application of thermochronology to hydrothermal ore deposits thermochronology finds many applications in economic geology utilizing temperature sensitive radiometric dating techniques to reveal low temperature upper crustal processes can elucidate many aspects of deposit genesis including timing and duration of mineralization processes rate of exhumation and erosion of intrusive ore deposits and comparative preservation potential the tools are utilized to best advantage when combined with other thermochronometry techniques that provide complementary information in addition when thermochronometers are combined with geochronometers e g zircon u pb over 800 c of thermal history is revealed from emplacement to erosion fig 1 with the advent of computational algorithms that provide more accurate and detailed models of thermochronology results the economic geologist has a powerful tool to use when assessing economic favorability of a region or prospect this chapter summarizes the various ways that low temperature thermochronometers have been utilized in studies of economic mineralization and primarily focuses on studies of porphyry ore deposits these deposits are well characterized and provide a good platform from which to demonstrate the extended understanding of ore formation processes that is provided by thermochronology studies in this section we review the fundamental application of u th he fission track and 40ar 39ar thermochronometry methods to mineralized systems we then present a synopsis of how these techniques can be used in thermal history analysis either alone or in combination with other chronometers in order to provide more information on deposit genesis the discussion is presented from low through to higher temperature thermochronometers corresponding to their presentation on figure 1 u th he thermochronology as documented earlier in the volume u th he thermochronology is based on measuring the accumulation of radiogenic 4he produced from u and th decay the daughter helium is retained until the mineral is heated to a temperature at which its structure and helium retentivity change this closure temperature varies from

historical development of the gravity method in exploration the gravity method was the first geophysical technique to be used in oil and gas exploration despite being eclipsed by seismology it has continued to be an important and sometimes crucial constraint in a number of exploration areas in oil exploration the gravity method is particularly applicable in salt provinces overthrust and foothills belts underexplored basins and targets of interest that underlie high velocity zones the gravity method is used frequently in mining applications to map subsurface geology and to directly calculate ore reserves for some massive sulfide orebodies there is also a modest increase in the use of gravity techniques in specialized investigations for shallow targets gravimeters have undergone continuous improvement during the past 25 years particularly in their ability to function in a dynamic environment this and the advent of

new standards for reducing gravity data the north american gravity database the north american gravity database as well as data bases from canada mexico and the united states are being revised to improve their coverage versatility and accuracy an important part of this effort is revising pro cedures for calculating gravity anomalies taking into ac count our enhanced computational power improved ter rain databases and datums and increased interest in more accurately defining long wavelength anomaly components users of the databases may note minor differences be tween previous and revised database values as a result of these procedures generally the differences do not impact the interpretation of local anomalies but do improve re gional anomaly studies the most striking revision is the use of the internationally accepted terrestrial ellipsoid for the height datum of gravity stations rather than the conven tionally used geoid or sea level principal facts of gravity observations and anomalies based on both revised and pre vious procedures together with germane metadata will be available on an interactive web based data system as well as from national agencies and data centers the use of the revised procedures is encouraged for gravity data reduc tion because of the widespread use of the global position ing system in gravity fieldwork and the need for increased accuracy and precision of anomalies and consistency with north american and national databases anomalies based on the revised standards should be preceded by the adjec tive ellipsoidal to differentiate anomalies calculated us ing heights with respect to the ellipsoid from those based on conventional elevations referenced to the geoid

longitudinal development of low latitude ionospheric irregularities during the geomagnetic storms of july 2004 1 during the period 22 28 july 2004 three geomagnetic storms occurred due to a sequence of coronal mass ejections in this paper we present and discuss the ionospheric observations from a set of in situ satellites and ground based gps total electron content and scintillation receivers a vhf radar and two chains of ionosondes 300 e and 120 e respectively that provide the evolutionary characteristics of equatorial and low latitude ionospheric irregularities versus longitude during these storm periods it is found that the irregularities occurred over a wide longitudinal range extending from around 300 e to 120 e on storm days 25 and 27 july 2004 on 25 july plasma bubbles pbs began premidnight in america and postmidnight in southeast asia on 27 july the occurrence of irregularities followed the sunset terminator and was observed sequentially after sunset from american to southeast asian longitudes past studies have reported that storm time low latitude ionospheric irregularities are mostly confined to a narrower longitude range 90 after sunset hours and are associated with the prompt penetration of eastward electric fields ppefs into low latitudes in june solstice months the occurrence of range type spread f or pbs is very low in southeast asian and south american sectors in contrast the present results indicate that geomagnetic storms triggered the wide longitudinal development of pbs in the american sector this was probably due to the effects of ppefs on both storm days however in the southeast asian sector the pbs on the 2 days probably arose from disturbance dynamo electric field ddef ppef and gravity wave seeding effects this study further shows that under complex storm conditions besides the long duration or multiple penetrations the combined effects of ppefs and ddefs could result in a wide longitude extent of ionospheric irregularities at times

detection of auroral activity using gps satellites gps global positioning system satellites and a receiver located at fairbanks alaska are used to detect auroral activity a technique for using gps total electron content tec data to detect auroral e ionization aei at all satellite line of sight elevations is presented the location of aei during auroral substorms is determined and is consistent with simultaneous magnetometer data maps of detected aei events reveal the distribution of aei in space and time additionally a technique is presented for identifying the effects of the auroral oval e layer on the tec data particle precipitation measured by the tiros satellite is closely related to variations in the tec data the effects of the oval are consistently seen in the tec data for a variety of magnetic conditions the location of the equatorward edge of the oval is determined during auroral substorms and compares well with a model of the oval and with individual tiros passes

the chemistry of geothermal waters in iceland ii mineral equilibria and independent variables controlling water compositions abstract the major element chemistry of icelandic geothermal waters is predictable provided two parameters are known this follows from an attainment of or a close approach to an overall chemical equilibrium in the geothermal systems at temperatures as low as 50 c it is considered that the geothermal system composition temperature and kinetic factors determine which alteration minerals form the system composition is not so much fixed by rock composition as by the rate of leaching of the various constituents from the fresh rock and the composition of inflowing water the water chemistry is determined by the system composition and the external variables acting on the system they include temperature and the mobility of chloride pressure which theoretically should be regarded as an external variable has insignificant effect on water compositions in the range 1 200 bars occurring in the geothermal systems

estimation of distant relief effect in gravimetry we analyze gravitational effects of distant topographic and bathymetric relief beyond the earth centered angular distance of 1 29 58 i e beyond the outer limit of the hayford bowie zone o or approximately 167 km using a spherical earth model our results support current procedures that neglect distant relief effects for most local gravity surveys but show their potential importance for continental and global scale surveys the distant relief can produce horizontal gradients as large as 0 3 e 0 03 mgal km in mountainous areas the gravitational effect of the distant relief is significant even for local surveys although the vertical gradient of the distant relief effect never exceeds 30 e 3 mgal km on the earth s surface

u th he chronology of the robe river channel iron deposits hamersley province western australia abstract channel iron deposits cid supply 40 of australia s iron ore but their genesis is still the subject of debate two well characterised samples of goethite hematite cid from a diamond drill core in mesa j of the robe river area in western australia were dated using u th he methods in order to constrain the timing of iron oxide formation and thereby provide a temporal context for cid genesis u th he ages he ages range from 25 7 0 6 to 7 0 0 8 ma and despite a high degree of scatter they corroborate relationships expected from the internal ooidal stratigraphy for individual ooids the hematitic core is older than or indistinguishable from the age of the surrounding goethitic cortex the goethitic cortices are in turn older than the ferruginised wood fragments recovered from the cementing goethitic matrix the data suggest the following paragenesis i hematitic cores in ooids formed in the early to middle miocene as documented by ages of 14 3 3 7 ma and 18 3 3 5 ma measured in the shallower 8 2 m deep and deeper 32 8 m sample respectively ii goethitic cortices of both samples formed in the late middle to early late miocene at 11 6 3 0 ma iii wood fragments form a prominent component of the matrix and were ferruginised during the late miocene he ages ranging from 9 4 0 5 to 8 2 0 4 ma in the deeper core and 8 4 0 9 to 7 0 0 8 ma in the shallower core the data suggest that the unique environmental conditions conducive to cid formation existed during the miocene and that a typical robe river cid sequence likely took 4 to 8 myr to accumulate a methodological implication of this study is that it confirms the previous observation of vasconcelos et al 2013 suggesting that the temperature utilised for he extraction from iron oxides has a critical impact on the mobility of parent nuclides the typical 1000 c laser heating used for crystalline minerals like apatite or zircon induces loss of u and th and results in erroneously old ages modest extraction temperature

ellipsoid geoid gravity geodesy and geophysics geophysics uses gravity to learn about the density variations of the earth s interior whereas classical geodesy uses gravity to define the geoid this difference in purpose has led to some confusion among geophysicists and this tutorial attempts to clarify two points of the confusion first it is well known now that gravity anomalies after the free air correction are still located at their original positions however the free air reduction was thought historically to relocate gravity from its observation position to the geoid mean sea level such an understanding is a geodetic fiction invalid and unacceptable in geophysics second in gravity corrections and gravity anomalies the elevation has been used routinely the main reason is that before the emergence and widespread use of the global positioning system gps height above the geoid was the only height measurement we could make accurately i e by leveling the gps delivers a measurement of height above the ellipsoid in principle in

global positioning system phase fluctuations and ultraviolet images from the polar satellite in a study designed to determine the temporal development of ionospheric irregularities in the auroral region in magnetic storm periods different types of simultaneous observations were compared for the storms of january 10 april 10 11 and may 15 1997 the data sets consisted of ultraviolet images uvi from the polar satellite phase fluctuations and total electron content tec from global positioning system gps recordings at a large number of sites magnetometer observations and hemispheric power precipitation the large scale global or macroscale picture of the magnetic storm showed the importance of universal time in the development of irregularities the hemispheric total power picture and the global indices such as kp show this macroscale picture of the entire storm period however individual sites show differences in localized magnetic field variations and the development of irregularities this we term the microscale the storms of january 10 and may 15 show the importance of local magnetic time and local magnetic variations at the sites while the storm of april 10 11 was dominated by the ut storm development during the intense activity of the storms total electron content shows minute by minute increases with the satellite moving to positions 6 km apart in the minute the structured precipitation either directly produces irregularities or indirectly sets instability conditions for irregularity development in the auroral region good correlation was established for the three storms between uvi intensity and phase fluctuation development the uvi lyman birge hopfield long 170 nm emission is sensitive to 100 200 km precipitation phase fluctuation development undoubtedly arises from perturbations in the f region as well topside and bottomside soundings have shown the high occurrence of spread f in the auroral region the comparison of the data sets from these storms and from other studies indicates that the creation of irregularities develops from conditions existing over a large range of bottomside heights i e at altitudes from 100 km to the f layer

reactivated basement structures affecting the sedimentary facies in a tectonically quiescent epicontinental basin an example from nw switzerland abstract the jurassic deposits in the southern part of central europe accumulated in a shallow epicontinental sea and their deposition has usually been believed to have corresponded to a phase of tectonic quiescence neither on conventional seismic records nor in outcrops obvious indications of synsedimentary tectonics were found nonetheless subtle variations in lithofacies and thickness occur above faults in the crystalline basement in fact preexisting structures became reactivated in the jurassic during major extensional phases when the tethys and the north atlantic opened this reactivation led to differential subsidence and or to rotation of fault bounded blocks but the sediments were deformed mainly flexurally as vertical movements in the basement were dissipated by triassic salt thus the depositional area was morphologically differentiated into swells and depressions in siliciclastic muddy environments swells were characterized by hardbottoms and hiatus beds depressions were filled by distal tempestites and gravity deposits in carbonate settings reefs nucleated on swells marls and muds were deposited in depressions many of them gravity deposits reactivation of faults occurred only during short episodes and was not synchronous throughout the study area and reactivation of individual faults was episodic and probably controlled by the palaeostress field and the faults orientation reactivation of deep rooted faults is also documented by hydrothermal activity which led to vein mineralization and alteration of minerals today exposed in nearby basement units the chronostratigraphic ages of the hydrothermal processes coincide with phases of enhanced subsidence during the sinemurian aalenian bajocian bathonian and oxfordian in turn facies changes of the sedimentary cover should be useful to predict basement structures when no seismic records are available

reliability of k ar dating of clays and silicifications associated with vein mineralizations in western europe k ar ages were determined on fine fractions and one massive silicification associated with vein mineralizations in uranium barium fluorine and related base metals in western europe the reliability of the potassic materials analysed once the mineralogical and geochemical relationships to the low temperature mineralization have been established is demonstrated the isotopic ages are concentrated between nearly 190 and 170 ma this epoch corresponds to that of the rifting of the future atlantic and tethys oceans this type of low temperature mineralization thus seems to be better explained by extensional phenomena

direct dating of hydrothermal w mineralization u pb age for hubnerite mnwo4 sweet home mine colorado abstract we have investigated the potential of hubnerite for u pb dating hubnerite forms typically at medium to low temperatures in a wide range of pneumatolytic hydrothermal mineral deposits particularly porphyry molybdenum and sn specialized granites hubnerite from the sweet home mine alma colorado formed in a pb rich u poor environment but still developed relatively radiogenic pb isotopic compositions the low pb common contents in hubnerite 0 075 to 0 155 ppm demonstrate that pb is efficiently excluded from the crystal lattice in contrast u may substitute for mn the u pb data of hubnerite scatter most of the scatter originates from samples with 206 pb 204 pb values below 50 where pb blank contributes up to 30 to pb total using the least radiogenic galena pb samples with 206 pb 204 pb values above 70 have overlapping 206 pb 238 u and 207 pb 235 u values and yield a 206 pb 238 u age of 25 7 0 3 ma 2 late stage apatite from the sweet home mine yields a 206 pb 204 pb 238 u 204 pb isochron corresponding to an age of 24 8 0 5 ma 2 a comparison of the u pb hubnerite ages with literature 40 ar 39 ar ages on earlier sericite and the u pb age on later apatite suggests that i hubnerite yields accurate u pb ages and ii the evolution of the sweet home mineralization from greisen type mineralization to medium temperature hydrothermal vein mineralization took place in a few hundred thousand years at most aqueous low n 2 bearing and aqueous inclusions in the dated hubnerite have homogenization temperatures between 325 and 356 c and moderate salinity up to 6 7 wt nacl equiv thus hubnerite represents one of the rare examples of a mineral that can be dated accurately and carries petrological information

u loss associated with laser heating of hematite and goethite in vacuum during u th he dating and prevention using high o2 partial pressure abstract single aliquot u th he dating of hematite has been used to study iron oxide precipitation in various environments but we show there is an important challenge to the method highly retentive hematite samples require temperatures of 1000 c to be completely degassed whereas the temperature for major u loss is 980 c this leads to erroneously high u th he ages through the analysis of u th and sm of hematite and goethite samples we establish the degree of u loss at this temperature and demonstrate that prolonged heating at temperatures of 950 c can lead to u loss we show that loss of u in goethite and hematite samples is associated with phase change from hematite to magnetite as fe is reduced the onset temperature of vacuum reduction of hematite can be increased from about 800 900 c in vacuum to approximately 1250 c in an oxygen partial pressure of 100 mbar we demonstrate that samples can be outgassed to extract helium at 1150 c without u loss in an o2 rich atmosphere during heating which does not increase the analytical blanks we describe our implementation and automation of the procedure an average age calculated on a reference hematite sample from replicate aliquots n 12 which were analyzed using this procedure has a relative uncertainty of 2 1 and is within uncertainty of the previously measured two aliquot age we suggest this o2 degassing procedure as a way to precisely and reproducibly determine single aliquot hematite and goethite u th he ages

helium isotope disequilibrium and geochronology of glassy submarine basalts the u th he dating method is the oldest method of geochronology that involves radioactivity but historically it has not been particularly successful even when problems of poor helium retention and loss due to radiation damage are circumvented by analysing suitable mineral phases1 4 problems frequently remain with inherited helium5 6 here we show that isotope disequilibrium in the 3he 4he ratio between helium trapped in vesicles and that dissolved in the glass phase of some young seamount basalts can be used to determine u th he ages for the basalts we use the 3he 4he in vesicles extracted by crushing in vacuo to correct the dissolved phase he by fusion of the remaining powder for the inherited component and compute the radiogenic helium concentration the method is applicable to rocks containing phases with different u th he and the results have implications for dating lavas in the age range of 103 to 106 years thus filling a gap between the limits of the 14c and k ar methods and for reconstructing the geochemical history of young volcanic systems

paragenetic specularite and adularia elba italy concordant u th he and k ar ages abstract in order to test the usefulness of the helium method for detecting young geological events in hematite u th and 4 he concentrations were analyzed in five specularite samples from rio marina type hematite deposits northeastern elba italy four specularite samples define a u 0 235th 4 he isochron age of 5 39 0 46 ma 2 the isochron intercepts the 4 he axis at 49 88 pl g 2 adularia which is paragenetic with specularite in one sample used for the isochron gives a meank ar age of 5 32 0 11 ma in addition two specularite samples one from rio marina and one from terra nera southeastern elba give helium model ages of 6 4 0 4 and 7 3 0 4 ma respectively depending on the model of genesis the high ages reflect incomplete 4 he degassing and or 4 he excess the study demonstrates that geologically meaningful helium ages as young as pliocene can be obtained from specularite in spite of expected interferences from initial helium if the 4 he axis intercept is a general measure of initial 4 he in hematite its effect on the calculated ages in mesozoic hematites in previous studies is negligible the age concordance implies that similar concordance should exist in samples with a known thermal history much older than pliocene moreover the helium method could also work on specularite with a thermal history younger than pliocene

geodetic versus geophysical perspectives of the gravity anomaly summary a gravity anomaly is essentially the difference between the gravitational acceleration caused by the earth s masses and that generated by some reference mass distribution however there are numerous subtleties to the definition and moreover to the practical realization of a gravity anomaly an attempt is made here to clarify the definition of a gravity anomaly from the geodetic and geophysical perspectives point out some of the key differences in terminology and philosophy and to identify some of the problems remaining in its practical realization from a variety of observation types it is argued that if the gravity anomaly is defined and realized in a rigorous and consistent manner this may lead to the improvement of its use in both geodesy and geophysics

u th he dating of apatite a potential thermochronometer abstract we found a gem quality crystal of durango fluorapatite to have a 4he content consistent with complete retention of radiogenic helium since its formation at about 31 ma isothermal heating and step heating analysis reveal 4he loss to occur systematically by volume diffusion at low temperatures the linear low temperature portion of the diffusion data yields an activation energy of 38 5 8 1 kcal mol and a frequency factor of in d 0 a 2 16 4 2 8 sec 1 corresponding to a closure temperature of 105 c 30 c cooling rate 10 c m y it appears that u th he dating of apatite might represent a useful new thermochronometer with a range similar to that of fission track dating of apatite from these results we infer that a number of the too young u th he dates reported in the literature on minerals such as zircon and magnetite may in fact represent valuable records of the low temperature thermal history of their host rocks

an exact solution for the gravity curvature bullard b correction the complete bouguer reduction includes in addition to the simple bouguer slab correction bullard a both curvature bullard b and terrain bullard c corrections a new closed form formula for the curvature correction is derived for which the calculated values differ from those published by swick by more than 0 5 mgal for high elevations these corrections reduce those of an infinite slab bullard a to that of a spherical cap having a surface radius of 166 7 km the spherical cap produces a lesser effect than the infinite slab because of the truncation of that part of the slab above the earth and extending to infinity but it produces a greater effect than the slab because of subslab earth resulting from curvature the physical significance of the correction lies in the combination of these two differences which are each a function of elevation the bullard b surface radius 166 7 km outer radius of the hayford bowie system is reaffirmed by the exact formula to be appropriate for exploration su

helium isotopes in ferromanganese crusts from the central pacific ocean abstract helium isotopes have been measured in samples of two ferromanganese crusts va13 2 and cd29 2 from the central pacific ocean with the exception of the deepest part of crust cd29 2 the data can be explained by a mixture of implanted solar and galactic cosmic ray produced gcr he in extraterrestrial grains and radiogenic he in wind borne continental dust grains 4he concentrations are invariant and require retention of less than 12 of the in situ he produced since crust formation loss has occurred by recoil and diffusion high 4he in cd29 2 samples older than 42 ma are correlated with phosphatization and can be explained by retention of up to 12 of the in situ produced 4he 3he 4he of va13 2 samples varies from 18 5 to 1852 ra due almost entirely to variation in the extraterrestrial he contribution the highest 3he 4he is comparable to the highest values measured in interplanetary dust particles idps and micrometeorites mms helium concentrations are orders of magnitude lower than in oceanic sediments reflecting the low trapping efficiency for in falling terrestrial and extraterrestrial grains of fe mn crusts the extraterrestrial 3he concentration of the crusts rules out whole undegassed 4 40 m diameter idps as the host instead it requires that the extraterrestrial he inventory is carried by numerous particles with significantly lower he concentrations and occasional high concentration gcr he bearing particles

gps phase scintillation at high latitudes during the geomagnetic storm of 17 18 march 2015 the geomagnetic storm of 17 18 march 2015 was caused by the impacts of a coronal mass ejection and a high speed plasma stream from a coronal hole the high latitude ionosphere dynamics is studied using arrays of ground based instruments including gps receivers hf radars ionosondes riometers and magnetometers the phase scintillation index is computed for signals sampled at a rate of up to 100 hz by specialized gps scintillation receivers supplemented by the phase scintillation proxy index obtained from geodetic quality gps data sampled at 1 hz in the context of solar wind coupling to the magnetosphere ionosphere system it is shown that gps phase scintillation is primarily enhanced in the cusp the tongue of ionization that is broken into patches drawn into the polar cap from the dayside storm enhanced plasma density and in the auroral oval in this paper we examine the relation between the scintillation and auroral electrojet currents observed by arrays of ground based magnetometers as well as energetic particle precipitation observed by the dmsp satellites equivalent ionospheric currents are obtained from ground magnetometer data using the spherical elementary currents systems technique that has been applied over the ground magnetometer networks in north america and north europe the gps phase scintillation is mapped to the poleward side of strong westward electrojet and to the edge of the eastward electrojet region also the scintillation was generally collocated with fluxes of energetic electron precipitation observed by dmsp satellites with the exception of a period of pulsating aurora when only very weak currents were observed

plasma irregularities in the high latitude ionospheric f region and their diamagnetic signatures as observed by champ 1 diamagnetic effects of ionospheric irregularities have been investigated at low latitudes before but no corresponding effort has been made at high latitudes in this study we demonstrate clear diamagnetic signatures of high latitude ionospheric irregularities as observed by the champ satellite we also present the climatology of these diamagnetic signatures for the years 2001 2010 and compare it with a previous study based on global positioning system gps scintillation measurements the climatology of the diamagnetic signatures is in reasonable agreement with that of the scintillations the occurrence rate of the ionospheric irregularities generally peaks along the auroral latitudes around the pole but it is not uniform zonally the occurrence rate exhibits a maximum at the dayside cusp and in the pre midnight ionosphere the occurrence rate increases with solar and or auroral activity the region of high occurrence rate expands equatorward with increasing auroral activity occurrence probabilities are higher in local winter than in local summer the overall occurrence rate is smallest around june solstice and largest around december solstice the ionospheric irregularities are generally accompanied by bursts of small scale field aligned currents facs and they are related to region 1 facs

temperature induced 4he degassing of specularite and botryoidal hematite a 4he retentivity study degassing of radiogenic 4he induced by stepwise heating in a vacuum was carried out on various grain size fractions of specular and botryoidal hematite in order to place constraints on their 4he retentivities samples from the vosges odenwald saarbergland and cumbria were used below 900 c specularite yields straight lines in arrhenius plots this is consistent with volume diffusion the diffusion distances correspond with the macroscopic mean grain size by contrast botryoidal hematite yields curved lines which are straight only below 250 c the actual diffusion distances appear to be commensurate with the microscopic size of the constituent crystals 0 1 to 10 m the diffusion coefficients of specular d20 and botryoidal hematite d20 r2 are 10 28 cm s 1 and 10 22 s 1 and the activation energies range from 110 to 130 and 130 to 210 kj mol respectively helium 4 closure temperatures tc of specularite grains with diameters of about 5 mm are above 200 c and for all grain fractions in botryoidal hematite 10 m the tc is above 90 160 c on the basis of tc both hematite varieties should be useful thermochronometers low temperature 4he losses of the order of a few percent during a few 100 m y are conceivable for botryoidal hematite

fe oxides in jasperoids from two gold districts in nevada characterization geochemistry and u th he dating abstract this study examines the whole rock geochemistry fe oxide texture and crystal morphology and fe oxide u th he date variation of jasperoids as well as the relationships between these characteristics in order to evaluate jasperoids as an indicator for gold mineralization jasperoid samples with a range of textures appearances and expected gold concentrations were collected from two gold districts in nevada the northern carlin trend gold quarry mine and the battle mountain district marigold mine battle mountain prospect in our jasperoid samples whole rock concentrations of au are positively correlated with as ag pb sb u w and tl the following fe oxide textures are associated with anomalous gold concentrations disseminated submicron crystals feathery and acicular crystal morphologies concentric zonation from hematite to goethite and botryoidal textures calculated closure temperatures for the u th he system in observed jasperoid fe oxide morphologies within our dataset range from 26 to 136 c indicating variable susceptibility to he diffusion at near surface conditions fe oxide u th he dates range from 29 4 0 5 ma to 0 11 0 01 ma displaying intra and intersample variation we attribute the date variation to multiple factors including he implantation parent isotope exchange and he loss through closure temperature sensitivity and alpha ejection the intra and intersample variation within the fe oxide u th he dates limits our ability to make geologic interpretations our case study identifies important limitations of the u th he method in jasperoids and provides insight on how he date variation might be avoided in future studies

sampling of brine in cores of precambrian granite from northern illinois the composition of groundwater in deep seated rocks is of great interest both geochemically and in connection with the disposal of radioactive waste however sampling of deep seated groundwater is expensive and often difficult we describe here a simple technique for the elution of pore fluid groundwater from cores of igneous rocks and we describe brine eluted from a core of precambrian granite from northern illinois drill hole uph 3 the brine is predominantly nacl and cacl2 with a ca na mole ratio of about 0 05 to 0 1 from analysis of soluble chloride in a crushed sample the chloride concentration in the pore water is estimated as 2 3 m the brine is similar to brine in the illinois basin and it was probably derived from the overlying sediments

hematite and mn oxide u th he dates from the buckskin rawhide detachment system western arizona gaining insights into hematite u th he systematics

inverse and 3d forward gravity modelling for the estimation of the crustal thickness of egypt abstract a 3d crustal density model for egypt was compiled it is constrained by available deep seismic refraction receiver functions analysis borehole and geological data in egypt seismic data are sparsely and irregularly distributed consequently we developed the crustal thickness model by integrating seismic and gravity data satellite gravity data was inverted to build an initial model which was followed by a detailed 3d forward gravity modelling the initial crustal thickness is determined by applying seismically constrained non linear inversion based on the modified bott s method and tikhonov regularization assuming spherical earth approximation moreover the gravity inversion based moho depth estimates are in good agreement with results of seismic studies and are exploited for the 3d forward modelling crustal thicknesses range from 25 to 30 km along the rifted margins of the red sea which thin toward the mediterranean sea thicknesses in southern egypt reach values between 35 and 40 km a maximum crustal thickness of 45 km is found in the southwestern part of egypt within the sinai peninsula the thickness varies from the shallow southern edge 31 km and increases toward the north 36 km our model revealed a thick lower crust beneath the southern part of egypt which can be associated with crustal modification that occurred during the collision of east gondwana and the saharan metacraton along the keraf suture zone during the final assembly of gondwana in the neoproterozoic finally the isostatic implications of the differences between the seismic and gravity derived mohos are thoroughly discussed in conclusion the developed 3d crustal thickness model provides high resolution moho depth estimates that closely resembles the major geological and tectonic features also the existing correlation between the topography bouguer anomalies and moho depths indicates that the investigated area is close to its isostatic equilibrium

insights from recent gravity satellite missions in the density structure of continental margins with focus on the passive margins of the south atlantic abstract we focus on new gravity and gravity gradient data sets from modern satellite missions goce grace and champ and their geophysical interpretation at passive continental margins of the south atlantic both sides south africa and south america have been targets of hydrocarbon exploration and academic research of the german priority program sample south atlantic margin processes and links with onshore evolution the achievable spatial resolution driven by goce is 70 80 km therefore most of the geological structures which cause a significant gravity effect by both size and density contrast can be resolved however one of the most important aspects is the evaluation of the omission error which is not always in the focus of interpreters it results from high frequency signals of very rough topographic and bathymetric structures which cannot be resolved by satellite gravimetry due to the exponential signal attenuation with altitude the omission error is estimated from the difference of the combined gravity model eigen 6c4 and the satellite only model goco05s it can be significantly reduced by topographic reductions simple 2d density models and their related mathematical formulas provide insights in the magnitude of the gravity effect of masses that form a passive continental margin they are contrasted with results from satellite only and combined gravity models example geophysical interpretations are given for the western and eastern margin of the south atlantic ocean where standard deviations vary from 25 to 16 mgal and 21 11 mgal respectively it could be demonstrated that modern satellite gravity data provide significant added value in the geophysical gravity data processing domain and in the validation of heterogeneous terrestrial data bases combined models derived from high resolution terrestrial gravity and homogeneous satellite data will lead to more detailed and better constrained lithospheric density models and hence will improve our knowledge about structure evolution and state of stress in the lithosphere

gps phase fluctuations in the equatorial region during the miseta 1994 campaign in this paper we present the first coordinated use of global positioning system gps multisite and multisatellite observations with ground based radar and optical diagnostics to investigate equatorial irregularity patterns thirty second samples of total electron content tec obtained from gps phase differences between 1 2 and 1 6 ghz signals are used to study phase fluctuations at several stations comparisons were made with various types of ground measurements during the multi instrument studies of the equatorial thermosphere aeronomy miseta period depletions of 6300a airglow emission from arequipa peru correlated with phase fluctuations recorded at the same site phase fluctuations at arequipa occurred at the times when the jicamarca radar backscatter returns from plumes were noted but were also seen on other nights when there were no radar returns from plumes levels of phase fluctuations noted at arequipa varied considerably on nights when only thin layers of irregularities were observed by the jicamarca radar differences of ionospheric conditions between the two sites separated by only 5 5 geographic longitude may account for the different behavior patterns of irregularities noted similar differences in the general behavior pattern of phase fluctuations were shown when data from arequipa and fortaleza brazil were compared these stations 33 apart but at the same dip latitude had different patterns for some days during a magnetic storm a very high altitude plume was observed by the radar and by phase fluctuations noted at santiago at 18 dip latitude this correlation of high plume altitude during some periods of magnetic activity was validated by additional examples of phase fluctuations from three other magnetic storms in the solar minimum years of 1994 and 1995

