investigating the role of the itoigawa shizuoka tectonic line towards the evolution of the northern fossa magna rift basin abstract the itoigawa shizuoka tectonic line istl fault system is considered to have one of the highest probabilities for a major inland earthquake occurrence in the whole of japan it is a complex fault system with the dip directions of the local fault segments changing from north to south between an east dipping low angle thrust fault a strike slip fault and a west dipping thrust fault the tectonic relations between the different parts of the fault system and the surrounding geological units are yet to be fully explained this study aims to reveal the juncture of the northern and central parts of the istl and investigate its contribution towards the shaping of the northern fossa magna rift basin we conducted 3 deployments of 1 or 2 linear arrays of seismic stations across the central and northern istl regions and observed local micro earthquakes for a period of 3 years each deployment recorded continuous waveform data for approximately 3 months using arrival times of 1193 local earthquakes we jointly determined earthquake locations and a 3d velocity model applying the tomography method we were able to image the regional crustal structures from the surface to a depth of 20 km with a spatial resolution of 5 km subsequently we used the obtained 3d velocity model to relocate the background local seismicity from 2003 to 2009 the juncture of the northern and central parts of the istl was well constrained by our results the depth extension of the northern parts of the istl fault segments follows the bottom of the miocene northern fossa magna rift basin nfm and forms an east dipping low angle fault in contrast the central parts of the istl fault segments are estimated to lie along the eastern boundary of the matsumoto basin forming an oblique strike slip fault fig 1

geology of panamint valley saline valley pull apart system california palinspastic evidence for low angle geometry of a neogene range bounding fault geological studies support the interpretation that northern panamint valley and saline valley southeast california form paired pull apart basins on opposite sides of the right slip hunter mountain fault zone eight to ten km of late cenozoic net slip can be established on the hunter mountain fault zone palinspastic reconstruction of northern panamint valley indicates that the valley was formed by movement on a shallow crustal low angle normal fault of 0 15 degree west dip during the last 3 0 ma this interpretation appears to contradict the notions that little extension is accomodated in the uppermost crust by low angle faulting and that the most recent extension in the basin and range province is accomodated exclusively by high angle faulting saline valley however is interpreted to have formed by extension on closely spaced rotated planar normal faults thus within one geometric system of paired pull apart basins extension appears to have been accommodated in the shallow crust in two different ways

experimental low grade alteration of biogenic magnetite indicates microbial involvement in generation of banded iron formations during the deposition of banded iron formation bif the downward flux of ferric oxyhydroxides and phytoplankton biomass should have facilitated fe iii reduction during burial with the end product being ferrous iron containing minerals including magnetite although earlier studies have attempted to quantify the significance of this pathway based on models of the ancient fe cycle the only direct evidences of a biological role in magnetite formation in bif are their iron isotope compositions and unique crystallography which are reminiscent of biologically generated magnetite however the biogenesis hypothesis lacks an explanation as to why modern biogenic magnetite crystals are generally a few hundred nm or smaller in size yet the magnetite crystals in bif are mostly tens of micrometers or larger in size in this study we demonstrate that biogenic magnetite crystals can grow in size upon reaction between oxyhydroxide and microbial biomass after compression and heating to 1 kbar and 150 1c respectively the magnetite crystals previously produced by thermoanaerobacter spp tor39 reach sizes in excess of 700 nm after the p t experiments while new magnetite grains 4 400 nm formed from the superparamagnetic magnetite dominated end product of shewanella sp culture this study indicates that the large magnetite crystals observed in bif can be derived through a three stage sequence beginning with dissimilatory iron reduction of an initial ferric iron rich sediment coupled to the oxidation of dead phytoplankton biomass followed by magnetite crystal aging and ultimately pressure temperature induced abiotic alteration of the biogenic magnetite during metamorphism

strain partitioning in the northern walker lane western nevada and northeastern california abstract paleomagnetic studies constrain both the kinematics and the timing of neogene intracontinental strain in the walker lane of northwestern nevada northeastern california the northwest trending walker lane is a zone of complex faulting and dextral offset along the boundary between the sierra nevada and the basin and range here an extensive tertiary volcanic section provides a paleomagnetic test for vertical axis rotation the 25 1 ma nine hill tuff covered the two structural domains of northern walker lane and parts of the adjacent provinces in the northernmost domain the pyramid lake domain the nine hill tuff is unrotated or rotated slightly counter clockwise in contrast nine hill tuff is rotated 35 44 clockwise in the northeastern part of the adjacent carson domain usable exposures of the tuff are lacking elsewhere in the carson domain but 9 13 ma basalts record 37 51 clockwise vertical axis rotation these basalts were sampled at three sites encompassing the n s length of the carson domain younger basalts from the carson domain show smaller clockwise rotations the paleomagnetic studies show that the deformation in the northern walker lane is partitioned into domains dominated by translation rotation and extension dextral slip along the walker lane is accommodated primarily by northwestward translation in the pyramid lake domain and by clockwise vertical axis rotation in the carson domain some neogene extension is also accommodated in the walker lane but most of it is occurring to the west of the walker lane along the edge of the sierra nevada comparison of paleomagnetic results from rocks of different ages constrains the timing of the present deformation regime in the walker lane the similar rotations recorded in 25 ma and 9 13 ma rocks indicates that virtually all of the rotation in the carson domain occurred after the eruption of the 9 13 ma basalts smaller rotations recorded in younger rocks constrain rotation rate

the 13c12c ratios of siderite and organic matter of a modern metalliferous hydrothermal sediment and their implications for banded iron formations abstract a hydrothermal ferruginous sediment precipitated by the activity of the microaerophilic chemolithotrophic bacterium galionella ferruginea has been sampled in a bay of nea kameni island santorini greece due to high fugacity of carbon dioxide precipitation of siderite also occurred the 13c value pdb was determined to be 6 5 in the siderite and 26 8 in the organic matter of mainly microbiological origin the enrichment of isotopically light carbon in carbonates of banded iron formations 13 c 10 has recently been discussed in literature the dilution of these marine carbonates by isotopically light carbon is suggested to have resulted from bacterial oxidation of reduced organic carbon during early diagenesis it is further suggested that fe iii in the newly precipitated sediment served as electron acceptor during oxidation in a hydrothermal model for the origin of banded iron formations this is consistent with the data presented here it is therefore postulated from the results presented that the reduced organic carbon in banded iron formations originates from microaerophilic chemolithotrophic bacteria

transtensional model for the sierra nevada frontal fault system eastern california active strike slip and normal faults along the eastern margin of the sierra nevada primarily accommodate northwestward translation of the sierra nevada central valley i e sierran microplate with respect to stable north america strike slip faults bordering the eastern sierran microplate are subparallel to small circles about the sierra nevada north american euler pole normal faults of the sierra nevada frontal fault system strike 45 clockwise of the small circle trajectories and exhibit well defined left stepping en echelon patterns consistent with formation in dextral transcurrent regime major graben bordering the northeastern sierran microplate are located in regions where the locus of range front deformation steps abruptly eastward in a releasing geometry relative to sierra nevada north american motion crustal shortening occurs at the northern end of the sierran microplate where a component of northwest dextral shear steps westward in a left restraining geometry across the sierran crest to the sacramento valley kinematic inversions of earthquake focal mechanisms from the walker lane belt bordering the eastern sierra nevada indicate that seismogenic deformation primarily is characterized by horizontal shearing and oblique crustal thinning directions of macroscopic dextral shear inferred from the inversions are subparallel to the trajectories of small circles about the sierra nevada north american euler pole normal faulting along most of the eastern sierran range front thus appears to primarily accommodate microplate translation rather than sierran uplift or regional basin and range extension

could bacteria have formed the precambrian banded iron formations banded iron formations bifs are prominent sedimentary deposits of the precambrian but despite a century of endeavor the mechanisms of their deposition are still unresolved interactions between microorganisms and dissolved ferrous iron in the ancient oceans offer one plausible means of mineral precipitation in which bacteria directly generate ferric iron either by chemolithoautotrophic iron oxidation or by photoferrotrophy on the basis of chemical analyses from bif units of the 2 5 ga hamersley group western australia we show here that even during periods of maximum iron precipitation most if not all of the iron in bifs could be precipitated by iron oxidizing bacteria in cell densities considerably less than those found in modern fe rich aqueous environments those ancient microorganisms would also have been easily supported by the concentrations of nutrients p and trace metals v mn co zn and mo found within the same iron rich bands these calculations highlight the potential importance of early microbial activity on ancient metal cycling

a 21 event 4 000 year history of surface ruptures in the anza seismic gap san jacinto fault and implications for long term earthquake production on a major plate boundary fault paleoseismic work completed at hog lake on the san jacinto fault sjf near anza california indicates that at least 21 surface ruptures have occurred in the anza seismic gap over the past 4 000 years the ages of the ruptures are constrained by 111 radiocarbon dates 97 of which fall in stratigraphic order the average recurrence interval for all ruptures for this period is about 185 105 years although some ruptures such as occurred in the april 1918 earthquake caused only minor displacement we rate the expression of each interpreted event in each of the twelve developed field exposures presented in this work by assigning numeric values for the presence of different criteria that indicate rupture to a paleo ground surface weakly expressed ruptures for example the deformation we interpret to be the result of the historical 1918 earthquake received low scores and are interpreted as smaller earthquakes from this analysis we infer that at least fifteen of the identified ruptures are indicative of large earthquakes similar to the penultimate earthquake inferred to be the m w 7 3 22 november 1800 earthquake the adjusted recurrence interval for large earthquakes lengthens to approximately 254 years comparison with the rupture history at the mystic lake paleoseismic site on the claremont strand indicates that it is plausible that several of the large ruptures identified at hog lake could have jumped the hemet step over at mystic lake and continued on the claremont strand or vice versa but most of the event ages do not match between the two sites indicating that most ruptures do not jump the step finally comparison with san andreas fault ruptures both to the north and south of its juncture with the sjf suggest that some northern sjf ruptures identified at mystic lake may correlate with events identified at wrightwood but that these northern ruptures have no match at hog lake and can not indicate rupture of the entire sjf onto the saf

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

evaluation of siderite and magnetite formation in bifs by pressure temperature experiments of fe iii minerals and microbial biomass abstract anoxygenic phototrophic fe ii oxidizing bacteria potentially contributed to the deposition of archean banded iron formations bifs before the evolution of cyanobacterially generated molecular oxygen o 2 by using sunlight to oxidize aqueous fe ii and precipitate fe iii oxyhydr oxides once deposited at the seafloor diagenetic reduction of the fe iii oxyhydr oxides by heterotrophic bacteria produced secondary fe ii bearing minerals such as siderite feco 3 and magnetite fe 3 o 4 via the oxidation of microbial organic carbon i e cellular biomass during deeper burial at temperatures above the threshold for life thermochemical fe iii reduction has the potential to form bif like minerals however the role of thermochemical fe iii reduction of primary bif minerals during metamorphism and its impact on mineralogy and geochemical signatures in bifs is poorly understood consequently we simulated the metamorphism of the precursor and diagenetic iron rich minerals ferrihydrite goethite hematite at low grade metamorphic conditions 170 c 1 2 kbar for 14 days by using 1 mixtures of abiotically synthesized fe iii minerals and either microbial biomass or glucose as a proxy for biomass and 2 using biogenic minerals formed by phototrophic fe ii oxidizing bacteria mossbauer spectroscopy and xrd showed that thermochemical magnetite formation was limited to samples containing ferrihydrite and glucose or goethite and glucose no magnetite was formed from fe iii minerals when microbial biomass was present as the carbon and electron sources for thermochemical fe iii reduction this could be due to biomass derived organic molecules binding to the mineral surfaces and preventing solid state conversion to magnetite mossbauer spectroscopy revealed siderite contents of up to 17 after only 14 days of incubation at elevated temperature and pressure for all samples with synthetic fe iii minerals and biomass whereas 6 of the initial fe iii was reduced to sideritic fe ii in biogenic fe iii minerals during incubation based on our data magnetite in bif is unlikely to be formed by thermochemical fe iii reduction in sediments of biogenic ferrihydrite hematite or goethite dominated sediments with complex microbial biomass present instead our results suggest that diagenetic magnetite in bif was either formed by microbial fe iii reduction during early diagenesis i e below 120 c or by thermochemical fe iii reduction with simple organic compounds at higher temperatures whereas siderite was formed by both microbial diagenetic fe iii reduction and thermogenic fe iii reduction with complex biomass thermochemical fe iii reduction coupled to biomass oxidation during metamorphism provides another origin for bif siderites and could have led to a significant increase in fe ii content in bif after deposition over geological timescales

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

east trending dextral faults in the western great basin an explanation for anomalous trends of pre cenozoic strata and cenozoic faults two postulated major east trending strike slip fault zones here named the coaldale and excelsior fault zones are delineated mainly on the basis of faults in cenozoic rocks in eastern california and western nevada and coincide with apparent major right lateral offsets in the distribution and facies of pre cenozoic rocks apparent right lateral offset of pre cenozoic rocks on the coaldale fault zone is 60 to 80 km and on the excelsior fault zone is 45 to 55 km this offset accounts for major disruption in trends of pre cenozoic rocks in eastern california and western nevada a disruption previously interpreted as the result of either an originally curving continental margin or tectonic distortion of originally linear trends by large scale bending oroflexural folding or by crustal scale folding related to north east southwest compression main offset on the coaldale and excelsior fault zones appears to be late mesozoic in age a pre mid cretaceous age is indicated because mid cretaceous and younger plutonic rocks are not cut by major strike slip faults on line with the fault zones major movement is probably younger than the dunlap formation which is dated paleontologically as early jurassic but which may also contain rocks as young as cretaceous local reactivation of the faults in the cenozoic perhaps under a different stress regime accounts for offset of cenozoic rocks the coaldale and excelsior fault zones terminate major northwest trending late cenozoic and possibly older faults the owens valley white mountain fault system in eastern california and the furnace creek fault zone in southeastern california and westernmost nevada terminate northward at the coaldale fault zone a system of south east trending right lateral and high angle faults in western nevada including the bettles well fault terminate southward at the excelsior fault zone major movement on northwest trending faults such as the furnace creek and bettles well fault may be mostly late cenozoic in age but present information does not preclude the possibility that these fault zones initiated prior to and are offset by the coaldale and excelsior fault system the unusual trends of pre tertiary rocks and of the coaldale and excelsior fault zones in eastern california and western nevada appear to be restricted to the walker lane belt a broad northwest trending structural zone characterized by right lateral shear in western nevada and eastern california possibly initial shear produced the northwest trending faults and a later kink in this system produced oroflexural folding and the east trending right lateral coaldale and excelsior fault zones this kink may have resulted from a change in the stress regime and structural complexities where the shear zone obliquely crossed the paleozoic continental margin

frictional behavior of materials in the 3d safod volume 1 we report on frictional properties of rocks within the 3 d crustal volume surrounding the san andreas fault observatory at depth safod samples include lithologies adjacent to the san andreas fault saf in the subsurface safod borehole rocks and synthetic fault gouge composed of talc serpentinite and quartz granodiorite arkosic sandstone and siltstone samples from the safod borehole are frictionally strong 0 56 0 66 sand and clay rich lithologies from outcrop exhibit friction in the range 0 56 0 68 natural serpentinite thought to abut the saf at depth exhibits low friction 0 18 0 26 our results indicate that 1 serpentinite exhibits low strength but is not weak enough to completely satisfy weak fault models 2 all other samples are consistent with a strong fault and crust and 3 if the saf is weak 0 2 due to the presence of serpentinite or talc these minerals would likely need to constitute over 50 by weight of the shear zone

holocene slip rates along the owens valley fault california implications for the recent evolution of the eastern california shear zone one of the largest historical earthquakes in california occurred in 1872 along the owens valley fault located along the western margin of the eastern california shear zone new paleoseismic and optically stimulated luminescence data are the first to bracket the timing of the pre 1872 rupture to between 3 3 0 3 and 3 8 0 3 ka these data yield an earthquake recurrence interval between 4100 and 3000 yr under the assumption of uniform return and indicate a holocene slip rate between 1 8 0 3 and 3 6 0 2 mm yr our data are broadly consistent with a model proposed for the space time evolution of the eastern california shear zone our holocene slip rate estimates for the owens valley fault are slower than present day slip rates determined from elastic half space models of geodetic data this discrepancy is reduced by using the recurrence interval estimated here and a viscoelastic model of geodetic data or by including geologic slip rates from adjacent faults

micro and nanobands in late archean and palaeoproterozoic banded iron formations as possible mineral records of annual and diurnal depositions abstract the microbands in precambrian banded iron formations bifs have been conjectured to record annual or even diurnal depositions however these bands have rarely been observed in high resolution at their true micro scale here i suggest that nanobands of fine grained hematite represent possible diurnal depositions and that microbands of chert jasper represent possible annual depositions in three sets of bifs 2460 myr bifs from the kuruman iron formation transvaal supergroup of south africa 2480 myr bifs from the dales gorge member of the brockman iron formation western australia and 2728 myr bifs from the hunter mine group abitibi greenstone belt canada observations made using scanning electron microscopy indicate that hematite and chert were syngenetic and that there was a hiatus between their precipitation and the genesis of the remainder of the minerals containing structural fe ii spindle like grains of hematite monocrystals of magnetite and ferro dolomite formed microbands of 30 70 m in thickness which appear cyclically in the matrix of the chert neither the band bound magnetite and dolomite nor the linear formations of the hematite spindles represent annual depositions due to their diagenetic features the thinnest microbands 3 12 m were observed in the chert and jasper and indicate depositional rates of 6 6 22 2 m myr in the bifs these rates are consistent with the integrated deposition rates calculated by geochronologic methods for the bifs if annual deposition is assumed the 26 nm nanobands observed only in hematite grains reflect an annual deposition of 18 6 m or 18 6 m myr which is also consistent with the depositional rate calculated by geochronologic methods it is tentatively suggested that these 26 nm nanobands were formed from the diurnal precipitation of fe iii resulting from the circadian metabolism of fe ii oxidizing or oxygen evolving photosynthetic microorganisms which slowed down the rise of atmospheric oxygen the diurnal precipitation of fe iii as hematite and the annual deposition of silica as chert jasper in the bifs provide internal clocks that may facilitate the examination of short term processes such as ecological oceanographic and climatic cycles that are recorded by the mineral or chemical compositions of bifs

evidence for exclusively inorganic formation of magnetite in martian meteorite alh84001 magnetite crystals produced by terrestrial magnetotactic bacterium mv 1 are elongated on a 111 crystallographic axis in a so called truncated hexa octahedral shape this morphology has been proposed to constitute a biomarker i e formed only in biogenic processes a subpopulation of magnetite crystals associated with carbonate globules in martian meteorite alh84001 is reported to have this morphology and the observation has been taken as evidence for biological activity on mars in this study we present evidence for the exclusively inorganic origin of 111 elongated magnetite crystals in alh84001 we report three dimensional 3 d morphologies for 1000 magnetite crystals extracted from 1 thermal decomposition products of fe rich carbonate produced by inorganic hydrothermal precipitation in laboratory experiments 2 carbonate globules in martian meteorite alh84001 and 3 cells of magnetotactic bacterial strain mv 1 the 3 d morphologies were derived by fitting 3 d shape models to two dimensional bright field transmission electron microscope tem images obtained at a series of viewing angles the view down the 110 axes closest to the 111 elongation axis of magnetite crystals 111 110 0 provides a 2 d projection that uniquely discriminates among the three 111 elongated magnetite morphologies found in these samples 111 elongated truncated hexa octahedron 111 tho 111 elongated cubo octahedron 111 eco and 111 elongated simple octahedron 111 eso all 111 elongated morphologies are present in the three types of sample but in different proportions in the alh84001 martian meteorite and in our inorganic laboratory products the most common 111 elongated magnetite crystal morphology is 111 eco in contrast the most common morphology for magnetotactic bacterial strain mv 1 is 111 tho these results show that 1 the morphology of 111 elongated magnetite crystals associated with the carbonate globules in martian meteorite alh84001 is replicated by an inorganic process and 2 the most common crystal morphology for biogenic mv 1 magnetite is distinctly different from that in both alh84001 and our inorganic laboratory products therefore 111 elongated magnetite crystals in alh84001 do not constitute as previously claimed a robust biosignature and in fact an exclusively inorganic origin for the magnetite is fully consistent with our results furthermore the inorganic synthesis method i e the thermal decomposition of hydrothermally precipitated fe rich carbonate is a process analogue for formation of the magnetite on mars namely precipitation of carbonate globules from carbonate rich hydrothermal solutions followed at some later time by a thermal pulse perhaps in association with meteoritic impact or volcanic processes on the martian surface

geodetic measurement of deformation in the central mojave desert california data from triangulation and trilateration surveys made during 1934 1982 are used to calculate shear strain rates in the central mojave desert of california for the region between the helendale and camp rock faults the shear strain rate was determined to be 0 16 0 03 strain yr with maximum right lateral shear strain occurring on a plane oriented n41 w 5 if we assume that this deformation is due to right lateral motion across the northwest trending local faults the average shear straining corresponds to a relative displacement of 6 7 1 3 mm yr across this portion of the network accounting for 12 of the predicted 56 mm yr of relative motion between the north american and pacific plates from the camp rock fault eastward across the network there is a transition from significant to very low strain rates examination of nine focal mechanisms and their relation to the local geology and the strain data suggests that most of the long term displacement occurs on the major northwest trending faults oriented nearly along the direction of relative motion between the north american and pacific plates secondary faulting controlled by a coulomb anderson failure mechanism or by slip on preexisting faults can account for the occurrence of earthquakes on faults of other orientations

formation of single domain magnetite by a thermophilic bacterium magnetite is a common product of bacterial iron reduction and may serve as a potential physical indicator of biological activity in geological settings here the authors report the formation of single domain magnetite under laboratory conditions by a thermophilic fermentative bacterial strain tor 39 that was isolated from the deep subsurface time course analyses were performed at 65 c to study the effect of bacterial activity on solution chemistry and magnetite formation during the growth of tor 39 run products were examined by transmission electron microscopy magnetite particles formed exclusively outside of bacterial cells and exhibited octahedral shapes having relatively equal length and width 15 difference tiny magnetite particles 12 nm nucleated between 10 and 11 h of incubation and increased to average lengths of 55 4 26 8 nm after 24 h of incubation between 24 h and 22 d of incubation magnetite particles maintained average lengths of 56 2 24 8 nm based on size constraints greater than 85 of the particles observed fell within the magnetic single domain little to no magnetite was detected in abiotic controls at 65 or 95 c or in tor 39 cultures whose activity was suppressed unlike mesophilic iron reducing bacteria e g gs 15 tor 39 produced crystals having shapes and sizesmore similar to some particles produced intracellularly by magnetotactic bacteria thus the single domain magnetite produced by thermophiles such as tor 39 may represent a heretofore unrecognized biological contribution to natural remanent magnetization in sedimentary basins and other geothermal environments less

source parameters of earthquakes in the nevada seismic zone 1915 1943 the nevada seismic zone has historically been one of the most active seismic regions of the intermountain west although all large m 7 0 earthquakes located within this zone occurred prior to the establishment of a worldwide seismograph network most have been well recorded instrumentally this study uses available instrumental data to determine the source parameters for some of the earliest earthquakes occurring within the region namely the 1915 m 7 6 pleasant valley and 1932 m 7 2 cedar mountain earthquakes and several smaller events of 5 5 m 6 5 occurring within the cedar mountain region between 1934 and 1943 results of body waveform inversions suggest that the pleasant valley earthquake at the northern end of the nevada seismic zone is a complex event best fit by a multiple source time function waveform and first motion information for the cedar mountain earthquake located within the walker lane suggest the earthquake was composed of two events each having significant components of right lateral strike slip motion rakes of 176 to 179 waveforms of the m 6 5 excelsior mountain earthquake located only 40 km southwest of cedar mountain suggest the earthquake was a simple rupture along a normal fault rake of 90 20 although surface faulting indicates that the event had a component of left lateral strike slip motion

