formation of chlorite during thrust fault reactivation record of fluid origin and p t conditions in the monte perdido thrust fault southern pyrenees the chemical and isotopic compositions of clay minerals such as illite and chlorite are commonly used to quantify diagenetic and low grade metamorphic conditions an approach that is also used in the present study of the monte perdido thrust fault from the south pyrenean fold and thrust belt the monte perdido thrust fault is a shallow thrust juxtaposing upper cretaceous paleocene platform carbonates and lower eocene marls and turbidites from the jaca basin the core zone of the fault about 6 m thick consists of intensely deformed clay bearing rocks bounded by major shear surfaces illite and chlorite are the main hydrous minerals in the fault zone illite is oriented along cleavage planes while chlorite formed along shear veins 50 m in thickness authigenic chlorite provides essential information about the origin of fluids and their temperature 18o and d values of newly formed chlorite support equilibration with sedimentary interstitial water directly derived from the local hanging wall and footwall during deformation given the absence of large scale fluid flow the mineralization observed in the thrust faults records the p t conditions of thrust activity temperatures of chlorite formation of about 240 c are obtained via two independent methods chlorite compositional thermometers and oxygen isotope fractionation between cogenetic chlorite and quartz burial depth conditions of 7 km are determined for the monte perdido thrust reactivation coupling calculated temperature and fluid inclusion isochores the present study demonstrates that both isotopic and thermodynamic methods applied to clay minerals formed in thrust fault are useful to help constrain diagenetic and low grade metamorphic conditions

fluid flow and volume loss during mylonitization an origin for phyllonite in an overthrust setting north carolina u s a abstract in the western blue ridge province of the southern appalachians north carolina granite gneisses are converted to phyllitic mylonites phyllonites along the base of the rector branch thrust sheet the mylonites show evidence for fluid infiltration and large volume losses with decreasing distance from the thrust and local shear zones feldspars undergo grain size reduction by cracking followed by chemical breakdown to muscovite sericite and zoisite the following reaction was important during mylonitization 3 k feldspar 2 h muscovite 2 k 6 sio 2 quartz displays evidence for dynamic recrystallization whereas feldspar deforms brittely which together with the secondary mineral assemblages suggest that deformation occurred at temperatures of between 300 c and 500 c in the presence of a fluid the mylonites are enriched by a factor of at least 2 5 in elements such as tio 2 p 2 o 5 zr y v la ce and depleted in sio 2 in comparison to their protolith gneisses the immobile element enrichments are attributed to enrichment in residual phases such as ilmenite zircon apatite and epidote in the mylonites and are interpreted as due to minimum volume losses of 60 mass balance calculations based on major element chemistry indicate the mylonites lost large amounts of sio 2 and smaller amounts of alkalies and were infiltrated by fluid rock weight ratios of between 10 2 and 10 3 phyllonitization as a process involves several deformation mechanisms including cataclasis and solution of feldspar as well as dislocation creep of quartz and micas reaction enhanced softening was apparently important in strain localization

holocene paleoseismicity temporal clustering and probabilities of future large m 7 earthquakes on the wasatch fault zone utah the chronology of m 7 paleoearthquakes on the central five segments of the wasatch fault zone wfz is one of the best dated in the world and contains 16 earthquakes in the past 5600 years with an average repeat time of 350 years repeat times for individual segments vary by a factor of 2 and range from about 1200 to 2600 years four of the central five segments ruptured between 620 30 and 1230 60 calendar years b p the remaining segment brigham city segment has not ruptured in the past 2120 100 years comparison of the wfz space time diagram of paleoearthquakes with synthetic paleoseismic histories indicates that the observed temporal clusters and gaps have about an equal probability depending on model assumptions of reflecting random coincidence as opposed to intersegment contagion regional seismicity suggests that for exposure times of 50 and 100 years the probability for an earthquake of m 7 anywhere within the wasatch front region based on a poisson model is 0 16 and 0 30 respectively a fault specific wfz model predicts 50 and 100 year probabilities for an m 7 earthquake on the wfz itself based on a poisson model as 0 13 and 0 25 respectively in contrast segment specific earthquake probabilities that assume quasi periodic recurrence behavior on the weber provo and nephi segments are less 0 01 0 07 in 100 years than the regional or fault specific estimates 0 25 0 30 in 100 years due to the short elapsed times compared to average recurrence intervals on those segments the brigham city and salt lake city segments however have time dependent probabilities that approach or exceed the regional and fault specific probabilities for the salt lake city segment these elevated probabilities are due to the elapsed time being approximately equal to the average late holocene recurrence time for the brigham city segment the elapsed time is significantly longer than the segment specific late holocene recurrence time

fluid rock interactions related to metamorphic reducing fluid flow in meta sediments example of the pic de port vieux thrust pyrenees spain in orogens shortening is mainly accommodated by thrusts which constitute preferential zones for fluid rock interactions fluid flow mass transfer and mineralogical reactions taking place along thrusts have been intensely investigated especially in sedimentary basins for petroleum and uranium research this study combines petrological investigations mineralogical quantifications and geochemical characterizations with a wide range of analytical tools with the aim of defining the fluid properties nature origin temperature and redox and fluid host rock interactions mass transfers recrystallization mechanisms and newly formed synkinematic mineralization in the pic de port vieux thrust fault zone pyrenees spain we demonstrate that two geochemically contrasted rocks have been transformed by fluid flow under low grade metamorphism conditions during thrusting the hanging wall triassic red pelite was locally bleached while the footwall cretaceous dolomitic limestone was mylonitized the results suggest that thrusting was accompanied by a dynamic calcite recrystallization in the dolomitic limestone as well as by leaching of iron via destabilization of iron oxides and phyllosilicate crystallization in the pelite geochemical and physical changes highlighted in this study have strong implications on the understanding of the thrust behavior tectonic and hydraulic and improve our knowledge of fluid rock interactions in open fluid systems in the crust

links between orogenic wedge deformation and erosional exhumation evidence from illite age analysis of fault rock and detrital thermochronology of syn tectonic conglomerates in the spanish pyrenees abstract we present new geochronologic data illuminating the tectonic and erosional history of the orogenic wedge exposed in the south central pyrenees spain we interpret illite age analyses from four fault gouges that record thrust belt development and document the importance of out of sequence thrusting fault activity occurs in pulses with slip occurring contemporaneously on multiple faults throughout the wedge new apatite fission track data from syn orogenic sediments of the sis conglomerate body reveal ages of 48 to 42 ma with no consistent variation upsection in strata deposited from 41 to 30 ma we interpret these data as well as thermal modeling of track length distributions to imply rapid cooling in the interior of the pyrenean wedge during the middle eocene the record of fault activity and erosion suggests that orogenic wedges may not evolve in a steady fashion but generally exhibit significant changes in rates of deformation and exhumation the observed correlation in the timing of tectonism and erosional exhumation provides evidence for links between tectonic and surface processes

frictional properties of natural fault gouge from a low angle normal fault panamint valley california 1 we investigate the relationship between frictional strength and clay mineralogy of natural fault gouge from a low angle normal fault in panamint valley california gouge samples were collected from the fault zone at five locations along a north south transect of the range bounding fault system spanning a variety of bedrock lithologies samples were powdered and sheared in the double direct shear configuration at room temperature and humidity the coefficient of friction was measured at a range of normal stresses from 5 to 150 mpa for all samples our results reinforce the intuitive understanding that natural fault gouge zones are inherently heterogeneous samples from a single location exhibit dramatic differences in behavior yet all three were collected within a meter of the fault core for most of the samples friction varies from 0 6 to 0 7 consistent with byerlee s law however samples with greater than 50 wt total clay content were much weaker 0 2 0 4 expandable clay content of the samples ranged from 10 to 40 wt frictional weakness did not correlate with expandable clays our results indicate that friction decreases with increasing total clay content rather than with the abundance of expandable clays the combination of field relations analytical results and friction measurements indicates a positive correlation between clay content fabric intensity and localization of strain in the fault core a mechanism based upon foliations enveloping angular elements to reduce friction is suggested for weakening of fault gouge composed of mixed clay and granular material we provide broad constraints of 1 5 km on the depth of gouge generation and the depth at which fault weakness initiates we show that slip on the panamint valley fault and similar low angle normal faults is mechanically feasible in the mid upper crust if the strength of the fault is limited by weak clay rich fault gouge

a least squares approach to mass transport calculations using the isocon method a statistically rigorous approach based on the isocon method grant 1986 to evaluate mass transport is presented chemical analyses of multiple samples of unaltered parent and altered rock are used to calculate the average oxide or element concentration and its standard deviation for each rock population in a typical application the uncertainties in element concentration associated with the lack of homogeneity in each population outweigh the analytical uncertainty an efficient algorithm is presented to select the immobile elements by identifying the maximum number of elements that are within their uncertainties compatible with the same isocon the actual isocon is constructed by forcing a line through the origin and optimizing its slope using a weighted least squares procedure for the selected immobile elements thus individual uncertainties for each immobile element are taken into account as an illustration the procedure is applied to a published set of data on potassic and sericitic alterations of quartz monzonite of the bingham porphyry copper system the surprising result indicates that the apparent increase of potassic alteration phases is a consequence of acid leaching of calcium and sodium no mass transport of potassium is indicated silica water and sulfur were added during alteration the best fit isocon requires a small mass increase during each alteration process which however is within the uncertainty obtained for the slope of the isocon a software package is available from the authors in the form of a fortran 77 source code

late quaternary activity along the lone pine fault eastern california the lone pine fault is a north trending secondary break of the owens valley fault zone 1 4 km west of lone pine california this fault forms an east facing scarp as much as 6 5 m high across an abandoned outwash fan of the tioga latest pleistocene glaciation the fault experienced large right lateral and smaller vertical displacement during the 1872 owens valley earthquake knowledge of the character and amount of slip at this site in and before 1872 is necessary for evaluations of earthquake hazard near owens valley and may help us to understand earthquakes along other parts of the eastern front of the sierra nevada and in the great basin scarp profiles indicate a 1 to 2 m component of dip slip in 1872 thus three 1872 type earthquakes could have created the scarp this number of events is also indicated by desert varnish patterns on boulders in the fault scarp by scarp morphology and by sediments near the fault horizontal offset of a relict channel on the fan is 12 to 18 m 3 earthquakes horizontal offset of a younger debris flow is 10 to 12 m apparently 2 earthquakes average horizontal offset for each earthquake including that of 1872 is 4 to 6 m the age of the fan surface is bracketed by a 21 ka shoreline of former lake owens and by the time of abandonment of the fan about 10 ka an average recurrence interval for 3 earthquakes is 5 000 to 10 500 yr the average recurrence interval combined with the average oblique offset for each event of 4 3 to 6 3 m gives an average late quaternary slip rate of 0 4 to 1 3 mm yr for the lone pine fault if we add the average horizontal slip component for the lone pine fault to the 1872 horizontal slip reported for the adjacent main owens valley trace of 2 7 to 4 9 m the combined 1872 horizontal slip component for the owens valley fault zone is approximately between 7 and 11 m a large value the associated horizontal slip rate for the owens vallev fault zone is 0 7 to 2 2 mm yr

stability of zircon in a low grade ultramylonite and its utility for chemical mass balancing the shear zone at mieville switzerland at mieville switzerland granitic basement rocks of the aiguilles rouges massif are cut by a subvertical shear zone the variscan shearing event produced a low grade ultramylonite zone which is up to 50 m wide and several kilometers long investigations of accessory zircons from the undeformed wall rock and from the most highly deformed ultramylonite show only minor alterations and mechanical damage of zircon crystals even in an extreme state of deformation this outstanding stability of zircon allows one to consider the element zr as immobile and therefore to use it as a passive marker for calculations of mass and volume changes during deformation processes application of this method confirms that the deformation at mieville proceeded under simple shear constant volume and isochemical conditions this is in agreement with the results of classical geochemical mass balancing in addition uncertainties inherent in the geochemical approach can be minimized by the new method

thermoluminescence dating of sand dunes in rajasthan india we report here a new application of thermoluminescence tl for dating sand dunes this application assumes that exposure to sunlight causes bleaching of the geological tl of a sediment to a residual value and that tl accumulation starts again when the sediment is buried under fresh deposit and is thus shielded from the sun although the tl method has been applied to loess1 2 and ocean sediments3 4 the application of this technique to sand dunes provides the first reliable dating control for dune dynamics palaeoclimatology and spread of deserts

integration of paleoseismic data from multiple sites to develop an objective earthquake chronology application to the weber segment of the wasatch fault zone utah we present a method to evaluate and integrate paleoseismic data from multiple sites into a single objective measure of earthquake timing and recurrence on discrete segments of active faults we apply this method to the weber segment ws of the wasatch fault zone using data from four fault trench studies completed between 1981 and 2009 after systematically reevaluating the stratigraphic and chro nologic data from each trench site we constructed time stratigraphic oxcal models that yield site probability density functions pdfs of the times of individual earth quakes we next qualitatively correlated the site pdfs into a segment wide earthquake chronology which is supported by overlapping site pdfs large per event displace ments and prominent segment boundaries for each segment wide earthquake we computed the product of the site pdf probabilities in common time bins which emphasizes the overlap in the site earthquake times and gives more weight to the narrowest best defined pdfs the product method yields smaller earthquake timing uncertainties compared to taking the mean of the site pdfs but is best suited to earth quakes constrained by broad overlapping site pdfs we calculated segment wide earthquake recurrence intervals and uncertainties using a monte carlo model five surface faulting earthquakes occurred on the ws at about 5 9 4 5 3 1 1 1 and 0 6 ka with the exception of the 1 1 ka event we used the product method to define the earthquake times the revised ws chronology yields a mean recurrence interval of 1 3 kyr 0 7 1 9 kyr estimated two sigma 2 range based on interevent recurrence these data help clarify the paleoearthquake history of the ws including the important question of the timing and rupture extent of the most recent earthquake and are essential to the improvement of earthquake probability assessments for the wasatch front region

reevaluation of holocene faulting at the kaysville site weber segment of the wasatch fault zone utah the 1978 kaysville utah trench excavated by swan and others 1980 across a large graben of the weber segment of the wasatch fault zone was reexcavated in 1988 to reevaluate the timing and nature of holocene faulting relogging of the trench reveals evidence for five or six faulting events younger than the provo phase of lake bonneville circa 13 000 14c years b p geometric reconstruction of net vertical offset in the last three events suggests a variation in coseismic vertical displacement at this site ranging from a net of 1 4 3 4 m per event the three latest faulting events occurred at shortly before 0 6 0 8 ka 2 8 0 7 ka and circa 3 8 7 9 ka earlier events cannot be directly dated because older graben fill sediments yielded thermoluminescence ages older than the time of deposition and some scarp derived colluvial wedges beneath the trench floor were not exposed the two younger faulting events we recognize at kaysville correlate reasonably well with faulting events on the same segment 25 km north near east ogden utah at circa 0 8 1 2 ka and 2 5 3 0 ka forman and others 1991 whereas the earlier kaysville event is significantly older than the earliest 3 5 4 0 ka event dated at east ogden the 3 5 4 0 ka ground rupture recognized at east ogden may have died out at a subsegment boundary between the two trench sites within the 61 km long weber segment

critical metals ree sc pge in ni laterites from cuba and the dominican republic ni laterites are considered worthy targets for critical metals cm exploration as rare earth elements ree sc and platinum group elements pge can be concentrated during weathering as a result

multidisciplinary approach to constrain kinematics of fault zones at shallow depths a case study from the cameros demanda thrust north spain thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts e g mylonites sheath folds shear bands in this paper a combination of techniques including structural analysis magnetic methods as anisotropy of magnetic susceptibility and paleomagnetism and paleothermometry is used to define thrusting conditions deformation and transport directions in the cameros demanda thrust north spain three outcrops were analyzed along this intraplate large scale major structure having 150 km of outcropping length 30 km of maximum horizontal displacement and 5 km of vertical throw results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analysis mixed layer illite smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust kinematic indicators foliation s c structures and slickenside striations indicate altogether a dominant nnw movement of the hanging wall in the western zone and ne in the eastern zone of the thrust thus implying strain partitioning between different branches of the main thrust the study of ams in fault rocks nearly 400 samples of fault gouge breccia and microbreccia indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direction onto the k max k int plane in sites with strong shear deformation paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting in spite of the shallow depth for deformation and a strong deformation or scattering of the magnetic remanence vectors in the fault zone the application of the described techniques and consistency of results indicate that the proposed multidisciplinary approach is useful when dealing with thrusts at shallow crustal levels

patterns of mineral transformations in clay gouge with examples from low angle normal fault rocks in the western usa abstract neoformed minerals in shallow fault rocks are increasingly recognized as key to the behavior of faults in the elasto frictional regime but neither the conditions nor the processes which wall rock is transformed into clay minerals are well understood yet understanding of these mineral transformations is required to predict the mechanical and seismogenic behavior of faults we therefore present a systematic study of clay gouge mineralogy from 30 outcrops of 17 low angle normal faults lanf s in the american cordillera to demonstrate the range and type of clay transformations in natural fault gouges the sampled faults juxtapose a wide and representative range of wall rock types including sedimentary metamorphic and igneous rocks under shallow crustal conditions clay mineral transformations were observed in all but one of 28 faults one fault contains only mechanically derived clay rich gouge which formed entirely by cataclasis clay mineral transformations observed in gouges show four general patterns 1 growth of authigenic 1m d illite either by transformation of fragmental 2m 1 illite or muscovite or growth after the dissolution of k feldspar illitization of fragmental illite smectite is observed in lanf gouges but is less common than reported from faults with sedimentary wall rocks 2 retrograde diagenesis of an early mechanically derived chlorite rich gouge to authigenic chlorite smectite and saponite mg rich tri octahedral smectite 3 reaction of mechanically derived chlorite rich gouges with mg rich fluids at low temperatures 50 150 c to produce localized lenses of one of two assemblages sepiolite saponite talc lizardite or palygorskite chlorite quartz and 4 growth of authigenic di octahedral smectite from alteration of acidic volcanic wall rocks these transformation groups are consistent with patterns observed in fault rocks elsewhere the main controls for the type of neoformed clay in gouge appear to be wall rock chemistry and fluid chemistry and temperatures in the range of 60 180 c

