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

nature of mantle source contributions and the role of contamination and in situ crystallisation in the petrogenesis of proterozoic mafic dykes and flood basalts labrador proterozoic tholeiitic dyke swarms share many compositional features with and pose similar petrogenetic problems to phanerozoic continental flood basalts but there are few extrusive equivalents of such swarms the mesoproterozoic 1 27 ga harp dyke swarm in labrador is one where possible extrusive equivalents exist in the seal lake group but are slightly displaced in space and time and can probably be related by models of progressive crustal extension here we try to evaluate the roles of crystal differentiation in situ crystallisation crustal assimilation and the relative contributions of asthenosphere and lithosphere derived melts in the petrogenesis of the mafic magmas modelling of the major and trace element variations both within individual dykes and between dykes and within the lava sequence does not suggest an important role for continental crust involvement while in situ crystallisation processes could account for some of the compositional variations the most successful models invoke mixing or contamination of asthenospheric magmas with by veined material in the lower lithosphere upper asthenosphere which carries the continental characteristics the results imply an important role for hydrous phases such as phlogopite and hornblende in the sub lithosphere mantle much of the low mgo character of mafic dykes may result from significant removal of mafic phases during in situ crystallisation within the lithosphere

petrology and geochemistry of potassic and ultrapotassic volcanism in central italy petrogenesis and inferences on the evolution of the mantle sources major trace element sr isotopic and mineral chemical data are reported for mafic volcanic rocks mg value 65 from the northern central sector of the potassic volcanic belt of central italy the rocks investigated range from potassic series ks and high k series hks to lamproitic lmp and kamafugitic kam through a transitional series trans thus covering the entire compositional spectrum of potassic and ultrapotassic magmas kam rocks are strongly silica undersaturated and compared with the other rock series have low sio2 al2o3 na2o sc and v and high cao k na na k al ks and hks have high al2o3 cao and variable enrichment in k2o and incompatible elements lmp rocks are saturated in silica and have high sio2 k2o k2o na2 mgo ni and cr and low al2o3 cao na2o sc and v trans rocks display intermediate compositional characteristics between lmp and ks all the rocks under study have fractionated hygromagmaphile element patterns with high lil hfs element values and negative anomalies of ti ta nb and ba negative sr anomalies are observed in the lmp and trans rocks lil elements show overall positive correlations with k2o whereas different trends of sr and hfse vs k2o are defined by lmp trans and ks hks kam 87sr 86sr range from about 0 710 to 0 716 ks hks and kam rocks have similar 87sr 86sr values clustering around 0 710 lmp and trans rocks have the highest 87sr 86sr values geochemical and isotopic data reported for the most primitive italian potassic and ultrapotassic rocks support the hypothesis that the interaction between crustal and mantle reservoirs was a main process in the genesis of italian potassic magmatism simple mass balance calculations exclude however an important role of crustal assimilation during ascent of subcrustal magmas to the surface and indicate that the sources of central italy volcanics underwent contamination with fluids and or melts released by upper crustal material previously brought into the mantle by subduction processes different trends of incompatible elements vs k2o observed in the studied rocks suggest distinct metasomatic processes for the sources of the investigated magmas liquids derived by bulk melting of pelitic sediments are believed to be the most likely contaminants of the source of lmp rocks fluids or melts rich in ca sr and with high lile hfse value and sr isotopic composition around 0 710 are the most likely contaminant of the source region of ks hks and kam volcanics variations in cao na2o and ferromagnesian element abundances and ratios suggest that in some zones the mantle source of potassic magmas experienced partial melting with extraction of basaltic liquids prior to metasomatism

morphometric classification of swell dominated embayed beaches abstract globally embayed beaches are common to hilly and mountainous coastlines they are typically characterised by two headlands that are a primary control on incident wave exposure and beach morphodynamics embayed beaches exist under a range of headland morphologies and degree of embaymentisation here we present a generalised embayment morphometric parameter e which classifies the geomorphological setting of embayed beaches based on the embayment indentation and area we apply this to 168 swell dominated embayed beaches from 6 regions using open access imagery the embayment morphometric parameter e was subjected to k means cluster analysis to identify 4 classes of embayed beaches with increasing e indicating greater headland influence and impact on incident wave exposure the classes range from 1 to 4 with increasing degree of embayment the most common is class 2 43 n 73 which represents embayed beaches that have moderate embayment indentation and headland influence there are clear trends in embayment geometry regardless of location wave climate or tidal regimes within the embayments there were 6 possible headland orientations types h1 h6 the most common 58 n 97 is when both headlands are orientated outwards from the beach h6 and may result in greater morphological beach response from less headland shadowing compared with headlands orientated inwards onto the beach h1 in summary we have developed a simple classification scheme for embayed beaches based on degree of indentation and headland orientation that can be applied to any embayed beach globally

polynomial and power functions for glacial valley cross section morphology an empirical evaluation of glacial trough cross section shape is performed on seven vertical cross sections in three sierra nevada valleys glaciated during the late quaternary power and second order polynomial functions are fitted by statistical regression power functions are very sensitive to subtle valley bottom topographic features and require precise specification of the valley bottom centre location this dependency is problematic given under representation of valley bottoms by conventional contour sampling methods and the common alteration of valley bottom morphology by non glacial processes power function exponents vary greatly in response to these and other non genetic factors and are not found to be reliable indicators of overall valley morphology second order polynomials express overall valley shape in a single robust function they are applied to both bedrock and sediment floored glacial valleys with negligible statistical bias except where side slopes are stepped or convex upward or where valley form is asymmetrical they can describe alluviated or severely eroded valleys and can objectively identify indi vidual components of polymorphic valleys because valley bottom and centre locations need not be specified mathematical expressions of parameters useful for geomorphic measurements and glaciological modelling are analytically derived from the polynomials as functions of the three polynomial coefficients these parameter equations provide estimates of valley side slopes mean and maximum depth midpoint location width area boundary length form ratio and symmetry

structural tectonic and glaciological controls on the evolution of fjord landscapes abstract the fjord landscape of south america stretching 1500 km between golfo corcovado 43 s and tierra del fuego 56 s is the largest continuous fjord landscape on earth this paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models first order geological structures are represented by strike slip faults forming lineaments up to hundreds of kilometres long the strike slip faulting has been active since late cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to 10 km long a detailed analysis of these second order lineaments from digital image data was carried out in three sectors in sector 1 located northwest of the north patagonian icefield there are three distinct mean orientations characterized by a main nearly orogen parallel orientation az 145 and two orogen oblique secondary orientations az 20 and az 65 in sector 2 located west of the south patagonian icefield there are also three separate mean orientations with most of the lineaments concentrated between azimuths 0 and 80 mean at 36 and two other orogen oblique means at azimuth 122 and 163 in sector 3 around the cordillera darwin there is a single main orogen parallel mean at 100 115 in all three sectors mapped fjord orientations bear a striking similarity to the structural data with fjords orientated preferentially in the same direction as structural lineaments we infer that successive glaciations followed the same ice discharge routes widening and deepening pre existing geological structures at the expense of the surrounding terrain to create the fjord landscape this study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

using parabolas to describe the cross sections of glaciated valleys it is widely accepted that the simple power curve y axb can be used to describe the cross section of glaciated valleys there are however good reasons to suppose that this particular form of equation is inappropriate for this purpose

erosion of sognefjord norway sognefjord is formed by a combination of exploitation of rock structure and subaerial and subglacial processes the fjord system follows zones of rock structural weakness above sea level the landforms are due mainly to subaerial processes and somewhat surprisingly not to glacial activity removal of erosive products and deepening of the fjord below sea level is due to glacial erosion

mesoscale coastal complexity and its relationship to structure and forcing from marine processes abstract this study investigates australia s coastline complexity to establish the relationship between geological inheritance and ocean processes as well as determine the characteristic length scales at which they operate each of australia s geological regions displays discrete complexity signatures indicating a correlation between coastal complexity and geology these mesoscale complexity signatures can vary enormously between regions over a range of length scales an angled measurement technique is used to quantify coastal complexity for a large number of random nodes at varying length scales around the australian continental margin cluster analysis are used to determine characteristic complexity signatures for random nodes and dimension reduction techniques and additive models are used to assess the relative effects of wave and tide power and physical variables in each geological region however although some geological regions are visibly distinct all geological regions are comprised of up to three basic classes or typologies furthermore this study demonstrates that at the mesoscale 1 100 km geological inheritance has the major influence in determining coastal complexity results show lithological mix to be an important factor and coastlines of a homogeneous lithology tend to be straighter than coastlines of mixed lithology they further demonstrate that wave action promotes a straight coastline if the lithology is homogeneous and a complex one if the lithology is heterogeneous this work will contribute to ongoing research in the classification of the australian continental margin by utilising available geophysical datasets that are fundamental to the establishment of rigorous boundaries in the regional marine planning process it provides important information about drivers responsible for coastal complexity at the mesoscale it is only from such studies that constructive quantitative approaches can be developed for robust regionalisation of coastal and marine systems

scale dependence of lithological control on topography bedrock channel geometry and catchment morphometry in western scotland abstract we propose that a scale dependent topographic signature of erodibility arises due to fluvial and glacial erosion acting on different parts of the landscape at different times for 14 catchments in western scotland we define three levels of substrate erodibility in order of decreasing resistance quartzite rocks nonquartzite rocks and zones of fault related fracture then using digital topographic and planimetric data coupled with field measurements we identify regression based scaling relationships between substrate erodibility and morphometric parameters at two spatial scales catchment scale morphometry shows a weak to variable relationship with substrate metrics overall erodibility can be inferred from catchment steepness indices i e channel steepness index and relief ratio but the existence of multiple exceptions could confound a more general application of this approach nonetheless major valley troughs trace fault zones and nonquartzite rocks leaving much of the higher and stee

