the effect of rupture complexity on estimates of source size a general technique is proposed for estimating rupture geometry from measurements of body wave durations wherein measurements of the overall signal duration or the duration of a single pulse identified in all of the arrivals are inverted to estimate the geometry of the overall rupture or of a specific subevent respectively the complexity of a waveform is determined by comparing the overall signal duration to the duration of the most prominent pulse in the waveform this complexity is used to estimate the ratio of the average rupture velocity to the subevent rupture velocity the shear waves radiated by eight moderate 3 6 ml 4 9 multiply recorded aftershocks of the 1975 oroville california earthquake are analyzed using measurements of the corner frequency the characteristic frequency the pulse duration and the signal duration comparison of these four different estimates of source size indicates that the corner frequency and the characteristic frequency are more sensitive to the dominant subevent size than to the overall event size the difference between the estimates of source size determined from the signal duration measurements and the spectral measurements increases as the rupture complexity increases

sm nd evidence for a major 1 5 ga crust forming event in the central grenville province the majority of gray gneisses from an 80 000 km 2 area in the central quebec grenville province define a sm nd isochron that yields an age of 1 53 0 07 ga major element trace element and initial nd isotopic data all point to a subduction related orogenic source for this terrane it is attributed to a major crustal extraction event that formed a mid proterozoic island arc the age of the terrane agrees with published data from the eastern and western grenville province in newfoundland and ontario respectively we suggest that 1 5 ga are fragments were accreted along much of the length of the laurentian foreland within 100 m y of their formation in an event marked by widespread granitoid plutonism

patterns of strain localization in heterogeneous polycrystalline rocks a numerical perspective the spatial and temporal patterns of strain localization in materials with pre existing heterogeneities are investigated via a series of two dimensional numerical models models include i a dynamic feedback process to simulate rheological weakening in response to the transition from non linear flow dislocation creep to linear flow diffusion creep grain boundary sliding and ii a time dependent strengthening process counteracting the weakening process different load bearing framework geometries with 20 weak component are used to evaluate the impact of geometry on the strength of the material and its ability to localize strain into an interconnected weak layer iwl our results highlight that during simple shear if dynamic weakening with or without strengthening feedbacks is present strain is quickly localized into an iwl where an increasing proportion of weak material increases the interconnections between the iwls thereby increasing the anastomosing character of the shear zones we establish that not only bulk strain localization patterns but also their temporal patterns are sensitive to the dominance of the weakening or strengthening process consequently shear zones are dynamic in time and space within a single deformation event hence the pattern of finite strain can be an incomplete representation of the evolution of a shear zone network

flow laws for rocks containing two non linear viscous phases a phenomenological approach abstract mylonitic rocks and rock analogue materials reveal two basic types of structure 1 a load bearing framework lbf of strong phase contains isolated pockets of weak phase 2 interconnected layers of weak phase iwl separate boudins and clasts of strong phase aggregates with the lbf microstructure are characterized by nearly uniform strain rate stress is concentrated in the load bearing framework in aggregates with an iwl microstructure strain rate and sometimes also stress are higher in the interconnected weak phase than in the boudins and clasts of strong phase the degree of stress and strain partitioning depends strongly on the viscous strength contrast and on the relative amounts of the constituent mineral phases based on these observations the rheology of two phase rock is modelled with separate functions for lbf and iwl microstructures a new flow law is derived for rock with iwl structure in which two phases undergo dislocation creep the flow law expresses composite creep strength in terms of temperature bulk strain rate and the volume proportions and creep parameters of the minerals in the rock strain rate and stress are averaged in the constituent phases and slip along phase boundaries maintains strain compatibility within the aggregate composite strengths predicted with the iwl flow law fall well within the uniform stress and uniform strain rate bounds and are generally consistent with the viscous strengths of experimentally deformed bimineralic aggregates a hypothesis of viscous strain energy minimization is used to determine the relative stability of the lbf and iwl microstructures during steady state creep the iwl microstructure is predicted to be stable over a broad range of two phase compositions and mineral strength contrasts whereas the lbf microstructure is stable only in rocks with low volume proportions of weak phase and low to moderate mineral strength contrasts the iwl flow law indicates that rheological stratification in the lithosphere depends strongly on rock composition especially in rocks with low volume proportions of a weak phase and high mineral strength contrasts

flow patterns around rigid inclusions in a multiple inclusion system undergoing bulk simple shear deformation abstract during deformation of an inclusion matrix system the velocity fields around individual inclusions mutually interfere with one another such interacting inclusions rotate at slower rates than non interacting single inclusions this paper presents a theoretical model that describes the flow pattern of matrix viscous material around interacting rigid inclusions of spherical shape in bulk simple shear deformation numerical simulations based on the velocity functions reveal that the volume concentration of inclusions is a crucial parameter controlling the flow pattern around rotating inclusions under interacting conditions at low volume concentrations v 0 1 transforms into a pattern with a bow tie shaped separatrix at a large volume concentration v 0 4 the separatrix assumes the geometry of a super ellipse we also present numerical models that illustrate the influence of volume concentration on the 1 nature of strain distribution 2 distortion patterns of passive foliations and 3 mantle structures around inclusions in an interacting state based on this theory it is shown that the rotational retardation of the inclusions slightly enhances the bulk viscosity of the inclusion matrix system

constraining the relative strengths of high grade metamorphic rocks using foliation refraction angles an example from the northern new england appalachians foliation refraction angles are used to estimate effective viscosity contrasts between metapelitic and metapsammitic layers in amphibolite facies metaturbidites in the presidential range of the white mountains in eastern new hampshire an early formed foliation developed during km scale nappe folding consistently displays larger bedding foliation angles in metapelitic units than metapsammitic units suggesting that the metapelitic units had higher effective viscosities during this deformation we collected bedding foliation angle measurements from a combination of outcrops and locally derived boulders to test the hypothesis that foliation refraction angles could be used to estimate the effective viscosity ratio between different rock types at high metamorphic grades our results show that the metapelitic layers were between 2 and 3 times more viscous than the metaspsammitic layers which we attribute to the presence of large up to 15 cm long abundant up to 30 vol effectively rigid andalusite porphyroblasts in the metapelitic layers we present a methodology for using foliation refraction angles to determine the effective viscosity ratios of different rock types address the practical limitations we encountered and suggest this method is an easy way of estimating the strength contrast between different rock types finally we hypothesize that metamorphism resulting in porphyroblast growth can strengthen large crustal volumes during orogenesis

deformation of ductile inclusions in a multiple inclusion system in pure shear this paper analyzes the deformational behavior of mutually interacting spherical inclusions in a multiple inclusion system considering two physical factors viscosity ratio between inclusion and matrix m and the ratio of inclusion diameter to mean inter inclusion distance a b for a given value of m the strain partitioning between a stiff inclusion and the bulk system i e ratio of their natural extension rates increases non linearly with increasing a b ratios and the gradient of increase becomes steeper when the inter inclusion distance is less than about twice their diameter i e a b about 0 5 the strain distribution within a deformed inclusion is homogeneous when the a b ratio is less than about 0 6 for larger values of a b the internal deformation becomes heterogeneous with the strain increasing or decreasing towards the core in the case of stiff m 1 and soft m 1 inclusions respectively the deformed shape of inclusions in section also shows departure from an ideal ellipse with an increase in the a b ratio stiff inclusions develop shapes similar to that of a super ellipse in contrast to soft inclusions that resemble a sub ellipse the heterogeneity of internal deformation is also reflected in the distortion of passive foliations initially at right angles to the bulk extension direction which become curved with convexity outward and inward respectively within stiff and soft inclusions

nd and sr isotope constraints on the origin of the cornubian batholith sw england combined nd and sr isotope data for the hercynian granites of sw england provide important new evidence for the origin of the cornubian batholith the nd isotope systematics are shown to be robust even in areas of extensive hydrothermal alteration e nd values for the main plutons range from 4 7 to 7 1 whereas values for the palaeozoic country rocks are significantly lower typically 8 to 11 depleted mantle nd model ages 1 3 1 8 ga indicate a heterogeneous source region for the granite magmas and imply that the age of the basement beneath southern england is significantly older than previously estimated calculated e nd values for the palaeozoic country rocks at the time of granite intrusion suggest that they were unlikely to have been the main source material for the magmas e nd e sr data for the granites do not define a simple binary mixing array between a mafic depleted mantle melt and proterozoic crust the best fit model is consistent with partial melting of a composite lower crustal source comprising immature metasedimentary and mafic meta volcanic rocks and mixing with a relatively minor contribution of basaltic magma extracted from a slightly enriched mantle source such hybrid magmas are thought to have been generated during an ivrea type underplating of the lower crust during continental collision their isotope signatures being determined by the relative proportions of crust and mantle material

plutonism in three orogenic pulses eastern blue ridge province southern appalachians department of geological sciences university of north carolina mitchell hall chapel hill nc 27599 3315

magnitude 7 level earthquakes a new lower limit of self similarity in seismic scaling relationships microfractures occurring in a rock sample that are called acoustic emission ae events show some similar features to earthquakes however it remains to be shown whether or not ae equate to ultramicroearthquakes in this study we show the existence of magnitude 7 level earthquakes based on seismological analyses of ae source parameters advances in multichannel broadband high speed continuous recording of ae under seismogenic pressure conditions has facilitated increasingly robust measurement source parameters of ae show that ae events satisfy the same scaling relationship as natural earthquakes in which seismic moment is inversely proportional to the cube of corner frequency this result suggests that both millimeter scale fractures and natural earthquakes of kilometer scale ruptures are highly similar as physical processes hence ae events can be interpreted as ultramicroearthquakes having a magnitude of about 7 these results demonstrate that laboratory observation is an effective approach in studying natural earthquake generation process

non ellipsoidal inclusions as geological strain markers and competence indicators abstract geological objects that do not deform homogeneously with their matrix can be considered as inclusions with viscosity contrast such inclusions are generally treated as initially spherical or ellipsoidal theory shows that ellipsoidal inclusions deform homogeneously so they maintain an ellipsoidal shape regardless of the viscosity difference however non ellipsoidal inclusions deform inhomogeneously so will become irregular in shape geological objects such as porphyroblasts porphyroclasts and sedimentary clasts are likely to be of this kind with initially rectilinear prismatic or superelliptical section shapes we present two dimensional finite element models of deformed square inclusions in pure shear parallel or diagonal to the square as a preliminary investigation of the deformation of non ellipsoidal inclusions with viscosity contrast competent inclusions develop marked barrel shapes with horn like corners as described for natural ductile boudins or slightly wavy rhombs incompetent inclusions develop dumb bell or bone shapes with a surprising degree of bulging of the shortened edges or rhomb to sheath shapes the results lead to speculation for inclusions in the circle to square shape range and for asymmetric orientations anticipated shapes range from asymmetric barrels lemons or flags for competent inclusions to ribbon or fish shapes for incompetent inclusions we conclude that shapes of inclusions and clasts provide an important new type of strain marker and competence criterion