reinterpretation of the exposed record of the last two cycles of lake bonneville western united states a substantially modified history of the last two cycles of lake bonneville is proposed the bonneville lake cycle began prior to 26 000 yr b p the lake reached the bonneville shoreline about 16 000 yr b p poor dating control limits our knowledge of the timing of subsequent events lake level was maintained at the bonneville shoreline until about 15 000 yr b p or somewhat later when catastrophic downcutting of the outlet caused a rapid drop of 100 m the provo shoreline was formed as rates of isostatic uplift due to this unloading slowed by 13 000 yr b p the lake had fallen below the provo level and reached one close to that of great salt lake by 11 000 yr b p deposits of the little valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods the maximum level of the little valley lake was well below the bonneville shoreline based on degree of soil development and other evidence the little valley lake cycle may be equivalent in age to marine oxygenisotope stage 6 the proposed lake history has climatic implications for the region first because the fluctuations of lake bonneville and lake lahontan during the last cycle of each were apparently out of phase there may have been significant local differences in the timing and character of late pleistocene climate changes in the great basin second although the bonneville and little valley lake cycles were broadly synchronous with maximum episodes of glaciation environmental conditions necessary to generate large lakes did not exist during early wisconsin time

quantification of mass transfers and mineralogical transformations in a thrust fault monte perdido thrust unit southern pyrenees spain abstract in fold and thrust belts shortening is mainly accommodated by thrust faults which are preferential zones for recrystallisation and mass transfer this study focuses on a detachment fault related to the emplacement of the monte perdido thrust unit in the southern pyrenees the studied fault zone consists of a 10 m thick intensively foliated phyllonite developed within the millaris marls of eocene age the lithological homogeneity of the hanging wall and footwall allows us to compare the millaris marls outside the fault zone with the highly deformed marls located in the fault zone and to quantify the chemical mineralogical and volumetric changes related to deformation processes along the fault the millaris marls are composed of detrital quartz illite chlorite minor albite and pyrite in a micritic calcite matrix in the fault zone the cleavage planes are marked by clay minerals and calcite chlorite veins attest to fluid mineral interactions during deformation the mineral proportions in all samples from both the fault zone and millaris marls have been quantified by two methods 1 x ray diffraction and rietveld refinement and 2 bulk chemical analyses as well as microprobe analyses to calculate modal composition the excellent agreement between the results of these two methods allows us to estimate mineralogical variations using a modification of the gresens equation during fault activation up to 45 wt of calcite was lost while the amounts of quartz and chlorite remained unchanged illite content remained constant to slightly enriched the mineralogical variations were coupled with a significant volume loss up to 45 mostly due to the dissolution of micritic calcite grains deformation was accompanied by pressure solution and phyllosilicates recrystallisation these processes accommodated slip along the fault they required fluids as catalyst but they did not necessitate major chemical transfers

on the rheology of till the deformation of subglacial till is instrumental in causing certain glacier surges the motion of rapid ice streams in ice sheets and ice sheet surges which are associated with heinrich events and consequent rapid climatic shifts during the last ice age it may also be the means whereby drumlins are formed and these in turn may act as a brake on large scale ice flow it is therefore important in building models to understand the rate at which till deforms and how this controls the basal ice velocity in recent years two paradigms have emerged on the one hand theoreticians have tended to use a viscous rheology though this lacks quantitative support on the other hand field and laboratory studies suggest that till behaves plastically in this paper i will examine some of the dynamic consequences of this latter assumption and show how the dichotomy between viscous and plastic may be less clearcut than previously thought

neotectonic fault activity in hong kong evidence from seismic events and thermoluminescence dating of fault gouge hong kong lies within a major ne trending fault zone that has been reactivated during several tectonic episodes since the palaeozoic three main faults sets are recognized in hong kong a dominant ne trending set an ene varying to e trending set and a subordinate nw trending set over the last 1000 years within a distance of 350 km of hong kong there have been about 40 earthquakes with magnitudes of over 4 75 and of these 11 had magnitudes of over 6 0 microseismic events in the last ten years are diffuse but may be associated with a major ne trending fault and a fault intersection thermoluminescence tl dates of fault gouge suggest that there have been three episodes of recent fault activity in hong kong these occurred at approximately at 100 000 190 000 and 270 000 years bp tl dating of alluvial sediments also indicates fault activity in the late pleistocene

evolution of a turbiditic foreland basin and analogy with an accretionary prism example of the eocene south pyrenean basin the south pyrenean tertiary basin was an east west trending foreland trough which developed from early eocene to miocene times in a north south trending compressive regime a turbiditic series of lower and middle eocene age hecho group enables us to define the typical features of the tectono sedimentary evolution of the basin 1 slope and shelf derived carbonate turbidites and megaturbidites bear witness to the seismic activity of the basin borders 2 the southern basin border evidenced by the onlap of the turbidites onto slope and shelf deposits migrated progressively southwards in time and 3 the deformation pattern is characterized in the meso cenozoic sediments by a complex thrust fold system of thin skinned tectonics style its specific geometry and kinematics were influenced by the pre deformation geometry onlap this thrust fold system is related to south directed basement nappes and its front advanced progressively southwards in time from this data we infer an evolutionary model for this highly mobile basin it was a flexural basin linked to the northward bending of the lithosphere in the foreland of a south directed crustal accretionary prism as the nappes advanced the basin migrated progressively southwards in the foreland direction as for the actual basin evolution many analogies with accretionary prism trench systems of active margins exist

mg metasomatism and formation conditions of mg chlorite muscovite quartzphyllites leucophyllites of the eastern alps w hungary and their relations to alpine whiteschists the lower austroalpine orthogneiss micachist complex of the sopron fertorakos area of w hungary contains mg chlorite muscovite quartzphyllites leuco phyllite and mg chlorite bearing kyanite quartzites whose chemical compositions differ greatly from their surrounding rocks formation of leucophyllites took place in shear zones and was associated with depletion in alkalies and iron and enrichment of magnesium and h2o mg zonation of relict igneous muscovites of leucophyllites and changes in the whole rock chemical compositions suggest mg metasomatism material gains and losses have been assessed using the composition volume relationship approach proceeding from metagranite through transition rocks to leucophyllites mgo h2o feo and alkalies show continuously increasing dispersion in isocon plots with mg enrichment even in sheared gneiss not in contact with leucophyllite the metasomatic processes that formed the mg rich rocks may be similar to those responsible for the formation of high pressure whiteschists in the central and western alps the geochemical characteristics of the dora maira whiteschists italy and their country gneisses are very similar to those of the sopron leucophyllites supporting the theory that mg metasomatism produced the whiteschist chemistry on the basis of oxygen isotope compositions of relict igneous muscovites the precursor granitic rock had a 18o value around 13 proving its crustal anatectic origin the leucophyllites have whole rock oxygen isotope compositions around 8 5 which is in conflict with the theory of an mg rich sedimentary protolith rather the low 18o values reflect fluid rock interaction with a low 18o fluid quartz mineral oxygen isotope fractionations yield a metamorphic temperature of 560 30 c which agrees with earlier estimates from mineral stabilities silicon contents of phengites correspond to a metamorphic pressure of 13 gpa at this temperature indicating eclogite facies metamorphism the fluids in equilibrium with leucophyllites had oxygen isotope compositions around 7 9 similar to those calculated for the ultrahigh pressure dora maira whiteschists 7 6 further supporting the genetic link between the leucophyllites and whiteschists hydrogen isotope compositions of mixed white mica chlorite samples from leucophyllites range from 40 to 35 correlating with chlorite contents the calculated endmember chlorite and white mica have d values of 30 and 40 respectively the similar d values of the white micas in leucophyllites gneisses and metagranites suggest an overall equilibration with respect to h isotopes the calculated d value of the fluid is approximately 0 suggesting a seawater origin this conclusion was also reached for the dora maira whiteschists a possible fluid source that satisfies both metasomatic and isotopic data is dehydration of hydrothermally altered oceanic crust the mafic ultramafic complex of the alpine penninic unit underlying the austroalpine nappes is a likely candidate the subduction and subsequent dehydration of the ophiolite series would supply the mg rich fluids whose migration brought about the metasomatic alteration of the overlying gneiss micaschist complexes

electron microprobe determination of minor and trace transition elements in silicate minerals a method and its application to mineral zoning in the peridotite nodule phn 1611 abstract we present a wds analytical technique for the determination by electron microprobe of low concentrations of the transition elements sc ti v cr mn co and ni in ferro magnesian silicate minerals the quality of measurements is improved by 1 optimization of counting times taking into account the anticipated analytical precision 2 monitoring instrumental and sample stabilities by a statistical analysis of peak and background intensity values sampled at intervals of 1 s simultaneous measurement of major elements is essential in evaluating bias related to instrumental drift 3 precise determination of background achieved by a least squares fitting of the measured background to a calculated one the latter is calculated by using a modified form of the kramer s equation this approach is also effective in correcting peak overlap interferences the efficiency of this method was checked by performing core to rim analysis of garnet clinopyroxene and orthopyroxene prophyroclasts in the peridotite nodule phn 1611 this led to precise determination of trace element chemical zoning in these minerals

thermoluminescence dating of fault scarp derived colluvium deciphering the timing of paleoearthquakes on the weber segment of the wasatch fault zone north central utah the timing of middle to late holocene faulting on the weber segment of the wasatch fault zone utah is constrained by thermoluminescence tl and radiocarbon age estimates on fine grained fault related colluvial sediments the stratigraphy in two trenches excavated across fault scarps is characterized by a stack of three colluvial wedges deposited in response to three separate faulting events the oldest of which buried a soil developed on a middle holocene debris flow thermoluminescence age estimates by the partial and total bleach methods and the regeneration method on fine grained colluvium from the trenches agree within 1 sigma and are concordant with the radiocarbon chronology a synthesis of the tl and 14c age estimates indicate that these three faulting events occurred sometime between 4500 and 3500 between 3200 and 2500 and between 1400 and 1000 years ago detailed investigation of a sequence of fine grained scarp derived distal colluvium shows that much of the sediment was deposited during 600 year intervals immediately after faulting the sedimentation rate of colluvium is inferred to increase shortly after faulting and tl dating of these sediments provides additional information to constrain the timing of faulting events

