calcic amphibole equilibria and a new amphibole plagioclase geothermometer there is currently a dearth of reliable thermobarometers for many hornblende and plagioclase bearing rocks such as granitoids and amphibolites a semi empirical thermodynamic evaluation of the available experimental data on amphibole plagioclase assemblages leads to a new thermometer based on the aliv content of amphibole coexisting with plagioclase in silica saturated rocks the principal exchange vector in amphiboles as a function of temperature in both the natural and experimental studies is left na square 1 right a left alsi 1 right t1 we have analysed the data using 3 different amphibole activity models to calibrate the thermometer reactions 1 edenite 4 quartz tremolite albite 1 2 pargasite 4 quartz hornblende albite 2 the equilibrium relation for both 1 and 2 leads to the proposed new thermometer t frac 0 677p 48 98 y 0 0429 0 008314 ln k and k left frac si 4 8 si right x ab plag where si is the number of atoms per formula unit in amphiboles with p in kbar and t in k the term y represents plagioclase non ideality rtln ab from darken s quadratic formalism dqf with y 0 for xab 0 5 and y 8 06 25 5 1 xab 2 for xab 0 5 the best fits to the data were obtained by assuming complete coupling between al on the t1 site and na in the a site of amphibole and the standard deviation of residuals in the fit is 38 c the thermometer is robust to ferric iron recalculation procedures from electron probe data and should yield temperatures of equilibration for hornblende plagioclase assemblages with uncertainties of around 75 c for rocks equilibrated at temperatures in the range 500 1100 c the thermometer should only be used in this temperature range and for assemblages with plagioclase less calcic than an92 and with amphiboles containing less than 7 8 si atoms pfu good results have been attained on natural examples from greenschist to granulite facies metamorphic rocks as well as from a variety of mafic to acid intrusive and extrusive igneous rocks our analysis shows that the pressure dependence is poorly constrained and the equilibria are not suitable for barometry

paraglacial rock slope stability glaciation and deglaciation along with their associated climatic and non climatic processes modify slope stresses and influence slope stability paraglacial slope failures are those that are a part of or influenced by the transition from glacial conditions to non glacial conditions gravitational failure of rock slopes is a primary and dominant process of slope evolution in mountainous terrain and is the subject of this paper which 1 reviews the approaches taken for researching paraglacial rock slope failure patterns and processes 2 summarises the spatial and temporal patterns of post glacial failures 3 assesses the factors influencing slope stability during glaciation and deglaciation 4 explores some of the applications of paraglacial research and 5 highlights some of the outstanding issues to be resolved and provides recommendations for terminology relating to paraglacial slope processes

lidar and 2d electrical resistivity tomography as a supplement of geomorphological investigations in urban areas a case study from the city of wroclaw sw poland in urbanized areas particularly in lowland terrains and floors of large river valleys the natural land configuration is often hard to recognize due to a long history of human activity accordingly archaeological works in cities which supply knowledge on settlement conditions are usually accompanied by geological and geomophological research lately data from light detection and ranging lidar have become a valuable source of information on urban land configuration geophysical methods are also becoming increasingly popular in background studies the paper presents a method of using and linking these sources of spatial information about landforms in such areas the main aim is to identify to what extent these complementary sources of data and the proposed method can be used in such a specific environment to reconstruct natural buried terrain morphology the city of wroclaw in central europe serves as an example to this end geomorphometric studies were conducted with the use of digital elevation models dems based on lidar scanning and derivated land surface parameters saga wetness index channel network base level and altitude above channel network the study also involved determining morphological edges and measurements of the meanders of the odra as well as expanding information on the spatial distribution of alluvia and the structure of slope breaks to this end geophysical measurements were conducted using the two dimensional electrical resistivity tomography method additionally five typical sequences of man made ground present within the perimeter of the city were distinguished as a result a map of the main landforms of wroclaw is presented finally we argue that although high resolution dem and derivate land surface parameters are very useful in terrain analysis places with thick man made ground or strongly levelled areas must be recognized by geoarchaeological excavations or geological bore holes the geophysical survey is useful to identify buried morphological edges and older relief elements in open areas

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

are granitic intrusions scale invariant published length l and thickness t data on 135 laccolith and 21 granite intrusions define power law relationships of the form l kt a typical of systems exhibiting scale invariant fractal behaviour both data sets are characterised by an exponent a 1 0 88 0 1 for laccoliths and 0 80 0 20 for plutons that reflects an inherent preference for scale invariant tabular sheet geometries these power law size relationships can be explained in mechanical terms by the need for an incoming magma sheet to travel laterally some distance before vertical thickening can occur sheet thickness is a function of available magma pressure which for an intrusion fed by a feeder dyke is proportional to the vertical magma transport distance

seismic site amplification induced by topographic irregularity results of a numerical analysis on 2d synthetic models abstract this study concerns the evaluation of seismic site effects and their relation to the local topographical characteristics of a slope the seismic amplification sa on the free surface is calculated by a numerical model using the finite elements fe method synthetic models by utilized in the fe analysis represent a slope with an inclination ranging from 10 to 41 at the crest and valley of the slope the models were considered horizontal and indefinite the site effects were calculated on the free surface in several nodal points the input motion used in the analysis was a sv seismic wave with variable frequency between 0 5 and 32 hz the seismic site analysis confirmed that in absence of sediments ground motion is more amplified at the upper slope break than in other points of the model in regard to seismic amplification vs the frequency we can affirm that seismic amplification reaches its maxima in the band 4 16 hz and with slope angle value computed at the highest degree it is also clear that a nonlinear seismic amplification response in the crest and valley zone while sa would seem to have a linear response in other zones we propose an empirical method to estimate the sa in the regular slope far from the crest and valley zone

why so few landslides triggered by the 2002 denali earthquake alaska abstract the 2002 m w 7 9 denali fault earthquake alaska provides an unparalleled opportunity to investigate in quantitative detail the regional hillslope mass wasting response to strong seismic shaking in glacierized terrain we present the first detailed inventory of 1580 coseismic slope failures out of which some 20 occurred above large valley glaciers based on mapping from multi temporal remote sensing data we find that the denali earthquake produced at least one order of magnitude fewer landslides in a much narrower corridor along the fault ruptures than empirical predictions for an m 8 earthquake would suggest despite the availability of sufficiently steep and dissected mountainous topography prone to frequent slope failure in order to explore potential controls on the reduced extent of regional coseismic landsliding we compare our data with inventories that we compiled for two recent earthquakes in periglacial and formerly glaciated terrain i e at yushu tibet m w 6 9 2010 and aysen fjord chile 2007 m w 6 2 fault movement during these events was similarly to that of the denali earthquake dominated by strike slip offsets along near vertical faults our comparison returns very similar coseismic landslide patterns that are consistent with the idea that fault type geometry and dynamic rupture process rather than widespread glacier cover were among the first order controls on regional hillslope erosional response in these earthquakes we conclude that estimating the amount of coseismic hillslope sediment input to the sediment cascade from earthquake magnitude alone remains highly problematic particularly if glacierized terrain is involved

10be exposure ages of a rock avalanche and a late glacial moraine in alta valtellina italian alps abstract a rock avalanche deposit was investigated in order to understand the chronological evolution of geological hazards and to evaluate the interaction of the triggering geodynamic processes in the valley val viola italian alps the deposit is situated west of the alpe dosde in a permafrost area with deep seated gravitational deformations dsgd along a tectonic line based on its geomorphologic context the rock avalanche was first interpreted as a result of slope stress release without exact timing this hypothesis was tested by measuring the 10 be exposure date of quartz from one boulder from the rock avalanche the age of 7430 460 years places the event in the early holocene the timing of the last deglaciation was constrained using the inner late glacial moraine of a moraine doublet in the valley alpe dosde situated at an altitude between 2140 and 2120 m a s l west of the rock avalanche the 10 be concentrations of quartz yield minimum exposure ages of 11 480 670 and 10 850 820 years different proposals for potential triggering factors of the rock avalanche include a melting of the local valley glacier and slope stress release in the val viola likely to play a minor role as trigger because of the time delay between the deglaciation and the rock avalanche event more likely are b enhanced crustal seismicity induced by post glacial regional isostatic glacial rebound coupled with tectonic stress or and c climate conditions with higher temperatures around 7430 460 years resulting in an upwards movement of the permafrost limit and destabilization of the rock walls

phase equilibrium constraints on the viscosity of silicic magmas 1 volcanic plutonic comparison by using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at 104 5 pa s irrespective of their temperature and level of emplacement magmas crystallizing as granitic plutons are not water poor and thus not more viscous than their extrusive equivalents instead comparison between pre eruption magma viscosities of extrusive silicic intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous given the typical strain rates in silicic magma chambers magma rheological behavior is expected to be dominantly newtonian bubbles having a minor rheological influence at depth although exceptions can exist thus whether a silicic intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors but not on the rheology of the magma itself however preemptive viscosities of extrusive magmas rarely exceed 106 pa s which suggests that crystal melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes the narrow range of viscosities displayed by silicic intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas considerations of the relationships between magma crystallinities bulk sio2 and preemptive melt h2o contents show that the higher the melt h2o content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted an empirical correlation is proposed that enables us to estimate preemptive melt h2o contents of erupted magmas by knowing their crystallinity and bulk sio2

thick and fast sedimentation in a pleistocene fiord lake of british columbia canada the central interior plateau of british columbia canada is dissected by numerous elongate glacially overdeepened lake basins akin to coastal fiords an air gun seismic reflection investigation 242 km of trackline of okanagan lake 120 km long 3 5 km wide shows that the pleistocene sediment fill is up to 792 m thick and that bedrock has been excavated by repeated pleistocene glacial erosion to nearly 650 m below sea level the depth of bedrock incision below the surrounding plateau is more than 2000 m exceeding that of the grand canyon in arizona the total volume of sediment infill within the narrow trenchlike basin is more than 90 km 3 and several lines of evidence suggest that this fill accumulated rapidly during a single phase of glaciolacustrine sedimentation during late wisconsin deglaciation of the region after 15 ka similar fiord lake basins up to 100 km long are common in the interior of british columbia if the data from okanagan are representative these basins may represent a major previously unrecognized component of the total glacial sediment flux to the ocean overdeepening below sea level and the focusing of large volumes of glacial sediment and meltwater into such basins are of considerable glaciologic significance and may record the fast unstable flow of ice streams during deglaciation of the cordilleran ice sheet

