deep hydrothermal circulation in a granite intrusion beneath larderello geothermal area italy constraints from mineralogy fluid inclusions and stable isotopes abstract a shallow 2 km granite body has been intersected by the mont 4 well in new producing areas of the larderello geothermal field the granite at 2 2 2 5 km and below 3 km underwent pervasive propylitic alteration that is dominated by the assemblage chlorite adularia quartz illite calcite albite epidote sphene fluid inclusion studies indicate two stages of alteration the first one is characterised by high temperature fluids that at 2218 m were trapped under boiling conditions at about 340 c and 15 mpa whereas at 3520 m evidence of boiling is not revealed and the temperature of the fluid was calculated to be about 350 c the second alteration stage shows a cooling of the system particularly evident in the shallower portion of the intrusion 235 c at 2218 m and 315 c at 3520 m the temperature of homogenisation for subsequent cooler inclusions approximates present day down hole temperatures and may be considered as representative of the fluid actually circulating in the granite in recent times calculated 18 o values of 0 1 for fluids in equilibrium at 340 c 2218 m and 350 c 3520 m with feldspar epidote and chlorite and d values of 51 to 61 for fluids in equilibrium with chlorite together with directly measured d values of 33 to 61 for fluid inclusions in quartz indicate derivation from meteoric waters the original meteoric signature of the fluids has been altered through water rock interaction but remains clearly distinguished from a primary magmatic signature for which no isotopic evidence was found active fracturing and the high structural relief of granite emplacement promoted hydrothermal circulation in the granitic body drilled by mont 4 well suggesting that such characteristics may be a pre requisite for such circulation at larderello

microstructural observations on natural syntectonic fibrous veins implications for the growth process abstract syntectonic antitaxial and ataxial fibrous veins were investigated using sem microprobe cathodoluminescence cl and optical microscopy in antitaxial calcite veins fibres and surrounding selvage grew simultaneously with similar growth rates of crystallographically differently oriented grains new material precipitated at the vein margin in antitaxial and bi mineralic ataxial microstructures bridges of country rock material formed during vein growth in an initial en echelon vein system in our antitaxial and bi mineralic ataxial samples the spacing of solid inclusions does not reflect individual crack seal openings

alpine tectonothermal evolution of the tuscan metamorphic complex in the larderello geothermal field northern apennines italy on the internal tyrrhenian side of the northern apennines high heat flow and geothermal gradient in the larderello geothermal field are evidence of a large scale thermal anomaly related to the emplacement of a large batholith of pliocene age extending from the upper to middle crust these intrusions relate to the miocene to recent northern apennines magmatism which developed as a result of crustal extension and upwelling of the asthenosphere at the base of the thinned crust in the subsurface of the larderello geothermal field medium and high grade metamorphic rocks tuscan metamorphic complex cored in several geothermal wells have previously been considered to be variscan basement new structural and petrographic data on these metamorphic rocks indicate an alpine tectonometamorphic history and provide evidence that medium to high grade mineral assemblages are related to pliocene thermal metamorphism centred on intrusions at shallow depth these data allow a new interpretation of the tuscan metamorphic complex as a tectonic wedge of the late palaeozoic triassic units and in particular highlight the considerable extent of pliocene thermal metamorphism and hydrothermal circulation as a result of convective cooling of intrusions

geological structure of a long living geothermal system larderello italy we have examined the data of 600 geothermal wells and re interpreted approximately 500 km seismic profiles through the field of larderello italy we conclude that the two main seismic reflectors present below the geothermal area host two different fluids 1 superheated steam in the upper h horizon reached by drillholes and 2 supercritical fluid in the deeper k horizon reached by few unproductive or damaged wells the superheated steam has the physical and chemical connotation of the geothermal fluid exploited so far at larderello whereas the supercritical fluid represents a potential unconventional deep seated resource still to be assessed the high temperatures existing in correspondence of the k horizon suggest that the silica rich rocks are close to a plastic state and the fluids should remain confined in a medium sealed to the confining rocks unless occasional fluid overpressure and abrupt high strain rates occur

