geology and petrogenesis of the edgecumbe volcanic field se alaska the interaction of basalt and sialic crust the edgecumbe volcanic field is a holocene volcanic province located on kruzof island se alaska exposed within the 260 km2 field are basalt andesitic basalt andesite dacite and rhyodacite the rhyodacites were erupted after the basalts and before the andesites the volcanics which are al rich 14 18 wt and lack an iron enrichment trend range from tholeiites 47 wt sio2 through rhyodacites 72 but a compositional gap of approximately 9 wt separates the dacites and rhyodacites initial 87sr 86sr ranges from 0 70297 in the basalts to 0 70440 in a pyroxene andesite 18o increases across the suite 5 8 to 7 9 plagioclase an32 86 is the dominant phenocryst in all but one lava olivine fo58 86 occurs in the basic lavas 53 wt sio2 but is replaced by orthopyroxene en43 73 and clinopyroxene en31wo41 en48wo40 in the more siliceous volcanics in the basalts and rhyodacites plagioclase is weakly zoned but extreme zoning 30 mole an is characteristic of phenocrysts in the intermediate lavas fractionation of the observed phenocryst assemblages could not have produced the more silicous volcanics instead they were generated by partial melting of intrusive basement 87sr 86sr 0 70487 18o 8 7 9 3 by basaltic magma and subsequent assimilation mass balance calculations show the rhyodacites are almost pure partial melt 5 basaltic component whereas the intermediate lavas contain between 30 and 60 partial melt

assessment of mineralogical and petrographic factors affecting petro physical properties strength and cracking processes of volcanic rocks abstract microtextural features influence the petrophysical and mechanical properties of rocks including the elastic properties and cracking processes under axial loads volcanic rocks with varying microtextural characteristics and compositions were evaluated to assess the effect of the main constituents mineralogical petrographic and micro structural features on the petrophysical properties elastic properties and strength furthermore detailed analyses were also used to understand the cracking processes under axial loads the analyses of the cracking processes were completed on thin sections obtained from the mechanically tested specimens the results from the quantitative mineralogical and petrographic studies and observations from thin sections revealed that the mineral mass fractions have an effect on the specific gravity and loss on ignition loi values on the other hand unconfined compressive strength ucs and elastic properties are mostly affected by petrographic variables e g mineral content the ucs values tend to decrease with a relative increase in the groundmass with respect to the phenocryst content and vice versa biotite is the only mineral that influences the ucs individually geometric features e g feret s diameter and perimeter of opaque minerals and biotite are determined to be important constituents influencing the young s modulus under axial loads crack propagation is strongly dependent on the proportional distribution of the phenocryst and groundmass it was observed that increasing groundmass content leads to predominantly axial cracks the cracks tend to bend or propagate as a boundary crack when they reach the boundary of an unaltered phenocryst thus axial and shear cracks co exist with increasing amounts of phenocrysts which hinders crack propagation occasionally cracks can penetrate the altered or opaque phenocrysts depending on the degrees of orientation with respect to applied load of the same minerals furthermore the synthesis of the measurements obtained from ucs tests and thin section observations reveals that an increase in the amount of phenocrysts which promote the formation of more shear cracks in addition to axial cracks causes an increase in the radial strain and poisson s ratio the other factors investigated had minor effects on physical and mechanical properties of studied rocks

samples from the crystallising boundary layer of a zoned magma chamber the spatial and chemical relationships between the melt occupying the reservoir and the mineral assemblages crystallising at the margins are reconstructed for the magma chamber which produced the 11000 yr b p tephra deposit of laacher see volcano the melt showed vertical chemical zonation immediately prior to eruption and throughout most of the magma volume only a small fraction of crystals were present the eruption also ejected crystal rich nodules ranging from mafic to felsic in composition which are samples of the materials crystallising at the boundaries of the chamber new data on nodule petrography and chemical compositions of whole rocks minerals and interstitial glasses are presented volume fraction of interstitial glass is not systematically related to mineral assemblage and varies typically between 1 and 20 vol i e the crystals interlock one exception is a group of mafic nodules with glass volume fractions between 25 and 40 vol bulk compositions of mafic nodules show strong enrichments or depletions in all major elements relative to the mafic phonolite interstitial melt felsic nodules show much less pronounced differences with their interstitial melt felsic nodules contain interstitial glasses with a range of compositions similar to that in the zoned bulk of the chamber and were probably derived from different heights on the walls mafic nodules have glass compositions similar to those at the base of the zoned liquid column and were probably derived from the floor modal mineralogy glass composition and mineral composition are systematically related in the nodules whereas in individual pumices samples derived from the main body of the chamber a broader range of mineral compositions are often found mineral assemblages were especially diverse in the upper part of the chamber it is deduced that the whole of the essentially liquid part of the chamber was emptied by the eruption that strongly contrasting mineral assemblages were forming simultaneously on the walls and floor that the gradient in crystal content in the crystallisation boundary layer was more gradual at the floor than at the walls and that the pumice mineralogy is not a simple phenocryst assemblage but is a mixture of crystals which grew from melts separated in space and or time

state of stress in the southern tyrrhenian subduction zone from fault plane solutions summary in this paper we present revised locations and original focal mechanisms computed for intermediate and deep earthquakes that occurred within the southern tyrrhenian subduction zone between 1988 and 1994 in order to improve our knowledge of the state of stress for this compressional margin in particular we define the stress distribution within a large portion of the descending slab between 40 and about 450 km depth the seismicity distribution reveals a continuous 40 50 km thick slab that abruptly increases its dip from subhorizontal in the ionian sea to a constant 70 dip in the tyrrhenian we computed focal mechanisms for events with magnitudes ranging from 2 7 and 5 7 obtaining the distribution of p and t axes for many events for which centroid moment tensor cmt solutions are not available thus enabling the sampling of a larger depth range compared to previous studies we define three portions of the slab characterized by different distributions of p and t axes a general down dip compression is found between 165 and 370 km depth whereas in the upper part of the slab 40 165 km depth the fault plane solutions are strongly heterogeneous below 370 km the p axes of the few deep events located further to the north have a shallower dip and are not aligned with the 70 dipping slab possibly suggesting that they belong to a separated piece of subducted lithosphere there is a good correspondence between the depth range in which the p axes plunge closer to the slab dip 70 and the interval characterized by the highest seismic energy release 190 370 km

the arcs of the western alps and the northern apennines an updated view abstract the arcs of the western alps and the northern apennines and the link between them are in the process of being investigated using the european geotraverse and they have historically been interpreted in many different ways new information particularly geophysical further constrains possible models both arcs have evolved in several stages sometimes complexly interrelated and sometimes independent of each other compressional belts produced in these stages have either been of the push arc type indentation into a deformable mass or the pull arc type backward migration of hinge of a subduction zone leading to small extensional basins known as back arc basins and pores with an arcuate mountain range on the subduction side extensional periods with the possible formation of pull arcs in the alps comprise the gosau period between the eo and meso alpine push arc phases and the oligocene lull period between the meso and the neo alpine push arc phases in the northern apennines remainders of the meso alpine nappes were involved in oligocene early miocene pull arc formation associated with spreading in the balearic sea followed by push arc formation particularly in the middle miocene and by renewed pull arc formation from the latest late miocene to the present during all of these developments the moho was modified by such processes as lithospheric stretching asthenospheric intrusions subhorizontal shearing and isostatic uplift the present moho configuration is consequently a collage of moho patches formed at different intervals both push and pull arcs are laterally bounded by complementary strike slip or transform zones these too were modified in the course of history and their final geometry is consequently of a very complex nature in the alps for instance the insubric fault zone appears to have been the main dextral transform fault of the neogene push arc until it was sinistrally kinked by the giudicarie fault zone and probably deactivated dextral transpression being briefly transferred to the en echelon brachyanticlines of the late alpine windows in the case of the oligocene apennines the sinistral rotations of corsica and sardinia otherwise hard to understand may be attributed in part to sinistral transform motions along the eastern border zone of the oligocene early miocene balearic extension