can the okhotsk plate be discriminated from the north american plate the plate geometry in northeast asia has been a long standing question with a major issue being whether the sea of okhotsk and northern japanese islands are better regarded as part of the north american plate or as a separate okhotsk plate this question has been difficult to resolve because earthquake slip vectors along the kuril and japan trenches are consistent with either pacific north america or pacific okhotsk plate motion to circumvent this difficulty we also use slip vectors of earthquakes along sakhalin island and the eastern margin of the japan sea and compare them to the predicted eurasia okhotsk and eurasia north america motions for a model with a separate okhotsk plate we invert 10 eurasia okhotsk and 255 pacific okhotsk slip vectors with pacific north america and eurasia north america nuvel 1 data alternatively for a model without an okhotsk plate those eurasia okhotsk and pacific okhotsk data are regarded as eurasia north america and pacific north america data respectively the model with an okhotsk plate fits the data better than one in which this region is treated as part of the north american plate because the improved fit exceeds that expected purely from the additional plate the data indicate that the okhotsk plate can be resolved from the north american plate the motions on the okhotsk plate s boundaries predicted by the best fitting euler vectors are generally consistent with the recent tectonics the eurasia okhotsk pole is located at northernmost sakhalin island and predicts right lateral strike slip motion on the nne striking fault plane of the may 27 1995 neftegorsk earthquake consistent with the centroid moment tensor focal mechanism and the surface faulting along the northern boundary of the okhotsk plate the north america okhotsk euler vector predicts left lateral strike slip consistent with the observed focal mechanisms on the nw boundary of the okhotsk plate the eurasia okhotsk euler vector predicts e w extension discordant with the limited focal mechanisms and geological data this misfit may imply that another plate is necessary west of the magadan region in southeast siberia but this possibility is hard to confirm without further data such as might be obtained from space based geodesy

mineralogical and microfabric characteristics of magnetite in the wuyang precambrian bifs southern north china craton implications for genesis and depositional processes of the associated bifs abstract precambrian banded iron formations bifs are widely distributed in the north china craton ncc among them the wuyang bifs located in the southern margin of ncc occur in the late archaean tieshanmiao formation and can be subdivided in two different sub types i quartz magnetite bifs qmb consisting of magnetite fine microcrystalline quartz and minor calcite and ii pyroxene magnetite bifs pmb composed of pyroxene fine microcrystalline quartz and subordinate feldspars both sub types display apparent discrepancies in terms of petrography and mineral composition as shown in electron backscattered diffraction ebsd images and micrographs magnetite grains from the qmb range in size from tens up to hundreds of m whereas magnetite crystals from the pmb can be up to a few tens of m across the x ray diffraction xrd structural data indicate that magnetite from both bif sub types is equiaxed cubic and was generated by sedimentary metamorphic processes the cell parameters of magnetite in the qmb are a b c 8 396 a and z 8 which deviate slightly from these of magnetite in the pmb a b c 8 394 a and z 8 the analytical results of raman spectroscopy analysis revealed micro structural signatures of both magnetite raman shifts near 552 cm 1 and 673 cm 1 and hematite raman shifts near 227 cm 1 295 cm 1 and 413 cm 1 in magnetite from both qmb and pmb the crystallinity degree is similar for magnetite micro structures but varies significantly for hematite micro structures oxygen fugacity fo2 conditions fluctuated during the recrystallization of magnetite in the qmb whereas no evident variation of fo2 occurred during the formation of magnetite in the pmb analytical results of laser ablation inductively coupled plasma mass spectrometry la icp ms show that the si al and mg abundances are higher in magnetite from the qmb whereas the ti and mn contents are more elevated in magnetite from the pmb magnetite composition also denotes that both bif sub types are sedimentary metamorphic origin whereas the deposition of pmb was also affected by volcanic activities overall data indicate that the differences in the depositional environment of each bif sub type are due to the involvement of volcanic eruption processes in the genesis of the pmb thus this paper indicated that the qmb was deposited by chemical deposition at the long term interval of volcanic eruptions and the pmb were the product of chemical deposition affected by the volcanic eruption

iron mineralization and taphonomy of microfossils of the 2 45 2 21 ga turee creek group western australia abstract we report a new assemblage of carbonaceous microfossils intimately associated with siderite and fe silicates from a black chert nodule included in iron formation of the ca 2 45 2 21 ga turee creek group western australia this chert comprises microbial fabrics dominated by filaments preserved in matrix of nano to micrometric quartz filaments occur in clumps and in a cobweb like fabric interspersed with coarse crystalline void filling quartz granules we studied this chert with optical microscopy combined with scanning transmission electron microscope observations of focused ion beam sections of microfossils this distinguished three types of well preserved fossil interpreted as polysaccharide sheaths that usually do not preserve chains of cells trichomes type 1 comprises narrow filaments with thin continuous kerogen sheaths type 2 comprises narrow filaments with thick granular sheaths and type 3 comprises broad filaments with thin sheaths type 4 filaments are poorly preserved as granular kerogen organic ultrastructures of type 2 4 microfossils are variably replaced by siderite crystals associated with minor fe silicates iron isotope analyses on bulk powder and reactive iron fraction show indistinguishable and highly positive 56 fe values 1 45 relative to the reference irmm 014 indicating that the bulk of siderite derives from reduction of fe iii oxides this provides indirect evidence that the microbial community was originally associated with fe iii oxides siderite and fe silicates are found with type 2 4 but not type 1 filaments suggesting that only the former were encrusted by fe iii oxides which may have been reduced in situ siderite and fe silicates could result from oxidation of organic matter in filaments coupled with microbial and or thermal reduction of fe iii bio minerals the increasing abundance of siderite correlated with decreasing organic matter preservation in filaments supports that this reaction occurred to variable extents in situ on each microfossil type 2 4 microfossils may thus represent iron oxidizing bacteria these microbial mats display strong similarities with those associated with immediately overlying carbonate rocks of the turee creek group where filaments were interpreted as sulfur oxidizing bacteria some filamentous bacteria can oxidize both iron and sulfur such metabolic versatility could have enabled benthic microbial mats to thrive in the drastically changing chemical conditions of the great oxidation event

contemporary tectonics seismicity and potential earthquake sources in the white mountains seismic gap west central nevada and east central california usa abstract the white mountains seismic gap wmsg is a broad area between the 1872 owens valley earthquake and the 1932 cedar mountain earthquake that has a complicated tectonic setting and seismicity patterns and is considered to have the potential for a strong or larger magnitude earthquake in the near future we take the sierra nevada block as the western boundary of the wmsg the pancake range lineament and the southernmost 1932 earthquake ruptures as its approximate northern boundary a change in structure tectonic rates and seismicity level as the eastern boundary and the northernmost 1872 earthquake ruptures as the southern boundary seismicity within the wmsg especially in the southern part has been at a very high level since 1978 this activity has included six events of magnitude 6 and their associated aftershocks in addition many earthquake swarms have occurred throughout the wmsg some of which are distinctly located at the ends of fault zones or near changes in structural orientation focal mechanisms show a predominance of strike slip solutions for both small and large earthquakes with nw trending right lateral and ne trending left lateral solutions for over half of the mechanisms these are similar to the sense of displacements and orientations of the larger faults in the wmsg thus seismic strain is consistent with the faulting pattern in the wmsg and is accommodating contemporary deformation through a conjugate set of strike slip and normal oblique slip faults examination and analysis of eighteen of the larger faults in the wmsg leads to the estimation of characteristic earthquakes ranging from magnitude 6 8 to 7 4 given the size of the seismic gap 100 km and the pronounced change in structure near the middle of the seismic gap it seems likely that it will require two or more magnitude m 7 events to fill the gap

talc bearing serpentinite and the creeping section of the san andreas fault the section of the san andreas fault located between cholame valley and san juan bautista in central california creeps at a rate as high as 28 mm yr 1 ref 1 and it is also the segment that yields the best evidence for being a weak fault embedded in a strong crust serpentinized ultramafic rocks have been associated with creeping faults in central and northern california and serpentinite is commonly invoked as the cause of the creep and the low strength of this section of the san andreas fault however the frictional strengths of serpentine minerals are too high to satisfy the limitations on fault strength and these minerals also have the potential for unstable slip under some conditions here we report the discovery of talc in cuttings of serpentinite collected from the probable active trace of the san andreas fault that was intersected during drilling of the san andreas fault observatory at depth safod main hole in 2005 we infer that the talc is forming as a result of the reaction of serpentine minerals with silica saturated hydrothermal fluids that migrate up the fault zone and the talc commonly occurs in sheared serpentinite this discovery is significant as the frictional strength of talc at elevated temperatures is sufficiently low to meet the constraints on the shear strength of the fault and its inherently stable sliding behaviour is consistent with fault creep talc may therefore provide the connection between serpentinite and creep in the san andreas fault if shear at depth can become localized along a talc rich principal slip surface within serpentinite entrained in the fault zone

iron formations a global record of neoarchaean to palaeoproterozoic environmental history abstract iron formations if represent an iron rich rock type that typifies many archaean and proterozoic supracrustal successions and are chemical archives of precambrian seawater chemistry and post depositional iron cycling given that if accumulated on the seafloor for over two billion years of earth s early history changes in their chemical mineralogical and isotopic compositions offer a unique glimpse into environmental changes that took place on the evolving earth perhaps one of the most significant events was the transition from an anoxic planet to one where oxygen was persistently present within the marine water column and atmosphere linked to this progressive global oxygenation was the evolution of aerobic microbial metabolisms that fundamentally influenced continental weathering processes the supply of nutrients to the oceans and ultimately diversification of the biosphere and complex life forms many of the key recent innovations in understanding if genesis are linked to geobiology since biologically assisted fe ii oxidation either directly through photoferrotrophy or indirectly through oxygenic photosynthesis provides a process for if deposition from mineral precursors the abundance and isotope composition of fe ii bearing minerals in if additionally suggests microbial fe iii reduction a metabolism that is deeply rooted in the archaea and bacteria linkages among geobiology hydrothermal systems and deposition of if have been traditionally overlooked but now form a coherent model for this unique rock type this paper reviews the defining features of if and their distribution through the neoarchaean and palaeoproterozoic this paper is an update of previous reviews by bekker et al 2010 2014 that will improve the quantitative framework we use to interpret if deposition in this work we also discuss how recent discoveries have provided new insights into the processes underpinning the global rise in atmospheric oxygen and the geochemical evolution of the oceans

micro scale tracing of fe and si isotope signatures in banded iron formation using femtosecond laser ablation we have detected micrometre scale differences in fe and si stable isotope ratios between coexisting minerals and between layers of banded iron formation bif using an uv femtosecond laser ablation system connected to a mc icp ms in the magnetite carbonate chert bif from the archean old wanderer formation in the shurugwi greenstone belt zimbabwe magnetite shows neither intra nor inter layer trends giving overall uniform d 56 fe values of 0 9 but exhibits intra crystal zonation bulk iron carbonates are also relatively uniform at near zero values however their individual d 56 fe value is highly composition dependent both siderite and ankerite and mixtures between both are present and d 56 fe end member values are 0 4 for siderite and 0 7 for ankerite the data suggest either an early diagenetic origin of magnetite and iron carbonates by the reaction of organic matter with ferric oxyhydroxides catalysed by fe iii reducing bacteria or more likely an abiotic reaction of organic carbon and fe iii during low grade metamorphism si isotope composition of the old wanderer bif also shows significant variations with d 30 si values that range between 1 0 and 2 6 for bulk layers these isotope compositions suggest rapid precipitation of the silicate phases from hydrothermal rich waters interestingly fe and si isotope compositions of bulk layers are covariant and are interpreted as largely primary signatures moreover the changes of fe and si isotope signatures between bulk layers directly reflect the upwelling dynamics of hydrothermal rich water which govern the rates of fe and si precipitation and therefore also the development of layering during periods of low hydrothermal activity precipitation of only small amounts of ferric oxyhydroxide was followed by complete reduction with organic carbon during diagenesis resulting in carbonate chert layers during periods of intensive hydrothermal activity precipitation rates of ferric oxyhydroxide were high and subsequent diagenesis triggered only partial reduction forming magnetite carbonate chert layers we are confident that our micro analytical technique is able to detect both the solute flux history into the sedimentary bif precursor and the bif s diagenetic history from the comparison between coexisting minerals and their predicted fractionation factors

