an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

some unique surface patterns on ignimbrites on earth a bird s eye view as a guide for planetary mappers abstract observations of terrestrial analogs are critical to aiding planetary mappers in interpreting surface lithologies on other planets for instance the presence of ignimbrites on mars has been debated for over three decades and is supported by analogy with deposits on earth critical evidence includes the geomorphic and surface expression of the deposits and those in the central andes of south america are amongst the most cited analogs herein we describe some prominent surface textures and patterns seen in ignimbrites on the scale of high resolution remotely sensed data 10 1 m per pixel these include pervasive joints and fractures that contribute to yardang form and development as well as prominent mounds fissures and fracture networks spiders bugs boxworks on ignimbrite surfaces while all these features are related to intrinsic cooling and degassing processes the involvement of external water buried by hot pyroclastic flows enhances fumarolic activity advective cooling and joint development observations of these geomorphic expressions using remote sensing are only possible with the highest resolution data and limited surface erosion for mars where similarly high resolution datasets are available for example the high resolution imaging sensor experiment or hirise extensive dust cover may limit the recognition of similar features there however significant relief on some of these features on earth indicate they might still be detectable on mars

fractal geometry characterization of geothermal reservoir fracture networks as a new procedure for modeling geothermal energy extraction systems a two dimensional modeling technique for subsurface fracture networks on the basis of fractal geometry is presented models of fracture networks are generated by distributing fractures randomly in space and by using the fractal relation between fracture length r and the number of fractures n expressed with a fractal dimension d as n cr exp d where c is a constant that signifies the fracture density within the rock mass this procedure makes it possible to characterize geothermal reservoirs by parameters measured from field data such as from core sampling in this characterization the fracture density parameter c of a geothermal reservoir is used as a parameter to model the subsurface fracture network using this fracture network model the connectivities of the water flow paths between wells are calculated by means of a monte carlo simulation and the result is then compared with that derived from a percolation model we show that many fewer fractures are required to connect two wells for the fracture network model than for the percolation model the transmissivities between wells for the fracture network model are also obtained as a function of the fracture density parametermore c the results show that the transmissivities in geothermal reservoirs are significantly dependent upon the fracture density of rock mass and they can be predicted from the fracture density parameter c of the reservoirs less

mantle flow in subduction systems the subslab flow field and implications for mantle dynamics 1 the character of the mantle flow field in subduction zones remains poorly understood despite its importance for our understanding of subduction dynamics in particular little attention has been paid to mantle flow beneath subducting slabs in order to identify processes that make first order contributions to the global pattern of subslab mantle flow we have compiled shear wave splitting measurements from subduction zones worldwide from previously published studies and estimated average splitting parameters for the subslab region globally the subslab region is overwhelmingly dominated by trench parallel fast splitting directions we tested for relationships between splitting delay time a measure of the strength of anisotropy and parameters that are indicators of tectonic processes such as trench migration velocity convergence velocity and obliquity age of subducting lithosphere and slab dip curvature seismicity and thickness we used several different plate motion models to describe plate and trench motions and evaluated the differences among the models we find that only one parameter namely the trench migration velocity in a pacific hot spot reference frame appears to correlate well with the strength of the subslab splitting signal this finding supports a model in which the mantle beneath subducting slabs is dominated by three dimensional flow induced by trench migration we explore several implications of our model for various aspects of mantle dynamics including the choice of a suitable reference frame s for mantle flow the existence of a thin decoupling zone between slabs and the subslab mantle and consequences for mass transfer between the upper and lower mantle

platinum group elements in silicate rocks of the lower critical and main zones at union section western bushveld complex concentration patterns of platinum group elements pge in the lower critical and main zones of the bushveld complex are modelled by a process of metal collection by segregating sulphide melt followed by fractional crystallization of monosulphide solid solution mss separation of os ir ru rh enriched mss cumulate ore and pt pd enriched residual sulphide melt is inferred to have occurred by upward percolation of interstitial silicate melt entraining sulphide melt whereas mss crystals are entrapped by early crystallizing chromite this process resulted in os ir ru rh enrichment of the chromitites and an upward increasing trend of pt pd os ir ru crystallization of platinum group minerals pgm from s undersaturated sulphide melt or from coalescing noble metal clusters are alternative possibilities to explain the observed pge patterns but remain difficult to model at present remobilization of pt and pd by percolating late magmatic hydrous fluids could have resulted in metal enrichment of pre existing magmatic sulphides but this model is not supported by the metal budget of the reefs and the field data there is no evidence for solid substitution of pge into oxides and silicates

kinematic structural restorations and discrete fracture modeling of a thrust trap a case study from the tarija basin argentina the integration between kinematic structural restorations and discrete fracture simulation is applied to a thrusted and fractured fault block in the tarija basin northern argentina the emphasis is on the influence of the factor time on the deformation history and fracture growth the structural evolution of the gas bearing santa rosa reservoir forms the basis for understanding the development of the 3d fracture system as simulated with 3d kinematic restorations during the restoration the cumulative dilatational strain was calculated and mapped and compared to traditional curvature analyses the strain maps are subsequently used to simulate geologically realistic discrete fracture networks that form the basis for further exploration and development of the field

connectivity permeability and channeling in randomly distributed and kinematically defined discrete fracture network models a major use of dfn models for industrial applications is to evaluate permeability and flow structure in hardrock aquifers from geological observations of fracture networks the relationship between the statistical fracture density distributions and permeability has been extensively studied but there has been little interest in the spatial structure of dfn models which is generally assumed to be spatially random i e poisson in this paper we compare the predictions of poisson dfns to new dfn models where fractures result from a growth process defined by simplified kinematic rules for nucleation growth and fracture arrest davy et al 2010 2013 this so called kinematic fracture model is characterized by a large proportion of t intersections and a smaller number of intersections per fracture several kinematic models were tested and compared with poisson dfn models with the same density length and orientation distributions connectivity permeability and flow distribution were calculated for 3d networks with a self similar power law fracture length distribution for the same statistical properties in orientation and density the permeability is systematically and significantly smaller by a factor of 1 5 to 10 for kinematic than for poisson models in both cases the permeability is well described by a linear relationship with the areal density p32 but the threshold of kinematic models is 50 larger than of poisson models flow channeling is also enhanced in kinematic dfn models this analysis demonstrates the importance of choosing an appropriate dfn organization for predicting flow properties from fracture network parameters

mesoscale strike slip faults and damage zones at marsalforn gozo island malta well exposed strike slip faults in limestones in the north western part of gozo show damage zones that can be grouped into three categories based on their location along faults tip damage linking damage and distributed damage the predominant fracture types within damage zones include extension fractures and secondary faults tip damage zones usually show wedge shaped patterns formed by antithetic faults and extension fractures commonly accompanied by block rotation several fractures are combined at linking damage zones typically with the concentration of a high intensity of fractures structures in distributed damage zones are typically similar to the classical riedel shear pattern evolutionary and 3d models are proposed in terms of the geometries of damage zones for small displacement strike slip fault zones different evolutionary routes depend on fault tip modes and locations

a scale independent approach to fracture intensity and average spacing measurement fracture intensity the number of fractures per unit length along a sample line is an important attribute of fracture systems that can be problematic to establish in the subsurface lack of adequate constraints on fracture intensity may limit the economic exploitation of fractured reservoirs because intensity describes the abundance of fractures potentially available for fluid flow and the probability of encountering fractures in a borehole traditional methods of fracture intensity measurement are inadequate because they ignore the wide spectrum of fracture sizes found in many fracture systems and the consequent scale dependence of fracture intensity an alternative approach makes use of fracture size distributions which allow more meaningful comparisons between different locations and allow microfractures in subsurface samples to be used for fracture intensity measurement comparisons are more meaningful because sampling artifacts can be recognized and avoided and because common thresholds of fracture size can be enforced for counting in different locations additionally quantification of the fracture size distribution provides a mechanism for evaluation of uncertainties estimates of fracture intensity using this approach for two carbonate beds in the sierra madre oriental mexico illustrate how size cognizant measurements cast new light on widely accepted interpretation of geologic controls of fracture intensity