fluid migration and origin of a mud volcano in the northern apennines italy the role of deeply rooted normal faults introductionsurface seeps of gas oil and salinewaters areconsideredtobeindicatorsof deep seated hydrocarbon accumu lationandhavebeenused forover60years as a guide to hydrocarbonprospectivity a wide spectrum ofseepages belongs to di erent geologi cal settings e g camerlenghi etal 1992 1995 thrasher etal 1996 schulz etal 1997 kopf etal 1998 graue 2000 spectacular seepagescan be found in basins with highsedimentation rates that generateoverpressureandmuddiapirism gu liev and feyzullayev 1996 up dipcarrier beds and active tectonic fea tures act as channels for subsurface uidandlocalizesurfaceemissionsuptotens orevenahundred kilometresfrom the reservoir thrasher etal 1996 during migration the domi nant mechanism that changeshydrocarbon composition is phasepartitioning migration of hydrocar bons is then largely the result ofbuoyancy of the free phase formedduringthisprocess matthews 1996 eventually thegeologyofthebasinisthe key to interpreting complicated uidmigrationpathways manystud ies simply focus on the oil and gascomponents of the migrating uidrather than on the characteristics ofthewaterandmudthatareassociatedwithhydrocarbonmigrationandalsoextruded by spontaneous seeps eventhough water is invoked as beingresponsibleforatleastlighthydrocar bon removal klusman and saaed 1996 watersofdi erentprovenancecontributetotheascending uidsandtheir geochemical characteristics canhelp in understanding their evolutionduring diagenesis and migration e g white 1965 hanor 1987 holyshandto th 1996 thispaperpresentssomeanalytical data from a spontaneoussurface seep bearing saline water mud gas and oil at the foothills ofthe northern apennines the aimsare i to provide some insight intothedepthandoriginofthe uidsandthe nature of the seepage pathway and ii tode nethelossofsubsurface uids accumulation related to thegeologicalpattern geological setting and structuralcontrol of the regnano mudvolcanoin the external portion of the nor thern apennines spontaneous uidemissions are distributed along twobelts borgia etal 1986 nanni andvivalda 1999 minissaleetal 2000 the rst belt stretches along the poplainfoothills whilethesecondoneisinternal and runs nearly parallel tothe main apenninic divide fig 1 theregnanomudvolcanoconsistsofmud breccias and mud ows spread ing over an area of 0 5km

pliocene crustal shortening on the tyrrhenian side of the northern apennines evidence from the gavorrano antiform southern tuscany italy the northern tyrrhenian sea and the inner northern apennines are classically regarded as a late miocene pleistocene back arc system developed as a consequence of slab rollback along active subduction zones we present new geological and structural data on the gavorrano antiform a key sector of the inner northern apennines lying close to the northern tyrrhenian sea it provides clear evidence of pliocene shortening deformation and magma emplacement the orientation of 1 n50 e n80 e derived by fault slip data inversion is consistent with a general ene wsw shortening direction furthermore this ene wsw trending orientation of 1 is compatible with the compressive deformation recorded in coeval sedimentary basins on this basis we suggest that the inner northern apennines were affected by crustal shortening during the pliocene this scenario matches well geophysical data suggesting that since the late messinian 6 5 ma subduction rollback and back arc extension strongly decreased in the northern tyrrhenian sea whereas they continued as active processes in the southern tyrrhenian sea

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

crustal models of the geothermal areas of southern tuscany italy abstract geological and geophysical data gathered in the geothermal areas of southern tuscany located in the inner part of the northern apennines indicate the presence of granite intrusions the most relevant data are 1 regional asthenospheric ascent to a depth of 40 50 km 2 granitic dykes as old as 3 8 2 9 ma and a widespread contact aureole found in several deep geothermal wells 3 very high heat flow values interpreted as the result of convective circulation of hot fluids above shallow magmatic bodies 4 the presence of low density bodies inferred from low gravity values often correlated with positive heat flow anomalies 5 the occurrence of a highly reflective horizon named k in a depth range of 3 12 km in the geothermal areas as shown by seismic reflection data 6 a 30 40 km wide low velocity body below the k horizon whose existence is supported by local earthquake tomography and teleseismic studies 7 the presence of a conductive body which correlates well with the anomalous tomographic and teleseismic body as revealed by magnetotelluric surveys the goal of the paper is to test different alternative crustal models by using these data the models are 1 granite intrusion 2 geopressurized fluids below impervious layers 3 contact metamorphic aureole 4 mylonite layers at the upper lower crust transition and 5 some combination of the four the occurrence of shallow intrusive bodies still partially molten and associated with saline brines is considered the most tenable model

fluid percolations in a fault zone a study of fluid inclusion planes in the st sylvestre granite northwest massif central france abstract a method for relating fluid flow evolution direction of fluid percolation to the bulk brittle network microfracture system at each state in a sequence of deformational events is presented fluids percolating through cracks are generally trapped as fluid inclusion planes alignment of fluid inclusions the method involves the use of fluid inclusions not only as a tool for the establishment of the physico chemical conditions under which fluids were entrapped but also as a microstructural marker of the geometry of permeability the study shows that through the determination of the paleopressures for each stage of fluid migration the chronology of the cracks and p t conditions prevailing during each crack formation can be established this methodology has focussed on a granitic example from the french massif central but may be applied to other geological environments

poisson s ratio values for rocks abstract compared to other basic mechanical properties of rocks poisson s ratio is an elastic constant of which the significance is generally underrated yet in rock mechanics there is a considerable number of diverse areas which require a prior knowledge or estimation of the value of poisson s ratio this paper examines the values and applications of poisson s ratio in rock mechanics following an historical account of the initial controversy whether it was a material constant or not the effects of poisson s ratio in the elastic deformation of materials intact rocks and rock masses are briefly reviewed also the reported values of poisson s ratio for some elements materials and minerals are compiled while typical ranges of values are presented for some rocks and granular soils finally poisson s ratio classifications are recommended for isotropic intact rocks

fluid regimes during late stages of a continental collision physical chemical and stable isotope measurements of fluid inclusions in fissure quartz from a geotraverse through the central alps switzerland fluid evolution during neo alpine metamorphism during late stages of the continental collision between europe and africa was studied by analyzing fluid inclusions in alpine fissure quartz collected in forty nine localities along a geotraverse through the central alps switzerland the methods employed include microthermometry micro raman spectroscopy k na thermometry and stable isotope analysis early fluid inclusions provide evidence of close to peak metamorphic temperatures of the late tertiary or neo alpine metamorphic event fluid composition evolved along the geotraverse from north to south as follows higher hydrocarbons were dominant in the low and medium grade diagenetic zones methane was the main volatile in the high grade diagenetic and low grade anchizone water dominated in the highgrade anchizone and low grade epizone with co2 10 mol in the high grade epizone and in the mesozone higher hydrocarbons and ch4 were the products of kerogen maturation and cracking of preexisting petroleum large water supplies originated from the dehydration of cooler metasedimentary rocks that were overthrust by crystalline basements of the lepontines aar and gotthard massifs carbon isotope analyses suggest that the co2 component was derived from oxidation of graphitic matter especially in the vicinity of sulfate bearing metasediments and from decarbonation reactions in the aar and gotthard massifs as well as in the helvetic axen nappe and its underlying north helvetic flysch high fluid pressures prevailed and favored nappe transport by contrast in the southern lepontine area very low early fluid pressures were probably related to dry rocks and scarce metasediments and to high geothermal gradients that resulted from intense uplift and erosion between 26 and 18 ma retrograde fluid evolution was recorded by a succession of fluid inclusion populations in each alpine fissure it was controlled by uplift and cooling and characterized by decreasing contents of volatiles and an increase in 18o of host quartz tectonic activity led to episodic pressure drops of at least 0 5 to 2 kbar and promoted fluid unmixing channelized flow and rapid growth of skeletal quartz channelized rather than pervasive fluid migration at temperatures 450 c and under conditions of brittle deformation is documented by episodic increases in salinity and by fluid flushing through the massifs there is stable isotope evidence for involvement of meteoric water only in late crystallizing quartz formation of alpine fissures and fissure minerals was the result of a unique coincidence of late continental collision 450 c fluid expulsion from overthrust metasediments uplift and erosion

fluid overpressure and stress drop in fault zones using the average aspect length maximum thickness ratios of 379 mineral filled extension mode i veins from an active fault zone the fluid overpressure during their development with reference to the minimum compressive principal stress 3 is estimated at 20 mpa emplacement of such veins increases 3 and can generate a temporary stress barrier to the propagation of subsequent hydrofractures on meeting a subhorizontal stress barrier vertically propagating hydrofractures may change into water sills where the fluid pressure is at or above lithostatic in this model stress barriers and thus water sills can form at any depth in and in any type of fault zones for such a high fluid pressure the product of the coefficient of sliding friction and the normal stress in the modified griffith criterion becomes essentially zero and the driving stress associated with faulting equal to twice the in situ tensile strength of the host rock for typical in situ tensile strengths of 2 3 mpa the driving stresses for slip on overpressured fault planes is 4 6 mpa these results are in good agreement with the commonly measured average static stress drops of 3 6 mpa during earthquakes

how local stress fields prevent volcanic eruptions recent studies show that dike injections in composite volcanoes and rift zones are much more common than dike fed eruptions although this observation is of fundamental importance in volcanic hazard studies and for understanding the formation and structure of the ocean crust the mechanisms that prevent dikes from reaching the surface are still poorly understood here we present new numerical models of magma chambers hosted by crustal layers of contrasting mechanical properties such as stiff lava flows and soft pyroclastic rocks the numerical models vary in sophistication from simple 4 layer models to a complex and realistic 30 layer model in the latter the layer thicknesses approach those of individual lava flows and pyroclastic flows as observed in the field in iceland and elsewhere more specifically for a magma chamber with a top at the depth of 1 5 km as is common in iceland each layer in the 30 layer model has a thickness of 50 m this is similar to the thicknesses of many pahoehoe lava flows and pyroclastic hyaloclastite and sedimentary units in iceland tilting of the lava pile is a general feature of volcanic areas to take this into account we also present several numerical models with dipping layers where in accordance with observations the dips of the layers increase with depth in the lava pile all the numerical models for thick and thin layers as well as for tilted layers yield some common results first that during magma chamber inflation local stresses in the stiff layers encourage dike propagation while those in the soft layers tend to arrest dike propagation and prevent volcanic eruptions second that the local stresses in the stiff layers may trigger seismogenic faulting while the soft layers remain seismically quiet the models with the dipping layers indicate that the general tilting of the lava pile may result in shifting of volcanic activity at the surface the shifting is because the local stresses that develop above a magma chamber located in a tilted lava pile control the pathways of injected dikes the direction of shifting is in the dip direction of the tilted lava pile and the amount of shifting increases with increasing dip all the results suggest that for an eruption to occur the stress conditions along the potential pathway of a dike must be basically homogeneous

fluid circulation in the upper brittle crust thickness distribution hydraulic transmissivity fluid inclusion and isotopic data of veins hosted in the oligocene sandstones of the macigno formation in southern tuscany italy abstract we present structural analysis fluid inclusion data on calcite and quartz and isotopic composition of calcite forming veins occurring in the upper crustal level and hosted in oligocene sandstone in southern tuscany italy the veins have been analysed in two sites few kilometres apart along well exposed coastal cliffs and in an abandoned quarry these two sites were at a different depths at the time of the vein formation with a h 100 m structural analysis of veins provided estimations of stress ratio 2 3 1 3 driving stress ratio r pf 3 1 3 and fluid overpressure po pf 3 at the time of vein formation the estimated po is in the range of 42 103 mpa 0 24 and r 0 45 indicating that fluid pressure was higher than the intermediate principal stress at the time of veins formation the veins thickness t shows a clear power law distribution d 1 8835 and r2 0 9762 in the lowermost site coast and a negative exponential distribution a 0 6943 and r2 0 9921 in the uppermost site abandoned quarry the vein thickness distributions have been used to compute the average transmissivity of the veins in the two sites the computed transmissivity for the vein formation is 10 4 m2 s 1 with higher values attained by the veins having negative exponential thickness distribution fluid inclusions studies highlighted that in both calcite and quartz water rich inclusions with salinities of 2 2 4 3 wt nacl equiv and methane rich inclusions were coevally trapped during fluid un mixing processes thermogenic origin from thermal maturation of organic matter present in the macigno formation is proposed for methane whereas the similarity between the 18o from 14 9 to 17 4 and 13c from 0 4 to 2 4 data of representative calcite veins and the isotopic composition 18o 16 1 13c 1 0 of host rock carbonate component indicates that the fluid which formed calcite was in isotopic equilibrium with the carbonates present in the oligocene sandstones the calculated pressure temperature conditions during the formation of these inclusions are prevalently within the 40 145 mpa and 160 260 c ranges the highest pressure values approximate the lithostatic pressure 120 mpa computed from geological data and are coherent with a geothermal gradient ranges of 35 45 c km whereas the lower pressure values are comparable with hydrostatic pressure conditions the pressure range indicated by fluid inclusion data is also comparable with the fluid pressure estimated from structural analysis the considerable pressure range can be related to pressure cycling between lithostatic and hydrostatic conditions as a consequence of fault valve actions and rock fracturing with subsequent pressure recover due to self sealing process

modelling the connection between earthquake preparation processes and crustal electromagnetic emission abstract the steadily increasing amount of information available today on the natural electromagnetic emission eme of the radio frequency band associated with seismic events raises the problem of the origin of this phenomenon a natural hypothesis is that eme is due to earthquake preparation processes the present paper is concerned with substantiating a model that postulates eme to be caused by cracking of surficial crustal layers in the zone of earthquake preparation the crust is assumed to have ordered hierarchical structure individual elements of that structure are formed of blocks of different scales and obey principles of similarity between the blocks are soft interlayers with a finite strength limit a regular periodic structure with a cubic lattice is studied as a result eme intensity as a function of magnitude is evaluated methodological recommendations are given for organization of field observations of eme in relation to earthquake prediction

storm induced precipitation variability control of long term erosion abstract erosion is often treated as a continuous process yet it occurs through discrete events such as floods and landslides of variable magnitude and periodicity it has also long been expected to be strongly dependent on precipitation however the influence of temporal rainfall variability upon long term evolution of landscapes remains unclear here we report high erosion rates 0 8 to 10 mm yr 1 over 70 ka estimated from paleovolcanic reconstructions across a steep rainfall gradient on reunion island which show that long term erosion rates are influenced by the cyclone induced variability of precipitation geostatistical analysis of 30 years of daily rainfall records reveals that erosion rates are high where the local climate is the driest and where the difference in intensity between extreme rainfall events and prevailing precipitation is the strongest this implies that the intrinsic variability of precipitation impacts landscape evolution not only through extreme meteorological events but also through background rainfall induced parameters such as humidity and dryness which modulate the erosion threshold of the earth s critical zone

new approach for the quantification of paleostress magnitudes application to the soultz vein system rhine graben france abstract quartz veins often appear in pre existing cracks and are the witnesses of paleofluid flows a new method of paleostress magnitude quantification is proposed in this paper based on the knowledge of i the geometrical distribution of vein poles ii empirical considerations of rupture criteria and iii the fluid pressure stress axis orientations deduced from the geometrical distribution of the vein poles define angular relations allowing the reduced stress tensor and the ratio characterization p f values quantified with fluid inclusion studies and intrinsic curves drawn with empirical relations depending on the rheologic properties of the pre fractured rock are combined to graphically fit the final mohr circle the resulting absolute stress magnitudes take into account the fluid pressure influence application of this method on the quartz vein system of soultz sous forets rhine graben france gives realistic magnitudes of the oligocene extension and are similar to those found in previous study with other methods

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

kinematics of crystal growth in syntectonic fibrous veins abstract detailed observations of a set of fibrous antitaxial calcite veins in a slate reveal that some of the calcite fibres do not connect material markers on both sides of the vein and can therefore not have tracked the full opening trajectory during vein growth this calls for a better understanding of the mechanisms of fibre formation and reliable criteria to test the tracking hypothesis based on surface roughness characteristics of the vein wall we develop a simple model for shape growth of crystals in a crack seal environment which can account for both tracking and non tracking behaviours and propose a set of tracking criteria for antitaxial veins finally we discuss ways by which the model can be tested against natural examples

pressure fluctuation during uplift of the northern apennines italy a fluid inclusions study abstract p t conditions existing after the main syn collision tectonic phase in the western part of the northern apenninic chain italy e g in the tuscan nappe outcropping in the la spezia area were estimated on the basis of a detailed microstructural structural petrographic and fluid inclusion study of quartz of syn tectonic d2 veins developed in the tertiary flysch at the top of the tuscan nappe macigno formation three main fluid events have been distinguished as follows during retrograde metamorphism d1 to d2 phase fluids in equilibrium with turbidites from the tuscan nappe were h2o ch4 mixtures issued from water organic matter interactions in temperatures conditions that may have reached at least 260 c or more 280 c depending on the considered depth estimates and maximum pressures around 210 250 mpa evidence of strong fluid pressure fluctuation between lithostatic and hydrostatic within the metamorphic formations up to 100 150 mpa possibly linked to fault valve activity at the beginning of the uplift triggered phase separation of the water methane fluids and production of methane rich and water rich fluids fluctuations in pressure during these events played a crucial role in quartz crystallization especially in extensional fissures formed perpendicular to the d2 folds axial foliation changes in the fluid regime and sources with time are evidenced by the input of brines which mix to distinct degrees and are trapped in healing microfissures during retrograde fluid evolution such mixing processes are an indication of the connection between separate fluid reservoirs with different temperature conditions consequently mass and heat transfer have to be taken into account as the downward percolation of cooler fluids probably accelerated the rate of cooling of the exhumed formations these processes are certainly common to most orogenic terrains and can be quantitatively studied through p v t x reconstruction using fluid inclusion data on the drainage zones where the mixing processes occurred this work confirms that fluid inclusion studies can provide accurate quantitative estimates of fluid pressure variations during the evolution of orogenic terrains and could therefore constitute a useful tool in tectonic interpretations at the light of the models developed for pressure variations in the upper crust

thickness and spatial distribution of veins in a porphyry copper deposit rosia poieni romania abstract a statistical analysis of the vein thickness distributions of veins in the rosia poieni porphyry copper deposit romania indicates that vein thickness data conform to a power law distribution whereas the spatial distribution of veins follows a negative exponential law a high clustering of the veins is indicated by both the spacing distribution and the cv values the similar vein densities observed at the open pit scale are representative of a saturation level of vein nucleation differences in the spacing distribution and in the mean vein thickness are explained by different initial nucleation rates in the deepest and the lowest parts of the porphyry copper the highly clustered organization of the system is explained by vein linkage processes during their growth and modification of the fluid pressure and local stress during the hydrofracturing

fractal analysis for natural hazards in the earth sciences the concept of fractals and scale invariance is well recognized in many natural objects however the use of fractals for spatial and temporal analyses of natural hazards has been less used and accepted in the earth sciences this book brings together 12 contributions that emphasize the role of fractal analyses in natural hazard research including andslides wildfires floods catastrophic rock fractures and earthquakes a wide variety of spatial and temporal fractal related approaches and techniques are applied to natural data experimental data and computer simulations these approaches include probabilistic hazard analysis cellular automata models spatial analyses temporal variability prediction and self organizing behaviour the main aims of this volume are a to present current research on fractal analyses as applied to natural hazards and b to stimulate the curiosity of advanced earth science students and researchers in the use of fractals analyses for the better understanding of natural hazards

regional distribution of al silicates and metamorphic zonation in the low grade verrucano metasediments from the northern apennines italy abstract mineralogical and petrological studies of triassic verrucano metasediments of the northern apennines are reported the widespread occurrence of al silicates allows the delineation of four metamorphic zones with increasing metamorphic grade 1 kaolinite zone well perugia 2 umbria 2 kaolinite pyro phyllite zone monte argentario and part of the verrucano of the monticiano roccastrada area and monti leoni 3 pyrophyllite zone monti pisani iano monti leoni the monticiano roccastrada area and some wells in the larderello region 4 kyanite zone massa area and some wells in the larderello area the four metamorphic zones correspond to temperatures ranging from 300 c to about 450 c on the basis of the si content of muscovite and geological arguments pressures of between 3 and 5 kbar are estimated the metamorphic zones are located more or less parallel to the bent north west south east trending structural zonation of the northern apennines with the concave side towards the tyhrrenian sea during the alpine orogeny the verrucano metasediments underwent three folding phases each of which has produced an axial plane schistosity s1 s2 s3 during the first folding phase the verrucano sediments were buried increasingly deeply within the crust from east to west the climax of alpine metamorphism was attained prior to the second folding phase with crystallization of porphyroblasts of kyanite and chloritoid in a central area located between massa and larderello the inferred paleo temperature distribution pattern resembles an asymmetric thermal high defined by the kyanite zone and surrounded by the pyrophyllite zone a similar pattern is still present in the tuscan crust as indicated by a series of geothermal anomalies passing through the northern apennines

high and low density fluids in a quartz vein from the irish variscides abstract combined microstructural and fluid inclusion studies on a multiple quartz vein from the irish variscides reveal a kinematic history consisting of three separate dynamically distinct extensional opening events the first of these is characterized by trapped fluid at densities of 0 87 0 98 g cm 3 indicative of pressures approximating the estimated lithostatic load while fluid densities associated with the following two events 0 76 0 91 g cm 3 clearly indicate sub lithostatic fluid pressures the combined evidence suggests that these later two opening events were extensional fractures occurring well below the critical depth for tensional 3 least effective principal stress it is argued here that the preservation of such low density fluids in an environment that conventionally requires supra lithostatic fluid pressures for hydraulic failure is due to i the influence of a preexisting material anisotropy in the rock that would result in hybrid extensional failure ii the effect of stress heterogeneities associated with the development of crude boudins in the vein

dikes emplaced into fractured basement timna igneous complex israel dikes are usually envisioned as arrays of parallel segments dilated perpendicular to the direction of the least compressive stress we describe here four dikes of highly irregular shape intruded in the fractured basement in the timna igneous complex southern israel the dikes include a doleritic dike 2 3 km long and 1 6 m to 32 m thick and three andesitic dikes up to 1 5 km long and 8 m thick the dikes each display significant variations of dip up to 60 strike up to 160 and thickness the thickness variations correlate better with the segment attitude than with the position along the dikes we show that the irregular shapes of the timna dikes are the result of emplacement into fractured host rock under different paleostress states and driving pressures three dilation styles that differ by the geometry of the initial cracks are analyzed an array of randomly oriented cracks style a a single linear crack style b and an array of interconnected nonparallel cracks style c the analysis of style a provides the stress state during dike emplacement including the orientations of the three principal stresses 1 2 3 the stress ratio 2 3 1 3 and the normalized driving pressure r pm 3 1 3 the stress ratio indicates the shape of the stress ellipsoid and it ranges from 0 for 2 3 prolate ellipsoid to 1 for 1 2 oblate ellipsoid the normalized driving pressure r indicates the relative magnitude of the internal magma pressure pm with respect to the tectonic stresses and it ranges from r 0 for pm 3 to r 1 for pm 1 we found that for three dikes in timna 0 25 indicating small differences between the two horizontal principal stresses and for one dike 0 9 indicating a large difference between the two horizontal principal stresses the normalized driving pressure r is about 0 08 in two horizontally propagating dikes and about 0 25 in two vertically propagating dikes style b predicts an elliptical thickness profile along the dike due to dilation of a linear crack this prediction agrees with the profile of one of the dikes the predicted thicknesses due to dilation of the interconnected array of cracks style c are in good agreement with the thickness variations of the doleritic dike and in fair agreement with two of the andesitic dikes deviations from the ideal geometry suggest separate stages of propagation and dilation in some of the dike segments

magma emplacement in a thrust ramp anticline the gavorrano granite northern apennines italy 1 magma emplacement in the upper crust is often associated with crustal extension whereby space for intrusions is made by dilation along transtensive and strike slip faults the lenticular shape of several intrusions indicates that a further mechanism for magma intrusion is laccolith emplacement with roof uplift of the overburden additionally melts exploit rheological discontinuities e g sedimentary layering during their ascent we present an emplacement model for intrusion of the shallow level gavorrano granite northern apennine italy which is located at the core of an open anticline the shape of the intrusion and structural features of the host rocks are indicative of a synkinematic emplacement in a growing thrust anticline space was provided by the opening of dilatation zones at the core of anticline as a consequence of different amounts of translation between hanging wall and footwall units which were separated by evaporitic rocks these evaporitic units acted as major decollement layers analog models provide results in good agreement with the structural setting of the anticline and emphasize the possibility that melts filled the dilatation zone with the decollement layers further facilitating intrusion