surface faulting accompanying the borah peak earthquake and segmentation of the lost river fault central idaho on the morning of 28 october 1983 the ms 7 3 borah peak earthquake struck central idaho and formed a y shaped zone of surface faults that is divided into a southern a western and a northern section the total length of the surface faults is 36 4 3 1 km and the maximum net throw is 2 5 to 2 7 m the near surface net slip direction determined from the rakes of striations in colluvium averaged 0 17 m of sinistral slip for 1 00 m of dip slip the 20 8 km long southern section is the main zone of surface faulting and coincides with the thousand springs segment of the lost river fault it has the largest amount of net throw most complex rupture patterns and best evidence of sinistral slip the surface faults include zones of ground breakage as much as 140 m wide en echelon scarps with synthetic and antithetic displacements and individual scarps that are nearly 5 m high the 14 2 km long western section diverges away from the lost river fault near the northern end of the southern section the net throw on this section is generally less than 0 5 m but locally is as much as 1 6 m the new ruptures are poorly developed across the crest and north flank of the willow creek hills they are mostly downhill facing arcuate scars perhaps incipient landslides that may overlie a deeper zone of tectonic movement the northern section at least 7 9 km long is on the warm spring segment of the lost river fault and has a maximum net throw of about 1 m the pattern of surface faulting on this section is simple compared to the other sections a 4 7 km long gap in 1983 surface faults separates the northern and southern sections but contains an older scarp of late pleistocene age geologic seismologic and geodetic data from the earthquake suggest that barriers confined the primary coseismic rupture to the thousand springs segment of the fault the rupture propagated unilaterally to the northwest from a hypocenter near the southeastern end of the segment the southeastern boundary of the segment is marked by an abrupt bend in the range front a 4 km long gap in late quaternary scarps and transverse faults of eocene age that intersect the lost river fault the northwestern boundary of the thousand springs segment is at the junction of the willow creek hills and the lost river fault here the southern and western sections of surface faults diverge and there is a gap in the 1983 scarps during the first few weeks after the main shock the large magnitude and large stress drop aftershocks clustered near this barrier later aftershocks were mainly northwest of the barrier on the warm spring and challis segments and showed that strain adjustments eventually affected the entire northern part of the lost river fault fault scarp morphology and the bedrock geology suggest that the boundary between the thousand springs and warm spring segments has probably ruptured less frequently and had less net slip during much of the late cenozoic than the interior of the adjacent segments the 1983 faulting shows that although segment boundaries can stop or deflect primary ruptures secondary surface faulting can occur on adjacent segments of the main fault a late pleistocene scarp in the 1983 gap suggests that infrequent earthquakes perhaps larger than the 1983 event might break through a segment boundary and thus release strain on two adjacent segments

late quaternary earthquake chronology from luminescence dating of colluvial and alluvial deposits of the arava valley israel abstract luminescence ages help provide a time scale for recurrent surface ruptures on a normal fault in the southern arava israel the dated samples come from alluvium and colluvium along a fault scarp north of elat the ages obtained mainly by infrared stimulation of sand size potassium feldspar grains accord with geomorphic age estimates from soils and degraded scarps four large earthquakes occurred between 37 000 and 14 000 yr ago five smaller earthquakes occurred thereafter continuing until recent times the mean recurrence interval for earthquakes of magnitudes greater than 6 is about 4000 yr

soil catenas to estimate ages of movements on normal fault scarps with an example from the wasatch fault zone utah usa trenches excavated across fault scarps on a 13 ka delta surface at brigham city utah usa document four types of soil catena phenomena first the relict summit soil is eroded at the scarp crest and its components incorporated into the accumulating colluvial wedge at the scarp base second the pre faulting soil weakens laterally as it is traced scarpward beneath the colluvial wedge from a relict position beyond the scarp toe third soils developed on individual colluvial wedges and on the underlying pre faulting surface merge downslope to form a cumulative soil profile at the scarp toeslope fourth soil horizons thicken downslope probably due to the combined affect of more available moisture water infiltration and sediment accumulation two soil catenas were used to evaluate the applicability of a continuity approach to paleoearthquake dating by which percentages of total development time represented by each soil at a fault scarp footslope could be estimated the continuity approach sets total soil development at the scarp footslope including any buried pre faulting soil plus the sum development of all colluvial wedge soils corrected by a slope factor f equal to total soil development at the scarp summit soil development was characterized by profile development index pdi and pedogenic clay parameters using facies models to estimate parent material values for genetically different colluvial units and recognizing inherited soil components in colluvial wedges as parent material properties the f slope factor used to correct colluvial wedge soils for development attributable to slope position rather than age was checked by using a nearby fluvial scarp as an independent control our soil data when compared to independent age estimates imply that rates of soil development have not been constant over the last 13 ka at brigham city but rather were considerably higher than average between 13 ka and 8 3 ka higher rates are probably due to a relatively high influx of eolian dust during the late pleistocene to early holocene following the lowering of lake bonneville a large paleolake in the western usa these variable rates of soil development preclude using the continuity approach for paleoearthquake dating at brigham city however promising results showing that generally consistent f factors can be calculated for fault and fluvial scarps leave open the possibility that in areas where soil development rates have been relatively constant over the time period in question the continuity approach may be a broadly applicable method for paleoearthquake dating

paleoseismological investigation of the oblique normal ekkara ground rupture zone accompanying the m 6 7 7 0 earthquake on 30 april 1954 in thessaly greece archaeological and geochronological constraints on ground rupture recurrence 1 observations in trenches excavated across the ekkara rupture zone erz the longest of the sporadic ground ruptures that accompanied the m 6 7 7 0 earthquake of 30 april 1954 on the domokos fault zone dfz identify a left lateral oblique normal fault with a slip vector aligned with the regional extension direction verifying the tectonic origin of the erz the paleoseismological interpretation of stratigraphic soil stratigraphic and tectonic features is discussed with emphasis on the issues related to strongly oblique fault kinematics two pre 1954 events of ground rupture are recognized e1 and e2 and an event of ground cracking only e1a shortly after e1 event e2 was accompanied by larger displacement than e1 and 1954 but this does not necessarily imply a stronger earthquake archaeological dating of transported ceramic sherds constrains e1 between 6750 and 4450 b p more likely 6450 5750 b p luminescence dating of colluvial deposits and 14c dating of pedogenic carbonates stone coatings place e2 at 17 500 2500 b p preferred age in the hazard wise most conservative interpretation recent recurrence intervals of erz activations exceed 3195 years the sporadic nature of the 1954 ruptures precludes certainty on whether the erz has recorded every past activation of the dfz unless data are also collected from other dfz rupture zones minimum limiting estimates of 0 3 0 5 mm yr slip rate are derived for the erz and the true slip rate is not expected to exceed 1 mm yr slip rate estimates for the erz may be minima for the dfz slip rate however because coseismic deformation in the past may have been distributed to more than one rupture zones at the surface

residual luminescence in modern debris flow deposits from western taiwan a single grain approach abstract in an active fold and thrust belt sediment is commonly transported in the form of debris and colluviums and the ages of such deposits can be important for seismic hazard assessment these sediments are mainly transported by high concentration flows that travel very short distances before burial and therefore have very few opportunities for daylight exposure and bleaching which limits the application of luminescence dating in such environments luminescence studies on modern debris flow deposits and channel sediments in central taiwan indicate a mixed population of bleached and unbleached grains the well bleached grains constitute a small proportion of the sediments and could only be identified using the single grain dating technique doing single aliquot analysis may result in overestimation of the age of such sediments by 3 25 ka the data reveal that outwash sediments are better bleached than debris flow sediments our results show that quartz that has experienced partial resetting can be used for luminescence dating only through the use of the single grain technique

evidence for limited ree leaching from the roffna gneiss switzerland a discussion of the paper by vocke et al 1987 cmp95 145 154

tectono thermal history of an exhumed thrust sheet top basin an example from the south pyrenean thrust belt this paper presents a new balanced structural cross section of the jaca thrust sheet top basin of the southern pyrenees combined with paleo thermometry and apatite fission track aft thermochronology data the cross section based on field data and interpretation of industrial seismic reflection profiles allows refinement of previous interpretations of the south directed thrust system involving the identification of new thrust faults and of the kinematic relationships between basement and cover thrusts from the middle eocene to the early miocene aft analysis shows a southward decrease in the level of fission track resetting from totally reset paleozoic rocks and lower eocene turbidites indicative of heating to tmax 120 c to partially reset middle eocene turbidites and no very weak resetting in the upper eocene lower oligocene molasse tmax 60 c aft results indicate a late oligocene early miocene cooling event throughout the axial zone and jaca basin paleo maximum temperatures determined by vitrinite reflectance measurements and raman spectroscopy of carbonaceous material reach up to 240 c at the base of the turbidite succession inverse modelling of aft and vitrinite reflectance data with the qtqt software for key samples show compatibility between vitrinite derived tmax and the aft reset level for most of the samples however they also suggest that the highest temperatures determined in the lowermost turbidites correspond to a thermal anomaly rather than burial heating possibly due to fluid circulation during thrust activity from these results we propose a new sequential restoration of the south pyrenean thrust system propagation and related basin evolution

