slip system domains 2 kinematic aspects of fabric development in polycrystalline aggregates abstract in the first paper of the present series cobbold and gapais 1986 we develop theoretical models of plane strain domainal deformation by slip along inextensible and indestructible fibres for such extreme mechanical conditions we show that deformation is largely controlled by kinematic factors we use our models to explain domainal patterns of natural slip systems including bedding and foliation planes faults ductile shear zones and lattice planes the present paper focusses on kinematic aspects of fabric development in polycrystalline aggregates a three dimensional kinematic model is developed it reveals that common quartz fabrics may develop domainally by reorientation and selection of inextensible slip directions a axes or slip planes with initially random orientation stable orientations of slip directions are close to both surfaces of no finite extension and orientations of large amount of shear we explain 1 1 common patterns of quartz a and c axis fabrics e g small circles and crossed girdles 2 2 characteristic differences between fabric patterns according to the shape of the finite strain ellipsoid 3 3 development of asymmetric fabrics during non coaxial deformation histories this last process involves selective destruction or replacement of certain orientation domains so that a preferred orientation of slip lines develops close to the bulk shear direction rotation recrystallization is shown to be an efficient natural selection mechanism the models also account for many microstructural features found in oriented polycrystalline rocks especially 1 1 alternating band like or kink like domains of twinned preferred orientations 2 2 individual grains or clusters of grains with retort like shapes and extensive recrystallisation at boundaries 3 3 small scale shear bands formed by strain partitioning and shear localization

numerical simulation of strain within lava domes abstract a new analytical and numerical method is presented to assess 3d deformation within lava domes the method allows any simultaneous combination of strain components even that of a pure shear and six elementary simple shear components the method s practical use is presented model results provide the following information for lava dome strain patterns in the upper part of a dome stretching is perpendicular to flow direction and in the lower part it is parallel flinn parameter values indicate a flattening strain ellipsoid through the dome except in a small zone in the centre where it is a constriction ellipsoid

arcades products of stress controlled and discontinuity related weathering abstract weathering patterns on sandstone cliff faces and sloping surfaces were studied from the viewpoint of gravity induced stress combined with the presence of planar discontinuities in the rock critical evaluation of hundreds of photos taken in various regions around the world numerical modelling using finite element method including automatic stress controlled element removal technique of erosion modelling and physical in situ modelling of friable sandstone revealed the formation of a specific sub group of weathering forms related to planar discontinuities due to their striking similarity with elements known from architecture these pits are introduced as arcades or arcade like forms these pits and cavities vary in size but they are similar in shape coalesced into trains along the discontinuities and separated from each other by hourglass shaped pillars in their origin and geometry these forms differ from widely known cavernous weathering forms such as honeycombs and tafoni we have shown that arcade shape and size are controlled by the redistribution of gravity induced stress along planar discontinuities and the resulting stress shadows the stress shadow zones along the discontinuities are characterized by material loss owing to various weathering and erosional mechanisms although overlooked as yet stress controlled weathering along discontinuities has a strong effect on rock surface morphology and arcades can be taken as its principal example

unravelling the development of a spheroidally weathered diorite gabbro santa margarita ecological reserve peninsular ranges southern california usa abstract within santa margarita ecological reserve smer southern california an 108 ma diorite gabbro pluton has weathered spheroidally resulting in the formation of concentric rindlets i e a rindlet zone around an unaltered ellipsoidal core of the parent rock to our knowledge little is known about how spheroidal weathering is produced in mediterranean climates like that characteristic of portions of the peninsular ranges hence we undertook a detailed study aimed at determining the textural and chemical changes associated with the spheroidal weathering of the diorite gabbro pluton the parental spheroidally weathered corestone is characterized by a hypidomorphic granular texture and consists primarily of plagioclase amphibole and biotite along with minor amounts of pyroxene and quartz within the corestone sericite and uncommonly calcite and chlorite replace plagioclase the latter mineral also infrequently replaces portions of amphibole and biotite such alteration products are derived from sub solidus deuteric alteration of the pluton xrd clay mineral analysis of the 13 rindlets indicates the presence of mostly kaolinite and vermiculite and a far lesser volume of green smectite thin section study of rindlet samples suggests that vermiculite is derived from the weathering of biotite the most extensively altered mineral in the rindlet zone such alteration is paralleled by statistically significant losses of k mass across the rindlet zone in addition statistically significant losses of ca and na mass across the rindlet zone likely reflect conversion of sericite to kaolinite in contrast the absence of statistically significant losses of mg fe and mn over most of the rindlet zone implies that fluids were mostly oxidizing and that any mg leached from amphibole was likely fixed within smectite while leached fe and mn precipitated out as oxides or oxyhydroxides though calcite was present in the corestone its absence in the rindlets indicates that fluids were sufficiently acidic to dissolve and remove it previous studies have shown that spheroidal weathering occurs when volume expansion produced by a positive v of reaction builds up internal elastic strain energy in the rock for example this type of reaction occurs when iron oxidizes within biotite resulting in an expansion of d 001 from 10 a to 10 5 a or when biotite is transformed into vermiculite leading to an expansion of d 001 from 10 a to 14 a data presented here suggest that the conversion of biotite to vermiculite and the resulting positive v produced the spheroidal fracturing of the corestone at smer hence these and other data discussed in this paper suggest that the weathering of biotite is the primary driving force in the formation of spheroidally weathered corestone in the mediterranean climate of the peninsular ranges

control on the emplacement of the andesite lava dome of the soufriere hills volcano montserrat by degassing induced crystallization lava solidification is controlled by two mechanisms external cooling and gas exsolution the latter inducing crystallization due to increasing liquidus temperature the andesite lava dome of the soufriere hills volcano montserrat is an extrusion dominated by crystallization caused by gas exsolution where cooling is unimportant in controlling emplacement in the magma chamber the magma has an estimated viscosity of 7 106 pa s during ascent gas exsolution caused the magma to extrude in a highly crystalline state with only 5 15 residual melt viscosities in the range 1013 1014 pa s and mechanical strength 1 mpa deformation can be heterogeneous with extrusion along shear zones rheological stiffening in the upper conduit also causes large overpressures shallow seismicity and cyclic patterns of dome extrusion gas rich porphyritic andesites tend to be the least mobile kind of lava because transition from magma into hot crystalline material was reached during ascent

structure and emplacement of a rhyolitic obsidian flow little glass mountain medicine lake highland northern california many rhyolitic obsidian flows show consistent stratigraphic relations among textural units exposed in the flow fronts of undissected flows and in cross sections of older flows the stratigraphy of the holocene little glass mountain rhyolitic obsidian flow consists of from bottom to top air fall tephra deposits basal breccia coarsely vesicular pumice obsidian finely vesicular pumice and surface breccia slightly crystalline rhyolite occurs near the vent areas a model of obsidian flow emplacement based on these textural relations is presented this stratigraphy may reflect the distribution of volatiles within the magma source region with the interlayered contact between coarsely vesicular pumice and overlying obsidian indicating stratification of volatiles in the magma body the distribution of pumiceous and glassy zones along with the orientations of flow banding can be used to map the surface structure of rhyolitic obsidian flows this complex structure as mapped on the little glass mountain flow reflects both the initial flow stratigraphy and subsequent deformational processes during emplacement of the lava three processes disrupt the initial flow configuration the rise of coarse pumice diapirs from the base of the flow the inward propagation of fractures in areas of extension and surface folding in sites of flow parallel compression subvertical flow banding in vent areas indicates that fracturing accompanies the emergence of lava most of the observed upper surface of a dome originates as a fracture plane the structure of domes that form over vent areas may reflect the orientation of dike like conduits as well as the local state of stress during extrusion

endogenous growth of dacite dome at unzen volcano japan 1993 1994 a dacite dome at unzen volcano grew mainly exogenously when it was small and the effusion rate was high but endogenously when the dome became large and the effusion rate declined the endogenous dome that has grown since late 1993 shows a shape classified as pelean whereas the earlier stage had a low lava dome shape the carapace of the endogenous dome moved like the crust of a basaltic lava pillow although the dome is several hundred times larger than such pillows the surface carapace was carried from the inside of the dome where it had been produced and it thickened as it cooled the crater floor was strongly deformed by the advancing endogenous dome the movement and crater floor deformation can be compared to that of a tractor tread moving on unconsolidated ground

deformation of partially molten granite a review and comparison of experimental and natural case studies experimental and natural investigations of partially molten granite are compared and reviewed experiments suggest that deformation of partially molten granite with low viscosity melt 104 pa s exhibits a rheological critical melt percentage rcmp in case of high viscosity melts 108 pa s however the relationship between melt fraction and log viscosity of the partially molten granite may be linear considerations about viscosity rheological thresholds and segregation of natural melts suggest that low viscosity melt experiments simulate natural conditions more realistically therefore an rcmp is to be expected under natural conditions both diffusion creep and dislocation creep may occur under natural conditions whereas cataclastic flow is only observed under experimental conditions a melt induced transition from dislocation creep to diffusion creep occurs under experimental and natural conditions melt topology is controlled by the magnitude of differential stress under experimental conditions if differential stress is higher than 100 150 mpa melt pockets are elongate and oriented at a low angle to the maximum compressive stress in contrast in nature melt pockets tend to be oriented subparallel to the foliation plane i e presumably at a high angle to the maximum compressive stress

rheology and microstructure of experimentally deformed plagioclase suspensions we present the result of the first deformation experiments at high temperatures and high pressures on synthetic magmatic suspensions of strongly anisometric particles the results highlight the interplay between the rheological response and the development of microstructures and they demonstrate the critical importance of the shape of crystals on the mechanical behaviour of magmas plagioclase suspensions with two crystal fractions 0 38 and 0 52 were deformed both in compression and in torsion in a paterson apparatus with increasing crystal fraction the rheological behaviour of the magmatic suspension evolves from nearly steady state flow to shear weakening this change being correlated with a microstructural evolution from a pervasive strain to a strain partitioning fabric magmatic suspensions of plagioclase have viscosities approximately five orders of magnitude higher than suspensions of equivalent crystallinities made of isometric particles such as quartz

coaxial progressive deformation textures in extrusive and shallow intrusive rocks southwest japan abstract fine grained rocks from an andesite dyke a dacite dome and a basalt flow contain microshear zones overprinting an aligned microlitic groundmass in each case the shear zones comprise conjugate sets bisected by the plane of crystal alignment this texture indicates coaxial or pure shear flow in contrast to simple shear which is generally considered to be the dominant kinematic flow type in extrusive and shallow intrusive rocks this is interpreted as resulting from a change from non coaxial to coaxial flow coinciding with increasing viscosity during emplacement this suggests that deformation of extrusive and shallow intrusive rocks in the near solid state during the latter stages of emplacement may be more important in the development of aligned rock textures than fluid state flow of the magma as is commonly envisaged

origin of honeycombs testing the hydraulic and case hardening hypotheses abstract cavernous weathering cavernous rock decay is a global phenomenon which occurs in porous rocks around the world although honeycombs and tafoni are considered to be the most common products of this complex process their origin and evolution are as yet not fully understood the two commonly assumed formation hypotheses hydraulic and case hardening were tested to elucidate the origin of honeycombs on sandstone outcrops in a humid climate mechanical and hydraulic properties of the lips walls between adjacent pits and backwalls bottoms of pits of the honeycombs were determined via a set of established and novel approaches while the case hardening hypothesis was not supported by the determinations of either tensile strength drilling resistance or porosity the hydraulic hypothesis was clearly supported by field measurements and laboratory tests fluorescein dye visualization of capillary zone vapor zone and evaporation front upon their contact demonstrated that the evaporation front reaches the honeycomb backwalls under low water flow rate while the honeycomb lips remain dry during occasional excessive water flow events however the evaporation front may shift to the lips while the backwalls become moist as a part of the capillary zone as the zone of evaporation corresponds to the zone of potential salt weathering it is the spatial distribution of the capillary and vapor zones which dictates whether honeycombs are created or the rock surface is smoothed a hierarchical model of factors related to the hydraulic field was introduced to obtain better insights into the process of cavernous weathering

dynamics of an unusual cone building trachyte eruption at pu u wa awa a hualālai volcano hawai i the pu u wa awa a pyroclastic cone and pu u anahulu lava flow are two prominent monogenetic eruptive features assumed to result from a single eruption during the trachyte dominated early post shield stage of hual lai volcano hawai i pu u wa awa a is composed of complex repetitions of crudely cross stratified units rich in dark dense clasts which reversely grade into coarser pumice rich units pyroclasts from the cone are extremely diverse texturally ranging from glassy obsidian to vesicular scoria or pumice in addition to fully crystalline end members the 100 m thick pu u anahulu flow is in contrast entirely holocrystalline using field observations coupled with whole rock analyses this study aimed to test whether the pu u wa awa a tephra and pu u anahulu lava flows originated from the same eruption as had been previously assumed crystal and vesicle textures are characterized along with the volatile contents of interstitial glasses to determine the origin of textural variability within pu u wa awa a trachytes e g magma mixing vs degassing origin we find that 1 the two eruptions likely originated from distinct vents and magma reservoirs despite their proximity and similar age 2 the textural diversity of pyroclasts forming pu u wa awa a can be fully explained by variable magma degassing and outgassing within the conduit 3 the pu u wa awa a cone was constructed during explosions transitional in style between violent strombolian and vulcanian involving the formation of a large cone and with repeated disruption of conduit plugs but without production of large pyroclastic density currents pdcs and 4 the contrasting eruption styles of hawaiian trachytes flow cone and pdc forming are probably related to differences in the outgassing capacity of the magmas prior to reaching the surface and not in intrinsic compositional or temperature properties these results further highlight that trachytes are kinetically faster magmas compared to dacites or rhyolites likely degassing and crystallizing more rapidly

widespread fluid infiltration during metamorphism of the witwatersrand goldfields generation of chloritoid and pyrophyllite chloritoid and pyrophyllite occur together in all major goldfields of the witwatersrand basin and are widespread in virtually all rock types of the upper witwatersrand supergroup including metaconglomeratic reefs and altered mafic rocks both minerals are particularly characteristic of the pelitic horizons intimately associated with reef packages but they are also developed locally in the regionally persistent metapelites that have basin wide extent pyrophyllite is particularly common in foliated zones adjacent to quartz veins and near unconformably overlying auriferous conglomerates the wide distribution of chloritoid and pyrophyllite in metapelites of the witwatersrand basin is attributed to alteration of chlorite rich shales rather than to unusual premetamorphic starting materials this alteration event involved the redistribution of many elements with up to 40 volume loss mainly due to removal of silica removal of most of the mg and some fe accounts for the stabilization of chloritoid and pyrophyllite relatively immobile elements included al ti nb cr v p la and ce whereas si fe mn zn co ni cu mg and ca were lost and k rb and ba were introduced by an infiltrating fluid the alteration event is inferred to have been within the chloritoid and pyrophyllite stability field and thus syn metamorphic as bulk chemical changes in metapelites are from chlorite directly towards chloritoid and then pyrophyllite rather than to lower grade minerals such as kaolinite muscovite chlorite chloritoid and muscovite chloritoid pyrophyllite assemblages are attributed to fluid buffering along appropriate curves as their production by metamorphism of lower grade mineral mixes is considered unlikely based on the present bulk rock compositional data a metamorphic timing for the alteration accounts for the correlation of strongly foliated areas with greater degrees of inferred alteration the transitions from chlorite to chloritoid to pyrophyllite define zones of increasing alteration widespread infiltration as part of peak metamorphism is suggested by the distribution of chloritoid and pyrophyllite quartz veining and textures fluid rock ratios calculated from a silica budget in one metapelitic horizon exceed 100 1 over many square kilometres these values need not imply multi pass fluid flow as much of the silica migration may be redistribution on a scale of a few metres from source rocks into veins although infiltration during metamorphism may have affected much of the upper witwatersrand succession channelized fluid flow within reef packages along faults and unconformities and in certain metaconglomerates and metapelites is inferred

rock cities and ruiniform relief forms processes terminology abstract spectacular rock cut landscapes consisting of closely spaced residual rock blocks separated by narrow intersecting corridors are variously termed as rock cities and ruiniform relief the former term has apparently never been formally defined except in the local czech literature whereas the latter was applied in various contexts making the terminology confusing this paper provides a global overview of forms processes and controls behind such rock city ruiniform landscapes and develops geomorphological terminology for such rock cut landscapes including the proposal that rock city becomes a legitimate scientific term rock cities and ruiniform relief are two different types of rock erosional morphology typified by the presence of a street pattern in the former and highly weathered surfaces of rock residuals in the latter although there is some overlap between the two examples of rock cities or ruiniform relief may be found in different lithologies and in a wide range of climates from hyper arid to humid classic localities include northern czechia and adjacent parts of poland and germany australia central sahara and the gran sabana in venezuela lithologies particularly suitable to the development of this type of erosional morphology include mainly sandstones followed by limestones dolomites conglomerates tuffs but igneous rocks such as granites or rhyolites are also known to support this type of relief the combination of sufficient rock strength to support steep rock faces and the presence of discontinuities which preferentially eroded turn to streets and squares in the rock cities appears as the basic prerequisite a wide range of processes are involved in their formation including surface and subsurface weathering mass movements salt tectonics karst processes in both carbonate and silicate rocks piping fluvial erosion and aeolian abrasion despite being spectacular landscapes very few models of long term evolution of rock city and ruiniform relief have been presented in the literature and it is unlikely that any one scenario would apply to all situations rather rock cities are examples of geomorphological convergence

the mechanism of flow and fabric development in mechanically anisotropic trachyte lava anisotropy of magnetic susceptibility ams and electron back scattered diffraction ebsd of magnetite and sanidine fabrics throughout an eroded trachyte lava dome in tertiary volcanic province of the nw czech republic revealed two fabric types the high degree of ams fabric is associated with sanidine textural domains similar to normal kink bands type i fabric and occupies the whole body except the sw margin folded fabric and low anisotropy of ams also in the sw margin reveals sanidine alignment domains resembling reverse kink bands type ii fabric the flow of trachyte lava occurred via simultaneous slip of sanidine crystals along their 010 planes and also by readjustment of the textural domain boundaries according to the fibre slip theory this microfabric study suggests that the type ii fabrics resulted from collapse of vertically anisotropic trachyte crystal mush above the feeding conduit type i fabric is interpreted to originate from type ii fabrics by further stretching of highly attenuated fold limbs asymmetric type i fabrics along margins of the dome are related to outflow of trachyte lava away from the conduit region due to divergent flow the trachyte fabric zonality is interpreted to reflect the process of successive emplacement of progressively rotated trachyte lava lobes within a lava dome that locally preserves the collapsed and folded vertical fabrics

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

strain partitioning during partial melting and crystallizing felsic magmas abstract the rheology of partly molten felsic systems changes dramatically during the onset of melting and through crystallization solid to liquid and liquid to solid transitions are not rheologically identical contradicting the concept of a unique rheological critical melt percentage we use four thresholds separating the successive stages according to the melt fraction for the melting transition 1 the liquid percolation threshold connects the melt pockets at about 8 of melt thus allowing local magma displacement at the metric scale and 2 for greater melt percentages 20 25 a melt escape threshold corresponds to the onset of transport over large distances of the melt and part of the residual solid phase leading ultimately to granitic bodies for the solidification transition 3 the first formation of a rigid framework of crystals which can accumulate stress although the melt can still flow corresponds to the rigid percolation threshold 55 solids and 4 the system becomes totally locked at about 72 75 solid which corresponds to the particle locking threshold the present paper focuses on strain partitioning induced by the coexistence of two contrasting rheological phases between these thresholds on a variety of scales non coaxial deformation is preferentially accommodated by the lower viscosity melt which increases the vorticity in the melt phase and reinforces asymmetries in the flow pattern strain partitioning also increases the scale length of the weakest phase during melting and magma ascent whereas strain partitioning decreases the scale length during crystallizing strain partitioning also affects the migration of melt by raising the particle locking threshold and lowering the melt escape threshold for three dimensional deformations such as transpression the direction of melt segregation e g horizontal may differ from the direction of melt migration e g vertical

crustal and uppermost mantle structure of the bohemian massif based on celebration 2000 data 1 the deep structure of the bohemian massif bm the largest stable outcrop of variscan rocks in central europe was studied using the data of the international seismic refraction experiment central european lithospheric experiment based on refraction celebration 2000 the data were interpreted by seismic tomographic inversion and by two dimensional 2 d trial and error forward modeling of p and s waves additional constraint on crustal structure was given by amplitude modeling using the reflectivity method and gravity modeling though consolidated the bm can be subdivided into several tectonic units separated by faults shear zones or thrusts reflecting varying influence of the cadomian and variscan orogeneses the saxothuringian barrandian moldanubian and moravian velocity models determine three types of crust mantle transition in the bm reflecting variable crustal thickness and delimiting contacts of tectonic units in depth the nw area the saxothuringian has a highly reflective lower crustal layer above moho with a strong velocity contrast at the top of this layer this reflective laminated lower crust reaches depths of 26 35 km and is characteristic for the saxothuringian unit which was subject to eastward subduction the moldanubian in the central part is characterized by the deepest 39 km and the most pronounced moho within the whole bm with a strong velocity contrast 6 9 8 1 km s 1 a thick crust mantle transition zone in the se with velocity increase from 6 8 to 7 8 km s 1 over the depth range of 23 40 km seems to be the characteristic feature of the moravian overthrusted by the moldanubian during variscan collision

the lithobiontic ecological niche with special reference to microorganisms abstract revised terminology is proposed that describes the ecological niches of microorganisms within hard mineral substrates organisms attached to the external surfaces of the rock are termed epiliths while those in the interior of the rock are all termed endoliths the latter are called chasmoendoliths if they inhabit fissures in rocks cryptoendoliths if they dwell within structural cavities and euendoliths if they actively penetrate calcareous substrates

magnetic fabric transposition in folded granite sills in variscan orogenic wedge abstract new approach involving evaluation of anisotropy of magnetic susceptibility ams data in stereoplots and jelinek s p j t space vollmer s eigenvalue and microstructural analyses is proposed to discriminate between homogeneous and superposed deformation in granites this method is used to decipher the internal ams fabric and microstructural evolution of a folded array of granitic sills the studied major sill shows a fabric and microstructural zonality marked by submagmatic and high temperature type i planar linear fabric developed at sill margins and the transpositional type ii subsolidus fabrics that formed at high to medium temperature deformation in the sill core while type i fabric is associated with dip slip magnetic lineations type ii subsolidus fabrics are marked by subhorizontal magnetic lineations striking parallel to the long axis of the sill the structural reconstruction of the fabrics in the granite and the host rocks as well as new u pb zircon ages suggest coeval emplacement of horizontal and vertical sills accounting for significant weakening of the host rock magma multilayer the model of folding of such multilayer and extrusion of residual magma parallel to axial planes is discussed with respect to structural record in other syn contractional granite sill arrays forming sheeted plutons worldwide

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

fast evolving conduits in clay bonded sandstone characterization erosion processes and significance for the origin of sandstone landforms abstract in strelec quarry the czech republic an underground conduit network 300 m long with a volume of 10 4 m 3 and a catchment of 7 km 2 developed over 5 years by groundwater flow in cretaceous marine quartz sandstone similar landforms at natural exposures conduits slot canyons undercuts are stabilized by case hardening and have stopped evolving the quarry offers a unique opportunity to study conduit evolution in sandstone at local to regional scales from the initial stage to maturity and to characterize the erosion processes which may form natural landforms prior to stabilization a new technique was developed to distinguish erodible and non erodible sandstone surfaces based on measurements of relative erodibility drilling resistance ambient and water saturated tensile strength ts at natural and quarry exposures three distinct kinds of surfaces were found 1 erodible sandstone exposed at 60 of surfaces in quarry this sandstone loses as much as 99 of ts when saturated 2 sub vertical fracture surfaces that are non erodible already prior to exposure at ground surface and which keep considerable ts if saturated 3 case hardened surfaces that start to form after exposure in favorable conditions they became non erodible and reach the full ts in just 6 years an increase in the hydraulic gradient from 0 005 to 0 02 triggered conduit evolution based on long term monitoring of water table in 18 wells and inflows to the quarry rapidly evolving major conduits are characterized by a channel gradient of 0 01 a flow velocity 40 cm s and sediment concentration 10 g l flow in openings with a discharge 1 ml s and hydraulic gradient 0 05 exceeds the erosion threshold and initiates piping in the first phase of conduit evolution fast concentrated flow mobilizes erodible sandstone between sets of parallel fractures in the shallow phreatic zone in the second phase the conduit opening mainly expands vertically upward into the vadose zone by mass wasting of undercut sandstone slabs mass wasting is responsible for 90 of mobilized sandstone sides of the mature conduits are protected by non erodible fracture surfaces natural landforms were probably formed very rapidly by overland flow piping and possibly fluidization during or at the end of the glacial periods when sandstone was not yet protected by case hardening

emplacement dynamics of phonolite magma into maar diatreme structures correlation of field thermal modeling and ams analogue modeling data abstract emplacement mode and original shape and dimensions of a well exposed phonolite body in the ceske st edoho i mountains czech republic were reconstructed using combined techniques of structural analysis of magmatic fabrics and columnar jointing together with analogue and thermal mathematical modeling of cooling for different shapes of experimental bodies phreatomagmatic rocks in the vicinity of some phonolite stocks in the area of interest suggest that the phonolite bodies were likely emplaced into maar diatremes our modeling revealed that intrusion of magma into phreatomagmatic maar diatreme craters can result in cryptodomes extrusive domes lava lakes or branched intrusions the fabric and columnar jointing pattern of the selected phonolite body reveals best fit with an asymmetric extrusive dome emplaced into the maar crater the scaling analysis and thermal modeling also suggest that the phonolite extrusion could have formed within 6 66 days and cooled to the background temperature after 10 000 years combined analogue and thermal modeling also revealed that the phonolite extrusions into maar diatreme craters are marked by upper tier collonade of vertical columns and lower tier of curved and outward flaring columns both tiers in the phonolite extrusions are divided by a subhorizontal suture

some remarks on fabric overprints and constrictional ams fabrics in igneous rocks during the ascent emplacement and post emplacement deformation of igneous rocks two or more phases of deformation that overprint each other are often depicted these overprints when magnetic minerals are present are recorded in magnetic fabric in this contribution overprints are studied by means of numerical modeling following several basic scenarios common to igneous rocks biotite and amphibole that occur often together in igneous rocks are considered as carriers of the anisotropy of magnetic susceptibility modeling shows that 1 a constrictional fabric with a low degree of anisotropy as commonly recorded in magmatic rocks may result from a deformation overprint and not necessarily from an extensional transtensional regime and 2 that the constrictional ams fabrics originates from orthogonal superimposition of a deformation event on an ams fabric inherited from earlier magma emplacement history therefore the interpretation of a constrictional fabric must be performed with caution numerical modeling may provide a suitable help in strengthening the interpretation of real magnetic fabric data

trace element rich brines in eclogitic veins implications for fluid composition and transport during subduction primary and pseudosecondary fluid inclusions occur in oscillatory and sector zoned omphacite in eclogitic veins from the monviso ophiolitic complex in the western alps the inclusions contain aqueous brines and daughter crystals of halite sylvite calcite dolomite albite anhydrite and or gypsum barite baddeleyite rutile sphene fe oxides pyrite and monazite this daughter mineral suite indicates high solubilites of na k ca mg fe zr ti p ba ce la th and s species and provides direct evidence for transport of high fieldstrenght large ion lithophile and light rare earth elements as dissolved species during subduction fluid inclusion heterogeneities preserved within and between adjacent grains in the veins however suggest that the scale of fluid equilibration was small a crack seal geometry in some of the veins implies that fluid release in pulses rather than steady flow controlled mineral deposition and growth in the veins from these observations we develop a model of fluid release and entrapment in which pulses of fluid are associated in time with increments of shear and tensile failure the rate of fluid release and the reduction in porosity both depend on the rate of plastic flow vein fluids may initially be derived from decreptitation of early fluid inclusions in the host eclogites small scale fluid heterogeneities implied by the fluid inclusions in the veins are best interpreted in terms of limited fluid flow and hence limited metasomatism we conclude that element recycling into the mantle wedge during subduction will depend at least as strongly on fluid transport mechanisms as on element solubilities in the fluid phase at monviso despite evidence for high trace element solubilities in saline brines the elements were not removed from the downgoing slab prior to teaching depths of 40 km

the role of microorganisms and biofilms in the breakdown and dissolution of quartz and glass three different types of silica 1 quartz sand 2 crystalline scepter quartz and 3 commercial glass subjected to biological growth were investigated for evidence of biologically induced breakdown the results of laboratory experiments with biofilms on quartz sand and glass were compared with material from the field microscopic optical and sem analysis of quartz sand weathered in vitro by a microbial community of cyanobacteria diatoms and heterotrophic bacteria demonstrate grain diminution of a sand fraction of north sea sediment the microbial community changes the minerals in the vicinity of the living cells which leave their mark on the quartz surface in form of imprints depressions and pits subsequently microbial growth on the surface brought about a general decrease of the grain size in the layer beneath a biofilm imprints of diatoms on glass surfaces colonized by diatoms and heterotrophic bacteria confirm the chemical etching activity of these organisms mixed cultures of diatoms and bacteria show depressions corresponding to the shape of individual cells our experiments confirm that diatoms heterotrophic bacteria and cyanobacteria from natural biofilms can actively attack quartz and glass microscopic analysis of an idiomorphic scepter quartz crystal from a tepui weathering environment reveals that the associated biofilms can create a local shift in the ph from 3 4 ph of water on the tepui to evidently higher than 9 necessary for quartz dissolution the quartz covered with a biofilm is partially perforated to a depth of more than 4 mm we conclude that biofilm growth in marine sub aquatic and terrestrial sub aerial conditions can significantly increase the breakdown of silica in the amorphous glass sub crystalline chert crystalline and granular forms of quartz microbial growth may therefore substantially modify the processes of transformation of a major rock forming mineral of great chemical and physical resistance

geochemistry and nd isotope signature of the collserola range palaeozoic succesion ne iberia gondwana heritage and pre mesozoic geodynamic evolution the collserola range includes a representative stratigraphic succession of the palaeozoic of the central part of the catalan coastal ranges ranging from cambro ordovician to carboniferous times in this paper we present an up to date review of the stratigraphy and structure of the palaeozoic of the collserola range and provide geochemical and sm nd isotope data to constrain the pre mesozoic crustal evolution of this sector of the variscan belt geochemical compositions indicate that the palaeozoic siliciclastic rocks of the collserola range were fed by a relatively mature heterogeneous source of sediment comprising quartz rich sediments to intermediate igneous rocks the siliciclastic rocks of the collserola range show great geochemical affinity with the turbidites of passive margins the sm nd signature of the siliciclastic rocks is compatible with those of the palaeozoic and late proterozoic fine grained siliciclastic rocks of the neighbouring terrains of sw europe there is a small decrease of the end t with decreasing age of sedimentation from the cambro ordovician to the carboniferous suggesting an increase of the amount of more juvenile material the presence of small volumes of alkaline basaltic rocks provides evidence for the input of juvenile material in the early palaeozoic basin and suggests that an extensional tectonic regime prevailed during the cambro ordovician sedimentation from a geodynamic point of view the overall analysis of the data implies that the palaeozoic rocks of the catalan coastal ranges were part of the northern gondwana passive margin before the closure of the rheic ocean and the subsequent variscan orogeny

nitrogen isotope fractionations during progressive metamorphism a case study from the paleozoic cooma metasedimentary complex southeastern australia abstract the well studied paleozoic cooma metamorphic complex in southeastern australia is characterized by a uniform siliciclastic protolith of uniform age with a continuous range of metamorphic grade from subgreenschist to upper amphibolite facies and migmatite grade in an annular pattern around the cooma granodiorite those conditions are optimal for investigating variations of n concentrations and 15 n values during progressive metamorphism nitrogen concentrations decrease and 15 n increases with increasing metamorphic grade sub chlorite zone 120 ppm n 15 n 2 3 chlorite zone 110 ppm n 15 n 3 0 biotite and andalusite zone 85 ppm n 15 n 3 8 sillimanite and migmatite zones 40 ppm n 15 n 10 7 covariation of k and n contents is consistent with n substituting for k as nh 4 in micas observed trends of increasing 15 n values with decreasing nitrogen concentrations can be explained by a continuous release of nitrogen depleted in 15 n with progressive metamorphism which causes an enrichment of 15 n in the residual nitrogen of the rock equilibrium models for rayleigh distillation and batch volatilisation for data of the greenschist and amphibolite facies metasedimentary rocks can be explained by n 2 nh 4 exchange at temperatures of 300 600 c whereas observed large fractionations for the upper amphibolite facies and melt products in the migmatite grade samples may be interpreted as nh 3 nh 4 exchanges at temperature of 650 730 c lower values in the highest grade zones may also stem in part from input of 15 n depleted fluids from the granodiorite the magnitude of isotope fractionation of nitrogen is about 1 2 during progressive metamorphism of metasedimentary rocks from sub chlorite zone to biotite andalusite zone which is consistent with previous studies consequently the large spread of 15 n values in archean greenschist facies metasedimentary rocks of 6 to 30 can be accounted for by variable mixtures of mantle plume dominated volatiles with a 15 n of 5 and a 15 n enriched marine sedimentary kerogen component inherited from a ci chondrite veneer having 15 n of 30 to 42

flow direction and groundmass shear zones in dykes shimane peninsula japan the groundmass of andesitic dykes at sezaki southwest japan has trachytic texture and contains microscopic shear zones the shear zones comprise a conjugate pair formed by flattening of the solidifying dyke rock probably caused by the magma pressure of the still molten part of the dyke this pressure shortened the solidifying rock perpendicular to the dyke margins and caused it to extrude parallel to the magma flow direction the groundmass shears indicate that locally the magma flowed 60 upward in the dykes it is concluded that while groundmass shears are a useful indicator of flow direction in dykes phenocryst alignment in dykes is strongly influenced by magma pressure flattening and thus may be a poor indicator of flow direction

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

shear thickening dilatancy in crystal rich flows abstract rheological models of molten rock are mostly based on behaviours in which viscosity is constant with respect to strain rate e g newtonian bingham plastic or viscosity decreases with increasing strain rate pseudo plastic or shear thinning rheological models in which viscosity increases with increasing strain rate shear thickening or dilatant models have rarely been used yet such behaviour is common in particulate systems whereas magmas with low crystal content may be appropriately modelled by the former behaviours greater crystal content may lead to particle interactions resulting in shear thickening behaviour the effect is illustrated using a powdered rhyolitic rock mixed with water which exhibits extreme shear thickening behaviour caused by particles moving apart as they move past each other the expansion of the grain fabric during flow is opposed by the applied loads such that dilatancy is invariably associated with shear thickening rheology crystal rich lava may exhibit shear thickening dilatancy a proposition supported by observations of glass rich microscopic shear zones disrupting crystal fabrics plutonic crystal mush may also exhibit shear thickening dilatancy which can explain synplutonic intrusion involving brittle fracture followed by ductile disruption in general strain rate is an important contributor to the transition from ductile to brittle behaviour in crystal rich igneous rocks

depositional systems and sequence stratigraphy of coarse grained deltas in a shallow marine strike slip setting the bohemian cretaceous basin czech republic deposits of coarse grained gilbert type deltas showing varying degrees of reworking of foresets by basinal currents were identified in middle turonian to early coniacian sandstones of the bohemian cretaceous basin the progradation of the deltaic packages earlier interpreted as large scale subaqueous dunes shelf ridges or subaqueous fault scarp accumulation terraces was controlled by high and low frequency relative sea level changes in a relatively slowly subsiding intracontinental strike slip basin end member types of the bohemian cretaceous coarse grained deltas are deep water deltas characterized by thick 50 80 m foreset packages with steep 10 30 foresets and shallow water deltas which deposited thin 15 m packages with foresets typically between 4 and 10 the differences in thickness and foreset slope angle were controlled predominantly by the accommodation available during progradation the depositional regime of the deltas was governed by i the fluvial input of abundant sand bedload with a minor proportion of gravel ii gravity flows most probably caused by liquefaction of the upper part of the unstable foreset slope and iii migration of sandy bedforms on the foreset slopes the bedform migration was driven by unidirectional currents of possible tidal origin individual foreset packages represent systems tracts or parts of systems tracts of depositional sequences a variety of stacking patterns of high frequency sequences exists in the basin caused by low frequency relative sea level changes as well as by local changes in sediment input because of generally low subsidence rates fluvial or beach topset strata were not preserved in the cases studied the absence of preserved fluvial facies which has been one of the main arguments against the fluvio deltaic origin of the sandstone bodies is explained by erosion of the topsets during transgression and their reworking into coarse grained lags of regional extent covering ravinement surfaces

biofilms and case hardening on sandstones from al quwayra jordan on cambrian and ordovician sandstone inselbergs at al quwayra in southern jordan many near vertical rock walls exhibit marked case hardening detailed examination of the case hardened layer from four sites on both red and white sandstones has been carried out using schmidt hammer simple chemical analyses scanning electron microscopy energy dispersive spectroscopy and inductively coupled plasma mass spectrometry these analyses reveal a range of types of case hardening often in association with cryptoendolithic bio lms containing cyanobacteria and fungi iron manganese and calcium are all found to be common constituents of cements within the case hardened layer micro organic bio lms may assist in the formation of case hardening through aiding cementation but are by no means a necessary component of all the hardened layers in the wadi rum area copyright 2004 john wiley sons ltd

the role of rock surface hardness and internal moisture in tafoni development in sandstone the development of cavernous weathering features such as tafoni remains poorly understood in particular the roles played by internal moisture and case hardening remain unclear in this study electric resistivity tomography ert has been used to map moisture distribution within inner walls of tafoni developed in sandstone and an equotip device used to measure rock surface hardness as a proxy measure of the degree of weathering and case hardening seven large tafoni in the golden gate highlands national park south africa varying in size and degree of development have been monitored a dynamic relationship between surface hardness degree of weathering and internal moisture regimes has been found we propose a new conceptual model which illustrates the complex interaction between case hardening and internal moisture and suggests a new direction for cavernous weathering research copyright 2011 john wiley sons ltd

diagnosis of weathering damage on rock cut monuments in petra jordan studies of many years combining in situ investigation and laboratory analysis have provided comprehensive information on weathering damage on the rock cut monuments in the ancient city of petra in jordan these rock cut monuments represent outstanding world heritage many hundred monuments were carved by the nabataeans from bedrock about 2000 years ago the awareness of increasing weathering damage on the monuments has resulted in international efforts towards their preservation the damage diagnosis has addressed the complex mutual relationships between stone types stone properties monument exposure regimes environmental influences weathering phenomena development and extent of weathering damage and weathering progression the rocks were classified lithostratigraphically and petrographically results on weathering forms weathering profiles and weathering products obtained from monument mapping in situ measurements and laboratory studies revealed a complex diversity of weathering phemomena with respect to type and intensity damage categories and damage indices were used to create a reproducible quantitative rating of weathering damage detailed results on weathering forms allowed the characterization and quantification of weathering progression including weathering prognoses stone properties and states of weathering damage were jointly considered for the rating of the rocks susceptibility to weathering the systematic evaluation of weathering damage and monument exposure regimes can enhance the assessment of weathering factors and processes

biologically initiated rock crust on sandstone mechanical and hydraulic properties and resistance to erosion abstract biocolonization on sandstone surfaces is known to play an important role in rock disintegration yet it sometimes also aids in the protection of the underlying materials from rapid erosion there have been few studies comparing the mechanical and or hydraulic properties of the birc biologically initiated rock crust with its subsurface as a result the overall effects of the birc are not yet well understood the objective of the present study was to briefly characterize the birc from both the mineralogical and biological points of view and especially to quantify the effect of the birc upon the mechanical and hydraulic properties of friable sandstone the mineralogical investigation of a well developed birc showed that its surface is enriched in kaolinite and clay to silt sized quartz particles total organic carbon increases with the age of the birc based on dna sequencing and microscopy the birc is formed by various fungi including components of lichens and green algae using the method of drilling resistance by measuring tensile strength and based on water jet testing it was determined that a birc is up to 12 times less erodible and has 3 35 times higher tensile strength than the subsurface friable sandstone saturated hydraulic conductivity of the studied birc is 15 300 times lower than the subsurface and was measured to also decrease in capillary water absorption 2 33 times water vapor diffusion is not significantly influenced by the presence of the birc the birc thus forms a hardened surface which protects the underlying material from rain and flowing water erosion and considerably modifies the sandstone s hydraulic properties exposing the material to calcination 550 c and experiments with the enzyme zymolyase indicated that a major contribution to the surface hardening is provided by organic matter in firmer sandstones the birc may still considerably decrease the rate of weathering as it is capable of providing cohesion to strongly weathered and disintegrated sandstone surfaces however only a near surface zone of the sandstone is stabilized by the birc and additional sources of stabilization gravity induced stress inorganic cement etc contribute to the resistance of the subsurface zone of sandstone exposures

behaviour of apatite during partial melting of metapelites and consequences for prograde suprasolidus monazite growth abstract the suprasolidus behaviour of apatite and monazite is examined for an average metapelite composition using phase equilibria modelling coupled with solubility equations of these minerals both closed and open system scenarios are considered partial melting above the solidus requires apatite and monazite breakdown in order to saturate the anatectic melt in phosphorus and the light rare earth elements in general melt loss is predicted to increase the stability of apatite and monazite at high temperature most apatite is predicted to survive up to ultrahigh temperature conditions except for rocks with low bulk phosphorus concentrations by contrast most monazite is expected to be consumed by uht conditions thorium substitution in monazite is expected to increase the stability of monazite to higher temperatures the presence of lree rich apatite decreases the stability of monazite above the solidus but the breakdown of this apatite during anatexis may generate prograde monazite at the apatite melt interface in local pockets of melt oversaturation however prograde suprasolidus monazite along grain boundaries is expected to be consumed during further partial melting or during melt homogenization when an interconnected melt network develops anatectic melts are predicted to be saturated with respect to apatite except at uht conditions and for rocks with low initial p2o5 bulk concentrations

internal strain within lava flows from analogue modelling internal strain within lava flows can be measured in the field from deformed bubbles or vesicle foliations preferred crystal orientation or ams studies these measurements have important implications for the determination of vertical velocity profiles and flow directions recent field studies show very contrasting strain patterns especially in vertical profiles an experimental study was conducted to relate variations in internal strain to different boundary conditions during flow results show that viscous flow in a straight channel along a basal slope produces three successive stretch trajectories in vertical flow planes these trajectories are related to the distribution with time of a simple shear component and a pure shear component viscous flow in a straight channel along a horizontal base reveals convex stretch trajectories in the vertical flow plane radial spreading at the mouth of a straight channel reveals concentric stretching perpendicular to the radial direction of displacement in the upper part of the flow strain components deduced from experiments may also explain fold formation during motion these experimental results provide a few end member strain patterns which may facilitate the interpretation of strain measurements in natural lava flows in terms of emplacement mechanisms

internal kinematics of salt diapirs the internal structure of intrusive and extrusive salt bodies elucidates their external shape and the mechanism and history of diapiric emplacement information relevant to petroleum exploration trace amounts of brine can act like heat to weaken salt and promote geologic creep by solution transfer mechanisms we compare natural strain markers in salt with the artificial markers used by fluid dynamicists stream lines are the smooth flow paths followed by fluid particles stream surfaces separate flow laminae and contain the stream lines grain shape fabrics in salt anneal readily and have strain memories so short that lineations map the stream lines and foliations map the stream surfaces of the last stages of deformation by contrast larger structures like folded beddi g have much longer strain memories as a result multiple generations of tonguelike recumbent flow folds formed by unsteady flow in the mother source layer rotate to upright sheath folds or spines in the stems of diapirs here they are constricted and refolded into steep curtain folds to form crescentic and other interference patterns visible in the roofs of salt mines mature diapirs can form crestal bulbs which may be balloon or mushroom shaped and which potentially form larger petroleum traps than previously supposed screens of country rock may be entrained between the stem and peripheral overhanging lobes caused by episodic sedimentation

internal fabric development in complex lava domes abstract viscous lava extrusions were modeled using plaster of paris with admixed magnetite dust which served as a tracer of the internal anisotropy of magnetic susceptibility fabric in model lava domes used analogue material showed pseudoplastic behavior and yield strength level proportional to increasing mixing ratio of plaster powder and water a series of models ranging from simple gravity flows to complex lava domes showing combined endogenous and exogenous growth were created by intrusion of plaster into a sandbox the similarity of model bodies is compared with natural lava domes on the basis of dynamic scaling analysis growth dynamics exogenous growth and internal fabric development in natural lava domes is critically discussed using the experimental results

evidence for major mass transfer and volume strain during regional metamorphism of pelites systematic examination of published sedimentary and metamorphosed pelite analyses has revealed evidence of significant mass transfer and volume strain during regional metamorphism statistical analysis of the data shows that barrovian zone metamorphism of pelitic schist generally causes increases in the whole rock concentrations of the low solubility elements ti and all the observed increases in ti and al contents as functions of metamorphic grade are almost certainly due to residual enrichment caused by the removal of other more soluble species application of mass balance principles to the petite compositional trends indicates that the average pelite may lose as much as 30 of its mass and volume during progressive metamorphism from subgreenschist to amphibolite facies conditions the bulk of the lost mass is silica not volatiles in addition other elements particularly ca na and k appear to be highly mobile in deep crustal metamorphism contrary to conventional interpretations it is concluded that the regional metamorphism of pelites is not an isochemical process

sandstone landforms shaped by negative feedback between stress and erosion the formation and preservation of sandstone landforms such as pillars and arches is enigmatic experiments and numerical modelling show that load bearing material weathers more slowly and thus the internal stress field can shape and stabilize sandstone landforms

textural evidence for dilatant shear thickening rheology of magma at high crystal concentrations investigation of the rheology of magmas at high crystal concentrations by experimental means has proved problematic an alternative approach is to study textures of igneous rocks that not only preserve evidence of the kinematics of magma flow such as flow direction but can also preserve evidence of rheology flow textures in multiply intruded trachyte dykes on fraser island eastern australia record evidence of dilatant flow during solidification this conclusion is reached by interpretation of microscopic ductile shear zones that disrupt the groundmass of aligned feldspar laths detailed three dimensional investigation demonstrates that the dihedral angle between conjugate micro shear zones is approximately 65 this conjugate angle is equivalent to that observed in dilatant granular materials such as sand dilatant behaviour is synonymous with shear thickening rheology indicating that the magma flow is time dependent and resists high flow rates some of the dykes contain autobrecciation fragments that may represent localities where the ductile flow rate threshold was exceeded newtonian or pseudoplastic shear thinning rheology of crystal poor magmas must progressively give way to shear thickening rheology during cooling and increasing crystal concentration

a laboratory simulation of rock breakdown due to freeze thaw in a maritime antarctic environment results of freeze thaw simulations on three large blocks of quartz micaschist are presented three types of water to ice phase change were identified from temperature and ultrasonic measurements it is suggested that the type of phase change results from a particular combination of rock moisture content solute concentration freeze amplitude and rate of fall of temperature the temperature at which ice thawed inside the rock 0 7 to 1 9 c was also found and this indicates the possibility of freeze thaw effects without positive temperatures approximately 80 per cent of the water that will freeze under natural conditions in the maritime antarctic environment under study appears to have done so by 6

strain accommodation about strike slip fault discontinuities in granitic rock under brittle to ductile conditions abstract brittle and ductile structures adjacent to fault terminations and echelon fault steps of left lateral strike slip faults in the lake edison granodiorite of the central sierra nevada california are related to stress perturbations caused by fault slip the structures associated with fault terminations change from dilatant splay fractures only to splay fractures and ductile fabrics on opposing sides of the fault to ductile fabrics ahead of the fault with decreasing distance from a younger neighboring pluton and presumably with increased temperatures the distributions of deformation mechanisms correlate with the inferred local magnitudes and spatial distributions of the maximum tensile stress the mean stress and the maximum shear stress displacements along the faults are transferred across echelon stepovers by mineralized dilatant fractures in extensional steps to accommodate slip transfer across contractional steps rock apparently was squeezed vertically out of the step by ductile flow concentrations of mobile and immobile elements indicate that diffusive mass transfer was not significant increased mean stress in contractional steps apparently enhanced crystal plastic flow of quartz a flow law that includes a pressure effect through correlation with pressure dependent solidus temperatures is more successful than other experimentally derived flow laws in predicting the observed distribution of ductile fabrics

progressive growth of the cerro bayo cryptodome chachahuen volcano argentina implications for viscous magma emplacement cryptodome and dome collapse is associated with volcanic hazards such as explosive eruptions pyroclastic flows and volcanic edifice collapse study of the growth and evolution of volcanic domes

experiments on internal strain in lava dome cross sections simple experiments have been conducted to study the strain evolution in lava dome cross sections a viscous fluid is injected vertically from a reservoir into a feeding conduit silicone putty is used as analogue magma two dimensional experiments allow the assessment of the internal strain within the dome particle paths are symmetrical on either side of a central line passing through the feeding conduit and display parabolic trajectories the highest strain zone is located above the extrusion zone in cross sections stretch trajectories show a remarkable concentric pattern wrapping around the extrusion zone of the analogue magma to the lateral margins a triple junction of stretch trajectories defines an isotropic point in the strain field in the main central part of the dome an intermediate zone of reversed sense of shearing is caused by a change in the sign of the velocity gradient with respect to that in the upper and lower zones knowledge of this evolving strain pattern can provide a better understanding of the evolution of natural domes also it can help to unravel the kinematic history of ancient domes partly removed by erosion

possible role of fluids in the process of earthquake swarm generation in the west bohemia vogtland seismoactive region abstract the west bohemia vogtland region in the western part of the bohemian massif known for periodic occurrence of earthquake swarms is also characterised by 0 2 0 5 ma old quaternary volcanoes rich co2 emissions anomalies of mantle derived he mineral springs and moffets the detailed analysis of the time space pattern of seismicity during the january 1997 swarm demonstrates the gradual and ordered migration of micro seismic activity suggesting the step by step penetration of fluids into a small fractured volume this scenario is supported by the similarity of the source mechanisms of the natural events of the january 1997 swarm with artificial injection induced micro earthquakes during the german deep drilling project ktb in neighbouring ne bavaria also the comparison of the west bohemia vogtland earthquake swarm region with other intraplate earthquake swarm regions and with earthquake swarms induced by current volcanic processes indicates a role of intrusions of magma and related fluids in generation process of earthquake swarms

controls on the geotechnical response of sedimentary rocks to weathering weathering reduces the strength of rocks and so is a key control on the stability of rock slopes recent research suggests that the geotechnical response of rocks to weathering varies with ambient stress conditions resulting from overburden loading and or stress concentrations driven by near surface topography in addition the stress history experienced by the rock can influence the degree to which current weathering processes cause rock breakdown to address the combined effect of these potential controls we conducted a set of weathering experiments on two sedimentary lithologies in laboratory and field conditions we firstly defined the baseline geotechnical behaviour of each lithology characterising surface hardness and stress strain behaviour in unconfined compression weathering significantly reduced intact rock strength but this was not evident in measurements of surface hardness the ambient compressive stress applied to samples throughout the experiments did not cause any observable differences in the geotechnical behaviour of the samples we created a stress history effect in sub sets of samples by generating a population of microcracks that could be exploited by weathering processes we also geometrically modified groups of samples to cause near surface stress concentrations that may allow greater weathering efficacy however even these pronounced sample modifications resulted in insignificant changes in geotechnical behaviour when compared to unmodified samples the observed reduction in rock strength changed the nature of failure of the samples which developed post peak strength and underwent multiple stages of brittle failure although weakened these samples could sustain greater stress and strain following exceedance of peak strength on this basis the multi stage failure style exhibited by weaker weathered rock may permit smaller magnitude higher frequency events to trigger fracture through intact rock bridges as well as influencing the characteristics of pre failure deformation these findings are consistent with patterns of behaviour observed in field monitoring results

creep of garnet in eclogite mechanisms and implications abstract the rheological properties of subducting rocks represent a fundamental parameter in the dynamics of subduction zones making robust predictions about these properties and the general strength evolution of subducting plates is hampered by a relatively restricted understanding of the mechanisms by which rocks deform at high and ultrahigh pressure this uncertainty is relates to the discrepancy between experimental and field based observations of eclogite deformation and in particular the role of garnet to further investigate this important aspect we performed a textural and micro structural investigation applying optical microscopy element mapping and electron backscatter diffraction on deformed garnet polycrystals from an eclogite mylonite the results were compared to those from a study of undeformed polycrystals that formed from a supercooled frictional melt at hp conditions the mylonites polycrystals are flattened parallel to the main high pressure foliation in the rock and individual grains were shortened by an average 15 although dislocation creep is commonly presumed to dominate garnet straining in eclogites no record of this mechanism was found instead the garnet grains have dissolution surfaces indicative of deformation by intergranular pressure solution the observations provide compelling evidence for the role of fluids and syn tectonic porosity in the weakening of garnet a supposedly rigid eclogite component such weakening represents a crucial step in the fundamental feedback loop between fluid ingress metamorphism and near instantaneous competence loss in rocks undergoing deep subduction

interpretation of domainal groundmass textures in basalt lavas of the southern lamington volcanics eastern australia the arrangement of crystals vesicles and glass in the matrix of a volcanic rock records information about the kinematics accompanying its formation simple rock textures involve homogeneous distributions of features such as aligned crystals whereas more complex rock textures involve inhomogeneous distributions comprising subregions or domains of homogeneous textural types in the groundmass of volcanic rocks two types of domainal textures are defined by 1 differences in the degree of alignment or direction of alignment of crystals and 2 different concentrations of crystals a petrographic survey of basalt lavas of the tertiary lamington volcanics in northeast new south wales australia reveals the presence of both crystal alignment and crystal concentration domainal textures alignment domains are interpreted as shear zones overprinting homogenous aligned textures during flow the formation of crystal concentration domains appears to involve multiple processes including 1 crystal clustering during flow 2 complex overprinting of dilatant groundmass shear zones 3 melt segregations due to stress or 4 postvesiculation processes

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

magnetic fabric and inferred flow direction of dikes conesheets and sill swarms isle of skye scotland abstract we have measured the ams of 16 dikes 35 conesheets and three sills associated with the cuillin hills magmatic center of the isle of skye in the inner hebrides of scotland and of nine dikes located in the regional dike swarm of skye sixty three intrusives totalling 734 samples were studied to determine the plumbing of the skye volcanic system low field susceptibility versus temperature k t identified three different mineral phases in the area namely ti rich magnetite pyrrhotite and titanomaghemite the petrofabrics of the 63 intrusives yielded coherent flow azimuths regardless of their time of emplacement three main types of magnetic fabric a c were found fabric type a plane kmax kint parallel to the dike plane represents the magma flow direction within the intrusives and is the dominant fabric 55 of all the intrusives within the cuillin hills magmatic center and its regional dike swarm the kmax inclinations show that 55 of the intrusives were fed by horizontal to sub horizontal ams inclination of the kmax axis is equal or less than 30 magma fluxes and the rest of them were fed by inclined to vertical fluxes horizontal magma flow means lateral magma injection inside fractures and becomes more probable as the source is located further away

slip system domains i plane strain kinematics of arrays of coherent bands with twinned fibre orientations abstract slip system in rocks often occupy domains each of uniform slip system orientation examples are conjugate faults shear zones folded bedding and crystal lattices domainal behaviour in plane strain is modelled as simple shearing along inextensible fibres an array of alternating band domains with coherent boundaries can undergo a uniform bulk strain with local perturbations in the domains if 1 domain boundaries are planes of mirror symmetry with respect to fibre attitude and 2 domains have alternating fractional widths a and 1 a motion in the models is shown to be a combination of three independent modes plus a bulk rigid motion during mode 1 motion domain boundaries stretch but do not migrate during mode 2 they do not stretch but migrate by lateral translation during mode 3 they migrate by translation and rotation orientation distribution functions odfs are defined by assigning frequencies a and 1 a to orientations and changes in are shown to be due to mode 1 alone changes in a to mode 2 alone mode 3 has no effect on an odf combinations of modes 1 2 and 3 can be used to accommodate an imposed bulk motion two examples are discussed a bulk simple shear and a rigid motion large amounts of simple shear are possible if fibres are on average parallel to the imposed shear direction if modes 1 and 2 are operative the resulting odf has a maximum peak close to the shear direction this may explain the asymmetry of preferred lattice orientations and the occurrence of unique fault sets in rocks that have undergone a progressive simple shear

deformation and magnetic fabrics in ductile shear zones a review abstract the anisotropy of magnetic susceptibility ams is a well established petrofabric tool for indicating relative strain and microstructural character and has been validated on various rock types and different structural settings the magnetic susceptibility of a rock k depends primarily on the nature and abundance of magnetic minerals the physical arrangement and lattice preferred orientation of these magnetic minerals give rise to magnetic anisotropy the ams scalar parameters most commonly used to constrain strain include the corrected degree of anisotropy p 1 a proxy for fabric intensity and the shape factor 1 t 1 an indicator of the magnetic fabric symmetry prolate vs oblate a number of studies have shown that a positive correlation generally exists between p and strain thus the ams shows a great potential as a tool for examining deformation in geologic structures characterized by large strain gradients such as shear zones however a number of caveats exist i the increase of p with strain cannot be solely attributed to deformation because p also increases with k regardless of deformation ii strain across shear zones is typically heterogeneous and is often localized in units of different lithology thus making the separation of the lithological and strain controls on ams difficult also deformation is commonly accompanied by mineral segregation or fluid rock interaction that induces changes in magnetic mineralogy iii even if the undeformed lithology was uniform across a shear zone variations in strain rate or temperature may result in different deformation mechanisms hence the relationship between p and strain depends strongly on both the mineral carriers of ams and on deformation mechanisms and iv the ams is unable to resolve composite fabrics such as those resulting from s c structures where minerals on the c and s planes respectively contribute to ams

microshear zones in a miocene submarine dacite dome of southwest japan microscopic shear zones have been found in the groundmass of glassy rocks of a miocene submarine dacite dome in southwest japan similar textures have been reported previously but only in dykes these textures give a valuable insight into the deformation of the dome during its emplacement by recording the orientations of the principal strains detailed textural analysis indicates that the microshear zones formed as a result of flattening and stretching of the magma simultaneously with quenching measured stretching directions are near parallel suggesting the magma flowed in one dominant direction rather than in a radial pattern the strain is believed to also be influenced by high magma pressure inside the dome being imposed on the high viscosity outer part of the dome

numerical modeling of the evolution of arcades and rock pillars abstract arcades i e lenticular and other specifically shaped hollows controlled by discontinuities have recently been recognized as a weathering form typical for sandstones weathered quartzites granites or tuffs they are produced by accelerated weathering and erosion in stress shadows related to the redistribution of gravity induced stress along planar discontinuities in the rock these forms occur worldwide in various settings inland humid arid and coastal the origin of arcades has been demonstrated via physical experiments and supported by a relatively simplistic numerical modeling however details on their shaping and the evolution of related forms have not been explained we performed an advanced numerical modeling to produce various shapes of arcades and rock pillars during the erosion of rock masses dissected by discontinuities we demonstrate that the erosion model in which erosion takes place when the maximum principal stress is below a certain critical value can adequately describe the formation of arcades in the modeling we set higher critical values for stresses at discontinuities than in a homogeneous material representing a rock mass to represent the higher tendency for disintegration of the discontinuity material which was weakened by the discontinuity formation processes by applying various discontinuity geometries and values of critical stresses we were able to reproduce the formation of various arcade shapes and complex three dimensional clusters of arcade cavities with rock pillars discontinuities and stress controlled erosion weathering are the only necessary conditions for arcade formation

ams measurements on obsidian from the inyo domes ca a comparison of magnetic and mineral preferred orientation fabrics abstract measurements of the anisotropy of magnetic susceptibility ams on lavas can yield information concerning flow directions deformation regimes and relative shear rates here we report results of measurements made on samples of rhyolitic obsidian collected from obsidian dome ca comparisons of ams measurements with previously determined 3d microlite orientation distributions in these samples serve as a calibration of the ams technique despite the low values of bulk susceptibility 1 06 7 04 10 3 si found in the dome relative to typical values in basalts 10 2 si the degree of anisotropy is extremely high in all specimens 3 4 10 7 furthermore susceptibility tensors exhibit a wide range of shapes varying from prolate to triaxial and flattened ellipsoids b parameter from 8 6 to 6 4 corresponding to various degrees of microlite dispersion our results also indicate that despite the tight clustering of principal susceptibility axes obtained on each site bulk flow directions inferred from the orientations of k max axes may be misleading because the orientation of the local extension changes from place to place within the dome however it is shown that the ams of each specimen provides a good measure of the direction of local extension consequently it is possible to interpret spatial variations in flow regime from systematic changes in the orientation of principal susceptibility axes as the proposed association between the local deformation regime and ams is strongly dependent on the aspect ratio of the crystals embedded in the flowing lava some caution must be exerted when interpreting ams results from other flows and a direct comparison between different flows may not be granted in many occasions

deformation patterns in a high viscosity lava flow inferred from the crystal preferred orientation and imbrication structures an example from salina aeolian islands southern tyrrhenian sea italy shape preferred orientation and imbrication structures of crystals have been measured on samples representative of the base centre and top of a highly viscous lava flow on salina aeolian islands southern tyrrhenian sea the data allow zones with different deformation patterns to be identified in the base and top of the flow deformation leads to the development of discrete preferred orientation and imbrication of the elongate crystals the sense of shear is right lateral at the base and left lateral at the top of the flow shear strain can be estimated by the analysis of crystal preferred orientation deformation increases from the flow centre to the outer more viscous boundary layers random orientation of crystals in the inner zone supports the presence of plug flow in a pseudoplastic lava the textural features of the studied lava may be related to different mechanisms i e lateral expansion we conclude that the observed crystal alignments and imbrication structures may be related to a plug flow moving between two non deforming walls the walls are represented by the solidified broken upper and basal crust of the flow the low shear strain values calculated in the outer margins of the flow are indicative of the last deformation event crystal preferred orientation and imbrication structures may be related to the occurrence of velocity gradients existing between the inner zone of the flow and its solidus or near solidus outer margins

oxygen isotope zoning in garnet a record of volatile transport abstract this study examines oxygen isotope zoning in garnets from a barrovian metamorphic terrane in eastern vermont using a co 2 laser extraction system previous strontium isotopic and structural studies of these garnets have shown that they grew over an approximately 10 ma interval during thrusting and nappe emplacement rosenfeld 1970 christensen et al 1989 our studies show that the garnets are strongly zoned in 18 o this zoning is the result of equilibration of garnet with water derived from dehydration of subjacent pelites during nappe stage deformation the magnitude and nature of 18 o zoning depends upon the garnet s location in the outcrop studied the garnets examined in this study come from an isotopically low 18 o paragonitic schist 18 o whole rock 9 that is adjacent to a relatively high 18 o schist 18 o whole rock 12 5 garnets from the paragonitic schists within 10 m of the contact with the isotopically heavier schists have relatively homogenous 18 o values varying from 9 5 in the core to 10 5 at the rim garnet in the paragonitic schists 85 m from the contact are more strongly zoned with 18 o ranging from a low of 6 0 in the cores to a high of 9 0 at the rims of the garnet these zoning patterns were produced by continuous infiltration of relatively high 18 o waters derived from the subjacent schists into the paragonitic schists during garnet grade metamorphism it is possible to determine the time integrated fluid fluxes by comparison of observed 18 o zoning profiles in garnet with those calculated from the equation describing combined advection diffusion of a tracer using this method we calculate time integrated fluid fluxes of 1 5 10 4 cm 3 cm 2 fluxes of this magnitude could have been produced by dewatering of 1 5 km of schist during garnet grade metamorphism

differential water distribution over dune slopes as affected by slope position and microbiotic crust negev desert israel runoff is one of the main water sources responsible for water redistribution within a given ecosystem water redistribution is especially important in arid regions and may be of great importance on sandy dunes where the likelihood of runoff is low owing to the high infiltration rates of sand redistribution of water may significantly affect plant and animal distribution and may explain vegetation patterns within an ecosystem runoff yield over sandy dune slopes in the western negev desert was measured under natural conditions during 1990 1994 the magnitude of runoff yield on different slope sections and on north and south exposures was established the results demonstrate that while slope position controlled the microbiotic crust cover crust cover and crust biomass controlled the amounts of runoff obtained whereas no runoff was measured on the upper dune sections devoid of crust only meagre quantities were measured on the midslope sections characterized by discontinuous crust cover substantially larger amounts were however obtained at the bottoms of the slopes characterized by continuous crust cover north facing slopes usually characterized by a chlorophyll a content of 29 41 mg m 2 yielded on average 3 2 times more runoff than south facing footslopes characterized by a 17 mg m 2 chlorophyll a content whereas microbiotic crust was found to be responsible for runoff generation additional water supply owing to runoff may also explain the occurrence of a high biomass crust and the dense vegetation belt at the dune interdune interface of the northern exposure where runoff tends to collect thus whereas crust may reduce infiltration in certain habitats runoff generated by crust may also be responsible for the promotion of crust growth in other habitats runoff may also be used to promote vegetation growth at the dune footslopes the possibility of using runoff to facilitate agroforestry is discussed copyright 1999 john wiley sons ltd

role of biological soil crust cover in bioweathering and protection of sandstones in a semi arid landscape torrollones de gabarda huesca spain sandstone structural landscapes in the semi arid torrollones de gabarda area province of huesca ne spain are often covered by a well developed biological soil crust of lichens mosses and cyanobacteria and black coatings on vertical surfaces by using scanning electron microscopy with backscattered detector imaging the biological soil crust studied evidenced high activity in the sandstone crust interface processes such as physical disintegration etching and dwelling as well as biomineralization by calcium oxalate and xation of mineral particles by extracellular polymeric substances were observed on the horizontal sandstone surfaces these processes may cause the occurrence of gnammas and the development of a protective coating that favours intense aking when the crust is disturbed on the sandstone cliffs columnar and tafoni weathering development is clearly guided by the protective action of the biological soil crust these qualitative observations are important to develop methodologies to address their quantitative importance in geomorphological processes in semi arid landscapes copyright 2004 john wiley sons ltd

grampian migmatites in the buchan block ne scotland rocks exposed along the scottish coast between fraserburgh and inzie head contain information critical to understanding the evolution of the buchan block the type locality for low p high t regional metamorphism and its relationship with the rest of the grampian terrane one of the major tectonostratigraphic components of the scottish caledonides the 8 km long section traverses a regional network of shear zones and at the highest grades around inzie head passes into the core of the buchan anticline a large scale open fold that is commonly regarded as a late structure post dating metamorphism the metasedimentary rocks increase in grade from upper amphibolite to granulite facies and preserve unequivocal evidence for partial melting the diatexite migmatites around inzie head along with other gneissose units within the buchan block have been regarded as allochthonous precambrian basement rocks that were thrust into their current position during the grampian orogenesis however field observations show that the onset of in situ partial melting in metapelitic rocks which was associated with the formation of garnet bearing aplites and associated pegmatites occurred around fraserburgh where shear fabrics are absent thus the rocks preserve a continuous metamorphic field gradient that straddles the shear zone network this observation supports an alternative interpretation that anatexis was the result of mid ordovician grampian metamorphism rather than an older tectonothermal event and that the inzie head gneisses are autochthonous using an average mid dalradian pelite as a plausible representative protolith phase equilibria modelling satisfactorily reproduces the observed appearance and disappearance of key minerals providing that peritectic garnet produced with the first formed melts represented by the garnet bearing aplites depleted the source rocks in mn the modelled metamorphic field gradient records a temperature increase of at least 150 c from 650 c near fraserburgh to in excess of 800 c at inzie head but is isobaric at pressures of 2 7 2 8 kbar suggesting the buchan anticline developed synchronous with partial melting the buchan anticline is likely an expression of crustal thinning and asthenospheric upwelling which produced voluminous gabbroic intrusions that supplied the heat for buchan metamorphism

structures and lithofacies of inferred silicic conduits in the parana etendeka lip southernmost brazil abstract extensive silicic units in the parana etendeka lip have been long interpreted as pyroclastic density currents rheomorphic ignimbrites derived from the messum complex in namibia in recent literature however they have been characterized as effusive lava flows and domes in this paper we describe structures and lithofacies related to postulated silicic lava feeder conduits at mato perso sao marcos and jaquirana cambara do sul areas in southern brazil inferred conduits are at least 15 25 m in width and the lithofacies include variably vesicular monomictic welded and non welded breccias in the margins to poorly vesicular banded spherulitic and microfractured vitrophyres in the central parts flat lying coherent vitrophyres and massive obsidian are considered to be the subaerial equivalents of the conduits large scale regional tectonic structures in southern brazil include the ne sw aligned porto alegre suture leao and acotea faults besides the antas lineament a curved tectonic feature accompanying the bed of antas river south of the antas lineament smaller scale nw se lineaments limit the exposure areas of the inferred conduits ne sw and subordinate nw se structures within this smaller scale lineaments are represented by the main postulated conduit outcrops and are parallel to the dominant sub vertical banding in the widespread banded vitrophyre lithofacies upper lava flows display flat lying foliation pipe like and spherical vesicles and have better developed microlites petrographic characteristics of the silicic vitrophyres indicate that crystal poor magmas underwent distinct cooling paths for each inferred conduit area the vitrophyre chemical composition is defined by the evolution of trachydacitic dacitic vitrophyres with 62 65 wt sio 2 to rhyodacite and rhyolite with 66 68 wt sio 2 the more evolved rocks are assigned to the latest intrusive grey vitrophyre outcropping in the center of the conduits degassing pathways formed during fragmentation and fracturing episodes within the conduits may have helped to inhibit the explosivity of the eruptions based on the documented lithofacies architecture we attribute the source of the silicic lava flows in the studied localities to tectonic controlled local conduits rather than pyroclastic density currents from distant vent areas

endolithic microorganisms in the antarctic cold desert in the frigid desert of the antarctic dry valleys there are no visible life forms on the surface of the soil or rocks yet in certain rock types a narrow subsurface zone has a favorable microclimate and is colonized by microorganisms dominant are lichens of unusual organization they survive not by physiological adaptation to lower temperatures but by changing their mode of growth being able to grow between the crystals of porous rocks their activity results in mobilization of iron compounds and in rock weatherning with a characteristic pattern of exfoliation this simple ecosystem lacks both higher consumers and predators

lichenic growth as a factor in the physical deterioration or protection of cappadocian monuments cappadocian monuments that are within tuff have serious deterioration problems understanding the effects of lichens on the tuffs is of utmost importance in this paper interactions between lichen coated surfaces of cappadocian monuments and the rock substratum have been studied thin sections and freshly cut sections were investigated by light and scanning electron microscopy the presence of clay minerals and zeolites as weathering by products produced by alteration and hydrolysis of glass and feldspars was assessed by xrd patterns furthermore some physical properties of the tuff coated by and free of lichens were measured and compared analysis of mineralogical data has shown that the main weathering mechanism can be identified as hydrolysis of some of the rock forming minerals the lichenic coat reduces the presence of water inside the rock thus protecting the rock material from physical decay and disintegration

the rheological transition in plagioclase bearing magmas 1 volcanological processes such as melt segregation ascent and eruption are directly dependent on the rheological behavior of magmatic suspensions an increase of the crystal fraction of the suspension leads to the formation of a solid particle network which abruptly increases magma viscosity the crystal fraction at which this rheological transition occurs depends on parameters such as the strain rate and the size shape and sorting of particles to determine the influence of the crystal shape on the rheological transition suspensions of plagioclase a representative anisometric crystal have been investigated at high temperatures and pressures synthetic suspensions with crystal fractions s ranging from 0 38 to 0 75 were deformed both in compression and torsion in a paterson apparatus at 300 mpa 900 c and 800 c and for strain rates between 1 0 10 5 and 1 0 10 3 s 1 all suspensions exhibit a non newtonian shear thinning rheological behavior the experimental results coupled with existing data and models at low crystal fractions s 0 3 allow several rheological domains to be identified from steady state flow to strain weakening each characterized by a specific microstructure in particular a progressive evolution from a pervasive to a strain partitioning fabric is found when increasing the crystal fraction our results highlight the influence of both the strain rate and the shape of crystals on the rheological behavior of magmas during crystallization magmatic suspensions of anisometric minerals such as plagioclase would develop a solid particle network earlier s 0 3 than suspensions of isometric minerals s 0 5 our study shows that localization of strain early in the crystallization history of mushy zones in the magma chamber near the conduit margins and at the base of lava flows would facilitate the mobilization the transfer and the final emplacement at the surface of highly viscous feldspar rich magmas

sandstone weathering in tropical climate results of low destructive investigations at the temple of angkor wat cambodia abstract investigations at the temple of angkor wat aimed at the explanation of the major weathering processes of building sandstone as well as at the role of both intrinsic factors i e sandstone petrography and properties and extrinsic factors i e climatic and environmental influences since material sampling at the temple was limited to a few boreholes because of the high artistic rank of the building non destructive and low destructive in situ investigation methods like ultrasonic wave and drilling resistance measurements had to be applied to obtain information about the material properties of sandstone and their changes due to weathering moreover hydric swelling behaviour of the sandstone was determined on undecorated pieces of fallen blocks from the walls additional random test stable isotopic investigations of environmental influences and salts and thorough investigations of the spatial distribution of salts in the ashlars at two selected places with typical weathering patterns completed the set of data the results demonstrate that the weathering process is mainly triggered by rain dry cycles salt load found in the stone is composed of gypsum and nitrate compounds sulphur stable isotope investigations of potential sources of gypsum lead to the conclusion that soluble components of bat droppings are the major source of salts influences of environmental factors like sulphate in rainwater or so2 from the air on salt formation are unlikely gypsum may reinforce the surface deterioration due to high swelling shrinking movements of the sandstone 1 mm m during intensive wetting drying cycles

dynamics of obsidian flows inferred from microstructures insights from microlite preferred orientations the flow of obsidian lava leads to crystal alignments that reflect both the accumulated strain and the type of flow across the surface microlite preferred orientations are used to investigate the emplacement dynamics strain history and structural evolution of obsidian dome eastern california measurements of three dimensional microlite trend and plunge in samples from the near vent region distal flow and flow front show 1 the flow directions along the dome margins 2 the deformation style e g pure versus simple shear at the dome margins and 3 the variation in strain as a function of position within the flow microlites form well developed lineations in the plane of flow banding in all samples stereographic projections indicate that lineations trend normal to the western flow front and plunge shallowly away from the margin the radial flow pattern indicated by measurements made along the western margin suggests that extrusion was from a roughly elliptical vent these results highlight a strong correlation between microlite trend and the bulk flow direction inferred from the geometry of the flow along most of the eastern periphery lineations trend parallel to the margin and likely reflect the local flow direction as influenced by compression against the thickening flow crust marginal talus piles and topography orientation distributions imply that radial spreading accompanied by flattening was the dominant mechanism for flow emplacement comparisons of measured orientation distributions with theoretical predictions suggest that microlite fabrics in flow front and nearvent samples developed in a pure shear flow microstructures in a sample from near the distal flow base records a component of simple shear variance in microlite trend provides a measure of the amount of strain acquired during flow standard deviation in trend decreases from the near vent region to the flow margins reflecting progressive alignment of microlites during transport pure shear strain inferred from orientation distributions increases from approximately 0 3 near the vent to about 1 1 at the flow front the difference between these strains 0 8 is an estimate of the strain associated with flow emplacement such strain is similar in size to that estimated from mesoscopic structures v1 and for horizontal spreading of a fluid whose volume is equal to that of obsidian dome v1 6 this suggests that flow on the surface was sufficient to produce observed microlite preferred orientations in the flow front these techniques can be applied to interpret older dissected lavas where erosion has erased much of the original flow front or where larger scale structures indicative of flow directions are poorly preserved fl 2002 elsevier science b v all rights reserved

folds produced by gravity spreading of a banded rhyolite lava flow abstract recumbent folds near the top of the minyon falls banded rhyolite flow in northeastern new south wales australia indicate lateral radial extension of lava as it flowed from the vent under the influence of gravity these structures occur near the vent of the flow and differ from the upright folds commonly observed near the tops of lava flows farther from the vent the fold patterns indicate lateral radial shortening and shearing as the spread of lava was impeded interpretation of the folds leads to a kinematic model of coaxial flow near the vent grading to simple shear and sub simple shear away from the vent

anisotropy of magnetic susceptibility in the ponta grossa dyke swarm brazil and its relationship with magma flow direction abstract measurements of anisotropy of magnetic susceptibility ams in 95 mafic dykes mainly tholeiites 10 200 m in width from the mesozoic ponta grossa swarm southern brazil revealed two main types of magnetic fabric type i fabric plane k 1 k 2 parallel to the dyke plane represents magma flow within the dykes whereas type ii plane k 1 k 3 parallel to the dyke plane is compatible with a fabric pattern reflecting vertical compaction of the magma column fabric type i dominates 51 of the dykes within the swarm whereas type ii 38 of the dykes concentrates mainly in the western region where the dykes intrude sediments considering the dykes with type i fabrics it is concluded that 58 of the dykes were fed by horizontal or sub horizontal k 1 inclinations less than 30 magmatic flow and 42 were fed by inclined to vertical k 1 inclinations more than 30 magma flow the latter are more frequent in the southeastern part of the swarm suggesting a magma source close to this area although there may have been other sources in other regions where dykes with inclined flow and distinct chemical characteristics are also found

measuring host rock volume changes during magma emplacement we use a technique to evaluate volume strains in contact aureoles during magma emplacement based on geochemical mass balance calculations dynamothermal contact metamorphism adjacent to the emigrant gap composite pluton sierra nevada california produced an 01 km wide thermal structural aureole consisting of an outer andalusite2cordierite zone and an inner potassium feldspar2sillimanite zone mass balance calculations using al as an immobile reference frame element in metapelites inside and outside of the aureole indicate that the percentage change in total rock mass between chlorite grade rocks outside of the thermal eaects of the pluton and the aureole is 11 1 21 4 mass balance calculations indicate that si was the major rock forming element depleted 0 16 from the aureole during contact metamorphism mass balance calculations and density measurements yield volume strains associated with mass transfer during contact metamorphism of 12 4 these data in conjunction with field relationships are interpreted to suggest that a element mobility during contact metamorphism is not restricted to volatiles and b volume losses within the contact aureole occur during magma emplacement and may contribute to the space making process during magma emplacement if intrusion spans the period necessary to engage hydrothermal circulation in the host rocks 1998 elsevier science ltd all rights reserved

silicic lava dome growth in the 1934 1935 showa iwo jima eruption kikai caldera south of kyushu japan the 1934 1935 showa iwo jima eruption started with a silicic lava extrusion onto the floor of the submarine kikai caldera and ceased with the emergence of a lava dome the central part of the emergent dome consists of lower microcrystalline rhyolite grading upward into finely vesicular lava overlain by coarsely vesicular lava with pumice breccia at the top the lava surface is folded and folds become tighter toward the marginal part of the dome the dome margin is characterized by two zones a fracture zone and a breccia zone the fracture zone is composed of alternating layers of massive lava and welded oxidized breccia the breccia zone is the outermost part of the dome and consists of glassy breccia interpreted to be hyaloclastite the lava dome contains lava with two slightly different chemical compositions the marginal part being more dacitic and the central part more rhyolitic the fold geometry and chemical compositions indicate that the marginal dacite had a slightly higher temperature lower viscosity and lower yield stress than the central rhyolite the high temperature dacite lava began to effuse in the earlier stage from the central crater the front of the dome came in contact with seawater and formed hyaloclastite during the later stage low temperature rhyolite lava effused subaerially as lava was injected into the growing dome the fracture zone was produced by successive fracturing ramping and brecciation of the moving dome front in the marginal part hyaloclastite was ramped above the sea surface by progressive increments of the new lava the central part was folded forming pumice breccia and wrinkles subaerial emplacement of lava was the dominant process during the growth of the showa iwo jima dome

structural analysis of flow related textures in lavas abstract the textures of coherent volcanic rocks including lavas and volcanic intrusives commonly contain features that are attributed to flowage previous applications of structural analysis to volcanic rocks are expanded here to provide a framework for analysis textures defined as the crystallinity granularity and shapes and arrangements of the components crystals glass and voids of a rock together with structures defined as individual features composed of the disposition attitude arrangement or relative positions of the components of a rock are first described second the spatial fabrics shapes and arrangements of the components of a rock and the orientation of textures and structures are identified third textures structures and fabrics are placed in the spatial and temporal geological context finally detailed interpretations of the kinematics and rheology of structures and fabrics is made leading to an integrated flow history of the rock illustrative case studies include rhyolite from the basal part of the tertiary minyon falls dome northeastern new south wales australia which has a texture comprising planar domains of differing crystal abundance flow bands multiple folds of these domains relatively homogeneous crystal alignment parallel to the fold axes and microfolding of these domains in the zone of interaction between phenocrysts and matrix including retrorotation of phenocrysts on short limbs of inequant folds trachyte dykes on fraser island queensland australia have a texture comprising crystal alignment planar concentration domains banding two planar domains of crystal alignment interpreted to be conjugate shear zones phenocrysts influence the spacing and distribution of the domains and interacted with shear zones by undergoing small amounts of rotation the shear zones overprinted a homogeneous crystal alignment during the last stage of flow before solidification as a result of dilatant granular interactions lava from miocene submarine banded silicic mafic domes on katsurajima on the coast of the shimane peninsula southwestern japan has a texture comprising crystal alignment irregular domains interpreted as the result of quenching local internal deformation of crystals including brittle boudinage and elongate vesicles and amygdales dacite from the late stages of the 1991 1995 eruption of mount unzen in western kyushu japan has a texture comprising crystal alignment deformation of phenocrysts and their surrounding matrix producing voids by mechanical means with the possible involvement of vapour phases the pervasive mechanical failure of the flowing magma may have triggered frontal collapse and the ensuing pyroclastic eruptions a spectrum of increasingly intense flow related textures can be recognised from simple planar alignments of crystals and vesicles to overprinting effects and domainal textures such as banding and shear zones and deformed domains pervasive ductile tearing and ultimately brittle fracture record flow during the transition from ductile magma to brittle rock the development of these flow related textures is controlled by the interplay of driving forces magma pressure gravity and resisting forces viscosity where driving forces are strong flow related textures are well developed when viscous resistance exceeds the driving forces flow and the development of flow related textures ceases