melonite group minerals and other tellurides from three cu ni pge prospects eastern desert egypt abstract melonite group minerals and other tellurides are described from three cu ni pge prospects in the eastern desert of egypt gabbro akarem genina gharbia and abu swayel the prospects are hosted in late precambrian mafic ultramafic rocks and have different geologic histories the gabbro akarem prospect is hosted in dunite pipes where net textured and massive sulfides are associated with spinel and cr magnetite michenerite merenskyite pd bi melonite and hessite occur mainly as inclusions in sulfides typical magmatic textures indicate a limited role of late and post magmatic hydrothermal processes at genina gharbia ore forms either disseminations in peridotite or massive patches in hornblende gabbro in the vicinity of metasedimentary rocks actinolitic hornblende epidote chlorite and quartz are common secondary silicates sulfide textures and host rock petrography suggest a prolonged late magmatic hydrothermal event michenerite merenskyite pd bi melonite altaite hessite tsumoite sylvanite and native te are mainly present in secondary silicates the abu swayel prospect occurs in conformable lens like mafic ultramafic rocks in metasedimentary rocks and along syn metamorphic shear zone the sulfide ore and host rocks are metamorphosed amphibolite facies 550 to 650 c 4 to 5 kbar and syn metamorphically sheared melonite group minerals are represented by merenskyite and pd bi melonite other tellurides comprise hessite altaite and joseite b melonite group minerals and tellurides occur as inclusions in mobilized sulfides and along cracks in metamorphic garnet and plagioclase the different geological history of the three prospects permits an examination of the role played by magmatic late magmatic and metamorphic processes on the mineralogy of melonite group minerals and diversity of tellurides the contents of pge and te in the ore and temperature of crystallization control the mineralogy and compositional trends of the melonite group minerals crystallization of the melonite group minerals over a wide range of temperatures in a te rich environment enhances the elemental substitutions merenskyite dominates the mineralogy of the group at low te activity while pd bi melonite is the common phase at high te activity

test of the frictional reactivation theory for faults and validity of fault slip analysis the notion that slip on faults is controlled by the balance between resolved shear stress and the magnitude of frictional resistance is examined in the light of the published orientations of ancient faults and slip lineations by compiling data from more than 1500 faults used in 228 stress analyses we observe that natural fault planes as well as lineations formed by fault slip display characteristic patterns of preferred orientation when rotated into the reference frame defined by the principal stress axes these patterns vary systematically according to the relative magnitudes of principal stresses determined by fault slip analysis furthermore these patterns are strikingly similar to those predicted by a frictional model for fault reactivation in which the potential for slip is equated to the ratio of the components of shear stress and normal stress on the fault plane our findings therefore make a compelling case for the concept of frictional slip tendency for the prediction of fault reactivation and lend support to the validity of fault slip methods for paleostress analysis

multivariate fracture intensity prediction application to oil mountain anticline wyoming the geometric characteristics of natural fractures significantly impact the hydraulic behavior of fractured reservoirs prediction of fracture geometry is therefore important for reservoir development decisions and production forecasting although many geometric kinematic mechanical geomechanical petrophysical sedimentary and geophysical attributes correlate to fracture intensity typically only the attribute with the highest absolute value correlation is chosen to be carried forward to influence prediction we employ a geostatistical bayesian updating approach that quantitatively accounts for multiple important attributes together impacting fracture geometry prediction the resulting models are more representative of the true geological complexity this methodology is applied to the oil mountain anticline outcrop near casper wyoming

a subduction zone reference frame based on slab geometry and subduction partitioning of plate motion and trench migration 1 the geometry of subducted slabs that interact with the transition zone depends critically on the partitioning of the subduction velocity vs at the surface into its subducting plate motion component vsp and trench migration component vt geodynamic models of progressive subduction demonstrate such dependence with five distinct slab geometries and corresponding partitioning ratios vsp vs slab draping vsp vs 0 5 slab draping with recumbent folds 0 5 vsp vs 0 8 slab piling 0 8 vsp vs 1 2 slab roll over with recumbent folds 1 2 vsp vs 1 5 and slab roll over vsp vs 1 5 the model findings have been applied to subduction zones in nature with well resolved slab geometries for which subduction partitioning ratios have been calculated during the last 20 million years in two global reference frames the indo atlantic and pacific hotspot reference frames the model nature comparison determines in which reference frame subduction partitioning ratios are most in agreement with observed slab geometries in the indo atlantic frame five out of five selected subduction zone segments with well resolved slab geometries plate velocities and trench velocities japan izu bonin mariana tonga kermadec agree with the geodynamic model predictions as calculated subduction partitioning ratios match the observed slab geometries in the pacific frame the partitioning ratio of only one subduction zone segment izu bonin matches observations it is thus concluded that the indo atlantic hotspot reference frame is preferred over the pacific one as a subduction zone reference frame in which to describe plate motions subduction kinematics and mantle flow

imaging of aseismic fault slip transients recorded by dense geodetic networks summary the large scale continuous gps networks that have emerged in the last decade have documented a wide range of aseismic deformation transients that resulted from physical processes such as aseismic fault slip and magma intrusion in particular a new class of m 7 slow earthquakes with durations ranging from days to months have been observed with gps arrays located above the downdip portion of subduction zone thrust interfaces interpretation of the displacement time series resulting from these events is not straightforward owing to the contaminating effects of multiple contributing signals such as fault slip local benchmark motion seasonal effects and reference frame errors we have developed a time dependent inversion algorithm based on the extended kalman filter which can separate the various signals and allow the space time evolution of these slow slip transients to be studied in detail we applied the inversion algorithm to the 1999 cascadia slow earthquake this event had two primary episodes of moment release separated by a two week period in which relatively little moment release occurred the cascadia event and other slow earthquakes share numerous similarities with both ordinary earthquakes and afterslip transients suggesting that they may represent fault slip under a conditionally stable regime

high temperature brine in chalcopyrite rich quartz vein 40 km southwest of sudbury ontario the lac panache nipissing gabbro intrudes huronian metasediments ca 40 km southwest of the sudbury igneous complex the gabbro contains disseminated sulfides and is in contact with a chalcopyrite rich quartz vein that crystallized from highly saline fluids 46 8 3 equivalent wt nacl at a minimum temperature of 420 27 c chloride and carbonate inclusions in opened fluid inclusion cavities in the vein suggest that the brine contained dissolved metals in addition to nacl such as fe cu mn and co the weakly altered quartz vein postdated regional metamorphism and was probably contemporaneous with the 1 7 ga felsic magmatism and attendant albite alteration in the area cl rich scapolite in the gabbro and highly saline fluid inclusions in the quartz vein suggest the existence of circulating hot brine throughout the tectonic evolution of the region the 2 2 ga old gabbro contains an abundance of cl rich scapolite intergrown with pyrrhotite and chalcopyrite that formed during the early hydrotherma

the roles of magmatic and hydrothermal processes in pge mineralization ferguson lake deposit nunavut canada the ferguson lake ni cu co platinum group element pge deposit in nunavut canada occurs near the structural hanging wall of a metamorphosed gabbroic sill that is concordant with the enclosing country rock gneisses and amphibolites massive to semi massive sulfide occurs toward the structural hanging wall of the metagabbro and a low sulfide high pge style of mineralization sulfide veins and disseminations locally occurs 30 50 m below the main massive sulfide water rock interaction in the ferguson lake ni cu co pge deposit is manifested mostly as widespread post metamorphic epidote chlorite calcite veins and replacement assemblages that contain variable amounts of sulfides and platinum group minerals pgm pgm occur as inclusions in magmatic pyrrhotite and chalcopyrite in both the massive sulfide and high pge zones at the contact between sulfides and hornblende or magnetite inclusions in the massive sulfide in undeformed sulfide veins and adjacent chlorite and or epidote halos in hornblende adjacent to hydrothermal veins and in plagioclase chlorite aggregates replacing garnet cemented by sulfide the pgm are mostly represented by the kotulskite pdte sobolevskite pdbi solid solution but also include michenerite pdbite froodite pdbi2 merenskyite pdte2 mertieite ii pd8 sb as 3 and sperrylite ptas2 and occur in variety of textural settings those that occur in massive and interstitial sulfides interpreted to be of magmatic origin and formed through exsolution from base metal sulfides at temperatures 600 c are dominantly bi rich i e te bearing sobolevskite whereas those that occur in late stage hydrothermal sulfide silicate veins and their epidote chlorite alteration halos tend to be more te rich i e bi bearing kotulskite the chemistry and textural setting of the various pgm supports a genetic model that links the magmatic and hydrothermal end members of the sulfide pgm mineralization the association of pgm with magmatic sulfides in the massive sulfide and high pge zones has been interpreted to indicate that pge mineralization was initially formed through exsolution from base metal sulfides which formed by magmatic sulfide liquid segregation and crystallization however the occurrence of pgm in undeformed sulfide bearing veins and in their chlorite epidote halos and differences in pgm chemistry indicate that hydrothermal fluids were responsible for post metamorphic redistribution and dispersion of pge

influence of the subducting plate velocity on the geometry of the slab and migration of the subduction hinge abstract geological observations indicate that along two active continental margins east asia and mediterranean major phases of overriding plate extension resulting from subduction hinge retreat occurred synchronously with a reduction in subducting plate velocity in this paper results of fluid dynamical experiments are presented to test the influence of the velocity of the subducting plate on the hinge migration velocity and on the geometry of the slab results show that hinge retreat decreases with increasing subducting plate velocity in addition phases of hinge retreat alternate with phases of hinge advance for relatively high subducting plate velocities due to interaction of the slab with the bottom of the box simulating the upper lower mantle discontinuity such slab kinematics could explain the episodic behaviour of back arc opening observed in convergent settings the geometry of the slab and the kinematics of subduction are significantly affected by the velocity of the subducting plate three subduction modes with accompanying slab geometry can be recognized a relatively low subducting plate velocity is accompanied by relatively fast hinge retreat with backward sinking of the slab and a backward draping slab geometry with increasing subducting plate velocity hinge migration is relatively small resulting in subvertical sinking of the slab and a folded slab piling geometry for a very high velocity the hinge migrates forward resulting in forward oriented subduction vectors and a forward draping slab geometry

cenozoic tectonics of western north america controlled by evolving width of farallon slab the basin and range province of western north america exemplified by the alternating mountain ridge and valley landscapes across nearly the entire u s state of nevada started to form 50 million years ago through a series of extensions of the continental crust prior to that massive mountain building collisions at the boundary between north america and the pacific ocean formed a subduction zone and compressed the continent by combining observations of global subduction zone velocities with numerical modeling schellart et al p 316 1 demonstrate that the thinning of the subducting portion of the oceanic plate controlled how and when the transition from compression to extension occurred even today where the much smaller remnant oceanic plate continues to slowly subduct below north america in the pacific northwest the width of the slab and not its age controls the velocity of subduction indeed this relation may explain the dynamics of other modern subduction zones from south america to japan 1 lookup doi 10 1126 science 1190366

geochemistry of the late permian no 30 coal seam zhijin coalfield of southwest china influence of a siliceous low temperature hydrothermal fluid this paper describes the influence of siliceous low temperature hydrothermal fluid on the elemental concentrations and mineralogical characteristics of the late permian anthracitic ro max 3 58 coal seam no 30 from the zhijin coalfield in western guizhou province sw china coal samples were examined using instrumental neutron activation analysis inductively coupled plasma mass spectroscopy inductively coupled plasma atomic emission spectrometry x ray fluorescence powder x ray diffraction scanning electron microscopy equipped with energy dispersive x ray and isotope analysis the modes of occurrence of elements were determined using a sequential chemical extraction procedure the studies indicate that the no 30 coal seam has a very high content of veined quartz vol 9 4 whose isotope values of 30si and 18o are 0 6 and 15 4 respectively indicating that the quartz originated from siliceous low temperature hydrothermal fluid formation temperature 160 220 c rather than detrital material of terrigenous origin or magmatic hydrothermal inputs results of scanning electron microscopy equipped with energy dispersive x ray and sequential chemical extraction procedure show that the veined quartz is the dominant source of fe cu u pd pt and ir which are as high as 2 31 356 8 2 1 2 43 and 0 006 g g in this coal seam respectively the studies have also found that elements such as fe and cu are mainly in the veined quartz and they do not occur as sulfides in this coal seam in sharp contrast to many other coal seams in china the geochemical and mineralogical anomalies of the coal are attributed to the siliceous low temperature hydrothermal fluid

pacific absolute plate motion since 145 ma an assessment of the fixed hot spot hypothesis 1 using the geometry and ages from 12 pacific seamount chains we have determined two new absolute plate motion models that now extend our self consistent and high resolution models with covariance estimates back to 145 ma the wk08 a model maps the full uncertainty in the age progressions into uncertainties in rotation opening angles yielding a relatively smooth plate motion model the wk08 g model relaxes the mapping of age uncertainties in order to better isolate secondary geometry changes seen along many coregistered chains both models have been used to assess the viability of the fixed hot spot hypothesis in the pacific in determining the models we found that only a small group of age samples had to be discarded on the grounds that they were discordant with the dominant trends we were able to connect plate motions for pre and post emperor age intervals by including the ratak gilbert ellice and musicians trails in our analysis however as no active hot spot locations exist for the older chains their inclusion adds additional model parameters both age and geometry misfits increase with age reflecting the observed increase in age uncertainties and the general widening of trails secondary and short lived changes in absolute plate motion mapped in wk08 g appear to correlate with the timing and sense of motion of known pacific rim tectonic events analysis of interchain distances between coeval samples from the hawaii and louisville chains suggests possible discrepancies during the older emperor stage that are compatible with predictions of hot spot drift we computed a new apparent polar wander path for the pacific and found a high degree of correspondence with paleomagnetically derived paths as long as solutions allowing for anomalous skewness were included in the latter our polar wander path suggests that there might have been some true polar wander during the emperor stage complemented by a smaller amount of hot spot drift than otherwise required we show that chain geometries and ages combined with future paleolatitude determinations from additional sites and chains could enable an observation based description of both hot spot and plate motions without relying on predictions of hot spot drift derived from mantle flow calculations

a model to explain joint patterns found in ignimbrite deposits the study of fracture systems is of paramount importance for economic applications such as co2 storage in rock successions geothermal and hydrocarbon exploration and exploitation and also for a better knowledge of seismogenic fault formation understanding the origin of joints can be useful for tectonic studies and for a geotechnical characterisation of rock masses here we illustrate a joint pattern discovered in ignimbrite deposits of south america which can be confused with conjugate tectonic joint sets but which have another origin the pattern is probably common but recognisable only in plan view and before tectonic deformation obscures and overprints it key sites have been mostly studied by field surveys in bolivia and chile the pattern is represented by hundreds of meters up to kilometre long swarms of master joints which show circular to semi circular geometries and intersections that have x and y patterns inside each swarm joints are systematic rectilinear or curvilinear in plan view and as much as 900 m long in section view they are from sub vertical to vertical and do not affect the underlying deposits joints with different orientation mostly interrupt each other suggesting they have the same age this joint architecture is here interpreted as resulting from differential contraction after emplacement of the ignimbrite deposit above a complex topography the set of the joint pattern that has suitable orientation with respect to tectonic stresses may act to nucleate faults

multi stage hydrothermal processes involved in low sulfide cu ni pge mineralization in the footwall of the sudbury igneous complex canada amy lake pge zone east range the amy lake pge zone is a low sulfide type cu ni pge mineralization in the east range footwall of the 1 85 ga sudbury igneous complex occurring in a 100 m wide sudbury breccia belt that coincides with an impact related major fracture zone bay fault zone detailed hydrothermal alteration mapping fluid inclusion trace element and stable isotope studies revealed a complex alteration and mineralization history in a multi source multi stage sudbury related hydrothermal system the two major stages of syn sudbury hydrothermal activity are characterized by similarly high salinity high temperature fluids that are 1 locally derived from footwall granophyre bodies and typified with high ni cu and pge s ratios and high ree contents magmatic hydrothermal stage and 2 a more voluminous cu ni pge rich fluid flux probably originated from the sudbury igneous complex footwall contact hydrothermal stage the second hydrothermal flux was introduced by brittle fractures in the area and resulted in a complex zonation of alteration assemblages and mineralization governed by local footwall composition the sudbury related hydrothermal event was overprinted by shear related epidote veining and calcite chlorite replacement both regionally present in the sudbury structure based on analogies the most important factors involved in the formation of hydrothermal low sulfide mineralization are proposed to be 1 accumulation of pge enriched fluids 2 large scale brittle structures as conduits to these fluids and 3 adequate host rock composition as a chemical trap resulting in sulfide and pgm precipitation in environments meeting these criteria hydrothermal pge mineralization is known to have formed not only in the sudbury footwall but also from mafic ultramafic intrusions associated with primary magmatic pge from several locations around the world

anoxic sediments an important environment for pge an overview anoxic sediments and metasediments have been recently recognized as important host environments for the platinum group elements pge economically significant pge concentrations have been reported from marine metal rich black shales in china yukon canada and poland these ore bearing horizons are characterized by extremely restricted vertical and sometimes larger horizontal extents they are associated with the evolution of intracontinental rifting structures without any magmatic activity suggesting a possible driving mechanism for mineralization processes complex pge associations including a significant relationship of pd and pt with ni bi se y and also with sb cu co au u and f are suggested using the results of a new statistical evaluation of available geochemical data these occurrences show more common features with other hydrothermal pge deposits the rift volcanic related marine metal rich black shales of the czech republic and finland however display lower pge values the mineralized layers are much thicker with a typically limited horizontal extent showing a close association with volcanic centres pd reveals a strong correlation with ni zn au and v pt exhibits a highly significant link with the cu and mo phases low average nicu ratios and pge au chondrite normalized patterns are similar to those of some magmatic pge deposits hosted in mafic and ultramafic rocks it is very likely that organic matter played an important role in the genesis of pge accumulations in metal rich black shales in both rift and rift volcanic related environments

deformation during the 12 november 1999 duzce turkey earthquake from gps and insar data only 87 days after the mw 7 5 17 august 1999 izmit earthquake the duzce earthquake ruptured a ca 40 km long adjoining strand of the north anatolian fault naf system to the east we used displacements of 50 global positioning system gps sites together with interferometric synthetic aperture radar insar range change data spanning the event to estimate the geometry and slip distribution of the coseismic rupture postseismic deformation transients from the duzce earth quake and the preceding i zmit event that are included in some of the measurements are corrected for using dislocation models fit to gps data spanning the various time periods nonlinear inversions for fault geometry indicate that the rupture occurred on a ca 54 north dipping oblique normal right lateral fault distributed slip inver sions indicate maximum strike slip near the center of the duzce fault close to the earthquake hypocenter slip magnitude and depth of faulting decrease to the west and east of the hypocenter both gps and insar data suggest that normal slip is restricted to the shallow portion of the rupture the duzce earthquake had the highest slip to rupture length ratio of any historic earthquake along the naf