optical dating of tsunami laid sands abstract the ages of some tsunami deposits can be determined by optical dating a key requirement being that the deposits are derived from sediment that was reworked and exposed to daylight by tidal currents waves wind or bioturbation during the last years before the tsunami measurements have been made using 1 4 ev infrared excitation of k feldspar grains separated from samples of prehistoric tsunami sand sheets and modern analogs of tsunami source sediments at four sites in washington state and british columbia source sands gave equivalent doses indicative of recent exposure to daylight tsunami sand at cultus bay washington yielded an optical age of 1285 95 yr calendric years before a d 1995 1 at 2 this age overlaps the range of from 1030 to 1100 yr determined through a combination of high precision radiocarbon dating and stratigraphic correlation tsunami sands at three sites near tofino and port alberni on vancouver island british columbia have optical ages of 260 20 325 25 and 335 45 yr historical records and radiocarbon dating show that the sand at each of the three sites is between 150 and 400 yr old these optical ages support the hypothesis that the vancouver island sands were deposited by a tsunami generated by a large earthquake on the cascadia subduction zone about 300 yr ago

late quaternary faulting and thermoluminescence dating of the east cache fault zone north central utah the east cache fault zone ecfz the southernmost of five en echelon quaternary normal faults between the wasatch and teton faults displays evidence of two large paleoearthquakes in the last 15 000 years 15 ka stratigraphic data from a trench on the central segment of the ecfz are augmented with one radiocarbon date the regional radiocarbon chronology and 14 thermoluminescence tl age estimates of the 14 tl analyses performed by alpha analytic inc only 8 satisfied our criteria for statistical acceptability 20 per cent coefficient of variation 50 per cent extrapolation to residual tl level the tl age estimates broadly bracket the earlier faulting event at between 8 7 1 0 and 17 4 3 0 ka and the later event at between 2 5 0 5 and 8 7 1 0 ka one radiocarbon age further constrains the earlier event to be younger than 15 540 130 yr bp correlation of local quaternary deposits to the regional radiocarbon chronology provides indirect but more tightly limiting age constraints of ca 4 to ca 7 ka for the later event and ca 13 ka to 15 540 130 yr bp for the earlier event both events had small vertical displacements at the trench site 0 8 to 1 8 m but the cumulative net vertical tectonic displacement elsewhere is up to 4 2 m suggesrive of m s 6 9 to 7 1 paleoearthquakes single event displacements and the extent of fault scarps suggest that these two paleoearthquake ruptures were probably limited to the 20 kin long central segment of the east cache fault zone near logan utah the elapsed time since the most recent event on the central segment ca 4 to ca 7 ka is somewhat less than the estimated recurrence interval between the latest two paleoearthquake 8 6 3 0 ka however comparison of only a single poorly constrained recurrence interval with the elapsed time does not result in a confident assessment of future earthquake potential

breakdown of feldspar volume gain and lateral mass transfer during mylonitization of granitoid in a low metamorphic grade shear zone abstract in a low metamorphic grade shear zone from quadrilatero ferrifero southeastern brazil granitoid rocks have been transformed into phyllonites and mylonites via activation of crystal plastic processes in quartz and fluid assisted reaction softening in feldspars quartz deformed by basal a and prism a slip with concurrent subgrain rotation recrystallization breakdown of matrix plagioclase an 22 35 via mica producing softening reactions required cationic exchanges between ca na and k forming replacement perthites in the k feldspar megacrysts which occupy around 60 of the original rock volume subsequent breakdown of the perthitic plagioclase an 12 15 led to disruption of the megacrysts enabling strain accommodation that localized the mylonite and phyllonite zones domainal volume and mass balance calculations based on major and minor elements indicate only small positive changes in mass and volume around 15 in the whole system however accentuated differences ranging from mass and volume losses of 25 and 35 at the margins to gains of 85 and 95 in the centre respectively exist between the individual longitudinal subzones occupied by the different tectonite types this scenario indicates that deformation proceeded as a nearly isochemical process although with lateral mobility of major elements principally si al and k within the shear zone these results are different from those previously reported for other granitic mylonites most of them indicating volume losses in compressional tectonic settings it is suggested that the extensional tectonic framework attributed to the moeda bonfim shear zone where mass volume losses are in principle not required enhanced the access of fluid and consequent transport of components into the shear zone principally fe si and k producing the small gains of mass and volume observed

an evaluation of thermoluminescence dating of paleoearthquakes on the american fork segment wasatch fault zone utah the accuracy of the thermoluminescence tl method for dating holocene paleoearthquakes was tested on fine grained sediments from three trenches excavated across the american fork segment of the wasatch fault zone utah sediments exposed in the trenches targeted for tl dating include a horizons of buried soils loessial silts and sag pond muds this study indicates that these sediments were fully light bleached prior to deposition and are suitable for tl dating equivalent dose estimates by the regeneration total and partial bleach methods are in general agreement and mean tl age estimates are concordant with radiocarbon ages combined radiocarbon and tl age estimates indicate three major episodes of faulting at 5 3 0 3 2 6 0 3 and 0 5 0 2 kyr ago

applications and limitations of thermoluminescence to date quaternary sediments abstract the thermoluminescence tl method dates sediment by quantifying time dependent dosimetric properties of mineral grains sunlight exposure of the sediment during transportation and deposition or heating resets the tl clock to time zero after burial of the mineral grains ionizing radiation from the decay of radioisotopes imparts a tl signal this accumulated tl signal is proportional to the equivalent dose ed which is a measure of radiation exposure during the burial period a tl age estimate is determined from the ratio of the ed to the environmental radiation dose rate the calculation of an ed is influenced by the susceptibility of sediments to optical bleaching the emission spectra of minerals and possible long and short term fading there are three basic methods for determining an ed regeneration total and partial bleach the regeneration technique may yield under estimates because of sensitivity changes with laboratory bleaching the latter two techniques are most useful for well and partially light bleached sediments respectively a number of sediments can be dated by the tl method eolian and a variety of terrestrial sediments yield apparently accurate tl age estimates though there are possible complications associated with pedogenesis it appears that some fluvial sediment can be accurately dated by tl but little is known about the efficiency of optical bleaching for fluvial depositional systems till and glacier proximal deposits are inadequately light bleached to be dated by tl sediments deposited distal from the glacier margin which are at least partially bleached are preferred for dating future research is needed to understand better the relationship between sedimentary environments and the extent of light bleaching also studies should concentrate on dating feldspar extracts from well dated sequences to more fully ascertain the temporal limitations of the method only by understanding the interplay of sedimentology tl dosimetry and environmental radiation can the tl method be effectively applied to the myriad of depositional environments spanning the late to middle pleistocene

earthquake recurrence in nw and central himalaya abstract in this study we compare himalayan seismic moment release estimates derived from strain rate observations with those derived from large historical earthquakes and to this end we use a reassessed catalogue of historical earthquakes from western and central himalaya since the beginning of the 16th century we have computed seismic moment rates within six contiguous segments along the himalayan arc and compared these using kostrov s formula with moment rates computed from recent global strain rate estimates and regional studies while the ratios between strain based moment rate estimates and those inferred from observed seismicity vary significantly between the segments we find on the average consistently larger strain based values by about a factor of two based on seismicity from the last 515 years the moment rate ratio is however significantly reduced when shorter catalogues are used to 1 28 for the last 215 years and to 1 05 for the last 115 years which is an almost perfect match the possible inclusion of afterslip in the model would further improve the 515 year match this is indicating that a significant part of the difference possibly most of it is likely to be caused by incompleteness of the longer earthquake catalogue possibly combined with underestimated magnitudes the difference between geodetic and seismic estimates for the more complete part of the catalogue is smaller than previously reported along the western himalayan frontal thrust in fact the only region where a significant moment rate difference is found in our study is in se himachal pradesh in terms of seismic hazard it is found that the moment rate reduction of about a factor of two when going from 115 to 515 years leads to a reduction in the 475 year pga of about 26 it is also found that using 50 years of usgs seismicity data between 1963 and 2012 leads to a 40 lower hazard as compared to using moment release for the last 115 years

microtectonic and geochemical characterization of thrusting in a foreland basin example of the south pyrenean orogenic wedge spain abstract in orogenic systems thrust faults play a major role in stacking different tectonic units and may act as conduits for the expulsion of large amounts of fluid of different origins metamorphic diagenetic meteoric this study focuses on the monte perdido thrust unit emplaced in the paleogene jaca thrust sheet top basin in the sw central pyrenees we aim to decipher the mechanisms and p t conditions of deformation in fault zones and characterize the related fluid involvement through combined microstructural geochemical and microthermometry analyses two thrust faults cutting platform limestones marls and siliciclastic turbidites of the lower part of the basin fill paleocene lower eocene have been studied the fault zones are characterized by metre thick shear zones with highly deformed foliated clay rich sediments foliation is underlined by preferentially oriented phyllosilicates several generations of shear and extension calcite quartz and chlorite bearing veins attest to fluid rock interactions during a multi stage deformation microstructural observations and stable isotope analyses on calcite from veins and host sediments suggest that deformation was aseismic and dominated by diffusive mass transfer from pressure solution sites along cleavage and stylolites to the precipitation sites in veins with mineralizing fluids in equilibrium with the host sediments our results suggest an essentially closed hydrologic system and imply the absence of significant fluid flow along the studied fault zones microthermometric study on fluid inclusions present in calcite and quartz veins and calcite quartz oxygen isotopic fractionation determined for the first generation shear veins allow a geothermal gradient of 34 c km to be estimated analytical results demonstrate an evolution of the fault zones in three stages the first stage was related to the emplacement of the monte perdido thrust unit during the middle eocene at a temperature of 208 c and a burial depth of 5 7 km the second stage corresponds to a fault reactivation at a temperature of 240 c and a burial depth of 6 5 km the latter deformation may have been related to folding of the monte perdido thrust unit during the emplacement of the underlying gavarnie thrust unit during the late eocene early oligocene with deeper burial resulting from aggradation of the thrust sheet top basin fill the last event corresponds to the formation of a dilatant vein system likely related to the exhumation of the massif

