holocene subaqueous paleoseismology of lake tahoe gravity flow deposits recovered in a suite of sediment cores in lake tahoe were examined to determine if the event deposits were triggered by strong shaking from earthquakes on active faults within and in close proximity to the lake tahoe basin the acoustic character and distribution of individual lacustrine deposits as well as potential source regions were constrained by high resolution seismic chirp reflection and multibeam bathymetric data between 14 and 17 holocene event deposits have been identified in lake tahoe and examination of their source areas suggests they originated from different initiation points along the steep margin with some being synchronous around the basin as opposed to flood related deposits lithologic characteristics magnetic susceptibility carbon and nitrogen isotopic signatures opal content and 14 c dating indicate that these event deposits are reworked lacustrine material radiocarbon dates indicate that the emplacement of these event deposit sediments correlates well with the late holocene paleoseismic earthquake record developed for the tahoe basin when taken alone the causality of these events may appear ambiguous but when the evidence is examined comprehensively it suggests that strong shaking may likely have been the primary trigger for many of the event deposits observed in the lake throughout the holocene for example four event deposits are assigned to tahoe basin faults the most recent earthquakes occurred on the incline village fault between 630 and 120 cal yr b p the southern segment of the west tahoe fault between 4510 and 4070 cal yr b p on the central and northern segments of the west tahoe fault 5600 5330 cal yr b p and on the west tahoe fault between 7890 and 7190 cal yr b p the oldest of the four associated tahoe basin events coincides with the beginning of an extended period when lake tahoe was likely not spilling or spilling intermittently and this suggests that active faulting and footwall uplift cut off the outlet at this time exaggerating drought conditions downstream likewise the event between 5600 and 5330 cal yr b p on the west tahoe fault may have exaggerated a smaller drought reflected downstream in pyramid lake this event may also be the most recent event mre on the largest segment of the west tahoe fault if correct the period since the last rupture is approximately twice the estimated average recurrence interval for the rubicon segment of the west tahoe fault a more complete holocene record of strong shaking greatly extends the paleoseismic record in the region and indicates a combined recurrence interval of between 750 and 800 yr for all faults in the region

the drenchwater deposit alaska an example of a natural low ph environment resulting from weathering of an undisturbed shale hosted zn pb ag deposit abstract the drenchwater shale hosted zn pb ag deposit and the immediate vicinity on the northern flank of the brooks range in north central alaska is an ideal example of a naturally low ph system the two drainages drenchwater and false wager creeks which bound the deposit differ in their acidity and metal contents moderately acidic waters with elevated concentrations of metals ph 4 3 zn 1400 g l in the drenchwater creek drainage basin are attributed to weathering of an exposed base metal rich massive sulfide occurrence stream sediment and water chemistry data collected from false wager creek suggest that an unexposed base metal sulfide occurrence may account for the lower ph 2 7 3 1 and very metal rich waters up to 2600 g l zn 260 g l cu and 89 g l tl collected at least 2 km upstream of known mineralized exposures these more acidic conditions produce jarosite schwertmannite and fe hydroxides commonly associated with acid mine drainage the high metal concentrations in some water samples from both streams naturally exceed alaska state regulatory limits for freshwater aquatic life affirming the importance of establishing base line conditions in the event of human land development the studies at the drenchwater deposit demonstrate that poor water quality can be generated through entirely natural weathering of base metal occurrences and possibly unmineralized black shale

on diagenesis dolomitisation and mineralisation in the irish zn pb orefield marine calcite cementation and lithification of carboniferous carbonate sediments hosting zn pb mineralisation in the irish orefield occurred at or near the seafloor a relatively early fine grained grey replacive dolomite preferentially developed in micrite is widely developed in the waulsortian limestone formation the main host to mineralisation and is pervasive in the southeastern midlands in proximity to the leinster massif this dolomite formed after the first four main stages of calcite cementation but probably also developed within tens of metres of the seafloor as evidenced by incorporation of clasts of dolomite in intraformational sedimentary breccias later coarse grained white dolomite preferentially replaced coarser components of the waulsortian limestone and infilled residual vuggy porosity whilst some of this coarse dolomite may be related to the fine replacive dolomite event a common spatial association with fault zones coupled with primary fluid inclusion data suggest that a significant proportion of this phase precipitated during the onset of fault controlled subsidence and widespread hydrothermal circulation within the irish midlands area fluids up to 250 c and 10 15 wt nacl equivalent sourced from a lower palaeozoic basement equilibrated fluid reservoir infiltrated the carbonate sequence via faults and fractures the more localised development of dolomite cemented breccias white matrix breccias that are frequently associated spatially with mineralisation was a consequence of the increased focusing of these hydrothermal fluids ore formation was broadly synchronous with development of the white dolomite breccias but only happened where mixing occurred between the hydrothermal ore fluids and localised near surface reservoirs of low temperature h2s rich brine in the waulsortian this process led to the precipitation of a distinctive black dolomite that forms a broad halo to massive sulphides although ore stage sulphides postdate significant diagenesis of the host rocks and often display epigenetic textures the fact that much of the cementation occurred soon after carbonate deposition means that mineralisation does not have to have formed after significant burial in fact the occurrence of clasts of hydrothermal dolomite and sulphides in intraformational debris flow breccias is only consistent with mineralising processes occurring in the near seafloor environment relatively soon after host rock deposition the regional development of a distinctive pink dolomite associated with faults and fractures was a post ore event and is considered to mark a regional brine migration linked to the onset of the variscan orogeny the development of this new tectonic and flow regime may have been responsible for the cessation of economic mineralisation in ireland

sedimentary processes across the continental rise of the southern antarctic peninsula abstract a series of large sediment mounds have been identified along the pacific portion of the antarctic peninsula continental rise these mounds are composed of sediment delivered to the continental rise during the advance and retreat of grounded ice across the shelf the stratigraphic development of one of these sediment deposits the tula sediment mound is examined to investigate how the onset of glaciation influenced the deep sea depositional environment along this portion of the margin the stratal relationships associated facies distribution and the physiography observed along the southern antarctic margin reflect the waxing and waning of the antarctic ice sheets various processes erode transport and deposit sediment along the outer shelf slope and rise throughout a glacial cycle a deep sea erosional unconformity is apparent at the base of the tula deposit this surface may reflect the first onset of intensified bottom water circulation along the margin perhaps induced by the tectonic opening of the drake passage the tula sediment mound is comprised predominantly of canyon overbank systems evidence for the onset of canyon cutting and the development of the thick overbank deposits 2 km is found immediately above the deep sea erosional unconformity relating increased canyon cutting across the continental rise to the fluctuation of ice across the shelf implies that the onset of predominantly glacial conditions commenced soon after the onset of intensified bottom water circulation along this margin the volume of sediment associated with the tula deposit and the apparent point source distribution of the channel systems suggests that much sediment was transported to the slope and rise perhaps by meltwater processes through these canyons

advection of fluids at the front of the sicilian neogene subduction complex abstract the sicilian accretionary prism shows a large southward imbricated system of thrust sheets the frontal part of the belt has been tectonically emplaced in plio pleistocene times major decollement surfaces and sole thrusts at the base of and inside the prism consist of melanges with a blocks in matrix fabric in the frontal part two superposed decollement levels are recognized the upper one located at the base of the paleogene neogene sedimentary series and the basal one at the base of duplexes triassic miocene sedimentary series syntectonic dewatering of the sedimentary sections occurred along decollements and thrust faults involving hydrofracture and mineralized vein development inside the deep sole thrusts rooted in the basal decollement hydrofractured blocks show different generations of syntectonic quartz and calcite extensional veins while in the upper decollement only calcite veins have been observed both quartz and calcite veins show aqueous primary fluid inclusions of low salinity with low trapping temperature for fluids in the upper decollement if we assume that at the time of deformation the main heat source was the regional conductive geothermal gradient the trapping temperatures of the fluids inside veins of the deep sole thrusts are higher than those predicted by the pilo pleistocene gradient for this subduction zone and correspond to a thermal anomaly we suggest that the frontal sicilian prism supported localized transient fluid flow of deep freshwater sourced from two different origins a shallow one for fluids now trapped in the upper decollement and a deep internal origin 6 10 km minimum depth for the hot fluids channelized along the basal decollement and now trapped inside the sole thrust of the mt scalpello duplex area

late pleistocene and holocene faulting in the western truckee basin north of truckee california evidence for active faulting in the truckee basin north of lake tahoe is observed in a meadow containing a scarp and small closed depression shallow hand dug trenches show offset marsh stratigraphy of holocene age lithostratigraphy descriptions and radiocarbon dates indicate the meadow was a marsh during the late quaternary that was abruptly infilled with the deposition of the 7000 yr b p tsoyawata tephra mt mazama the tephra is offset up to 80 cm across a narrow sub vertical north south striking fault zone additional offset of 30 cm occurred across the same structure during the late pleistocene our study provides direct stratigraphic evidence for at least one surface faulting event during the holocene and another in the late pleistocene within the truckee fault zone and provides new constraints on seismic sources capable of significant ground rupture and or shaking in the greater reno tahoe truckee area

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

terrestrial cosmogenic surface exposure dating of moraines at lake tahoe in the sierra nevada of california and slip rate estimate for the west tahoe fault abstract two sets of pleistocene moraines tioga and tahoe are preserved at cascade lake along the west side of lake tahoe the 10 be terrestrial cosmogenic nuclide surface exposure ages for two younger tioga moraines yield an average age of 22 3 1 2 ka coincident with the global last glacial maximum the ages suggest that the tioga glaciation may have reached its maximum several thousand years earlier in the lake tahoe basin than to the south along the east flank of the sierra nevada the oldest 10 be age 120 8 ka determined for an additional suite of 10 boulders exhibiting significant scatter in 10 be ages is interpreted to be the minimum age of formation for older tahoe moraines in the tahoe basin suggesting they were deposited during marine oxygen isotope stage 6 the moraines at cascade lake are displaced by the west tahoe fault that strikes northward for 45 km along the western edge of the lake tahoe basin vertical displacements of the crests of the tahoe and tioga moraines are 59 10 and 32 12 m respectively averaged over the time since the formation of the tahoe and tioga moraines the average vertical separation rates are

60 k y record of extension across the western boundary of the basin and range province estimate of slip rates from offset shoreline terraces and a catastrophic slide beneath lake tahoe deformation across three major fault strands within the lake tahoe basin has been mapped by using a novel combination of high resolution seismic chirp airborne laser and acoustic multibeam derived bathymetry and deep and shallow water sediment cores submerged erosional terraces of late pleistocene age 19 2 6 1 8 ka record vertical de formation across fault strands that ranges between 10 and 15 m offset of 10 m is observed across the southern part of the west tahoe fault avalanche deposits from the catastrophic mckinney bay slide ca 60 ka are offset across the stateline fault by at least 21 25 m the submerged shoreline terraces and debris avalanche provide marker beds with which to constrain the extensional history of the region for the past 60 k y this history is then used to assess the future seismic hazard of the region data on deformation across these two important marker beds combined with chronological control from 14 c and optically stimulated luminescence measurements yield an estimate of extension across the lake tahoe basin that is 0 4 0 5 mm yr on the basis of these measurements there exists the potential for a large seiche wave generating m7 earthquake every 3 k y late pleisto cene and holocene vertical deformation rates within the tahoe basin are characteristic of basin and range faulting and place the tahoe basin within the western limits of the extensional basin and range province

controls on stylolite development morphologic lithologic and temporal evidence from bedding parallel and transverse stylolites from the u s appalachians quantification of morphology of bedding parallel and transverse or tectonic stylolites from the southern appalachians reveals that regardless of tectonic setting or stylolite orientation lithologic heterogeneity controls stylolite development for example stylolites in more heterogeneous carbonate lithologies packstones and grainstones are more serrate than those in wackestones and mudstones similarly early forming stylolites are more serrate than late forming stylolites and computer simulations suggest that decreases in porosity or other lithologic heterogeneity cause the less serrate nature of late forming stylolites the linkage of a stylolite s morphology to its time of development should allow field estimation of timing of stylolitization and thus of timing of loading or compression although bedding parallel and transverse stylolites generally result from different kinds of compression morphological relations indicate that their development follows the same fundamental patterns bedding

active faulting in the north valleys region of reno nevada a distributed zone within the northern walker lane abstract at the latitude of reno nevada usa 15 25 of the pacific north american plate boundary strain is accommodated east of the sierra nevada through a combination of normal oblique dextral slip along the eastern sierra nevada range front and dextral slip along faults in the northern walker lane the north valleys region sits within the northern walker lane directly east of the sierra range front and is characterized by a series of small north striking basins bound by quaternary active faults that accommodate dextral oblique extension geodetic studies of the north valleys estimate that the faults collectively accommodate 0 9 1 7 mm y of extension and in this paper geologic observations on the tectonic geomorphic expression and relative activity of faults within and bounding the north valleys are described including the last chance petersen mountain fred s mountain and spanish springs valley fault zones and several un named faults in lemmon and hungry valleys geologic observations from the interpretation of lidar derived hillshade images aerial photographs satellite imagery and field reconnaissance indicate that the faults all exhibit evidence of late quaternary deformation including offset alluvial fan deposits and abrupt range front escarpments the results indicate that the faults of the north valleys are capable seismic sources characterized by extension rates on the order of hundredths to tenths of millimeters per year the faults act to transfer slip from the sierra nevada range front to the northeastern walker lane by accommodating dextral oblique extension consistent with pull apart basin kinematics within a simple shear right lateral system

sierra nevada basin and range transition near reno nevada two stage development at 12 and 3 ma relative and absolute elevations of the sierra nevada and adjacent basin and range province timing of their differentiation and location amount and timing of strike slip movement between them are controversial the provincial boundary near reno developed in two stages 1 at ca 12 ma the 700 km 2 verdi boca sedimentary basin formed across what was to become the boundary probably as a result of a small magnitude but regional extensional episode that affected much of the western basin and range 2 at 3 ma the basin was complexly faulted and folded during a larger magnitude extensional episode that established the modern sierran structural and topographic boundary in this area the boundary is really a transition zone with a western edge along the donner pass california fault zone which is farther west than previously placed both episodes appear to have resulted from east west extension only which suggests that northwest motion of the sierra nevada relative to the basin and range shown by geodetic data began after 3 ma or was taken up farther east

active transtensional boundary zone between the western great basin and sierra nevada block western u s cordillera the walker lane and northern part of the eastern california shear zone form a boundary zone accommodating differential motion between the sierra nevada and western great basin within the boundary zone global positioning system velocities show a westward increase from 2 3 mm yr in the central great basin to 14 mm yr in the sierra nevada and a clockwise rotation from west northwest to northwest in the same region incremental extensional strain axes recorded by earthquake focal mechanisms and fault slip inversion show an east to west counterclockwise rotation of 50 from parallel with the velocity field in the central great basin to nearly orthogonal to the velocity field along the eastern flank of the sierra nevada unlike plane strain deformation within the central great basin the progressive deviation between the orientation of extension axes and the velocity field in the boundary zone is a product of nonplane strain the boundary zone records active constriction formed in conditions varying from wrench dominated to extension dominated transtension

automated recognition of valley lines and drainage networks from grid digital elevation models a review and a new method abstract the literature on valley and drainage line recognition from grid digital elevation models dems is reviewed two problems preventing the successful delineation of fully connected drainage networks of single line width are identified a the positioning of the ends of drainage networks and b the assignment of drainage directions to a dem in particular the assignment of drainage directions across flat areas and at closed depressions in the dem pits a new method for drainage network delineation is suggested which incorporates an alternative method for drainage direction assignment over a dem this method is found to produce realistic directions and performs well on two complex dems

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

chronology for fluctuations in late pleistocene sierra nevada glaciers and lakes mountain glaciers because of their small size are usually close to equilibrium with the local climate and thus should provide a test of whether temperature oscillations in greenland late in the last glacial period are part of global scale climate variability or are restricted to the north atlantic region correlation of cosmogenic chlorine 36 dates on sierra nevada moraines with a continuous radiocarbon dated sediment record from nearby owens lake shows that sierra nevada glacial advances were associated with heinrich events 5 3 2 and 1

wisconsin glaciation of the sierra nevada 79 000 15 000 yr b p as recorded by rock flour in sediments of owens lake california chemical analyses of the clay sized fractions of 564 continuous sediment samples 200 yr resolution from composite core ol90 92 allow quantification of an abundance of glacial rock flour rock flour produced during glacier advances is represented by clay sized plagioclase k feldspar and biotite in homogeneous internal composition the abundance of rock flour is deemed proportional to the intensity of glacies advances age control for the composite section is provided by combining previously published radiocarbon dates on organics u th dates on ostracode shells and u th dates on saline minerals from nearby searles lake correlated to ol92 by pollen the rock flour record displays three levels of variability 1 a dominant one of about 20 000 yr related to summer insolation and precipitation 2 an intermediate one of 3000 5000 yr perhaps related to north atlantic heinrich events and 3 a minor one of 1000 2000 yr perhaps related to north atlantic thermohaline driven air temperature variation

late pleistocene and holocene paleoearthquake activity of the olinghouse fault zone nevada paleoseismic trenching and fault surface trace mapping indicate that the olinghouse fault zone a northeast trending left lateral strike slip fault located in the northern walker lane nevada has been the source of multiple latest pleistocene and holocene surface rupturing earthquakes a trench exposure near the eastern end of the fault records two and possibly three earthquakes after 3360 190 cal yr b p and two trenches at the western end of the fault contain evidence for two earthquakes after 19 800 630 cal yr b p with the most recent earthquake occurring after 1935 70 cal yr b p the apparent higher frequency of recent earthquakes at the eastern end of the fault may reflect triggered slip on the olinghouse fault zone due to earthquakes on the conjugate northwest trending right lateral pyramid lake fault repeated late pleistocene and holocene earthquakes on the olinghouse fault zone demonstrate that northwest directed right lateral shear of the northern walker lane is accommodated in part by northeast trending left lateral faults

duration and severity of medieval drought in the lake tahoe basin droughts in the western u s in the past 200 years are small compared to several megadroughts that occurred during medieval times we reconstruct duration and magnitude of extreme droughts in the northern sierra nevada from hydroclimatic conditions in fallen leaf lake california stands of submerged trees rooted in situ below the lake surface were imaged with sidescan sonar and radiocarbon analysis yields an age estimate of w1250 ad tree ring records and submerged paleoshoreline geomorphology suggest a medieval low stand of fallen leaf lake lasted more than 220 years over eighty more trees were found lying on the lake floor at various elevations above the paleoshoreline water balance calculations suggest annual precipitation was less than 60 normal from late 10th century to early 13th century ad hence the lake s shoreline dropped 40e60 m below its modern elevation stands of pre medieval trees in this lake and in lake tahoe suggest the region experienced severe drought at least every 650e1150 years during the mid and late holocene these observations quantify paleo precipitation and recurrence of prolonged drought in the northern sierra nevada published by elsevier ltd

holocene paleoclimate history of fallen leaf lake ca from geochemistry and sedimentology of well dated sediment cores abstract millennial scale shifts in aridity patterns have been documented during the holocene in the western united states yet the precise timing severity and regional extent of these shifts prompts further study we present lake sediment core data from fallen leaf lake a subalpine system at the southern end of the lake tahoe basin for which 80 of the contemporary inflow is derived from snowpack delivered by pacific frontal storm systems a high quality age model has been constructed using 14c ages on plant macrofossils 210pb and the tsoyowata tephra datum 7 74 7 95 cal kyr bp one core captures the transition from the late tioga younger dryas glaciolacustrine package to laminated opaline clay at 11 48 cal kyr bp early holocene sedimentation rates are relatively high 1 9 mm year and cooler winter temperatures are inferred by the presence of pebbles interpreted to be transported out into the lake via shore ice there is a geochemically distinct interval from 4 71 to 3 65 cal kyr bp that is interpreted as a late holocene neopluvial characterized by depleted 13c and lower c n that point to reduced runoff of terrigenous organic matter increased winter precipitation and increased algal productivity the largest holocene signal in the cores occurs at the end of the neopluvial at 3 65 cal kyr bp and marks a shift into a climate state with variable precipitation yet is overall more arid than the neopluvial this new climate state persists for 3 ka until the little ice age low sedimentation rates 0 5 mm year the homogeneous opaline sediment and steadily increasing contributions of terrestrial vs algal organic matter in these cores suggest that the lowstand state of fallen leaf lake may have been the norm from 3 65 to 0 55 cal kyr bp punctuated by short term high precipitation years or multi year intervals capable of rapid short duration lake level rise fallen leaf lake is strongly influenced by changes in winter precipitation and temperature manifested largely by the geochemical proxies and highlights unique advantages of subalpine lakes in regional paleoclimate reconstructions

the palos verdes fault offshore southern california late pleistocene to present tectonic geomorphology seascape evolution and slip rate estimate based on auv and rov surveys the palos verdes fault pvf is one of few active faults in southern california that crosses the shoreline and can be studied using both terrestrial and subaqueous methodologies to characterize the near seafloor fault morphology tectonic influences on continental slope sedimentary processes and late pleistocene to present slip rate a grid of high resolution multibeam bathymetric data and chirp subbottom profiles were acquired with an autonomous underwater vehicle auv along the main trace of pvf in water depths between 250 and 600 m radiocarbon dates were obtained from vibracores collected using a remotely operated vehicle rov and ship based gravity cores the pvf is expressed as a well defined seafloor lineation marked by subtle along strike bends right stepping transtensional bends exert first order control on sediment flow dynamics and the spatial distribution of holocene depocenters deformed strata within a small pull apart basin record punctuated growth faulting associated with at least three holocene surface ruptures an upper shallower landslide scarp a buried sedimentary mound and a deeper scarp have been right laterally offset across the pvf by 55 5 52 4 and 39 8 m respectively the ages of the upper scarp and buried mound are approximately 31 ka the age of the deeper scarp is bracketed to 17 24 ka these three piercing points bracket the late pleistocene to present slip rate to 1 3 2 8 mm yr and provide a best estimate of 1 6 1 9 mm yr the deformation observed along the pvf is characteristic of strike slip faulting and accounts for 20 30 of the total right lateral slip budget accommodated offshore southern california

the potential hazard from tsunami and seiche waves generated by large earthquakes within lake tahoe california nevada we investigate the potential of local earthquakes to generate tsunamis and seiches within lake tahoe we calculated the long wavelength oscillations generated by 3 hypothetical m w 7 earthquake scenarios for faults with normal slip directly under and outside the lake basin the scenarios involving fault slip under the lake are the north tahoe incline village and west tahoe dollar point scenarios the genoa scenario involves a fault that crops out 10 km east of the lake faulting beneath the lake generates a tsunami followed by a seiche that continues for hours with waves as large as 3 to 10 m the seiche potentially threatens low lying lakeside communities and lifelines we also compare the spectral characteristics of synthetic tide gauge records with wind swell observations the fundamental mode calculated for a seiche is consistent with the wind swell observations

