the influence of clay content salinity stress and wettability on the dielectric properties of brine saturated rocks 10 hz to 10 mhz complex impedance measurements have been performed on 14 shaly sand samples berea sandstone and ottawa sand bentonite packs in a frequency range of 10 hz to 10 mhz using both the two and four electrode techniques measurements have been conducted at an effective radial stress varying from ambient pressure to 4000 psi for brine saturated oil wet and water wet samples the dielectric permittivity is found to correlate with the clay volume fraction the cation exchange capacity and electrochemical potential of the rock samples and to depend strongly on the salinity of the brine used stress and wettability are shown to have a small influence on the dielectric constant of fully brine saturated rocks a lower critical frequency is found to characterize the geometry of the pore space empirical correlations between the dielectric constant frequency permeability cation exchange capacity and porosity are presented for the shaly sands used in this study these correlations provide a means of estimating important petrophysical parameters such as the permeability and the clay content from a nondestructive complex impedance sweep of shaly sands fully saturated with brine

a new hypothesis on parameters controlling the formation and size of porphyry copper deposits implications on thermal gradient of subducted oceanic slab depth of dehydration and partial melting along the kerman copper belt in iran abstract porphyry copper deposits in the tethyan metallogenic belt broadly occur in early mesozoic late mesozoic paleogene and neogene within a wide range of tectonic setting these deposits in iran often occur within the cenozoic urumieh dokhtar magmatic arc udma mostly in the kerman porphyry copper belt kpcb located in the southeast of this arc these deposits along the udma are mainly associated with the granitoids of miocene age 18 82 9 20 ma in this research geochemical characteristics pb and sr isotopes tectonic environment oxidizing conditions and source of magmas for the most important porphyry copper deposits of the udma have been compared and discussed on the basis of trace element discrimination diagrams the kerman belt granitoids formed in a volcanic arc type setting whereas the jebal barez granitoids seem to have formed in a different tectonic setting the eu eu of granitoids from the kerman belt are greater than 1 2 representing the oxidizing conditions for the crystallization of the granitoid magma whereas jebal barez granitoids were formed under reducing conditions the sr y ratio for kerman granitoids is greater than 60 indicating adakitic affinities and la yb n for these granitoid rocks is between 17 and 35 suggesting that their parental magma was generated from a deep garnet bearing source based on 87sr 86sr i values for kerman belt granitoids of 0 704 0 705 it is suggested that parental magmas originated from a subducted oceanic slab in the sarcheshmeh porphyry copper deposit the thermal gradient of the oceanic slab at depth was less than 9 c km warm cold slab the oceanic slab was highly hydrated and more than 80 of the water within the oceanic slab was released in the deep zone of the sub arc region at a depth of 110 130 km under saturated conditions the oceanic slab partially melted 20 25 a large volume of magma and magmatic water formed sarcheshmeh as a giant porphyry copper deposit in the iju deposit a small porphyry copper deposit the oceanic slab was slightly hydrated and minor water was released at the depth of 110 130 km a small volume of magma was formed due to water undersaturated melting conditions finally a new hypothesis is introduced regarding the roles of down dip thermal gradient of the oceanic slab water content depth of dehydration and degree of partial melting of oceanic slab which are important controls on the formation and size of the porphyry copper deposits within continental volcanic arcs

cretaceous ridge subduction along the lower yangtze river belt eastern china the lower yangtze river belt is one of the most important metallogenic belts in china the mechanisms responsible for ore genesis and the formation of related cretaceous igneous rocks such as adakite a type granitoid and nb enriched basalt remain controversial mesozoic granitoids in the lower yangtze river belt were mostly formed in the early cretaceous 140 125 ma and three granitoid belts the inner the south and the north have been defined according to petrological and geochemical characteristics previously based mainly on negative end and high initial sr isotope values the adakitic rocks were generally attributed to partial melting of thickened or delaminated lower crust both of which require crustal thickening mesozoic crustal thickening however is not supported by the development of extensional basins in the region from the late jurassic to cretaceous eastern china was closely associated with subduction of the pacific plate in the south and the izanagi plate in the north the midocean ridge mor between these two plates was drifting toward and likely subducting under the lower yangtze river belt a ridge subduction model can therefore explain the distribution of different magmatic rocks and ore deposits in the belt partial melting of subducting young hot oceanic slabs close to the ridge formed adakitic rocks the negative end values of adakitic rocks can be plausibly interpreted by mixing between adakitic magmas and enriched components in the lithospheric mantle and or crustal materials through afc process a slab window opened during ridge subduction as indicated by a type granitoids in the center of the inner belt nb enriched basalt found in the belt was likely formed by partial melting of a mantle wedge metasomatized by fluids released from the subducting slab at shallow depths

direct reservoir parameter estimation using joint inversion of marine seismic ava and csem data a new joint inversion algorithm to directly estimate reservoir parameters is described this algorithm combines seismic amplitude versus angle ava and marine controlled source electromagnetic csem data the rock properties model needed to link the geophysical parameters to the reservoir parameters is described errors in the rock properties model parameters measured in percent introduce errors of comparable size in the joint inversion reservoir parameter estimates tests of the concept on synthetic one dimensional models demonstrate improved fluid saturation and porosity estimates for joint ava csem data inversion compared to ava or csem inversion alone comparing inversions of ava csem and joint ava csem data over the north sea troll field at a location with well control shows that the joint inversion produces estimated gas saturation oil saturation and porosity that is closest as measured by the rms difference l1 norm of the difference and net over the interval to the logged values whereas csem inversion provides the closest estimates of water saturation

petrology and isotope geochemistry of san vincenzo rhyolites tuscany italy two groups of rhyolites have been recognized at san vincenzo tuscany italy group a rhyolites are characterized by plagioclase quartz biotite sanidine and cordierite mineral assemblages they show constant mgo and variable cao and na2o contents initial87sr 86sr ratios in group a samples range between 0 71950 and 0 72535 whereas the nd isotopic compositions are relatively constant 0 51215 0 51222 group b rhyolites are characterized by orthopyroxene and clinopyroxene as additional minerals and show textural mineralogical and chemical evidence of interaction with more mafic magmas the sr and nd isotopic ratios range between 0 71283 0 71542 and 0 51224 0 51227 respectively magmatic inclusions of variable size 1 mm to 10 cm were found in groups b rhyolites these inclusions consist mainly of diopsidic clinopyroxene and minor olivine and biotite they are latitic in composition and represent blobs of hybrid intermediate magmas entrained in the rhyolitic melts these magmatic inclusions have relatively high sr contents 996 1529 ppm and sr and nd isotope ratios of 0 70807 0 70830 and 0 51245 0 51252 respectively 87sr 87sr data on minerals separated from both group a and b rhyolites and magmatic inclusions reveal strong isotopic disequilibria due to the presence of both restitic and newly crystallized phases in group a rhyolites and due to interaction of rhyolites with a mantle de rived magma in group b rhyolites isotopic data on whole rocks and minerals allow us to interpret the group a rhyolites as representative of different degrees of melting of an isotopically fairly homogeneous pelitic source conversely group b rhyolites underwent interactions with a mantle derived magma the crustal source as inferred from isotopic systematics would be characterized by87sr 86sr and143nd 144nd ratios close to 0 7194 and 0 51216 respectively the sub crustal magma would have sr isotopic composition close to 0 7077 and a143nd 144nd ratio greater than or equal to 0 51252 these isotopic features are different from those reported for the parental magmas postulated for vulsini and alban hills in the nearby roman magmatic province and are similar to those of the vesuvius and ischia magmas

destruction of the north china craton induced by ridge subductions abstractthe destruction of the north china craton ncc mainly occurred in the cretaceous and has been attributed to a top down rapid delamination bottom up long term thermal chemical erosions or hydration by subduction released fluids on the basis of the distribution of one jurassic and two early cretaceous adakite belts and the drifting history of the paleo pacific plate we propose that three ridge subduction events dominated the large scale decratonization in the ncc both physical erosion and magmatism induced by ridge subduction contributed to the destruction of the ncc the last ridge subduction at ma was the key driving force in the final destruction we present mineralogical geochemical and isotopic data in support of the ridge subduction model flat subduction of a spreading ridge resulted in stronger physical erosion on the thick lithosphere mantle of the ncc consequently slab melting occurred during ridge subduction forming adakites with mantle mg isotope compositions followed b

consistent joint elastic electrical differential effective medium modelling of compacting reservoir sandstones abstract improved reservoir characterization and monitoring can be achieved by combining seismic and controlled source electromagnetic techniques this requires developing coherent rock physics descriptions in this paper we demonstrate consistent joint elastic electrical modelling according to the differential effective medium theory we test our modelling against data from a compaction experiment on a set of 11 sandstone core samples from the same quarry location the presented approach is analogous to calibrating a rock physics model to a particular reservoir based on data from possible well logs and core samples for simplicity we choose to use multivariable non linear regression in the inversion it shows that this technique is able to identify solutions that are physically sound however a more rigorous inversion method might be considered in future implementations to identify the critical parameters we test the elastic electrical sensitivity of the various unknown variables involved the most sensitive parameters identified are then perturbed during the modelling the mineralogy consists mainly of quartz which we assume to be spherical and kaolinite we use the resistivity to calibrate the aspect ratio of the clay grains and estimate the porosity reduction due to compaction these values are in turn used in inverse modelling of the bulk and shear moduli the solid minerals make up the inclusion material in the differential effective medium modelling for both the elastic and electrical properties hence this formulation constitutes a consistent joint elastic electrical modelling scheme we achieve good fits between the model results and the laboratory measurements for most of the samples the reason for the less good fit with some of the samples might be due to measurement errors in the laboratory this is supported by the observed abnormal stiffness compaction trends associated with those samples

lunar megaregolith mixing by impacts spatial diffusion of basin melt and its implications for sample interpretation abstract the formation ages of lunar impact basins are critical to understanding the late accretion history of the inner solar system furthermore the correct interpretation of the provenance and isotopic dates of basin derived impact melt basin melt is essential for the calibration of lunar chronology function however abundances of basin melt in the lunar near surface are not well understood basin melt has been gardened by a long sequence of subsequent impact events altering its abundance and size distribution we developed a numerical model to investigate this process by means of the monte carlo method in a spatially resolved model the fraction of melt in ejecta was tracked globally and at the apollo 14 17 and luna 20 sampling sites and was compared with k ar age distributions of lunar impact melt breccias it was found that melt produced by the very large spa basin as well as the relatively late forming imbrium basin should be dominant in the near surface top one meter the simulation shows that the melt component at the apollo 14 17 and luna 20 sites is strongly affected by nearby mid to late forming basins imbrium melt should be abundant in apollo 14 17 samples crisium melt is the most significant component of basin sourced melt in luna 20 samples all the apollo 14 17 and luna 20 samples could include melt from serenitatis and the spa basin nectaris melt should occur in apollo 16 apollo 17 and luna 20 samples and orientale melt has no significant mixing in the apollo 14 17 and luna 20 sampling sites in general besides a prominent age peak at 3 9 ga related to the imbrium basin the model predicts pronounced abundance peaks of older basin melt 3 9 ga which tend to be absent from distributions of k ar ages of impactites from landing sites the diffusion characteristics of basin melt suggest that for future sampling aimed at collecting early basin melt the re excavation zones of late impact craters larger than tens of kilometer in diameter inside basins may provide the highest abundances of melt from early basins

feasibility of chemical u th total pb baddeleyite dating by electron microprobe abstract we evaluate the potential for applying the electron microprobe em chemical dating technique to the mineral baddeleyite zro 2 an accessory phase commonly used to determine crystallization ages of mafic rocks in conventional isotopic u pb studies baddeleyite is well suited for em chemical dating because it has relatively high concentrations of u negligible common pb and is highly resistant to pb loss em chemical and isotope dilution u pb ages are presented for five baddeleyite reference samples including the 780 ma faber lake gabbro sheet great bear magmatic zone canada the 1109 ma moore lakes gabbro churchill province canada the 1269 ma muskox intrusion slave craton canada the 2060 ma phalaborwa carbonatite s africa and the 2410 ma binneringie gabbro dyke yilgarn craton australia overall the em chemical ages show good correlation with the conventional u pb ages three of the reference samples yielded em ages within 30 60 ma of the conventional ages well within analytical uncertainty for reasons that are not known two of the samples yielded em chemical ages that are systematically old by 140 ma we conclude from these data that the em chemical dating technique provides reasonable first order age information for typical precambrian baddeleyite the systematic variation of u and pb at the micron scale in baddeleyite coupled with the excellent spatial resolution of the em 1 m allows for determination of chemical u th total pb isochrons from individual baddeleyite crystals in polished thin section em chemical dating offers a non destructive time efficient a matter of hours for each sample and cost effective way to obtain contextural age information from baddeleyite in mafic rocks with a grain size too small for isolation and conventional u pb dating

age of carbonatite and phoscorite magmatism of the phalaborwa complex south africa abstract the phalaborwa complex south africa has been dated by u pb analysis of uranothorianite and baddeleyite yielding an age of 2047 11 8 ma for caronatite and phoscorite magmatism baddeleyite yields an age comparable to the age determined on uranothorianite and provides a reliable age indicator ages of carbonatite and silicate magmatism cannot be resolved as different events confirmation of k rich alkaline magmas produced in the mantle as early as 2047 ma suggests that significant chemical heterogeneities existed prior to 2000 ma

nature of surface electrical conductivity in natural sands sandstones and clays the electrical conductivity of rocks results from conduction through the bulk solution occupying the pores and from surface conduction occurring at the fluid grain interface the nature of the surface electrical conductivity of shaly and clean sands and sandstones is examined surface conduction is characterized by the specific surface conductance which is the sum of three contributions i conduction within the electrical diffuse layer which makes a negligible contribution to the total specific surface conductance ii conduction in the stern layer which is shown to vary significantly with the salinity of the pore fluid at low salinities 10 6 to 10 3 mol 1 1 but becomes independent of salinity at higher salinities iii a mechanism operating directly on the mineral surface independent of salinity and perhaps associated with proton transfer at salinities higher than 10 3 mol 1 1 and at 25 c the specific surface conductance of quartz and clays is equal to 8 9 10 9 s and 2 5 10 9 s respectively equations describing the influence of surface conductivity and microstructure upon the macroscopic electrical conductivity of sands sandstones and shales are also developed

cross property rock physics relations for estimating low frequency seismic impedance trends from electromagnetic resistivity data estimating the low frequency seismic impedance trend is critical for reservoir characterization based on seismic inversions conventional seismic reflection data have an information gap between 2 and 10 hz and do not contain information about the background impedance trend on the other hand controlled source electromagnetic csem data are typically low resolution and contain information about the earth s resistivity structure thus cross property rock physics relations between elastic and electrical properties can extract information from the csem data to provide constraints on the low frequency seismic impedance trend this concept is tested with well log data and applied to a resistivity section inverted from csem data results show that appropriate cross property rock physics relations can capture the background low frequency impedance trend and provide useful constraints on models for inversion

resistivity velocity transforms revisited velocity and density measured in a well are crucial for synthetic seismic generation which is in turn a key to interpreting real seismic amplitude in terms of lithology porosity and fluid because velocity and density curves are sometimes of poor quality or simply absent in older wells it is important to be able to reconstruct these curves from reliable measurements such as resistivity and gamma ray gr a recent example of this approach is by xu et al 2003 where mechanical compaction curves and velocity porosity relations are used to reconstruct a full suite of the needed log data the earliest attempt to reconstruct a sonic curve from resistivity is by faust 1953 where both the velocity and resistivity are empirically related to depth and lithology from these two relations an equation follows that links the sonic velocity to the depth and formation factor where the formation factor is defined as usual as the ratio of the resistivity of water saturated rock to the resistivity of water

buffering of melt oxygen fugacity by sulphur redox reactions in calc alkaline magmas calculated oxygen fugacities of magmas from lascar volcano northern chile and the 1991 eruption of mount pinatubo phillipines are seen to increase with decreasing temperature relative to the fayalite magnetite quartz buffer isopleths of constant h2s so2 at moderate pressures 2 4 kbar lie parallel to the data we conclude that magma mixing prior to eruption liberated large quantities of so2 gas by oxidation of dissolved sulphide in the mafic end member oxygen fugacity of the magmas was then buffered by reduction of this gas to h2s leading to increasingly oxidized magmas such a process might be used to explain the highly oxidized nature of other sulphur rich evolved calc alkaline magmas notably the el chichon trachyandesite

measurements of elastic and electrical properties of an unconventional organic shale under differential loading abstractwe have developed an experimental approach to simultaneously measure the stress dependence of ultrasonic wave velocities at 1 mhz and therefore the components of the undrained elastic stiffness tensor as well as the components of the complex conductivity tensor in the frequency range from 100 mhz to 10 hz we performed the experiments on a cylindrical core sample from the haynesville formation porosity of approximately 0 08 bound water excluded and clay content mostly illite approximately 30 40 wt we performed experiments under controlled confining and pore fluid pressures achieving differential pressure states representative of autochthonous reservoir conditions directional measurements were made using independent acquisition arrays piezoelectric crystals and nonpolarizing electrodes distributed azimuthally on the core sample external surface the bedding plane being along the axis of the cylindrical core sample ultrasonic waveforms were recorded on a high resolution oscilloscope

a model for low pressure facies metamorphism during crustal thickening low pressure metamorphic facies i e high t p ratios are widespread in a wide range of tectonic settings explanations offered for the occurrence of these facies include extensional and or magmatic models however these fail to explain that the low p facies metamorphism is commonly coeval with a phase of pervasive crustal thickening with t p ratios increasing during or slightly lagging behind the thickening we propose an alternative explanation based on the approximate synchroneity of crustal thickening and erosion thinning of the mantle lithosphere