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

bending mechanics and mode selection in free subduction a thin sheet analysis summary to elucidate the dynamics of free buoyancy driven subduction of oceanic lithosphere i study a model in which a 2 d sheet of viscous fluid with thickness h and viscosity 1 subducts in an infinitely deep ambient fluid with viscosity 1 numerical solutions for the sheet s evolution are obtained using the boundary element method bem starting from an initial configuration comprising a short protoslab attached to a longer horizontal plate that is free to move laterally beneath an impermeable traction free surface interpretation of the solutions using thin viscous sheet theory shows that the fundamental length scale controlling the subduction is the bending length lb defined at each instant as the length of the portion of the sheet s midsurface where the rate of change of curvature is significant geophysically speaking lb is the sum of the lengths of the slab and of the region seaward of the trench where flexural bulging occurs the bending length in turn enters into the definition of the sheet s dimensionless stiffness s h lb 3 which controls whether the sinking speed of the slab is determined by the viscosity of the sheet itself s 1 or by that of the ambient fluid s 1 motivated by laboratory observations of different modes of subduction retreating versus advancing trench folding versus no folding etc in fluid layers with finite depth i calculate numerically the dip d of the slab s leading end as a function of and the normalized depth d h to which it has penetrated the contours of the function d d h strongly resemble the intermode boundaries in the laboratory based regime diagram of schellart supporting the hypothesis that the mode of subduction observed at long times in experiments is controlled by the dip of the slab s leading end when it reaches the bottom of the layer in particular the bem solutions explain why trenches advance in the laboratory only when lies in an intermediate range and why they retreat when is either smaller or larger than this application of the bem model to wu et al s compilation of the minimum curvature radii of subducted slabs suggests 140 510 for the earth this is too small to permit the laboratory type trench advancing mode in agreement with the lack of tomographic evidence for slabs that are bent over backwards

the lac des iles complex ontario petrology and platinum group elements mineralization in an archean mafic intrusion the lac des iles complex is a late archean mafic to ultramafic complex that is host to 20 4 106 t pt pd and au mineralization with an average grade of 6 34 g t platinum group elements pge the 30 km2 complex located in the wabigoon subprovince consists of several coalescing mafic to ultramafic intrusive centers the complex is emplaced into early gneissic tonalite and is contemporaneous with late granitoids the magmatic evolution of the complex reflects the emplacement of multiple pulses of previously fractionated magma some of which underwent subsequent in situ fractionation distinct magma sequences are recognized on the basis of intrusive relationships differences in the cumulus minerals crystallization order and trace element chemistry these sequences are 1 hornblende gabbro 2 gabbro and gabbronorite and 3 ultramafic where there is evidence of intrusive relations the most primitive sequences are emplaced late and occur toward the north end of the complex microprobe analyses in

gold and platinum in shales with evidence against extraterrestrial sources of metals abstract few black shales contain concentrations of precious metals higher than average continental crust i e 5 ppb au yet au and pt alloys have been reported from the kupferschiefer in poland moreover thin sulfide beds in certain chinese and canadian shales contain several hundred ppb au pd and pt and average 4 mo and 2 5 ni in an association that is difficult to explain volcanic and non volcanic exhalations hydrothermal epigenesis involving either igneous or sedex fluids biogenic processes and low temperature secondary enrichment are among the possible factors involved in deriving ni pge and au for black shales and sulfide beds in black shales extraterrestrial sources have been invoked in some cases e g the cambrian of china however available data on abundances of pge indicate relatively low values for ir

discrete fracture network model of the vapor zone leakages at the copahue geothermal field abstract the volcano hosted geothermal system of copahue is one of the most promising resources of renewable energy in argentina it is driven by a layered reservoir composed of a steam cap above a deep liquid dominated reservoir we study the surficial leakages of the shallow steam zone by performing a discrete fracture network model and a 3d forward strain stress model of the upper caprock unit the hydrothermal zones linked to steam cap leakages are subordinated to deep rooted n60 striking faults associated damage zones exhibit higher values of fracture intensity vertical and anisotropy of permeability than the host rocks joints and cross joints likely control leakage zones where the formers are subject to high dilation tendency the anfiteatro monocline might constitute the northwestern boundary of the shallow steam zone variations of h2o co2 ratio helium isotopic signature and co2 between hydrothermal zones are explained in terms of petrophysical properties of the upper ignimbrites and changes in their structural control our results suggest that the upper caprock ignimbrite avoids the decompression of the reservoir because it provides the low fractured and low permeability layer that seals the geothermal system conversely ignimbrites affected by the extensional faults system enhance the shallow vapor zone given its high fracture density and permeability

a large scale flow and tracer experiment in granite 2 results and interpretation water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock in a companion paper the experimental design and performed experiments are described the present paper describes the interpretation of flow and tracer movement in the rock outside the drift the tracer movement was measured by the more than 160 individual tracer curves the tracer experiments have permitted the flow porosity and dispersion to be studied the possible effects of channeling and the diffusion of tracers into stagnant waters in the rock matrix and in stagnant waters in the fractures have also been addressed

structural architecture releasing deep sourced carbon dioxide diffuse degassing at the caviahue copahue volcanic complex abstract the link between carbon dioxide diffuse degassing and its structural control was examined in the caviahue copahue volcanic complex over an area of approximately 10 km2 that encompasses five hydrothermal sites namely anfiteatro copahue town las maquinitas i las maquinitas ii and las maquinas both geochemical and structural approaches were applied in order to investigate the structural scenario releasing hydrothermal fluids in this area also the first isotopic analysis of soil co2 degassing in the andean region is presented the geochemical analysis shows well defined co2 diffuse degassing structures in copahue town las maquinitas i las maquinitas ii and las maquinas hydrothermal sites soil diffuse co2 is fed by multiple sources a deep magmatic hydrothermal source a biogenic source and a mixed source the structural analysis indicates the presence of an extensional regime that gives place to three structural trends consisting of ne sw trending normal faults nw se sinistral strike slip faults and ene wsw right lateral strike slip faults the comparison between diffuse degassing structures directions and faults directions suggests that there is a structural control on diffuse degassing diffuse co2 is released through an early extensional setting and it is emitted through normal faults strike slip faults and through areas with higher structural damage such as relay areas between fault segments and terminations of individual fault segments

from decades to epochs spanning the gap between geodesy and structural geology of active mountain belts geodetic data from the global navigation satellite system gnss and from satellite interferometric radar insar are revolutionizing how we look at instantaneous tectonic deformation but the significance for long term finite strain in orogenic belts is less clear we review two different ways of analyzing geodetic data velocity gradient fields from which one can extract strain dilatation and rotation rate and elastic block modeling which assumes that deformation is not continuous but occurs primarily on networks of interconnected faults separating quasi rigid blocks these methods are complementary velocity gradients are purely kinematic and yield information about regional deformation the calculation does not take into account either faults or rigid blocks but where gnss data are dense enough active fault zones and stable blocks emerge naturally in the solution block modeling integrates known structural geometry with idealized earthquake cycle models to predict slip rates on active faults future technological advances should overcome many of today s uncertainties and provide rich new data to mine by providing denser more uniform and temporally continuous observations

platinum group element mineralization in a hydrothermal cu ni sulfide occurrence rathbun lake northeastern ontario pt pd and au are concentrated in a hydrothermal cu ni sulfide occurrence near rathbun lake northeastern ontario the mineralization is associated with a sheared zone of the wanapitei intrusion where hydrothermal fluids have altered relatively pristine gabbronorite to chlorite sericite quartz epidote and biotite chalcopyrite and pyrite the principal sulfide minerals occur as massive and disseminated mineralization bismuthian merenskyite and to a lesser extent kotulskite michenerite and temagamite are the pd bearing minerals whereas pt occurs primarily in sperrylite 64 percent of the pd mineral grains are associated with altered silicates rather than sulfides although grains within sulfides may have been exsolved the size and number associated with silicates suggest many were precipitated independently grab samples average 9 percent cu 0 2 percent ni 20 829 ppb pd 9 736 ppb pt and 3 053 ppb au values for the other platinum group elements are near background levels no correlation is evident between cu and the platinum group elements or au the ratio of pt pd os ir ru is much larger than for tholeiitic hosted deposits of magmatic origin and probably reflects the relative solubilities of the platinum group elements