neotectonics geodesy and seismic hazard in the northern walker lane of western north america thirty kilometers of crustal shear and no strike slip article i nfo roughly 30 km of cumulative right lateral crustal displacement and 5 6 mm yr of the ongoing relative right lateral motion between the pacific and north american plates are observed in the northern walker lane the right lateral shear has been accommodated in large part by the development of a set of discontinuous en echelon normal fault bounded basins and perhaps significant vertical axis rotations of the intervening crust the observations provide an illustrative example of how large amounts of crustal shear may be accom modated in the absence of strike slip faults and point to difficulties attendant to melding geologic and geo detic observations in the analysis of seismic hazard in this particular case the assumption that all geodetically observed shear across the area will be recorded by earthquake displacements may be flawed

kinematics of the southern walker lane belt and motion of the sierra nevada block california deformation in the southern walker lane belt region of the southwestern great basin accommodates significant portions of both pacific north america transform motion and basin and range extension apparent kinematic inconsistencies between geodetic and fault slip data in this region have made it difficult to understand the nature of the interaction between these deformation processes and to infer the regional kinematics we model the kinematics of this region in a manner that enforces kinematic consistency and includes fault geometry and slip rate data global positioning system gps survey data and very long baseline interferometry very long baseline array vlbi vlba site velocity data a model is found that is consistent with the set of available data and this model differs significantly from prior models for the region our model has the sierra nevada block which bounds the western margin of the great basin moving n50 w 5 at 12 7 1 5 mm yr with only minor amounts of counterclockwise rotation left lateral slip on the western garlock fault is a consequence of the relatively great westerly component of sierra nevada velocity we also find that the basin and range extension east of our study area occurs at a rate of about 2 5 mm yr which is slower than the rate in the central great basin

tracing element sources of hydrothermal mineral deposits ree and y distribution and sr nd pb isotopes in fluorite from mvt deposits in the pennine orefield england fluorite from mississippi valley type mvt deposits in the south pennine orefield england displays significantly different distributions of rare earths and yttrium rey compared to fluorite from similar mvt deposits in the north pennine orefield samples from the south pennine orefield display negative ce and positive gd and y anomalies but lack any eu anomaly indicating that the rey were mobilized from relatively pure marine sedimentary carbonates in marked contrast fluorite from the north pennine orefield lacks any ce and gd anomalies but shows a pronounced positive eu anomaly suggesting that the rey were provided by different source rock s that the mineralizing hydrothermal fluid had experienced higher temperatures prior to fluorite precipitation and that it was derived from deeper crustal levels in the north compared to the south the isotopic composition of sr in blue john fluorite from the south pennine orefield suggests that sr was mobilized from lower carboniferous tournaisian limestones whereas pb isotopes suggest that in contrast to rey and sr pb was derived from aluminosilicate rocks neither nd nor sr or pb isotopes can be used to radiometrically date the formation of blue john fluorite all isotope systems studied indicate that the limestone host rock of this fluorite mineralization did not contribute to the trace element budget of the hydrothermal fluid our results show that different solutes in a natural water hydrothermal fluid groundwater etc may be derived from different sources and that the study of a small set of elements or isotope ratios may not provide full insight into the genesis or history of a mineralization or a hydrothermal fluid our data provide evidence for the uncoupling of sr nd and pb during fluid rock interaction and fluid migration and show that the use of plots such as 87sr 86sr vs end to learn about mixing relationships as is commonly done in igneous geochemistry is unreliable when applied to natural waters and their precipitates

the treatment of flat areas and depressions in automated drainage analysis of raster digital elevation models methods developed to process raster digital elevation models dem automatically in order to delineate and measure the properties of drainage networks and drainage basins are being recognized as potentially valuable tools for the topographic parameterization of hydrological models all of these methods ultimately rely on some form of overland flow simulation to define drainage courses and catchment areas and therefore have difficulty dealing with closed depressions and flat areas on digital land surface models some fundamental assumptions about the nature of these problem topographic features in dem are implicit in the various techniques developed to deal with them in automated drainage analysis the principal assumptions are 1 that closed depressions and flat areas are spurious features that arise from data errors and limitations of dem resolution 2 that flow directions across flat areas are determined solely by adjacent cells of lower elevation and 3 that closed depressions are caused exclusively by the underestimation of dem elevations it is argued that while the first of these assumptions is reasonable given the quality of dems generally available for hydrological analysis the others are not rather it seems more likely that depressions are caused by both under and overestimation errors and that flow directions across flat areas are determined by the distribution of both higher and lower elevations surrounding flat areas two new algorithms are introduced that are based on more reasonable assumptions about the nature of flat areas and depressions and produce more realistic results in application these algorithms allow breaching of depression outlets and consider the distribution of both higher and lower elevations in assigning flow directions on flat areas the results of applying these algorithms to some real and hypothetical landscapes are presented 1998 john wiley sons ltd

a comparison of drainage networks derived from digital elevation models at two scales abstract automated generation of drainage networks has become increasingly popular with powerful analytical functions in geographic information systems gis and with the increased availability of digital elevation models dems this paper compares drainage networks derived from dems at two scales 1 250 000 250k and 1 24 000 24k using various drainage parameters common in hydrology and geomorphology the comparison of parameters derived from the 250k dems with those from the 24k dems in 20 basins ranging from 150 to 1000 km2 in west virginia shows that the goodness of fit between parameter estimates based on the dems varies results clearly show that superior estimations are produced from the 24k dems better estimates can be obtained from the 250k dems for stream length and frequency parameters than for gradient parameters however the estimation of the mean gradient parameters based on the 250k dems seems to improve with increasing terrain complexity finally basin size does not strongly affect the accuracy of parameter estimates based on the 250k dems

the unusual temporal and spatial slip history of the wassuk range normal fault western nevada usa implications for seismic hazard and walker lane deformation we document temporal and spatial variations in vertical displacement rate across 6 temporal orders of magnitude to better understand how the 100 km long east dipping wassuk range normal fault system has accommodated strain in the context of the walker lane a tectonically active nnw trending zone of dextral and extensional deformation that affects significant portions of western nevada and eastern california we combine 10 be and 26 al cosmonuclide exposure ages with shallow seismic and gravity data from the buried hanging wall of the wassuk fault to derive a post 113 ka 10 5 yr time scale vertical displacement rate of 0 82 0 16 mm yr we also perform large scale fault scarp analysis to constrain the long term 1 ma 10 6 yr time scale displacement rate our fault scarp analysis results imply similar vertical displacement rates with higher long term vertical displacement rates along the southern fault 1 1 mm yr relative to the northern fault vertical displacement rate data at the 10 6 10 5 10 3 and 10 1 yr time scales this study and others support a constant vertical displacement rate between 0 75 and 1 0 mm yr for the wassuk range fault since ca 4 ma an anomalously high vertical displacement rate at the 10 4 yr time scale is best explained by an earthquake cluster between ca 15 5 ka and ca 10 5 ka potentially linked to rapid filling of the walker lake basin immediately prior to the ca 13 ka sehoo highstand of ancestral lake lahontan we hypothesize that this flood event induced seismicity by placing an additional load on the hanging wall of the wassuk range fault and by increasing the pore fluid pressure within and adjacent to the fault although an earthquake cluster like this is consistent with wallace type fault behavior we suggest that a nontectonic stressor induced the cluster resulting in the apparent discrepancy in vertical displacement rate at the 10 4 yr time scale thus we posit that the long term slip along wassuk fault is better explained by slip predictable reid type behavior which deviates from the behavior of other well documented fault systems based on these results we suggest that similar unrecognized nontectonic stressors may influence rates of strain release along other major fault systems worldwide finally we present a revised model of central walker lane kinematics based on data from this and other recent studies

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

deriving flow directions for coarse resolution 1 4 km gridded hydrologic modeling 1 the national weather service hydrology laboratory nws hl is currently testing a grid based distributed hydrologic model at a resolution 4 km commensurate with operational radar based precipitation products to implement distributed routing algorithms in this framework a flow direction must be assigned to each model cell a new algorithm referred to as cell outlet tracing with an area threshold cotat has been developed to automatically accurately and efficiently assign flow directions to any coarse resolution grid cells using information from any higher resolution digital elevation model although similar to previously published algorithms this approach offers some advantages use of an area threshold allows more control over the tendency for producing diagonal flow directions analyses of results at different output resolutions ranging from 300 m to 4000 m indicate that it is possible to choose an area threshold that will produce minimal differences in average network flow lengths across this range of scales flow direction grids at a 4 km resolution have been produced for the conterminous united states

a new triangular multiple flow direction algorithm for computing upslope areas from gridded digital elevation models 1 gridded digital elevation data often referred to as dems are one of the most widely available forms of environmental data topographic analysis of dems can take many forms but in hydrologic and geomorphologic applications it is typically used as a surrogate for the spatial variation of hydrological conditions topographic indices and flow routing here we report on a new flow routing algorithm and compare it to three common classes of algorithms currently in widespread use the advantage of the new algorithm is that unrealistic dispersion on planar or concave hillslopes is avoided whereas multiple flow directions are allowed on convex hillslopes we suggest that this new triangular multiple flow direction algorithm md1 is more appropriate for a range of flow routing and topographic index applications

river reach length and slope estimates for large scale hydrological models based on a relatively high resolution digital elevation model application of regular grid based distributed hydrological models requires information related to river drainage networks such as flow directions flow accumulated areas basin delineation and length and slope of river reaches for every grid cell most of those data may be extracted automatically from digital elevation models dem however when dealing with large basins available dems are usually in higher spatial resolution than the model grid upscaling procedures have therefore been developed to extract low resolution flow directions and flow accumulated areas from relatively high resolution dems this paper presents a new methodology which extends the upscaling method to automatically extract length and slope of river reaches for large scale grid based hydrological models the proposed method is new and is believed to be the first attempt to produce such information automatically from dems the methodology was applied to parts of the uruguay river basin in south america using the globally wide available dem produced by the shuttle radar topography mission srtm 90m quality of results was assessed by comparing calculated river lengths with distances measured over vectorized river networks which were assumed to be correct it was shown that the proposed methodology adequately assigns river lengths to every model cell while ensuring that the whole length of the streams is considered the effect of dem resolution on calculated river length errors was analyzed by resampling the srtm dem to three different cell sizes with best results obtained for the higher resolution dem the modification of the original high resolution dem through the process known as stream burning was also tested largely improving the quality of the results finally optimal distance transforms were used for the calculation of distance increments instead of euclidean local distances giving results that were generally better the quality of results for calculated slope values could not be assessed because no reliable data were available for comparison

improving hydrological information acquisition from dem processing in floodplains extraction of hydrological information from digital elevation models dems is a required step when conducting any spatially distributed hydrological modelling in particular automated methods are proposed to extract the drainage structure from the dem however a realistic river network is not always derived from conventional dem processing methods indeed inaccuracy occurs in flat areas corresponding to floodplains in these areas additional sources of information are required to extract the correct drainage direction from the dem in this study it is demonstrated that traditional approaches of dem preprocessing such as the commonly known stream burning fail to provide correct maps of drainage directions and catchment areas when the extension of flat areas is large a new method is proposed to take advantage of available imagery data this method is based on a double dem burning process dem is first burned in the main rivers using the channel network and then in the floodplain using the spatial distribution of floodplains provided by classified satellite images in this sense the method has been referred to as the floodplain burning approach or simply fb approach spatial distribution of floodplains is derived from a multitemporal sar image classification a system of equations is used to vary the elevation offset required to be burnt in each cell representing the floodplain according to the minimal distance from the channel network which is calculated by a distance transformation the fb approach was applied to a sub basin located within the larger amazon river basin the region is characterized by large floodplain extensions basin delineation maps derived from the new method were compared with those obtained from the traditional stream burning method and highlighted more realistic results copyright 2008 john wiley sons ltd

new constraints on deformation slip rate and timing of the most recent earthquake on the west tahoe dollar point fault lake tahoe basin california high resolution seismic compressed high intensity radar pulse chirp data and piston cores acquired in fallen leaf lake fll and lake tahoe provide new paleoseismic constraints on the west tahoe dollar point fault wtdpf the western most normal fault in the lake tahoe basin california paleoearthquake records along three sections of the wtdpf are investigated to determine the magnitude and recency of coseismic slip chirp profiles image vertically offset and folded strata along the southern and central sections that record deformation associated with the most recent event mre on the wtdpf three faults are imaged beneath fll and the maximum vertical offset observed across the primary trace of the wtdpf is 3 7 m coregis tered piston cores in fll recovered sediment and organic material above and below the mre horizon radiocarbon dating of organic material constrained the age of the mre to be between 3 6 and 4 9 k y b p with a preferred age of 4 1 4 5 k y b p in lake tahoe near rubicon point approximately 2 0 m of vertical offset is observed across the wtdpf based on nearby core data the timing of this offset occurred be tween 3 10 k y b p which is consistent with the mre age in fll offset of tioga aged glacial deposits provides a long term record of vertical deformation on the wtdpf since 13 14 k y b p yielding a slip rate of 0 4 0 8 mm yr in summary the slip rate and earthquake potential along the wtdpf is comparable to the nearby genoa fault making it the most active and potentially hazardous fault in the lake tahoe basin

linked sequence stratigraphic and structural evolution of propagating normal faults two distinct phases in the structural evolution of normal faults can be identified in the miocene gulf of suez rift 1 an initial growth fold stage when the fault is a buried structure and 2 a subsequent surface faulting stage during the growth fold stage strata thin and become truncated toward the fault zone and are rotated and diverge away from the buried fault into growth synclines in contrast once the fault breaks surface strata form a divergent wedge which is rotated and thickens into the fault the two tectono stratigraphic styles also occur contemporaneously along the length of a single fault segment growth folding characterizes deformation around the ends of fault segments where the fault is blind whereas the center of fault segments are characterized by surface faulting these observations suggest that marked along strike variation in stratal surfaces and facies stacking patterns will occur in depositional sequences in areas of normal faulting

investigation of late pleistocene and holocene activity in the san gregorio fault zone on the continental slope north of monterey canyon offshore central california abstract we provide an extensive high resolution geophysical sediment core and radiocarbon dataset to address late pleistocene and holocene fault activity of the san gregorio fault zone sgfz offshore central california the sgfz occurs primarily offshore in the san andreas fault system and has been accommodating dextral strike slip motion between the pacific and north american plates since the mid miocene our study focuses on the sgfz where it has been mapped through the continental slope north of monterey canyon from 2009 to 2015 the monterey bay aquarium research institute collected high resolution multibeam bathymetry and chirp sub bottom profiles using an autonomous underwater vehicle auv targeted samples were collected using a remotely operated vehicle rov to provide radiocarbon age constraints we integrate the high resolution geophysical data with radiocarbon dates to reveal pleistocene seismic horizons vertically offset less than 5 m on nearly vertical faults these faults are buried by continuous reflections deposited after 17 5 ka and likely following erosion during the last sea level lowstand 21 ka bracketing the age of faulting to 32 21 ka clearly faulted horizons are only detected in a small area where mass wasting exhumed older strata to within 25 m of the seafloor the lack of clearly faulted holocene deposits and possible highly distributed faulting in the study area are consistent with previous interpretations that late pleistocene and holocene activity along the sgfz may decrease to the south this study illustrates the complexity of the sgfz offshore central california and demonstrates the utility of very high resolution data from combined auv geophysical rov seabed sampling surveys in offshore studies of fault activity

multistory duplexes with forward dipping roofs north central brooks range alaska the endicott mountains allochthon has been thrust far northward over the north slope parautochthon in the northern brooks range progressively younger units are exposed northward within the allochthon to the south the incompetent hunt fork shale has thickened internally by asymmetric folds and thrust faults northward the competent kanayut conglomerate forms a duplex between a floor thrust in hunt fork and a roof thrust in the kayak shale to the north the competent lisburne group forms a duplex between a floor thrust in kayak and a roof thrust in the siksikpuk formation both duplexes formed from north vergent detachment folds whose steep limbs were later truncated by south dipping thrust faults that only locally breach immediately overlying roof thrusts within the parautochthon the kayak lisburne and siksikpuk equivalent echooka formation form a duplex identical to that in the allochthon this duplex is succeeded abruptly northward by detachment folds in lisburne these folds are parasitic to an anticlinorium interpreted to reflect a fault bend folded horse in north slope basement with a roof thrust in kayak and a floor thrust at depth these structures constitute two northward tapered internally deformed wedges that are juxtaposed at the base of the allochthon within each wedge competent units have been shortened independently between detachments located mainly in incompetent units the basal detachment of each wedge cuts upsection forward northward to define a wedge geometry within which units dip regionally forward these dips reflect forward decrease in internal structural thickening by forward vergent folds and hindward dipping thrust faults

high ree and y concentrations in co cu au ores of the blackbird district idaho analysis of 11 samples of strata bound co cu au ore from the blackbird district in idaho shows previously unknown high concentrations of rare earth elements ree and y averaging 0 53 wt percent ree y oxides scanning electron microscopy indicates ree and y residence in monazite xenotime and allanite that form complex intergrowths with cobaltite suggesting coeval co and ree y mineralization during the mesoproterozoic occurrence of high ree and y concentrations in the blackbird ores together with previously documented saline rich fluid inclusions and cl rich biotite suggest that these are not volcanogenic massive sulfide or sedimentary exhalative deposits but instead are iron oxide copper gold iocg deposits other strata bound co deposits of proterozoic age in the north american cordillera and elsewhere in the world may have potential for ree and y resources iocg deposits with abundant light ree should also be evaluated for possible unrecognized heavy ree and y mineralization

late quaternary morphostratigraphy of lake st joseph southeastern canadian shield evolution from a semi enclosed glacimarine basin to a postglacial lake abstract this paper reports and describes multibeam echosounder subbottom profiler and sediment sampling data collected in lake st joseph southern quebec a formerly glacimarine sedimentary basin that has been glacio isostatically uplifted to form a small lake its study provides a unique opportunity for investigating changes in sedimentary environments from a glacial sea to a postglacial lake multibeam bathymetry allows the observation of two basins separated by a bathymetric ridge and of mass movement deposits in both basins high resolution seismic stratigraphy reveals the presence of seven seismic units these seven units relate to the advance and retreat of the laurentide ice sheet over the region following ice retreat transparent u3 and high amplitude reflection u4 units were deposited during the champlain sea invasion the transparent unit likely represents a rapidly retreating glacier which allowed the deposition of massive silt and clay whereas the high amplitude reflectors which are internally composed of transparent to chaotic lenses are interpreted as the result of a deceleration of ice retreat or a stabilization of the glacier and of glacio isostatic rebound overlying the champlain sea sediments a unit composed of smaller laminations u5 suggests that it was deposited during the marine to lacustrine transition in a paraglacial environment this is supported by its presence in the northern basin where the riviere aux pins mouth is located and its absence in the southern basin where no river is observed the bathymetric ridge between the two basins thus limited sediment transport following the complete retreat of the champlain sea organic rich sediments u7 were deposited in the lake in the northern basin the presence of the riviere aux pins allowed their deposition in the form of rhythmites whereas the absence of rivers in the southern basin resulted in the deposition of an acoustically transparent unit a mass movement u6 identified during the deposition of unit 7 occurred around 1250 ad and is interpreted as earthquake triggered

cementation hydrothermal alteration and zn pb mineralization of carbonate breccias in the irish midlands textural evidence from the cooleen zone near silvermines county tipperary a reply sir we are delighted to respond to the comments of reed and wallace on our paper on the origin of breccia hosted base metal mineralization in the irish ore field lee and wilkinson 2002 reed and wallace s thesis is that the mineralized breccias we have described within the mississippian waulsortian limestone formation at cooleen are not of sedimentary origin and therefore by extension that synsedimen tary breccias do not exist elsewhere in the ore field if correct one of a number of lines of evidence that have been used to infer a near sea floor origin for at least a component of sulfide mineralization in ireland that of reworked clasts of sulfide within sedimentary breccias would be invalidated contrary to the suggestion of reed and wallace the existence of sedimentary breccias spatially associated with mineralization in the waulsortian is universally accepted in the literature mine based investigations that include underground observations as well as drill core data and sedimentological studies have concluded that the stratiform wedge shaped breccia bodies commonly developed within the waulsortian limestone facies are sedimentary debris flows of courceyan age boyce et al 1983 taylor 1984 andrew 1986 clifford et al 1986 somerville et al 1992 submarine fault scarp sedimentary breccias are common in sediment hosted zn pb deposits e g goodfellow et al 1993 and display the same characteristics as the breccias at cooleen hitzman and beaty 1996 p 125 also recognized that synsedimentary breccias are present within the waulsortian at both silvermines and lisheen but went on to state that textural and field relationships clearly show that the principal episode of brecciation postdated regional burial dolomiti zation inferring a hydrothermal origin for the ore hosting breccias while we would not agree with this conclusion particularly in relation to the silvermines area we accept that the ore hosting breccias at lisheen galmoy and silvermines have been

seismic stratigraphy buried beach ridges and contourite drifts the late quaternary history of the closed lago cardiel basin argentina 49 s the results of a seismic stratigraphic analysis of a closed lake basin lago cardiel in southernmost south america are reported very few high resolution continental records spanning the late quaternary have been obtained from this region seismic sequence stratigraphic analysis allows a reconstruction of lake level variations two major hiatuses of unknown age occurred during the early evolution of the basin with the deposition of an alluvial fan in a restricted area in the intervening time period following the development of a relatively shallow lake during the late pleistocene and a short desiccation pulse around 11 220 14c yr bp a transgression of over 135 m occurred at the beginning of the holocene the transgression was associated with the formation of beach ridges preserved in the lake stratigraphy on the floor of the modern lago cardiel at four different elevations the preservation of largely unreworked beach ridges indicates a stepwise rise in the lake level there is no seismic evidence of a major lowering of the lake below modern level during the entire holocene deposition since the mid holocene is marked by strong lateral differences in sediment accumulation with a depocentre slightly to the north of the basin midpoint and a pronounced mounded distribution seismic reflection geometries as well as sedimentological characteristics indicate a lacustrine contourite drift covering an area of 80 100 km2 as lago cardiel is under the influence of westerly winds these most likely drove lake circulation the identification of drowned beach ridges and of contourite drifts illustrates that high resolution seismic stratigraphy is not only a powerful tool in reconstructing past lake level elevations for closed lake basins but it can also provide information about the rate of lake level changes and the presence and strength of lake currents

rare earth elements and hydrothermal ore formation processes abstract the geochemical behaviour of ree is influenced by nearly all important hydrothermal ore formation processes including fluid rock interactions fluid precipitations adsorption and scavenging onto particles and changes in fluid temperature pressure ph eh alkalinity and ligand concentration destabilization of ree complexes in response to these physicochemical changes and possible chemical crystallographic controls determine the concentration and distribution of ree within hydrothermal minerals mineraloids and amorphous phases alteration assemblages of intrusive related mineralisations may exhibit a wide range of ree distributions and ree fractionation trends the ree distribution within these hydrothermally altered lithologies will depend on the ree concentration in the rock and the fluid the partitioning behaviour of the ree between the rock phases and the fluid and the types of alteration reactions which take place reactive rocks such as carbonate rich lithologies of skarn deposits may gain or loose significant amounts of ree during fluid rock interactions ree geochemical investigations combined with fluid inclusion and stable isotope studies may point to the origin of alteration products and the source s of ore fluids ancient massive sulphide ores commonly exhibit anomalous eu concentrations similar to many recent submarine hydrothermal precipitates the recognition of hydrothermal fluid seawater sedimentary or volcanically derived ree distributions within ores chemical sediments and hydrothermally altered lithologies may help to constrain genetic modelling of massive sulphide deposits care should be taken with the interpretation of ree distributions from metamorphosed hydrothermal ore deposits becase metamorphic and diagenetic alteration reactions may change the ree distributions mobility of ree may occur during diagenesis of carbonate rich rocks and during the development of shear zones and migmatites in contrast very large fluid rock ratios are necessary to cause significant changes in ree patterns of silicate rich rocks during diagenesis and regional metamorphism

zinc isotopes in sphalerite from base metal deposits in the red dog district northern alaska analyses of sphalerite samples from shale hosted massive sulfide and stratigraphically underlying vein breccia deposits in the red dog district in northern alaska show a range of 66zn values from zero to 0 60 per mil the lowest values are observed in the vein breccia deposits and the stratigraphically overlying but structurally displaced shale hosted massive sulfide deposits show a systematic trend of increasing 66zn values from south to north main aqqaluk paalaaq anarraaq the 66zn values are inversely correlated with sphalerite fe mn ratio and also tend to be higher in low cu sphalerite consistent with precipitation of lower 66zn sphalerite closer to the principal hydrothermal fluid conduits the most likely control on isotopic variation is rayleigh fractionation during sulfide precipitation with lighter zinc isotopes preferentially incorporated in the earliest sphalerite to precipitate from ore fluids at deeper levels vein breccias and close to the principal fluid conduits in the orebodies followed by precipitation of sulfides with higher 66zn values in shallower and or more distal parts of the flow path there is no systematic variation among the paragenetic stages of sphalerite from a single deposit suggesting an isotopically homogeneous zinc source and consistent transport deposition conditions and or dissolution reprecipitation of earlier sphalerite without significant fractionation decoupled zn and s isotope compositions are best explained by mixing of separate metal and sulfur bearing fluids at the depositional site the results confirm that zn isotopes may be a useful tracer for distinguishing between the central and distal parts of large hydrothermal systems as previously suggested and could therefore be of use in exploration

pattern and rates of faulting in the central nevada seismic belt and paleoseismic evidence for prior beltlike behavior the central nevada seismic belt cnsb is a concentration of historical 1915 1932 1954 surface faulting in the western basin and range province forming a linear nearly continuous 300 km long rupture zone previous results are integrated in this study with new paleoseismic and exploratory trenching data from the historical zones to look for evidence of older similar beltlike patterns or elevated slip rates that could indicate whether the cnsb is a zone of focused long term crustal strain the data show that the continuous rupture belt produced by the seven earthquakes occurring between 1915 and 1954 is unique in the available paleoseismic record at the 1954 fairview peak fault the lack of prehistorical faulting in deposits containing the wilson creek bed 19 tephra eliminates the possibility of an identical seismic belt in the past 35 4 ka our studies also show that the faults have net slip rates ranging from a low of 0 09 mm yr on the fairview peak fault to a high of 0 7 mm yr on the 1932 cedar mountain fault these are considered moderate to low rates that are similar to most late quaternary faults in the western basin and range province a space time comparison shows that the paleoseismic histories for these multiple rupture zones are diverse and the number and timing of events in each of the zones indicate that there is little evidence for older contemporaneous ruptures of these same faults based on these results we reach several conclusions regarding the longer term holocene behavior of the cnsb although paleoseismic data preclude an older identical rupture belt among the historical zones consideration of associated holocene faults within the greater cnsb region indicates that several similar but not identical beltlike rupture patterns are plausible during the past 13 ka although each requires seismic gaps in the along strike pattern although long term strain represented by density of young faults does appear to increase from east to west into the cnsb the slip rate data demonstrate that the cnsb is not a belt of concentrated or elevated crustal strain compared with areas that extend west to the sierra nevada the increase in the distribution of holocene fault activity from east to west into the cnsb is consistent with a marked increase in the 1992 2002 gps velocity field at the latitude of the 1954 rupture sequence however a comparison of the geologic rates across the belt at this same latitude indicates that the extension rates 0 59 1 37 mm yr are systematically lower than both the campaign and continuous gps rates 2 20 3 13 mm yr by factors of 2 5 these discrepancies may be due to postseismic strain or to some form of off fault deformation we conclude that the results of our study of fault behavior in the cnsb best support the belt migration model proposed by wallace 1987 for the western basin and range province in which temporal tectonic pulses are believed to migrate regionally activating different beltlike combinations of late quaternary faults in an as yet unknown pattern of migration

abyssal current influence on the southwest bermuda rise and surrounding region abstract echograms 3 5 khz and bottom photographs reveal that the northward flowing antarctic bottom water aabw has strongly influenced the modern depositional regime on the southwest bermuda rise the spatial distribution of echo character types the orientation and nature of current controlled structures and limited current meter data show that aabw flows with varying intensities along three primary pathways around and over the southwest bermuda rise the main core of aabw flows clockwise around the eastern and western flanks of the southern bermuda rise roughly parallel to the 5400 m isobath this current bifurcates at 28 30 n 69 w where a portion flows northeast over the southwest bermuda rise and the remainder continues north along the physiographic boundary between the southwest bermuda rise and the hatteras abyssal plain secondary ribbons of aabw branch off the main core of aabw during its southerly journey along the southeastern bermuda rise and flow west through fracture zones finally a diffuse northward flowing aabw sweeps the entire southwest bermuda rise a progression of current controlled bedforms occurs beneath the main path of the aabw reflecting the spatially varying current velocities and sediment supply the main core of aabw flows west through the narrow vema gap creating erosional furrows along the border between the southwest bermuda rise and the vema gap current velocities greater than 20 cm s 1 are inferred from the bedforms in this region farther north along the southwestern edge of the bermuda rise sediment waves become more prevalent this transition from erosional to more depositional bedforms results from diminished current velocities 5 15 cm s 1 and increased sediment supply although some of these bedforms on the southwest bermuda rise appear to be relict their orientation is consistent with current meter data and abyssal current direction inferred from bottom photographs

crustal deformation across the sierra nevada northern walker lane basin and range transition western united states measured with gps 2000 2004 1 global positioning system gps data collected in campaigns in 2000 and 2004 were processed and interpreted with other gps data in the western basin and range province to provide new constraints on the rate style and pattern of deformation of the central and northern walker lane wl which lies near the western boundary of the basin and range across the central wl near 38n latitude the velocities with respect to north america increase westward by 10 mm yr inducing dextral shear farther north between 40 and 41n latitude a western zone of 7 mm yr relative motion undergoes dextral shear and an eastern zone of 3 mm yr relative motion undergoes extension and shear these data show that the northern wl is essentially a dextral shear zone experiencing minor net dilatation ed 2 6 0 8 nstrain yr near most holocene normal faults dilatation inferred from the velocity field is not greater than the uncertainties however near the central nevada seismic belt we detect significant dilatation expressed as extension in a direction approximately normal to the range fronts ed 23 0 3 9 nstrain yr some of which is attributable to transient postseismic deformation following large historic earthquakes a block model constrained by velocities corrected for transient effects shows that the sum of dextral slip rates across the honey lake warm springs east pyramid fault system and mohawk valley faults is 7 mm yr the wl is a zone whose width and dilatation rate increase northwestward consistent with counterclockwise rotation of the sierra nevada microplate and transfer of deformation into the pacific northwest

reactive surface area control of the dissolution kinetics of biogenic silica in deep sea sediments abstract flow through dissolution experiments demonstrate that the specific reactive surface area of biogenic silica decreases significantly with depth in surficial sediments of the southern ocean specific surface areas obtained from nitrogen gas bet adsorption isotherms however do not exhibit the systematic changes of the specific reactive surface area inferred from the kinetic experiments furthermore the decrease in surface reactivity of the siliceous skeleton fragments continues at depths in the sediments where there is no longer a net release of silicic acid to the pore waters thus the specific reactive surface changes most likely reflect a progressive reduction of the surface density of reactive sites aging during burial rather than the preferential dissolution of a more reactive fraction of siliceous debris deposited from the water column the observed aging of the silica surfaces has important consequences for the benthic regeneration of nutrient silicic acid from deep sea sediments

