age and emplacement of late variscan granites of the western bohemian massif with main focus on the hauzenberg granitoids european variscides germany abstract the variscan hauzenberg pluton consists of granite and granodiorite that intruded late to postkinematically into ht metamorphic rocks of the moldanubian unit at the southwestern margin of the bohemian massif passauer wald u pb dating of zircon single grains and monazite fractions separated from medium to coarse grained biotite muscovite granite hauzenberg granite ii yielded concordant ages of 320 3 and 329 7 ma interpreted as emplacement age zircons extracted from the younger hauzenberg granodiorite yielded a 207 pb 206 pb mean age of 318 6 4 1 ma the hauzenberg granite i has not been dated the pressure during solidification of the hauzenberg granite ii was estimated at 4 6 0 6 kbar using phengite barometry on magmatic muscovite corresponding to an emplacement depth of 16 18 km the new data are compatible with pre existing cooling ages of biotite and muscovite which indicate the hauzenberg pluton to have cooled below t 250 400 c in upper carboniferous times a compilation of age data from magmatic and metamorphic rocks of the western margin of the bohemian massif suggests a west to northwestward shift of magmatism and ht lp metamorphism with time both processes started at 325 ma within the south bohemian pluton and magmatism ceased at ca 310 ma in the bavarian oberpfalz the slight different timing of ht metamorphism in northern austria and the bavarian forest is interpreted as being the result of partial delamination of mantle lithosphere or removal of the thermal boundary layer

fission track lengths in the apatite annealing zone and the interpretation of mixed ages abstract measurements of confined fission tracks in apatites from deep boreholes show that their mean length is reduced and the length distribution becomes progressively broader through the fission track annealing zone at subsurface temperatures of around 100 c and above the length distribution characteristically becomes very broad without a pronounced peak the lengths of the longest tracks remain essentially constant at all stages of natural annealing observed in the boreholes this pattern is similar to that found in laboratory annealing of spontaneous fission tracks in apatite from an outcrop sample of the same formation these observations show that confined track lengths can be used as important indicators of the type of thermal history that a sample has experienced in the temperature zone of increasing track stability the length distributions reported here provide a basis for interpretation of fission track ages that might otherwise be ambiguous an apatite age which results from a uniform slow cooling history will have a broad negatively skewed length distribution while a bimodal distribution provides clear evidence of a two stage history involving partial annealing by a discrete thermal event the apparent fission track age associated with a bimodal length distribution will be a mixed age intermediate between the original age and that of the later event

structure related geochemical ree and isotopic k ar rb sr δ18o characteristics of clay minerals from rotliegend sandstone reservoirs permian northern germany abstract euhedral illite cementing the gas bearing sandstone reservoirs of the rotliegend in the niedersachsische rift system northern germany was studied along a horst to graben cross section to examine its chemical and isotopic characteristics the data show that differentiated illite particles grew during a tectono thermal event marked by distinct episodic hydrothermal activities along fault drains and in the poral space of sandstones at 210 ma and at 195 to 190 ma in horst positions at 185 to 175 ma in the nearby graben and at 170 to 165 ma in both the horst and graben varied ree distribution patterns and initial 87sr 86sr ratios from 0 7124 to 0 7142 relative to illite particle size outline a high chemical variability of the fluids during illite growth the 18o values of illite range from 20 0 to 12 4 and those of chlorite from 12 0 to 6 9 the changing 18o values of the minerals most likely relate to varied 18o values of the fluids or to different water rock ratios during crystallization differences among the ree and 87sr 86sr tracers and the 18o values of different generations of illite also suggest a changing fluid chemistry relative to time significant positive eu anomalies and negative ce anomalies in the ree distributions of illite suggest feldspar alteration by the migrating fluids in oxidizing environments

rb sr and k ar dating of clay diagenesis in jurassic sandstone oil reservoir north sea rb sr and k ar isotopic determinations were combined with scanning electron microscopy sem observations and x ray diffractometry xrd controls to date the diagenetic formation of clay minerals from oil bearing sandstones of the middle jurassic brent sandstone in the north sea the separated clay fractions often contain detrital components especially k feldspars which are reduced to sizes smaller than 0 4 m either by intense in situ alteration or by destructive sample preparation direct rb sr and k ar isotopic dating of diagenetic illite therefore was not possible isotopic data obtained on mixtures of detrital and newly formed components showed however that illite formed about 40 to 45 ma this value also was obtained directly on clay fractions separated by a gentle method of disaggregation illitization is related to emplacement of hydrocarbons and associated waters into the formation aqueous and hydrocarbon fluids simultaneously trapped in quartz overgrowth inclusions indicate late silicification contemporaneous with this fluid migration minimum trapping temperatures of at least 110 c for these fluid inclusions are too high for the present burial depth hot fluids are assumed to have originated in deep source rocks beneath the brent reservoirs and migrated upward during the middle eocene

displacement rates on the toroweap and hurricane faults implications for quaternary downcutting in the grand canyon arizona the toroweap and hurricane faults considered to be the most active in arizona cross the uinkaret volcanic field in the western grand canyon these normal faults are downthrown to the west and the colorado river crosses these faults as it flows west in the grand canyon cosmogenic 3 he 3 he c dates on basalt flows and related landforms are used to calculate vertical displacement rates for these faults the two faults cross unruptured alluvial fans dated as 3 ka toroweap and 8 ka hurricane and 10 other landforms that range in age from 30 to 400 ka are displaced middle and late quaternary displacement rates of the toroweap and hurricane faults are 70 180 and 70 170 m m y respectively on the basis of these rates the combined displacement of 580 m on these faults could have occurred in the past 3 to 5 m y all 3 he c dates are younger than existing k ar dates and are consistent with new 40 ar 39 ar dates and existing thermoluminescence tl dates on basalt flows these different dating techniques may be combined in an analysis of displacement rates downcutting rates for the colorado river in the eastern grand canyon 400 m m y are at least double the downcutting rates west of the faults 70 160 m m y faulting probably increased downcutting in the eastern grand canyon relative to downcutting in the western grand canyon during the late quaternary

laser microprobe 40ar 39ar analysis of pseudotachylyte and host rocks from the tatra mountains slovakia evidence for late palaeogene seismic tectonic activity laserprobe 40ar 39ar data from fault related pseudotachylytes and granitic host rocks from the tatra mountains central western carpathians resolve the controversy over the age of propagation of the sub tatra detachment fault this major structure has resulted in exhumation of crystalline basement to the north west and subsidence and sediment deposition in the palaeogene central carpathians basin to the south east host rock biotite ages range from 331 ma to 322 ma and pseudotachylyte spot ages range from 164 ma to 28 ma of these the youngest group identify the maximum timing of the early stages of tatra mountains uplift which continued in the miocene 20 10 ma and culminated during the quaternary the wide ranging older ages are an artefact of an unsupported 40ar component that is most likely a combination of both inherited and excess argon

an empirical evaluation of the argon diffusion geometry in muscovite the temperature time significance of 40ar 39ar muscovite ages is difficult to evaluate quantitatively because of ambiguities in the choice of an appropriate model diffusion geometry the effective diffusion dimension and large uncertainties in experimentally determined diffusion parameters laser 40ar 39ar studies of natural 40ar concentration gradients suggest that argon loss in muscovite occurs primarily via cylindrical volume diffusion commonly with an effective diffusion dimension equal to the crystal diameter the present study tests the cylinder model geometry and the control of physical grain size on the effective diffusion dimension by measuring the anisotropy of a natural40ar diffusion gradient parallel and perpendicular to 001 in a single euhedral muscovite phenocryst the new data combined with previous studies clearly indicate loss of 40ar via cylindrical volume diffusion and strongly suggest that loss of 40ar across the 001 sheets slab diffusion geometry is minimal in undeformed crystals

supracrustal intraplate thickening of variscan basement due to alpine foreland compression results from the superdeep well ktb bohemian massif germany until its final depth of 9101 m the superdeep well ktb kontinentales tiefbohrprogramm der bundesrepublik deutschland drilled through variscan basement rocks which suffered strong brittle ductile and brittle deformation during late and post variscan times investigations of faults and mineralized tension gashes revealed the following deformation stages 1 upper carboniferous subvertical tension gashes 2 upper carboniferous reverse faults 3 cretaceous subhorizontal tension gashes and reverse faults 4 neogene normal faults clear depth dependent variations of metamorphic conditions of the post variscan deformation structures are obvious whereas the upper carboniferous structures show almost no variations with depth this refers to the metamorphic index minerals as well as to the deformation fabrics in quartz we explain this considerable lack of gradients as being the result of reactivative reverse faulting that led to considerable vertical thickening of the upper crust the fault geometry indicates an antiformal stack the frontal ramp of which was drilled by ktb at 7000 m depth there is strong evidence that this frontal ramp referred to as the franconian lineament at the surface rises from a subhorizontal detachment at about 10 km depth which corresponds to the brittle ductile boundary layer of quartz bearing rocks the considerable amount of supracrustal vertical thickening above the franconian lineament results from repeated movements along this detachment since upper carboniferous times it seems reasonable to suppose that in intraplate tectonic settings the brittle ductile boundary layer is prone to form a long lived decoupling horizon along which the upper brittle crust is detached from the viscous middle and lower crust

slip rates along active faults estimated with cosmic ray exposure dates application to the bogd fault gobi altai mongolia dating morphological features displaced along active faults presents a major difficulty in evaluation of slip rates we used in situ produced 10 be to calculate minimum ages for alluvial surfaces misaligned by movement along a major active fault in the gobi altai western mongolia the maximum slip rate of 1 2 mm yr suggested by this method contrasts strongly with rates of 20 mm yr that we estimated by correlation of alluvial deposition with warm humid periods associated with the last glacial termination estimated to have occurred about 12 ka in western tibet the 10 be based slip rate indicates that strong earthquakes can occur along faults with low slip rates and demonstrates the contribution of cosmic ray exposure dating in quaternary tectonic analyses

sr isotope systematics of k feldspars in plutonic rocks revealed by the rb sr microdrilling technique sr 86 sr isotope variation was studied in subareas of k feldspar megacrysts from late palaeozoic granodiorite diorite and syenite of the bavarian forest most samples were collected close to the bavarian pfahl shear zone and feldspars from these sites reveal remarkably constant initial 87 sr 86 sr isotope ratios these ratios are similar to those of the bulk groundmass or feldspar crystals from the groundmass individual feldspar grains however define isochron ages that are considerably younger by 15 to 30 ma than the crystallisation age of the host rocks as defined by u pb and pb pb zircon geochronology the rb sr feldspar data probably reflect diffusion controlled isotopic homogenisation under hydrous conditions between 290 310 ma a pink feldspar crystal from a hydrothermally altered syenite reveals comparatively large degree of isotopic variation indicating local disturbance of the rb sr system caused by hydrothermal alteration during permian triassic pfahl quartz precipitation a diorite from the furstenstein pluton displays some isotopic scatter and slight differences in the initial 87 sr 86 sr ratios between the more radiogenic feldspar megacryst and the less radiogenic bulk groundmass this rock type was subsequently intruded by the saldenburg granite and the more radiogenic 87 sr 86 sr isotope signature of the feldspar relative to the groundmass is interpreted as being consistent with the feldspar having exchanged with the fluids derived from the granite this study shows that k feldspar crystals from slowly cooled plutonic rocks do not necessarily preserve their original sr isotope composition however sr isotope traverses through single crystals can give robust records of the mm scale isotope system behaviour also in older plutonic rocks relevant for solving petrological or geochronological problems d 2005 elsevier b v all rights reserved

k ar dating of fault gouge in the northern sydney basin nsw australia implications for the breakup of gondwana abstract the occurrence of synkinematic and authigenic clay minerals is a common feature in fault gouges few attempts have been made to date fault gouges we present the first age data in australia for synkinematic illite smectite growth in two fault zones of the northern sydney basin nsw the faults occur at burwood beach nsw in the northern part of the sydney basin and are hosted by early permian siltstones tuffs and coals of the lambton formation newcastle coal measures the faults are 1 5 m apart show normal displacement and trend n s with steep easterly dips foliated gouge zones comminution and dilational breccias are developed along both fault surfaces k ar ages extracted from samples in the gouge and tuffs in the damage zones are 172 6 10 m to 119 ma 2 m 237 245 ma for the

surface textural analysis of quartz sand grains from odp site 918 off the southeast coast of greenland suggests glaciation of southern greenland at 11 ma shipboard analysis of the 1 183 m sedimentary section recovered at site 918 in the irminger basin during ocean drilling program leg 152 revealed material of glacial origin diamictons ice rafted debris ird and dropstones as deep as 543 m below sea floor bsf the sediment containing the deepest dropstone was biostratigraphically dated shipboard as approximately 7 ma pushing back the date for the onset of glaciation on southern greenland by 5 ma thin layers of fine sand were found as much as 60 m deeper in the core raising the possibility of an even earlier date for glaciation to determine the sedimentary history of these deeper sand layers the surface textures on quartz grains from eleven cores bracketing the interval of interest were analyzed by scanning electron microscope the results suggest that the grains in the 60 m interval below the deepest dropstone have a glacial history at that level an 11 ma sr isotope date was obtained from planktonic foraminifers this late miocene timing is supported biostratigraphically by both nanofossil and foraminifer assemblages indicating a new minimum age for the onset of glaciation on southern greenland and in the north atlantic

dating pseudotachylyte of the nojima fault using the zircon fission track method 1 the zircon fission track analysis of pseudotachylyte answered how old the nojima fault is which was activated during the 1995 kobe earthquake in japan the time of seismic fault motions at the crustal interior can be constrained by dating pseudotachylyte formation we succeeded in separating zircons from the pseudotachylyte layer of the fault as well as in dating them by the fission track method here we show that the layer has a significantly younger age 56 4 ma than the initial cooling age of the host rock suggesting that the fault was already initiated at 56 ma much older than the previous estimate based on the spatial distribution of sediments around the fault

dating fault reactivation by ar ar laserprobe an alternative view of apparently cogenetic mylonite pseudotachylite assemblages apparently cogenetic mylonite pseudotachylite assemblages are commonly reported in major fault zones they represent two very incompatible modes of deformation and complex formation mechanisms have been proposed to explain this paradox we report here one such assemblage from central norway in which apparently synchronous mylonite and pseudotachylite formation is separated by 100 ma mean muscovite ar ar laserprobe spot ages from mylonite and pseudotachylite matrix are 406 11 ma and 290 10 ma respectively in preference to a complex cogenetic model we invoke fault reactivation as a viable alternative and suggest that assumed contemporaneity in such assemblages may be invalid in many cases

modeling of the temperature sensitivity of the apatite u th he thermochronometer apatite u th he apparent ages will generally reflect residence for extended periods at temperatures where helium is neither quantitatively retained nor lost by diffusion to characterize the response of apatite he ages to thermal histories involving partial he retention we explored solutions to the he production diffusion equation under thermally static conditions the analytical solution to this equation coupled with published diffusivity data demonstrates that the zone of partial he retention extends from about 40 c to 85 c this zone lies at temperatures 35 c cooler than the analogous fission track partial annealing zone he ages within the partial retention zone ultimately achieve a balance between he production and loss yielding a steady state age both the ultimate age and the time it takes to achieve this age are temperature dependent for example an apatite held at 75 c equilibrates to an age of 2 ma after 17 myr regardless of whether equilibrium is approached from a higher or a lower initial he age for representative dynamic thermal histories we evaluated apatite he ages using a numerical solution to the ingrowth diffusion equation the results illustrate the sensitivity of he ages to various geologic histories and are useful for understanding he age elevation relationships and for testing time temperature paths derived from apatite fission track length distributions in addition although he diffuses rapidly from apatite at shallow crustal temperatures modeling of ambient temperature fluctuations indicates that he ages are nearly unaffected by surficial processes

late variscan magmatism revisited new implications from pb evaporation zircon ages on the emplacement of redwitzites and granites in ne bavaria pb evaporation zircon analyses coupled with a detailed cathodoluminescence cl study on the complete series of granitoids from the northern oberpfalz ne bavaria provide new evidence for the commencement and timing of late variscan magmatism all granitoids analysed in this study were dated before by rb sr and or k ar methods investigated samples comprise medium grained i type dioritic rocks redwitzites i s type granites leuchtenberg marktredwitz g1 zainhammer and s type granites falkenberg liebenstein mitterteich friedenfels steinwald flossenburg barnau the zircon evaporation technique reveals three groups of 207pb 206pb ages which are interpreted to represent magmatic crystallisation 1 ages of 324 321 ma are found in all analysed redwitzites and in almost all i s type granites 2 the granites of falkenberg and liebenstein yield ages of 315 ma 3 ages between 312 and 310 ma are recorded in the mitterteich friedenfels steinwald and flossenburg granites titanite crystals from different redwitzite bodies yield conventional u pb ages of 325 322 ma identical to the pb evaporation zircon data of these rocks the s type granites of groups 2 and 3 contain zircons with relict cores but only a small number of them yield older ages indicating that some of the cores must have lost their radiogenic pb from the geochronological data we infer that metamorphic conditions of the variscan crust produced different granite types at different times the data support a model involving an early period of mantle related magmatism which postdates the final convergence stage of the variscan orogen this magmatic activity was at the same time as the thermal peak of regional metamorphism and is followed by a late period of crustal anatexis which is probably related to post collisional extension of the thickened variscan crust

time calibration of a p t path from a variscan high temperature low pressure metamorphic complex bayerische wald germany and the detection of inherited monazite a temperature time path was constructed for high temperature low pressure ht lp migmatites of the bayerische wald internal zone of the variscan belt germany the migmatites are characterised by prograde biotite dehydration melting peak metamorphic conditions of approximately 850 c and 0 5 0 7 gpa and retrograde melt crystallisation at 800 c the time calibration of the pressure temperature path is based on u pb dating of single zircon and monazite grains and titanite separates on 40ar 39ar ages obtained by incremental heating experiments on hornblende separates single grains of biotite and k feldspar and on 40ar 39ar spot fusion ages of biotite determined in situ from sample sections additionally crude estimates of the duration of peak metamorphism were derived from garnet zoning patterns suggesting that peak temperatures of 850 c cannot have prevailed much longer than 2 5 ma the temperature time paths obtained for two areas approximately 30 km apart do not differ from each other considerably u pb zircon ages reflect crystallisation from melt at 850 800 c at 323 ma southeastern area and 326 ma northwestern area the u pb ages of monazite mainly coincide with those from zircon but are complicated by variable degrees of inheritance the preservation of inherited monazite and the presence of excess 206pb resulting from the incorporation of excess 230th in monazite formed during ht lp metamorphism suggest that monazite ages in the migmatites of the bayerische wald reflect crystallisation from melt at 850 800 c and persistence of older grains at these temperatures during a comparatively short thermal peak the u pb ages of titanite 321 ma and 40ar 39ar ages of hornblende 322 316 ma and biotite 313 309 ma reflect cooling through the respective closure temperatures of approximately 700 570 500 and 345 310 c published in the literature most of the feldspars ages 305 296 ma probably record cooling below 150 300 c while two grains most likely have higher closure temperatures the temperature time paths are characterised by a short thermal peak by moderate average cooling rates and by a decrease in cooling rates from 100 c my at temperatures between 850 800 and 700 c to 11 16 c my at temperatures down to 345 310 c further cooling to feldspar closure for ar was probably even slower the lack of decompressional features the moderate average cooling rates and the decline of cooling rates with time are not easily reconciled with a model of asthenospheric heating rapid uplift and extension due to lithospheric delamination as proposed elsewhere instead the high peak temperatures at comparatively shallow crustal levels along with the short thermal peak require external advective heating by hot mafic or ultramafic material

age constraints on faulting and fault reactivation a multi chronological approach movement within the earth s upper crust is commonly accommodated by faults or shear zones ranging in scale from micro displacements to regional tectonic lineaments since faults are active on different time scales and can be repeatedly reactivated their displacement chronology is difficult to reconstruct this study represents a multi geochronological approach to unravel the evolution of an intracontinental fault zone locality along the danube fault central europe at the investigated fault locality ancient motion has produced a cataclastic deformation zone in which the cataclastic material was subjected to hydrothermal alteration and k feldspar was almost completely replaced by illite and other phyllosilicates five different geochronological techniques zircon pb evaporation k ar and rb sr illite apatite fission track and fluorite u th he have been applied to explore the temporal fault activity the upper time limit for initiation of faulting is constrained by the crystallization age of the primary rock type known as kristallgranit at 325 7 ma whereas the k ar and rb sr ages of two illite fractions 2 m 266 255 ma are interpreted to date fluid infiltration events during the final stage of the cataclastic deformation period during this time the kristallgranit was already at or near the earth s surface as indicated by the sedimentary record and thermal modelling results of apatite fission track data u th he thermochronology of two single fluorite grains from a fluorite quartz vein within the fault zone yield cretaceous ages that clearly postdate their late variscan mineralization age we propose that later reactivation of the fault caused loss of helium in the fluorites this assertion is supported by geological evidence i e offsets of jurassic and cretaceous sediments along the fault and apatite fission track thermal modelling results are consistent with the prevalence of elevated temperatures 50 80 c in the fault zone during the cretaceous

conjugate shear zones in the southern bohemian massif austria implications for variscan and alpine tectonothermal activity abstract mylonitic fabrics developed within conjugate wrench ductile shear and fault systems in the southern bohemian massif display both dextral nw se trending systems and sinistral ne sw trending systems shear senses contrasting temperature conditions of deformation can be observed in the different shear zones temperatures above 650 c were reached in the pfahl shear zone shearing under greenschist facies conditions took place in the rodl and danube shear zones brittle deformation dominated in the vitis and diendorf shear zones 40 ar 39 ar dating of various size fractions of muscovite formed and or deformed during mylonitization yield ages of ca 287 ma the nw se trending system and ca 288 281 ma the ne sw trending system the shear zones are interpreted as a late variscan conjugate system 40 ar 39 ar age spectra of fine grained newly grown sericite or rejuvenation of ages give evidence for post variscan reactivation of the shear zones brittle deformation within the shear zones was probably associated with maintenance of very high fluid pressure during variscan deformation foreland deformation during the alpine orogeny also played a significant role leading not only to the development of the ceske budejovice graben but also to local reactivation of the shear zones at higher crustal levels

use of 230th u ages of striated carnotites for dating fault displacements crusts of uranium minerals carnotite and tyuyamunite were found along some fault planes in the northern negev israel field microscope and scanning electron microscope sem examinations of the carnotite showed that they crystallized on previously formed faults and then underwent a later deformation this deformation is evidenced by slickensides and striations that developed on the three scales on the crusts the carnotites were dated by the 230th u method and found to be between 123 and 19 ka indicating that the most recent displacement along the faults occurred during late pleistocene to holocene time hence the u series of deformed carnotite is suggested as a method for dating young displacement along faults

the evolution of illite to muscovite mineralogical and isotopic data from the glarus alps switzerland thirty five illite and muscovite concentrates were extracted from triassic and permian claystones shales slates and phyllites along a cross section from the diagenetic alpine foreland tabular jura and borehole samples beneath the molasse basin to the anchi and epimetamorphic helvetic zone of the central alps concentrates and thin sections were investigated by microscopic x ray infrared mossbauer thermal dta and tg wet chemical electron microprobe k ar rb sr 40ar 39ar and stable isotope methods with increasing metamorphic grade based on illite crystallinity data xrd and ir the following continuous changes are observed i the 1md 2m1 polymorph transformation is completed in the higher grade anchizone ii k2o increases from 6 8 wt diagenetic zone to 8 5 10 anchizone to 10 11 5 epizone reflecting an increase in the total negative layer charge from 1 2 to 2 0 iii a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone epizone boundary iv a shift of an endothermic peak in differential thermal curves from 500 to 750 c v k ar and rb sr apparent ages of the fraction 2 m decrease from the diagenetic zone to the epizone k ar ages being generally lower than rb sr ages the critical temperature for total ar resetting is estimated to be 260 30 c k ar and rb sr ages become concordant when the anchizone epizone boundary is approached the stable isotope data on the other hand show no change with metamorphic grade but are dependent on stratigraphic age these results suggest that the prograde evolution from 1 md illite to 2m1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals however this is not a recrystallization process this restructuration is completed approximately at the anchizone epizone boundary the isotopic data indicate significant diffusive loss of 40ar and 87sr prior to any observable lattice reorganization the restructuration progressively introduces a consistent repartition of ar and k in the mineral lattices and is outlined by the 40ar 39ar age spectra concordant k ar and rb sr ages of around 35 30 ma with concomitant concordant 40ar 39ar release spectra are representative for the main phase of alpine metamorphism calanda phase in the glarus alps a second age group between 25 and 20 ma can probably be attributed to movements along the glarus thrust ruchi phase while values down to 9 ma in regions with higher metamorphic conditions suggest thermal conditions persisting at least until the middle tortonian

mineralogy 40ar 39ar dating and apatite fission track dating of rocks along the castle mountain fault alaska abstract the castle mountain fault is a 200 km long right lateral fault that forms the northern boundary of the cook inlet basin and matanuska valley alaska fault gouge and fault rock at six localities contain the clay minerals illite smectite chlorite and interstratified illite smectite at one locality gouge contains deformed illite smectite with very little wall rock chlorite contamination fine 36 24 0 08 ma for fine to coarse sizes respectively argon retention ages obtained from 40ar and 39ar retained in the three size fractions of illite at room temperature during neutron irradiation are 37 36 0 15 42 11 0 14 and 47 20 0 10 respectively apatite fission track ages were measured in arkose at a locality on the fault 60 km west of the gouge locality three samples of arkose were dated one within 10 m of the fault core one 170 m from the fault and one 335 m from the fault the sample nearest to the fault yielded an age of 29 3 2 8 ma but it only had four track lengths at 10 13 m two apatite grains from the intermediate sample yielded a pooled age of 34 3 6 1 ma the distant sample 25 grains counted 101 track lengths yielded an age of 32 0 2 9 ma this sample has a broad distribution of track lengths and a broad distribution of individual grain ages ranging from 14 8 5 1 to 67 8 8 8 ma monte carlo modeling of the apatite age and track length data is consistent with hydrothermal mineralization at 37 39 ma followed by rapid uplift and cooling after 10 ma the 40ar 39ar total gas ages k ar are minimum ages and the argon retention ages are maximum ages the thermal model derived from the fission track data and the argon retention age for the finest illite fraction of 37 ma date a hydrothermal mineralization event on the fault

chemistry of hydrothermal quartz in the post variscan bavarian pfahl system f r germany abstract chemical analyses of hydrothermal quartz by means of instrumental neutron activation coulometric dewatering and decrepitation analysis are combined with previously published microthermometric and isotopic data in order to unravel the processes involved in the formation of the post variscan hydrothermal system bavarian pfahl the bavarian pfahl is interpreted as a fossil zone of tectonic activity and large scale channelized fluid movement in the upper continental crust the predominance of k relative to ca and na in quartz as well as in fluid inclusions strongly supports the hypothesis that incongruous dissolution of feldspar during wall rock alteration and k metasomatism during fluid ascent along the shear zone accompanied by intense silicification are characteristic features of important fluid pathways in the crust the element contents detected in quartz along a 70 km long profile can be correlated with variable wall rock compositions high concentrations of ba as rb sr and cs are found in the vicinity of sedimentary basins at the western margin of the bohemian massif elevated element contents in this part of the profile probably result from intense water rock interaction within the adjoining sedimentary basin high ba contents in the vicinity of the fluorite barite mining district of nabburg wolsendorf indicate a genetic relationship between both mineralizations low cl br ratios can be generated either by interaction with carbonaceous sediments in these basins or by interaction with graphite in basement rocks the calculated salinities of the fluid inclusions vary widely but correlate well with microthermometric data and indicate mixing of basement or sedimentary brines with high salinity and meteoric water with low salinity the effects of polyphase cataclasis a result of seismic pumping on the fluid inclusion population and the mechanical properties of quartz have been studied by combined dewatering and decrepitation analyses despite minor regional variations in the chemical composition of quartz along the profile the overall uniform element pattern supports homogeneity of the hydrothermal system over distances of at least 70 km and probably over the total length of about 150 km the fluid volume required for the formation of the bavarian pfahl is estimated to correspond to the volume of the baltic sea approx 23 000 km3 in analogy with hydrothermal springs in the vicinity of recently active shear zones and faults the lifetime of the hydrothermal system bavarian pfahl is estimated to be about 160 000 years

dating fault gouges geological faults are fractures in the earth s crust along which there has been some displacement and are thus zones of weakness which are of importance in planning civil engineering projects constructing underground caverns and conducting earthquake research to assess the potential for future displacements and fluid circulation along faults it is helpful to establish the age of the latest episode of mineral growth in fault zones however there have been few attempts to date recrystallized and newly grown minerals developed in fault zones at low temperature1 4 here we report k ar and rb sr ages for clay fractions from two fault zones in the eastern alps and compare them with ages of the same fine fractions from the undeformed host rock the results suggest that the bulk of the clays along these faults were formed during early cretaceous and tertiary times respectively no major displacements seem to have taken place in recent times

burial and exhumation of corsica france in the light of fission track data 1 the mesozoic and cenozoic exhumation and cooling history of corsica is reconstructed by fission track ft data on basement and sedimentary rocks apatite ages are 105 16 ma zircon ages are 160 145 ma the jurassic and cretaceous ages show that parts of the variscan basement escaped alpine influence the basement was thermally affected by rifting prior to jurassic opening of the ligurian piedmont ocean then it cooled to near surface temperatures in paleocene eocene times subduction buried parts of the basement and overlying flysch to greater depth in the oligocene both collapse of the nappe stack and rifting prior to opening of the ligurian provencal basin affected the apatite ft system of the basement in different partly overlapping areas causing a complex age pattern the study shows that thorough analysis of ft data and thermal modeling allow to assign age populations to distinct cooling processes even when several thermotectonic events contributed to generate an intricate age pattern

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

fluorite u th he thermochronology constraints on the low temperature history of yucca mountain nevada abstract fluorite is one of the secondary minerals precipitated in pore spaces at the future nuclear waste repository site at yucca mountain nevada the authors have conducted u th he dating of this fluorite in an attempt to constrain the temperature and timing of paleo fluid flux into the site repeated analysis of colourless fluorite yielded a weighted average age of 9 7 0 15 ma 2 younger than previously determined sanidine 40ar 39 ar ages 12 8 ma for deposition of the tuff laboratory he diffusion experiments conducted on the yucca fluorite yield a preliminary he closure temperature tc of 90 10 c cooling rate of 10 c ma and previous studies have determined that the fluorite precipitated from warm fluids 65 80 c at depths of it was observed that the purple coloured outer portion of the fluorite nodule yielded non reproducible and invariably older ages than colourless fluorite several possible reasons are suggested

kar systematics of illite smectite in argillaceous rocks from the ordos basin china abstract conventional k ar dating x ray diffraction analyses illite crystallinity determinations and quantitative infrared spectroscopy mineral analyses were carried out on clay materials of the mesozoic and paleozoic argillaceous rocks from the ordos basin china in order to date the illite smectite diagenesis and to evaluate the influence of detrital contamination on the k ar ages a clay mineral assemblage of illite i s chlorite kaolinite was determined two different stages of illite diagenesis were distinctly identifiable which can be correlated to two thermal and or fluid flow events accompanying well known major tectonic movements in china a jurassic diagenetic event 170 160 ma is related to the early yanshanian movement whereas a silurian devonian diagenetic age 420 370 ma corresponds to the late caledonian movement no influence of the jurassic event is evident on the silurian devonian diagenetic illite attesting to the good retentivity of diagenetic illite for argon principles for estimating any influence on the k ar data of a size fraction by detrital contamination are discussed decreasing illite crystallinity and increasing or constant k ar data with increasing depth indicate that authigenic illite predominates and that the k ar data are diagenetic with little detrital influence furthermore the correlation between k ar ages and depth can reveal the temperature controlled mechanisms of the diagenetic illitization process increasing k ar ages with depth reflects burial diagenesis while constant k ar ages with depth indicates a diagenetic event caused by a short lived thermal event as shown in our study

the genesis of an inter field marine sandwave and the associated anti asymmetry migration of neighboring crests 1 a series of high resolution multibeam echo sounding surveys near san francisco ca suggests the occasional migration of marine sandwave crests in the direction opposite to that indicated by the shape asymmetry of the individual sandwaves in contrast to all previous observations of the relationship between bedform shape asymmetry and migration the anti asymmetry migration occurs over approximately the same time period that a new sand wave crest is formed within the large and relatively stable field the new sandwave crest appears approximately midway between two larger crests in the vicinity of structural defects in a nearly two dimensional portion of the field the sandwaves in the vicinity of the new crest are found to have migrated away from the new crest regardless of their shape asymmetry later a large section of the new crest disappears and the neighboring sandwaves migrated back toward the vacated crest location this migration occurs for sandwaves up to at least ten wavelengths away from the new crest