origin of late variscan granitoids from ne bavaria germany exemplified by ree and nd isotope systematics sm nd isotopic results are presented for late and post tectonic granitoids comprising peraluminous granites and subordinate metaluminous dioritic rocks redwitzites from the fichtelgebirge fg and northern oberpfalz nop ne bavaria the data combined with a number of earlier geochromological studies on these granitoids place severe constraints on the crustal evolution of this region during the carboniferous and pre carboniferous epoch redwitzites range in nd t from 4 to 0 inclusive data from p k holl and coworkers the nd t values of the granites s s are restricted to overlapping ranges of 8 to 3 fg and 8 to 2 nop in both domains the older granites 330 325 ma are characterized by nd t values of 4 whilst the younger granites 315 305 and 290 ma have nd t values of 4 the diversity observed in nd isotopic characteristic is interpreted in terms of different source material the nd isotopic compositions of the redwitzites exhibit source heterogeneity suggesting mixing between mantle magma and crust the nd isotopic features of the older granites are consistent with the magmatic precursors having been generated by partial melting of pre existing mature crust variably contaminated by mantle material or alternatively by melting of chemically less evolved crust resembling paragneisses of teh zev structural unit the origin of the younger granites can be confidently linked to anatexis of common moldanubian and saxothuringian metasediments two stage nd model ages tdm of the granitoids are in the range 1 1 1 7 ga these ages provide further support of substantial involvement of pre phanerozoic crust in the generation of the granitoids the leuchtenberg granite and the g2 and g3 granites yield late variscan sm nd isochron ages which are concordant with previous rb sr data on these granites by contrast the nd isotopic data for barnau and flossenburg define pseudo isochrons suggestive of mixing between contrasting felsic melts

brittle deformation events at the western border of the bohemian massif germany investigations of brittle deformation structures present within the crystalline rocks of the bavarian oberpfalz reveal a complex late to post variscan crustal evolution upper carboniferous mainly westphalian granites were emplaced into semibrittle to brittle rocks of the zev zone of erbendorf vohenstraus and the egz erbendorf greenschist unit respectively from both the alignment of the granites and the direction of granite related tension gashes a north east south west extension must be assumed for the period of magmatic activities apart from the granite intrusions rapid crustal uplift about 1 5 km my led to an increase in the geothermal gradient from 40 c km late variscan post granitic the increased geothermal gradient persisted during the succeeding reverse faulting which results from late carboniferous probably stephanian east west and northeast south west compression although not evidenced directly in the area considered strike slip faults seem to have played an important part during the late variscan crustal evolution particularly in the early permian the strike slip events indicate further crustal shortening and indentation under north south compression a similar indentation was present in cretaceous time after a weak phase of early cretaceous reverse faulting which results from north south compression strike slip faults formed under north west south east and north south compression all these faults in particular the strike slip faults seem to be related to the cretaceous and lowermost tertiary convergence of the alpine carpathian orogeny a late stage of crustal extension characterized by a radial stress tensor 2 3 is indicated through high angle normal faults which probably formed during the subsidence of the adjacent neogene eger graben

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

estimating the p t x_ h_ 2 o conditions during crystallization of low calcium granites the pressure and temperature at which the alkali feldspar plagioclase boundary curve intersects the h 2 o saturated liquidus of a granitic composition defines the minimum pressure at which alkali feldspar can be the liquidus phase and the minimum temperature at which plagioclase can be stable at the liquidus the intersection may also define the maximum water content for a magma that had plagioclase at the liquidus the key pieces of information required to estimate a p t projection from p t x h 2 o space for a granite liquidus are 1 the solubility of water in the melt composition of interest 2 the location and shape of the liquidus surface in p t x h 2 o space and 3 the pressure and temperature at which the two feldspar boundary curve intersects the saturated liquidus our review of recent data suggests that burnham s 1979 model predicts water solubility in granitic melts within about 5 10 mole near the saturated liquidus but that there are unresolved problems in the undersatura

u pb whole rock and mineral dating of the falkenberg granite in northeast bavaria u pb and pb pb isotope ratios of 10 whole rock samples 3 k feldspars 3 muscovites 3 biotites and 7 apatites from the falkenberg granite northeast bavaria define a three dimensional discordia plane yielding intersection ages of307 22ma and59 91ma an age of 316 9 ma was calculated from a pb pb isochron for these samples the whole rock samples appear to be only slightly disturbed by a later event which is documented by fission track ages of the apatites about 50 ma the apparent u pb isochron age of 304 ma and the th pb isochron age of 303 ma cannot be accepted as ages because the high mswd values classify them as scatterchrons the results are in agreement with the results of rb sr and k ar dating however dates derived from zircons scatter between 320 and 360 ma these older ages are interpreted as due to relicts in the zircons

quantitative refinement of calibrated 14c distributions abstract a new method is presented for using known ordering or other relationships between 14c samples to reduce 14c dating uncertainty the order of sample formation is often known from for example stratigraphic superposition dendrochronology or crosscutting field relations constraints such as a minimum time between dates and limits from historical information are also readily included dendrochronologically calibrated calendric date histograms initially represent each date the method uses bayes theorem and the relational constraints to upweight date ranges in each date distribution consistent with the other date distributions and the constraints and downweight unlikely portions the reweighted date distributions retain all dating possibilities present in the initial calibrated date distributions but each date in the result now reflects the extra information such as ordering supplied through the constraints in addition one may add information incrementally and thus analyze systematically its effect on all the date distributions thus the method can be used to assess the consistency of the quantitative data at hand the bayesian approach also uses the empirical calibrated date distributions directly so information is not lost prematurely by summarized dates to a mean and variance or confidence intervals the approach is illustrated with data from two densely sampled paleoseismic sites on the san andreas fault in southern california an average reduction in 14 c date distribution variance of 59 is achieved using ordering information alone and 85 is achieved by also applying sedimentation rate constraints and historical information

petrological and geochemical characteristics of archean gneisses and granitoids from bastar craton central india implication for subduction related magmatism the gneisses and granitoids of bastar craton with rock suites up to 3 5 ga show calc alkaline trondhjemitic characteristics the rocks are enriched in both lile and hfse than primordial mantle they have also relatively higher abundances of lile and strong depletion at p and ti in the multielement diagram the depletion of ti and p indicates retention of these elements by titanite and or apatite during partial melting it is proposed that subduction of an oceanic slab and its consequent melting led to the formation of the protoliths of the gneisses without much interaction with the mantle wedge the granitoids represent temporally distinct suites formed in response to further melting of slab at greater depth and interaction of magma with the mantle wedge during their transport to the crust

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

towards a more practical two feldspar geothermometer the thermodynamic basis of several recent attempts to formulate a simple two feldspar geothermometer is discussed together with a review of earlier empirical geothermometers and ones based on experimental studies in the ternary feldspar system it is shown that double binary thermometers which involve the combination of regular solution mixing models for the binary alkali feldspar system with ideal mixing in plagioclases do not give a satisfactory representation of two feldspar relations especially for albite rich compositions where a critical point exists thermometers based on mixing parameters for ordered alkali feldspar frameworks are even more unjustified both because low plagioclases are certainly non ideal and because of uncertainty in knowing the degree of al si order in the alkali feldspar when exchange equilibrium was achieved a thermodynamic thermometer requires knowledge of ternary activities which are at present unknown experimental determinations of relationships in the ternary feldspar system are reviewed and the correct general form of the thermometer constructed using mainly the experimental data of seck 1971a and smith and parsons 1974 chemographic tests for equilibrium between feldspar pairs are suggested and petrographie features discussed in an appendix new values are given of margules parameters calculated for binary disordered alkali feldspars from recent solvus data up to 15 kbars and their physico chemical basis examined we suggest that accurate representations of the mixing properties of disordered alkali feldspars using margules parameters are at present premature

intrusion of igneous rocks physical aspects igneous rocks occur in two predominant modes the plutonic mode is characterized by intrusive emplacement under compressional tectonic stress regimes the volcanic mode is dominated by the eruption of large volumes of magma through fault controlled dyke structures in extensional tectonic stress regimes

microthermometric study of silicate melt inclusions in variscan granites from se germany volatile contents and entrapment conditions melt inclusions in granitic rocks are generally crystalline and must oberpfalz regions along the northern margin of the be homogenized to glass before analysis we employ a simple kinetic bohemian massif some of these granites particularly in technique with microthermometry to estimate total volatile contents the german erzgebirge are highly evolved geochemically and p t conditions of trapping of the melts from their hoand famous for the tin and uranium mineralization mogenization behaviour this information complements chemical associated with them several publications have condata from microprobe or ion probe analysis and can be obtained centrated on the geology geochemistry and ore from inclusions too small for direct analysis we present here values associations of the granites forster tischendorf 1994 for volatile contents as equivalent wt h2o trapping temperatures seltmann 1994 tischendorf forster 1994 hecht et and trapping pressures derived from studies of melt inclusions in some al 1997 siebel et al 1997 but their magmatic volatile variscan granites of the erzgebirge fichtelgebirge and oberpfalz contents and emplacement level are difficult to determine germany the volatile concentrations range from 3 to 10 equiv wt and have not often been addressed the granites from h2o microprobe analysis shows that the most volatile rich these regions contain abundant melt inclusions and these inclusions contain up to 8 wt f estimates of trapping offer the potential of constraining melt water contents pressures and temperatures suggest that crystallization began at an and conditions of trapping emplacement level of 3 6 5 km near 700 c with normal biotite all three regions contain composite plutons or plutonic and two mica granites and ended with topaz albite granite complexes which range in composition from un 650 c and pegmatitic phases down to 520 c this wide differentiated biotite granites to more highly evolved tworange of trapping temperatures and volatile contents is a general mica granites and finally to extremely evolved granites feature of melt inclusions in granites many of the granites studied containing li micas and topaz in some cases this comare highly evolved geochemically but the extreme volatile enrichment positional range is covered by different units of a single typical for these also occurs locally in the unspecialized granites pluton e g falkenberg granite oberpfalz whereas in other places individual plutons are more restricted in composition the erzgebirge region is particularly rich

timing of large earthquakes since a d 800 on the mission creek strand of the san andreas fault zone at thousand palms oasis near palm springs california paleoseismic investigations across the mission creek strand of the san andreas fault at thousand palms oasis indicate that four and probably five surface rupturing earthquakes occurred during the past 1200 years calendar age estimates for these earthquakes are based on a chronological model that incorporates radiocarbon dates from 18 in situ burn layers and stratigraphic ordering constraints these five earthquakes occurred in about a d 825 770 890 mean 95 range a d 982 840 1150 a d 1231 1170 1290 a d 1502 1450 1555 and after a date in the range of a d 1520 1680 the most recent surface rupturing earthquake at thousand palms is likely the same as the a d 1676 35 event at indio reported by sieh and williams 1990 each of the past five earthquakes recorded on the san andreas fault in the coachella valley strongly overlaps in time with an event at the wrightwood paleoseismic site about 120 km northwest of thousand palms oasis correlation of events between these two sites suggests that at least the southernmost 200 km of the san andreas fault zone may have ruptured in each earthquake the average repeat time for surface rupturing earthquakes on the san andreas fault in the coachella valley is 215 25 years whereas the elapsed time since the most recent event is 326 35 years this suggests the southernmost san andreas fault zone likely is very near failure the thousand palms oasis site is underlain by a series of six channels cut and filled since about a d 800 that cross the fault at high angles a channel margin about 900 years old is offset right laterally 2 0 0 5 m indicating a slip rate of 4 2 mm yr this slip rate is low relative to geodetic and other geologic slip rate estimates 26 2 mm yr and about 23 35 mm yr respectively on the southernmost san andreas fault zone possibly because 1 the site is located in a small step over in the fault trace and so the rate is not be representative of the mission creek fault 2 slip is partitioned northward from the san andreas fault and into the eastern california shear zone and or 3 slip is partitioned onto the banning strand of the san andreas fault zone

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

isotopic dating in metamorphic belts isotopic dating in metamorphic rocks is concerned with the timing of processes whose operation is controlled by continually changing physical conditions of these temperature has a pervasive influence and the use of physical models to elucidate the ways in which temperature is likely to vary is briefly reviewed the central concept of closure temperature is critically discussed and quantitative estimates for biotite and hornblende are evaluated in order to illustrate the factors which control closure temperatures and limit their application in practice the possibility of dating crystallization using minerals which crystallize below their respective closure temperatures is examined taking examples involving k ar rb sr sm nd and u pb analyses the indirect dating of metamorphism via structurally dated plutons is briefly considered and the problems of interpreting both discordant u pb zircon ages and rb sr whole rock isochrons in metamorphosed granites are discussed the value of near concordant zircon ages is emphasized the extent of isotopic equilibration during metamorphism specifically of sr isotopes in metasediments is shown not to be a simple function of metamorphic grade the flow of fluids produced by metamorphic reactions appears to be crucial and there is a potential for dating metamorphism using whole rock samples where such flow can he demonstrated independently the concluding discussion briefly examines existing data for the dalradian and indicates the potential for further progress using both well established and novel approaches

evidence for large earthquakes on the san andreas fault at the wrightwood california paleoseismic site a d 500 to present we present structural and stratigraphic evidence from a paleoseismic site near wrightwood california for 14 large earthquakes that occurred on the southern san andreas fault during the past 1500 years in a network of 38 trenches and creek bank exposures we have exposed a composite section of interbedded debris flow deposits and thin peat layers more than 24 m thick fluvial deposits occur along the northern margin of the site the site is a 150 m wide zone of deformation bounded on the surface by a main fault zone along the northwest margin and a secondary fault zone to the southwest evidence for most of the 14 earthquakes occurs along structures within both zones we identify paleoearthquake horizons using in filled fissures scarps multiple rupture terminations and widespread folding and tilting of beds ages of stratigraphic units and earthquakes are constrained by historic data and 72 14c ages mostly from samples of peat and some from plant fibers wood pine cones and charcoal comparison of the long well resolved paleoseimic record at wrightwood with records at other sites along the fault indicates that rupture lengths of past earthquakes were at least 100 km long paleoseismic records at sites in the coachella valley suggest that each of the past five large earthquakes recorded there ruptured the fault at least as far northwest as wrightwood comparisons with event chronologies at pallett creek and sites to the northwest suggests that approximately the same part of the fault that ruptured in 1857 may also have failed in the early to mid sixteenth century and several other times during the past 1200 years records at pallett creek and pitman canyon suggest that in addition to the 14 earthquakes we document one and possibly two other large earthquakes ruptured the part of the fault including wrightwood since about a d 500 these observations and elapsed times that are significantly longer than mean recurrence intervals at wrightwood and sites to the southeast suggest that at least the southermost 200 km of the san andreas fault is near failure

cooling and inferred uplift erosion history of the grenville orogen ontario constraints from 40ar 39ar thermochronology stepwise 40ar 39ar degassing experiments of 57 mineral separates of hornblende muscovite biotite and perthitic microcline have been used in conjunction with petrologic observations to place regional constraints on the postmetamorphic cooling and the inferred uplift and erosion history of the grenville orogen in ontario the 40ar 39ar data support an interpretation of slow nearly uniform cooling 1 4 c m y from temperatures of 500 c to below 150 c in the central gneiss belt cgb hornblendes cooled through ar closure between 930 and 1025 ma whereas in the central metasedimentary belt cmb hornblendes record the following range in 40ar 39ar cooling ages 1104 ma in the frontenac terrane 1007 1067 ma in the sharbot lake terrane 919 1026 ma in the elzevir terrane and 972 ma in the central metasedimentary belt boundary zone regional uplift erosion rates of 0 03 0 14 km m y have been estimated for the grenville orogen in ontario based on the 40ar 39ar data a model retrograde p t path for rocks of the cgb and an upper time constraint provided by flat overlying cambrian and ordovician sediments these erosion rates are consistent with rates estimated for other proterozoic or archean granulite terranes but are an order of magnitude slower than active orogens such as the alps and himalayas a regular variation in hornblende 40ar 39ar cooling ages is observed in rocks that traverse highly strained often mylonitic shear zones that separate the four major terranes of the cmb the pattern of 40ar 39ar ages is interpreted to reflect late tectonic extension consistent with field observations in the central metasedimentary belt boundary zone and elsewhere in the cmb up to 13 km of vertical displacement is inferred for some rocks in the cmb between the time they cooled below closure to argon diffusion in hornblende 500 c and their exposure at the surface 25 c

irregular recurrence of large earthquakes along the san andreas fault evidence from trees old trees growing along the san andreas fault near wrightwood california record in their annual ring width patterns the effects of a major earthquake in the fall or winter of 1812 to 1813 paleoseismic data and historical information indicate that this event was the san juan capistrano earthquake of 8 december 1812 with a magnitude of 7 5 the discovery that at least 12 kilometers of the mojave segment of the san andreas fault ruptured in 1812 only 44 years before the great january 1857 rupture demonstrates that intervals between large earthquakes on this part of the fault are highly variable this variability increases the uncertainty of forecasting destructive earthquakes on the basis of past behavior and accentuates the need for a more fundamental knowledge of san andreas fault dynamics

evaluation of multiple emplacement mechanisms the huichizi granite pluton qinling orogenic belt central china three end member granite emplacement mechanisms host rock ductile shortening hrds host rock rigid displacement hrrd and magmatic absorption ma are identified in this study of the huichizi pluton the internal fabrics are mainly flattening typesona 0 4 0 9u and strain is highoesa 1 0 0 6u near the boundaries and lowoesa 0 7 0 30u toward the central parts of the pluton in the 1 5 km wide contact aureole extension e is measured in syn emplacement deformed veins and the calculated average shortening normal to the sides and tips of the pluton are 1 14 km and 0 74 km respectively from this we conclude that the hrds produced only about 20 space for the present volume of the pluton the regional hrrd derived from the uplift by about 8 km of the qinling group in a flower structure contributed 19 032 space ms including stoping and material transfer processes yielded another 37 space of this stoping contributed a minimum of 1 space estimated from the surface area of 2 8 km 2 covered by xenoliths transfer processes provided about 36 of the needed space deduced from the average 64 36 ratio of hybridization of mantle derived to crustal qinling group derived magma the three mechanisms may act nearly simultaneously as a multiple emplacement mechanism this situation may apply to many other plutons as well 2000 elsevier science ltd all rights reserved

a 100 year average recurrence interval for the san andreas fault at wrightwood california evidence for five large earthquakes during the past five centuries along the san andreas fault zone 70 kilometers northeast of los angeles california indicates that the average recurrence interval and the temporal variability are significantly smaller than previously thought rapid sedimentation during the past 5000 years in a 150 meter wide structural depression has produced a greater than 21 meter thick sequence of debris flow and stream deposits interbedded with more than 50 datable peat layers fault scarps colluvial wedges fissure infills upward termination of ruptures and tilted and folded deposits above listric faults provide evidence for large earthquakes that occurred in a d 1857 1812 and about 1700 1610 and 1470

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

faults and veins in the superdeep well ktb constraints on the amount of alpine intra plate thrusting and stacking of variscan basement bohemian massif germany the crystalline rocks of the superdeep well ktb 9101 m depth display abundant late to post variscan brittle ductile and brittle deformation structures clear depth dependent variations in metamorphic conditions are obvious concerning cretaceous subhorizontal tension gashes and reverse faults whereas the upper carboniferous structures subvertical tension gashes and reverse faults show almost no variations with depth the lack in depth dependent gradients can be explained by strong cretaceous reverse faulting that led to an intra plate antiformal stack the frontal ramp of this stack a broad fault bundle referred to as the franconian lineament was drilled at 7300 m depth it rises from a flat lying detachment at approximately 9 km depth which corresponds to the brittle ductile transition zone of quartz bearing rocks supracrustal stacking and thickening along and above this ramp was particularly active during alpine upper cretaceous foreland compression close to the franconian lineament the alpine impact strongly affected the variscan crustal edifice disturbing the variscan and late variscan depthdependent gradients in ktb

k ar geochronology of different tectonic units at the northwestern margin of the bohemian massif abstract the polymetamorphic moldanubian mo of the northeasthern margin of the bohemian massif has been thrust to the north onto the mainly paleozoic sedimentary saxothuringian of the fichtelgebirge fg these two units have undergone polyphase deformation and the last regional event to affect both units was a low pressure metamorphism in which temperatures decreased towards the north in contrast the nappe units of the erbendorf vohenstrauss zone zev and the erbendorf greenschist zone egz which partly cover the border of the moldanubian and the saxothuringian and the munchberg nappe pile mm which lies on the saxothuringian were in parts subjected to a late medium pressure metamorphic event the zev the egz the mo and the fg are intruded by late carboniferous granites conventional k ar analyses mainly of hornblendes and muscovites from the autochthonous fg and mo the units beneath the nappes have yielded exclusively carboniferous dates the oldest dates point to a regional cooling of the rocks which outcrop at the present day surface at about 330 320 ma i e at the early late carboniferous boundary the late carboniferous cooling history was largely governed by the thermal influence of the post kinematic granites 320 295 ma especially in the fg and the northern mo the high grade metamorphic rocks in the western part of the zev and in the upper three nappes of the mm mostly yield dates around 380 ma i e early devonian the results show a relatively wide scatter moreover biotites frequently appear to be older than the coexisting muscovites both observations indicate that the rocks underwent a later thermal influence whether some groups of older dates e g 400 ma are due to excess argon or to inherited argon is still open to discussion slightly scattered muscovite dates around 366 ma were obtained for the prasinite phyllite series one of the lower nappes of the mm a single hornblende from the egz gave the same age these two nappes have therefore probably been affected by a late devonian thermal and or tectonic event the muscovite dates obtained from the paleozoic bavarian lithofacies the lowermost nappe of the mm and the hornblende dates from the eastern part of the zev are indistinguishable from those of the autochthonous units fg and mo

problems encountered with the 14c dating of peat abstract pairs of neighbouring short columns of peat from two sites in northern england were divided into contiguous 1 cm thick slices that were sub sampled for pollen and plant macro fossil analysis for each slice the remaining peat was then split into humic acid humin and fulvic acid fractions and radiocarbon dated this research demonstrates that significant variations can occur in the radiocarbon content of discrete chemically defined fractions of peat a total of 127 radiocarbon dates was obtained the results from the four columns of peat are highly variable and mutually inconsistent the fulvic acid fraction although normally younger than the corresponding humic acid and humin fractions has very little effect on a combined date in these samples however it is removed from all samples prior to dating in order to remove any carbonates which could contaminate samples the variations in the ages obtained for the humic acid and corresponding humin fractions range from the humin fraction being 630 years older than the humic acid srr 4029 to the humic acid being 1210 years older than the humin fraction srr 4007 even when a two sigma confidence is allowed no correlation was apparent between pollen concentration 13 c enrichment degree of humification and the conventional radiocarbon ages

depth of intrusion and thermal modeling of the falkenberg granite oberpfalz germany the late carboniferous falkenberg granite exposed 2 km to the east of the german continental deep drilling ktb drill site has solidified at a depth of approximately 9 12 km the initial temperature of the intrusion was 780 800 c the shape of the pluton is approximately that of a horizontal plate with an assumed original thickness of approximately 9 km 3 km of which having now been removed by erosion the results of simple one dimensional thermal modeling based on conductive heat transfer suggest cooling to 400 and 350 c over approximately 6 and 15 m y respectively with respect to the cooling ages of micas this suggests that the intrusion is somewhat older than previously assumed the lack of thermal influence in the nearby crustal section recovered by ktb compared with the width of the contact aureole inferred from the model is explained by considerable convergence between contact and drilling site the initial synemplacement distance between the granite wall rock contact and the ktb location was at least twice the recent value this is consistent with mesozoic crustal shortening which has resulted in the antiformal stack geometry of the supracrustal slices drilled by ktb

subsurface granites in the franconian basin as the source of enhanced geothermal gradients a key study from gravity and thermal modeling of the bayreuth granite the franconian basin in ne bavaria is a region of gravity low between the bohemian massif in the east and the kraichgau terrane in the west borehole measurements have identified the northern part of the franconian basin as a regional geothermal anomaly and new heat flow calculations give values of 100 mw m2 distinct negative bouguer anomalies observed in this basin are modeled as granitic intrusions in the saxothuringian basement that underlies the permo mesozoic units the interpretation of gravity gradients in combination with the filtering of gravity data gives the possible depth constraints of the intrusive bodies the resulting depths were cross checked using microstructural studies of quartz veins in the basement rocks at 1341 m depth the quartz shows structures typical for low temperature plasticity and we infer a deformation temperature of ca 300 c this indicates a considerable pre permian uplift of at least 7 km for parts of the saxothuringian basement and supports depth estimates from gravity data the heat supply of granitic intrusions by radiogenic decay is modeled considering several scenarios for the geological conditions recovered by the obernsees borehole model for conductive heat transfer the 1390 m deep drillhole is in a marginal position to the most pronounced negative bouguer anomaly it could be shown that the saxothuringian basement including heat producing granites heat production rates 4 6 w m3 covered by the insulating sedimentary rocks 1 35 km of permian to lower jurassic units can account for the enhanced geothermal gradient 38 c km that were measured in the borehole