contributions to geotechnique 1948 2008 engineering geology rock mechanics and rock engineering throughout its history geotechnique has regularly published papers on the fundamentals of engineering geology the core concepts of rock mechanics and the practice of rock engineering in totality these papers provide a concise history of the development of these areas of geotechnics here a review of many of these papers is presented in terms of the specific themes of engineering geology rock slope instability behaviour of intact rock and discontinuities in rock field measurements in rock mechanics discontinuous rock masses numerical modelling and rock engineering papers covering a wide range of issues within these themes are outlined together with an indication of how they have influenced later developments the review clearly demonstrates how geotechnique has been at the forefront of rock mechanics rock engineering and engineering geology for the whole of its 60 year existence

impact of biomineralization on the preservation of microorganisms during fossilization an experimental perspective abstract the biogenicity of fossil microbial biomorphs is often debated because their morphologies are poorly informative and the chemical structural and isotopic signatures of putative biogenic organic molecules have been altered during their incorporation into the sediments and the geological history of the host rock here we investigated the effect of encrustation by biominerals on the morphological and chemical degradation of escherichia coli cells during experimental thermal treatments non calcified e coli cells and e coli cells encrusted by calcium phosphates were exposed to heating under an argon atmosphere at two different temperatures 300 c 600 c for 20 h two additional experiments were performed on non calcified e coli cells at 300 c for 2 h and 100 h to discuss the influence of experiment duration organic residues of all experiments were characterized at a multiple length scale using a combination of scanning electron microscopy transmission electron microscopy raman microspectroscopy electron paramagnetic resonance epr spectroscopy fourier transform infrared ft ir spectroscopy and x ray absorption near edge structure spectroscopy xanes at the carbon k edge in the absence of encrusting biominerals the morphological structure of the organic residues of e coli cells was completely lost after heating at 300 or 600 c even after short 2 h long heating experiments the content of aromatic functional groups of the organic residues of non calcified e coli cells increased during heat treatment at 600 c for 20 h while the amide functional groups were lost as indicated by ft ir spectroscopy consistently the epr spectrum of these organic residues indicated important transformation as a comparison this spectrum appeared similar to epr spectra of ancient organic carbons such as carbons from the apex chert ca 3460 myr indicating a similar concentration of aromatic moieties in contrast calcified e coli exposed to the same conditions showed only limited morphological alteration as observed by electron microscopy as well as lower chemical transformation as detected by ft ir and epr spectroscopies despite the difficulties to relate experimental conditions directly to geological conditions these experiments evidence the influence of cell encrustation by minerals on their chemical and morphological preservation potential during fossilization processes

structure and morphology of magnetite anaerobically produced by a marine magnetotactic bacterium and a dissimilatory iron reducing bacterium intracellular crystals of magnetite synthesized by cells of the magnetotactic vibroid organism mv 1 and extracellular crystals of magnetite produced by the non magnetotactic dissimilatory iron reducing bacterium strain gs 15 were examined using high resolution transmission electron microscopy electron diffraction and57fe mo ssbauer spectroscopy the magnetotactic bacterium contained a single chain of approximately 10 crystals aligned along the long axis of the cell the crystals were essentially pure stoichiometric magnetite when viewed along the crystal long axis the particles had a hexagonal cross section whereas side on they appeared as rectangules or truncated rectangles of average dimension 53 35 nm these findings are explained in terms of a three dimensional morphology comprising a hexagonal prism of 110 faces which are capped and truncated by 111 end faces electron diffraction and lattice imaging studies indicated that the particles were structurally well defined single crystals in contrast magnetite particles produced by the strain gs 15 were irregular in shape and had smaller mean dimensions 14 nm single crystals were imaged but these were not of high structural perfection these results highlight the influence of intracellular control on the crystallochemical specificity of bacterial magnetites the characterization of these crystals is important in aiding the identification of biogenic magnetic materials in paleomagnetism and in studies of sediment magnetization

microstructures crystallography and geochemistry of magnetite in 2500 to 2200 million year old banded iron formations from south africa western australia and north china abstract as a major mineral in banded iron formation bif magnetite can provide information on depositional environment and mechanism of bif it can provide insights into precambrian biological process the crystallography and microstructures of magnetite in bif have been poorly studied due to its simple chemical composition here we report an integrated crystallographic and geochemical study on various magnetites from four bifs of 2500 to 2200 million year old for a better understanding on their geneses and alterations euhedral magnetite crystals from the 2480 ma dales gorge and 2460 ma kuruman bifs all show pure and homogeneous colors in their ebsd phase euler and ipf maps suggesting they are well crystallized and devoid of inclusions or fractures these crystals are recognized as silician magnetite with appreciable structural si ave 1 22 and 2 05 wt respectively but rare al ave 0 27 and

shrimp u pb zircon ages for the palaeoproterozoic kuruman iron formation northern cape province south africa evidence for simultaneous bif deposition on kaapvaal and pilbara cratons abstract stilpnomelane rich tuffaceous mudrocks are an important component of the palaeoproterozoic kuruman and griquatown iron formations in the northern cape province they document volcanic activity during the deposition of these iron formations and the zircon populations that they contain record syn depositional volcanism resedimentation and post depositional isotopic disturbance the trace element signatures of tuffaceous samples suggest that although zircons are felsic volcanogenic in origin mixing of felsic ash with basaltic ash and or muds in the water column was also likely in addition these rocks record minor terrigenous input and some samples indicate mixing with iron rich clays oxides and smectites moreover they reflect a shift from mafic volcanism e g mafic tuffs in the underlying gamohaan formation towards more felsic volcanism that is a trend also recorded for tuffaceous rocks in the brockman iron formation the best estimate of the depositional age for the top of the riries member and hence the kuruman iron formation is 2460 ma where most of the zircon populations were derived from volcanism coeval with bif deposition ages obtained in this study that are older than the 2465 5 ma age for the lower riries member probably represent resedimented pyroclastic deposits i e give eruptive ages from earlier eruptions that contain an unimodal zircon population and as such only provide maximum depositional ages although a compacted sedimentation rate csr for the entire kuruman iron formation is 3 4 m per million years a csr of about 22 m per million years is deduced for the riries member suggesting that there are cryptic gaps within the kuruman stratigraphic record the latter is comparable to the csr of 33 m per million years calculated for hamersley province bifs ages of the tuffaceous horizons in the kuruman iron formation are comparable to those from the brockman iron formation of the hamersley province the 2460 5 ma age for the top of the riries member corresponds to the 2459 3 ma age for the base of the joffre member and the 2463 5 ma whaleback shale member of the brockman iron formation although ca 2468 2478 ma ages reflect detrital or syn depositional zircon populations they are comparable to the 2470 4 ma s13 and the 2479 3 ma s9 macrobands of the dales gorge member brockman iron formation moreover the zircon age spectra and pb loss histories of both the kuruman and brockman iron formation tuffaceous sediments are strikingly similar without doubt the kuruman and brockman iron formations were deposited synchronously whether they were a response to global magmatic events or were deposited in the same basin are questions still being debated

active displacement transfer and differential block motion within the central walker lane western great basin velocities determined for 50 global positioning system sites within the central walker lane indicate differential motion among tectonic blocks forming a boundary zone between the great basin extensional province and the sierra nevada the velocity field is related to displacement transfer from the owens valley and furnace creek fault systems of east ern california to transtensional structures of the walker lane and extensional faults of the central nevada seismic belt block boundaries are sharp and appear to be inherited from pre tertiary crustal structure the block geometries exert strong influence on dif ferential displacements concentrated along boundaries as belts of divergent transcurrent and convergent motion the aggregate velocity accounts for about 25 of the relative motion between the pacific and north american plates about 5 mm yr of the motion is localized along the eastern margin of the sierra nevada whereas about 10 mm yr is stepped 100 km east along a belt of east northeast trending transtensional faults that merge with northwest trending transcurrent structures of the walker lane about 6 mm yr of the velocity field is transferred to north northeast trending extensional faults of the central nevada seismic belt the heterogeneous distribution of motions is consistent with partitioning of a regional velocity field formed by westward extension and n408w directed shear

banded iron formations through much of precambrian time similarities between proterozoic 1 8 2 5 gyr and archean 2 5 gyr banded iron formations are probably more significant than their differences the contrasts largely reflect differences in the tectonic settings of proterozoic and archean terrains archean banded iron formations are not as thick nor laterally as extensive as the major proterozoic iron formations nevertheless some archean iron formations have strike lengths of over 150 200 km and may have been quite extensive prior to the deformation that has affected most archean terrains stratigraphic sequences in which iron formations occur are highly variable and indicate that iron formations formed in many depositional environments sedimentary textures in the iron formations are dominated either by granules and oolites or laminations including microbanding reflecting differences in their physical conditions of deposition granular and oolitic textures are abundant in only three proterozoic depositional basins and most precambrian iron forma

making magnetite late again evidence for widespread magnetite growth by thermal decomposition of siderite in hamersley banded iron formations abstract banded iron formations bifs are marine chemical sedimentary rocks that were widely deposited before the start of the great oxidation event 2 45 2 32 ga they represent an important archive into the chemistry of the precambrian oceans and atmosphere and the evolution of the marine biosphere it is believed that bifs were derived from ferric oxides hydroxides that were deposited by iron oxidizing bacteria or by reaction with oxygen released by cyanobacteria hematite is traditionally interpreted to represent the dehydrated product of the ferric oxide hydroxide precipitate whereas magnetite is thought to have formed from ferric oxides hydroxides via bacterial iron reduction and oxidation of microbial biomass however studies are equivocal about when and how magnetite formed in bifs we present the results of a detailed petrographic study of magnetite in bifs of the hamersley group western australia we find no evidence that magnetite was precipitated from seawater or was a product of bacterial iron reduction instead most of the magnetite formed by replacement of siderite and other ferrous rich minerals after burial our observations suggest that magnetite growth was linked to the breakdown of siderite during metamorphism published experimental data indicate that in the presence of water and under the metamorphic conditions experienced in the southern pilbara craton 200 350 c the thermal decomposition of siderite could account for much of the magnetite in the hamersley bifs 3feco3 h2o fe3o4 3co2 h2 the relationship between magnetite and the primary precipitates which are preserved as greenalite nanoparticles and microgranules in chert bands suggests that much of the magnetite formed in siderite rich iron silicate bands that developed by compaction of non silicified iron silicate muds these bands acted as reactive pathways for fluid flow and the formation of magnetite if most of the magnetite formed after burial then it is necessary to reassess assumptions about the chemistry of the original precipitates and the role of microbial life in the redox cycling of iron our results are consistent with models for the deposition of bifs that center around a precursor sediment comprising greenalite precipitates and diagenetic siderite that was partially replaced by magnetite and hematite after burial

surface rupturing earthquakes repeated in the 300 years along the istl active fault system central japan surface rupturing earthquakes produced by intraplate active faults generally have long recurrence intervals of a few thousands to tens of thousands of years we here report the first evidence for an extremely short recurrence interval of 300 years for surface rupturing earthquakes on an intraplate system in japan the kamishiro fault of the itoigawa shizuoka tectonic line istl active fault system generated a mw 6 2 earthquake in 2014 a paleoseismic trench excavation across the 2014 surface rupture showed the evidence for the 2014 event and two prior paleoearthquakes the slip of the penultimate earthquake was similar to that of 2014 earthquake and its timing was constrained to be after a d 1645 judging from the timing the damaged area and the amount of slip the penultimate earthquake most probably corresponds to a historical earthquake in a d 1714 the recurrence interval of the two most recent earthquakes is thus extremely short compared with intervals on other active faults known globally furthermore the slip repetition during the last three earthquakes is in accordance with the time predictable recurrence model rather than the characteristic earthquake model in addition the spatial extent of the 2014 surface rupture accords with the distribution of a serpentinite block suggesting that the relatively low coefficient of friction may account for the unusually frequent earthquakes these findings would affect long term forecast of earthquake probability and seismic hazard assessment on active faults

why joints are more abundant than faults a conceptual model to estimate their ratio in layered carbonate rocks it is a commonplace field observation that extension fractures are more abundant than shear fractures the questions of how much more abundant and why are posed in this paper and qualitative estimates of their ratio within a rock volume are made on the basis of field observations and mechanical considerations a conceptual model is also proposed to explain the common range of ratios between extension and shear fractures here called the j f ratio the model considers three major genetic stress components originated from overburden pore fluid pressure and tectonics and assumes that some of the remote genetic stress components vary with time i e stress rates are included other important assumptions of the numerical model are that i the strength of the sub volumes is randomly attributed following a weibull probabilistic distribution ii all fractures heal after a given time thus simulating the cementation process and therefore iii both extensional jointing and shear fracturing could be recurrent events within the same sub volume as a direct consequence of these assumptions the stress tensor at any point varies continuously in time and these variations are caused by both remote stresses and local stress drops associated with in situ and neighbouring fracturing events the conceptual model is implemented in a computer program to simulate layered carbonate rock bodies undergoing brittle deformation the numerical results are obtained by varying the principal parameters like depth viz confining pressure tensile strength pore fluid pressure and shape of the weibull distribution function in a wide range of values therefore simulating a broad spectrum of possible mechanical and lithological conditions the quantitative estimates of the j f ratio confirm the general predominance of extensional failure events during brittle deformation in shallow crustal rocks and provide useful insights for better understanding the role played by the different parameters for example as a general trend it is observed that the j f ratio is inversely proportional to depth viz confining pressure and directly proportional to pore fluid pressure while the stronger is the rock the wider is the range of depths showing a finite value of the j f ratio and in general the deeper are the conditions where extension fractures can form moreover the wider is the strength variability of rocks i e the lower is the m parameter of the weibull probabilistic distribution function the wider is the depth range where both fractures can form providing a finite value of the j f ratio natural case studies from different geological and tectonic settings are also used to test the conceptual model and the numerical results showing a good agreement between measured and predicted j f ratios

extending the upper temperature limit for life the upper temperature limit for life is a key parameter for delimiting when and where life might have evolved on a hot early earth the depth to which life exists in the earth s subsurface and the potential for life in hot extraterrestrial environments a combination of geological and

the joffre banded iron formation hamersley group western australia assessing the palaeoenvironment through detailed petrology and chemostratigraphy abstract the joffre member of the brockman iron formation is by volume the largest single known banded iron formation bif in the world here we present detailed petrology and chemostratigraphy through the entire 355 m core section of this 2 45 billion year old unit oxide bif and silicate carbonate oxide bif dominate the lithology with minor amounts of interbedded stilpnomelane mudrock stilpnomelane rich tuffaceous mudrock and calcareous mudrock besides chert and magnetite the prominent mineralogy is riebeckite ankerite hematite stilpnomelane and crocidolite the bif is characterized by an average of 50 wt sio 2 and 44 5 wt fe 2 o 3 and an overall low abundance of al 2 o 3 2 sn of 0 24 the rey patterns also show a positive la sn anomaly no ce sn anomaly and a weakly developed positive y sn anomaly iron isotopes 56 fe with positive 56 fe values of 0 04 to 1 21 suggest that a large part of the hydrothermal iron was partly oxidized in the upper water column and subsequently precipitated as ferric oxyhydroxides no epiclastic grains have been found rather submarine hydrothermal fluids and fine grained volcanogenic detritus controlled bif chemistry the former source is reflected through a constant positive eu sn anomaly throughout the core average eu sn anomaly of 1 6 with a peak of 2 1 between 100 and 155 m depth while the latter source is best reflected through the stilpnomelane rich tuffaceous mudrock consisting of volcanic ash fall tuff with relict shards set in a stilpnomelane matrix the mudrock is overlain by well preserved wavy laminae and laminae sets of stilpnomelane microgranules that likely originated from re worked volcanic ash formed either on the seafloor or in the water column prior to deposition an enriched hree to lree pattern a high iron content 30 wt and a 56 fe value of 0 59 collectively imply that the mudrock facies interacted with the fe rich seawater prior to deposition the tio 2 zr ratio of the bif and the associated mudrocks suggest a felsic only source related to the same style of volcanics as the slightly younger woongarra rhyolites given the observation that the dominant control on the seawater chemistry was associated with felsic volcanics we speculate that the fine grained pelagic ash particles may have sourced bio available nutrients to the surface water this would have facilitated enhanced biological productivity including bacterial fe ii oxidation which is now recorded as the positively fractionated 56 fe iron oxide minerals in the joffre bif alongside submarine hydrothermal input to the basin the dominant control on the ocean chemistry seems to have been through volcanic and pyroclastic pathways thereby making the joffre bif poorly suited as a chemical proxy for the study of atmospheric oxygen and its weathering impact on local landmasses

variations in strength and slip rate along the san andreas fault system convergence across the san andreas fault saf system is partitioned between strike slip motion on the vertical saf and oblique slip motion on parallel dip slip faults as illustrated by the recent magnitude m s 6 0 palm springs m s 6 7 coalinga and m s 7 1 loma prieta earthquakes if the partitioning of slip minimizes the work done against friction the direction of slip during these recent earthquakes depends primarily on fault dip and indicates that the normal stress coefficient and frictional coefficient vary among the faults additionally accounting for the active dip slip faults reduces estimates of fault slip rates along the vertical trace of the saf by about 50 percent in the loma prieta and 100 percent in the north palm springs segments

biogeochemical cycling of iron in the archean paleoproterozoic earth constraints from iron isotope variations in sedimentary rocks from the kaapvaal and pilbara cratons abstract iron isotope compositions of low metamorphic grade samples of archean paleoproterozoic sedimentary rocks obtained from fresh drill core from the kaapvaal craton in south africa and from the pilbara craton in australia vary by 3 in 56 fe 54 fe ratios reflecting a variety of weathering and diagenetic processes depositional ages for the 120 samples studied range from 3 3 to 2 2 ga and fe c and s contents define several compositional groups including samples rich in fe organic carbon carbonate and sulfide the 56 fe values for low c org low c carb and low s sedimentary rocks are close to 0 the average of igneous rocks this range is essentially the same as that of c org poor late cenozoic loess aerosol river loads and marine sediments and those of c org poor phanerozoic proterozoic shales that these 56 fe values are the same as those of igneous rocks suggests that fe has behaved conservatively in bulk sediments during sedimentary transport diagenesis and lithification since the archean these observations indicate that if atmospheric o 2 contents rose dramatically between 2 4 and 2 2 ga as proposed by many workers such a rise did not produce a significant change in the bulk fe budget of the terrestrial sedimentary system if the archean atmosphere was anoxic and fe was lost from bedrock during soil formation any isotopic fractionation between aqueous ferrous fe fe aq 2 and fe bearing minerals must have been negligible in contrast if the archean atmosphere was oxic fe would have been retained as fe 3 hydroxides during weathering as it is today which would produce minimal net isotopic fractionation in bulk detrital sediments siderite rich samples have 56 fe values of 0 5 0 5 and experimentally determined fe aq 2 siderite fractionation factors suggest that these rocks formed from fe aq 2 that had similar or slightly higher 56 fe values the 56 fe values calculated for fe aq 2 overlaps those of modern submarine hydrothermal fluids but it is also possible that fe aq 2 had 56 fe values higher than those of modern hydrothermal fluids depending upon the fe aq 2 fe carbonate fractionation factor that is used in contrast c org rich samples and magnetite rich samples have strongly negative 56 fe values generally between 2 3 and 1 0 and available fluid mineral fractionation factors suggest that the fe bearing minerals siderite and magnetite in these rocks formed in the presence of fe aq 2 that had very low 56 fe values between 3 and 1 reduction of fe 3 hydroxide by sulfide precipitation of sulfide minerals or incongruent dissolution of silicate minerals are considered unlikely means to produce significant quantities of low 56 fe fe aq 2 we interpret microbial dissimilatory fe 3 reduction dir as the best explanation for producing such low 56 fe values for fe aq 2 and our results suggest that dir was a significant form of respiration since at least 2 9 ga

holocene slip rate and earthquake recurrence on the honey lake fault zone northeastern california the honey lake fault zone a major right lateral fault in the basin and range province of eastern california is one of a broad system of faults that accommodate some of the relative motion between the pacific and north american plates these right lateral faults may have significantly higher slip rates and thus greater earthquake hazards than the normal faults for which the basin and range is more commonly known in the honey lake valley the fault forms a 50 km long zone of landforms typical of active strike slip faults right lateral offset of an incised creek channel is used to estimate a holocene slip rate of between 1 1 and 2 6 mm yr a fault exposure in holocene alluvium shows evidence for at least four late holocene surface faulting earthquakes

a multistage origin for neoarchean layered hematite magnetite iron formation from the weld range yilgarn craton western australia abstract the origins of iron formations remain somewhat enigmatic despite much progress over the past decades this is due in part to continuing research demonstrating that these deposits do not have a single origin but rather can be formed under various and variable conditions this study describes a formation pathway for an algoma type banded iron formation bif from the 2 75 billion year old weld range of western australia based on petrographic and fe isotope analyses of drill core samples the bif is composed of alternating layers of jaspilitic and fe poor chert magnetite layers of varying thickness and abundance and rare pyrite petrographic analysis indicates the minerals formed in the order hematite magnetite and then pyrite with the latter two clearly replacive of primary bedded hematite hematite 56fe values from all portions of the drill core are positive and essentially identical 56fe 0 61 0 05 magnetite 56fe values are positive as well 56fe 0 51 0 07 but vary systematically with total magnetite content of the core samples pyrite 56fe values are positive and higher than both hematite and magnetite 56fe 1 03 0 05 combined these analyses reveal a multistage formational model for the weld range bif initial deposition occurred by the partial oxidation of hydrothermally sourced aqueous fe ii to form a fe iii si co precipitate probably by anoxygenic photosynthetic iron oxidizers this material would have been converted to hematite under equilibrium conditions with excess aqueous fe ii magnetite formed by a later intrusion of reducing fluids mostly along bedding planes but also as cross cutting veins this produced large quantities of magnetite layers parallel and sub parallel to the original bedding but that do not represent a primary depositional feature pyrite was produced in some portions of the unit likely under equilibrium conditions by later infiltration of reducing fluids containing sulfide the entirely positive 56fe values for all fe phases in the weld range bif stands in stark contrast to the more massive superior type bifs of the paleoproterozoic hamersley and transvaal basins of western australia and south africa respectively which have 56fe values that average close to 0 but vary over nearly the entire range of 56fe values measured in nature 56fe 2 5 to 2 6 the weld range bif 56fe values are similar to those of older algoma type bifs such as the paleoarchean isua bif of greenland but are less positive on average this overall trend of decreasing average 56fe values through time likely records an overall increasing trend of oxygenation of the archean surface ocean from 3 8 to 2 45 billion years ago

geochemical and mineralogic effects of contact metamorphism on banded iron formation an example from the transvaal basin south africa intrusion of a diabase sill into the paleoproterozoic kuruman iron formation transvaal basin south africa makes it possible to distinguish between effects of contact and regional metamorphism on mineralogic elemental and isotopic compositions of banded iron formation bif lithofacies temperatures within the aureole of contact metamorphism likely did not significantly exceed 450 c as suggested by the presence of early diagenetic carbonates greenalite and stilpnomelane formed prior to intrusion in chert rich facies as close as 4 m from the sill in sediments 32 m away from the intrusion a temperature of 280 c is indicated by the magnitude of 18o fractionation between successive chert and siderite microbands in unmetamorphosed equivalents similar isotopic analyses on whole rock samples yield temperature estimates between 150 and 230 c in comparison with samples of similar lithofacies from the underlying campbellrand kuruman transition zone carbonates from within the metamorphic aureole are depleted in 13c and 18o the abundance and c isotopic composition of total organic c toc in whole rock samples is lower and more enriched in 13c than those in samples outside of the zone of contact metamorphism within 5 m of the diabase sill the abundance of fe increases dramatically and the oxidation state of the sediments fluctuates considerably more than in sediments outside of the metamorphic aureole isotopic and mineralogic systematics in the zone of contact metamorphism in the kuruman iron formation are similar to those in siliceous dolomites and limestones altered by similar thermal processes as the most distinct isotopic and elemental variations occur within 10 m of the diabase sill it is suggested that volatilization and fluid infiltration associated with the intrusion were the main processes of alteration consideration of the effects of metamorphism both contact and regional as well as early diagenesis on the mineralogy and isotopic chemistry of bif sediments may be a key to our understanding of primary mineralogies and oxidation state of these enigmatic deposits

magnetite biomineralization in ferruginous waters and early earth evolution abstract burial of large quantities of magnetite fe ii fe iii 2o4 in iron formations ifs likely contributed to the protracted oxidation of earth s surface during the precambrian eons magnetite can form through a diversity of biological and abiotic pathways and its preservation in ifs may thus be variably interpreted as the result of some combination of these processes such interpretations give rise to divergent pictures of the precambrian earth system and models for its evolution through time new knowledge on the contribution of specific magnetite formation pathways is therefore needed to accurately tether our conceptual and numerical models to the geologic record to constrain pathways of magnetite formation under ferruginous conditions we conducted geochemical and multi method microspectroscopic analyses on particles obtained from the water columns and sediments of ferruginous lakes matano and towuti in indonesia we find that biologically reactive fe iii mineral phases are reduced in the anoxic waters of both lakes causing the formation of primary authigenic magnetite directly in the water column this water column magnetite often takes conspicuous framboidal forms which given the link to microbial fe iii reduction may provide a biological signature on early earth and by extension other planetary bodies the consumption of more biologically reactive forms of fe iii and the resulting delivery of primary magnetite to underlying sediments promotes the burial of oxidized equivalents and implies that primary magnetite formation could have been a principal pathway of fe delivery to ifs combined the removal of fe from earth s surface through biologically induced magnetite formation and subsequent burial in ifs suggests that seawater chemistry and the microbially mediated reactions that cause magnetite formation played key roles in earth system evolution and in setting the pace for planetary oxidation through the precambrian eons

displacement and geometrical characteristics of earthquake surface ruptures issues and implications for seismic hazard analysis and the process of earthquake rupture there now exist about three dozen historical earthquakes for which in vestigators have constructed maps of earthquake rupture traces accompanied by de scriptions of the coseismic slip observed along the fault strike the maps and slip distributions are compiled here to place observational bounds on aspects of seismic hazard analysis and fault mechanics analysis leads to an initial statistical basis to predict the end points of rupture and the amount of surface slip expected at sites along the strike during earthquakes on mapped faults the observations also give support to the ideas that there exists a process zone or volume of about 3 4 km in dimension at the fronts of large laterally propagating earthquake ruptures within which stress changes may be sufficient to trigger slip on adjacent faults and that the ultimate length of earthquake ruptures is controlled primarily by the geometrical complexity of fault traces and variations in accumulated stress levels along faults that arise due to the location of past earthquakes to this may be added the observation that the form of earthquake surface slip distributions is better described by asymmetric rather than symmetric curve forms and that earthquake epicenters do not appear to correlate in any systematic manner to regions of maximum surface slip observed along strike online material maps of surface ruptures digitized values and curve fits to surface slip distributions and notes and references for tables 1 and 2

thermochronological constraints on the timing and magnitude of miocene and pliocene extension in the central wassuk range western nevada apatite fission track and u th he thermochronological data provide new constraints on the timing of faulting and exhumation of the wassuk range western nevada where east dipping normal faults have accommodated large magnitude ene wsw oriented extension extensional deformation has resulted in the exhumation of structurally coherent fault blocks that expose sections of preextensional mostly granitic upper crust in the grey hills and central wassuk range these fault blocks display westward tilts of 60 and expose preextensional paleodepths of up to 8 5 km based on the structural reconstruction of tilted preextensional tertiary andesite flows that unconformably overlie mesozoic basement rocks apatite fission track and u th he thermochronological data from the fault blocks constrain the onset of rapid footwall exhumation at 15 ma fission track modeling results indicate rapid fault block exhumation occurred between 15 and 12 ma which is in agreement with miocene volcanic rocks that bracket the tilting history in addition fission track and u th he data suggest reduced rates of cooling following major extension as well as renewed cooling related to active high angle faulting along the present day range front starting at 4 ma thermochronological data from structurally restored fault blocks indicate a preextensional miocene geothermal gradient of 27 5 c km the thermochronological constraints on the timing of extensional faulting and the eruptive history in the wassuk range imply a model for extension where crustal heating and volcanism precede the onset of rapid large magnitude extension and where synextensional magmatism is suppressed during the highest rates of extension

ground rupturing earthquakes on the northern big bend of the san andreas fault california 800 a d to present paleoseismic data on the timing of ground rupturing earthquakes constrain the recurrence behavior of active faults and can provide insight on the rupture history of a fault if earthquakes dated at neighboring sites overlap in age and are considered correlative this study presents the evidence and ages for 11 earthquakes that occurred along the big bend section of the southern san andreas fault at the frazier mountain paleoseismic site the most recent earthquake to rupture the site was the mw7 7 7 9 fort tejon earthquake of 1857 we use over 30 trench excavations to document the structural and sedimentological evolution of a small pull apart basin that has been repeatedly faulted and folded by ground rupturing earthquakes a sedimentation rate of 0 4 cm yr and abundant organic material for radiocarbon dating contribute to a record that is considered complete since 800 a d and includes 10 paleoearthquakes earthquakes have ruptured this location on average every 100 years over the last 1200 years but individual intervals range from 22 to 186 years the coefficient of variation of the length of time between earthquakes 0 7 indicates quasiperiodic behavior similar to other sites along the southern san andreas fault comparison with the earthquake chronology at neighboring sites along the fault indicates that only one other 1857 size earthquake could have occurred since 1350 a d and since 800 a d the big bend and mojave sections have ruptured together at most 50 of the time in mw 7 3 earthquakes

ancient geochemical cycling in the earth as inferred from fe isotope studies of banded iron formations from the transvaal craton variations in the isotopic composition of fe in late archean to early proterozoic banded iron formations bifs from the transvaal supergroup south africa span nearly the entire range yet measured on earth from 2 5 to 1 0 in 56fe 54fe ratios relative to the bulk earth with a current state of the art precision of 0 05 for the 56fe 54fe ratio this range is 70 times analytical error demonstrating that significant fe isotope variations can be preserved in ancient rocks significant variation in fe isotope compositions of rocks and minerals appears to be restricted to chemically precipitated sediments and the range measured for bifs stands in marked contrast to the isotopic homogeneity of igneous rocks which have 56fe 0 00 0 05 as well as the majority of modern loess aerosols riverine loads marine sediments and proterozoic shales the fe isotope compositions of hematite magnetite fe carbonate and pyrite measured in bifs appears to reflect a combination of 1 mineral specific equilibrium isotope fractionation 2 variations in the isotope compositions of the fluids from which they were precipitated and 3 the effects of metabolic processing of fe by bacteria for minerals that may have been in isotopic equilibrium during initial precipitation or early diagenesis the relative order of 56fe values appears to decrease in the order magnetite siderite ankerite similar to that estimated from spectroscopic data although the measured isotopic differences are much smaller than those predicted at low temperature in combination with on going experimental determinations of equilibrium fe isotope fractionation factors the data for bif minerals place additional constraints on the equilibrium fe isotope fractionation factors for the system fe iii fe ii hematite magnetite fe carbonate 56fe values for pyrite are the lowest yet measured for natural minerals and stand in marked contrast to the high 56fe values that are predicted from spectroscopic data some samples contain hematite and magnetite and have positive 56fe values these seem best explained through production of high 56fe 54fe reservoirs by photosynthetic fe oxidation it is not yet clear if the low 56fe values measured for some oxides as well as fe carbonates reflect biologic processes or inorganic precipitation from low 56fe ferrous fe rich fluids however the present results demonstrate the great potential for fe isotopes in tracing the geochemical cycling of fe and highlight the need for an extensive experimental program for determining equilibrium fe isotope fractionation factors for minerals and fluids that are pertinent to sedimentary environments

late pleistocene fault slip rate earthquake recurrence and recency of slip along the pyramid lake fault zone northern walker lane united states 1 up to 25 of pacific north america plate relative transform motion is accommodated east of the sierra nevada most of that 25 is taken up by deformation in the walker lane a discontinuous zone of strike slip and normal faults approximately parallel to the san andreas the pyramid lake fault zone is a northwest trending right lateral fault in the northern walker lane nevada recent geodetic surveys report 6 2 mm year of right lateral shear strain accumulation across the northern walker lane interpretation of displaced geomorphic features preserved in post lake lahontan 15 500 cal yr b p surfaces indicate the pyramid lake fault zone has accommodated at least 2 6 0 3 mm year of right lateral shear during the late pleistocene additionally a minimum of two earthquakes have occurred since deposition of the mazama tephra 7630 cal yr b p and at least four earthquakes have occurred on the fault after desiccation of lake lahontan 15 5 ka with the most recent earthquake occurring after 1705 175 cal yr b p the observations indicate that the pyramid lake fault zone accommodates the major portion 25 70 of right lateral slip east of the sierra nevada at the latitude of 39 45 n

deposition of banded iron formations by anoxygenic phototrophic fe ii oxidizing bacteria the mechanism of banded iron formation bif deposition is controversial but classically has been interpreted to reflect ferrous iron fe ii oxidation by molecular oxygen after cyanobacteria evolved on earth anoxygenic photoautotrophic bacteria can also catalyze fe ii oxidation under anoxic conditions calculations based on experimentally determined fe ii oxidation rates by these organisms under light regimes representative of ocean water at depths of a few hundred meters suggest that even in the presence of cyanobacteria anoxygenic phototrophs living beneath a wind mixed surface layer provide the most likely explanation for bif deposition in a stratified ancient ocean and the absence of fe in precambrian surface waters

elongated prismatic magnetite crystals in alh84001 carbonate globules potential martian magnetofossils using transmission electron microscopy tem we have analyzed magnetite fe 3o 4 crystals acid extracted from carbonate globules in martian meteorite alh84001 we studied 594 magnetites from alh84001 and grouped them into three populations on the basis of morphology 389 were irregularly shaped 164 were elongated prisms and 41 were whisker like as a possible terrestrial analog for the alh84001 elongated prisms we compared these magnetites with those produced by the terrestrial magnetotactic bacteria strain mv 1 by tem again we examined 206 magnetites recovered from strain mv 1 cells natural darwinian selection in terrestrial magnetotactic bacteria appears to have resulted in the formation of intracellular magnetite crystals having the physical and chemical properties that optimize their magnetic moment in this study we describe six properties of magnetite produced by biologically controlled mechanisms e g magnetotactic bacteria properties that collectively are not observed in any known population of inorganic magnetites these criteria can be used to distinguish one of the modes of origin for magnetites from samples with complex or unknown histories of the alh84001 magnetites that we have examined the elongated prismatic magnetite particles 27 of the total are indistinguishable from the mv 1 magnetites in five of these six characteristics observed for biogenically controlled mineralization of magnetite crystals

primary hematite in neoarchean to paleoproterozoic oceans banded iron formations bifs are ironand silica rich chemical sedimentary rocks formed throughout the archean and paleoproterozoic eras the presence of hematite fe2o3 and magnetite fe3o4 in bifs has led to the widespread assumption that fe ii oxidation must have occurred in the ancient oceans via either a biological or chemical mechanism however it is unclear whether the ferric iron now present in bif represents the original ferric oxyhydroxide e g ferrihydrite fe oh 3 precipitated in the water column or if it is the result of later stage circulation of oxidizing fl uids through the sediment pile in this study we conducted high resolution microscopic investigations on bif from the 2728 ma abitibi greenstone belt located in the superior province of the canadian shield and the 2460 ma kuruman iron formation in south africa to ascertain the timing and paragenesis of the hematite three types of hematite are identifi ed by high resolution electron microscopic characterization and selected area electron diffraction 1 3 5 nm ultrafi ne hematite particles in the iron oxide rich bands h1 2 submicrometer subhedral to euhedral hema tite crystals randomly distributed in the chert matrix of transitional zones between iron oxide and chert rich bands h2 and 3 needle like radial and fi brous hematite that replaced stilpnomelane or carbonates and is distributed along fractures or layer boundaries h3 we interpret the fi rst two types as primary minerals dehydrated from precursor ferric oxyhydroxides h1 remains ultrafi ne in size while h2 has undergone an ostwald coarsening process facilitated by internal fl uids produced during amorphous silica to quartz transformation h3 is a later stage mineral formed by external fl uid mediated replacement of iron silicates or carbonates these results indicate that a signifi cant fraction of the hematite in the bif originated from ferric oxyhydroxide precursors importantly this implies that photosynthetic fe ii oxidation by either a direct or indirect biological mechanism did exist in seawaters from which some bif material was deposited

geneses and evolutions of iron bearing minerals in banded iron formations of 3760 to ca 2200 million year old constraints from electron microscopic x ray diffraction and mossbauer spectroscopic investigations abstract minerals preserved in banded iron formations bifs are diagenetic and or metamorphic rather than primary knowing their geneses and evolutions are essential for understanding the interactions between the atmosphere ocean and biosphere in the first two billion years of life history on earth here we use high resolution electron microscopy x ray diffraction and mossbauer spectroscopy to investigate the mineralogy of six bifs aged from 3760 ma to ca 2200 ma with a variety of genetic conditions the results reveal that each major iron mineral magnetite hematite carbonate and silicate has a range of structural and morphological features that represent different geneses and evolutionary histories euhedral magnetite crystals with homogeneous internal structures and compositions 3 5 nm hematite particles aggregated in iron rich bands and submicrometer sized euhedral hematite in chert matrix of fe si transitional bands are identified to have transformed from precursors directly precipitated from seawaters these minerals retain some primary environmental information when bifs are deposited the other mineral phases display features of alteration due to multi redox reactions hydrothermal or supergene processes such as crosscutting mineral replacement or overgrowth deformation fracture and porous structures that have overprinted the primary signatures such minerals include 1 massive magnetite with fragmentation structures 2 partly to completely oxidized magnetite crystals 3 acicular fibrous hematite in fractures or iron and silica layering 4 microplaty hematite 5 hematite oxidized from other fe ii bearing minerals e g magnetite and stilpnomelane 6 carbonates with heterogeneous chemical compositions 7 carbonates replacing other minerals e g siderite thin film coating the euhedral magnetite crystals 8 irregular carbonate cementing other minerals e g magnetite 9 preferentially orientated fibrous spindle like silicates cutting iron and silica rich bands and 10 massive silicate pieces this study provides detailed mineralogical and petrologic characterizations of bif minerals that can serve as a reference for future in situ geochemical measurements by recent developed techniques

a fault scarp in an urban area identified by lidar survey a case study on the itoigawa shizuoka tectonic line central japan abstract a light detection and ranging lidar survey was conducted in a densely built up area to generate a high resolution digital elevation model dem to look for active faults the urban district of matsumoto city in central japan is located in a 3 km 2 basin along the itoigawa shizuoka tectonic line active fault system one of japanese onshore fault systems with the highest earthquake probability a high resolution dem at a 0 5 m grid interval was obtained after removing the effects of laser returns from buildings clouds and vegetation it revealed a continuous scarp up to 2 m in height borehole data and archaeological studies indicate the scarp was formed during the most recent faulting event associated with historical earthquakes in addition the fault scarp strongly supports that the urban district is in a pull apart basin related to a fault step over between two left lateral strike slip faults consequently accurate interpretation of fault geometry is crucial to provide estimates of future surface deformation and to allow modeling of basin structure and strong ground motion thus the lidar mapping survey in urban districts is effective for detailed active fault mapping in order to constrain basin structure and to forecast the exact location of surface rupturing associated with large earthquakes

iron formation in neoarchean deltaic successions and the microbially mediated deposition of transgressive systems tracts abstract neoarchean deltaic deposits present in superior province canada contain an excellent record of shallow water siliciclastic and iron formation if deposition the deltas were fed by braided fluvial systems which commonly resulted in the development of small active lobes that repeatedly cycled through progradation and abandonment although a thick progradational deltaic assemblage was also investigated magnetite rich chemical sediments interbedded with siltstones and slates are present on flooding surfaces overlying shore proximal fluvial channels and distributary mouth bars of the braid delta deposits magnetite laminae are also interbedded with some distributary mouth sediments draping reactivation surfaces in ripples to barforms thicker accumulations of if up to 73 m form portions of transgressive systems tracts where chemical sedimentation dominated offshore equivalents of these successions do not contain chemical sediments sedimentologic data imply that if deposition in this well mixed nearshore water mass was not compatible with slow rates of constant iron compound precipitation in the world ocean combined with siliciclastic sediment starvation the model presented for iron precipitation relies on an elevated flux of continentally derived nutrients in the nearshore stimulating photosynthetically induced oxidation of fe2 under these conditions elevated accumulation rates precluded the development of condensed intervals characteristic of transgressive systems tracts

biogenic fe iii minerals from formation to diagenesis and preservation in the rock record abstract fe metabolizing bacteria are intimately linked to the cycling of fe in modern environments and have likely been key players in the evolution of the earth s biogeosphere fe minerals have also been suggested as a key preservative of cell organic matter in sediments keeping otherwise labile phases conserved at least on time scales of 100 000 years the interpretation of a biological influence on the fe rock record is difficult without a deeper understanding of the mechanisms of biogenic fe iii and fe ii mineral formation the character of these minerals and their diagenesis over short and long time scales here we present the recent advances in the study of abiogenic and biogenic fe iii minerals in particular we focus on the role of fe ii oxidizing bacteria in the deposition of ancient banded iron formations bif we discuss this work within the framework of the main challenge separating biogenic from abiogenic processes over deep time we describe how efforts in isotope geochemistry biomarker research mineral analysis and biogeochemistry are helping to establish a window to the past finally we present some new approaches that help investigate the main processes leading to the formation and potential fate of fe organic matter aggregates

surface faulting and paleoseismic history of the 1932 cedar mountain earthquake area west central nevada and implications for modern tectonics of the walker lane the 1932 cedar mountain earthquake m s 7 2 was one of the largest historical events in the walker lane region of western nevada and it produced a complicated strike slip rupture pattern on multiple quaternary faults distributed through three valleys primary right lateral surface ruptures occurred on north striking faults in monte cristo valley small scale lateral and normal offsets occurred in stewart valley and secondary normal faulting occurred on north northeast striking faults in the gabbs valley epicentral region a reexamination of the surface ruptures provides new displacement and fault zone data maximum cumulative offset is estimated to be 2 7 m and newly recognized faults extend the maximum width and end to end length of the rupture zone to 17 and 75 km respectively a detailed quaternary allostratigraphic chronology based on regional alluvial geomorphic relationships tephrochronology and radiocarbon dating provides a framework for interpreting the paleoseismic history of the fault zone a late wisconsinan alluvial fan and piedmont unit containing a 32 36 ka tephra layer is a key stratigraphic datum for paleoseismic measurements exploratory trenching and radiocarbon dating of tectonic stratigraphy provide the first estimates for timing of late quaternary faulting along the cedar mountain fault zone three trenches display evidence for six faulting events including that in 1932 during the past 32 36 ka radiocarbon dating of organic soils interstratified with tectonically ponded silts establishes best fit ages of the pre 1932 events at 4 5 12 15 and 18 ka each with 2 ka uncertainties on the basis of an estimated cumulative net slip of 6 12 m for the six faulting events minimum and maximum late quaternary slip rates are 0 2 and 0 7 mm yr respectively and the preferred rate is 0 4 0 5 mm yr the average recurrence interseismic interval is 3600 yr the relatively uniform thickness of the ponded deposits suggests that similar size characteristic rupture events may characterize late quaternary slip on the zone a comparison of event timing with the average late quaternary recurrence interval indicates that slip has been largely regular periodic rather than temporally clustered to account for the spatial separation of the primary surface faulting in monte cristo valley from the epicenter and for a factor of two to three disparity between the instrumentally and geologically determined seismic moments associated with the earthquake we hypothesize two alternative tectonic models containing undetected subevents either model would adequately account for the observed faulting on the basis of wrench fault kinematics that may be associated with the walker lane the 1932 cedar mountain earthquake is considered an important modern analogue for seismotectonic modeling and estimating seismic hazard in the walker lane region in contrast to most other historical events in the basin and range province the 1932 event did not occur along a major range bounding fault and no single throughgoing basement structure can account for the observed rupture pattern the 1932 faulting supports the concept that major earthquakes in the basin and range province can exhibit complicated distributive rupture patterns and that slip rate may not be a reliable criterion for modeling seismic hazard

alternating si and fe deposition caused by temperature fluctuations in precambrian oceans precambrian banded iron formations contain thin alternating layers of iron and silica rich minerals microbial culture experiments show that these alternations could be caused by changes in the relative dominance of microbial iron oxidation and abiotic silica precipitation driven by fluctuating ocean temperature

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

magnetofossils the magnetization of sediments and the evolution of magnetite biomineralization magnetite fe 3o 4 is one of the most stable carriers of natural remanent magnetization nrm in sedimentary rocks and paleomagnetic studies of magnetite bearing sediments such as deep sea cores and pelagic limestones have provided a detailed calibration between the biostratigraphic and magnetic polarity time scales despite this important role there is as yet a very poor understanding of how ultrafine grained 0 1 m magnetite is formed transported and preserved in marine environments a major conceptual advance in our understanding of these processes is the recent discovery that biogenic magnetite formed by magnetotactic bacteria and or other magnetite precipitating organisms is responsible for much of the stable magnetic remanence in many marine sediments and sedimentary rocks since these magnetite particles are of biogenic origin they are termed properly magnetofossils kirschvink chang 1984

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

conditions of riebeckite formation in the iron formation of the dales gorge member hamersley group western australia stability relations in the system na fe mg si c o h at low temperature and pressure at constant temperature riebeckite is stable to lower fo 2 conditions than hematite and higher ph values than magnetite or hematite where riebeckite coexists with carbonates its stability field is enlarged by a decrease of total carbonate at constant ph riebeckite assemblages in the dales gorge member can be divided into two groups carbonate free and carbonate bearing modified journal abstract

the formation of magnetite in the early archean oceans abstract banded iron formations bifs are iron and silica rich chemical sedimentary rocks that were deposited throughout much of the precambrian the biological oxidation of dissolved fe ii led to the precipitation of a ferric oxyhydroxide phase such as ferrihydrite in the marine photic zone upon burial ferrihydrite was either transformed into hematite through dehydration or it was reduced to magnetite via biological or abiological fe iii reduction coupled to the oxidation of buried microbial biomass however it has always been intriguing as to why the oldest bifs are characteristically magnetite rich while bifs formed after the neoarchean are dominated by hematite here we propose that some magnetite in early archean bif could have precipitated directly from seawater through the reaction of settling ferrihydrite and hot fe ii rich hydrothermal fluids that existed in the deeper waters we conducted experiments that showed the reaction of fe ii with biogenic ferric iron mats under strict anoxic conditions lead to the formation of a metastable green rust phase that within hours transformed into magnetite our model further posits that with the progressive cooling and oxidation of the earth s oceans the above reaction shuts off and magnetite was subsequently restricted to reactions associated with diagenesis and metamorphism

active faulting in the walker lane 1 deformation across the san andreas and walker lane fault systems accounts for most relative pacific north american transform plate motion the walker lane is composed of discontinuous sets of right slip faults that are located to the east and strike approximately parallel to the san andreas fault system mapping of active faults in the central walker lane shows that right lateral shear is locally accommodated by rotation of crustal blocks bounded by steep dipping east striking left slip faults the left slip and clockwise rotation of crustal blocks bounded by the east striking faults has produced major basins in the area including rattlesnake and garfield flats teels columbus and rhodes salt marshes and queen valley the benton springs and petrified springs faults are the major northwest striking structures currently accommodating transform motion in the central walker lane right lateral offsets of late pleistocene surfaces along the two faults point to slip rates of at least 1 mm yr the northern limit of northwest trending strike slip faults in the central walker lane is abrupt and reflects transfer of strike slip to dip slip deformation in the western basin and range and transformation of right slip into rotation of crustal blocks to the north the transfer of strike slip in the central walker lane to dip slip in the western basin and range correlates to a northward broadening of the modern strain field suggested by geodesy and appears to be a long lived feature of the deformation field the complexity of faulting and apparent rotation of crustal blocks within the walker lane is consistent with the concept of a partially detached and elastic brittle crust that is being transported on a continuously deforming layer below the regional pattern of faulting within the walker lane is more complex than observed along the san andreas fault system to the west the difference is attributed to the relatively less cumulative slip that has occurred across the walker lane and that oblique components of displacement are of opposite sense along the walker lane extension and san andreas contraction respectively despite the gross differences in fault pattern the walker lane and san andreas also share similarities in deformation style including clockwise rotations of crustal blocks leading to development of structural basins and the partitioning of oblique components of slip onto subparallel strike slip and dip slip faults