the anso transect of the southern pyrenees basement and cover thrust geometries a balanced geological section through the western central pyrenees allows the alpine geometry of hercynian basement to be determined this shows marked differences with other transects of the southern part of the chain basement involved thrust sheets do not form an antiformal stack but are imbricated and define steps separated by frontal culmination limbs basement thrusts propagate upwards and have formed distinct thrust systems in the cover in this transect the north pyrenean zone is bounded to the south by gently dipping thrusts of large displacement and the axial zone massif at its western termination area is a flat topped culmination caused by a single thrust fault the gavarnie thrust this thrust emerges to the south in the interior of the syntectonic jaca basin the geometry of which is also controlled by underlying basement thrusts various generations of structures can be correlated with distinct episodes of syntectonic sedimentation a sequential restoration of the section illustrates how successive foreland sedimentary wedges were generated and progressively involved in deformation tectonic shortening is 48 km almost half of that estimated further to the east for the southern pyrenees the structure deduced at the ecors pyrenees seismic section cannot be translated to this transect

fluid mixing and recycling during pyrenean thrusting evidence from fluid inclusion halogen ratios abstract syntectonic fluids have been sampled through fluid inclusion microthermometry and crush leach analyses cations and halogens from a 50 km n s transect through the central southern pyrenees the fluid inclusions are contained in syntectonic quartz veins in triassic redbeds cretaceous carbonates and hercynian basement rocks with some calcite and dolomite data from limestones and evaporites in more external parts of the belt the main datasets come from 1 alpine shear zones cutting the neouvielle granodiorite in the hercynian axial zone at the north end of the transect 2 an imbricate zone beneath the alpine gavarnie thrust at the pic de port vieux 3 several localities in the footwall and hangingwall of the gavarnie thrust on the southern margin of the axial zone the inclusion fluids generally decrease in salinity from 27 35 at the northern end of the transect to 7 22 on the southern margin of the axial zone the majority of the inclusions have cl br ratios lower than seawater and are interpreted as relict fluids after seawater evaporation and halite precipitation in the upper trias this interpretation is supported by cl br na systematics which are consistent with a change from halite to halite sylvite precipitation with progressive evaporation fluids in the basement shear zones are interpreted to have essentially the same evaporitic origin as those still contained in sedimentary formations although it is possible that final concentration of brines in the neouvielle massif involved retrograde hydration reactions with removal of water by precipitation of hydrous minerals the fluids are also very similar in salinity and halogen chemistry to those found in veins associated with mesozoic pb zn f deposits which predate the thrusting the lower salinities seen at the southern margin of the axial zone are interpreted to reflect mixing of the brines with a higher level fluid connate or meteoric water circulating within the mesozoic carbonates of the higher thrust sheets at one locality where triassic evaporites are still present high cl br ratios at relatively low salinities are present in inclusions within the underlying triassic redbeds but low cl br ratios at higher salinities are seen lower in the sequence this is consistent with dissolution of halite by a dilute fluid but with limited penetration downwards we suggest that the fluid history of the pyrenees evolved through a series of stages 1 upper triassic evaporite formation with sinking of brines into underlying redbeds and fractured basement rocks 2 circulation of brines with formation of pb zn deposits along faults at some time between the triassic and the upper cretaceous 3 renewed extension with erosion of triassic rocks in many areas and further drawing down of triassic brines into the basement 4 deposition of u cretaceous and palaeocene carbonates containing connate waters of marine origin 5 formation of the pyrenean thrust belt with overpressuring and expulsion of the brines along shear zones and faults 6 creation of topography with a high level circulation system in the mesozoic thrust sheets driven largely by topography at the southern margin of the axial zone there was limited mixing of the deeper overpressured brines with these more dilute hydrostatically pressured fluids an important point is that because of their density hypersaline brines are difficult to expel from the upper crust and may be involved in a succession of alteration and mineralisation events in the same general area over hundreds of millions of years

temperature micro mapping in oscillatory zoned chlorite application to study of a green schist facies fault zone in the pyrenean axial zone spain oscillatory compositional zoning in minerals has been observed in hydrothermal magmatic and metamorphic environments and is commonly attributed to chemical or physical cyclical changes during crystal growth chemical zoning is a common feature of solid solutions which has been rarely reported in phyllosilicates in this study oscillatory zoning in chlorite is described in samples from the pic de port vieux thrust a minor thrust fault associated to the major gavarnie thrust fault zone central pyrenees spain the pic de port vieux thrust sheet comprises a 1 20 m thick layer of triassic red pelite and sandstone thrust over mylonitized cretaceous dolomitic limestone the thrust fault zone deformation comprises secondary faults and cleavage affecting the triassic pelite and sandstone an important feature responsible to this deformation is a set of veins filled by quartz and chlorite chlorite is present in crack seal extension veins and in shear veins both structures opened under the same stress conditions in some shear veins chlorite occurs as pseudo uniaxial plates arranged in rosette shaped aggregates these aggregates appear to have developed as a result of radial growth of the chlorite platelets oscillatory zoning has been imaged by backscattered scanning electron microscopy and by x ray quantitative micro mapping these oscillations correspond to chemical zoning with alternating iron rich and magnesium rich bands the chlorite composition ranges from a fe rich pole to a mg rich pole fe 3 fe values were measured in chlorite using xanes spot analyses and vary from 0 23 to 0 44 the highest values are in the fe rich area temperature maps built from standardized microprobe x ray images and redox state using the program xmaptools indicate oscillatory variations from about 310 to 400 50 c during chlorite crystallization these temperature variations are correlated with a fe 3 fe variation by al 3 fe 3 1 and di trioctahedral substitutions highlighted by mg and fe tot contents fe mg zoning chemical variations could be then explained by alternation of cooling times and cyclical pulses of a fluid hotter than the host rock it is however not excluded that kinetic effects influence the incorporation of mg or fe during chlorite crystallization

fluid channelling during ductile shearing transformation of granodiorite into aluminous schist in the tauern window eastern alps ductile shearing in the core of the tauern window austria transformed metagranodiorite into si undersaturated garnet chlorite staurolite schist at a depth of c 35 40 km during the alpine orogeny four distinct zones have been recognized extending from the wallrock into the centre of the shear zone zone i unaltered metagranodiorite with subordinate amphibolite zone ii biotite white mica garnet schist zone iii biotite phengite schist zone iv quartz absent garnet chlorite staurolite schist with garnets up to 10 cm across whole rock analyses show a dramatic decrease in sio2 from 65 wt in zone i to 35 wt in zone iv ca na and sr also decrease across the shear zone whereas al ti fe mg p cr ni zn and rb all increase towards zone iv mass balance calculations indicate that shearing was accompanied by up to 60 volume loss near the centre of the shear zone comparison of the tauern window samples with other shear zones in granitic hosts indicates that silica loss accompanied by gains in mg fe and ti is typical for volume loss shear zones but is distinctly different from the element behaviour exhibited in shear zones that are thought to represent approximately isovolumetric behaviour in the samples studied here volume loss appears to have resulted from channellized fluid flow during shearing producing time integrated fluid fluxes of 108 cm3 cm 2 in zone iv this large volume of fluid may have originated in part from dehydration of flysch carried beneath the metagranodiorites during eocene movement on the north penninic subduction zone development of an inverted thermal gradient during subduction would have allowed the fluid to scavenge large amounts of silica from the shear zone during ascent and heating

soils as a tool for estimating ages of quaternary fault scarps in a hyperarid environment the southern arava valley the dead sea rift israel abstract on the alluvial fan of nahal shehoret in the extremely arid region of the negev desert israel reg soils developed on stable alluvial surfaces in colluvium along terrace risers and in colluvial units on a complex fault scarp were compared the degree of soil profile development provided an age estimate of the surface that was faulted a maximum age estimate of the scarp or terrace riser and an estimate of the maximum recurrence intervals of faulting events irsl dates of the tectonically displaced alluvial surfaces and colluvial units at the same site enabled us to re evaluate the use of reg soils for relative dating the major faulting event started at 34 8 4 3 ka it displaced a late pleistocene surface of the nahal shehoret alluvial fan dated at 56 10 8 ka renewed fluvial activity and deposition of alluvium on the downfaulted block had almost terminated by 13 6 2 3 ka the scarp was formed during the latest pleistocene and was followed by smaller faulting events which had only minor effects on the fault scarp morphology the similarity of age estimates from irsl dating and the degree of soil development in this environment indicates that soils can be used to date surfaces and colluvial units