fluid geochemical transect in the northern apennines central northern italy fluid genesis and migration and tectonic implications chemical and isotopic characteristics of natural gas and thermal water discharges from the western back arc tyrrhenian sea across the apennine thrust belt to the po valley and adriatic coast foredeep basins in the northern apennines central northern italy reveal a large scale fluid motion in the upper crust both vertically and horizontally on the basis of gas compositions two different domains of rising fluids have been distinguished 1 co2 rich he poor 3he 4he high domain in the western peri tyrrhenian extensional sector 2 ch4 rich he rich 3he 4he low domain in the eastern adriatic compressional sector such gases rising from various depths are crossed by a huge lateral n2 rich water flow in the peri tyrrhenian sector of ca so4 hco3 meteoric derived waters that move in a regional wide aquifer hosted in a quite thick mesozoic carbonate series morphologically the co2 vents consist of mud basins with high gas rate emission where the rising fluids move upwards through diatremes on the other hand ch4 emissions seep out from typical mud volcanoes with a reduced gas flow rate where the fluid motion is likely related to saline diapir extrusions and the methane is mostly carried to the surface by the associated mud the two rising mechanisms described locate southwest and northeast of the apennine watershed respectively from a seismic point of view the ch4 domain in the thrust belt and foredeep areas is characterized by a large number of earthquakes indirectly pointing to a different rheological behavior of the terrains with respect to the more internal peri tyrrhenian area owing to the quite high thermal gradient of the latter the boundary of the brittle ductile crust in the peri tyrrhenian sector can be located at a 10 km shallow depth although the presence of several post orogenic basins would suggest widespread extensional tectonics in all areas west of the apennine watershed those located in the easternmost part display gas vents with typical crustal 3he 4he ratios as this ratio is very sensitive to deep fluids rising from the mantle we hypothesize that such basins at the foot of the apennines are not due to tensive stress as suggested by their morphological shape they are piggy back thrust top basins developed and evolved in a still acting compressive tectonic regime

radiogenic isotopes in fluid inclusions radiogenic isotopes studied in fluid inclusions are still a limited field with great potential for expansion as analytical techniques improve the main limitation for sr ar and he isotope work is the very small number of radiogenic atoms produced in a typical fluid inclusion the requirements to analysts are correspondingly high examples show that isotopic tracing on fluid inclusion fluids can be a decisive tool in solving geological problems

a metrological approach to measuring 40ar concentrations in k ar and 40ar 39ar mineral standards in geochronology isotopic ages are determined from the ratio of parent and daughter nuclide concentrations in minerals for dating of geological material using the k ar system the simultaneous determination of 40ar and 40k concentrations on the same aliquot is not possible therefore a widely used variant the 40ar 39ar technique involves the production of 39ar from 39k by neutron bombardment and the reliance on indirect natural calibrators of the neutron flux referred to as mineral standards many mineral standards still in use rely on decades old determinations of 40ar concentrations resulting uncertainties both systematic and analytical impede the determination of higher accuracy ages using the k ar decay system we discuss the theoretical approach and technical design of a gas delivery system which emits metrologically traceable amounts of 40ar and will allow for the sensitivity calibration of noble gas mass spectrometers the design of this system is based on a rigorous assessment of the uncertainty budget and detailed tests of a prototype system a number of obstacles and proposed resolutions are discussed along with the selection of components and their integration into a pipette system

the effect of clay distribution on the elastic properties of sandstones the shape and location of clay within sandstones have a large impact on the p wave and s wave velocities of the rock they also have a large effect on reservoir properties and the interpretation of those properties from seismic data and well logs numerical models of different distributions of clay structural laminar and dispersed clay can lead to an understanding of these effects clay which is located between quartz grains structural clay will reduce the p wave and s wave velocities of the rock if the clay particles become aligned or form layers the velocities perpendicular to the alignment will be reduced further s wave velocities decrease more rapidly than p wave velocities with increasing clay content and therefore poisson s ratios will increase as the velocities decrease these effects are more pronounced for compacted sandstones small amounts of clay that are located in the pore space will have little effect on the p wave velocity due to the competing influence of the density effect and pore fluid stiffening the s wave velocity will decrease due to the density effect and thus the poisson s ratio will increase when there is sufficient clay to bridge the gaps between the quartz grains p wave and s wave velocities rise rapidly and the poisson s ratios decrease these effects are more pronounced for under compacted sandstones these general results are only slightly modified when the intrinsic anisotropy of the clay material is taken into account numerical models indicate that there is a strong nearly linear relationship between p wave and s wave velocity which is almost independent of clay distribution s wave velocities can be predicted reasonably accurately from p wave velocities based on empirical relationships however this does not provide any connection between the elastic and petrophysical properties of the rocks numerical modelling offers this connection but requires the inclusion of clay distribution and anisotropy to provide a model that is consistent with both the elastic and petrophysical properties if clay distribution is ignored predicting porosities from p wave or s wave data for example can result in large errors estimation of the clay distribution from p wave and s wave velocities requires good estimates of the porosity and clay volume and verification from petrographic analyses of core or cuttings for a real data example numerical models of the elastic properties suggest the predominance of dispersed clay in a fluvial sand from matching p wave and s wave velocity well log data using log based estimates of the clay volume and porosity this is consistent with an interpretation of other log data

genesis of the yandong porphyry cu deposit in eastern tianshan nw china evidence from geology fluid inclusions and isotope systematics abstract the yandong porphyry cu deposit 372 mt at 0 58 cu is located in the center of the eastern tianshan xinjiang nw china multiple stage hydrothermal activities have resulted in potassic chlorite sericite phyllic and propylitic alteration in this deposit the yandong deposit formed in four stages i e an early quartz magnetite pyrite stage i a quartz pyrite chalcopyrite stage ii a quartz chalcopyrite pyrite molybdenite stage iii and a late quartz carbonate stage iv three evolutionary episodes were observed by a detailed fluid inclusion study 1 early ore stage i fluids were trapped under two phase conditions as evidenced by the coexistence of vapor rich v type inclusions homogenization temperatures 410 494 c average salinity 2 2 wt nacl equiv liquid rich l type inclusions homogenization temperatures 311 430 c average salinity 9 5 wt nacl equiv and hypersaline h type inclusions trapped at 300 bars or a depth of approximately 1 km assuming lithostatic pressure conditions 2 main ore stage ii and iii fluid inclusions in quartz were also trapped under two phase conditions boiling as identified by the coexistence of v and l type fluid inclusions l type inclusions homogenized between 161 and 390 c average 270 c with salinities of 1 6 9 9 wt nacl equiv average 4 9 wt nacl equiv and a depth of 1 km 100 bars hydrostatic pressure conditions 3 late ore stage iv fluids are represented by inclusions in barren quartz carbonate veinlets characterized by homogenization temperatures ranging from 123 to 261 c average 179 c and salinities between 0 7 and 4 7 wt nacl equiv average 2 0 wt nacl equiv the initial hydrothermal fluids are characterized by high temperature high salinity and high oxygen fugacity belonging to a h 2 o nacl system hydrogen and oxygen isotope data indicate that the hydrothermal fluids have a dominantly magmatic signature and mixed with abundant meteoric waters in the quartz carbonate stage sulfur stable isotope suggests that the ore forming metals came primarily from the tonalite magma that sourced from the subducted oceanic slab involving some mantle peridotites during ascent the cu mineralization of the yandong porphyry deposit occurred at a shallow crustal level approximately 1 km and the fluid boiling or phase separation decrease of temperature as well as fluid rock interaction were likely important factors responsible for metal accumulation and deposition in the magmatic hydrothermal system

a comparison of laboratory and field measurements of p wave anisotropy1 p wave velocity anisotropy determined from a cross hole survey at the imperial college borehole test site compares favorably with that measured in the laboratory on core from the holes the holes penetrate a layered sequence of sandstones shales and carbonates of the namurian upper limestone group the laboratory measurements of the vertical and horizontal velocities of core samples indicate that the shales exhibit p wave anisotropies of over 20 but that the sandstones and limestones are only slightly anisotropic these discrete measurements have been used in combination with wireline data to produce a log of p wave anisotropy including the anisotropic information vastly improves the match between observed and synthetic traveltimes from the cross hole data set this implies that there is little frequency dependence of intrinsic p wave anisotropy inversion of the cross hole traveltimes highlights the need for good angular coverage in order to resolve the anisotropy parameters the observed p wave anisotropy of the field data is due to the combined effect of sedimentary layering and the intrinsic anisotropy of the rocks the intrinsic anisotropy is found to be the dominant factor

evaluation of porosity and saturation degree by laboratory joint measurements of velocity and resistivity a model improvement this paper illustrates the laboratory procedures and experiments carried out on samples with different lithologies and reconstructed samples in order to test and implement an electroseismic model carrara et al 1994 which allows the evaluation of porosity and the saturation degree of rocks the testing was conducted by comparing porosity and saturation degree s w values obtained from measured resistivity and elastic wave velocity v p by means of appropriate formulations with the values of and s w previously calculated by geotechnics and employed as standards the experimental results have led to a good definition of the model to be proposed as an application method in the field of hydrogeology

