formation of chlorite during thrust fault reactivation record of fluid origin and p t conditions in the monte perdido thrust fault southern pyrenees the chemical and isotopic compositions of clay minerals such as illite and chlorite are commonly used to quantify diagenetic and low grade metamorphic conditions an approach that is also used in the present study of the monte perdido thrust fault from the south pyrenean fold and thrust belt the monte perdido thrust fault is a shallow thrust juxtaposing upper cretaceous paleocene platform carbonates and lower eocene marls and turbidites from the jaca basin the core zone of the fault about 6 m thick consists of intensely deformed clay bearing rocks bounded by major shear surfaces illite and chlorite are the main hydrous minerals in the fault zone illite is oriented along cleavage planes while chlorite formed along shear veins 50 m in thickness authigenic chlorite provides essential information about the origin of fluids and their temperature 18o and d values of newly formed chlorite support equilibration with sedimentary interstitial water directly derived from the local hanging wall and footwall during deformation given the absence of large scale fluid flow the mineralization observed in the thrust faults records the p t conditions of thrust activity temperatures of chlorite formation of about 240 c are obtained via two independent methods chlorite compositional thermometers and oxygen isotope fractionation between cogenetic chlorite and quartz burial depth conditions of 7 km are determined for the monte perdido thrust reactivation coupling calculated temperature and fluid inclusion isochores the present study demonstrates that both isotopic and thermodynamic methods applied to clay minerals formed in thrust fault are useful to help constrain diagenetic and low grade metamorphic conditions

fluid flow and volume loss during mylonitization an origin for phyllonite in an overthrust setting north carolina u s a abstract in the western blue ridge province of the southern appalachians north carolina granite gneisses are converted to phyllitic mylonites phyllonites along the base of the rector branch thrust sheet the mylonites show evidence for fluid infiltration and large volume losses with decreasing distance from the thrust and local shear zones feldspars undergo grain size reduction by cracking followed by chemical breakdown to muscovite sericite and zoisite the following reaction was important during mylonitization 3 k feldspar 2 h muscovite 2 k 6 sio 2 quartz displays evidence for dynamic recrystallization whereas feldspar deforms brittely which together with the secondary mineral assemblages suggest that deformation occurred at temperatures of between 300 c and 500 c in the presence of a fluid the mylonites are enriched by a factor of at least 2 5 in elements such as tio 2 p 2 o 5 zr y v la ce and depleted in sio 2 in comparison to their protolith gneisses the immobile element enrichments are attributed to enrichment in residual phases such as ilmenite zircon apatite and epidote in the mylonites and are interpreted as due to minimum volume losses of 60 mass balance calculations based on major element chemistry indicate the mylonites lost large amounts of sio 2 and smaller amounts of alkalies and were infiltrated by fluid rock weight ratios of between 10 2 and 10 3 phyllonitization as a process involves several deformation mechanisms including cataclasis and solution of feldspar as well as dislocation creep of quartz and micas reaction enhanced softening was apparently important in strain localization

fluid rock interactions related to metamorphic reducing fluid flow in meta sediments example of the pic de port vieux thrust pyrenees spain in orogens shortening is mainly accommodated by thrusts which constitute preferential zones for fluid rock interactions fluid flow mass transfer and mineralogical reactions taking place along thrusts have been intensely investigated especially in sedimentary basins for petroleum and uranium research this study combines petrological investigations mineralogical quantifications and geochemical characterizations with a wide range of analytical tools with the aim of defining the fluid properties nature origin temperature and redox and fluid host rock interactions mass transfers recrystallization mechanisms and newly formed synkinematic mineralization in the pic de port vieux thrust fault zone pyrenees spain we demonstrate that two geochemically contrasted rocks have been transformed by fluid flow under low grade metamorphism conditions during thrusting the hanging wall triassic red pelite was locally bleached while the footwall cretaceous dolomitic limestone was mylonitized the results suggest that thrusting was accompanied by a dynamic calcite recrystallization in the dolomitic limestone as well as by leaching of iron via destabilization of iron oxides and phyllosilicate crystallization in the pelite geochemical and physical changes highlighted in this study have strong implications on the understanding of the thrust behavior tectonic and hydraulic and improve our knowledge of fluid rock interactions in open fluid systems in the crust

links between orogenic wedge deformation and erosional exhumation evidence from illite age analysis of fault rock and detrital thermochronology of syn tectonic conglomerates in the spanish pyrenees abstract we present new geochronologic data illuminating the tectonic and erosional history of the orogenic wedge exposed in the south central pyrenees spain we interpret illite age analyses from four fault gouges that record thrust belt development and document the importance of out of sequence thrusting fault activity occurs in pulses with slip occurring contemporaneously on multiple faults throughout the wedge new apatite fission track data from syn orogenic sediments of the sis conglomerate body reveal ages of 48 to 42 ma with no consistent variation upsection in strata deposited from 41 to 30 ma we interpret these data as well as thermal modeling of track length distributions to imply rapid cooling in the interior of the pyrenean wedge during the middle eocene the record of fault activity and erosion suggests that orogenic wedges may not evolve in a steady fashion but generally exhibit significant changes in rates of deformation and exhumation the observed correlation in the timing of tectonism and erosional exhumation provides evidence for links between tectonic and surface processes

frictional properties of natural fault gouge from a low angle normal fault panamint valley california 1 we investigate the relationship between frictional strength and clay mineralogy of natural fault gouge from a low angle normal fault in panamint valley california gouge samples were collected from the fault zone at five locations along a north south transect of the range bounding fault system spanning a variety of bedrock lithologies samples were powdered and sheared in the double direct shear configuration at room temperature and humidity the coefficient of friction was measured at a range of normal stresses from 5 to 150 mpa for all samples our results reinforce the intuitive understanding that natural fault gouge zones are inherently heterogeneous samples from a single location exhibit dramatic differences in behavior yet all three were collected within a meter of the fault core for most of the samples friction varies from 0 6 to 0 7 consistent with byerlee s law however samples with greater than 50 wt total clay content were much weaker 0 2 0 4 expandable clay content of the samples ranged from 10 to 40 wt frictional weakness did not correlate with expandable clays our results indicate that friction decreases with increasing total clay content rather than with the abundance of expandable clays the combination of field relations analytical results and friction measurements indicates a positive correlation between clay content fabric intensity and localization of strain in the fault core a mechanism based upon foliations enveloping angular elements to reduce friction is suggested for weakening of fault gouge composed of mixed clay and granular material we provide broad constraints of 1 5 km on the depth of gouge generation and the depth at which fault weakness initiates we show that slip on the panamint valley fault and similar low angle normal faults is mechanically feasible in the mid upper crust if the strength of the fault is limited by weak clay rich fault gouge

stability of zircon in a low grade ultramylonite and its utility for chemical mass balancing the shear zone at mieville switzerland at mieville switzerland granitic basement rocks of the aiguilles rouges massif are cut by a subvertical shear zone the variscan shearing event produced a low grade ultramylonite zone which is up to 50 m wide and several kilometers long investigations of accessory zircons from the undeformed wall rock and from the most highly deformed ultramylonite show only minor alterations and mechanical damage of zircon crystals even in an extreme state of deformation this outstanding stability of zircon allows one to consider the element zr as immobile and therefore to use it as a passive marker for calculations of mass and volume changes during deformation processes application of this method confirms that the deformation at mieville proceeded under simple shear constant volume and isochemical conditions this is in agreement with the results of classical geochemical mass balancing in addition uncertainties inherent in the geochemical approach can be minimized by the new method

a least squares approach to mass transport calculations using the isocon method a statistically rigorous approach based on the isocon method grant 1986 to evaluate mass transport is presented chemical analyses of multiple samples of unaltered parent and altered rock are used to calculate the average oxide or element concentration and its standard deviation for each rock population in a typical application the uncertainties in element concentration associated with the lack of homogeneity in each population outweigh the analytical uncertainty an efficient algorithm is presented to select the immobile elements by identifying the maximum number of elements that are within their uncertainties compatible with the same isocon the actual isocon is constructed by forcing a line through the origin and optimizing its slope using a weighted least squares procedure for the selected immobile elements thus individual uncertainties for each immobile element are taken into account as an illustration the procedure is applied to a published set of data on potassic and sericitic alterations of quartz monzonite of the bingham porphyry copper system the surprising result indicates that the apparent increase of potassic alteration phases is a consequence of acid leaching of calcium and sodium no mass transport of potassium is indicated silica water and sulfur were added during alteration the best fit isocon requires a small mass increase during each alteration process which however is within the uncertainty obtained for the slope of the isocon a software package is available from the authors in the form of a fortran 77 source code

numerical simulations of glacial valley longitudinal profile evolution glaciers shape alpine landscapes they broaden valley bottoms enhance local valley relief generate multiple steps overdeepen valley floors and cause tributary valleys to hang these distinctive glacial signatures result from 10 4 10 5 yr of erosion during which swings in climate drive advances and retreats of alpine glaciers we use a numerical model of glacial erosion to explore the development of the longitudinal profiles of glaciated valleys the model is driven by the past 400 k y of variable climate because both sliding speed which dictates abrasion rate and water pressure fluctuations which strongly modulate quarrying rate should peak at the equilibrium line altitude ela we expect the locus of most rapid erosion to follow the transient ela simulations of a single glacial valley show rapid flattening of the longitudinal profile inclusion of a tributary glacier creates a step immediately downvalley of the tributary junction that persists over multiple glaciations and commonly leaves the tributary valley hanging steps and overdeepenings result from an increase in ice discharge immediately below the tributary junction which is accommodated primarily by increased ice thickness and hence sliding rate the size of the step increases with the ratio of tributary to trunk ice discharge while the height of a hanging valley reflects the difference in the time integrated ice discharge in tributary and trunk valleys and therefore increases as the discharge ratio decreases

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

slope distributions threshold hillslopes and steady state topography digital elevation models of two steady state mountain ranges the olympic mountains om and oregon coast range ocr are used to examine relationships between slope distributions the development of threshold hillslopes and steady state topography plots of drainage area versus slope for these mountain ranges exhibit substantial scatter that complicates comparison of range form to analytical theories and landscape evolution models contour plots of the density of such data reveal an attractor at the scale of the transition from hillslope processes to channel processes and log bin averaging reveals trends that parallel predictions of steady state erosion laws but with different rate laws for five distinct process domains hillslopes valley heads and colluvial bedrock and alluvial valley segments slope histograms computed for 100 km2 areas defined by a 10 10 km grid throughout the om exhibit approximately normal or exponential distributions in areas of active rock uplift and depositional topography respectively local slope distributions in the ocr also tend to be normally distributed but some are left skewed in areas with gentler slopes mean slopes determined both over the above referenced grid and a 10 km diam moving window are relatively invariant in the core of the om in spite of strong contrasts in bedrock erodibility and gradients in long term rock uplift rates in contrast the mean slopes in the ocr parallel latitudinal gradients in rock uplift rates and bedrock erodibility hence the slope distributions in the om and ocr reflect distinct relationships between development of threshold bedrock and soil mantled hillslopes and steady state topography

critical metals ree sc pge in ni laterites from cuba and the dominican republic ni laterites are considered worthy targets for critical metals cm exploration as rare earth elements ree sc and platinum group elements pge can be concentrated during weathering as a result

quantification of mass transfers and mineralogical transformations in a thrust fault monte perdido thrust unit southern pyrenees spain abstract in fold and thrust belts shortening is mainly accommodated by thrust faults which are preferential zones for recrystallisation and mass transfer this study focuses on a detachment fault related to the emplacement of the monte perdido thrust unit in the southern pyrenees the studied fault zone consists of a 10 m thick intensively foliated phyllonite developed within the millaris marls of eocene age the lithological homogeneity of the hanging wall and footwall allows us to compare the millaris marls outside the fault zone with the highly deformed marls located in the fault zone and to quantify the chemical mineralogical and volumetric changes related to deformation processes along the fault the millaris marls are composed of detrital quartz illite chlorite minor albite and pyrite in a micritic calcite matrix in the fault zone the cleavage planes are marked by clay minerals and calcite chlorite veins attest to fluid mineral interactions during deformation the mineral proportions in all samples from both the fault zone and millaris marls have been quantified by two methods 1 x ray diffraction and rietveld refinement and 2 bulk chemical analyses as well as microprobe analyses to calculate modal composition the excellent agreement between the results of these two methods allows us to estimate mineralogical variations using a modification of the gresens equation during fault activation up to 45 wt of calcite was lost while the amounts of quartz and chlorite remained unchanged illite content remained constant to slightly enriched the mineralogical variations were coupled with a significant volume loss up to 45 mostly due to the dissolution of micritic calcite grains deformation was accompanied by pressure solution and phyllosilicates recrystallisation these processes accommodated slip along the fault they required fluids as catalyst but they did not necessitate major chemical transfers

multidisciplinary approach to constrain kinematics of fault zones at shallow depths a case study from the cameros demanda thrust north spain thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts e g mylonites sheath folds shear bands in this paper a combination of techniques including structural analysis magnetic methods as anisotropy of magnetic susceptibility and paleomagnetism and paleothermometry is used to define thrusting conditions deformation and transport directions in the cameros demanda thrust north spain three outcrops were analyzed along this intraplate large scale major structure having 150 km of outcropping length 30 km of maximum horizontal displacement and 5 km of vertical throw results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analysis mixed layer illite smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust kinematic indicators foliation s c structures and slickenside striations indicate altogether a dominant nnw movement of the hanging wall in the western zone and ne in the eastern zone of the thrust thus implying strain partitioning between different branches of the main thrust the study of ams in fault rocks nearly 400 samples of fault gouge breccia and microbreccia indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direction onto the k max k int plane in sites with strong shear deformation paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting in spite of the shallow depth for deformation and a strong deformation or scattering of the magnetic remanence vectors in the fault zone the application of the described techniques and consistency of results indicate that the proposed multidisciplinary approach is useful when dealing with thrusts at shallow crustal levels

patterns of mineral transformations in clay gouge with examples from low angle normal fault rocks in the western usa abstract neoformed minerals in shallow fault rocks are increasingly recognized as key to the behavior of faults in the elasto frictional regime but neither the conditions nor the processes which wall rock is transformed into clay minerals are well understood yet understanding of these mineral transformations is required to predict the mechanical and seismogenic behavior of faults we therefore present a systematic study of clay gouge mineralogy from 30 outcrops of 17 low angle normal faults lanf s in the american cordillera to demonstrate the range and type of clay transformations in natural fault gouges the sampled faults juxtapose a wide and representative range of wall rock types including sedimentary metamorphic and igneous rocks under shallow crustal conditions clay mineral transformations were observed in all but one of 28 faults one fault contains only mechanically derived clay rich gouge which formed entirely by cataclasis clay mineral transformations observed in gouges show four general patterns 1 growth of authigenic 1m d illite either by transformation of fragmental 2m 1 illite or muscovite or growth after the dissolution of k feldspar illitization of fragmental illite smectite is observed in lanf gouges but is less common than reported from faults with sedimentary wall rocks 2 retrograde diagenesis of an early mechanically derived chlorite rich gouge to authigenic chlorite smectite and saponite mg rich tri octahedral smectite 3 reaction of mechanically derived chlorite rich gouges with mg rich fluids at low temperatures 50 150 c to produce localized lenses of one of two assemblages sepiolite saponite talc lizardite or palygorskite chlorite quartz and 4 growth of authigenic di octahedral smectite from alteration of acidic volcanic wall rocks these transformation groups are consistent with patterns observed in fault rocks elsewhere the main controls for the type of neoformed clay in gouge appear to be wall rock chemistry and fluid chemistry and temperatures in the range of 60 180 c

a theoretical model coupling chemical weathering rates with denudation rates uplift of the himalayas has been proposed to have locally accelerated chemical weathering thus leading to enhanced co2 sequestration and global cooling this hypothesis assumes that rapid erosion exposes fresh highly reactive minerals at earth s surface empirical studies quantifying the relationship between erosion and weathering have produced apparently conflicting results where the nature of the relationship is dependent on the weathering regime of the sampled landscapes we derive a quantitative model that defines this relationship across the range of weathering regimes from supply limited to kinetically limited conditions the model matches trends in field data collected by others and reconciles apparently conflicting results the model also demonstrates that as erosion rates increase potential increases in weathering rate from the exposure of fresher materials are offset by the decrease in the total volume of minerals exposed due to thinner regolith we conclude that the relationship between weathering and erosion is one of diminishing returns in which increases in erosion rate lead to progressively smaller increases in weathering rate indeed at the highest erosion rates weathering rates may decline the ability therefore of accelerated uplift and erosion to stimulate greater co2 sequestration may be significant in landscapes eroding at rates of 10 102 t km 2 yr 1 however where erosion rates are greater than 102 t km 2 yr 1 increases in denudation may not be matched by increases in chemical weathering finally our results suggest that watersheds with regolith thicknesses of 0 5 m will yield the greatest solute fluxes

positive feedbacks associated with erosion of glacial cirques and overdeepenings the principal points of water input to a glacier are the bergschrund in cirques and crevasse fields lower on the glacier crevasse fields commonly occur over convexities at the heads of overdeepenings in glacier beds the amplitude of subglacial water pressure fluctuations is large just down glacier from these points of water input erosion by quarrying is likely in such areas erosion is thus inferred to be localized on the headwalls of cirques and overdeepenings in the case of overdeepenings this leads to a positive feedback process in which a perturbation in the bed causes crevassing at the surface resulting in erosional forces that accentuate the perturbation when subglacial water flows up an adverse bed slope leading out of a cirque or overdeepening much of the viscous energy dissipated is used to warm the water to keep it at the pressure melting temperature as the ice thins and the pressure decreases in such situations subglacial conduits are maintained by high water pressures rather than by melting of conduit walls in the limit water pressures apparently become so high that water is forced out along the ice bed interface and the conduits collapse the products of erosion are then no longer flushed out and a protective till layer accumulates by limiting erosion on such adverse bed slopes this till layer controls the geometry of these overdeepened basins

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

evolution of a turbiditic foreland basin and analogy with an accretionary prism example of the eocene south pyrenean basin the south pyrenean tertiary basin was an east west trending foreland trough which developed from early eocene to miocene times in a north south trending compressive regime a turbiditic series of lower and middle eocene age hecho group enables us to define the typical features of the tectono sedimentary evolution of the basin 1 slope and shelf derived carbonate turbidites and megaturbidites bear witness to the seismic activity of the basin borders 2 the southern basin border evidenced by the onlap of the turbidites onto slope and shelf deposits migrated progressively southwards in time and 3 the deformation pattern is characterized in the meso cenozoic sediments by a complex thrust fold system of thin skinned tectonics style its specific geometry and kinematics were influenced by the pre deformation geometry onlap this thrust fold system is related to south directed basement nappes and its front advanced progressively southwards in time from this data we infer an evolutionary model for this highly mobile basin it was a flexural basin linked to the northward bending of the lithosphere in the foreland of a south directed crustal accretionary prism as the nappes advanced the basin migrated progressively southwards in the foreland direction as for the actual basin evolution many analogies with accretionary prism trench systems of active margins exist

mg metasomatism and formation conditions of mg chlorite muscovite quartzphyllites leucophyllites of the eastern alps w hungary and their relations to alpine whiteschists the lower austroalpine orthogneiss micachist complex of the sopron fertorakos area of w hungary contains mg chlorite muscovite quartzphyllites leuco phyllite and mg chlorite bearing kyanite quartzites whose chemical compositions differ greatly from their surrounding rocks formation of leucophyllites took place in shear zones and was associated with depletion in alkalies and iron and enrichment of magnesium and h2o mg zonation of relict igneous muscovites of leucophyllites and changes in the whole rock chemical compositions suggest mg metasomatism material gains and losses have been assessed using the composition volume relationship approach proceeding from metagranite through transition rocks to leucophyllites mgo h2o feo and alkalies show continuously increasing dispersion in isocon plots with mg enrichment even in sheared gneiss not in contact with leucophyllite the metasomatic processes that formed the mg rich rocks may be similar to those responsible for the formation of high pressure whiteschists in the central and western alps the geochemical characteristics of the dora maira whiteschists italy and their country gneisses are very similar to those of the sopron leucophyllites supporting the theory that mg metasomatism produced the whiteschist chemistry on the basis of oxygen isotope compositions of relict igneous muscovites the precursor granitic rock had a 18o value around 13 proving its crustal anatectic origin the leucophyllites have whole rock oxygen isotope compositions around 8 5 which is in conflict with the theory of an mg rich sedimentary protolith rather the low 18o values reflect fluid rock interaction with a low 18o fluid quartz mineral oxygen isotope fractionations yield a metamorphic temperature of 560 30 c which agrees with earlier estimates from mineral stabilities silicon contents of phengites correspond to a metamorphic pressure of 13 gpa at this temperature indicating eclogite facies metamorphism the fluids in equilibrium with leucophyllites had oxygen isotope compositions around 7 9 similar to those calculated for the ultrahigh pressure dora maira whiteschists 7 6 further supporting the genetic link between the leucophyllites and whiteschists hydrogen isotope compositions of mixed white mica chlorite samples from leucophyllites range from 40 to 35 correlating with chlorite contents the calculated endmember chlorite and white mica have d values of 30 and 40 respectively the similar d values of the white micas in leucophyllites gneisses and metagranites suggest an overall equilibration with respect to h isotopes the calculated d value of the fluid is approximately 0 suggesting a seawater origin this conclusion was also reached for the dora maira whiteschists a possible fluid source that satisfies both metasomatic and isotopic data is dehydration of hydrothermally altered oceanic crust the mafic ultramafic complex of the alpine penninic unit underlying the austroalpine nappes is a likely candidate the subduction and subsequent dehydration of the ophiolite series would supply the mg rich fluids whose migration brought about the metasomatic alteration of the overlying gneiss micaschist complexes

electron microprobe determination of minor and trace transition elements in silicate minerals a method and its application to mineral zoning in the peridotite nodule phn 1611 abstract we present a wds analytical technique for the determination by electron microprobe of low concentrations of the transition elements sc ti v cr mn co and ni in ferro magnesian silicate minerals the quality of measurements is improved by 1 optimization of counting times taking into account the anticipated analytical precision 2 monitoring instrumental and sample stabilities by a statistical analysis of peak and background intensity values sampled at intervals of 1 s simultaneous measurement of major elements is essential in evaluating bias related to instrumental drift 3 precise determination of background achieved by a least squares fitting of the measured background to a calculated one the latter is calculated by using a modified form of the kramer s equation this approach is also effective in correcting peak overlap interferences the efficiency of this method was checked by performing core to rim analysis of garnet clinopyroxene and orthopyroxene prophyroclasts in the peridotite nodule phn 1611 this led to precise determination of trace element chemical zoning in these minerals

hypsometric analysis to identify spatially variable glacial erosion 1 relatively little research has been undertaken on the use of digital elevation models to recognize the spatially variable glacial imprint of a landscape using theoretical topographies and a landscape evolution model we investigate to what extent the hypsometric analysis of digital elevation models may be used to recognize the glacial signature of mountain ranges a new morphometric parameter which we term the hypsokyrtome from the greek ipsos elevation kyrtoma curvature is derived from the gradient of the hypsometric curve the efficacy of the hypsometric integral and hypsokyrtome is tested through the study of the ben ohau range new zealand whose glacial imprint has been described previously with a numerical model we further test the geomorphic parameters in describing the morphologies of regions subject to diverse climatic and tectonic conditions the hypsokyrtome is highly sensitive to glacial erosion and the maps produced provide insights into the spatial distribution of glacial erosion we use srtm data and focus on two alternative geomorphic settings the european alps and the apennines the former has been affected by both fluvial and glacial erosion while the latter mainly exhibits a fluvially dominated morphology the correlation between elevations with increased glacial erosion and last glacial maximum lgm equilibrium line altitudes elas suggests the prevalence of a glacial buzz saw in the alps indicating that climate may put a limit on alpine topography

evidence for limited ree leaching from the roffna gneiss switzerland a discussion of the paper by vocke et al 1987 cmp95 145 154

tectono thermal history of an exhumed thrust sheet top basin an example from the south pyrenean thrust belt this paper presents a new balanced structural cross section of the jaca thrust sheet top basin of the southern pyrenees combined with paleo thermometry and apatite fission track aft thermochronology data the cross section based on field data and interpretation of industrial seismic reflection profiles allows refinement of previous interpretations of the south directed thrust system involving the identification of new thrust faults and of the kinematic relationships between basement and cover thrusts from the middle eocene to the early miocene aft analysis shows a southward decrease in the level of fission track resetting from totally reset paleozoic rocks and lower eocene turbidites indicative of heating to tmax 120 c to partially reset middle eocene turbidites and no very weak resetting in the upper eocene lower oligocene molasse tmax 60 c aft results indicate a late oligocene early miocene cooling event throughout the axial zone and jaca basin paleo maximum temperatures determined by vitrinite reflectance measurements and raman spectroscopy of carbonaceous material reach up to 240 c at the base of the turbidite succession inverse modelling of aft and vitrinite reflectance data with the qtqt software for key samples show compatibility between vitrinite derived tmax and the aft reset level for most of the samples however they also suggest that the highest temperatures determined in the lowermost turbidites correspond to a thermal anomaly rather than burial heating possibly due to fluid circulation during thrust activity from these results we propose a new sequential restoration of the south pyrenean thrust system propagation and related basin evolution

breakdown of feldspar volume gain and lateral mass transfer during mylonitization of granitoid in a low metamorphic grade shear zone abstract in a low metamorphic grade shear zone from quadrilatero ferrifero southeastern brazil granitoid rocks have been transformed into phyllonites and mylonites via activation of crystal plastic processes in quartz and fluid assisted reaction softening in feldspars quartz deformed by basal a and prism a slip with concurrent subgrain rotation recrystallization breakdown of matrix plagioclase an 22 35 via mica producing softening reactions required cationic exchanges between ca na and k forming replacement perthites in the k feldspar megacrysts which occupy around 60 of the original rock volume subsequent breakdown of the perthitic plagioclase an 12 15 led to disruption of the megacrysts enabling strain accommodation that localized the mylonite and phyllonite zones domainal volume and mass balance calculations based on major and minor elements indicate only small positive changes in mass and volume around 15 in the whole system however accentuated differences ranging from mass and volume losses of 25 and 35 at the margins to gains of 85 and 95 in the centre respectively exist between the individual longitudinal subzones occupied by the different tectonite types this scenario indicates that deformation proceeded as a nearly isochemical process although with lateral mobility of major elements principally si al and k within the shear zone these results are different from those previously reported for other granitic mylonites most of them indicating volume losses in compressional tectonic settings it is suggested that the extensional tectonic framework attributed to the moeda bonfim shear zone where mass volume losses are in principle not required enhanced the access of fluid and consequent transport of components into the shear zone principally fe si and k producing the small gains of mass and volume observed

rock slope failure and the river long profile this study examines the geomorphic effects of large 10 6 m 3 rock slope failures on long profiles of rivers in the swiss alps and the new zealand southern alps regression of channel slope versus drainage basin area objectively highlights knickpoints separating incised from aggraded reaches that often correspond to locations of large rock slope failures for a fixed concavity index the highest values of the steepness index and erosion index along a given profile spatially coincide with breach channels cut into formerly river damming rockslide debris as old as 10 k y assuming that the knickpoints do not predate slope failure data show that high profile steepness and inferred specific stream power are not always the cause but often a result of large river blocking rock slope failure in mountain basins omission of rockslide data from slope area plots lowers the steepness index and increases the concavity index on average yet only in few cases more than one standard deviation

the anso transect of the southern pyrenees basement and cover thrust geometries a balanced geological section through the western central pyrenees allows the alpine geometry of hercynian basement to be determined this shows marked differences with other transects of the southern part of the chain basement involved thrust sheets do not form an antiformal stack but are imbricated and define steps separated by frontal culmination limbs basement thrusts propagate upwards and have formed distinct thrust systems in the cover in this transect the north pyrenean zone is bounded to the south by gently dipping thrusts of large displacement and the axial zone massif at its western termination area is a flat topped culmination caused by a single thrust fault the gavarnie thrust this thrust emerges to the south in the interior of the syntectonic jaca basin the geometry of which is also controlled by underlying basement thrusts various generations of structures can be correlated with distinct episodes of syntectonic sedimentation a sequential restoration of the section illustrates how successive foreland sedimentary wedges were generated and progressively involved in deformation tectonic shortening is 48 km almost half of that estimated further to the east for the southern pyrenees the structure deduced at the ecors pyrenees seismic section cannot be translated to this transect

microtectonic and geochemical characterization of thrusting in a foreland basin example of the south pyrenean orogenic wedge spain abstract in orogenic systems thrust faults play a major role in stacking different tectonic units and may act as conduits for the expulsion of large amounts of fluid of different origins metamorphic diagenetic meteoric this study focuses on the monte perdido thrust unit emplaced in the paleogene jaca thrust sheet top basin in the sw central pyrenees we aim to decipher the mechanisms and p t conditions of deformation in fault zones and characterize the related fluid involvement through combined microstructural geochemical and microthermometry analyses two thrust faults cutting platform limestones marls and siliciclastic turbidites of the lower part of the basin fill paleocene lower eocene have been studied the fault zones are characterized by metre thick shear zones with highly deformed foliated clay rich sediments foliation is underlined by preferentially oriented phyllosilicates several generations of shear and extension calcite quartz and chlorite bearing veins attest to fluid rock interactions during a multi stage deformation microstructural observations and stable isotope analyses on calcite from veins and host sediments suggest that deformation was aseismic and dominated by diffusive mass transfer from pressure solution sites along cleavage and stylolites to the precipitation sites in veins with mineralizing fluids in equilibrium with the host sediments our results suggest an essentially closed hydrologic system and imply the absence of significant fluid flow along the studied fault zones microthermometric study on fluid inclusions present in calcite and quartz veins and calcite quartz oxygen isotopic fractionation determined for the first generation shear veins allow a geothermal gradient of 34 c km to be estimated analytical results demonstrate an evolution of the fault zones in three stages the first stage was related to the emplacement of the monte perdido thrust unit during the middle eocene at a temperature of 208 c and a burial depth of 5 7 km the second stage corresponds to a fault reactivation at a temperature of 240 c and a burial depth of 6 5 km the latter deformation may have been related to folding of the monte perdido thrust unit during the emplacement of the underlying gavarnie thrust unit during the late eocene early oligocene with deeper burial resulting from aggradation of the thrust sheet top basin fill the last event corresponds to the formation of a dilatant vein system likely related to the exhumation of the massif

fluid mixing and recycling during pyrenean thrusting evidence from fluid inclusion halogen ratios abstract syntectonic fluids have been sampled through fluid inclusion microthermometry and crush leach analyses cations and halogens from a 50 km n s transect through the central southern pyrenees the fluid inclusions are contained in syntectonic quartz veins in triassic redbeds cretaceous carbonates and hercynian basement rocks with some calcite and dolomite data from limestones and evaporites in more external parts of the belt the main datasets come from 1 alpine shear zones cutting the neouvielle granodiorite in the hercynian axial zone at the north end of the transect 2 an imbricate zone beneath the alpine gavarnie thrust at the pic de port vieux 3 several localities in the footwall and hangingwall of the gavarnie thrust on the southern margin of the axial zone the inclusion fluids generally decrease in salinity from 27 35 at the northern end of the transect to 7 22 on the southern margin of the axial zone the majority of the inclusions have cl br ratios lower than seawater and are interpreted as relict fluids after seawater evaporation and halite precipitation in the upper trias this interpretation is supported by cl br na systematics which are consistent with a change from halite to halite sylvite precipitation with progressive evaporation fluids in the basement shear zones are interpreted to have essentially the same evaporitic origin as those still contained in sedimentary formations although it is possible that final concentration of brines in the neouvielle massif involved retrograde hydration reactions with removal of water by precipitation of hydrous minerals the fluids are also very similar in salinity and halogen chemistry to those found in veins associated with mesozoic pb zn f deposits which predate the thrusting the lower salinities seen at the southern margin of the axial zone are interpreted to reflect mixing of the brines with a higher level fluid connate or meteoric water circulating within the mesozoic carbonates of the higher thrust sheets at one locality where triassic evaporites are still present high cl br ratios at relatively low salinities are present in inclusions within the underlying triassic redbeds but low cl br ratios at higher salinities are seen lower in the sequence this is consistent with dissolution of halite by a dilute fluid but with limited penetration downwards we suggest that the fluid history of the pyrenees evolved through a series of stages 1 upper triassic evaporite formation with sinking of brines into underlying redbeds and fractured basement rocks 2 circulation of brines with formation of pb zn deposits along faults at some time between the triassic and the upper cretaceous 3 renewed extension with erosion of triassic rocks in many areas and further drawing down of triassic brines into the basement 4 deposition of u cretaceous and palaeocene carbonates containing connate waters of marine origin 5 formation of the pyrenean thrust belt with overpressuring and expulsion of the brines along shear zones and faults 6 creation of topography with a high level circulation system in the mesozoic thrust sheets driven largely by topography at the southern margin of the axial zone there was limited mixing of the deeper overpressured brines with these more dilute hydrostatically pressured fluids an important point is that because of their density hypersaline brines are difficult to expel from the upper crust and may be involved in a succession of alteration and mineralisation events in the same general area over hundreds of millions of years

temperature micro mapping in oscillatory zoned chlorite application to study of a green schist facies fault zone in the pyrenean axial zone spain oscillatory compositional zoning in minerals has been observed in hydrothermal magmatic and metamorphic environments and is commonly attributed to chemical or physical cyclical changes during crystal growth chemical zoning is a common feature of solid solutions which has been rarely reported in phyllosilicates in this study oscillatory zoning in chlorite is described in samples from the pic de port vieux thrust a minor thrust fault associated to the major gavarnie thrust fault zone central pyrenees spain the pic de port vieux thrust sheet comprises a 1 20 m thick layer of triassic red pelite and sandstone thrust over mylonitized cretaceous dolomitic limestone the thrust fault zone deformation comprises secondary faults and cleavage affecting the triassic pelite and sandstone an important feature responsible to this deformation is a set of veins filled by quartz and chlorite chlorite is present in crack seal extension veins and in shear veins both structures opened under the same stress conditions in some shear veins chlorite occurs as pseudo uniaxial plates arranged in rosette shaped aggregates these aggregates appear to have developed as a result of radial growth of the chlorite platelets oscillatory zoning has been imaged by backscattered scanning electron microscopy and by x ray quantitative micro mapping these oscillations correspond to chemical zoning with alternating iron rich and magnesium rich bands the chlorite composition ranges from a fe rich pole to a mg rich pole fe 3 fe values were measured in chlorite using xanes spot analyses and vary from 0 23 to 0 44 the highest values are in the fe rich area temperature maps built from standardized microprobe x ray images and redox state using the program xmaptools indicate oscillatory variations from about 310 to 400 50 c during chlorite crystallization these temperature variations are correlated with a fe 3 fe variation by al 3 fe 3 1 and di trioctahedral substitutions highlighted by mg and fe tot contents fe mg zoning chemical variations could be then explained by alternation of cooling times and cyclical pulses of a fluid hotter than the host rock it is however not excluded that kinetic effects influence the incorporation of mg or fe during chlorite crystallization

fluid channelling during ductile shearing transformation of granodiorite into aluminous schist in the tauern window eastern alps ductile shearing in the core of the tauern window austria transformed metagranodiorite into si undersaturated garnet chlorite staurolite schist at a depth of c 35 40 km during the alpine orogeny four distinct zones have been recognized extending from the wallrock into the centre of the shear zone zone i unaltered metagranodiorite with subordinate amphibolite zone ii biotite white mica garnet schist zone iii biotite phengite schist zone iv quartz absent garnet chlorite staurolite schist with garnets up to 10 cm across whole rock analyses show a dramatic decrease in sio2 from 65 wt in zone i to 35 wt in zone iv ca na and sr also decrease across the shear zone whereas al ti fe mg p cr ni zn and rb all increase towards zone iv mass balance calculations indicate that shearing was accompanied by up to 60 volume loss near the centre of the shear zone comparison of the tauern window samples with other shear zones in granitic hosts indicates that silica loss accompanied by gains in mg fe and ti is typical for volume loss shear zones but is distinctly different from the element behaviour exhibited in shear zones that are thought to represent approximately isovolumetric behaviour in the samples studied here volume loss appears to have resulted from channellized fluid flow during shearing producing time integrated fluid fluxes of 108 cm3 cm 2 in zone iv this large volume of fluid may have originated in part from dehydration of flysch carried beneath the metagranodiorites during eocene movement on the north penninic subduction zone development of an inverted thermal gradient during subduction would have allowed the fluid to scavenge large amounts of silica from the shear zone during ascent and heating

late pleistocene glacial equilibrium line altitudes in the colorado front range a comparison of methods abstract six methods for approximating late pleistocene pinedale equilibrium line altitudes elas are compared for rapidity of data collection and error rmse from first order trend surfaces using the colorado front range trend surfaces computed from rapidly applied techniques such as glaciation threshold median altitude of small reconstructed glaciers and altitude of lowest cirque floors have relatively high rmses 97 186 m because they are subjectively derived and are based on small glaciers sensitive to microclimatic variability surfaces computed for accumulation area ratios aars and toe to headwall altitude ratios thars of large reconstructed glaciers show that an aar of 0 65 and a thar of 0 40 have the lowest rmses about 80 m and provide the same mean ela estimate about 3160 m as that of the more subjectively derived maximum altitudes of pinedale lateral moraines rmse 149 m second order trend surfaces demonstrate low elas in the latitudinal center of the front range perhaps due to higher winter accumulation there the mountains do not presently reach the ela for large glaciers and small front range cirque glaciers are not comparable to small glaciers existing during pinedale time therefore pleistocene ela depression and consequent temperature depression cannot reliably be ascertained from the calculated ela surfaces

disentangling magnetic subfabrics and their link to deformation processes in cleaved sedimentary rocks from the internal sierras west central pyrenees spain abstract here we present a detailed study of the magnetic fabrics and subfabrics of remagnetized upper cretaceous limolites that crop out in the internal sierras west central pyrenees affected by a penetrative pressure solution cleavage the bulk magnetic fabrics of these rocks rt ams show variable orientations that do not conform to what is typically reported for cleaved sedimentary rocks in contrast the paramagnetic subfabrics lt ams show remarkably constant directional properties so that their k max and k min axes cluster parallel to the intersection lineation and to the poles to bedding respectively these lt ams subfabrics indicate a preferred orientation of phyllosillicates that is consistent with a syn sedimentary late cretaceous period of nne oriented layer parallel shortening noticeably these phyllosillicate subfabrics are not further altered by the subsequent formation of cleavage in the late eocene early oligocene the ferrimagnetic subfabrics aarm also show remarkably constant orientation so that their k max axes are strikingly parallel to the shortening direction in the area we interpret this preferred orientation of ferrimagnetic grains as being caused by subhorizontal shear associated to cleavage formation which is consistent with the age and mechanisms authigenic growth and rotation of pre existing magnetite grains proposed for the pervasive remagnetization that affects the studied rocks

postglacial adjustment of steep low order drainage basins canadian rocky mountains 1 it is generally argued that pleistocene glaciation results in increased sediment flux in mountain systems an important but not well constrained aspect of pleistocene glacial erosion is the geomorphic decoupling of cirque basins from main river systems this study provides a quantitative link between glacier induced basin morphology postglacial erosion and sediment delivery for mountain headwaters with basin area 28 respectively and ii larger fan sizes at outlets of noncirque basins compared to cirques although small headwater basins represent the steepest part of mountain environments and erode significant postglacial sediment the majority of sediment remains in storage under interglacial climatic conditions and does not affect large scale mountain river systems

glacial erosion evolution of river long profiles and the organization of process domains in mountain drainage basins of coastal british columbia 1 in glaciated british columbia canada quaternary climate changes are responsible for profound spatial reorganization of earth surface processes these changes have left a landscape characterized by topographic anisotropy associated with a hierarchy of glacial troughs the evolution of glaciated landscapes is examined by analyzing the structure of geomorphic process domains and channel long profiles to identify process domains we use channel surveys and gis analysis to construct slope area transects of the channel network this analysis reveals generalized process form disequilibrium with a mismatch between topographic signatures and currently active geomorphic process domains at the landscape scale of source colluvial channels contributing area 1 km2 the glacial paraglacial signature commonly overrides that produced by contemporary debris flows along the axis of former ice flows relict glacial cirques introduce a hanging fluvial domain at contributing areas as small as 8 10 2 km2 and produce complex channel long profiles similar to those observed for rivers responding to tectonic forcing slope area relations typical of unglaciated equilibrium environments do not apply here the concept of process domains appears to hold however some major glacially forced modifications in the alluvial colluvial transition are observed and the definition of a depositional colluvial subdomain is proposed comparison between field and gis measured slopes reveals that gis associated error is not uniform between process domains and that gis based plots do not successfully discriminate field based process domains the combination of glacial and post glacial fingerprints and the effects of ongoing earth surface processes generate a complex landscape whose glacial signatures may persist until the onset of the next ice age

the effect of mineralogy and effective normal stress on frictional strength of sheet silicates abstract phyllosilicates are common constituents of upper crustal faults and subduction forearcs we studied the effect of mineralogy and controlled effective normal stress between 5 mpa and 100 mpa on frictional strength although the effect of mineralogy on frictional strength of single phase phyllosilicate gouges has been previously studied the influence of effective normal stress has not we conducted water saturated and vacuum dry frictional tests on single phase phyllosilicate gouges using a triaxial apparatus minerals included talc pyrophyllite kaolinite lizardite illite montmorillonite chlorite muscovite phlogopite and biotite particle size 20 mpa dry friction coefficients are constant and wet friction coefficients show a small increase this is attributed to loss of water and increased contact area the results indicate that frictional strength of clay rich faults increases at depths less than 1 km under hydrostatic pore fluid pressures

conditions and mechanism for the formation of iron rich montmorillonite in deep sea sediments costa rica margin coupling high resolution mineralogical characterization and geochemical modeling abstract iron rich smectite is commonly described in the diagenetic fraction of deep sea sediment as millimeter to centimeter aggregates dispersed in the sediment or as a coating on sedimentary particles or nodules this study examines several factors to elucidate formation mechanisms of a particular iron rich smectite and its potential transformation to glauconite the study combines a detailed mineralogical investigation on natural samples and a chemical modeling approach to assess mineralogical reactions and pathways transmission electron microscopy tem observations and analytical electron microscopy tem aem analyses were conducted on microtomed samples of millimeter to centimeter long green grains these grains are widespread in pelagic calcareous sediment from the costa rica margin they are composed of pyrites that are partially dissolved and are surrounded by amorphous or very poorly crystallized iron rich particles iron rich montmorillonite grows from an amorphous precursor and its formation requires the input of si o mg k na and ca our results suggest that these inputs are supported by the dissolution of sedimentary phases such as volcanic glasses siliceous fossils and silicates thermodynamic modeling of fluid sediment interactions was conducted with the geochemical computer code phreeqc using mineralogical and pore fluid compositions from sediment samples and calculated estimates for thermodynamic constants of smectites that are not maintained by the computer code simulations confirm the possibility that the green grains are the product of pyrite alteration by seawater under oxidizing conditions the extent of smectite production is controlled by the kinetics of pyrite dissolution and fluid migration the absence of aluminum in the costa rica margin system explains the formation of an iron rich montmorillonite instead of glauconite whereas the presence of calcite that buffers the system explains the formation of an iron rich montmorillonite instead of iron oxides

the evolution of illite to muscovite mineralogical and isotopic data from the glarus alps switzerland thirty five illite and muscovite concentrates were extracted from triassic and permian claystones shales slates and phyllites along a cross section from the diagenetic alpine foreland tabular jura and borehole samples beneath the molasse basin to the anchi and epimetamorphic helvetic zone of the central alps concentrates and thin sections were investigated by microscopic x ray infrared mossbauer thermal dta and tg wet chemical electron microprobe k ar rb sr 40ar 39ar and stable isotope methods with increasing metamorphic grade based on illite crystallinity data xrd and ir the following continuous changes are observed i the 1md 2m1 polymorph transformation is completed in the higher grade anchizone ii k2o increases from 6 8 wt diagenetic zone to 8 5 10 anchizone to 10 11 5 epizone reflecting an increase in the total negative layer charge from 1 2 to 2 0 iii a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone epizone boundary iv a shift of an endothermic peak in differential thermal curves from 500 to 750 c v k ar and rb sr apparent ages of the fraction 2 m decrease from the diagenetic zone to the epizone k ar ages being generally lower than rb sr ages the critical temperature for total ar resetting is estimated to be 260 30 c k ar and rb sr ages become concordant when the anchizone epizone boundary is approached the stable isotope data on the other hand show no change with metamorphic grade but are dependent on stratigraphic age these results suggest that the prograde evolution from 1 md illite to 2m1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals however this is not a recrystallization process this restructuration is completed approximately at the anchizone epizone boundary the isotopic data indicate significant diffusive loss of 40ar and 87sr prior to any observable lattice reorganization the restructuration progressively introduces a consistent repartition of ar and k in the mineral lattices and is outlined by the 40ar 39ar age spectra concordant k ar and rb sr ages of around 35 30 ma with concomitant concordant 40ar 39ar release spectra are representative for the main phase of alpine metamorphism calanda phase in the glarus alps a second age group between 25 and 20 ma can probably be attributed to movements along the glarus thrust ruchi phase while values down to 9 ma in regions with higher metamorphic conditions suggest thermal conditions persisting at least until the middle tortonian

rock matrix structures in a zone influenced by a stylolite abstract a stylolitic structure is one of the visible manifestations of the pressure solution process in a rock the stylolitic process zone as defined in previous studies on both sides of a stylolite is studied by sem the chosen samples concern tectonic stylolites within a high porosity limestone 16 without tension gashes this zone corresponds to a local increase of porosity and comprises a large number of stylolitic joints showing a decreasing size from the macroscopic structure to simple contact between two grains two hypotheses are presented for the stylolite formation 1 the macroscopic stylolite is the result of the coalescence of earlier minor pressure solution structures 2 small stylolites nucleate gradually from a major stylolite joint the mass transfer can be realized either by diffusion between particles or by seepage through previously undescribed process zone fractures the mass deposition can be localized in the porous volume and the microcracks without requiring any additional tectonic openings including tension gashes the rock deformation is therefore limited to shortening parallel to 1 without normal extension

jurassic lake t oo dichi a large alkaline saline lake morrison formation eastern colorado plateau a large alkaline saline lake lake t9oo9dichi9 occupied the entire eastern part of the colorado plateau region during deposition of the brushy basin member of the upper jurassic morrison formation the lake extended from near the site of albuquerque new mexico to near the site of grand junction colorado and occupied a region that encompassed the san juan and ancestral paradox basins making it the largest ancient alkaline saline lake known the lake was typically shallow and frequently evaporated to dryness although the water table was probably never far beneath the surface intermittent streams carried detritus from source areas to the west and southwest far out into the lake basin a reflection of a low depositional gradient and the ephemeral nature of the lake prevailing westerly winds carried silicic volcanic ash to the lake basin from an arc region to the west and southwest a lateral hydrogeochemical gradient characterized by increasing salinity and alkalinity from the margin of the lake to the center developed in pore waters of the lacustrine sediments and resulted in alteration of the ash to a variety of authigenic minerals that define concentric zones within the lake basin the basinward progression of diagenetic mineral zones is smectite clinoptilolite analcime potassium feldspar albite a concomitant lateral zonation of mixed layer illite smectite developed from highly smectitic in the outermost zones to highly illitic in the central zone authigenic albite and illitic mixed layer clay minerals previously thought to require elevated temperatures for formation crystallized during early diagenesis at syndepositional temperatures in the lacus trine sediments of lake t9oo9dichi9 this study presents evidence for a syndepositional origin for both of these minerals these findings have important implications in terms of limiting the use of these minerals as geothermometers recognition of alkaline saline lake deposits in the morrison formation significantly alters interpretations of depositional environments of this formation and it also has important implications for paleoclimatic interpretation late jurassic climate was apparently much more and than had previously been thought in fact sedimentologic evidence suggests that the lake basin was typically dry for extended periods and enjoyed only brief wet intervals this conclusion has important consequences for environmental interpretation of the habitat that was favorable for large herbivorous dinosaurs which thrived in the late jurassic

effects of glacial meltwater in the giss coupled atmosphereocean model 1 north atlantic deep water response varying magnitudes of freshwater input through the st lawrence are added to different versions of the giss coupled atmosphere ocean model the results show a generally linear response in percentage north atlantic deep water nadw reduction to the volume of water added without any obvious threshold effects when the estimated best guess freshwater input for the allerod younger dryas interval is added only small reductions in nadw production occur in less than a century with complete cessation requiring more than 300 years if the ocean circulation was weaker in the allerod preceding the younger dryas somewhat larger percentage reductions occur and it would take 150 200 years for a complete shutdown the freshening is aided by a positive feedback associated with the reduction in evaporation relative to precipitation in the north atlantic amounting to some 20 30 of the added freshwater runoff when the freshwater input is stopped after complete nadw shutdown nadw production does not resume with complete nadw cessation cooling eventually occurs throughout the northern hemisphere including regions where it is not thought to have arisen during the younger dryas and the globe cools by 1 c due primarily to the sea ice albedo feedback while in many regions the observed cooling is reproduced the cooling in greenland is much less than is estimated with only 50 nadw cessation cooling is primarily around the north atlantic no rapid warming is seen in response to freshwater cessation the sensitivity displayed here for nadw reduction due to freshwater input from the st lawrence is roughly similar to that associated with increased precipitation accompanying global warming in the next century so a similar sensitivity may arise with younger dryas freshwater inputs from other suspected locations greenland europe

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget