numerical simulation of metamorphic pressure temperature time paths and fluid production in subducting slabs in order to investigate metamorphic reactions and fluid production in subduction zones a 2 dimensional finite difference model has been constructed the model simulates heat transfer in a subduction zone with a 27 dip a spatial resolution of 1 km is used in the region of the subduction thrust in order to carefully monitor metamorphic reactions elsewhere the spatial resolution is 5 km in these calculations the oceanic crust is assumed to contain 2 wt bound volatiles distributed homogeneously within the 7 5 km thick crust fluids are released by continuous and discontinuous end members of three different dehydration models pressure sensitive temperature sensitive and amphibole negative dp dt dehydration subduction zone pressure temperature time p t t paths predicted by the model intersect the wet basaltic solidus only at the initiation of subduction in mature subduction zones and in the absence of significant frictional heating and induced mantle convection p t t paths encounter subsolidus conditions at depths of 100 150 km beneath magmatic arcs suggesting that slab dehydration reactions play an important role in arc magma genesis metamorphic dehydration reactions that consume 50 kj kg result in p t t paths that are only 5 k cooler than models that neglect such reactions in both the temperature and amphibole dehydration models the fluid production region moves to greater depths over time as the subduction zone cools within the oceanic crust fluid production starts at the top of the crust and migrates downward in the temperature and amphibole dehydration models this phenomenon coupled with the weakening effect of devolatilization reactions may result in the accretion of oceanic crust to the hanging wall of the subduction zone for a convergence rate of 3 cm yr average fluid fluxes out of the subducting slab range from 0 1 kg fluid m yr for the continuous reaction models to 1 kg fluid m yr for the discontinuous pressure and amphibole dehydration models vertical fluid fluxes on the order of 1 kg fluid m yr can substantially perturb the thermal structure of overlying rocks and can cause large scale hydration and metasomatism of the overlying mantle wedge in contrast the thermal effect of fluid flow parallel to the subduction thrust zone is insignificant compared to the thermal effect of subducting oceanic lithosphere

development of a shear flow test apparatus and determination of coupled properties for a single rock joint abstract a new laboratory technique for coupled shear flow tests of rock joints was developed and used to investigate the coupled effect of joint shear deformation and dilatancy on hydraulic conductivity of rock joints this technique was used to carry out coupled shear flow tests with an artificial created granite joint sample under constant normal loads and up to residual shear deformations of 20 mm the hydraulic conductivity was estimated by using a finite difference method and an approximate equation assuming the cubic law the shear flow testing results revealed that the change of hydraulic conductivity is approximately similar to that of the dilatancy of a joint the hydraulic conductivity increases rapidly by about 1 2 1 6 orders of magnitude for the first 5 mm of shear displacement after passing the residual shear stress the hydraulic conductivity becomes gradually a constant value with increasing shear displacement on the other hand the hydraulic conductivity after shearing is about one order of magnitude larger than that prior to shearing shear flow coupling characteristics obtained from these tests have a consistent trend with barton s model prediction during the initial shear process however increasing deviation between measured and predicted hydraulic conductivity of rock joint samples has been observed with increasing shear displacement

exhumation of late paleozoic blueschists in queensland australia by extensional faulting blueschists in southeastern queensland australia record a carboniferous history of subduction and metamorphism at 6 kbar a later thermal overprint associated with intrusion of s type granitoids ca 306 ma and regional greenschist facies metamorphism accompanied formation of ductile fabrics in the lower plate of an oceanic protolith metamorphic core complex late carboniferous extensional deformation in this part of the new england orogen may have accompanied outstepping of the subduction trench or rollback and steepening of the paleo pacific plate during development of a wide zone of asthenospheric upwelling and continental back arc extension authors

conductive structures in southwestern canada a regional magnetometer array study an array of 33 three component recording magnetometers was operated in june and july 1980 in alberta and british columbia south of the edmonton prince rupert highway this very large array with its stations dispersed through 550 000 km2 and on average 150 km apart had limited resolution and was designed to confirm known conductive structures discover new ones and locate them sufficiently for suitable placement of further arrays with closer spaced stations and therefore higher resolution magnetograms and three sets of fourier transform anomaly maps are presented they show the general attenuation of the vertical component of variation fields west of the rocky mountain belt known from previous work and generally attributed to a conductive layer in the lower crust or upper mantle two prominent local anomalies are shown by variation fields of periods 15 30 min the first indicates induced currents near tete jaune cache west of jasper the highly conductive structure carrying the induced currents ma

the new england batholith constraints on its derivation from nd and sr isotopic studies of granitoids and country rocks abstract nd and sr isotopic compositions are reported for the granitic suites which comprise the late palaeozoic to earliest mesozoic new england batholith of eastern australia some of the granitic suites are typically i type in their mineralogy chemistry and isotopic compositions implying a derivation from igneous infracrustal source rocks whereas other suites have characteristics consistent with a derivation from a protolith which was predominantly sedimentary and relatively felsic s types the i type granitoids of the nundle suite have nd values 3 3 to 6 1 that are amongst the most primitive yet documented for a relatively felsic sio 2 65 plutonic suite and these values imply a derivation from either a depleted upper mantle source or more probably a complex source region involving both volcanic arc rocks and detrital material their compositions are distinctly more primitive than those of the new england super suite which constitutes the permian core of the batholith this extensive super suite comprising granitoids traditionally designated as i type has an overall range in initial nd and sr isotopic compositions of 1 7 to 4 6 and 0 70458 to 0 70624 respectively although the majority of plutons have initial nd isotopic compositions which fall into a very narrow range 1 0 1 5 units this limited range is remarkable considering the extreme lithological diversity and range in chemical composition of the analysed samples sio 2 47 74 and implies a source region of considerable volume having reasonably uniform isotopic compositions but variation in chemistry a similarly uniform source isotopically is also indicated for the s type granitoids of the carboniferous hillgrove suite and carboniferous permian bundarra suite with initial nd values of 0 8 to 2 3 and initial 87 sr 86 sr compositions of 0 70474 to 0 70577 showing only limited ranges five pelites three felsic and four mafic greywackes representing typical country rocks from different stratigraphic levels have initial nd values 1 7 to 6 6 and initial 87 sr 86 sr compositions 0 70378 to 0 70585 which essentially mirror the compositional variation in the granitoids a chemical mineralogical and isotopic bimodality in these sediments indicates two very distinctive sources one felsic rhyodacitic the other relatively mafic andesitic which were separated spatially and temporally in many but not all areas of early to mid palaeozoic new england a model is presented in which the s type granitoids are derived from a predominantly felsic source i e pelites and felsic greywackes whereas some of the granitoids belonging to the new england super suite may have been derived from source rocks consisting of both felsic and mafic sedimentary components the distinction between many s type and i type granitoids in new england is unclear for two principal reasons a because the granitoids and their respective source rocks are relatively young geologically so that their isotopic systems have not evolved to any considerable extent and b because of the intrinsic igneous chemical compositions of any sedimentary component that may be involved in their genesis

