crustal concealing of small scale core field secular variation summary the earth s magnetic field is mainly produced within the earth s liquid and electrically conducting core as a result of a process known as the geodynamo many other sources also contribute to the magnetic signal accessible to observation at the earth s surface partly obscuring the main core magnetic field signal thanks to a series of very successful satellites and to advances in magnetic field modelling techniques considerable progress has however been made in the recent years toward better identifying the signal of each of these sources in particular temporal changes in the field of internal origin happen to be detectable now in spherical harmonic degrees up to perhaps 16 all of these changes are usually attributed to changes in the core field itself the secular variation on the ground that the lithospheric magnetization cannot produce such signals it has however been pointed out on empirical grounds that temporal changes in the field of internal origin produced by the induced part of the lithospheric magnetization could dominate the core field signal beyond degree 22 this short note revisits this issue by taking advantage of our improved knowledge of the small scale field changes and of the likely sources of the lithospheric field we rely on a simple extrapolation of the observed spatial spectrum of the field changes beyond degree 16 and use a forward approach based on a recent geological model of lithospheric magnetization this leads us to confirm that the main cause of the observed changes in the field of internal origin up to some critical degree n c is indeed likely to be the secular variation of the core field but that the signal produced by the time varying lithospheric field is bound to dominate and conceal the time varying core signal beyond that critical degree in very much the same way the permanent component of the lithospheric field dominates and conceals the permanent component of the core field beyond degree 14 all uncertainties taken into account we estimate n c to lie between 22 and 24 we however also note that in practice the main limitation to the observation of the core field small scale secular variation is not so much its concealing by the field of lithospheric origin but its fast changing nature and small magnitude this leads us to conclude that whereas cumulative small scale lithospheric field changes might be detected some day detection of core field secular variation beyond degree 18 is likely to remain a severe challenge for some time

dynamo tests for stratification below the core mantle boundary abstract evidence from seismology mineral physics and core dynamics suggests a layer with an overall stable stratification in the earth s outer core possibly thermal in origin extending below the core mantle boundary cmb for several hundred kilometers yet vigorous deep mantle convection with locally elevated heat flux implies locally unstable thermal stratification below the cmb consistent with interpretations of non dipole geomagnetic field behavior that favor upwelling flows in places below the cmb to resolve this apparent inconsistency we investigate the structure of convection and magnetic fields in the core using numerical dynamos with laterally heterogeneous boundary heat flux strongly heterogeneous boundary heat flux generates localized convection beneath the cmb that coexists with an overall stable stratification there our partially stratified dynamos are distinguished by their time average magnetic field structures without stratification or with stratification confined to a thin layer the octupole component is small and the cmb magnetic field structure includes polar intensity minima with more extensive stratification the octupole component is large and the magnetic field structure includes intense patches or high intensity lobes in the polar regions comparisons with the time averaged geomagnetic field are generally favorable for partial stratification in a thin

scalar magnetic anomaly maps of earth derived from pogo and magsat data a new pogo scalar magnetic anomaly map at 400 km altitude is presented which consists of spherical harmonics of degree 15 60 on the basis of the common features of this map with two new magsat anomaly maps dawn and dusk two scalar magnetic anomaly maps of the earth are presented using two selection criteria with different levels of stringency these selection criteria suppress the noncrustal components of the original maps by different amounts the more stringent selection criteria seek to eliminate as much contamination as possible at the expense of suppressing some anomaly signal this map is represented by spherical harmonics of degree 15 60 the less stringent selection criteria seek to retain as much crustal signal as possible at the expense of also retaining some contaminating fields this map is represented by spherical harmonics of degree 15 65 the resulting two maps are highly correlated with degree correlation coefficients greater than 0 8

intermediate sulfidation epithermal gold base metal deposits in tertiary subaerial volcanic rocks sahinli tespih dere lapseki western turkey abstract gold in the sahinli and tespih dere intermediate sulfidation gold base metal deposits in western turkey occurs in relatively deep epithermal quartz veins along with base metal minerals which have epithermal textures including plumose quartz vug infills comb and cockade textures and matrix supported milled breccias the total sulfide content of the veins in the area is variable ranging from fluid inclusions in main stage quartz at sahinli are only liquid rich with homogenization temperatures ranging from 220 to 322 c and the majority of th values between 250 and 300 c salinity ranges from 4 3 to 6 9 wt nacl equiv first ice melting temperatures tmf between 24 5 and 19 0 c indicate that the fluids were dominated by nacl h2o during mineralization the relatively higher average th at the tespih dere deposit 295 c is attributed to a relatively deeper level of exposure calculated 18o values indicate that ore forming hydrothermal fluids in the study area had 18oh2o ranging from 1 1 to 9 7 average 3 8 strongly 18o enriched compared with present day hydrothermal meteoric water in the area 18o 8 5 d values of fluid inclusions in quartz range from 58 to 93 and d values of clay minerals and alunite from 40 to 119 d values from intermediate argillic alteration average 68 in the study area are very similar to d values of the present day local geothermal system average d 54 whereas d values from advanced argillic alteration average d 33 are very different from the present day local geothermal system the 34s values in samples from the sahinli and tespih dere deposits average 2 9 for pyrite 3 3 for chalcopyrite 5 4 for sphalerite and 7 6 for galena these data are consistent with derivation of the sulfur from either igneous rocks or possibly from local wallrock

elevated paleomagnetic dispersion at saint helena suggests long lived anomalous behavior in the south atlantic earth s magnetic field is presently characterized by a large and growing anomaly in the south atlantic ocean the question of whether this region of earth s surface is preferentially subject to enhanced geomagnetic variability on geological timescales has major implications for core dynamics core mantle interaction and the possibility of an imminent magnetic polarity reversal here we present paleomagnetic data from saint helena a volcanic island ideally suited for testing the hypothesis that geomagnetic field behavior is anomalous in the south atlantic on timescales of millions of years our results supported by positive baked contact and reversal tests produce a mean direction approximating that expected from a geocentric axial dipole for the interval 8 to 11 million years ago but with very large associated directional dispersion these findings indicate that on geological timescales geomagnetic secular variation is persistently enhanced in the vicinity of saint helena this in turn supports the south atlantic as a locus of unusual geomagnetic behavior arising from core mantle interaction while also appearing to reduce the likelihood that the present day regional anomaly is a precursor to a global polarity reversal

thickness of the magnetic crust of mars 1 to estimate the thickness of the magnetic crust of mars six observational magnetic spectra are fitted with the theoretical spectrum expected from a novel bimodal distribution of magnetic sources observational spectra differ for each comes from a different map or model of variously selected and analyzed mars global surveyor magnetometer electron reflectometer measurements of the vector magnetic field around mars the new theoretical spectrum represents fields from both compact sources and extended laterally correlated sources on a spherical shell so the estimated shell depth can now be doubled to obtain layer thickness this typical magnetic crustal thickness is put at 47 8 8 4 km the extensive sources are enormous typically 650 km across and account for over half the magnetic energy at low degrees there is some indication that these sources are relatively shallow but the typical area remains about 330 000 km2 granted such extended sources represent magnetization of mars ancient crust in a core source field dominated by a reversing areocentric paleodipole each one arguably formed during a single polarity chron how did such vast regions of magnetic crust form a survey of many eligible mechanisms suggests magnetization of cooling igneous rock at minimal rates of about 1 to 0 1 km3 a during superchrons of order 15 to 150 ma long