construction of a pluton evidence from an exposed cross section of the searchlight pluton eldorado mountains nevada a top to bottom cross section of the searchlight pluton is exposed in a large tilt block in the colorado river extensional corridor of southern nevada hornblende barometry and geologic relations indicate that the pluton was about 10 km thick extending from approximately 3 to 13 km depth the pluton is stratified with about 2 km of fine grained quartz monzonite below the roof 2 km of granite in the center and 6 km of coarser more mafic quartz monzonite at the bottom the lower unit has a pronounced magmatic foliation that was subhorizontal prior to tilting contacts between the units are gradational over a few centimeters to about 20 m geometry field relations and elemental and isotopic data suggest that the three units mark the terminal stages of evolution of magma that filled a very thick magma chamber the upper unit formed as a solidification front that migrated downward from the roof and the middle unit granite and the lower unit represent complementary segregated melt and crystal rich cumulate thus the dominant part of the pluton appears to have solidified in monotonic fashion from more or less uniform magma that was compositionally similar to the upper unit the basal quartz monzonite and the lower part of the granite enclose widely scattered synplutonic hornblende gabbro and diorite pods that range from centimeter to kilometer scale these rocks are commonly fine grained and formed as quenched mafic melts they are isotopically distinct from the main sequence and represent discrete injections into the magma chamber the mafic magmas were contaminated by but did not strongly affect the main sequence magma the nd and sr isotopic compositions of the main sequence magma are intermediate between those of regional crust and enriched mantle derived basalts like those represented by the mafic pods this suggests that the principal magma was a hybrid with about 60 mantle component and thus the pluton represents both addition to and internal reorganization of the crust

importance of seasonal and annual layers in controlling backscatter to radar altimeters across the percolation zone of an ice sheet radar altimeters are one of the main tools for measuring elevation changes across the antarctic and greenland ice sheets and larger ice caps a ground based radar was deployed in autumn 2004 and spring 2006 in the percolation zone of the greenland ice sheet this radar is a high bandwidth system operating in the ku band the same frequency as several satellite altimeters measurements were made over an elevation range of 1795 to 2350 m along with snow pit and shallow core studies these measurements demonstrate the spatial and temporal variations in the backscatter relative strengths of surface and volume reflections change dramatically between spring and autumn and there is also high spatial variability across the percolation zone the extent of percolation will affect elevation estimates made by radar altimeters

an exact solution for effects of topography on free rayleigh waves an exact solution for the effects of topography on rayleigh wave amplification is presented the solution is obtained by incorporating conformal mapping into complex variable stress functions developed for free rayleigh wave propagation in an elastic half space with a flat upper surface results are presented for free rayleigh wave propagation across isolated symmetric ridges and valleys it is found for wavelengths that are comparable to ridge widths that horizontal rayleigh wave amplitudes are amplified at ridge crests and that vertical amplitudes are strongly reduced near ridge crests relative to horizontal and vertical amplitudes of free rayleigh waves in the flat case horizontal amplitudes are strongly deamplified at valley bottoms relative to those for the flat case for rayleigh wavelengths comparable to valley widths wave amplitudes in the symmetric ridges and valleys asymptotically approach those for the flat case with increased wavelengths increased ridge and valley widths and with horizontal distance from and depth below the isolated ridges and valleys also prograde particle motion is predicted near crests of narrow ridges and near the bottoms of narrow valleys finally application of the theory at two sites known for topographic wave amplification gives a predicted surface wave amplification ratio of 3 80 at the ridge center for a frequency of 1 0 hz at robinwood ridge in northern california and a predicted surface wave amplification ratio of 1 67 at the ridge center for the same frequency at the cedar hill nursery site at tarzana in southern california

probing the accumulation history of the voluminous toba magma the age and compositional zonation in crystals from the youngest toba tuff record the prelude to earth9s largest quaternary eruption we used allanite crystals to date and decipher this zoning and found that the crystals retain a record of at least 150 000 years of magma storage and evolution the dominant subvolcanic magma was relatively homogeneous and thermally stagnant for 110 000 years in the 35 000 years before eruption the diversity of melts increased substantially as the system grew in size before erupting 75 000 years ago

the role of landslides in downslope transport of caprock derived boulders in sedimentary tablelands stolowe mts sw poland abstract escarpment slopes in sedimentary tablelands are often mantled by extensive boulder blankets while lithology shows beyond doubt that caprock is the source of boulders the processes involved in boulder movement and their distribution patterns are rarely examined in this paper we investigate the role of landslides initiated within middle and lower escarpment slopes in redistributing boulder covers on the example of the stolowe mountains in sw poland quartz sandstones form caprock and give rise to precipitous albeit rather low 30 m high at most typically 10 15 m uppermost slope sections and are the source of boulders which occur at distances even 1 km away from the caprock on the nearly flat footslope sedimentary series beneath caprock include fine grained rocks such as mudstones claystone and calcareous sandstones geomorphological mapping and geomorphometric analysis of a high resolution dem allowed us to identify landform patterns interpreted as resulting from landslides both rotational and translational the latter produced distinctive tread and riser topography with risers up to 10 m high results of geophysical prospecting using electrical resistivity tomography ert confirm the presence of allochthonous sandstone derived upper layer that wedges out downslope and indicate resistivity contrasts at depth of 5 15 m interpreted as basal boundaries of landslide material sandstone boulders rafted on top of slid masses and reached very distant footslope settings the primary role of landsliding consists of transporting allochthonous boulders further than would be possible otherwise and accumulating boulders in clusters and linear belts across the slope notably on risers

pathways of geomorphic evolution of sandstone escarpments in the gory stolowe tableland sw poland insights from lidar based high resolution dem abstract the tableland of the stolowe mountains sw poland with its prominent mesas and sandstone capped escarpments belongs to the most spectacular geomorphic landscapes of central europe while the gross morphological features of the area have long been recognized the evolutionary pathways of densely forested and poorly accessible escarpment slopes remained poorly understood in this paper we use lidar data to shed a new light on landform inventories within the escarpments their spatial patterns and using process from form reasoning on the longer term evolution of the escarpments four sites two on each major escarpment have been subject to detailed analysis which involved examination of shaded relief slope plan and profile curvature and topographic wetness index in each case the 1 1 m model was used while for the most complex site at mt szczeliniec wielki the results were compared with the 5 5 m model to check the impact of model resolution on geomorphic interpretation despite some loss of information involved in model re interpolation to the coarser scale the main features of escarpment morphology could still be recognized on the other hand automatic landform classification based on the calculation of topographic position index from the 10 10 m model and performed for the entire tableland failed to reveal differences between various sections of the escarpments detectable on finer models the analysis of spatial patterns of minor landforms within the escarpments identified on lidar derived models shows that no single pathway of escarpment evolution exists both the upper slopes in sandstone caprock and the mid slopes in weaker rocks show signs of instability and these are not necessarily coupled large scale caprock failures do occur but seem rare and localized sandstone free faces are rather subject to continuous slow retreat by detachment of individual joint bound blocks another zone of instability occurs well below the caprock and the dominant processes are shallow landslips initiated within weak deformable rocks

exhaustion and steady state models for predicting landslide hazards in the canadian rocky mountains abstract the temporal distribution of landslides can be evaluated by steady state and exhaustion models the probability of landsliding remains constant through time in the steady state model but the probability decreases in the exhaustion model as more slopes fail rock sliding down bedding surfaces on overdip slopes exhausts hazardous sites to leave stable dipslope landforms in kananaskis country in the canadian rocky mountains the distribution of rock slides in this area can be better explained by the exhaustion model than by the steady state model

the role of fluvial and glacial erosion in landscape evolution the ben ohau range new zealand a morphometric comparison of valleys has been made for the ben ohau range in the central southern alps of new zealand the range is undergoing rapid tectonic transport and uplift the humid north of the range is a glacial trough and arete landscape with a temperate glacial climate the dry south has rounded divides and plateau remnants dissected by fluvial valleys assuming that space time substitution allows today s spatial valley form transition to represent evolutionary stages in valley development the tectonic history allows time constraints to be placed on the rate of transition to an alpine glacial landscape morphometric change has been quantified using hypsometric curves and distance elevation plots of cirque and valley floor altitudes ancestral fluvial valleys have less concave long profiles but are stepped at altitude owing to the presence of high level cirques and remnant plateau surfaces and possess a low proportion of land area at low elevation increasing glacial influence is manifest as smoother more deeply concave long profiles and u shaped cross profiles associated with a higher proportion of the land area at lower elevation the full morphological transition has involved up to 2 4 km of vertical denudation over the 4 ma lifetime of the mountain range of which 80 per cent would have occurred by preglacial fluvial erosion combining the trajectory of tectonic transport with reconstructed glaciation limits and climatic history it is indicated that about 200 ka of temperate glacial erosion produces recognizable trough and areete topography mean and modal relief increase where glacial activity is confined to cirques but decrease when trough incision by ice becomes established as a dominant process in the landscape 1997 by john wiley sons ltd

effects of the vertical component of ground shaking on earthquake induced landslide displacements using generalized newmark analysis abstract the popular newmark method calculates the cumulative permanent displacement of a landslide having a known critical acceleration as it is subjected to the effects of an earthquake acceleration time history for an infinite slope this method considers ground acceleration as parallel to the slope and downslope which results in two important limitations 1 vertical downslope acceleration only is considered 2 the ratio of vertical to horizontal acceleration only depends on the inclination of the slope surface in the model developed herein the ground acceleration is not parallel to the slope the ratio of vertical to horizontal acceleration called the vertical accelerometric parameter depends on the seismic situation of the slope magnitude earthquake source distance style of faulting and the vertical acceleration acts alternately upslope and downslope application of the principles of classical mechanics leads to the pseudo static factor of safety and hence to the seismic horizontal critical acceleration of a potential landslide which depends not only on its static factor of safety geometry geotechnical properties and hydrogeologic conditions but also on its seismic situation it is shown that newmark s model is in fact a particular case of the general model and in most cases the seismic horizontal critical acceleration results from vertical upslope acceleration and is lower than newmark s critical acceleration as a consequence the displacements d resulting from the model developed herein will be greater than the displacements dn calculated from newmark s approach for some potential landslides the difference d dn is considerable and results in significant consequences in the seismic stability analysis of the affected slopes which justifies the importance of the effects of vertical ground shaking

regional coseismic landslide hazard assessment without historical landslide inventories a new approach currently regional coseismic landslide hazard analyses require comprehensive historical landslide inventories as well as detailed geotechnical data consequently such analyses have not been possible where these data are not available a new approach is proposed herein to assess coseismic landslide hazard at regional scale for specific earthquake scenarios in areas without historical landslide inventories the proposed model employs fuzzy logic and geographic information systems to establish relationships between causative factors and coseismic slope failures in regions with well documented and substantially complete coseismic landslide inventories these relationships are then utilized to estimate the relative probability of landslide occurrence in regions with neither historical landslide inventories nor detailed geotechnical data statistical analyses of inventories from the 1994 northridge and 2008 wenchuan earthquakes reveal that shaking intensity topography and distance from active faults and streams are the main controls on the spatial distribution of coseismic landslides average fuzzy memberships for each factor are developed and aggregated to model the relative coseismic landslide hazard for both earthquakes the predictive capabilities of the models are assessed and show good to excellent model performance for both events these memberships are then applied to the 1999 chi chi earthquake using only a digital elevation model active fault map and isoseismal data replicating prediction of a future event in a region lacking historic inventories and or geotechnical data this similarly results in excellent model performance demonstrating the model s predictive potential and confirming it can be meaningfully applied in regions where previous methods could not for such regions this method may enable a greater ability to analyze coseismic landslide hazard from specific earthquake scenarios allowing for mitigation measures and emergency response plans to be better informed of earthquake related hazards

isotopic disequilibrium among commingled hybrid magmas evidence for a two stage magma mixing commingling process in the mt perkins pluton arizona this is the publisher s version also available electronically from http www jstor org stable 30070774 seq 1 page scan tab contents

mafic replenishments into floored silicic magma chambers commingling between contemporaneous mafic and felsic magmas is now widely recognized in a broad range of intrusions and intrusive complexes these interactions are important features for two main of reasons 1 the rapidly chilled margins of mafic magma against silicic magma commonly preserve the compositions of mafic liquids and 2 because the mafic magma solidifies rapidly the resulting final configurations of mafic and felsic magmas can provide insights into physical processes and changing viscosity contrasts and rheologies of magmas and felsic crystal mush during crystallization of the mafic magma mingling of contrasted magmas was first recognized in the 1950s wider recognition of interactions between mafic and silicic liquids led to concepts of net veining in the 1960s intramagmatic flows chilled basaltic layers separated by felsic cumulates in the 1970s and in the 1990s to mafic silicic layered intrusions masli which could be as much as a few kilometers thick and more than 100 km2 in area it was quickly appreciated that these masli preserved stratigraphic records of mafic replenishments into silicic magma chambers floored by felsic crystal mush volcanic studies had anticipated the occurrence of this last type of intrusion on the grounds that extensive ponding of basaltic magmas beneath silicic chambers was seen to be essential to keep large silicic systems like yellowstone active for millions of years this paper looks at the history of changing perceptions and interpretations of magma mingling and whether or not sill complexes are distinct from mafic silicic layered intrusions the stratigraphy of mafic silicic layered intrusions records changing magmatic compositions events and processes in a temporal framework comparable to that provided by coeval volcanic rocks as a result careful study of masli has great potential for linking plutonic and volcanic processes and events

the importance of earthquake induced landslides to long term slope erosion and slope failure hazards in seismically active regions abstract this paper describes a general method for determining the amount of earthquake induced landsliding that occurs in a seismically active region over time this determination can be used as a quantitative measure of the long term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope erosion rates and landscape evolution the method uses data from historical earthquakes to relate total volume of landslide material dislodged by an earthquake to the magnitude m and seismic moment m0 of the earthquake from worldwide data a linear regression relation between landslide volume v and m0 is determined as v m0 1018 9 0 13 where v is measured in m3 and m0 is in dyn cm to determine the amount of earthquake generated landsliding over time this relation is combined with data on seismic moment release for a particular region which may be derived from either earthquake history or fault slip data the form of the m0 v relation allows the rate of production of earthquake induced landslides over time to be determined from total rate of seismic moment release without regard to the distribution of individual events thus simplifying and generalizing the determination application of the method to twelve seismically active regions with areas ranging from 13 275 to 2 308 000 km2 shows that erosion rates from earthquake induced landslides vary significantly from region to region of the regions studied the highest rates were determined for the island of hawaii new zealand western new guinea and the san francisco bay region of california significantly lower rates were determined for iran tibet the sierra nevada great basin region of california and central japan for the time period from 715 ad to the present intermediate rates were determined for peru southern california onshore california turkey and central japan for the time period from 1586 ad to the present to determine the relative long term importance of seismically triggered landslides these erosion rates are compared to erosion rates calculated for other slope processes and to rates calculated from fluvial sediment discharge comparisons with other slope processes indicate that earthquake induced landslides are the predominant agents of slope erosion on the island of hawaii in the san francisco bay region and in western new guinea for hawaii the san francisco bay region and sierra nevada great basin region of california the erosion rates calculated for earthquake induced landslides also exceed the regional erosion rates calculated from fluvial sediment discharge

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

the effect of glaciation on the intensity of seismic ground motion seismicity is known to contribute to landscape denudation through its role in earthquake triggered slope failure but little is known about how the intensity of seismic ground motions and therefore triggering of slope failures may change through time topography influences the intensity of seismic shaking generally steep slopes amplify shaking more than flatter slopes and because glacial erosion typically steepens and enlarges slopes glaciation may increase the intensity of seismic shaking of some landforms however the effect of this may be limited until after glaciers retreat because valley ice or ice caps may damp seismic ground motions two dimensional numerical models flac 6 0 were used to explore how edifice shape rock stiffness and various levels of ice inundation affect edifice shaking intensity the modelling confirmed that earthquake shaking is enhanced with steeper topography and at ridge crests but it showed for the first time that total inundation by ice may reduce shaking intensity at hill crests to about 20 50 of that experienced when no ice is present the effect is diminished to about 80 95 if glacier ice level reduces to half of the mountain slope height in general ice cover reduced shaking most for the steepest sided edifices for wave frequencies higher than 3 hz and when ice was thickest and the rock had shear stiffness well in excess of the stiffness of ice if rock stiffness is low and shear wave velocity is similar to that of ice the presence of ice may amplify the shaking of rock protruding above the ice surface the modelling supports the idea that topographic amplification of earthquake shaking increases as a result of glacial erosion and deglaciation it is possible that the effect of this is sufficient to have influenced the distribution of post glacial slope failures in glaciated seismically active areas copyright 2012 john wiley sons ltd

escarpment retreat in sedimentary tablelands and cuesta landscapes landforms mechanisms and patterns abstract although the general concept that escarpments in layered rocks retreat through time was offered more than 150 years ago recognizing the exact mechanisms patterns and rates of retreat remains a challenge in this paper we provide the state of the art of the theme of escarpment retreat reviewing both the classic contributions often forgotten but important case studies and the latest research in separate parts of the paper we discuss 1 terminology applied to the geomorphology of escarpments 2 the main assumptions and pathways of long term evolution of escarpments including conceptual models presented so far 3 processes involved in cliff retreat mainly weathering mass movements and erosion 4 the role of spring erosion and fluvial processes leading to fluvial dissection and development of canyons present in many tablelands 5 the possible role of climate change in escarpment evolution 6 rates of escarpment retreat in conclusions we summarize the major advances in our understanding of escarpment evolution of the last two three decades such as the recognition of the key role of emerging groundwater in non uniform escarpment retreat of an important role of silica dissolution and underground removal of dissolved solids increasing appreciation of rock properties in governing the patterns of escarpment retreat the proposal that cliffs do not necessarily retreat via catastrophic rock slope failures but may disintegrate in situ and the first attempts to date escarpment retreat using cosmogenic isotopes finally the remaining gaps and possible research priorities for the future are identified

crystal capture sorting and retention in convecting magma the mystery of producing strong compositional diversity among suites of comagmatic igneous rocks is investigated by considering the dynamic evolution of basaltic magma in a sheet like chamber a central conclusion is that inward progressing crystallization produces strong viscosity and temperature gradients that promote convection only near the leading edge of the upper thermal boundary layer convection is apparently confined to an essentially isoviscous isothermal region that hugs the downward growing roof zone strong changes in viscosity with crystallization divide the upper and lower thermal boundary layers into regions of decreasing viscosity and crystallinity n called rigid crust n 0 5 mush 0 5 n 0 25 and suspension n 0 25 the strong increase in viscosity near the mush suspension interface acts as a capture front that overtakes and traps slowly settling crystals initial phenocrysts mostly escape capture but crystals nucleated and grown in the suspension zone can escape only if the capture front slows to a critical rate attainable only in bodies thicker than about 100 m escaping crystals are redistributed and sorted by convection driven by the advance of the capture front itself crystal laden plumes traverse the central hot core of the body and deposit partially resorbed and sorted crystals within the lower suspension zone convection is never vigorous but is part of an overall intimate balance between roofward heat loss rigid crust growth crystallization kinetics and transport and sorting of sinking escaped crystals there is a strong similarity between these processes and those producing both varves and saline pan deposits it is clear that lavas lava lakes and sills are indeed examples of true magma chambers strongly exhibiting certain aspects of this over all process these aspects commonly also characterize the large mafic magmatic bodies because strong compositional changes in the residual melt occur largely outward that is at lower temperatures and higher crystallinities of the capture front which is immobile and mostly within rigid crust the possible range in comagmatic compositions available for eruption anywhere within the active magma is very limited this is in broad agreement with the compositional range observed in basaltic lava lakes sills and plutons like skaergaard the tuning of convection crystallization kinetics and phase equilibria in chambers of this type can produce a variety of textures and layering but not a diversity of compositions

chronologic and isotopic framework for early proterozoic crustal evolution in the eastern mojave desert region se california the early proterozoic geologic evolution of the eastern mojave desert region as defined by characteristics of its supracrustal rocks granitoids metamorphism structural history and pb and nd isotopic signature contrasts sharply with other proterozoic provinces of the southwestern united states the oldest supracrustal rocks of the mojave desert region contain zircons over 2 0 ga corroborating nd isotopic evidence for a much older crust here than elsewhere in the southwestern united states granitoids widely emplaced within these supracrustal rocks range from 1 76 to 1 64 ga the earlier plutons and surrounding supracrustal rocks were metamorphosed to granulite and high amphibolite facies throughout the province at about 1705 ma in a migmatite producing event that we term informally the ivanpah orogeny subsequent granitoids emplaced from 1 69 to 1 67 ga were voluminous along a north trending belt in the middle of the mojave province younger plutons were emplaced at about 1 66 ga in several places and at about 1 64 ga along the extreme southern part of the province commonalities between the proterozoic evolutions of the mojave and arizona crustal provinces do not conclusively establish the time that the provinces were juxtaposed the data only suggest that the juxtaposition occurred between about 1 76 and 1 64 ga

a seismologically consistent expression for the total area and volume of earthquake triggered landsliding we present a new seismologically consistent expression for the total area and volume of populations of earthquake triggered landslides this model builds on a set of scaling relationships between key parameters such as landslide spatial density seismic ground acceleration fault length earthquake source depth and seismic moment to assess the model we have assembled and normalized a catalog of landslide inventories for 40 shallow continental earthquakes low landscape steepness causes systematic overprediction of the total area and volume of landslides when this effect is accounted for the model predicts the total landslide volume of 63 of 40 cases to within a factor 2 of the volume estimated from observations r2 0 76 the prediction of total landslide area is also sensitive to the landscape steepness but less so than the total volume and it appears to be sensitive to controls on the landslide size frequency distribution and possibly the shaking duration some outliers are likely associated with exceptionally strong rock mass in the epicentral area while others may be related to seismic source complexities ignored by the model however the close match between prediction and estimate for about two thirds of cases in our database suggests that rock mass strength is similar in many cases and that our simple seismic model is often adequate despite the variety of lithologies and tectonic settings covered this makes our expression suitable for integration into landscape evolution models and application to the anticipation or rapid assessment of secondary hazards associated with earthquakes

differential glacio isostatic uplift of crustal blocks at glen roy scotland abstract detailed measurements of the altitudes of the shorelines of former ice dammed lakes in glen roy and vicinity in the scottish highlands prove erroneous the conventional view that former shorelines in areas affected by glacio isostatic uplift are uniformly tilted and or gently warped the measurements demonstrate differential uplift of blocks of the earth s crust the surfaces of some blocks have no detectable tilt whereas others have gradients up to at least 4 6 m km and are tilted in different directions in three areas 0 7 2 0 km long shorelines are distorted by crustal movements all these areas have landslides attributed to earthquakes that accompanied the release of stress in the area of greatest local distortion three shorelines rose about 3 m above their average altitudes for the immediately surrounding area and a fault scarp was produced possibly these local distortions accompanied catastrophic lake drainage by jokulhlaup analogous to crustal movements associated with man made lakes a relationship between crustal movement and the limit of a glacial advance is demonstrated these findings have implications for other parts of the world affected by glacioisostatic uplift

the effects of normal and shear stress wave phasing on coseismic landslide displacement predictive models used to assess the magnitude of coseismic landslide strain accumulation in response to earthquake ground shaking typically consider slope parallel ground accelerations only and ignore both the influence of coseismic slope normal ground accelerations and the phase relationship between dynamic slope normal and slope parallel accelerations we present results of a laboratory study designed to assess the significance of the phase offset between slope normal and slope parallel cyclic stresses on the generation of coseismic landslide displacements using a dynamic back pressured shearbox that is capable of simulating variably phased slope normal and slope parallel dynamic loads we subjected sediment samples to a range of dynamic loading scenarios indicative of earthquake induced ground shaking we detail the variations in strain accumulation observed when slope normal and slope parallel stresses occur independently and simultaneously both in and out of phase using a range of dynamic stress amplitudes our results show that the instantaneous phasing of dynamic stresses is critical in determining the amount of coseismic landslide displacement which may vary by up to an order of magnitude based solely on wave phasing effects instantaneous strain rate is an exponential function of the distance normal to the mohr coulomb failure envelope in plots of shear stress against normal effective stress this distance is strongly controlled by the phase offset between dynamic normal and shear stresses our results demonstrate that conditions considered by conventional coseismic slope stability models can either overestimate or underestimate earthquake induced landslide displacement by up to an order of magnitude this has important implications for accurate assessment of coseismic landslide hazard

the little red hill seismic experimental study topographic effects on ground motion at a bedrock dominated mountain edifice the kinematic response of a bedrock dominated mountain edifice to seismic shaking near lake coleridge in the southern alps of new zealand was examined a small elongated and bedrock dominated mountain ridge little red hill was equipped with a seismic array seven earss instruments mark l 4 3d seismometers were installed along the ridge crest the flank and at the base of the 210 m high 500 m wide and 800 m long mountain edifice from february to july 2006 seismic records of local and regional earthquakes were used to provide information on amplification and deamplification effects as well as on the frequency response at different parts on the edifice the ground motion records were analyzed using three different methods comparisons of peak ground accelerations power spectral density analysis and standard spectral ratio analysis time and frequency domain analyses show that site amplification is concentrated along the elongated crest of the edifice where amplifications of up to 1100 were measured relative to the motion at the flat base the field experiment also highlighted the extreme variations in amplification with regard to closely located sites but at contrasting topographic locations theoretical calculations and frequency analyses of field data indicate a maximum response along the ridge crest of little red hill for frequencies of about 5 hz which correlate to wavelengths approximately equal to the half width or height of the edifice the consequence of amplification effects on the stability and degradation of rock masses can be seen areas showing high amplification effects overlap with the spatial distribution of seismically generated block fields at little red hill it is concluded that topography geometry and distance to the seismic source play key roles in causing amplification effects of seismic ground motion and supporting dilation and degradation of rock mass across bedrock dominated mountain edifices

beyond debuttressing mechanics of paraglacial rock slope damage during repeat glacial cycles cycles of glaciation impose mechanical stresses on underlying bedrock as glaciers advance erode and retreat fracture initiation and propagation constitute rock mass damage and act as preparatory factors for slope failures however the mechanics of paraglacial rock slope damage remain poorly characterized using conceptual numerical models closely based on the aletsch glacier region of switzerland we explore how in situ stress changes associated with fluctuating ice thickness can drive progressive rock mass failure preparing future slope instabilities our simulations reveal that glacial cycles as purely mechanical loading and unloading phenomena produce relatively limited new damage however ice fluctuations can increase the criticality of fractures in adjacent slopes which may in turn increase the efficacy of fatigue processes bedrock erosion during glaciation promotes significant new damage during first deglaciation an already weakened rock slope is more susceptible to damage from glacier loading and unloading and may fail completely we find that damage kinematics are controlled by discontinuity geometry and the relative position of the glacier ice advance and retreat both generate damage we correlate model results with mapped landslides around the great aletsch glacier our result that most damage occurs during first deglaciation agrees with the relative age of the majority of identified landslides the kinematics and dimensions of a slope failure produced in our models are also in good agreement with characteristics of instabilities observed in the field our results extend simplified assumptions of glacial debuttressing demonstrating in detail how cycles of ice loading erosion and unloading drive paraglacial rock slope damage

magmatic stoping as an important emplacement mechanism of variscan plutons evidence from roof pendants in the central bohemian plutonic complex bohemian massif the presence of numerous roof pendants stoped blocks and discordant intrusive contacts suggests that magmatic stoping was a widespread large scale process during the final construction of the central bohemian plutonic complex bohemian massif the measured total length of the discordant contacts that cut off the regional cleavage and were presumably formed by stoping corresponds to about half of all contacts with the upper crustal host rocks in addition at least some of the straight cleavage parallel intrusive contacts may also have recorded complex intrusive histories ending with piecemeal stoping of thin cleavage bounded host rock blocks into the magma chamber based on the above we argue that the fast strain rates required for emplacement of large plutons of the central bohemian plutonic complex into brittle upper crustal host rocks over relatively short time span could not have been accommodated entirely by slow ductile flow or slip along faults instead the emplacement was largely accommodated by much faster thermal cracking and extensive stoping independent of regional tectonic deformation finally we emphasize that magmatic stoping may significantly modify the preserved structural patterns around plutons may operate as an important mechanism of final construction of upper crustal plutons and thus may contribute to vertical recycling and downward transport of crustal material within the magma plumbing systems in the crust

structural reconstruction and zonation of a tilted mid crustal magma chamber the felsic chemehuevi mountains plutonic suite structural relief resulting from middle tertiary extensional deformation in the chemehuevi mountains of california exposes a unique cross section through an extensive 280 km 2 calc alkalic compositionally zoned sill like granitic intrusion of late cretaceous age minimum estimates for emplacement pressure 4 to 6 kbar imply that the chemehuevi mountains plutonic suite was initially intruded at mid crustal depths and has undergone 10 to 15 of postemplacement tilting tectonic denudation and erosion reconstruction of the pre tertiary pre tilt configuration suggests that this metaluminous to peraluminous granitic suite exhibits crude normal vertical and temporal zonation from granodiorite to granite the zonation involves a decrease in age and an increase in silica away from the walls and roof the youngest and most evolved members being concentrated toward the center and floor of the intrusion the lower part of the intrusion had a flat floor which was penetrated by at least three feeder dikes providing magma to the chamber the chamber grew laterally in stages each pulse being more evolved than the preceding one structural reconstruction indicates that the roof is less than 1 km above the exposed top of the intrusion suggesting a tabular geometry with an aspect ratio of about 5 1 the magma apparently ponded along the contact between undeformed proterozoic basement above and subhorizontally foliated mylonitic gneisses below and was therefore structurally controlled this reconstruction provides information on the geometry of mesozonal intermediate to silicic magma chambers in addition the restoration provides a rare opportunity to observe crosscutting relations between different types of mid crustal structures thick mylonitic shear zones granitic intrusions and temporally unrelated detachment faults the geometry of which emphasizes the need for careful evaluation of seismic reflection profiles across complexly deformed and intruded continental crust

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

investigating the effect of earthquakes on open pit mine slopes abstract this paper develops a database for studying the circumstances under which dynamic loading of earthquake can cause slope failure in deep open pit mines with a long lifetime the database includes 177 open pit mines hit by earthquake and 95 natural slopes and 37 tailing dams which have been failed by earthquakes both earthquake parameters and geomechanical characteristics involved in each case study are investigated from this information the elements playing role in the earthquake triggered failures in natural slopes and tailing dams are identified and used to indicate conditions that may result in earthquake induced failures in open pit mines the result shows that even though the valley shape geometry and absence of the top weathered layer make open pit mines less prone to earthquake induced failures excessive pore pressure in pit slopes still carries the risk of earthquake triggered failures in open pit slopes only limited numbers of open pit mines have been so far exposed to earthquakes with the same parameters as those causing failure in natural slopes and tailing dams that is the response of open pit mines to higher magnitude shallower and closer earthquakes is still unknown studying the earthquakes that have caused failure in other slopes it is concluded that open pit mines may still experience reportable failures if struck by earthquakes with local depth of less than 40 km epicentral distance of less than 100 km and magnitude of greater than 6 0 the necessity of accounting for seismic loading in slope stability analyses and active dewatering for open pit mines located in seismically active areas are also discussed

slip rate variations on normal faults during glacial interglacial changes in surface loads geologic and palaeoseismological data document a marked increase in the slip rates of the wasatch fault and three adjacent normal faults in the basin and range province during the late pleistocene early holocene epochs the cause of this synchronous acceleration of fault slip and the subsequent clustering of earthquakes during the holocene has remained enigmatic although it has been suggested that the coincidence between the acceleration of slip and the shrinkage of lake bonneville after the last glacial maximum may indicate a causal relationship here we use finite element models of a discrete normal fault within a rheologically layered lithosphere to evaluate the relative importance of two competing processes that affect fault slip postglacial unloading the removal of mass which decreases the slip rate and lithospheric rebound which promotes faster slip we show that lithospheric rebound caused by regression of lake bonneville and deglaciation of adjacent mountain ranges provides a feasible mechanism for the high holocene rates of faulting in the wasatch region our analysis implies that climate controlled changes in loads applied to earth s surface may exert a fundamental control on the slip history of individual normal faults

rock slope failure following late pleistocene deglaciation on tectonically stable mountainous terrain the ages of 31 postglacial rock slope failures rsfs in scotland and nw ireland derived from 89 cosmogenic isotope exposure ages are employed to analyse the temporal pattern of failure and its relationship to the timing of deglaciation rates of glacio isostatic crustal uplift and periods of rapid climate change rsf ages span almost the whole period since ice sheet retreat from 18 2 1 2 ka to 1 7 0 2 ka or from 17 1 1 0 ka to 1 5 0 1 ka depending on the production rate used in 10 be age calculation but catastrophic failure of rock slopes was w4 6 times more frequent prior to w11 7 ka than during the holocene 95 of dated rsfs at sites deglaciated during retreat of the last ice sheet occurred within w5400 years after deglaciation with peak rsf activity 1600e1700 years after deglaciation this time lag is inferred to represent 1 stress release initiated by deglacial unloading leading to 2 time dependent rock mass strength degradation through progressive failure plane development and ultimately 3 to either spontaneous kinematic release or failure triggered by some extrinsic mechanism by contrast 11 dated rsfs at sites reoccupied by glacier ice during the younger dryas stade yds of w12 9e11 7 ka exhibit no clear temporal pattern suggesting that glacial reoccupance during the yds was ineffective in preconditioning a renewed cycle of enhanced rsf activity comparison of timing of individual rsfs with that of deglaciation and rapid warming events at w14 7 ka and w11 7 ka suggests that glacial debuttressing enhanced joint waterpressuresduringdeglaciationandthawofpermafrosticeinrockjointscouldhavetriggeredfailurein only a small number of cases conversely the timing of maximum rsf activity following ice sheet deglaciation corresponds broadly with maximum rates of glacio isostatic crustal uplift suggesting that the two are linked by enhanced seismic activity a seismic failure trigger is consistent with full slope failure at all sites where failure planes are clearly defined our results indicate that numerous rsfs must have occurred in areas that were reoccupied by glacier ice during the yds but have not been identified because runout debris was removed by yds glaciers more generally they provide the first reliably dated body of evidence to support the view that retreat of the last ice sheets in tectonically stable mountainous terrain initiated a period of enhanced rock slope failure due to deglacial unloading and probably lateglacial seismic activity implying that most undated rsfs in such areas are probably of lateglacial or veryearly holocene age they also demonstrate however that a low frequency of rsf activity extended throughout the holocene

impacts of post glacial rebound on landslide spatial distribution at a regional scale in northern iceland skagafjorður in de glaciated areas para glaciation i e the conditioning of landscapes by prior glaciation has often been considered a major predisposing factor in landslide occurrence its consequences have been particularly well identified at a fine scale especially on bedrock jointing hitherto the relative impacts of para glaciation on hillslope dynamics at a regional scale had nevertheless not been quantified statistically we examine skagafjor ur area northern iceland where landslides are widespread at least 108 were mapped in an area of c 3000km2 we compare the role of para glaciation debuttressing influence of post glacial rebound with that of classic factors topography lithology etc in landslide occurrence and location using a spatial analysis based on a chi square test on the one hand the results highlight that landslides are over represented in areas where post glacial rebound was at its maximum with a stronger concentration of landslides in the northern part of the fjord on the other hand the distribution of landslides did not show any clear relationship with the pattern of glacial debuttressing tschuprow coefficient highlights that the influence of post glacial rebound on landslide location is higher than the combined influence of slope gradient curvature or geological structure this result is supported by our initial evidence for the timing of landslides in the area most landslides occurred during the first half of the holocene and a period of hillslope instability was initiated when the post glacial uplift was at its maximum finally the mechanisms that link post glacial rebound and landsliding as well as the geomorphic impacts of landslides are discussed

implications of paleomagnetic data on miocene extension near a major accommodation zone in the basin and range province northwestern arizona and southern nevada paleomagnetic data from volcanic and crystalline rocks elucidate the evolution of a major miocene accommodation zone in the northern colorado river extensional corridor the accommodation zone is a 10 km wide belt of intermeshing conjugate normal faults that facilitates reversals in the dominant tilt direction of fault blocks and dip direction of major normal fault systems tilt corrected means e g n 28 sites d 353 4 i 61 3 95 6 7 k 17 4 from miocene volcanic strata overlap expected miocene directions at the 95 confidence level these data and geologic relations suggest that at exposed structural levels the accommodation zone did not facilitate distributed strike slip displacement between opposing tilt block domains vertical axis rotations are probably negligible in most of the corridor as the miocene structural grain generally mimics that in the zone discrepancies between characteristic remanent magnetizations chrm in crystalline rocks and expected directions are therefore attributed to rotations about horizontal i e tilting or flexing axes chrms from cretaceous and miocene intrusions suggest 50 90 of tilting of large crystalline terranes on either side of the accommodation zone the magnitude of tilting inferred from the paleomagnetic data is similar to that of tertiary strata in nearby fault blocks implying that these crystalline terranes are parts of highly tilted fault blocks rather than flexed lower plate rocks major low angle normal faults that bound highly tilted parts of these crystalline terranes probably nucleated at steep dips and were rotated to gentle dips by block tilting paleomagnetic data indicative of negligible tilting e g miocene intrusions northern black mountains crystalline terrane n 13 sites d 359 i 55 95 9 k 24 and geologic relations imply that lower plate rocks may surface in both the east and west tilted domains 35 50 km away from the zone the trend toward shallower structural levels with respect to miocene extension and tapering of highly extended terrane toward the accommodation zone imply that the magnitude of upper crustal extension decreases toward the zone temporal patterns of major extension especially an apparently continuous northward younging across both the east and west tilted domains further suggest that the accommodation zone served as a long lived rupture barrier between conjugate normal fault systems rather than as a short term boundary between opposing systems that propagated toward and converged at the zone

glacier shrinkage and modeled uplift of the alps 1 present day glacier reduction in the alps estimated from glacier inventories and induced viscoelastic response of a stratified earth s model is responsible for sizable uplift rates patches of 0 4 0 5 mm yr due to ice mass loss of largest ice complexes overprint a characteristic area of slower uplift of 0 1 0 2 mm yr signature of the phenomenon in the whole alpine chain viscous stress relaxation in the lower crust due to glacier mass loss after the end of the little ice age is expected to produce uplift rates of 0 32 mm yr leading to a total viscoelastic response up to 0 8 mm yr our predictions in the western alps show that viscoelastic response to present day glacier shrinkage forms a substantial fraction half of the observed uplift data attempts to constrain the contributions arising from active alpine tectonics and drainage must account for this uplift signal citation barletta v r c ferrari g diolaiuti t carnielli r sabadini and c smiraglia 2006 glacier shrinkage and modeled uplift of the alps geophys res lett 33 l14307 doi 10 1029 2006gl026490