u th ne and multidomain u th he systematics of a hydrothermal hematite from eastern grand canyon a hydrothermal hematite from the redwall limestone in eastern grand canyon arizona usa was analyzed for u th he and u th ne systematics the dense polycrystalline aggregate has u and th concentrations of 16 ppm each neon produced by particle capture on 18 o is abundant in the sample it constitutes 90 of total 21 ne and indicates a u th ne age of 217 5 ma this value provides a lower bound for the formation age of the sample but detailed interpretation is not possible given the current absence of neon diffusion data for hematite the 130 2 ma u th he age is much younger than the ne age and therefore must be a cooling age highly reproducible step heating he release experiments reveal the existence of a spectrum of diffusion domain sizes spanning about 3 orders of magnitude in radius corresponding to he closure temperatures ranging from 0 to 150 c these domains may correspond to crystallites in the specimen which are observed to range from smaller than a few nm to a few m 4he 3he age spectra acquired from the same experiments define a distinctive sigmoidal shape with step ages increasing monotonically from 0 to 210 ma this pattern clearly records the presence of the multiple domains as the hematite acquired its radiogenic helium coupling of the 4he 3he spectra and the diffusion data allow modeling of permissible time temperature paths experienced by the hematite these paths can be compared with independent thermal history reconstructions for eastern grand canyon characterized by 170 m yr of sedimentary burial followed by regional unroofing and canyon incision beginning at 80 ma the unroofing portion of the path inferred from the hematite is in good agreement with apatite u th he and fission track data the results permit rapid cooling in late cretaceous early tertiary time suggest a subsequent period of slow cooling through temperatures of 50 70 c with accelerated cooling ensuing after 20 ma in contrast the hematite data demand temperatures in some part s of the mesozoic that are at least 100 c hotter than expected based on burial depth estimates this may indicate that the sample experienced a reheating event associated with the passage of fluids similar to those observed at nearby mineralized breccia pipes overall these data provide motivation for further work to understand he and ne behavior in hematite and their potential use in thermochronometry

dating of vein specularite using internal u th 4he isochrons hematite an ubiquitous iron oxide is commonly found enriched with uranium and other elements supplied by the ore solution from which it had formed the decay of the incorporated uranium to stable lead produces alpha particles which become 4he atoms via electron capture in hematite this helium production may provide a convenient clock which records the time elapsed since the iron oxide became closed enough to prevent quantitative helium escape wernicke and lippolt 1993a 1993b recently lippolt et al 1993 reported high retention qualities of specular hematite for 4he over geologic periods of time activation energies above 116 kj mol and diffusion coefficients smaller than 10 30 m2 s 1 at room temperature and closure temperatures above 200 c here the concentrations of u and th have been measured together with radiogenic 4he at four different locations inside two specularites the u he concentrations co varied sufficiently among the locations for an internal helium isochron of late jurassic age to be obtained from each specularite the study suggests that specularite is a prolific chronometer and might allow a routine approach of the helium isochron method to obtain crystallization cooling ages

salt poor and salt rich fluid inclusions in quartz from two boreholes in northern switzerland abstract microthermometric studies on fluid inclusions in quartz from two boreholes in northern switzerland which cored the bottstein granite at bottstein and the crystalline basement with the overlying permo carboniferous trough sediments at weiach enable to elucidate the evolution and the p t trapping conditions of the fluid compositions two fluid groups one salt poor and the other salt rich were identified within inclusions from boreholes the salt poor inclusions are older than the salt rich inclusions whose age is post stephanian the salt poor fluids consist mainly of nacl and are trapped under relatively high temperatures up to 350 400 c the salt rich inclusions reached temperatures of at least 100 130 c low temperatures observed during the first melting 70 to 37 c indicate that other chloride salts besides nacl i e cacl2 mgcl2 etc must be present these salt rich fluids probably originated in the permian and or triassic evaporites and imply significant vertical fluid migration

botryoidal hematite from the schwarzwald germany heterogeneous uranium distributions and their bearing on the helium dating method abstract neutron induced fission tracks of small grain mounts of two co genetic botryoidal hematites eisenbach hematite manganese mineralization district mittelschwarzwald germany reveal substantial heterogeneous 235 u distributions 235 u fission tracks in the three shells of one hematite yield total uranium concentrations of 26 48 and 160 ppm 2 errors of approximately20 respectively the other hematite consists of a coherent mineralogical unit devoid of shell type features in which four localities have been probed with a range in total uranium between 26 and 600 ppm induced fission tracks from a larger section of the single unit hematite show a subparallel arrangement of five well defined 235 u zones with densities ranging from about 10 6 tracks cm 2 in zone 5 to approximately 25 10 6 tracks cm 2 in zone 2 additionally in zones 3 5 gradual internal track density variations of over 100 can be recognized a traverse shows that there is an overall decrease in radioactivity from zone 1 to zone 5 an autoradiograph confirms the existence of five zones with different activities and allows correlation of the high activity zone 2 with a 0 5 mm thin internal hematite micro layer analyses by mass spectrometer of the triple shell hematite resulted in the following concentrations 26 45 and 166 ppm uranium 2 errors of1 and 0 55 3 25 l g 4 he 2 errors of3 the four probed localities in the single unit hematite show smaller variations at 40 73 ppm uranium 2 errors of0 5 and 0 75 1 37 l g 4 he 2 errors of3 spectrometry of thorium yields values in the 1 5 ppm range for both hematites the uranium and 4 he concentration differences measured allow construction of two internal u th he isochrons yielding identical ages 2 error of 156 1 ma and 155 6 ma concordance of both isochrons in our opinion is strong evidence for a geologically significant age we interpret the data as emplacement ages further we suggest that botryoidal hematite has the potential to be a prolific chronometer for the helium method on mesozoic hematite bearing mineralizations

high resolution mapping of tec perturbations with the gsi gps network over japan two dimensional total electron content tec perturbations over japan are mapped with the geographical survey institute gsi gps network geonet gps earth observation network its spatial resolution is 0 15 latitude 0 15 longitude and temporal resolution is 30 seconds two dimensional tec observations with these high resolutions revealed spatial structures and temporal evolutions of traveling ionospheric disturbances tids in the nighttime mid latitude ionosphere on july 03 1997 a preliminary result of the tec perturbation mapping indicates that it would be a strong tool to investigate the ionospheric structures in detail coordinated observations with other ionospheric observation techniques such as incoherent scatter is radars airglow imagers and ionosondes are needed to clarify the vertical structure of the ionosphere

weathering geochronology by u th he dating of goethite nine samples of supergene goethite feooh from brazil and australia were selected to test the suitability of this mineral for u th he dating measured he ages ranged from 61 to 8 ma and were reproducible to better than a few percent despite very large variations in u and th in all samples with internal stratigraphy or independent age constraints the he ages corroborated the expected relationships these data demonstrate that internally consistent he ages can be obtained on goethite but do not prove quantitative 4he retention to assess possible diffusive he loss stepped heating experiments were performed on two goethite samples that were subjected to proton irradiation to produce a homogeneous distribution of spallogenic 3he the 3he release pattern indicates the presence of at least two diffusion domains one with high helium retentivity and the other with very low retentivity at earth surface conditions the low retentivity domain which accounts for 5 of 3he contains no natural 4he and may represent poorly crystalline or intergranular material which has lost all radiogenic 4he by diffusion in nature diffusive loss of 3he from the high retentivity domain is independent of the macroscopic dimensions of the analyzed polycrystalline aggregate so probably represents diffusion from individual micrometer size goethite crystals the 4he 3he evolution during the incremental heating experiments shows that the high retentivity domain has retained 90 95 of its radiogenic helium this degree of retentivity is in excellent agreement with that independently predicted from the helium diffusion coefficients extrapolated to earth surface temperature and held for the appropriate duration considering both the high and low retentivity domains these data indicate that one of the samples retained 90 of its radiogenic 4he over 47 5 ma and the other retained 86 over 12 3 ma thus while diffusive loss corrections to supergene goethite he ages are required these initial results indicate that the corrections are not extremely large and can be rigorously quantified using the proton irradiation 4he 3he method

multi aliquot method for determining u th he ages of hydrothermal hematite returning to elba abstract we have used a multi aliquot method to obtain precise u th he ages of hydrothermal hematite and to assess the extent to which he loss from fine grained hematite caused by diffusion and recoil hematite n 6 from the rio marina mine elba italy yields u th he ages that range from 5 36 0 33 to 5 64 0 11 ma giving a weighted mean age of 5 53 0 14 ma and an isochron age of 5 25 0 20 ma 40ar 39ar data from cogenetic adularia yield flat age spectra with analytically indistinguishable plateau ages 5 575 0 008 and 5 583 0 013 ma an additional adularia has a more complex spectrum and yields an interpreted age of 5 64 0 03 ma the hematite u th he ages overlap the 40ar 39ar ages albeit they are less precise 2 6 vs 0 2 0 5 this indicates that the loss of in situ radiogenic 4he from complex fine grained hematite either by diffusion and recoil is insignificant the study shows that multi aliquot method has the potential to reliably deliver precise and accurate ages for iron oxide mineralisation that has not suffered significant post crystallisation thermal perturbation

4he diffusion in 40ar retentive minerals abstract 4he vacuum diffusion experiments were carried out by stepwise degassing minerals normally used in k ar chronometry such as hornblende nepheline and others the study aims at 4he diffusion parameters for uppermost crustal temperatures and thus at he retentivities of the minerals the results indicate long time near quantitative 4he retention in hornblende pyroxene langbeinite and perhaps nepheline for 0 5 mm grains at least at temperatures below about 70 c sanidine and muscovite lose 4he over geologic periods at lower temperatures only the minerals of the first group are possible u th he chronometers or geothermometers provided that other dating problems such as alpha loss and u migration can be settled closure temperatures for rapidly cooling 2 mm hornblende crystals are found to be in the range of 190 to 170 c tentative u he indices indicate that diffusion parameters of the same order of magnitude as determined for the he retentive minerals may be used to select minerals to be further examined for their u th he datability e g ore minerals

the theory of the bouguer gravity anomaly a tutorial although the corrections which bring about a bouguer gravity anomaly are well established the reasons for doing them are not well understood one cause of this common misunderstanding is that the subject has been poorly presented in many of the basic texts this claim was quantified by t r lafehr a major figure in gravity exploration for 30 years in 1991 when he wrote in geophysics that nine of 15 english language textbooks contain erroneous statements on this subject

inclusions of sedimentary brines in post variscan mineralizations in the federal republic of germany a study by neutron activation analysis abstract the post variscan vein mineralizations in the federal republic of germany are characterized by highly saline fluid inclusions t e t mice 26 to 20 c t h 1 ca 22 000 60 000 mg kg 1 cl 85 000 200 000 mg kg 1 and br 550 2 600 mg kg 1 composition and salinity of the inclusion solutions are similar to brines in deep sedimentary basins it is assumed that formation waters of the na ca cl type migrated out of permo triassic sediment troughs into culmination zones of the variscan orogen where they were heated and caused mineralizations through cooling and mixing with sulfate bicarbonate waters when reascending

first observations of sbas waas scintillations using collocated scintillation measurements and all sky images to study equatorial plasma bubbles 1 the first observations of amplitude scintillations on a space based augmentation system sbas satellite signal are presented the scintillations occurred on the signal transmitted by a wide area augmentation satellite waas on 8 9 september 2004 from 2250 0045 lt the gps receiver that measured the scintillations is located on haleakala hawaii geomagnetic 21 3 n 271 4 e with a maximum s4 0 35 corresponding to a peak to peak snr variation of 8 db the scintillations are relatively weak which is to be expected for a site poleward of the equatorial anomaly during declining solar conditions using a collocated all sky imager features of the irregularity structuring in the equatorial plasma bubbles are resolved the satellite signals scintillate when the ray path intersects the three main bubbles the scintillation intensity tends to peak near the walls and decreases slightly in the interior of the bubbles in this case the bubbles leading east walls contain smaller scale size irregularities than the trailing west walls

u th he evidence of jurassic continuous hydrothermal activity in the schwarzwald basement germany abstract u th he model and isochron ages of 21 botryoidal hematites collected from the hohberg base metal vein system in the triberg granite complex mittelschwarzwald germany cover most of the jurassic period the possibility of quantitative 4 he loss triggered by successive hydrothermal events although conceivable for individual hematites based on a 4 he retentivity study and calculated opening temperatures of hematite for 4 he of 90 180 c can largely be ruled out thus the range of model and isochron ages indicates that the majority of the hematites are not cogenetic this is supported by a broad range of pb total concentrations in the hohberg botryoidal hematites 150 2700 ppm by comparison with virtually identical pb total concentrations found in cogenetic hematites from four different vein systems in the schwarzwald the th u ratios of the hematites vary by a factor of 700 0 01 7 25 mainly as a result of the range of th concentrations 0 1 74 ppm the incorporation of substantial amounts of th in hematite is thought to result from increased th transport mobility possibly caused by association with colloids and or complexing in the ore solution 18 o analyses of a 160 ma old cogenetic hematite quartz pair indicate that precipitation occurred from a fluid of magmatic origin at a temperature of 180 c the regional temperature peak in the basement at the present erosional surface during the jurassic 130 c provides a lower temperature limit of hematite formation this implies that hematite emplacement occurred at temperatures roughly ranging between 130 and 180 c the jurassic continuous hydrothermal activity suggests that the pre rifting european craton is characterized by local thermal fluxes during a long time span

4he age discordance and release behavior of a double shell botryoidal hematite from the schwarzwald germany abstract microprobe analyses of a double shell botryoidal hematite from the fahlenbach vein system schwarzwald germany show an fe3 depletion of 3 4 with respect to al3 and silicon within a 0 5 mm wide zone of alteration which separates both shells and probably is the result of a subsequent hydrothermal event induced 235u fission tracks of grain mounts from both shells reveal several grain populations within a range of 3 to 22 ppm total uranium mass spectrometer u and photometer analyses th of various localities probed within each shell vary significantly at about 5 and 12 ppm u as well as at 11 and 19 ppm th the th u ratios vary from 1 5 to 2 4he concentrations correlate with u 0 23 th heterogeneities which permits construction of two shell internal isochrons the 4he ages are discordant inner shell although mineralogically older 150 ma outer shell 182 ma 4he release by stepwise heating of one sample from each shell yielded activation energies of 124 8 and 142 7 kj mol the extrapolated 4he diffusion coefficients at 20 c logd 20 r 2 values of 19 7 0 7 and 22 2 0 6 sec 1 reveal a higher 4he retentivity at earth s surface temperatures for the outer shell 4he closure temperatures after dodson 1973 are lower for the inner shell hematite by 50 c probably also indicating earlier opening during heating the age discordance could be the result of a younger hydrothermal event which probably also has caused the observed alteration zone such an event is potentially related to the emplacement of the nearby rappenloch hematite generation ii 156 ma ago complete rejuvenation of the inner shell hematite had occurred whereas the 4he age of the outer shell was only slightly lowered due to the higher 4he retentivity

bouguer reduction density why 2 67 one of the most widely recognized parameters in solid earth geophysics is the assumed density of the surface rocks of the continental crust 2 67 g cm 3 or 2670 kg m 3 in today9s preferred si units in the calculation of bouguer and isostatic gravity anomalies which are widely used for geological studies the gravitational effect of the earth mass between an observation site and a datum is calculated assuming an infinite flat slab of a specified density that approximates the mass the datum for most surveys is sea level or in the case of surveys of limited areas it may be the elevation of the lowest station in the survey although the choice of datum is arbitrary commonly sea level is used in an attempt to standardize anomalies from different surveys similarly a density of 2 67 g cm 3 is generally assumed for the density of the included mass in regional gravity surveys

global positioning system phase fluctuations at auroral latitudes using observations of a diversity of propagation paths of global positioning system satellites from each of 11 high latitude stations it was possible to determine the behavior pattern for the development of phase fluctuations in the auroral and subauroral irregularity regions the coverage comprised a large range of longitudes and latitudes with all data measuring the same parameter i e phase fluctuations starting with characteristics of the irregularity development on magnetically quiet days it was noted that the start and stop times of phase fluctuations correlated with the entry and exit into the irregularity oval maximum occurrence of phase fluctuation took place near magnetic midnight during magnetic storms the irregularity oval expands equatorward and poleward and phase fluctuations increase in intensity using the time difference of the development of irregularities between stations considerably separated in longitude the conclusion was reached that during a magnetic storm there is a long time feeding of the turbulent energy that develops irregularities in the oval while the geographic position of the station relevant to the oval is important during storms the dynamics of each storm modifies the simple behavior shown during quiet times observations at corrected geomagnetic latitudes 80 indicate that phase scintillation intensities were lower than those in the oval during both quiet and disturbed conditions in years of low solar flux since the technique yields a measure of total irregularity intensity for the total propagation path it was not possible solely from these data to determine the altitude of the irregularities in case studies it was found that during magnetically quiet periods when irregularities are noted on propagation paths in the irregularity oval f layer critical frequencies and thicknesses were greater than those of the e layer during magnetic storm periods e layer critical frequencies are for various periods of time greater than those of the f layer during storms there are probably contributions from both layers with different mechanisms for the development of irregularities operating as a function of time storm development and latitude

secondary fe mn oxides in minerals heavily damaged by α recoil possible implications for palaeomagnetism sub micron fe mn oxides in columbite tantalite minerals are bound to metamict domains in the host these nano oxides are secondary minerals as the metamict zones formed through accumulation of damages from recoil each of which in a small volume destroys the crystal lattice of the u and th bearing columbite tantalite host transmission electron microscope investigations demonstrate that the oxides fall in the compositional range of magnetite jacobsite iwakiite fe mn 3o4 and of hematite type minerals along the fe2o3 mn2o3 join i e minerals that are known to be major carriers of magnetic remanence measured magnetic properties of isolated columbite tantalite crystals demonstrate in some samples magnetic remanence which is bound to sub micron pseudosingle domain crystals rather than to the host thus the magnetic remanence is not related to the formation of columbite tantalite but to the crystallization of the nano oxides which occur in metamict domains of the host and therefore are secondary depending on the content and distribution of u and th the nano oxides may form diachronously within an individual and among several host crystals magnetic secondary nano oxides are not restricted to columbite tantalite minerals but may occur in other minerals where high contents of fe and mn are associated with high contents of u and th rocks that show the same spatial distribution for u and fe as for instance some red sandstones may display magnetic properties that are controlled by recoil induced growth of secondary fe oxides

analysis of the global ionospheric disturbances of the march 2015 great storm the global ionospheric storm in march 2015 was investigated using data from over 3000 gps stations worldwide in this study total electron content tec rate of tec rot and rot s standard deviation roti as well as the second order difference operator tect were considered as main characteristic methods to distinguish ionosphereic disturbances the results show that 1 based on the multiple methods above we all observed that for the first time there were three equatorward traveling ionospheric disturbances tids in the main phase of this storm in north america the disturbance zone expanded to 40 n the disturbance periods and ae peak stages were roughly synchronous we suggest that these three tids were induced by the propagation of agws to low latitudes under the action of ae 2 the most intense positive storm occurred over south america and the south atlantic over 300 enhancement 00 00 05 00 ut march 18 whereas a negative storm was observed in the corresponding region of the nh such inverse hemispheric asymmetry in intensity and structure can be explained by the variations of the thermospheric composition the imf by component and the geomagnetic intensity 3 on march 18 a negative storm dominated globally except at certain low latitudes and tended to propagate equatorward and decay with time which could be largely attributed to the storm circulation theory and the evolution of the negative storm was further characterized by the fof2 variations of ionosondes

reply by the author to t r lafehr and k c chan discussion on the normal vertical gradient of gravity geophysics 48 1011 1031 july 1983 discussion geophysics 51 1505 1508 july 1986 frequently geophysical methods can be useful to those without detailed knowledge of physics buried conducting objects can be found by a beachcomber using only a crude metal detector conducting ore bodies can be located with an em instrument distinct basement units can be mapped on an aeromagnetic map as magnetic terrains and salt domes are apparent on gravity maps of the gulf coast in all of these cases anomalous values of some measurement stand out distinctly against their background values however this is not the case with ground gravity surveys in areas of high topographic relief where elevation corrections can be far greater than the target anomalies

comparative analysis of spread f signature and gps scintillation occurrences at tucuman argentina 1 we analyze data recorded from october 2010 to september 2011 during the ascending phase of the 24th solar cycle from an advanced ionospheric sounder istituto nazionale di geofisica e vulcanologia ionosonde and a gps ionospheric scintillation and total electron content tec monitor scintillation receiver colocated at low latitude in the southern american longitudinal sector tucuman 26 9 s 294 6 e magnetic latitude 15 5 s argentina the site offers the opportunity to perform spread f and gps scintillation statistics of occurrence under the southern crest of the equatorial ionospheric anomaly spread f signatures classified into four types strong range spread f ssf range spread f frequency spread f fsf and mixed spread f the phase and amplitude scintillation index and s4 respectively the tec and the rate of tec parameter marker of the tec gradients that can cause scintillations are considered the seasonal behavior results as follows the occurrence of all four types of spread f is higher in summer and lower in winter while the occurrence of scintillations peaks at equinoxes in the postsunset sector and shows a minimum in winter the correspondence between ssf and scintillations seems to be systematic and a possible correlation between s4 and fsf peaks is envisaged at the terminator the investigation focused also on two particular periods from 12 to 16 march 2011 and from 23 to 29 september 2011 both characterized by the simultaneous presence of ssf signatures and scintillation phenomena allowing to discuss the role of traveling ionospheric disturbances as a strong candidate causing ionospheric irregularities

the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a abstract land l s and prezbindowski d r 1981 the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 51ndash 74 systematic chemical variation exists in formation water collected from a dip section through lower cretaceous rocks of south central texas chemical variation can be explained by an interactive water rock diagenetic model the cyclic lower cretaceous shelf carbonates of the edwards group dip into the gulf of mexico coast geosyncline and can be considered to a first approximation as part of a complex aquifer contained by paleozoic basement beneath and by relatively impermeable upper cretaceous clay and chalk above the hydrodynamic character of this carbonate system is strongly controlled by major fault systems major fault systems serve as pathways for vertical movement of basinal brines into the lower cretaceous section formation water movement in this sytem has strong upfault and updip components the parent na ca cl brine originates deep in the gulf of mexico basin at temperatures between 200 and 250 c by the reaction halite detrital plagioclase quartz water albite brine other dissolved components originate by reaction of the fluid with the sedimentary phases k feldspar calcite dolomite anhydrite celestite barite and fluorite significant quantities of pb zn and fe have been mobilized as well as the brine moves updip out of the overpressured deep gulf of mexico basin and encounters limestones of the stuart city reef trend the buried platform margin small amounts of galena precipitate in late fractures continuing to rise upfault and updip the brine becomes progressively diluted on encountering significant quantities of dolomite in the backreef facies the ca rich brine causes dedolomitization although thermochemical consideration suggests that small amounts of several authigenic phases should precipitate most have yet to be found minor amounts of several kinds of calcite spar are present however as the brine evolves by dilution and by cooling no systematic changes in any cation cl ratio occur except for regular updip gain in mg as a result of progressive dedolomitization the formation water highly diluted by meteoric water eventually discharges along faults as hot mineral water

an overview of the early november 1993 geomagnetic storm this paper describes the development of a major space storm during november 2 11 1993 we discuss the history of the contributing high speed stream the powerful combination of solar wind transients and a corotating interaction region which initiated the storm the high speed flow which prolonged the storm and the near earth manifestations of the storm the 8 day storm period was unusually long the result of a high speed stream maximum speed 800 km s emanating from a distended coronal hole storm onset was accompanied by a compression of the entire dayside magnetopause to within geosynchronous earth orbit geo for nearly 12 hours the near earth environment was in a state of tumult a super dense plasma sheet was observed at geo and severe spacecraft charging was reported the effects of electrons precipitating into the atmosphere penetrated into the stratosphere subauroral electron content varied by 100 and f layer heights oscillated by 200 km equatorial plasma irregularities extended in plumes to heights of 1400 km later energetic particle fluxes at geo recovered and rose by more than an order of magnitude a satellite anomaly was reported during the interval of high energetic electron flux model results indicate an upper atmospheric temperature increase of 200 k within 24 hours of storm onset joule heating for the first 24 hours of the storm was more than 3 times that for typical active geomagnetic conditions we estimate that total global ionospheric heating for the full storm interval was 190 pj with 30 of that generated within 24 hours of storm onset

fast fourier based error propagation for the gravimetric terrain correction abstractwe have identified a gap in the literature on error propagation in the gravimetric terrain correction therefore we have derived a mathematical framework to model the propagation of spatially correlated digital elevation model errors into gravimetric terrain corrections as an example we have determined how such an error model can be formulated for the planar terrain correction and then be evaluated efficiently using the 2d fourier transform we have computed 18 3 billion linear terrain corrections and corresponding error estimates for a 1 arc second 30 m digital elevation model covering the whole of the australian continent

high latitude ionospheric irregularity drift velocity estimation using spaced gps receiver carrier phase time frequency analysis the conventional spaced receiver approach uses amplitude scintillations to estimate equatorial ionospheric irregularity drift velocities this approach is less applicable at high latitudes where there is a lack of substantial amplitude scintillations this paper presents a method to estimate ionosphere irregularity horizontal drift velocities based on gps signal carrier phase measurements joint time frequency analysis of the carrier phase measurements using an adaptive periodogram technique generates time varying spectrograms of ionospheric irregularity induced phase fluctuations cross correlation of the spectrograms between antenna pairs provides time lag information on propagating radio signals through the same ionospheric structure the time lag information is combined with known positions of the receiver array satellite orbits and assumed irregularity altitude to infer ionospheric irregularity horizontal drift velocity this paper presents the methodology and demonstrates its feasibility using data collected by a gps receiver array at gakona alaska the potential error sources of this method are also analyzed

on the normal vertical gradient of gravity by j h karl geophysics 48 1011 1013 july 1983 in his reply to c j swain s 1984 discussion karl states that no one has disagreed with his proposed 0 265 mgal m average value for the normal gravity gradient and that his global terrain model can be used to challenge the validity of the traditional approach to data reduction our investigations show that karl is in error on both counts and we hope that the following analyses will help toward a clearer understanding of this question

global maps of the crust 2 0 crustal components stripped gravity disturbances we use the crust 2 0 crustal model and the egm08 geopotential model to compile global maps of the gravity disturbances corrected for the gravitational effects attractions of the topography and of the density contrasts of the oceans sediments ice and the remaining crust down to the moho discontinuity techniques for a spherical harmonic analysis of the gravity field are used to compute both the gravity disturbances and the topographic and bathymetric corrections with a spectral resolution complete to degree 180 of the spherical harmonics the ice stripping correction is computed with a spectral resolution complete to degree 90 the sediment and consolidated crust stripping corrections are computed in spatial form by forward modeling their respective attractions all data are evaluated on a 1 1 arc degree grid at the earth s surface and provided in data sets s1 s5 in the auxiliary material for the scientific community for use in global geophysical studies the complete crust stripped gravity disturbances globally having a range of 1050 mgal contain the gravitational signal coming dominantly from the global mantle lithosphere upper mantle morphology and density composition and partially from the sublithospheric density heterogeneities large errors are expected because of uncertainties of the crust 2 0 model i e deviations of the crust 2 0 model density from the real earth s crustal density heterogeneities and the moho relief uncertainties

a comparative study of ionospheric irregularity drift velocity derived from a gnss receiver array and poker flat incoherent scatter radar measurements during high latitude ionospheric scintillation the conventional ionospheric scintillation based spaced receiver technique uses global navigation satellite systems gnss signal intensity measurements it is not suitable however for high latitude regions where phase scintillations occur much more often than amplitude scintillations this paper demonstrates that gnss signal carrier phase scintillations observed from a spaced receiver array can be used to infer horizontal ionospheric drift velocities via time domain correlation drift velocities measured by the colocated poker flat incoherent scatter radar are cross compared against the estimated results from the gnss receiver array a comparative study is conducted based on two case studies on 20 and 31 december 2015 both accompanied by intense geomagnetic storms overall the comparison results show statistical agreement between the gnss receiver array estimation and incoherent scatter radar measurements

palaeomagnetic evidence for the age of the cumbrian and manx hematite ore deposits implications for the origin of hematite mineralization at the margins of the east irish sea basin uk examples of epigenetic hematite mineralization located at the margins of the east irish sea basin have been sampled for palaeomagnetic investigation to establish the timing of ore formation samples collected from 10 sites in cumbria are dominated by hematite of near pure composition and characterized by dual polarity and in part dual component magnetizations that yield palaeopoles nine sites between 50 n 130 e and 50 n 150 e in contrast samples recovered from seven sites on the isle of man have more varied mineralogical compositions that include ferromagnets with lower unblocking temperatures manx hematite mineralization also exhibits dual polarity but magnetizations yield steeper inclinations with palaeopoles lying between 55 n 130 e and 70 n 150 e steeper directions probably reflect minor tilting of the manx block following hematite emplacement correlation of poles with the european apparent polar wander path indicates that these ore deposits formed during the middle triassic results show that hematite mineralization sited at the margins of the east irish sea basin is essentially contemporaneous and establishes for the first time an underlying temporal relationship between these geographically dispersed ore bodies dating places the mineralization within a broader extensional geotectonic regime associated with the early rifting of pangaea in the north atlantic the context implies a causal link between crustal extension development of ore forming fluids within the evolving east irish sea basin and subsequent migration of fluids to basin margins where iron was precipitated as hematite supplementary materials locations and details of palaeomagnetic sample sites and a tabulation of selected reference palaeomagnetic poles defining the triassic and early jurassic segment of the apparent polar wander path for the european sector of the eurasian plate are available at www geolsoc org uk sup18691

standardization in gravity reduction gravity reduction standards are needed to improve anomaly quality for interpretation and to facilitate the joining together of different data sets to the extent possible data reduction should be quantitative objective and comprehensive leaving ambiguity only to the interpretation process that involves qualitative subjective and geological decisions the term bouguer anomaly describes a field intended to be free of all nongeologic effects not modified by a partial geologic interpretation measured vertical gradients of gravity demonstrate considerable variation but do not suggest as often reported that the normal free air gradient is in error or needs to be locally adjusted such gradients are strongly influenced by terrain and to a lesser extent by the same geologic sources which produce bouguer anomalies a substantial body of existing literature facilitates the comprehensive treatment of terrain effects which may be rigorously implemented with current computer technology although variations in topographic rock density are a major source of bouguer anomalies a constant density appropriate to the area under investigation is normally adopted as a data reduction standard leaving a treatment of the density variations to the interpretation a field example from british columbia illustrates both the variations in vertical gravity gradients which can be encountered and the conclusion that the classical approach to data reduction is practically always suitable to account for the observed effects standard data reduction procedures do not and should not include reduction to datum the interpreter must be aware however that otherwise smooth regional bouguer anomalies caused by regional sources do contain high frequency components in areas of rugged topography

hematite fault rock thermochronometry and textures inform fault zone processes abstract minerals on fault surfaces record fluid rock interaction strain and or heat during fault slip fault hosted hematite is amenable to u th he he thermochronometry hematite he dates reflect fault related processes or exhumation depending on hematite growth above or below the grain size controlled closure temperature and processes that promote open system behavior deconvolving these phenomena requires multi scale hematite textural characterization and constraints on the ambient thermal history from conventional thermochronometry two examples of this approach include investigations of hematite coated fault surfaces from exhumed damage zones in the seismically active wasatch fault zone wfz ut and painted canyon fault pcf paralleling the southern san andreas fault mecca hills ca wfz fault mirrors preserve sub m scale polygonal grain textures and hematite he data patterns that together with host rock apatite he data are consistent with localized friction generated heat hematite he loss and hematite recrystallization during damage zone seismicity