bayesian inversion for the filtered flow at the earth s core mantle boundary the inverse problem of determining the flow at the earth s core mantle boundary according to an outer core magnetic field and secular variation model has been investigated through a bayesian formalism to circumvent the issue arising from the truncated nature of the available fields we combined two modeling methods in the first step we applied a filter on the magnetic field to isolate its large scales by reducing the energy contained in its small scales we then derived the dynamical equation referred as filtered frozen flux equation describing the spatiotemporal evolution of the filtered part of the field in the second step we proposed a statistical parametrization of the filtered magnetic field in order to account for both its remaining unresolved scales and its large scale uncertainties these two modeling techniques were then included in the bayesian formulation of the inverse problem to explore the complex posterior distribution of the velocity field resulting from this development we numerically implemented an algorithm based on markov chain monte carlo methods after evaluating our approach on synthetic data and comparing it to previously introduced methods we applied it to a magnetic field model derived from satellite data for the single epoch 2005 0 we could confirm the existence of specific features already observed in previous studies in particular we retrieved the planetary scale eccentric gyre characteristic of flow evaluated under the compressible quasi geostrophy assumption although this hypothesis was not considered in our study in addition through the sampling of the velocity field posterior distribution we could evaluate the reliability at any spatial location and at any scale of the flow we calculated the flow uncertainties we determined are nevertheless conditioned by the choice of the prior constraints we applied to the velocity field

scanning electron microscope cathodoluminescence analysis of quartz reveals complex growth histories in veins from the butte porphyry copper deposit montana scanning electron microscope cathodoluminescence sem cl analysis of quartz reveals textures that cannot be observed using optical microscopy or backscattered electrons these cryptic textures yield insight into timing and physical conditions of quartz growth especially in environments with multiple quartz precipitation events hydrothermal quartz from quartz sulfide veins in the porphyry copper deposit in butte montana was analyzed by sem cl revealing the following textures euhedral growth zones wide nonluminescing bands that cut across multiple quartz grains rounded luminescent quartz grain cores with euhedral overgrowths nonluminescing splatters of quartz connected by networks of cobweb like nonluminescing quartz in otherwise luminescent quartz concentric growth zones and wide nonluminescent grain boundaries these textures indicate that many veins have undergone fracturing dilation growth of quartz into fluid filled space quartz dissolution and recrystallization of quartz precipitation and dissolution textures indicate that early quartz molybdenite veins formed as a result of pressure fluctuations between lithostatic and hydrostatic at high temperatures and later pyrite quartz veins formed near hydrostatic pressure in response to temperature decrease through and beyond the field of retrograde quartz solubility

regional stratification at the top of earth s core due to core mantle boundary heat flux variations earth s magnetic field is generated by turbulent motion in its fluid outer core although the bulk of the outer core is vigorously convecting and well mixed some seismic geomagnetic and geodynamic evidence suggests that a global stably stratified layer exists at the top of earth s core such a layer would strongly influence thermal chemical and momentum exchange across the core mantle boundary and thus have important implications for the dynamics and evolution of the core here we argue that the relevant scenario is not global stratification but rather regional stratification arising solely from the lateral variations in heat flux at the core mantle boundary using our extensive suite of numerical simulations of the dynamics of the fluid core with heterogeneous core mantle boundary heat flux we predict that thermal regional inversion layers extend hundreds of kilometres into the core under anomalously hot regions of the lowermost mantle although the majority of the outermost core remains actively convecting sufficiently large and strong regional inversion layers produce a one dimensional temperature profile that mimics a globally stratified layer below the core mantle boundary an apparent thermal stratification despite the average heat flux across the core mantle boundary being strongly superadiabatic stratification of the earth s outer core is regional not global and created by lateral heat flux variations at the core mantle boundary according to numerical simulations of fluid core dynamics

direct observation and measurement of au and ag in epithermal mineralizing fluids abstract colloidal gold particles have been observed in c 300 c low salinity fluids from the arapucandere intermediate sulphidation epithermal base metal au deposit in nw turkey this is the first time colloidal gold has been recorded in an ancient mineralizing fluid growth in veins of large euhedral quartz crystals after the deposition of sulphides occurred in a number of stages from the introduction of fresh pulses of fluid the quartz overgrowths have a fibrous texture which facilitated trapping of large elongate fluid inclusions between the quartz fibres which grew perpendicular to the crystal faces of the pre existing quartz episodic periods of intense trapping of fluid inclusions occurred throughout the growth of quartz trapped within primary fluid inclusions are numerous particles of gold the largest observed is c 1 m but most are smaller bse element mapping shows these to contain au ag cu hg la icp ms profiles of the fluid inclusions confirm au and ag is not present in solution being present as numerous particles we have quantified the concentration of gold in fluid inclusions which are orders of magnitude greater than has been previously measured or thought likely in crustal fluids the average ag concentration is c 32 ppm and au is c 41 ppm but the maximum concentrations of both may reach several 100 s to 1000 ppm calcite forms a coating on the inner surface of the inclusions and barite pyrite galena sphalerite and unidentified minerals are also present with the au ag particles it is clear that the au ag particles could not have precipitated in the fluid inclusions therefore they must have precipitated elsewhere and been carried with the hydrothermal fluid the high concentrations and their colloidal nature have implications for the enrichment of gold in mineral deposits

chemical and boron isotope compositions of tourmaline from the jaduguda u cu fe deposit singhbhum shear zone india implications for the sources and evolution of mineralizing fluids abstract the proterozoic jaduguda u cu fe deposit in the singhbhum shear zone eastern india hosts the oldest and most productive uranium mine in india the polymetallic ores in jaduguda are hosted in altered sheared and metamorphosed volcano sedimentary rocks and this complexity has lead to a confusion in ore genetic models for the deposit a characteristic of the mineralization is the presence of abundant tourmaline locally exceeding 50 vol which is spatially associated with u and cu mineralization in all rock types and its chemical and b isotopic variations provide important constraints on fluid source s and ore deposit affinity we examined tourmaline from the u cu ore zone and adjacent footwall and hanging wall meta sedimentary rocks tourmaline grew in three different stages pre kinematic tourmaline 1 represented by fractured and porphyroblastic grains is ubiquitous in the wall rocks and the u cu zone syn kinematic tourmaline 2 and post kinematic tourmaline 3 are found exclusively in the u cu zone where intense shear deformation has focussed fluid flow alteration and metamorphism all tourmalines belong to the alkalic group and most are dravitic systematic contrasts in major element compositions between tourmaline 1 and tourmaline 2 are attributed to the influence of high fluid rock ratios in the u cu ore zone tourmaline from the jaduguda deposit exhibits a wide overall range of 11b values from 6 8 to 17 2 positive values of tourmaline 1 are irrespective of host rock and ore association u or u cu and range between 2 3 to 17 2 n 44 the calculated 11b values of fluid in equilibrium with this tourmaline for mineralization temperatures of 300 450 c range from 4 to 20 the 11b values of syn kinematic tourmaline 2 are much lower than tourmaline 1 between 6 8 and 4 n 7 and the corresponding fluid 11b values are 4 8 6 the high values of 11b for tourmaline 1 and early fluid suggest a marine evaporite or basinal brine was the source of boron and this fits with abundant mineralogical and geochemical evidence for highly saline fluids during mineralization we propose that the isotopically lighter fluid associated with tourmaline 2 and related syn kinematic mineralization mobilization was derived from the metamorphic volcano sedimentary rocks at high fluid rock ratios in and around the shear zone post kinematic tourmaline 3 is compositionally and isotopically 11b 4 to 11 1 n 5 similar to tourmaline 1 in the same samples suggesting it formed by local recrystallization of the early tourmaline or from a renewed influx of saline fluids similar to those which formed the pre kinematic mineralization integrating the results of this tourmaline study with the geological and geochemical characteristics of the jaduguda u cu fe mineralization suggests that it is best regarded as a variant of the fe oxide cu u ree or iocg class of deposits

geology mineralogy and fluid inclusion data from the arapucan pb zn cu ag deposit canakkale turkey abstract the arapucan pb zn cu ag deposit occurs as hydrothermal veins in diabase and altered triassic metasandstones adjacent to calc alkaline intrusive igneous rocks the deposit is an important commercial source of base metal in northwestern turkey potential by products are silver and gold the geology of the area includes a paleozoic metamorphic basement triassic sedimentary rocks with carbonate blocks tertiary granitoids and neogene volcanics the mineral assemblage includes galena quartz calcite sphalerite chalcopyrite and pyrite as well as minor bismuthinite tetrahedrite pyrolusite hematite scheelite malachite magnetite limonite and rutile silver is associated with tetrahedrite early hydrothermal activity was responsible for the formation of three hypogene alteration types of decreasing intensity silicification sericitization and argillic alteration these alteration styles show a rough spatial zonation the ore stage clearly postdates hydrothermal alteration as indicated by the occurrence of ore minerals in vuggy cavities and fractures in silica bodies the deposit contains evidence of at least two periods of hypogene mineralization separated by a period of faulting in addition to pb zn cu ag and au the ores contain substantial quantities of w bi sb and te average 34s values for galena and pyrite are 3 95 and 2 24 respectively suggesting an igneous source for both the sulphur and metals however geological and geochemical interpretations suggest that at least some of the metals were leached from the metasandstones and diabases fluid inclusions in main stage sphalerite homogenize at 229 384 c with salinities ranging from 1 7 to 18 5 eq wt nacl the deposits formed as the result of the interaction of two aqueous fluids a higher salinity fluid probably magmatic and a dilute meteoric fluid the narrow range of 34s galena and pyrite values 5 2 to 1 2 cdt suggests that the sulphur source of the hydrothermal fluids was the same during deposition of the metals

a model of ocean basin crustal magnetization appropriate for satellite elevation anomalies a model of ocean basin crustal magnetization measured at satellite altitudes is developed which will serve both as background to which anomalous magnetizations can be contrasted and as a beginning point for studies of tectonic modification of normal ocean crust the model is based on published data concerned with the petrology and magnetization of the ocean crust and consists of viscous magnetization and induced magnetization estimated for individual crustal layers thermal remanent magnetization and chemical remanent magnetization are excluded from the model because seafloor spreading anomalies are too short in wavelength to be resolved at satellite altitudes the exception to this generalization is found at the oceanic magnetic quiet zones where thermal remanent magnetization and chemical remanent magnetization must be considered along with viscous magnetization and induced magnetization

efemcukuru b rich epithermal gold deposit izmir turkey efemcukuru located in the aegean region turkey is an example of vein type epithermal gold deposit with related stockwork and replacement mineralisation the veins are hosted by late cretaceous paleogene flysch facies rocks of the izmir ankara zone which were intruded by rhyolites from of neogene volcanism gold mineralisation is associated with late pulses of magmatic hydrothermal activity and is present in zones of hydraulic brecciation adjacent to veins or stockwork zones around a dome shaped small intrusion the intrusion and later epithermal mineralisation are both controlled by nw setrending faults and mineral deposits occur along strike with dips 60j to 80j to the northeast individual quartz veins associated with sulphide minerals and mineralised hornblende facies hornfels are other important ore bearing formations the alteration associated with mineralisation is represented mainly by rhodonite rhodochrosite axinite quartz calcite and adularia in veins and stockwork zone and chlorite sericite illite and kaolinite in the wall rock homogenisation temperatures of 200 300 jc reflect emplacement of ore distant from inferred magmatic heat in epithermal environment due to wide range in salinity of the fluids 0 9 eq wt nacl sulphide diversity in the deposit is rather rich than the low sulphidation epithermal systems the fluid inclusion data indicate that a complicated geothermal system existed both the gas data and the microthermometry data indicate that there was fluid mixing each type of mineralisation has been studied with the aim of clarifying the paragenetic relationships among the different minerals arsenopyrite pyrite marcasite sphalerite galena and chalcopyrite are the main minerals with pyrrhotite fahlore group sphene rutile and gold occurring as accessories pyrolusite limonite goethite lepidocrocite covellite chalcocite malachite and azurite are of secondary origin d 2003 elsevier science b v all rights reserved

earth s core internal dynamics 1840 2010 imaged by inverse geodynamo modelling inverse geodynamo modelling seeks to estimate the dynamic state of earth s core from geo magnetic data and the statistical information brought by a prior self consistent 3 d numerical model of the geodynamo the method rests on the use of least squares inversions under constraints and estimates hidden quantities by taking advantage of linear relations and long range statistical correlations with the magnetic observations the data together with their error statistics are provided by geomagnetic field models cov obs gufm sat q3 and cm4 covering epochs 1840 2010 the prior numerical model is the recently published coupled earth dynamo the output of which presents a high degree of morphological semblance to the geomagnetic field while reproducing the main features of its secular variation an analysis of the inversion misfits to the data shows that the prior model generally accounts well for the main field and secular variation data within their specified errors throughout the investigated time period inverted core flows are confirmed to be mainly organized in columns parallel to the earth s rotation axis a previously observed giant eccentric columnar gyre of westward drifting flow is found to be present from epoch 1870 onwards and its structure is shown to slowly rotate westwards at a rate up to 0 1 yr 1 confirming an earlier prediction based on direct numerical modelling temporal variations in the axisymmetric part of the gyre accurately account for observed variations of the length of the day in recent epochs inverted magnetic structures support a mechanism of azimuthal flux expulsion by convective columns to explain the origin of low latitude magnetic flux patches existing beneath the atlantic the 1840 2010 time average of the inverted density anomaly field has a longitudinal hemispheric structure with most of the buoyancy in the eastern hemisphere consistent with rapid surges of convective columns imaged in this hemisphere with earlier proposals of a faster inner core freezing there and with a possible east to west convective translation of the solid inner core the typical timescales of flow variation observed in the inversions are two to three times shorter than those naturally produced by a direct simulation of the prior model underlining its limits in fully rendering the earth s core short timescale dynamics

array based iterative measurements of smks travel times and their constraints on outermost core structure vigorous convection in earths outer core led to the suggestion that it is chemically homogeneous however there is increasing seismic evidence for structural complexities close to the outer cores upper and lower boundaries both body waves and normal mode data have been used to estimate a p wave velocity vp at the top of the outer core the e layer which is lower than that in the preliminary reference earth model however these low vp models do not agree on the form of this velocity anomaly one reason for this is the difficulty in retrieving and measuring smks arrival times to address this issue we propose a novel approach using data from seismic arrays to iteratively measure smks skks differential travel times this approach extracts individual smks signal from mixed waveforms of the smks series allowing us to reliably measure differential travel times we successfully use this method to measure smks time delays from earthquakes in the fiji tonga and vanuatu subduction zones smks time delays are measured by waveform cross correlation cc between smks and skks and the cc coefficient allows us to access measurement quality we also apply this iterative scheme to synthetic smks seismograms to investigate the 3d mantle structures effects the mantle structure corrections are not negligible for our data and neglecting them could bias the vp estimation of uppermost outer core after mantle structure corrections we can still see substantial time delays of s3ks s4ks and s5ks supporting a low vp at the top of earths outer core

geomagnetic evidence for fluid upwelling at the core mantle boundary summary previous studies both geomagnetic and seismic have been unable to show conclusively whether or not there is fluid upwelling at the core mantle boundary here a new method is developed in which an attempt is made to invert geomagnetic secular variation data measured at the earth s surface for a frozen flux purely toroidal core mantle boundary cmb velocity field under the assumption that the mantle is electrically insulating and flux is frozen in at the cmb these data have previously been inverted for the core mantle boundary radial secular variation from which the appropriate fit between model and data is known two different main field models were used to assess the effect of uncertainty in its radial component at the cmb the conclusions were the same in both cases frozen flux purely toroidal motions provide a poor fit a statistical test allows very firm rejection of the hypothesis that the residuals are not significantly larger whereas there is no statistical difference between the residuals of inversions for radial secular variation and frozen flux velocity fields at the cmb if upwelling and down welling is included the inherent non uniqueness in the velocity field obtained is not of concern since only their statistical properties are utilized and no physical significance is attached to the flows obtained

grimm the gfz reference internal magnetic model based on vector satellite and observatory data summary in this paper the new gfz reference internal magnetic model grimm is presented the model has been derived from nearly 6 yr of champ satellite data and 5 yr of observatory hourly means at high latitudes full vector satellite data are used at all local times which allows a separation between on one hand the fields generated by ionosphere and field aligned currents and on the other hand the fields generated in the earth s core and lithosphere this selection technique leads to a data set without gaps during the polar summers resulting in a core field model that has an unprecedented time resolution the modelled static core field secular variation and lithospheric field are all in good agreement with previously published magnetic field models order five b splines are used to model the variation in time of the core field the energy in the secular acceleration has therefore a smooth behaviour in time and increases continuously from 2003 5 mapping the field acceleration from 2001 5 to 2005 5 reveals its rapid and complex evolution over this time period at the earth s surface due to the applied regularization technique the acceleration energy in spherical harmonics 6 11 is significantly larger than for other models and we show that such a spectrum is acceptable

tectonic implications of mars crustal magnetism mars currently has no global magnetic field of internal origin but must have had one in the past when the crust acquired intense magnetization presumably by cooling in the presence of an earth like magnetic field thermoremanent magnetization a new map of the magnetic field of mars compiled by using measurements acquired at an 400 km mapping altitude by the mars global surveyor spacecraft is presented here the increased spatial resolution and sensitivity of this map provide new insight into the origin and evolution of the mars crust variations in the crustal magnetic field appear in association with major faults some previously identified in imagery and topography cerberus rupes and valles marineris two parallel great faults are identified in terra meridiani by offset magnetic field contours they appear similar to transform faults that occur in oceanic crust on earth and support the notion that the mars crust formed during an early era of plate tectonics

low sulfidation type au ag mineralization at bergama izmir turkey abstract bergama the center of bergama county is located in western turkey and includes the villages of ovacik narlica and saganci the ovacik epithermal gold silver deposit is located in the western anatolian volcanic and extensional province adjacent to the ene trending bergama graben some 100 km north of the city of izmir gold of economic grades at the ovacik deposit reserves 4 19 mt at 7 6 g t occurs in epithermal quartz veins which display low temperature epithermal textures including crustiform banding quartz pseudomorphs after bladed calcite and multiphase hydrothermal breccias alteration minerals at both ovacik and narlica are dominated by smectite mixed layer illite smectite chalcedonic quartz and adularia whereas major kaolinite and minor mixed layer smectite illite 13 4 a occur at saganci the total sulfide content at ovacik is low geochemical variations in altered wall rocks at ovacik and narlica are generally characterized by two fold enrichments in k rb cs and 25 to 93 depletions in sr ca mg na and even higher depletions 96 to 99 decrease in the quartz adularia vein zone lanthanum ce pr hf zr sm eu gd tb and ho also exhibit up to 50 depletions in the wall rock and even more so up to 90 depletion for la and nd in the vein structure wall rock enrichment in au ag as hg and sc is by factors of 60 150 88 8 and 3 respectively the ranges of ree in both the altered volcanic rocks and quartz adularia veins are wide and may reflect either significant mobilization of ree during alteration and mineralization or their dilution by the metasomatic processes from fresh volcanic rocks through montmorillonite illite adularia altered wallrock to quartz adularia veins high rb sr ratios in adularia illite altered areas are closely related to the presence of k rich alteration minerals low rb sr ratios and corresponding low k values at saganci are due to acid leaching of volcanic rocks positive correlation coefficients between au and ag pb zn cd cu and sb in epithermal quartz veins all of which are 0 51 are significant silver and sb are remarkably enriched at higher levels of the deposit no correlation occurs between au and as or ag and as the ovacik quartz in au ag bearing veins has 18o values ranging from 9 5 to 15 7 whereas d values of fluid inclusions in quartz range from 89 to 125 however the narlica quartz in au ag bearing veins returned 18o values ranging from 5 9 to 8 3 whereas the d values of fluid inclusion in quartz range from 82 to 99 18o results indicate that ore forming hydrothermal fluids at ovacik and narlica had 18oh2o values ranging from 2 9 to 3 5 average 0 24 and from 2 96 to 0 6 average 1 6 respectively they are thus 18o enriched in comparison with present day meteoric and hydrothermal meteoric waters 5 4 18o 18oh2o and d values suggest that mineralizing solutions were a mixture of meteoric and magmatic waters the 34s sulfide data at ovacik and narlica range from 2 1 to 5 3 average 1 7 and from 4 6 to 2 7 average 0 36 respectively these 34s sulfide values are consistent with a magmatic source for s

mapping geomagnetic secular variation at the core mantle boundary summary data from recent satellite missions have vastly increased the resolution of models of the geomagnetic field and itsfirst and second time derivatives secular variation sv and secular acceleration sa the spectra of both sv and sa are blue at the core mantle boundary both well fit by functions proportional to l l 1 where l is the spherical harmonic degree the ratio of the two spectra defines a timescale for geomagnetic variations of approximately 10 yrs for all resolvable harmonic degrees the blue spectra should prevent meaningful maps of the sv being generated nevertheless the coherence of the maps up to harmonic degree 13 suggests that it is possible to obtain useful insight from their examination low sv is confirmed under the pacific but also revealed under the north atlantic and antarctica these features are more readily explained in terms of dynamo control through thermal core mantle coupling than by electromagnetic screening comparison with maps from measurements prior to the recent satellites using the comprehensive model suggests that models back to at least 1970 are sufficiently good to enable direct comparison of the sv

mathematical geophysics a survey of recent developments in seismology and geodynamics n j vlaar g nolet m j r wortel s a p l cloetingh editors reidel dordrecht 1988 xi 407 pp dfl 120 00 49 00 37 35 hardback

constraints from material properties on the dynamics and evolution of earth s core the material properties of the earth s core have been better constrained by recent technical and computational advances the properties imply that the core was once hot but is cooling quickly and the inner core is young

small scale structure of the geodynamo inferred from oersted and magsat satellite data the geodynamo in the earth s liquid outer core produces a magnetic field that dominates the large and medium length scales of the magnetic field observed at the earth s surface1 2 here we use data from the currently operating danish oersted3 satellite and from the us magsat2 satellite that operated in 1979 80 to identify and interpret variations in the magnetic field over the past 20 years down to length scales previously inaccessible projected down to the surface of the earth s core we found these variations to be small below the pacific ocean and large at polar latitudes and in a region centred below southern africa the flow pattern at the surface of the core that we calculate to account for these changes is characterized by a westward flow concentrated in retrograde polar vortices and an asymmetric ring where prograde vortices are correlated with highs and retrograde vortices with lows in the historical 400 year average magnetic field4 5 this pattern is analogous to those seen in a large class of numerical dynamo simulations6 except for its longitudinal asymmetry if this asymmetric state was reached often in the past it might account for several persistent patterns observed in the palaeomagnetic field7 8 9 10 we postulate that it might also be a state in which the geodynamo operates before reversing

mapping and modeling of magnetic anomalies in the northern polar region of mars vector crustal magnetic field maps of the northern polar zone 60 n to 90 n are constructed from selected mars global surveyor magnetometer data obtained during the period from may 28 to september 13 1998 two medium anomalies amplitudes 50 nt at 170 km altitude are mapped in locations consistent with earlier studies no visible surface features correlate with the anomalies suggesting that the sources lie beneath the visible veneer of polar deposits and volcanic lava flows if so then they formed prior to the immediate end of the heavy bombardment upper hesperian period modeling of anomaly vector field components combined with independent constraints on the depth to the curie isotherm yields lower limits on bulk magnetization intensities 0 4 0 9 a m that are significantly greater than those measured for martian snc meteorite samples rocks that contain substantially more titanomagnetite than snc meteorites or that contain magnetic phases in addition to titanomagnetite possibly resulting from hydrothermal alteration are therefore suggested alternatively remanence acquisition in a field of earthlike intensity 50 t rather than in the relatively weak inferred paleointensities for snc meteorites 1 10 t would also help to explain the relatively strong inferred remanent magnetizations the approximate south paleomagnetic pole positions corresponding to these two anomaly sources are located in a region between olympus mons and the present north rotational pole this region is adjacent to the approximate location predicted by melosh 1980 for the paleopole prior to the formation of the tharsis gravity anomaly

δd values of fluid inclusion water in quartz and calcite ejecta from active geothermal systems do values reflect those of original hydrothermal water one of the most common methods for estimating paleohydrothermal d values in epithermal quartz veins is hydrogen isotope analysis of h 2 o extracted from fluid inclusions in quartz by thermal decrepitation the validity of the method is questioned the d values of water extracted from fluid inclusions in clear euhedral quartz from active geothermal systems are up to 30 per mil more negative than the d value 42 of the geothermal water measured d values of the fluid inclusion water are dependent on the temperature at which the water in the quartz was extracted water extracted at 800 c has d values about 10 to15 per mil lower than fluid inclusion water extracted at 500 c 53 to 61 fluid inclusion water in calcite from an active geothermal well has d values that match those of the geothermal water calcite is thus potentially a more suitable mineral for estimating paleohydrothermal d values

statistical treatment of crustal magnetization summary we present a general statistical theory for relating magnetic fields to the magnetization of their source region when the geometry of the source is spherical and the magnetization is a realization of a stationary isotropic random process for the case of gaussian statistics considered here the second order statistics are sufficient to determine the process uniquely observed high degree coefficients from a spherical harmonic expansion of the field appear to be consistent with this model we find simple models of crustal magnetization that are compatible with observational constraints namely the values of the magnetic power spectra believed to be derived from the crust and the total crustal power any statistical model of the crust can be used to pre whiten observations prior to modelling the core field in a way described previously by jackson

a time dependent model of the earth s magnetic field and its secular variation for the period 1980 2000 1 this study presents an investigation and description of the secular variation of the earth s magnetic field between 1980 and 2000 a time dependent model c3fm continuous covariant constrained endpoints field model of the main field and its secular variation between 1980 and 2000 is developed with gauss coefficients expanded in time on a basis of cubic b splines this model is constrained to fit field models from high quality vector measurements of magsat in 1980 and orsted in 2000 and to fit both magnetic observatory and repeat station secular variation estimates for the period in between these secular variation estimates first time derivatives are derived from observatories monthly or annual means and repeat station data in order to reduce the contributions of crustal noise annual and semiannual variation on average the model input consists secular variation estimates of the x y and z components at 130 locations per month treatment of covariance between the different components allows a higher temporal sensitivity of the model due to the exclusion of some external field variation the model is computed up to degree and order 15 the model is a useful extension of the hitherto existing time dependent description of the secular variation gufm which describes the secular variation until 1990 it reveals a short term secular variation on subdecadal timescale and has a higher spatial resolution than previously resolved the model is also valuable to test the frozen flux hypothesis and to link features of the radial field at the core mantle boundary to the geodynamo

an improved geomagnetic data selection algorithm for global geomagnetic field modelling a spherical harmonic degrees 60 global internal field model is described called bgs g l 0706 this model includes a degree 15 core and piecewise linear secular variation model and is derived from quiet time orsted and champ satellite data sampled between 2001 0 and 2005 0 for the satellite data selection a wide range of geomagnetic index and other data selection filters have been used to best isolate suitably quiet magnetospheric and ionospheric conditions only a relatively simple degree one spherical harmonic external field model is then required it is found that a new vector magnetic disturbance index vmd the existing longitude sector a indices the auroral zone index ie and the polar cap index pc are better than kp and dst at rejecting rapidly varying external field signals at low middle auroral and polar latitudes the model quality is further enhanced by filling spatial and temporal gaps in the quiet data selection with a second selection containing slightly more disturbed data it is shown that vmd provides a better parametrization than dst of the large scale rapidly changing external field the lithospheric field model between degrees 16 and 50 is robust and displays good coherence with other recently published models for this epoch bgs g l 0706 also shows crustal anomalies consistent with other studies although agreement is poorer in the southern polar cap intermodel coherency reduces above about degree 40 most likely due to incompletely filtered signals from polar ionospheric currents and auroral field aligned currents the absence of the pc index for the southern hemisphere for 2003 onwards is a particular concern

a 50 degree spherical harmonic model of the magnetic field of mars this paper presents a 50 degree and order spherical harmonic model of the magnetic field of mars derived at 120 km altitude using the three orthogonal components of the vector magnetic field data acquired by the mars global surveyor within the 80 to 200 km altitude range the downward continued vector magnetic field components to the surface of mars delineate details of the martian magnetic field the strong magnetic anomalies in the southern hemisphere do not show compelling evidence for magnetic lineations similar to those associated with the seafloor spreading on earth the anomalies are more or less equidimensional the magnetic signatures surrounding the impact basins hellas argyre and isidis show that the prominent magnetic anomalies are older than the impact events an average magnetization of 2 a m is estimated for the upper crust surrounding hellas basin four isolated magnetic anomalies are modeled by vertical prisms with circular cross sections of 170 to 190 km radius and 20 to 30 km thickness the magnetization of the model prisms is 5 a m more than that of the surroundings

physico chemical controls on ore deposition in the arapucandere pb zn cu precious metal deposit biga peninsula nw turkey abstract arapucandere is one of a number of similar cu zn pb au ag epithermal deposits in the biga peninsula which are mineralogically and tectonically similar fluid inclusions have very low salinities between 1 7 and 0 wt nacl and a wide range of temperatures from 360 to 160 c there was extensive boiling and flashing of the hydrothermal fluids which initiated mineral deposition the range of temperatures is consistent with emplacement of the veins at 700 m depth with the pressure decreasing from near lithostatic to near hydrostatic and a decrease in temperature to 250 c due to adiabatic expansion of the fluids there is evidence of a limited amount of boiling but the temperature and pressure decrease was close to the liquid vapour curve flashing of the fluids was caused by sudden drops to sub hydrostatic pressures and even lower temperatures mineralization was caused by these pressure related temperature decreases as there is no evidence of cooling and dilution of the ore fluids 34 s values of sulphides indicate a magmatic source but the more negative than usual values also suggest boiling affected isotopes d and 18 o of the fluids indicate a mixing between meteoric waters and magmatic fluids with the large range of d due to boiling la icp ms analyses of fluid inclusions reveal high cu zn pb concentrations in the fluids despite their low salinity transported as chloride complexes exceptional pressure and temperature decrease causing the fluids to flash was likely to have been in response to earthquakes

p t x constraints on the koru epithermal base metal au deposit biga peninsula nw turkey abstract the koru deposit is a typical intermediate sulfidation base metal au example of volcanic volcaniclastic hosted mineralization in the biga peninsula and northwestern turkey ore deposition was associated with the collisional and post collisional tectonics related to the closure of the tethys ocean galena baryte and quartz are main minerals accompanied by minor amounts of sphalerite pyrite chalcopyrite covellite and marcasite the homogenization temperature of fluid inclusions indicates two distinct fluid pulses one at a temperature commensurate with epithermal mineralization and boiling near boiling conditions at c 350 c with the second approximately 150 200 c lower salinity in both instances was from 11 0 to 0 2 wt nacl the d and 18o values of water in equilibrium with early quartz and fluid inclusions plot close to the magmatic water box indicating the source of the high temperature fluid was magmatic d and 18o values from early and late baryte trend towards the meteoric water line mwl but this is not due to mixing with meteoric water rather equilibration with alteration assemblages at decreasing temperature la icp ms analyses of fluid inclusions reveal high cu zn pb concentrations in the fluids despite their low salinity transported as chloride complexes the range of temperatures within the early quartz and sphalerite mineralization can be explained by pressure variations during vein and fracture opening

accounting for magnetic diffusion in core flow inversions from geomagnetic secular variation summary we use numerical dynamos to investigate the possible role of magnetic diffusion at the top of the core we find that the contribution of radial magnetic diffusion to the secular variation is correlated with that of tangential magnetic diffusion for a wide range of control parameters the correlation between the two diffusive terms is interpreted in terms of the variation in the strength of poloidal flow along a columnar flow tube the amplitude ratio of the two diffusive terms is used to estimate the probable contribution of radial magnetic diffusion to the secular variation at earth like conditions we then apply a model where radial magnetic diffusion is proportional to tangential diffusion to core flow inversions of geomagnetic secular variation data we find that including magnetic diffusion does not change dramatically the global flow but some significant local variations appear in the non frozen flux core flow models termed diffusive the hemispherical dichotomy between the active atlantic and quiet pacific is weaker a cyclonic vortex below north america emerges and the vortex below asia is stronger our results have several important geophysical implications first our diffusive flow models contain some flow activity at low latitudes in the pacific suggesting a local balance between magnetic field advection and diffusion in that region second the cyclone below north america in our diffusive flows reconciles the difference between mantle driven thermal wind predictions and frozen flux core flow models and is consistent with the prominent intense magnetic flux patch below north america in geomagnetic field models finally we hypothesize that magnetic diffusion near the core surface plays a larger role in the geomagnetic secular variation than usually assumed

major and trace element and multiple sulfur isotope composition of sulfides from the paleoproterozoic surda copper deposit singhbhum shear zone india implications for the mineralization processes abstract the present study combines major and trace element composition and sulfur s isotope data of pyrite and chalcopyrite from the surda copper sulfide deposit in the singhbhum shear zone the most important copper and uranium producing belt singhbhum cu u belt in india three textural and compositional types of both pyrite and chalcopyrite were distinguished unzoned to partially zoned pyrite ia with high co up to 54900 ppm and low ni content is earliest followed by oscillatory zoned pyrite ib with high as up to 25600 ppm and co up to 46800 ppm both occurring in pyrite i chalcopyrite i pyrrhotite magnetite apatite vein cobaltite type substitution fe1 xcox s1 xasx 2 is suggested for pyrite ib gold occurs in pyrite i as minor invisible gold and as electrum inclusions it also occurs along with cu mn ni hg ag pb sb zn ce y u and th in micro fractures that transgress the primary zoning pattern defined by as co and ni in pyrite ib the early inclusion rich chalcopyrite generation chalcopyrite i contains high concentration of zn and se and minor to trace amounts of co ni hg pb sb te and bi appeared in between pyrite i and ii low co high ni up to 37700 ppm content pyrite ii and inclusion free chalcopyrite ii enriched in co ni hg bi mn ag sb v and pb are cogenetic and occurring in pyrite ii pyrrhotite pentlandite chalcopyrite ii violarite vein low co and ni containing pyrite iii chalcopyrite iii occur mainly as disseminated grains the relative timing of formation of pyrite ii chalcopyrite ii with pyrite iii chalcopyrite iii remains uncertain pyrite chalcopyrite textures indicate that all pyrite chalcopyrite formed at some time prior to the end of deformation and metamorphism both in situ and mineral separates of all pyrite types and associated chalcopyrite yield a narrow range of positive 34s values between 3 8 and 6 9 suggesting sulfur being derived from a similar source consistent positive 34s values and other circumstantial evidence indicate that most sulfur was derived from seawater sulfate or modified seawater brine evaporite 33s values revealed mass dependent fractionation mdf signature it is proposed that incorporation of mdf sulfur of the mineralization event in paleoproterozoic singhbhum cu u belt took place after the great oxidation event the high se concentrations 260 400 ppm and se s ratios for both pyrite i and ii from surda deposit 4 4 5 7 10 4 suggest a low temperature of the cu rich ores 250 350 c and precipitation from a metalliferous fluid with a high se s ratio 10 4 to 10 3 consistent with igneous input of these elements

on core surface flows inferred from satellite magnetic data abstract satellite data allows the magnetic field produced by the dynamo within the earth s core to be imaged with much more accuracy than previously possible with only ground based data changes in this magnetic field can in turn be used to make some inferences about the core surface flow responsible for them in this paper we investigate the improvement brought to core flow computation by new satellite data based core magnetic field models it is shown that the main limitation now encountered is no longer the now high accuracy of those models but the non modelled secular variation produced by interaction of the non resolvable small scales of the core flow with the core field and by interaction of the partly resolvable large scales of the core flow with the small scales of the core field unfortunately masked by the crustal field we show how this non modelled secular variation can be taken into account to recover the largest scales of the core flow in a consistent way we also investigate the uncertainties this introduces in core flows computed with the help of the frozen flux and tangentially geostrophic assumptions it turns out that flows with much more medium and small scales than previously thought are needed to explain the satellite data based core magnetic field models it also turns out that a significant fraction of this flow unfortunately happens to be non recoverable being either non resolvable because too small scale or invisible because in the kernel of the inverse method even though it produces the detectable non modelled secular variation applying this to the magsat 1980 to orsted 2000 field changes leads us to conclude that a flow involving at least strong retrograde vortices below the atlantic hemisphere some less resolved prograde vortices below the pacific hemisphere and some poorly resolved and partly non resolvable polar vortices is needed to explain the 1980 2000 satellite era average secular variation the characteristics of the fraction of the secular variation left unexplained by this flow are also discussed

wavelet characterization of external magnetic sources as observed by champ satellite evidence for unmodelled signals in geomagnetic field models praveen kunagu 1 2 georgios balasis 3 vincent lesur 1 e chandrasekhar2 and c papadimitriou3 1helmholtz centre potsdam gfz german research centre for geosciences germany 2department of earth sciences indian institute of technology bombay powai mumbai 400076 india email esekhar iitb ac in 3institute for astronomy astrophysics space applications and remote sensing national observatory of athens greece

on the occurrence and wider implications of anomalously low δd fluids in quartz veins south cornwall england a chemical and hydrogen isotopic study has been carried out on quartz hosted fluid inclusions from three different quartz carbonate sulphide sulphate veins from southwest england two fluid types have been identified in these veins by fluid inclusion microthermometry 1 a low temperature 80 150 c saline 20 27 wt nacl cacl2 equiv nacl cacl2 brine and 2 a moderate temperature 200 c low salinity 0 5 wt nacl equiv fluid d values for the brines range from 39 to 103 and values for the dilute fluids are in the range 46 to 79 both fluid types have at least some values of d which are defined as anomalous i e cannot be directly related to either a low d source fluid or to modification of a source fluid by common physicochemical processes such as evaporation or boiling examination of these data in the given geological context suggest the anomalously low values are unlikely to be attributable to analytical artifacts or post entrapment changes of the fluid inclusions similarly fluid interaction with a suitable mineral or organic phase cannot adequately explain the data we conclude that an as yet unidentified process is responsible for producing low d fluids in southwest england and that this may be a common phenomenon in low temperature basinal environments

genetic investigation and comparison of kartaldag and madendag epithermal gold deposits in canakkale nw turkey two epithermal gold deposits kartaldag and madendag located in nw turkey have been characterized through the detailed examinations involving geologic mineralogical fluid inclusion stable isotope whole rock geochemistry and geochronology data the kartaldag deposit 0 01 17 65 ppm au hosted by eocene dacite porphyry is associated with four main alteration types with characteristic assemblage of i chlorite smectite illite kaolinite ii quartz kaolinite iii quartz alunite pyrophyllite iv quartz pyrite the last being characterized by three distinct quartz generations comprising massive vuggy early fine medium grained vug lining early and banded colloform comb late textures observed sulfide minerals are pyrite covellite and sphalerite oxygen and sulfur isotope analyses performed on quartz delta o 18 quartz 7 93 to 8 95 parts per thousand and calculated delta o 18 h2o 7 95 to 1 4 parts per thousand and pyrite delta s 34 pyrite 4 8 parts per thousand and calculated delta s 34 h2s 6 08 to 7 20 parts per thousand separates suggest a meteoric water source for water in the hydrothermal fluid and an igneous source for the sulfur dissolved in ore related fluids microthermometric analyses of primary fluid inclusion assemblages performed on quartz late quartz generation yield temperatures th dominantly in the range of 245 285 degrees c and generally low salinity values at 0 to 1 7 wt nacl eq based on the quartz textures and the associated base metal concentrations along with fluid inclusion petrography the early vug lining quartz is considered to have been associated with the mineralization possibly through a boiling and a late mixing process at 285 degrees c the madendag deposit 027 20 60 ppm au hosted by paleozoic mica schists is associated with two main alteration types sericite illite kaolinite and quartz pyrite dominated by two distinct quartz generations i early colloform comb and banded quartz and ii late quartz forming the cement in hydrothermal breccia whereas oxygen isotope analyses of quartz delta o 18 quartz 9 55 to 18 19 parts per thousand and calculated delta o 18 h2o 2 97 to 5 54 parts per thousand suggest varying proportions of meteoric and magmatic sources for the ore bearing fluid sulfur isotope ratios delta s 34 pyrite 2 2 parts per thousand and calculated delta s 34 h2s 3 63 to 3 75 parts per thousand point to an essentially magmatic source for sulfur with or without contribution from sedimentary sources microthermometric analysis carried out on primary fluid inclusion populations of a brecciated sample early quartz give a temperature th range of 235 255 degrees c and 0 0 to 0 7 wt nacl eq salinity based on the textural relationship base metal and high gold contents the ore precipitation stage is associated with late stage quartz formation via a possible boiling process the presence of alunite pyrophyllite and kaolinite vuggy quartz and covellite suggest a high sulfidation type of epithermal deposit for kartaldag on the other hand madendag is identified as an adularia sericite type owing to the presence of significant sericite neutral ph clays mostly illite chlorite smectite and kaolinite low temperature quartz textures e g colloform comb and banded quartz and limited sulfide minerals given the geographical proximity of kartaldag and madendag deposits the similar temperature and salinity ranges obtained from their fluid inclusions and the similar ages of igneous rocks in both deposits kartaldag 40 80 036 to 42 19 0 45 ma madendag 43 34 0 85 ma the mineralizing systems in both deposits are considered to be genetically related c 2013 elsevier b v all rights reserved

comment on origin and evolution of hydrothermal fluids in epithermal pb zn cu au ag deposits at koru and tesbihdere mining districts canakkale biga peninsula nw turkey by mustafa cicek and tolga oyman ore geology review 2016 78 176 195

geomagnetic jerks and rapid hydromagnetic waves focusing at earth s core surface geomagnetic jerks are abrupt changes in the second time derivative the secular acceleration of earth s magnetic field that punctuate ground observatory records as their dynamical origin has not yet been established they represent a major obstacle to the prediction of geomagnetic field behaviour for years to decades ahead recent jerks have been linked to short lived temporally alternating and equatorially localized pulses of secular acceleration observed in satellite data associated with rapidly alternating flows at earth s core surface here we show that these signatures can be reproduced in numerical simulations of the geodynamo that realistically account for the interaction between slow core convection and rapid hydromagnetic waves in these simulations jerks are caused by the arrival of localized alfven wave packets radiated from sudden buoyancy releases inside the core as they reach the core surface the waves focus their energy towards the equatorial plane and along lines of strong magnetic flux creating sharp interannual changes in core flow and producing geomagnetic jerks through the induced variations in magnetic field acceleration the ability to numerically reproduce jerks offers a new way to probe the physical properties of earth s deep interior geomagnetic jerks in the earth s magnetic field are caused by the arrival of hydromagnetic waves and could be generated by sudden releases of buoyancy in the earth s core suggest geodynamic numerical model simulations

magnetic boundary layers in numerical dynamos with heterogeneous outer boundary heat flux abstract it has been proposed that magnetic flux expulsion due to outer core fluid upwellings may affect the geomagnetic secular variation on the core mantle boundary bloxham 1986 in this process intense horizontal field lines are concentrated below the outer boundary introducing small radial length scales and consequently strong radial diffusion here we explore such magnetic boundary layers in numerical dynamo simulations with heterogeneous outer boundary heat flux inferred from a tomographic model of lower mantle seismic shear waves velocity anomalies our scheme associates magnetic boundary layers to peak horizontal magnetic fields at the top of the shell in our models mean magnetic boundary layer thickness ranges 200 400 km and decreases with increasing magnetic reynolds number extrapolation or interpolation to earth s core conditions based on total core flow amplitude or its poloidal part gives mean magnetic boundary layer thickness of 220 and 260 330 km respectively we find magnetic boundary layers associated with the azimuthal field at the equatorial region whereas magnetic boundary layers associated with the meridional field are found at mid latitudes negative outer boundary heat flux anomalies yield preferred locations of expulsion of azimuthal field below africa and the pacific while positive outer boundary heat flux anomalies yield preferred locations of expulsion of meridional field below the americas and east asia furthermore we find a tendency of the azimuthal field to low latitudes of the northern hemisphere our results suggest that the local diffusion time is on the order of several kyr and the local magnetic reynolds number is on the order of 10 both much smaller than classical estimates

a coherent model of the crustal magnetic field of mars 1 the immense amount of the mapping phase mars global surveyor mgs magnetic data allows us to derive a highly accurate magnetic map of mars the data acquired at nighttimes within the first 3 years of the mapping phase are divided into two almost equal parts and each part is expressed in spherical harmonics of degree up to 90 the two models are almost identical over harmonics of degree up to 62 but show appreciable differences over higher degree harmonics indicating that the higher degree harmonic coefficients have appreciable noncrustal contribution the most repeatable components of the two models are combined to produce an accurate 62 degree harmonic model of the magnetic field of the martian crust it is further demonstrated that the altitude of mgs is the major limiting factor of the resolution of the mapping phase data the small scale features of the data with wavelengths shorter than 400 km have significant contribution from noncrustal sources they are not useful for delineating the details of the magnetic source bodies in the crust

ovacik gold deposit an example of quartz adularia type gold mineralization in turkey the ovac1k gold deposit is located 100 km north of izmir in western turkey it lies adjacent to the east northeast trending bergama graben and it consists of a series of high grade gold bearing epithermal quartz veins hosted by subaerial andesitic dacitic lava dome facies of lower miocene age the region is underlain by paleozoic metamorphic rocks and limestone which are cut by medium to high level intrusions and overlain by subaqueous and subaerial andesitic to dacitic lava domes that host the ovac1k gold deposit middle to late miocene extensional tectonic activity was responsible for the formation of north northeast south southwest to northeast southwest trending grabens the extensional activity was accompanied by normal faulting with a later variable sinistral strike slip component oriented east west and northwest southeast it is probable that these faults were critical in controlling the development of epithermal quartz veins both mineralized and unmineralized two of four nearly east west trending epithermal veins at ovac1k contain significant au mineralized areas and display typical low temperature epithermal textures including crustiform banding quartz pseudomorphs after bladed calcite and multiphase hydrothermal breccias veins crop out throughout a maximum strike length of 400 m and surface widths are up to 35 m mineralized areas extend down dip for at least 200 m gold appears to be related mainly to earlier formed quartz adularia veins and breccias the gold occurs mainly in clasts of earlier vein material that has been transported from deeper levels in the vein system little gold is contained in the matrix of the breccias the alteration associated with mineralization consists of secondary albite or adularia together with quartz and clays such as smectite interlayered illite smectite and illite chlorite illite and chlorite metallic minerals occur generally only in trace amounts and include chalcopyrite pyrite arsenopyrite sphalerite bornite chalcocite covellite galena and electrum the mineralizing fluids had temperatures ranging from 150 to 250 c and salinities between 7 0 and 8 0 wt percent nacl equiv the veins have a distinct trace element signature including high au ag as and sb high au and ag with low as and sb contents are found in the quartz adularia veins whereas low au and ag with high as and sb are found in the silicified hanging wall and footwall zones drilling has confirmed continuity of mineralized rock to a vertical depth of 175 m to date a resource of 2 980 000 tonnes at 9 0 g t au containing 862 000 ounces has been delineated other deposits of this type should be sought where late oligocene to early miocene volcano plutonic rocks are cut by major northeast southeast trending grabens with associated northwest southeast to east west oriented normal to sinistral strike slip faults volcanic rocks with strong adularia sericite alteration and silicification accompanied by quartz veins with epithermal textures are primary targets

mineralogy of the sources for magnetic anomalies on mars abstract recent discovery of intense magnetic anomalies on mars which are due to remanent magnetization requires some explanation for the possible minerals responsible for the anomalous signature thermoremanent magnetization trm in single domain sd and multidomain md sized magnetite hematite and pyrrhotite all potential minerals are considered the intensity of trm in 0 05 mt is in descending order sd sized magnetite sd sized pyrrhotite md sized hematite md sized pyrrhotite md sized magnetite sd sized hematite the trm intensity is 50 of the sirm each of these minerals and estimated concentrations of magnetic remanence carriers assumed to be titanomagnetite in the shergotty nakhlaxhassigny martian meteorites are used in a thin sheet approximation model to reveal the concentration of each mineral required for the generation of an observed magnetic anomaly 1 500 nt at 100 km altitude assuming trm acquisition in a 0 05 mt magnetic field