geochronology of the mesoproterozoic state farm gneiss and associated neoproterozoic granitoids goochland terrane virginia the goochland terrane is an isolated block of mesoproterozoic crust in the piedmont province of central virginia we report u pb zircon dates and whole rock major and trace element data for the state farm gneiss one of the main units in the terrane and additional results for a newly recognized suite of neoproterozoic granitoids that intrude the gneiss the state farm gneiss ranges in bulk composition from quartz monzodiorite to granite and three samples yield u pb zircon dates of 1046 7 6 ma 1039 18 11 ma and 1023 10 ma we interpret these dates as igneous crystallization ages which indicate a maximum emplacement interval of ca 1057 1013 ma for these samples neoproterozoic granitoids including the fine creek mills and flat rock granites are more alkaline than the state farm gneiss and display all compositional characteristics of a type granites e g high fe mg ga ga al nb zn y zr u pb zircon analyses from five separate bodies indicate crystallization ages from ca 654 to 588 ma but all results are complicated by mesoproterozoic ca 1 ga inheritance coupled in some cases with secondary pb loss we interpret the ages and compositions of the younger rocks to reflect neoproterozoic rifting of the goochland terrane but its location during rifting is uncertain the terrane may have been separated from laurentia during the neoproterozoic breakup of rodinia and later reattached

modelling the bulk viscosity of two phase mixtures in terms of clast shape abstract the rheological behaviour of many rock types will depend on how mixtures of different minerals and rock clasts behave together this paper develops two dimensional modelling of the bulk viscosity of two phase viscous mixtures with different shape fabrics in pure shearing based on self consistent mechanics and behaviour of inclusion matrix systems an equation is presented for the bulk viscosity in terms of the phase viscosity contrast phase fractions and clast shape results are given for idealised two dimensional mixtures of circles squares or ellipses with a variety of phase viscosity contrasts in pure shearing parallel perpendicular to the shape fabric the normalised bulk viscosities of all these mixtures fall between the theoretical upper and lower viscous bounds given by homogeneous strain rate and homogeneous stress respectively but nearer to the upper bound with increasing shape fabric mixtures with a particular geometry are shown to have a constant relative horizontal distance between these two bounds as proposed by p d bons using graphs for the normalised bulk viscosities of mixtures with variably elliptical aligned shape fabrics the results for fabrics orthogonal to pure shearing can be extrapolated to a diagonal fabrics in pure shearing and b orthogonal or diagonal fabrics in simple shearing these reveal the bulk viscous anisotropy of mixtures with shape fabric in two dimensions it is speculated that during a progressive finite deformation two phase mixtures might undergo changes in bulk viscosity over time with steady stiffening during pure shear and perhaps cyclic stiffening and softening during simple shear the two dimensional models provide an approximation to the three dimensional properties of mixtures with shape fabrics with potential applications to rocks including conglomerates

correlating mechanical data with microstructural observations in deformation experiments on synthetic two phase aggregates abstract a simple method of analysing the results of deformation experiments on synthetic two phase aggregates is presented and applied to some tests on calcite halite aggregates the approach involves replacing the observed mechanical behaviour of real two phase materials of coarse microstructure with a phase volume fraction weighted mechanically equivalent representation in which each phase is assigned its own single valued stress and its own single valued strain such a representation can be solved for the stresses and strains in the two phases and the results compared with the stresses and strains as determined from the deformation microstructures in principle it is then possible to constrain which of the features of the microstructure are mechanically significant the stresses supported by the synthetic calcite halite aggregates suggest a strong partitioning of the deformation into the halite at all volume fractions of calcite and yet analysis of the halite strains from the deformation microstructures indicates that there is little or no strain partitioning between the phases however these conflicting results may be reconciled by using the calcite contiguous volume rather than the actual calcite volume fraction to characterize the strength of the aggregates with respect to those of their component phases

a micromechanical approach for simulating multiscale fabrics in large scale high strain zones theory and application 1 deformation fabrics in earth s crust and mantle are commonly used to constrain the tectonic history deformation mechanisms and rheological properties of the lithosphere their formation involves heterogeneous and multiscale deformation processes that current single scale models cannot capture here we present a micromechanics based multiorder power law approach mopla for the simulation of multiscale fabrics in crustal scale high strain zones we consider the progressive deformation in a crustal high strain zone on three different scales on the macroscopic scale representing the average assemblage of rock units at a point we regard the rock mass as a continuum made of many first order elements the progressive deformation of first order elements in the macroscopic flow field simulates tectonic transposition on the scale of an individual first order element we regard it as an eshelby inhomogeneity embedded in a poly element continuum we apply eshelby s inhomogeneity formalism for power law materials to relate the flow field inside a first order element to the macroscopic flow field on the scale pertinent to structures observed on the outcrop or smaller scale the partitioned flow fields inside individual first order elements are used to examine the fabric development we implement mopla in mathcad apply the approach to a natural example of the cascade lake shear zone and discuss the implications of multiscale deformation our model predicts lineation patterns observed in natural high strain zones that have remained unexplained by single scale models

high strain deformation of conglomerates numerical modelling strain analysis and an example from the wutai mountains north china craton abstract conglomerates have been widely used to investigate deformation history and rheology strain vorticity and viscosity previous studies reveal that several factors such as pebble shapes and concentrations as well as material properties affect conglomerate deformation however how pebble concentration and interaction between pebbles affect deformation is not understood very well we use the 2d numerical modelling platform elle coupled to the full field crystal visco plasticity code vpfft to simulate the deformation of conglomerates with various viscosity contrasts between pebbles and matrix and different pebble concentrations with both linear stress exponent n 1 and power law n 3 viscous rheologies under simple shear conditions up to a shear strain of ten pebbles can behave as effectively passive deformable or effectively rigid an increase in pebble concentrations viscosity contrasts enhances pebble deformation but reduces their rotation a mean aspect ratio rf orientation plot is proposed to gain an estimate of pebble deformation behaviour and the amount of bulk strain closely spaced rigid or deformable pebbles can form clusters that mechanically act as single inclusions rigid clusters rotate and survive for only short strain increments whereas the more stable deformable ones keep on elongating with minor rotation we provide a natural example of deformed conglomerates from the wutai mountains north china craton these consist of banded iron formation bif pebbles embedded in a schistose matrix using the mean rf plot a finite strain of 6 under simple shear could be determined the viscosity of the pebbles is estimated at about 5 8 times that of the matrix for a linear rheology n 1 or 2 to 5 times if a power law rheology with n 3 is assumed

geophysical and geochemical evidence for a hercynian magmatic arc maryland to georgia the distribution of hercynian granitic plutons in the central and southern appalachians is compatible with their being generated in a continental magmatic arc environment isotopic and geochemical data show a consistent pattern of lesser degree of crustal involvement in the most easterly plutons both gravity and aeromagnetic anomaly data suggest that the plutons were either synchronous with or postdate the development of the geophysical anomalies and are unlikely to be a part of any major allochthon

nd isotopic evidence for juvenile crust in the carolina terrane southern appalachians nd isotopic analyses of whole rock samples from the older portion of the carolina terrane one of the largest terranes in the appalachian orogen demonstrate that part of this terrane is composed of juvenile mantle derived crust these data suggest that the terrane may not have originally been built upon old evolved basement material but rather may have been built upon oceanic crust a recent study by other workers demonstrates a more crustally evolved nd isotopic signature for younger components of the carolina terrane these data may indicate that the terrane interacted with evolved crust at a later time possibly by amalgamation with a more evolved crustal fragment before final accretion to laurentia rather than indicating a primary old basement a juvenile nature for the older portion of the terrane contrasts with models that suggest it is an evolved crustal fragment that formed in a continental margin setting a scenario proposed to explain the high proportion of felsic volcanic rocks within the terrane it is herein suggested that carolina is a chemically evolved but isotopically juvenile crustal fragment because it remained in an oceanic setting for an unusually long time in this regard the carolina terrane is similar to some of the large accreted terranes in the canadian cordillera such as wrangellia and alexander the presence of juvenile crust in the carolina terrane documents that at least part of the southern appalachian orogen is not composed solely of reactivated pre existing continental crust the importance of this part of the orogen in terms of the volume of juvenile phanerozoic crustal material in north america may be larger than previously thought however until additional major appalachian terranes have been isotopically characterized the volume of juvenile crust in the whole orogen remains unknown the isotopic make up of a terrane can be an important aspect of terrane analysis as different terranes may have significantly different isotopic compositions while even widespread pieces of a single terrane should have very similar isotopic characteristics the nd isotopic data for the carolina terrane form the beginning of an isotope database for terranes in the southern appalachians

estimation of viscosity contrast and finite strain from deformed elliptical inclusions a method of strain analysis is described which takes into account a possible competence difference between the strain markers and the rest of the rock using data consisting of the sectional shapes and orientations of groups of inclusions from conglomerate like rocks limits are placed on the possible effective viscosity contrast between the inclusions and the rock as a whole as well as on the bulk finite strain suffered by the rock these results are calculated using a computer program based on the theory for the deformation of elliptical cylinders the method can be considered an extension of the rf method but provides more information and involves less restrictive assumptions

the influence of viscosity contrast on the strain pattern and magnitude within and around dense blocks sinking through newtonian rock salt abstract dense inclusions in salt cover a wide range of materials and therefore material properties depending on their origin we have modelled the deformation associated with gravity driven sinking of horizontal initially rectangular blocks of dense material through newtonian salt our two dimensional finite differences models analyse the influence and interaction of two parameters 1 the size i e the aspect ratio ar of the block and 2 the viscosity contrast between the salt and the more viscous block over four orders of magnitude the results demonstrate that during gravity driven sinking the blocks are folded and sheared the strain magnitude within the block increases with increasing block ar and decreases with increasing viscosity contrast sinking velocities of the blocks are in the range of 6 mm a 1 and are a function of block and salt deformation that depend on the block mass and ar as well as on the viscosity contrast salt deformation is characterised by the development of an array of characteristic structures that include folds and shear zones as well as a zone characterised by extreme vertical stretching above the block termed entrainment channel strain in the salt is locally more than two orders of magnitude higher than in the block and increases with increasing block ar and viscosity contrast salt deformation is distributed in closely spaced high and low strain zones concentrated in the block vicinity and the entrainment channel

the effects of porphyroblast growth on the effective viscosity of metapelitic rocks implications for the strength of the middle crust numerical models are used to examine the effects of porphyroblast growth on the rheology of compositionally layered rocks metapelites and metapsammites and by extension the middle crust during prograde metamorphism as porphyroblast abundance increases during prograde metamorphism metapelitic layers will strengthen relative to porphyroblast free metapelitic units and potentially relative to quartzofeldspathic metapsammitic units as metapelitic layers become stronger the integrated strength of compositionally layered successions increases potentially causing large volumes of mid crustal rock to strengthen altering the strain rate distribution in the middle crust and affecting the geodynamic evolution of an orogenic belt the growth of effectively rigid porphyroblasts creates strength heterogeneities in the layer undergoing porphyroblast growth which leads to complex strain rate distributions within the layer at the orogen scale the strengthening of large crustal volumes on the order of thousands of cubic kilometres changes the strain rate distribution which may change exhumation rates of high grade metamorphic rocks the geothermal structure and the topography of the orogen the presence of a strong zone in the middle crust causes strain rate partitioning around the zone suppressed uplift rates within and above the zone and leads to the development of a basin on the surface

flow variations in power law multilayers implications for competence contrasts in rocks abstract an idealized bilaminate multilayer of alternating competent and incompetent layers with different proportional thicknesses is used to model theoretically the manner in which flow in rocks may vary from layer to layer during deformation the layers are assumed to flow according to a power law with stress exponent n of 1 newtonian flow 3 or 5 which is in accordance with current experimental data for flow in rocks the theoretical analysis concentrates first on incompressible plane flow and is then extended to some forms of incompressible three dimensional flow strain rate variations from competent to incompetent layers are illustrated for two dimensional flows on rheology graphs of log stress vs log strain rate three types of bulk multilayer deformation are illustrated layer parallel pure shearing lpps layer parallel simple shearing lpss and layer oblique straining in different orientations the degree of flow partitioning varies with the bulk flow layer thicknesses and layer n values for all systems in plane two dimensional flow the greatest partitioning occurs for 45 bulk shortening lpss and is most extreme for high n values such that the strain rate is virtually zero in competent members however for three dimensional flows preliminary results suggest that the value of n may play a less significant role in flow partitioning particularly for bulk pure flattening or constrictional flows these theoretical flow variations provide some meaning to competent contrast in rocks and reveal possible links between relative competence and deformation history such flow variations in space and time may provide the driving mechanism for folding in ductile multilayered systems

the behaviour of deformable ellipsoidal particles in three dimensional slow flows implications for geological strain analysis abstract eshelby s equations governing the motion of a viscous inclusion embedded in a matrix of contrasting viscosity are solved numerically for arbitrarily shaped and arbitrarily oriented ellipsoidal particles the theory has important implications for geological strains and strain analysis specifically it predicts that particles more competent than their matrix will have deformed shapes with larger k values than equivalently shaped and oriented passive markers the effect is significant even for viscosity ratios as low as r 1 5 and increases with increase in r for general applications numerical solutions must be sought nevertheless there are useful exceptions 1 1 the two dimensional deformed shape of viscous particles can be computed graphically provided the matrix strain is irrotational pure shear and the section ellipse is a principal plane of the particle ellipsoid for sections through a three dimensional system with arbitrarily oriented particles this method and those based on sections through an elliptic cylinder is inaccurate the reliability is further diminished for simple shear 2 2 irrotational deformations in three dimensions can be computed on transformed flinn plots if the particle or average particle axial orientations are parallel with the applied flow similar diagrams may be used to make independent estimates of viscosity contrasts in polymict conglomerates

strength evolution and the development of crystallographic preferred orientation during deformation of two phase marbles abstract we conducted conventional triaxial compression and confined torsion tests on calcite rocks at 1023 k and equivalent strain rates between 10 6 and 10 3 s 1 to investigate the influence of variations in volume fraction and geometry of a second phase on the evolution of strength and cpo nominally dense two phase marbles were made by hot isostatic pressing of mixtures of calcite and amorphous carbon the carbon grains were either spheres or splinters with known size distributions were chemically inert and are nearly rigid adding 1 vol spheres caused only small changes in strength or cpo strengths were consistent with the activation of slip on f 10 1 1 the hardest system in calcite adding 10 vol splinters increased the strength at low strains and strain rates but had smaller effects at high strains or rates the cpo of rocks containing splinters were similar to those in pure samples but with reduced intensity when 10 vol spheres were added the aggregate strength under confined torsion was less than that of the pure material distinct and intense cpos developed the reduced stresses were consistent with those necessary for slip on systems weaker than f viscoplastic self consistent calculations used to model the texture evolution required slip on f 10 1 1 and c 1 2 1 0 to match the cpo of pure samples results were consistent with the inclusion of slip on r 1 2 1 0 in samples containing 10 vol spheres deformed in torsion slip activity on the harder systems was decreased the exact cause of the strength reduction in these experiments is not understood but it is possible that adding smooth spheres enhanced grain boundary sliding thereby decreasing activity on f 10 1 1 thus shape and volume fraction of second phases may be important in determining cpo and strength and it is important to consider the loading geometry

strain localization during high temperature creep of marble the effect of inclusions abstract the deformation of rocks in the earth s middle and lower crust is often localized in ductile shear zones to better understand the initiation and propagation of high temperature shear zones induced by the presence of structural and material heterogeneities we performed deformation experiments in the dislocation creep regime on carrara marble samples containing weak limestone or strong novaculite second phase inclusions the samples were mostly deformed in torsion at a bulk shear strain rate of 1 9 10 4 s 1 to bulk shear strains between 0 02 and 2 9 using a paterson type gas deformation apparatus at 900 c temperature and 400 mpa confining pressure at low strain twisted specimens with weak inclusions show minor strain hardening that is replaced by strain weakening at 0 1 0 2 peak shear stress at the imposed conditions is about 20 mpa which is 8 lower than the strength of intact samples strain progressively localized within the matrix with increasing bulk strain but decayed rapidly with increasing distance from the inclusion tip microstructural analysis shows twinning and recrystallization within this process zone with a strong crystallographic preferred orientation dominated by r and c slip in recrystallization induced weakening starts at local shear strain of about 1 in the process zone corresponding to a bulk shear strain of about 0 1 in contrast torsion of a sample containing strong inclusions deformed at similar stress as inclusion free samples but do not show localization the experiments demonstrate that the presence of weak heterogeneities initiates localized creep at local stress concentrations around the inclusion tips recrystallization induced grain size reduction may only locally promote grain boundary diffusion creep accordingly the bulk strength of the twisted aggregate is close to or slightly below the lower isostress strength bound determined from the flow strength and volume fraction of matrix and inclusions

the analysis of progressive deformation in rock analogues abstract two dimensional deformation experiments using analogue materials such as octachloropropane and camphor have proven to be a powerful tool in the investigation of microstructural development since they make it possible to observe the specimen throughout its deformation history the addition of dispersed marker particles makes it possible to trace the movement of material points during deformation from this information the flow and deformation can be interpolated for any point within the specimen at any time the geometry of the flow and deformation can then be visualized in the form of grids contour plots strain ellipses and other methods despite this apparently ideal setting for studying flow and deformation the need to use marker particles to trace material points introduces unexpected problems in the analysis we present a computer program to analyse the movement of marker particles digitization of the positions of the particles is improved by the use of video input and semi automatic digitization the use of polynomials to describe the complete path of marker particles and least squares best fit solving improves the analysis of the data

generation segregation ascent and emplacement of alleghanian plutons in the southern appalachians the carboniferous permian alleghanian orogeny in the southern appalachians produced a distinctive 45 m y long intrusive event that formed a ne trending band of dispersed composite plutons covering 10 500 km 2 of these plutons 75 are metaluminous biotite or amphibole biotite granitoids with lower crustal sources and 20 are peraluminous biotite muscovite garnet or cordierite biotite granitoids with more evolved crustal sources the remaining 5 are gabbroids intermediate rocks and possible alkaline granitoids the granitoid to gabbroid intermediate rock area ratio is 180 1 the exposed intrusive rocks were produced at a relatively slow rate of 2 km 3 linear km m y along the orogen indicating an inability of the source to produce much melt inefficient melting mechanisms or difficulty of magma segregation and ascent the absence of spatial trends in rock composition and age of emplacement the small amount but relative abundance of the granitoids and coincidence with con

mullions in the high ardenne slate belt belgium numerical model and parameter sensitivity analysis in the high ardenne slate belt belgium pre existing layer perpendicular quartz veins in psammite layers acted as mechanical boundaries due to the difference in competence between vein quartz and psammite this caused the formation of mullions during layer parallel shortening in this paper the process of mullion formation is modelled using finite element techniques a parameter sensitivity analysis of the mullion model demonstrates that the stress exponent of psammite the total horizontal shortening of the psammite layers the initial aspect ratio of the psammite segments between the veins and the competence contrast between psammite and vein quartz are the controlling parameters for the shape of the mullions our results suggest that the morphology of the mullions can be used to constrain the rheology of psammite deforming in the middle crust moreover the parameter sensitivity analysis illustrates the range of layer parallel shortening extension structures associated with layer perpendicular quartz veins that can be expected in nature e g dogbones inverted mullions and creates future perspective for the use of the model as a paleorheological gauge for these structures

the sources of energy for crustal melting and the geochemistry of heat producing elements crustal melting to produce granite magmas requires a tremendous amount of energy in principle there are three main mechanisms of heating that can extensively melt a fertile crust radiogenic heat caused by the decay of 40k 230th 235u and 238u increased subcrustal heat flux caused by the upwelling of deeper therefore hotter mantle materials advection of heat caused by the emplacement and crystallization of hot mantle magmas two dimensional finite elements modeling reveals that a fertile crust thickened to 65 70 km would produce copious granite magmatism after 30 40 m y if its average heat production is a 1 2 w m 3 but it would scarcely melt if a 0 65 w m 3 increasing the subcrustal heat flow from the normal value of qm 0 025 w m 2 to qm 0 04 w m 2 may also lead to extensive crustal melting especially if the crust does not thin to less than 30 35 km very high qm 0 06 w m 2 affecting the continental crust is unlikely but the combination of moderately high qm 0 04 w m 2 and a thick fertile crust with a 1 2 w m 3 such as often happens in the volcanic and back arc areas of subduction zones is ideal to produce copious granite magmatism lastly the emplacement of hot mantle magmas in a fertile crust can produce crustal melts in just a few thousand years but the volume of these is equal to or less than the volume of the intruding magma a clue for understanding the relative importance of each of these three mechanisms comes from the radiogenic heat production of granite rocks calculated from the concentration of 40k 230th 235u and 238u at the time of their formation this parameter estimated on more than 3400 granites samples of different ages and provenance reveals a strongly asymmetric distribution peaking around 2 4 w m 3 a value much higher than the average continental crust about 1 1 2 w m 3 and certainly much higher than the average lower continental crust about 0 4 0 8 w m 3 only those granite rock types that are clearly connected with mantle heat sources such as the archean ttg post archean subduction related trondhjemites and recent adakites have a heat production equal to or smaller than the lower continental crust since the bulk melt solid partition coefficient of the heat producing elements hpe k th and u is k 1 the elevated hpe contents of granites indicates that most of them have been derived from hpe rich sources we conclude that radiogenic heating is often essential and always advantageous for generating large volumes of granite magmas and that granite magmatism is the main cause of the accumulation of hpe in the upper crust

apparent stress scaling for tectonic and induced seismicity model and observations abstract a macroscopic model of seismic sources provides a scaling relationship for the apparent stress treated as a function of three independent parameters seismic moment rupture area size and average slip acceleration these parameters represent three different factors kinematic geometric and material this relationship allows us to distinguish and explain the following statistical characteristics of the log apparent stress versus log seismic moment plot the regional trends represented by a series of 1 2 slope lines are related to the averaged shape of slip velocity pulses so they reflect kinematic characteristics of the rupture process the global trend represented by the 1 6 slope line is expected to characterize sets of events of wide range of rupture area sizes and assumes dependence of rupture area size on total slip so it is related to the rupture initiation propagation and arrest conditions therefore it reflects earthquake rupture dynamics additional shiftings among the trend lines obtained for the smallest induced tremors larger tectonic earthquakes and slow tsunami earthquakes reflect differences between the intact rock failure and the frictional slip failure that is between fracture energies of these different earthquake classes

flow laws of multiphase rocks calculated from experimental data on the constituent phases abstract an attempt has been made to develop expressions for the flow laws of polyphase rocks in terms of the volume fractions and flow laws of their constituent phases the flow strengths predicted by the proposed model for granite diorite diabase and lherzolite are in good agreement with previously determined experimental values the study allows one to calculate to the first approximation the flow laws of a large number of rocks at geologic conditions based on the experimentally determined flow laws of a relatively small number of monomineralic aggregates

alleghanian deformation and metamorphism in the eastern north carolina piedmont rb sr isotopic data document alleghanian ages for the metamorphic event which formed the upper greenschist to amphibolite grade raleigh belt and for the d 3 deformational event which formed regional scale folds and mylonite zones in the eastern north carolina piedmont the butterwood creek granite which straddles the eastern boundary between the raleigh belt and the eastern slate belt has a whole rock isochron age of 292 31 ma biotite ages indicate that the eastern undeformed part of the pluton cooled rapidly after intrusion whereas a younger biotite age of 251 ma indicates slow cooling for the western foliated portion of the granite which lies in the raleigh belt other biotite ages within the raleigh belt range from 247 238 ma the thermal maximum for the raleigh belt probably accompanied the intrusion of numerous granitic plutons during the time 315 to 285 ma the biotite ages indicate that the raleigh belt remained at elevated temperatures and did not cool to the blocking temperature of biotite until 250 240 ma rapid cooling of the eastern part of the butterwood creek helps define the eastern boundary of the alleghanian thermal event which corresponds to the eastern limit of the high grade rocks of the raleigh belt the s 3 tectonic biotite foliation in the western part of the butterwood creek and in other alleghanian plutons of the raleigh belt associated regional f 3 folds and the d 3 hollister mylonite zone which cuts the butterwood creek pluton formed between the time of intrusion of the butterwood creek at 292 ma and regional cooling by 250 240 ma this study further defines the narrow alleghanian thermotectonic belt along the eastern piedmont which is known as the raleigh belt in virginia and north carolina and reappears as the kiokee belt in south carolina and georgia

geochemical and ndsrpb isotopic composition of alleghanian granites of the southern appalachians origin tectonic setting and source characterization abstract we report major element trace element and nd and sr isotopic ratios for 35 samples of late mississippian early permian alleghanian granites that intrude the carolina terrane eastern slate belt inner piedmont and kiokee belt of the southern appalachians major element compositions indicate that most plutons are high potassium k 2 o 4 metaluminous granites initial e nd depleted mantle model ages and initial 87 sr 86 sr ratios respectively of the plutons range from 8 2 to 3 4 940 1020 ma and 0 70642 0 72798 for the inner piedmont 2 3 to 2 0 660 1130 ma and 0 70421 0 71035 for the kiokee belt 2 7 to 2 4 660 870 ma and 0 70353 0 70816 for the eastern slate belt and 6 7 to 1 9 690 1140 ma and 0 70391 0 70739 for the carolina terrane the chemical and isotopic data are most consistent with formation of the granites by anatexis of continental crust rather than derivation from a depleted mantle source rocks of the carolina terrane have e nd 300 ma values and pb isotopic ratios indistinguishable from those of most alleghanian granites suggesting it is a likely source some alleghanian granites within the carolina terrane require a more evolved source than exposed carolina terrane rocks suggesting that evolved crust possibly grenville basement occurs structurally below or within the terrane the chemical and isotopic compositions of granites intruding the kiokee belt eastern slate belt and carolina terrane are similar suggesting that these terranes are geochemically similar in contrast alleghanian granites within the inner piedmont have higher initial 87 sr 86 sr and lower 143 nd 144 nd ratios indicating that their sources are isotopically more evolved the virtual absence of alleghanian plutons with mafic intermediate compositions and the lack of geographic trends in chemical and isotopic composition across the orogen makes a subduction origin for the granites unlikely the consistency of the geochemical data with a crustal anatectic origin of the granites together with the observation that they intruded synchronously with alleghanian thrusting in the valley and ridge province suggests strongly that they are collisional in origin the crustal heating events that produced the granites might have been caused by delamination of mantle lithosphere during collision of laurentia with gondwana 1 2 alternatively adequate heating may have occurred by crustal thickening during emplacement of thrust sheets 3

the robustness of seismic moment and magnitudes estimated using spectral analysis we present an assessment of how microseismic moment magnitude mw e stimates vary with the method and parameters used to calculate seismic moment this is an important topic for operators and regulators who require good magnitude estimates when monitoring induced seismicity it is therefore imperative that these parties know and understand what errors exist in given magnitude values something that is poorly reported this study concentrates on spectral analysis techniques and compares mw computed in the time and frequency domains using recordings of mw 1 5e vents at cotton valley east texas the maximum discrepancy between mw estimated using the different methods is 0 6 units a significant variation by adjusting parameters in the mw calculation we find that the radiation pattern correction term can have the most significant effect on m w generally up to 0 8 units following this investigation we make a series of recommendations for estimating microseismic m w using spectral methods noise should be estimated and removed from recordings and an attenuation correction should be applied the spectral level can be measured by spectral fitting or taken from the low frequency level significant factors in obtaining reliable microseismic mw estimates include using at least four receivers recording at 1000 hz and making radiation pattern corrections based on focal mechanism solutions not average values

genesis of granitoid batholiths of peninsular malaysia and implications for models of crustal evolution evidence from a ndsr isotopic and upb zircon study nd sr and u pb isotopic data for the late triassic west coast province batholiths and permian to triassic east coast province batholiths of peninsular malaysia allow estimates of the ages of the crustal fragments comprising the peninsula to be made initial nd and sr values for granitoids from the west coast province range from 6 to 10 and 160 0 716 to 660 0 751 respectively nd model ages calculated based on a depleted mantle evolution model tdmnd range from 1300 ma to 1800 ma and are in general agreement with the mid proterozoic upper intersection ages of u pb zircon reverse discordia 1500 1700 ma initial nd and sr values for granitoids from the east coast province range from 0 8 to 6 and 10 0 705 to 130 0 714 respectively calculated tdmnd ages of 900 1400 ma for these granitoids are comparable to two u pb zircon reverse discordia intercepts that yield 800 ma and 1350 ma the general agreement of u pb zircon inheritance ages and tdmnd ages are interpreted to correspond to the proterozoic crust formation ages of the continental fragments represented by the west coast and east coast batholithic provinces mid proterozoic 1300 1900 ma crust formation ages are commonly shown by other phanerozoic continental margin plutonic and volcanic belts the ubiquitous mid proterozoic crust formation ages and the absence of archaean signatures suggest voluminous juvenile additions to the continental crust in the mid proterozoic such ages at continental margins would imply that many continental blocks had achieved very much their present day extent by the mid proterozoic

tectonics of the southern and central appalachian internides the appalachian orogen was constructed along the ancient precambrian continental margin of eastern north america by a series of compressional events that began in the ordovician and episodically spanned much of the paleozoic era the processes of accretion of suspect and exotic terranes together with terrane collision and ultimately completion of the wilson cycle by continent continent collision resulted in construction of the appalachian orogen figure 1 these paleogeographic elements are rep resented by the various lithotectonic units visible today in the southern and central appalachians figure 2 these subdivisions represent the late precambrian rifted margin and early paleozoic platform that were formed directly upon north american grenvillian basement cumberland allegheny plateau valley and ridge and western blue ridge the offshore north american slope rise assemblage hamburg klippe southern appalachian eastern blue ridge and inner piedmont and higher thrust sheets of the maryland northern virginia piedmont and the exotic carolina or avalon and wilmington terranes the carolina ter rane contains the alleghanian high grade metamorphic core these elements form the basis for this analysis and review of the present state of knowledge of the tectonic history of the southern and central appalachian internides the appalachian orogen has been the subject of study by geologists at least since the early nineteenth century early fundamental concepts such as the geosynclinal theory of mountain building dana 1873 hall 1883

rheology of synthetic anorthite diopside aggregates implications for ductile shear zones 1 we investigated the high temperature creep strength of fine grained anorthite diopside rocks at temperatures ranging from 1323 k to 1523 k and at 300 mpa confining pressure in a paterson type gas medium deformation apparatus flow stress varied between 20 and 450 mpa resulting in strain rates between 6 1 10 7 s 1 and 7 5 10 4 s 1 pure diopside and anorthite samples were hot pressed from crushed natural single crystals and glass powders respectively two phase samples were produced by hot isostatic pressing of mechanically mixed powders of anorthite glass with 25 50 and 75 vol diopside particles arithmetic mean grain size of the anorthite matrix is dan 3 5 m three different ranges of diopside particle size were used ddi 25 m 35 m and 45 m water content of as is samples was about 0 05 0 02 wt h2o and predried samples contain about 0 004 0 001 wt h2o at experimental conditions as is samples are assumed to be water saturated water content of predried samples is about 3 times less than that of starting diopside single crystals the specimens contain about 1 vol glass located at fluid inclusions and some multiple grain junctions two grain boundaries examined by high resolution transmission electron microscopy did not show amorphous layers to a resolution of 1 nm at experimental conditions pure diopside aggregates are about 2 3 orders of magnitude stronger than pure anorthite samples for as is and predried specimens respectively in general strength of the two phase aggregates increases with increasing diopside content but remains between isostress and isostrain rate bounds aggregate strengths predicted from continuum mechanics models are in good agreement with the experimental data for dilute diopside particle mixtures and high volume fractions when diopside particles form a load bearing framework at low stresses 100 200 mpa the stress exponent is n 1 suggesting diffusion controlled creep at higher stresses mechanical data and microstructures suggest that samples deformed in the transition region between diffusion controlled creep and dislocation creep for pure anorthite and diopside aggregates deforming in dislocation creep we estimated stress exponents of n 3 and n 5 5 respectively for the two phase aggregates n is between n 3 and n 5 depending on diopside content at low stresses deformation microstructures indicate load transfer from a weak anorthite matrix to stronger diopside particles creep activation energies for pure diopside and anorthite mixtures range from 286 kj mol 1 for wet anorthite deformed at low stresses to 691 kj mol 1 for dry diopside deformed at high stresses activation energies of two phase mixtures are between or close to those of the end members as is samples have significantly lower activation energies than predried samples

flow laws of multiphase materials and rocks from end member flow laws abstract rheological properties of polyphase rocks play an important role in the dynamics of the lithosphere and asthenosphere however flow laws for large portions of the polyphase rocks in the earth s crust and mantle have not been well determined an analysis based on the theory of mixtures has been made to calculate the general flow laws of coarse 5 m nearly equant grained aspect ratio 3 and massive polyphase rocks and materials for which only the flow laws and volume fractions of the constituents are taken into consideration in the modeling of the bulk rheology and effects of microstructure could be ignored the theoretical analysis is based on three assumptions 1 the polyphase composite and the monophase aggregates of its constituents obey the same kind of flow laws linear power or exponential 2 there is no change in the operative deformation mechanism of each phase when it is in the composite as compared to when it is in a monophase aggregate and 3 neither chemical metamorphic reactions take place among the constituent phases nor eutectic melting occurs due to the phase mixing the proposed iterative process allows to predict to the first approximation the flow laws for a large number of polyphase rocks in terms of the experimentally determined flow laws of a relatively small number of monomineralic aggregates applications of this approach to typical polyphase rocks such as granite diorite diabase aplite and websterite as well as to synthetic two phase materials such as forsterite enstatite mixtures and water ice ammonia dehydrate aggregates yield quite accurate approximations to the experimental values

non steady homogeneous deformations computational techniques using lie theory and application to ellipsoidal markers in naturally deformed rocks abstract the dynamic theory of deformable ellipsoidal inclusions in slow viscous flows was worked out by j d eshelby in the 1950s and further developed and applied by various authors we describe three approaches to computing eshelby s ellipsoid dynamics and other homogeneous deformations the most sophisticated of our methods uses differential geometric techniques on lie groups this lie group method is faster and more precise than earlier methods and perfectly preserves certain geometric properties of the ellipsoids including volume we apply our method to the analysis of naturally deformed clasts from the gem lake shear zone in the sierra nevada mountains of california usa this application demonstrates how given three dimensional strain data we can solve simultaneously for best fit bulk kinematics of the shear zone as well as relative viscosities of clasts and matrix rocks

anisotropic viscosity of a dispersion of aligned elliptical cylindrical clasts in viscous matrix abstract self consistent averaging using an auxiliary solution for an elliptical anisotropic viscous inclusion in an anisotropic viscous host provides estimates of the principal bulk viscosities of a dispersion of aligned elliptical viscous clasts in an isotropic or anisotropic viscous matrix analysis and results are for a two dimensional analog of a composite rock with clasts that are cylinders with axes normal to the plane of flow the ratio of principal viscosities n in clast parallel extension or shortening s in clast parallel shear m n s is smaller than that obtained using an auxiliary solution in which the host is isotropic results for the limiting case of rigid clasts indicates that the latter procedure overestimates the stress concentration in axis parallel extension or shortening at intermediate clast volume fraction f if the matrix is anisotropic bulk anisotropy derives from both the shape anisotropy and the intrinsic anisotropy of the matrix and unsymmetrical relations for the principal viscosities and m f result the results suggest that rheological anisotropy in rocks with a planar fabric is greatly reduced if the components are lenticular in form rather than continuous layers a general solution is given for an elliptical inclusion for the case that the principal axes of anisotropy in both the host and the inclusion are oblique to the axes of the elliptical section and the host is subjected to homogeneous stress far from the inclusion

nd and sr isotopic constraints on the source of alleghanian granites in the raleigh metamorphic belt and eastern slate belt southern appalachians u s a abstract pennsylvanian permian granites that intrude the raleigh metamorphic belt and the eastern slate belt of the southern appalachian orogen account for 40 of the total volume of granite produced during the alleghanian orogeny we report major and trace element concentrations and initial nd and sr isotopic compositions from 31 samples of allegahanian granites that intrude these belts to further constrain the nature of the sources of the granites nd isotopic compositions of three raleigh metamorphic belt orthogneisses and two eastern slate belt metavolcanic rocks are also presented to further constrain the nature of the crust in this region of the orogen major and trace element concentrations of raleigh metamorphic belt and eastern slate belt alleghanian granites are similar for every element examined major element concentrations of the alleghanian granites indicate that they are high k 2 o 3 5 wt slightly peraluminous al 2 o 3 cao na 2 o k 2 o 0 96 1 12 trace element compositions of the alleghanian granites are similar to those of granites produced in both volcanic arc and continental collision settings initial nd isotopic compositions of raleigh metamorphic belt granites range from e nd 300 ma 4 4 to 3 0 and initial 87 sr 86 sr ratios from 0 703 to 0 708 eastern slate belt granites have nd 300ma between 2 7 and 2 2 and initial 87 sr 86 sr ratios range between 0 703 and 0 706 depleted mantle model ages of granites from both belts range from 600 to 1070 ma gneisses from the raleigh metamorphic belt and volcanic rocks of the eastern slate belt have e nd 300 ma values of 4 4 to 4 4 similar to those of the alleghanian granites suggesting that anatexis of the crust in these belts could have produced the granites the neodymium isotopic compositions of the gneisses from the raleigh metamorphic belt are significantly more radiogenic than that of grenville crust the granites that intrude the raleigh metamorphic belt also show no evidence of interaction with grenvillian crust suggesting that neither the surface rocks nor unexposed portions of the raleigh metamorphic belt are predominantly composed of grenville crust thus in contrast to previous suggestions the raleigh metamorphic belt is significantly different than the adjoining goochland terrane but is similar to the nearby carolina terrane

oxygen isotopic compositions of the late orogenic granites in the southern piedmont of the appalachian mountains u s a and their relationship to subcrustal structures and lithologies abstract data were acquired from 143 whole rock samples from 20 late orogenic post metamorphic hercynian age granitic plutons from the piedmont of the southern appalachians principally in georgia and south carolina these plutons exhibit a regional gradient in oxygen isotopic compositions in which the granites confined to the inner piedmont to the northwest are 18 o enriched 11 4 to 7 9 whereas those toward the southeast within the charlotte slate and portions of the kiokee belts have distinctly lower 18 o 16 o compositions 8 2 to 5 5 one body that lies along the southeastern edge of the piedmont in south carolina however appears to be anomalously 18 o enriched 8 9 most plutons display 18 o 16 o variations of 18 o enriched plutons occupy areas characterized by negative anomalies whereas low 18 o bodies are invariably restricted to regions of positive anomalies 2 87 sr 86 sr data where granites with 18 o values 18 o enriched plutons 9 have ratios 0 710 3 contrasting chemical and accessory mineral compositions in which many 18 o depleted granites have a number of i type characteristics whereas several of the most 18 o enriched plutons exhibit a number of s type features it can be inferred from these data that the 18 o enriched granites were formed from continental crustal protoliths that underlie much of the inner piedmont and portions of the kiokee belt whereas the low 18 o plutons were derived from more mafic sources beneath the charlotte slate and portions of the kiokee belt the overall correspondence between the regional 18 o 16 o patterns exhibited by the granites and gravity data implies that these grantes may be essentially rooted to their protoliths in turn suggesting that the large scale translational movement recently proposed for the southern piedmont may have occurred prior to intrusion of these granites 320 m y ago

high pressure deformation in two phase aggregates abstract we investigate the rheological behavior of multi phase aggregates at high pressure and high temperature using synchrotron x ray radiation as the probing tool we are able to quantify the stress state of individual phases within the aggregates this method provides fundamental information in interpreting the behavior of two phase multi phase mixtures which contribute to our understanding of the deformation process at deep earth conditions we choose mgal2o4 spinel and mgo periclase as our model materials mixtures of various volume proportions were deformed in a multi anvil high pressure deformation apparatus at pressure of 5 gpa and elevated temperatures stress is determined from x ray diffraction providing a measure of stress in each individual phase of the mixture in situ during the deformation macroscopic strain is determined from x ray imaging we compare the steady state strength of various mixtures at 1000 c and 800 c and at the strain rate in the range of 1 8 to 8 8 10 5 s 1 our data indicate that the weak phase mgo is responsible for most of the accumulated strains while the strong phase spinel is supporting most of the stress when the volume proportion is 75 spinel and 25 mgo the intermediate compositions 40 60 are much weaker than either of the end members while the grain sizes for the intermediate compositions submicrons are much smaller than the end members 5 10 m we conclude that a change in flow mechanism resulting from these smaller grains is responsible for the low strength of the intermediate composition mixtures this study demonstrates an approach of using synchrotron x rays to study the deformation behaviors of multi phase aggregates at high pressure and high temperature

mineral fish their morphological classification usefulness as shear sense indicators and genesis mineral fish are sheared and commonly asymmetric mineral grains or clusters of grains this work reports 11 sub types of mineral fish showing a top to se sense of ductile shearing in the karakoram metamorphic complex kmc the mineral fish are of three broad geometries sigmoid lenticular and parallelogram reliable senses of shear are indicated by the overall asymmetry and inclination of mineral fish on the other hand the true shear sense is not always indicated by either the orientations of their cleavage planes or those of the individual grains in composite mineral fish the ranges of local orientations of single sigmoid mineral fish that include the lower values 23 in the kmc indicate their extensive ductile shearing the studied mineral fish were products of a range of deformation mechanisms including homogeneous deformation simple shear intra granular slip crystal plastic deformation fracturing and synthetic shearing additionally some examples might have undergone duplex slips and a few nucleated and grew either prior to or during the top to se shearing

numerical simulations of magmatic enclave deformation abstract present in both plutonic and volcanic rocks enclaves are inclusions of magma into a compositionally distinct magmatic host classical relationships between their shapes and the dynamical conditions that prevailed during their formation have been drawn from fluid fluid analogies and from solid rock mechanics magmas however are hydrogranular suspensions with a rheology distinct from these two end members this work presents results from computational fluid dynamics with discrete element modeling cfd dem aimed at deforming crystal rich enclaves in pure shear the cfd dem approach explicitly resolves solid solid interactions such as contact and friction while taking into account fluid coupling the first series of deformation involved only pure fluids to validate the setup the second series comprised seven runs aimed at reproducing magmatic conditions enclaves were made of a cylindrical suspension of particles embedded into a host with different characteristics in both media particles and fluids had densities viscosities elastic characteristics and sizes tailored to the geological constraints of the adamello batholith italy each run corresponds to a temperature along the two respective crystallization paths and span crystal contents from 10 to 62 vol results show that to first order deformation does not depend on differences in melt viscosities crystal contents or bulk viscosity contrast this is due to the formation of force chains parallel to the main compression direction which transmits stress across the enclave a simple first order relationship could be fitted to our data to relate shear and enclave deformation which we applied to the case of the adamello pluton there is a second order dependence of deformation on the onset of particles contacts and force chains which are both related to particle concentration the main control of these second order effects is the host crystal content enclave particles pack early quickly erasing differences in initial content and building force chains parallel to the compression axis that transmit stresses to the host whether the host is able to transmit those stresses across its own volume is controlled by host crystal content

high resolution mechanics of a microearthquake sequence unique data from microseismic ms and acoustic emission ae systems monitoring a common rock volume have been analyzed from the underground research laboratory in canada the two 16 sensor systems were installed to investigate stress induced microcracking around clay and concrete bulkheads as part of the tunnel sealing experiment single and double ms events are found to be spatially associated with clusters of between 19 86 higher frequency ae events each ae cluster is elongated with the longest axis between 15 and 50 cm the ae events occurring before the associated ms event are termed foreshocks and for two of the three analyzed ae clusters an acceleration in the ae frequency and cumulative magnitude occurs upto the time of the ms event however with one ae cluster very few foreshocks are recorded possibly indicating a more homogeneous failure plane time independent moment tensors were determined with the ms events showing significant deviatoric sources the majority of the ae events have deviatoric mechanisms with a few crack opening and crack closure type events also determined this study highlights the benefits of using small scale seismic systems to investigate the temporal fracture mechanics of microcrack formation and allows comparisons with larger more damaging seismicity

viscous anisotropy of two phase composites and applications to rocks and structures abstract anisotropy of viscosity in rocks has a significant effect on the development of geological structures as demonstrated in several theoretical and analogue model studies this paper develops the results of a self consistent mechanics approach to modelling the bulk viscous properties of two phase composites to reveal the strength of the viscous anisotropy anisotropy factor is defined as the ratio of normal to shear viscosity n s the value of is determined for different types of composites of two viscous phases with varying viscosity ratio m 5 10 100 ranging from bilaminates to those with elliptical shape fabrics given by axial ratio r bilaminates with equal layer thickness are the most highly anisotropic systems where simply depends on m these results are applied to rocks modelled as two phase composites of competent and incompetent lithologies with the aim of quantifying the viscous anisotropy that is associated with natural rock deformation and the formation of geological structures it is deduced that m 5 or 10 is an appropriate maximum viscosity contrast for many metasedimentary rocks e g psammite pelite composites but that m 100 might be effectively reached in limestone marl pairs or in rocks containing surfaces of slip or zones of recrystallisation or grain boundary sliding these m values give rise to maximum values of 3 5 5 and 25 5 respectively an anisotropy factor of 25 is effectively a composite of a rigid and a viscous phase and may only be achieved in solid melt mixtures anisotropic rocks whether layered or containing a strong shape fabric will develop folds more easily than isotropic rocks characteristic structures are similar folds chevron folds kink bands and shear bands geometric features of folds especially fold angularity may provide methods of quantifying the viscous anisotropy of rocks and composites

analysis of the cleburne texas earthquake sequence from june 2009 to june 2010 on 9 june 2009 an graphic 1 2 8 earthquake shook cleburne texas a community not known to have previously experienced earthquakes over 50 small earthquakes followed by the end of december 2009 a temporary network of four and then five iris passcal broadband systems was deployed from june 2009 to june 2010 recording data that were used to locate 38 events with the most confident p and s arrival picks event locations were distributed along a 2 km long north northeast trend the location centroid was at 32 298 n 97 372 w and at 3 6 km depth this location is approximately 1 3 km from a saltwater disposal well that began injection in october 2007 and 3 2 km away from a second injection well that was active from september 2005 to late july 2009 focal mechanisms estimated for the best recorded events suggest a north northeast south southwest trending normal fault with a dip of 50 and a component of oblique motion rake of 80 this average solution is generally consistent with the north northeast trending extensional faults that are prevalent across parts of texas oklahoma louisiana and arkansas stress drops calculated from p and s spectra for seven different events ranged from 3 9 to 90 bars with most estimates between 40 and 50 bars typical values for intraplate earthquakes because there were no known previous earthquakes and the located events were close to the two injection wells and near the injection depth the possibility exists that earthquakes may be related to fluid injection online material tables of absolute and relative earthquake locations and a figure summarizing focal mechanism solutions 1 embed inline graphic 1 gif

extensional detachment at the inclusion matrix interface in a multiple inclusion system abstract this paper deals with a theoretical analysis of extensional fissures around spherical rigid inclusions hosted in a ductile matrix undergoing bulk shear the analysis shows that the mechanical interaction of inclusions is a function of the inclusion concentration a b 2 a and 2 b are the inclusion diameter and mean inter inclusion distance respectively and intensifies the tensile stress imparted by the flowing matrix on the inclusion matrix interface inclusion concentration a b thus appears to be a crucial parameter in perturbing the inclusion matrix coherence and leading to formation of extensional fissures around an inclusion we performed numerical simulations to delineate the fields for coherent and incoherent interfaces in the t o a b space where t o is the tensile strength of the interface normalized to where and are the viscosity of matrix and bulk shear rate respectively for a given a b the interface cannot remain coherent unless the tensile strength is greater than a critical value the critical t o increases almost linearly at a gentle gradient with increasing a b however for a b 0 7 this increases nonlinearly assuming a large value when the concentration is high a b 0 8 it is also revealed that under the same deformation conditions the instantaneous opening in fissures may vary depending upon the a b values

rheology of fine grained siliciclastic rocks in the middle crust evidence from structural and numerical analysis constitutive models to describe the rheology of the crust are based on a combination of indirect methods and many aspects are still unknown and controversial here we present a new method to quantify the rheology of fine grained siliciclastic rocks which are common in the middle crust and deform by solution precipitation processes we use a combination of structural analysis at different scales and a geomechanical model to develop a parameter estimation scheme to calculate rheological parameters at 350 400 8c and geologic strain rates the results of this study demonstrate that fine grained siliciclastic rocks in the middle crust have a newtonian viscous rheology approximately 10 times weaker than wet quartz this is in agreement with observed microstructures our results imply that the strength of polyphase quartz rich rocks located in the middle crust is much lower than predicted by conventional models based on flow laws for dislocation creep because fine grained siliciclastic rocks control the rheology of the middle crust in many sedimentary basins our results provide new quantitative parameters for geodynamic modelling in settings where dissolution precipitation creep is important d 2005 elsevier b v all rights reserved

rheological and kinematical responses to flow of two phase rocks abstract numerical simulations have been performed to investigate the strain dependent behaviour of rheological and kinematical responses to flow of two phase rocks using the commercial finite difference program flac2d it was assumed that the two phases have maxwell rheology plane strain and velocity boundary condition which produces a simple shear deformation were also assumed two types of geometries were considered strong phase supported sps and weak phase supported wps we calculated strain dependent variations of effective viscosity and partitioning of strain rate vorticity and kinematic vorticity number during deformation in both sps and wps structure models the results show that the strain dependent behaviour is largely influenced by the geometry of the composite sps models show both strain hardening and strain softening during the simulations with strain hardening preceding strain softening a critical shear strain is necessary to begin the strain softening behaviour strain hardening and strain softening are accompanied by a reduction and an increase of the partition of strain rate into the weak phase respectively on the other hand wps models show only weak strain hardening and strain softening being the strain dependent behaviour close to a steady state flow in addition the following results are obtained on vorticity and kinematic vorticity number 1 in both sps and wps models the partition of vorticity into weak phase increases with progressive shear strain i e the strong phase becomes less rotational 2 in sps models weak inclusions changes from sub simple shear to super simple shear with progressive strain whereas the strong matrix changes from super simple shear to sub simple shear 3 in wps models the strong inclusions with high viscosity contrasts are less rotational but can be in super simple shear condition to high strains the observed strain dependent behaviours have been compared with previous proposed analytical models the degree of agreement is variable balshin and ryshkewitch duckworth models are only applicable to sps models ji generalized mixture rule model is applicable to both models the results suggest that polyphase rocks with sps structure during ductile shear deformation respond as strain softening materials after an initial strain hardening stage that may drive to the strain localization into the material

structural geology meets micromechanics a self consistent model for the multiscale deformation and fabric development in earth s ductile lithosphere abstract earth s lithosphere is made of rheologically heterogeneous elements of a wide range of characteristic lengths a micromechanics based self consistent multiorder power law approach is presented to account for lithospheric deformations and the accompanying multiscale fabric development the approach is principally based on the extended eshelby theory for the motion of a power law viscous ellipsoid in a power law viscous matrix and the idea of embedding inhomogeneities within inhomogeneities the extended theory provides a general means for investigating deformation partitioning in heterogeneous rocks the inhomogeneities within inhomogeneities method allows multi hierarchical levels of flow field partitioning and hence multiscale deformations to be investigated partitioned flow fields are used to investigate fabric development being based fully on micromechanics the approach generates model predictions of both kinematic quantities strain strain rates and vorticity and stress histories the former can be directly compared with field and laboratory structural observations while the latter can help to understand the physics of natural deformations the self consistent and multiscale approach is applied to a natural example of the cascade lake shear zone in the east sierra nevada of california the modeling shows that the fabrics are most consistent with a steeply dipping transpression zone with a convergence angle of 20 and a strike slip displacement about 26 km further the strength evolution of the model zone confirms that a transpression zone is a weakening system with respect to the simple shearing component and a hardening one for the pure shearing component this is consistent with slip partitioning in obliquely convergent plate boundaries boundary normal convergence tends to spread over a broad area whereas boundary parallel shear tends to localize in major strike slip zones

a tale of two viscosities abstract we describe a series of 12 large strain two dimensional simple shear numerical experiments on two phase linear and non linear viscous materials the modal percentage of the two phases their relative viscosities and the stress exponent of the dependence of viscosity on stress were systematically varied allowing us to observe the effects of these parameters on the flow behaviour of the system all experiments exhibited localisation but the extent and type of localisation varied considerably and the range of parameters allows both classical sc as well as sc structures to form the inter granular finite strain geometries also varied systematically although there is a tradeoff between non linearity of viscosity and the viscosity contrast that results in similar geometries for quite different mechanical behaviour the finite rotation of the harder phases was similar within any one experiment originally parallel passive marker lines thus remain sub parallel after deformation and rotation which may be mistaken for non rotation the internal deformability and interaction between grains allows meta stable grain elongation orientations to form without any additional consideration of external slip surfaces the slight variability of initial grain geometry and subsequent grain interactions leads to a wide variability in final grain shapes for the same initial viscosities

studies of strain and rheology of conglomerates abstract conglomerates can show significant strain variations among their component rock types previous studies have exploited this feature as a method of quantifying the effective viscosity ratios among different rock types using inclusion matrix models that we review here we further investigate the rheology of conglomerates via models of multiphase mixtures of spherical clasts with varying phase fractions using idealised models with two to four phases we can quantify the influence of phase viscosities and volume fractions on the bulk viscosity and reveal how this controls the strain partitioning among the different phases we consider practical methods of analysing conglomerates and choose r f analysis for measuring clast strain and fry analysis for whole rock strain the methods are illustrated through case studies of two very different conglomerates the port askaig tillite scotland and cesson conglomerate brittany we define the important rock phases in each and assess their strain variations although providing strain measurements of regional interest our main purpose is to quantify the viscosity ratios among the component rocks we find that among the most common rock types semipelite quartzite psammite volcanics granite the viscosity ratios span about one order of magnitude agreeing with previous studies these small numerical values for viscosity ratios among many rock types in many conglomerates lead us to conclude that these rocks each deformed at approximately constant viscosity i e as linearly viscous rather than according to a power law

u pb geochronologic nd isotopic and geochemical evidence for the correlation of the chopawamsic and milton terranes piedmont zone southern appalachian orogen abstract we report u pb crystallization ages from four metavolcanic rocks and two granitic gneiss samples as well as whole rock chemical analyses and sm nd isotopic ratios from 25 metaigneous and metasedimentary rocks from the chopawamsic and milton terranes southern appalachian orogen a metarhyolite sample from the chopawamsic formation and a metabasalt sample from the ta river formation in the chopawamsic terrane have indistinguishable u pb crystallization ages of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 471 4 pm 1 3

source parameters of picoseismicity recorded at mponeng deep gold mine south africa implications for scaling relations abstract we investigate the source parameters of picoseismic and nanoseismic events m w 4 1 recorded with a high sensitivity seismic network at the mponeng gold mine in south africa to gain new insights into the scaling of small seismic events the japanese german underground acoustic emission research in south africa jaguars network composed of one three component 3c accelerometer sensitivity 50 hz to 25 khz and 8 acoustic emission ae sensors sensitivity 1 khz to 180 khz is located at a depth of 3268 m and covers the limited volume of approximately 300 300 300 m the ae sensors are calibrated with respect to the 3c accelerometer in the frequency band 400 hz 17 khz the waveform data of two datasets are analyzed 1 the aftershock sequence of an m w 1 9 event that occurred approximately 30 m from our network and 2 the postblasting activity recorded during working days located at a distance 90 m from the network at the exploitation level for the analysis we applied spectral fitting and spectral ratio methods the calculated values of m w range from 0 8 down to 4 1 with corner frequencies 0 8 khz 13 6 khz source sizes from 8 cm to 1 3 m we observe static stress drops ranging from 1 mpa to 10 0 mpa with apparent stresses of 0 01 mpa 1 00 mpa stress drops are independent of the moment suggesting self similar behavior in the analyzed magnitude range 4 1 m w

age and origin of anorthosites charnockites and granulites in the central virginia blue ridge nd and sr isotopic evidence rb sr isotopic data for anorthosites charnockites ferrodioritic to quartz monzonitic plutons and high grade gneisses of the blue ridge of central virginia show evidence of post emplacement metamorphism but in some cases retain grenville ages the pedlar river charnockite suite yields an isochron age of 1021 36 ma initial 87sr 86sr ratio of 0 7047 6 which agrees with published u pb zircon ages five samples of that unit which contain paleozoic mylonitic fabrics define a regression line of 683 ma interpreted as a mixing line with no age significance samples of the roseland anorthosite complex show excessive scatter on a rb sr evolution diagram probably due to paleozoic 475 m y metamorphism data from the ferrodioritic to quartz monzonitic plutons of the area yield an age of 1009 26 ma inital ratio 0 7058 4 which is in the range of the u pb zircon ages of 1000 1100 ma the stage road layered gneiss yields an age of 1147 34 ma initial ratio of 0 7047 5 sm nd data for the pedlar river charnockite suite reflect a pre grenville age of 1489 118 ma nd 6 7 1 2 data for the roseland anorthosite complex and the ferrodioritic to quartz monzonitic plutons yield grenville isochron ages of 1045 44 ma nd 1 0 0 3 and 1027 101 ma nd 1 4 1 0 respectively two roseland anorthosite samples plot far above the isochron demonstrating the effects of post emplacement disturbance of sm nd systematics while mylonitized pedlar river charnockite suite samples show no evidence of sm nd redistribution the disparity of the sm nd age and other isotopic ages for the pedlar river charnockite suite probably reflects a sm nd source age suggesting the presence of an older crust within this portion of the ca 1 ga old basement

tectonic evolution of the easternmost piedmont north carolina the northeastern north carolina piedmont is made up of a basement sequence of unknown age possibly a southern extension of the grenville age goochland terrane of eastern virginia structurally overlain by a volcanogenic sequence of probable late precambrian to early paleozoic age an eastward continuation of lithologies occurring in the carolina slate belt a model is proposed in which the basement and volcanogenic sequences are separated by a pre alleghanian taconic decollement northwestward and westward vergence of associated folds of the upper plate suggests that the volcanogenic sequence was thrust from the southeast or east over the basement terrane this deformation occurred during a greenschist grade m 1 metamorphic event alleghanian granites 313 to 285 ma intrude both the basement and volcanogenic sequences clearly cutting the inferred decollement in some areas this alleghanian plutonism was accompanied by regional heating to produce the upper greenschist to amphibolite grade m 2 assemblages of the raleigh belt the raleigh belt remained hot until late alleghanian compression produced regional scale f 3 folds and d 3 mylonite zones with the resultant uplift and cooling of this belt by 250 240 ma

strength of strained two phase mixtures application to rapid creep and stress amplification in subduction zone melange aseismic creep may occur by distributed deformation in melange shear zones comprising weak matrix and stronger clast materials slow slip events or steady tectonic displacement can be distributed over 100 m thick shear zones if weak matrix controls bulk shear zone deformation we use 2 d numerical models to quantify the rheology of moderately strained shear strain 1 75 melange for various volumetric proportions of competent clasts melange deformation with 50 clasts is matrix dominated and can accommodate steady creep at higher clast proportions melange viscosity increases more than tenfold after small strains because strong clasts interact and form force chains clast shear stress is amplified above the imposed shear stress by a factor of 14 where force chains develop slow slip events may occur due to a temporary absence of force chains while localized regions of high shear stress generate coincident fracturing and potentially tremor events

the deformational behaviour of bimineralic limestone halite aggregates abstract a compositional foliation banding develops within synthetic limestone halite aggregates experimentally deformed in axially symmetric compression and in simple shear the strength of the bulk aggregate decreases as the foliation becomes stronger foliation weakening in calcite rich specimens the development of foliation starts with the formation of cataclastic shear systems in calcite domains between isolated halite domains with increasing deformation halite is sheared into these systems the halite domains coalesce into halite rich shear systems and accommodate an increasing amount of the bulk deformation the bulk strength of bimineralic aggregates at a given amount of strain increases with decreasing halite content the influence of halite on the bulk strength is much greater than would be expected from its volume fraction and becomes dominant with increasing deformation due to the development of the foliation it is postulated that such processes also occur during natural deformation of polyphase rocks competent clasts within a weaker ductile matrix showing no recrystallization differ in shape and rotational behaviour from recrystallizing clasts such as feldspar augen these competent clasts denoted as type clasts may cause problems in deducing the sense and direction of shear when formed as almost exact mirror images of type recrystallizing clasts

comparison of fry strain ellipse and ams ellipsoid trends to tectonic fabric trends in very low strain sandstone of the appalachian fold thrust belt abstract in moderately to highly strained sandstones both the long axis of the bedding parallel finite strain ellipse as calculated by the normalized fry method and the projection of the long axis of the ams ellipsoid on the plane of bedding align well with local structural grain trends of cleavage folds and faults this relationship implies that results of both 2d fry and ams analyses represent the local layer parallel tectonic strain component do both methods provide comparable results for very low strain sandstone e g

effects of object ellipticity on strain and implications for clast matrix rocks we examine the influence of object shape on strain taking the example of an elliptical object in a matrix of different viscosity the eshelby bilby equation for the cross sectional strain of circular cylindrical objects in a matrix of different viscosity is differentiated to express the relationship of developing sectional ellipticity on incremental strain this leads to an expression for the strain of initial elliptical objects whose axes are parallel or perpendicular to pure shearing graphs show that competent elliptical objects with axial ratios of ri 3 or more will strain significantly more than circular objects of the same viscosity less if the objects are incompetent while the effect is likely to be insignificant for competent objects with initial ellipticity of 2 which is indicated from statistics for undeformed pebbles in conglomerates any clast with greater ellipticity such as ri 5 to 10 could deform significantly more than an equant clast and thus appear to be materially less competent these principles have implications for geological strain studies and for competence contrasts in rocks

pure shear deformation of square objects and applications to geological strain analysis abstract geological objects that deform differently from the rock matrix such as pebbles or other clasts are unlikely to have been originally circular or elliptical in section and must therefore be expected to deform heterogeneously and change shape irregularly we investigate this process with finite element models of pure shear deformation of square objects in three orientations square skew and diagonal in a matrix with different viscosity modelling shows that squares deform irregularly with competent objects becoming barrel shaped and fish mouthed cf boudins whereas incompetent objects become bone shaped or elongate lobes the object aspect ratios r o are less different from the bulk strain ratio r s than for equivalent circular objects in contrast diagonal squares deform almost homogeneously into rhombs with aspect ratios closer to those for circles asymmetrically oriented skew squares behave intermediately developing skew flag and hooked shapes according to competence contrasts that might be misdiagnosed as shear criteria all these square objects and circles in theory show almost linear strain paths of object versus bulk r 1 with slope related to viscosity ratio object shape and orientation linear relationships are also found for concavity convexity shape factors for squares the results have implications for strain analysis and competence contrasts in rocks

flow strength of highly hydrated mg and na sulfate hydrate salts pure and in mixtures with water ice with application to europa 1 we selected two europan ice shell candidate highly hydrated sulfate salts for a laboratory survey of ductile flow properties mgso4 7h2o epsomite and na2so4 10h2o mirabilite called ms7 and ns10 respectively polycrystalline samples in pure form and in mixtures with water ice i were tested using our cryogenic high pressure creep apparatus at temperatures 232 t 294 k confining pressures p 50 and 100 mpa and strain rates 4 10 8 7 10 5 s 1 grain size of ns10 samples was 100 m the flow strength of pure ms7 was over 100 times that of polycrystalline ice i at comparable conditions that of pure ns10 over 20 times that of ice in terms of the creep law a n e q rt where r is the gas constant we determine parameter values of a 1012 1 mpa ns 1 n 5 4 and q 128 kj mol for pure ns10 composites of ice i and ns10 of volume fraction ns10 have flow strength c ns10 ns10j 1 ns10 iceij 1 j where j 0 5 making the effect on the flow of ice with low volume fractions of ns10 much like that of virtually undeformable hard rock inclusions being much stronger and denser than ice massive sulfate inclusions in the warmer ductile layer of the europan ice shell are less likely to be entrained in convective ice flow and more likely to be drawn to the base of the ice shell by gravitational forces and eventually expelled with only smaller dispersed sulfate inclusions at probable sulfate 0 2 the shell may be treated rheologically as pure polycrystalline ice with boundary conditions perhaps influenced by the high density and low thermal conductivity of the hydrated salts

seismic estimates of stress release five seismic estimates of stress release are compared for eight multiply recorded aftershocks of the 1975 oroville california earthquake the dynamic stress drop the arms stress drop and the apparent stress provide stable estimates which are strongly correlated across the data set the uncertainties of these estimates the standard error of the mean divided by the mean are approximately 15 estimates of the brune stress drop are uncorrelated with estimates of the average static stress drop calculated from the seismic moments and the rupture geometries of the aftershocks determined from the signal durations of the recorded s waves the brune stress drops are most strongly correlated with the arms stress drops implying that the brune stress drop provides an estimate of the average dynamic stress drop as brune originally proposed

are viscosity ratios of rocks measurable from cleavage refraction abstract in this questions contribution i consider some of the accepted methods of measuring viscosity ratios in rocks and pose a new one for a wide range of strain and orientations it can be shown that the bedding normal is immeasurably close to the xy plane and this has applications to the relationship between cleavage and strain i therefore propose that with some limitations cleavage refraction can provide a measure of effective viscosity ratios in layered rocks examples show that cleavage refraction across competence contrasts yields surprisingly small viscosity ratios this method might also provide a way of distinguishing newtonian from non newtonian behaviour of rocks over time and space

the german bank pluton offshore sw nova scotia age petrology and regional significance for alleghanian plutonism permian plutonism is widespread in the u s appalachians but not in the canadian sector of the appalachians the german bank pluton sampled in two boreholes offshore southwestern nova scotia gave a u pb age of 300 1 ma determined by isotope dilution thermal ionization mass spectrometry id tims on thermally annealed and chemically etched zircon grains electron microprobe dating of monazite yielded an age of 308 13 ma late paleozoic plutonism in the canadian appalachians was dominated by northwestward subduction of the rheic ocean whereas the rheic ocean in the u s appalachians closed by southeasterly subduction a slab tear therefore developed at the southwestern margin of the rheic ocean slab beneath the canadian appalachians the high sr and ba metaluminous magnetite granite of the german bank pluton resulted from melting of underplated lower crust and or lithospheric mantle by a rising asthenospheric diapir related to this slab tear geochemically the german bank pluton is similar to most 300 265 ma plutons of the southern appalachians except in its strongly negative nd isotopic composition that results from the underthrusting of a ca 2 ga lower crustal block of saharan craton

an analysis of anisotropy of rocks containing shape fabrics of rigid inclusions abstract this paper presents a theoretical basis for estimation of mechanical anisotropy in homogeneous rocks containing shape fabrics of rigid inclusions the analysis is based on two types of viscous models one containing linear fabrics of prolate a b c inclusions cf l tectonite and the other containing planar fabrics of oblate a b c inclusions cf s tectonite models show contrasting bulk viscosities in stretching normal viscosity and shearing shear viscosity parallel to the fabric the axial ratio r a b and the volume concentration v of rigid inclusions appear to be the principal parameters in determining the viscosity contrast in anisotropic models with linear fabrics normal viscosity p increases monotonically with increase in r whereas shear viscosity s increases to a maximum and then drops down to a near stationary value in anisotropic models with planar fabrics the normal viscosity increases little with increasing flatness of inclusions but the variation assumes a steep gradient when the latter is large shear viscosity on the other hand is relatively less sensitive to the shape of inclusions the ratio of normal and shear viscosities conventionally described as anisotropy factor in both the models is always greater than 1 indicating that normal viscosity will be essentially greater than shear viscosity irrespective of the axial ratio of inclusions forming the fabric models with a linear fabric show contrasting normal viscosities in pure shear flow along and across the linear fabric the anisotropy is expressed by the ratio of longitudinal and transverse normal viscosities anisotropic factor it is revealed that the transverse viscosity is essentially less than the longitudinal viscosity as observed in test models

magnitude of weakening during crustal scale shear zone development we describe and apply a field based approach for calculating the bulk strength of a heterogeneous material to a crustal scale shear zone defining the margin of the ma parry sound domain in the grenville province of southeastern ontario using a numerical method we calculate bulk strength defined as effective viscosity as the ratio between the surface traction needed to deform a square block in simple shear and the velocity gradient across that block we use natural shear zone geometries to define the internal block structure and assign internal relative viscosities based primarily on textural criteria the margin of the parry sound domain developed into the km scale twelve mile bay shear zone accommodating several tens of km of transport while the domain interior remained rigid fracturing and fluid infiltration drove development of an amphibolite facies meter scale shear zone network that evolved into the twelve mile bay structure we analyzed three sites across the w5 km wide strain gradient from near the granulitic domain to the large scale shear zone the rocks at the shear zone margin weakened by approximately 30 those in the core weakened by at least 77 and probably by an order of magnitude these values lie between but differ substantively from the isostress and isostrain rate bounds indicating that a numerical approach such as presented here markedly improves the accuracy of bulk strength calculations

automatic time domain calculation of source parameters for the analysis of induced seismicity abstract a time domain methodology for the automatic on line calculation of source parameters is introduced the method is based on applying parseval9s theorem to the spectral equations proposed by andrews 1986 the appropriateness of the technique for the analysis of induced seismicity was tested by comparing on line values of seismic moment seismic energy and static stress drop with those obtained in the frequency domain off line for an aftershock sequence of events recorded underground at creighton mine ontario our analysis shows that the calculated on line and off line source parameters are in good agreement with an average slope offset of 4 from the 1 1 line suggesting that the proposed method is reliable additionally by applying empirical on line attenuation corrections coda q similar results are obtained to those calculated using off line corrections spectral decay improving the average slope offset to 1

juvenile middle proterozoic crust in the adirondack highlands grenville province northeastern north america nd isotope data indicate that minimal amounts of significantly older crust have contributed to the genesis of the oldest ca 1 3 13 5 ga plutons in the adirondack highlands these are magmatic arc tonalites with positive initial epsilon sub nd values and sm nd depleted mantle model ages t sub dm that are within 70 m y of the time of their crystallization granitoids of the anorthosite mangerite charnockite granite suite dated at 1 156 1 134 ma as well as the 1 100 1 050 ma plutons associated with the ottawan phase of the grenvillian orogenic cycle also have positive initial epsilon sub nd values and t sub dm ages similar to the tonalites derivation of both groups of granitoids by crustal melting of the magmatic arc is consistent with the available isotopic and geochemical data juvenile late middle proterozoic crust that formed during or just prior to the grenville cycle appears to dominate the southwestern grenville province as well as the grenville inliers to the south in contrast most of the contiguous grenville province in canada comprises largely reworked older crust

source mechanisms of mine related seismicity savuka mine south africa we report full moment tensor solutions for 76 mine tremors with moment magnitudes mw between 0 5 and 2 6 recorded by a network of 20 high frequency geophones in a deep gold mine in south africa source mechanisms convey important information on how in mine stresses are relaxed and understanding the nature of such mechanisms is essential for improving our assessment of rock mass response to mining our approach has consisted of minimizing the l2 norm of the difference between observed and predicted p sv and sh spectral amplitudes with visually assigned polarities to constrain all six independent components of the seismic moment tensor our results reveal the largest principal stresses in the mine are com pressive oriented near vertically and relaxed through a mix of volumetric closure and normal faulting consistent with a gravity driven closure of the mined out areas pre vious moment tensor studies in deep mines had suggested that the distribution of seis mic sources in terms of the volumetric shear mix was bimodal a bimodal distribution is compatible with our moment tensor solutions only for moment magnitudes above 2 2 events in the 0 5 mw 2 2 moment magnitude range display a continuous distribution of their volumetric shear mix online material focal parameters for mine tremors at savuka

the development of bone shaped structures in initially segmented layers during layer parallel extension numerical modelling and parameter sensitivity analysis in orogenic zones the geometric occurrence of specific tectonic structures can often be related to contrasting rheological properties of rock materials one of such tectonic structures is layer perpendicular naturally fractured layers with vein infill that underwent subsequent deformation internal deformation by coaxial extension of these segmented layers with host rock material less competent than the vein material gives rise to the development of bone shaped structures i e dogbones in this paper the formation of such dogbones is modelled using finite element techniques a parameter sensitivity analysis of the model demonstrates that the degree of extension of the host rock segments their initial aspect ratio and the competence contrast between vein material and host rock are the controlling parameters for the final shape of the dogbones during coaxial extension the results moreover suggest that the specific geometry of the dogbones can serve to quantify competence contrasts between the host rock and vein material during flow at geological strain rates

geochemical comparison between himalayan and hercynian leucogranites abstract isotopic sr pb nd o ree and trace element data from three himalayan nepal and six hercynian brittany france leucogranites are compared for the himalayan granites makulu mustang and especially manaslu the 87sr 86sr versus 87rb 86sr scatter diagrams and hence variability of the initial 87sr 86sr ratios reflect heterogeneity of the source materials these ratios are very high 0 730 0 770 for manaslu the very high 207pb 204pb ratios 15 8 at the corresponding 206pb 204pb ratio of 18 8 the very low 143nd 144nd ratios i nd 13 to 17 and the very high 18o 16o ratios 12 confirm the crustal origin with the paragneisses of the tibetan slab formation i as the probable parent source for the six hercynian granites with an individual rb sr isochron established for many of them the initial 87sr 86sr ratios range from 0 706 to 0 717 the lead neodymium and oxygen isotope compositions confirm their crustal source of presumably palaeozoic age but not specifically identified the rare earth patterns and thorium contents are comparable to those for himalayan granites the similarities of the geochemical signatures isotopes and trace elements of the himalayan and hercynian leucogranites suggest that the petrogenetic processes were comparable and that the himalayan continental collision model can be applied to the hercynian the depletion in ree and th implies either interaction of the granitic liquids with fluid or more probably early precipitation of monazite the increase in sm nd in the granites compared to their parent materials implies that the neodymium model ages of primary mantle extraction are maximum rather than minimum ages in contrast to the hercynian leucogranites the extremely radiogenic sr of the himalayan leucogranites reflects the very long crustal residence time before the melting event the apparent uniformity of the initial 87sr 86sr ratios of the individual hercynian granites may be related to an aging effect where the straight line fitting improves with increase in age of the pluton

it s a matter of size magnitude and moment estimates for microseismic data microseismic mapping is a valuable tool for assessing hydraulic fracture stimulations during a stimulation treatment borehole near surface or surface geophones record passive seismic data the microseismic events are thought to be shear failures that occur around the opening of a tensile hydraulic fracture as it grows over the past several years there has been a large growth in the number of hydraulic fracture monitoring surveys along with the number of vendors who acquire and process microseismic data here we discuss two attributes of microseismic data which are associated with the size of the passive event seismic moment and magnitude