a more precise chronology of earthquakes produced by the san andreas fault in southern california improved methods of radiocarbon analysis have enabled us to date more precisely the earthquake ruptures of the san andreas fault that are recorded in the sediments at pallett creek previous dates of these events had 95 confidence errors of 50 100 calendar years new error limits are less than 23 calendar years for all but two of the dated events this greater precision is due to larger sample size longer counting time lower background noise levels more precise conversion of radiocarbon ages to calendric dates and better stratigraphic constraints and statistical techniques the new date ranges with one exception fall within the broader ranges estimated previously but our estimate of the average interval between the latest 10 episodes of faulting is now about 132 years variability about the mean interval is much greater than was suspected previously five of the nine intervals are shorter than a century three of the remaining four intervals are about two to three centuries long despite the wide range of these intervals a pattern in the occurrence of large earthquakes at pallett creek is apparent in the new data the past 10 earthquakes occur in four clusters each of which consists of two or three events earthquakes within the clusters are separated by periods of several decades but the clusters are separated by dormant periods of two to three centuries this pattern may reflect important mechanical aspects of the fault s behavior if this pattern continues into the future the current period of dormancy will probably be greater than two centuries this would mean that the section of the fault represented by the pallett creek site is currently in the middle of one of its longer periods of repose between clusters and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in california the greater precision of dates now available for large earthquakes recorded at the pallett creek site enables speculative correlation of events between paleoseismic sites along the southern half of the san andreas fault a history of great earthquakes with overlapping rupture zones along the mojave section of the fault remains one of the more attractive possibilities

disentangling magnetic subfabrics and their link to deformation processes in cleaved sedimentary rocks from the internal sierras west central pyrenees spain abstract here we present a detailed study of the magnetic fabrics and subfabrics of remagnetized upper cretaceous limolites that crop out in the internal sierras west central pyrenees affected by a penetrative pressure solution cleavage the bulk magnetic fabrics of these rocks rt ams show variable orientations that do not conform to what is typically reported for cleaved sedimentary rocks in contrast the paramagnetic subfabrics lt ams show remarkably constant directional properties so that their k max and k min axes cluster parallel to the intersection lineation and to the poles to bedding respectively these lt ams subfabrics indicate a preferred orientation of phyllosillicates that is consistent with a syn sedimentary late cretaceous period of nne oriented layer parallel shortening noticeably these phyllosillicate subfabrics are not further altered by the subsequent formation of cleavage in the late eocene early oligocene the ferrimagnetic subfabrics aarm also show remarkably constant orientation so that their k max axes are strikingly parallel to the shortening direction in the area we interpret this preferred orientation of ferrimagnetic grains as being caused by subhorizontal shear associated to cleavage formation which is consistent with the age and mechanisms authigenic growth and rotation of pre existing magnetite grains proposed for the pervasive remagnetization that affects the studied rocks

changes in holocene paleoseismic activity in the hula pull apart basin dead sea rift northern israel abstract paleoseismic analysis of the azaz fault segment of the dead sea fault northern israel indicates that this region was subjected to intermittent periods of strong seismicity and quiescence during the latest pleistocene and the holocene the azaz fault forms the eastern margin of the hula valley a pull apart basin between two left stepping segments of the dead sea fault the fault is currently inactive but it displaces a 25 30 ka travertine in the northeastern corner of the hula valley and near surface marsh sediments inside the valley two trenches excavated across a 15 20 m high fault scarp near kefar szold expose fluvial and colluvial sequences showing clear evidence of recent tectonics one trench exposes well sorted bedded alluvial sediments comprising two upward fining units each capped by a weakly developed paleosol the sediments were deposited on the down faulted block and are bounded in the east by the fault scarp the second trench uncovers fine colluvial sediments cross cut by a wide fault parallel fissure filled by collapsed sediments in both trenches the lower sedimentary unit is capped by a coarse colluvium containing boulders up to 1 5 m in size the colluvium shows no clear bedding and has a weakly developed paleosol on top optically stimulated luminescence dating of the lower fluvial sequence shows that its age ranges between 12 ka at the base to 6 ka at the top while the middle part of the overlying colluvium is ca 4 8 ka the relation between the lower fluvial units and the fault indicates that at least two large scale earthquakes occurred in the early holocene each one resulting in a 1 1 5 m high fault scarp during this seismically active period no coarse colluvial sediments were deposited along the fault trace and thus the region must have had low tectonic relief the clear contact with the overlying coarse colluvium reflects a middle holocene rapid change to the present high steep relief this change was achieved by frequent strong seismic events which triggered colluvial processes and prevented stratification and soil formation on the slope the soil on the present slope reflects a quiescent period that has lasted at least several hundred years during which stress has accumulated and seismic risk increased

the effect of mineralogy and effective normal stress on frictional strength of sheet silicates abstract phyllosilicates are common constituents of upper crustal faults and subduction forearcs we studied the effect of mineralogy and controlled effective normal stress between 5 mpa and 100 mpa on frictional strength although the effect of mineralogy on frictional strength of single phase phyllosilicate gouges has been previously studied the influence of effective normal stress has not we conducted water saturated and vacuum dry frictional tests on single phase phyllosilicate gouges using a triaxial apparatus minerals included talc pyrophyllite kaolinite lizardite illite montmorillonite chlorite muscovite phlogopite and biotite particle size 20 mpa dry friction coefficients are constant and wet friction coefficients show a small increase this is attributed to loss of water and increased contact area the results indicate that frictional strength of clay rich faults increases at depths less than 1 km under hydrostatic pore fluid pressures

late quaternary faulting on the manas and hutubi reverse faults in the northern foreland basin of tian shan china abstract the tian shan range lies in the actively deforming part of the india asia collision zone in the northern foreland basin of tian shan the strata were intensively deformed by cenozoic folding and faulting slip rate studies along these faults are important for understanding the dynamics of crustal deformation and evaluating the seismic hazards in the region two reverse faults the manas and hutubi faults in the northern foreland basin were investigated due to past faulting events along these faults the terrace treads along the manas river were ruptured forming fault scarps several meters in height loess deposits were trapped and preserved at the surface ruptures along these scarps the thickness of the trapped loess is dependent on the size of the ruptures the minimum and maximum ages of these scarps are constrained by dating the loess preserved at the surface ruptures and the terrace treads respectively using the quartz optically stimulated luminescence osl dating technique our dating results suggest that the loess trapped at the ruptures was deposited from the early to mid holocene at the hutubi fault and from the mid to late holocene at the manas fault the vertical displacements of the faults were evaluated by measuring the topographic profiles across the investigated fault scarps using the differential global position system dgps our results suggest that during the late quaternary in the studied region the vertical slip rates of the manas fault were between 0 74 mm yr and 1 6 mm yr while the hutubi fault had a much lower vertical slip rate between 0 34 mm yr and 0 40 mm yr the tectonic implications of our results are discussed

conditions and mechanism for the formation of iron rich montmorillonite in deep sea sediments costa rica margin coupling high resolution mineralogical characterization and geochemical modeling abstract iron rich smectite is commonly described in the diagenetic fraction of deep sea sediment as millimeter to centimeter aggregates dispersed in the sediment or as a coating on sedimentary particles or nodules this study examines several factors to elucidate formation mechanisms of a particular iron rich smectite and its potential transformation to glauconite the study combines a detailed mineralogical investigation on natural samples and a chemical modeling approach to assess mineralogical reactions and pathways transmission electron microscopy tem observations and analytical electron microscopy tem aem analyses were conducted on microtomed samples of millimeter to centimeter long green grains these grains are widespread in pelagic calcareous sediment from the costa rica margin they are composed of pyrites that are partially dissolved and are surrounded by amorphous or very poorly crystallized iron rich particles iron rich montmorillonite grows from an amorphous precursor and its formation requires the input of si o mg k na and ca our results suggest that these inputs are supported by the dissolution of sedimentary phases such as volcanic glasses siliceous fossils and silicates thermodynamic modeling of fluid sediment interactions was conducted with the geochemical computer code phreeqc using mineralogical and pore fluid compositions from sediment samples and calculated estimates for thermodynamic constants of smectites that are not maintained by the computer code simulations confirm the possibility that the green grains are the product of pyrite alteration by seawater under oxidizing conditions the extent of smectite production is controlled by the kinetics of pyrite dissolution and fluid migration the absence of aluminum in the costa rica margin system explains the formation of an iron rich montmorillonite instead of glauconite whereas the presence of calcite that buffers the system explains the formation of an iron rich montmorillonite instead of iron oxides

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

comparison of amino acid racemization geochronometry with lithostratigraphy biostratigraphy uranium series coral dating and magnetostratigraphy in the atlantic coastal plain of the southeastern united states the results of an integrated study comprising litho and biostratigraphic investigations uranium series coral dating amino acid racemization in molluscs and paleomagnetic measurements are compared to ascertain relative and absolute ages of pleistocene deposits of the atlantic coastal plain in north and south carolina four depositional events are inferred for south carolina and two for north carolina by all methods the data suggest that there are four pleistocene units containing corals that have been dated at about 100 000 yr 200 000 yr 450 000 yr and over 1 000 000 yr some conflicts exist between the different methods regarding the correlation of the younger of these depositional events between charleston and myrtle beach lack of good uranium series dates for the younger material at myrtle beach makes the correlation with the deposits at charleston more difficult