the mineralogy mineral chemistry and origin of the wuyang banded iron formations north china craton abstract several banded iron formations bifs occur in precambrian strata of the north china craton ncc two sub types of bif occur in the wuyang area quartz magnetite qmb and pyroxene magnetite bifs pmb however the genesis of pyroxene and the how the bifs formed are not well understood magnetite grains in qmb are relatively large with a straight boundary and sharp corners and display a pronounced alignment whereas magnetite in pmb is disseminated and has a smaller grain size x ray diffraction xrd analyses indicate that the crystal parameters of magnetite in qmb are a b c 8 396 a and z 8 whereas those of the magnetite in pmb are a b c 8 394 a and z 8 these parameters are consistent with magnetite forming in sedimentary iron formation based on scanning electron microscopy and energy dispersive spectroscopy eds results magnetite of both bifs possesses high stabilities of geochemical property compared with magnetite in pmb magnetite in qmb has higher concentrations of sio2 na2o al2o3 cao k2o mgo sc co y nb ta and u the enrichment of these elements is consistence with their derivation from seawater due to the strong adsorption capability of precursor iron hydroxide a spider diagram of trace elements reveals that magnetite in qmb is enriched in ta whereas magnetite of pmb is depleted in ce based on raman and electron probe micro analysis of pyroxene in pmb synchronous and compositional zoning are found in the degrees of crystallinity fwhm values of gaussian fitting for raman shift next to 1014 cm 1 and the concentration of sio2 al2o3 mgo mno cao and feo of pyroxene from core to rim the two types of bif formed in different sedimentary environments from different precursors the precursor to the qmb bif is almost pure chemical sediment whereas a that for pmb contains a volcanic ash component the qmb was likely deposited during a period of hydrothermal sedimentation in the wuyang basin that was associated with neoarchean magmatism activity while the pmb was deposited during periods of volcanic paroxysm

depositional environment of the paleoproterozoic yuanjiacun banded iron formation in shanxi province china the paleoproterozoic 2 38 2 21 ga yuanjiacun banded iron formation bif located in shanxi province is a superior type bif in the north china craton this bif is within a metasedimentary rock succession of the yuanjiacun formation in the lower luliang group which has undergone lower greenschist facies metamor phism iron oxide magnetite and hematite carbonate and silicate facies are all present within the iron rich layers the eastward transition from carbonate into oxide facies iron formations is accompanied by a change in mineralogical composition from siderite in the west through magnetite ankerite and magnetite stilpnomelane assemblages in the transition zone to magnetite and then hematite in the east these distinct lateral facies are also observed vertically within the bif i e the iron mineral assemblage changes upsection from sider ite through magnetite into hematite rich iron formation the oxide facies bif formed near shore whereas carbonate siderite and silicate facies assemblages formed in deeper waters based on detailed analyses of these variations on a basinal scale the bif precipitated during a transgressive event within an environment that ranged from deep waters below storm wave base to relatively shallow waters the bif samples display distinctively seawater like rees y profiles that are characterized by positive la and y anomalies and hrees enrichment relative to lrees in post archean australian shale normalized diagrams consistently positive eu anomalies are also observed which are typical of reduced high temperature hydrothermal fluids in addition slightly negative to positive ce anomalies and a large range in ratios of light to heavy rees are present in the oxide facies bif these characteristics in combination with consistently positive 56fe values suggest that deposition of the bif took place along the chemocline where upwelling of deep anoxic iron and silicarich hydrothermal fluids mixed with shallower and slightly oxygenated seawater the ankerite displays highly depleted 13c values and the carbonate rich bif has a high content of organic carbon suggesting dissimilatory fe iii reduction of a ferric oxyhydroxide precursor during burial of biomass deposited from the water column that same biomass was likely tied to the original oxidation of dissolved fe ii the fact that the more ferric bif facies formed in shallower waters suggests that river sourced nutrients would have been minimal thus limiting primary productivity in the shallow waters and minimizing the organic carbon source necessary for reducing the hematite via dissimilatory fe iii reduction by contrast in deeper waters more proximal to the hydrothermal vents nutrients were abundant and high biomass productivity was coupled to increased carbon burial leading to the deposition of iron rich carbonates the deposition of the yuanjiacun bif during the onset of the great oxidation event goe ca 2 4 2 2 ga confirms that deep marine waters during this time period were still episodically ferruginous but that shallow waters were sufficiently oxygenated that fe ii oxidation no longer needed to be tied directly to proximal cyanobacterial activity

simulating precambrian banded iron formation diagenesis abstract post depositional diagenetic alteration makes the accurate interpretation of key precipitation processes in ancient sediments such as precambrian banded iron formations bifs difficult while microorganisms are proposed as key contributors to bif deposition the diagenetic transformation of precursor fe iii minerals associated with microbial biomass had not been experimentally tested we incubated mixtures of ferrihydrite proxy for biogenic ferric oxyhydroxide minerals and glucose proxy for microbial biomass in gold capsules at 1 2 kbar and 170 c both wet chemical analysis and mineralogical methods microscopy x ray diffraction and mossbauer spectroscopy were used to analyze the reaction products under these conditions ferrihydrite fe iii oh 3 transforms to hematite fe 2 iii o 3 magnetite fe ii fe 2 iii o 4 and siderite fe ii co 3 silica coated ferrihydrite prepared at conservative si fe ratios as predicted for the precambrian oceans and mixed with glucose yielded hematite and siderite whereas magnetite could not be identified microscopically our results show that electron transfer from organic carbon to fe iii minerals during temperature pressure diagenesis can drive the production of key bif minerals our results also demonstrate that the post depositional mineralogy of bif does not directly archive the oceanic or atmospheric conditions present on earth during their lithification as a consequence atmospheric composition regarding concentrations of methane and co 2 during the time of bif mineral deposition cannot be directly inferred from bif mineralogical data alone

preservation of fe isotope heterogeneities during diagenesis and metamorphism of banded iron formation we present the iron isotope composition of primary diagenetic and metamorphic minerals in five samples from the contact metamorphosed biwabik iron formation these samples attained peak meta morphic temperatures of 1 on the millimeter scale minerals in the lowest grade samples consistently show a sequence in which d 56 fe of magnetite silicate carbonate the inter mineral fe isotope differences vary in a fashion that cannot be reconciled with theoretical temperature dependent fractionation factors textural evidence re veals that most if not all magnetite in the biwabik formation is diagenetic not primary and that there was tremendous element mobility during diagenesis the short duration of contact metamorphism allowed diagenetic magnetite compositions to be preserved throughout prograde metamorphism until at least the appearance of olivine magnetite compositions there fore act as an isotope record of the environment in which these sediments formed larger scale fluid flow and longer timescales may allow equilibration of fe isotopes in regionally metamorphosed rocks to lower temperatures than in contact metamorphic environ ments but weakly regionally metamorphosed rocks may preserve small scale fe isotopic heterogeneities like those observed in the biwabik iron formation importantly fe isotope compositions that are charac teristic of chemical sedimentation or hydrothermal processes are preserved at low grade in the form of large inter mineral variations and at high grade in the form of unique bulk rock compositions this observa tion confirms earlier work that has suggested that fe isotopes can be used to identify sedimentary processes in the precambrian rock record

mineral ecophysiological data provide growing evidence for microbial activity in banded iron formations the phosphorus composition of banded iron formations bifs has been used as a proxy for precambrian seawater composition and the paleoeredox state of earth s surface environment however it is unclear whether the phosphorus in bifs originally entered the sediment as a sorbed component of the iron oxyhydroxide particles or whether it was incorporated into the biomass of marine phytoplankton we conducted high resolution mineral analyses and report here the first detection of an fe iii acetate salt as well as nanocrystals of apatite in association with magnetite in the 2 48 ga dales gorge member of the brockman iron formation a bif hamersley western australia the clusters of apatite are similar in size and morphology to biogenic apatite crystals resulting from biomass decay in phanerozoic marine sediments while the formation of an fe iii acetate salt and magnetite not only implies the original presence of biomass in the bif sediments but also that organic carbon likely served as an electron donor during bacterial fe iii reduction this study is important because it suggests that phytoplankton may have played a key role in the transfer of phosphorus and other trace elements from the photic zone to the seafloor

the link between biomineralization and fossilization of bacteria insights from field and experimental studies abstract fossil biominerals and fossils of microorganisms in ancient rocks contain important biogeochemical signals decoding this record may reveal crucial information about the evolution of life on earth and terrestrial paleoenvironments however the identification of traces of life especially in very old rocks is extremely challenging because the morphological and chemical signatures of biominerals and microfossils are subtle of microscopic size and inevitably altered with aging in this review we stress on the fact that biomineralization is often the first step of fossilization and produces particular chemical structural and morphological features that can be preserved in fossil biominerals or microfossils with a special focus on fe biomineralization the taphonomic processes affecting biominerals and microfossils and altering their morphology and or chemical composition over time are then discussed in light of experimental fossilization simulations and field sample analyses we suggest that taxonomic biases observed in the fossil record may be related to differential abilities of species to trigger biomineralization this calls for studies of the effective biomineralizing activity and fossilization potential of each species present in highly diverse natural microbial communities finally recent analytical developments leave little doubt that very substantial progress in the study of biomineralization processes and ancient biostructures will be achieved in the near future

reconciling short recurrence intervals with minor deformation in the new madrid seismic zone at least three great earthquakes occurred in the new madrid seismic zone in 1811 and 1812 estimates of present day strain rates suggest that such events may have a repeat time of 1000 years or less paleoseismological data also indicate that earthquakes large enough to cause soil liquefaction have occurred several times in the past 5000 years however pervasive crustal deformation expected from such a high frequency of large earthquakes is not observed this suggests that the seismic zone is a young feature possibly as young as several tens of thousands of years old and no more than a few million years old

late cenozoic history and slip rates of the fish lake valley emigrant peak and deep springs fault zones nevada and california several well dated stratigraphic markers permit detailed assessment of the temporal and spatial variation in slip rates along the interconnected faults of the fish lake valley emigrant peak and deep springs fault zones in west central nevada and east central california right lateral motion on the fish lake valley fault zone apparently began ca 10 ma 11 9 8 2 ma associated extensional faulting probably began ca 5 ma 6 9 4 ma and resulted in the opening of fish lake valley and deep springs valley the long term lateral slip rate for the fish lake valley fault zone since about 10 ma is 5 mm yr 3 12 mm yr our preferred lateral slip rate for the central most active part of the fish lake valley fault zone decreased from about 6 to 3 mm yr from the late miocene to the early pleistocene increased to about 11 mm yr during the middle pleistocene and decreased to about 4 mm yr during the late pleistocene extension may account for some of the change in lateral slip rate during the pliocene the large increase in lateral slip rate during the middle pleistocene is circumstantially linked to an increase in vertical slip rates on the fish lake valley and deep springs fault zones at about the time of the eruption of the bishop ash 0 76 ma vertical slip rates along the three fault zones are also related to fault strike vertical rates are highest on north striking faults and approach zero on northwest striking faults the long lived slip history of the fish lake valley fault zone fits a tectonic model in which the death valley furnace creek fish lake valley fault system is integrated with right lateral shear on faults of the central walker lane and the eastern california shear zone to accommodate part of the pacific north american relative plate motion our research demonstrates that the fish lake valley fault zone accounts for about half the rate of 10 12 mm yr of pacific north american plate boundary shear accommodated within the basin and range province between about lat 37 and 38 n

lateral offsets and revised dates of large prehistoric earthquakes at pallett creek southern california recent excavation and new radiocarbon dates of sediments at pallett creek are the basis for new conclusions regarding the late holocene history of the san andreas fault systematic dissection of a 50 m long 15 m wide 5 m deep volume of earth centered on the fault enables documentation in three dimensions of fault patterns lateral offsets and vertical deformation associated with large earthquakes of the past the excavations expose evidence for 12 earthquakes that occurred between about 260 and 1857 a d with an average recurrence interval of about 145 years prehistoric slip events that occurred in 1720 50 1550 70 1350 50 1080 65 and 845 75 a d have lateral offsets that are comparable to those of the most recent great earthquake of 1857 thus all of these events represent earthquakes of large magnitude the lateral offsets of two other events in 935 85 and 1015 100 a d are an order of magnitude smaller and may be interpreted in several ways with regard to the size of these events the new data constrain the average recurrence interval for large earthquakes at this site to between 145 and 200 years but suggest a monotonic decrease in individual intervals to below this range during the past 900 years on the basis of these data the probability of a large earthquake with surficial fault rupture at this site is between 0 2 and 5 during 1984 and 7 and 60 by the year 2000