concentrations and origins of platinum group elements in late paleozoic coals of china the platinum group elements pges in 63 samples collected from the late paleozoic coal bearing strata in western guizhou province and north china were determined using high resolution inductively coupled plasma mass spectrometry hr icp ms the study shows that pges in coal have five different sources magmatic hydrothermal inputs low temperature hydrothermal fluids synsedimentary volcanic ash detrital minerals of terrigenous origin and seawater this study indicates that the first three sources can lead to enrichment of pges in these chinese coals the typical low contents of pges in most of the studied coals defined as background contents in this work mainly originate from detrital minerals the background content of pd 150 ng g is higher than that of pt 30 ng g and much higher than that of ru 5 ng g rh 14 ng g and ir 1 ng g the pd content is nearly 15 fold higher than the crustal abundance in contrast pt content is lower than its crustal abundance the relatively good correlation between pd pt and ash contents suggests that the pges are associated with minerals

structural controls on fluid circulation at the caviahue copahue volcanic complex ccvc geothermal area chile argentina revealed by soil co 2 and temperature self potential and helium isotopes abstract natural geothermal systems are limited areas characterized by anomalously high heat flow caused by recent tectonic or magmatic activity the heat source at depth is the result of the emplacement of magma bodies controlled by the regional volcano tectonic setting in contrast at a local scale a well developed fault fracture network favors the development of hydrothermal cells and promotes the vertical advection of fluids and heat the southern volcanic zone svz straddling chile and argentina has an important yet unexplored and undeveloped geothermal potential studies on the lithological and tectonic controls of the hydrothermal circulation are therefore important for a correct assessment of the geothermal potential of the region here new and dense self potential sp soil co 2 and temperature t measurements and helium isotope data measured in fumaroles and thermal springs from the geothermal area located in the north eastern flank of the copahue volcanic edifice within the caviahue caldera the caviahue copahue volcanic complex ccvc are presented our results allowed to the constraint of the structural origin of the active thermal areas and the understanding of the evolution of the geothermal system ne striking faults in the area characterized by a combination of sp co 2 and t maxima and high 3 he 4 he ratios up to 8 16 0 21ra whereas atmospheric ra is 1 382 10 6 promote the formation of vertical permeability preferential pathways for fluid circulation wnw striking faults represent low permeability pathways for hydrothermal fluid ascent but promote infiltration of meteoric water at shallow depths which dilute the hydrothermal input the region is scattered with sp co 2 and t minima representing self sealed zones characterized by impermeable altered rocks at depth which create local barriers for fluid ascent the ne striking faults seem to be associated with the upflowing zones of the geothermal system where the boiling process produces a high vapor dominated zone close to the surface whereas the wnw striking faults could act as a boundary of the copahue geothermal area to the south

mafic intrusions in the footwall of the sudbury igneous complex origin of the sudbury impact melt sheet and its associated ore deposits abstract the majority of the mafic intrusions and volcanic rocks in the footwall of the sudbury igneous complex sic which is believed to have formed from a melt sheet produced by the impact of a very large bolide belong to one of two large mafic igneous suites viz the 2450 ma east bull lake ebl suite of intrusions or the 2200 ma nipissing diabase suite of intrusions this has been established by u pb la icp ms dating of zircons from the newly recognized frood intrusion which hosts the frood and stobie ore bodies and two of the sudbury gabbro intrusions and comparison of the geochemistry of these intrusions with that of the ebl intrusive suite and the nipissing diabase suite the age of the frood intrusion 2421 32 ma falls within error of other ebl type intrusions whereas the ages of the nairn 2203 11 ma and totten 2168 11 ma intrusions fall within error of published ages for the nipissing diabase moreover the primitive mantle normalized patterns of the petrogenetic trace elements on extended spidergrams of the nairn and totten sudbury gabbros are similar to those of the nipissing diabase as are those of the frood intrusion to other members of the ebl intrusive suite the ni cu pge sulfide deposits at sudbury are associated with the lower contact of the sic where a discontinuous inclusion rich norite contains much of the mineralization at the contact and an inclusion bearing quartz diorite is directly associated with the mineralization of the radial and concentric offset dykes the sublayer rocks and the overlying unit of melanocratic norites provide strong evidence for a relationship between the ore deposits and both inclusions and melts of mafic ultramafic target rocks the most common pre impact mafic ultramafic target rocks are intrusions of the ebl and nipissing diabase suites although there are also archean aged mafic ultramafic enclaves in the gneisses beneath the north range of the sic the totten orebody in the worthington offset and the kelly lake ore body in the copper cliff offset are directly associated with footwall rocks comprising sudbury gabbro and nipissing gabbro respectively whereas the frood stobie offset and the associated frood and stobie ore deposits are sandwiched in a breccia belt containing large rafts of amphibole megacrystic gabbro belonging to the extensively broken up frood intrusion olivine bearing mafic and ultramafic rocks some of which exhibit shock metamorphic features but others do not are common inclusion types and occur in diverse sublayer environments the unshocked melanorite and olivine melanorite inclusions share common geochemical characteristicsde indicating that they were derived from a similar source their geochemistry is also similar to that of the frood intrusion as well as the east bull lake intrusion this indicates that they may have been sourced from east bull lake type intrusions that were incorporated into the melt sheet at the time of melt generation mass balance calculations indicate that the felsic country rocks which account for 77 of the total volume of the sic and contain 18 ppm ni and 21 ppm cu together with the sulfide poor mafic country rocks which account for 23 of the sic and contain 133 ppm ni and 92 ppm cu have too little ni and cu to account for the ni and cu contents of the quartz diorite the composition of which provides an indication of that of the initial melt sheet calculations using the r factor equation of campbell and naldrett 1979 indicate that the magmas that formed the norites and the ore deposits had 137 ppm ni and 121 ppm cu mass balance calculations have been used to determine if the country rocks have sufficient ni and cu in them to generate the ore deposits the weighted median ni content of the sulfide poor

the role of boundary conditions in numerical models of subduction zone dynamics abstract numerical studies of subduction zone dynamics on a regional scale usually use a limited spatial extent for their models and therefore need to define boundary conditions on all model edges these boundary conditions imply a choice for the mechanical and thermal state of the surrounding regions which may influence the evolution of the model system we investigate the role of the surface and lateral boundary conditions for simple mechanical subduction models using a standard finite element method we find that subduction is only possible if the slab can decouple from the surface this decoupling can be achieved by a true free surface a free slip surface with a weak crust for the subducting plate or a free slip surface with a layer of low viscosity low density material sticky air between the model surface and the crust models of slab dynamics that employ a free slip surface reproduce trench migration slab sinking velocities and slab geometry of models with a free surface as long as they use either a weak crust which can be viscous viscoelastic and or brittle or a sticky air layer the vertical topography will however not be reproduced for free slip models without a sticky air layer for ocean ocean convergent models we find that the application of inflow boundary conditions at the edges of the subducting or overriding lithosphere controls trench motion and the geometry of the subducting slab inflow on the overriding side causes trench retreat and a slab resting on the lower mantle whereas inflow restricted to the subducting side can cause trench advance and a slab which folds on the lower mantle

seismic tomography with p and s data reveals lateral variations in the rigidity of deep slabs abstract regional seismic tomography of the northwest pacific island arcs using p and s wave arrival time data with similar path coverage reveals an oceanic lithospheric slab deflected in the mantle transition zone beneath the izu bonin region in good agreement with the results of earlier tomographic and other seismic studies in the region the s wave images however do not show clearly the deflection of the slab this implies that the stagnant lithospheric slab in the transition zone is more likely a bulk sound structure which is strongly supported by our results from joint inversions for bulk sound and shear wavespeeds for the izu bonin region where trench migration has been reported the properties of the deflected slab lying on top of the 660 km discontinuity show strong bulk sound and weak shear signatures in contrast to the descending slab itself there is an indication in the shear images that a component of the former oceanic lithosphere is penetrating into the top of the lower mantle suggesting that a slab split has occurred

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

fracture prediction for the 1980 el asnam algeria earthquake via elastic dislocation modeling 1 geomechanical models based on linear elasticity have been used to predict the mode and distribution of subseismic fractures around larger faults these models can be tested against field observations of surface breaks fractures formed in the aftermath of large earthquakes this paper presents forward models based on elastic dislocation theory of the deformation due to the ms 7 3 earthquake at el asnam algeria in 1980 using fault parameters from previous geodetic studies to define a set of larger faults our models calculate the deformation field in the surrounding rock volume we compare predicted strain and stress fields with the surface deformation measured in the area following the 1980 earthquake using a combination of the redistributed elastic dislocation stress due to slip on the major faults and a small component of overburden stress the models successfully predict normal faults and tensile fractures in the hanging wall of the reverse fault system orientations of the predicted faults vary along strike of the fault system being parallel to the main reverse fault in the south but oblique to it along the central segment agreeing with observed surface breaks the results of our forward modeling are not sensitive to the magnitude or direction of a regional tectonic stress the predicted fractures are controlled by the near field short term redistributed stresses due to coseismic slip the agreement between modeled and measured deformation patterns adds confidence in the use of elastic dislocation theory to accurately predict small faults generated by coseismic slip on large faults

mineralogy and geochemistry of a late permian coal in the dafang coalfield guizhou china influence from siliceous and iron rich calcic hydrothermal fluids abstract this paper describes the influence of siliceous and iron rich calcic low temperature hydrothermal fluids lthf on the mineralogy and geochemistry of the late permian no 11 coal anthracitic r r 2 85 in the dafang coalfield in northwestern guizhou province china the no 11 coal has high contents of vein ankerite 10 2 vol and vein quartz 11 4 vol with formation temperatures of 85 and 180 c respectively indicating that vein ankerite and vein quartz were derived from low temperature calcic and siliceous hydrothermal fluids in two epigenetic episodes the vein quartz appears to have formed earlier than vein ankerite did and at least three distinct stages of ankerite formation with different ca sr and fe mn ratios were observed the two types of mineral veins are sources of different suites of major and trace metals scanning electron microscope and sequential extraction studies show that in addition to fe mg and ca vein ankerite is the dominant source of mn cu ni pb and zn in the coal and the contents of these five elements are as high as 0 09 and 74 0 33 6 185 and 289 g g respectively in contrast vein quartz is the main carrier mineral for platinum group elements pges pd pt and ir in the coal and the contents of pd pt and ir are 1 57 0 15 and 0 007 g g respectively sequential extraction showed a high pge content in the silicate fraction up to 10 4 g g pd 1 23 g g pt and 0 05 g g ir respectively it is concluded that the formation of ankerite and quartz and the anomalous enrichment of trace elements in the no 11 coal in the dafang coalfield guizhou result from the influx of calcic and siliceous low temperature hydrothermal fluids

gas geochemistry of the magmatic hydrothermal fluid reservoir in the copahue caviahue volcanic complex argentina abstract copahue volcano is part of the caviahue copahue volcanic complex ccvc which is located in the southwestern sector of the caviahue volcano tectonic depression argentina chile this depression is a pull apart basin accommodating stresses between the southern liquine ofqui strike slip and the northern copahue antinir compressive fault systems in a back arc setting with respect to the southern andean volcanic zone in this study we present chemical inorganic and organic and isotope compositions 13c co2 15n 3he 4he 40ar 36ar 13c ch4 d ch4 and d h2o and 18o h2o of fumaroles and bubbling gases of thermal springs located at the foot of copahue volcano sampled in 2006 2007 and 2012 helium isotope ratios the highest observed for a southern american volcano r ra up to 7 94 indicate a non classic arc like setting but rather an extensional regime subdued to asthenospheric thinning 13c co2 values from 8 8 to 6 8 vs v pdb 15n values 5 3 to 5 5 vs air and co2 3he ratios from 1 4 to 8 8 109 suggest that the magmatic source is significantly affected by contamination of subducted sediments gases discharged from the northern sector of the ccvc show contribution of 3he poor fluids likely permeating through local fault systems despite the clear mantle isotope signature in the ccvc gases the acidic gas species have suffered scrubbing processes by a hydrothermal system mainly recharged by meteoric water gas geothermometry in the h2o co2 ch4 co h2 system suggests that co and h2 re equilibrate in a separated vapor phase at 200 220 c on the contrary rock fluid interactions controlling co2 ch4 production from sabatier reaction and c3h8 dehydrogenation seem to occur within the hydrothermal reservoir at temperatures ranging from 250 to 300 c fumarole gases sampled in 2006 2007 show relatively low n2 he and n2 ar ratios and high r ra values with respect to those measured in 2012 such compositional and isotope variations were likely related to injection of mafic magma that likely triggered the 2000 eruption therefore changes affecting the magmatic system had a delayed effect on the chemistry of the ccvc gases due to the presence of the hydrothermal reservoir however geochemical monitoring activities mainly focused on the behavior of inert gas compounds n2 and he should be increased to investigate the mechanism at the origin of the unrest started in 2011

an experimental study of subduction and slab migration results of fluid dynamical experiments on the behavior of subducted slabs are presented that address two important characteristics of subduction slab penetration through the transition zone and horizontal slab migration cold negatively buoyant molded slabs of concentrated sucrose solution with viscosities of 3 5 106 p were introduced into a more dilute two layered sucrose solution representing the upper and lower mantle the transition zone was modeled by a step increase in both density and viscosity ratios of slab thickness to upper layer depth the relative viscosities in each layer and the effective rayleigh number were close to mantle values the initial configuration consisted of two plates separated by a trench gap with one plate attached to a dipping slab simulating a developing subduction zone with an overriding plate two different boundary conditions were used at the trailing ridge end of the subducting plate 1 fixed end corresponding to zero ridge motion and 2 free end corresponding to zero ridge resistance based on results from 15 experiments with various combinations of upper layer lower layer and slab densities u l s and viscosities we find that slab penetration depth is sensitive to both the normalized slab density anomaly r s l s u and the dip angle three penetration regimes are recognized r 0 5 in which the slab sinks into the lower layer without distortion 0 2 r 0 5 which permits limited penetration the amount dependent on dip angle in this regime the slab develops a thick root just beneath the transition zone and r 0 2 in which the slab is deflected by the transition and little or no penetration occurs retrograde slab motion and trench migration occurred in nearly every case with the overriding plate moving parallel to but faster than the trench causing the gap between subducting and overriding plates to close with time prograde trench motion was never observed and the trench remained stationary only in the extreme case free ridge condition with equal upper and lower layer densities these results suggest that the transient extension found in many back arc basins may be a direct consequence of the tendency for retrograde subduction and the amount of extension may be governed in part by the degree of slab penetration through the transition zone

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

transport behavior in three dimensional fracture intersections 1 flow and transport patterns in three dimensional fracture intersections are investigated with emphasis on the occurrence and effects of local flows around each intersection flow and transport simulations indicate that local flow circulations referred to as local flow cells arise because of an interplay between intersection geometry and corresponding boundary conditions for flow along the fracture boundaries local flow cells are thus unique features in three dimensional fracture networks the analysis here suggests that local flow cells have little effect on the overall fluid flow in a fracture network but may constitute an effective mechanism which contributes to the long breakthrough tailing and retardation often observed in transport through discrete fracture networks

structural model and slip dilation tendency analysis at the copahue geothermal system inferences on the reservoir geometry the copahue volcano host one of the most attractive geothermal resources of argentina several studies focused on both the volcanic activity and the related geothermal manifestations including a feasibility report during the 90s however limited unclear and usually contradictory structural interpretations are found in the literature and the role of the main faults over the geothermal system remains thus unsolved this paper provides the first structural characterization and role assessment of the faults over the fluid flow and the reservoir geometry a 3d structural model has been constructed to achieve this goal and a fault plane striations survey has been carried out at anfiteatro termas and maquinitas hydrothermal zones using this dataset a slip and dilation tendency analysis over the main structures have been performed the 3d structural model indicates that the copahue geothermal field is bounded by an n60 trending fault set and constrained to the north by the trolope fault and to the south by the chancho co fault both with wnw ese trend the collected fault plain striations data was inverted to obtain the paleostress tensor related to the formation of the copahue village fault system cvfs the structure that controls the hydrothermal areas the subvertical maximum principal stress axis obtained defines a well constrained tensional regime with a subhorizontal nw se minimum principal stress consistent in all the surveyed locations both the 3d model and the inverted paleostress tensor indicate that the geothermal field and probably the entire northeastern slope of the volcano is subjected to an extensional faulting regime our analysis shows that the n 60 trending fault set is critically stressed for dilation and probably behaves as an active hydrological fault system whereas the n105 and n135 fault sets have intermediate and low dilation tendency respectively these tendencies might lead to a northeast trend fluid path between the chancho co and the n135 faults and might define the extension of the steam cap we propose a compartmentalized reservoir model made up by three fault segmented blocks while a steam cap over a deeper reservoir controlled by the cvfs characterizes the central segment a pressurized liquid dominated reservoir could prevail to the west of termas and the east of maquinas hydrothermal zones this model explains the differences between the fumaroles inside the cvfs i e termas to maquinas fumaroles and outside this structural system i e anfiteatro is consistent with the steam cap identified by the exploration boreholes and is consistent with the 3d structural framework proposed also the model suggests that the collapse of the eastern slope of the chancho co hill might constitute the initial state of the current configuration of the geothermal system additional studies are needed to verify the proposed reservoir model before defining deep exploration targets including magnetotellurics discrete fracture network analysis and preliminary thermodynamical models 2019 elsevier b v

platinum group elements in a 3 5 ga nickel iron occurrence possible evidence of a deep mantle origin the bon accord ba ni fe deposit occurs in chemically depleted ultramafic rocks of the circa 3 5 ga jamestown ophiolite complex in the barberton greenstone belt of the kaapvaal craton south africa the host rocks of the ba body are high temperature ultramafic tectonites which probably represent the upper mantle residue from which the overlying magmatic rocks were separated during partial melting ba is unusual both mineralogically and chemically it consists of a rare ni rich assemblage ni oxide bunsenite spinels trevorite nichromite and silicates e g liebenbergite the ni end member olivine and their altered equivalents nio average 38 and feo fe2o3 average 34 are the major chemical constituents the cu and s contents are very low both 2000 c lower mantle high ni fe and ni co ratios relative to c 1 chondrite suggest that ba might have been derived from siderophile rich material that remained in the lower mantle after inefficient core formation a model is presented wherein such a metal silicate heterogeneity is fractionated and oxidized during ascent through the mantle in a thermal plume which originates in the lowermost mantle the d layer some of its residue is finally incorporated as pods into the lithospheric mantle during formation of the archean oceanic crust inclusion of such fractionated pods in the old subcontinental keel of the kaapvaal craton might constitute a potential pge source which could have been tapped by subsequent magmatic activity