geoelectrical and seismic prospections in hydrogeology model and master curves for the evaluation of porosity and water saturation the prevailing purpose of geoelectrical exploration is the location of acquifers as resistivity is strongly sensitive to the presence of water through this method valuable information on the structure and volume of storage rocks may be acquired however the evaluation of saturation and porosity which plays a strong role in the estimation of hydraulic parameters is hitherto affected by a large uncertainty therefore it is necessary to carry out expensive and often numerous drillings in addition to the calibration ones in this paper we argue how the uncertainty can be substantially reduced by carrying out a joint seismic and geoelectrical prospection

excess argon in k ar and ar ar geochronology the k ar and ar ar dating techniques occasionally produce anomalously old ages attributed to excess argon and such data is often rejected as not offering any insight into the age thermal history or geochemistry of the rock however improvements in the quantification of argon geochemistry now provide a framework to model excess argon in both open and closed systems solubility data for argon in hydrous fluids melts and emerging data for minerals can be used to understand the behaviour of excess argon and provide valuable insights into the environment in which the samples cooled to their argon retention or closure temperature treating excess argon as a trace element also throws light on its behaviour in minerals above the closure temperature in deeply buried dry systems such as eclogites blueschists granulites and even in the lithospheric mantle extremely low partition coefficients between k feldspar and hydrous fluid phases predict lower excess argon susceptibility than micas and this is observed in fluid poor systems variation of partition coefficients can lead to excess argon in fluids being introduced into minerals or removed from minerals as grain boundary fluids change during flow through a rock however excess argon can also be introduced or removed from minerals by varying temperature without the need for fluid flow high mineral melt and mineral fluid partition coefficients are also the reason why excess argon is often concentrated in inclusions within minerals partition coefficients between minerals and hydrous fluids as low as 10 6 lead fluid inclusions to dominate the radiogenic argon budget particularly in low potassium minerals melt inclusions are less dominant but become critical in dating younger samples

the relationships between the velocities attenuations and petrophysical properties of reservoir sedimentary rocks1 the authors have measured the velocities and attenuations of compressional and shear waves in 29 water saturated samples of sandstones and shales at a confining pressure of 60 mpa and at frequencies of about 0 85 mhz the measurements were made using a pulse echo method in which the samples diameter 5 cm length 1 5 cm to 2 5 cm were placed between perspex buffer rods inside a high pressure cell the velocity of each seismic wave was determined from the travel time difference of equivalent phase points corrected for diffraction effects of the signals reflected from the top and from the base of each samples attenuation was determined in a similar way by comparison of the diffraction corrected amplitudes of the signals the attenuation data are presented as quality factors q sub p and q sub s for compressional and shear waves respectively and shear waves respectively the results show that qs is strongly correlated with v sub s that q sub p is weakly correlated with v sub p and that q sub p is strongly correlated with q sub s center dot q sub p is strongly dependent on the volume percentage of the assemblage of intra pore minerals whether they are clays or carbonates it is concluded that themore attenuation mechanism is due to the local fluid flow arising from the differential dilation of the solid rock frame and the intra pore mineral assemblage which is a results of their very different elastic moduli less

early fluid migration in a deep part of the larderello geothermal field a fluid inclusion study of the granite sill from well monteverdi 7 abstract metamorphic magmatic to hydrothermal fluids trapped in fluid inclusion planes fip were studied in a microfractured granite sill from a deep level 3483 3486 m b g l of the well monteverdi 7 larderello geothermal field this granite has recorded a complex succession of fluid migration through a dense set of healed microcracks nine generations of fluids trapped within specific microcrack networks are distinguished and include vapors and liquids of the c h o n s system aqueous liquids and brines with distinctive sets of cation chlorides licl nacl nacl cacl 2 and nacl detailed studies of the geometrical and chronological relationships between the fluid inclusion planes allow the establishment of a clear relative chronology with the c h o n s and licl fluids being earlier than the nacl cacl 2 and nacl aqueous liquids and brines in particular it can be shown that the c h o n s and licl fluids are strongly associated in space and time since the corresponding fluid inclusion planes display evidence of mutual contamination of inclusions within the planes significant changes in the physical chemical parameters occurred in the conditions of fluid trapping during the evolution of the larderello field all observed paleofluids have compositions differing from that encountered in the present day fluids and record a complex p t t x evolution from an early stage dominated by magmatic and metamorphic derived fluids towards a later stage dominated by more surficial waters at the early stage hydrothermal circulation occurred under lithostatic pressure at a depth of ca 4 5 km at temperatures as high as 450 500 c such conditions are very reminiscent of contact metamorphism and were probably created by the deep intrusive body detected by geophysical studies batini et al 1983 1985 the involved fluids are c h o n s vapors and liquids of metamorphic derivation and aqueous li bearing brines of probable magmatic derivation they are consistent with the hypothesis of the intrusive being a granite at the later stage physical conditions had evolved towards hydrostatic pressure at a depth close to the present 3 5 km one and temperatures of 400 350 c still higher than the present day ones early fluids were no longer present the observed fluids record the involvement of more surficial waters both meteoric and connate transient boiling events were probably occurring heralding the present day conditions vapor dominated geothermal system nevertheless no trapped fluids display similar composition and density with the present day geothermal fluids at larderello in old geothermal fields such as larderello it must be emphasized that the use of fluid inclusions in order to reconstruct past hydrothermal evolution is strongly dependent onto pressure estimation since significant temperature corrections may be needed in the larderello case failing to take in account the pressure effects would have led to seriously misleading conclusions

cross property relations between electrical conductivity and the seismic velocity of rocks cross property relations are useful when some rock properties can be measured more easily than other properties relations between electrical conductivity and seismic velocity stiffness moduli and density can be obtained by expressing the porosity in terms of those properties there are many possible ways to combine the constitutive equations to obtain a relation each one representing a given type of rock the relations depend on the assumptions to obtain the constitutive equations in the electromagnetic case the equations involve archie s law and its modifications for a conducting frame the hashin shtrikman hs bounds and the self similar and complex refraction index method crim models in the elastic case the stress strain relations are mainly based on the time average equation the hs bounds and the gassmann equation also expressions for dry rocks and for anisotropic media using backus averaging are analyzed the relations are applied to a shale saturated with brineoverburden and to a sandstone saturated with oilreservoir tests with sections of a north sea well log show that the best fit is given by the relation between the gassmann velocity and the crim selfsimilar and archie models for the conductivity

simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell a feasibility study adaptations of existing triaxial cells for ultrasonic p and s wave measurements are well documented this paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions by employing the top cap and the pedestal of the cell as electrodes axial resistivity measurements are now feasible in order to minimize the polarization effect of this two electrode arrangement careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band radial resistivity measurements are also included in the system by introducing a strap electrode system in a reservoir under production changes in both saturations temperature if steam injection and stresses can take place therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters the feasibility of the system to obtain such reliable information is demonstrated employing a small selection of core samples in the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion

precise pb baddeleyite geochronology by the thermal extraction thermal ionization mass spectrometry method abstract the ability to easily obtain precise 0 1 age determinations on mafic rocks can facilitate identification of contemporaneous magmatic events across continents and hence open new avenues of research investigations related to large scale mantle processes we present high precision pb age determinations on baddeleyite zro 2 a common accessory mineral in mafic rocks using the recently developed thermal extraction thermal ionization mass spectrometer te tims procedure for dating of zircon in order to constrain the conditions for thermal extraction of pb from baddeleyite a sequence of sem back scattered electron images were acquired along with energy dispersive x ray spectroscopy spot analysis of baddeleyite grains embedded in silica beads at progressively increasing temperature between 1200 and 1590 c replicate analyses of twelve preheated at 1250 c and silica embedded baddeleyite grains from the paleoproterozoic phalaborwa carbonatite using this procedure have yielded a 207 pb 206 pb weighted mean age of 2060 3 0 4 ma consistent with previously reported 207 pb 206 pb ages for this carbonatite occurrence determined by the conventional u pb isotope dilution thermal ionization mass spectrometry id tims technique fourteen baddeleyite fractions from a large paleoproterozoic n s striking mafic dyke swarm in the dharwar craton yielded a 207 pb 206 pb weighted mean age of 2215 9 0 3 ma also consistent with previously determined conventional ages all data were corrected for mass fractionation of 0 18 amu as determined previously on zircon both data sets scatter outside measurement errors implying an external 2 sigma error of 0 055 in the case of the carbonatite and 0 043 for the mafic dyke which we suggest represents the reproducibility of the fractionation correction our results demonstrate that thermal extraction 207 pb 206 pb ages are comparable with the conventional u pb ages in both accuracy and precision this procedure does not need ultra clean laboratory conditions

geochronology and isotope transport systematics in a subsurface granite from the larderello travale geothermal system italy abstract a monzogranite here referred to as the montieri pluton was encountered along two depth profiles from ca 2 to 4 km depth in wells of the larderello travale geothermal system italy we obtained high resolution petrographic and microchemical data on seven fresh samples of the montieri pluton these data are required to correctly interpret the combined isotope data for the rb sr and k ar systems biotite and k feldspar from all samples were analyzed by rb sr and 39ar 40ar rb sr analyses gave extremely variable two point rb sr apparent ages and sr initials indicating that biotite did not equilibrate with feldspar bulk dissolution of k feldspars does not define a rb sr alignment that could have proved a common origin of all k feldspar samples from a single magma batch the leachable fractions of k feldspar separates have much more homogeneous 87sr 86sr ratios around 0 712 which may reflect the isotopic composition of a late stage circulating fluid because of the anatectic origin of the granites from the larderello travale geothermal system it is likely that every k feldspar separate contains at least three isotopically distinct feldspar generations relics of the hercynian gneiss basement pliocene magmatic minerals and hydrothermal retrogression products such heterogeneity can be confirmed and quantified by petrographical observations and electron microprobe analyses the 39ar 40ar age spectra of the biotite samples show some internal discordance because of deviations from stoichiometry biotite discordance can be attributed both to chlorite intergrowths as predicted from the active fluid circulation and to the presence of multiple biotite generations such as have already been documented from other micas from the larderello travale geothermal system and as indeed confirmed by high resolution petrography total k ar biotite ages on cluster around 3 ma and broadly agree with a rb sr age obtained by regressing only the biotite analyses this suggests that the montieri pluton whose known volume is at least 25 km3 was emplaced at that time the k feldspar spectra are strongly discordant no step age approaches the zero age which would be predicted by ar diffusivity modelling the extraneous ar in the feldspars is not excess ar but inherited ar instead ar inheritance in the feldspar separates correlates with inheritance of sr arrhenius trajectories of the apparent ar diffusivities for all seven feldspars are astonishingly identical despite the heterochemism amongst samples however the apparent diffusivity calculated from the step heating experiments led to irreproducible models for the thermal history along the depth profile as well as time scales shorter than the historical record this indicates that ar diffusivities calculated from laboratory experiments must not be extrapolated to geological conditions

kca chronology of lunar granites abstract k ca age determinations were undertaken for three lunar granitic samples 14321 1062 14303 206 and 12013 141 k ca isotopic analyses of bulk samples of seven pristine lunar igneous rocks including four mare basalts 10017 15555 14321 1394 and 14305 304 371 one norite 15445 17 one anorthosite 60025 one kreep basalt 72275 543 and seven meteorites juvinas pasamonte moore county stannern y75011 84b zagami and shergotty were also performed the k ca mineral isochron for lunar granitic clast 14321 1062 yields an age of 4 06 0 07 ga for 40k 0 5543 ga 1 and an initial 40 ca 44 ca of 47 141 0 010 normalized to 42 ca 44 ca 0 31221 the k ca age is in excellent agreement with the rb sr and sm nd ages and is slightly older than the average 39ar 40ar and u pb zircon ages low precision k ca ages of 4 04 0 64 ga and 3 76 0 72 ga were obtained for lunar granites 14303 206 and 12013 141 respectively due to their lower k ca ratios initial 40 ca 44 ca values for seven lunar and seven meteoritic bulk samples are similar and yield an average initial 40 ca 44 ca of 47 136 0 002 2 m and 0 006 2 p assuming this value as the lunar initial 40 ca 44 ca a ten to twenty fold fractionation for k ca during the formation of granite 14321 is calculated for a two stage model the large k ca enrichment is consistent with a granite genesis model involving a silicate liquid immiscibility process literature data for lunar granites studied so far exhibit a wide range of ages from 3 9 to 4 4 ga thus lunar granites probably represent samples from about eight different intrusive bodies the positive k and k ca correlations of lunar rocks strongly supports an early global lunar differentiation however most granites were probably not directly produced from this early differentiation event

fluid evolution of the tongkuangyu porphyry copper deposit in the zhongtiaoshan region evidence from fluid inclusions abstract the tongkuangyu porphyry copper deposit is located in the zhongtiaoshan region southern margin of the north china craton more than 2 8 million tons of cu average cu grade 0 68 is hosted in the paleoproterozoic quartz monzonite porphyry 2122 10 ma the ore forming processes of the tongkuangyu porphyry cu deposit are divided into three mineralization stages namely the early main and late mineralization stages the majority of cu ores were formed in the main stage which is characterized by veinlets and disseminated chalcopyrite and minor molybdenite pyrite magnetite and hematite quartz is the major gangue mineral which occurs as veinlets and associates with metallic minerals through systematic petrographic observation the ore bearing quartz veins a type quartz and the quartz hosted in chalcopyrite b type quartz were studied in detail to investigate the fluid evolution of the tongkuangyu porphyry cu deposit four types of fluid inclusions were recognized in the a type quartz which include 1 pure vapor or vapor rich v type inclusions 2 co 2 h 2 o c type inclusions 3 liquid rich l type inclusions and 4 daughter mineral bearing s type inclusions s type inclusions in the main stage a type quartz contain mainly halite and minor sylvite calcite hematite chalcopyrite and anhydrite with homogenization temperatures of 233 450 c v type inclusions coexisting with the s type inclusions homogenize to vapor phase at 282 375 c suggesting that the ore forming fluids may have experienced boiling in the main mineralization stage the late stage s type inclusions have homogenization temperatures of 186 245 c and contain largely halite with minor sylvite fluid inclusions in the b type quartz intergrown with chalcopyrite are closely associated with the ore forming processes the main stage b type quartz contains predominantly s type inclusions with homogenization temperatures of 250 412 c and minor v type inclusions on the other hand the late stage b type quartz contains abundant s type inclusions with homogenization temperatures of 195 230 c and less l type inclusions our results show that the s type inclusions in both the a and b type quartz of the same ore stage have very similar homogenization temperatures therefore fluid boiling may have promoted the cu enrichment in the high salinity fluids and the brine phase is the main metal transport medium in the tongkuangyu porphyry cu deposit the common occurrence of hematite and anhydrite daughter minerals in the s type inclusions further suggests that ferrous ion oxidization may have caused sulfate reduction this process may have played an important role during the cu precipitation event the progressive cooling of fluids and the incorporation of meteoric water in the late mineralization stage possibly resulted in the small scale vein type mineralization

the squirt flow mechanism macroscopic description we introduce a poroelasticity model that incorporates the two most important mechanisms of solid fluid interaction in rocks the biot mechanism and the squirt flow mechanism this combined biot squirt bisq model relates compressional velocity and attenuation to the elastic constants of the drained skeleton and of the solid phase porosity permeability saturation fluid viscosity and compressibility and the characteristic squirt flow length squirt flow length is a fundamental rock property that does not depend on frequency fluid viscosity or compressibility and is determined experimentally we find that the viscoelastic response of many sandstones is dominated by the squirt flow component of the bisq mechanism and that the viscoelastic properties of these rocks can be expressed through a single dimensionless parameter omega r 2 kappa where omega is angular frequency r is the characteristic squirt flow length and kappa is hydraulic diffusivity the biot mechanism alone does not give an adequate explanation of the observed velocity dispersion and attenuation and the viscoelastic behavior of many sandstones

structure and late cenozoic evolution of the upper lithosphere in southwest tuscany italy abstract geological and geophysical data on southwest tuscany are reviewed in order to define the structure and evolution of the upper lithosphere from the miocene to the quaternary petrologic studies reveal the existence below all of tuscany of hercynian and older polyphased metamorphic rocks and of hercynian granite whose top is an important seismic reflecting horizon the basement is characterized by ne sw trending structures in contrast with the main nw se alpine structures of the uppermost levels the heat flow map shows two broad areas with values higher than 80 mw m2 reaching maximum values of 10 5 and 15 h f u in the geothermal areas which are also characterized by negative bouguer anomalies a landsat study revealed a ne sw band of subcircular structures passing through larderello and coinciding with a regional fault system and a steep rise in the moho petrologic geochemical and radiometric data on the tuscan igneous rocks show that partial melting took place in the tuscan crust at different levels and to varying degrees from the miocene to quaternary producing a continuous alpine granitic layer the known tuscan intrusive bodies and two batholiths below the larderello and mt amiata geothermal fields represent culminations of the alpine granite the rise of the tuscan magmas was closely correlated to a post tortonian tensional tectonics and followed its n e migration tensional tectonics started after the last compressional phase 10 11 ma b p as a consequence of the anticlockwise rotation of italy the opening of the tyrrhenian sea and the swelling of the mantle below southwest tuscany

geochronology and excess ar geochemistry of the lhotse nup leucogranite nepal himalaya abstract 40ar 39ar dating experiments on several coexisting minerals from two close by leucogranite outcrops near lhotse nup glacier nepal himalaya reveal a complex behaviour four biotite and muscovite ages cluster around 15 5 ma a lower value than literature rb sr ages on splits of the same four micas suggesting a discrepancy with the ideal cooling age sequence observed in the alps a strongly discordant ar ar spectrum on tourmaline does not allow a chronological interpretation a potassium feldspar shows a slow cooling staircase spectrum with a superimposed saddle diagnostic of excess ar hf leaching removed excess ar but caused great perturbations to the minimum step ages isochron plots and the release of reactor produced ar isotopes the present data require that the currently fashionable interpretations of feldspar systematics be radically changed the main chronological conclusions rely on the eight mica ages their decrease from 18 2 to 15 3 ma dates the cooling of the lhotse nup leucogranite