segmentation and configuration of subducted lithosphere in italy an important control on thrust belt and foredeep basin evolution the apennine foredeep basin system located on continental crust consists of four roughly parallel basin segments each containing a flexural outer rise and an inner trough that deepens continuously toward the thrust belt flexural modeling of subsidence data across the basin indicates that this foredeep basin results mainly from deep subsurface loads acting on the subducted slab from within the subduction zone rather than from the topographic load of the apennine mountains the geometry of the four basin segments observed within the apennine foredeep is thus inferred to reflect subduction of segmented lithosphere where each lithospheric segment corresponds to a segment of the foredeep basin beneath the basin and in the foreland the lithosphere is continuous segmentation occurs only at depth beneath the thrust belt this pattern olf segmentation of the subducted lithosphere at depth is reflected in the large scale geometry of the outer part of the apennine thrust belt and appears to control it similarly the pattern of segmentation also appears to control the position of the eastern limit of back arc type extension in western italy these relations strongly suggest a genetic relation between subduction zone processes foredeep basin geometry and thrust belt evolution in which the configuration of the subducted lithosphere largely controls the large scale surface deformation observed in the apennine system

digital image based numerical modeling method for prediction of inhomogeneous rock failure abstract this paper presents a two dimensional digital image based numerical modeling method for prediction of inhomogeneous rock failure behavior under loadings actual inhomogeneities of granitic rocks are extracted from color images of the granite cross sections they are represented as the internal spatial distribution of three main granite minerals quartz feldspar and biotite the actual mineral spatial distribution on granite cross section is then incorporated into conventional numerical software packages to examine the rock failures under loading some digital image processing algorithms are presented to isolate and identify the main internal minerals and their distribution from color digital images a simple method is proposed to transform the actual image data into vector data for generation of finite meshes or grids the vector data are used directly as uniform square element meshes or grids that can be inputted into the existing software packages the finite difference software package flac is used as an example for the present investigation the conventional mohr coulomb and tensile stress failure criteria are used to examine the failure behavior of a circular granite cross section under the conventional brazilian indirect tensile test loading conditions the numerical results indicate that the vertical tensile crack initiates in a biotite located near the geometrical center of the granite cross section and the actual spatial distribution of the three minerals plays an important role in modifying the propagation pattern of the tensile crack from its theoretical position at the central vertical diameter of a homogeneous circular cross section the numerically predicted failure load and tensile strength values for inhomogeneous granite are much lower than the expected values

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

effect of heterogeneity of brittle rock on micromechanical extensile behavior during compression loading a grain based universal distinct element code model was developed to generate a deformable polygonal grain like structure to simulate the microstructure of brittle rock it takes into account grain scale heterogeneity including microgeometric heterogeneity grain scale elastic heterogeneity and microcontact heterogeneity the microgeometric heterogeneity can be used to match the grain size distribution of the rock the discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy the modeling approach was evaluated using lac du bonnet granite and a aspo diorite the microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading the crack initiation stress was found to be controlled primarily by the microscale geometric heterogeneity while the microcontact heterogeneity controlled the strength characteristics the effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined

identifying crack initiation and propagation thresholds in brittle rock recent work at the underground research laboratory of atomic energy of canada limited in pinawa manitoba has shown that high compressive stresses near the tunnel face significantly contribute to

genesis and evolution of regoliths evidence from trace and major elements and sr nd pb u isotopes abstract regoliths encompass different materials from the fresh bedrock to the top of the organic horizons the occurrence and evolution of these materials are determined by deposition erosion and weathering processes that are specific for each region the origin and interaction of the regolith layers are still important issues in the study of critical zone functioning studies that attempt to understand the processes responsible for the structure and the evolution of regoliths often focus either on the soil or on the bedrock compartment and often from a narrowly focused approach using just a single tool such as major element patterns or mineralogy this limits the understanding of the complete regolith composition and evolution the present study proposes the combination of mineralogy major and trace element concentrations and sr nd pb u isotopes as an extremely useful procedure for tracking the spatial and temporal origin of regolith materials and understanding their stratification this multi tracer approach was applied on a regolith profile from the south western edge of the rhenish massif which is characterised by the occurrence of slate bedrocks and overlying pleistocene periglacial slope deposits ppsd the data allowed the differentiation of three compartments within the regolith 1 the organic compartment where low 206pb 207pb and 87sr 86sr isotopic ratios reflected the impact of atmosphere derived components 2 the ppsd compartment whose upper horizons were characterised by the presence of atmosphere derived particles rich in cd sn sb hg and pb and by relatively low 206pb 207pb and 87sr 86sr ratios whereas the lower horizons showed nb enrichments in their matrix and a mineralogical composition pointing to ancient volcanic events and 3 the weathered slate compartment whose weathering progression and genetic relationship with the ppsd were particularly well tracked with 87sr 86sr and 143nd 144nd isotope ratios 234u 238u activity ratios and positive ce anomalies the results prove the efficiency of radiogenic isotope measurements combined with the analysis of major and trace elements to complete regolith studies moreover these isotopes and elements are shown to be potential geochemical tracers of exchange processes at the water mineral interface this approach allows for the first time the description of an evolution scheme of a complete slate regolith which covers a large part of the rhenish massif

phase equilibria of the lower laacher see tephra east eifel germany constraints on pre eruptive storage conditions of a phonolitic magma reservoir laacher see volcano erupted about 12 900 years ago resulting in a tephra blanket widely dispersed in central europe the eruption tapped a chemically and mineralogically strongly zoned phonolitic magma reservoir in order to better constrain the pre eruptive storage of that magma hydrothermal phase equilibria experiments have been performed on a powdered sample from the highly evolved phonolite of the lower laacher see tephra llst experiments were run at water pressures of 75 175 mpa and temperatures of 725 800 c stability fields of sanidine and amphibole the most common crystal phases in llst suggest that the magma last equilibrated at temperatures of 750 760 c and pressures of 115 145 mpa those conditions suggest the magma should have contained between 5 and 6 wt water which agrees well with water contents of 5 7 wt found in glass inclusions that agreement along with the observation that cl and s vary with the composition of the inclusions suggest that the laacher see magma was saturated at depth with a water rich fluid and thus was stored at pressures near those estimated from our experiments such pressures roughly correspond to depths of 5 6 km clinopyroxene and plagioclase did not occur in the experimental runs although present in the natural pumice sample it seems likely that these phases are not inherent to the llst they were formed in other parts of the chemically stratified column and later redistributed a recalculation of the magma density together with a new estimate of the temperature and pressure range suggests a steep density gradient and a thin withdrawal layer which is typical for volatile enriched magma bodies and confirms earlier models of convective fractionation in the laacher see magma reservoir

geological and hydraulic characterisation of the excavation disturbed zone in the opalinus clay of the mont terri rock laboratory abstract the fracture network in the excavation disturbed zone edz of an argillaceous formation the opalinus clay in the mont terri rock laboratory in northwest switzerland is characterised using structural and hydrogeological techniques sampling of unloading fractures is done by analysing resin injected overcores taken from the edz resulting in a structural data set of fracture orientations frequencies and extent of the edz these parameters are derived in tunnel sections which were excavated by blasting pneumatic hammering and road header techniques pneumatic and hydrogeological tests are subsequently carried out to derive hydraulic parameters such as permeability and transmissivity distributions of the fracture network synthesis of the structural and hydrogeological data led to a conceptual model of the edz in the mont terri rock laboratory which is defined by a 2 m plastically deformed zone around the tunnel this plastic zone is further divided into an inner 1 m zone consisting of an air filled fracture network and an outer zone with mostly saturated and isolated fractures transmissivities in the inner zone are orders of magnitude higher than those of the undisturbed opalinus clay finally a methodology is proposed for the structural and hydrogeological characterisation of the edz this methodology is not site specific and is thus applicable at any argillaceous underground facility

investigating the effects of micro texture and geo mechanical properties on the abrasiveness of volcanic rocks abstract the abrasiveness of rocks is a fundamental rock property that affects sawing and cutting performance wear of tunnel boring machine tbm heads the cerchar abrasiveness index cai test is a commonly used procedure to define rock abrasivity this paper investigates the relationship between quantitative mineralogical and petrographic data and cai values for some selected volcanic rocks in addition the research examines the relationship between physical e g effective porosity and p wave velocities and mechanical e g uniaxial compressive strength ucs brazilian tensile strength bts young s modulus e properties including brittleness values and cai values quantitative mineralogical and petrographic analyses reveal the variations in micro textural properties as defined by different groundmass phenocryst ratios analyses also suggest that the dimensions of opaque minerals and plagioclase feldspar apparently have individual effects on cai values additionally the combined effects of grain size and primary types of constituent minerals have a significant on cai values additionally results of physical and mechanical tests indicate that as p wave velocities increase cai values increase the increasing values of ucs bts and e cause cai values to increase significantly however only one of three brittleness values was found to have a considerable relationship with cai values this research demonstrates the importance of evaluating the micro textural variations and the combined effects of micro texture physical properties and mechanical properties on the cai values of volcanic rocks

the role of constraints on joint hypocentre determination in seismotectonic studies in this paper we show how the performance of the joint hypocentre determination jhd method can be improved leading to reduced instability in cases close to singularity the method has been extended by imposing a number of constraints introduced by other authors and adding a new one we tested the stability of the method and the relative advantages of the various constraints by simulating a geometrical space distribution of hypocentres recorded by a regional seismic network we then applied this method to deep earthquakes that occurred in the southern tyrrhenian sea subduction zone and to the seismicity of the northern apennines which is moderately deeper than the typical shallow seismicity of the apennines the results obtained from the analysis of synthetic data and actual earthquakes confirm that the jhd method produces less scatter in the hypocentral determinations with respect to the standard locations the main conclusion of our study is that we can significantly reduce the systematic mislocations that result from applying jhd to very clustered seismicity if we introduce the appropriate set of constraints

an estimate of hypocentre location accuracy in a large network possible implications for tectonic studies in italy summary data recorded by the italian telemetered seismic network itsn of the istituto nazionale di geofisica ing have been widely used in recent years to image slab structures and to find evidence for active processes along the italian peninsula however the use of seismic data for geostructural purposes may be affected by the well known trade off between earthquake location and seismic velocity parameters furthermore the confidence ellipse predicted by standard procedures may be inadequate for the representation of the probable error of a computed localization this paper evaluates the probable errors on the hypocentre determinations of the seismic events recorded by the itsn using a monte carlo method we compute synthetic arrival times using a 1 d velocity model appropriate as an average for the italian area the hypocentres used are ail those recorded by the itsn during the period january 1992 to march 1994 1972 events station locations are those of the current itsn configuration the synthetic arrival times are perturbed with a gaussian distribution of errors and input to ings standard hypocentral location procedure but using crustal velocities differing by 10 per cent from those used to generate them each simulation is repeated at least 30 times average absolute shifts of hypocentres are assessed in grid cells of linear dimension 33 km covering the whole italian region for regions within the itsn shifts are typically 5 10 km in location and up to 20 km in depth however for offshore and coastal regions they are much greater 50 km or more in both location and depth far exceeding the equivalent uncertainties quoted by ing bulletins possible consequences of this are highlighted by producing a cross section of subcrustal hypocentres from the adriatic to the tyrrhenian sea where the large uncertainty in depth precludes any confident interpretation of dipping tectonic features

seismicity of the adriatic microplate abstract the adriatic microplate was previously considered to be a unique block tectonically active only along its margins the seismic sequences that took place in the basin from 1986 to 1990 give new information about the geodynamics of this area three subsets of well recorded events were relocated by the joint hypocentre determination technique on the whole this seismic activity was concentrated in a belt crossing the southern adriatic sea around latitude 42 in connection with regional e w fault systems some features of this seismicity similar to those observed in other well known active margins of the adriatic plate support a model of a southern adriatic lithospheric block detached from the northern one other geophysical information provides evidence of a transitional zone at the same latitude

seventeenth canadian geotechnical colloquium the effect of cohesion loss and stress path on brittle rock strength stress strain curves for brittle rocks show three characteristic stress levels crack initiation long term strength and peak strength damage controlled testing at low confining stresses has shown that the long term and peak strengths are sensitive to the amount of induced damage i e the greater the amount of damage the lower the long term and peak strengths these tests also showed that the brittle failure process is characterized by a loss of cohesion as friction is mobilized excavation of a circular test tunnel in massive brittle rock resulted in failure around the tunnel the back calculated strength for the failed rock around the tunnel is approximately one half of that measured in laboratory tests crack induced damage of lac du bonnet granite both in the laboratory and in situ begins when the load exceeds approximately one third of the unconfined compressive strength however the stress level associated with failure is a function of loading path in the laboratory where the loading path monotonically increases the ultimate strength of an unconfined sample is 225 mpa numerical studies suggest that in situ the loading path around the tunnel is more complex involving stress increase and decrease and stress rotation for this loading path failure initiates at a stress between 100 and 120 mpa conventional frictional failure criteria did not adequately predict the extent of brittle failure measured around the circular tunnel the results from the damage controlled laboratory tests and the microseismic monitoring carried out during tunnel construction indicate a constant deviatoric stress criterion is a reliable indicator for predicting the onset of damage this criterion was also found to give a reasonable prediction for the maximum depth of failure around the test tunnel the fundamental assumption in the constant deviatoric stress criterion is that at low confining stresses such as those which occur around underground openings the brittle failure process is dominated by cohesion loss

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

dynamic models of subduction geophysical and geological evidence in the tyrrhenian sea summary predictions based on a 2 d finite element model for subduction underneath the calabrian arc in southern italy are compared with a variety of geophysical and geological data such as the present day stress pattern within the slab uplift from the elevation of marine terraces in calabria and subsidence in the tyrrhenian marsili basin from odp leg 107 we model the behaviour of the slab driven by slab pull in agreement with the present tectonic style in this part of the mediterranean as suggested by several investigators the model accounts for the crustal lithospheric and mantle structures in a vertical cross section perpendicular to the calabrian subduction zone the shape of the slab is constrained on the basis of new tomographic images in the southern tyrrhenian sea which were obtained from the regional seismic stations of the istituto nazionale di geofisica while the rheological properties of the mantle are taken from global dynamic models density contrasts between the subducted slab and the surrounding mantle based on petrological models drive the flow in our viscoelastic model stress values displacements and vertical velocities at the surface are sampled at different times after loading until dynamic equilibrium is reached our estimates are appropriate for a time window of 100 kyr the validity of our comparison with the geological record is based on the assumption that the tectonic configuration in the past was not substantially different from that of the present day two families of models with unlocked and locked subduction faults are considered the unlocked models allow for roll back of the trench of about 20 mm yr in agreement with some geological estimates the same family of models predicts uplift of the calabrian arc of about 1 mm yr l and subsidence in the marsili basin of 1 2 mm yr in agreement with geological surveys the deviatoric stress obtained from the unlocked model is consistent with the continuous distribution of deep seismicity in the southern tyrrhenian sea with minor concentration within the lithospheric wedge locked models fail to reproduce these geophysical and geological observations predictions derived from a detached slab model are not consistent with the continuous hypocentral distribution of deep seismicity in the southern tyrrhenian sea deformation at the surface and the stress patterns at depth for a detached slab differ substantially from those of a continuous plate dynamic topography and horizontal motions are reduced when compared with the continuous plate with deviatoric stresses concentrated within the relict slab our results indicate that subduction is a major tectonic process in the southern tyrrhenian sea

magma mixing versus xenocryst assimilation the genesis of trachyandesites in sancy volcano massif central france sr and nd isotopic compositions have been determined on basaltic and acid trachyandesites bta ata from the sancy volcano mont dore massif france these represent more than 80 of the lavas erupted during its activity between 0 9 and 0 2 ma these lavas have been recently interpreted as the result of two component magma mixing during and after repeated injections of basaltic magmas in trachytic reservoirs magmatic heterogeneities in the ata s large to small enclaves banded lavas megacrysts testify to the mingling event complete mixing is supposed to have been achieved in the hybrid bta s which contain sanidine plagioclase and clinopyroxene megacrysts in disequilibrium with their host the megacrysts are interpreted as relicts of the trachytic end member isotopic data on basic comagmatic enclaves and host ata matrix samples from three different cycles of mingling succession of heterogeneous pyroclastics heterogeneous ata lava flows or domes and occasionally homogeneous bta lava flows are not incompatible with two component mixing but could just reflect the heterogeneity of the analysed samples however the bta s have sr contents and sr isotopic ratios which are too high to be simple binary mixing products between the postulated end members three hypotheses are considered to explain this discrepancy 1 the analysed end members are not those involved in bta genesis 2 some crustal contamination occurred during and after the mixing event 3 sr rich sanidine xenocrysts with radiogenic 87sr86sr have been assimilated and digested in the bta s in this third hypothesis that i favour it is not necessary to resort to magma mixing to explain the genesis of the bta s assimilation of xenocrysts by basaltic hawaiitic or mugearitic magmas accounts for both mineralogical disequilibria and isotopic characteristics of these lavas

evolution of the laacher see magma chamber evidence from sims and tims measurements of uth disequilibria in minerals and glasses abstract u th disequilibrium was measured by secondary ion mass spectrometry th and thermal ionization mass spectrometry u in mineral separates from pumices and cumulate nodules from the laacher see volcano 12 5 0 5 kyr corrected 14 c age in east eifel germany phonolitic glasses all plot to the left of the equiline with higher u th observed in the most felsic glasses measured partitioning of u and th in the mineral phases is consistent with the observed increase in u th with progressive fractional crystallization apparent ages of crystallization inferred from internal isochrons in the pumices from the main part of the magma chamber are about 13 3 kyr indistinguishable from the eruption age this implies that the residence time of these phenocrysts did not exceed 1 2 kyr older less precise ages for the upper part of the magma chamber 30 kyr suggest mixing of older crystals from cumulates and or longer residence times mineral isochrons for cumulate nodules are not well defined with ages ranging from 10 to 30 kyr suggesting in situ cumulate formation 10 20 kyr prior to the eruption the time required to explain the 230 th 232 th difference between parental basanite and laacher see phonolite is inferred to be about 100 kyr together these observations favor a cooling model where differentiation of parental basanite takes place in a deep magma body over about 100 kyr followed by emplacement of the resulting mafic phonolite into an upper crustal chamber and continued differentiation toward evolved phonolite the time scale for the development of zonation in the laacher see magma chamber is estimated to be 10 20 kyr at most

volatile composition of the phonolitic laacher see magma 12 900 yr bp implications for syn eruptive degassing of s f cl and h 2 o a volatile rich and chemically zoned phonolitic magma reservoir was tapped successively during the eruption of laacher see volcano ca 12 900 years bp and produced a tephra sequence consisting of phenocryst poor highly evolved phonolite at the base and phenocryst rich more mafic phonolite at the top the stratospheric volatile loading was estimated by comparing pre and post eruptive s f cl and h2o contents of undegassed glass inclusions and partially degassed matrix glasses glass inclusions 150 1490 ppm s and host matrix glasses 150 820 ppm s both document a strong s decrease during progressive magmatic differentiation which is interpreted to be partially caused by crystallization of hauyne the s6 stotal ratio of the pre eruptive melt increased with differentiation from 8 to 71 as indicated by s k wavelength shift measurements in glass inclusions sulfate rich highly evolved phonolitic magma was erupted during plinian and sulfide rich more mafic phonolitic magma during late phreatomagmatic phases f and cl became enriched during late stages of differentiation glass inclusions 690 4060 ppm f 1770 4400 ppm cl matrix glasses 680 3660 ppm f 2130 4330 ppm cl the most differentiated melts maximum 13 wt na2o occur only as matrix glass and are extremely f enriched 5080 8780 ppm but cl depleted 460 2820 ppm suggesting that f was retained in the melt whereas some cl was lost during pre and or syn eruptive degassing the h2o contents of glass inclusions increase irregularly with differentiation 2 5 5 7 wt matrix glasses are h2o depleted 0 2 2 8 wt compared to most glass inclusions showing that most h2o was released to the atmosphere by explosive degassing a mass balance calculation yields a syn eruptive volatile release of 1 9 tg stotal 6 6 tg cl and 403 tg h2o from the melt this is a minimum estimate since s and cl could have accumulated in a separate fluid phase as indicated by fluid inclusions in hauyne and pre eruption h2o contents close to saturation level at the likely pressure temperature conditions in the laacher see magma reservoir we estimate that at least ca 20 tg so2 were injected into the stratosphere causing a significant negative climate forcing as reflected by several paleoclimate proxies and as shown by recent modeling

structure and dynamics of the laacher see magma chamber eifel germany from major and trace element zoning in sanidine a cathodoluminescence and electron microprobe study microtextures and zoning patterns in sanidine phenocrysts from the phonolitic laacher see tephra germany were investigated in order to constrain processes occurring in the magma chamber before eruption the laacher see tephra unit is chemically zoned and has been inferred to represent the product of eruption of an inverted layered magma chamber samples from various levels in the deposit were investigated we used a combination of textural studies optical microscopy and back scattered electron bse imaging electron microprobe emp analysis of major minor and trace elements ca na k al si ba sr fe and ti and element mapping the samples studied contain two feldspar phases and the ternary composition of the sanidine thus constrains the temperature of crystallization whereas its trace element content reflects the melt composition the large diversity in textures found in the sanidine crystals can be classified into three types composite c type pseudooscillatory po type and resorbed patchy r type trace elementpoor lamellar composite alkali feldspars c type are found in samples inferred to represent the top and the middle part of the magma chamber they grew as composite crystals from the melt at temperatures as low as 650 c in a highly differentiated and volatilerich boundary layer at the magma chamber roof or wall pseudooscillatory zoning with resorption surfaces po type is found in sanidinesfromsamplesinferredtorepresentthemiddlepartandthebase of the magma chamber repeated large an variations 1 4 mol reflect temperature variations of 100 300 ca ssociated with changes in water content variations of minor and trace elements ba sr and ti in sanidine decoupled from the pseudo oscillations of the major elements reflect chemical changes in the melt and are damped by chemicaldiffusioninthemelt bothmajorandminorelementvariations inpo typecrystalsareinterpretedastheprogressiveinfluenceofamore mafic hotter melt this may be partly explained by the settling of crystals through the thermal and chemical gradient existing in the magma chamber however the additional role of magma recharge may be required to explain the large temperature variations resorbed patchy zoned crystals r type found mainly in samples corresponding to the middle part of the magma chamber reflect early growth in a differentiated boundary layer followed by resorption and overgrowthinthemainmagmabody manyofthelaacherseesanidine crystals did not crystallize for the most part in the melt in which they were erupted in the presence of preserved major and trace element zonation in the magma this observation indicates crystal dispersion within a layered magma chamber without large scale mixing and overturn

tomographic studies of the upper mantle beneath the italian region teleseismic p arrivals at seismological stations are inverted into a model of velocity perturbations down to a depth of about 470 km directionally independent average residuals computed from steeply inciding waves are transformed into a model of lithospheric thickness both models show a good correspondence with the main tectonic features of the italian peninsula positive velocity perturbations are observed beneath the alps and in depths over 200 km also beneath the po basin a high velocity anomaly of the tyrrhenian subduction is less pronounced probably due to a directional dependence of p velocities in the mantle negative velocity perturbations indicate several low velocity regions e g beneath the northern apennines the sicily region and in the upper 100 km beneath the po basin the amplitudes of velocity perturbations beneath the depth of 200 km are smaller on the average than those in the upper two layers the whole region is characterized by large undulations of the lithosphere base which reaches depths from less than 60 km to more than 150 km the most prominent lithospheric root beneath the alps is a product of the collision between the european and the adriatic plates while the lithospheric thickening beneath the calabrian coast is likely to be connected with the eastern wing of the tyrrhenian subduction the dramatic changes of lithosphere thickness between the northern and the southern apenninic arcs and northern calabria as well as the thinnings at the western closure of the po basin indicate important deep seated boundaries of lithospheric blocks of autonomous geodynamic development

methodological approach to earthquake location procedures application to italian seismicity the joint hypocenter determination jhd and a standard location procedure are compared in an effort to determine the relative accuracy of the two techniques the jhd technique was applied to two italian regions affected by large azimuthal gaps in station distribution and or poor knowledge of the seismic velocity model the two techniques show large differences concerning the depth estimations for many events the standard location method has problems of convergence requiring the use of procedures blocking the variation of depth in some instances as a result of synthetic data analysis we observed that the use of the jhd technique reduces the influence of the seismic velocity model and of random reading errors

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

evolution of magma mixing in an alkaline suite the grande cascade sequence monts dore french massif central geochemical modelling abstract trachyandesitic lavas from an alkaline suite grande cascade sequence monts dore french massif central have been investigated for evidence of mechanical magma mixing a wide variety of textures are present in the sequence as pillow like enclaves bandings and emulsified facies the grande cascade flows and pyroclasts range from basalt to trachyte 44 67 wt sio 2 pillow like enclaves intricate commingling and local diffusive mixing at the mafic felsic interface in emulsified types show that mafic inclusions were incorporated in their trachytic host as blobs of magma such inclusions were probably dispersed throughout the trachytic magma by mechanical mixing different stages of the evolution of a mechanical mixing process were recognized in relation with the stratigraphy and chronology of the products the most heterogeneous features enclaves bandings are restricted to the bottom of the sequence where basalt and trachyte coexist at the top texturally homogeneous trachyandesites occur relict phenocrysts are observed in both basaltic enclaves oligoclase fe rich clinopyroxene sanidine of the trachyte and trachytic hosts mg rich olivine mg rich clinopyroxene ca rich plagioclase of basalt the intermediate rocks basic trachyandesites contain xenocrysts of mg rich olivine clinopyroxenes oligoclase sanidine together with reversely zoned plagioclase and pyroxene phenocrysts this assemblage is presumed to result from the incorporation of xenocrysts related both to mafic and felsic endmembers all mineral assemblages are out of equilibrium reversed compositional zoning profiles in plagioclase and clinopyroxene crystals were produced by the mixing event we are able to identify the compositional characteristics of the components that were mixed a primary alkaline basalt mg olivine labrador mg clinopyroxene magnetite and a silicic trachyte oligoclase fe clinopyroxene sanidine are the endmembers of mixing observed chemical variations in major and trace elements can be modelled as pure binary mixtures between basaltic and trachytic endmembers using the best mixing line method provost and allegre 1979 the calculations emphasize that trachyandesites are the result of complete hybridization between basalt and trachyte the data on mesostasis show that melt mixing and not only crystal transfers has produced the intermediate lavas of the grande cascade sequence textural criteria petrography mineral chemistry and geochemical data major and trace elements support the magma mixing model

the open system geochemical evolution of alkalic cap lavas from haleakala crater hawaii usa lavas ranging from alkalic basalt to mugearite are exposed in a continuous stratigraphic section in haleakala crater on the island of maui these lavas define a series of discrete magma batches separated by sharp compositional breaks characterized by upsection increases in incompatible element e g k2o nb ree th ba rb contents al2o3 cao ratios and la sm ratios and complementary decreases in compatible element e g mgo ni cr v sc contents within magma batches there are systematic upsection decreases in incompatible element contents al2o3 cao ratios and la sm ratios and systematic increases in compatible element contents the observed compositional cyclicity can be explained as the result of alternating periods of low and high magma chamber recharge rates the upsection interbatch compositional breaks represent periods of low or negligible magma chamber recharge during which eruption is suppressed and the geochemical effects of crystal fractionation dominate those imposed by magma mixing at the initiation of recharge the influx of mafic magma into the magma chamber produces an eruption resulting in partial evacuation of the magma chamber following eruption recharge magma mixes with magma remaining in the magma chamber continued recharge and mixing during these eruptive periods cause the compositions of lavas to become more mafic with time thus during a recharge period the bulk composition of the magma chamber approaches that of the recharge magmas the most mafic lavas i e the youngest lavas within each magma batch typically are relatively evolved mg 48 mgo 7 wt and therefore cannot represent primary magmas evidence for polybaric fractionation suggests that these lavas represent recharge magmas that have undergone crystal fractionation in a deeper level reservoir prior to injection into the shallow level haleakala magma chamber the observed fine scale geochemical cyclicity is superimposed over the larger scale systematic changes in isotope ratios and highly incompatible trace element ratios that are attributed to time dependent changes in the proportions of distinct mantle components in the source of these lavas these contrasting scales of temporal geochemical variability illustrate how shallow level magma chamber processes have imposed short time period 2000 years compositional controls on magmas whose compositions were also changing over relatively long time periods 800 000 years due to source related effects the decrease in magma supply rates during the alkalic cap phase of hawaiian volcanism probably results in increased magma chamber residence times thus creating the greater magmatic diversity observed the specifics of the petrologic and geochemical evolution of individual hawaiian volcanoes during this period differ at least in part because of differences in magma supply rates

relationship between density compressive strength tensile strength and aggregate properties of andesites from hungary aggregate properties and strength parameters of four andesites from two operating hungarian quarries of nogradkovesd one lithotype and gyongyossolymos three lithotypes are presented in this paper air dry water saturated and freeze thaw subjected specimens were tested on core drilled cylindrical specimens and the aggregate properties were also determined from the remaining part of the drilled rock blocks tensile strength values rapidly decreased from air dry to water saturated and finally to freeze thaw subjected specimens linear relationships between air dry and water saturated bulk densities and between ucs and modulus of elasticity were found micro fabric influences strength and aggregate parameters of studied andesites fine porphyritic andesite has the highest ucs and tensile strength and the best micro deval results while coarser porphyritic andesite has lower strength and aggregate parameters test results were compared with previously published rock mechanical data of intermediate and basic igneous rocks a good exponential correlation was found between micro deval and ucs values of this paper and previously published data sets but there was no indication that micro deval values correlate well with los angeles values

digital features of main constituents in granite during crack initiation and propagation abstract the purpose of this study is to investigate the digital features of various constituents on granite specimen in the crack initiation and propagation process the test video image photographed during laboratory uniaxial compression test and digital image processing techniques were used to conduct this study the video image was first converted into the format easily recognized in programming a multiple object tracking technique was then developed to detect the locations of the individual cracks at any time the initiation of each crack was determined by the occurring instant of the bounding box including the cracks the length width and area of each crack at any time were thereafter recorded the relation of the propagation process with digital features of the constituents in various locations was furthermore investigated it shows that two cracks propagated respectively along the vertical and horizontal directions as uniaxial compression test was performed a limit box technique can be used to determinate the initiation instants of the multi cracks on the specimen surfaces during propagation the width of the cracks increased quickly just after initiation and then fluctuated around a magnitude until the completely failure of the specimen the constituents near the crack would split as the crack initiated the shape features of biotites feldspar and quartz changed in different manners during crack s initiation and propagation the technique presented herein may be referable in investigating the failure mechanism of rock materials

eruption and emplacement of a basaltic welded ignimbrite during caldera formation on gran canaria the 14 1 ma old composite ignimbrite cooling unit p1 45 km3 on gran canaria comprises a lower mixed rhyolite trachyte tuff a central rhyolite basalt mixed tuff and a slightly rhyolite contaminated basaltic tuff at the top the basaltic tuff is compositionally zoned with a an upward change in basalt composition to higher mgo content 4 3 5 2 wt b variably admixed rhyolite or trachyte commonly 5 wt and c an upward increasing abundance of basaltic and plutonic lithic fragments and cognate cumulate fragments the basaltic tuff is divided into three structural units i the welded basaltic ignimbrite which forms the thickest part c 95 vol and is the main subject of the present paper ii poorly consolidated massive bomb and block rich beds interpreted as phreatomagmatic pyroclastic flow deposits and iii various facies of reworked basaltic tuff tuff unit i is a basaltic ignimbrite rather than a lava flow because of the absence of top and bottom breccias radial sheet like distribution around the central tejeda caldera thickening in valleys but also covering higher ground and local erosion of the underlying p1 ash a gradual transition from dense rock in the interior to ash at the top of the basaltic ignimbrite reflects a decrease in welding the shape of the welding profile is typical for emplacement temperatures well above the minimum welding temperature a similar transition occurs at the base where the ignimbrite was emplaced on cold ground in distal sections in proximal sections the base is dense where it was emplaced on hot felsic p1 tuff the intensity of welding especially at the base and the presence of spherical particles and of mantled and composite particles formed by accretion and coalescence in a viscous state imply that the flow was a suspension of hot magma droplets the flow most likely had to be density stratified and highly turbulent to prevent massive coalescence and collapse model calculations suggest eruption through low pyroclastic fountains 1000 m high with limited cooling during eruption and turbulent flow from an initial temperature of 1160 c the large volume of 26 km3 of erupted basalt compared with only 16 km3 of the evolved p1 magmas and the extremely high discharge rates inferred from model calculations are unusual for a basaltic eruption it is suggested that the basaltic magma was erupted and emplaced in a fashion commonly only attributed to felsic magmas because it utilized the felsic p1 magma chamber and its ring fissure conduits evolution of the entire p1 eruption was controlled by withdrawal dynamics involving magmas differing in viscosity by more than four orders of magnitude the basaltic eruption phase was initially driven by buoyancy of the basaltic magma at chamber depth and continued degassing of felsic magma but most of the large volume of basalt magma was driven out of the reservoir by subsidence of a c 10 km diameter roof block which followed a decrease in magma chamber pressure during low viscosity basaltic outflow

natural fractures in tight gas volcanic reservoirs and their influences on production in the xujiaweizi depression songliao basin china lower cretaceous volcanic rocks that contain major natural fractures are the main natural gas reservoirs in the deep xujiaweizi depression of the northern songliao basin in china natural fractures are mainly tectonic fractures in addition to some shrinkage dissolution and cryptoexplosive fractures analyzing various sources of data revealed that fractures are generally better developed in the rhyolites and trachytes of the crater and near crater group also tectonic fractures are developed to a higher degree in the hanging wall of faults with the degree of development decreasing with increasing distance from the fault planes more than 85 of these fractures are found to be unfilled and when connected by pores provide the main effective storage volume for these volcanic reservoirs up to 75 natural gas production is closely related to the linear density p10 of unfilled tectonic fractures and the angle between the orientation of unfilled tectonic fracture and the corresponding direction of the maximum horizontal stress component the results show that natural gas production is elevated when the average p10 exceeds 2 m 1 and the average included angle is less than 30 finally it was concluded that within the study area unfilled tectonic fractures of near east west strikes which have smaller included angles 30 with respect to the maximum horizontal stress direction are under minimal compressive stresses and make the best fluid flow pathways in the reservoir

the control of mineral constituents and textural characteristics on the petrophysical mechanical pm properties of different rocks of the himalaya abstract petrophysical and mechanical pm properties of a rock are primarily controlled by its mineral constituents and various textural parameters similar rock types in different tectonic setups may be characterized by different mineralogical compositions and textural properties because they might have suffered different deformational processes this paper presents a study on the mineralogical and textural control on various pm properties in quartzites granitoids gneisses metabasics and dolomite collected from different tectonic set ups the inter relationships among mineral constituents various textural parameters unconfined compressive strength ucs schmidt hammer rebound r value seismic wave both p and s waves velocity and their attenuation characteristics were obtained using regression analyses it has been concluded that there exists no relation between ucs and seismic wave velocity in quartzite granitoids and gneisses moderate positive relationship in metabasics and strong negative relationship in dolomite it has further been noted that in quartzite and dolomite monominerelic rocks grain size dominantly control the seismic wave velocity as the relatively coarser grained samples have higher seismic wave velocity whereas ucs is strongly controlled by grain size as well as the quantity and the orientation of the weak minerals like muscovite biotite calcite etc in gneisses and granitic gneisses preferred orientation of minerals especially the mica minerals although in present small quantity is the main factor controlling ucs and seismic velocity both these properties increase with the increase in intensity of preferred alignment of minerals whereas in metabasics it is the presence of amphibole pyroxene minerals feldspar that dominantly controls the seismic wave velocity

seismogenic structures activated during the 1987 seismic sequences along the adriatic coast summary in order to obtain a better spatial definition of the structures which were activated during the marche adriatic coast seismic sequences in summer 1987 we relocated the earthquakes epicentres by means of an original computer code based on the joint hypocentre determination technique the sequences took place at sites which are considered of moderate seismicity although historical files contain information about stronger events that occurred in the surrounding areas the activated structures belong to the outer apennines front range and adriatic foreland folds respectively the spatial trend shown in the results of our seismological analysis agrees with the main geological features known from literature

the aspo pillar stability experiment part ii rock mass response to coupled excavation induced and thermal induced stresses a 1 m thick pillar was subject to coupled excavation and thermal induced stresses to induce brittle rock mass yielding the yielding strength of the heterogeneous and fractured rock mass consisting of aspo diorite was evaluated at eighteen discrete locations using data from the displacement acoustic emission and thermal monitoring systems the average rock mass yielding strength was determined to be 0 59 of the uniaxial compressive strength the onset of dilation in uniaxial laboratory tests determined from strain gauge data was found to occur at approximately 0 45 of the uniaxial compressive strength it was shown that that the onset of acoustic emission events in situ also occurred when the tangential stress exceeded 0 43 of the uniaxial compressive strength for sites with absence of in situ data it is recommended that this lower bound value determined from laboratory data may be used for assessing the in situ rock mass yielding strength visual observation and displacement monitoring showed that extent of rock mass yielding is sensitive to small changes in the tangential stress magnitudes it was determined using three dimensional modelling that changes in the tangential stress magnitude of approximately 1 mpa was sufficient to cause yielding of the pillar to propagate in what appeared to be intact rock observations suggest that without this small stress change yielding of the rock mass would not occur in other words there appeared to be a well defined boundary and if the stresses reached this boundary yielding was observed however if stresses were only slightly below this boundary yielding or time dependant processes were not observed over the monitoring period used in the experiment

replenished magma chambers effects of compositional zonation and input rates several recent publications have reported investigations of the dynamical effects and geological consequences of the replenishment of a homogeneous magma chamber by the rapidinjection of hot relatively dense fresh magma the new magmaforms a separate layer at the base of the chamber whereit cools and crystallizes until the density of the residual liquid in the lower layer becomes equal to that of the upperlayer at which time the fluid in the two layers becomes intimately mixed the fluid dynamical aspects of this modelwere confirmed by laboratory experiments using aqueous solutions this paper reports three experimental variations on the basic theme which examine the effects of the rate of injection into homogeneous and compositionally stratified chambers first the rapid injection of a hot dense layer beneath a fluid with a lower temperature and a vertical compositional gradient is considered a series of layers gradually builds up from the base of the upper gradient region while the lower layer cools crystallizes and finally overturns in this situation however the rise of the lower layer fluid is restrained by the density gradient and mixing takes place with only part of the upper fluid second the slow influx of a hot dense liquid beneath a cold less dense homogeneous layer is considered a considerable quantity of the input fluid coolsand crystallizes immediately releasing some lighter fluid to mix with the fluid in the homogeneous layer with time some dense input fluid spreads along the bottom so that locally the situation is the same as the one considered in the previous studies with a local overturning occurring when the density of the lower fluid has decreased sufficiently the deposition of crystals continues and some rather fine chimney like structures can develop which bear a resemblance to the black smokers recently discovered on the sea floor third a combination of the first two variations is studied by the consideration of the slow influx of hot dense liquid beneath a uniformly cooler fluid with a vertical compositional gradient the input fluid is constrained in its rise by the density gradient as the influx continues the additional thermal energy is also confined and causes the crystals to redissolve and build up a lower layer as was observed in the case of a rapid injection beneath a compositional gradient

correlation of mineralogical and textural characteristics with engineering properties of selected granitic rocks from turkey abstract granitic rocks show a variety of engineering properties that may affect quarrying operations tunneling mining slope stability and the use of rock as a construction material the physical and mechanical properties are a function of the mineralogical and textural characteristics of the rock the purpose of this study is to apply correlation analysis to investigate the relationships between petrographical and engineering properties of granitic rocks a variety of granitic rock samples from different parts of turkey were subjected to petrographic studies the same samples were then tested to determine specific gravity dry and saturated unit weight water absorption effective and total porosity sonic velocity schmidt hardness point load strength index uniaxial compressive strength tensile strength and modulus of elasticity the relationships between these properties and the petrographical characteristics are described by simple regression analyses the study revealed that the influence of the textural characteristics on the engineering properties appears to be more important than the mineralogy it also determined that the types of contacts grain mineral shape and size significantly influence the engineering properties of the granitic rocks

zoning and exsolution in alkali feldspars from laacher see volcano western germany constraints on temperature history prior to eruption compositional zoning and exsolution patterns of alkali feldspars in carbonatite bearing cognate syenites from the 6 3 km3 d r e phonolitic laacher see tephra lst deposit in western germany 12 9 ka are reported these rocks represent the cooler outer portion and crystal rich products of a cooling magma reservoir at upper crustal levels major and trace element difference between cores and rims in sanidine crystals represent two generations of crystal growth separated by unmixing of a carbonate melt trace element differences measured by la icp ms are in accordance with silicate carbonate unmixing across the core rim boundary we extracted gray scale profiles from multiple accumulations of back scattered electron images gray scales directly represent k na ratios owing to low concentrations of ba and sr 30 ppm diffusion gradients are modeled to solve for temperature using known pre eruptive u th zircon ages 0 20 ky of each sample schmitt et al j petrol 51 1053 1085 2010 estimated temperatures range from 630 c to 670 c for the exsolution boundaries a diffusive homogenization model is constrained by the solvus temperature of 712 725 c and gives short time scales of only 15 50 days based on our results we present a model for the temperature time history of these rocks the model also constrains the thermal variation across the cooling crystal rich carapace of the magma reservoir over 20 ka and suggests a thermal reactivation of cumulates the cooling carapace and probably the entire system only a few years prior to the explosive eruption of the remaining molten core of the phonolitic magma reservoir

evidence for magma mixing within the laacher see magma chamber east eifel germany abstract the final pyroclastic products of the late quaternary phonolitic laacher see volcano east eifel w germany range from feldspar rich gray phonolite to dark olivine bearing rocks with variable amounts of feldspar and al augite megacrysts petrographically and chemically homogeneous clasts occur along with composite lapilli spanning the compositional range from phonolite mgo 0 9 to mafic hybrid rock mgo 7 0 for all major and trace elements both a basanitic and a phonolitic phenocryst paragenesis occur within individual clasts the phonolite derived phenocrysts are characterized by glass inclusions of evolved composition rare inverse zoning and strong resorption indicating disequilibrium with the mafic hybrid matrix basanitic magnesian clinopyroxene and olivine in contrast show skeletal normally zoned overgrowths indicative of post mixing crystallization in accord with petrographical and other chemical evidence mass balance calculations suggest mixing of an evolved laacher see phonolite containing variable amounts of mineral cumulates and a megacryst bearing basanite magma magma mixing occurred just prior to eruption hours of the lowermost magma layer of the laacher see magma chamber but did not trigger the volcanic activity

the bag tephra a widespread tephrochronological marker in middle europe chemical and mineralogical investigations the bag tephra is a widespread tephra layer interbedded in quaternary loess deposits along the danubian valley of hungary and slovakia its age is poorly defined between 788 and 380 ka b p the glass and mineral composition micropumice clasts of phono tephrite and blocky shards of tephri phonolite associated with two kinds of clinopyroxene fassaitic diopside and salite is very distinctive this tephra could be used as a chronological marker as soon as its age is refined the probable origin is the middle italian volcanic area

constraints on the pre eruptive magmatic history of the quaternary laacher see volcano germany ba zonation patterns in sanidine phenocrysts from mafic and intermediate phonolite and crystal rich cumulates from the laacher see volcano 12 9 ka in western germany document diffusion times suggestive of periodic recharge events throughout the magma reservoir s entire lifespan of 24 ky phenocrysts analysed from samples that formed late at the base of the compositionally zoned magma reservoir by mixing and mingling between a resident phonolite magma and recharging basanite show resorption and thin 2 10 m late stage ba rich overgrowth short diffusion profiles across these boundaries give diffusion times of 1 5 3 years at most which are interpreted to be the maximum duration between the most recent recharge by the basanite and eruption the lack of such late overgrowth in samples from other parts of the phonolite reservoir suggests that effect of this mixing and mingling was limited to the crystal rich base sanidines in the cumulates by contrast are generally devoid of zoned crystals only rare cumulate crystals with resorbed outer boundaries and very thin overgrowths a few microns with very sharp compositional changes imply the remobilization of cumulates only months before eruption based on the diffusion timescales and storage temperatures obtained in a previous study we present a genetic model for the conditions and timing of storage and re activation of the magma system prior to the eruption of laacher see which is the largest volcanic event in central europe since the last glaciation

separated earthquake location we present a practical method of locating earthquakes in laterally varying media the procedure has two distinct phases an estimation phase and an application phase in the estimation phase all existing arrival time residuals relative to some reference one dimensional velocity model for a region are used to estimate a set of path anomalies station corrections that vary as a function of source position this is done by sorting earthquakes into groups localized in space and applying a novel multiple event location algorithm this algorithm uses a pair of complementary projection operators to combine a priori information about the lateral structure that is indeterminate from the available data with the information that can be determined uniquely from the available data having estimated path anomalies as a function of source location we can generate a table of path anomalies that can be accessed and interpolated for future earthquake location this is the application phase of the method we have tested the method on synthetic data designed to study how well earthquakes can be located in the vicinity of the rupture zone of the 1984 morgan hill california earthquake we found precise absolute locations could be obtained provided the a priori information was specified appropriately distortion of relative locations occurred near large lateral velocity gradients and for groups of events spread over large areas because of the inadequacy of fitting a single set of path anomalies to the whole group

tomographic images of the upper mantle below central europe and the mediterranean results from delay time tomography of the european mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes slab like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath spain the tyrrhenian basin and the aegean these structures are interpreted as images of subducted slabs large aseismic regions with positive velocity anomalies are found beneath the western mediterranean italy the alps dinarides the pannonian basin northern greece and the aegean these anomalies can also be linked to subducted lithosphere from the anomaly patterns it is deduced that subduction occurred below the western mediterranean and along both sides of the adriatic micro plate beneath the dinarides and northern greece the velocity structures suggest detachment of the slab from the surface

subducting oceanic crusts of the philippine sea and pacific plates and weak zone normal compression in the kanto district japan summary oceanic crusts subducting into the mantle were detected by analyses of mantle earthquakes in the kanto district central japan earthquakes in a depth range of 30 80 km in the southwestern ibaraki prefecture were relocated by a modified method of joint hypocentre determination we obtained a good distribution map of hypocentres and focal mechanisms a boundary layer between the eurasian and philippine sea plates was found where thrust earthquakes with p axes in the nw se direction and of which low angle nodal planes dip northward occurred in a layer with a thickness of about 4 km the p wave velocity in this layer is estimated to be less than about 7 0kms l another boundary layer between the philippine sea and pacific plates exists about 15 km beneath the above boundary layer thrust earthquakes with p axes in the ew direction and of which low angle nodal planes dip westward occurred in this layer that also has a thickness of about 4km furthermore normal faulting earthquakes of which the p axes are almost perpendicular to the boundary layers were found immediately outside the boundary layers combining these results we can conclude that the boundary layers are oceanic crusts that exist at the top of the subducting philippine sea and pacific plates weak zone normal compression was proposed to result from the existence of low velocity oceanic crusts at plate boundaries this hypothesis can be explained because only stress caused by relative motion of the two plates is consumed inside the weak oceanic crust the remnant stress after subtracting the above stress from the tectonic one applied at the plate boundary is the stress of which the p axis is normal to the plate boundary

seismicity and p wave velocity image of the southern tyrrhenian subduction zone summary this paper focuses on the deep earth structure and earthquake distribution within the southern tyrrhenian subduction zone we discuss seismological observations which provide insight into the mechanics of subduction processes for an unusual compressional margin the motivation for this work derives from the recognition that little is known about one of the most intriguing geodynamic features of the italian peninsula and the fact that a large amount of information can be extracted from data collected by the istituto nazionale di geofisica national seismic network we show that the hypocentres of intermediate and deep earthquakes that have occurred since 1988 image a nw dipping plane continuous from the ionian sea to the tyrrhenian down to 450 km depth we also present a 3 d model of the deep structure beneath southern italy derived using deep earthquake seismic tomography tomographic images reveal a high velocity body dipping from the apulian and iblean forelands towards the tyrrhenian basin in the crust and upper mantle at least down to 320 km depth this high velocity body may be related to the cold subducted ionian lithosphere earthquake hypocentres are confined within the high velocity body delineating the subduction beneath the calabrian arc

the deep seismicity of the tyrrhenian sea the deep seismicity of the tyrrhenian sea is analysed using data from a new instrumental catalogue of the seismicity of the italian area we use algorithms for the determination of absolute and relative hypocentral locations and for the evaluation of the geometry and coherence of the state of stress within the subducting slab the structure of the benioff zone although simpler than previously indicated reveals anomalous traits both in the seismicity distribution and in the stress geometry confirming that standard subduction models cannot be applied in the tyrrhenian region the velocity anomaly and the location of few isolated events indicate that the subducted slabs extend to the north along the apenninic chain approximately to the latitude of the irpinia region in central italy 42 n

joint hypocentral location in media with lateral velocity variations and interpretation of the station corrections abstract the application of a new implementation of the joint determination of hypocenters origin times and station correction terms jhd technique to data from the arkansas swarm usa the campi flegrei italy and the nazca plate argentina throws new light onto the problem of earthquake location in all these cases good quality p and s wave arrival times were available the main results are as follows 1 large lateral velocity variations llvv are generally associated with relatively large station corrections these corrections in turn are usually much larger than the average of the station residuals determined when the same set of events is located using a single event location sel method 2 the locations determined by the jhd and sel methods may be substantially different 3 since the effect of llvv on jhd locations is not well established simple 3 d velocity models are constructed so that the jhd technique applied to synthetic data generated using these models produce station corrections similar to those observed 4 the analysis of the synthetic data also shows that the locations determined by the jhd method are much closer to the true locations than the locations determined with the sel method the use of the weighted average of the sel station residuals as station corrections does not give better located events although there is a large decrease in the r m s residual computed for each event therefore the use of r m s residuals to estimate the quality of event locations is not always warranted in view of these results it is possible to conclude that the jhd station corrections can be used to detect lateral velocity variations and to produce locations substantially less affected by these variations than the locations determined by the sel method furthermore under appropriate conditions the jhd station corrections can also be used in a forward modeling scheme to get a semiquantitative velocity model such a model may be the only information that can be obtained from a data set when the station and event distributions are not adequate for 3 d velocity inversion

micro textural effects on crack initiation and crack propagation of andesitic rocks abstract the onset of dilation and uniaxial compressive strength ucs of rocks are known to be affected by mineralogical petrographic and microstructural features therefore micro textural variations are essential for understanding variation in strength and failure behaviour of rocks in this study volcanic rock samples with different micro textural characteristics from different locations in turkey were evaluated the mechanical tests revealed considerable variations in unconfined uniaxial compressive strength and the crack initiation ci threshold the ucs ranges between 108 289 mpa and ci ranges between 46 130 mpa detailed quantitative petrographic and mineralogical analyses were carried out on each tested specimen to understand these strength variations additionally microstructural studies were carried out on thin sections before and after mechanical perturbation to analyze 1 the effect of the main constituents of the rock specimens and mineral heterogeneity on crack initiation and propagation and 2 the orientation and distribution of micro and macro cracks formed during laterally unconfined compression the synthesis of mechanical mineralogical petrographic and microstructural data suggests that both the crack initiation threshold and peak strength are influenced by the ratio of the area of fine grain groundmass grains smaller than 200 m to amphibole and plagioclase phenocrysts in addition ci and ucs decrease with an increasing normalized area of biotite phenocryst

subcrustal earthquakes in the northern apennines italy evidence for a still active subduction previously unreported subcrustal earthquakes have been located up to 90 km depth beneath the northern apennines italy these earthquakes occur beneath a zone of abundant upper crustal seismicity mostly confined to the upper 20 km of the crust although there are relatively few well located subcrustal earthquakes there appears to be a general southwestward deepening of the hypocenters from the adriatic to the tyrrhenian sea consistent with other geophysical data which suggest that the adriatic lithosphere is presently subducting beneath the northern apennines

stable isotope relations in an open magma system laacher see eifel frg 18o 16o and d h ratios have been measured for matrix glasses and phenocrysts from the zoned phonolitic laacher see tephra sequence 11000 y b p east eifel volcanic field frg to study open system behaviour of the associated magma system mineral and glass 18o values appear to be largely undisturbed by low temperature secondary alteration record isotopic equilibrium and confirm previous conclusions based on radiogenic isotope evidence of early small scale crustal assimilation during differentiation of parental magmas in a crustal magma chamber one sanidine glass pair possibly documents the late stage influx of meteoric fluids into the topmost magma layer prior to eruption a sealing carapace of chilled magma which itself was strongly contaminated prevented large scale fluid exchange up to the point prior to eruption when this carapace was fractured and meteoric water gained access to parts of the magma system d h measurements of various glass types glass inclusions dense and pumiceous glass and amphiboles gave conflicting results suggesting a combination of degassing volatile exchange with country rocks and hydration stable isotope ratios for primitive parental magmas 18o 5 5 to 7 0 and mantle megacrysts 18o 5 5 to 6 0 d 21 to 38 for amphiboles and phlogopite resp suggest a rather variable fluid composition for the sub eifel mantle

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out

assessment of rock geomechanical quality by quantitative rock fabric coefficients limitations and possible source of misinterpretations abstract rock microfabrics were quantified by image measurement system petrographic image analysis of thin sections along with common measured parameters grain area and size length of major and minor axes and their orientation some quantitative parameters aspect ratio grain boundary smoothness and fabric coefficients micropetrographic quality index k texture coefficient tc indexes of interlocking t and grain size homogeneity g were determined the reliability of these parameters for the evaluation of geomechanical properties was tested on the set of granitic rocks showing pronounced variability in rock mechanical properties none of the tested rock fabric coefficients or parameters proved a close correlation to rock mechanical properties except grain size based on experimental findings the grain size is along with porosity the controlling factor of rock mechanical properties of genetically and mineralogically similar rocks obliteration of the real effects of rock fabric parameters on the mechanical properties of rocks by application of complex fabric coefficients disables their practical use in petrography applied to geomechanics

mineralogical controls on the engineering behavior of hydrothermally altered granites under uniaxial compression effective engineering characterization of granites altered through processes of kaolinization is critical for safe extraction and design of slopes for the china clay industry in south west england by considering this important issue representative samples taken from a range of decomposition grades of altered granite were used to assess the controlling influence of changes in mineralogy on uniaxial compressive strength elastic modulus dry density and ultrasonic velocity dramatic reduction in uniaxial compressive strength occurs between alteration grades ii and iii analysis of acoustic emission data constrained by evaluation of scanning electron microscope sem images and strain gauge deformation readings has been used to identify crack propagation stages during uniaxial compression quantitative evaluation of mineralogy was determined from x ray diffraction xrd analysis of representative samples in order to establish relationships between mineralogy such as kaolinite and uniaxial compressive strength for the different alteration grade material the results of the testing confirm that the degree of alteration or kaolinization and associated changes in mineralogy of the granite is directly related to reduction in uniaxial compressive strength and dry density