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

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

evaluation of sampling methods for fracture network characterization using outcrops outcrops provide valuable information for the characterization of fracture networks sampling methods such as scanline sampling window sampling and circular scanline and window methods are available to measure fracture network characteristics in outcrops and from well cores these methods vary in their application the parameters they provide and therefore have advantages and limitations we provide a critical review on the application of these sampling methods and apply them to evaluate two typical natural examples 1 a large scale satellite image from the oman mountains oman 120 000 m2 1 291 669 ft2 and 2 a small scale outcrop at craghouse park united kingdom 19 m2 205 ft2 the differences in the results emphasize the importance to 1 systematically investigate the required minimum number of measurements for each sampling method and 2 quantify the influence of censored fractures on the estimation of fracture network parameters hence a program was developed to analyze 1300 sampling areas from 9 artificial fracture networks with power law length distributions for the given settings the lowest minimum number of measurements to adequately capture the statistical properties of fracture networks was found to be approximately 110 for the window sampling method followed by the scanline sampling method with approximately 225 these numbers may serve as a guideline for the analyses of fracture populations with similar distributions furthermore the window sampling method proved to be the method that is least sensitive to censoring bias reevaluating our natural examples with the window sampling method showed that the existing percentage of censored fractures significantly influences the accuracy of inferred fracture network parameters

influence of fracture scale heterogeneity on the flow properties of three dimensional discrete fracture networks dfn while permeability scaling of fractured media has been so far studied independently at the fracture and network scales we propose a numerical analysis of the combined effect of fracture scale heterogeneities and the network scale topology the analysis is based on 2 106 discrete fracture network dfns simulations performed with highly robust numerical methods fracture local apertures are distributed according to a truncated gaussian law and exhibit self affine spatial correlations up to a cutoff scale lc network structures range widely over sparse and dense systems of short long or widely distributed fracture sizes and display a large variety of fracture interconnections flow bottlenecks and dead ends at the fracture scale accounting for aperture heterogeneities leads to a reduction of the equivalent fracture transmissivity of up to a factor of 6 as compared to the parallel plate of identical mean aperture at the network scale a significant coupling is observed in most cases between flow heterogeneities at the fracture and at the network scale the upscaling from the fracture to the network scale modifies the impact of fracture roughness on the measured permeability this change can be quantified by the measure a2 which is analogous to the more classical power averaging exponent used with heterogeneous porous media and whose magnitude results from the competition of two effects i the permeability is enhanced by the highly transmissive zones within the fractures that can bridge fracture intersections within a fracture plane ii it is reduced by the closed and low transmissive areas that break up connectivity and flow paths citation de dreuzy j r y meheust and g pichot 2012 influence of fracture scale heterogeneity

a new device for characterizing fracture networks and measuring groundwater and contaminant fluxes in fractured rock aquifers this paper presents the fundamental theory and laboratory test results on a new device that is deployed in boreholes in fractured rock aquifers to characterize vertical distributions of water and contaminant fluxes aquifer hydraulic properties and fracture network properties e g active fracture density and orientation the device a fractured rock passive flux meter frpfm consists of an inflatable core assembled with upper and lower packers that isolate the zone of interest from vertical gradients within the borehole the outer layer of the core consists of an elastic fabric mesh equilibrated with a visible dye which is used to provide visual indications of active fractures and measures of fracture location orientation groundwater flux and the direction of that flux beneath the outer layer is a permeable sorbent that is preloaded with known amounts of water soluble tracers which are eluted at rates proportional to groundwater flow this sorbent also captures target contaminants present in intercepted groundwater the mass of contaminant sorbed is used to quantify cumulative contaminant flux whereas the mass fractions of resident tracers lost are used to provide measures of water flux in this paper the frpfm is bench tested over a range of fracture velocities 2 20 m day using a single fracture flow apparatus fracture aperture 0 5 mm test results show a discoloration in visible dye corresponding to the location of the active fracture the geometry of the discoloration can be used to discern fracture orientation as well as direction and magnitude of flow in the fracture average contaminant fluxes were measured within 16 and water fluxes within 25 of known imposed fluxes

north eastward subduction followed by slab detachment to explain ophiolite obduction and early miocene volcanism in northland new zealand oligocene miocene models for northern new zealand involving south westward subduction to explain early miocene northland volcanism do not fit within the regional southwest pacific tectonic framework a new model is proposed which comprises a north east dipping south loyalty basin slab that retreated south westward in the eocene earliest miocene and was continuous with the north east dipping subduction zone of new caledonia in the latest oligocene the trench reached the northland passive margin which was pulled it into the mantle by the slab resulting in obduction of the northland allochthon during and after obduction the slab detached from the unsubductable continental lithosphere inducing widespread calc alkaline volcanism in northland the new model further explains contemporaneous arc volcanism along the northland plateau seamount chain and sinking of the northland basement followed by uplift and extension in northland

a continuum representation of fracture networks part ii application to the aspo hard rock laboratory abstract a method to represent fracture networks in a continuum model is evaluated by an application to the aspo hard rock laboratory hrl the basic approach of the method is to first generate a fracture network based on data from field measurements and then represent the network as grid cell conductivities using a staggered grid arrangement it is argued that the resulting conductivity fields capture the correlation and anisotropy structures as well as the mean conductivity of the rock in a realistic way the main objective is to evaluate if the suggested method can be used in an application to a real site the objective is formulated in three questions can the method utilize available field data can the generated fields be calibrated and conditioned and are realistic distributions of pressure flow and density obtained from the application to the aspo hrl it is concluded that the hydraulic conductivity fields generated by the suggested method can utilize field data and be calibrated it is also demonstrated that realistic distributions of pressure flow and density can be simulated

a comparative study of discrete fracture network and equivalent continuum models for simulating flow and transport in the far field of a hypothetical nuclear waste repository in crystalline host rock abstract one of the major challenges of simulating flow and transport in the far field of a geologic repository in crystalline host rock is related to reproducing the properties of the fracture network over the large volume of rock with sparse fracture characterization data various approaches have been developed to simulate flow and transport through the fractured rock the approaches can be broadly divided into discrete fracture network dfn and equivalent continuum model ecm the dfn explicitly represents individual fractures while the ecm uses fracture properties to determine equivalent continuum parameters we compare dfn and ecm in terms of upscaled observed transport properties through generic fracture networks the major effort was directed on making the dfn and ecm approaches similar in their conceptual representations this allows for separating differences related to the interpretation of the test conditions and parameters from the differences between the dfn and ecm approaches the two models are compared using a benchmark test problem that is constructed to represent the far field 1 1 1 km 3 of a hypothetical repository in fractured crystalline rock the test problem setting uses generic fracture properties that can be expected in crystalline rocks the models are compared in terms of the 1 effective permeability of the domain and 2 nonreactive solute breakthrough curves through the domain the principal differences between the models are mesh size network connectivity matrix diffusion and anisotropy we demonstrate how these differences affect the flow and transport we identify the factors that should be taken in consideration when selecting an approach most suitable for the site specific conditions

stochastic simulation of radionuclide migration in discretely fractured rock near the aspo hard rock laboratory we study the migration of sorbing tracers through crystalline rock by combining relatively simple transport measures with particle tracking in a discrete fracture network the rock volume is on a 1

the 2012 2016 eruptive cycle at copahue volcano argentina versus the peripheral gas manifestations hints from the chemical and isotopic features of fumarolic fluids this study presents the chemical and isotopic compositions of hydrothermal gases from fumaroles discharging around copahue volcano argentina gas samples including those from two fumaroles at the active summit crater were collected during 13 surveys carried out by different research teams from 1976 to february 2016 the time series of h2 co and light hydrocarbons showed episodic increases related to the main events of the last eruptive cycle that started on 19 july 2012 concentration peaks were likely caused by enhanced input of hot magmatic fluids affecting the hydrothermal reservoir these data contrast with the temporal variations shown by rc ra and 13c co2 values in 2012 2014 which indicated an increasing input from a crustal fluid source in 2015 2016 however these isotopic parameters showed opposite trends their composition became closer to that of the two summit fumaroles which possibly corresponds to that of the deep magmatic related end member the delayed and reduced compositional changes in the peripheral hydrothermal fluid discharge in response to the 2012 2016 eruptive events suggest that geochemical surveys of these emissions are unlikely to provide premonitory signals of volcanic unrest if the volcanic activity remains centered in the main crater instead an instrument which is able to provide measurements of volcanic gases in the air e g multigas may be used to detect changes at the summit crater otherwise monitoring of seismic activity and ground deformation as well as the periodic measurement of the chemistry of the water in the rio agrio which is fed by thermal discharge from the summit crater seem to represent the most reliable means of monitoring at copahue however the relative compositional stability of the hydrothermal reservoir is a great advantage in terms of geothermal resource exploitation and could encourage new investments in the copahue geothermal project which was abandoned in the 1990s

pt pd reefs in magnetitites of the stella layered intrusion south africa a world of new exploration opportunities for platinum group elements the 3033 ma stella layered intrusion of south africa consists largely of magnetite gabbros and gabbros that are hosted by greenstones of the kraaipan belt the intrusion contains a 100 m thick platinum group element pge enriched interval that includes a number of laterally continuous pge reefs constituting the oldest mineralization of this type known on earth the richest of the reefs is hosted by magnetitite and contains 10 15 ppm pt pd over 1 m representing by far the highest pge grades known up to this time in magnetitite hosted pt pd reefs the pges are interpreted to have been concentrated by sulfide melt after s saturation had been reached in the advanced stages of magmatic differentiation in response to magnetite crystallization reaction between sulfide melt and oxides led to late magmatic s loss causing a paucity of sulfides in most of the pge mineralized interval as a result the reefs cannot be distinguished macroscopically from their unmineralized host rocks and we suggest that similar mineralization may have been overlooked in the upper parts of other tholeiitic intrusions elsewhere

use of hydraulic tests at different scales to characterize fracture network properties in the weathered fractured layer of a hard rock aquifer the hydrodynamic properties of the weathered fractured layer of a hard rock pilot watershed in a granitic terrain are characterized using hydraulic tests at different scales the interpretation of numerous slug tests leads to characterize the statistical distribution of local permeabilities in the wells the application of flowmeter profiles during injection tests determines the vertical distribution of conductive fracture zones and their permeabilities it appears that the extension of the most conductive part of the weathered fractured layer is limited down to 35 meters depth the partition of drainage porosity between blocks 90 and fractures 10 is determined thanks to the interpretation of pumping tests using a double porosity model the application of anisotropic and single fracture analytical solutions on pumping test data allows to determine respectively the degree of anisotropy of permeability and the radius 4 to 16 meters of the horizontal conductive fractures crossed by the wells two different scales of fractures networks are identified the primary fracture network pfn which affects the matrix on a decimeter scale by contributing to an increase in the permeability and storage capacity of the blocks and the secondary fracture network sfn which affects the blocks at the borehole scale sfn is composed of two sets of fractures the main set of horizontal fractures is responsible for the sub horizontal permeability of the weathered fractured layer a second set of less permeable sub vertical fractures insures the connectivity of the aquifer at the borehole scale the good connectivity of fractures networks is shown by fractional dimension flow solutions the absence of scale effect in the study area suggests that the hydraulic conductivity at the borehole scale is laterally homogeneous finally the analysis and synthesis of the hydrodynamic properties allow to propose a comprehensive hydrodynamic model of the fractured weathered layer many geological and hydrogeological indicators suggest that a continuous and laterally homogeneous weathering process is responsible for the origin of the fractures and permeability encountered in the aquifer these results confirm the major role played by weathering in the origin of fractures and on resulting hydrodynamic parameters in the shallow part of hard rock aquifers

kinematics and flow patterns in deep mantle and upper mantle subduction models influence of the mantle depth and slab to mantle viscosity ratio 1 three dimensional fluid dynamic laboratory simulations are presented that investigate the subduction process in two mantle models an upper mantle model and a deep mantle model and for various subducting plate mantle viscosity ratios sp m 59 1375 the models investigate the mantle flow field geometrical evolution of the slab sinking kinematics and relative contributions of subducting plate motion and trench migration to the total rate of subduction all models show that the subducting plate is always moving trenchward resulting from slab pull furthermore all deep mantle models show trench retreat as do upper mantle models in the initial stage of subduction before slab tip transition zone interaction upper mantle models with a low sp m 66 217 continue to show trench retreat after interaction upper mantle models with a high sp m 378 709 show a period of trench advance after interaction followed by trench retreat upper mantle models with a very high sp m 1375 show continued trench advance after interaction the difference in trench migration behavior and associated slab geometries is attributed to both sp m and the mantle depth to plate thickness ratio tm tsp which both affect the slab bending radius to mantle thickness ratio rb tm four subduction regimes can be defined regime i with rb tm 0 3 trench retreat slab draping and a concave trench regime ii with 0 3 rb tm 0 5 episodic trench migration slab folding and a concave trench regime iii with rb tm 0 5 trench advance slab rollover geometries and minor trench curvature and regime iv with rb tm 0 8 trench retreat slab draping and a rectilinear trench in all models slab parallel downdip motion induces poloidal mantle flow structures in addition trench retreat and rollback motion of the slab induce quasi toroidal return flow around the lateral slab edges toward the mantle wedge rollback induced poloidal flow around the slab tip is not observed in any of the experiments finally comparison between the slab geometries observed in the upper mantle models and slab geometries observed in nature imply that the effective viscosity ratio between slab and ambient upper mantle in nature is less than 103 and of the order 1 7 102 with a best estimate of 1 3 102

percolation conditions in fractured hard rocks a numerical approach using the three dimensional binary fractal fracture network 3d bffn model 1 we numerically investigate fracture connectivity and percolation conditions in fractured hard rocks using a three dimensional binary fractal fracture network 3d bffn model based on three fractal geometric parameters the fractal dimensions d2 of the spatial distribution of fractures the exponent of the power law cumulative fracture length distribution a and the maximum fracture length lmax normalized by the domain length l lmax l numerical results clarify that the percolation threshold in 3d bffn models is strongly controlled by fractal geometric parameters and is independent of any anisotropy in the orientations in addition when a 0 55 are percolated domains the zone of percolation within seismogenic fracture networks between mi and ki reveals that the networks formed from seismic swarm related seismogenic fractures over a 7 week period related to the intrusion of a dyke inferred previously from seismicity and deformation data

differentiation and source of the nipissing diabase intrusions ontario canada major and trace element data are presented for 2 2 ga proterozoic diabase sills from across the nipissing magmatic province of ontario in situ differentiation of the magma coupled with assimilation of huronian supergroup roof sediments is responsible for the variation in composition between quartz diabase and granophyric diabase seen within many of the differentiated intrusions uniform trace element and isotope ratio signatures such as la sm 2 8 3 7 and endchur 2 7 to 5 9 characterize chilled margins and undifferentiated quartz diabases these chemical signatures suggest the existence of a single magma source that was parental to intrusions throughout the magmatic province this magma has higher la sm and lower ti y than primitive mantle and is displaced towards the composition of shales most chilled diabases and quartz diabases have a similar mg 0 64 and 0 60 and ni content 98 and 127 ppm and it is argued that the magma differentiated at depth and was emplaced as a uniform low mg magma

carbon dioxide diffuse emission and thermal energy release from hydrothermal systems at copahue caviahue volcanic complex argentina abstract the north western sector of caviahue caldera argentina close to the active volcanic system of copahue is characterized by the presence of several hydrothermal sites that host numerous fumarolic emissions anomalous soil diffuse degassing of co2 and hot soils in march 2014 measurements of soil co2 fluxes in 5 of these sites namely las maquinas las maquinitas i las maquinitas ii anfiteatro and termas de copahue allowed an estimation that 165 t of deeply derived co2 is daily released the gas source is likely related to a relatively shallow geothermal reservoir containing a single vapor phase as also suggested by both the geochemical data from the 3 deep wells drilled in the 1980s and gas geoindicators applied to the fumarolic discharges gas equilibria within the h c o gas system indicate the presence of a large probably unique single phase vapor zone at 200 210 c feeding the hydrothermal manifestations of las maquinas las maquinitas i and ii and termas de copahue a natural thermal release of 107 mw was computed by using co2 as a tracer of the original vapor phase the magmatic signature of the incondensable fumarolic gases the wide expanse of the hydrothermal areas and the remarkable high amount of gas and heat released by fluid expulsion seem to be compatible with an active magmatic intrusion beneath this portion of the caviahue caldera