the geomorphic impact of glaciers as indicated by tors in north sweden aurivaara 68 n abstract geomorphological investigations carried out on 15 tor like features located on the aurivaara plateau north sweden 68 n provide new insights in the greatly debated age of these landforms erratics and till trapped deep in the tor joints support a pre weichselian age for tor formation moreover the occurrence of various weathering stages in allochtonous material the joint width up to 1 5 m requiring long term weathering and the frequent association of tors with pediment like forms suggest pre quaternary tor formation the juxtaposition of fresh erratics and in situ old weathering features mushroom rocks concentrically weathered well rounded corestones and grus indicates a predominantly cold based regime for the scandinavian ice sheet with erratics carried by the overlying moving ice being repeatedly deposited on tor summits during deglaciation phases the relationships between tors and ice action indicated for the aurivaara plateau result in the proposal of a morphodynamical succession of five tor subtypes ranging from the preservation of well rounded corestones still embedded in grus suggesting negligible glacial erosion to the almost complete removal of tor features by ice scouring a comparison with tors in similar geological and topographical contexts from the unglaciated dartmoor area allows a tentative evaluation of an average overall glacial erosion of 0 10 m on the northern sweden plateaus in sharp contrast with the 190 m overdeepening of the nearby tornetrask basin thus this case study of swedish tors provides additional support to the recent interpretations of relict landscapes in previously glaciated areas and is in accordance with the classical model of glacial selective erosion established in the nordic and arctic mountains

analysis of spatial relationships among geomorphic petrographic and structural characteristics of the dartmoor tors the granite tors of dartmoor are characterized by using the regional spatial patterns of 21 geomorphic petrographic and structural variables the data were derived from topographic maps field measurement and laboratory analysis of rock samples collected in the field identification of spatial patterns and comparison of patterns between variables were made on contour maps generated from the data using arc info three tor types summit tors valleyside tors and spur tors are semiquantitatively characterized using these data and procedures the three types of tors are distinguished with respect to variations in relative relief joint spacing and joint type rock texture grain size and composition summit tors have the highest relative relief mean 125 7 m contain the most potassium feldspar 30 per cent and have the most widely spaced primary vertical 300 cm and secondary horizontal joints 10 cm the rocks are the most megacrystic 15 per cent and the coarsest grained plagioclase is also abundant in summit tors valleyside tors have the lowest relative relief mean 72 9 m and the most widely spaced horizontal joints primary 60 200 cm secondary 10 cm grain size vertical joint spacing and quartz and potassium feldspar abundances are intermediate the shapes of valleyside tors are controlled by horizontal joints and the rocks are either very feebly magcrystic or equigranular in texture spur tors have intermediate relative relief mean 115 4 m the narrowest joint spacing vertical joints 200 cm 50 75 cm horizontal joints 60 cm 10 cm and the finest grain in addition the rocks are feebly magacrystic

granite geomorphology and its geological controls serra da estrela portugal abstract serra da estrela is an elevated granite massif in central portugal characterized by extensive plateau surfaces incised by deep valleys affected by quaternary glaciation bounded by steep fault generated escarpments the presence of seven major textural variants of granite provides an opportunity to study the relationships between lithology and relief whereas dem analysis helped to show the relationships between lithology and topography objectively the higher ground is associated with fine to medium grained granites and is typified by planar surfaces of low gradient with occasional angular tors and rock pedestals block fields built by angular material are common in the parts that were not previously glaciated less elevated parts of the plateau are supported by medium to coarse grained granites and show more varied topography with an abundance of tors boulder piles and depressions lithological boundaries locally coincide with slope breaks but this is not the rule in the northern part of the massif a deep topographic basin has evolved in biotite granite whereas deeply incised valleys follow major fault lines geological controls show a hierarchy in that gross relief reflects the pattern of tectonic uplift and subsidence whereas lithology and then fracture patterns become more and more important if one focuses on smaller and smaller landforms

foraminiferal inventory and lithologic description of the lower cretaceous albian hulcross shale monkman area northeastern british columbia correlation of an arenaceous microfauna of 41 species 44 subspecies from the hulcross formation of the monkman pass area with that found in the hulcross shale on the peace river has a further corroboration in matching spectra of volcanic ash beds at both localities the monkman pass equivalents of both the basalmost portion and the upper part of the hulcross beds on the peace river are in sandy to continental facies diatoms are plentiful in the monkman pass section in the shaly facies the foraminiferal genera include bathysiphon thuramminoides psammosphaera hippocrepina saccammina reophax glomospira ammodiscus psamminopelta haplophragmoides ammobaculites trochammina textulariopsis pseudobolivina verneuilinoides uvigerinammina gaudryina eggerella and dorothia only thuramminoides haplophragmoides and trochammina occur in abundance indicating water of depth around 100 m at time of deposition and of salinity close to that of normal seawater the low degree of bioturbation and the pres

controls of tor formation cairngorm mountains scotland tors occur in many granitic landscapes and provide opportunities to better understand differential weathering we assess tor formation in the cairngorm mountains scotland by examining correlation

the gravity field in the central pacific from satellite to satellite tracking satellite to satellite doppler tracking between the ats 6 and the geos 3 spacecraft is used to measure the high degree and order gravity field over an 80 area in the central pacific ocean doppler tracking provides velocity measurements of geos 3 as a function of time which are easily converted to line of sight accelerations since the low degree and order gravity field is known well each geos 3 revolution is reduced relative to a twelfth degree and order field model the method is then capable of measuring wavelengths in the range from about 3500 to 1000 km accelerations computed along 40 revolutions roughly half of them descending and the others ascending can be contoured into a map of the gravity field at the geos 3 altitude of 840 km the dominant wavelength of the map is about 2000 km a comparison of this field with an altimeter derived geoid and the gem 10b gravity field shows good agreement since each map is essentially independent of the others this comparison is critical in establishing the validity of any of the maps each map shows virtually the same areas of positive and negative anomalies these areas are essentially the same in the central pacific as those found in our earlier study compared with surface amplitudes these anomalies are only one tenth as large at the geos 3 altitude this observation and the correlation of gravity with residual depth anomalies imply that the cause of some of these anomalies may be due to bumps in the upper surface of the lithosphere that are compensated at depths of about 30 100 km some of the anomalies apparently do not correlate with residual depth anomalies

scale issues in weathering studies a review of the major scale issues in weathering studies reveals concerns over the fundamental spatio temporal distributions of weathering phenomena as well as issues of upscaling microscope based observations and linking different scales of observations in explanations of landform development various strategies are proposed which can be used to tackle these issues many rooted in non linear dynamical systems ideas as an initial step spatio temporal scale distributions are estimated here for weathering processes landforms and controls based on a range of empirical data two case studies of phytokarst in grand cayman and blistering and scaling of building stones are presented to illustrate the types of data that might be used to establish more convincing scale linkages in weathering investigations

a test of petrological control in the development of bornhardts and koppies on the matopos batholith zimbabwe this paper investigates the reasons for the presence of both domed inselbergs bornhardts and boulder inselbergs koppies on the matopos batholith zimbabwe xrf and microprobe analyses of rock samples from 16 bornhardts and 24 koppies have shown no significant chemical or mineralogical differences which might indicate greater weathering resistance of the bornhardts many bornhardts are located on massive bodies of slowly cooled porphyritic granite which were emplaced at a relatively late stage in the evolution of the batholith the surrounding rocks are less porphyritic and appear to have been foliated during deformation associated with emplacement of the later bodies the entire batholith has been affected by post emplacement tectonism which has created three major fracture systems the morphological differences between bornhardts and koppies in this area are therefore considered to reflect differences in jointing which arise both from the primary igneous emplacement process and from tectonic deformation

failure mechanisms and stability analyses of granitic boulders focusing a case study in galicia spain abstract granitic boulders are widespread geomorphological elements particularly found in humid granitic areas although they seldom represent a hazard for people or infrastructures sometimes their location in steep or natural slopes may jeopardise their stability and potentially affect people or infrastructures in addition their complex geometry makes the instability mechanisms difficult to identify so it is even more difficult to compute factors of safety regarding their stability in this paper the authors analyse potential failure mechanisms of granite boulders based on analytical mechanic calculations and physical tilt tests permitting understanding the phenomena under scrutiny then they study the stability of one of these boulders the pena do equilibrio or equilibrium rock to do that they resort to standard geotechnical characterization and advanced geometrical characterization derived from uav photogrammetric and 3d laser scanning of the boulder the presented results exemplify how the application of these recently available topographic technologies in combination with rock mechanics approaches enable a rigorous analysis of the stability of granite boulders

geochemistry of the granitic rocks and their minerals from serra da estrela central portugal abstract several types of hercynian peraluminous granitic rocks ranging from biotite muscovite granodiorite to muscovite granite occur in the horst of serra da estrela variation diagrams of most major and trace elements of the rocks and biotites and cr and v of muscovites show fractionation trends however nb li rb k rb li mg variation diagrams of the rocks and muscovites and also of sn cs cs k of the muscovites indicate that the muscovite granite probably originated by another mechanism least squares analysis of major elements and modelling of trace elements indicate that the coarse grained porphyritic biotite muscovite granite granite porphyry and fine to medium grained muscovite biotite granite were derived from the granodiorite magma by fractional crystallization of plagioclase quartz and biotite emplacement of granodiorite magma took place at 3 5 3 kb and 720 c granites and granite porphyry probably originated about 690 c but were completely crystallized about 520 c o2 was about 10 17 for the granodiorite and hcl hf was higher whereas log h2o hcl was lower in the granodiorite than in the other granitic rocks of the fractionated series the coarse grained porphyritic biotite muscovite granite was hydrothermally altered between 400 350 c and 260 230 c at about 1 5 1 kb the hydrothermal fluids were probably mainly meteoric in origin but some fluids released during the late stage of granite solidification might also have been involved

on the tectonic origin of iberian topography the present day topography of the iberian peninsula can be considered as the result of the mesozoiccenozo ic tectonic evolution of the iberian plate including rifting and basin formation during the mesozoic and compression and mountain building processes at the borders and inner part of the plate during the tertiary followed by neogene rifting on the mediterranean side and surface processes acting during the quaternary the northern central part of iberia corresponding to the geological units of the duero basin the iberian chain and the central system shows a mean elevation close to one thousand meters above sea level in average some hundreds of meters higher than the southern half of the iberian plate this elevated area corresponds to i the top of sedimentation in tertiary terrestrial endorheic sedimentary basins paleogene and neogene and ii planation surfaces developed on paleozoic and mesozoic rocks of the mountain chains surrounding the tertiary sedimentary basins both types of surfaces can be found in continuity along the margins of some of the tertiary basins the bouguer anomaly map of the iberian peninsula indicates negative anomalies related to thickening of the continental crust correlations of elevation to crustal thickness and elevation to bouguer anomalies indicate that the dierent landscape units within the iberian plate can be ascribed to dierent patterns 1 the negative bouguer anomaly in the iberian plate shows a rough correlation with elevation the most important gravity anomalies being linked to the iberian chain 2 most part of the so called iberian meseta is linked to intermediate elevation areas with crustal thickening this pattern can be applied to the two main intraplate mountain chains iberian chain and central system 3 the main mountain chains pyrenees and betics show a direct correlation between crustal thickness and elevation with higher elevation crustal thickness ratio for the central systemvs the betics and the pyrenees other features of the iberian topography namely the longitudinal pro le of the main rivers in the iberian peninsula and the distribution of present day endorheic areas are consistent with the tertiary tectonic evolution and the change from an endorheic to an exorheic regime during the late neogene and the quaternary some of the problems involving the timing and development of the iberian meseta can be analysed considering the youngest reference level constituted by the shallow marine upper cretaceous limestones that indicates strong dierences induced by i the overall tertiary and recent compression in the iberian plate responsible for dierences in elevation of the reference level of more than 6 km between the mountain chains and the endorheic basins and ii the eect of neogene extension in the mediterranean margin responsible for lowering several thousands of meters toward the east and uplift of rift shoulders a part of the recent uplift within the iberian plate can be attributed o sostatic uplift in zones of crustal thickening

geopotential orbit variations applications to error analysis the position and velocity errors of a near circular orbit due to geopotential uncertainty are developed in fourier series current satellite gravity models generate position uncertainties of up to 50 m alongtrack for close satellites 1000 km altitude in shallow resonance periods less than 5 days from coefficients of order 13 14 smaller radial errors are due to resonance and to first order terms poorly seen in current satellite geopotentials correlation of errors is strong by order and the same degree parity application of the development is made to 1 the prediction of errors for a future altimeter satellite 2 the capability of earth based tracking of a close mars orbiter in resolving that planet s gravity potential and 3 improvement of the resolution of the low degree geopotential from the geopotential research mission using tracking data from the global positioning system

a review of the structure petrology and dynamic deformation characteristics of some enigmatic terrestrial structures abstract we review three categories of enigmatic terrestrial structures that have a variety of macroscopic and microscopic dynamic deformation features the first category includes the midcontinent united states cryptoexplosion structures they are of shallow origin and illustrate the effects that might be expected from a meteorite impact on a sedimentary rock terrane the second category includes the well known vredefort and sudbury plutons or basement uplifts the lesser known precambrian basement uplifts at steen river manson and carswell and the diatreme breccia dikes at the slate islands they are of relatively deep seated origin and illustrate the effects that might be expected from deep crustal or mantle processes of an explosive nature the third category includes the large landslides in areas of crystalline rocks at koefels and langtang the dynamic deformation features at these latter locations appear to be related to high strain rate tectonic processes associated with the landslide itself we conclude that microscopic dynamic deformation features which occur in natural materials may have originated from meteorite impacts from internal explosions or from high strain rate tectonic process

on upper mantle seismic heterogeneities beneath fennoscandia abstract three dimensional seismic mapping of the upper mantle beneath fennoscandia baltic shield using an ach type of inversion technique in combination with p wave travel time residual observations from the local seismograph network gave the following results the central parts of the baltic shield are characterized by relatively high seismic velocities down to approximately 300 km those parts of the shield most affected by the caledonide orogeny exhibit relatively low velocities particularly in the uppermost 100 km depth interval the lower part of the upper mantle 300 600 km does not exhibit pronounced seismic velocity anomalies and in this respect is in contrast to results from similar studies in regions subjected to neotectonic processes like parts of central and southeastern europe the seismic anomaly pattern in the presumed thickened lithosphere is in quantitative agreement with similar ones derived from surface wave dispersion analysis and inversion of electrical measurements the general orientation of these anomalies coincides with that of the glacial uplift

climate and relief induced controls on the temporal variability of denudation rates in a granitic upland how soil erosion rates evolved over the last about 100 ka and how they relate to environmental and climate variability is largely unknown this is due to a lack of suitable archives that help to trace this evolution we determined in situ cosmogenic beryllium 10 10be along vertical landforms tors boulders and scarps on the sila massif to unravel their local exhumation patterns to develop a surface denudation model over millennia due to the physical resistance of tors their rate of exhumation may be used to derive surface and thus soil denudation rates over time we derived soil denudation rates that varied in the range 0 0 40 mm yr 1 the investigated boulders however appear to have experienced repositioning processes about 20 25 ka bp and were therefore a less reliable archive the scarps of the sila upland showed a rapid bedrock exposure within the last 8 15 ka overall the denudation rates increased steadily after 75 ka bp but remained low until about 17 ka bp the exhumation rates indicate a denudation pulse that occurred about 17 5 ka bp since then the rates have continuously decreased we identify three key factors for these developments climate topography and vegetation between 75 and 17 ka bp climate was colder and drier than today the rapid changes towards warmer and humid conditions at the pleistocene holocene transition apparently increased denudation rates a denser vegetation cover with time counteracted denudation topography also determined the extent of denudation rates in the upland regime on slopes denudation rates were generally higher than on planar surfaces by determining the exhumation rates of tors and scarps soil erosion rates could be determined over long timescales and be related to topography and particularly to climate this is key for understanding geomorphic dynamics under current environmental settings and future climate change

palaeocontinental configurations and geoid anomalies reconstructions of past continental configurations help our understanding of the evolution of planetary surface morphology and impose valuable constraints on the models for planetary dynamics the problem is that although well established palaeogeographical maps now exist for mesozoic and later times1 2 thanks to excellent agreement between palaeomagnetic and marine magnetic deductions this is not true for earlier times mainly due to the lack of independent palaeogeophysical control over otherwise longitudinally ambiguous palaeomagnetic data the prospect of relating palaeocontinental configurations to geoid anomalies recently raised by anderson3 has thus given a fresh perspective to this problem here his continental insulation model is shown to be an inadequate explanation of the undulations of subduction compensated geoid instead the geoid highs and lows are shown to correlate well with the overall divergent and convergent plate tectonism since the middle palaeozoic and are thus ascribed respectively to the ascending and descending patterns of lower mantle convection

mcmurray formation foraminifera within the lower albian lower cretaceous loon river shales of northern alberta early cretaceous paleogeography and biostratigraphy of western canada are reviewed in light of a reassessment of foraminiferal and microfloral data from unpublished university theses on the early a

long wavelength heterogeneities in the upper mantle as seen by satellites abstract modern satellite methods have made it possible to study the gravity field of the earth with methods that primarily give increased information of the lower harmonics in a spherical harmonic expansion for areas covered with water we have recently obtained very interesting results from the seasat satellite earlier studies of the gravity field have mainly resulted in geophysical evaluations for the very low degrees which mostly reflect information from the core and the lower mantle now available studies seem to give evidence for geophysical activities which originate from convection currents as well as glacio isostatic uplifts most of this information is probably generated in the upper mantle methods for mapping of the terrestrial gravity field with satellite technique are presented and some of the problems with the geophysical evaluation are further discussed

a review of alpine tectonics in portugal foreland detachment in basement and cover rocks abstract the alpine foreland in portugal was deformed by compressional tectonism during the miocene in the nne ssw oriented lusitanian basin most folds and thrusts in the meso cenozoic cover are oriented ene wsw parallel to the alpine front in the betic cordillera and verge towards the north northwest and south southeast the thrusts are connected by lateral ramps most of these are oriented nne ssw to n s and show sinistral movement and some are transpressional the lateral ramps result from reactivation of older extensional faults related to crustal thinning of the continental margin in the e w oriented algarve basin a simpler basin inversion occurred with older e w normal faults reactivated as essentially pure thrusts in both basins alpine structures formed above decollements in the hettangian evaporite clastic complex variscan basement was also deformed by ene wsw reverse faults during miocene time the similarity in orientation and style of the basement structures to those in the cover suggests that they also occurred by detachment but their larger scale indicates that the detachment is deep and involves much of the crust thus we interpret the central cordillera in which basement rocks are thrust over miocene sediments on both sides as a pop up of crustal scale elevated above downward flattening faults that dip towards each other and merge into a single deep detachment alpine structures in the iberian foreland are therefore similar in structural style to those of the appalachian and laramide forelands of north america and the alpine foreland of northwest europe

the seasat altimeter mean sea surface model gridding techniques are used to combine an 18 day set of seasat altimeter data and two precisely computed seasat ephemerides in order to arrive at global contour maps of the mean sea surface topography the altimeter data have an rms agreement of 111 cm with the ss3 mean sea surface computed by means of the pgs s3 ephemerides and of 70 cm with the ss4 mean surface derived from the pgs s4 ephemerides while comparisons with the gem 10b 1 x 1 deg gravimetric geoid have yielded rms differences of 2 8 m those with a global mean sea surface derived from geos 3 altimeter data show rms differences of 1 3 m and 1 1 m for the cases of the ss3 and ss4 surfaces respectively an ss4 mean sea surface topograph is featured among the study findings presented further improvements in the representation of mean sea surface topography are expected with the development of more accurate gravity models for orbit computation

radiometric dating of a tuff bed in the middle albian hulcross formation at hudson s hope british columbia u pb rb sr and k ar methods were employed to estimate the age of a thin crystal tuff bed in the middle albian hulcross formation at hudson s hope northeastern british columbia ten different gravity fractions of altered biotite define an rb sr isochron that passes through the plotted rb sr data point for cogenetic plagioclase the biotite plagioclase isochron yields an age of 102 4 1 0 20 x mswd1l2 ma mswd is mean square weighted deviate and an initial ratio of 0 71311 0 00030 different size fractions of clear prismatic zircons define a u pb discordia line that intersects the concordia at 102 5 20 ma the four heaviest gravity fractions of biotite give a k ar age of 106 0 1 8 20 ma the most probable age of deposition of the tuff bed is estimated to be very close to or a little more than 102 ma but does not exceed 106 ma

the determination of rates of land uplift in norway it is the task and the responsibility of the geodetic section within the geographical survey of norway to establish and maintain the national horizontal and vertical geodetic primary control networks of that country provided that relative crustal movements take place within norway they will cause deformations to these networks there is no geodetic proof that any horizontal deformations of the surface layer of the crust take place in continental norway and there is no established geological evidence of such movements either in 1984 a small geodetic control network was established and measured for the first time across a possibly active fault it is not expected that horizontal movements will cause any serious problems in the maintenance of the horizontal network vertical movements of the ground however are causing us problems both in the establishment and in the maintenance of a national height system

in search for a relationship between harmonic resolutions of the geoid convective stress patterns and tectonics in the lithosphere a possible explanation for the betic rif orocline abstract convective stress fields implied by the runcorn model have been integrated with geological structures in the overlying lithosphere this is dangerous since small scale convection patterns in the mantle might have remained stationary for at least 50 ma while particular parts of the lithosphere are likely to have passed over distinct convective stress regimes in such periods the mantle component of the stress history of lithospheric structures younger than 32 ma is potentially tractable if a mean plate velocity of 5 cm y 1 is assumed this is because the satellite gravity data used here allow the detection of convection cells with horizontal length scales of the order of 1600 km which the lithosphere may cross in 32 ma for example the sublithospheric stress field might have accounted for the uplift and subsequent subsidence of the alboran sea basin w mediterranean between 25 and 20 ma ago an immature diapiric rise of the mantle due to upwelling is likely to have occurred beneath this region between 25 and 20 ma ago the resulting lithospheric swell caused extensive tectonic unroofing by nappe spreading with or without some sliding the subsidence of the alboran sea after the rise of the dome seems an excellent example of the combined effects of lithospheric cooling connected with ceasing mantle diapirism and mechanical thinning of the lithosphere by nappe translations

petrological influence on differential weathering and inselberg development in the kora area of central kenya in the kora area of central kenya domed inselbergs are well developed on outcrops of granitoid migmatite while positive relief features are rare on the surrounding gneiss block strewn vegetated hills occur on restricted areas of granoblastite gabbro and metagabbro schmidt hammer measurements have shown that the apparent differences in resistance to weathering and erosion are not due to variations in rock hardness since all the rock types have similar r values the results of geochemical analyses have shown that the migmatites are significantly more potassic than the surrounding gneiss samples of migmatite from the inselbergs were also found to be slightly richer in potassium than migmatite samples from the inter inselberg areas the variations in potassium content probably reflect differences in protolith composition chemical fractionation during partial melting and the effects of metasomatism these findings support earlier suggestions that other things being equal potassium rich granitoid rocks weather more slowly than less potassic rocks

lithological mapping of the troodos ophiolite cyprus using airborne lidar topographic data traditional field based lithological mapping can be a time consuming costly and challenging endeavour when large areas need to be investigated where terrain is remote and difficult to access and where the geology is highly variable over short distances consequently rock units are often mapped at coarse scales resulting in lithological maps that have generalised contacts which in many cases are inaccurately located remote sensing data such as aerial photographs and satellite imagery are commonly incorporated into geological mapping programmes to obtain geological information that is best revealed by overhead perspectives however spatial and spectral limitations of the imagery and dense vegetation cover can limit the utility of traditional remote sensing products the advent of airborne light detection and ranging lidar as a remote sensing tool offers the potential to provide a novel solution to these problems because accurate and high resolution topographic data can be acquired in either forested or non forested terrain allowing discrimination of individual rock types that typically have distinct topographic characteristics this study assesses the efficacy of airborne lidar as a tool for detailed lithological mapping in the upper section of the troodos ophiolite cyprus morphometric variables including slope curvature and surface roughness were derived from a 4 m digital terrain model in order to quantify the topographic characteristics of four principal lithologies found in the area an artificial neural network the kohonen self organizing map was then employed to classify the lithological units based upon these variables the algorithm presented here was used to generate a detailed lithological map which defines lithological contacts much more accurately than the best existing geological map in addition a separate map of classification uncertainty highlights potential follow up targets for ground based verification the results of this study demonstrate the significant potential of airborne lidar for lithological discrimination and rapid generation of detailed lithological maps as a contribution to conventional geological mapping programmes

geochemical and isotopic constraints on the petrogenesis of early ordovician granodiorite and variscan two mica granites from the gouveia area central portugal abstract a biotite granodiorite and seven sn bearing two mica granites crop out in the gouveia area central portugal a shrimp u th pb zircon age from the granodiorite and monazite ages from four of the two mica granites show that they are of early ordovician 480 ma and permo carboniferous i e variscan 305 and 290 ma age respectively the variscan two mica granites are late and post d3 major and trace element variation in the granitic rocks and their biotite and muscovite indicate mainly individual fractionation trends the granitic rocks are mostly depleted in hree relative to lree the biotite granodiorite is probably derived from igneous lower crust as evidenced by low initial 87 sr 86 sr 0 7036 high e nd t 2 5 and moderate 18 o 8 8 the two mica granites are probably derived by partial melting of heterogeneous mid crustal metasediments mainly metapelite and some metagraywacke as evidenced by their high initial 87 sr 86 sr 0 7076 0 7174 18 o 10 7 13 4 and major element compositions however variation diagrams for major and trace elements from two of the muscovite biotite granites and their micas define fractionation trends rb sr whole rock analyses from the two granites are perfectly fitted to a single isochron and the rocks have sub parallel ree patterns the younger granite is derived from the older by fractional crystallization of quartz plagioclase biotite and ilmenite tested by modelling major and trace elements most of the sn bearing granites are derived from distinct magma batches they result from partial melting of a heterogeneous mid crustal metasediment they do not represent a crustal anomaly in tin fractional crystallization is responsible for the increase in the sn contents of the granites and their micas muscovite has a higher sn content than coexisting biotite and is the principal host mineral for sn in these rocks

newest results obtained in studying the fennoscandian land uplift phenomenon abstract the fennoscandian land uplift phenomenon has been studied using geodetic gravimetric and seismologic material results obtained show that the greatest part of the phenomenon is of glaciological origin in the geoid there is a depression approx eight meters in depth a seismic map showing data gathered over 500 years shows also a certain tectonic pattern

combined numerical and geomorphological reconstruction of the serra da estrela plateau icefield portugal abstract the paper focuses on reconstructing a plateau icefield surface from field geomorphological data and a physical based glacier model the results allow the analysis of the patterns of glacial erosion and the estimation of the palaeo equilibrium line altitudes ela the study area is the serra da estrela a plateau in central portugal rising to 2000 m asl the glaciated area during the last maximum of the serra da estrela glaciation lmgse was 66 km 2 the reconstruction of the topography of the icefield and valley glaciers in the lmgse is based on the schilling and hollin model it iterates along the valley longitudinal profile and is based on the gradient on valley shape indices and on yield basal shear stresses these variables influence ice thickness and therefore also the slope of the ice surface allowing for its reconstruction the key variable is basal yield shear stress and its value was included in the model manually starting from the points of maximum extent of the valley glaciers and following a range known to occur in contemporary conditions the input values are validated by matching the resulting ice surface to geomorphological features where these are absent a constant value of 100 kpa was used the icefield was reconstructed from a radiating set of long sections along which ice thicknesses were calculated a dem of the ice surface was constructed allowing the estimation of the hypsometric curves of the distinct glacier catchments and the calculation of the palaeo elas the results show a regional ela at 1650 m asl with spatial variations across the icefield reflecting mainly the effect of eastward snow drift the lmgse glaciers were very sensitive to minor climatic changes especially due to the large area of the plateau icefield and to the positioning of the elas close to or in the flat part of the hypsometric curve the model of the ice surface is of significant value for the analysis of the patterns of glacial erosion at the landscape level in the serra da estrela most of the glacial erosion occurred near the plateau margins and in valley heads where glacier surface slope was steeper allowing for a faster ice flow and where ice flow concentrated strong glacier erosion in the zezere valley is linked to the tectonic setting but also to the confluence of glaciers and to the overfeeding of snow from the plateau

the absolute age of the eifelian tioga ash bed pennsylvania the tioga ash bed bed b of the zeigler pit union county pennsylvania lies in the polygnathus costatus costatus zone of the eifelian stage of the middle devonian series the 27 5 cm thick bed contains igneous zircon and monazite crystals that have been dated by precise u pb techniques zircons are characterized by inherited pb that occurs as barely perceptible interior regions enriched in inclusions the zircons are discordant and do not reveal the igneous age of the bed in contrast high quality monazite crystals lack any evidence of inheritance or loss of pb and multiple analyses have overlapping 207 pb 235 u ages of 390 0 pm 0 5 ma the monazite analyses are concordant or very slightly reversely discordant the consistency of the monazite data provides a new precise estimate of age for the lower eifelian

the relief of the swiss alps and adjacent areas and its relation to lithology and structure topographic analysis from a 250 m dem abstract in this paper we discuss the large scale geomorphological characteristics of the swiss alps based on numerical analysis of a digital elevation model and compare these to an erodibility map constructed from a geotechnical map of switzerland and regional geomorphological studies comparing the erodibility map with the large scale morphometry shows an intimate relationship between mountain scale erodibility and topography on average higher mean elevations and steeper mean slopes correlate with regions where rocks of low erodibility prevail areas with high peaks as well as the main water divides are controlled by the presence of bedrock with low to very low detachability the drainage network of the swiss alps shows a close relationship to the lithological differences as well major longitudinal valleys follow easily erodible units in the eastern and western part of the swiss alps the highest values of local relief are located to the south of the main water divide whereas in the central part local relief is higher to the north of the main water divide the large scale geomorphic characteristics regarded in the framework of the geological history of uplift and denudation suggest that low and very low erodibilities lead to the development of areas of high elevations which are likely to persist over periods of 10 15 ma as the analysis of the lepontine area shows 20 ma after cessation of exhumation such high elevations are likely to be worn down and to manifest themselves as high relief only

glacial modification of granite tors in the cairngorms scotland a range of evidence indicates that many granite tors in the cairngorms have been mod ified by the flow of glacier ice during the pleistocene comparisons with sw england and the use of a space time transformation across 38 tor groups in the cairngorms allow a model to be developed for progressive glacial modification tors with deeply etched surfaces and no or limited block removal imply an absence of significant glacial modification the removal of superstructure and blocks locally forming boulder trains and the progressive reduction of tors to stumps and basal slabs repre sent the more advanced stages of modification recognition of some slabs as tor stumps from which glacial erosion has removed all superstructure allows the original distribution of tors to be recon structed for large areas of the cairngorms unmodified tors require covers of non erosive cold based ice during all of the cold stages of the middle and late pleistocene deformation beneath cold based glacier ice is capable of the removal of blocks but advanced glacial modification requires former wet based glacier ice the depth of glacial erosion at former tor sites remains limited largely to the partial or total elimination of the upstanding tor form cosmogenic nuclide exposure ages phillips et al 2006 together with data from weathering pit depths hall and phillips 2006 from the surfaces of tors and large erratic blocks require that the glacial entrainment of blocks from tors occurred in marine isotope stages mis 4 2 6 and probably at least one earlier phase the occurrence of gla cially modified tors on or close to the main summits of the cairngorms requires full ice cover over the mountains during these stages evidence from the cairngorms indicates that tor morphology can be regarded as an important indicator of former ice cover in many formerly glaciated areas particularly where other evidence of ice cover is sparse recognition of the glacial modification of tors is impor tant for debates about the former existence of nunataks and refugia copyright 2006 john wiley sons ltd

on gravity from sst geoid from seasat and plate age and fracture zones in the pacific our earlier measurements of the high degree and order n m 12 gravity in the central pacific using the method of satellite to satellite tracking sst have been extended with an additional 50 passes of data the sst method utilizes line of sight doppler tracking between the very high geosynchronous ats 6 spacecraft and the much lower 840 km orbiting geos 3 spacecraft the observed changes in velocity with time are reduced in relation to the well determined low degree and order n m 12 goddard earth model gem field model and accelerations are found by differentiation of the range rates because this new map is essentially identical to the earlier results we have produced a composite map by combining all 90 passes of sst data the resolution of the map is at worst about 5 and is much better in most places a comparison of this map with conventional gem models shows very good agreement a reduction of the seasat altimeter data has also been carried out for an additional comparison although the seasat geoid contains much more high frequency information it agrees very well with both the sst and the gem fields the maps are dominated especially in the east by a pattern of roughly east west anomalies with a transverse wavelength of about 2000 km a further comparison with regional bathymetric data shows a good correlation of gravity and geoid with plate age each anomaly band is framed by major fracture zones whose regular spacing 10 seems to account for the fabric in these fields there are other anomalies that are accounted for by hot spots and altogether the immediate source of at least part of these pacific anomalies is in the lithosphere itself it therefore seems that most of the anomalies in the east half of the pacific could be partly caused simply by regional differences in plate age the amplitude of these geoid or gravity anomalies caused by age differences should decrease with absolute plate age and large anomalies 3 m over old smooth seafloor may indicate a further deeper source within or perhaps below the lithosphere however because of the significant effect of plate structure on the geoid and gravity fields especially over young 80 ma seafloor lithospheric effects must be eliminated before these anomalies can be systematically ascribed to deeper sources such as small scale convection

weathering profiles in granitoid rocks of the sila massif uplands calabria southern italy new insights into their formation processes and rates abstract in this paper we characterized several weathering profiles developed on granitoid rocks in the sila massif upland calabria southern italy integrating detailed macro and micromorphological observations with physico mechanical field tests and petrographic mineralogical and geochemical analyses we focused our attention on the main weathering and pedogenetic processes trying to understand apparent discrepancies between weathering grade classes based on field description and geomechanical properties and two common weathering indices such as the micropetrographic index ip and the chemical index of alteration cia our results showed that sericite on plagioclase and biotite chloritization that represent inherited features formed during late stage hydrothermal alteration of granitoid rocks may cause an overestimation of the real degree of weathering of primary mineral grains under meteoric conditions especially in lower weathering grade classes moreover the frequent identification of fe mn oxides and clay coatings of illuvial origin rather than or in addition to those formed in situ both at the macro and microscale may also explain an overestimation of the weathering degree with respect to field based classifications finally some apparent inconsistencies between field geomechanical responses and chemical weathering were interpreted as related to physical weathering processes cryoclastism and thermoclastism that lead to rock breakdown even when chemical weathering is not well developed hence our study showed that particular caution is needed for evaluating weathering grades because traditional field and geochemical petrographic tools may be biased by inherited hydrothermal alteration physical weathering and illuvial processes on the basis of chronological constraints to soil formation obtained from a 42 ka old volcanic input mixed to granite parent materials detected in the soil cover of the sila massif upland a first attempt to estimate soil formation rates was achieved for different depths of corresponding weathering profile zones soil formation rates ranged from 0 01 0 07 mm a 1 for a and bw horizons weathering class vi to 0 04 0 36 mm a 1 for the underlying saprolite c and cr layers class v by comparing these results with the corresponding erosion rates available in the literature for the study area that range from

pleistocene deglaciation and the global gravity field the present day global geoid and free air gravity anomaly signals induced by pleistocene deglaciation have been computed along with their secular variations a revised green function has been derived for the free air gravity anomaly and we find that an earth model with a lower mantle viscosity moderately larger than the upper mantle value satisfies observations of the anomaly over both hudson s bay and fennoscandia using this preferred earth model the predicted global geoid anomaly map is characterized by peak negative values of 36 7 9 4 and 21 9 m over hudson s bay northern europe and antarctica respectively and by a smooth small amplitude 2 5 m upwarping over the major ocean basins although the field has an order of magnitude less power than the observed there is a significant spatial correlation between the two inferences of mantle viscosity based upon comparisons between the observed geoid and the computed deglaciation induced anomaly are hampered by the large contribution from the convective circulation in the earth s mantle we have subtracted a predicted convection signal based on seismic tomography from the observed field however the residual geoid thus obtained is still too inaccurate to allow a useful comparison in contrast a filtered version of the observed geoid over canada which retains harmonic coefficients in the degree range 10 22 provides a relatively uncontaminated by convection datum that is indeed satisfied by the preferred earth model secular variations in the earth s gravitational field are naturally dominated by the signal from pleistocene deglaciation in this respect we compute zonal harmonics in the expansion of the present day rate of change of the geopotential and in particular we predict amplitudes comparable to that for the previously analysed j2 for j4 j5 j7 and j9 all of which reflect in large part the response due to the melting of the massive laurentide ice sheet this analysis suggests that measurement of these higher order secular variations of the zonal harmonics based upon analysis of long time series of lageos ranging data could provide very useful additional constraints on the radial variation of mantle viscosity these constraints along with all others described in this paper are shown to be relatively insensitive to assumptions concerning the deflection during the glacial isostatic adjustment process of the 400 and 670 km density discontinuities within the mantle

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

the distribution of inselbergs and their relationship to geomorphological structural and lithological controls in southern zimbabwe abstract the gneissic granitic basement of southern zimbabwe is characterized by a wide variety of inselbergs preferentially developed on the granitoid rocks however there are significant differences in the frequency of inselbergs and most inselbergs occur in the younger granitoid rocks particularly in rocks with microcline as the dominant k feldspar but their distribution is not uniform completely isolated inselbergs are rare and most inselbergs are arranged in clusters or are associated with plateaus or they occur as the detached ends of spurs and ridges chemical and mineralogical investigations indicate significant differences in the composition of the older and younger granitoid rocks the latter are characterized by a higher content of alkali feldspars and a lower content of plagioclase and mafic minerals the influences of texture fabric and fracture characteristics on the resistance of the rocks vary in the southern part of the study area the majority of rock domes is associated with porphyritic granites and fine grained granites whilst inselbergs of the large batholith complexes in the northern part of the study area show virtually no relationships to the grain size of the rocks thin sections analysis indicate that the rocks of the terrains with a higher density of inselbergs are characterized by an intense intergrowth of minerals and a higher number of contacts between quartz and alkali feldspars particularly in the case of the porphyritic granites the influence of texture on the frequency of rock domes is linked with two factors these are a high content of microcline minerals that have filled the interstices of the surrounding mineral framework and enclosed the surrounding minerals overgrowths and replacement micro structures indicate a long lasting crystallization which appears to be responsible for a lower density of cooling fractures enclosure of the more vulnerable minerals in the more resistant microcline megacrysts retards the loosening of the rock constituents the marked differences in the lithological and structural characteristics of the various granitoid rocks influence the weathering behaviour of the rocks and illustrate that the divergent weathering characteristics of the rocks are strongly dependent on lithological and structural factors

stelckiceras and other gastroplitinae ammonitina from the albian lower cretaceous fort st john group peace river area northeastern british columbia stelckiceras jeletzky 1980 and pseudopulchellia imlay 1961 emend j a jeletzky in 1980 are illustrated from the ammobaculites wenonahae subzone of the albian lower cretaceous hasler formation of the fort st john group on the peace river in northeastern british columbia species of gastroplites mclearn 1930 pseudopulchellia imlay 1961 pseudogastroplites jeletzky 1980 and stotticeras jeletzky 1980 are illustrated from the ammobaculites sp and haplophragmoides multiplum subzones of the subjacent cadotte member of the boulder creek formation and the underlying hulcross formation two new species gastroplites bahani and gastroplites jeletzkyi are described the presence of several arctic exotic ammonites suggests that the middle albian interior seaway was not entirely isolated from the arctic basin numerous foraminifera are known to be common to both basins and current inflow may have prevented endemic gastroplites s st and stelckiceras from migrating northward biostratigraphic conclusio

magmatic structures and kinematics emplacement of the variscan granites from central portugal serra da estrela and castro daire areas abstract the late d3 variscan granites which represent the most important volume of granites of central portugal are studied here for their magmatic and solid state fabrics by means of the anisotropy of magnetic susceptibility ams technique in a 5000 km 2 area located between guarda and castro daire including the serra da estrela region two main directions n150e and n20e of stretching lineations are found indicating that the emplacement of these late kinematic granitoids was tectonically controlled a three stage model is proposed in which a openings along n150 striking dextral strike slip faults allow the first granitic magmas to be emplaced in the upper crust of palaeozoic metasediments and syn d3 granitoids b openings along n20 striking possibly sinistral strike slip faults conjugates to the prior strike slip faults and allow the enlargement of the granitic plutons and c the final emplacement of this huge volume of granitic rocks was mainly controlled by the magma pressure which explains the rarity of structures related to this stage of granites emplacement in the country rocks this structural study of granitic rocks yields new constraints on the tectonic evolution of this part of the variscan orogenic belt at c 300 ma

spatial and temporal variability of periglaciation of the iberian peninsula abstract active periglacial processes are currently marginal in the iberian peninsula spatially limited to the highest mountain ranges however a wide variety of periglacial deposits and landforms are distributed in low and mid altitude environments which shows evidence of past periods of enhanced periglacial activity the purpose of this paper is to summarize the present knowledge of past periglacial activity in the iberian peninsula the chronological framework takes four main stages into account the last glaciation deglaciation holocene and present day processes this study focuses on the highest massifs pyrenees cantabrian range nw ranges central range iberian range sierra nevada as well as other lower elevation environments namely the central iberian meseta during the last glaciation the periglacial belt extended to much lower altitudes than today reaching current sea level in the nw corner of the iberian peninsula a wide range of geomorphological landforms and sedimentary records is indicative of very active periglacial processes during that phase in some cases related to permafrost conditions i e block streams rock glaciers most of the inactive landforms and deposits in low and mid elevations in iberia are also related to this phase the massive deglaciation of the iberian massifs was caused by a gradual increase in temperatures the deglaciation phase was only interrupted by a short period with colder conditions the younger dryas that reactivated periglacial processes in the formerly glaciated cirques of the highest lands specifically with the widespread development of rock glaciers during the holocene periglacial processes have been only active in the highest ranges shifting in altitude according to temperature regimes and moisture conditions the little ice age saw the reactivation of periglacial activity in lower elevations than today currently periglacial processes are only active in elevations exceeding 2500 m in the southern ranges and above 2000 2200 m in the northern massifs higher in sierra nevada in the south of iberian peninsula

large scale distributed deformation controlled topography along the western africa eurasia limit tectonic constraints in the interior of the iberian peninsula the main geomorphic features mountain ranges and basins seems to be arranged in several directions whose origin can be related to the n s plate convergence which occurred along the cantabro pyrenean border during the eocene lower miocene time span the iberian variscan basement accommodated part of this plate convergence in three e w trending crustal folds as well as in the reactivation of two left lateral nne ssw strike slip belts the rest of the convergence was assumed through the inversion of the iberian mesozoic rift to form the iberian chain this inversion gave rise to a process of oblique crustal shortening involving the development of two right lateral nw se shear zones crustal folds strike slip corridors and one inverted rift compose a tectonic mechanism of pure shear in which the shortening is solved vertically by the development of mountain ranges and related sedimentary basins this model can be expanded to nw africa up to the atlasic system where n s plate convergence seems also to be accommodated in several basement uplifts anti atlas and meseta and through the inversion of two mesozoic rifts high and middle atlas in this tectonic situation the microcontinent iberia used to be firmly attached to africa during most part of the tertiary in such a way that n s compressive stresses could be transmitted from the collision of the pyrenean boundary this tectonic scenario implies that most part of the tertiary eurasia africa convergence was not accommodated along the iberia africa interface but in the pyrenean plateboundary a broad zone of distributed deformation resulted from the transmission of compressive stresses from the collision at the pyrenean border this distributed intraplate deformation can be easily related to the topographic pattern of the africa eurasia interface at the longitude of the iberian peninsula shortening in the rif betics external zones and their related topographic features must be conversely related to more local driven mechanisms the westward displacement of the exotic alboran domain other than n s convergence the remaining nnw sse to nw se latest miocene up to present convergence is also being accommodated in this zone straddling iberia and morocco at the same time as a new ill defined plate boundary that is being developed between europe and africa

seismotectonics of portugal and its adjacent area in the atlantic abstract new elements on the seismicity of portugal and new focal mechanism solutions of earthquakes with epicentres situated off the coast of the portuguese mainland and in the azores region are presented historical seismicity data show that in the territory of the portuguese mainland there are active faults that are responsible for earthquakes that have caused important damage and many casualties however most of the intraplate earthquakes with epicentres situated in the portuguese mainland or near the shore are normally of small magnitude and this renders difficult their interpretation in the light of focal mechanisms a solution for one earthquake with magnitude 5 and epicentre at the nazare submarine canyon is presented southwestwards of cape st vincent there is an important seismic zone responsible for high magnitude earthquakes such as that of 1 november 1755 this zone is situated in the region where the extension of the messejana fault into the ocean joins with the azores gibraltar fault the seismicity of the area situated between the western coast of the portuguese mainland and the azores increases approximately along the 15 w meridian from the latitude of the azores gibraltar fault up to 44 n focal mechanisms of earthquakes with epicentres situated along this line show very similar solutions the interpretation of the focal mechanism solutions of the earthquakes with epicentres situated in the studied area shows that the stress field trends approximately nw se it is assumed that this stress field results from the interaction of the eurasian and african plates however this direction is not maintained in the azores region

cenozoic tectonic activity in a variscan basement evidence from geomorphological markers and structural mapping nw iberian massif abstract the nw iberian massif is part of an ancient basement that has been considered a seismically stable area with no outstanding cenozoic tectonics however recent seismic activity revealed the need for better knowledge of the cenozoic structures in the area because of the lack of mesozoic deposits and the scarcity of cenozoic sediments as well as the intense deformation of the pre mesozoic variscan basement it is difficult to study the cenozoic tectonic structures in this work the combination of detailed structural mapping and study of geomorphological markers in the variscan basement has allowed recognition of cenozoic tectonic structures kinematics and processes that otherwise would not have been identified the identified structures have been gathered into three groups a ne sw trending strike slip faults mainly sinistral b nnw vergent thrusts that uplift the caurel mountains and galaico leoneses mountains and c e w and ene wsw thrusts that uplift the ancares mountains in a pop up structure the structures cut the pre cenozoic erosion surface and affect the drainage network that shows patterns characteristic of tectonic activity the three groups of structures define sectors with different relief showing a strong link between geomorphological elements and tectonic structures the intense drainage reorganisations observed in the area and the deformation of miocene pliocene deposits point out to a significant late miocene tectonic activity in the region thus the cenozoic tectonic activity in the northwest of the iberian peninsula takes place during an extensive period of time which started with the episodes of compression in the cantabrian margin and it is identified nowadays by the recent seismic activity recorded in the north western iberian peninsula 1995 and 1997 lugo events the seismicity is related to the cenozoic structures identified in the area which move under the present se nw horizontal maximum compression and coincide with the proposed seismogenic faults

tomographical mapping of the lithosphere and asthenosphere beneath southern scandinavia and adjacent areas abstract in this paper we report on a seismic tomographical survey of the lithosphere asthenosphere beneath southern scandinavia and adjacent areas the ach inversion technique has been used and the observational data in the form of p wave travel time residuals have been obtained from seismogram records from networks in denmark southern norway and southern sweden the volume under investigation subdivided into four levels layers of 7 7 knots blocks each for estimation of velocity perturbations covers the area 54 62 n and 7 20 e and depth range 0 600 km major findings are as follows level 1 0 100 km pronounced velocity lows beneath southern jutland zealand the variscan foredeep and the sveco norwegian province of southeastern norway 1500 ma old the svecofennides of southeastern sweden exhibit relatively high velocities while the sveco norwegian province of southwestern sweden 1700 ma old is characterized by moderately high velocities the transition between velocity highs and lows coincides with the tornquist teisseyre line ttl or fennoscundian border zone level 2 100 300 km velocity anomalies are less pronounced at this level although velocity lows are found beneath the northern jutland zealand area and slightly northwestwards of the oslo rift the only velocity high is found beneath the southeasternmost part of sweden the ttl does not appear to have a clear counterpart in the velocity anomaly pattern in this depth range although a clearly unambiguous answer here would require far more extensive observational data a research goal of the future level 3 300 500 km and level 4 500 600 km velocity anomalies are weak which is not unexpected for the upper mantle beneath shield areas