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

strain accumulation across the wasatch fault near ogden utah deformation of a 70 by 40 km trilateration network spanning the north trending wasatch fault near ogden utah has been monitored from 1972 through 1990 all but nine of the 200 measurements are consistent with deformation that is linear in time we presume that those nine observations are contaminated by some blunder in making the measurements and that deformation is linear in time the strain rate over the 1972 1990 interval across a 40 km wide zone west of the wasatch fault hanging wall block is adequately approximated by a 0 04 0 01 strain yr n85 e 5 uniaxial extension adequate coverage of the footwall block is available only over the 1981 1990 interval and the strain rate across a 30 km wide zone there is approximated by a 0 07 0 03 strain yr n20 e 12 uniaxial extension the observed extension of the hanging wall block in the direction normal to fault strike suggests that the wasatch fault may be listric a planar fault would produce a zone of contraction normal to the fault at the surface of the hanging wall block the component of extension parallel to fault strike observed on the footwall block is unexplained

fault slip rates and initiation age based on diffusion equation modeling wasatch fault zone and eastern great basin models of the evolution of fault scarp morphology provide time elapsed since slip initiated on a faulted surface and may therefore provide more accurate estimates of slip rate than the rate calculated by dividing scarp offset by the age of the ruptured surface to accomplish this task linear and nonlinear models of sediment transport are calibrated from the morphology of lake bonneville shoreline scarps and fault scarps formed by multiple surface rupturing earthquakes along the wasatch fault zone wfz profile modeling of scarps formed by several events distributed through time is done using a constant slip rate csr solution and yields a value of a 1 2 slip rate diffusivity time elapsed since slip initiated on a fault is determined by establishing a value for and measuring total scarp offset csr nonlinear modeling 0 2 8 1 1 m2 kyr wfz of faults along the west slope of the oquirrh mountains indicates a slip rate of 0 1 mm yr since 50 to 65 ka which is corroborated by cosmogenic dating 10be 26al age 75 ka the slip rate along the west flank of the stansbury mountains varies from 0 04 to 0 2 mm yr for time frames of 10 to 100 ka with the most recent rupture on the northern portion of the fault zone 10 ka scarp analysis of the southern end of the nephi segment wfz suggests either temporal clustering or variable slip rate as indicated by differences in the short term 1 3 mm yr for 4 3 ka versus long term 0 4 mm yr for 70 ka slip rates

rock matrix structures in a zone influenced by a stylolite abstract a stylolitic structure is one of the visible manifestations of the pressure solution process in a rock the stylolitic process zone as defined in previous studies on both sides of a stylolite is studied by sem the chosen samples concern tectonic stylolites within a high porosity limestone 16 without tension gashes this zone corresponds to a local increase of porosity and comprises a large number of stylolitic joints showing a decreasing size from the macroscopic structure to simple contact between two grains two hypotheses are presented for the stylolite formation 1 the macroscopic stylolite is the result of the coalescence of earlier minor pressure solution structures 2 small stylolites nucleate gradually from a major stylolite joint the mass transfer can be realized either by diffusion between particles or by seepage through previously undescribed process zone fractures the mass deposition can be localized in the porous volume and the microcracks without requiring any additional tectonic openings including tension gashes the rock deformation is therefore limited to shortening parallel to 1 without normal extension

jurassic lake t oo dichi a large alkaline saline lake morrison formation eastern colorado plateau a large alkaline saline lake lake t9oo9dichi9 occupied the entire eastern part of the colorado plateau region during deposition of the brushy basin member of the upper jurassic morrison formation the lake extended from near the site of albuquerque new mexico to near the site of grand junction colorado and occupied a region that encompassed the san juan and ancestral paradox basins making it the largest ancient alkaline saline lake known the lake was typically shallow and frequently evaporated to dryness although the water table was probably never far beneath the surface intermittent streams carried detritus from source areas to the west and southwest far out into the lake basin a reflection of a low depositional gradient and the ephemeral nature of the lake prevailing westerly winds carried silicic volcanic ash to the lake basin from an arc region to the west and southwest a lateral hydrogeochemical gradient characterized by increasing salinity and alkalinity from the margin of the lake to the center developed in pore waters of the lacustrine sediments and resulted in alteration of the ash to a variety of authigenic minerals that define concentric zones within the lake basin the basinward progression of diagenetic mineral zones is smectite clinoptilolite analcime potassium feldspar albite a concomitant lateral zonation of mixed layer illite smectite developed from highly smectitic in the outermost zones to highly illitic in the central zone authigenic albite and illitic mixed layer clay minerals previously thought to require elevated temperatures for formation crystallized during early diagenesis at syndepositional temperatures in the lacus trine sediments of lake t9oo9dichi9 this study presents evidence for a syndepositional origin for both of these minerals these findings have important implications in terms of limiting the use of these minerals as geothermometers recognition of alkaline saline lake deposits in the morrison formation significantly alters interpretations of depositional environments of this formation and it also has important implications for paleoclimatic interpretation late jurassic climate was apparently much more and than had previously been thought in fact sedimentologic evidence suggests that the lake basin was typically dry for extended periods and enjoyed only brief wet intervals this conclusion has important consequences for environmental interpretation of the habitat that was favorable for large herbivorous dinosaurs which thrived in the late jurassic

the potential of using thermoluminescence to date buried soils developed on colluvial and fluvial sediments from utah and colorado u s a preliminary results the natural tl intensity for surface and buried holocene and pleistocene a horizons developed on flood plain silts near denver colorado exponentially decreases with time this signal is approaching saturation by ca 130 ka the a horizon of the modern flood plain soil is not fully light bleached the tl properties and age estimates are presented for radiocarbon dated eolian enriched buried a horizons developed on fault derived colluvium from the american fork segment of the wasatch fault zone utah dating of these buried soils provide a close age estimate on paleoearthquake events mean tl age estimates by regeneration and total bleach techniques for buried a horizons are 0 5 0 1 ka and 2 7 0 4 ka which are in agreement with corresponding radiocarbon dates of 980 70 years bp and 2620 70 years bp a surface sag pond mud formed within an antithetic grabben is well light bleached and yielded a tl age estimate by the total bleach method of 240 60 years bp in agreement with its known age of 300 years bp this study indicates that relatively brief periods of pedogenesis are not sufficient to light bleach sediment and that eolian additions enhance the reduction of tl in soils

luminescence dating of hillslope deposits a review abstract luminescence dating determines the last exposure to light of quartz and feldspar mineral grains and thus the time a sediment was laid down prerequisite is that the sediment grains were sufficiently exposed to light prior to deposition for eolian deposits this seems a fair assumption although exceptions may well exist for other depositional environments light exposure prior to burial is often restricted in duration intensity and spectral composition and may result in an age overestimation recent developments now allow dating of sediments that were exposed to only little light prior to deposition the main developments are single aliquot techniques and statistical tests that allow extraction of valid age estimates even from deposits in which bleached and unbleached grains are mixed these developments in combination with the fact that the great majority of sediments near the earth s surface are not of eolian origin have resulted in the large interest in the luminescence dating of non eolian deposits here we review possibilities and challenges of luminescence dating of colluvial deposits we summarize techniques for the detection and handling of insufficiently bleached sediments a common condition in colluvial deposits we give an overview how luminescence dating has been applied on hillslope sediments for reconstructing landscape response to climate change to analyze past fault activity and unravel human induced soil erosion we discuss sampling strategies and give guidelines as to which techniques are best suited to establish luminescence chronologies for colluvium

a cenozoic seawater sr ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes a cenozoic multi species record of benthic foraminiferal calcite sr ca has been produced and is corrected for inter specific offsets typically less than 0 3 mmol mol and for the linear relationship between decreasing benthic foraminiferal sr ca and increasing water depth the water depth correction determined from holocene late glacial maximum and eocene paleowater depth transects is not vert similar0 1 mmol mol km the corrected cenozoic benthic foraminiferal sr ca record ranges from 1 2 to 2 0 mmol mol and has been interpreted in terms of long term changes in seawater sr ca enabling issues related to higher resolution variability in sr ca to be ignored we estimate that seawater sr ca was not vert similar1 5 times modern values in the late cretaceous but declined rapidly into the paleogene following a minimum in the eocene seawater sr ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late miocene by assuming scenarios for changing seawater calcium concentration and using published carbonate accumulation rate data combined with suitable values for sr partition coefficients into carbonates the seawater sr ca record is used to estimate global average river sr fluxes these fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity tectonic outgassing to calculate changes in global average river 87sr 86sr through the cenozoic the absolute magnitude of sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties nevertheless our results suggest that river sr flux increased from 35 ma to the present day roughly two fold accompanied by an overall increase in 87sr 86sr by not vert similar0 to 0 001 between 75 and 35 ma river 87sr 86sr also increased by not vert similar0 001 to 0 002 but was accompanied by a decrease two to three fold in river sr flux

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

topographic constraints on deviatoric stress field in the indo eurasian collision region seismo tectonic implications the deviatoric stress field are computed from the inversion of gravitational potential energy gpe for the indo eurasian plate collision region including the himalaya and the tibet plateau the resulting stress pattern in combination with stress and strain rates obtained by inverting respectively the focal mechanism solution of large earthquakes and gps derived plate motions are used to study the nature of the present day deformations a narrow belt bordering the himalayan collision zone from the south is characterized by strong compressive stresses the variations in stress pattern along this belt coincide with arc normal ridges extending into the himalaya and are able to explain arc parallel segmentation of seismicity gravitational collapse seems to play an important role in the southeastern tibet plateau depth sensitivity of the seismic derived stresses and gps derived surface strain rates coupled with evidence of arcuate shaped high electrical conductivity favour strong ductile flow around the eastern himalaya syntaxis ehs at mid crustal depth the deflection of crustal flow indicted by the viscous resistance offered by the rigid sichuan basin adds to the traction stresses to cause clockwise rotation of the block around ehs

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget