viscous flow and deformation of regional metamorphic belts at convergent plate boundaries 1 viscous flow and deformation of a newtonian fluid between rigid boundaries have been modeled for investigating deformation of a forearc wedge and a regional metamorphic belt as a weak deforming zone between the plates at convergent boundaries three types of analytic formulations together with numerical formulations for a newtonian fluid with a constant viscosity are used for investigating various flows and deformation 1 flows induced by squeezing between two parallel boundaries 2 flows induced by squeezing and heterogeneous mass influx in the wedge between two oblique boundaries e g accretionary wedge over the subducting plate with the continental plate as a backstop and 3 flows induced by dragging along the boundaries and by homogeneous mass influx in the wedge as in type 2 all cases include strike slip movements of the boundaries which allows us to investigate three dimensional 3 d deformation e g 3 d corner flow the corresponding flow deformation of infinitesimal and finite elements and the timescale of flow are calculated for each configuration with various mechanical boundary conditions the model results show that configuration and mechanism of the flow can be inferred from the spatial variation of finite deformation e g deformed radiolarians as a strain marker and geometry of folding as finite deformation of a large block in particular prolate strain nearly parallel to the strike of subduction zone together with a large scale folding can be a good indicator for deformation in the forearc wedge associated with 3 d corner flow induced by oblique subduction deformation observed in the cretaceous regional metamorphic belts in southwest japan can be explained by this mechanism

metasomatic control of k rb ratios in amphibolites abstract amphibolite facies metamorphism of gabbroic dykes together with their quartzo feldspathic granulite facies country rock archean basement west greenland transformed the gabbroic rocks into amphibolites with remarkably high k rb values up to 2300 average 727 reflecting correspondingly high k rb values in the country rock a similar dyke transformation in an amphibolite facies complex precambrian basement southwest sweden produced amphibolites with more common k rb values average 375 similar to those found in the country rock as the protolith chemistry and the p t conditions of origin for the two amphibolite occurrences are very similar it is concluded that the difference in k rb distribution is caused by the difference in country rocks the k and rb values in the two amphibolite occurrences lie between protolith and country rock values suggesting an exchange of k and rb between basic rock and quartzo feldspathic country rock probably through the hydrothermal fluids which assisted in the amphibolite formation

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

mineralogy and phase relations in the blueschist facies of the black butte and ball rock areas northern california coast ranges microprobe study of minerals in rocks of the blueschist facies from the black butte and ball rock areas of the south fork mountain schist northern california coast ranges is the basis in this report for analysis of reactions and phase relations among lawsonite pumpellyite epidote and associated minerals observed assemblages are intermediate in a progression from those observed elsewhere in high p low t schists of the franciscan e 9 panoche pass where lawsonite is present in nearly all lithologies to the relatively low phigh t assemblages of the shuksan blueschist washington where epidote is ubiquitous two successive reactions in this sequence in order of increasing temperature are l lawsonite na amphibole epidote quartz albite chlorite hzo 2 na amphibole pumpellyite quartz epidote ca amphibole albite chlorite h2o the pressure of metamorphism for the black butte and ball rock areas is estimated from the jadeite content of pyroxene and from the stability of aragonite to have been approximately 7 kbar temperature estimates are not tightly constrained by mineral equilibria but are suggested to be in the range of 250 to 300 c

strain stress and uplift strain distribution across the high pressure type sambagawa regional metamorphic belt was measured by studies of shape change of initially spherical radiolaria strains change from 5 to 2000 with increasing metamorphic temperatures aburpt strain increase apparently occurs in the intermediate metamorphic grades of the terrane deformation stresses during metamorphism were inferred using the grain sized quartz piezometer method which is applicable to dynamically recrystallized quartzose rocks stress distribution across the terrane was composed of two levels the stress level in the lower grade zones was about 130 mpa but in the higher grade zones was about 50 mpa combining stress distribution strain distribution and temperatures of the studied metamorphic terrane the activation energy of the deformation of these quartzose rocks is estimated to have been about 80 90 kj mol the huge amount of deformation of the deep seated sambagawa metamorphic terrane which was formed probably at the lower crustal to uppermost mantle levels over the subducting lithosphere was sufficient to bring about the uplift of parts of the terrane to the earth s surface

geometry and development of relay ramps in normal fault systems relay ramps occur between normal fault segments that overstep in map view the geometry and evolution of exposure scale relay ramps are described from the somerset coast england and are compared with larger scale ramps from elsewhere relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments these groups are interpreted as being evolutionary stages in stage 1 the segments do not interact stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp in stage 3 connecting fractures start to break the relay ramp stage 4 is when the relay ramp is destroyed to produce a single fault that has an along strike bend these evolutionary stages can develop through ti e but they can also be seen spatially a branch line between normal faults or an along strike bend may represent a stage 4 relay with progressively earlier stages occurring updip or downdip characteristic variability in displacement distance profiles for fault segments and linked faults accompanies the interaction and linkage processes displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps relay ramps often contribute to a minimum in total fault displacement at a linkage point

petrologic structural and age relations of serpentinite amphibolite and blueschist in the shuksan suite of the iron mountain gee point area north cascades washington part of the shuksan blueschist terrane near iron mountain and gee point north cascades washington has associated serpentinite amphibolite barroisite schist blueschist rare eclogite and blackwall type metasomatic rock field petrographic and microprobe observations indicate that the amphibolite and barroisite schists were metamorphosed in contact with peridotite and suggest that the peridotite may have been a heat source the serpentinite and associated rocks are structurally concordant with the regional blueschists and have been overprinted by blueschist metamorphism isotopic dating gives metamorphic ages of 148 5 to 164 6 m y for the amphibolite and barroisite schist and 129 5 m y for nearby regional shuksan blueschists the origin of the serpentinite amphibolite blueschist assemblage is interpreted to be the result of sequential events in a subduction zone as subduction began oceanic crustal materials underwent high temperature metamorphism along the hot ultramafic hanging wall and were converted to amphibolites materials that were subducted later came in contact with a cooler hanging wall and recrystallized as blueschist this hypothesis may be applicable to the origin of similar rock associations in the franciscan terrane and other orogenic belts

a fluid model for the shape of accretionary wedges in this paper the accretionary wedges landward of most oceanic trenches are modelled assuming a newtonian fluid rheology it is shown that lubrication theory is applicable and that the addition of material to the wedges can be neglected in determining the shape of the wedges the predicted shape of the wedges is in good agreement with bathymetric profiles across the kurile ryukyu and aleutian wedges from the shape of the above wedges it is deduced that accretionary sediments have viscosities between 1018 and 1019 poise

strains and folds within thrust sheets an analysis of the heilam sheet northwest scotland abstract the changes of shape and orientation of fossil worm burrows have been used to carry out a detailed strain analysis of the heilam thrust sheet in the moine thrust zone northwest scotland the strains have been factorised into components of layer parallel shear 1 layer normal shear 2 and layer parallel shortening or elongation variations in the 1 shear are largely lithologically controlled some strain is due to flexural processes as the thrusts and overlying beds change dip over thrust ramps or are tightened by later deformation while there may also be a component of drag which increases towards the overlying thrust this predating the shear due to flexure a contoured map of the values suggests that major folds within the thrust sheet developed as a result of stick or drag on the floor thrust prior to ramp climb this led to differential movement in the transport direction causing layer parallel shortening accompanied or followed by buckling of the layers a map showing layer normal shear strains 2 suggests that the heilam sheet forms a major surge zone the central part having moved further wnw than the northern and southern parts this has led to components of lateral shear along parts of the sheet especially in the north producing curvature of the imbricate faults

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

the geology of the rough gas field summary the rough gas field was discovered in 1968 it lies in the united kingdom continental shelf blocks 47 3d and 47 8b and produces from the permian rotliegendes sandstone in a faulted anticlinal structure initial reserves were 384 bcf the field was on production until 1980 when the british gas corporation began developing rough as a gas storage facility to meet peak season demand in the mid to late 1980 s three main facies associations are recognised from core studies of the rotliegendes reservoir aeolian sands proximal fluvial sands and conglomerates and distal sheet flood sands the vertical arrangement of these associations within the rotliegendes sequence define three sedimentary units which represent semi arid alluvial fan progradation and abandonment these units can also be recognised on electric logs and can be correlated across the field reservoir porosity and permeability is largely controlled by the texture and mineralogy of the sedimentary facies with a concomitant diagenetic influence the geological model of facies distribution and trends in reservoir quality together with well test data has been used to optimise future development locations and update reservoir simulation of field behaviour in the storage mode

long range high resolution stratigraphic correlation of rotliegend fluvial fan deposits in the central dutch offshore abstract the rotliegend feather edge area in the central part of the endorheic southern permian basin in the dutch offshore is characterized by a predominance of mud prone evaporite bearing playa and lake deposits with a subordinate amount of interbedded thin fluvial sheet sandstones the distribution and lateral facies changes of the sandstone bodies have been analyzed by generating a long range high resolution chronostratigraphic correlation framework the correlation technique of pattern matching of gr logs was applied supported by calculating spectral trend curves flooding events are the primary near synchronous correlation surfaces which can be traced up to and over 100 km the basin setting of the southern permian basin the studied sandstone depositional architecture logs and sedimentary characteristics core are analogous to the depositional setting of laterally amalgamated terminal lobes of dryland river systems in an endorheic basin such as the holocene altiplano basin in bolivia present day lake eyre australia and the miocene ebro basin spain the integrated approach has yielded a stratigraphic reservoir architecture framework in which the reservoir sandstones with net sand up to 10 m have been identified as amalgamated terminal splay sandstone sheets formed at the end of dryland river pathways alternating with lacustrine mudstone layers deposited during short duration high magnitude flooding in intermittent wet climate periods

the kamuikotan zone in hokkaido japan tectonic mixing of high pressure and low pressure metamorphic rocks in the kamuikotan zone central hokkaido japan two distinct types of metamorphic rocks are tectonically mixed up along with a great quantity of ultramafic rocks one type consists of high pressure metamorphic rocks and the other of low pressure ones the high pressure metamorphic rocks are divided into two categories 1 prograde greenschist to glaucophaneschist facies rocks derived from mudstone sandstone limestone a variety of basic rocks such as pillow and massive lavas hyaloclastite and tuff and radiolarian valanginian to hauterivian chert among which the basic rocks and the chert and occasionally the sandstone occur as incoherent blocks or inclusions enveloped by mudstone 2 retrograde amphibolites with minor metachert and glaucophane calcite rock which are tectonic or exotic blocks enclosed within prograde mudstone or serpentinite or separated from these prograde rocks by faults the k ar ages of the prograde metamorphic rocks 72 107 and 116 ma on phengitic muscovites are younger than those of the retrograde rocks 109 132 135 and 145 ma on muscovites and 120 ma on hornblende the low pressure metamorphic rocks consist of the mafic members of an ophiolite sequence with a capping of radiolarian tithonian chert with the metamorphic grade ranging from the zeolite facies through the greenschist partly actinolite calcic plagioclase facies to the amphibolite partly hornblende granulite facies the low pressure metamorphism has a number of similarities with that described for ocean floor metamorphism the tectonic evolution of such a mixed up zone is discussed in relation to mesozoic plate motion

healing behavior of simulated fault gouges from the groningen gas field and implications for induced fault reactivation we investigated the frictional strength recovery healing and subsequent reactivation and slip weakening behavior of simulated fault gouges derived from key stratigraphic units in the seismogenic groningen gas field n e netherlands direct shear slide hold slide shs experiments were performed at in situ conditions of 100 c 40 mpa effective normal stress and 10 15 mpa pore fluid pressure synthetic formation brine sheared gouges were allowed to heal for periods up to 100 days before subsequent reshearing the initial coefficient of steady sliding friction was highest in the basal zechstein caprock 0 65 0 02 and slochteren sandstone reservoir 0 61 0 02 gouges and the lowest in the ten boer claystone at the reservoir top 0 38 0 01 and in the carboniferous shale substrate 0 45 healing and subsequent reactivation led to a marked increase in static friction coefficient of up to 0 16 in basal zechstein and 0 07 in slochteren sandstone gouges for the longest hold periods investigated followed by a sharp strength drop up to 25 and slip weakening trajectory by contrast the ten boer and carboniferous gouges showed virtually no healing or strength drop healing rates in the basal zechstein and slochteren sandstone gouges were significantly affected by the stiffness of different machines used in line with the ruina slip law and with a microphysical model for gouge healing our results point to marked stratigraphic variation in healed frictional strength and healing rate of faults in the groningen system and high seismogenic potential of healed faults cutting the reservoir and basal zechstein caprock units upon reactivation

finite strain patterns in some alpine nappes abstract the patterns of finite strain in some alpine nappes and thrust sheets are reviewed together with their tectonic evolution glarus nappe the finite strain pattern approximately that of heterogeneous simple shear was acquired during upper oligocene times when the helvetic thrust block was deformed together with its infrastructure and basement the glarus thrust was formed during miocene times and modified by pliocene to recent differential uplift morcles nappe this large recumbent fold nappe overrode the aiguilles rouges massif and its cover towards the northwest the finite strain pattern resulted from successive diagenetic compaction multilayer buckling and heterogeneous simple shear high strains occur along the inverted limb of the nappe and fold hinges are oriented subperpendicular to the nw stretching lineation final emplacement of the nappe during the miocene was perhaps a later event chartreuse massif 33 e w shortening was developed across this fold and thrust belt during post helvetian times by decollement along the oxfordian shales in response to thrusting and uplift in the belledonne basement the oxfordian shales had earlier accommodated a pre helvetian probably oligocene deformation in the basement and its trias bajocian cover when n030 trending subhorizontal folds cleavage and a stretching lineation 18 n030 stretching were developed digne nappe detached along the keuper evaporites the cover was displaced westwards in two stages 1 late oligocene with folding cleavage development formation of the frontal slices and an overall e w shortening of 20 and 2 late miocene pliocene after emplacement of the embrunais nappes in the east producing the digne thrust it is concluded that for these alpine nappes geological criteria must be used to establish their evolution if the internal deformation can then be assigned to part of this evolution the pattern of finite strain can be used to quantify and elucidate that part a maximum of information is gained if the incremental deformation history can also be obtained from study of syntectonic fibres

development of n w europe s southern permian gas basin summary the southern permian basin contains over 4 1 10 12 m 3 of recoverable non associated gas most of which is found in early permian rotliegend sandstones the most important source of this gas is carboniferous coal deposited in a proto tethys foredeep basin where the coals were overlain by rotliegend desert sands and by late permian zechstein halite the scene was set for creating important reservoirs for gas deformation of the reservoir and seal to create a trap and the generation and migration of carboniferous gas resulted from the structural history of the area which was shaped in part by underlying crustal blocks and zones of crustal weakness much of this history was related to events most clearly expressed beyond the limits of n w europe in the north atlantic and tethys 1 e w tension which gave rise to the oblique slip induced subsidence of many sub basins within the southern permian basin caused the consecutive creation of the viking central graben system and rockall trough and ended with the crustal spreading of the atlantic ocean and 2 the early mesozoic opening of tethys its cretaceous closure and ensuing alpine orogeny which induced inversion in many areas of the southern permian basin that are now gas bearing

strain analysis of a northern apennine shear zone using deformed marble breccias abstract the alpi apuane region of the northern apennines appears to have been deformed within a large scale low angle shear zone with an overthrust sense of movement the presence of mineral stretching lineations folds progressively rotated into the x strain direction and schistosities which intersect the nappe boundaries at small angles suggest that a component of shear strain occurred during the deformation the strain ratios and orientations on two dimensional sections have been determined from deformed marble breccias reduction spots and oncalites data from three or more non perpendicular non principal sections have been combined to determine the finite strain ellipsoids at 33 sites within the shear zone the finite strains have been separated into components of simple shear longitudinal strain and volume change algebraic expressions have been derived and graphs constructed which enable components of and and and to be determined directly from a knowledge of strain ratio r within the shear zone and the angle between the principal strain direction and the shear zone boundary the alpi apuane data indicate that neither simple shear alone nor simple shear with volume change can satisfactorily explain the observed strains consideration of simple shear plus longitudinal strain leads to a general relationship in which the value of shear increases and the values of longitudinal strain change along a sw ne profile across the zone integration of the resulting shear strain distance curves gives a minimum displacement of 4 km within the shear zone combination of the finite strains with the total time of deformation known from k ar studies leads to average strain rates from 1 4 to 9 6 10 15 sec 1 a characteristic flat ramp flat geometry initially formed the boundaries of what was later to develop into the overthrust shear zone and deformation of the underlying crystalline basement is believed to have occurred by ductile shearing estimates of 21 crustal shortening for the region suggest that the crustal thickness prior to deformation was approximately 20 km in this part of the northern apennines

the rotliegend sedimentation history of the southern north sea and adjacent countries in this study more than 900 well logs and 125 core descriptions from the uk the netherlands and germany are analyzed and integrated into a refined tectono stratigraphic subdivision three periods of rotliegend deposition schneverdingen slochteren and hannover correspond to distinct phases of basin extension a climatic cyclicity of drying upward sequences is superimposed upon the tectonically driven phases of sediment accumulation resulting in a fine scale cyclicity that can be correlated across a variety of facies in the southern permian basin the fluvial aeolian and sabkha and lake environments are represented by conglomerates sandstones and claystones respectively the aeolian facies identified in this study include a variety of deposits found in a modern desert environment and range from sheet sand minor dune barkhan dune transverse dune and star dune to longitudinal dune the main controlling factors that were responsible for the sedimentological differences across the basin are the evolution of the tectonic elements the increasingly arid climate and the westward prograding extension of the basin these distinctive features are retained and enhanced during post rotliegend basin evolution prevailing winds blowing from the north east explain in part the distribution of the various aeolian facies across the basin

two types of ductile deformation regional metamorphic belt abstract the geometry of plastic strains of regional metamorphic rocks is divided into two types one is the uniaxial extension strain prolate and the other the biaxial shortening strain oblate from the plane strain simple shear to the uniaxial shortening geometry the uniaxial extension geometry is found in deformation of metamorphic rocks of the sambagawa ryoke kamuikotan and franciscan belts while the biaxial type is seen in deformation of the shimanto the alpine the appalachian and the caledonian metamorphic rocks the classification of the metamorphic belts by means of strain geometry and strain path is independent of the metamorphic facies series the difference in strain geometry of metamorphic belts is responsible mainly for the tectonic stress regime in metamorphism it is suggested that the biaxial type belongs to the collision type orogeny and the uniaxial type to the cordilleran type orogeny

importance of mineral surface areas in rotliegend sandstones for modeling co2 water rock interactions abstract investigations of rotliegend sandstones from the ne netherlands have been carried out to determine the mineralogical composition and spatial mineral distribution specific mineral and whole rock surface areas and the integration of these results in geochemical water rock co 2 simulations therefore two scenarios were considered 1 volumetric rock composition derived from point counting on thin sections and 2 effective mineralogy derived from 2d pore lining image analysis data which represent the percentage amount of each mineral phase exposed within open or accessible pores specific mineral surface areas were defined for each mineral phase respectively and integrated in both model scenarios based on point counting data the volumetric compositions of the sandstones are dominated by the mineralogy of detrital grains like quartz and k feldspar authigenic minerals esp clays volumetrically make up a small portion of the bulk rock volume only but are exposed due to their small crystal size nm to m scale and a large specific surface area 13 to 195 m 2 g in comparison to e g feldspar grains 0 03 to 1 79 m 2 g hence the size distribution and accessibility of detrital and authigenic minerals regulate the availability of chemical species for water rock interactions in the pore space the effective mineralogy of the sandstones is a function of the presence of grain covering and pore filling authigenic minerals in the two rotliegend sandstones studied approximately 23 and 43 of the detrital grains are covered by cements blocking the grain surface areas accessible for potential water rock interactions these minerals are fe oxide clay cutans mainly illite kaolinite quartz carbonate dolomite ankerite and siderite sulfate anhydrite and barite and galena the specific surface area ssa of each mineral was calculated using electron microscopy to determine the sample geometry e g size thickness and standard density values for the volumetric and effective mineralogy data the total specific surface area of the bulk rock was calculated by summing the specific mineral surface areas in relation to their relative content in the rock as determined using x ray diffraction these results were compared to surface area values determined using low pressure n 2 adsorption bet method of the bulk rock mean value 1 4 m 2 g it is shown that the ssa values using the effective mineralogy approach mean value of 0 46 m 2 g are closer to the whole rock bet than the ssa for volumetric mineralogy 0 05 m 2 g these different values for the volumetric and the effective mineralogy show significant differences in geochemical modeling results the initial amount of k feldspar kaolinite hematite and carbonate controls the availability of species for clay mineral precipitation e g mg smectite during co 2 storage effective mineral carbonation is calculated using the volumetric compared to the effective mineralogy within the first 100 years carbonate precipitation occurs for the volumetric mineralogy but is absent for the effective mineralogy opposing trends are observed for long term reactions 100 years similarly when using the effective mineralogy the porosity increases over the entire simulation time of 10 000 years while it initially decreases for the volumetric mineralogy followed by an increase and a net zero porosity change after 10 000 years this implies that different results for co 2 trapping can be expected depending upon the mineral assemblage and its effective mineralogy

comparison of quartz microfabric with strain in recrystallized quartzite abstract the relationship between quartz c axis microfabric and strain is examined in six specimens of recrystallized quartzite conglomerate in which strain was measured using pebble shapes four rocks subjected to plane strain display a direct relationship between the strength of preferred orientation and the strain intensity the c axis distributions in these rocks as well as a rock subjected to moderate extensional strain are crossed girdles with maxima near the intermediate principal strain axis and connecting girdles at acute angles to the direction of maximum shortening a rock subjected to moderate flattening strain has several maxima clustered near the direction of maximum shortening and a weak connecting girdle through the intermediate principal strain axis these results are generally similar to those of other studies comparing strain and tectonite fabrics and also with experimental and computer simulation studies of fabrics the degree of preferred orientation is related to total strain and therefore microfabrics in quartzites may be cautiously interpreted as qualitative indicators of strain intensity uncertainties are greater however for correlations of fabric patterns with shapes of the strain ellipsoid an observed increase in recrystallized grain sizes with increasing strain suggests that flow stress was lower in the more strained rocks