esr dating of fault movement using various defect centres in quartz the case in the western south fossa magna japan the dates of movements of the itoigawa shizuoka tectonic line i s t l and minobu fault in the western south fossa magna have been obtained by esr dating measurements were made on various lattice defects of the ohc ge al and e centres in quartz grains of fault clay and quartz veins intruded at the time of movement all the dates obtained from these centres in quartz grains from two localities of the i s t l and iwo localities of the minobu fault fall in the range of 0 30 0 55 ma this suggests that all the centres were annihilated completely and that the obtained age can be admitted as the actual data of the latest fault movement meanwhile esr dates of quartz vein and fault clay in other localities locations 3 6 7 are divided into 0 30 0 55 ma and 1 5 2 0 ma which suggest incomplete resetting the dates of 0 30 0 55 and 1 5 2 0 ma might correspond to the clino unconformities observed in plio pleistocene sequence of this region

short paper low grade metamorphism of the welsh basin lower palaeozoic succession an example of diastathermal metamorphism the lower palaeozoic succession of the welsh basin has suffered the effects of low grade metamorphism which shows features that do not accord with classical models of regional or burial metamorphism textural evidence demonstrates the development of greenschist facies metamorphism prior to deformation and cleavage development while mineralogical characters indicate a low pressure facies series in order to accommodate these features it is suggested that the area has suffered diastathermal metamorphism in which an enhanced thermal flux develops early in the tectonic cycle in response to an extensional setting temperatures remained relatively high during final closure associated with deformation of the basin sediments and consequent cleavage development such a model adequately resolves previously conflicting interpretations of burial and deformation related metamorphism

esr studies for absolute dating of fault movements the principle of absolute dating of fault movements is based on the initialization or resetting of some clock system by faulting in the case of esr dating heating is more effective in resetting esr signals than fracturing according to a computer simulation of resetting by shear heating during faulting the esr signals can never be completely reset at depths of less than 100 200 m below the surface of the earth therefore esr samples must be collected from depth by coring or tunnelling or from outcrop with consideration of the rate of exhumation of the fault outcrop in general unpaired electrons trapped at lattice defects in crystals can diffuse much more easily than atoms hence samples for other dating methods which are based on the diffusion of atoms should be collected at even greater depth on the other hand if no esr signal is observed from unfractured quartz in the wall rocks one may directly determine the age of the fault movement using esr signals in the fractured quartz whose precursors were formed by faulting the age obtained t should then satisfy the following relationship t b t t e where t b and t e are the ages of the beginning and end of the fault movements and it may show the time of a fault movement

basement controls on sediment hosted zn pb deposits a pb isotope study of carboniferous mineralization in central ireland lead isotope ratios of galenas from carbonate hosted zn pb or ba or cd or ag deposits in central ireland are homogeneous within individual deposits but vary between deposits the variation correlates directly with geographic position defining isoplumbs and not with style of mineralization age of host rock or structural or physico chemical factors the least radiogenic pb occurs in the northwest and the most radiogenic in the southeast this pattern elegantly reflects irish pre caledonian basement geology lewisian gneisses in the northwest and late proterozoic upper crustal rocks in the southeast that the northwestern end member of the irish pb mixing trend is ultimately lewisian is demonstrated by the concordance of the irish pb isotope trend with the trends defined in proterozoic to tertiary rocks and ores of scotland which contain pb of demonstrably lewisian derivation although geologic relations and pb isotope ratios unambiguously implicate basement in the ore forming process we are unable to discriminate between lewisian gneisses themselves and detritus derived from lewisian rocks in the caledonian metamorphic complex as the direct source of pb comparison of the irish deposits with mcarthur river and mississippi valley deposits leads us to conclude that style of mineralization syngenetic syndiagenetic epigenetic is not a fundamental aspect of sediment hosted zn pb deposits but is a reflection of local stress regimes and physico chemical conditions the fundamental link between the types of sediment hosted zn pb deposits may be the onset of a condition such as extension or compression that provides a mechanism for driving fluids in extensional regimes seismic pumping processes may channel fluids toward the surface or into fractures or favorable pore spaces resulting in a wide variety of styles of mineralization the lack of dilatency in sediments in compressional regimes however may inhibit surface exhalation and favors epigenetic styles of mineralization

esr isochron dating of the nojima fault gouge southwest japan using icp ms an approach to fluid flow events in the fault zone