geological mapping and chronology of lunar landing sites apollo 11 abstract crater size frequency distribution csfds measurements allow the derivation of absolute model ages amas for geological units across various terrestrial bodies in the solar system based on body specific adjustments to the lunar chronology e g hartmann 1970 neukum et al 1975 1983 2001 stoffler and ryder 2001 stoffler et al 2006 hiesinger et al 2012 robbins 2014 thus it is important to revisit and test the accuracy of the lunar chronology using data from recent lunar missions e g hiesinger et al 2000 2012 2015 rajmon and spudis 2004 stoffler et al 2006 as well as newer analyses of lunar samples e g gaffney et al 2011 meyer 2012 snape et al 2016 welsh et al 2018 we generated a new detailed geological map of the apollo 11 landing region based on spectral characteristics topography and albedo maps which shows several mare units adjacent to the lunar module lunar reconnaissance orbiter camera lroc images were used to measure new csfds and derive the cumulative number of craters with diameters 1 km or n 1 for the apollo 11 landing site the newly derived n 1 values are consistent with the presence of only one surficial unit at the landing site the group a high k high potassium young mare basalt as described in meyer 2012 we reviewed the radiometric ages for apollo 11 samples that have been determined since the calibration of the lunar cratering chronology used our new geological map to reinterpret their provenance and correlated them with the new n 1 values these are plotted and compared with the lunar chronology of neukum et al 1983 our calibration point for the apollo 11 landing site is consistent with the earlier values thus confirming neukum s 1983 and neukum and ivanov s 2001 lunar chronology curves

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

dating fault generated pseudotachylytes comparison of 40ar 39ar stepwise heating laser ablation and rb sr microsampling analyses three different geochronological techniques stepwise heating laser ablation 40ar 39ar rb sr microsampling have been evaluated for dating fault generated pseudotachylytes sampled along the periadriatic fault system paf of the alps because pseudotachylytes are whole rock systems composed of melt clast and alteration phases chemical control from both ar isotopes cl k ca k ratios and empa analyses is crucial for their discrimination when applied to stepwise heating 40ar 39ar analyses this approach yields accurate melt related ages even for complex age spectra the spatial resolution of laser ablation 40ar 39ar analyses is capable of contrasting melt clast and alteration phases in situ provided the clasts are not too fine grained the latter of which results in integrated mixed ages without geological information elevated cl k and ca k ratios were found to be an invaluable indicator for the presence of clast admixture or inherited 40ar due to incomplete isotopic resetting during frictional melting rb sr microsampling dating did not furnish geologically meaningful ages on the basis of isotopic disequilibria among pseudotachylyte matrix phases and independent rb sr microsampling dating of cogenetic ultra mylonites the concordant 40ar 39ar pseudotachylyte ages are interpreted as formation ages the investigated pseudotachylytes altogether reveal a cretaceous to miocene history for the entire paf consistent with independent geological evidence individual faults however consistently reveal narrower intervals of enhanced activity lasting a few million years electronic supplementary material to this paper can be obtained by using the springer link server at http dx doi org 10 1008 s00410 002 0381 6

diffusion in mineral geochronometers present and absent abstract in solid state physics and materials science fick s law diffusion is a well established process in earth sciences laboratory experiments on garnet olivine and other anhydrous minerals do document the intra grain element concentration gradients that follow the functional form required by fick s law natural gradients in minerals have rarely been analyzed with the necessary spatial resolution reports of actual observations of diffusion profiles of element concentrations are rare in the literature and diffusion profiles of isotope ratios in minerals used for geochronology are absent an in depth re examination of recent and older literature suggests that isotope transport in minerals is instead often dominated by fluid mediated retrogression reactions imaging microtextures by cathodoluminescence or back scattered electron maps provides ubiquitous evidence of patchy or dendritic replacement structures which correspond to multiple growth stages in zircon monazite muscovite biotite k feldspar etc the u pb k ar and rb sr systems in these partly retrogressed minerals show isotopic inheritance that survived the retrograde reactions at least in part in close correspondence with the petrologic relicts depending on the relative rates of the petrological processes relevant for isotope transport geochronometers can be grouped in two classes class i thermochronometers are those for which the diffusivity of a given radiogenic isotope is faster than the rate of dissolution and or reprecipitation and class ii hygrochronometers are those for which aqueous dissolution reprecipitation is the faster process all of the abovementioned geochronometers for which patchy dendritic textures formed by diachronous mineral generations and isotopic inheritance were observed must be assigned to class ii class ii samples in petrologic equilibrium can but need not record purely thermal diffusion of daughter isotopes the isotope record of class ii minerals in petrologic disequilibrium being controlled by inheritance and retrogression reactions depends chiefly on the reaction promoting factors water activity and strain the dependence of class ii mineral ages on thermal diffusion is subordinate and never unique

sulfur abundance and its speciation in oxidized alkaline melts abstract the sulfur concentrations and the relative proportions of s2 and s6 were measured by electron microprobe in a series of melt inclusions trapped in phenocrysts from different subduction related and within plate volcanoes the melt inclusions correspond to potassic and shoshonitic primary melts to tholeiitic and hawaiitic primitive melts in the tholeiitic and the transitional basaltic melt inclusions sulfur is mainly present as s2 s 6 s total 0 03 to 0 08 and varies from 0 13 to 0 18 wt the occurrence of immiscible sulfides attests to their saturation in shoshonitic and potassic primary melts sulfur s 0 12 to 0 32 wt is dissolved as both s2 and s6 s 6 s total 0 3 to 0 7 their oxygen fugacity estimated from the s 6 s total ratios ranges from ninio to ninio 1 log unit hawaiitic melts may also dissolve up to 0 3 wt sulfur possibly because of their oxidation state close to ninio as illustrated by samples from mt etna italy variations of sulfur at constant s 6 s total ratio and temperature in both the potassic and shoshonitic primary melts indicate that these melts are undersaturated with respect to a s rich condensed phase in agreement with their relatively high oxidation state it strongly suggests that sulfur behavior in relatively oxidized primary alkaline melts is controlled by the mantle source melting conditions

conjunctive k ca and rb sr dating of glauconies the glaucony series of which glauconitic mica is the k rich end member is one of the few widely occurring minerals in the sedimentary record so their isotopic ages determined mainly by the k ar method represent a major database for the geologic time scale many k ar ages were however found to be too young and often also discordant with available corresponding rb sr ages this discrepancy may reflect the disparate responses of the chemically contrasting daughter elements ar and sr to postdepositional processes and renders either age equivocal a potentially promising approach to evaluate the intrinsic potential of glauconies and other k rich minerals for direct and reliable dating of sediments is the conjunctive use of the chemically very similar k ca and rb sr systems the relationship between k ca and rb sr ages may show a coherence or regularity indicative of a geologically meaningful age like in the case of the well known chemically identical dual u pb decay systems as a crucial first step this report presents the first successful precise k ca dating in conjunction with rb sr dating of an ordovician glauconite using the same sample aliquot chemical procedure and mass spectrometer

two different types of granitoids in the suyunhe large porphyry mo deposit nw china and their genetic relationships with molybdenum mineralization abstract the suyunhe large porphyry mo deposit 0 57 mt molybdenum located in the west junggar nw china is the largest known porphyry mo deposit in xinjiang granitoids in this deposit are mainly characterized by three closely spaced intrusive centers known as stocks i ii and iii respectively the stocks i and iii mainly consist of barren granodiorite porphyry and tonalite porphyry whereas the stock ii is mainly composed of fertile monzonitic granite porphyry and granite porphyry based on detailed major and trace element and sr nd isotopic analyses two distinct compositional groups can be identified the first group of high silica end members hse is characterized by high sio 2 mostly 75 wt low mgo 0 07 0 69 wt and mg 0 19 0 36 significant eu depletion in the chondrite normalized diagram and low sr y and la yb as well as noticeably negative anomalies of ba sr p and ti in the primitive mantle normalized diagram the second group of low silica end members lse however displays adakite like features with lower sio 2 0 4 and higher sr y mostly 20 and la yb 8 the depleted sr nd isotopic characteristics e nd t 3 5 6 4 and i sr 0 7026 0 7055 and young two stage model ages of hse and lse indicate that they were both derived from partial melting of juvenile lower crust that might be triggered by asthenosphere upwelling subsequent to a slab rollback event however the depths of initial melting might be different the current evidence demonstrates that hse in the suyunhe deposit formed by partial melting of juvenile crust at depths of less than 33 km with a plagioclase residue whereas that for lse occurred at depths of 40 km where a garnet residue existed and the crust was thickened the lower source depth as well as subsequently strong plagioclase fractionation results in the absence of adakite like characteristics in hse the ce 4 ce 3 and eu n eu n ratios in zircons of hse are much lower than ore forming intrusions from porphyry cu deposits in the central asian orogenic belt but noticeably higher than barren intrusions from the lachlan fold belt and ore bearing intrusions from small intermediate porphyry mo deposits from the east qinling dabie and the nanling metallogenic belts china indicating that neither too high nor too low oxygen fugacities are favorable for large porphyry mo deposits based on previous studies of adakitic rocks in the world adakite like lse in the suyunhe deposit are believed to have higher oxygen fugacities and thus be less fertile than hse we finally suggest that adakites and adakite like rocks are unproductive for porphyry mo deposits

laboratory determined transport properties of berea sandstone we report laboratory measurements of electrical resistivity water permeability k and compressional wave velocity vp for both intact and fractured berea sandstone samples as functions of temperature from 20 c to 200 c and effective pressure pe from 2 5 mpa to 50 mpa for the intact sample vp increases from 3 52 km s to 4 16 km s as pe goes from 3 to 50 mpa with increasing temperature vp decreases at rates of about 3 percent per 100 c at pe of 5 mpa and about 1 5 percent per 100 c at pe of 38 mpa data from the fractured sample are qualitatively similar but velocities are about 10 percent lower for both intact and fractured samples increases less than 15 percent as pe increases from 2 5 mpa to 50 mpa although both samples show a larger decrease in resistivity with increasing temperature most of this change is attributed to the decrease in resistivity of the pore fluid over that temperature range for both samples k decreases with increasing pressure and temperature the intact sample permeabi

comparison of in situ and laboratory acoustic measurements on lough hyne marine sediments compressional wave velocity and attenuation were measured at frequencies of 200 1500 hz on seafloor sediments at lough hyne ireland using a mini boomer source and hydrophone array velocity and attenuation were also measured in the laboratory at 200 800 khz on a 1 m long sediment core taken from the site the in situ results indicate an average sediment phase velocity of about 1600 m s and sediment quality factor of 10 20 the laboratory core measurements give an average phase velocity of 1793 26 m s and quality factor of 16 5 the poorly sorted lough hyne sediments are highly attenuating and highly dispersive when compared to values published in the literature for well sorted marine sediments such as clean sands and marine clays the results are consistent with the few published data for poorly sorted sediments and indicate that intrinsic attenuation is highest when the mass ratio of mud clay silt to sand grade particles is close to unity it is proposed that compliance heterogeneities are most abundant when mud and sand grade particles are present in roughly equal proportions and that the observations support local viscous fluid flow as the most likely loss mechanism

giant versus small porphyry copper deposits of cenozoic age in northern chile adakitic versus normal calc alkaline magmatism cenozoic magmatic activity in northern chile led to the formation of two contrasting porphyry copper belts 1 a paleocene early eocene belt comprising small porphyry copper deposits e g lomas bayas of normal calc alkaline affinity and 2 a late eocene early oligocene belt hosting huge porphyry copper deposits e g chuquicamata of adakitic affinity although the first belt comprises both volcanic and plutonic rocks andesitic basaltic and rhyolitic lavas and tuffs and associated sub volcanic porphyries and felsic stocks the latter only includes intrusions mostly granodioritic types including porphyry copper deposits we suggest that the late eocene early oligocene belt formed when fast and oblique convergence between the south america and farallon plates led to flat subduction and direct melting of the subducting plate hence giving rise to plutonic rocks of adakitic affinity the absence of volcanism under prevailing compressional conditions prevented the escape of so2 from the adakitic sulfur rich highly oxidized magmas closed porphyry system which allowed formation of huge mineral deposits on the contrary coeval volcanic activity during formation of the paleocene early eocene calc alkaline porphyries allowed development of open systems hence to outgassing and therefore to small mineral deposits

a new approach for deriving pseudovelocity logs from resistivity logs1 this paper describes a method of generating pseudovelocity logs using measurements of electrical resistivity a theoretical relation between electrical resistivity and transit time which is applicable to a wide range of lithologies has been developed the application of this relation using a method which defines lithoresistivity zones as lithological intervals related to the same formation and showing small resistivity variations has been tested in the reconcavo sedimentary basin in bahia brazil a comparison of derived pseudovelocity logs with actual sonic logs for five wells shows the validity of the present approach

porphyry copper gold mineralization at yulong china promoted by decreasing redox potential during magnetite alteration the yulong porphyry cu au deposit occurs on the eastern margin of the tibetan plateau and is one of the largest porphyry cu au deposits in china containing more than 6 million tons of cu metal similar to other porphyry cu deposits in the world the yulong porphyry is highly oxidized sulfate is the dominant sulfur species in fluid inclusions hosted by magmatic quartz phenocrysts and no sulfide is observed indicating an oxygen fugacity above the sso buffer during magmatic processes the sulfur species changed from sulfate dominant during magmatic processes to sulfide dominant during the main mineralization processes with sulfate and sulfide mineral assemblages observed in fluid inclusions in mineralized quartz veinlets and only sulfides in the orebodies corresponding to a decrease in redox potential from the porphyry to the hydrothermal fluid magnetite crystallization was coincident with the onset of major sulfate reduction indicating that magnetite isolated trivalent iron reducing sulfate and consequently leading to the formation of porphyry cu au mineralization most porphyry cu au ore deposits are spatially associated with and genetically related to oxidized felsic magmas our results indicate that sulfate reduction promoted by magnetite crystallization is essential for the final precipitation of cu au bearing sulfides i e decreasing redox potential of the fluid is the key to and direct cause of ore formation in yulong initial high redox potential is a prerequisite for and may be an indirect indicator of most mineralization of this kind because it enables efficient transportation of cu au redox potential fluctuations can be well preserved in zircon a resistant accessory mineral commonly found in porphyries which might be developed as a handy and reliable exploration tool for porphyry cu deposits associated with magnetite

joint elastic electrical properties of reservoir sandstones and their relationships with petrophysical parameters we measured in the laboratory ultrasonic compressional and shear wave velocity and attenuation 0 7 1 0 mhz and low frequency 2 hz electrical resistivity on 63 sandstone samples with a wide range of petrophysical properties to study the influence of reservoir porosity permeability and clay content on the joint elastic electrical properties of reservoir sandstones p and s wave velocities were found to be linearly correlated with apparent electrical formation factor on a semi logarithmic scale for both clean and clay rich sandstones p and s wave attenuations showed a bell shaped correlation partial for s waves with apparent electrical formation factor the joint elastic electrical properties provide a way to discriminate between sandstones with similar porosities but with different clay contents the laboratory results can be used to estimate sandstone reservoir permeability from seismic velocity and apparent formation factor obtained from co located seismic and controlled source electromagnetic surveys

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

response to the comment by w h schwarz et al on joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by p r renne et al 2010

direct elastic properties to resistivity transforms abstractnumerous publications have dealt with estimations of resistivity from elastic parameters and vice versa attempts have been made in the cross property relationship of elastic and electric properties in particular velocity to resistivity using different parameters such as porosity and water saturation these types of transforms are currently used to predict background seismic velocities and resistivities or even start models for seismic or controlled source electromagnetic csem inversions however they are not reliable predictors because they depict the regional elastic or electric variations with limited accuracy we present a novel approach for the development of models capable of estimating the regional subsurface resistivity based on information from regional wells and seismic inversions we apply multivariate nonlinear regression on data derived from regional wells and seismic inversions and subsequently produced an estimation of subsurface horizontal resistivity that could be either us

rb sr and k ar ages on minerals at temperatures of 300 400 c from deep wells in the larderello geothermal field italy rb sr and k ar ages have been obtained on six biotites two muscovites and one hornblende from samples of micaschist gneiss and amphibolite of lower paleozoic to precambrian age at a depth exceeding 2 000 m in basement rocks of the larderello travale geothermal region most of the data cluster in the range 2 5 3 7 ma revealing the existence of a pliocene thermal event to which the origin of the field may be attributed the resulting duration of the larderello geothermal field is unexpectedly long in the basement levels of the two wells examined unstabilized minimum temperatures of 290 and 380 c were measured all the biotites show almost complete 40ar and 87sr retention at the measured well temperatures petrologic evidence stilpnomelane stability and experimental data activation energies and diffusion coefficients also favour a closure temperature above 400 c for rb sr and k ar in biotites in agreement with recent direct experimental determinations

compressional wave velocity and attenuation at ultrasonic and sonic frequencies in near surface sedimentary rocks laboratory ultrasonic measurements of compressional wave velocity and attenuation were made as a function of effective pressure on samples of limestone sandstone and siltstone taken from a shallow borehole test site the results indicate that the sandstones are pervaded by grain contact microcracks which dramatically affect their compressional wave attenuations clean sandstone shows a compressional wave quality factor q sub p of 24 2 at 5 mpa effective pressure close to the estimated in situ burial pressure and a q sub p of 83 29 at 60 mpa the q sub p of limestones and siltstones at the site show negligible and small increases with pressure in the laboratory respectively the strong pressure dependence of q sub p in clean sandstone was used to infer the presence of in situ microcracks sediment velocities measured in the laboratory at about 1 mhz were compared with those from the full waveform sonic log at about 10 khz implies that they must also be highly attenuating over a significant part of the frequency range 10 khz to 1 mhz to account for the magnitude of the observed velocity dispersion assuming the laboratory q sub p values measured at 5 mpa remain constant down to 10 khzmore predicts the observed dispersion quite well furthermore the sonic log velocities of sandstones limestones and siltstones after normalizing each lithology for porosity and clay content were found to reflect the same pressure depth trends observed in the laboratory the results provide evidence for the existence of in situ microcracks in near surface sediments less

relationships among compressional wave attenuation porosity clay content and permeability in sandstones anelastic attenuation is the process by which rocks convert compressional waves into heat and thereby modify the amplitude and phase of the waves understanding the causes of compressional wave attenuation is important in the acquisition processing and interpretation of high resolution seismic data and in deducing the physical properties of rocks from seismic data we have measured the attenuation coefficients of compressional waves in 42 sandstones at a confining pressure of 40 mpa equivalent to a depth of burial of about 1 5 km in a frequency range from 0 5 to 1 5 mhz the compressional wave measurements were made using a pulse echo method in which the sample 5 cm diameter 1 8 cm to 3 5 cm long was sandwiched between perspex lucite buffer rods inside the high pressure rig the attenuation of the sample was estimated from the logarithmic spectral ratio of the signals corrected for beam spreading reflected from the top and base of the sample the results show that for these samples compressio

dynamic poroelasticity a unified model with the squirt and the biot mechanisms the velocities and attenuation of seismic and acoustic waves in rocks with fluids are affected by the two most important modes of fluid solid interaction 1 the biot mechanism where the fluid is forced to participate in the solid s motion by viscous friction and inertial coupling and 2 the squirt flow mechanism where the fluid is squeezed out of thin pores deformed by a passing wave traditionally both modes have been modeled separately with the biot mechanism treated in a macroscopic framework and the squirt flow examined at the individual pore level we offer a model which treats both mechanisms as coupled processes and relates p velocity and attenuation to macroscopic parameters the biot poroelastic constants porosity permeability fluid com pressibility and viscosity and a newly introduced microscale parameter a characteristic squirt flow length the latter is referred to as a fundamental rock property that can be determined experimentally we show that the squirt flow mechanism dominates the biot mechanism and is responsible for measured large velocity dispersion and attenuation values the model directly relates p velocity and attenuation to measurable rock and fluid properties therefore it allows one to realistically interpret velocity dispersion and or attenuation in terms of fluid properties changes e g viscosity during thermal enhanced oil recovery eor or to link seismic measurements to reservoir properties as an example of the latter transformation we relate permeability to attenuation and achieve good qualitative correlation with experimental data

constraining the 40 k decay constant with 87 rb 87 sr 40 k 40 ca chronometer intercomparison abstract a literature survey reveals that the k ar chronometer gives ages that are ca 1 younger than u pb ages this offset is generally attributed to an inaccurate 40k decay constant three geological samples selected from a shortlist of eight with known u pb ages were investigated using detailed petrological methods and subsequently the rb sr and k ca chronometers in order a to evaluate if they meet the requirement of a geological history reflecting a point like event i e isochronous formation and subsequent ideal closure of chronometers and b to narrow down the systematic uncertainty on the 40k decay constant by investigating the metrologically traceable k ca decay branch lepidolite of the rubikon pegmatite namibia was dated with rb sr at 504 7 4 2 ma and the phlogopite and apatite from the phalaborwa carbonatite complex south africa yielded a rb sr age of 2058 9 5 2 ma both rb sr ages agree with published u pb ages the rb sr age of the late archean siilinjarvi carbonatite finland records a later regional metamorphic event at 1869 10 ma only the samples from the phalaborwa complex represent a point like magmatic event and meet all the criteria to make them suitable for the 40k decay constant intercalibration the phalaborwa k ca isochron has a slope of 1 878 0 012 forcing the k ca isochron to coincide with the u pb and rb sr ages gives one equation with two unknowns assuming that the branching ratio of the k ca branch bca lies in the interval k 2 of all published references 0 8925

laboratory study of the electrical and hydraulic properties of rocks under simulated reservoir conditions abstract experimental results are presented for resistivity and permeability measurements on clay free sandstone and shaly synthetic rock samples at simulated reservoir conditions of pressure and temperature some details of a novel multi sample high pressure and temperature rock testing system and a new technique for making synthetic shaly samples are also presented a significant influence of pressure and temperature on both the electrical and the hydraulic properties of sandstone and synthetic rocks has been observed the combined effect of pressure and temperature on the electrical properties of the sandstones tested is approximately the sum of their individual effects the effect of clay minerals on the electrical and hydraulic properties of rocks has also been investigated the experimental results obtained lead to a better understanding of the mechanisms of the pressure and temperature effects on the geophysical properties of sedimentary rocks

evaluation of the 87rb decay constant by age comparison against the u pb system abstract the rb sr decay system is one of the most widely used geochronometers for obtaining ages and cooling rates of terrestrial magmatic metamorphic and hydrothermal events it has also been extensively applied to date extraterrestrial early solar system events the accuracy of rb sr ages however strongly depends on the accuracy of the 87 rb decay constant 87 rb we determined 87 rb relative to the decay constants of 235 u and 238 u by comparing rb sr ages of minerals with u pb ages obtained from the same intrusion comparison of u pb emplacement ages with high precision rb sr mineral ages from three rapidly cooled igneous rocks covering an age range of ca 2 5 ga yields an unweighted mean 87 rb of 1 393 0 004 10 11 yr 1 i e 0 3 corresponding to a half life of 49 76 10 9 years because this decay constant is 2 lower than the presently recommended one many previously published ages are 2 too young and the resulting geologic interpretations may need revision

diagnostics of seismic time lapse effects of sandstones based on laboratory data we evaluated a viscoelastic modeling of p and s wave velocity dispersion attenuation pressure and fluid effects for a set of siliciclastic rock samples our analysis used a published laboratory data set of 63 sandstones with a wide range of compositional heterogeneities we observed a notable correlation between the velocity and attenuation pressure sensitivity and the abundance lack of quartz in the samples we included compliant pores low aspect ratio proportionally to the content of secondary minerals to account for the differential sensitivity to pressure the observed velocity and attenuation were well reproduced by the applied viscoelastic modeling we found that pores of significantly different scale required pore fluid relaxation time constants of proportionally different magnitudes to reproduce the velocity and attenuation measurements the relaxation time constant of crack sized pores can be one order of magnitude smaller than the constant of mesopores moreover the velocity dispersion and attenuation signatures revealed that a pore textural model dependent on lithological composition is critical in the prediction of time lapse fluid and pressure responses

the influence of shale effects upon the electrical resistivity of reservoir rocks the roots of the so called shaly sand problem in hydrocarbon evaluation lie in the effect of relatively fine grained minerals upon measured electrical parameters of granular reservoirs this influence manifests itself as an excess conductivity over and above that due to the purely geometric effects of electrolyte distribution within the pore space for formations with low shaliness this excess conductivity is usually insignificant in typical oilfield situations the influence of shaliness upon observed values of formation resistivity has been appraised by collating core sample data from four different reservoirs it has been demonstrated that during the course of electrical measurement under conditions of full electrolyte saturation any given lithology can exhibit both negligible and highly significant shale effects depending upon the resistivity of the interstitial aqueous electrolyte the effects of shaliness are also governed by the degree of water saturation because the manifestation of shaliness in electrical data is not a function of lithology alone recourse is made to a more realistic concept of shale effects whereby a formation or section of a formation is classified as effectively clean or effectively shaly according to whether it obeys or defies respectively the fundamental empirical laws of archie 1942 in particular since an intrinsic formation factor can be obtained directly in fully saturated effectively clean reservoirs whereas only an apparent quantity may be recorded directly in fully saturated effectively shaly reservoirs the ratio of apparent to intrinsic formation factor serves as a useful conceptual indicator of shale effects attaining the limiting value of unity only under effectively clean conditions in the context of electrical measurement the terms shaliness and shale effects are evidently not synonymous and it is the latter which should be considered when selecting equations for the computation of water saturation the implications for well log analysis follow through formulated guidelines that describe the relative levels of shale effects in different zones of lithologically uniform reservoirs

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in

high sr y arc magmas and porphyry cu mo au deposits just add water porphyry cu mo au deposits are commonly associated with intermediate composition arc related igneous rocks with high sr y and la yb ratios and such rocks are equated by some researchers with melts derived from subducted oceanic crust undergoing eclogite facies metamorphism adakites however similar geochemical characteristics are readily developed in normal asthenospheric mantle wedge derived magmas by fractionation of amphibole and or garnet and or by interaction with crustal materials during ascent through the upper plate lithosphere while there is widespread evidence for such fractionation and contamination processes in porphyry magmas there is little direct evidence for an origin by slab melting the enhanced fertility of arc magmas relates primarily to their high water content which is required for the formation of magmatic hydrothermal systems upon shallow crustal emplacement magmatic water contents 4 wt percent h 2 o cause abundant amphibole garnet fractionation but suppression of plagioclase crystallization at deep crustal levels resulting in increasing sr y and la yb ratios with differentiation commonly into adakitic ranges but not reflecting slab melting additional factors that affect arc magma fertility are relatively high oxidation states and sulfur content but these are secondary to the requirement for sufficient water thus arc magmatic suites with high sr y ratios and evidence for the presence of hydrous phenocryst phases hornblende and or biotite are indeed prospective for porphyry cu mo au deposits but only because these parameters indicate high magmatic water content