magnetotelluric observations along the lithoprobe southeastern canadian cordilleran transect as part of the lithoprobe southern cordilleran transect investigations twenty seven wideband magnetotelluric mt responses were obtained along 150 km of the reflection seismic lines the mt profile begins to the east on the rocky mountain trench above autochthonous north american basement traverses across the purcell anticlinorium the kootenay arc the nelson batholith and ends on the east side of the valhalla gneiss complex sites near kootenay lake respond to a major near surface conductivity anomaly that is probably due to either graphitic schists or to an extension of the silver bearing mineralization found further north the short period 1 s data are highly complex and exhibit 3d regional features inversions of the data from the two sites on the valhalla complex yield 1d models with interfaces in electrical conductivity at depths that agree with an increase in the number of reflectors at 9 km the base of layered reflections at 22 km and the mono at 35 km of major significance to our understanding of the current composition and state of the lower continental crust is that although for the valhalla complex there are few reflections below 22 km the mt responses indicate that the zone is conducting this is the only location known to the authors where the lower crust is seismically transparent but electrically conductive

structural history of high pressure metamorphic rocks in the southern vanoise massif french alps and their relation to alpine tectonic events abstract a nappe of amphibolite facies metamorphic rocks of pre permian age in the southern vanoise massif the arpont schist has been affected by an alpine hp lt metamorphism the first mesoscopically recognizable deformation d 1 post dated the high pressure peak jadeitic pyroxene quartz glaucophane lawsonite and was associated with glaucophane epidote d 1 produced a flat lying schistosity and a nw trending glaucophane lineation and was probably associated with nappe displacement involving nw directed subhorizontal shear d 2 formed small scale folds and a foliation associated with chlorite albite the changing parageneses during the period pre d 1 to d 1 to d 2 suggest decreasing pressure so that the deformation appears to have been related to the uplift history rather than to the process of tectonic burial d 2 was followed by a static metamorphism green biotite chlorite albite possibly of lepontine age se directed backthrusting and folding d 3 and later differential uplift along steep faults took place under low grade conditions

porphyroclast systems as kinematic indicators porphyroclasts of relatively strong minerals in mylonites commonly have an internal monoclinic shape symmetry defined by tails of dynamically recrystallized material the geometry of a porphyroclast and its tails called a porhyroclast system can serve as a valuable indicator of the sense of vorticity porphyroclast systems have been divided into and types on the basis of the geometry of the tails types have wedge shaped recrystallized tails whose median lines lie on opposite sides of a reference plane parallel to the tails and containing the symmetry axis for the system types are further subdivided into a a types in which the porphyroclast is isolated in a relatively homogeneous matrix and b types in which the porphyroclast system is associated with a shear band foliation in the matrix types typically have narrow recrystallized tails whose median lines cross the reference plane adjacent to the porphyroclast consequently embayments of matrix material occur adjacent to the porphyroclasts and the tails display characteristic bends a porphyroclast system in a mylonite develops when the relatively weak dynamically recrystallized grain aggregate in the porphyroclast mantle changes its shape due to non coaxial flow in the adjacent matrix this behaviour has been modelled in shear box experiments passive marker lines around rigid cylinders embedded in silicone putty were subjected to simple shear the experiments were modified to simulate a change in recrystallization rate r with respect to rate of deformation by decreasing the diameter of the rigid cylinder during deformation at variable rates the ratio r appears to be one of the most important factors in determining which porphyroclast system will develop at high r values flow of recrystallized material away from the porphyroclast is continuously appended by the production of new grains and wedge shaped a type tails develop at low r values relatively few new grains are added to the tails which become thinned and deflected by drag due to the spinning motion of the porphyroclast in addition most porphyroclast systems at low shear strains are of a type or lack monoclinic symmetry whereas types are only developed at high shear strain values complex porphyroclast systems characterized by two generations of tails are observed in many of the natural and model shear zones studied and may form due to fluctuating r conditions that allow isolated a and type porphyroclast systems to be used as sense of vorticity indicators are the systems should have a monoclinic shape symmetry matrix grain size should be small with respect to porphyroclast size matrix fabric should be homogeneous deformation history should be simple and observations should be made on sections normal to the inferred bulk vorticity vector for the mylonite

mechanisms of blueschist creation and preservation in an a type subduction zone mount olympos region greece deformation and metamorphism in the mount olympos region greece are the result of subduction of continental crust a type subduction during the alpine orogeny new structural and petrologic data from this region provide insight into the creation of low geothermal gradients in a type subduction zones and the preservation of blueschist facies assemblages early convergent deformation was accompanied by greenschist amphibolite facies metamorphism blueschist facies mineral assemblages overprinted higher grade assemblages during large scale episodic shortening that occurred during and after continental collision prehnite pumpellyite facies assemblages are postkinematic with respect to contractional fabrics but predate a prolonged period of extension that was not accompanied by metamorphism under plating and extension permitted unroofing and preservation of the blueschists with no over printing by greenschist facies assemblages

conductive structures under the canadian rocky mountains the paper reports results from an array of 33 three component magnetometers that recorded time varying fields in 1981 over an area of some 56 000 km2 in the canadian cordillera the array was centr

experimental investigations of blueschist greenschist transition equilibria pressure dependence ofal2o3 contents in sodic amphiboles a new geobarometer

regional distribution of white k mica polymorphs and their phengite content in the central alps some 150 white k micas from the central alps were analysed for their polymorph and phengite content

sedimentary fabrics in alpine ophicalcites south pennine arosa zone switzerland many ultramafic complexes in the south pennine nappes of eastern switzerland are covered by serpentinite breccias known as ophicalcites the breccias are overlain by radiolarites or younger oceanic sediments their fabric and their components document a combined tectonic sedimentary origin of the breccias in the davos area the breccias occur along distinct zones in the ultramafic host rock typically nonfragmented peridotite serpentinite grades rapidly through a narrow zone of host rock cut by different generations of dikes into complex breccias dominated by a carbonate matrix the breccias are of polyphase origin as shown by the different phases of fragmentation and generations of cementation and sediment infill these are distinguished by color differences and by a bimodal grain size distribution that also exhibits geopetal structures comparison with breccias from present day oceanic fracture zones suggests that the tethyan serpentinite breccias may have formed in a transform setting a sinistral transform margin along the northern edge of the apulian microplate or promontory is in line with current plate kinematic reconstructions

comment and reply on deep crustal seismic reflection profiling new england orogen eastern australia telescoping of the crust and a hidden deep layered sedimentary sequence comment

single grain argon laser probe dating of phengites from the blueschist to greenschist transition on sifnos cyclades greece measurements of 40ar 39ar age spectra on single white mica crystals of tertiary age is a new means of obtaining detailed geochronological information of alpine blueschists internal consistency of the data set as well as excellent agreement with previous conventional k ar results demonstrates that this new technique can be used with confidence to obtain information on the thermal evolution of young metamorphic belts

electromagnetic exploration for fluids in the earth s crust abstract electromagnetic geophysical techniques yield information on the spatial distribution of electrical conductivity a parameter sensitive to fluids in the rocks the paper describes electromagnetic techniques of use through the earth s crust including magnetovariation mv arrays magnetotelluric mt sounding and dc resistivity sounding field studies using these techniques lead to a discussion of various causes of high crustal conductivity including aqueous fluids silicate partial melt and films of graphite or magnetite on grain surfaces water in the crust is proposed as the preferred cause of high conductivity in the juvenile crust of tectonically active regions in particular where the anomalous conductivity is correlated with high heat flow and other geophysical and geological parameters

phase relations of epidote blueschists phase diagrams have been computed for minerals in the system ncmash using the optimised thermodynamic data base of berman 1988 augmented by data on glaucophane and pumpellyite to illustrate the relationships between rocks containing epidote and sodic amphibole and those containing assemblages characteristic of neighbouring metamorphic facies the stoichiometries of stable bounding equilibria yield a simple list of mineral parageneses that serves to define an epidote blueschist facies and surrounding metamorphic facies the calculations suggest that when iron free the pairs zoisite glaucophane and clinozoisite glaucophane do not possess a stability field the natural fe bearing paragenesis of epidote sodic amphibole occupies a closed field in the pt diagram whose size increases dramatically as the ratio fe3 al in the minerals is increased where garnet is involved in bounding reactions such as with respect to eclogite and garnet bearing albite epidote amphibolite the epidote blueschist field decreases in size as the ratio fe2 mg is increased the classic blueschist to greenschist transition reaction is best developed in rocks with large fe3 and fe2 contents and is possibly metastable in mgal rich rocks in the latter a wedge of albite epidote actinolite barroisite amphibolite separates the epidote blueschist from the greenschits paragenesis field a first occurrence of garnet divides the epidote blueschist field into a lower temperature garnet free zone and a higher temperature garnet bearing zone although the temperatures calculated for this garnet isograd seem high the locations of all the facies boundaries are influenced by h2o activity however even minor amounts of co2 in the fluid phase x co2 0 005 render the epidote sodic amphibole paragenesis metastable so that facies boundaries cannot be shifted by varying the co2 content of the fluid phase below 600 c no mutual boundaries exist between the amphibolite facies and the epidote blueschist and eclogite facies respectively the calculated low pressure limit for the eclogite paragenesis pyralspite omphacite jd 50 quartz typical metabasite compositions is 12 to 14 kbars with h2o activity 0 9 or 1 5 to 2 kbar lower for jd 30

middle ordovician high pt metamorphic rocks in eastern australia evidence from k ar ages phengite separated from a metagabbro three blueschist and one metabasite that occur as blocks in serpentinite melange in the new england fold belt eastern australia has yielded k ar ages of 465 480 ma significantly older than the age of most components of the belt the schists and metabasite contain either glaucophane and or crossite intergrown with the phengite providing the first conclusive evidence for early paleozoic subduction accretion associated with the east gondwana margin the tectonic affinity of the blocks is uncertain they and other small early paleozoic convergent margin elements in the new england fold belt may be allochthonous remnants of an arc system accreted in the devonian or carboniferous or they may be related to early paleozoic convergent margin components found farther inboard in the paleozoic fold belts of eastern australia

opposite vergence of nappes and crustal extension in the french italian western alps in the internal pennine zone of the french italian western alps dora maira monviso rocciavre massifs and queyras region the structural trends define an apparent dome geometry that is truncated to the east by the po basin this geometry is classically interpreted as a backthrusting system the kinematic history of the area has been investigated using structural metamorphic and geochronologic data on the basis of which two main deformation episodes have been distinguished that occurred under differing metamorphic conditions 1 the first deformation occurred under greenschist facies metamorphism it caused a regional scale foliation and an ew trending lineation that lie parallel to ductile deformation zones and thrust contacts sense of shear indicators associated with the lineation indicate contradictory top to the east and top to the west senses of shear from these it is deduced that coeval east and west vergent thrust faulting accommodated major displacements between nappes phengite ar ar data yield late eocene early oligocene ages for the greenschist facies metamorphism 2 the second deformation caused the widespread development of high angle shear bands and normal faults on opposite sides of the dora maira massif resulting in the apparent dome geometry of the massif a steep 50 80 network of west dipping normal faults is particularly well developed on the west side of the dora maira massif differences of 2 3 kbar and 100 150 c between juxtaposed monviso rocciavre and queyras nappes implies 8 km of vertical displacement along the monviso upper tectonic contact these normal faults formed in a more brittle regime only a post early oligocene age can be estimated from microstructural studies for these final movements these deformations postdate hp lt metamorphism and resulted in the juxtaposition of nappes of distinctly different origin age grade and p t t history a kinematic model is presented in which opposite vergence of nappes followed by large scale crustal extension occurred in response to uplift during the convergence between the european and south alpine plates this model may account for rapid uplift rapid unroofing and cooling of high pressure low temperature rocks thereby explaining the absence of amphibolite facies metamorphism overprint in this part of the alps that may have led to the preservation of coesite bearing rocks in the southern part of the dora maira massif

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

seismic reflectors conductivity water and stress in the continental crust the uppermost 10 15 km of the earth s continental crust differs in several geophysical properties from the lower crust the upper crust is electrically resistive seismically transparent contains nearly all intracontinental earthquake hypocentres and responds to stress elastically with brittle fracture the lower crust is electrically conductive contains many seismic reflectors is aseismic and shows ductile response to stress i show here that the characteristics of both regions can be explained if the entire crust contains saline water in separated cavities in the compressively stressed rocks of the upper crust but in the lower crust forming an interconnected film on the crystal surfaces the model may apply principally to technically active parts of the continental crust beneath shields the lower crust may be dry

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

role of tectonic denudation in warping and uplift of low angle normal faults large displacement on a low angle normal fault results in isostatic uplift of the lower plate in response to tectonic denudation simple models of the denudation process predict warping of the lower plate into a broad antiform or antiform synform pair with axes perpendicular to the direction of extension the amount of warping is strongly influenced by initial fault geometry surface topography the amount of extension and the distribution of extension within the upper plate late stage processes that augment antiform growth include one sided denudation of the antiform reverse faulting due to concave upward flexure and wholesale detachment and reverse drag folding of the antiform antiformal uplifts now exhumed by erosion form mountain ranges in the southwestern united states where conditions were favorable for warping during mid tertiary crustal extension four major structural domains are apparent in transects across these uplifts and adjacent areas 1 unextended area 2 synformal upper plate 3 antiformal uplift and 4 wedge shaped upper plate each domain is separated from adjacent domains by the traces of a master low angle normal fault

a two step homogenization based permeability model for deformable fractured rocks with consideration of coupled damage and friction effects abstract the permeability variation induced by anisotropic damage of rock blocks and nonlinear deformation of fractures is modeled with a two step homogenization technique for deformable fractured rocks containing arbitrarily distributed penny shaped microcracks in rock blocks separated by multiple sets of critically orientated fractures of much large scales the proposed model accounts for the influences of the microstructural alteration of rock blocks and fractures at the laboratory scale and the development pattern of the fracture system as well as the rock fracture interaction at the field scale on the permeability of a fractured rock under mechanical loading or excavation condition the proposed model was first validated by laboratory data of compression tests with permeability measurements on the beishan granite coupled shear flow tests with hydraulic conductivity measurements on a granite fracture and anisotropic strength tests on the martinsburg slate with good agreement between the model predictions and the laboratory measurements numerical simulations were finally performed to examine the excavation induced permeability change in the surrounding granitic rock of the stripa tunnel demonstrating the importance in considering both the damage of rock blocks and the deformation of fractures for better understanding the excavation induced permeability change in the surrounding rock near the excavation surface

underplated units in an accretionary complex melange of the shimanto belt of eastern shikoku southwest japan imbricated thrust stacks composed of melange and oceanic slabs occur in the shimanto belt eastern shikoku sw japan the melanges are divided into two types melange i consists of lenticular sandstone blocks surrounded by scaly shale matrix and melange ii is composed of blocks of oceanic material such as basalts cherts and red shale in a scaly matrix of shale melange ii is observed only near the boundaries between melange i and oceanic slabs the fabric of melange i indicates progressive deformation during underthrusting of originally coherent trench fill turbidites layer parallel extension characterizes early deformation and is divided into two stages an early stage formed during normal faulting and a subseguent stage formed perpendicular to the early extension the early extension is interpreted in terms of riedel shear associated with layer parallel shearing and tectonically induced loading normal to the layering the second extension is due to sticking thrust movement late deformation of melange i is represented by folding in association with layer parallel shearing this appears to be related to compression just before or during underplating of melange i beneath the accretionary prism layer parallel shear extends downward due to strain hardening of sheared sediments and then reaches to the base of the sediments subsequently the shear zone penetrates pelagic sediments and finally oceanic basement at this time melange ii is formed by the shearing an imbricated stack of melanges i ii and oceanic slabs forms duplexes during the underplating process the weak metamorphism of the melange complex in the study area suggests that underplating occurs at shallow depths where trench fill is thin

the use of discrete fracture network simulations in the design of horizontal hillslope drainage networks in fractured rock abstract characteristics of fracture networks are explored in a discrete fracture network framework to provide design guidelines for horizontal drainage networks in fractured rock central to the study is defining how fracture attributes relate to fracture network structure and network scale fluid flow and in turn how flow characteristics of fracture networks influence horizontal drain length and orientation multiple realizations of stochastic fracture networks generated from both synthetic and field specific data sets serve as a basis for understanding physical fracture network structure and resultant global flow and for performing intersection analyses of hillslope drains with flowing fractures study results indicate that the logarithm of the standard deviation of fracture transmissivity log t is the single most important attribute for drainage network design as higher values of log t describe heterogeneous flow patterns where only a small portion of the network conducts a significant quantity of fluid thus recommended drain lengths for intersecting significantly conductive fractures increase with increases in log t fracture trace length orientation and density also play a role albeit secondary to the distribution of transmissivity in defining drain length as a function of drain orientation relative to the mean fracture set orientation the spatially discontinuous nature of fracture networks and the wide range in transmissivity values found in natural fracture networks tend to produce high degrees of variability in computed intersection distances between drains and fractures conducting significant quantities of fluid to account for this variability a conservative approach is recommended where horizontal drain lengths along a pre defined orientation are scaled by discrete fracture network computed intersection distances equal to the upper 95th confidence interval

structural evidence for extensional exhumation of blueschist bearing serpentinite matrix melange new england orogen southeast queensland australia the footwall of a normal fault in the north d aguilar block in eastern australia contains blueschist blocks within a serpentinite matrix melange the melange contains mass flow deposits and was derived by erosion and redeposition of oceanic lithosphere exposed on the ocean floor by faulting in mid carboniferous time the melange was metamorphosed in the epidote blueschist facies mylonitized and underplated to the hanging wall of a subduction zone an s type granitoid intruded at 306 307 ma was probably derived by partial melting of subducted metasediments during the peak of a greenschist facies overprint that accompanied transposition of an early high p low t fabric mylonitic rocks below the normal fault absorbed a component of top to the west simple shear related to movement on that originally west dipping fault and resulted in juxtaposition of very low grade accretionary sequences above polydeformed blueschists in a metamorphic core complex at deeper levels in the footwall of the fault bulk deformation was approximately irrotational later the low angle fault was folded and its displacement was transferred westward into a more planar fault splay the juxtaposition of high p serpentinite melange against upper plate rocks probably reflects the mechanical weakness of serpentinite in deformed oceanic sequences and the role serpentinite plays in strain softening that concentrates deformation along major extensional shear zones

deep crustal seismic reflection profiling new england orogen eastern australia telescoping of the crust and a hidden deep layered sedimentary sequence australian bureau of mineral resources bmr deep crustal seismic reflection profiling in the new england orogen of eastern australia has revealed a thick deeply buried layered sequence that was telescoped by thrusting into a stack 20 km thick the seismic character suggests that the sequence is probably sedimentary and comparable in style to that revealed by the consortium for continental reflection profiling cocorp beneath the menimack synclinorium in new hampshire the beenleigh terrene a metamorphosed paleozoic accretionary wedge that overlies the deep layered sequence is thin skinned and has a maximum thickness of about 4 6 km the boundary between the sequence and the new england orogen is a well defined west dipping thrust fault which extends to at least 14 km we suggest that telescoping of the deep layered sequence occurred away from the new england orogen and that it and the beenleigh terrene were later accreted to the orogcn by underthrusting between 265 and 235 ma

tectonic history of subduction zones inferred from retrograde blueschist p t paths many phanerozoic convergent plate junctions are marked by discontinuous blueschist belts reflecting relatively high pressure p prograde trajectories common blueschist paragneisses such as those of the western alps exhibit widespread overprinting by greenschist and or epidote amphibolite facies assemblages for this type of high p belt retrograde metamorphism involved fairly rapid nearly isothermal decompression some terranes underwent continued heating during early stages of pressure release uplift probably occurred as a consequence of the entrance of an island arc oceanic plateau or segment of continental crust into the subduction zone collision resulting in marked deceleration or cessation of underflow and buoyant approximately adiabatic rise of the stranded recrystallized subduction complex other high p belts such as the franciscan of western california preserve metamorphic aragonite and lack a low p overprint retrogression approximately retraced the prograde p t temperature path or for early formed high grade blocks occurred at even higher p t ratios parts of this type of metamorphic belt evidently migrated slowly back up the subduction zone in response to isostatic forces during continued plate descent and refrigeration upward motion took place as tectonically imbricated slices as laminar return flow in melange zones and perhaps partly a lateral spreading extension of the underplated accretionary prism retrograde p t trajectories of high pmore belts therefore provide important constraints on the tectonic evolution of convergent plate junctions less

formulation of strain dependent hydraulic conductivity for a fractured rock mass abstract by characterizing rock masses as anisotropic continua with one or multiple sets of critically oriented fractures a methodology is developed in this paper to address the change in hydraulic conductivity resulted from engineering disturbance material nonlinearity and anisotropy an equivalent elastic perfectly plastic constitutive model with non associated flow rule and mobilized dilatancy is developed to describe the global nonlinear response of the rockmass under complex loading conditions by separating the deformation of fractures from that of the equivalent medium a strain dependent hydraulic conductivity tensor is formulated this not only considers the normal compressive deformation of the fractures but also and more importantly integrates the effect of material nonlinearity and post peak shear dilatancy using this methodology a closed form solution is derived to describe the hydraulic behavior of a single fracture during combined normal and shear loading processes the closed form solution is validated by an existing coupled shear flow test under wide ranges of normal and shear loads numerical simulations are performed to investigate the changes in hydraulic conductivities of a cubic block of fractured rock mass under triaxial compression and shear loading as well as a circular underground excavation in a biaxial stress field at the stripa mine sweden the simulation results agree well with the in situ experimental observations and an existing elastic strain dependent analytical solution respectively the evaluation results clearly demonstrate that the proposed model is capable of predicting the changes in hydraulic properties of fractured rock masses under loading or excavation

structural styles in mesozoic and cenozoic melanges in the western cordillera of north america the term melange is currently used to describe several different kinds of mudstone rich rocks that are broadly characterized by an obscure stratigraphy stratal disruption or a chaotic block in matrix fabric four types of melange which can be defined in outcrop on the basis of mesoscopic fabric and lithologic composition are particularly widespread and distinctive type i includes sequences of originally interbedded sandstone and mudstone that record incipient to thorough disruption and fragmentation of strata accomplished largely by layer parallel extension type ii consists of similarly deformed thin layers of green tuff radiolarian ribbon chert and minor sandstone originally interbedded with black mudstone disruption in both types i and ii which probably occurred while the sediments were incompletely consolidated has been ascribed to either imbricate faulting in accretionary wedges or gravitationally driven deformation type iii comprises inclusions of diverse shapes sizes and compositions enveloped in a locally scaly pelitic matrix the ultimate source of fragments is obscure because the majority were not derived by either the progressive disruption of interbedded sediments or in situ tectonic plucking and abrasion of adjacent rocks although some type iii melanges may have originated deep within accretionary prisms final emplacement as olistostromes muddy debris flow deposits or mud diapirs seems likely type iii melanges are mechanically analogous to scaly sheared serpentinites many probably have been tectonically remobilized or even intruded into shallow level fault zones type iv consists of lenticular inclusions bounded by an anastomosing network of subparallel faults their fabric records progressive slicing in brittle fault zones each of the four types of melange described here could in theory have formed in a variety of settings on or within an accretionary wedge at an active convergent margin none can yet be singled out as a uniquely diagnostic subduction melange

a review of existing methods used to evaluate the hydraulic conductivity of a fractured rock mass we review the existing methods for evaluating the hydraulic conductivity of a rock mass rock mass permeability may be assessed using empirical analytical and numerical approaches empirical methods use data from in situ field tests to derive the relationship between depth and permeability by applying a curve fitting method and establishing the relationship between hydraulic conductivity and a geological index analytical methods rely on darcy and cubic laws to estimate the permeability of a rock mass by taking into account the geometrical characteristics of the joint sets analytical equations of the flow rate into underground excavations are also developed by solving the laplace equation for homogeneous and isotropic aquifers under various boundary conditions numerical modeling can evaluate the outcomes of both empirical and analytical approaches and vice versa and can provide a sensitivity analysis of the parameters that affect rock mass permeability the importance of stress and joint set characteristics is often investigated via numerical modeling as are the scale effect and directional permeability in this review paper we provide a comprehensive review of these approaches for studying rock mass permeability we summarize the advantages and disadvantages of existing methods and highlight potential future research directions

low temperature thermochronology of the northern thomson orogen implications for exhumation of basement rocks in ne australia abstract the tasmanides of eastern australia record much of the phanerozoic tectonic development of the retreating pacific australia plate boundary and are an oft cited example of an orogen that has undergone tectonic mode switching to begin to constrain the timing of exhumation of basement rocks that are now exposed in portions of the ne tasmanides we measured apatite and zircon u th he ages from the thomson orogen and overlying paleozoic strata in the back arc of the new england orogen in ne australia zircon u th he ages from basement samples including those recovered from boreholes at depths of up to 1 1 km are characterized by large inter and intra sample variability and range from approximately 180 ma early jurassic to 375 ma late devonian u th he zircon ages from several individual samples are negatively correlated with effective uranium eu a pattern that is also true of the dataset as a whole suggesting that variations in u and th zoning and radiation damage are partially responsible for the age variability the oldest zircon u th he cooling ages coincide with the formation of regionally extensive late devonian early carboniferous back arc basins suggesting that late devonian extension played a significant role in exhumation of parts of the northern thomson orogen apatite u th he ages from a basement sample and a late permian sandstone in the overlying bowen basin which are also marked by intra sample variability and age eu correlations span from the early cretaceous through oligocene in general agreement with previous apatite fission track data in conjunction with observations of key geologic relationships and prior k ar and 40ar 39ar data our results suggest four overall phases in the thermal history of the northern thomson orogen 1 cambrian early silurian metamorphism during the delamerian and benambran orogenies 2 protracted cooling during the late devonian through mid permian that likely resulted from extensional exhumation 3 permian triassic reheating during burial beneath thick sedimentary basins and 4 cretaceous and paleogene cooling during uplift and erosion

considerations of the dilatancy angle in rocks and rock masses the present study responds to the poor treatment given to dilatancy in classical rock mechanics post failure problems such as tunnel or mine pillar design a comprehensive review of the literature and observations in regard to published test results would indicate that dilatancy is highly dependent both on the plasticity already experienced by the material and confining stress moreover it also appears that scale may play a non negligible role in our article we provide a detailed analysis of published test data with a view to proposing a sufficiently significant but conveniently simple formulation of the dilatancy angle that reflects these dependencies and that can be readily implemented in numerical codes the model is then tested demonstrating that it is capable of representing rock sample strain behaviour in compressive tests finally the model is applied to the resolution of ground reaction curves for tunnels in poor to average quality rock masses showing a good correlation with results obtained using practical rock engineering techniques r 2005 elsevier ltd all rights reserved

the southern cape conductive belt south africa its composition origin and tectonic significance abstract magnetometer array studies have led to the discovery and mapping of the southern cape conductive belt sccb crossing the southern tip of africa from west to southeast coasts the sccb lies just south of the namaqua natal belt of cratonic rocks remobilized about 1000 m y b p it is shown that it coincides with a zone of weakness which has been exploited by three major geosynclinal accumulations over some 600 m y relationships between the sccb and the basement geochronology geology and tectonics are considered in detail these relationships support the view that the conductive belt was formed by an accumulation of marine sediments and oceanic lithosphere at the top of a proterozoic subduction which stopped about 1000 to 800 m y b p associated with this subduction we propose a proterozoic range of andean mountains whose roots are now exposed in the namaqua natal belt later subduction further south near the present south coast is proposed to account for the intrusion between the south coast and the sccb of the cape granites in the time interval 600 500 m y b p there is some evidence for a third yet more distant subduction episode off permian gondwanaland after outlining this tectonic history the paper turns to a closer examination of the hypothesis that the southern cape conductive belt consists of partly serpentinized basalt accumulated at the top of a proterozoic subduction a large static magnetic anomaly which correlates with the sccb over most of its length is well fitted by a model which strongly supports this hypothesis bouguer gravity anomalies along western and central profiles likewise support the hypothesis a discussion follows of the process of formation of the proposed block of serpentinized marine rocks beginning with serpentinization of the crust near oceanic ridges by reaction of warm porous newly extruded basalt with seawater convecting through it the serpentinized basalt is stable at crustal temperatures and pressures and so is transported in the seafloor until it reaches a subduction where it accumulates because of its low density examples of such accumulations are cited finally it is shown that any iron in the olivine and pyroxene in the original basalt precipitates when these silicates are hydrated to serpentine as magnetite which is the dominant mineral conferring high electrical conductivity and high magnetic susceptibility on serpentinites in particular the beattie static magnetic anomaly requires in our model calculation a very high susceptibility readily attainable in basalt at 15 20 serpentinization the authors know of no other rock able to provide this high susceptibility a similar percentage of serpentinization provides the density required to model the gravity anomalies

orogenesis without collision stabilizing the terra australis accretionary orogen eastern australia the neoproterozoic to end paleozoic terra australis orogen extended along the gondwana margin of the paleo pacific ocean and it now provides a detailed record of orogenic activity and continental stabilization within an ongoing convergent accretionary plate margin new geochronological data from end paleozoic plutonic and volcanic rocks associated with the gondwanide orogeny in the new england region of eastern australia integrated with information on the nature and timing of associated sedimentation deformation and metamorphism allow resolution of a high fidelity record of orogenesis at the end of the carboniferous around 305 ma convergent margin magmatism which had been active along the western margin of the new england region terminated and was followed by a short pulse of regional compressional deformation and metamorphism marking the commencement of the tablelands phase of gondwanide orogenesis deformation was almost immediately followed by the onset of clastic sedimentation and local calc alkaline volcanism dated at 293 ma in the extensional barnard basin emplacement of the two new england s type granitic suites the bundarra and the hillgrove suites along with localized high temperature low pressure metamorphism was essentially contemporaneous ranging in age from 296 to 288 ma and overlapped in time with i type magmatism and the switch from regional compression to extension and barnard basin rifting the hunter bowen phase of the gondwanide orogeny commenced with contractional deformation resulting in termination of sedimentation in the barnard basin and regional deformation and metamorphism across new england and into the sydney and gunnedah basins to the west at around 265 260 ma contractional loading of the sydney and gunnedah basins resulted in their conversion from extensional to foreland basins which received ongoing pulses of sediment from the new england orogenic welt until 230 ma the hunter bowen phase was associated with widespread i type plutonism and volcanic activity in new england that ceased around 230 ma marking the termination of gondwanide orogenesis orogenesis occurred in an evolving convergent plate margin setting s and i type magmatic activity ranging in age from ca 300 to 230 ma represents a stepping out of arc magmatism from the western margin of new england prior to 305 ma into the preexisting arc trench gap there is no evidence that deformation was related to the collision of the convergent margin with a major lithospheric mass and the widespread development of extensional basins in the eastern third of australia in the early permian indicates control by phenomena acting on a continental scale probably changing plate kinematics associated with the amalgamation of pangea

permeability tensor for discontinuous rock masses rock masses which commonly contain a large number of discontinuities are treated as homogeneous anisotropic porous media to formulate the corresponding permeability tensor this has been successfully achieved by introducing a symmetric tensor crack tensor which depends only on the geometry of the related cracks aperture size and orientation the principal directions associated with the symmetric crack tensor are coaxial with those of the permeability tensor the first invariant of the crack tensor is proportional to the mean permeability while the deviatoric part is related to the anisotropic permeability these results are well supported by numerical experiments on the permeability of cracked media by long remer wilson and witherspoon an actual rock mass moderately jointed granite was studied to see whether the crack tensor can be determined in situ stereology based on geometrical statistics provides a sound basis for determining the crack tensor in situ the crack tensor is obtained by

clinopyroxene a mineral telescoped through the processes of blueschist facies metamorphism textural evolution and compositional variation of clinopyroxenes in ward creek metabasites are described pyroxenes change with increasing grade from finegrained aggregates through fan shaped medium grained prisms to blocky coarse crystals characteristic features of metamorphic pyroxenes include 1 the occurrence of coexisting pyroxene pairs the compositions of which are used to delineate compositional gaps 2 the existence of large compositional variations of pyroxenes within a single specimen which record a considerable span of p and or t for crystallization and 3 the development of compositional trends in single specimens and in three metamorphic zones which are progressive in nature the first formed clinopyroxene jd20aug65ac15 in the lower lawsonite zone mimics the composition of relict igneous augite it changes continuously with increasing grade at nearly constant low xjd content towards acmite at a composition around jd20aug30ac50 the trend turns towards jadeite and intersects a solvus to form two coexisting clinopyroxenes in the middle lawsonite zone at higher grade the compositional gap becomes restricted towards the jadeite omphacite join and clinopyroxene increases in xjd toward jadeite a reversed compositional trend occurs at higher grade clinopyroxenes decrease in jadeite component at nearly constant aug ac ratio of 50 50 and finally become omphacite in the uppermost pumpellyite and epidote zones the na ca pyroxenes close to the binary join jd ac occur in the lawsonite and pumpellyite zones ranging from xjd 1 0 0 30 together with ab and qz the ubiquitous occurrence of aragonite at temperature estimates of 170 240 c by taylor coleman 1968 for these zones does not support the low temperature extrapolation of the jd ab qz curve by holland 1980 the estimated metamorphic field gradient indicates an inflection point at 7 kbar 200 c below this blueschist facies metamorphism proceeded under dominant pressure increase from 4 to 7 kbar at nearly constant temperature about 150 200 c whereas at higher grade recrystallization above the inflection point the metamorphic temperature increased from 200 to 350 c at nearly constant pressure about 7 8 kbar such an inflection point suggests the depth of underplating of either seamounts or accretionary packages in a subduction zone

crustal extension in the northern apennines the transition from compression to extension in the alpi apuane core complex an interpretation of northern apennine geology is presented which relates the temporal and spatial occurrence of both compressional and extensional deformation features in terms of the changing dynamic evolution within an accretionary wedge after a model proposed by platt 1986 followed by the initiation and development of continental rifting during cretaceous to eocene time an accretionary wedge formed as remnant tethyan oceanic crust subducted beneath the rotating corsica sardinia microplate microplate collision during the oligocene was characterized by the rapid imbrication of buoyant continental crust of the italian continental margin the record of which is preserved within the duplex structure geometry of the alpi apuane region the overthickened wedge geometry returned to a more stable configuration by developing extensional features during the miocene both listric normal faults at upper crustal levels and shear zones indicating evidence of distributed ductile extensional strain at mid crustal levels are recorded it is proposed that large scale regional extension with associated volcanism beginning in the messinian was represented by the intrusion of asthenospheric material from the subducted plate into the already attenuated accretionary complex further rifting perhaps aided by subduction and back arc processes in the southern apennines led to the formation of the tyrrhenian sea as an oceanic basin both the apennines and north american core complexes record evidence of crustal thickening followed by crustal thinning and finally of continental rifting this suggests that the similar histories of these regions with vastly different plate tectonic settings may both be explained by processes linked to the changing internal dynamics of accretionary wedges

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

estimation of rev size and three dimensional hydraulic conductivity tensor for a fractured rock mass through a single well packer test and discrete fracture fluid flow modeling abstract a new methodology is presented to determine the representative elementary volume rev size and three dimensional 3 d hydraulic conductivity tensor for a fractured rock mass first a 3 d stochastic fracture network model was built and validated for a gneissic rock mass based on the fracture data mapped from scanline surveys at the site this validated fracture network model was combined with the fracture data observed on a borehole to generate a stochastic deterministic fracture network system in a cubic block around each packer test conducted at a different depth region in the same borehole each packer test was simulated numerically applying a developed discrete fracture fluid flow model to estimate the influenced region or effective range for the packer test a cubic block of size 18 m with the packer test interval of length about 6 5 m located at the centre of this block was found to be suitable to represent the influenced region using this block size the average flow rate per unit hydraulic gradient defined as the transmissivity multiplied by mean width of flow paths field for fractures was calibrated at different depth regions around the borehole by numerically simulating the packer tests conducted at different depth regions the average flow rate per unit hydraulic gradient of the fractures that intersect the borehole was considered to be quite different to the average flow rate per unit hydraulic gradient of the fractures that do not intersect the borehole a relation was developed to quantify the ratio between these two parameters by studying the directional hydraulic conductivity behaviour of different cubic block sizes having the validated stochastic fracture network and calibrated hydraulic parameters a rev for the hydraulic behaviour of the rock mass was estimated to be a block size of 15 m the hydraulic conductivity tensor in 3 d computed through regression analysis using the calculated directional hydraulic conductivity values in many directions was found to be significantly anisotropic the principal directions of the hydraulic conductivity tensor were found to be agreeable with the existing fracture system of the site further the geometric hydraulic conductivity calculated was found to be comparable to the hydraulic conductivity estimated through the radial flow assumption in continuum porous media

evidence for east west crustal extension in the eastern alps implications for the unroofing history of the tauern window the contact between the western border of the tauern window and the overlying austroalpine nappes austria and italy is marked by a structural petrologic and geochronologic discontinuity that developed in the early stages of unroofing of the window within the window pressure temperature time paths j selverstone 1985 indicate that significant ductile thinning occurred shortly after the cessation of thrusting paleocene eocene sense of shear indicators rotated porphyroblasts asymmetric augen and pressure shadows s c fabrics associated with a west plunging stretching lineation indicate that this thinning occurred in response to top to the west low angle normal shear during metamorphism the same sense of normal shear is present in the mesozoic members of the austroalpine sequence west of the window in these rocks however west directed shear occurred at low temperatures 300 c after the thermal peak of metamorphism structural data and the regional geometry imply that the western end of the tauern window is a low angle normal fault brenner line that juxtaposed brittlely deformed rocks of the austroalpine nappes against more ductilely deformed rocks from the window biotite k ar and rb sr data suggest a miocene age for final movement on the brenner line these data indicate a prolonged history of east west extension in the eastern alps that affected all crustal levels early ductile thinning of lower crust followed by mid to upper crustal low angle normal faulting a model is presented that relates the young east west extension to displacement transfer from dextral movement on the periadriatic lineament in this model the brenner line and by analogy the simplon line can be thought of as detachment faults that tectonically unroofed the tauern window and lepontine thermal highs respectively

hydraulic properties of partially saturated rock fractures subjected to mechanical loading abstract this study presents a methodology for estimating the unsaturated hydraulic properties of rock fractures under deformation conditions the surface morphology of an artificial granite rock fracture was examined using a high resolution three dimensional laser scanner and the aperture distribution of the fracture was found to follow a gaussian distribution by virtue of the aperture distribution function and applying the young laplace equation to local apertures a novel model was presented to predict the capillary pressure saturation relationship and the relative hydraulic conductivity of rough walled rock fractures subjected to normal and shear loading the proposed model was partially validated against existing laboratory data on the unsaturated hydraulic properties of rock fractures and can be readily applied to various engineering practices such as transport phenomena in fractures landslide mitigation or underground oil storage

australian palaeozoic palaeomagnetism and tectonics ii a revised apparent polar wander path and palaeogeography abstract new palaeomagnetic data from mid to late palaeozoic rocks in australia have enabled us to revise the palaeozoic apparent polar wander path apwp this modified australian apwp is supported by data from other parts of gondwanaland the palaeomagnetic poles indicate that during the early and mid palaeozoic australia underwent rapid rotation first clockwise during the mid ordovician to the early silurian then counterclockwise from the mid silurian until the end of the devonian while it remained at low to equatorial latitudes this was succeeded by a rapid southward movement during mid carboniferous times the implications of the palaeomagnetic data for the tectonic relationship between the lachlan fold belt lfb and cratonic australia are consistent with the tectonic evidence that the lfb has been in place since the mid devonian

dipping seismic reflectors electrically conductive zones and trapped water in the crust over a subducting plate the lithoprobe program across the northern cascadia subduction zone at vancouver island has obtained geophysical data that suggest a dipping zone of trapped free pore water in the overlying continental crust land and marine multichannel seismic reflection profiles show several bands of reflectors the primary one at a depth of about 30 km is about 5 km thick dips inland and appears to coincide with an electrically conductive layer defined by magnetotelluric data the downgoing oceanic crust is imaged as a thin reflector dipping at about 15 and 10 km deeper than the primary reflector a location that is consistent with seismicity and seismic refraction data both the reflectors and the conductor have been modeled by near horizontal lamellae with 1 4 saline water porosity detailed geothermal measurements defining heat flow that decreases inland indicate that the dipping bands are nearly isothermal at a temperature of 400 500 c it is suggested that free water generated by dehydration of the downgoing oceanic plate migrates upward until reduced temperature results in hydration reactions and mineral precipitation that forms an impermeable barrier low vertical permeability is required to keep the water from separating to the top of the layer this can be reconciled with the low electrical resistivity if pore interconnection is through thin grain boundary tubes as predicted by theoretical equilibrium pore geometry although very small effective grain size is necessary an abrupt transition from high permeability to very low permeability is predicted at a several percent porosity in agreement with the modeled porosity such pore geometry with low permeability may be restricted to temperatures above about 400 c i e in greenschist to amphibolite facies conditions where grains will deform to equilibrium geometry and cracks are annealed the region above the reflective and conductive band is estimated to be within blueschist conditions consistent with the inferred high seismic velocity from refraction data and high density from gravity data

an equivalent continuum model for coupled stress and fluid flow analysis in jointed rock masses to provide a set of governing equations for solving the coupled stress and fluid flow a rock mass which commonly contains a large number of geological discontinuities is treated as an anisotropic elastic porous medium with the corresponding elastic compliance and permeability tensors hydro mechanical equivalents to the discontinuous mass the hydromechanical equivalents with the special emphasis on the permeability tensor are formulated on the assumption that any crack can be replaced by a set of parallel planar plates connected by two springs two dimensional numerical analyses on seepage flow networks support the validity of the permeability tensor some field evidence is analyzed to examine the applicability of the present model for the practical purpose of rock hydraulics

late miocene ductile extension and detachment faulting mykonos greece the geometry and style of structural relations at map to microscopic scale on mykonos cyclades aegean sea greece suggests ductile extension and detachment faulting during the late miocene this island is dominated by granitic rocks that have a well developed shallowly dipping mylonitic foliation and a northeast southwest trending mineral elongation lineation kinematic indicators in these rocks exhibit a top to the northeast down dip sense of shear textural relations suggest that conditions during mylonitic deformation were greenschist to amphibolite facies and published k ar geochronology suggests a late miocene age for this deformation event mylonitic rocks lie in the footwall of a low angle fault and fault striae parallel to the elongation lineation suggest kinematic coordination between mylonitic deformation and movement along the fault translation along the fault juxtaposes younger tilted sedimentary rocks of low metamorphic grade upon the once deeper mylonitic rocks the style and geometry of deformational fabrics and map relations on this island are strikingly similar to those observed in metamorphic core complexes of the western united states

tectonic setting of blueschist and island arc terranes of west central baja california mexico diverse oceanic rocks exposed in west central baja california mexico are assigned to three shallowly dipping tectonic units the lower plate is a subduction complex consisting of regionally metamorphosed blueschists and divided into structurally and petrologically distinct subterranes the upper plate consists of triassic lower cretaceous are rocks and overlapping mid cretaceous turbidites a fault bounded serpentinite matrix melange between lower and upper plate rocks contains blueschist eclogite amphibolite and variably serpentinized mafic and ultramafic blocks lower plate blueschists were metamorphosed in the late early cretaceous and uplifted along shallowly dipping normal faults during conditions of steady state subduction exotic blocks of blueschist eclogite and amphibolite are derived from a cryptic terrane or terranes record varied p t t histories and were uplifted via tectonic emplacement or diapiric rise of serpentinite along the normal faults