intra arc deformations with vertical rotation axes the case of the pre middle miocene terranes of southwest japan abstract various folds bends with vertical or subvertical rotation axes occur in the pre middle miocene terranes of southwest japan they are variable in shape conical folds accordion folds megakink bands and so on and some are accompanied with strike slip faults they range from several kilometers to more than 100 km in width and some of their hinge surfaces are traceable more than a few tens of kilometers their shapes which resemble megakink band or buckle folds indicate that they were produced by horizontal compression with vertical or subvertical 2 axes in a shallow level of the crust they were superimposed on the pre middle miocene fold and thrust structures or nappe melange complexes and are regarded to have been formed mostly during the middle miocene contemporaneous with the clockwise rotation of southwest japan related to the fan shaped opening of the sea of japan geometrical analysis clearly suggests that the drifting southwest japan behaved as a non rigid body and the formation of these structures resulted from the differential rotation of the terranes and the collision of the izu bonin arc with eastern southwest japan

lead and sulfur isotope microstratigraphy in galena crystals from mississippi valley type deposits the development of an analytical procedure for lead and sulfur isotope analysis by secondary ion microprobe mass spectrometry allowed us to provide in situ isotopic microanalyses of galena crystals we performed analyses across the growth zones of two crystals of galena from mississippi valley type ore deposits with a spatial resolution of 50 mu m and a spacing of 250 mu m these analyses show frequent variations for both lead and sulfur isotope compositions which occurred during the time of the crystal growth we can demonstrate that for both elements these variations involved changes in the sources of the brines which formed the ore deposits the comparison of lead and sulfur isotope behavior suggests that for the picher deposit lead and sulfur originated from common sources whereas for the buick mine deposit lead and sulfur had separate sources the two galenas exhibit rapid and frequent changes in isotopic composition this suggests numerous and discontinuous inputs of lead and sulfur to the ore deposits this model agrees well with a physical model for mississippi valley type deposits proposed by cathles and smith 1983 the isotopically different sources were probably different sedimentary layers and perhaps basement rocks in the same basin whose formation waters were channeled in preferred water conduits to the ore deposit location during the subsidence of the basin allowing mixing between the different sources to occur during the brines travel

criteria for complete zeroing of esr signals during faulting of the san gabriel fault zone southern california in using electron spin resonance esr to date the time of the last movement on a fault it is essential to demonstrate that the esr signal was fully zeroed at the time of faulting if the signal was not completely reset then the esr age obtained will be too great we have refined the criteria for complete zeroing of esr signals at the time of fault movement samples of fault rocks were collected from surface outcrops of the san gabriel fault zone in the little tujunga region near los angeles southern california using quartz grains of 250 m the estimated ages for either e or ohc signals in all fault rock samples analyzed decrease with grain size down to a plateau value for particles smaller than some critical grain size in some cases the al signal in the smallest grains yields the same age as the plateau age of either the e or ohc signal plateau ages of reactivated younger gouges were indeed smaller than those of the older fault host rocks within the plateau region different grain size fractions show different radiation sensitivity for a single esr signal but all converge to the same de equivalent dose value this indicates that the complete resetting probably occurred during fault movement the depth of fault rocks during fault movement can be estimated from uplift rates and the esr ages the estimated uplift rates was about 0 3 cm yr for the holocene and 0 03 cm yr for the late pleistocene menges et al 1979 the estimated plateau esr ages ranged from 1200 to 135 ka the depths at the time of the last fault movements in the little tujunga region were in the range of 68 360 m the measured maximum horizontal stresses at this depth in southern california range from 5 to 10 mpa for a depth of 70 m the calculated vertical stress is 1 16 mpa and measured maximum horizontal stress is about 5 mpa the angle between the strike of the san gabriel fault and the direction of maximum horizontal stress is about 85 using above values calculated shear stress on the fault is about 0 67 mpa and the normal stress to the fault is about 5 mpa if we assume mean displacements of 4 cm m 4 to 1 m m 7 these conditions were sufficient to reset esr signals in quartz below critical grain size at the time of fault activity

structural analysis of coseismic normal fault zones of the 2011 mw 6 6 fukushima earthquake northeast japan the 2011 m w 6 6 fukushima earthquake occurred in iwaki city 250 km southwest of the epicenter of the 2011 m w 9 0 tohoku japan earthquake and produced two subparallel 15 23 km long surface rupture zones with distinct displacements along two pre existing normal faults the shionohira and yunodake faults which strike north northwest south southeast and northwest southeast both dipping southwest respectively field investigations and structural analysis of the coseismic shear zones developed within the shionohira and yunodake fault zones reveal that 1 the coseismic shear zones consist of a fault core that includes a narrow fault gouge zone of 10 cm in width generally 1 5 cm a fault breccia zone of 50 cm in width and a damage zone of 5 50 m in width that is composed of cataclastic rocks fractures and subsidiary faults 2 the foliations characterized by s c fabrics developed in the shear zones indicate a dominantly normal fault slip sense consistent with that observed along the coseismic surface ruptures and 3 veinlet cataclastic rocks composed of unconsolidated fault gouges and fine grained materials occur as simple discrete veinlets and multiple cross cutting interconnected networks of veinlets these newly documented structural characteristics for two coseismic fault shear zones and associated cataclastic rocks indicate that the locations of coseismic slip zones associated with the 2011 fukushima earthquake were controlled by pre existing fault shear zones central to the shionohira and yunodake faults which have repeatedly moved as seismogenic normal faults since the timing of formation of associated cataclastic rocks our results demonstrate that the structural analyses of coseismic shear fault zones provide a powerful tool to study the nature and active faulting history of seismological faults

the genesis of sediment hosted exhalative zinc lead deposits large sediment hosted lead zinc deposits like mount isa mcarthur river navan rammelsberg and sullivan form a distinctive group characterised by stratiform syngenetic sulphide ores that formed in local basins on the sea floor as a result of protracted hydrothermal activity accompanying continental rifting generally there is a development of a sedimentary pre ore phase mineralization often featuring manganese followed by zinc lead iron and chert lower main phase zinc lead lenses are usually almost devoid of copper but cu tenors increase toward the middle or top of the ore sequences hanging wall trace element haloes are common these characteristics are accounted for by deriving the ore solutions from subsurface convective circulation of modified highly saline seawater the circulation is initiated during rifting and driven by a high geothermal gradient as a result of continued extensional strain and cooling of the rock column the brittle to ductile transition zone is depressed and the circulation penetrates to greater depth with time of the ore metals the downward penetrating convection fluids first leach and transport zinc and lead but with increasing temperature are later able to leach and transport some copper unless convective circulation ceases the metal sequence generally reverses as the cooling phase sets in the minimum distance separating major coeval orebodies of this type is 18 km which is a function of the size of the convective systems

lead isotope zoning in galena an ion microprobe study of a galena crystal from the buick mine southeast missouri ion microprobe techniques have been used to determine the variations of pb isotope ratios within a single octahedral crystal of galena from the buick mine southeast missouri the crystal shows uniform concentric zonation of pb isotope ratios with a total variation of approximately 3 percent in 208 pb 206 pb and approximately 4 percent in 207 pb 206 pb and with the crystal margin being less radiogenic lower 206 204 than the core the range in the observed 208 pb 206 pb ratio is larger than that observed previously for bulk galena analyses from throughout the mine and is almost as large as the total variation reported for the whole southeast missouri ore district the ion probe results are demonstrated to be accurate to 0 1 0 2 percent by comparison with conventional mass spectrometric analyses performed on microsamples of the same crystal the ion probe technique holds promise for establishing a pb isotope chronostratigraphy for the ore bearing solutions which will be useful in delineating temporal and spatial aspects of the fluid circulation patterns

metallogenic evolution in wales constraints from lead isotope modelling galena has been collected from different styles of mineralization throughout wales galenas from the ordovician volcanogenic mineralization at parys mountain north wales give highly variable lead isotope ratios which could have been produced either by a two stage history or by the mineralizing fluids interacting and mixing with radiogenic lead derived from uranium rich upper crust the variation in the lead isotopic ratios of galena from veins cutting lower palaeozoic sediments is considered to be due to separate periods of mineralization during the early devonian and early carboniferous the most likely source for this mineralization is the thick sequence of lower palaeozoic basinal mudstones both the disseminated galena in mesozoic sedimentary rocks and galena from veins within the underlying carboniferous limestone give triassic and jurassic model lead ages which agree with mineralization ages deduced from geological considerations it is suggested that the source for this lead mineralization is the underlying carboniferous shales these and other galenas from wales have significantly different isotope ratios to those from the irish carbonate hosted ore deposits which would indicate that the mineralizing fluids had either different sources or evolutionary histories

reconstruction of hydrological changes and response to effective moisture variations from north central usa lake sediments abstract ratios of the stable isotopes of oxygen and carbon in benthic ostracodes and marl from cores taken from two lakes in north central minnesota reflect holocene hydrological and vegetation changes oxygen isotopes show that williams and shingobee lakes located in the same watershed but with different positions along a hydrologic gradient were connected before 9 8 ka as part of a larger lake lake willobee from 9 8 7 7 ka the level of lake willobee fell as a result of glacial retreat and increasing evaporation leaving small separated basins further decreases in lake level after 7 7 ka due to increasing aridity triggered the inflow of ground water in williams lake at about 7 ka and in shingobee lake at about 5 ka after 4 ka effective moisture increased the carbon isotope record reflects changes in vegetation with higher 13 c values during the prairie period 7 7 4 ka and lower values during preceding and succeeding forest periods the differences in timing of hydrological events show that the biotic and geochemical response of the lakes to climate variations is mediated by their hydrologic systems the response may be strongly spatially heterogeneous and can result in contrasting information from geochemical and biotic proxies from the same paleorecord

current challenges to esr dating abstract electron spin resonance dating is applicable to a wide range of materials found at quaternary sites and which can generally be assured to exhibit zero signals at the time to be dated t 0 local inhomogeneity in external dose rates may contribute to dispersion in apparent dates but average dates may still be good estimates of site ages testing of u uptake models by u series measurements shows that both early and continuous uptake can occur possibly even in the same site problems of signal lifetime determination and diagenesis are reviewed

esr dating of the subsidiary faults in the yangsan fault system korea abstract the yangsan fault system is located near heavy industrial complexes and nuclear power plants in the korean peninsula we carried out esr dating of fault rocks from the wonwonsa and ihwa faults two subsidiary faults of the yangsan fault system esr ages are divided into three groups in order of decreasing confidence multiple plateau esr ages single plateau esr ages and maximum esr ages the wonwonsa fault was reactivated at least 4 times and the ihwa fault at least 2 times within the quaternary period long term cyclic fault activity of some subsidiary faults of the yangsan fault system occurred in the pleistocene and suggests the possibility of continued activity on this fault system

esr dating of fault gouge the effect of grain size abstract esr signals of quartz grains in fault gouge have been partially or completely reset by movements on the fault which allows the dating of the last fault movement in order to better understand the zeroing process we have studied the variation in esr signal ad and age in various grain sizes since it can be expected that larger grains will be less affected by stress than smaller grains we propose that a plateau of constant lower age for the smallest grains indicates total resetting this is confirmed in gouge from a fault in california only such samples should be used for dating

dating of a volcanic rock by electron spin resonance the age of a volcanic rock has been determined by esr dating using the ge center in quartz the total dose of natural radiation and the age obtained from the ge center are 460 krad and 2 07 0 50 ma respectively and those from the unidentified defect at g 2 011 are 484 krad and 2 16 0 21 ma respectively these dates agree well with the age of 2 0 0 5 ma determined by the fission track method high stress or temperature destroy these accumulated defects but in the same time produce a lot of new diamagnetic precursors which enable us to observe the clear esr signal

increase of radiation sensitivity of esr centres by faulting and criteria of fault dates abstract the esr spectra and ages of the fractured rocks along the itoigawa shizuoka tectonic line a major fault in japan were measured the esr signal intensities tend to become larger with decreasing distance from the fault boundary because the radiation sensitivities of the esr centres have increased by faulting according to fracturing and heating experiments when the radiation sensitivities of esr centres have visibly increased the signals may have been almost completely reset by faulting as a result of the increase of radiation sensitivity the error range of the td values for incompletely reset esr signals is comparatively large whereas it is smaller in the case of completely reset signals therefore by assessing the error range of td values we can determine whether esr signals were completely reset at the time of faulting

basement geology and tectonic evolution of ireland as deduced from pb isotopes in ireland lead isotope data collected on carboniferous hosted zn pb deposits can and has been interpreted to indicate that lead and other metals were derived from the underlying basement rocks in order to test this hypothesis whole rock lead isotope measurements were made on greywackes from the longford down inlier which represent the along strike continuation of the northern part of the caledonian basement underlying the base metal deposits the lead isotope data define a linear array on a 207 pb 204 pb versus 206 pb 204 pb plot with end points at 207 pb 204 pb 15 542 206 pb 204 pb 18 456 and 207 pb 204 pb 15 461 206 pb 204 pb 17 973 no evidence of lead isotope overprinting by the mineralizing event could be found in the samples studied when the lead isotope data are corrected for addition of radiogenic lead since the time of base metal mineralization c 350 ma ago there is a 1 1 correlation between the lead isotopic composition of galenas in the base metal deposits and the longford down grewyackes these results support the hypothesis that lead and other metals were derived from the greywackes underlying the base metal mineralization on a 208 pb 204 pb versus 206 pb 204 pb plot neither whole rock greywacke nor galena lead isotope data define a linear array the 208 pb 204 pb 206 pb 204 pb trend is best explained by tectonic or sedimentological mixing of three isotopically distinct lead isotope end members these end members are 1 old unradiogenic basement in nw ireland lewisian complex precursor 2 ordovician arc material from nw ireland and 3 ordovician arc material form se ireland isotopic modelling of these end members shows that the present day mixing line seen in the ordovician and silurian sediments can be calculated back to values inferred for the ordovician arc end members using the same values of as were used to back calculate the lead isotopic composition of the greywackes to the time of mineralization this information is further confirmation of the sediment mixing model presented a tectonic model developed from these and established geological data suggest a late ordovician closure of the iapetus ocean and that the silurian greywackes are a by product of eroded ordovician arc material from nw and se of the iapetus suture

the pontesford lineament welsh borderland the ne trending pontesford lineament centres on the pontesford linley and adjacent faults in the shelve longmynd inlier to the ne it is usually drawn along the se edge of the cheshire basin and to the sw along a variety of lines parallel to or converging with the church stretton fault new mapping and reassessment of published data suggest that sw of the pontesford linley fault the lineament is logically drawn along the clun forest disturbance a post pridoli late silurian fold fault belt then across the nw side of the llandrindod inlier to flank the tywi lineament the lineament was intermittently active at least from mid ordovician through to triassic time with both strike slip and dip slip displacements that involved the upper part of the precambrian basement late ordovician and early silurian strike slip was particularly important the lineament controlled the sites of several silurian sedimentary basins ordovician contrasts across the lineament can be explained either by contemporary fault control or by subsequent large displacements juxtaposing unlike terranes the long history of reactivation and basement control on the pontesford lineament is typical of lineaments throughout wales and the borderland it suggests that both caledonian and variscan structural trends n of the variscan front may be inherited from older pre silurian or even precambrian basement structures

relative and absolute dating of land surfaces abstract the dating of land surfaces has long posed problems for geomorphologists relative methods stratigraphic geomorphic topographic are sound and convincing exhumed forms may complicate identification and relationships for both epigene and etch forms have been buried and exhumed but in tectonically undisturbed areas the higher surfaces are older than those preserved at lower levels also surfaces have an age range the relationship of surfaces with volcanic deposits old shorelines and genetically related sedimentary sequences provides sound ages and correlation with dated duricrusts and faults is also useful there are no temporal limits to relative dating for the methods are equally applicable to the dating say of proterozoic surfaces as of those of pleistocene age the disadvantage of such methods is that the necessary evidence is frequently either not preserved or not exposed the so called absolute physical numerical methods and especially those based on exposure age dating with in situ cosmogenic radionuclides are appealing because they produce direct numerical ages and appear to be widely applicable but there are severe temporal limitations and sampling problems complicate and may invalidate interpretation absolute age determinations must be consistent with the stratigraphic and geomorphologic settings the best results are obtained when physicists and earth scientists pool their knowledge and experience a background in local and regional geology is especially important

sm nd evidence for the age and origin of a mississippi valley type ore deposit mississippi valley type mvt ore deposits represent the relatively common product of large scale fluid transport in the continental lithosphere yet the models for their genesis have been more controversial and unconstrained than those of any other class of giant ore deposit1 2 here we show that sm nd isotope data can be used to determine the age and origin of an mvt deposit sm nd data for fluorites from the north pennine orefield are difficult to explain unless some of the mineralization is of mesozoic rather than the traditionally accepted palaeozoic age furthermore the nd and sr isotopie compositions of the fluorites do not support a variety of recent models that include derivation of the components from the mantle the lower palaeozoic basement or the underlying buried granite which served to focus the flow of hydrothermal fluids

the possible bearing of the granite of the uph deep drill holes northern illinois on the origin of mississippi valley ore deposits the pb pb th pb and u pb systems of whole rock drill core samples of the granite of uph record at least one postcrystallization event treatment of the data on a concordia plot indicate the timing of this disturbance was probably 260 35 m y ago and probably no older than 400 m y ago the upper intercept age on concordia is 1416 20 m y and the pb pb isochron age for the four least disturbed rocks plus the four potassium feldspars is 1451 19 m y these ages are in close agreement with rb sr whole rock and u pb zircon ages determined by others and should be the age of granite formation considerable pb loss is indicated for many of the shallower samples that have a more red rather than pink color probably to a factor of two to three or more as a result of the disturbance although the granite remains pb rich today 40 80 ppm in some other studies of disturbed u th pb systems the radiogenic lead has been taken up by potassium feldspars however the pb for most samples seems to have been lost from the system for the granite of uph one sample with an unusually high pb content of about 195 ppm has the most radiogenic pb of any sample but normal values of th u this sample has obviously gained radiogenic pb by more than a factor of four and confirms that pb was indeed mobilized in parts of the system within the limits of the uncertainties equal amounts of pb were lost or gained in both the u pb and th pb systems which is compatible with mobilization being restricted to lead there is some tendency however for the more affected samples to have lower th u values and higher u contents a complex model in which u is gained pb lost and 208pb lost preferentially to 207pb and 206pb cannot be ruled out u and th have somewhat different crystallographic locations and decay energies so that 208pb might be in more accessible sites than the other pb isotopes fission track mapping of the samples indicates most of the u today is located in submicroscopic sites along edges and cleavages of biotite and iron oxides so u is readily available for remobilization lead extraction with only minor u or th removal may have been accomplished by chloride rich brines lead isotope data on the granite of uph indicates that some of the pb in the ore in the nearby upper mississippi valley lead zinc district may have been derived from these granites an even better match is made with the ores of southeastern missouri although a granite like that of uph would only be one end member most likely the radiogenic end member of a mixed source curiously similar aged and heavy metal rich granites from southeastern missouri are not a good match for theckn nearby ores basement rocks such as the granite of uph must be reconsidered as an important contributor to the ores of the mississippi valley but it is unlikely that they constitute the sole source

electron spin resonance esr dating abstract esr dating has been systematically applied in earth sciences and archaeology since 1975 when ikeya dated a stalactite from the akiyoshi cave in japan in the meantime this new technique has been successfully applied to the dating of materials such as speleothems spring deposited travertines mollusc shells corals and tooth enamel the present research focuses on the dating of quartz which allows the age assessment of heated ceramics volcanic rocks intrafault material or windblown sediments esr dating is based on the measurement of the number of paramagnetic centers in a mineral these centers are generated by alpha beta and gamma radiation of the matural radioelements such as u th and k and have accumulated over time two parameters have to be determined the accumulated dose ad and the dose rate d to which the sample was exposed this review comprises three major parts a introduction into esr dating b application of the method and c appendices giving detailed description of dose rate calculation physical basis of electron spin resonance the esr spectrometer and esr lines the major emphasis lies on the outline of the application of esr dating this includes the discussion of the esr signals of the various materials sampling sample preparation and measurement techniques

applicability of esr dating using multiple centres to fault movement the case of the itoigawa shizuoka tectonic line a major fault in japan abstract no direct method for dating the fault movement has been hitherto established except esr dating whose applicability is disputed however the most serious question in esr dating is whether accumulated esr signals are completely reset at the time of fault movement when the defect centres are partially preserved at the time of previous faulting the date obtained is uncertain we have shown fukuchi et al 1985 1986 however that we can judge correctly whether esr signals were completely reset or not when the esr signal counting is done for multiple esr centres of different stabilities for resetting from the data for completely reset centres actual date of fault movement can be calculated this multiple centre method was tested with samples whose esr signal intensities are judged to be about zero at the time of fault movement the result which confirms the applicability for the fault movement dated back to 100 ka bp is presented in this paper

pine point a case history of lead isotope homogeneity in a mississippi valley type district the lead isotope compositions of 32 galena samples from 20 different deposits in the pine point district are essentially identical within error avg 206 pb 204 pb 18 175 or 0 008 and indicate a remarkable uniformity of isotope composition over a mineralized area of several hundred square kilometers the isotope homogeneity could result from an homogeneous source or from thorough mixing during extraction and subsequent precipitation of lead the homogeneity of the lead isotope data allows an interpretation in terms of a single stage lead evolution model and calculation of a model age of mineralization of about 290 ma late pennsylvanian this age is substantially younger than the middle devonian host rocks 375 ma but much earlier than the post early cretaceous approximately 100 ma tectonic events along the western margin of the mackenzie basin that have been credited with initiating the regional hydrologic regime that resulted in mineralization more complex multistage models are possible but cannot be more precisely defined by present data the homogeneity and nonradiogenic composition of pine point leads is in marked contrast to those reported for devonian carbonate hosted pb zn deposits of the mackenzie platform this discrepancy may be due in part to the different paleogeographic positions of the two groups of deposits the more radiogenic inhomogeneous group is situated on the western edge of the platform adjacent to deep water shales of the selwyn basin pine point in contrast lies more than 500 km to the east within the carbonate platform

observations on the micro texture and esr spectra of quartz from fault gouge abstract we have investigated fault gouge samples from a variety of sites in eastern china with esr optical and scanning electron microscopy sem x ray diffraction and cathodoluminescence the results reveal two different types of quartz a macrocrystalline and a microcrystalline variety the macrocrystalline samples show increasing esr intensities of the e centre with increasing grain size whilst the microcrystalline samples show the opposite trend we also found that the dissolution of quartz grains and secondary quartz precipitation on the surface of the grains is significant in some samples indicating active chemical weathering in these fault zones the occurrence of secondary quartz has serious implications for the reliability of any dating attempt

isotopic composition of lead in galenas from the viburnum trend missouri the isotopic composition of lead in crystals of galena from the no 28 magmont brushy creek fletcher and ozark mines along the viburnum trend has been determined by ion microprobe variations in the isotopic composition of lead along traverses perpendicular to growth zoning are generally complex patterns of lead isotope variation from the center to the edge of galena crystals can be correlated for distances up to 200 m our lead isotope data together with earlier data for galena from the viburnum trend and the old lead belt lie along a linear band on 207 pb 206 pb 208 pb 206 pb diagrams lead in the paragenetically early octahedral galena is less radiogenic than lead in the paragenetically late cubic galena there is no significant geographic variation in the isotopic composition of the galena leads within the viburnum trend most of the isotopic variations can be explained in terms of the mixing of a normal lead isotope component from oil field brines and a radiogenic lead component derived from the precambrian basement the lead in these brines is derived from a source with a lower time integrated th u value than that of the source of the lead for analyzed oil field brines the isotopic composition of the radiogenic component is most consistent with derivation from a grenvillian 1 0 1 2 b y source the composition of lead in the cubic galenas may also be influenced by the admixture of lead derived from the dissolution of earlier octahedral galena

pb isotope evidence on the origin of the west shropsh orefield england pb isotope data on ore galenas from the west shropshire orefield show a significant spread of 20 pb 204 pb values with minor variation in 207pb 204 pb and 208pb 204 pb ratios these indicate that lead was derived from multiple sources some of them uranium enriched and incompletely mixed prior to ore deposition four possible mineralizing agents are considered circulating sea water metamorphic waters basinal brines and convecting formation waters pb isotope data exclude a circulating sea water origin for the mineralization and best support a convecting formation water mineralizing agent a model involving a single fluid tapping multiple lead sources is proposed to explain the observed pb isotope variation

origin of a giant orebody at navan ireland the navan base metal deposit in ireland formed 360 myr ago1 and is one of the world s largest orebodies with 70 million tonnes of 12 zn pb much of the mineralization was sedimentary exhalative other well known examples of this class of the so called sedex deposits are mount isa in australia sullivan in canada and meggen in germany several models for the formation of such deposits have been suggested here we report the first systematic stratigraphic pb isotopic study of galenas in any giant exhalative zn pb orebody we document evidence that the sources of pb in the navan orebody evolved to produce increased dispersion and less radiogenic averages of lead isotopic compositions this is as expected if the orebody formed from a hydrothermal convection cell which expanded to scavenge metals from progressively deeper parts of the continental crust

direct esr dating of fault gouge using clay minerals and the assessment of fault activity abstract the esr dating method has been applied to the fault gouge of the nojima fault the outcrop of which arose due to the southern hyogo prefecture earthquake on january 17th 1995 and to the fault gouge of the median tectonic line mtl which is a major active fault in japan without considering the resetting of esr signals the esr ages obtained for clay minerals in the fault gouges are considered to indicate the age of the beginning of the fault movements at the outcrop assuming no radon loss and the general values of water content and ray efficiency the esr ages of the fault gouges of the nojima fault and mtl are estimated as 0 55 1 16 and 6 76 9 28 ma respectively the esr age of the nojima fault is consistent with the age of the beginning of the rokko movements in the kinki districts estimated geologically on the other hand the esr age obtained from the mtl is younger than the k ar age about 11 ma which is presumably overestimated due to the existence of the source minerals in the k ar dating sample since it is geologically known that the mtl at the outcrop had moved until the late pleistocene holocene the fault movement of the mtl at this outcrop probably began at 6 76 9 28 ma b p after the intrusion of the felsitic dyke 12 16 ma which is the source rock of the fault gouge into the fault boundary the esr dating of clay minerals in the fault gouge may be effective for assessing fault activity if no quaternary deposit exists at the outcrop the younger the esr age of the fault gouge is the higher the fault activity is if not indurated and the freshest clay gouge can be collected at the outcrop the esr age of the most recent movement may be obtained from the clay gouge

electron spin resonance esr dating of pre quaternary faults in the sichuan basin sw china abstract the electron spin resonance esr dating method is thought to be limited to the quaternary period in this study we attempt to expand the esr dating range to the pre quaternary using three fault zone samples collected from faults in the sichuan basin and its surroundings we adopt a ray radiation dose of up to 2 104 gy which is much greater than that typically employed and find that the esr intensity of the e1 center a type of signal for esr dating in quartz continuously increases with the ray dose and is slightly influenced by the radiation dose rate this indicates the potential of esr to date pre quaternary faults by simulating environmental radiation under geological burial conditions we use esr to date the latest extension event in the western hubei and hunan thrust belt to 9 17 0 76 ma and the thrusting of the longmenshan fault zone toward the sichuan basin to approximately 6 14 0 73 ma conversely the saturated esr intensity of fault zone samples from the daba fault zone suggests a lack of strong tectonic activity in the southern daba fault zone in the last 10 ma our results are consistent with fission track ages and the regional tectonic evolution history therefore esr is a practical method for dating pre quaternary faults in structural and petroleum geology applications

mississippi valley type deposits products of brine expulsion by eustatically induced hydrocarbon generation an example from northwestern australia mechanisms for fluid flow such as compactive dewatering gravity driven hydrologic flow and seismic pumping are not geologically plausible for mississippi valley type mvt mineralization in the lennard shelf canning basin northwestern australia sulfides at cadjebut and the other lennard shelf mvt deposits precipitated from overpressured hydrocarbon rich brines the deposits lie below a major mid carboniferous unconformity that is linked to a global sea level fall independent evidence at cadjebut also constrains the time of mineralization to the mid carboniferous a sea level fall at this time could have raised the sediment water interface above the thermocline thereby increasing the temperature of the basin by minus 16 degree c model calculations show that a rise in basin temperature would induce sufficient hydrocarbon gas maturation to expel 1005 km sup 3 of brine this brine volume would be more than sufficient to transport and deposit the metal budget of the known mvt deposits on the lennard shelf the existence worldwide of mvt deposits below unconformities suggests that sea level induced hydrocarbon generation could have assisted mvt mineralization in other provinces 33 refs 2 figs

experimental investigations on dating the last earthquake event using osl signals of quartz from fault gouges abstract obtaining a reliable age of the latest seismic slip event along an active fault is important for seismic hazard assessment here we observe changes in the optically stimulated luminescence osl signal of quartz crystals due to frictional heating in artificial fault gouges comprising a mixture of quartz grains and ca bentonite powder the fault gouge was deformed using a high velocity rotary shear apparatus at room temperature and room humidity at a seismic slip rate of 1 31 m s 1 intense slip localization occurred along a very thin layer 300 m thick within the simulated fault zones 1 mm thick the estimated temperature of the slip localized layer sll increased by 475 c from frictional heating the quartz osl signals of the gouges were fully reset most noticeably for the sll in contrast there was rare slip localization at subseismic slip rates 0 06 0 001 m s 1 for which the estimated temperature rise in the sll was 120 c hence the quartz osl signal was not reset under this condition the results suggest that quartz osl dating can be used to constrain the age of the latest seismic event in natural quartz bearing fault zones where a sll occurs

esr plateau dating of fault gouge abstract the use of esr dating to determine the time of last motion on a fault requires that the signals must have been fully zeroed at the time of last motion zeroing can be demonstrated by comparing the ages of successively finer grain sizes of quartz if a plateau of low ages is found for the finest grains this should represent the age of last motion testing this model on various strands of the san gabriel fault zone in southern california we find low age plateaus in all samples and also convergence of ages for two different esr signals in most samples esr dating of single samples of quartz with larger grains than those of the plateau will result in too large an age of last motion and may fail to observe convergence between ages given by two or more esr signals

microfractures within the fault damage zone record the history of fault activity 1 for faults without sedimentary covers there is no robust method to obtain paleoseismic data that is crucial for the prediction of future damaging earthquake events sudden failure along faults during earthquakes induces off fault damage surrounding such basement faults we showed that the quaternary active fault has the damage zone characterized by a fracture density that decays exponentially with distance from the fault for both healed and open microfractures in contrast quaternary inactive faults contain only healed microfracture damage zone cross cutting relationships between microfractures and a minimum healing temperature of 100 c suggest that healed microfractures formed before and at deeper levels than did unhealed microfractures the damage zone defined by open microfractures reflects the recent fault movement during exhumation associated with erosion and regional uplift from the maximum depth at which microfractures may remain unhealed microfracture analysis can therefore be used to examine the history of basement fault activity