equilibrium disequilibrium and nonequilibrium landforms in the landscape abstract landscapes are composed of a diversity of landforms that may be characterized as equilibrium disequilibrium or nonequilibrium equilibrium is a constant relation between input and output or form toward which a landform tends or around which it fluctuates in time because of recent environmental changes and long relaxation times however many landforms are not adjusted to present inputs disequilibrium landforms are those that tend toward equilibrium but have not had sufficient time to reach such a condition some landforms called nonequilibrium do not tend toward equilibrium even with relatively long periods of environmental stability but rather undergo frequent and large change in form nonequilibrium may be caused by high magnitude thresholds that cause low frequency weather events to dominate form positive feedbacks and or nonlinearities that result in deterministic chaos landscapes contain mixtures of equilibrium disequilibrium and nonequilibrium landforms and these types of landforms interact in geomorphic systems such as sediment cascades the three types of behavior may coexist in the same landscape and the outputs of such mixed geomorphic systems reflect the combined effects of equilibrium disequilibrium and nonequilibrium subsystems this classification provides a framework for analysis and modeling of complex landscapes

metamorphism melting and extension age constraints from the high himalayan slab of southeast zanskar and northwest lahaul abstract we present evidence for two distinct stages of tertiary metamorphism m1 and m2 in the high himalayan slab of southeast zanskar and northwest lahaul as well as evidence for an older pre himalayan metamorphism pre m1 the m1 was a regional barrovian type event related to crustal shortening and thickening of the indian plate margin while m2 was associated with crustal melting and the emplacement of the gumburanjon leucogranite into the zanskar shear zone at the top of the slab u pb dating of metamorphic and magmatic accessory phases constrains the timing of m1 between 30 and 37 ma and the crystallization and emplacement age of the gumburanjon leucogranite at 21 22 ma inherited accessory phases in metamorphic and magmatic samples suggest that the protoliths of the slab are at least lower paleozoic in age and that they experienced a major pre m1 thermal perturbation at ca 450 500 ma whether this was associated with a regional barrovian type metamorphism or whether it was a thermal event rel

quantifying the eocene to pleistocene topographic evolution of the soutwestern alps france and italy we evaluate the topographic evolution of the southwestern alps using eocene to pleistocene pollen data combined with existing sedimentological petrographic and detrital geo and thermochronological data we report 32 new pollen analyses from 10 sites completed by an existing dataset of 83 samples from 14 localities situated across the southwestern alps including both the pro and the retro foreland basins the presence of microthermic tree pollen mainly abies picea indicates that this part of the mountain belt attained elevations over 1900 m as early as the oligocene inferred rapid surface uplift during the mid oligocene coincided with a previously documented brief phase of rapid erosional exhumation when maximum erosion rates may have reached values of up to 1 5 2km myr slower long term average exhumation rates of 0 3km myr since the late oligocene helped maintaining the high alpine topography of the southwestern alps until today the relative abundances of meso microthermic tree pollen cathaya cedrusand tsuga and microthermic tree pollen abies picea in the pro and retro foreland basin deposits indicate that the present day asymmetric topography with a relatively gentle western flank and steeper eastern flank was established early in the southwestern alps at least since

isotopic constraints on the structural relationships between the lesser himalayan series and the high himalayan crystalline series garhwal himalaya nd and sr isotope systematics may provide important constraints on the location of major thrust systems that separate lithologically similar sedimentary sequences the potential of the technique is illustrated by this isotopic study of the main central thrust system of the himalaya nd isotope data from the garhwal himalaya indicate that metasedimentary rocks from the vaikrita group nd 14 to 19 correlate closely with those from the high himalayan crystalline series which constitutes the hanging wall lithologies of the main central thrust in contrast metasedimentary rocks from the munsiari group nd 23 to 28 show marked similarities to the lesser himalayan series in the footwall of the main central thrust sr isotopes support the correlations in that the vaikrita group shows partial reequilibration at 500 ma whereas the munsiari group has not undergone sr isotope homogenization since 1800 ma thus the vaikrita thrust that juxtaposes these two formations is recognized as the main central thrust in garhwal himalaya the thrust coincides approximately with the location of the kyanite isograd confirming that inverted metamorphism is characteristic of both hanging wall and footwall of the main central thrust along the tons thrust known locally as the srinagar thrust 50 km south of the main central thrust low grade quartzarenites with nd sr isotope and trace element characteristics typical of lesser himalayan formations have been emplaced on phyllites and siltstones with geochemical characteristics of the high himalayan crystalline series the field relationships most probably result from out of sequence thrusting in which lesser himalayan series rocks to the north were emplaced over low grade equivalents of the high himalayan crystalline series preserved in the external part of the orogen this study establishes the value of isotope data for lithostratigraphic correlations within orogenic belts

early proterozoic nappe formation an example from sodankyla finland northern baltic shield the central lapland greenstone belt comprises rift related metavolcanic and metasedimentary rocks representing one of the largest supracrustal belts in the baltic shield the sodankyla area in the central part of the belt represents a complex thrust duplex within a nappe overlying belomorian archaean basement and autocthonous luirojoki calc silicate rocks here an early d 1 schistosity is axial planar to at least three coaxial generations of southward verging subhorizontal e w plunging d 1 folds associated with major southwards thrusting d 2 is represented by broad map scale upright ne trending folds in the south and crenulations in the north staurolite grade metamorphism represented by post tectonic andalusite staurolite kyanite assemblages occurred after d 2 folding later d 3 deformation was limited to local nw trending folds and sinistral faults the internal nappe like structure of the central lapland greenstone belt suggests that it represents the foreland of a large collisional complex cored by the lapland granulite belt

two phase orogenic convergence in the external and internal sw alps the nw se trending sector of the sw alps includes the dora maira massif where tertiary eclogites record ultrahigh pressures and rapid exhumation along a ne sw crustal cross section italy france compiled pressure temperature time data in internal zones are correlated with tertiary stratigraphy in external zones to reconstruct orogen evolution revealing a coherent two phase convergence history during the first subduction accretion phase eocene 55 34 ma rapid north south plate convergence caused the subduction and exhumation of high pressure and ultrahigh pressure uhp rocks in a steady state subduction channel this coincided with the north to nnw migration of an underfilled flexural basin across the european foreland nappe stacking within the subduction channel did not create significant relief implying that primarily subduction forces generated this flexural basin from 34 ma onward the second collisional phase was characterized by slower nw se plate convergence the internal units of the sw alps underwent considerable anticlockwise rotation as they became involved in a nw se oriented sinistral transpression zone between the european and adriatic plates to the north of the orogen the north alpine foreland basin became overfilled as a result of high sediment supply from increasing orogen relief in contrast in se france active flexure of the european plate appears to have ceased and sedimentation became limited to small thrust sheet top basins created by continuing gentle ne sw shortening internal units were exhumed slowly from depths of c 20 km principally by erosion in the sw alps the transition between these two phases was marked by the rapid subduction and exhumation of the dora maira uhp unit assuming lithostatic pressure this unit would have been exhumed from 100 km depth requiring a rate that exceeds that generated by plate convergence therefore either exhumation was accelerated by additional stresses locally generated by transpression slab breakoff or high density contrasts or more controversially the ultrahigh pressure occurred at a considerably shallower depth as a result of local overpressure

pore properties as indicators of breakdown mechanisms in experimentally weathered limestones the results are reported of four experimental weathering tests freeze thaw wetting and drying slake durability and salt weathering on five different types of limestone effective porosity mercury intrusion porosimetry and scanning electron microscopy were used to evaluate changes in pore properties while weight loss and fracture density were used to assess deterioration severity a primary aim was to observe modifications in porosity due to weathering and to draw inferences about the internal rock deterioration mechanisms taking place it is concluded that the five limestones not only show a wide range of resistance to weathering in general but considerable difference in resistance to particular weathering processes consequently when assessing durability it is essential to consider rock properties in the context of the weathering process to which the rock is subject the type of deterioration indicator used is also important in interpretation of durability a variety of pore modification mechanisms operate including changes in pore connectivity pore infilling and the introduction of additional void space there are indications that changes to the internal pore structure of rocks due to weathering may be a precursor to more substantial macrodeterioration copyright 2001 john wiley sons ltd

changing climate changing process implications for salt transportation and weathering within building sandstones in the uk salt weathering is a crucial process that brings about a change in stone from the scale of landscapes to stone outcrops and natural building stone facades it is acknowledged that salt weathering is controlled by fluctuations in temperature and moisture where repeated oscillations in these parameters can cause re crystallisation hydration de hydration of salts bringing about stone surface loss in the form of for example granular disaggregation scaling and multiple flaking however this traditional view of how salt weathering proceeds may need to be re evaluated in the light of current and future climatic trends indeed there is considerable scope for the investigation of consequences of climate change on geomorphological processes in general building on contemporary research on the deep wetting of natural building stones it is proposed that as stone may be wetter for longer ion diffusion may become a more prominent mechanism for the mixing of molecular constituents and a shift in focus from physical damage to chemical change is suggested data from ion diffusion cell experiments are presented for three different sandstone types demonstrating that salts may diffuse through porous stone relatively rapidly in comparison to for example dense concrete pore water from stones undergoing diffusion experiments was extracted and analysed factors controlling ion diffusion relating to time of wetness within stones are discussed continued saturation connectivity of pores mineralogy behaviour of salts sedimentary structure and potential changes in system dynamics as a result of climate change are addressed system inputs may change in terms of increased moisture input translating into a greater depth of wetting front salts are likely to be stored differently in stones with salt being in solution for longer periods during prolonged winter wetness this has myriad implications in terms of the movement of ions by diffusion and the potential for chemical change in the stone especially in more mobile constituents leading to a weakening of the stone matrix grain boundary cementing the output may be mobilisation and precipitation of elements leading to for example uneven cementing in the stone this reduced strength of the stone or compromised ability of the stone to absorb stress is likely to make crystallisation a more efficacious mechanism of decay when it does occur thus a delay in the onset of crystallisation while stonework is wet does not preclude exaggerated or accelerated material loss when it finally happens

salt weathering simulations under hot desert conditions agents of enlightenment or perpetuators of preconceptions because of access difficulties and inhospitable environmental conditions our understanding of rock weathering in hot deserts has been strongly influenced by laboratory simulations however a risk exists that results may come to owe more to experimental design than to actual environmental conditions experienced at the atmosphere rock surface interface this was especially true in early salt weathering simulations that seemingly sought to reinforce the orthodoxy of a physically dominated weathering environment driven by extremely high absolute temperatures and large diurnal temperature ranges however improvements in environmental sensors over the last 20 years have established the complexity of desert climates and the importance of microclimatic controls and allowed considerable refinement of experimental design this overview evaluates the implications of recent simulation studies and presents new information on possible fatigue effects of differential thermal expansion of salts and the salt weathering of test blocks under compressive loading in doing so it demonstrates how physical rock properties change during experimentation the importance of short term surface temperature fluctuations distinctions between the weathering of unconfined debris and larger rock surfaces the importance of moisture and salt applications that replicate their availability in deserts the importance of rock thermal properties in controlling their weathering response in environments dominated by radiative heating and cooling and the overall complexity of weathering regimes

rock warming and drying under simulated intertidal conditions part ii weathering and biological influences on evaporative cooling and near surface micro climatic conditions as an example of biogeomorphic ecosystem engineering the way in which rocks and engineering materials heat up and dry out in the intertidal zone is of relevance to both weathering and ecology these behaviours can be measured in the laboratory under controlled conditions designed to replicate those occurring in the field previous studies have demonstrated differences in thermal behaviours between rock types and through time as a result of soiling in terrestrial environments but the influence of weathering and colonization on rock behaviours in the intertidal zone has not been previously assessed we measured the warming and drying of blocks of rock limestone and granite and marine concrete during low tide events simulated in the laboratory before and after a period of exposure eight months on rock platforms in cornwall uk as well as differences between the material types temperatures of control unexposed and field exposed blocks differed in the order of 1 to 2 c drying behaviours were also different after field exposure differences during the first few hours of exposure to air and heat were attributed to discolouration and albedo effects over longer periods of time changes in the availability of near surface pore water as a result of micro scale bioerosion of limestone and the development of bio chemical crusts on marine concrete observed using scanning electron microscopy sem are suggested as mechanisms enhancing and reducing respectively the efficiency of evaporative cooling the retention of moisture by epilithic biofilms may also influence thermal and drying behaviours of granite these observations represent one of the first examples of cross scalar biogeomorphic linkages in the intertidal zone the significance of the results for the subsequent efficiency of weathering and near surface micro climatic conditions experienced by colonizing organisms is discussed the involvement of microorganisms in the creation of more or less ecologically stressful conditions through the alteration of substratum geomorphic properties and behaviours is suggested as an example of biogeomorphic ecosystem engineering copyright 2011 john wiley sons ltd

emplacement of the cuera and picos de europa imbricate system at the core of the iberian armorican arc cantabrian zone north spain new precisions concerning the timing of arc closure the final stages of the variscan orogeny mostly carboniferous in the western european variscan belt involved the development of the iberian armorican arc which is cored by the cantabrian zone nw iberia the cantabrian zone is the foreland of the western european variscan belt and it is interpreted to record the waning stages of the closure of the rheic ocean the distalmost tectonic units within the cantabrian zone the cuera unit and the picos de europa province were the last tectonic units emplaced at the core of the western european variscan belt orocline together they form an imbricate system and associated wedge top basins that are key to understanding the development of the orocline the emplacement of the cuera unit and the picos de europa province occurred in the latest pennsylvanian between moscovian and gzhelian times new detailed mapping together with stratigraphic sedimentologic and biostratigraphic data analysis of syntectonic successions and structural information constrain the timing and evolution of this imbricate system our analysis indicates that the thrust sheets were emplaced roughly perpendicular to previous tectonic units of the cantabrian variscan foreland fold and thrust belt most probably during the oroclinal bending of the sw european variscan belt that formed the iberian armorican arc the n s directed imbricate system was characterized by a shallow dip of the topographic surface 150 15 km and complex structure of the orogenic wedge are thought to result from the progressive increase in the dip of the basal decollement during bending of the underlying gondwana lithosphere and may reflect the closure of the iberian armorican arc

the crystalline units of the high himalayas in the lahul zanskar region northwest india metamorphic tectonic history and geochronology of the collided and imbricated indian plate in the high himalayan belt of northwest india crustal thickening linked to palaeogene collision between india and eurasia has led to the formation of two main crystalline tectonic units separated by the syn metamorphic miyar thrust the high himalayan crystallines sensu stricto hhc at the bottom and the kade unit at the top these units are structurally interposed between the underlying lesser himalaya and the very low grade sediments of the tibetan nappes they consist of paragneisses orthogneisses minor metabasics and chiefly in the hhc leucogranites the hhc registers a polyphase metamorphism with two main stages designated as m1 and m2 a metamorphic zonation with high temperature recrystallization and migmatization at middle structural levels and medium temperature assemblages at upper and lower levels in contrast the kade unit underwent a low temperature metamorphism rb sr and u th pb isotope data point to derivation of the orthogneisses from early palaeozoic granitoids while the leucogranites formed by anatexis of the hhc rocks and were probably emplaced during miocene time most of the complicated metamorphic setting is related to polyphase tectonic stacking of the hhc with the cooler kade unit and lesser himalaya during the himalayan history however a few inconsistencies exist for a purely himalayan age of some ml assemblages of the hhc as regards the crustal derived leucogranites the formation of a first generation mixed with quartzo feldspathic leucosomes was possibly linked to melt lubricated shear zones which favoured rapid crustal displacements at upper levels they intruded during stage m2 and the latest movements along the syn metamorphic miyar thrust but before juxtaposition of the tibetan nappes along the late metamorphic zanskar fault

comparative studies of the lichen rock interface of four lichens in vingen western norway abstract sandstone samples from vingen western norway have been analysed to find whether different lichen taxa may explain variations in the degree of weathering at this site the samples were analysed by high performance thin layer chromatography hptlc thin layer chromatography tlc scanning electron microscopy sem x ray diffraction xrd and x ray fluorescence spectroscopy xrf followed by descriptive statistics and principal component analysis pca the study of the weathering rinds beneath four lichens indicates differences in weathering effect between the studied taxa those rinds beneath ophioparma ventosa and to a lesser extend pertusaria corallina are in general deeper and show a higher degree of mineral dissolution and crumbling of the rock surface compared to fuscidea cyathoides and ochrolechia tartarea a very high concentration of fungal hyphae within the weathering rind beneath o ventosa and p corallina compared to the other two taxa may be the cause of the increased biophysical and biochemical weathering o ventosa and f cyathoides contain similar amounts of oxalate which also in general are much higher than for p corallina and o tartarea the studied taxa also contain different lichen compounds differences in content of lichen compounds seem thus to be a more likely explanation for the variations in chemical weathering than differences in oxalic acid production in addition to biological mediated physical and chemical weathering the water holding capacity of lichens may increase the chemical dissolution and frost wedging of rock surfaces the thallus and the endolithic fungal hyphae bind the partly fragmented rock surface and protect it from abrasion and erosion however when the thallus dies loose mineral grains and fragments from the upper lichen mineral interface will be removed and a new surface will be exposed and available for colonization and biodegradation it is thus likely that lichens enhance weathering rates except at locations with extremely high abrasion where they may protect the surface

erratic shortening from balanced cross sections of the western himalayan foreland basin causes and implications for basin evolution abstract balanced cross sections from the western himalayan foreland foothill belt reveal a variation in shortening amounts from 22 to 71 3 over a lateral distance of 85 km the large variation may be attributed to the fact that the method of cross section balancing considers the initial layering as horizontal which is an unlikely situation in foreland basins simple trigonometric relationships are used to minimize the error in shortening estimates however the suggested corrections could not be applied to the himalayan foreland basin because of unavailability of the required data on initial basin geometry the study also indicates that shortening rates for the area based on these shortening amounts cannot be used for earthquake prediction

geostatistical analysis in weathering studies case study for stanton moor building sandstone geostatistical techniques for spatial prediction and spatial simulation have been used in an innovative application to the study of weathering of natural building stone the study investigates the differences in the spatial variation of permeability characteristics between fine and coarse grained stanton moor building sandstone non destructive permeability measurements using an unsteady state portable probe permeameter were made on three adjacent faces of two cubic blocks representative of fine to medium grained and medium to coarse grained stanton moor sandstone the findings provide greater understanding in the investigation of the durability characteristics of the stanton moor sandstone and show that the spatial distribution and variability of permeability is more important in predicting the overall strength and weathering properties than mean permeability and absolute minimum and maximum values the results suggest that both primary textural characteristics such as grain size and extent of cementation appear to be important factors in determining the overall durability properties of stanton moor sandstone as a building stone geostatistical analysis has been shown to be an important tool in the characterization of spatial variation for the investigation of weathering of building stones copyright 2006 john wiley sons ltd

sand rich turbidite system of the late oligocene northern apennines foredeep physical stratigraphy and architecture of the macigno costiero coastal tuscany italy

source tracing of detrital serpentinite in the oligocene molasse deposits from the western alps barreme basin implications for relief formation in the internal zone we present the first contribution of tracing the source area of ophiolitic detritus in the alpine molasse deposits by raman spectroscopy the lower oligocene molasse deposits preserved in the barreme basin in the sw foreland of the western alpine arc are known for the sudden arrival of the first exotic detritus coming from the internal alpine zones among them the pebbles of serpentinized peridotites have so far not been studied we show that they only consist of antigorite serpentinite implying that they originate from erosion of high temperature blueschists in contrast the upper oligocene lower miocene molasse shows mixed clasts of serpentine including antigorite and lizardite without any evidence of chrysotile this suggests that they were derived from a less metamorphosed unit such as the low temperature blueschist unit taking into account the sediment transport direction in the basin and the varied metamorphic characteristics of the other ocean derived detritus we constrain the lithologic nature of the source zones and the location of the relief zones identified as the internal alps se of the pelvoux external crystalline massif available structural data and in situ thermochronological data allow the reconstruction of the oligocene to early miocene collisional geometry of the palaeogene subduction wedge this phase corresponds to two major phases of uplift evolving from a single relief zone located above the ivrea body during early oligocene times and persisting up to early miocene times then during late oligocene early miocene times a second relief zone developed above the brianconnais zone at that time the internal western alps acquired its double vergency

cavernous weathering dynamical instability and self organization cavernous weathering may be conceptualized as a self reinforcing process characterized by positive feedback within the weathering system a morphometric study of caverns in the valley of fire state park nevada usa demonstrates the applicability of a dynamically unstable or conditionally unstable model of cavernous weathering systems outcrop surfaces displaying caverns tend to show increasing fragmentation of the surface in the early stages of cavernous weathering succeeded by convergent evolution of the surface in which caverns tend to grow and coalesce a paradoxical relationship exists between the weathering system output at the scale of individual forms and the outcrop scale caverns tend toward minimum interior surface area by developing a spheroidal form yet the outcrop surface tends toward maximum exposed surface area by increasing the degree of fragmentation of the surface copyright 2004 john wiley sons ltd

the origin of honeycomb weathering honeycomb weathering occurs throughout the world but the origin remains a matter of controversy wind erosion exfoliation frost shattering and salt weathering have been proposed as explanations although few attempts have been made to substantiate these hypotheses with chemical or mineralogical studies chemical analyses and field observations indicate that honeycomb weathering in coastal exposures of arkosic sandstone near bellingham washington results from evaporation of salt water deposited by wave splash microscopic examination of weathered surfaces show that erosion results from disaggregation of mineral grains rather than from chemical decomposition thin walls separating adjacent cavities seem to be due to protective effects of organic coatings produced by microscopic algae inhabiting the rock surface cavity walls are not reinforced by precipitation of elements released by weathering as has often been suggested at other locations honeycomb weathering develops rapidly and can be observed on surfaces that were planar less than a century ago

tracing exhumation and orogenic wedge dynamics in the european alps with detrital thermochronology detrital cooling ages from the pro foreland and retro foreland basins of the european alps record distinctive exhumation trends that correlate with orogenic wedge states inferred from thrust front propagation rates periods of rapid hinterland exhumation correlate with relatively slow propagation of deformation toward the foreland and are interpreted to represent subcritical wedge conditions whereas periods of slow hinterland exhumation correlate with rapid propagation of deformation toward the foreland and indicate supercritical wedge conditions similar lag time trends recorded in both the pro foreland and retro foreland thus mimic orogenic wedge behavior and suggest that local tectonics and or climate events do not overprint the regional signal

tectonic significance of cenozoic exhumation and foreland basin evolution in the western alps the alps are the archetypical collisional orogenic system on earth and yet our understanding of processes controlling topographic growth in the cenozoic remains incomplete whereas ideas and models on the alps are abundant data from the foreland basin record able to constrain the timing of erosion and sedimentation mechanisms of basin accommodation and basin deformation are sparse we combine seismic stratigraphy micropaleontology white mica 40ar 39ar detrital zircon u th he and apatite fission track thermochronology to miocene pliocene samples from the retro wedge foreland basin saluzzo basin in italy and to oligocene miocene sedimentary rocks from the pro wedge foreland basin b rreme basin in france of the western alps our new data show that exhumation in the oligocene miocene was non uniform across the western alps topographic growth was underway since the oligocene and exhumation was concentrated on the pro side of the orogenic system rapid and episodic early miocene exhumation of the western alps was concentrated instead on the retro side of the orogen and correlates with a major unconformity in the proximal retro foreland basin a phase of orogenic construction is recorded by exhumation of the proximal pro foreland in both the central and western alps at ca 16 ma this is associated with high sedimentation rates and by inference erosion rates and suggests that an increase in accretionary flux associated with the dynamics of subduction of europe under adria controlled orogenic expansion in the miocene

age of metamorphism in the lesser himalaya and the main central thrust zone garhwal india results of illite crystallinity 40 ar 39 ar fusion and k ar studies

isotopic constraints on the age and provenance of the lesser and greater himalayan sequences nepalese himalaya the main central thrust of the central himalaya juxtaposes the lesser himalayan sequence footwall with the greater himalayan sequence hanging wall both of which are regarded as components of the northern passive margin of india considerable uncertainty surrounds their respective ages and sedimentary derivation u pb and sm nd isotopic studies of samples from the langtang area central nepal demonstrate important distinctions between the two rock packages the greater himalayan sequence had a sedimentary provenance that included a major source of 0 8 1 0 ga zircons implying a late proterozoic age the source of the precambrian part of the lesser himalayan sequence contained 1 87 2 60 ga zircons and its depositional age is probably middle proterozoic nd isotopic characteristics of the two sequences are different at 21 ma the greater himalayan rocks had end values between 14 6 and 18 5 while their lesser himalayan counterparts had values between 21 4 and 25 9 giving rise to major differences in their model ages the lesser and greater himalayan sequences at langtang are interpreted as correlative to the lower and upper parts of the vindhyan supergroup currently exposed south of the gangetic plain in northern india on the basis of available age data the exposed hanging wall of the main central thrust in central and eastern nepal contains no archean early proterozoic basement if the fault does root into the basement at depth it must do so farther north than recently published cross sections indicate this implies a total displacement on the fault that is substantially greater than the 140 210 km required by tectonic overlap in the eastern himalayas

proterozoic crustal evolution in the nw himalaya india as recorded by circa 1 80 ga mafic and 1 84 ga granitic magmatism abstract single zircon dating of the rampur metabasalts of the larji kullu rampur window in the lesser himalayas yielded an evaporation age of 1800 13 ma the zircon age is considerably younger than the previously published whole rock sm nd age of 2510 90 ma suggesting that the sm nd age may be geologically meaningless and that the sm nd whole rock array may have resulted from mixing in the nw himalaya there is also evidence for extensive silicic melt generation in the paleoproterozoic zircons from a metarhyodacite in the larji kullu rampur window yielded an evaporation age of 1840 16 ma which we interpret as the minimum age of magmatism the main central thrust granitic mylonites are interpreted as the basement of the neoproterozoic haimanta group metasediments together with the granitic rocks from the lesser himalaya they were derived from pre existing continental crust prior to 1 84 ga the nd depleted mantle model ages are in the range of 2 6 2 4 ga suggesting a contribution of archean crust a recycled archean component is also documented by a 2 9 ga domain in one of the zircons

observations of three dimensional salt distribution in building sandstone observations of three dimensional salt distributions within three sandstone blocks after 120 years of exposure in an aggressive urban environment are presented based on measurements of soluble ion concentrations results indicate a complex distribution of sulphur and chloride where distributions are not consistent between salt types dictated by conditions at the six surfaces of the blocks this highlights the dangers of extrapolating the results of salt weathering simulations with regard to salt accumulation patterns or the results of fieldwork which rely on single surface samples from individual stones the widely held perception that urban environments are dry with shallow surface wetting of building stone does not appear to hold true for certain building stone copyright 2000 john wiley sons ltd

sandstone weathering processes damaging prehistoric rock paintings at the albarracin cultural park ne spain the rock paintings in cliff foot caves of the albarracin cultural park are known as some of the most important evidences of the levantine prehistoric art of spain 8000 3000 bp the paintings are on sandstone buntsandstein facies of triasic age which may develop intense weathering the analysis of the variables controlling the weathering indicate that salt and wetting drying weathering are responsible for granular disintegration and flaking which lead to rock painting deterioration

younger hanging wall rocks along the vaikrita thrust of the high himalaya a model based on inversion tectonics abstract in sharp contrast to the common observed characteristic of areas of thrust tectonics where older rocks are thrust over younger along the vaikrita thrust in the high himalaya younger hanging wall rocks i e vaikrita group late mesoproterozoic to early neoproterozoic lie above the older footwall rocks i e munsiari formation paleoproterozoic the phenomenon is explained by an inversion tectonics based model where normal faulting and metamorphism were followed by thrusting in which the thrust displacement was less than the displacement during the earlier normal faulting the present day hanging wall tilt towards north may have been caused by a later thrust initiated as a piggy back sequence accompanied by folding and himalayan metamorphism

on the interaction of geology measurement and statistical analysis of small scale permeability measurements sedimentary rocks exhibit small scale mm permeability variations which can be detected with a probe permeameter the structure of the laminations may provide evidence about the characteristics of the measurement device the statistical interpretation of these measurements using averages and variograms is enhanced when the geological character of the rock is taken into consideration the three aspects of rock characterization namely geology measurement and statistical analysis are best assessed in concert this theme is illustrated using probe data taken from sections of the rannoch and etive formations northern north sea

precollision and postcollision thermal events in the himalaya illite crystallinity and b o spacing analyses of rocks from the lesser himalaya show that the upper paleocene lower eocene subathu formation deposited immediately prior to or early in the india asia collision shows distinctly lower metamorphic grades than the anchiepizone upper precambrian lower paleozoic rocks the latter have been affected by a precollision metamorphic event the probable age of which is paleozoic although a mesozoic age is not ruled out thermal effects of the main central thrust are restricted to a section 1300 m below the thrust therefore the le fort model for metamorphic inversion and granite formation needs modifying because the exposed main central thrust footwall rocks could not have generated the fluids responsible for anatectic melting

reconstruction of tertiary palaeovalleys in the south alpine foreland basin of france eocene oligocene of the castellane arc abstract the dynamics of depositional environments and the spatial deformation of drainage networks in foreland basins reflect the tectonic and erosional dynamics associated with the development of mountain belts the spatial and temporal organization of the eocene oligocene 40 25 ma sedimentation in the external part of the south alpine foreland basin of france was reconstructed using an integrated cartographic sedimentological and petrographic analysis of the tertiary sedimentary successions the depositional geometries and variations in facies and thickness of the palaeogene nummulitic succession as well as the observed flow directions in various continental and marine sediments suggest that the barreme blieux and taulanne synclines were present as palaeovalleys since the eocene the sedimentological analysis of the nummulitic succession allows the identification of three depositional sequences separated by transgressive surfaces that are recognized in the barreme blieux and taulanne synclines correlation of these sequences between the three synclines suggests that these palaeovalleys were connected by a local valley network that recorded the same sea level fluctuations during the marine nummulitic sedimentation the palaeovalley network was structurally controlled by the east west axes of the blieux and taulanne synclines and the north south axis of the barreme syncline formed during the pyrenean provencal late cretaceous middle eocene shortening and the first stage of the alpine history middle eocene respectively later on the westward alpine compression since the early oligocene induced local depocenter migration and reversal in flow direction however compared to the modern river pattern the palaeovalley orientation highlights a geometrical stability since their formation about 40 ma suggesting a long term stability of the early structures in the foreland basin this constancy can be explained by the location of the study area in a piggy back basin transported at the top of the provencal thrust sheet that facilitated the preservation of the overall axis orientation of the palaeovalleys

role of inversion tectonics in structural development of the himalaya abstract analysis of surface and subsurface structures variation of shortening amounts obtained by restoration of deformed cross sections and occurrence of younger hangingwall rocks over the older footwall rocks across the vaikrita thrust in the higher himalaya suggests reactivation of early normal faults as thrusts based on this an inversion tectonics model is proposed for structural development of the himalaya the model explains the geometrical shape of the himalaya as primary arcuation and helps in resolving superimposed deformation in the region

tafoni on coastal slopes south devon u k cavernous weathering tafoni development occurs on coastal slopes in greenschist bedrock at elevations up to 40 m above sea level the freshly weathered surfaces of the cavern interiors are irregular in morphology discordant to major rock structure formed by substantially weakened rock and associated with granular weathering debris the weathering debris contains soluble elements in proportions similar to those present in seawater and the penetration of elements associated with sea salts into the weathering surface to estimated depths of at least 0 1 0 2 m is indicated by the presence of chlorine scanning electron microscopy and microprobe analyses suggest that rock breakdown occurs principally through limited chemical weathering at grain boundaries the mechanism for the emplacement of marine salts within sheltered rock surfaces in the tafoni is postulated to be a combination of dry deposition under turbulent atmospheric conditions and wetting by coastal fog

a review of definitions of the himalayan main central thrust most workers regard the main central thrust mct as one of the key high strain zones in the himalaya because it accommodated at least 90 km of shortening because that shortening exhumed and buried hanging wall and footwall rocks and due to geometric and kinematic connections between the main central thrust and the structurally overlying south tibet detachment geologists currently employ three unrelated definitions of the mct metamorphic rheological age of motion structural or protolith boundary structural these disparate definitions generate map and cross section mct positions that vary by up to 5 km of structural distance the lack of consensus and consequent shifting locations impede advances in our understanding of the tectonic development of the orogen here i review pros and cons of the three mct definitions in current use none of these definitions is flawless the metamorphic rheological and age of motion structural definitions routinely fail throughout the orogen whereas the protolith boundary structural definition may fail only in rare cases all limited to sectors of the eastern himalaya accordingly a definition based on high strain zone geometry and kinematics combined with identification of a protolith boundary is the best working definition of the mct

experimental salt weathering of limestones in relation to rock properties a total of 21 different types of british and european mesozoic limestones have been subjected to simulated salt weathering using sodium sulphate na2so4 with the following aims assessment of the relative durabilities of different types of limestone assessment of the importance of modulus of elasticity and other factors in affecting durability and assessment of the use of impulse excitation techniques to monitor changes in rock modulus of elasticity the rocks showed a wide spectrum of durabilities while rocks with high values of modulus of elasticity lower water absorption capacities high densities and low salt uptakes tended to be durable there were anomalies the explanation for which probably lies in their pore structures non destructive testing techniques showed that although the more durable rocks failed to lose weight or to show visual signs of disintegration their modulus of elasticity values did tend to decline indicating a loss in strength copyright 1999 john wiley sons ltd

preliminary observations on the impact of complex stress histories on sandstone response to salt weathering laboratory simulations of process combinations historic sandstone structures carry an inheritance or a memory of past stresses that the stone has undergone since its placement in a facade this inheritance which conditions present day performance may be made up of long term exposure to a combination of low magnitude background environmental factors for example salt weathering temperature and moisture cycling and superimposed upon these less frequent but potentially high magnitude events or exceptional factors for example lime rendering severe frost events fire the impact of complex histories on the decay pathways of historic sandstone is not clearly understood but this paper seeks to improve that understanding through the use of a laboratory process combination study blocks of quartz sandstone peakmoor from nw england were divided into subsets that experienced different histories lime rendering and removal fire and freeze thaw cycles in isolation and combination that reflected the event timeline of a real medieval sandstone monument in ne ireland bonamargy friary mccabe et al 2006b these subsets were then subject to salt weathering cycles using a 10 salt solution of nacl and mgso4 that represents the every day stress environment of for example sandstone structures in coastal or polluted urban location block response to salt weathering was monitored by collecting drying and weighing the debris that was released as blocks were immersed in the salt solution at the beginning of each cycle the results illustrate the complexity of the stone decay system showing that seemingly small variations in stress history can produce divergent response to salt weathering cycles applied to real world historic sandstone structures this concept may help to explain the spatial and temporal variability of sandstone response to background environmental factors on a single facade and encourage conservators to include the role of stress inheritance when selecting and implementing conservation strategies

isotopic and structural constraints on the location of the main central thrust in the annapurna range central nepal himalaya five isotope enhanced geologic transects in the southern annapurna range of central nepal elucidate structural geometries near the main central thrust whole rock nd isotopes and u pb ages of detrital zircons unambiguously distinguish greater himalayan hanging wall and lesser himalayan footwall metasedimentary rocks nd 0 values for lower lesser himalayan rocks typically range from 20 to 26 whereas greater himalayan rocks usually have nd 0 values of 19 to 12 lower lesser himalayan rocks yield detrital zircons with an age peak at ca 1880 ma and no detrital zircons younger than ca 1550 ma in contrast greater himalayan rocks yield detrital zircons with a prominent broad peak of ages at ca 1050 ma and no detrital zircons younger than ca 600 ma the protolith boundary between greater and lesser himalayan rocks is up to 1 km farther south than usually mapped on the basis of lithology field and microstructural observations indicate the presence of a top to the south ductile shear zone superimposed on this boundary confirming this shear zone as the main central thrust no evidence exists for large scale structural mixing of greater and lesser himalayan rocks along the main central thrust in the annapurna range

comparative investigation of the spatial distribution of past weathering impacts on sandstone masonry abstract inspection of the deterioration of both natural outcrops and historical built stone facades reveals that patterns of disruption are not uniform indicating the influence of material and environmental properties sandstones have a spatial variability in weathering response for this reason geostatistical techniques have been applied to studies of sandstone properties mineralogical and structural that influence susceptibility to decay for this study a comparative analysis of permeability data acquired from a quarry fresh stone and a weathered sample is undertaken the depositional processes that resulted in the formation of sandstone also create structures of spatial variation such as laminations or larger bedding planes within the material using geostatistical techniques the permeability variance observed within quarry fresh blocks of sandstone indicates the subsampling of larger geological structures when cut from the quarry face once blocks have been emplaced within a building they will be subjected to the increased stress of the urban environment these conditions result in exacerbated weathering through processes such as salt and chemical weathering weathering can alter material properties such as permeability with the creation of a secondary permeability produced by the opening pores and alteration of pore connectivity through the application of geostatistics in the analysis of permeability data observed from the weathered block variography reveals the presence of smaller scale structures this suggests that alteration of the sandstone s permeability has led to the creation of new weathering structures within the stone overwriting the initial sedimentary structures these weathering related structures will affect both the magnitude and spatial distribution of permeability within the weathered block the interconnected pathways of permeability created by past weathering facilitate the migration of moisture and salts in solution through the substrate this work has demonstrated that through a geostatistical approach with the application of co kriging these potential moisture pathways can be identified and visualised

sandstone response to salt weathering following simulated fire damage a comparison of the effects of furnace heating and fire fire has long been recognized as an agent of rock weathering our understanding of the impact of fire on stone comes either from early anecdotal evidence or from more recent laboratory simulation studies using furnaces to simulate the effects of fire this paper suggests that knowledge derived from simulated heating experiments is based on the pre conceptions of the experiment designer when using a furnace to simulate fire the operator decides on the maximum temperature and the duration of the experiment these are key factors in determining the response of the stone to fire and if these are removed from real world observations then knowledge based on these simulations must be questioned to explore the differences between heating sandstone in a furnace and a real fire sample blocks of peakmoor sandstone were subjected to different stress histories in combination lime rendering and removal furnace heating or fire frost and salt weathering block response to furnace heating and fire is discussed with emphasis placed on the non uniformity of the fire and of block response to fire in contrast to the uniform response to surface heating in a furnace subsequent response to salt weathering by a 10 solution of sodium chloride and magnesium sulphate was then monitored by weight loss blocks that had experienced fire showed a more unpredictable response to salt weathering than those that had undergone furnace heating spalling of corners and rapid catastrophic weight loss were evidenced in blocks that had been subjected to fire after periods of relative quiescence an important physical side effect of the fire was soot accumulation which created a waxy relatively impermeable layer on some blocks this layer repelled water and hindered salt ingress but eventually detached when salt able to enter the substrate through more permeable areas concentrated and crystallized behind it resulting in rapid weight loss and accelerated decay copyright 2007 john wiley sons ltd

thermobarometric constraints on the thermal history of the main central thrust zone and tibetan slab eastern nepal himalaya the main central thrust mct south of mt everest in eastern nepal is a 3 to 5km thick shear zone separating chlorite bearing schist in the lower plate from sillimanite bearing migmatitic gneiss in the overlying tibetan slab the metamorphic grade increases through the mct zone toward structurally higher levels previous workers have suggested that either post or synmetamorphic thrust movement has caused this inversion of metamorphic isograds in an effort to quantify the increase in grade and to constrain proposed structural relations between metamorphism and slip on the fault four well calibrated thermobarometers were applied to pelitic samples collected along two cross strike transects through the mct zone and tibetan slab results show an increase in apparent temperature up section in the mct zone from 778 k to 990 k and a decrease in temperature to 850 k in the lower tibetan slab which is consistent with synmetamorphic thrust movement a trend in calculated pressures across this section is less well defined but on average decreases up section with a gradient of 28mpa km resembling a lithostatic gradient pressure temperature paths for zoned garnets from samples within the mct zone modelled using the gibbs method show a significant decrease in temperature and a slight decrease in pressure from core to rim which might be expected for upper plate rocks during synmetamorphic thrust movement samples from the uppermost tibetan slab yield higher temperatures and pressures than those from the lower tibetan slab which may be evidence for later resetting of thermobarometers by intrusion of the large amounts of leucogranite at that structural level

signatures of divergence and self organization in soils and weathering profiles abstract complex system behaviors such as self organization are difficult to address in geology system evolution often cannot be directly observed and in geology models and theory must be reconciled with field evidence however self organization can be addressed within the historical interpretive paradigm by applying a measure of the degree of self organization of geologic features using standard interpretive methods to determine the nature of changes and determining whether those changes result in an increase or decrease in organization in this way stable non self organizing convergent development can be distinguished from unstable chaotic self organizing divergent development kolmogorov entropy k entropy was used as a measure of the self organization of soil profiles in eastern north carolina in general the profiles are low in k entropy indicating a generally high level of predictability and information in the vertical arrangement of pedogenetic horizons as a broad generality the study p

thermal evolution of the greater himalaya garhwal india the hanging wall of the main central thrust mct in garhwal india roughly 79 n 80 e 30 n 31 n exhibits an inverted metamorphic gradient sillimanite potassium feldspar assemblages near the top of the hanging wall or greater himalayan sequence are underlain by kyanite grade rocks near the fault textural relationships in pelitic samples from the alaknanda and dhauli river valleys indicate that the inversion is the product of two distinct metamorphic events an early harrovian event m1 which affected the entire greater himalayan sequence and a later buchan event m2 the effects of which are most obvious in the upper part of the sequence rim thermobarometry garnet inclusion thermobarometry and thermodynamic modeling of garnet zoning reveal that the basal portions of the metamorphic sequence experienced peak m1 conditions of 900 k and 960 mpa roughly 36 km depth before following an erosion controlled uplift path e g england and richardson 1977 m2 metamorphic temperatures in the upper part of the sequence also exceeded 900 k but maximum pressures 317 523 mpa indicate paleodepths of only 12 19 km calculated pressure temperature paths indicate that m2 was characterized by temperature increases of 80 k and roughly 5 km of tectonic burial we attribute m1 to tectonic burial of the greater himalayan sequence during the early stages of india eurasia collision we believe that the uplift and cooling path of the sequence was interrupted in late oligocene miocene time by a second burial and heating event m2 related to thrust imbrications in southern tibet this burial was coincident with the generation of leucogranites which are abundant near the top of the greater himalayan sequence but are virtually absent near the mct field relations do not constrain whether the leucogranites were derived from some presently unexposed portion of the greater himalayan sequence and were injected at their present structural level or were melted in situ if the granites were injected then they may have provided some of the heat necessary for m2 metamorphism although our data suggest no direct relationship between the main central thrust as mapped in garhwal and metamorphism in the greater himalaya anatectic melting of an unexposed portion of the greater himalayan sequence could have been associated with movement along a blind thrust with characteristics similar to the mapped mct in central nepal cf le fort 1981 if the granites were produced by in situ m2 melting then we must appeal to a heat source within the upper part of the greater himalayan sequence such as locally high concentrations of heat producing elements cf pinet and jaupart 1987

case hardening of sandstone the case hardened crust developed on the aztec sandstone in the valley of fire nevada has been characterized by a variety of techniques including electron microscopy and infrared spectroscopy the case hardened crust consists mainly of host rock with a fine grained cement and wind deposited kaolinite the cement is usually calcite but in some cases the hydrated calcium borate colemanite was found to be the case hardening cement

rock warming and drying under simulated intertidal conditions part i experimental procedures and comparisons with field data the wetting drying and warming cooling behaviours of rock and stone are known to influence the nature and rate of weathering the way materials warm up and dry out also influences their suitability as biological substrata while rock thermal behaviours have been measured under controlled laboratory conditions previous experiments have largely been restricted to terrestrial simulations due to practical constraints where efforts have been made to simulate intertidal conditions expansion and contraction of rocks or rates of breakdown i e sediment production and weight loss have been measured while detailed observations of thermal and drying behaviours have rarely been made a simple semi automated procedure is described that enabled measurement of surface temperatures and desorption evaporative water loss for different material types rock and concrete under simulated semidiurnal tide conditions some preliminary results are presented illustrating the types of data that were obtained and comparisons are made with temperature data collected on a rock platform in the uk to assess the ability of the procedure to adequately represent field conditions copyright 2011 john wiley sons ltd

variable weathering response in sandstone factors controlling decay sequences differences in weathering response characteristics of fine and coarse grained stanton moor sandstone samples were assessed in a laboratory weathering simulation experiment using a variable combination of salt weathering and freeze thaw cycles preliminary analysis of permeability characteristics identified similar mean values for each type of stanton sandstone but significant differences in the range of values between the two sample sets with coarse grained samples of stanton moor sandstone displaying a restricted range of values in comparison to fine grained samples which showed much greater within block variation data indicated that the greater the range in initial permeability values the greater the potential for salt and moisture ingress and retention and hence eventual disruption of the fabric of the stone experimental data also identified different stages in decay sequences with significant structural change occurring during the initial preparatory stage before material breakdown and loss became apparent evidence suggests that relatively minor structural and mineralogical differences between samples of the same stone type can have a significant influence on weathering behaviour resulting in distinct rates and patterns of breakdown copyright 2005 john wiley sons ltd

lithostratigraphic correlations in the western himalaya an isotopic approach we present the results of a whole rock nd isotopic study of two contrasting regions of the western himalaya using the neodymium model age approach on the scale of a single orogen high grade metasedimentary rocks from zanskar yield model ages t dm that are similar to those of the high himalayan crystalline series t dm 1 2 2 0 ga nd 6 to 16 and distinct from values from the lesser himalaya t dm 2 3 3 4 ga nd 18 to 27 hence these two lithological sequences can be recognized for 2000 km along the strike of the orogen data for the basement of the nanga parbat massif at the western extremity of the himalaya t dm 2 3 2 8 ga nd 18 to 30 suggest that these rocks are not equivalent to the high himalaya as previously supposed but have affinities with the lesser himalaya a thin metasedimentary cover sequence on the margins of the nanga parbat massif is isotopically indistinguishable from the high himalaya t dm 1 6 1 8 ga nd 10 to 14 the prior misidentification of the provenance of the massif stems from its high metamorphic grade characteristic of the high himalaya but in this case related to the unique neogene history of the nanga parbat massif which has exhumed a higher grade equivalent of the lesser himalaya that is not seen elsewhere

hangingwall bed rotation and the development of contractional and extensional structures around a thrust fault geometric and experimental models abstract tectonic inversion of normal faults and development of extensional and contractional structures in the vicinity of thrust faults were studied using two models i a geometric or rigid model and ii an experimental or brittle ductile model the first model is based on simple trigonometric relationships between shortening rotation of layers along a thrust and dip of the thrust the model may be used to understand the structures at upper levels of the earth s crust in a predominant brittle regime the second model is based on a series of experiments performed with clay analogues it simulated the structures forming at a deeper level in a brittle ductile regime and incorporates folding as an essential feature the results of the study reveal that structures near a thrust fault depend on the thrust geometry and dip amount the initial orientation of hangingwall layers and their rheological properties in the absence of frictional effects along a thrust surface the rotation of layers and consequent displacement is directly proportional to the thrust dip since the listric faults are characterized by a decrease of dip with depth the variation in the rotation of layers in a profile section may result in formation of dilation spaces that may serve as potential sites for secondary mineral deposits or oil traps a large rotation of hangingwall layers results in a reverse fault drag and a small rotation caused by frictional effects along the fault produces normal fault drag

thrust tectonics crustal shortening and the structure of the far eastern nepal himalaya balanced and restored structural sections across the far eastern nepal himalaya have been constructed in order to determine the structure and evolution of the himalayan orogenic wedge and the amount of tectonic shortening the region has undergone since the initiation of thrusting along the main central thrust mct the far eastern nepal himalaya is comprised of three distinct thrust bound tectonic packages the higher himalayan crystalline thrust sheet the lesser himalayan metasediment thrust package and the sub himalayan imbricate fan the higher himalayan crystallines consisting of kyanite and sillimanite bearing gneisses intruded by the miocene jannu leucogranites have been thrust over the lesser himalayan metasediments along the mct for a distance of 140 km to 175 km the lesser himalayan metasediments are a 12 km thick unit consisting primarily of phyllites metaquartzites and mylonitic augen gneisses in which garnet biotite and chlorite metamorphic zones are exposed in progressively deeper structural levels the lesser himalayan metasediment thrust package is underlain by a decollement the main detachment fault mdf which lies at a calculated depth of between 6 and 10 km underneath the mahabharat lekh and at a calculated depth of 20 to 25 km north of the tamar khola dome the tamar khola dome overlies a footwall ramp along the mdf where the mdf cuts upsection through the lesser himalayan metasediments the lesser himalayan thrust package probably has an internal structure aproximating a hinterland dipping duplex with the mct and the mdf corresponding to the roof and floor thrusts respectively both the tamar khola thrust an out of sequence breach thrust and the main boundary thrust mbt are splay thrusts off of the mdf the sub himalaya consisting of nonmetamorphosed sedimentary rocks displays an emergent imbricate fan geometry and is underlain by the southern continuation of the mdf which lies at a depth of 5 5 km to 6 km beneath the siwalik hills folding and thrusting within the lesser himalayan thrust package and the sub himalayan imbricate fan have accomodated 45 to 70 km of tectonic shortening total north south shortening across the higher lesser and sub himalaya of far eastern nepal south of the tibetan plateau has been of the order of 185 km to 245 km and has occurred at an average rate of 7 4 mm to 15 3 mm per year since the initiation of the mct between 16 and 25 ma

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

tectonic implications drawn from differences in the surface morphology on two joint sets in the appalachian valley and ridge virginia surface morphology distinguishes two joint sets in the virginia west virginia appalachians and points to a difference in rupture velocity between the two sets the earlier joint set j1 propagated prior to or during fault related folding and was subsequently tilted as folds grew to have steeper limb dips j1 is characterized by a rougher surface displaying a symmetrical plumose pattern created during the propagation of a simple rupture front in ceramics such morphology is the product of a faster rupture under relatively high stress intensity k i k ic where k ic indicates critical stress intensity this relatively fast joint growth is consistent with an effective tensile stress sustained by oblique plate convergence at the onset of the alleghanian orogeny the later joint set j2 propagated normal to the allegheny front in a subvertical orientation independent of local bed dip a multilobed rupture leaves a smooth surface on j2 joints by analogy with ceramics such a surface is indicative of slower propagation by subcritical crack growth k i k ic this slow joint growth is consistent with the slow generation of effective tensile stress arising from hydrocarbon maturation postdating fold growth during the waning stages of the alleghanian orogeny

metamorphic evolution of the high himalayan crystallines in se zanskar india the high himalayan crystallines hhc of se zanskar consist of biotite paragneisses of orthogneisses that derive from early palaeozoic granitoids of minor metabasics and of post metamorphic leucogranites of miocene age two main metamorphic events have been documented in the hhc the first event occurred at p 12 0 0 5 kbar and t 750 50 c in rare metabasics intruded by early palaeozoic granitoids in the biotite paragneisses thermobarometric estimates of the first event point to comparable t at p 4 5 kbar lower the first event is followed by a pervasive syn tectonic crystallization characterized by lower p and t on the basis of the cooling ages of the metamorphic minerals and on the geological evidence the second event is referred to the tertiary himalayan crystallization further petrological and geochronological studies are necessary to prove whether a few mineral relics ascribed to the first event define a polyphase himalayan evolution or if they record the incomplete obliteration of an older history during the himalayan event the hhc of se zanskar show a decrease in metamorphic grade from the middle structural levels upward close to the kade unit and downward close to the lesser himalaya from sillimanite k feldspar biotite bearing assemblages to kyanite staurolite muscovite bearing assemblages this metamorphic zonation is probably a consequence of the polyphase history of intracontinental thrusts and of the tectonic emplacement of hot crustal slabs within shallower and colder thrust sheets at relatively late stages of the continental collision between india and eurasia

corroded cobbles in southern death valley their relationship to honeycomb weathering and lake shorelines in southern death valley pits similar in morphology to honeycomb weathering herein referred to as corrosion pits occur on the surfaces of cobbles that are associated with wave produced benches the pitted cobbles include a variety of igneous metamorphic and siliciclastic rocks corrosion pits are rare to absent in limestones or dolomites pit morphology is controlled by cobble lithology in massive rocks the pits are arcuate elongate and gently tapering corrosion of laminated or foliated rocks has produced irregular more jagged pits the presence of desert varnish has strongly inhibited the corrosion process the corroded cobbles are inferred to reflect both chemical and physical weathering of rocks along pleistocene lacustrine strandlines corrosion took place through salt weathering and or heat moisture expansion processes and through chemical dissolution of selected minerals as a result of splash zone wetting and drying the ancient lake waters may have had high ph and high total dissolved solids contents the recognition of corroded cobbles may be important in the reconstruction of the position of ancient shorelines for certain types of alkaline lakes and in the reconstruction of their ancient chemistries

dynamical instability in surface permeability characteristics of building sandstones in response to salt accumulation over time abstract this paper explores how the surface permeability of sandstone blocks changes over time in response to repeated salt weathering cycles surface permeability controls the amount of moisture and dissolved salt that can penetrate in and facilitate decay connected pores permit the movement of moisture and hence soluble salts into the stone interior and where areas are more or less permeable soluble salts may migrate along preferred pathways at differential rates previous research has shown that salts can accumulate in the near surface zone and lead to partial pore blocking which influences subsequent moisture ingress and causes rapid salt accumulation in the near surface zone two parallel salt weathering simulations were carried out on blocks of peakmoor sandstone of different volumes blocks were removed from simulations after 2 5 10 20 and 60 cycles permeability measurements were taken for these blocks at a resolution of 20 mm providing a grid of 100 permeability values for each surface the geostatistical technique of ordinary kriging was applied to the data to produce a smoothed interpolation of permeability for these surfaces and hence improve understanding of the evolution of permeability over time in response to repeated salt weathering cycles results illustrate the different responses of the sandstone blocks of different volumes to repeated salt weathering cycles in both cases after an initial subtle decline in the permeability reflecting pore blocking the permeability starts to increase reflected in a rise in mean maximum and minimum values however between 10 and 20 cycles there is a jump in the mean and range permeability of the group a block surfaces coinciding with the onset of meaningful debris release after 60 cycles the range of permeability in the group a block surface had increased markedly suggesting the development of a secondary permeability the concept of dynamic instability and divergent behaviour is applied at the scale of a single block surface with initial small scale differences across a surface having larger scale consequences as weathering progresses after cycle 10 group b blocks show a much smaller increase in mean permeability and the range stays relatively steady this may be explained by the capillary conditions set up by the smaller volume of the stone allowing salts to migrate to the back of the blocks and effectively relieving stress at the front face

experimental frost weathering of sandstone by various combinations of salts weathering experiments are reported combining frost and a range of salts that occur naturally on rock faces in western and central europe potassium and ammonium alums enhanced frost weathering quite considerably both singly and in combination though they were less potent than halite the destructiveness of which at sub zero temperatures was again confirmed by contrast alunogen and gypsum had little or no effect on rates of frost weathering either singly or in combination combining halite and gypsum produced breakdown that was intermediate between that of the two salts individually as did the combination of gypsum and potassium alum breakdown in solutions of ammonium alum and gypsum and in a combination of potassium and ammonium alum with gypsum caused greater breakdown over 25 cycles of freeze thaw than was recorded with the salts singly the results extend the range of salts known to enhance frost weathering and show that it is difficult to predict the aggressiveness of combinations of salts by experimenting with each salt separately copyright 2001 john wiley sons ltd

tafoni in the el chorro area andalucia southern spain using a combination of field laboratory and micromorphological evidence this study examines tafoni singular tafone in the el chorro area of andalucia southern spain and makes inferences concerning the processes responsible for their formation twenty five tafoni were randomly selected for field examination the morphology of these cavernous rock domes is characterized by a helmet shaped outer roof and an arched shaped cavern often with a partially overhanging visor measurements of height width and depth of the caverns revealed marked variations in size the presence or absence of lichen cover surface varnish overhanging visor cavern backwall stripes rock flaking weathering pits and cavern floor sediments was also noted surface hardness values obtained using a schmidt hammer are relatively low but significantly higher on the outer roof of the tafoni than on the inner cavern walls analysis of sediment samples collected from the cavern backwalls and floors indicates predominantly sandy textures alkaline ph values and some base cation enrichment micromorphological analysis of thin sections prepared from undisturbed blocks reveals large quantities of pore filling cement consisting mainly of calcite mineral grains affected by weathering and pseudomorphic replacement and dark rounded nodules with a metallic appearance in terms of their formation different processes appear to act on different parts of the landform on the outer roof surfaces case hardening resulting from near surface cementation and surface varnish development is dominant on the inner cavern surfaces however core softening resulting from granular disintegration and flaking dominates exfoliation weathering running water and wind deflation also appear to play an important role in tafone formation a phased model of tafone evolution is proposed whereby the features pass through four phases of development initiation enlargement amalgamation and degradation in the study area there are examples of tafoni in each of these phases much of the evidence suggests that the tafoni are actively developing under current environmental conditions

evolution of a thrust sheet top basin the tertiary barreme basin alpes de haute provence france in the french sector of the tertiary alpine mountain belt of southern europe the early stages of compression established an initial thrust front a long distance into the foreland 30 40 km rearward of the terminal thrust front an extensive region of thrust sheet top basins was established behind this initial thrust front particularly after a regional marine transgression in late eocene time priabonian these basins were initially connected but became increasingly compartmentalized as the thrust belt evolved the basins are now preserved as a series of structurally isolated synclinal remnants in the external zones of the alpine thrust belt one of these remnants known as the barreme basin has a preserved fill that is 900 m thick spans 18 m y and is exposed over 50 km 2 the tertiary basin fill comprises initial nonmarine deposits overlain by a marine succession and subsequent continental strata and includes evidence of submarine gravity slides growth structures and abrupt changes in sediment transport directions and provenance evolution of the basin fill was influenced by both far field and more localized near field deformation events the latter being dominated by the progressive growth of a steep thrust related anticline that defined the eastern margin of the basin this basin fill records several key steps in the evolution of the alpine mountain belt such as the first incursion of clasts derived from the emplacement of major thrust structures in the inner parts of the mountain belt ca 32 30 ma synsedimentary volcanic activity and the growth of an important out of sequence anticline that progressively separated the barreme basin from the gres d9annot basin to the east in addition the basin preserves the progression from an early underfilled flysch basin to a subsequent overfilled molasse basin in early oligocene time rupelian between ca 33 and 30 ma records of these events are not available from the fill of the younger foreland basin preserved beyond the final thrust front and this remnant of the thrust sheet top basin province therefore provides a unique record of the early structural and stratigraphic evolution of the alpine mountain belt

rapid exhumation and mountain building in the western alps petrology and 40ar 39ar geochronology of detritus from tertiary basins of southeastern france 1 tertiary convergence high pressure low temperature hp lt metamorphism and subsequent exhumation in the internal western alps were concurrent with detrital deposition in foreland basins at the external periphery of the orogen in the present work we have probed the geochronology and chemistry of white mica grains and metamorphic pebbles from the foreland basins of se france in order to gain additional perspective on exhumation rates and mountain building processes in the internal domain of the tertiary orogen our data indicate that throughout the tertiary these basins were mainly fed from a relatively low pressure source dominated by si poor micas yielding pre alpine 40ar 39ar ages small amounts of detritus composed of high pressure minerals and pebbles are first detected in early oligocene 30 32 ma strata of the barreme basin the 40ar 39ar geochronology of phengites from garnet blueschist pebbles from these strata yielded 34 3 ma ages indicating rapid ascent and exposure of hp lt rocks in the internal part of the orogen shortly after metamorphism to explain the preponderance of pre alpine micas alongside the rare presence of alpine hp lt detritus we suggest that the general architecture of the western alps whereby inner hp lt metamorphic units are cut off from the se france basins by a low grade lid of brianconnais back thrusts was rapidly built in the early oligocene and did not change significantly since then

origin of the inverted metamorphism of the lower himalayas central nepal abstract the southern slope of the central nepal himalayas is divided geologically by the main central thrust zone into the underlying midland metasediment zone lower himalayas in the south and the overlying himalayan gneiss zone higher himalayas in the north the former zone consists of a thick pile of various kinds of metasediments folded into an anticlinorium and the latter zone consists of high grade crystalline rocks with a north dipping homoclinal structure and is further overlain by the tethys himalayas composed of non or slightly metamorphosed tethyan sediments the main central thrust zone shows a characteristic lithology such as calcareous schist quartzite phyllitic schist and augen gneiss and is intensely mylonitized the mineral composition and paragenesis of the rocks in the present area indicate an inverted metamorphism from the midland metasediment to the main central thrust zones that is the metamorphic grade of the midland metasediment zone increases upward toward the thrust zone from the chlorite to the biotite zones of the greenschist facies and the greenschist amphibolite transitional zone is attained in the thrust zone the himalayan gneiss zone is apparently much higher in metamorphic grade than the thrust zone on the basis of the compositional zoning of garnets and muscovite compositions however it is concluded that the himalayan gneisses suffered a polymetamorphism the younger metamorphism resulted in a retrograde metamorphism of the himalayan gneisses together with the above mentioned inverted metamorphism and an anatectic melting in depth this was caused by shear heating due to the thrust movement along the main central thrust zone during the alpine tectonism the older metamorphism which seems to be precambrian in age was much higher in metamorphic grade than the younger one and formed the pyrope rich cores of garnets in the himalayan gneisses the maximum metamorphic temperature of 550 c estimated from the mineral paragenesis in the thrust zone is compatible with that caused by shear heating due to the thrusting with thrusting velocity of 5 10 cm yr maximum stress of 300 bars and thrusting distance of 250 km bird 1978