structural control on the presence and character of calas observations from balearic islands limestone rock coast macroforms abstract calas are characteristic embayed rocky coastline landforms related to steep sided drowned valleys that were deeply incised during low sea level stages into carbonate plateaus this paper studies the factors that control the presence and character of calas in three different islands of the balearic archipelago mallorca menorca and formentera by means of digital elevation model dem reconstructions embayment and catchment morphometric analysis and through the compilation of fault and joint orientations all islands exhibit emerged carbonate platforms upper miocene in age characterised by horizontal or very gently dipping bedding two distinct patterns observed at all study sites are the absence or poor development of calas when carbonate plateaus exhibit strong coast parallel structures and a greater variability of cala embayment size according to stream catchment size lithology or their catchment distance from the coastline furthermore the amount of stream incision and consequently the characteristics of a cala at its mouth depends on the proportion of impermeable rocks exposed in each drainage basin and on the density and spacing of fractures karst collapse dolines and valley infilling associated with quaternary sea level oscillations are also important in determining the shape and size of calas

processing of regional seismic events using data from small aperture arrays abstract a regional on line array processing package ronapp has been developed and tested on data from a small aperture seismic array noress at norsar consisting of 12 sensors spaced with distances up to about 2 km the processing package automatically detects and locates regional seismic events in the distance range from a few kilometers to the maximum propagation range of regional s type waves sn or lg the package contains a conventional sta lta detector which works on a set of filtered beams deployed at typical phase velocities of pn and lg sn 8 0 and 4 5 km sec when a detection is found data within a certain time window around the detection time are used for estimates of refined arrival time and signal frequency and a wavenumber analysis is then performed following a proper prefiltering this gives in addition to arrival time and frequency estimates of phase velocity azimuth and signal to noise ratio for each detection following each processed detection an event location based on azimuth and s p travel times is performed if the last detection is identified as an s type wave phase velocity below 6 km sec and a preceding p wave phase velocity above 6 km sec has been detected with about the same direction of approach appropriate procedures are developed to allow for several detections within the p and s coda to keep track of used and unused detections and to identify epicenter locations that override preliminary ones as the analysis progresses through the s wave train of the event the processing package has been tested off line and on line on a number of data intervals for various experimental noress array configurations the automatic processing package provides detection results for regional events that compare favorably with those from the full norsar array and location results that deviate from locations by the fennoscandian network of seismological stations by typically 30 km which is of the order of the location uncertainty of the network

scratching the surface estimating dimensions of large igneous provinces a study of five major basaltic provinces including oceanic plateaus volcanic passive margins and continental flood basalts shows that they are voluminous constructions of extrusive igneous rock underlain by intrusive rock crustal thickness ranges from 20 to 40 km and lower crust is characterized by high 7 0 7 6 km s seismic velocities volumes and emplacement rates derived for two oceanic plateaus the ontong java and kerguelen broken ridge reveal short lived pulses of increased global crustal production and suggest an origin involving the lower mantle the ontong java rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid ocean ridge system despite the importance off large igneous provinces in studies of mantle dynamics and the global environment scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features

lithospheric thinning by midplate mantle plumes and the thermal history of hot plume material ponded at sublithospheric depths mantle plumes supply hot material to the asthenospheric channel which spreads beneath initially normal oceanic lithosphere at midplate hotspots the fate of this material and the thermal structure of the lithosphere depend on the vigor of secondary convection through the steep thermal gradient above the ponded plume material it has been proposed either that 1 secondary convection is so vigorous that material hotter than the normal mantle adiabat is cooled a short distance downstream of the hotspot such that the geotherm resembles that of younger lithosphere or 2 that the plume material retains its excess temperature for a significant time and the lithosphere thins slowly a parameterized method of modeling transient secondary convection is developed to examine this question calculations indicate that secondary convection is likely to be sluggish unless partial melting greatly lowers viscosity in addition vigorous secondary convection would greatly retard upstream asthenospheric flow of plume material beneath the nose of the hawaiian swell and asthenospheric flow of hot material away from hotspots on slowly moving plates like cape verde this conclusion is compatible with limited seismic evidence that indicates that the lithosphere is not detectably thinned beneath the hawaiian swell

drainage network evolution and patterns of sedimentation in an experimental wedge in fold and thrust belts drainage organization and patterns of sedimentation depend conceptually on the ability or not for preexisting reaches to incise uplifting thrust sheets in this study we investigate experimentally the dynamics of drainage network in a wedge submitted to shortening and erosion it allows us to reproduce and to monitor the interactions between tectonics erosion and sedimentation during the development of up to five successive thrust sheets in the experiments channels adjust to uplift rate by both increasing their slope and narrowing their channels as it is observed in nature the series of experiments shows that the proportion of persistent preexisting transverse channels increases with the ratio of rainfall over shortening rates the experiments confirm the view that the competition between discharge and tectonic uplift controls along strike variations in sediment flux in sedimentary basins by controlling the drainage organization if the transverse channels draining a wedge are not diverted a line source dispersal system develops in front of the active structure if channels are diverted in the backlimb of the frontal structure it results in point sourced depositional systems separated by areas fed only by small channels developing in the front of the wedge fans accumulated in front of the active structures reveal two stages of sedimentation one of progradation while the frontal structure is active and a second one of valley backfilling and thrust sealing during internal deformation of the wedge the experiments also suggest that spatial variations in rock uplift rate along a thrust front may be evidenced by minimum discharge variations of persistent transverse channels

the scourie dyke suite petrogenesis and geochemical nature of the proterozoic sub continental mantle the petrogenesis of bronzite picrite olivine gabbro norite and quartz tholeiite dykes which make up the 2 39 b y scourie dyke swarm cutting the archaean lewisian gneisses of n w scotland is interpreted on the basis of their major and trace element geochemistry most of the dykes bear primary amphibole and or phlogopite and with one exception are all hypersthene or quartz normative apart from one tholeiite dyke which shows relative light rare earth element depletion all the dykes show enrichment in light rare earths and large ion lithophile elements they do not however show an equivalent enrichment in other incompatible high field strength ions such as nb and ta and in this respect resemble island arc and calc alkaline basalts the different dyke types have distinctive rare earth patterns and other trace element ratios which are maintained over a range of major element compositions

rock slope instability and erosion toward improved process understanding rock slopes in a range of environments are among the landscape elements most sensitive to climate change the latter affecting rock mass properties altering slope boundary conditions and changing geosystem configurations major climate dependent influences promoting destabilization include stress redistribution with changing glacial ice extents degradation of mountain permafrost altered slope hydrology and weathering environments loading and unloading due to deposition and erosion and changes in the spectrum of magnitude and frequency of driving forces in steep bedrock terrain erosional processes control slope morphology by modulating rates of i weathering in response to climate and pre disposition ii rock slope retreat in response to magnitude and frequency of detachment and iii channel incision or valley infilling in response to variable sediment supply modelling landscape evolution and anticipating natural hazards in these environments thus requires deeper insights into the processes driving rock slope instability and erosion this special issue emphasizes new understanding of rock slope processes through a collection of manuscripts at the forefront of research in the field copyright 2014 john wiley sons ltd

strength of jointed rock masses jointed rock masses comprise interlocking angular par ticles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials the strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which in turn depends on the number orientation spacing and shear strength of the discontinuities a complete understanding of this problem presents formidable theoretical and experi mental problems and hence simplifying assumptions are required in order to provide a reasonable basis for estimating the strength of jointed rock masses for engineering design purposes this paper summarizes some of the basic information upon which such simplifying assumptions can be made a simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples des masses jointives de rochers comprennent des particules angulaires enchevetrees ou des

petrogenetic relationship between palaeoproterozoic tholeiitic dykes and associated high mg noritic dykes labrador canada abstract trace element and sr nd isotopic studies of the palaeoproterozoic 2235 ma kikkertavak dyke swarm in labrador provide information on early sub continental lithosphere development there are three distinct chemical dyke types two are tholeiitic the third of high mg norite composition petrogenetically it is not possible to relate any of the chemical groups one to another by simple fractional crystallisation processes nor can they be derived by contaminating asthenospheric magmas with local crustal components from their sr nd isotopic characteristics in relation to their rare earth and multielement patterns it is clear that significant heterogeneity existed in the source regions of the dyke magmas at the time they were generated and that the mantle processes responsible can be linked with the phase of crustal growth in the region at 3 0 ga modelling suggests that the observed compositions can be accounted for by lower lithosphere asthenosphere mantle sources which have been variably depleted by previous episodes of basalt magma extraction and then re enriched by a lamproitic melt component and possibly by progressive infiltration of melts from a subducted sediment or subduction component high mg noritic dykes are relatively common worldwide in the palaeoproterozoic and are often broadly coeval with tholeiitic dykes but are much less common in younger dyke suites most have compositions which require a refractory major element composition coupled with significant re enrichment in incompatible lithophile elements recent models for cyclic mantle overturns with related deep mantle plumes begin to provide the right thermal and compositional environment beneath immature lithosphere which can generate the dyke types observed

sedimentary basin inversion caused by igneous underplating northwest european continental shelf a considerable body of evidence indicates that many of the extensional sedimentary basins in the vicinity of the british isles underwent permanent exhumation during the tertiary the most dramatic indicator of this process is the present day absence of as much as 4 km of anticipated postrift thermal subsidence in basins just north and west of scotland any explanation of this observation must take into account the fact that the entire region has very small long wavelength free air gravity anomalies this important constraint implies either that the crust has been thickened or that low density material has been added to or formed from the lithosphere and rules out models that invoke flexural effects arising from the opening of the north atlantic tertiary epeirogeny is often attributed to compression that is assumed to be related in a general sense to alpine mountain building however to remove 3 km of sedi mentary rock from a basin 100 km wide requires 15 km of shortening minor tertiary compression is observed all over the continental shelf but nowhere is it sufficient to account for the required amount of uplift and erosion in addition exhumation dramatically increases from south to north whereas the observed compression decreases markedly in the same direction at the beginning of the tertiary rifting associated with the initiation of the iceland plume generated substantial volumes of melt inversion of rare earth element concentrations of mgorich igneous rocks suggests that a minimum of 5 km of melt was produced beneath at least part of the continental shelf we infer that much of this melt remains trapped within the lithosphere presumably close to the moho which acted as a density filter such underplating will generate rapid uplift

fluvial clastic sediment yield in canada scaled analysis this report presents a set of maps of regional fluvial sediment yield in canada based mainly on the water survey of canada archive of riverine suspended sediment observations regional scaling rel

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

glacial outlet valley size ice drainage area relationships some considerations previous work indicates that large variations in the power law relationship relating glacial outlet valley size to ice drainage area may occur between different glaciological settings in this paper we take issue with methods used to quantify the relationships of outlet valley size to drainage area size and propose a general method for comparing power law relationships between study areas to determine whether or not such power law scalings are similar based on this method we demonstrate that outlet valleys have a similar sensitivity to variation in ice contributing area irrespective of their glaciological setting contrary to earlier findings minor variation in such relationships may reflect the different lithological and glaciological settings of the study sites and provide an insight into the physics of glacial erosional development of landscapes despite their limitations we conclude that power law relationships are valid and when interpreted carefully provide a useful basis for comparing the efficiency of glacial erosion processes in different locations copyright 2003 john wiley sons ltd

a reassessment of the role of ice sheet glaciation in the long term evolution of the east greenland fjord region abstract the long term evolution of the east greenland fjord region is investigated using geomorphological and stratigraphical evidence to 1 assess the nature of landscape modification caused by late cenozoic ice sheet glaciation and 2 relate patterns of glacial landscape modification to first order i e continent margin scale topography and geology geomorphological and stratigraphical evidence demonstrates evolution of the first order topography and incision of at least part of the present first order fjord system by 55 ma this hypothesis is tested using apatite u th he ages for samples from two bedrock profiles near kong oscar fjord the thermochronology supports landscape evolution before 55 ma followed by relative tectonic stability because it indicates rapid denudation around the time of rifting that occurred prior to continental breakup i e between 75 and 55 ma the nature of landscape modification caused by late cenozoic glacial erosion appears to have been controlled by first order topography and geology with selective ice sheet erosion in areas of high elevation caledonian basement and apparently little glacial erosion of low elevation mesozoic sedimentary strata nevertheless fjord morphometry demonstrates systematic evolution of the first order fjord system from confined and overdeepened fjords in caledonian basement to wider and disproportionately larger fjords in mesozoic strata the latter indicates that changes in lithological strength enabled the development of more efficient fjord morphology under full glacial conditions that may have promoted fast ice flow

lithological and drainage network determinants of the character of drowned embayed coastlines the perception that coastal character reflects lithology via lithology s control on embayment size is tested by an examination of embayment sizes along a tectonically stable coastline to which ancient river systems drain the new south wales coast this coastline is comprised of four distinct geological provinces exhibiting a wide range of lithological and structural variation and is taken to be representative of physiographic settings controlling coastline configuration on a wide range of continental margin types our analysis shows that embayment size l the length of the embayment from headland to headland at sea level is related to the size of the river draining to the embayment catchment area a such that l 0 60 a 0 82 documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc

seismic event detection and source location using single station three component data the seismic event detection and source location scheme presented in this paper uses single station seismic data to analyze seismic events to detect events the detection scheme combines the signals on the horizontal components in a manner analogous to beam steering once an event is detected the location scheme estimates the location of the source with respect to the receiver by estimating the polarization direction of the pn phase the range estimate is then obtained from the relative timing of different phases

petrology and geochemistry of metabasalts from the 1 95 ga jormua ophiolite northeastern finland the jormua ophiolite exposes a unique fragment of red seatype oceanic crust formed in a setting related to continental break up 1950 ma ago two distinct types of basalt are represented the early dykes and the main basalt suite early dykes have fractionated h ree patterns oib like trace element patterns low 2j nb 6 and ejwfyss ga 0 6 indicative of their derivation from an enriched source the remaining dykes and all lavas belong to the second e morb like main basalt suite which is characterized by high mg number and cr contents flat ree patterns zr b 6 17 chondritic th ta and only moderately depleted isotopic signatures zjufi gs a 4 1 9j most main suite samples cannot be related solely by fractional crystallization to a common parental magma rather they represent distinct melt fractions that underwent variable amounts of chromite olivine plagioclase fractionation during ascent a significant part of the compositional diversity of the main basalt suite can be explained by mixing a depleted source with a relatively uniform proportion of an enriched component similar to that represented by the oib like early dykes it is probable that during the latest stages of continental rifting the oib type melts metasomatized the upper part of the depleted asthenospheric mantle which became the source of the main basalt suite soon after the old continental lithosphere was ruptured the complete absence of any evidence for a subduction related component in the basalts implies that jormua is not a back arc ophiolite

uphill facing antislope scarps in the coast mountains southwest british columbia uphill facing scarps are examined at affliction creek a glacierized area within the meager creek volcanic complex of southwest british columbia scarps occur directly downslope of tension cracks and are considered to have developed from a combination of 1 antithetic movement between partly toppled slices of rock defined by a master joint set dipping into the slope and 2 erosion of the upslope face of each tension crack leaving the downslope face prominent as an antislope scarp a kinematic test for toppling failure is described glacial erosion and rapid glacial downwasting are probable causes of toppling lichenometric data indicate significant scarp development since affliction glacier attained its maximum neoglacial dimensions about 140 yr ago dilatancy is cited as a possible mechanism for scarp stabilization

assimilation and high pressure fractional crystallization afc recorded by paleo proterozoic mafic dykes southeast greenland abstract the northern margin of the nagssugtoqidian mobile belt in southeast greenland exposes a suite of moderately fractionated fe rich tholeiitic dykes of paleo proterozoic age the dykes were intruded during extension of the crust prior to the development of the nagssugtoqidian mobile belt although the dykes recrystallized under amphibolite facies conditions during proterozoic orogenesis they suffered little deformation excluding two very evolved samples the compositions range between 7 8 4 6 wt mgo 44 5 52 9 wt sio2 and 1 8 6 9 wt total alkalis one group of mafic dykes shows distinct mantle normalized trace element patterns with high abundance of low field strength elements and light rare earth elements and low abundances of high field strength elements these characteristics are consistent with a process of fractional crystallization coupled with assimilation of the regional granulitic crust relatively high rates of assimilation to fractional crystallization 0 7 are required to generate the level of incompatible trace elements this points to lower crustal conditions and the assimilation is believed to have taken place at the base of the continental crust trace element variations indicate fractionation at high pressure involving clinopyroxene as the main extracted phase we evaluate two fractionation models corresponding to a pressure of 0 9 and 1 5 gpa respectively and show that the trace element variations require polybaric fractionation at pressures from a maximum of 1 5 gpa to a minimum of 0 9 gpa

remobilisation of the continental lithosphere by a mantle plume major trace element and sr nd and pb isotope evidence from picritic and tholeiitic lavas of the noril sk district siberian trap russia the late permian to early triassic siberian traps have been sampled by drill core core sg 9 and from surface exposure section 1f in the noril sk region of the siberian platform russia combined major trace element and nd sr and pb isotope data on selected samples through the siberia trap offer new chemostratigraphic criteria for the identification and characterisation of two fundamentally different magma types and 9 of the 11 formations of lava developed near noril sk a lower sequence of sub alkalic basalts tholeiites and picritic basalts upwards these are the ivakinsky syverminsky and gudchichinsky formations are overlain by an upper sequence of picritic basalts and tholeiites interbedded with tuffs upwards these are the khakanchansky tuklonsky nadezhdinsky morongovsky mokulaevsky and kharayelakhsky formations the gudchichinsky and tuklonsky formations contain both picritic and tholeiitic lavas the tuklonsky formation tholeiites and picrites have moderate gd yb 1 6 1 8 low tio2 0 45 0 95 wt a significant negative ta and nb anomaly nb la 0 42 0 57 and unradiogenic nd nd chur to 4 6 in contrast both the gudchichinsky formation tholeiites and picrites have high gd yb 2 3 3 1 and tio2 1 2 2 3 wt no significant nb or ta anomaly nb la 0 8 1 1 and radiogenic nd nd chur to 7 3 the low ti and nb la high la sm and unradiogenic nd isotope signatures of the picritic tuklonsky formation lavas and the tholeiitic lavas of the upper sequence are characteristic of magmas strongly influenced by material from the continental lithosphere whereas the high ti and nb la low la sm and radiogenic nd isotope signatures of the lower sequence are more comparable to deeper asthenospheric mantle plume generated lavas similar to oceanic island basalts the lavas overlying the tuklonsky formation have mg numbers of 0 63 to 0 68 and are more evolved than the tuklonsky mg number 0 62 and have more radiogenic nd chur tuklonsky 0 03 to 4 66 mokulaevsky 0 60 to 1 61 but have many of the incompatible trace element features of the tuklonsky sky type magma these lavas show a progressive upwards decline in sio2 55 49 wt la sm 4 6 2 0 and ur sr 67 to 13 which has previously been attributed to a decrease in the proportion of crustal material contributed to the magma this paper explores and alternative model where a component of the crustal contribution might be derived from within an ancient region of the mantle lithosphere as recycled sediment rather than from the overlying continental crust

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

temporal constraints on glacial valley cross profile evolution two thumb range central southern alps new zealand abstract a key problem in understanding valley evolution in alpine landscapes has been the lack of an independent timescale against which to measure morphological change here we outline that by using space as a proxy for time the role of glaciation in producing classic u shaped valleys can be quantified the two thumb range in new zealand s central southern alps is undergoing rapid tectonic transport and uplift as it is advected towards the alpine fault repeated cycles of glacial erosion during the quaternary have fashioned an alpine landscape in the north of the range close to the main divide and alpine fault while valleys in the less glaciated south of the range have rounded divides and convex fluvial cross profiles using known rates of tectonic transport and uplift of the southern alps coupled with an offshore oxygen isotope 18o record from the chatham rise and glacio geological reconstructions time constraints can be applied to the erosional development of valleys it is possible to estimate the duration of glacial occupancy of valleys in the two thumb range and the pattern is one of very limited glaciation of the southern valleys with glacial occupancy increasing northwards the key trend identifiable is that valley cross profiles become u shaped with c 400 600 kyr of glacial occupancy other models have shown a flattening of valley long profiles with increased glaciation implying glaciers erode larger volumes of rock from mountains than rivers from a cross profile perspective the simple change in geometry from v to u shape concurs with these models indeed the transition from v to u shape with increasing relief and glaciation indicates glaciers may erode greater volumes of rock from mountain belts than rivers

wave train model for knickpoint migration rivers respond to a drop in their base level by incising the topography the upstream propagation of an incision as usually depicted by a knickpoint migration is thought to depend on several parameters such as the drainage area lithology and the amplitude of the base level drop we first investigate the case of the messinian salinity crisis that was characterized by the extreme base level fall 1500 m of the mediterranean sea at the end of the miocene the response of drainage areas of three orders of magnitude 103 to 106 km2 highlights the dominant role of the drainage area with a square root relationship in controlling the knickpoint migration after a base level fall a compilation of mean rates of knickpoint propagation for time durations ranging from 102 to 107 years displays a similar relationship indicating that successive wave trains of knickpoint can migrate in a river first wave trains linked to the release of the alluvial cover and then wave trains related to the bedrock incision which correspond to the real time response of rivers wave trains with very low retreat rates long lived knickpoints 1 my rather correspond to the response time of regional landscape

a discussion of hirano and aniya s 1988 1989 explanation of glacial valley cross profile development in a rational explanation of cross profile morphology for glacial valleys and of glacial valley development hirano and aniya 1988 present an explanation for the apparent catenary form of glaciated valley cross profiles based on the assumption that glacial erosion works towards minimizing friction between a glacier and its channel however as there is as yet no convincing justification for the application of such extremum principles to this problem it is not clear how useful this type of analysis might be in more detail hirano and aniya s analysis includes assumptions about patterns of basal water pressures and the controls on friction inconsistent with other work in this area furthermore as hirano and aniya 1989 point out the catenary solution they derive is the maximum rather than the minimum friction solution the underlying reason for this surprising result is that the variational principle hirano and aniya use is inappropriately structured for the problem being addressed as it does not involve a cross section area i e ice discharge constraint hirano and aniya also discuss the progressive development of glacial valley cross profiles but their analysis is hindered by the fact that most of the data they present are purely morphological and thus cannot be used to assess form development as a function of either time or extent of glacial erosion the only possible exceptions are graf s 1970 data which give morphological parameters as a function of valley order but these do not unequivocally support hirano and aniya s conclusions and are used with implicit assumptions about the relationship between valley order and time of glacial occupation or magnitude of glacial erosion that are incorrect or uncorroborated respectively however if we accept the common assumption that glacial erosion results in a progression from initial v shaped to broadly u shaped parabolic or catenary forms hirano and aniya s argument that there are two distinct types of form development incision in alpine situations versus valley widening under ice sheets is justified and is an important observation that needs to be addressed in future models of glacial valley development

convection and crystal settling in sills it has been advocated that convective and crystal settling processes play significant and perhaps crucial roles in magmatic differentiation the fluid dynamics of magma chambers have been extensively studied in recent years both theoretically and experimentally but there is disagreement over the nature and scale of the convection over its bearing on fractionation and possibly over whether it occurs at all the differential distribution of modal olivine with height in differentiated alkaline basic sills provides critical evidence to resolve this controversy at least for small to medium large magma chambers our own and others published data for such sills show that irrespective of overall olivine content modal olivine contents tend to increase in a roughly symmetrical manner inwards from the upper and lower margins of the sill i e the distribution patterns are more often approximately d shaped rather than the classic s shape generally ascribed to gravity settling we concur with the majority of other authors that this is an original feature of the filling process which has survived more or less unchanged since emplacement we therefore conclude that the magmas have not undergone turbulent convection and that gravity settling has usually played only a minor modifying role since the intrusion of these sills we offer a possible explanation for the apparent contradiction between fluid dynamical theory and the petrological evidence by suggesting that such sills rarely fill by the rapid injection of a single pulse of magma rather they form from a series of pulses or a continuous pulsed influx over a protracted interval during which marginal cooling severely limits the potential for thermal convection

knickpoint recession rate and catchment area the case of uplifted rivers in eastern scotland knickpoint behaviour is a key to understanding both the landscape responses to a base level fall and the corresponding sediment fluxes from rejuvenated catchments and must be accommodated in numerical models of large scale landscape evolution knickpoint recession in streams draining to glacio isostatically uplifted shorelines in eastern scotland is used to assess whether knickpoint recession is a function of discharge here represented by its surrogate catchment area knickpoints are identified using ds plots log slope versus log downstream distance a statistically significant power relationship is found between distance of headward recession and catchment area such knickpoint recession data may be used to determine the values of m and n in the stream power law e kamsn the data have too many uncertainties however to judge definitively whether they are consistent with m n 1 bedrock erosion is proportional to stream power and kps should be maintained and propagate headwards or m 0 3 n 0 7 bedrock incision is proportional to shear stress and kps do not propagate but degrade in place by rotation or replacement nonetheless the e scotland m and n values point to the dominance of catchment area discharge in determining knickpoint retreat rates and are therefore more consistent with the stream power law formulation in which bedrock erosion is proportional to stream power copyright 2005 john wiley sons ltd

glacial landscape and paleoglaciation in terra sabaea evidence for a 3 6 ga polythermal plateau ice cap abstract in a previous study we demonstrated with a comparative morphometrical analysis the first morphometric evidence of a glacial landscape composed of glacial cirques and glacial valleys in the south of terra sabaea at an elevation 1000 m in two impact craters and one mountain the purpose of this study is to use the same method to seek other geomorphologic evidence of glacial landscapes elsewhere in terra sabaea based on a comparison between current and old glacial landscapes on earth and mars we identified 81 glacial valleys and possible evidence for a former plateau ice cap dated at 3 6 ga at the highest elevation in terra sabaea the identified glacial valleys have the same morphometric properties as terrestrial and martian glacial valleys with u shaped cross sectional profiles a v index 0 2 a length to with ratio 1 and a cross sectional area to drainage area ratio four times higher than the fluvial ones moreover these properties are different from terrestrial and martian fluvial valleys we did not find well preserved glacial cirques in this area this absence questions the origin of glacial valleys however the presence of an extensive flat plateau from which the long valleys radiate could have hosted an ancient plateau ice cap which was the source of these glacial valleys a comparison with the cantal and the shaluli shan in the southeastern tibetan plateau on earth reveals morphometrical similarities with our study area in fact long glacial valleys originating radially from a plateau at higher elevation are characteristics of an ancient plateau ice cap this analysis allowed us to propose a polythermal regime for martian glacial landscape namely a cold based ice cap except at the margin where the regime is warmed based due to the steeper topography this topography created shear stress which increased the heat at the base of the ice and created the outlet glacial valleys near the plateau the radial valleys are u shaped with a v index 0 2 but downstream to the low elevation area these valleys become more v shaped with a v index around 0 1 this hypothesis is supported by the presence of an open basin paleolake making the transition between inlet glacial valleys upstream and an outlet v shaped valley downstream so the morphometry of the radiating valleys suggests that liquid water played a role in the formation of this landscape

event location at any distance using seismic data from a single three component station this paper demonstrates the usefulness of a novel technique for analysis of single site three component seismogram records for reliable epicenter determinations for even small seismic events at any distance parameters that may be extracted by this technique are p phase identifications in terms of x 2 probabilities and the associated slowness vectors using data from short period and broadband seismometers installed in the new noress norway array single site event locations are demonstrated azimuth estimates are found directly from the slowness vector while epicenter distance estimates are derived from differential arrival times between pn pg sn and lg sg simultaneous inversion for crustal model and hypocenter data indicate a crustal thickness beneath noress of 33 5 km if sn and or lg are well recorded focal depth estimates are often accurate to within a few kilometers locating teleseisms is problematic since secondary phases are not fully readily identifiable and hence distance can be estimated only by conversion of the measured apparent phase velocity for distances out to approximately 1000 km event location errors as compared to network solutions seldom exceed 50 km and are due mainly to errors in azimuth estimates with sn phases available focal depth errors appear to be of the order of 4 km for teleseismic p waves short period location errors occasionally exceeded 7 and were due mainly to poor distance estimates using broadband records from relatively strong events location errors were about 1 further refinements seem feasible by using seismicity information and or recognition of stationarity in the p wave decomposition pattern for events within the same region at least in certain cases such approaches reflect genuine location refinements as demonstrated

morphodynamic characteristics and classification of beaches in england and wales abstract the use of beach classification models has become widespread in literature in recent years beach classification models that recognise distinct modal beach states in response to environmental conditions are most widely used these models were developed largely in high energy micro to meso tidal sandy environments and subsequent attention has focussed on extending their use into other beach environments here the applicability of these traditional beach classification models to the highly diverse coastline of england and wales was assessed through collection of detailed morphodynamic characteristics of 92 beaches yielding a comprehensive multi variate data set containing morphological sedimentological and hydrodynamic information the complex and diverse study region incorporates beach morphology covering the full spectrum from reflective to dissipative and non barred to multi barred cluster analysis supplemented by mds ordination resulted in the identification of 9 distinct beach types traditional morphodynamic indices and rtr were found to be effective in discriminating between beach groups providing some support for the beach state models derived using information from australian beaches it was found that absolute wave energy wave power is important as well in controlling beach type for intermediate beaches a wave energy flux p h 2 t value of 3 kw m 1 was found to differentiate between beaches with p 3 kw m 1 and without p 1 three dimensional bar rip morphology a key component controlling recreational beach hazard levels observations presented here inform a beach classification model to be used as the basis for a national beach risk assessment programme beach classification models based on environmental parameters are by necessity simplifications and should be used as tools for understanding morphodynamic systems rather than beach type prediction

outlet glacier trough size drainage area relationships fiordland new zealand abstract this paper examines relationships between the area supplying ice to fiord troughs and various measures of fiord size such as depth width and length in fiordland new zealand the size of the outlet troughs was found to be adjusted to the discharge of ice following a similar relationship to that encountered with fiords developed under essentially cold based ice sheets in british columbia however the fiordland outlet troughs were substantially shorter and shallower than their counterparts in british columbia this difference may reflect contrast in mode of erosion in each case although the major dimensions of the fiords undoubtedly reflect the controlling influence of the pre glacial lanscape upon which ice caps were superimposed with their rediating outlet glaciers

a rational explanation of cross profile morphology for glacial valleys and of glacial valley development the fact that the cross profile of the glacial valley could be well approximated by parabolas y axb b 2 0 is explained by the variation principle assuming that the glacier erosion works towards minimizing thefriction between ice and bedrock the variation principle proves that the ideal or fully developed morphology of the glacial valley should be a catenary the curve which a chain hanging from two fixed points forms maclaurin s series expansion of the catenary equation shows that a parabola is a very good approximation of the catenary hence the good approximation of the cross profile by parabolas different catenaries are generated by changing the form ratio depth rim width and are then approximated by y axb by the method of last squares the b values obtained become only fractionally larger than 2 0 with invreasing form ratios of up to 1 0 indicating that b values would range in practice between 1 0 and about 2 0 two types of trend in the relationship between b values and the form ratio were obtained from several glaciers for one type the b value becomes larger with increasing form ratios and for the other the opposite the first type is called the rocky mountain model after its source of data and represents overdeepening of the glacial valley development the second type is caalled the patagonia antarctica model representing a widening instead of a deepening process of development these differences are attributed to the nature of the glaciers which produced these valleys i e alpine glaciers and continental ice sheets

the contribution of discontinuous rock mass failure to glacier erosion geomechanical rock mass properties control the response of bedrock to applied stresses and can be summarized in a linear mohr coulomb equation which defines the principal parameters determining failure nevertheless in studying the erosion of bedrock by glacier ice little attention has been paid to failure criteria though a coincidence of erosion all and forms with fracture systems at regional and local scales has been demonstrated few studies have analysed the precise nature of the fracture geometry or proposed its mechanical impact in association with glacier ice this investigation proposes that since almost all bedrock possesses identifiable fracture systems the properties of discontinuous rock mass drm be regarded as defining primary conditions of stress and stability which are subsequently modified directly and indirectly by glacier ice consequent rock mass failure modes are prescribed by discontinuity geometry and applied stresses and evidence from north wales confirms the validity of the theoretical treatment of rock mass properties and explains the accordance of landforms with structure

morphometric evidence of 3 6 ga glacial valleys and glacial cirques in martian highlands south of terra sabaea abstract the climate of early mars remains unclear and the debate is topical recently climatic models have suggested a cold climate during the noachian early hesperian on mars which goes against the wet and warm climate often put forward the purpose of this study is to seek geomorphologic evidence of this early cold climate to achieve this a step by step study of the geometry and morphology of several martian valleys has been done in the southern highlands the analysis highlights the morphometric properties which enable the identification of martian glacial landscapes we identified 100 cirques and 83 glacial valleys in two craters and on one mountain in the southern part of terra sabaea the studied morphologies have the same morphometric characteristics and trends as terrestrial and martian glacial valleys and glacial cirques in contrary these trends are very different from those observed in fluvial valleys on earth and on mars 1 the martian glacial valleys are u shaped with a large flat floor and a v index 0 20 while martian and terrestrial fluvial valleys are v shaped with a v index 1 while for fluvial valleys this ratio is 1 3 finally the cross sectional area and the elevation are higher for the glacial valleys compared to the fluvial ones these glacial valleys often originate with a topographic hollow which have the same properties than terrestrial glacial cirque the glacial landscapes identified in southern terra sabaea are restricted to elevations 1000 m and are dated by crater counting to be 3 6 ga this study strongly supports glacial processes as the origin of these valleys and cirques and is the first morphometric evidence of glacial valleys associated with glacial cirques in the southern highlands in agreement with the climatic models we propose that the martian climate during the late noachian early hesperian was characterized by glaciated highlands at elevations 1500 m and at lower elevations where fluvial valley network has been identified

the influence of rock mass strength on glacial valley cross profile morphometry a case study from the southern alps new zealand the erosional morphology in the vicinity of the main divide of the southern alps and fiordland new zealand appears to be a product of the interaction between alpine fault induced tectonic processes rock mass strength of the uplifted and eroded bedrock and the processes acting to denude the developing mountain landscape the magnitude of the effects of glacial erosion on the landscape is directly controlled by the size and physical properties of the glaciers whilst the form of the trough is a direct consequence of the rock mass strength rms properties of the slope rock realistic models of development of the cross profile shape of glacial valleys must take into consideration the rms properties of the eroded substrate

the lower crust of se belarus petrological geophysical and geochemical constraints from xenoliths abstract highly altered alkaline lamprophyre tuffs of devonian age from se belarus contain lower crustal xenoliths that vary from feldspar rich mafic granulites to rarer feldspar poor eclogitic granulites together with coarse grained hornblendites textural evidence mineral compositions and t p data 700 800 c 0 9 1 1 gpa of the garnet granulite xenoliths indicate that equilibration occurred in the lower crust and therefore we consider that these xenoliths represent samples of the in situ lower crust they are highly altered but the main primary minerals are almandine garnet diopside and andesine plagioclase k feldspar scapolite biotite apatite ilmenite ti magnetite and rutile are accessory minerals a subsequent metasomatic event post dating the granulite facies metamorphism has introduced widespread pargasitic amphibole the granulites are basic in composition are enriched in the most incompatible trace elements and have large negative nb anomalies la n nb n range from 3 to 12 inferring a subduction related origin ree patterns show variable lree enrichment la yb 6 27 and some positive eu anomalies indicating plagioclase accumulation trace element and ree patterns for one sample suggest a melt composition the granulites may represent a gabbroic underplate of unknown age and may be petrogenetically related to the osnitsk mikashevichi plutonic belt hornblendite xenoliths are relatively unaltered and consist of pargasite or pargasite plus magnetite and apatite amphibole compositions are very homogeneous and resemble those in the granulite xenoliths the 40 ar 39 ar plateau age is 381 2 ma lree enriched patterns low 87 sr 86 sr ratios and textural constraints suggest that these hornblendites precipitated from a magma formed from a small degree partial melt of a garnet bearing mantle they may be petrogenetically related to the host lamprophyres possibly as a cumulate from an earlier flux of magma and related to the metasomatic event that affected the granulites whole rock vp values calculated from modal mineralogies of the granulite xenoliths range from 6 7 to 7 5 km s assuming equilibration at 800 c 1 0 gpa they are compatible with seismic velocity measurements of the lower crust beneath se belarus which reach 7 2 km s xenoliths with the least modal plagioclase and to some extent the most modal clinopyroxene and garnet give the highest whole rock vp values calculated vp values for hornblendite xenoliths 6 75 km s at 800 c 1 0 gpa suggest that identification of hornblendite in the lower crust from vp values alone would be difficult

controls on the stability and inclinations of hillslopes formed on hard rock in identifying controls on rock slope form a distinction is made between 1 rock slopes with joints which dip steeply out of a cliff and hence are subject to mass failure of the rock mass above a critical joint and 2 rock slopes with inclinations which are either in equilibrium with the mass strength of their rocks or have profiles which will develop towards strength equilibrium as cross joints open in the first class of slope stability results not just from the basic frictional resistance of the rock but also from the frictional roughness along the critical joint and from the normal stress acting across that joint stability may be reduced by weathering and loss of strength of the joint wall rock as a result of normal stress variations with depth induced by overburdens high cliffs which are not undercut have a concave profile the second group of slopes includes those with inclinations controlled at the scale of individual joint blocks buttressed slopes and those on unjointed rock masses buttressed and unjointed rock masses develop towards a condition of mass strength equilibrium as cross joints open strength equilibrium slopes may be recognized by application of a rock mass strength classification proposed for geomorphic purposes eleven propositions are formulated which identify controls on rock slope development and some consequences of these controls

identification of strength equilibrium rock slopes further statistical considerations strength equilibrium slopes are rock slopes whose gradient and rock mass strength rms are in adjustment the identification of such slopes depends on the accurate specification of the strength equilibrium envelope previous attempts to delimit the envelope are reviewed and modifications are proposed that permit its more rigorous statistical definition because can be measured much more reliably than rms the structural relation between these variables is estimated by regressing rms on and the strength equilibrium envelope is defined by the 95 per cent confidence limits the analysis is performed on a data set of 268 rock slopes representing all the data on rms and hitherto employed in published studies of strength equilibrium slopes

a reply to a discussion of hirano and aniya s 1988 1989 explanation of glacial valley cross profile development by jonathan m harbor the extremum principle is again justified as a valid and relevant approach to cross sectional form of the glacial valley it is accepted that the extremum previously obtained was a maximum and not a minimum for friction but this still appears to be a valid application of the principle harbor s more detailed discussion is recognized as valid assuming the presence of appreciable water pressures and that hallet s theory is to be preferred over boulton s but these assumptions do not always seem appropriate while the importance of time for valley evolution is fully accepted the extremum approach is still thought to be useful for example in maximizing cross section for a given resistance

magmatism and continental break up in the south atlantic high precision40ar 39ar geochronology abstract a detailed ar ar study of the parana etendeka continental flood basalts cfb has been undertaken using laser spot analysis data provide information not only on the age of the samples but also on the variability of the non radiogenic ar component and state of alteration the results indicate the parana etendeka cfb were erupted over 10 million years between 137 and 127 ma providing a minimum overall eruption rate of 0 1 km3 yr 1 this is an order of magnitude less than that previously proposed for this the deccan and siberian cfb provinces but it is similar to estimates for hawaii iceland and the columbia river cfb in detail the new ar ar analyses indicate that magmatism within the parana etendeka province migrated from nw to se prior to and during the opening of the south atlantic providing an explanation for the asymmetry of the cfb lavas about the south atlantic moreover chemically defined magma types were erupted at different times in different places and so within the paranathey may not be used as reliable chronostratigraphic units rather such magmatic units may reflect the extent of compositionally distinct source regions in the uppermost mantle and indicate that partial melting took place over a wide area under the paranabasin the nw se migration of the onset of magmatism might be interpreted as a plume trace but the inferred rate of movement is 3 times faster than that inferred from subsequent magmatism on the rio grande rise it is argued that the onset of magmatism reflected extensional tectonics normal to the ponta grossa dyke swarm given that magmatism preceded the main phase of rifting and that extension across the ponta grossa was moderate current plume models have difficulty in predicting sufficient melting within the asthenosphere

the role of fluorine and oxygen fugacity in the genesis of the ultrapotassic rocks the effects of h2o co2 ch4 and hf on partial melting of a model phlogopite harzburgite mantle are considered with regard to the production of ultrapotassic magmas fluorine has a polymerising effect in h2o poor conditions but in the presence of abundant h2o where hf rather than f is dominant the overall effect is depolymerisation methane also dissolves by forming oh groups and so has a depolymerising effect group i ultrapotassic rocks lamproites probably originate from primary magmas with sio2 contents ranging from around 40 wt to at least 52 wt this range can be explained by differing depths of origin from a similar source with a similar reduced h2o ch4 hf volatile mixture the formation of silica rich initial melts from a model phlogopite harzburgite is assisted by the presence of ch4 and hf dissociation of less than 0 1 wt h2o driven by h2 loss is sufficient to cause oxidation during emplacement to observed oxidation states silica poor ultrapotassic rocks could be produced at higher pressures in a reduced environment or in an oxidised environment with high co2 co2 h2o ratios

trace element variations in atlantic ocean basalts and proterozoic dykes from northwest scotland their bearing upon the nature and geochemical evolution of the upper mantle abstract trace element data on ocean floor and ocean island basalts from the atlantic and from early proterozoic dyke swarms are considered in relation to the nature and causes of upper mantle heterogeneity studies of dredged and drilled basalts from the north atlantic have enabled the compositions of erupted ridge basalts to be monitored in space and time and have revealed the following features a that while melting processes may give rise to appreciable ree variation at a particular site ratios of the more incompatible elements remain remarkably consistent in basalts erupted at a particular ridge segment for tens of millions of years and b that there are major differences in incompatible element ratios in basalts erupted at different ridge segments the relationships suggest that the volumes of mantle with these characteristic incompatible element ratios must be large but that the processes associated with basalt generation are not capable of significantly changing incompatible element ratios nevertheless the processes which have produced these incompatible element variations must be incorporated into any model for mantle evolution our preferred model invokes both crustal extraction and incipient mantle melting as the major mechanisms for changing incompatible element mantle source regions both represent very small degrees of mantle melting a depleted upper mantle variably veined with incompatible element enriched liquids or fluids derived through incipient melting at greater depths is most consistent with the trace element and isotopic compositions of north atlantic basalts many of which are not normal mid ocean ridge basalts n type morb ocean island basalts may represent more intensely veined and in some cases at least more refractory sources sampled at lower degrees of partial melting mantle from which incipient melts have been removed probably represents the n type morb source extraction of crustal material having high contents of the large ion lithophile elements but low contents of the high field strength ions ie ta and nb from a veined metasomatized mantle source leaves the upper mantle residue enriched in ta and nb relative to the large ion lithophile elements this might explain the enrichment of ta and nb in most mantle sources of continental and ocean island basic lavas mantle sources enriched by incipient melting processes are continually dissipated by mantle convection but may be preserved for a significant time beneath stable continents trace element data on early proterozoic tholeiitic to picritic dyke swarms from scotland suggest that short term mantle heterogeneities may have existed beneath the region at that time and could have been related to the processes of crustal generation 600 m y earlier

evidence from magnetic fabric for the flow pattern of magma in the mackenzie giant radiating dyke swarm continental flood basalts and their associated swarms of mafic dykes are thought to result from melting in mantle plumes1 3 but the processes by which the resulting magma makes its way from mantle to crust remain obscure here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the proterozoic mackenzie dyke swarm our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm and then travelled horizontally at all further distances out to at least 2 100 km the sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the mackenzie igneous events

comparison of late pleistocene and modern glacier extents in central nepal based on digital elevation data and satellite imagery abstract late pleistocene and modern ice extents in central nepal are compared to estimate equilibrium line altitude ela depressions new techniques are used for determining the former extent of glaciers based on quantitative objective geomorphic analyses of a 90 m resolution digital elevation model dem for every link of the drainage network valley form is classified as glacial or fluvial based on cross valley shape and slope statistics down valley transitions from glacial to fluvial form indicate the former limits of glaciation in each valley landsat multispectral scanner imagery for the same region is used to map current glacier extents for both full glacial and modern cases elas are computed from the glacier limits using the dem and a toe to headwall altitude ratio of 0 5 computed ela depressions range from 100 900 m with a modal value of 650 m and a mean of 500 m values consistent with previously published estimates for the central himalaya but markedly smaller than estimates for many other regions we suggest that this reflects reduced precipitation rather than a small temperature depression consistent with other evidence for a weaker monsoon under full glacial conditions

anorogenic magmatism and the grenvillian orogeny the grenvillian orogeny was preceded by extensive anorogenic volcanism and plutonism in the period 1500 1300 ma in the form of rhyolites epizonal granites anorthosites gabbros alkaline complexes and basic dykes an analogue for the mid proterozoic anorogenic complexes is provided by the 2000 km by 200 km belt of anorogenic complexes in the hoggar niger and nigeria which contain anorthosites gabbros and peralkaline granites and were generated in a cambrian to jurassic rift that farther south led to the formation of the south atlantic an analogue for the 1 106 km2 area of 1500 1350 ma rhyolites and associated epizonal granites that underlie the mid continental united states is provided by the 1 7 106 km2 area of jurassic tobifera rhyolites in argentina which were extruded on the stretched continental margin of south america immediately preceding the opening of the south atlantic the mid proterozoic complexes were intruded close to the continental margin of the grenvillian ocean and were c

glacial abrasion and sliding their dependence on the debris concentration in basal ice a model of bedrock abrasion by a temperate glacier is developed that takes into account the significant impeding effect of scattered rock fragments at the ice rock interface on glacier sliding an increase in the debris concentration above a relatively low value can reduce the abrasion rate by decreasing both the flux of rock fragments and the effective forces which press fragments against the bed abrasion of a simple wavy bed is shown to be most rapid for a relatively low debris concentration above which the abrasion varies inversely with the debris content a similar concentration dependence of abrasion is expected for beds of arbitrary geometry but low roughness sliding glaciers will tend to abrade until the basal ice is nearly stagnant at which point rocks of all sizes start to lodge against the bed

distribution and characteristics of overdeepenings beneath the greenland and antarctic ice sheets implications for overdeepening origin and evolution das thanks the national cooperative for the disposal of radioactive waste nagra switzerland for their role in stimulating new research on the topic of focused glacial erosion and das and hp further thank nagra for funding the quantitative study of overdeepening morphology on which this paper is based grant 11 716 fcu bys hp also acknowledges support by the research council of norway through its centres of excellence funding scheme grant 223259 and the petromaks project glaciations in the barents sea area glacibar grant 200672 j

159 ma kjakebeinet lamproites dronning maud land antarctica and their implications for gondwana breakup processes lamproite dykes that cross cut middle jurassic karoo related flood basalts in vestfjella dronning maud land antarctica have been dated at 158 7 1 6 ma by 40ar 39ar incremental heating of phlogopite compared to most lamproites these dykes are unusually low in sio2 40 09 40 18 wt and high in cao 12 35 16 24 wt and p2o5 3 03 3 81 wt they have broad affinities to spatially and temporally related group ii kimberlites of southern africa but the geochemically closest correlatives are cao and p2o5 rich diopside madupitic lamproites from leucite hills usa the kjakebeinet lamproites are notably high in incompatible elements show negative initial end values 6 0 6 7 and positive initial esr values 14 17 with tdm model ages of c 1 1 ga and probably record melting of metasomatized subcontinental lithospheric mantle beneath western dronning maud land their emplacement records the youngest recognized magmatic event in the region coincides with the proposed second and final stage of gondwana breakup between africa and antarctica and may be associated with deep seated coast parallel strike slip faulting in dronning maud land survival of old easily fusible lithospheric mantle material 20 ma after the eruption of voluminous flood basalt magmas suggests that the latter were emplaced within narrow zones of lithospheric thinning and that the source of lamproites remained largely intact between these zones

a numerical model of landform development by glacial erosion the jagged peaks knife edged ridges and steep sided valleys of alpine landscapes are well known products of glaciation yet little is known about how the dynamics of ice flow and glacial erosion give rise to such landforms by linking a finite element model for ice flow through a valley with a model for glacial erosion we have simulated the gradual evolution of one of the most striking of glacial landforms the u shaped valley incorporating realistic glacier sliding laws and spatial variations in rock resistance our simulations illustrate how ice flow erosion patterns and topography interact in the long term evolution of glacial landforms in addition our results indicate for the first time that the formation of a steady state u shaped valley takes approximately 105 years

high resolution reconstruction of the last ice sheet in nw scotland reconstructions of the last late devensian british ice sheet have hitherto been based on assumptions regarding its extent and form here we employ observational evidence for the maximum altitude of glacial erosion trimlines on mountains that protruded through the ice palaeonunataks to reconstruct the form of the ice sheet over 10 000 km2 of nw scotland contrasts in the clay mineralogy of soils and exposure ages of rock surfaces above and below these trimlines confirm that they represent the upper limit of late devensian glacial erosion the reconstruction yields realistic values of basal shear stress and is consistent with independent evidence of ice movement directions the ice sheet reached 950 m altitude over the present n s watershed descended northwards and north westwards was deflected around an ice dome on skye and an independent outer hebrides ice cap and probably extended across the adjacent shelf on a bed of deforming sediments

refinement of a technique for determining rock mass strength for geomorphological purposes use of a field technique recently devised by selby for the measurement of rock mass strength has resulted in the understanding of the relationship between rock mass strength and slope form it is suggested that the accuracy of rock mass strength assessments may be enhanced by further subdividing the rating scales for intact rock strength and the spacing of partings the relationship between rock mass strength and gradient is reformulated using southern african data and statistically based confidence limits for identifying strength equilibrium slopes are proposed

quantification of rock control in geomorphology abstract rock control the influence of rock properties on landform development has for long been a relatively under researched topic but numerous techniques have been developed especially by geotechnical engineers and stone conservationists that are now being applied to geomorphological issues by geomorphologists these techniques range in scale from the quantification of major discontinuities through to analysis of micro pores rock control studies that have taken place over the last few decades have contributed important insights into our understanding of such diverse phenomena as 1 river terraces bedrock channel forms and gradients pot hole development drainage density and gully badland development 2 slope forms and failures especially with respect to rock mass strength 3 the form of glacial troughs and of subglacial erosional landforms 4 weathering controls on rock durability and the association of weathering with porosity 5 classic karst features including various types of karren 6 sandstone landforms 7 inselbergs and tors and 8 cliffs and shore platforms

an on line analysis system for three component seismic data method and preliminary results this paper presents the basic method and algorithm of a system for automatic on line analysis of seismic data at three component stations and gives preliminary experimental results data processing consists of four steps 1 preliminary detection and estimation of the signal arrival time by using the energy based ydetector 2 refinement of signal parameters arrival time amplitude period and coda duration 3 estimation of the azimuth and incident angle of the seismic ray by using polarization analysis and 4 approximate estimation of event parameters epicenter coordinate origin time and magnitude from teleseismic p waves for a constrained focal depth the software package which is called seismostansia has been tested in an on line environment at an experimental seismic station in eastern kazakhstan testing results show that the system can handle an input flow of up to 100 signals in a 24 hr period comparison of the results of automatic detection with data of the station bulletin obtained by visual analysis of analog seismograms shows that 1 with the present threshold setting the automatic system detects practically all teleseismic signals seen by the analyst together with typically 10 to 15 signals per day not confirmed by visual analysis 2 in 70 per cent of the cases the residual between the arrival time obtained from the automatic and subjective procedures is 0 5 sec or less for snr 10 and 1 sec or less for snr 10 3 in 70 per cent of the cases the residual between the signal period obtained from the automatic and subjective procedures is 0 2 sec or less analysis of data indicates that an effective means of identifying false alarms with low snr can be the level of polarization rectilinearity of p and s waves by analyzing azimuth estimates for a suite of explosions at the nevada test site it is shown that a systematic bias forms the main contribution to the residual relative to true azimuth in the general case the azimuth residuals are due to the features of the medium both at the epicenter and at the station and consequently depend on both azimuth and epicentral distance an analysis of azimuth residuals points to a periodic dependence on azimuth the value of the period is about 120 additional information azimuth and angle of incidence reported from threecomponent stations to data centers is shown to improve significantly the reliability of phase association in the processing of data from a global seismic network

experimental study of barium partitioning between phlogopite and silicate liquid at upper mantle pressure and temperature barium partition coefficients for phlogopite crystallized from a natural lamproite at 10 30 kbar and 900 1150 c show a three fold decrease in partition coefficient d with increasing pressure from 10 to 30 kbar e g from 0 75 to 0 23 and 35 50 increase in d with increasing temperature from 1000 to 1100 c at 10 and 15 kbar e g from 0 51 to 0 75 the variation with temperature is contrary to most recorded variations of d and is attributed to a compositional control in the phlogopite d correlates with substitution of titanium in the phlogopite thus as the titanium content increases with increasing temperature the barium content and hence d increases application of partitioning data for barium in models for lamproite genesis suggests that phlogopite of metasomatic origin and possibly some barium rich accessory phases are present in the source rocks for lamproite and phlogopite plays a major role in the generation of lamproitic magma

rb sr geochronology of the archaean maggo gneiss from the hopedale block nain province labrador the maggo gneiss a typical grey gneiss from the hopedale block of coastal labrador southern nain province preserves structures of two major archaean tectonothermal events the hopedalian and the younger fiordian rb sr whole rock analyses of four suites representing the hopedalian event 3140 95 ma 1 3125 43 ma 3028 199 ma and 3025 163 ma fall within the early middle archaean and represent a period of cratonization of the hopedale block two suites with a younger fiordian structural fabric 2899 116 ma and 2804 100 ma fall within the late middle archaean and are interpreted as dating a period of reworking that locally reset the rb sr isotopic systematics of the maggo gneiss fiordian ages were also determined from four suites 2927 50 ma 2884 86 ma 2854 83 ma and 2764 89 ma that do not display the fiordian structural fabric indicating that chemical and mechanical components of the fiordian event did not occur simultaneously age determinations of the fiordian do not dat

morphometric analysis of the river thamirabarani sub basin in kanyakumari district south west coast of tamil nadu india using remote sensing and gis the quantitative analysis of the drainage morphometric system is vital to understand the hydrological and environmental interaction and its processes of an area the present study deals with quantitative characteristics of morphometry of steep slope and short length sub basin of r thamirabarani in kanyakumari district tamilnadu india using geospatial technology in this study the digital elevation model data product aster dem landsat etm image and survey of india topographical map were used to delineate slope relief and drainage system structures such as drainage pattern stream order stream network and stream length of the sub basin using arcgis 9 3 software the morphometric analysis deals with hydrologic processes such as stream frequency bifurcation ratio circulatory ratio and length of overland flow of the sub basin area and their influences on the local morphologic landforms the quantitative measurement of these characteristics is used to explore the basin s contribution to the hydrological cycle and the shape size and formation of the local landscapes in the region moreover the hypsometric analysis and denudation rate were estimated for understanding the quantitative geomorphological characteristics of the sub basin the relationship of the morphometric parameters reveals that the drainage network is strongly controlled by geological and geomorphological structures of the area the geometry of streams exhibits dendritic drainage pattern associated with coarse drainage texture in primary order of streams present on hilly terrain surface and semi dendritic pattern in higher stream order flow on less elevated surface with gentle slope the drainage density of the study area ranges from 0 1 to 1 89 km km2 and the maximum density value was found along the higher stream order the mean bifurcation ratio of this area is 4 21 and the high ratio was measured between the third and fourth order of stream segments the morphometry of this area is depicted by the length of the stream segment drainage pattern and stream flow direction which are influenced by relief steep slope and local geological structure furthermore the sub basin is found to be strongly elongated in shape with a length of 42 78 km and the circularity ratio of this area is measured as 0 33 and elongation ratio as 0 57 the textural dissection of the landforms shows low drainage density in the high elevated hilly terrain in the north and high level in the plain areas in the southern part the values of the circulatory ratio length of overland flow and elongation ratio are relatively close to one another and the relationship among them shows their influences on the process of surface runoff and sediment deposition along the estuary landforms in the study area moreover it is observed that the hypsometric curve of this study area is characterized by convex up shape in nature and represents the youth stage inequilibrium of landscapes consequently the hypsometric integral value 0 49 reflects the distribution of a major volume of the landmass 435 32 km2 at relatively low elevations 180 m the morphometric parameters induced denudation rate of this study area is 65 14 t km2 year and indicates the occurrence of a wide range of denudation intensities throughout the sub basin which is relatively proportional to the suspended sediment yield that is transported in the suspension per unit area based on the realistic output it is proved that remote sensing and gis are effective tools for morphometric studies of the drainage basin

melting of a subduction modified continental lithospheric mantle evidence from late proterozoic mafic dike swarms in central australia geochemical and nd isotopic studies of two postorogenic late proterozoic 1083 23 ma high mg tholeiitec dike swarms in central australia indicate that the dike swarms were derived by partial melting of the continental lithospheric mantle which was modified by subduction processes during major crust formation events in the region both dike swarms stuart and kulgera which intrude the arunta and musgrave inliers respectively resemble island arc tholeiites in terms of geochemical features they yield whole rock sm nd ages of 1853 189 ma with nd 4 2 4 2 stuart and 1589 165 ma with nd 1 7 3 6 kulgera the two whole rock ages and initial nd values are remarkably similar to the oldest u pb zircon ages and initial nd values obtained from the corresponding basement blocks these isotopic data are interpreted as recording sm nd fractionation events in the continental lithospheric mantle associated with major episodes of crust formation in the early proterozoic

a rational explanation of cross profile morphology for glacial valleys and of glacial valley development a further note the authors discovered a misinterpretation in their original paper which is corrected here

early precambrian crustal development changing styles of mafic magmatism the work of sutton watson 1951 was one of the cornerstones in the interpretation of the evolution of early precambrian archaean and early proterozoic gneiss complexes and in the documentation of mafic dyke swarms that intruded recently accreted archaean cratons since then the concept of geological terranes and terrane accretion has been extended back to the archaean and different events can be distinguished by increasingly precise isotopic dating techniques there is growing evidence that with certain clear provisos the principle of uniformitarianism can be applied as equally to the early precambrian as it can through the rest of the geological record in terms of mafic magmatism there are similarities between some ancient and modern suites both intrusive and extrusive but there are also some major differences such as the presence of komatiites in the archaean and the formation of large scale layered intrusions and extensive dyke swarms at the end of the late archaean and in the early proterozoic the mantle has evolved continuously with the progressive extraction of mafic magmas but allowing for this continental tholeiites appear to have changed little with time ancient mid ocean ridge basalts are elusive because of their poor preservation record the geochemistry of mafic volcanics occurring in many greenstone belts commonly suggests a continental contamination component and that these volcanic rocks are most closely akin to those from present day arc systems the relative abundance of early precambrian intrusive mafic suites parallels the crustal growth curve reflecting the global crustal accretion differentiation superevent towards the close of the archaean bimodal tholeiitic noritic mafic magmatism associated with many of these intrusive suites stems from this rapid turnover in the mantle mafic crust continental crust system this in turn gives a possible link between the respective evolutions of archaean to recent komatiitic noritic and boninitic suites

significance of anisotropy of magnetic susceptibility fabrics in proterozoic mafic dykes hopedale block labrador abstract anisotropy of magnetic susceptibility fabrics have been studied in a suite of mafic early proterozoic kikkertavak dykes and two mid proterozoic kokkorvik sills in the hopedale block of labrador two sets of en echelon dyke arrays from the kikkertavak swarm are considered to represent two linear dyke intrusions at depth three main fabrics were revealed in the kikkertavak dykes in the first the maximum susceptibility axis is sub horizontal or gently inclined and parallel to the dyke walls and is interpreted as the primary magma flow direction a second fabric affects only dykes along strike from a much younger dyke and is interpreted as the result of local stress anisotropy the third fabric with significantly lower susceptibility is only locally developed in the southeast near the mid proterozoic kanairiktok shear zone and is also interpreted as the result of local superimposed tectonic stress the kokkorvik sheets preserve a single flow induced fabric sub parallel to the measured crack propagation lineation indicating that the magma flow was parallel to the crack propagation direction the gently inclined magma flow direction inferred for the kikkertavak dykes is believed to reflect later stage magmatic emplacement when consolidation had already commenced at this stage the buoyancy contrast between magma and host rock had been reduced to the point when the initially vertical magma flow was no longer sustainable and was replaced by lateral flow

multiple scales in river basin morphology existing data reveal that the steepness s of many river basins with mountainous headwaters defined as the ratio of total relief to total length of a basin is related to the logarithm of basin size the relief of these same river basins is observed to be non linearly related to basin steepness with maximal values of relief occurring in basins for which the value of s is about 0 03 or equivalently in basins in which the average slope is about 2 these systematic relationships between size relief and steepness of some basins which span nine orders of magnitude of area are inter preted in terms of an intermediate limit process bounded by well separated spatial scales the lower limiting scale corresponds to a threshold between channel formation and significant mass wastage and the upper limiting scale corresponds to the size of the largest landmass if the observed relationships between basin size relief and steepness indeed reflect a limit process then they are independent of the details of the physics contributing to landscape development and instead result from the constraints imposed by the bounding spatial scales exceptions to the limiting relationships explored here are readily noted however and are interpreted to reflect regional geological and temporal controls the delineation of the importance of multiple scales provides a potentially powerful basis for the examination of morphological relation ships in river basins introduction river basins dominate the landscape and the study of their morphology reveals important information about their formation sediment yield and fill i examine here the quantitative relationship between the area and steepness of river basins which drain mountainous terrain in terms of the bounding and intermediate length scales imposed by geological process and form the steepness of a river basin is considered in terms of the ratio of its total relief to its total length this ratio is a dimensionless number that has found wide use in the comparison of basins schumm 1956 1963 and other landscape features such as alluvial fans melton 1965 which vary greatly in size its value represents the average slope of the longitudinal profile of a basin and thus represents the basin wide magnitude of the gravitational component of landscape forming processes in the next section i review ideas regarding the existence and separation of spatial scales in fluvial landscapes this is followed by a simple analysis of physical systems bounded exclusively by two well separated spatial scales the results of the analysis are then used to examine the relationships observed between river basin area steepness and relief additional points of interest are explored in the discussion these include the situation when an intermediate spatial scale is imposed by regional geological structure and the evaluation of a denudational time scale and its relationship to basin size i conclude with a summary of important findings separation of multiple bounding scales in river basin morphology montgomery and dietrich 1992 found a simple relationship between the length l of a drainage basin and its area a given by

quantifying bedrock fracture patterns within the shallow subsurface implications for rock mass strength bedrock landslides and erodibility 1 the role of bedrock fractures and rock mass strength is often considered a primary influence on the efficiency of surface processes and the morphology of landscapes quantifying bedrock characteristics at hillslope scales however has proven difficult here we present a new field based method for quantifying the depth and apparent density of bedrock fractures within the shallow subsurface based on seismic refraction surveys we examine variations in subsurface fracture patterns in both fiordland and the southern alps of new zealand to better constrain the influence of bedrock properties in governing rates and patterns of landslides as well as the morphology of threshold landscapes we argue that intense tectonic deformation produces uniform bedrock fracturing with depth whereas geomorphic processes produce strong fracture gradients focused within the shallow subsurface additionally we argue that hillslope strength and stability are functions of both the intact rock strength and the density of bedrock fractures such that for a given intact rock strength a threshold fracture density exists that delineates between stable and unstable rock masses in the southern alps tectonic forces have pervasively fractured intrinsically weak rock to the verge of instability such that the entire rock mass is susceptible to failure and landslides can potentially extend to great depths conversely in fiordland tectonic fracturing of the strong intact rock has produced fracture densities less than the regional stability threshold therefore bedrock failure in fiordland generally occurs only after geomorphic fracturing has further reduced the rock mass strength this dependence on geomorphic fracturing limits the depths of bedrock landslides to within this geomorphically weakened zone

rocky coasts their role as depositional environments abstract the role of rocky coasts as depositional environments has been generally neglected by rock and depositional coast workers although rock coasts can be hostile sedimentary environments they frequently host a variety of deposits consisting of mixes of boulders and megaclasts to sand and cobbles these deposits include pockets of sand and pebble trapped in topographic depressions or at the foot of scarps and cliffs isolated boulders pocket beaches trapped between headlands and sand to boulder beaches in shallow bays exposed to strong wave action the tectonic setting which is reflected in the degree of geological heterogeneity alongshore together with the wave regime and other elements of the morphogenic environment help to determine the amount and mobility of the sediment and consequently whether it plays an essentially abrasional or protectional role many beaches have a resistant rock foundation which will modulate their response to rising sea level and possibly increased storminess during this century wave refraction and temporal and spatial changes in sediment abrasional and protectional efficacy influence the development of crenulated planforms on coasts with a high degree of geological heterogeneity and possibly on more geologically homogeneous coasts with longshore variations in cliff height or in the amount of sediment theory suggests that these coasts may develop equilibrium planforms with uniform rates of erosion in bays and on headlands or they may undergo a series of cyclical transformations involving alternating increases and decreases in the depth of the bays relative to the headlands