ganges basin geometry records a pre 15 ma isostatic rebound of himalaya the tertiary continental strata of the himalayan foreland basin are subdivided into two groups but the meaning of this subdivision was previously unclear from the analysis of drill holes seismic lines dated sections outcrops and balanced cross sections we find that the southward migration rate of the depositional pinch out of the younger group is 19 5 mm yr and equals the himalayan shortening rate this equality shows that the flexural foreland basin development is mainly controlled by the motion of the thrust load the long term pinch out migration rate was slower for the older synorogenic group erosion locally occurred at the end of its deposition due to tectonic reactivation of lineaments of the indian shield we suggest that this change in the basin development is linked to the detachment of the subducted indian lithosphere that decreased the slab pull and increased the mean compressive stress within the indian plate whereas the plate motion remained constant the most important implication of our work is that the associated isostatic rebound could have increased the himalayan elevation prior to 15 ma

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

estimation and applicability of attenuation characteristics for source parameters and scaling relations in the garhwal kumaun himalaya region india abstract source parameters of the small to moderate earthquakes are significant for understanding the dynamic rupture process the scaling relations of the earthquakes and for assessment of seismic hazard potential of a region in this study the source parameters were determined for 58 small to moderate size earthquakes 3 0 m w 5 0 occurred during 2007 2015 in the garhwal kumaun region the estimated shear wave quality factor q f values for each station at different frequencies have been applied to eliminate any bias in the determination of source parameters the q f values have been estimated by using coda wave normalization method in the frequency range 1 5 16 hz a frequency dependent s wave quality factor relation is obtained as q f 152 9 7 f 0 82 0 005 by fitting a power law frequency dependence model for the estimated values over the whole study region the spectral low frequency spectral level and corner frequency and source static stress drop seismic moment apparent stress and radiated energy parameters are obtained assuming 2 source model the displacement spectra are corrected for estimated frequency dependent attenuation site effect using spectral decay parameter kappa the frequency resolution limit was resolved by quantifying the bias in corner frequencies stress drop and radiated energy estimates due to finite bandwidth effect the data of the region shows shallow focused earthquakes with low stress drop the estimation of zuniga parameter e suggests the partial stress drop mechanism in the region the observed low stress drop and apparent stress can be explained by partial stress drop and low effective stress model presence of subsurface fluid at seismogenic depth certainly manipulates the dynamics of the region however the limited event selection may strongly bias the scaling relation even after taking as much as possible precaution in considering effects of finite bandwidth attenuation and site corrections although the scaling can be improved further with the integration of large dataset of microearthquakes and use of a stable and robust approach

thermotectonic history of the chiplakot crystalline belt in the lesser himalaya kumaon india constraints from apatite fission track thermochronology abstract fission track ages and confined track length distribution of apatite samples separated from the chiplakot crystalline belt ccb of the lesser himalayan crystalline lhc zone located to the south of the main central thrust mct munsiari thrust mt in kumaon india have been determined ages from the ccb along the kali and darma valleys fall in two distinct groups in the northern part of the ccb the ages range from 9 8 0 6 to 7 6 0 6 ma with a weighted mean of 9 6 0 1 ma while in the southern part the ages vary from 17 9 0 9 to 12 9 1 1 ma with a weighted mean of 14 1 0 1 ma the bimodal distribution of track lengths indicates that the ages are mixed ages rather than simple cooling ages the apatite fission track aft ages and already published structural data of the ccb suggest a complex erosional denudation history within the upper 3 4 km of the crust of the ccb the ages further indicate that the ccb was thrust into place earlier than the middle miocene i e at the time of development of the mct since then these rocks have remained within the upper 3 km of crust and were affected by only moderate to slow erosion and exhumation these results have important implications for the tectonic evolution of the lhc zone to the south of the mct mt the exhumation of the lhc zone in different parts of the himalaya was not uniform in the kumaon himalaya it was not controlled as in the himachal himalaya by any major tectonic event since it was thrust over the lesser himalayan meta sedimentary lhms zone and underwent moderate to slow erosion and exhumation

imaging the moho and the main himalayan thrust in western nepal with receiver functions the crustal structure of western nepal is studied for the first time by performing receiver function analysis on teleseismic waveforms recorded at 16 seismic stations the moho geometry is imaged as it deepens from 40 km depth beneath the foothills and the lesser himalaya to 58 km depth beneath the higher himalayan range a midcrustal low velocity zone is detected at 15 km depth along 55 km horizontal distance and is interpreted as the signature of fluids expelled from rocks descending in the footwall of the main himalayan thrust our new image allows structural comparison of the moho and of the main himalayan thrust geometry along strike of the himalayas and documents long wavelength lateral variations the general crustal architecture observed on our images resembles that of central nepal therefore western nepal is also expected to be able to host large m w 8 megathrust earthquakes as the 1505 ce event plain language summary we investigate the earth s crust in western nepal we use 16 stations to detect waves from faraway earthquakes and using these we make an image of the structure of the crust we find that the crust is getting thicker beneath the himalaya and that fluids are locally present in the upper part of the crust as this image is similar to the one we know in central nepal where major earthquakes happened it is possible that major earthquakes will also happen in western nepal in the future without knowing when

stratigraphy correlation and sedimentary history of adelaidean late proterozoic basins in australia abstract adelaidean late proterozoic time is represented by the precambrian portion of the thick sequence in the adelaide geosyncline its stratotype basin in south australia comparable adelaidean sedimentation including the deposition of glaciogenic sediments is recorded in other intracratonic and epicratonic basins extending northwards across australia in the adelaide geosyncline which lies to the east of the gawler craton and its cratonic platform cover the stuart shelf up to 15 km of mainly shallow water sediments accumulated partly in intracratonic troughs and perhaps partly on a miogeoclinal continental shelf the earliest sedimentation is associated with rifting and basic volcanism with an estimated age of ca 1100 ma it commenced with basal blanket sands shelf carbonates and basaltic volcanics followed by mixed carbonate clastic and evaporitic beds callanna beds the overlying burra group consists of a number of west derived possibly deltaic cycles and magnesite bearing platform carbonates the unconformably overlying late adelaidean umberatana group contains the lower glacial beds including the sturt tillite interglacial siltstone dated at about 750 ma and carbonate and the upper glacial beds the post glacial wilpena group commences with a distinctive cap dolomite above the upper glacials and contains mainly fine to medium clastics and the ediacara metazoan assemblage late adelaidean sedimentation patterns are sufficiently similar in the officer amadeus ngalia and georgina basins of central australia and in the kimberley region western australia to suggest interconnection with the adelaide geosyncline to the south in the amadeus basin the early adelaidean sequence is younger than about 1050 ma but cannot be directly correlated with the early adelaidean formations of the adelaide geosyncline however the late adelaidean glacial and younger sequences are readily correlated they include the lower glacial areyonga formation and the arumbera sandstone i containing elements of the ediacara assemblage in the georgina and ngalia basins mainly late adelaidean sequences including thick glacials can mostly be correlated with the amadeus basin in the kimberley region earliest adelaidean clastics may be represented but only the late adelaidean glaciogenic and associated sediments can be correlated with confidence the tillites commonly overlie glaciated pavements the lower glacials are represented only in a graben while the upper glacials and succeeding sequence are more widespread post glacial shales have been dated at ca 670 640 ma the dominantly carbonate and clastic sequences of the bangemall basin western australia cannot be directly correlated with any type adelaidean but geochronology suggests an earliest adelaidean age ca 1050 ma

spatiotemporal variation in exhumation of the crystallines in the nw himalaya india constraints from fission track dating analysis abstract during himalayan orogeny coeval thrusting along the main central munsiari thrust mct mt and extension along the south tibetan detachment system stds are widely responsible for rapid exhumation of the higher himalayan crystalline hhc zone apatite and zircon fission track data along the kaliganga and darma valleys in the kumaon himalaya serve to document the shallow bedrock exhumation history of the hhc taking into account sample location within the hhc with respect to the mct mt the apatite fission track aft data sets along the darma 1 0 0 1 to 2 8 0 3 ma and kaliganga 1 4 0 2 to 2 4 0 3 ma which are sharing same structural setting and rock types and being separated by 40 km show very similar patterns of exhumation histories since plio quaternary in the kumaon himalaya data sets along darma and kaliganga are very similar to data set of adjacent traverse 50 km away along the goriganga valley studied by patel and carter 2009 whole data sets within the hhc in kumaon himalaya provide clear evidence for plio quaternary tectonic activity along the vaikrita thrust vt precipitation in this region exerts a strong influence on erosional surface processes fluvial erosional unloading along the himalaya is focused on the high mountainous region of the hhc where the orographic barrier forces out the maximum percentage of annual rainfall ft cooling ages reveal coincidence between rapid erosion and exhumation that is focused in a 25 30 km wide sector of the hhc rather than covering the entire orogen similarity of aft age pattern and exhumation rates along all three major traverses goriganga darma and kaliganga indicates that the region has been experiencing constant rate of crustal uplift and erosion since long time comparison of fission track ages from the kumaon himalaya with other segments of the nw himalaya shows spatiotemporal variation in exhumation it is described due to the development of local structures such as dome window in jammu and kashmir and himachal himalayas and quaternary active thrusting along the vt and mct mt in the garhwal kumaon himalaya

control of detachment geometry on lateral variations in exhumation rates in the himalaya insights from low temperature thermochronology and numerical modeling 1 the himalayan range is commonly presented as largely laterally uniform from west to east however geological structures topography precipitation rate convergence rates and low temperature thermochronological ages all vary significantly along strike here we focus on the interpretation of thermochronological data sets in terms of along strike variations in geometry and kinematics of the main crustal detachment underlying the himalaya the main himalayan thrust mht we report new apatite fission track aft ages collected along north south transects in western and eastern central nepal at the latitudes of the annapurna and langtang massifs respectively aft ages are consistently young 3 ma along both n s transects in the high relief zone of the higher himalaya and increase 4 to 6 ma toward the south in the lesser himalaya we compare our new data to published low temperature thermochronological data sets for nepal and the bhutan himalaya we use the full data set to perform both forward and inverse thermal kinematic modeling with a modified version of the pecube code in order to constrain potential along strike variations in the kinematics of the himalayan range our results show that lateral variations in the geometry of the mht in particular the presence or absence of a major crustal scale ramp strongly control the kinematics and exhumation history of the orogen

fission track and 40ar39ar evidence for episodic denudation of the gangotri granites in the garhwal higher himalaya india abstract in order to document quantitatively the cooling and denudation history of the higher himalayan granites bordering the tethyan sedimentary zone fission track ft apatite and 40 ar 39 ar mica ages have been determined on the gangotri leucogranites and biotite granites in the garhwal region of india gangotri is the source area of the ganges river and lies in the midst of the highest himalayan peaks in india a total of 15 apatite ages from a vertical profile 2580 4370 m on the gangotri granites yields ft ages in the range of 1 5 0 6 to 2 4 0 5 ma indicating that the rock column with a relief of 1800 m cooled through 130 10 c within only 1 million years during the late pliocene an average denudation rate of 2 mm yr is estimated for the past 2 4 million years from the gangotri granites we also report a muscovite 40 ar 39 ar age of 17 9 0 1 ma and a biotite age of 18 0 0 1 ma these reflect cooling of the rocks through 300 350 c probably related to an early miocene pulse of denudation caused by a basement cover detachment the martoli normal fault above the leucogranites time temperature pathways indicate that the cooling of the rocks in the late pliocene quaternary was five to six times the magnitude of cooling between 18 and 2 ma indicating a distinct pulse of rapid denudation in the late pliocene quaternary we interpret these young apatite ages and fast denudation as a geomorphic response increased erosion and cooling of the rocks to a major pulse of tectonic uplift in the higher himalaya shortly before 2 4 ma the effect of climatic cooling on this denudation is considered secondary to the role of tectonic forcing and indeed produced a positive feedback to the primary cause although our study is confined to the garhwal region it is probable that other granitic bodies of the higher himalaya bordering the tethyan sedimentary rocks and forming the loftiest summits in the himalaya have also experienced episodic denudation one major pulse in the early miocene which was mainly tectonic denudation and another in the late pliocene quaternary which was mainly erosional the latter is well recorded by apatite ft data and is consistent with the hypothesis that rapid uplift and denudation of the himalayan rocks may have influenced the initiation of the ice ages in the northern hemisphere

interseismic strain accumulation on the himalayan crustal ramp nepal the departement of mines and geology has been monitoring the seismicity of the central himalayas of nepal since 1985 intense microseismicity and frequent medium size earthquakes ml 4 tend to cluster beneath the topographic front of the higher himalaya this 10 20km deep seismicity also correlates with a zone of localized uplift that has been evidenced from geodetic data both microseismic and geodetic data indicate strain accumulation on a mid crustal ramp that had been previously inferred from geological and geophysical evidence this ramp connects a flat decollement under the lesser and sub himalaya with a deeper decollement under the higher himalaya and probably acts as a geometric asperity where strain and stress build up during the interseismic period the large himalayan earthquakes could nucleate there and probably activate the whole flat and ramp system up to the blind thrusts of the sub himalaya

1d velocity structure and characteristics of contemporary local seismicity around the tehri region garhwal himalaya abstract a 1d velocity model of the tehri region in the garhwal himalaya is estimated from the travel time inversion of 145 well located local events having 1177 p and 1090 s arrivals the velocity model consists of six layers up to 24 km depth with p and s wave velocities ranging from 4 42 to 6 78 km s and 2 41 to 3 71 km s respectively the depth of the moho estimated using travel time curves of crustal phases is about 46 km a low velocity layer deciphered between 12 and 14 km depths is ascribed to fractured basement thrust representing the upper surface of the indian plate using the proposed velocity model 1457 events are relocated about 70 of the locatable events occur in the inner lesser himalaya between the main central thrust mct and the srinagar thrust the postulated depth of the basement thrust in the vicinity of the mct is about 10 12 km the depth distribution of events delineates the geometry of the seismically active main himalayan thrust mht below a 300 km long segment of the mct the mht is composed of two shallow dipping fracture zones that seem to represent seismically active thrust zones dipping in opposite directions two seismicity zones at 10 and 15 km depths with a 5 km vertical separation define a flat ramp flat type structure of the mht in the vicinity of the mct the postulated front of the underthrusting indian plate is at a depth of about 15 18 km the lower flat seismicity zone bifurcates into two indicating further slicing of the lower flat zone the postulated thickness of the brittle part of the underthrusting indian crust is about 20 km in the vicinity of the mct

dating of geomorphological processes using dendrogeomorphological methods abstract the object of this study was to develop methods for investigating recent geomorphodynamics of aggradation processes by dendrogeomorphological analyses of the stems and the roots of partially buried spruces every accumulation process causes growth reactions in the affected trees which is reflected in the growth rings analysis of the growth rings enables us to determine the time and the magnitude of burial yet the critical burial depth which when exceeded causes the death of the tree is 1 6 to 1 9 m the burial of a spruce stem causes the sprouting of adventitious root horizons a single event may cause simultaneous sprouting of up to six root horizons of which the uppermost horizon usually is the strongest one the dating of the onset of sprouting of the oldest adventitious roots among each root system enables one to establish absolute dates of debris flow events with an accuracy 0 to 3 years yet this method is very time consuming the simplest dating method proved to be the determination of burial events by the onset of a pronounced reduction of increment in the stem wood of the affected trees with only one core to be taken of each tree this method therefore allows a spatiotemporal reconstruction of aggradation processes the information recorded on the stem cross section of stem by the growth ring pattern lessens with increasing burial depth though

depositional environment and regional stratigraphic significance of the serle conglomerate a late proterozoic submarine fan complex south australia abstract the serle conglomerate is a lenticular unit 8 km 160 m at the top of the late proterozoic sturtian glacigenic yudnamutana subgroup in the northeastern part of the adelaide geosyncline in its type area at the west end of the fitton trough it can be subdivided into five stratigraphic units interpreted as the products of deposition in the mid to upper portions of a submarine fan complex progradation of submarine fans under conditions of eustatic sea level rise was probably due to concomitant fault activity and isostatic readjustments along the basin margins in an area about 10 km west of the type area similar conglomerates overlie glacigenic rocks of the yudnamutana subgroup with an erosional contact and therefore are younger than them there is no definitive evidence of glacial influence during deposition of the serle conglomerate so that previous correlations with glacigenic diamictites elsewhere in the adelaide geosyncline are unlikely there is no justification in this area for inferring two separate early sturtian glaciations

a large scale meandering submarine canyon outcrop example from the late proterozoic adelaide geosyncline south australia the late proterozoic adelaide geosyncline along with overlying cambrian strata comprises a thick sequence of sediments and sparse volcanics which accumulated in a major rift and passive margin setting during late syn rift or early post rift phases large volumes of terrigenous and carbonate sediments of the late proterozoic umberatana and wilpena groups and cambrian hawker group filled the rift submarine canyon development was related to at least four of these depositional cycles the most notable of which resulted in incision and subsequent filling of the major several kilometres in width and up to 1 5 km deep submarine canyons by the wonoka formation the wonoka formation canyons are not obviously fault controlled they are interpreted to have been eroded by turbidity currents during a relative low stand of sea level they were subsequently filled by a fining upwards suite of sediments which reflects subsequent relative rise of sea level and carbonate platform development ultimately the canyon complex was buried by north westerly progradation of overlying fluvial and slope sequences billy springs beds and possibly correlative upper pound subgroup it is considered likely that more distal elements of this prograding clastic wedge provided the necessary material for canyon erosion prior to canyon filling and ultimate burial by what may have been elements of the same depositional cycle it is considered possible that the series of isolated outcrops of canyon cross sections within the wonoka formation are sections of a single canyon thalweg developed within a considerably broader zone of slope degradation if this interpretation is correct then the gorge like patsy springs canyon lies in more proximal regions of the basin slope whereas 40 km to the north east the lower slope is cut by the fortress hill canyon complex palaeocurrent analyses of channel fill turbidites within the canyons imply that the fortress hill complex is in fact the outcropping western edge of a sinuous incised canyon thalweg the wonoka formation canyons containing basal sedimentary breccias but only minor conglomerates are considered typical of passive margin canyon development they are contrasted with the generally highly conglomeratic channel fills observed in outcropping tertiary and cretaceous examples of active margin canyons and upper fan valleys

spatial and temporal analysis of mass movement using dendrochronology tree growth and inclination on sloping land is affected by mass movement suitable analysis of tree growth and tree form can therefore provide considerable information on mass movement activity this paper reports a new automated method for studying the temporal and spatial aspects of mass movement activity ringwidth data from only a few cores per tree are required the method uses filtering techniques and statistical time series analysis preliminary results for two landslides in the barcelonnette area of the french alps show a relative stability of movement activity over the last hundred years no trend and short periodicity six to seven year periods of mass movement activity the advantages of the method over other mostly visual methods are its clearness flexibility repeatability and rapidity however further testing is needed to examine its reliability

short term bank gully retreat rates in mediterranean environments abstract in this study short term headcut retreat was monitored from 46 active bank gullies selected in the guadalentin and the guadix basin in southeast spain the measurements were carried out manually using an orthogonal reference system fixed by erosion pins around the gully heads between april 1997 and april 1999 with a 1 year interval the average volumetric retreat rate for all gullies was 4 0 m 3 year 1 corresponding with an average linear retreat rate of 0 1 m year 1 but more erosion took place during the first monitored year 1997 1998 compared to the second 1998 1999 an interplay of spatial variations in rainfall distribution and tension crack activity is assumed to be responsible for the important difference in annual headcut retreat compared to the small difference in annual rainfall amounts statistical analysis showed that the present drainage basin area a p was the most important topographical factor explaining average gully headcut retreat rate both in terms of annual eroded volume v e and annual linear retreat r l and expressed by the power relationships v e 0 04 a p 0 38 r 2 0 39 and r l 0 01 a p 0 23 r 2 0 39 the v e a p relationship was compared with the relationship between original drainage basin area a o and total eroded bank gully volume vol i e vol 1 71 a o 0 60 r 2 0 65 the importance of runoff generation from a drainage basin is shown by the positive correlation of linear headcut retreat and the runoff curve number cn representative for the conditions in the drainage basin high cn values tend to coincide with higher annual eroded volumes in the relationship between present drainage basin area a p and annual eroded volume v e but this effect was not observed in the relationship between original drainage basin area a o and total eroded bank gully volume vol stepwise multiple regression selected the relevant environmental parameters explaining annual eroded volume and linear retreat in both equations the present drainage basin area explained the largest part of the variation the cn was selected as another common parameter height of the headcut was the second most important variable explaining annual eroded volume indicating the role of energy transfers and undercutting at the headcut linear retreat was further explained by the average slope of the present drainage basin area representing the effect of decreasing transmission losses and increasing flow velocity with steeper catchment slopes and by the sand content decreasing the cohesion of the soil material promoting soil fall and headcut retreat spatial extrapolation of the measured volumetric retreat rate of 4 0 m 3 year 1 revealed that active bank gully heads contribute up to 6 of the sediment yearly filling up the puentes reservoir estimated gully ages i based on the ergodic principle and ii by linear extrapolation of actual gully retreat rates in the past range between 63 years and 1539 and between 64 and 1720 years respectively the high correlation between the gully ages estimated by the two methods is attributed to the fact that most gullies have not reached the evolutionary stage of significantly declining retreat rates since medium term gully retreat rates are more dependent on drainage basin area compared to the short term retreat rates obtained in this study the estimated gully ages represent maximum values assuming that present land use and climate conditions prevailed over the last two millennia

classic and new dating methods for assessing the temporal occurrence of mass movements abstract establishing landslide chronologies is essential both for understanding causes of mass movements as part of fundamental geomorphological research and for the assessment of landslide hazards as part of applied geomorphology we discuss the applicability of different methods for determining landslide chronologies frequencies and dynamics in relation to the type of material being dated sampling location and type of mass movement the emphasis is on the possibilities and limitations of the different dating methods established methods such as radiocarbon dating lichenometry and dendrochronology are briefly discussed the paper focuses however on 1 new analytical techniques like accelerator mass spectrometry ams thermally ionising mass spectrometry tims and laser fusion which have led to significant improvements of established dating methods and on 2 new dating methods like optically stimulated luminescence osl dating and alpha recoil track art dating

joint approach combining damage and paleoseismology observations constrains the 1714 a d bhutan earthquake at magnitude 8 0 5 the region of bhutan is thought to be the only segment of the himalayas not having experienced a major earthquake over the past half millennium a proposed explanation for this apparent seismic gap is partial accommodation of the india asia convergence further south across the shillong plateau yet the seismic behavior of the himalayan megathrust is unknown here we present historical documents from the region reporting on an earthquake in 1714 ad and geological evidence of surface rupture to constrain the latest large event in this area we compute various earthquake scenarios using empirical scaling relationships relating magnitude with intensity source location and rupture geometry our results constrain the 1714 ad earthquake to have ruptured the megathrust in bhutan most likely during a m7 5 8 5 event this finding reclassifies the apparent seismic gap to a former information gap and implies that the entire himalayan arc has a high level of earthquake potential

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

seismotectonics and crustal stress field in the kumaon garhwal himalaya abstract we present fault plane solutions of 94 well located small to moderate sized 1 5 ml 5 4 earthquakes which occurred in the kumaon garhwal himalaya during 2005 2008 using p wave polarity and body wave amplitudes these earthquakes show a mixture of thrust normal and strike slip type mechanism with a majority of thrust type most of the thrust earthquakes occur at a depth of 8 22 km in the main central thrust mct zone and the lower himalaya the spatial distribution of these earthquakes suggest that the strain resulting from the ongoing collision of the indian plate with the eurasian plate is being consumed by thrust fault movement mainly on the north dipping munsiari thrust and south dipping tons thrust the strike slip earthquakes are mainly observed in the lower himalaya as well as around the munsiari region in the mct zone the normal earthquakes are also observed in different parts of the kumaon garhwal himalaya and the gangetic plain their occurrence is attributed to the local structure s as well as the flexure of the indian plate stress tensor inversion of the calculated fault plane solutions indicates that the maximum compressive stress in the gangetic plain is n s directed and near vertical whereas in the kumaon garhwal himalaya it is near horizontal and nne ssw directed and correlating with the prevailing stress condition due to northward movement of indian plate

one dimensional reference velocity model and precise locations of earthquake hypocenters in the kumaon garhwal himalaya we report an optimum 1d velocity model of the kumaon garhwal himalaya based on analysis of 5000 seismograms generated at 50 digital broadband seismic stations in the region during april 2005 and june 2008 these include data from 385 local earthquakes with azimuth gaps of 180 each of which had a minimum of seven p and five s phase readings this velocity model was then used to map the locations of 1150 earthquakes 1 m 5 that occurred in the region a majority 75 of these earthquakes occurred in the upper 20 km of the crust largely above the main himalayan thrust and forms an 10 km wide band along the surface trace of the munsiari thrust however we also find another parallel band of earthquakes about 70 km to its southwest through the tehri dam in the lesser himalaya and a significant number 15 both in the tethys himalaya and within the flexed crust of the underthrusting indian plate beneath the ganga basin furthermore unlike the reported absence of seismicity in the lower crust of the nepal himalaya and its reappearance in the shallow mantle the kumaon garhwal himalayan crust is found to be seismically active throughout with no event reliably recorded in the shallow mantle of this region during the epoch of our seismic recording online material figures show constrains and distribution of data used in joint inversion and table shows p and s wave corrections obtained from travel time inversion

himalayan megathrust geometry and relation to topography revealed by the gorkha earthquake the himalayan mountain range has been the locus of some of the largest continental earthquakes including the 2015 magnitude 7 8 gorkha earthquake competing hypotheses suggest that himalayan topography is sustained and plate convergence is accommodated either predominantly on the main plate boundary fault or more broadly across multiple smaller thrust faults here we use geodetic measurements of surface displacement to show that the gorkha earthquake ruptured the main himalayan thrust fault the earthquake generated about 1 m of uplift in the kathmandu basin yet caused the high himalaya farther north to subside by about 0 6 m we use the geodetic data combined with geologic geomorphological and geophysical analyses to constrain the geometry of the main himalayan thrust in the kathmandu area structural analyses together with interseismic and coseismic displacements are best explained by a steep shallow thrust fault flattening at depth between 5 and 15 km and connecting to a mid crustal steeper thrust we suggest that present day convergence across the himalaya is mostly accommodated by this fault no significant motion on smaller thrust faults is required furthermore given that the gorkha earthquake caused the high himalayan mountains to subside and that our fault geometry explains measured interseismic displacements we propose that growth of himalayan topography may largely occur during the ongoing post seismic phase

microearthquake activity in some parts of the himalaya and the tectonic model abstract microearthquake data from temporary permanent networks in different parts of the himalaya shed new light on understanding the earthquake generating processes and their relation to tectonic models of the region the microearthquake activity in arunachal pradesh northeastern himalaya is found to be pronounced at the main boundary thrust mbt and to its south the subcrustal earthquakes depth 50 80 km occur much below the plane of detachment of the tectonic models proposed by seeber et al 1981 ni and barazangi 1984 the mbt is not the seismogenic fault the earthquakes are generated by strike slip movement on deep seated hidden faults transverse to the mbt the high seismic activity in the shillong plateau about 200 km south of the mbt in the northeast region is due to the influence of himalayan collision tectonics to the north and burmese arc subduction tectonics to the east the activity in the plateau is not directly related to the himalayan thrust belt or seismic belt these are mostly crustal earthquakes depth 10 30 km and are caused by local active faults lineaments in the eastern himalaya in the sikkim and darjeeling area the seismic activity is found to be clustered mostly to the north of the mbt the earthquakes occur at a depth range 0 50 km the majority of them occur below the detachment plane by thrust faulting in the central part in the nepal himalaya lateral variations of the seismic activity are observed which represent lateral segmentation of the mbt by transverse tectonic features in the western himalaya however the tectonic models fit well with the microearthquake data in the himachal pradesh of the western himalaya the microearthquakes are mostly recorded in the mbt zone and the hypocentres depth 0 20 km are confined above the plane of detachment or on the basement thrust the earthquakes mostly occur to the south of the main central thrust mct which suggests that the mct is not seismogenic it is rather a dormant fault no single tectonic model explains the himalayan earthquakes

strong seismic coupling underneath garhwal kumaun region nw himalaya india abstract no great earthquake has occurred in the garhwal kumaun region of nw himalaya in the past 500 years or more we report results of continuous gps measurements from 28 sites from the region to suggest that the convergence rate in this part of the himalaya is about 18 mm yr which is leading to strain accumulation in the region the main himalayan thrust mht in the frontal part of the himalaya under the outer and southern lesser himalaya is strongly coupled for a width of about 85 km the midcrustal ramp where earthquakes of himalayan seismic belt occur exhibits low coupling strong coupling on the mht beneath the outer and lesser himalaya is homogeneous except in the very shallow updip part of the mht subduction of sediments of the indo gangetic plains or the delhi hardwar ridge does not seem to influence coupling a high rate of strain accumulation which has continued for more than 500 years on a strongly coupled mht makes this one of the most earthquake vulnerable segments of the himalayan arc

timing and mechanisms of central himalayan exhumation discriminating between tectonic and erosion processes the ability to deduce exhumation mechanisms from thermochronological data is hampered by the fact that assumptions on the thermal state of the lithosphere have to be made additional argumentation is generally required to discriminate between erosion controlled and tectonically induced exhumation this problem can be overcome by studying the spatial distribution of zircon and apatite u th he and fission track data in this work the variation of four different low temperature isotopic systems generating age trends along a sampling line is used to infer mechanisms of quaternary exhumation in the central high himalayan metamorphic belt observed zircon age trends with southwards increasing cooling ages from 0 5 to 1 7 ma are attributed to tectonically induced exhumation the uniform apatite cooling ages clustered c 0 5 ma are attributed to erosion

structural control on downdip locking extent of the himalayan megathrust author s lindsey eo almeida r mallick r hubbard j bradley k tsang llh liu y burgmann r hill em abstract 2018 the authors geologic reconstructions of the main himalayan thrust in nepal show a laterally extensive midcrustal ramp hypothesized to form the downdip boundary of interseismic locking using a recent compilation of interseismic gps velocities and a simplified model of fault coupling we estimate the width of coupling across nepal using a series of two dimensional transects we find that the downdip width of fault coupling increases smoothly from 70 to 90 km in eastern nepal to 100 110 km in central nepal then narrows again in western nepal the inferred coupling transition is closely aligned with geologic reconstructions of the base of the midcrustal ramp in central and eastern nepal but in western nepal the data suggest that the location is intermediate between two proposed ramp locations the result for western nepal implies either an anomalous coupling transition that occurs along a shallowly dipping portion of the fault or that both ramps may be partially coupled and that a proposed crustal scale duplexing process may be active during the interseismic period we also find that the models require a convergence rate of 15 5 2 mm year throughout nepal reducing the geodetic moment accumulation rate by up to 30 compared with earlier models partially resolving an inferred discrepancy between geodetic and paleoseismic estimates of moment release across the himalaya

the vendian succession of northeastern spitsbergen petrogenesis of a dolomite tillite association abstract the sedimentary record of late precambrian time is magnificently displayed in the highland snowfields of northeastern spitsbergen svalbard vendian strata are represented essentially by the polarisbreen group which consists mostly of dolostone and includes two dolomitic glacial units the oldest sediments in the polarisbreen group compose the elbobreen formation c 400 m which is divided into four laterally persistent members the lower carbonate member e1 125 m contains a distinctive basal dark grey limestone with microspar filled synaeresis cracks suggested to be of lagoonal origin and associated with minor dolostone shale and chert higher parts of the member are dominantly dolostone partly stromatolitic with some shale and sandstone shallow subtidal to intertidal deposition is indicated by the dominance of intraclastic lithologies and relics of anhydrite penecontemporaneous dolomite is partially overprinted by microsparry dolomite thought to be of groundwater origin the redefined petrovbreen member e2 consists of diamictite and other detrital dolostone pronounced thickness variations 2 40 m are thought to be original depositional features the member represents the deposits of a short glacial period in which the following depositional processes are inferred lodgement massive diamictite subaqueous meltout massive and bedded diamictite ice rafting lithologies bearing dropstones and possibly also diamictite redeposition by sediment gravity flows some diamictite and conglomerate rhythmite and shale current winnowing thin tabular conglomerate subaerial or subaqueous meltwater action channelled conglomerate and sandstone periglacial shrinkage diamictite wedge fillings the macdonaldryggen member e3 230 m is a monotonous succession of shaly dolostone of lagoonal origin it grades up into the slangen member e4 25 m which consists of subtidal to intertidal dolarenite with anhydrite relics succeeded by fenestral dolostone that was fractured and cemented by saline groundwaters in an emergent environment the wilsonbreen formation 160 m represents a return to glacial deposition but this time longer lasting and with substantial extra basinal material represented the gropbreen member w1 28 107 m and the ormen member w3 44 139 m consist dominantly of dolomitic diamictite with subordinate conglomerate and sandstone and are separated by a middle carbonate member w2 3 30 m which contains distinctive rhythmitic and stromatolitic limestone as well as sandstone the same depositional processes can be recognised as in the petrovbreen member but the wilsonbreen formation is overall of somewhat more continental aspect lower proportion of rhythmite and dropstone structures in addition there are basal breccia and crack fillings formed by frost shattering of the underlying cemented dolostone tabular sandstone thought to be formed by wave reworking of outwash a striated terrestrial cobble pavement supraglacially derived breccia horizons periglacial wedges filled by sand and the w2 assemblage of possible lacustrine origin the dracoisen formation 525 m represents an abrupt return to non glacial conditions an upward deepening wave dominated succession of pure dolostone d1 20 m and impure dolostone d2 105 m is succeeded by offshore black shale d3 150 m and then by a very shallow water succession of evaporite lacustrine aspect with a dolostone containing evaporite relics d5 10 m separating dolomitic sandstone and shale d4 80 m and d6 150 m the contact with the transgressive cambrian sandstones above is poorly exposed deposition of the succession dominantly under marine conditions is inferred but it is difficult to rule out a lacustrine environment at any particular horizon this dolomite tillite association can be explained by penecontemporaneous and minor secondary dolomite formation in marginal environments with warm climatic indicators at some levels being sharply interrupted because of rapid climatic changes by glacial sediments containing abundant detrital dolomite since the latter sediments make up only 17 of the 1080m thick succession glacial conditions only occupied a small proportion of vendian time

structural and thermochronological studies of the almora klippe kumaun nw india implications for crustal thickening and exhumation of the nw himalaya

a device for measuring gully headwall morphology this paper describes a low cost device for measuring the three dimensional morphology of a gully headwall the device was designed to operate in a gully system with the following characteristics overhanging banks caused by a thick dense root mat retreat of the underlying unconsolidated sediments through small slab failures leading to a considerable variation in retreat rate at each point on the headwall and changes in the orientation of the headwall owing to changes in sediment properties and the topographical and hydrological controls of gully growth the device is used to measure a series of closely spaced vertical profiles of the headwall and the collected data are combined to draw a contour map showing the distance from the plane of the instrument to the headwall comparing maps for sequential times enables retreat rates for the diffferent proportions of the headwall to be quantified

assessment of soil losses by ephemeral gully erosion using high altitude stereo aerial photographs the objective of this study is to explore in a critical way the potential of high altitude stereo aerial photographs for the assessment of ephemeral gully erosion rates on 28 may 1995 an intensive rainfall event 30 mm h 1 during 30 min return period 3 years occurred in central belgium ephemeral gullies formed within an area of 218 ha study area 1 were mapped and measured both in the field and by high altitude aerial photos taken at the same time comparison of these two methods shows that if only one of the two surveying techniques had been used only 75 per cent of the total ephemeral gully length would have been detected so that the combination of aerial and field data leads in fact to the best possible determination of total gully length within the selected area a correction factor c is proposed so that the results of an ephemeral gully erosion survey based on high altitude stereo aerial photos can be adjusted for the undetected gullies next a sequential series of high altitude stereo aerial photographs taken in six different years was analysed in order to determine ephemeral gully erosion rates in three selected study areas study areas 2 3 and 4 selection criteria were chosen so that these three areas were similar to study area 1 and representative for the cultivated areas in central belgium where intense soil erosion regularly occurs ephemeral gullies were mapped and their total length was measured from the aerial photos using a mean gully cross section of 0 2635 m2 determined in study area 1 the average eroded volume is 1 89 m3 ha 1 in six months for study area 1 0 86 m3 ha 1 in six months for area 2 1 44 m3 ha 1 in six months for area 3 and 2 37 m3 ha 1 in six months for area 4 according to the correction factor c these mean ephemeral gully erosion volumes have to be increased by 44 per cent the ephemeral gully erosion rates based on high altitude stereo aerial photos correspond well with the results of other surveys carried out in the belgian loess belt copyright 1999 john wiley sons ltd

patterns and controls of gully growth along the shoreline of lake huron an empirical approach was used to examine the morphology and behaviour of gullies along the eastern shoreline of lake huron canada gully and watershed dimensions and percentage vegetation cover of a sample of 44 gullies were measured from aerial photographs between 1930 and 1992 gullies with larger watersheds had higher area growth rates larger gullies continue to expand over time while small gullies are more likely to become stable growth rates increased between 1955 and 1978 because of increased snowfall extreme flow events the extension of municipal drains and the use of subsurface drainage after 1970 efforts to rehabilitate gullies using drain pipes and check dams contributed to a decrease in gully growth rates 1997 john wiley sons ltd

assessing quaternary reactivation of the main central thrust zone central nepal himalaya new thermochronologic data and numerical modeling we study the recent dynamics of the central nepal himalaya focusing on possible reactivation of the footwall of the main central thrust which is marked by an abrupt topographic transition different tectonic mechanisms such as overthrusting of a major crustal ramp underplating or out of sequence thrusting have been suggested to explain the morphology and exhumation patterns in this area we present 25 new apatite fission track ages collected along a north south transect in central nepal as well as two age elevation profiles ages are consistently younger than 3 ma old in the main central thrust zone and increase continuously to 4 6 ma old in the south no jump in apatite fission track ages is observed across the topographic transition apparent exhumation rates from age elevation relationships vary from 0 46 0 13 0 09 km ma in the palung granite south of kathmandu to 4 4 4 8 1 5 km ma in the main central thrust zone the latter rate is probably overestimated by a factor of two due to topographic effects as shown by a new numerical model these strongly varying exhumation rates can be explained by overthrusting of a crustal ramp which exerts a primary control on age patterns and do not require out of sequence reactivation of thrusts in the main central thrust zone

characteristics and controlling factors of bank gullies in two semi arid mediterranean environments abstract bank gullies are gullies that are formed due to a height drop caused by a terrace or a river bank which develop by headward retreat in erodible hillslopes this study aims i to investigate the morphology of actively eroding bank gullies i e geometrical characteristics resulting from past erosion and active erosion processes shaping the gully and ii to find relationships with environmental site characteristics such as topographical parameters material properties and climate the ultimate goal is to identify the most important controlling factors of past and present bank gully erosion fifty five active bank gullies formed in different lithologies by various erosion processes have been selected in the guadalentin basin and the surroundings of guadix southeast spain for each bank gully site geometrical and topographical parameters of both the channel and the drainage basin were measured erosion features indicating activity at the gully head such as tension cracks plunge pools undercutting fluting piping and rill or sheet erosion on sloping side walls were mapped and samples were taken from distinct lithological layers that were considered to influence the type and intensity of erosion processes a relationship could be shown between the presence of piping and fluting and a number of material characteristics including particle size distribution dispersion behaviour and electrical conductivity on the other hand lithology appeared not to be a differentiating factor on gully development in the long run as expressed by the total eroded volume v this parameter was most strongly related to the drainage basin area in which the entire bank gully had been formed a o explaining 66 of the variance the relationship is v 1 75 a o 0 59 no significant difference was found between regression lines through sub datasets of different soil textural classes finally multiple regression was used to include both topographical parameters and material characteristics in an explanatory and or predictive equation for the total eroded bank gully volume the results of the analyses using the entire dataset including the sites in the guadalentin as well as in the guadix area have been compared with the results for the separate study areas differences are not only related to topographical and lithological characteristics but may also be the consequence of a different climate in the two areas

thrust geometries and deep structure of the outer and lesser himalaya kumaon and garhwal india implications for evolution of the himalayan fold and thrust belt the kumaon garhwal region of the himalaya lies near the center of the himalayan fold and thrust belt we have drawn two balanced cross sections 100 km apart through the outer and lesser himalaya the cross sections incorporate all the surface well log and earthquake seismic data currently available from the region two branch line maps showing trailing and leading branch lines and cutoff lines of the major thrusts in the region are also drawn the three dimensional deep structure of the outer and lesser himalaya is interpreted based on the balanced cross sections and the branch line maps deep structure of the higher and tethyan himalaya is extrapolated based on surface geology and is subject to revision as more surface and seismic data become available from these areas a sequential evolutionary model for the kumaon himalaya along the eastern pindari section is proposed according to this model the kumaon himalaya evolved by an overall forelandward progression of thrusting with some reactivation along the munsiari thrust mt the main boundary thrust mbt and the main central thrust mct we use structural stratigraphic and radiometric criteria to place time constraints on the motion of these thrusts earliest motion along the mbt may have occurred in early middle paleocene but the main episode probably started in late eocene and may still be continuing emplacement of the mt had occurred by middle late eocene whereas the mct shows activity around 20 ma thus exhibiting break back thrusting with respect to the mt shortening estimates are obtained from the pindari section minimum shortening in the sedimentary thrust sheets of the outer and lesser himalaya is 161 km or 65 as a first approximation we have also restored the crystalline sheets in order to obtain shortening estimates for the entire himalaya minimum shortening for the himalaya after restoring the mct sheet varies from 354 76 to 421 km 79 these estimates were further combined with published data from the area between the mct sheet and the indus tsangpo suture zone itsz minimum shortening between the indo ganga foreland and the itsz thus obtained lies in the range 687 754 km or 69 72 we compare our shortening estimates with those available from the pakistan and nepal himalaya

modeling of the temperature sensitivity of the apatite u th he thermochronometer apatite u th he apparent ages will generally reflect residence for extended periods at temperatures where helium is neither quantitatively retained nor lost by diffusion to characterize the response of apatite he ages to thermal histories involving partial he retention we explored solutions to the he production diffusion equation under thermally static conditions the analytical solution to this equation coupled with published diffusivity data demonstrates that the zone of partial he retention extends from about 40 c to 85 c this zone lies at temperatures 35 c cooler than the analogous fission track partial annealing zone he ages within the partial retention zone ultimately achieve a balance between he production and loss yielding a steady state age both the ultimate age and the time it takes to achieve this age are temperature dependent for example an apatite held at 75 c equilibrates to an age of 2 ma after 17 myr regardless of whether equilibrium is approached from a higher or a lower initial he age for representative dynamic thermal histories we evaluated apatite he ages using a numerical solution to the ingrowth diffusion equation the results illustrate the sensitivity of he ages to various geologic histories and are useful for understanding he age elevation relationships and for testing time temperature paths derived from apatite fission track length distributions in addition although he diffuses rapidly from apatite at shallow crustal temperatures modeling of ambient temperature fluctuations indicates that he ages are nearly unaffected by surficial processes

exhumation of the central wasatch mountains utah 2 thermokinematic model of exhumation erosion and thermochronometer interpretation 1 the wasatch fault is a 370 km long normal fault in utah that marks the boundary between the stable colorado plateau to the east and the extending basin and range to the west understanding the thermokinematic evolution of this fault can provide insights into intracontinental extensional tectonics and deformation processes in other rift zones e g east africa rift transantarctic mountains we explore the thermokinematics of footwall exhumation and erosion in the cottonwood intrusive belt of the central wasatch mountains emphasis is placed on using low temperature thermochronometers to quantify 1 the spatial and temporal variability of exhumation and erosion rates 2 the geometry of footwall tilt 3 the fault dip angle and 4 the magnitude and duration of exhumation these processes are investigated using two dimensional 2 d thermal kinematic models coupled with cooling rate dependent kinetic models which predict exhumed apatite fission track aft and u th he ages the range of model parameters considered includes footwall exhumation and erosion rates at the fault between 0 2 and 2 0 mm yr 1 footwall tilt hinge positions between 15 and 40 km distance from the fault a single planar normal fault with dip angles of 45 and 60 and exhumation magnitudes of up to 15 km at the fault simulations include the formation of a low thermal conductivity sedimentary basin and erosion of heat producing layers erosion maintains a constant topographic profile the kinematic and exhumation history of the wasatch mountains is investigated by comparing model predicted thermochronometer ages to observed aft zft and u th he ages predicted and observed ages are compared using a reduced chi square analysis to determine a best fit kinematic model for the wasatch mountains the preferred model includes exhumation occurring on either a 45 or 60 dipping fault a footwall hinge located a minimum of 20 25 km from the fault and a step decrease deceleration in the footwall exhumation rate at the fault from 1 2 to 0 8 mm yr 1 at around 5 ma the model also suggests an exhumation duration of 12 myr 2 myr index terms 1035 geochemistry geochronology 8010 structural geology fractures and faults 8015 structural geology local crustal structure 8109 tectonophysics continental tectonics extensional 0905 8130 tectonophysics heat generation and transport keywords exhumation erosion normal faults numerical modeling heat flow thermochronometers

thrusting and back thrusting as post emplacement kinematics of the almora klippe insights from low temperature thermochronology abstract crystalline klippen over the lesser himalayan sequence lhs in the kumaon and garhwal regions of nw himalaya are the representative of southern portion of the main central thrust mct hanging wall these were tectonically transported over the juxtaposed thrust sheets berinag tons and ramgarh of the lhs zone along the mct these klippen comprise of nw se trending synformal folded thrust sheet bounded by thrusts in the south and north in the present study the exhumation histories of two well known klippen namely almora and baijnath and the ramgarh thrust sheet in the kumaon and garhwal regions vis a vis himalayan orogeny have been investigated using apatite fission track aft ages along a 60 km long orogen perpendicular transect across the almora klippe and the ramgarh thrust sheet 16 aft cooling ages from the almora klippe and 2 from the ramgarh thrust sheet have been found to range from 3 7 0 8 to 13 2 2 7 ma and 6 3 0 8 to 7 2 1 0 ma respectively from lhs meta sedimentary rocks only a single aft age of 3 6 0 8 ma could be obtained three aft ages from the baijnath klippe range between 4 7 0 5 and 6 6 0 8 ma aft ages and exhumation rates of different klippen show a dynamic coupling between tectonic and erosion processes in the kumaon and garhwal regions of nw himalaya however the tectonic processes play a dominant role in controlling the exhumation thrusting and back thrusting within the almora klippe and ramgarh thrust sheet are the post emplacement kinematics that controlled the exhumation of the almora klippe combining these results with the already published aft ages from the crystalline klippen and the higher himalayan crystalline hhc the kinematics of emplacement of the klippen over the lhs and exhumation pattern across the mct in the kumaon and garhwal regions of nw himalaya have been investigated

the kumaun and garwhal lesser himalaya india part 2 thermal and deformation histories an integrated petrologic thermochronologic and numerical modeling study constrains the thermal evolution of the lesser himalayan sequence in the kumaun and garwhal regions of india south of the tons thrust peak metamorphic temperatures do not exceed 330 c on the northern side a transition toward higher temperatures adjacent to the main central thrust hanging wall is documented in the immediate footwall of the main central thrust peak temperatures average 550 c an inverted thermal field gradient of 30 c km beneath the vaikrita thrust is calculated an inverted thermal field gradient of 20 c km is also documented beneath a klippe of the main central thrust hanging wall 25 km south of the vaikrita thrust and a peak footwall temperature of 530 c is recorded close to the shear zone at the base of the klippe the mechanism for thermal metamorphism in the lesser himalayan sequence is interpreted to be conduction of heat from the main central thrust fault and or hanging wall to the footwall a localized thermal field gradient is also associated with the tons thrust the 40 ar 39 ar thermochronology reveals that the exposed rock in the kumaun and garwhal lesser himalaya underwent cooling below the closure temperature tc for white mica at different times in the late tertiary the proximal footwall of the munsiari thrust experienced cooling below the white mica tc at ca 8 5 ma south of the munsiari thrust in the proximal footwalls of the chaukori and askot klippen muscovites ages are ca 11 5 ma 3 ma older than samples to the north the age differences in samples from northern and southern exposures are interpreted to document cooling related to thermal relaxation following passage of the main central thrust hanging wall atop the lesser himalayan sequence results of thermal modeling achieve good fits to the data when scenarios involve an early miocene phase of overthrusting of a hot hanging wall over a downgoing footwall followed by the initiation of a duplex within lesser himalayan sequence rocks

geometry and internal characteristics of archaean submarine channel deposits pilbara block western australia abstract well preserved submarine fan deposits of early archaean age ca 3 3 ga occur in the pilbara block of western australia channel interchannel lobe and basin plain deposits are recognizable in two facies associations termed respectively conglomerate sandstone shale and sandstone shale unitary upper fan channel deposits are recognizable in the conglomerate sandstone shale facies association the channel deposits consist of inverse to normal graded and graded stratified resedimented conglomerates and sandstones these facies accumulated respectively in the thalweg and on the adjacent terrace of the upper fan channel and grade laterally into thin bedded cde turbidites of levee origin the coarse channel facies are enclosed within interchannel shales iron formations and carbonates the morphology of midfan channel deposits is strongly influenced by grain size reflecting different provenances where conglomeratic in the west these deposits are laterally continuous tabular bodies consisting of scour based graded stratified conglomerate sandstone couplets grading predominates but associated horizontal and cross stratification indicates periodic late stage traction reworking these midfan sediments are considered to have accumulated in shallow laterally switching channels on a braided suprafan arenaceous midfan channel deposits occur in the southeast and comprise narrow lenses of amalgamated bouma a or ab sandstones displaying an upward decrease in bed thickness sedimentation took place in laterally confined channels within cohesive argillaceous banks he enclosing interchannel shales contain abundant overbank sandstones often with complete bouma sequences both midfan channel types grade basinwards into upward coarsening basin plain to lobe deposits basin plain shales and iron formations are considered to be analogues of holocene hemipelagic and pelagic sediments

dendrogeomorphological analysis of mass movement a technical note on the research method dating of mass movement events by examining the course of eccentricity of the annual rings of trees inclined as a result of these movements can be a problem in the case of multiple inclined trees showing compound trunk curvature and complex reaction wood these problems however can be solved when sampling of ring width cores is based on accurate analysis of the form of the trunk

the kumaun and garwhal lesser himalaya india part 1 structure and stratigraphy our understanding of the geologic evolution of the himalaya remains incomplete particularly in regard to structural and geochronologic details of the proterozoic paleozoic lesser himalayan sequence we conducted an integrated field mapping geochronological study and geochemical analysis of the lesser himalayan sequence strata in the kumaun and garwhal himalaya of nw india 78 00 80 30 e structural observations reveal a systematic change in deformation styles from lower to higher structural levels in the main central thrust footwall in the south and at lower structural levels the main central thrust footwall is characterized by parallel folding and sparse development of axial cleavage quartz microstructures indicate that deformation occurred at temperatures below 350 c in contrast in the north and at higher structural levels close to the main central thrust deformation is characterized by replacement of original bedding the development of penetrative cleavage and schistosity locally folds are tight in places isoclinal and overturned the corresponding quartz microstructures indicate that deformation occurred above 350 c dating of detrital zircons from lesser himalayan sequence metasedimentary units and igneous zircons from schistose gneisses throughout the lesser himalayan sequence allow refinements to the stratigraphic framework first unlike has been observed in western nepal immediately west of our study area u pb zircon dating suggests the absence of paleoproterozoic strata in the ramgarh thrust hanging wall this suggests that the thrust cuts upsection laterally along strike second u pb detrital zircon dating suggests that metasedimentary strata in the ramgarh thrust hanging wall are correlative with basal units of the outer lesser himalayan sequence removing the necessity that the ramgarh thrust hanging wall was allochthonous with respect to its footwall lesser himalayan sequence units schistose gneisses with u pb ages of ca 1850 ma are older than lesser himalayan sequence units in the area suggesting that they are thrust emplaced lesser himalayan sequence basement we conclude that the ramgarh thrust is an out of sequence thrust postdating a folding event in its footwall the earlier proposal that neoproterozoic cambrian lesser himalayan sequence strata are the southern extension of the tethyan himalayan sequence requires that the tons thrust which separates the distal and proximal facies of the lesser himalayan sequence be a major south directed structure with a slip magnitude of 50 100 km

initiation and evolution of gullies along the shoreline of lake huron over one hundred gullies are deeply incised into algonquin bluff along the eastern shoreline of lake huron aerial photographs between 1930 and 1992 were used to measure temporal changes in area and length of a sample of forty four gullies regression analysis shows that gully area and length have increased in a linear fashion and that gully initiation occurred in the nineteenth century gully initiation coincides with deforestation and settlement of the area surface drainage was redirected into drainage ditches concentrating the flow and enhancing gully erosion natural processes associated with climatic fluctuations are probably insufficient to cause gully initiation but may contribute to ongoing gully expansion

proterozoic sedimentation and pan african geodynamic development in the himalaya abstract the purana or proterozoic lower cambrian continental margin sedimentary succession of the lesser himalaya comprises three lithological divisions a lower argillo arenaceous group a middle carbonate succession and an upper argillo calcareous assemblage the poorly sorted basal sediments consisting of wacke slate alternations of the lower group were emplaced by currents including turbidity currents which in the early stage flowed northwards from the aravalli and satpura mountains of peninsular india lenticular deposits of diamictite within the flysch succession represent submarine slides penecontemporaneous basaltic lavas and associated tuffs interbedded with shallow water arenites making up the bulk of the upper part of the lower group were related to rifting of the basins the overlying dolomites and dolomitic limestones were laid down on a very shallow stable shelf and are characterised by columnar branching stromatolites and lenticular units of crystalline magnesite and associated talc lenticular diamictites towards the top of the upper group of slates and limestone are harbingers of tectonic movements culminating towards the end of the early cambrian in an upheaval which abruptly terminated sedimentation throughout the lesser himalaya and peninsular india and caused a pronounced interruption of sedimentation in the tethyan domain in the northern himalaya the cambro ordovician 500 25 ma granites intruding the lesser himalayan thrust sheets of lower proterozoic metamorphic rocks and the upwarped northern front of the himalaya signify an important tectonic event that terminated the purana proterozoic lower cambrian sedimentation in the indian subcontinent this seems to be related to the tectonic movements that occurred towards the close of the late proterozoic or early cambrian

soft sediment deformation structures and their implications for late quaternary seismicity on the south tibetan detachment system central himalaya uttarakhand india abstract the south tibetan detachment system stds defines the lithological and tectonic boundary between the higher himalayan crystallines and the tethyan sedimentaries earlier studies have suggested that the stds has been dormant since its inception during the miocene along with the main central thrust mct however recent studies indicate that the stds was active during the pleistocene holocene period we provide additional support for this more recent activity based on the occurrence of seismically induced soft sediment deformation structures ssds preserved in relict lake sediments in the dhauli ganga gori ganga and kali ganga river basins of the central himalaya the relict lakes are located on the hanging wall of the stds an optical chronology of the lake sediments brackets the seismically induced ssds between 20 ka and 11 ka with a major seismic event of magnitude 6 5 occurring between 17 ka and 13 5 ka since mct and stds are considered to be the coupled structures our observation supports the hypothesis that the stds is providing accommodation space to the strain gradient arising due to the north south compression in the himalaya during the late quaternary

palaeoclimate implications from deep drilling of neoproterozoic strata in the officer basin and adelaide rift complex of australia a marine record of wet based glaciers abstract two prominent episodes of neoproterozoic glaciation in australia are recorded in the cryogenian sturtian

spatial distribution of gully head activity and sediment supply along an ephemeral channel in a mediterranean environment abstract in this study we examined the factors that control the spatial distribution of bank gully heads along a reach of an ephemeral river rambla salada in an area threatened by desertification in southeast spain the activity of 458 gully heads was assessed in the field by pre defined criteria such as sharp edges presence of a plunge pool tension cracks recent deposited sediments flow marks and vegetation re growth the results showed that land use has a significant impact on bank gully head activity recent land use changes involving the extension of almond cultivation appears to intensify bank gully head activity also lithology has a clear impact on the bank gully extension it was further investigated whether the gully heads were important sediment sources that contributed to reservoir sedimentation the density of very active bank gully heads along the study reach was one per 17 m of channel length average annual retreat volumes were derived from measurements at 46 active gully heads 4 0 m3 y 1 by selecting all the channel sections in the catchment of the puentes reservoir with a similar pattern of bank gullies using aerial photographs an estimate of basin wide sediment production of bank gully heads was established it was estimated that the retreat of active bank gully heads alone in the 12 760 ha study area representing 12 of the total catchment area of the puentes reservoir produced 6 of the sediment filling up the reservoir considering that the sediment is also derived from other sources such as channel walls channel beds and hillslopes the overall conclusion is that bank gully expansion in southeast spain is a major point source of sediment and therefore a major process of land degradation

mountain building in the nepal himalaya thermal and kinematic model we model crustal deformation and the resulting thermal structure across the nepal himalaya assuming that since 20 ma shortening across the range has been primarily taken up by slip along a single thrust fault the main himalayan thrust mht fault and that the growth of the himalayan wedge has resulted mainly from underplating and to the development of a duplex at midcrustal depth we show that this process can account for the inverse thermal metamorphic gradient documented throughout the lesser himalaya lh the discontinuity of peak metamorphic temperatures across the mct as well as the distribution of age of exhumation across the range this study suggests that the metamorphic evolution of the range over about the last 20 million years is compatible with the kinematics of recent crustal deformation deduced from morphotectonic and geodetic studies

characterizing the main himalayan thrust in the garhwal himalaya india with receiver function ccp stacking abstract we use common conversion point ccp stacking of ps receiver functions to image the crustal structure and moho of the garhwal himalaya of india our seismic array of 21 broadband seismometers spanned the himalayan thrust wedge at 79 80 e between the main frontal thrust and the south tibet detachment in 2005 2006 our ccp image shows the main himalayan thrust mht the detachment at the base of the himalayan thrust wedge with a flat ramp flat geometry seismic impedance contrasts inferred from geologic cross sections in garhwal imply a negative impedance contrast velocity decreasing downward for the upper flat located beneath the lower himalaya and a positive impedance contrast velocity increasing downward for the ramp located beneath the surface trace of the munsiari thrust or mct i at the lower flat located beneath the higher himalaya spatially coincident measurements of very high electrical conductivities require the presence of free fluids and we infer a negative impedance contrast on the mht caused by ponding of these fluids beneath the detachment our seismic image indicates that the upper flat of the mht is 10 km below sea level and dips north at 2 connecting to a mid crustal ramp which is 10 km high and dips at 16 the lower flat is 20 25 km below sea level and dips at 4 the main central thrust mct appears as a negative impedance contrast dipping at 16 the moho is nearly horizontal at 35 45 km depth beneath the sub himalaya and lower himalaya deepening to 50 km or more beneath the higher himalaya this depth is 10 25 km shallower than in the nw indian himalaya and 5 10 km shallower than in central nepal requiring significant along strike variations in crustal thickness the observed thickness of subducted indian crust in garwhal is 20 28 km

development of gullies and sediment production in the black soil region of northeastern china abstract gully erosion is an important environmental hazard in the black soil region of northeastern china it is a primary sediment source in the region which needs appropriate soil conservation practices gully incision in rolling hills typical of this region was monitored using real time kinematic gps to assess the rates of gully development and the resultant sediment production from 2002 to 2005 gully heads in the study area retreated between 15 4 and 33 5 m giving an average retreat rate of 8 4 m yr 1 field measurements showed that total sediment production due to gully erosion during the three years ranged between 257 and 1854 m3 yr 1 which is equivalent to 326 to 2355 t yr 1 with gully head retreat accounting for 0 to 21 7 4 4 in average the sediment delivery ratio was especially high during the summer rainy season 56 in average sediment production by ephemeral gullies and permanent gullies was 1 5 times greater than that from surface erosion gully heads retreated faster in the spring freeze thaw period than in the summer the stage of gully development could be identified based on short term changes in the gully erosion rate

post emplacement kinematics and exhumation history of the almora klippe of the kumaun garhwal himalaya nw india revealed by fission track thermochronology tectonically transported crystalline thrust sheet over the lesser himalayan meta sedimentary zone along the main central thrust mct is represented by almora baijnath askot and chiplakot crystalline klippen the almora dadeldhura klippe in the kumaun garhwal and western nepal himalaya is the witness and largest representative of these crystalline klippen south of mct here we investigate the post emplacement kinematics and exhumation history of the almora klippe the newly derived zircon fission track zft ages combined with published apatite fission track aft 40ar 39ar ages from the almora dadeldhura klippe and ramgarh thrust sheet to quantify the temporal variation in cooling ages and exhumation rates using 1 d numerical modelling approach we calculate the transient exhumation rates with respect to different time intervals new zft cooling ages along 50 km long orogeny perpendicular transect across the almora klippe range between 13 4 0 6 and 21 4 0 9 ma published aft ages and 40ar 39ar ages from the almora dadeldhura klippe range 3 7 0 8 13 2 2 7 and 18 20 25 69 ma respectively aft ages reported from ramgarh thrust sheet range 6 3 0 8 7 2 1 0 ma in kumaun region and 10 3 0 5 14 4 2 2 ma in western nepal the linear age trend along with youngest zft age 14 ma close to the north almora thrust nat in its hanging wall suggests rapid uplift close to the nat due to its reactivation as back thrust the transient exhumation rates of almora klippe agree that the erosion rate was rapid 0 58 mma 1 close to the nat in its hanging wall and relatively slow 0 31 mma 1 close to the sat in its hanging wall during 15 11 ma we interpret that the fission track ages and transient exhumation rate pattern of crystalline klippen show a dynamic coupling between tectonic and erosion processes in the kumaun garhwal himalaya however the tectonic processes play the major role in controlling the exhumation pattern

crustal velocity structure and earthquake processes of garhwal kumaun himalaya constraints from regional waveform inversion and array beam modeling abstract in order to understand present day earthquake kinematics at the indian plate boundary we analyse seismic broadband data recorded between 2007 and 2015 by the regional network in the garhwal kumaun region northwest himalaya we first estimate a local 1 d velocity model for the computation of reliable green s functions based on 2837 p wave and 2680 s wave arrivals from 251 well located earthquakes the resulting 1 d crustal structure yields a 4 layer velocity model down to the depths of 20 km a fifth homogeneous layer extends down to 46 km constraining the moho using travel time distance curve method we then employ a multistep moment tensor mt inversion algorithm to infer seismic moment tensors of 11 moderate earthquakes with m w magnitude in the range 4 0 5 0 the method provides a fast mt inversion for future monitoring of local seismicity since green s functions database has been prepared to further support the moment tensor solutions we additionally model p phase beams at seismic arrays at teleseismic distances the mt inversion result reveals the presence of dominant thrust fault kinematics persisting along the himalayan belt shallow low and high angle thrust faulting is the dominating mechanism in the garhwal kumaun himalaya the centroid depths for these moderate earthquakes are shallow between 1 and 12 km the beam modeling result confirm hypocentral depth estimates between 1 and 7 km the updated seismicity constrained source mechanism and depth results indicate typical setting of duplexes above the mid crustal ramp where slip is confirmed along out of sequence thrusting the involvement of tons thrust sheet in out of sequence thrusting indicate tons thrust to be the principal active thrust at shallow depth in the himalayan region our results thus support the critical taper wedge theory where we infer the microseismicity cluster as a result of intense activity within the lesser himalayan duplex lhd system

an exceptionally thick upper proterozoic sturtian glacial succession in the mount painter area south australia the yudnamutana subgroup is a thick succession of upper proterozoic sturtian glacigenic rocks preserved in the yudnamutana trough in the northeastern part of the adelaide geosyncline in ascending order the subgroup comprises the fitton bolla bollana and lyndhurst formations the name hamilton creek member is proposed for a locally developed conglomeratic facies at the base of the fitton formation these rocks are interpreted as the products of two glacial advances the first is evidenced by the hamilton creek member which includes sediment gravity flows derived from subaqueous glacial outwash the fitton formation is composed mainly of basinal siltstones and mudstones with associated coarser grained rocks that are largely sediment gravity flows diamictites in the upper part of the formation signify the onset of a second glacial advance thick diamictites of the bolla bollana formation are interpreted as rainout deposits from floating ice derived from ice streams debouching from a steep and high hinterland into a fault controlled basin the lyndhurst formation is mainly fine grained rocks dropstones and sparse diamictites attest to the presence of some floating ice but some of the diamictites are probably mass flow deposits paleocurrent data from the yudnamutana subgroup indicate transport to the west northwest the sturtian glacigenic rocks are overlain by a transgressive shale stratigraphic similarities exist between the yudnamutana subgroup and thinner successions to the west these stratigraphic similarities probably reflect paleoclimatic changes the twice repeated sequence of diamictite followed by mudstone is attributed to two glacial advance retreat cycles local variations in thickness and stratigraphic succession are probably related to contemporaneous faulting

sequence stratigraphy and the interpretation of neoproterozoic earth history abstract the application of sequence stratigraphy to neoproterozoic successions is important for improving the resolution of time correlation within individual sedimentary basins and potentially at a global scale the methodology is illustrated in this paper by reference to two contrasting examples from the flinders ranges adelaide geosyncline of south australia where the younger part of the neoproterozoic to earliest cambrian succession 770 ma to 540 ma has been divided into thirteen unconformity bounded depositional sequences one of the most prominent sequence boundaries at or near the base of the wonoka formation is characterized by a series of buried canyons as much as 1 km deep high resolution sequence stratigraphic studies at umberatana syncline continue to support the view that the canyons were cut subaerially and filled by fluvial and shallow water sediments in contrast to the wonoka canyons sequence boundaries interpreted at the base of the nuccaleena formation seacliff sandstone and near the top of the abc range quartzite are relatively subtle with only limited evidence for erosion and valley incision four sequence boundaries at the level of the sturtian and marinoan varanger glacial deposits and in the vicinity of the precambrian cambrian boundary are thought to correlate with surfaces in the amadeus basin of central australia other prominent sequence boundaries including the wonoka canyons and surfaces within the upper part of the wonoka formation and at the base of the ediacara member of the rawnsley quartzite correspond with a relatively condensed section in the amadeus basin and their lateral persistence beyond the adelaide geosyncline is therefore difficult to evaluate given the lack of precision in biostratigraphy and isotope geochemistry in neoproterozoic rocks and in a marked departure from phanerozoic practice we recommend placement of a terminal proterozoic gssp at a sequence boundary a prime candidate in australia is the sequence boundary at the base of the nuccaleena formation seacliff sandstone immediately above the marinoan glacial rocks in the adelaide geosyncline and its likely correlative at or near the base of the gaylad sandstone in the amadeus basin

precursor seismicity foreshocks and aftershocks of the uttarkashi earthquake of october 20 1991 at garhwal himalaya abstract the uttarkashi earthquake m b 6 6 of october 20 1991 occurred in a complicated geological tectonic setting at the main central thrust mct zone of the himalaya the main shock was preceded by a precursory earthquake activity which continued for about eight years and then there was a quiescent period for about three years three foreshocks m 4 0 occurred 48 h before the main shock two aftershocks m 4 0 occurred within 12 h of the main shock which was then followed by another two aftershocks m 4 0 after about seven days on october 27 1991 the largest aftershock m 5 2 occurred within 12 h the aftershocks magnitude less than 4 0 continued for about two months and it decayed at a rate t 0 87 about 1000 earthquakes magnitude less than 1 0 and above were recorded by a closely spaced five station temporary microearthquake meq network out of these 124 aftershocks which occurred inside the network are located by homogeneous station method spatial variation of the aftershocks with time was observed fault plane solutions of the main shock and aftershocks indicate dominantly thrust faulting based on the hypocentral data depth estimate of the plane of detachment is made and a fault interaction model is presented the model shows that the main shock occurred at the juncture of mct zone plane of detachment and the basement thrust the north dipping uttarkashi fault a parallel fault at the mct zone has been activated by the tectonic stress generated due to relative movement of the tibetan plate over the indian plate

stratigraphy and sedimentology of sturtian glacigenic deposits in the western part of the north flinders basin south australia abstract the late proterozoic sturtian succession in the northern part of the adelaide geosyncline is disposed in a southward closing arcuate outcrop belt that is largely fault bounded on its southern margin on the west side the glacigenic portion of the sturtian succession is between 100 and 800 m thick a thin discontinuous basal breccia is present on the older rocks of the burra group this is followed by a locally developed diamictite with associated lenticular sandstones interpreted as a tillite and glacial outwash deposits respectively the succeeding sturtian units are much more widespread unit 2 is a mudstone dominated heterogeneous succession of siliciclastic rocks formed by traction currents gravity flows and rain out from floating ice a second diamictite unit 3 is massive in the southeasterly part of the study area near the town of copley but is stratified and heterogeneous in an area to the northwest this diamictite is probably a marine deposit formed in the south by rapid rain out from floating ice and in the north by a variety of processes that largely reworked the glacigenic sediment the topmost unit 4 is also heterogeneous and resulted from the interplay of gravity flows traction currents and ice rain out palaeocurrents indicate a dominantly southeasterly transport but some herringbone cross bedding suggests tidal activity dolostones are present in unit 4 and stromatolitic bioherms were noted in the basal diamictite in this region the sturtian succession is considered to be the product of glaciation centred to the west and north feeding into an elongate basin here termed the north flinders basin palaeocurrent data and thickness changes suggest that the basin may have opened to the east in late proterozoic time this basin may have been separated from the main part of the adelaide geosyncline to the southeast by the shallow to emergent central flinders zone

plio plistocene in sequence thrust propagation along the main central thrust zone kumaon garhwal himalaya india new thermochronological data abstract the kumaon and garhwal himalayas nw india have similar geologic tectonic topographic and precipitation pattern however low temperature thermochronological age pattern varies significantly along the strike as well as across the strike of major faults here we interpret the new set of thermochronological age data across the strike of major faults namely vaikrita thrust vt munsiari thrust mt berinag thrust bt and the baijnath nappe along pindari valley in the kumaon garhwal himalaya in the present work 18 new apatite fission track aft ages of samples collected along a north south transect have been reported ages in the hanging wall of vt which range from 2 1 0 2 to 4 2 0 7 ma have been found to be becoming younger linearly with distance from north to the vt this trend crosses the vt with significant jump in ages in the south of the vt ages are lying between 0 3 0 1 and 3 9 0 8 ma and show linear variation with distance from the vt to bt no significant jump in ages across the mt is observed and the linear trend of younging southward is continuing till the bt the break and displacement in age pattern with youngest ages close to thrusts possibly indicate progressive late thrust movement it reflects sequential uplift and cooling towards the south from the vt to bt which is consistent with an in sequence style of thrust propagation we compare our new data to the published thermochronological data from its adjacent traverses along the goriganga and dhauliganga valleys 25 km away from the present traverse towards east and west respectively in the kumaon garhwal himalaya in order to understand potential along strike variations in the kinematics our observations indicate a dynamic coupling between tectonic and surface processes in the garhwal kumaon himalaya and support that the geometry of crustal scale faults and their associated kinematics control exhumation pathways of rocks

a method for dendrochronological assessment of medium term gully erosion rates abstract a method based on dendrochronology to estimate gully erosion rates was developed as an alternative of traditional methods for assessing medium term gully retreat rates such as field monitoring of headcuts or aerial photo interpretation of gully retreat the method makes use of trees or parts of a tree affected by gully erosion revealing information on the history of the erosion process by datable deviations of their normal growth pattern hence defined as datable objects these include roots exposed by erosion browsing scars made by ungulates on exposed roots or on above ground parts of fallen trees exposed and dead root ends root suckers stems branches and leading shoots of fallen trees and a sequence of trees within a gully the method is based on the differentiation between three main conditions depending on the relation between the dynamics of the datable object part of the tree and the development of the gully the first condition implies that the datable object was created before erosion of the gully volume to be dated e g exposed tree roots according to the second condition the datable object developed as an immediate consequence of the erosion event e g growth reactions of a fallen tree the third condition implies that the datable object was created some time after the erosion event took place e g trees colonising the gully bed each principle has consequences for the accuracy and the correct interpretation of the estimated erosion rate i e whether the true erosion rate is underestimated exact or overestimated in spite of methodological limitations and dendrochronological dating problems the method was successfully applied in southeast spain conservative estimations of gully head retreat rate resulted in an average medium term 3 46 years value of 6 m3 year 1 n 9 for gully sidewall processes the average minimum erosion rate per unit sidewall length amounted 0 1 m3 year 1 m 1 n 9 a strong correlation was found between the headcut retreat rate vm ortho m3 year 1 and the drainage basin area a m2 of the gullies expressed by vm ortho 0 02a0 57 r2 0 93 n 9 comparing the findings from this study with those obtained by short term headcut retreat monitoring suggests a high reliability of the estimated retreat rates supporting the applicability of the developed dendrochronological method

fabric development during shear deformation in the main central thrust zone nw himalaya india abstract quartz microfabrics and associated microstructures have been studied on a crustal shear zone the main central thrust mct of the himalaya sampling has been done along six traverses across the mct zone in the kumaun and garhwal sectors of the indian himalaya the mct is a moderately north dipping shear zone formed as a result of the southward emplacement of a part of the deeply rooted crust that now constitutes the central crystalline zone of the higher himalaya over the less metamorphosed sedimentary belt of the lesser himalaya on the basis of quartz c and a axis fabric patterns supported by the relevant microstructures within the mct zone two major kinematic domains have been distinguished a noncoaxial deformation domain is indicated by the intensely deformed rocks in the vicinity of the mct plane this domain includes ductilely deformed and fine grained mylonitic rocks which contain a strong stretching lineation and are composed of low grade mineral assemblages muscovite chlorite and quartz these rocks are characterized by highly asymmetric structures microstructures and quartz c and a axis fabrics that indicate a top to the south sense that is compatible with south directed thrusting for the mct zone an apparently coaxial deformation domain on the other hand is indicated by the rocks occurring in a rather narrow belt fringing and structurally above the noncoaxial deformation domain the rocks are highly feldspathic and coarse grained gneisses and do not possess any common lineation trend and the effects of simple shear deformation are weak the quartz c axis fabrics are symmetrical with respect to foliation and lineation moreover these rocks contain conjugate and mutually interfering shear bands feldspar quartz porphyroclasts with long axes parallel to the macrosopic foliation and the related structures microstructures suggesting deformation under an approximate coaxial strain path on moving towards the mct the quartz c and a axis fabrics become progressively stronger the c axis fabric gradually changes from random to orthorhombic and then to monoclinic in addition the coaxial strain path gradually changes to the noncoaxial strain path all this progressive evolution of quartz fabrics suggests more activation of the basal rhomb and a slip systems at all structural levels across the mct