the role of the mantle during crustal extension constraints from geochemistry of volcanic rocks in the lake mead area nevada and arizona one of the fundamental questions in areas of large magnitude extension and magmatism is the role of the mantle in the extension process the lake mead area is ideally suited for developing models that link crustal and mantle processes because it contains both mantle and crustal boundaries and it was the site of large magnitude crustal extension and magmatism during miocene time in the lake mead area the boundary between the amagmatic zone and the northern colorado river extensional corridor parallels the lake mead fault system and is situated just to the north of lake mead this boundary formed between 11 and 6 ma during and just following the peak of extension and corresponds to a contact between two mantle domains during thinning and replacement of the lithospheric mantle in the northern colorado river extensional corridor the lithospheric mantle in the amagmatic zone remained intact contrasting behavior to the north and south of this boundary may have produced the mantle domain boundary the domain to the north of the boundary is characterized by mafic lavas with a lithospheric mantle isotopic and geochemical signature nd 3 to 9 87 sr 86 sr 0 706 0 707 to the south of the boundary in the northern colorado river extensional corridor lavas have an ocean island basalt oib mantle signature and appear to have only a minor lithospheric mantle component in their source nd 0 to 4 87 sr 86 sr 0 703 0 705 mafic lavas of the northern colorado river extensional corridor represent the melting of a complex and variable mixture of asthenospheric mantle lithospheric mantle and crust pliocene alkali basalt magmas of the fortification hill field represent the melting of a source composed of a mixture of asthenospheric mantle high u pb himu like mantle and lithospheric mantle depth of melting of alkali basalt magmas remained relatively constant from 12 to 6 ma during and just after the peak of extension but probably increased between 6 and 4 3 ma following extension miocene and pliocene low nd and high 87 sr 86 sr magmas and tholeiites at malpais flattop were derived from a lithospheric mantle source and were contaminated as they passed through the crust the shift in isotopic values due to crustal interaction is no more than 4 units in nd and 0 002 in 87 sr 86 sr and does not mask the character of the mantle source the change in source of basalts from lithospheric mantle to asthenospheric mantle with time the oib character of the mafic lavas and the himu like mantle component in the source are compatible with the presence of rising asthenosphere as an upwelling convective cell or plume beneath the northern colorado river extensional corridor during extension the lake mead fault system a major crustal shear zone parallels the mantle domain boundary the lake mead fault system may locally represent the crustal manifestation of differential thinning of the lithospheric mantle

application of the topographic position index to heterogeneous landscapes topographic position index tpi is an algorithm increasingly used to measure topographic slope positions and to automate landform classifications we applied tpi to a geoarchaeological research project in northwestern belgium but its use led to erroneous landform classifications in this heterogeneous landscape we asked whether deviation from mean elevation dev was a better method for landform classification than tpi we found that it enabled more accurate geomorphological assessment when using northwestern belgium as a case study

reply to comments on is stoping a volumetrically significant pluton emplacement process the 188th meeting of the geological society of washington was devoted to a consideration of the methods of igneous intrusion the discussion was opened by mr whitman cross who directed it to the methods by which the large igneous masses such as laccoliths stocks and batholiths have

active deformation in the eastern swiss alps post glacial faults seismicity and surface uplift abstract post glacial tectonic faults in the eastern swiss alps occur as single lineaments clusters of faults or extensive fault zones consisting of several individual faults aligned along the same trend the orientation of the faults reflects the underlying lithology and the pre existing structures joints pervasive foliations within these lithologies most post glacially formed faults in the area around chur which undergoes active surface uplift of 1 6 mm year trend e w and cut across alpine and glacial features such as active screes and moraines additionally there are nnw and ene striking faults reactivating pervasive alpine foliations and shear zones based on a comparison with the nodal planes of recent earthquakes e w striking faults are interpreted as active faults because of very short rupture lengths and mismatches of fault location with earthquake distribution magnitude and abundance the faults are considered to be secondary faults due to earthquake shaking cumulative deformation in post or interseismic periods or creep and not primary earthquake related faults the maximum of recent surface uplift rates coincides with the youngest cooling of the rocks according to apatite fission track data and is therefore a long lived feature that extends well into pre glacial times isostatic rebound owing to overthickened crust or to melting of glacial overburden cannot explain the observed surface uplift pattern rather the faults earthquakes and surface uplift patterns suggest that the alps are deforming under active compression and that the aar massif basement uplift is still active in response to ongoing collision

regional patterns of earthquake triggered landslides and their relation to ground motion 1 we have documented patterns of landsliding associated with large earthquakes on three thrust faults the northridge earthquake in california chi chi earthquake in taiwan and two earthquakes on the ramu markham fault bounding the finisterre mountains of papua new guinea in each case landslide densities are shown to be greatest in the area of strongest ground acceleration and to decay with distance from the epicenter in california and taiwan the density of co seismic landslides is linearly and highly correlated with both the vertical and horizontal components of measured peak ground acceleration based on this observation we derive an expression for the spatial variation of landslide density analogous with regional seismic attenuation laws in its general form this expression applies to our three examples and we determine best fit values for individual cases our findings open a window on the construction of shake maps from geomorphic observations for earthquakes in non instrumented regions

chapter 3 structural development of a major extensional accommodation zone in the basin and range province northwestern arizona and southern nevada implications for kinematic models of continental extension

boulder aprons indicate long term gradual and non catastrophic evolution of cliffed escarpments stolowe mts poland abstract caprock crowned escarpments are characteristic geomorphic features of the sandstone tableland of the stolowe mountains sw poland their mid and lower slopes truncate weaker sedimentary formations but are littered with sandstone boulders of various size often more than 5 m long which form nearly continuous aprons a model of escarpment retreat by rock fall has been widely accepted in literature but in the stolowe mountains it has never been tested against field evidence in addition no rock fall events except one minor fall in 1921 have been recorded in historical times in this paper we erected five hypotheses of how escarpments may have evolved through time to result in widespread boulder presence on the slopes mapping boulder extent and slope morphology run out distance simulations using conefall software and rock strength determinations using the schmidt hammer carried out on boulders along eight representative slope profiles provide data about characteristics of the boulder covers systematic decrease in intact rock strength with an increasing distance from the sandstone cliffs suggests that the boulder aprons are diachronic and record long term retreat of escarpments there exists no conclusive evidence of widespread boulder downslope movement although in a few localities shallow landslides have rafted boulders far away from the cliff lines modelling exercise shows that the actual extent of boulders is 2 3 times bigger than suggested by conefall predictions these findings coupled with observations along the cliff lines themselves lead us to propose a model of free face in situ disintegration as the most likely hypothesis to explain block detachment and release from rock faces as cliff lines recede and the slope surface below is lowered remnant boulders occupy a position increasingly further away from escarpment rims but experience little actual movement this model complements the existing models of tableland evolution which tend to emphasize catastrophic mass movement processes on cliffed escarpments

sources of the early cretaceous plutons in the turtle and west riverside mountains california anomalous cordilleran interior intrusions ages and initial isotopic ratios of early cretaceous 100 ma plutons of the cordilleran interior in the southern turtle and west riverside mountains distinguish them from late cretaceous plutons in surrounding ranges in the eastern mojave desert furthermore the studied plutons have isotopic and geochemical characteristics more similar to plutons of cretaceous age in the coastal batholiths peninsular ranges and sierra nevada than to most mesozoic plutons in the cordilleran interior the studied plutons are calcic in contrast to the mostly cak alkaline mesozoic plutons of the eastern mojave desert distinctive isotopic signatures of the granitoids include lower initial 87sr 86sr of 0 705 0 710 18o of 6 3 to 7 7 208pb 204pb of 38 3 39 5 and higher end of 3 86 to 9 60 than the late cretaceous plutons in the region the distinctive characteristics of these early cretaceous plutons are probably both location and time specific and result from 1 emplacement in a cold untapped mojave type proterozoic upper crust 2 a significant component of basaltic magmas partially melted from the asthenosphere or subcontinental lithosphere and 3 a magmatic component derived from proterozoic mafic lower crust they interacted less with their crustal hosts than did the later more voluminous late cretaceous plutons

a new seismic hazard model for new zealand we present a new probabilistic seismic hazard analysis psha for new zealand an important feature of the analysis is the application of a new method for the treatment of historical distributed seismicity data in psha the psha uses the seismicity recorded across and beneath the country to define a three dimensional grid of a values i e parameter a of a gutenberg richter distribution log n yr a bm in which n yr is the number of earthquakes per year recorded inside each grid cell equal to or greater than magnitude m parameter b and the limiting maximum cutoff magnitude of the gutenberg richter distribution are defined from the surrounding region 14 crustal and 23 subcrustal seismotectonic zones are defined for the country and then smoothed across the boundaries of the zones the methodology therefore combines the modern method of defining continuous distributions of seismicity parameters frankel 1995 frankel et al 1996 with the traditional method of defining large area sources and the associated seismicity parameters e g algermissen et al 1990 the methodology provides a means of including deep subduction zone seismicity in a psha preserves the finer scale spatial variations of seismicity rates across a region avoids the undesirable edge effects produced in the traditional method when adjacent area sources enclose areas of significantly different seismicity rates and also enables parameters most reliably defined at a regional scale parameter b and maximum cutoff magnitude of a gutenberg richter distribution and slip type to be incorporated into the psha the psha combines the modeled seismicity data with geological data describing the location and earthquake recurrence behavior of 305 active faults and new attenuation relationships for peak ground acceleration and spectral acceleration developed specifically for new zealand different attenuation expressions are used for crustal and subduction zone earthquakes the resulting psh maps for a 150 year return period show the highest hazard to occur in the center and southwest of the country in the areas of highest historical crustal and deep subduction zone seismicity in contrast the longer return period maps 475 and 1000 year return period show the highest hazard to occur from the southwest to northeast ends of the country along the faults that accommodate the majority of the motion between the pacific and australian plates the maps are currently being used to revise new zealand s building code which has previously been based on pshas that did not explicitly include individual faults as earthquake sources manuscript received 10 april 2001

a fault scarp in an urban area identified by lidar survey a case study on the itoigawa shizuoka tectonic line central japan abstract a light detection and ranging lidar survey was conducted in a densely built up area to generate a high resolution digital elevation model dem to look for active faults the urban district of matsumoto city in central japan is located in a 3 km 2 basin along the itoigawa shizuoka tectonic line active fault system one of japanese onshore fault systems with the highest earthquake probability a high resolution dem at a 0 5 m grid interval was obtained after removing the effects of laser returns from buildings clouds and vegetation it revealed a continuous scarp up to 2 m in height borehole data and archaeological studies indicate the scarp was formed during the most recent faulting event associated with historical earthquakes in addition the fault scarp strongly supports that the urban district is in a pull apart basin related to a fault step over between two left lateral strike slip faults consequently accurate interpretation of fault geometry is crucial to provide estimates of future surface deformation and to allow modeling of basin structure and strong ground motion thus the lidar mapping survey in urban districts is effective for detailed active fault mapping in order to constrain basin structure and to forecast the exact location of surface rupturing associated with large earthquakes

silicic magma chambers as traps for basaltic magmas the cadillac mountain intrusive complex mount desert island maine the cadillac mountain intrusive complex located on mount desert island maine provides a superb record of episodic invasion of a floored silicic magma chamber by many pulses of basaltic magma the complex consists of three units the cadillac mountain granite cmg the somesville granite sg and gabbro diorite g d basaltic magmas were emplaced before during and after the emplacement and crystallization of the granitic plutons and the chambers of silicic magma acted as traps for basaltic magma basaltic magma emplaced into the surrounding country rocks crystallized as homogeneous diabase and gabbro while basaltic magma emplaced within the perimeter of the granite displays abundant evidence for commingling with silicic magma the g d unit about 1 5 km thick consists of interlayered gabbroic dioritic and granitic rocks although thin 1 m thick gabbroic layers in the g d unit are typically chilled on all margins thicker layers of gabbro commonly form the lower parts of macrorhythmic units

hafnium oxygen neodymium strontium and lead isotopic constraints on magmatic evolution of the supereruptive southern black mountains volcanic center arizona u s a a combined lass zircon whole rock study the 700 km 3 peach spring tuff pst erupted at 18 8 ma from the silver creek caldera in the southern black mountains volcanic center sbmvc of western arizona is the only supereruption scale ignimbrite in the northern colorado river extensional corridor the sbmvc contains pre and post caldera volcanic rocks and caldera related intrusions 19 17 ma that provide a detailed petrologic record of ignimbrite antecedence and aftermath whole rock sr nd pb hf isotopic data combined with complementary zircon o and hf isotopic data from a suite of pre through post pst samples provide robust constraints on 1 how the sbmvc evolved with respect to magmatic sources and processes throughout its 2 ma history and 2 the petrogenetic relationships between the pst and slightly younger intracaldera plutons both pre and post pst units have isotopic ranges nd 8 3 to 11 6 hf 8 2 to 14 0 87 sr 86 sr i 0 709 0 712 206 pb 204 pb 18 19 18 49 207 pb 204 pb 15 60 15 62 208 pb 204 pb 38 95 39 29 that fall within the spectrum of miocene colorado river extensional corridor rocks and are consistent with mixing of substantial fractions of proterozoic mojave crust and juvenile material derived from regional enriched mantle compared to the pst which has relatively uniform isotopic ratios nd 11 4 to 11 7 hf 13 8 to 14 3 87 sr 86 sr i 0 709 0 712 206 pb 204 pb 18 20 18 29 207 pb 204 pb 15 60 15 62 208 pb 204 pb 39 02 39 33 individual pre and post pst units are isotopically more variable and generally more primitive consistent with whole rock isotopes zircon hf 8 to 14 and oxygen 18 o 4 5 to 7 2 for most pre and post pst units also have wider ranges and more mantle like values than those of the pst 12 to 15 6 1 to 7 1 moreover zircon isotopic compositions decrease in post pst samples a few zircons from post pst intrusions have 18 o values lower than mantle values whole rock and zircon elemental and isotopic analyses indicate that 1 most pre and post pst units are less evolved and less homogenized than the pst itself 2 intrusions in the silver creek caldera are petrogenetically distinct from the pst and therefore represent discrete magmatic pulses not unerupted pst mush 3 enriched mantle input increased in the sbmvc following the paroxysmal pst eruption 4 post pst history of the sbmvc was characterized by periodic influx of magmas with varying juvenile fractions into pre existing mushy or solidified intrusions resulting in variable and incomplete hybridization and 5 melting and assimilation of hydrothermally altered crust played a relatively minor role in the generation and evolution of magmas in the sbmvc

contribution to the theory of scarpland development from observations in central queensland australia abstract theories of scarpland geomorphology developed over the past century have been characterized by divergent conceptual frameworks and have been hindered by language barriers here we review the main theories and assess them with reference to field evidence from central queensland this region provides exceptional scope for such an assessment because of the detailed k ar chronology available for basalt that is draped extensively over scarps and valleys the basalt provides the key to deciphering the pattern and rate of denudation erosion began in the late mesozoic and was greatly advanced when volcanism occurred during the middle cenozoic postbasaltic erosion has been dominated by the incision of the basaltic caprock and by the lengthening of canyons rather than by scarp retreat canyons have extended headward by 1 2 km m yr widened by 150 250 m m yr and deepened by 6 25 m m yr while scarps between canyons have retreated by only 18 130 m m yr canyon cutting both on the scarp front and on t

application of airborne lidar to mapping seismogenic faults in forested mountainous terrain southeastern alps slovenia results are presented of the first airborne lidar survey ever flown in europe for the purpose of mapping the surface expression of earthquake prone faults detailed topographic images derived from lidar data of the idrija and ravne strike slip faults in nw slovenia reveal geomorphological and structural features that shed light on the overall architecture and kinematic history of both fault systems the 1998 mw 5 6 and 2004 mw 5 2 ravne fault earthquakes and the historically devastating 1511 m 6 8 idrija earthquake indicate that both systems pose a serious seismic hazard in the region because both fault systems occur within forested terrain a tree removal algorithm was applied to the data the resulting images reveal surface scarps and tectonic landforms in unprecedented detail importantly two sites were discovered to be potentially suitable for fault trenching and palaeo seismological analysis this study highlights the potential contribution of lidar surveying in both low relief valley terrain and high relief mountainous terrain to a regional seismic hazard assessment programme geoscientists working in other tectonically active regions of the world where earthquake prone faults are obscured by forest cover would also benefit from lidar maps that have been processed to remove the canopy return and reveal the forest floor topography

timing and periodicity of paraglacial rock slope failures in the scottish highlands abstract many formerly glaciated mountains exhibit a high density of postglacial rock slope failures rsfs in the form of rockslides rock avalanches or deep seated gravitational slope deformations such rsfs are often termed paraglacial as they reflect pre conditioning by glaciation and deglaciation the temporal pattern of paraglacial rsfs is unknown we employ 47 cosmogenic isotope exposure ages obtained for 17 catastrophic rsfs in the scottish highlands to test models of changes in rsf frequency since deglaciation our results show that rsf activity spans almost the entire postglacial period from 17 ka until 1 5 ka and that the periodicity of sampled postglacial rsfs is statistically indistinguishable from a pattern of uniform periodicity 1 ka 1 our data do not conform to proposed models of declining rsf frequency with time elapsed since deglaciation but suggest that the temporal distribution of postglacial rsfs is best described by a combination of rapid response enhanced rsf frequency during or immediately after deglaciation followed by approximately constant periodicity our findings are consistent with near surface fracturing of rock when glacially induced confining stresses are removed causing some failures during or immediately after deglaciation and reducing other slopes to critical conditional stability so that failure is triggered by progressive rock mass weakening or by transient triggering mechanisms neither permafrost degradation thaw of ice in joints nor seismic activity offers a general explanation for triggering scottish rsfs but could be contributory in some cases the quasi constant periodicity inferred for holocene rsfs implies that the probability of rsfs in this seismically quiescent intraplate area has not changed in the past 10 ka and that further though infrequent catastrophic rsfs are likely to occur in the future

the effect of topography on earthquake ground motion a review and new results a brief review of experimental and theoretical results about the effect of topography on seismic motion shows that they are consistent only on a qualitative basis amplification at mountain tops for wavelengths comparable with mountain widths is predicted and observed but the numerical simulations often underestimate the actual observed effects we propose that this disagreement is because current models are not complex enough we therefore computed the response to incident sh waves of a set of different complex configurations that include two dimensional surface topography with or without periodic ridges and subsurface layering the results show that 1 the topographic effect in itself is difficult to isolate from other effects like surface layering and therefore the amplification on top of geomorphologically complex sites cannot be predicted by a priori estimations based solely on topography and 2 the high crest base amplification ratio observed in the field cannot usually be matched even with complex two dimensional structures with incident plane sh waves which suggests that more complex models are needed to incorporate more complex wave fields e g sv surface and three dimensional geologic configurations

use of lidar derived images for mapping old landslides under forest large deep seated landslides are common features in the flemish ardennes belgium as most of these old 100 years landslides are located under forest in this hilly region aerial photograph interpretation is not an appropriate landslide mapping method this study tested the potential of lidar light detection and ranging images for mapping old landslides under forest landslide inventory maps were created for a 125 km2 area by applying the expert knowledge of seven geomorphologists to lidar derived hillshade slope and contour line maps in a gis environment each of the seven lidar based landslide inventories was compared i with the other six ii with a detailed field survey based inventory and iii with a comparable study in which topographic data were extracted from a topographical map the combination of the percentage of field landslides indicated by an expert and the percentage of positional discrepancies expressed in terms of positional mismatch were used to evaluate the quality of the lidar based inventory maps high quality lidar derived landslide inventory maps contain more than 70 per cent of the landslides mapped during the field survey and have positional discrepancies smaller than 70 per cent when compared with the field survey based inventory map four experts and the combination map of all experts satisfied these criteria together the seven experts indicated all landslides mapped in the field importantly lidar enabled the experts to find ten new landslides and to correct the boundaries of eleven of the 77 landslides mapped during the field survey hence this study showed that large scale lidar derived maps analysed by experienced geomorphologists can significantly improve field survey based inventories of landslides with a subdued morphology in hilly regions copyright 2006 john wiley sons ltd

tilting burial and uplift of the guadalupe igneous complex sierra nevada california it is often incorrectly assumed that plutons have a relatively uneventful structural history after emplacement the 151 ma guadalupe igneous complex gic in the foothills terrane california was involved in three post emplacement events 1 30 of southwestside up tilting during ductile regional faulting and contraction 2 burial of the pluton from 4 to 12 km during crustal thickening of the wall rocks and 3 uplift with only minor tilting in the late cretaceous tilting of the pluton is indicated by 1 southwest to northeast gradational changes from layered gabbros and diorites to granites and granophyres 2 northeastward dips of layering in gabbro internal contacts and bedding of overlying coeval volcanic rocks 3 northeastward decrease in wall rock metamorphic grade and 4 paleomagnetic data from 14 localities across the pluton we argue that tilting occurred between 146 135 ma during southwest northeast directed regional contraction this contraction is indicated by widespread folds and cleavages and by reverse motion on the bear mountains fault zone bmfz a large northeast dipping shear zone that bounds the gic on its southwest side burial of the gic which overlapped in time but outlasted tilting is suggested by 1 post emplacement contractional faulting folding and cleavage development 2 analyses of strains associated with widespread cleavage that indicate vertical thickening of 100 and 3 microstructural and mineral assemblage data that indicate shallow emplacement of the gic in contrast to mineral assemblage and limited geobarometric data from adjacent 120 110 ma plutons that indicate moderate emplacement levels late cretaceous uplift is indicated by 95 75 ma sedimentary rocks that unconformably overlie the 120 110 ma plutons this geologic history is interesting for several reasons first although the gic participated in extensive post emplacement deformation it lacks internal structural evidence of these events except locally along the bear mountains fault zone second the agreement between paleomagnetic and structural evidence for tilting suggests that no large latitudinal displacement of the gic is required third the paleomagnetic data also help to define the geometry of the magma chamber now represented by the gic lack of streaking of paleomagnetic site mean directions demonstrates that the pluton acted as a single unit after cooling through the blocking temperature 450 560 c of low titanium titanomagnetite however variations in the dip of internal layering and contacts from 70 at the base to 30 near the top of the pluton indicate that not all of these features were horizontal and planar when they formed we propose that this variation in dip of layering is most consistent with sidewall crystallization of magma resulting in drape of layering along the walls of the intrusion therefore internal layering within this pluton does not record paleohorizontal

field and model constraints on silicic melt segregation by compaction hindered settling the role of water and its effect on latent heat release to investigate how large volumes of silicic melts segregate to form granitic plutons we conducted a case study of a zoned pluton in which sio 2 increases from intermediate 69 wt to highly silicic compositions 74 wt toward the contact with metasedimentary wallrock in the outer 25 m of the pluton all other major minor and trace elements vary systematically with sio 2 and indicate that outward increasing sio 2 is due to a decrease in mafic elements and minerals whole rock oxygen isotopes and elemental variation diagrams do not support mixing with wallrock as an explanation for the si rich boundary layer instead mafic enclaves which are common in the pluton also decrease in abundance in the outer 25 m of the pluton suggesting a mechanical origin for the si rich boundary layer the coupling of mechanical and geochemical boundary layers combined with geochemical modeling indicate that the silica rich enclave poor boundary layer formed by hindered settling or compaction of a crystal rich crystal fractions 60 magmatic mush segregation of melts at high crystal fraction is known to be a slow process however petrography and zr based thermometry indicate that the residual si rich liquids were water saturated water decreases melt viscosity which helps expulsion but equally importantly water also delays much of the latent heat release to late in the thermal and crystallization history of a cooling magma we show that the higher the water content the longer the time interval over which a magma chamber resides at the stage when water saturated high silica liquids form allowing sufficient time for exfiltration of silicic liquids before the magma body freezes

synkinematic intrusion of the anorogenic 1425 ma beer bottle pass pluton southern nevada the tectonic setting of a transcontinental belt of 1500 1300 ma granitic intrusions that extends from southern california to labrador is controversial however the granites are conventionally considered to be anorogenic detailed field microstructural and geochronologic data from the 1425 ma beer bottle pass pluton southern nevada indicate that major mylonite zones recording dextral contractile strains were probably active during and or shortly after pluton emplacement and suggest that the anorogenic interpretation for this pluton requires reevaluation mylonite zones up to 100 m thick strike northeast dip moderately northwest and contain a consistent west plunging elongation lineation mylonites occur along 15 of the exposed granite wall rock contact and extend into both the pluton and the wall rock mesoscopic and microscopic kinematic indicators record an oblique dextral reverse pluton side down movement sense synkinematic mineral assemblages of hornblende and biotite and dynamic recrystallization of feldspars suggest that deformation occurred minimally under amphibolite facies conditions a k ar biotite date of 1399 32 ma obtained from a sample of mylonitic granite suggests that deformation took place during or soon following pluton crystallization we reject forcible emplacement of the beer bottle pass pluton as a mechanism for formation of the mylonite zones because 1 rocks near the granite wall rock contact are largely unstrained 2 the mylonite zones conform only locally to the pluton wall rock contact 3 mylonite zones strike at high angles to and truncate the intrusive pluton wall rock contact 4 the pluton side down shear sense is more compatible with a uniform sense simple shear zone than a forcibly intruding pluton and 5 fabrics indicative of noncoaxial deformation dominate over flattening fabrics we suggest that the beer bottle pass pluton is fundamentally synkinematic with respect to either 1 a local contractile deformational event or 2 regional strains produced by distant plate tectonic processes operative between 1500 and 1300 ma as suggested by nyman and karlstrom 1994 the timing and kinematics of shear zones associated with other circa 1400 ma plutons in the western united states e g graubard and mattinson 1990 nyman et al 1994 kirby et al this issue support the latter interpretation our kinematic data are more consistent with a contractile or transpressive tectonic setting at circa 1400 ma nyman and karlstrom 1994 nyman et al 1994 than with models involving regional extension e g windley 1993

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

detection of subtle tectonic geomorphic features in densely forested mountains by very high resolution airborne lidar survey abstract despite successes elsewhere in the world 2 m resolution dems from a standard airborne lidar survey failed to detect small tectonic geomorphic features in densely forested high relief mountains of central japan our new 0 5 m dems from an unprecedentedly high resolution lidar survey along the neodani fault now reveal a number of previously unknown fault scarps as well as other hidden geomorphic features the survey achieves a ground return density of 6 2 m 2 out of a total shot density of as much as 12 7 m 2 the main factor to gain sufficient ground returns in unfavorable conditions is a large side lap of 70 between flight swaths which means that any specific area in the target zone is scanned three or more times from different angles evaluation of dems with resolution from 0 25 to 10 m assures that a 0 5m resolution lidar dem is necessary for the detection of subtle tectonic breaks another key factor for complete detection of small tectonic geomorphic features is the application of a recently developed dem visualization red relief image map rrim which allows mapping of all the small features with various sizes orientations and morphology overcoming major drawbacks of classic dem visualizations a very high resolution lidar survey aided with rrim visualization as used in this study provides a more reliable approach for the detailed mapping of slight active fault traces hidden under dense vegetation

the mount perkins block northwestern arizona an exposed cross section of an evolving preextensional to synextensional magmatic system the steeply tilted mount perkins block northwestern arizona exposes a cross section of a magmatic system that evolved through the onset of regional extension new 4oar 39ar ages of variably tilted 0 90 o volcanic strata bracket extension between 15 7 and 11 3 ma preextensional intrusive activity included emplacement of a composite miocene laccolith and stock trachydacite dome complex and east striking rhyolite dikes related volcanic activity produced an 18 16 ma stratovolcano cored by trachydacite domes and flanked by trachydacite trachyandesite flows and 16 ma rhyolite flows similar compositions indicate a genetic link between the stratovolcano and granodioritic phase of the laccolith magmatic activity synchronous with early regional extension 15 7 14 5 ma generated a thick felsic volcanic sequence a swarm of northerly striking subvertical rhyolite dikes and rhyolite domes field relations and compositions indicate that the dike swarm and felsic volcanic sequence are cogenetic modes of magma emplacement changed during the onset of extension from subhorizontal sheets east striking dikes and stocks to northerly striking subvertical dike swarms as the regional stress field shifted from nearly isotropic to decidedly anisotropic with an east west trending horizontal least principal stress preextensional trachydacitic and preextensional to synextensional rhyolitic magmas were part of an evolving system which involved the ponding of mantle derived basaltic magmas and ensuing crustal melting and assimilation at progressively shallower levels major extension halted this system by generating abundant pathways to the surface fractures which flushed out preexisting crustal melts and hybrid magmas remaining silicic melts were quenched by rapid upper crustal cooling induced by tectonic denudation these processes facilitated eruption of mafic magmas accordingly silicic magmatism at mount perkins ended abruptly during peak extension 14 5 ma and gave way to mafic magmatism which continued until extension ceased

observations from the floor of a granitoid pluton inferences on the driving force of final emplacement an east west profile across the tilted bergell pluton exposes a 10 km thick interval in terms of crustal depth consequently the floor as well as the root and side of the main intrusive body of the pluton crop out at the surface and a tentative three dimensional geometry is constructed at the highest crustal level the geometry and deformation features at the margin of the pluton indicate ballooning whereas the folded floor of the main intrusive body indicates synmagmatic shortening related to regional deformation these contrasting features are best explained by shortening of the base of the pluton which caused an expansion at a higher crustal level final emplacement of the pluton into higher crustal levels was therefore not driven primarily by buoyancy but rather by regional deformation within deeper levels of the crust

on the dynamics of magma mixing by reintrusion implications for pluton assembly processes many plutons have formed by repeated intrusion with complex internal contacts characterized by sharp and diause kinematic and compositional domains we performed numerical experiments of mixing following magma chamber recharge that explicitly considers the fluid dynamics of multiphase mixtures in the limit of zero diausivity of intensive scalar quantities and low stokes number mingling by fluid instability is equivalent to deformation and persistent fluid structures are kinematic attractors three distinct regimes are exemplified and can be described by their multiphase reynolds or grashof number for a reynolds number greater than about 100 an internal intrusive contact will collapse by internal wave breaking and chaotic magma mingling and mixing yield a nearly chamber wide stratification this flow may scour mushy regions at the walls and widely distribute previously crystallized material for reynolds numbers from 10 to 100 the internal wave does not break and the stratification occupies less of the chamber leaving islands of unmixed material for reynolds numbers around 1 internal slumping and folding can occur and is the most likely to be preserved by a mineral fabric internal sub vertical contacts require a high absolute viscosity in the resident magma representing a time break between episodes of reintrusion the shape of perched mafic domains captures the progress of sinking from higher levels into regions of increasing strength and crystallinity 7 2000 elsevier science ltd all rights reserved