stacking paleointensity and oxygen isotope data for the last 1 5 myr piso 1500 coupled relative geomagnetic paleointensity rpi and oxygen isotope records are used to construct rpi and oxygen isotope stacks for the last 1 5 myr the coupled correlations are accomplished using the match algorithm lisiecki l e and lisiecki p a 2002 application of dynamic programming to the correlation of paleoclimate records paleoceanography 17 1049 doi 10 1029 2001pa000733 to simultaneously correlate isotope and rpi records the simultaneous match reduces the degree of freedom associated with correlations using rpi or oxygen isotope records alone the overall compatibility of rpi and oxygen isotopes indicates a dominant global but independent component in both signals the local wavelet power spectrum lwps for the rpi stack indicates little significant orbital power although the accompanying oxygen isotope stack has all the lwps characteristics expected of a high resolution oxygen isotope record containing orbital frequencies the piso 1500 stack represents a new stratigraphic template that can be used to correlate among marine sediment records and link them to polar ice cores via variations in cosmogenic nuclide production scaling the stack to values for virtual axial dipole moment vadm indicate maxima at 15 1022 am2 and minima that imply a threshold of 2 5 1022 am2 below which values are associated with either polarity reversals or magnetic excursions

space time distribution patterns of destructive earthquakes in the inner belt of central japan part 3 seismic hazard assessment abstract on the basis of the strike and sense of active faults the inner belt of central japan can be divided into the chubu and kinki districts the chubu district can be subdivided into four blocks by lines linking major nw se trending active faults a number of inner belt earthquakes of magnitudes m 6 4 or greater m japan meteorological agency scale have been documented or recorded since 599 a d whereas most epicenters of these earthquakes were located along lines linking active faults a few occurred in intra block areas in the first paper of this series the analysis of space time distribution patterns of destructive earthquakes revealed seismic cycles which consist of an active period of earthquakes and a quiet period with no activity seismic gaps were also detected in which no earthquakes have occurred during the present active period the second paper demonstrated that the average rates of seismic moment release calculated from the average slip rates of active faults which constitute the major tectonic or block boundary lines are nearly equal to those released by the historic earthquakes on the basis of the results of the two former papers two seismic maps a hazard map and an earthquake potential map of the inner belt of central japan are constructed since the seismic activity along tectonic and block boundary lines is much greater than that of the intra block areas the lines and intra block areas are separately evaluated in these seismic maps the hazard map shows the seismic activity by making use of the average rate of seismic moment release while the average rates of the lines range from 0 010to0 030 10 26 dyne cm y those of the intra blocks have values of less than 0 005 10 26 dyne cm y with one exception since regions of higher moment release rate experienced historic earthquakes with larger maximum magnitude the moment release rate is a good indicator for estimating the maximum magnitude of future earthquakes during the present active period future earthquakes will probably occur along seismic gaps these seismic gaps are illustrated in the earthquake potential map the two seismic maps are useful in reducing earthquake disasters by designing earthquake resistant buildings and structures in the earthquake prone regions of central japan

magnetic petrology of equatorial atlantic sediments electron microscopy results and their implications for environmental magnetic interpretation 1 the magnetic microparticle and nanoparticle inventories of marine sediments from equatorial atlantic sites were investigated by scanning and transmission electron microscopy to classify all present detrital and authigenic magnetic mineral species and to investigate their regional distribution origin transport and preservation this information is used to establish source to sink relations and to constrain environmental magnetic proxy interpretations for this area magnetic extracts were prepared from sediments of three supralysoclinal open ocean gravity cores located at the ceara rise geob 1523 1 3 49 9 n 41 37 3 w the mid atlantic ridge geob 4313 2 4 02 8 n 33 26 3 w and the sierra leone rise geob 2910 1 4 50 7 n 21 03 2 w sediments from two depths corresponding to marine isotope stages 4 and 5 5 were processed this selection represents glacial and interglacial conditions of sedimentation for the western central and eastern equatorial atlantic and avoids interferences from subsurface and anoxic processes crystallographic elemental morphological and granulometric data of more than 2000 magnetic particles were collected by scanning and transmission electron microscopy on basis of these properties nine particle classes could be defined detrital magnetite titanomagnetite fragmental and euhedral titanomagnetite hemoilmentite intergrowths silicates with magnetic inclusions microcrystalline hematite magnetite spherules bacterial magnetite goethite needles and nanoparticle clusters each class can be associated with fluvial eolian subaeric and submarine volcanic biogenic or chemogenic sources large scale sedimentation patterns are delineated as well detrital magnetite is typical of amazon discharge fragmental titanomagnetite is a submarine weathering product of mid ocean ridge basalts and titanomagnetite hemoilmenite intergrowths are common magnetic particles in west african dust this clear regionalization underlines that magnetic petrology is an excellent indicator of source to sink relations hematite encrustations magnetic spherules and nanoparticle clusters were found at all investigated sites while bacterial magnetite and authigenic hematite were only detected at the more oxic western site at the eastern site surface pits and crevices were seen on the crystal faces indicating subtle early diagenetic reductive dissolution it was observed that paleoclimatic signatures of magnetogranulometric parameters such as the ratio of anhysteretic and isothermal remanent magnetizations can be formed either by mixing of multiple sources with separate relatively narrow grain size ranges western site or by variable sorting of a single source with a broad grain size distribution eastern site hematite goethite and possibly ferrihydrite nanoparticles occur in all sediment cores studied and have either high coercive or superparamagnetic properties depending on their partly ultrafine grain sizes these two magnetic fractions are generally discussed as separate fractions but we suggest that they could actually be genetically linked

textural and stable isotopic evidence for the genesis of the tynagh base metal deposit ireland at the tynagh mine county galway four major stages of mineralization can be recognized that span the diagenetic and postlithification history of the host waulsortian limestones 1 growth of colloform and granular pyrite clots during the early diagenesis of the micritic host 2 rapid geopetal precipitation of microcrystalline sphalerite galena barite and dolomite within a dilatant fracture system that developed as a consequence of the forceful injection of metalliferous fluids into the coherent waulsortian carbonate mudbanks adjacent to the tynagh fault 3 veining and replacement of the host and previously precipitated phases by tennantite chalcopyrite bornite arsenopyrite medium to coarsely crystalline galena and coarse sparry barite and 4 finally precipitation of calcite within veinlets and cavities and dolomitization of large bodies of previously unmineralized waulsortian limestones sulfur isotope ratios indicate that contemporaneous lower carboniferous seawater acted as the source of sulfate for precipitation of barite delta 34 s 21 1 to 17 4ppm stage 1 delta 34 s 3 1 to 15 5ppm and stage 2 delta 34 s 4 1 to 26 0ppm sulfides were precipitated by reduced sulfur generated during open system bacterial reduction of this sea water sulfate source isotopically heavier delta 34 s or 0ppm reduced sulfur of deep seated origin was introduced from the fault zone during stage 3 this mixed with bacteriogenic sulfur migrating into the waulsortian bank limestones to precipitate stage 3 sulfides and sulfosalts delta 34 s 11 1 to 23 0ppm mineralized limestones delta 13 c 2 1 to 4 0ppm delta 18 o 17 6 to 27 1ppm ore stage carbonates delta 13 c 2 8 to 3 4ppm delta 18 o 17 1 to 26 9ppm and postore carbonates delta 13 c 4 0 to 2 6ppm delta 18 o 15 9 to 25 8ppm are depleted in the heavier isotopes of carbon and oxygen with respect to unmineralized limestones delta 13 c 3 1 to 4 1ppm delta 18 o 22 2 to 28 1ppm the depletion in 13 c is attributed to the mixing of host derived carbon with bacterially oxidized carbon and during stage 4 deep seated carbon the 18 o depletion of the mineralized host is a consequence of isotopic exchange with the ore fluids an oxygen isotope fractionation temperature of 200 degrees c and a delta 18 o smow value of 10 5 per mil for the coexisting water is obtained from a single stage 3 quartz albite pair collected from the fault zone if these values are accepted the delta 18 o values of stage 3 carbonates can only be interpreted in terms of mixing of this isotopically heavy water introduced from the fault with isotopically lighter water already present or migrating into the bank limestones

palaeoreconstruction of the amazon river freshwater and sediment discharge using sediments recovered at site 942 on the amazon fan a continuous reconstruction of palaeoclimate has been generated for the last 12 000 c 14 yr bp from odp site 942 5 degrees 45 n 49 degrees 6 w at a water depth of 3346 m drilled to the west of the amazon fan records from the site suggest that during the younger dryas the amazon basin was extremely dry and amazon river discharge was low this increased aridity is hypothesised to be due predominantly to reduced precipitation in addition there is evidence for a discharge event at the end of the younger dryas coeval with termination 1b that produced an estimated amazon river outflow equivalent to present day values and an increase in sediments derived from the andes the timing of this event coincident with the warming of the andean ice sheet suggests that it was at least partly driven by meltwater produced by the retreat of andean glaciers but also required an increase in regional rainfall resulting from changes in climate site 942 also demonstrates that the sediment input to the western part of the amazon fan from the river ceased between 9900 and 9500 c 14 yr bp at a time when sea level was 40 50 m below the present level if this value is truly indicative of the sea levels at which the sediment supply to the fan switched off then it is far greater than the 30 m below current sea level suggested previously copyright c 2000 john wiley sons ltd

evidence for multiple paleomagnetic intensity lows between 30 and 50 ka bp from a western equatorial pacific sedimentary sequence abstract a paleomagnetic study was carried out on the radiocarbon dated md97 2134 core located in the western equatorial pacific southern papua new guinea margin rock magnetic investigations revealed changes of the magnetic mineralogy along the hemi pelagic sedimentary sequence but the reconstruction of past direction and relative paleointensity variations of the geomagnetic field remained feasible four successive paleointensity drops are recorded between 30 and 50 ka bp the largest one is associated with an abrupt swing of declination and inclination interpreted as a smoothed signature of the laschamp excursion 41 ka bp the succession of four events of weak intensity between 30 and 50 ka bp introduces a complex behaviour of the geomagnetic field in the time interval spanning over the laschamp and the mono lake excursions

the nature of mineralizing fluids of the kipushi zn cu deposit katanga democratic repubic of congo quantitative fluid inclusion analysis using laser ablation icp ms and bulk crush leach methods fluid inclusions from the epigenetic zn cu deposit of kipushi central african copper belt katanga democratic republic of congo have been subjected to an integrated microthermometric bulk crush leach and laser ablation inductively coupled plasma mass spectrometric la icp ms study to elucidate the physicochemical conditions of ore formation and the origin of the mineralizing fluids the kipushi deposit is hosted in carbonates and partly in siliciclastic rocks that have undergone regional low grade greenschist facies metamorphism and which were strongly deformed during the lufilian orogeny main deformation phase 550 ma investigation of host rock gangue and ore samples enabled reconstruction of the paragenesis of ore deposition the main zn cu ge pb sulfide mineralization was accompanied by three generations of hydrothermal dolomite and a generation of coarse grained quartz primary and pseudosecondary fluid inclusions in these minerals contain predominantly halite saturated aqueous brines 30 43 wt nacl equiv with locally unidentified trapped solids these inclusions mostly decrepitate upon heating before total homogenization which could suggest that they also trapped excess carbonic vapor they show petrographic and microthermometric evidence for postentrapment reequilibration prohibiting their use as accurate geothermometers and geobarometers previous studies on chlorite and sphalerite geothermometry framed the formation temperature of the kipushi cu zn deposit between 290 to 380 c younger fluids are present as secondary inclusions in the gangue minerals and as primary fluid inclusions in sphalerite from a minor secondary mineralization phase these two phase aqueous inclusions have a slightly lower salinity 23 31 wt nacl equiv and have homogenization temperatures ranging from 170 to 80 c in successive fluid inclusion assemblages sporadically some mixed aqueous carbonic and gaseous co2 ch4 inclusions are present but their genetic position is un clear and they are insignificant with regard to the mineralization process as a whole crush leach bulk analysis of the fluid inclusions show that the mineralizing fluids had a molar cl br ratio close to or somewhat higher than the seawater value which rules out a major contribution from bittern brines and suggests that the fluids gained their salinity primarily by the dissolution of evaporites younger fluids that circulated through the deposit after the main phase of ore formation have cl br and na br signatures indicative of a greater involvement of halite dissolution brines values much higher than that of seawater la icp ms analyses of the mineralizing fluids reveal that they have molar li na ca na mg na mn na and sr na in the range of natural high salinity fluids in metamorphic environments worldwide however they have relatively high molar fe na zn na pb na and especially very high ba na ratios their molar k na is also somewhat higher than for other low grade metamorphic fluids but is nevertheless in agreement with the values predicted by the k na geothermometer at the conditions of ore formation this suggests that the major element composition of the fluids was buffered by fluid mineral equilibria their relatively high metal contents ba zn fe and pb suggest that they interacted with and leached these elements from felsic basement rocks at higher temperatures whatever the origin of the fluids their salinity and the metals their uniformly high ba and ore metal content together with the absence of barite and the occurrence of ba silicates at kipushi indicates that sulfide mineralization occurred when the metal bearing fluids encountered a reducing h2s rich reservoir the ubiquitous presence of preexisting metamorphosed carbonic material shungite in the sulfides and host rock and a sulfur isotope signature of the ores in agreement with thermogenic sulfate reduction suggests that this condition was likely created due to the high initial reduced carbon content of the host rocks at kipushi which seems to be exceptional in the copper belt therefore we postulate that a critical factor in the formation of major vein type zn cu mineralization was the presence of a hydrocarbon rich facies of the lower nguba carbonates at kipushi

detransformation of the british geomagnetic secular variation record for holocene times in this note we replot the british post glacial secular variation curve in terms of actual values of declination and inclination rather than the transformed declination and inclination system used in our original paper turner thompson 1981 this should facilitate the comparison of our record with contemporaneous european archaeomagnetic data our composite record was obtained by averaging the dated records from 10 cores of lake sediment the sequence of unit vectors describing the magnetic direction record of each core was rotated so as to place its mean direction the mean over the section of core dated between 0 and 7000 bp the time span of the shortest core at zero transformed declination and inclination dt o it 0 the transformed coordinate frame of each core is thus derived from its mean direction assumed to represent the mean geomagnetic field direction over the 7000 yr period rather than from the core tube and its orientation during coring hence the problem of not knowing the azimuthal orientation and inclination of the corer during core collection is avoided and the 10 records can be averaged in this coordinate system transformed coordinates then provide a convenient generalised method of plotting averaged sediment records however in the archaeomagnetic method sample orientation is straightforward and the results can readily be plotted as absolute declination and inclination values so for consistency when comparing the two we have attempted here to detransform our record the following procedures assumptions and approximations were taken to produce the detransformed magnetograms and bauer type plots of figs 1 and 2 1 amplitude correction although the combination of 10 data sets produces a good estimate of the signature of the geomagnetic variations the following factors contribute to an overall loss of amplitude in both declination and inclination a the quality of magnetic recording varies widely between different sediments depending on the porosity of the sediment the size and shape distributions and the nature of the magnetic carrier verosub 1979 the loch lomond sediments carry a good high amplitude pattern of remanent directions of which the most recent closely follow the london observatory records the much wetter and less compacted sediments of llyn geirionydd on the

variscan veins record of fluid circulation and variscan tectonothermal events in upper palaeozoic limestones of the moravian karst czech republic numerous variscan syntectonic calcite veins cross cut palaeozoic rocks in the moravian karst a structural petrographic and stable isotopic analysis of the calcite veins and a microthermometric study of fluid inclusions in these vein cements have been carried out to determine the origin of the variscan fluids and their migration during burial and deformation the isotopic parameters of white older more deformed and rose younger calcites are 87 sr 86 sr is between 0 7078 and 0 7082 white and 0 7086 rose 18 o is between 17 7 and 26 1 white and between 14 8 and 20 7 smow rose 13 c ranges from 0 1 to 2 5 white and from 0 3 to 1 6 v pdb rose the isotopic signatures point to precipitation in an older fluid system buffered by the host rock white calcites and to an open younger fluid dominated system rose calcites parent fluids h 2 o nacl system had salinities between 0 35 and 17 25 eq wt nacl the pressure corrected and confined homogenization temperatures suggest formation of the calcite veins from a fluid with a temperature between 120 and 170 c a pressure of 300 880 bar at a depth between 2 1 and 3 2 km the fluids were most likely confined to a particular sedimentary bed as a bed scale fluid migration white older calcite veins or later to a pile of palaeozoic sediments as a stratigraphically restricted fluid flow rose younger calcite veins the low temperatures and pressures during precipitation of calcites which took place close to a peak of burial deformation confirm the distal position of the moravian karst region within the variscan orogen

br cl geochemistry of hydrothermal brines associated with proterozoic metasediment hosted copper mineralization at mount isa northern australia abstract instrumental neutron activation analyses inaa of small bulk samples of vein quartz are used to estimate the br cl ratio of saline fluid inclusions associated with late metamorphic copper mineralization in quartz dolomite breccias at mount isa the results are compared with similar data from veins associated with district scale metasomatism in potential copper source rocks near mount isa and with quartz samples from other locations in northern australia which may have trapped fluids approaching the br cl composition of paleoproterozoic halite evaporites br cl ratios in some of the evaporite related samples are similar to present day seawater 0 0035 while others range up to 0 015 all samples from the mount isa copper ores fluids with total salinities mostly between 10 and 25 wt nacl eq have consistently high br cl ratios between 0 008 and 0 018 on average 3 5 times higher than modern seawater fluids associated with district scale alteration of metabasalts up to 30 km away from the deposit have high br cl ratios identical to those of the ore fluids this indicates a common source of the salts and supports a tentative correlation between mine and district scale alteration events and may ultimately help to trace potential fluid flow paths to or from the site of ore deposition the observed fluid compositions are contrary to the low br cl ratios that would be expected from a simple model of ascending fluids derived by prograde metamorphism of salt bearing paleoproterozoic metasediments mass balance calculations based on mine and district scale alteration suggest that the high br cl fluids may have originated above the present level of erosion as basin brines which infiltrated the terrain during the waning stages of regional metamorphism they may have formed in an inferred evaporitic cover sequence of mesoproterozoic age as residual bitterns or by diagenesis and partial dissolution of halite similar to modern br enriched basin brines secular variation in oceanic br cl preferential chlorine removal from evaporite derived metamorphic fluids by fluid rock interaction or an unusually br rich magma source beneath the deposit could provide alternative explanations for the high br cl ratios of the mount isa brines but are considered to be less likely processes in light of the available geologic data

dating recent hawaiian lava flows using paleomagnetic secular variation hawaiian paleomagnetic secular variation sv is defined from samples at 67 sites on lava flows of known age paleomagnetic directions range through 40 of inclination and 30 of declination angular dispersion within sites is commonly dating precision is limited by dispersion of 4 5 among sites of apparently similar age the main dispersion sources are in 14 c dates 3 0 intra flow deformations 2 0 and local magnetic anomalies 1 5 results from 68 sites on undated flows show that 95 of kilauea9s surface is younger than 1 000 yr a hiatus in volcano growth 1 000 1 500 yr ago coincides with the filling of a large caldera averaging of available data yields an sv reference curve which is fairly reliable to 1 500 yr ago contains gaps and ambiguities 1 500 3 000 yr ago and remains highly uncertain 3 000 6 000 yr ago the sv dating method can be precise but is limited by the need for a calibrated sv history it can be a powerful correlation tool even if a history is unavailable

liquefaction and flowage at archaeological sites in the inner belt of central japan tectonic and hazard implications abstract all archaeological data gathered at 55 archaeological sites excavated in the alluvial plains and basins of the inner belt of central japan revealed the occurrence and age of events of liquefaction and flowage the alluvial plains and basins are bounded on one or both sides by active faults representing tectonic or block boundary lines the excavated sites with liquefaction and flowage events identified are found distributed within a 15 km wide zone along the tectonic or block boundary lines of the alluvial plains and basins this suggests that seismic hazards caused by liquefaction and flowage mainly occur within this 15 km wide zones along the tectonic lines sand filled dikes of various shapes were found and are thought to represent evidence of liquefaction and flowage the sand filled dikes can be classified into two main types a lenticular type arrangeden echelon and a cylindrical type opening upward in a fan shape archaeological age estimates indicate that the liquefaction and flowage were induced by earthquakes which occurred during three periods around 1000 b c between 0 and 500 a d and after 1500 a d suggesting that active seismic periods occurred at an interval of approximately 1000 years

block rotation by strike slip faulting structural and paleomagnetic evidence geometric analysis shows that motion of sets of strike slip faults should cause block rotation otherwise the distorted fault domain would not fit with its surrounding the sense of the block rotation depends on the sense of fault slip and the spacing and orientation of the faults all of which can be obtained from structural data the predictions of the geometric model can then be independently tested by paleomagnetic measurements the model was tested in northern israel structural data reveal several domains of contemporaneous right and left lateral strike slip faults paleomagnetic measurements show that in a domain of nnw trending left lateral faults blocks rotated 23 3 8 2 clockwise and in a domain of right lateral faults blocks rotated 22 4 9 0 anticlockwise these results are in agreement with the prediction of the geometric analysis of the structure the combined results of the heterogenous deformation of the area resembles a pure shear which allows n s extension by about 1 3 in other domains rotations of 34 6 9 1 and 53 1 11 0 were found in their original orientation the left and right lateral faults intersected at angles of 60 70 enclosing the principal axis of shortening in accordance with theories of brittle failure as a result of block rotations this angle is now larger and may reach 110 the results demonstrate large block rotations in different senses in domains of strike slip faults the independent structural and paleomagnetic data can be interpreted within the framework of a simple geometric model northern israel is considered to be a good model for this efficient mechanism of intraplate deformation which is expected to occur in similar tectonic settings elsewhere

in situ raman spectroscopic quantification of aqueous sulfate experimental calibration and application to natural fluid inclusions abstract sulfate is an important component of geological fluids which is often encapsulated in fluid inclusions fis analyses of the composition of such fis can provide important information on the origin and properties of the fluids inside however conventional microthermometric analyses are often hampered due to the complex composition of such fluids alternatively in situ raman spectroscopy is a powerful method to determine the aqueous sulfate concentration of fis unfortunately the effect of a common component chloride on the analytical results has not been well addressed yet in addition disagreements also exist in the current spectrum processing method which also prevents the application of this method in various geological cases in this study a series of fused silica capillary capsules fsccs containing aqueous na2so4 0 01 1 5 mol kg and na2so4 nacl mna2so4 0 05 and 0 5 mol kg mnacl 0 1 4 0 mol kg solutions were prepared as standards in situ raman spectra for the stretching vibration of so42 v1 so42 the bending vibration v2 h2o and the stretching vibration vs h2o of water were collected at room temperature results show that for sulfate solutions both v2 h2o and vs h2o bands can be used as internal standards for the determination of aqueous sulfate concentration mso42 the peak area a ratios between v1 so42 and v2 h2o or vs h2o bands increased nearly linearly with mso42 in na2so4 solutions consequently the relationships between mso42 and the spectral parameters i e a v1 so42 a v2 h2o and a v1 so42 a vs h2o were established however the calculated mso42 will be underestimated when applying the above calibration curve to nacl na2so4 solutions using a v2 h2o as an internal reference in this case the influence of chloride on the calculated mso42 will be largely eliminated when using a vs h2o as an internal reference or fitting the vs h2o band with two gaussian components at 3230 cm 1 and 3450 cm 1 and then using the total peak area as internal reference it should be noted that our calibration results allow comparisons across different laboratories because the spectral intensity was corrected to reduce the response function of the spectrometer and the temperature and wavenumber dependence then the a v1 so42 a vs h2o mso42 relationship was applied to natural fis in fluorite from the dalucao hydrothermal ree deposit southwestern china and in halite from the paleogene evaporite in the jianghan basin south china the mso42 in pre ree stage fluorite hosted fis can reach 0 37 mol kg indicating that sulfate are responsible for the hydrothermal transport of ree the mso42 in the halite hosted fis were found to be in close association with the mineral assemblage serving as an indicator for the degree of evaporation or sedimentary facies

contrasting sources for lead in cu polymetallic and zn pb mineralisation in ireland constraints from lead isotopes devonian red bed hosted deposits in sw ireland occur either as low grade stratiform disseminations and minor veinlets with bornite and djurleite or as major quartz veins with copper polymetallic deposits pb isotopic ratios vary according to the style of mineralisation for disseminated sulphides there is a considerable scatter of lead isotope compositions these appear to define a mixing line between a basement source and a more radiogenic component which may have been granite derived detrital minerals in the red beds for minor veinlets there is a more restricted distribution of lead isotopic data which could be interpreted in terms of fluid flow homogenising the wide spread of pb isotope ratios from the disseminated sulphides this is consistent with published sulphur isotope data major quartz veins show a clustered array of pb isotopic ratios and it is suggested that the bulk of the metals were derived after variscan compression from a basement source with a minor contribution from red beds lower carboniferous limestone hosted deposits form three groups cu ag hg as sb u epigenetic vein hosted deposits cu as zn pb ag co ni stratabound deposits and cu as pb ag mo co ni epigenetic vein deposits lead isotope compositions for the stratabound deposits have a very restricted range for each locality and plot close to the same mixing line as the carboniferous zn pb deposits of central ireland it is suggested that the lead in both areas has been derived from a similar basement source the model age of ca 350 10 ma for stratabound mineralisation is close to that of their host rocks lead isotope data for the epigenetic cu as vein deposits suggest a similar source but a younger age of 280 10 ma for mineralisation this 280 10 ma age has important implications for the timing of the variscan orogeny in sw ireland because chalcopyrite tennantite occurs along pressure solution cleavage planes that have been deformed by thrusting the emplacement of the mineralised tectonic ross island sheet west of killarney must post date 280 ma the difference in the ore assemblage between the limestone hosted cu polymetallic deposits of ireland and the penecontemporaneous zn pb deposits of central ireland may be because of differences in the underlying lithology in the sw up to 6 km of red beds underlie the limestone hosted stratabound cu polymetallic deposits whereas in central ireland the zn pb ore bearing carbonate rocks are underlain by lower palaeozoic greywackes with a minimal thickness of late devonian red beds however the isotopic evidence only indicates a major red bed source of metals at ardtully elsewhere unless the metals in the red beds originated from a basement rather than a granite source a significant red bed contribution to the metals seems unlikely an alternative possibility is that copper ores were derived from an extension of the ordovician island arc of se ireland

a late quaternary geomagnetic secular variation record from lake waiau hawaii and the question of the pacific nondipole low a continuous paleomagnetic record for the last 13 000 years was obtained from the sediments of lake waiau located near the summit of mauna kea volcano on the island of hawaii the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the hypothesis that there has been anomalously low geomagnetic sv in the central pacific was tested using angular dispersion analysis the inclination record has a mean value of 27 that is much lower than the 35 predicted by the geocentric axial dipole hypothesis the spectrum obtained from spectral analysis shows major inclination peaks at periodicities of approximately 3600 and 7900 years and major declination peaks at periodicities of approximately 1100 2000 3300 and 7800 years the approximately 8000 and 3500 year periodicities shown in both inclination and declination spectrums may represent the dipole and nondipole variation respectively the approximately 1100 and 2000 year periodicities are probably derived from either the sources that affect declination only or the offsets between the core sections in addition bauer plots of the magnetic vector are dominated by clockwise motion the angular dispersion calculated from lake sediments is 5 9 with respect to the mean virtual geomagnetic pole vgp and 9 1 with respect to the geographic pole both values are much lower than the 13 5 expected from paleosecular variation model g which separates the angular dispersion into components from the dipole and the quadruple families our results support the hypothesis that an anomalously low secular variation is a characteristic feature of the central pacific furthermore this geomagnetic behavior persists on time scales of 104 years regional anomalies in temperature topography or electrical conductivity at the core mantle boundary are inferred to cause the low sv

late metamorphic veins record deep ingression of meteoric water a la icpms fluid inclusion study from the fold and thrust belt of the rhenish massif germany abstract the fluid evolution of late metamorphic quartz vein systems in the fold and thrust belt of the rhenish massif has been studied by microthermometry and la icpms microanalysis the quartz veins are hosted by very low grade organic matter rich metasiltstones and metapelites of the hunsruck nappe complex the veins record two major stages of textural evolution a massive vein filling assemblage with elongate blocky quartz chlorite albite and apatite and a later open space filling assemblage with euhedral crystals of quartz ankerite dolomite and minor calcite and sulfides the euhedral quartz crystals host well preserved fluid inclusion assemblages which made it possible to reconstruct the chemical evolution of the fluid system with time the fluid inclusions are all aqueous two phase with low salinity and three successive fluid generations record a systematic decrease in salinity from 4 7 5 3 to 3 1 3 9 and then to 1 4 1 7 wt eqv nacl the salinity decrease is paralleled by a decrease in homogenization temperatures from 210 225 c to 148 164 c and 124 139 c using la icpms microanalysis of individual fluid inclusions reproducible elemental concentrations of li na k rb cs mg ca ba sr b al as sb s cl and br could be determined the concentrations of the alkali metals and of boron arsenic and antimony are correlated with the fluid salinity element concentrations are highest in the early fluid generation and decrease systematically in the latter two generations the systematic changes in fluid composition salinity homogenization temperature and elemental concentrations are best explained by fluid mixing between a hot metamorphic fluid of moderate salinity that carried elevated concentrations of b as and sb and a cooler dilute fluid that was of meteoric origin the fluid evolution therefore signals deep ingression of meteoric water during late metamorphic exhumation and uplift the molar cl br ratios of the fluid inclusions lie on a linear array that extends from close to seawater to values that are substantially below seawater because evaporitic sources are conspicuously absent in the shallow water marine sequence of the rhenish massif the elevated br concentrations and cl br ratios below seawater are best explained by fluid rock interaction and liberation of br from the organic matter in the metasediments

a sequence of destructive earthquakes and the coupling of fault systems in central japan abstract in the western part of central japan large successive inland earthquakes have occurred causing serious damage the 1891 m 8 0 nobi earthquake was followed by the 1909 m 6 8 anegawa the 1945 m 6 8 mikawa and the 1948 m 7 1 fukui earthquakes the two major fault systems termed the tsurugawan isewan tectonic line titl and the fukui neodani block boundary line fnbb have been identified as lines linking nw se oriented active faults in the study area an examination of the vertical displacement of ground surfaces indicates that tilting of the central part of the fnbb caused by the nobi earthquake begins around the sekigahara fault on the central part of the titl ruptures and vertical displacements can also be found along the ogaki kisozaki fault close to the titl therefore it was concluded that the influence of the nobi earthquake extended to a part of the titl eighteen years after the nobi earthquake the anegawa earthquake occurred along the sekigahara fault these features and the earthquake sequence can be explained by a block rotation model with strike slip faulting the nobi earthquake created en echelon ruptures over an 80 km long line with a left lateral slip of up to 8 m along the neodani fault according to the model this left lateral slip must be accompanied by a clockwise rotation of the block between the fnbb and titl the block rotation should in turn induce a left lateral slip on the titl since the titl exhibits a sharp bend along the sekigahara fault a transtensional region should appear along the fault owing to the left lateral slip of the titl the expected transtensional region is consistent with areas damaged by the anegawa earthquake suggesting that the earthquake occurred in the transtensional regime about 40 years after the anegawa earthquake the mikawa and fukui earthquakes were generated on the southern and northern ends of the fnbb respectively this implies that the fault movement of the nobi and anegawa earthquakes created a concentration of stress at both ends of the fnbb resulting in the mikawa and fukui earthquakes approximately two years prior to the nobi earthquake seismic activity was initiated over a wide zone along the fnbb also notable earthquakes aligned along the titl were observed ten years prior to the anegawa earthquake the onset of seismicity along a fault system can be used in predicting destructive inland earthquakes which eventually occur along the fault

the earthquake deformation cycle at the nankai trough southwest japan geodetic measurements made landward of the nankai trough site of great subduction zone thrust earthquakes in 1854 and 1946 provide a uniquely detailed picture of the strain buildup process supply constraints on the mechanism of strain accumulation and allow for improved estimates of earthquake recurrence provided the two most recent movement cycles are similar the observations dating from about 1890 may be used to reconstruct a single complete deformation cycle coseismic strain release postseismic transients interseismic strain accumulation very complete leveling and tidal gage data indicate that postseismic deformation extends more than 300 km inland from the plate boundary persists for at least 30 years and shows a clear tendency to become longer wavelength with increasing time the transient movements have two timescales the first of about a year or less corresponds to deformation largely uplift concentrated close to the coseismic fault and is most easily explained by aseismic slip or very localized deformation downdip of the earthquake rupture plane the second longer timescale is associated with a diffusion like spread of the deformation further landward an effect qualitatively similar to that first predicted by elsasser to be an expected consequence of faulting in an elastic plate overlying a viscoelastic asthenosphere cumulative uplift since 1890 correlates well with the distribution of uplifted marine terraces although average post 1890 tilt rates exceed late quaternary and holocene averages by at least a factor of three because of the nonlinearity of strain buildup and the significant permanent deformation simple recurrence calculations typically overestimate the true interval between great earthquakes by a factor of 2 to a factor of 3 strict application of the time predictable model assumed correct overcomes these difficulties provided the cumulative transient deformation and the proportion of permanent deformation per cycle can be estimated

global geomagnetic field models for the past 3000 years transient or permanent flux lobes psvmod1 0 is a compilation of globally distributed palaeodirectional data from archaeomagnetic artefacts lava flows and lake sediments at 24 sites evaluated at 100 year intervals from 1000 bc to ad 1800 we estimate uncertainty in these measures of declination and inclination by comparison with predictions from standard historical models in time intervals of overlap and use the 100 year samples and their associated uncertainties to construct a sequence of minimum structure global geomagnetic field models global predictions of radial magnetic field at the coremantle boundary cmb as well as inclination and declination anomalies at the earth9s surface provide an unprecedented view of geomagnetic secular variations over the past 3000 years and demonstrate a consistent evolution of the field with time resolution of the models is poorest in the southern hemisphere where only six of the 24 sites are located several with incomplete temporal coverage low flux regions seen in the historical field near the north pole are poorly resolved but the northern hemisphere flux lobes are clearly visible in the models these lobes are not fixed in position and intensity but they only rarely venture into the pacific hemisphere the pacific region is seen to have experienced significant secular variation a strong negative inclination anomaly in the region like that seen in 0 5 ma models persists from 1000 bc until ad 1000 and then gradually evolves into the smaller positive anomaly seen today on average between 1000 bc and ad 1800 the non axial dipole contribution to the radial magnetic field at the core mantle boundary is largest in the north central pacific and beneath central asia with clear non zonal contributions at the earth9s surface average inclination anomalies are large and negative in the central pacific and most positive slightly to the east of central africa inclination anomalies decrease with increasing latitude average declinations are smallest in equatorial regions again with strong longitudinal variations largest negative departures are centred over australia and eastern asia secular variation at the earth9s surface is quantified by standard deviation of inclination and declination about their average values and at the cmb by standard deviation in radial magnetic field all three show significant geographical variations but appear incompatible with the idea that secular variation in the pacific hemisphere is permanently attenuated by greatly enhanced conductivity in d 00 beneath the region

sub greenschist facies metamorphism from the variscides of sw ireland an early syn extensional peak thermal event illite crystallinity studies on metaclastics from the variscides of sw ireland range in value from 0 18 to 0 25 2 indicating a metamorphic grade in the upper anchizone lower epizone c 275 325 c chlorite geothermometry yields a similar metamorphic temperature range 280 315 c combining these data with known overburden estimates for the area c 5km implies late palaeozoic geothermal gradients in excess of 60 ckm 1 fluid inclusion studies on quartz veins in these metaclastics reveal two vein types characterized by fluid densities of 0 7 0 93 g cm 3 group 1 and 0 9 1 0gcm 3 group 2 respectively this variation in fluid density is thought to be dominantly controlled by temperature with group 1 veins linked to late palaeozoic extension and high geothermal gradients and group 2 veins associated with subsequent variscan deformation and lower temperature conditions

post acadian sediment recycling in the devonian old red sandstone of southern ireland abstract the upper devonian munster basin of southern ireland has traditionally been viewed as a post orogenic molasse deposit that was sourced from the caledonides of central ireland and subsequently deformed by the end carboniferous variscan orogenic event the basin fill is composed of super mature quartz arenite sandstone that clearly represents a second cycle of deposition the source of this detritus is now recognized as lower devonian dingle basin red bed sequences to the north this genetic link is based on the degree of similarity in the detrital mica chemistry in both of these units micas plot in identical fields and define the same trends in addition the two sequences show increased textural and chemical maturity up sequence and define indistinguishable 40 ar 39 ar age ranges for the detrital mica grains partial resetting of the ar ages can be attributed to elevated heat flow in the region caused by munster basin extension and subsequent variscan deformation the combined evidence from southwest ireland therefore points to a caledonian or possibly taconian primary source area that initially shed detritus into the lower devonian dingle basin which was subsequently recycled into the upper devonian munster basin following mid devonian acadian basin inversion

geomagnetic secular variations over the last 6500 years as recorded by sediments from the lakes of south argentina summary regional type curves depicting secular variations in declination and inclination through the last 6700 calendar years constructed for southwestern argentina about 41 s 71 30 w by stacking palaeomagnetic data derived from lake sediment cores are described and analysed the data consist of records from four lakes which have been previously studied el trebol brazo campanario moreno and escondido and are here integrated within lake correlation was based on magnetic susceptibility and intensity of the natural remanent magnetization nrm interlake correlation was derived from declination and inclination patterns and a set of radiocarbon age determinations the secular variation sv of the geomagnetic field was studied using spectral analysis and precession analysis of the magnetic vector the spectrum obtained from spectral analysis of declination d and inclination i at the same time shows major peaks at periodicities of about 3400 1600 and 1200 yr for both parameters in order to test the stability of the periodicities obtained spectral analysis has been applied to every 3500 yr time span at intervals of 500 yr for both records patterns of circularity during the last 6700 yr appear to recur with a near constant interval of about 2000 yr both open and closed loops are associated with clockwise and counter clockwise circularity

geochemistry of tectonically expelled fluids from the northern coast ranges rumsey hills california usa tectonic compression has created abnormally high pressure on deep basinal fluids causing their expulsion from areally exposed upper cretaceous rock along the eastern margin of the california coast ranges the fluids emerge as near neutral perennial sodium chloride springs at high elevations with flow rates as high as 10 l per min higher spring discharges are more common around the exposure of a west vergent fault propagation fold axis spring waters range from 1000 to 27 000 mg l tds the least saline water 18o 7 5 closely represents local meteoric water that mixes with saline fluid 18o 5 3 and forms a slope of 3 5 on a d vs 18o plot a na 125 to 8000 mg l vs cl 150 to 17 000 mg l plot shows a linear dilution trend that extends close to but below the values for modern seawater calcium 75 3000 mg l is considerably enriched relative to seawater and forms a nonlinear trend with chloride in detail the na deficit defined by the difference between the measured na content and the na concentration on a hypothetical seawater dilution line is approximately balanced by the ca excess similarly defined by the seawater dilution line this relationship strongly suggests that the fluid is diluted seawater that is being modified by active albitization of plagioclase at different depths simultaneous b and 18o enrichment of the fluids accompanied by deuterium depletion further suggest that the seawater modification is influenced by clay diagenesis bicarbonate and sio2 concentrations show an inverse correlation with cl with most waters being saturated or slightly oversaturated with calcite and quartz at the discharge temperatures some freshwater springs with near meteoric stable isotope values may represent mixing of young groundwater from perched aquifers but in many cases the freshwater springs emerge along the same structures and have the same perennial nature as the saline fluids and expulsion of an older fresh groundwater component that is under abnormal fluid pressures cannot be ruled out basinal fluids elsewhere commonly show dilution trends with local meteoric water and in the case of the rumsey hills some of the dilute saline waters may indicate deep penetration of meteoric water 1 km in the pleistocene before the latest tectonic uplift geothermometry of the spring waters maximum 90 c suggest an origin from as deep as 4 0 km this depth is consistent with the depth of the core of a fault propagation anticline below the surface of the rumsey hills developed by active internal deformation of an east tapering wedge beneath the southwestern sacramento valley active tectonic compression causes near lithostatic fluid pressures in the shallow subsurface below the rumsey hills and volume strain within the core of the anticline that results in upward expulsion of the saline fluids from the indicated depths

major changes in glacial and holocene terrestrial temperatures and sources of organic carbon recorded in the amazon fan by tetraether lipids the amazon basin is a major component of the global carbon and hydrological cycles a significant natural source of methane and home to remarkable biodiversity and endemism reconstructing past climate changes in the amazon basin is important for a better understanding of the effect of such changes on these critical functions of the basin using a novel biomarker proxy based on the membrane lipids of soil bacteria with a new regional calibration we present a reconstruction of changes in mean annual air temperatures for the amazon catchment during the last 37 kyr b p biomarkers were extracted from ocean drilling program sediment core odp942 recovered from the amazon fan the amazon fan is a major depository for terrestrial sediments with the advantage that the terrestrial material captured reflects a regional integration of the whole river catchment the reconstructed tropical amazonian temperatures were similar to 5 degrees c cooler at the last glacial maximum similar to 21 degrees c compared to modern values similar to 26 degrees c this is in agreement with previous estimates of tropical continental temperatures in the tropical amazon basin and tropical africa during the last glacial maximum moreover we also illustrate how the soil bacterial membrane lipid record reveals major changes in basin dynamics and sediment provenance during the glacial holocene transition impacting the biomarker reconstructions from similar to 11 kyr onward

full vector paleomagnetic secular variation records from latest quaternary sediments of lake malawi 10 0 s 34 3 e abstract we have conducted a paleomagnetic study of late quaternary sediments from lake malawi east africa in order to develop a high resolution record of paleomagnetic secular variation psv this study has recovered psv records from two cores 3p 6p in northern lake malawi 10 0 s 34 3 e the psv appears to be recorded in fine grained detrital magnetite titanomagnetite grains detailed af demagnetization of the natural remanence nrm shows that a distinctive characteristic remanence chrm is demagnetized from 20 to 80 mt which decreases simply toward the origin the resulting directional psv records for 3p and 6p are easily correlatable with 29 distinct inclination features and 29 declination features the statistical character of the psv in both cores is consistent with holocene psv noted at other holocene equatorial sites radiocarbon dating of the cores is based on 18 independent radiocarbon dates and four dated stratigraphic horizons that can be correlated into each core the final directional psv time series cover the last 24 000 years with an average sediment accumulation rate of 30 cm kyr we have also developed a relative paleointensity estimate for these psv records based on normalizing the nrm after 20 mt af demagnetization by the sirm after 20 mt af demagnetization changing sedimentation patterns complicate any attempt to develop a single paleointensity record for the entire core lengths we have developed a relative paleointensity record for the last 6000 years that has 14 correlatable features including 5 notable peaks in intensity three of these peaks are synchronous with paleointensity highs farther north in se europe sw asia egypt but two of the peaks are at times of low paleointensity farther north we interpret this to indicate that lake malawi 10 s is at least partly under the influence of a different flux regeneration region of the outer core dynamo a relative paleointensity record was also developed for 11 000 24 000 ybp the general pattern appears to be consistent with other published records but our confidence in the correlations is more limited

vitrinite reflectance data from the kinsale harbour old head of kinsale area southern ireland and its bearing on the interpretation of the munster basin vitrinite reflectance of the upper devonian carboniferous succession in the kinsale harbour old head of kinsale area ranges from 4 06 5 21 m and 6 21 7 82 max which is indicative of meta anthracite coal rank no correlation is apparent between vitrinite reflectance and stratigraphic position through c 2 km of section suggesting that near maximum temperatures were maintained until after variscan folding low reflectance values of 0 62 and 0 30 0 35 m at the local base of the jurassic succession in the north celtic sea basin well 48 30 1 and onshore at cloyne respectively indicate a major discontinuity in the maturation profile in the region comparison with high reflectance gradients from upper palaeozoic successions in the halen and turnhout boreholes in belgium and the munsterland no 1 borehole in west germany suggests that a thick 5 7 km cover of pre permo tnassic rocks must once have been present in the munster basin to account for the high maturation levels observed whether the cover was emplaced by silesian sedimentation or by late palaeozoic thrusting is unclear

structural evolution of the irish variscides the effects of the variscan orogeny on the upper palaeozoic succession are recognizable throughout central and southern ireland the deformation can be zoned using structural styles and trends which illustrate a northward decrease in deformation intensity coupled with increasing control by pre variscan structures in the basement the most intense deformation occurs to the south of the dingle dungarvan line where shortening approaches 50 as a result of layer parallel shortening followed by buckling and finally thrusting the deformation is considered to have developed above a shallow dipping sole thrust which has been located offshore by the swat seismic reflection profiles cross faults which are common throughout the orogen resulted from n s shear couples this is consistent with their origin as accommodation structures due to differential shortening along strike the original shape of the munster basin has exerted a control on the distribution and overall facing of the major structures the sole thrust extends to the north of the dingle dungarvan line and the structural zonation of the orogen is due to variations in the stratigraphic level of this thrust the leinster massif is considered to be essentially autochthonous slip on the sole thrust decays towards the massif which acted as a rigid passive block and was partially responsible for the arcuate trend of the orogen

space time distribution patterns of destructive earthquakes in the inner belt of central japan activity intervals and locations of earthquakes abstract based on a block structure model of the inner belt of central japan an examination was conducted of the space time distribution patterns of destructiv magnitudes m 6 4 or greater m japan meteorological agency scale the distribution patterns revealed a periodicity in earthquake activit seismic gaps major nw se trending left lateral active faults divide the inner belt of central japan into four blocks 20 80 km wide the occurrenc a d with m 6 4 which have caused significant damage were documented in the inner belt of central japan the epicenters of these earthquakes close to the block boundaries using the relationship between the magnitude of earthquakes which occurred in the japanese islands and the active length of faults that generated them movement is calculated for each historical earthquake space time distributions of earthquakes were obtained from the calculated lengths the latitud of generation when an active period begins a portion or segment of the block boundary creates an earthquake which in turn appears on the ground surf active period ends when the block boundary generates earthquakes over the entire length of the block boundary without overlapping five seismic gaps with fault lengths of 20 km or longer can be found in the inner belt of central japan it is predicted that the gaps will generate ea magnitudes of 7 0 these data are of significance for estimating a regional earthquake risk over central japan in the design of large earthquake resist the time sequences of earthquakes on the block boundaries reveal a similar tendency with alternating active periods with seismic activity and quiet pe activity the inner belt of central japan is now in the last stage of an active period the next active period is predicted to occur around 2500 a d

measurement of the degree of smoothing in sediment paleomagnetic secular variation records an example from late quaternary deep sea sediments of the bermuda rise western north atlantic ocean abstract replicate paleomagnetic secular variation psv records for the last 15 000 yr have been recovered from two deep sea sediment gravity cores on the bermuda rise western north atlantic ocean the records have been correlated using several different parameters and dated by correlation to a nearby piston core which has a high resolution 14 c chronology the psv records are systematically subdued with respect to the expected local magnetic field variability during the holocene when sedimentation rates were about 10 cm kyr during the late pleistocene when sedimentation rates were a factor of 2 3 higher the psv variability was significantly larger we attribute this to smoothing of the psv records by a depositional post depositional remanence drm pdrm acquisition process with a 10 20 cm lock in interval the degree of psv smoothing was evaluated by comparing the vgp angular dispersion and vector spectral content of the bermuda rise cores with high resolution psv records from north america and great britain these results suggest a 50 reduction in the drm pdrm recording of vector variability during the holocene on the bermuda rise with most of the psv reduction occurring for features of less than 2000 yr in duration we can reproduce the subdued psv pattern with a mathematical model that simulates the site drm pdrm remanence acquisition process finally the replicate gravity cores document that psv records may be reproducible on a local scale even though they only retain a low pass filtered record of true magnetic field variability

stress state evolution of the brittle upper crust during compressional tectonic inversion as defined by successive quartz vein types high ardenne slate belt germany abstract in the frontal part of the rhenohercynian fold and thrust belt high ardenne slate belt germany two successive types of quartz veins oriented normal and parallel to bedding respectively are interpreted to reflect the early variscan compressional tectonic inversion of the ardenne eifel sedimentary basin fracturing and sealing occurred in lower devonian siliciclastic multilayers under very low grade metamorphic conditions in a brittle upper crust a geometrical and microthermometric analysis of these veins has helped to constrain the kinematic and pressure temperature conditions of both vein types allowing the reconstruction of the stress state evolution in a basin during tectonic inversion it is demonstrated that bedding normal extension veins which developed under low differential stresses and repeatedly opened and sealed crack seal under near lithostatic fluid pressures reflect the latest stage of an extensional stress regime bedding parallel veins which developed at differential stresses that were still low enough to allow the formation of extension veins cross cut the bedding normal veins and preceded the regional fold and cleavage development these veins show a pronounced bedding parallel fabric reflecting bedding normal uplift and bedding parallel shearing under lithostatic to supra lithostatic fluid pressures during the early stages of a compressional stress regime this kinematic history corroborates that fluid overpressures are easy to maintain during compressional tectonic inversion at the onset of orogeny

remobilization and mineralization of selenium tellurium in metamorphosed red beds evidence from the munster basin ireland abstract selenium and tellurium are vital elements for the ongoing development of carbon free energy generation but are only recovered in small volumes as by products of base and precious metal processing security of supply of these commodities is of high importance as their demand is forecast to increase in the near future thus more research is required on the varying mineralization systems where their occurrence and behavior are poorly understood such as sedimentary basins and metasedimentary terranes the munster basin of southern ireland is a good study area for sedimentary se te in such environments as it has a regionally high soil selenium anomaly and is characterized by devonian terrestrial red beds which were metamorphosed during the hercynian variscan orogeny the area also contains ore grade biogenic sediment hosted copper and remobilized vein hosted copper sulfides which are prospective for chalcophile selenium and tellurium quartz vein hosted se te mineralization was identified across the munster basin accompanied by trace gold silver mercury accessory phases new sulfur isotope data reinforces the model of sulfur and selenium remobilized from a biogenic red bed source which reflects a wider association of selenium deposits with oxidizing environments the co occurrence of tellurium mineralization suggests that it too may be concentrated in oxidizing environments associated traces of gold add to a growing body of evidence that gold is also transported and precipitated in oxidizing conditions in continental basins

the vein hosted copper deposits of the allihies mining area sw ireland a new structural and chronological evaluation this paper presents new data for historical vein hosted copper sulfide deposits in the late paleozoic munster and south munster basins of sw ireland detailed mapping 3d modelling fluid inclusion microthermometry and geochronology from the allihies area of the beara peninsula have led to a new interpretation of the timing and development of ore mineralization macro and microstructural studies reveal that the ore bearing mainly east west striking quartz veins are directly related to early extensional basinal normal faults molybdenite re os dating of the main stage cu lode yields ages from 367 3 5 5 to 366 4 1 9 ma this early vein system experienced subsequent late carboniferous variscan deformation including cleavage development sinistral sw ne strike slip faulting cataclastic deformation and recrystallization the new timing of cu mineralization in sw ireland has major implications for its relationship to the base metal deposits of the irish midlands supplementary material a video file showing a 3d model of the major lodes and the underground workings at mountain mine and excel spreadsheets showing fluid inclusion measurements and sample locations of the allihies copper mining district are available at https doi org 10 6084 m9 figshare c 4875015

a fluid inclusion study of fluid pressure and salinity variations in the footwall of the rector branch thrust north carolina u s a abstract last melting and homogenization temperatures of fluid inclusions from plastically deformed bedding parallel quartz veins in the footwall of the rector branch thrust north carolina were studied as a function of distance from the thrust fluid inclusions and microstructures in mylonitic rocks within the thrust zone were also examined fluid inclusions in quartz veins which display evidence for intracrystalline plasticity e g subgrain polygonization occur along subgrain boundaries and have higher homogenization temperatures tn and a wider range 120 320 c compared to less deformed samples maximum th values which approach the temperature of deformation 300 20 c apparently reflect leakage of inclusions along subgrain boundaries minimum th values 120 160 c on the other hand record near lithostatic conditions 2 6 kb at 300 c maximum last melting temperatures tm increase from 20 to 4 c with decreasing distance to the thrust corresponding to a decrease in salinity of the fluid from 23 to 3 wt nacl equivalent the decrease in salinity towards the fault is interpreted as due to infiltration of the fault at depth to approximately 10 km by surface derived waters during periods of fault zone dilatancy inclusions along healed microcracks in quartz from the fault zone display higher salinity 17 26 wt nacl equiv and are interpreted to reflect enhanced fluid rock interaction in the fault zone due to hydration reactions the fluid pressure and salinity variations are consistent with a combined dilatancy hydraulic fracturing model for the rector branch thrust previously documented bulk rock volume losses for this fault zone are inferred to have been produced by the fluxing of the fault zone with undersaturated surface derived fluids

geochemistry of mineral waters and associated gases of the sakhalin island far east of russia abstract isotopic and chemical data on the mineral water mud volcanoes fluid and associated gases from the biggest russian island sakhalin together with previous stable isotope data d 18 o dd 13 c allow elucidation of their origin and general evolution the water fluid circulation is mainly related to marine environment inducing three distinct types na hco 3 cl alkali carbonate groundwaters na cl hco 3 highly evolved saline and na cl mature groundwaters indicating different evolution chemical evolution of groundwater on sakhalin island demonstrated cation exchange and salinization as dominant evolutionary pathways isotopic composition of groundwaters varies from meteoric to metamorphic waters these metamorphic waters consist of water hydration from the clay and seawater are traced in fluids of yuzhno sakhalin mud volcano despite modification by mixing with meteoric waters and water rock interaction processes fault systems that define the areas of highly mineralized water circulation appear to play a major role in the co 2 migration to the surface and ch 4 generation the 13 c co 2 values have pointed that gas phase in high pco 2 waters mostly consists of mantle derived co 2 the carbon isotope signature of methane 13 c ch 4 and d ch 4 indicates its distinct origin which is specified by tectonics methane manifestation in the south of the sakhalin island is mainly related to thermogenic reservoirs as they are more often dislocate by tectonics and crossed by active and permeable faults the sources of biogenous methane in the north of sakhalin island is related to younger and shallower reservoirs and less affected by tectonic processes the determinations of 222 rn have allowed observing that maximal radon flux is associated with high pco 2 waters

the structural evolution of the western irish variscides an example of obstacle tectonics abstract detailed mesostructural and strain analysis investigations across the killarney mallow fault i e the traditional variscan front in southwest ireland reveal that this structural line separates two distinct tectonic regimes north of the killarney mallow fault bulk shortening orthogonal to orogenic strike is estimated to be 12 all of which is accounted for by late stage buckling microscopic strain analysis reveals that there is only local development of a tectonic fabric south of the front bulk shortening is 40 due to combined layer parallel shortening lps buckling and faulting variscan deformation is presented as being essentially coaxial the regional finite strain pattern outlined above is thought to be primarily controlled by the combined effect of a buried basement obstacle in eastern iveragh and increased sedimentary pile thickness at the western end of the orogen

a comparison of holocene paleomagnetic secular variation records from north america the comparison of nine holocene 0 12 000 years b p records of paleomagnetic field secular variation psv obtained from across north america indicates that distinctive field features in inclination and declination often can be traced for more than 4000 km without significant change in pattern independent age determinations corroborate these correlations while also suggesting that westward or eastward drift is not significant on the other hand northward drift may be a significant process at least between 1500 and 5500 years b p several methods of analyzing the overall psv character point to circularity vector looping as a preferred means of defining coherent space time vector variations which are termed waveforms a few distinctive waveforms each discernible for about 1400 years dominate psv across north america during the holocene 4 5 loops and 2 loops being associated with clockwise and counterclockwise circularity respectively the clockwise loops appear to be periodic occurring every 2400 years and most likely result from the recurrence of a distinctive regional dynamo source in the outer core the pattern of circularity noted in north america during the last 3000 years correlates in time with similar circularity changes seen globally this may indicate that there is some degree of coupling between different regional dynamo sources within the outer core the fact that some north american waveforms are almost identical to waveforms observed elsewhere around the world at different times may indicate that similar distinctive regional dynamo sources recur randomly throughout the outer core

the time averaged paleomagnetic field 0 5 ma persistent departures from the geocentric axial dipole field model of the time averaged paleomagnetic field over the past 5 myr have been analyzed using oceanic data from deep sea cores and continental data from igneous rocks and sediments the data set comprises the equivalent of 9490 spot readings of the field 5831 normal and 3659 reverse from 930 groups of data variations in declination anomalies between groups of data strongly suggest the existence of second order tectonic effects small rotations that make it difficult if not impossible to identify any nonzonal terms that might exist inclination anomalies have therefore been modeled in terms of low degree zonal harmonics the calculated inclination anomalies within 10 latitude bands are widely scattered for both oceanic and continental data and do not appear to have been drawn from distributions with common means we attribute this large scatter to previously undetected or uncorrected second order tectonic effects in the continental data or in the oceanic data to small departures from the vertical in deep sea cores if it is assumed that these effects are random between groups of data and without a systematic bias they can be averaged out to a large extent if there are sufficient numbers of groups within each latitude band this method also has the major advantage that it maximizes time averaging of the field when this is done an acceptable fit to the inclination anomaly data is found using a zonal harmonic model although the point estimates for the reverse polarity zonal quadrupole term are consistently larger than those for the normal polarity zonal quadrupole term the difference is not significant and is likely due to contamination effects this finding is true for a combination of all the data or for separate combinations of continental igneous rocks and ocean sediments this conclusion differs from all previous analyses the major differences occur in model estimates of the zonal octupole term the estimates varying widely depending on the particular data combination we show that false octupole terms can be introduced by several factors including inclination errors in sediments and lavas the use of unit vectors in the analyses and incomplete magnetic cleaning particularly of reversely magnetized rocks thus we cannot impute a geomagnetic significance to the estimates of a zonal octupole term we suggest that the best estimates for the zonal quadrupole g2 g20 g10 are obtained from the combined brunhes age igneous rocks and oceanic normal data 0 033 0 019 and for the combined matuyama age igneous rocks and oceanic reverse data 0 042 0 022 when these two sets are combined the overall best estimate of g2 is 0 038 0 012

holocene paleomagnetic secular variation records from the western equatorial pacific ocean abstract we have carried out detailed rock magnetic and paleomagnetic studies on a suite of four deep sea sediment cores from indonesia and the philippine islands which form a transect from 6 3 n to 10 6 s the cores have average sediment accumulation rates of 35 65 cm kyr that all yield high resolution paleomagnetic secular variation psv records the psv records contain 44 correlatable inclination and declination features that corroborate the individual psv records and indicate that they are all continuous with no significant stratigraphic gaps thirty four ams radiocarbon dates provide a high resolution time stratigraphic framework for the psv records which extend from 0 18 000 yrs bp these are the first high resolution holocene psv records ever recovered from anywhere on earth within 17 of the equator almost 1 3 of the earth s surface area statistical analysis of the holocene psv records indicates that they have i anomalies of 5 to 9 consistent with 5 ma averaged results the strong similarity in i anomaly pattern of holocene and longer term 5 ma averaged psv data suggest that the dynamo process causing the anomaly is largely described by holocene psv by contrast the holocene psv records have vgp angular dispersions that are significantly lower than 5 ma averaged psv data yet significantly higher than psv data averaged over only the last few thousand years this difference indicates that whatever dynamo process causes the overall directional variability of the earth s magnetic field is not totally described by recent last few thousand year psv or even by late quaternary last 20 000 yrs psv

pore fluid and seismogenic characteristics of fault rock at depth on the wasatch fault utah fluid inclusions and structural fabric in fault rock in the exhumed footwall of the wasatch fault allow measurement of fluid pressure temperature and composition and estimation of rheological characteristics of fault behavior hydrothermally altered and deformed oligocene quartz monzonite of the little cottonwood stock forms a partially preserved footwall carapace at the southern end of the salt lake segment of the wasatch normal fault zone cataclasite and phyllonite contain two syndeformational alteration mineral assemblages that formed during progressive faulting and displacement of the footwall an early epidote chlorite sericite magnetite alteration assemblage developed in phyllonite and cataclasite and a later laumontite prehnite hematite alteration assemblage developed during cataclasis fluid inclusions associated with the formation of alteration minerals are preserved in healed fractures in quartz grains fluid inclusions that record the transition temperature from quasi plastic flow to frictional deformation are associated with hydrothermal alteration to chlorite epidote and sericite and were trapped at minimum temperatures of 223 c 353 c and minimum fluid pressures of 1150 2800 bars the fluids average 13 mol co2 and 8 2 wt nacl a radiometric age of hydrothermal sericite suggests that the age of the alteration is 17 6 0 7 m y if maximum fluid pressure is near lithostatic the minimum depth of formation of the alteration was 11 km at 337 c consistent with a thermal gradient of 30 c km the ratio of pore fluid pressure to lithostatic pressure varied from 0 52 to nearly 1 0 and indicates that effective normal stress on the fault at these depths may have approached zero structural fabrics and fluid inclusion characteristics are used to estimate seismogenic characteristics of the fault cleavage lineation and s c bands in the phyllonite indicate that deformation at temperatures above 350 c and depths greater than 11 km was dominated by aseismic creep unstable fracture propagation in cataclasite developed during seismic slip at shallower levels the downdip seismogenic length of the salt lake segment is estimated as 16 km using a fault zone dip of 45 and a minimum depth of 11 km for the quasi plastic frictional transition the segment strike length is 35 km and the seismogenic area is about 600 km2 compatible with generation of m 7 0 earthquakes

the distribution of fe and mn between chlorite and fluid evidence from fluid inclusions abstract the fe mn ratio of fluid inclusions from low grade metamorphic quartz veins has been analyzed by an improved crush leach method when compared with fe and mn in coexisting vein chlorites exchange between fluid and chlorite is shown to vary with the redox state of the wall rocks but is independent of the salinity of the fluid agreement between our results and theoretical predictions of fe mn partitioning between fluid and chlorite are good for veins from relatively oxidized rocks but vein fluids from reduced hosts are enriched in fe

holocene geomagnetic secular variation records from north eastern australian lake sediments summary secular variation records have been obtained from cores from lakes barrine and eacham two north eastern australian volcanic crater lakes the results from several cores have been stratigraphically correlated and then stacked and smoothed the chronology provided by radiocarbon dating indicates that the lake eacham sequence spans the last 5700 calendar years the time scale for the lake barrine record is less weil constrained but it

source or sink an assessment of the role of the old red sandstone in the genesis of the irish zn pb deposits the zn pb ba deposits of central ireland are hosted by lower carboniferous waulsortian limestone and navan group carbonate sediments the deposits are located near the margins of subbasins in close association with extensional faults the source of metals and the flow pathways utilized by the hydrothermal fluids responsible for ore genesis have long been a matter of conjecture the devonian to lower carboniferous old red sandstone has been suggested as a possible regional aquifer and metals source therefore a petrographic and lead isotope study of this unit was conducted to assess its putative role in ore formation hydrothermally unaltered old red sandstone has 206pb 204pb 207pb 204pb and 208pb 204pb ratios ranging from 18 71 to 22 45 15 52 to 15 86 and 38 57 to 42 71 respectively the sedimentological characteristics of the red beds coupled with results of isotopic modeling support the conclusion that the lead isotope signature of the unit is predominantly controlled by radiogenic caledonian granite detritus that has an avalonian like character the modeled lead isotope composition of the old red sandstone at the time of the lower carboniferous ore forming event is too radiogenic for it to have acted as the main source of lead for the irish ore field examination of drill core outcrop and underground exposures reveals that hydrothermal alteration within the old red sandstone forms a halo around faults indicating that fluid flow in the unit was predominantly structurally focused these hydrothermally altered sediments have 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 18 21 to 21 77 15 54 to 15 91 and 38 02 to 41 57 respectively unlike the unaltered sediments several altered samples have lead isotope compositions similar to galena from the lower carboniferous deposits petrographic examination reveals that these samples contain trace hydrothermal sulfides that are probably responsible for the orelike signature therefore it appears that at least locally the old red sandstone functioned as a sink for lead during the lower carboniferous mineralizing event the conclusions from this study eliminate the old red sandstone as the main source of lead in the ore field and suggest that deposit lead is derived primarily from lower paleozoic rocks precambrian crystalline basement in view of these results regional gravity driven fluid flow models calling upon an old red sandstone focused flow regime and metals source can be discounted rather deep circulation of fluids through the fractured basement underlying central ireland plays an integral role in the evolution of the ore forming system

space time correlations between inland earthquakes in central japan and great offshore earthquakes along the nankai trough implication for destructive earthquake prediction abstract based on the tectonic framework of central japan including the surrounding submarine areas the space time relationship between destructive inland earthquakes of magnitudesm 6 4 or greater and great offshore earthquakes along the nankai trough was examined from east to west four tectonic lines are defined as lines linking active faults the itoigawa shizuoka tectonic line istl the tsurugawan isewan tectonic line titl the hanaore kongo fault line hkfl and the arima takatsuki tectonic line attl the titl divides central japan into the chubu and kinki districts and probably extends southward to the nankai trough the chubu district is subdivided into four blocks by boundary lines linking nw se trending active faults having left lateral strike slip in the kinki district n s trending active reverse steep dip faults are dominant in the triangular region north of the median tectonic line between the titl and hkfl forming a basin and range province starting from 1586 a d a seismic space time sequence of high seismic activity in the chubu district in which earthquake occurrence migrates from the eastern to western tectonic lines of central japan was identified the sequence also revealed that inland earthquakes preceded great offshore earthquakes which occurred along the nankai trough it was also found that a destructive earthquake tends to occur on the hkfl within 30 years after the occurrence on the titl and that the western nankai trough generated great earthquakes ofm 7 0 at intervals ranging from 8 to 49 years after the hkfl earthquakes if the eastern nankai trough is coupled with the western nankai trough a forthcoming greater earthquake measuringm 8 5 may be expected since such great earthquakes are always accompanied by large tsunamis much attention should be focussed on possible tsunami disasters along the pacific coast of central japan based on its tectonic structure a tectonic model of central japan is proposed the seismic space time sequence which attempts to explain the cause of the sequential earthquake generation is also discussed

late quaternary paleomagnetic secular variation recorded in deep sea sediments from the demerara rise equatorial west atlantic ocean abstract we have carried out a paleomagnetic rock magnetic study of two gravity cores and two multicores from the demerara rise 8 n adjacent to ne south america the magnetic measurements indicate that there is a stable natural remanent magnetization nrm carried primarily by detrital magnetite titanomagnetite that preserves the local pattern of paleomagnetic secular variation psv the two gravity cores have consistent patterns of directional variability the rock magnetic intensities in both gravity cores vary by less than a factor of three relative paleointensity estimates have been derived by normalizing the nrm to chi arm and sirm both gravity cores show the same pattern of relative paleointensity variability 27 calibrated radiocarbon dates from our studied gravity cores and one additional piston core huang et al 2014 have been used to build chronologies for the two gravity cores core 25ggc has bulk sedimentation rates varying from 18 to 22 cm ky and contains a psv record for the last 19 ka core 9ggc has bulk sedimentation rates of 9 17 cm ky and contains a psv record for the last 28 ka there are no other published good quality well dated full vector psv records within 4000 km of the sites a region which constitutes almost 20 of the earth s surface area our relative paleointensity records are consistent with other global records under the assumption of field intensity being largely a global scale process we have compared our directional psv data statistically with eight other good quality well dated low latitude psv records our statistical analysis shows that our demerara rise directional psv records are consistent with those other studies and that the late quaternary equatorial field variability is significantly lower than much longer duration 780 ka to 5 ma variability

rapid dewatering of the crust deduced from ages of mesothermal gold deposits the large scale migration of fluids through the continental crust has been well documented but there is no consensus regarding the timing of fluid migration relative to orogenic episodes or rates of crustal dewatering1 here we present40ar 39ar dates for muscovites from quartz veins along a major shear zone in southeast alaska which show that the veins were emplaced in the early eocene during the late stages of orogenic deformation hydrother mal activity took place for only about 1 myr and along a distance of at least 200 km the fluids were generated by metamorphic reactions in subducted crust along the north american plate margin and were apparently trapped in the crust by the low permeabilities accompanying a convergent tectonic regime until 56 myr ago the rapid dewatering event coincided with a change in plate motion at 56 55 myr which caused a shift from convergent to partly transcurrent tectonics we suggest that this change in tectonic regime led to increased crustal permeabilities and hence the possibility of large scale fluid migration

evolution of fluid driving forces and composition within collisional orogens subaerial collisional mountain belts have a predictable asymmetric two sided wedge geometry the major driving forces for crustal fluid flow in this framework arc thermal and topographic gradients it is possible to predict both a time averaged fluid state and the evolution of the fluid regime during orogenesis with three distinct fluid flow regimes the outboard toe where material is incorporated into the orogen a transitional zone of concentrated deformation and a zone of rapid exhumation along the inboard slope adjacent to the indentor as rocks move into the outboard wedge relatively low temperature compaction and head driven fluid flow dominates mid crustal material undergoes disequilibrium dehydration as rock fluid packets move into the transition zone producing a dominantly aqueous metamorphic fluid in the inboard region rapid uplift produces geothermal gradients in excess of 80 c km which encourage vigorous free convection advecting fluids evolve through immiscibility towards increasing co2 content during uplift of the rock fluid packets mixing of thermally driven and head driven fluids occurs at depths of 5 10 km the southern alps of new zealand the european alps and the himalaya represent variants of this orogenic hydrothermal system

paleomagnetic secular variation and relative paleointensity during the holocene in south china huguangyan maar lake revisited the scarcity of reliable paleomagnetic secular variation psv records from east asia especially from low latitude regions impedes better understanding of global psv mechanisms here we report on a radiocarbon dated holocene psv record from a composite 6 7 m long core collected from the high sedimentation rate huguangyan maar lake hml in subtropical tropical south china rock magnetic results demonstrate that the natural remanent magnetization resides in single domain magnetite alternating field demagnetization experiments at 1 cm spacing on u channel samples reveal six distinct inclination highs at 7 500 bce 5 100 bce 4 600 bce 3 600 3 400 bce 1 600 1 200 bce and 600 800 ce three inclination lows at 4 800 bce 600 300 bce and 1 000 1 300 ce and three eastward declination trends at 3 600 3 200 bce 2 600 2 400 bce and 400 bce to 200 ce the similarity between the hml psv record and other independently dated records from east asia and geomagnetic field models corroborates the robustness of our age model and holocene psv record strikingly centennial to millennial scale psv features of the hml are comparable within age uncertainties with other holocene records from europe north america and canada suggesting that such directional patterns are likely to be hemispheric in scale although relative paleointensity data of hml are affected by environmental factors e g organic matter diagenesis the record still provides a regionally important new psv reference curve whose conspicuous features may serve as stratigraphic markers for east asian paleorecords

deep structure of southern ireland a new geological synthesis using birps deep reflection profiling the birps deep seismic reflection data of wire west of ireland 1 1b from galway bay to the celtic sea are integrated with geological and other geophysical data to produce a synthesis of the fundamental tectonic character of the crust in and around southern ireland the iapetus suture forms a zone of north dipping reflectors which projects up between the shannon estuary and the dingle peninsula and is overlain by a late caledonian reflector with a shallow south dip across the iapetus suture zone the crust thickens southward and the lower crust becomes less reflective it is proposed that the lower palaeozoic volcano sedimentary rocks which form the leinster massif extend southwestward beneath the variscan province and at least 30 km offshore to the wire lines we argue that the weak south dipping reflectors in the upper and middle crust south of the iapetus suture represent an early caledonian fault system linked to a mid crustal detachment which formed during the south dipping subduction event recorded onshore by the ordovician volcano sedimentary successions these faults were selectively reactivated causing the predominant ene trend of younger regional tectonic features in and around southern ireland the three onshore upper palaeozoic basins close east of the wire lines we point out that the variscan front is only a map line across the british isles with no consistent tectonic character thus the south dipping reflector below the north margin of the north celtic sea basin on swat 4 generally referred to as the variscan front is correlated by us with the northern boundary of the rosslare complex thus making it the northern tectonic boundary of the caledonian basement block known as the rosslare monian terrane furthermore the north dipping south irish sea lineament on winch 4 can be correlated with the menai straits lineament and could thus be the southern boundary of this terrane the south dipping reflector on swat 2 also previously called the variscan front is correlated with the johnston benton fault system in southwest wales

the secular variation of earth s magnetic field models of the magnetic field at the core mantle boundary at selected epochs from 1715 0 to 1980 0 reveal novel features in the field at the core these suggest that the flow of core fluid is coupled to the mantle and that magnetic diffusion is significant

constraints on the origins of fluids forming irish zn pb ba deposits evidence from the composition of fluid inclusions the numerous zn pb deposits in the irish midlands together with the quantity and grade of the ore make this a world class base metal province despite significant exploration and research there is still disagreement on the origin of the mineralizing fluids in this study we have measured the composition of fluid inclusions using a crush leach technique these data constrain the possible sources of the fluids both during and after mineralization chloride and br concentrations indicate that the main ore fluid at tynagh and silvermines was seawater that had evaporated until the salinity was between 12 and 18 wt percent however na k and li data show that water rock interactions have resulted in the depletion of na and the enrichment of k and li relative to the concentrations expected for evaporated seawater the fluids that produced postore dolomitization were also derived from seawater that had evaporated to higher salinities and had precipitated halite the concentrations of na k and li are what would be expected for seawater at this degree of evaporation and show that these fluids did not interact with the same lithologies as the ore fluids the major change to their fluid composition was exchange of mg for ca during dolomitization we suggest that the ore fluids could only have reached their high salinity by evaporation of seawater on the extensive shallow water shelf regions that existed over much of the irish midlands

lake sediment record of the geomagnetic secular variation in britain during holocene times summary a palaeomagnetic record of the geomagnetic secular variation during the last 10000 years has been obtained from 10 cores of sediment from loch lomond scotland lake windermere north england and llyn geirionydd north wales a time scale is provided by 30 radiocarbon age determinations and pollen analyses on several of the cores the main swings and much fine detail of both declination and inclination records repeat well between cores and between lakes and the overall record is much more detailed than previous european records the new record shows that neither declination nor inclination swings have been periodic over the past 10000 years but that the main swings have become progressively shorter in duration during that time each swing is characterized by fine detail which enables use of the record as a secondary method of dating other european sediments the motion of the geomagnetic vector has been predominantly clockwise throughout the time period spanned but confirms a period of anticlockwise motion from 1100 to 600 bp first discovered by british archaeomagnetic investigations the record agrees with british and czechoslovakian archaeomagnetic records but not with japanese archaeomagnetic or north american lake sediment records this suggests that the secular changes are controlled by local growing and decaying drifting sources rather than by wobbling of the main geomagnetic dipole

a nested fault system with block rotation caused by left lateral faulting the neodani and atera faults central japan abstract a detailed study of outcrops existing around the neodani and atera faults which are large scale left lateral faults oriented nw se in central japan revealed they were accompanied by two distinct fault systems of different scale and slip sense intermediate scale parallel right lateral faults and small scale parallel left lateral kink bands or faults a nested fault model with different geometric scales is proposed to explain the hierarchical occurrence of the fault systems in this model the secondary fault system is contained within the primary fault system as a mirror image of it left lateral movement of the atera or neodani fault induces right lateral movement of intermediate scale faults and results in counterclockwise rotation of the blocks between the faults this right lateral movement in turn induces left lateral movement of small scale faults or kink bands which causes clockwise rotation of the small blocks between them since the angle of the counterclockwise rotation of the primary fault systems is the same as that of the clockwise rotation of the secondary fault system these rotations cancel each other while the large scale fault movements cause block rotation the small blocks eventually show no rotation

the use of a combined structural stable isotope and fluid inclusion study to constrain the kinematic history at the northern variscan front zone bettrechies northern france abstract a detailed structural stable isotope and fluid inclusion study of distinct vein generations has been performed in a kilometre scale syncline to correlate the temperature pressure conditions of vein formation with specific deformation episodes the structural relationship of the veins with cleavage folds faults and with one another allows the identification of pre syn and post variscan carbonate vein generations the stable isotope composition of the vein calcites and dolomites is very similar to that of the surrounding limestones and dolostones respectively this indicates that the cements were precipitated from fluids buffered by the host rock and implies that the temperature pressure characteristics of the fluids reflect the thermal history of the deformation history within the syncline microthermometric data of primary fluid inclusions were used to estimate the temperature pressure conditions at precipitation time and thus of the deformation pressure corrected trapping temperatures for the veins show a temperature evolution from pre variscan 310 c to variscan 260 200 c and post variscan 75 c this evolution indicates that the syncline developed not at a specific depth but rather as an active progressive deformation process during transport along the northern variscan thrust front

holocene sedimentation on the distal amazon fan demerara abyssal plain abstract we have studied the rock magnetic characteristics of 31 multicores and 7 gravity cores from deep sea sediments of the distal amazon fan and demerara abyssal plain this study has permitted us to delineate the space time pattern of holocene physical sedimentation along the northeastern margin of south america associated with the amazon river sediment plume the rock magnetic variability is correlatable over the entire study region this degree of correlation has permitted us to develop a composite picture of holocene rock magnetic and overall physical clastic sedimentation 26 radiocarbon dates have been combined with the rock magnetic correlations to provide a composite holocene chronostratigraphy for that variability we have built isopach maps of overall sedimentation for three windows in the holocene 3000 4500 and 7000 calendar years bp the overall sedimentation in the center of our region is 5 cm kyr but sedimentation rates are faster closer to the coastline and associated with the distal clastic flux from the amazon plume there is a secondary high in sediment accumulation under the north brazil current retroflection our maps suggest that the retroflection has been active at the millennial scale for at least the last 7000 years we estimate that the mid holocene 4 5 9000 calendar years bp pattern of sedimentation was distinctly different from that of the last few thousand years the clastic sediments were 25 reduced in concentration with the biogenic sediments similarly increased by 25 they were finer grained and significantly less rich in ferric iron phases hematite goethite we think these three covarying clastic parameters are due to an interval of reduced clastic flux from the amazon river plume with a reduced proportion of amazon basin sediments as opposed to andes derived sediments we hypothesize this was due to significantly drier amazon basin environmental conditions during that time interval

formation of fossil hydrothermal chimneys and mounds from silvermines ireland sulphur isotope analyses reveal that the fossil hydrothermal pyrite mound and tubes at silvermines were produced by the reaction of hydrothermal fe ii with bacteriogenically reduced sulphur species 34s range 18 4 to 42 5 this took place in a brine pool dominated by hyper saline carboniferous seawater this is in contrast to their modern but considerably larger morphological counterparts forming by direct precipitation of hydrothermal sulphides on the east pacific rise at 21 n

seismotectonics of the median tectonic line in southwest japan implications for coupling among major fault systems the relationship between the slip activity and occurrence of historical earthquakes along the median tectonic line mtl together with that of the fault systems extending eastward has been examined the mtl is divided into three segments each containing diagnostic active faults no historical earthquakes have been recorded along the central segment although the segment has faster quaternary slip rates compared with the other segments that have generated historical earthquakes this discrepancy between earthquake generation and slip rate can be explained by a microplate model of southwest japan the microplate model also provides spatial and temporal coupling of slip on adjacent fault systems in the context of this model slip on adjacent faults reduces the normal stress on the mtl historical data and paleoseismic evidence indicate that slip on this segment occurs without significant strong ground motion we interpret this as indicating anomalously slow seismic slip or aseismic slip slip on the central segment of the mtl creates transpressional regions at the eastern and western segments where historical earthquakes were recorded alternatively the earthquakes at the eastern and western segments were triggered and concentrated shear stress at the edge of the segments resulted in postseismic slip along the central segment the sequence of historical events suggests that the mtl characteristically does not produce great earthquakes the microplate model also provides a tectonic framework for coupling of events among the mtl the adjacent fault systems and the nankai trough

decreased influence of antarctic intermediate water in the tropical atlantic during north atlantic cold events abstract antarctic intermediate water aaiw is a key player in the global ocean circulation contributing to the upper limb of the atlantic meridional overturning circulation amoc and influencing interhemispheric heat exchange and the distribution of salinity nutrients and carbon however the deglacial history of aaiw flow into the north atlantic is controversial here we present a multicore top neodymium isotope calibration which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition e nd values in their authigenic coatings we then present the first foraminifera based reconstruction of e nd from three sediment cores retrieved from within modern aaiw in the western tropical north atlantic our records reveal similar glacial and interglacial contributions of aaiw and a pronounced decrease in the aaiw fraction during north atlantic deglacial cold episodes heinrich stadial 1 hs1 and younger dryas yd our results suggest two separate phases of reduced fraction of aaiw in the tropical atlantic during hs1 with a greater reduction during early hs1 if a reduction in aaiw fraction also reflects reduced amoc strength this finding may explain why in many regions there are two phases of hydrologic change within hs1 and why atmospheric co2 rose more rapidly during early than late hs1 our result suggesting less flow of aaiw into the atlantic during north atlantic cold events contrasts with evidence from the pacific where intermediate depth e nd records may indicate increased flow of aaiw into the pacific during the these same events antiphased e nd behavior between intermediate depths of the north atlantic and pacific implies that the flow of aaiw into atlantic and pacific seesawed during the last deglaciation

interaction of the san jacinto and san andreas fault zones southern california triggered earthquake migration and coupled recurrence intervals two lines of evidence suggest that large earthquakes that occur on either the san jacinto fault zone sjfz or the san andreas fault zone safz may be triggered by large earthquakes that occur on the other first the great 1857 fort tejon earthquake in the safz seems to have triggered a progressive sequence of earthquakes in the sjfz these earthquakes occurred at times and locations that are consistent with triggering by a strain pulse that propagated southeastward at a rate of 1 7 kilometers per year along the sjfz after the 1857 earthquake second the similarity in average recurrence intervals in the sjfz about 150 years and in the mojave segment of the safz 132 years suggests that large earthquakes in the northern sjfz may stimulate the relatively frequent major earthquakes on the mojave segment analysis of historic earthquake occurrence in the sjfz suggests little likelihood of extended quiescence between earthquake sequences

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

upper crustal fluid migration an example from the variscides of sw ireland the density and composition of single generation fluids in quartz veins from two similar host lithologies located either side of the irish variscan front were investigated using fluid inclusion microthermometry and crush leach analysis the front marks the northern boundary of a distinctive cleavage developed under sub greenschist facies conditions and coincides with the margin of a fault controlled inverted half graben the late devonian munster basin trapped fluids in variscan veins north of this basin have medium salinities 4 14 wt nacl eq and densities generally compatible with the expected p t conditions of deformation in the area fluids in veins south of the half graben margin can be grouped into those in a syn compressional veins with moderate salinities 8 16 wt and b late stage veins associated with post orogenic extension which have trapped high salinity fluids 22 27 wt fluid densities for both vein types are broadly compatible with estimated p t conditions of both trapping events crush leach analyses reveal that all the fluids analysed have br cl ratios close to smow variations in i cl ratios and cation chemistry indicate significant water rock interaction for medium salinity fluids on either side of the front the marked internal consistency in br cl ratios from northern and southern fluids coupled with the broad ranges of cation to chloride ratios suggests that an early homogenous marine brine was subsequently modified by differing migration histories during the late palaeozoic tectono sedimentary evolution of the area it is contended that on a megascopic scale gravity driven fluid flow controlled by megascopic fold geometries was the dominant mechanism of fluid migration associated with the buckling phase of the orogen while expulsion of supra hydrostatically pressurised fluids is associated with late stage orogenic extension

a comparison of acoustic and rock magnetic properties of equatorial atlantic deep sea sediments paleoceanographic implications compressional wave p wave velocities and magnetic susceptibilities were measured on gravity ggc and piston cores pc and ocean drilling program odp leg 108 advanced piston cores apc from the equatorial atlantic to test our hypothesis that climatically driven changes in terrigenous and biogenic fluxes and in carbonate dissolution control the interrelationships between the two signals in pleistocene sediments deposited above the calcium compensation depth ccd we observed changes in p wave velocity and magnetic susceptibility that are 1 inversely correlated and 2 coherent to changes in glacial interglacial climate glacials show low p wave velocities and relatively high magnetic susceptibilities in contrast interglacials show high p wave velocities and relatively low magnetic susceptibilities these temporal changes in p wave velocity and magnetic susceptibility reflect the climatic history recorded in the sediments and are related to 1 the production of biogenic carbonate mainly planktonic foraminifera and 2 the terrigenous sediment supply that contains magnetic minerals below the ccd this pattern disappears and consistently low p wave velocities and distinctly higher magnetic susceptibilities prevail the distinct decrease of large p wave velocity fluctuations is due to the dissolution of carbonate sediments which cause a distinct decrease in sand grain sizes and a consistently low carbonate content 10 dilution of magnetic material by the carbonate fraction is minor and the high magnetic susceptibility values and the relatively high amplitude variations in magnetic susceptibility are due to changes in the magnetic mineral concentration of the terrigenous non carbonate fraction in early pliocene sediments we also observed covarying velocity and magnetic susceptibility signals that may reflect a predominatly terrigenous control on sedimentation our preliminary results demonstrate that a combined use of non destructive measurements of acoustic and rock magnetic signals provides a potential paleoceanographic tool for characterizing 1 glacial interglacial pelagic sedimentation 2 pelagic sedimentation above the ccd 3 increases in carbonate dissolution and 4 areas below the ccd furthermore rock magnetic fluctuations in sediments below the ccd may provide an important stratigraphic tool for the deep carbonate free basins of the world s oceans

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

the interplay between fluids folds and thrusts during the deformation of a sedimentary succession abstract in this paper field evidence is presented to support the idea that fluid pressures in excess of lithostatic pressure were operating during the initiation and reactivation of large thrusts and folds in the wenlock shales of llangollen north wales it is also argued that as major thrusts are reactivated and as major folds amplify into finite structures they in turn exert an influence on the subsequent migration and concentration of fluids within the deforming sedimentary succession

chemistry source and behavior of fluids involved in alpine thrusting of the central pyrenees quartz veins occupying extensional fractures that formed relatively late in the alpine thrusting history of the pyrenees contain abundant inclusions of hypersaline brines small amounts of bitumen also occur a range of brine compositions is apparent from the freezing behavior of fluid inclusions from different samples with large variations in na ca ratio but many individual samples contain only one brine composition all brine types display a bimodal distribution of homogenization temperature which is interpreted as the result of fluctuation in fluid pressure from a maximum value equal to lithostatic at 5 7 km depth and around 270 c to a value up to 700 bars lower this is ascribed to dilatancy pumping chemical analyses of brines leached from two samples yields balanced analyses for 14 elements both analyses appear to represent sedimentary formation waters and are closely analogous to oil field brines a basement origin is precluded by the presence of bitumens and the low k ca ratios differences between the analyses probably reflect different source bed mineralogy including the presence or absence of dolomite but triassic red beds are likely to be a major source the occurrence of these brines in the fault planes provides constraints on both the sources and movement of the fluids involved in thrusting significant infiltration of either surface waters or metamorphic water of dehydration can be ruled out because of the high salinities typically 20 25 wt dissolved salts hence although permeability was locally high due to fracturing around the faults fluids were pumped into these fractures from sedimentary formations adjacent to the fault individual fluid pathways were short lived relative to the duration of the deformation event so that different fluids were pumped into the faults at different times in response to local fault propagation

geomagnetic secular variations 0 14 000 yr bp as recorded by lake sediments from argentina summary palaeomagnetic and sedimentological studies carried out on the bottom sediments from three lakes in western argentina are described at the within lake level five lithological units could be broadly defined and were useful as a general guide in defining detailed correlations based on the magnetic susceptibility k and intensity of remanent magnetization j in one of the three lakes el trebol it was possible to derive a closer lithologically based correlation and this was consistent with that based on the magnetic parameters inter lake correlation was derived from the inclination and declination patterns considered as a pair also taking account of a set of radiocarbon age determinations to remove any ambiguities all the individual measurements were transformed to a time scale prior to stacking to produce type curves the records for laguna el trebol and brazo de campanario extend back to about 6000 radiocarbon years before present while lago morenito provides a record extending back to about 14000 radiocarbon years before present the records exhibit variations with similar overall characteristics to those previously obtained for europe and north america but there appears to be no correlation with the northern hemisphere patterns on a swing to swing basis both clockwise and anticlockwise precession of the geomagnetic vector is evident both from spectral analysis of declination inclination pairs and vgp paths

sulfate brines in fluid inclusions of hydrothermal veins compositional determinations in the system h2o na ca cl so4 sulfate is among the most abundant ions in seawater and sulfate bearing brines are common in sedimentary basins among other environments however the properties of sulfate bearing fluid inclusions during microthermometry are as yet poorly constrained restricting the interpretation of fluid inclusion compositions where sulfate is a major ion the schwarzwald mining district on the eastern shoulder of the upper rhinegraben rift is an example of a geologic system characterized by sulfate bearing brines and constraints on the anion abundances chloride versus sulfate would be desirable as a potential means to differentiate fluid sources in hydrothermal veins in these regions here we use the pitzer type formalism to calculate equilibrium conditions along the vapor saturated liquidus of the system h2o na ca cl so4 and construct phase diagrams displaying the predicted phase equilibria we combine these predicted phase relations with microthermometric and crush leach analyses of fluid inclusions from veins in the schwarzwald and upper rhinegraben to estimate the compositions of these brines in terms of bulk salinity as well as cation and anion loads sodium versus calcium and chloride versus sulfate these data indicate systematic differences in fluid compositions recorded by fluid inclusions and demonstrate the application of detailed low temperature microthermometry to determine compositions of sulfate bearing brines thus these data provide new constraints on fluid sources and paleo hydrology of these classic basin hosted ore forming systems moreover the phase diagrams presented herein can be applied directly to compositional determinations in other systems