for similar deposits in north america fennoscandia and south africa available paleomagnetic data suggest low latitude 5 11 glaciation for the north american south african and west australian deposits

tidal sandwaves and related storm deposits in the transgressive protoproterozoic chaibasa formation india abstract despite deformation and metamorphism the 2 3 ga fine grained siliciclastic chaibasa formation of eastern india locally retains an excellent record of sandwave migration under the influence of tides and storms within a precursor sandstone facies in a largely subtidal setting and provides a rare opportunity to detect tidal periodicities in the finer facies locally preserved minor features provide glimpses of the depositional mechanisms and settings the silt dominated precursor heterolithic silt mud facies contain numerous slides and slumps and was formed on a relatively steep slope between the fairweather and storm wave bases the shale facies formed in a deeper setting beneath the wave base earthquakes occasionally have interrupted normal sedimentation and massflow products are present in all the facies but with increasing frequency within the finer facies the sandstone facies units which were emplaced during repeated lowstands were first subjected to progradation and subsequently drowned in an overall transgression trend

the tsaoling landslide triggered by the chi chi earthquake taiwan insights from a discrete element simulation article i nfo in the village of tsaoling in yunlin county taiwan a major landslide was triggered by the chi chi earthquake in 1999 with more than 125 10 6 m 3 of rock displaced the kinematic behaviour of this landslide is simulated using a 2d discrete element model pfc2d code our numerical model is composed of discs bonded together the initial boundary conditions are applied along the ball wall contacts by using derived velocities integrated from the strong motion data with a duration of 160 s including the peak acceleration near tsaoling the constraints are mainly issued from the final geometry of the landslide including its capacity to cross the river valley and reach a significant elevation on the opposite mountain flank they also result from a variety of geological and hydrological observations including the local levels of material disruption and the location of survivors our modelling thus indicates that a low friction coefficient about 0 15 and a medium strength are required to account for the actual landslide characteristics a self lubrication mechanism probably accounts for the low residual friction our model also suggests that the maximum velocity of sliding reached 50 m s a result that cannot be checked in the absence of actual measurements in addition to friction the strength of sliding block is of special importance because it controlled the possibility for the upper layer fragments to roll and get buried and hence the probability of survival

palaeoproterozoic terrestrial sedimentation in the beasley river quartzite lower wyloo group western australia abstract pre 2 2 ga aeolianite deposits are relatively rare in the geological record due to reworking of aeolianites either by fluvial systems transgression or non recognition here we present high resolution sedimentary facies analysis of a section through the 2 2 ga beasley river quartzite lower wyloo group western australia the unambiguous presence of terrestrial fluvial aeolian deposition is documented in the form of fluvial architectural elements channel bar lateral accretion and overbank deposits and aeolian features dune pin stripe lamination wind streaks and adhesion features these observations contrast strongly with a previous interpretation of marine deposition which is discounted our data is consistent with the dominantly terrestrial depositional mode of the rest of the lower wyloo group including the basal three corners conglomerate member and the subaerial cheela springs basalt we conclude that the lower wyloo succession formed in a terrestrial regime during continental rifting

palaeoproterozoic sedimentation on the singhbhum craton global context and comparison with kaapvaal the singhbhum craton has a limited palaeoproterozoic supracrustal record which suggests a three part history comprising a long period of high freeboard and palaeosol formation on granitoids subsequent rift related mafic ultramafic volcanism and subordinate sedimentation c 2 25 2 1 ga dhanjori and jagannathpur basin fills possibly also simlipal malangtoli and ongarbira basin fills which overlapped locally with mafic soil formation and a major regression at around2 0 ga followinga longhiatus theapproximately 1 6 gadhalbhum dalmasuccession was laid down probably under continental conditions this rather truncated record stands in con trast to the chronologically and geographically much more widespread supracrustal basin fills of the kaapvaal craton and there appears to be an overall poor comparison between these two early precambrian crustal blocks however on kaapvaal three analogous events are identified widespread approximately 2 2 ga mafic volcanism followed by a well developed palaeosol and a major transgression prior to 2 05 ga the three shared events between the two cratons are com patible with the postulate of a global approximate 2 45 2 2 ga shutdown of magmatic and tec tonic geodynamics with the origin of the triumvirate directly reflecting its resumption again after about 2 2 ga we recognize here that a large diversity of views on singhbhum s geodynamic history exists predicated on a lack of precise geochronology and commonly poor outcrops and the current hypotheses are presented with these factors in mind

evolution of the proterozoic rift margin sediments north singhbhum mobile belt jharkhand orissa india abstract the proterozoic north singhbhum mobile belt nsmb a proterozoic rift basin registered a complex interplay of tectonism and sedimentation the siliciclastic sedimentary succession developed along the southern margin of the nsmb offers a deep insight into the changing pattern of sedimentation in response to crustal dynamism along a rift margin stratigraphic sedimentologic structural and tectonic studies of the proterozoic sedimentary succession bisrampur formation indicate deposition in a series of half grabens developed successively along the margin of the rift basin under the influence of lithospheric stretching analyses of the sedimentary facies attributes and the architecture of the studied sedimentary succession and paleocurrent patterns indicate filling of the half grabens by archean basement derived siliciclastic sediments in an alluvial fan fan delta environment the structural elements developed in these sediments and neighboring rock units suggest that deformation and final collapse of the half graben basins took place during a terminal orogeny on the basis of an integrated analysis of the dataset generated in the present study and the database available in published work a comprehensive evolutionary model of the north singhbhum mobile belt is reconstructed

two paleoproterozoic glacio eustatic cycles in the turee creek group western australia widespread glaciations in the period 2 42 2 22 ga have led to the suggestion of a paleoproterozoic snowball earth yet this hypothesis has been difficult to substantiate here we report the discovery of two paleoproterozoic glacio eustatic cycles from a predominantly marine succession in western australia where previously only one had been recorded sedimentary facies characteristics reveal that each cycle sharply commenced with a falling stage systems tract and terminated with a transgressive systems tract consistent with drawdown and subsequent release of large volumes of seawater from and into waxing and waning ice sheets respectively this discovery provides support for the widespread nature of paleoproterozoic glaciations and a major climatic change accompanying the rise in atmospheric oxygen

a marine to fluvial transition in the paleoproterozoic koolbye formation turee creek group western australia abstract although no unambiguous biogenic criteria exist to discriminate precambrian shallow marine successions from fluvial deposits physical sedimentological evidence including an association of primary sedimentary structures and textures stratigraphic position and comparison with phanerozoic and modern examples has been found useful in identifying these deposit types our high resolution sedimentary facies analysis coupled with new mapping clearly indicates shallow marine to beach aeolian to fluvial sedimentation in the paleoproterozoic koolbye formation of the turee creek group western australia a falling stage systems tract within the koolbye formation has been documented our sedimentary facies analysis in combination with sedimentological analysis of the underlying kungarra formation indicates development of at least three falling stage systems tracts within the turee creek group across the rise of atmospheric oxygen the great oxidation event

geological and morphological study of the jiufengershan landslide triggered by the chi chi taiwan earthquake the jiufengershan rock and soil avalanche is one of the largest landslides triggered by the chi chi earthquake taiwan 1999 the landslide destabilized the western limb of the taanshan syncline along a weak stratigraphic layer it involved a flatiron remnant which was almost entirely mobilized during the earthquake the avalanche was slowed down by ns trending ridges located downstream along the jiutsaihu creek the landslide affected a 60 m thick and 1 5 km long sedimentary pile composed of shales and sandstones which dip 228se toward a transverse valley the triggering mechanism and the sliding process were analyzed by means of geological and morphological data from aerial photographs and observed in the field a high resolution airborne light detection and ranging lidar image taken 2 5 years after the landslide allows the identification of morphological structures along the sliding surface and the landslide accumulation the sliding surface shows several deformation structures such as fault scarps and folds these structures are interpreted in terms of basal shear stresses created during the avalanche three major joint sets were identified at the sliding surface the isopach map of the landslide was calculated from the comparison between elevation models before and after the earthquake the coseismic volume of mobilized material and landslide deposit data are 4210 6 m 3 and 5010 6 m 3 respectively the geometry of the landslide accumulation in the field has an irregular star shape the morphology of the deposit area shows a sequence of smooth reliefs and depressions that contrast with the neighboring ridges d 2005 elsevier b v all rights reserved

the archaean nucleus of singhbhum the present state of knowledge abstract the supracrustal rocks of the older metamorphic group omg consisting of metasediments and ortho amphibolite constitute the oldest unit in the archaean nucleus of singhbhum however there are indications that still older 3 4 3 8 ga crust of both sialic and mafic composition existed in this region the omg ortho amphibolites were formed by partial melting of mantle with near chondritic composition ca 3 3 ga ago probably as a result of plume activity shortly afterwards partial melting of the underplated mafic material produced a tonalitic melt older metamorphic tonalitic gneiss omtg which intruded the omg supracrustals and the entire suite was deformed and metamorphosed to upper amphibolite facies subsequent to this melting of the omg ortho amphibolites and the lower crustal material of probable andesitic composition produced melts varying in composition from tonalite to granite and these intruded in different phases to produce plutons of singhbhum granite bonai granite and kaptipada granite which together form volumetrically the major part of the archaean nucleus the older omg and omtg occur as enclaves within these younger granitoids the time difference between the emplacements of the omtg and the early phases of younger granitic intrusion was of the order of 100 200 ma thus serial additions of juvenile material led to the formation of a stable microcontinent by 3 2 ga thermally triggered stretching in this microcontinent produced basins peripheral to the present day singhbhum granite pluton and in these basins the younger supracrustal rocks of the iron ore group iog consisting of bif associated argillaceous and subordinate arenaceous rocks and mafic lavas were laid down there is inadequate field or geochronological evidence to resolve the issue of whether the different iron ore basins were coeval or not meagre geochronological data suggest that some of the bifs are older than ca 3 1 ga post iog activity is confined to the intrusion of mafic dyke swarms and formation of intracratonic basins the ages of both being uncertain

composition and weathering conditions of paleoproterozoic upper crust of bundelkhand craton central india records from geochemistry of clastic sediments of 1 9ga gwalior group abstract the 1 9 ga gwalior group represents one of the major paleoproterozoic depositional basin of bundelkhand craton and is comprised of 1 km thick unmetamorphosed and undeformed sedimentary succession with basal clastic sequence of sandstone shale association par formation and an upper chemogenic bif rich sequence morar formation the geochemical examinations of the basal clastic rocks are the subject of present study the compositional maturity and extreme quartz enrichment in sandstones of gwalior group suggest slow upliftment and high in situ weathering of basement terrains in a stable platformal setting these clastic sediments are characterized by strong depletion of mobile constituents like ca sr and na high plagioclase index of alteration pia values and strong positive correlation between al 2 o 3 and tio 2 indicating severe weathering of upper crust positive correlation between feo t and tio 2 suggests fe retention in paleoweathering profiles and is attributed to oxygenated atmosphere post depositional potash metasomatism is indicated in a cn k systematics of these sediments and k enrichment from near zero to as high as 38 is inferred with most of the shale samples show 30 extraneous k 2 o additions depleted transition element ni cr co sc contents elevated large ion lithophile element lile k rb ba th light rare earth elements lree contents fractionated rare earth element ree patterns strong negative eu anomalies in these sediments point toward k rich intracrustal granitic source component steeper ree patterns avg la yb n 12 57 compared to basement granites and conspicuous depletion of y over other liles in auc normalized spidergram also suggest a heavy rare earth element hree depleted ttg source component minor contribution from tholeiitic mafic rock is evidenced from th sc sc la sc sc th systematics and positive correlation of transition elements with feo t and tio 2 mixing calculations on the ree data suggest that upper continental crust of bundelkhand craton was constituted of 40 granite 40 ttg and 20 mafic rocks this is in contrast with the present day composition of bundelkhand granite gneiss complex bggc that contains 90 high k granite the data suggest unroofing of granite batholiths by means of erosion and upliftment of supracrustal ttg cover

petrochemistry of the lavas from proterozoic dalma volcanic belt singhbhum eastern india the dalma volcanic belt of the singhbhum precambrian terrain in eastern india is developed along the median zone of a linear basin flanked by archaean cratonic basement to the south the lavas in a low grade metamorphic environment preserve a strong compositional bimodality with highly magnesian picritic volcanics developed at the base and low k basalt flows above constituting the bulk of the lava pile the ultrabasic lavas have low concentrations of immobile incompatible elements ratios of which are probably controlled by the source character dalma mafic flows are closely comparable in geochemical character to modern day mid oceanic ridge basalts morb with a dominance of light ree depleted basalts and ferrobasalts however in terms of certain element ratios th ta deviation from morb characteristics toward island arc tholeiites is apparent in this respect the dalma basalts appear to have a modified morb composition and the closest chemical analogy may be basalts from back arc basins i e a supra subduction zone environment the bimodality of ultrabasic and mafic lavas is reminiscent of archaean komatiitic provinces the geochemical signature of the dalma lavas and the geological framework of the terrain strongly point to a marginal basin domain developed in this crustal segment during the proterozoic

3 35ga komatiite volcanism in the western dharwar craton southern india constraints from nd isotopes and whole rock geochemistry abstract we present field petrographic sm nd whole rock isochron and whole rock geochemical data for komatiites from sargur group greenstone belts of the western dharwar craton field evidence such as pillow structure indicates their eruption in a marine environment petrographic data reveal that the igneous mineralogy has been altered during post magmatic hydrothermal alteration processes corresponding to greenschist to lower amphibolite facies conditions with rarely preserved primary olivine and orthopyroxene a 16 point sm nd whole rock isochron gives an age of 3352 110 ma for the timing of eruption of komatiite lavas about 60 of the studied komatiite samples show al depletion whilst the remaining are al undepleted the al depleted komatiites are characterised by high cao al2o3 ratios 1 01 1 34 and low al2o3 tio2 5 16 whereas al undepleted komatiites show lower cao al2o3 ratios 0 59 0 99 and higher al2o3 tio2 17 26 trace element distribution patterns of komatiites suggest that most of the primary geochemical and nd isotopic compositions are preserved with only minor influence of post magmatic alteration processes and negligible crustal contamination the chemical characteristics of al depleted komatiites such as high gd yb n together with lower hree y zr and hf imply their derivation from deeper upper mantle with garnet majorite involvement whereas lower gd yb n slightly higher hree y zr and hf suggest derivation from shallower upper mantle without garnet involvement the observed chemical characteristics cao al2o3 al2o3 tio2 mgo ni cr nb zr y hf ree indicate derivation of the komatiite magmas from different depths in a plume setting whereas sub contemporaneous felsic volcanism and ttg accretion can be attributed to an arc setting in order to explain the spatial association of komatiite volcanism with contemporaneous mafic felsic volcanism and ttg accretion we propose a combined plume arc setting nd isotope data of the studied komatiites indicate depleted mantle reservoirs which may have evolved by early 4 53 ga global differentiation of the silicate earth as suggested by boyet and carlson boyet m carlson r w 2005 142nd evidence for early 4 53 ga global differentiation of silicate earth science 309 577 581 or extraction of continental crust during the early archaean

sedimentation history of the paleoproterozoic singhbhum group of rocks eastern india and its implications abstract this paper reviews the sedimentological geochemical and stratigraphic characteristics of the paleoproterozoic chaibasa and dhalbhum formations the singhbhum group of eastern india and presents a comparative study with other paleoproterozoic lithostratigraphic units of india both the formations are entirely siliciclastic and deformed and metamorphosed generally at greenschist to upper amphibolite facies the older chaibasa formation consists of sandstone shale and sandstone shale interbanded heterolithic facies it conformably overlies the late archean paleoproterozoic dhanjori formation of terrestrial alluvial fan fluvial origin the lower chaibasa member formed in a marine setting the shale and heterolithic facies formed in a continental shelf setting below and above the storm wave base respectively the sandstone facies formed in a subtidal setting during sea level fall in contrast the upper chaibasa member formed in a shallow marine setting both the shale and heterolithic facies formed above the storm wave base in significant contrast the overlying dhalbhum formation is dominated by finer clastics with much lower proportion of sandstones the base of the terrestrial dhalbhum formation is a sequence boundary unconformity sedimentary facies analysis clearly shows two broad facies association of terrestrial origin fluvial and aeolian the aeolian facies association overlies the fluvial facies association the dhalbhum sandstones show typical ree pattern of quartz dilution with lower concentrations compared to the mudstones the dhalbhum finer clastics mimic typical ree patterns resembling abundances in the continental crust rare earth element plots display a good match with post archean australian shales paas including similar concentrations steep negative slope for lrees negative eu anomaly and nearly flat hrees the singhbhum paleoproterozoic succession is devoid of both chemical sediments and paleoproterozoic glacial deposits in contrast to neighboring cratons

dynamic analysis of a slope failure from the 6 august 1979 coyote lake california earthquake abstract the coyote lake california earthquake of 6 august 1979 m l 5 7 provided a rare opportunity to perform a dynamic numerical analysis of a seismically induced slope failure using actual strong motion records the earthquake displaced a preexisting slump on the northeast shore of lake anderson and formed a fissure 20 m long offsets of 9 mm vertically and 18 mm horizontally were measured across the fissure the slump is 9 km northwest of the located epicenter but within 100 m of the mapped trace of the calaveras fault two strong motion records were written in the vicinity of the slump coyote creek 5 km to the southeast and gilroy 6 15 km to the southeast these records combined with field measurements of the slope estimates of the material properties and a dynamic numerical model based on the newmark analysis of seismic slope stability to calculate a predicted displacement for the landslide a displacement of 27 mm calculated using the n50 e component of the gilroy 6 record is in excellent agreement with the displacement measured in the field 21 mm however displacements of only 0 12 mm calculated using the 250 component of the coyote creek strong motion record reflect significant local variations in seismic shaking intensity because strong motion records and slope failures rarely coincide this landslide provides an important test case for our understanding of the dynamics of seismically induced landslides as well as a warning that local seismologic variations need to be considered in any design applications

characteristics and triggers of earthquake induced landslides of pyroclastic fall deposits an example from hachinohe during the 1968 m7 9 tokachi oki earthquake japan abstract this work characterizes the geomorphological features and describes the factors controlling earthquake induced landslides of pyroclastic fall deposits statistical analysis of the distribution of landslides caused by the 1968 m7 9 tokachi oki earthquake and prior high magnitude earthquakes was conducted using 0 5 m resolution light detection and ranging data and aerial photographs most of the 1968 co seismic landslides were shallower than 3 5 m and occurred on sliding surfaces with slope angles of less than 34 average angle of 26 4 the fitting relationship between the height and length of the 1968 co seismic landslides was h 0 226l with a modal apparent friction angle of 12 14 indicating high mobility the 1968 co seismic landslide crowns were primarily located near ridge crests the hillslope morphology and seismic arias intensity direction greatly influenced the direction of the earthquake induced landslides which were predominantly oriented in a northwest north east direction these earthquake induced landslides occurred in a cluster where fine marginal portions of towada hachinohe pyroclastic flow deposits i e to h pfl thinly

depositional history of diamictites from the late paleoproterozoic dalma formation e india abstract the paleoproterozoic dalma formation situated on the singhbhum craton in eastern india consists almost entirely of mafic to ultramafic rocks that were deposited by effusive volcanic activity and as pyroclastic deposits the main focus of the present study however is on diamictites consisting like both other rock types exclusively of chlorite and actinolitic hornblende that are intercalated with these volcanic rocks these diamictites are interpreted as mass flow deposits the textures and mineralogical composition of the diamictites suggests a volcanic origin of the material most probably they are reworked pyroclastic deposits with the same mineralogy as the dalma lavas on this basis it is concluded that the diamictites represent the deposits of one or more volcanic mudflows they must have formed of material that had already travelled over a considerable distance in the form of grain by grain transport as indicated by the presence of both rounded and distinctly broken clasts and by the relatively small size of the clasts both the grain by grain and the mass transport must have occurred following pathways that were covered all over with volcanic material of mafic composition this transport must have taken place under terrestrial conditions as no marine or lacustrine clasts or matrix is included the results of the study suggest that the diamictites within the dalma formation cannot be seen as a possible equivalent of paleoproterozoic glacigenic sediments such as known from australia and south africa

dating the oldest greenstone in india a 3 51 ga precise u pb shrimp zircon age for dacitic lava of the southern iron ore group singhbhum craton abstract this article reports a precise 3506 8 2 3 ma u pb shrimp zircon age for dacitic lava in a well preserved low grade metamorphic and low strained greenstone belt succession of the southern iron ore group singhbhum craton india this age makes the succession the oldest known greenstone belt succession in india and one of the oldest low strain greenstone successions in the world after the 3 51 ga coonterunah group of the pilbara craton western australia and the moderately deformed 3 54 ga theespruit formation of the barberton greenstone belt kaapvaal craton south africa the geochemical composition of the dacitic lava and related volcanic rocks suggests that they formed in a volcanic arc setting the succession also contains a major 120 m thick oxide facies banded iron formation that distinguishes it from the slightly older successions of the pilbara and kaapvaal cratons this banded iron formation may well be one of the oldest and most well preserved and together with associated volcanics

influence of surface normal ground acceleration on the initiation of the jih feng erh shan landslide during the 1999 chi chi taiwan earthquake the 1999 chi chi taiwan earthquake triggered numerous landslides throughout a large area in the central range to the east southeast and south of the fault rupture among them are two large rock avalanches at tsaoling and at jih feng erh shan at jih feng erh shan the entire thickness 30 50 m of the mio cene changhukeng shale over an area of 1 km 2 slid down its bedding plane for a distance of about 1 km initial movement of the landslide was nearly purely trans lational we investigate the effect of surface normal acceleration on the initiation of the jih feng erh shan landslide using a block slide model we show that this ac celeration currently not considered by dynamic slope stability analysis methods significantly influences the initiation of the landslide

life on land in the precambrian microfossils have been discovered in cavity fill and replacement silica that occurs between chert breccia clasts in 1200 million year old paleokarst at the top of the mescal limestone central arizona and in 800 million year old paleokarst at the top of the beck spring dolomite southeastern california microbial communities on precambrian g550 million years ago land may have been extensive enough to affect weathering erosion sedimentation and geochemical processes

shallow marine and coastal eolian quartz arenites in the neoarchean palaeoproterozoic karutola formation dongargarh volcano sedimentary succession central india abstract the neoarchean palaeoproterozoic karutola formation a 200 m thick supermature quartz arenite occurs interlayered between two thick units of intermediate to basic volcanic rocks of the dongargarh group despite metamorphism and deformation detrital texture and sedimentary structures are well preserved allowing detailed process based facies analysis the facies recognised include 1 inner shelf 2 shoreface 3 delta mouth lower delta plain 4 tidal flat and 5 foreshore backshore a coastal sand sheet dominated by adhesion structures and consisting of alternating eolian and foreshore aqueous deposits records eolian processes operative in the karutola coastal area textural characteristics hint at a significant eolian contribution to the shallow marine sand overall palaeocurrent indicates a nw se shoreline trend with hinterland to the west of the present outcrop belt a surface indicating an abrupt increase in the water depth divides the formation into two units the lower part encloses inner shelf to foreshore backshore deposits and the upper part of the succession records deposition from the shoreface to lower deltaplain environment a tidal flat sandstone mudstone unit is developed only in the north western end of the study area a granite gneiss source terrain cropping out to the west and a hot humid climate appears to have supplied the abundant quartz sand to the karutola shoreline and the sand population attained textural maturity through eolian and aqueous reworking it is postulated that the aqueous eolian interaction inferred for the karutola sand should be common in sandy depositional environments that lacked land vegetation

geochemical and ion microprobe u pb zircon constraints on the archaean evolution of singhbhum craton eastern india abstract geochemical and shrimp u pb zircon analyses were obtained for nine samples of the singhbhum craton to investigate major regional granite intrusion volcanism sedimentary deposition metamorphism and deformation episodes detrital zircons within a recrystallized sandstone enclave within tonalitic gneiss provided a maximum time for deposition of 3375 3 ma all uncertainties are at 95 confidence unless otherwise specified for the host sandstone igneous crystallization dates between 3380 and 3299 ma were obtained for tonalite gneiss and foliated trondhjemite samples from widely dispersed sites whereas unfoliated granitic samples provided igneous crystallization dates

dynamic discrete analysis of an earthquake induced large scale landslide abstract the chiu fen erh shan landslide estimated to have a volume of 36 million cubic meters was triggered by the m w 7 6 taiwan chi chi earthquake of 1999 the debris covered an area of 1 95 km 2 and claimed 36 lives during the sliding the landslide mass disintegrated with its debris acquiring high speeds to reach over 1 km of travel distance the main objectives of the study were to investigate if it was possible to numerically model the landslide progression including slope disintegration and to reproduce the post failure configuration toward these goals the study employed a discrete element method called discontinuous deformation analysis for the dynamic analysis by incorporating the spacing and orientation information of the joints and bedding planes the slope was modeled as an assemblage of discrete deformable blocks horizontal and vertical ground motions were simultaneously applied the near field digital strong records were affected by the large uplift of the hanging wall of the reverse thrust fault and corrections were made to address this issue the study showed that the methodology adopted was able to capture essential characteristics of the landslide and gave a post failure configuration resembling that observed in the field