continuous lake sediment records of glaciation in the sierra nevada between 52 600 and 12 50014c yr b p the chemistry of the carbonate free clay size fraction of owens lake sediments supports the use of total organic carbon and magnetic susceptibility as indicators of stadial interstadial oscillations owens lake records of total organic carbon magnetic susceptibility and chemical composition of the carbonate free clay size fraction indicate that tioga glaciation began 24 500 and ended by 13 60014c yr b p many of the components of glacial rock flour e g tio2 mno bao found in owens lake sediments achieved maximum values during the tioga glaciation when valley glaciers reached their greatest extent total organic carbon and sio2 amorphous concentrations reached minimum values during tioga glaciation resulting from decreases in productivity that accompanied the introduction of rock flour into the surface waters of owens lake at least 20 stadial interstadial oscillations occurred in the sierra nevada between 52 600 and 14 00014c yr b p total organic carbon data from a pyramid lake sediment core also indicate oscillations in glacier activity between 39 500 and 13 60014c yr b p alpine glacier oscillations occurred on a frequency of 1900 yr in both basins suggesting that millennial scale oscillations occurred in california and nevada during most of the past 52 600 yr

multistage hydrothermal silicification and fe tl as sb ge ree enrichment in the red dog zn pb ag district northern alaska geochemistry origin and exploration applications geochemical analyses of major trace and rare earth elements ree in more than 200 samples of variably silicified and altered wall rocks massive and banded sulfide silica rock and sulfide rich and unmineralized barite were obtained from the main aqqaluk and anarraaq deposits in the red dog zn pb ag district of northern alaska detailed lithogeochemical profiles for two drill cores at aqqaluk display an antithetic relationship between sio2 al2o3 and tio2 zr which together with textural information suggest preferential silicification of carbonate bearing sediments data for both drill cores also show generally high tl sb as and ge and uniformly positive eu anomalies eu eu 1 0 similar high tl sb as ge and eu eu values are present in the footwall and shallow hanging wall of zn pb ag sulfide intervals at anarraaq but are not as widely dispersed net chemical changes for altered wall rocks in the district on the basis of average al normalized data relative to unaltered black shales of the host kuna formation include large enrichments 50 of fe ba eu v s co zn pb tl as sb and ge at both red dog and anarraaq si at red dog and sr u and se at anarraaq large depletions 50 are evident for ca at both red dog and anarraaq for mg p and y at red dog and for na at anarraaq at both red dog and anarraaq wall rock alteration removed calcite and minor dolomite during hydrothermal decarbonation reactions and introduced si eu and ge during silicification sulfidation reactions deposited fe s co zn pb tl as and sb barite mineralization introduced ba s and sr light ree and u were mobilized locally this alteration and mineralization occurred during mississippian hydrothermal events that predated the middle jurassic cretaceous brookian orogeny early hydrothermal silicification at red dog took place prior to or during massive sulfide mineralization on the basis of the dominantly planar nature of zn pb veins which suggests filling of fractures that developed in previously lithified rock uniformly low ca and mg and uniformly negative ce anomalies in highly siliceous red dog wall rocks reflect hydrothermal decarbonation reactions and pervasive silicification owing to conductive cooling of oxidized metalliferous fluids similar ca and mg depletions are evident at anarraaq but generally lack associated silicification possibly because temperatures of the hydrothermal fluids were too low 180 c or because the thermal contrast between the fluids and wall rocks was smaller owing to the greater depth of alteration and mineralization there compared with red dog chalcophile element anomalies fe zn pb tl as sb in wall rocks at both red dog and anarraq are attributed to sulfidation reactions coeval with subsurface zn pb ag mineralization during the mixing of oxidized metalliferous fluids with h2s rich fluids derived locally within the kuna formation sedimentary wall rocks in the red dog district are characterized by a distinctive suite of geochemical anomalies especially for zn pb tl as sb ge and eu eu at the aqqaluk deposit wall rocks without visible sphalerite or galena 300 ppm zn pb have anomalous eu eu tl sb and as for up to 100 m stratigraphically below zn rich silica rock at anarraaq the tl anomaly is most extensively developed and enrichment relative to unaltered black shale of the kuna formation is present up to 62 m above the highest zn pb sulfide zones the magnitude of the enrichment and systematic behavior of tl in the district make tl a promising geochemical exploration guide for red dog type zn pb ag deposits elsewhere

silica and germanium in pacific ocean hydrothermal vents and plumes dissolved silica si and inorganic germanium ge concentrations were measured in hydrothermal fluids from black smoker vents on the east pacific rise 21 n epr and the southern juan de fuca ridge 45 n sjdfr north and south cleft sites axial volcano these typically display end member concentrations ranging from 16 to 23 mm si and 150 to 280 nm ge and end member ge si ratios clustering between 8 and 14 10 6 more than 10 fold greater than the ratio entering the ocean via rivers 0 54 10 6 and being recycled in seawater 0 7 10 6 excess concentrations of dissolved si and ge above oceanic background are observed in mid water hydrothermal plumes over mid ocean ridge mor spreading centers on the southern epr sepr 10 20 s and the sjdfr the largest si and ge concentration anomalies occur over the north cleft segment of the sjdfr these are a factor of three greater than anomalies over the sepr 10 20 s excess ge correlates with excess3he in plumes at a ge 3he molar ratio of about 1 104 approximately the same ratio as in black smokers these observations combined with low abundances of ge in femn rich metalliferous sediments suggest that ge and si behave conservatively in mid ocean ridge hydrothermal plumes a simple ocean si and ge balance constrained by the global river silica flux and ge si ratios in hydrothermal vents rivers and biogenic silica suggests that the global hydrothermal silica flux is about 1 4 1011 mole yr 1 much lower than that estimated from3he either 1 70 80 of the ge flux to the ocean is removed in as yet undiscovered sinks not opal or 2 only 10 of the mantle to ocean3he and heat fluxes is associated with mor hydrothermal convection through the 350 c isotherm 90 is off ridge or 3 the oceanic ge si 3he and87sr86sr balances today are far from steady state

concealed quaternary strike slip fault resolved with airborne lidar and seismic reflection the grizzly valley fault system northern walker lane california 1 the grizzly valley fault system gvfs strikes northwestward across sierra valley a low relief basin situated within a network of active dextral slip faults in the northern walker lane california quaternary motion along the grizzly valley fault system has not been previously documented we used high resolution 0 25 m airborne lidar data in combination with high resolution p wave seismic reflection imaging to evaluate quaternary deformation associated with the gvfs we identified suspected tectonic lineaments using the lidar data and collected seismic reflection data along six profiles across the lineaments the seismic reflection images reveal a deformed basal marker that we interpret to be the top of tertiary volcanic rocks overlain by a 120 450 m thick suite of subhorizontal reflectors that we interpret to be plio pleistocene lacustrine deposits three profiles image features that we interpret to be the principal active trace of the gvfs which is a steeply dipping fault zone that vertically offsets the volcanic rocks and the lacustrine basin fill these data suggest that the gvfs may have been active in latest quaternary time because 1 the lidar data show subtle surficial geomorphic features that are typical of youthful faulting including a topographic lineament marked by an 1 m high ridge composed of discontinuous left stepping lobes and 2 the seismic profiles demonstrate shallow faulting of the lacustrine strata that coincides with the left stepping ridge this investigation illustrates the potential for unidentified low rate strike slip faults in basins and emphasizes the value of high resolution topographic data and subsurface imaging as a means of identifying these structures

strain accumulation and rotation in western nevada 1993 2000 1 the positions of 44 gps monuments in an array extending from the sierra nevada at the latitude of reno to near austin nevada have been measured several times in the 1993 2000 interval the western half of the array spans the walker lane belt whereas the eastern half spans the central nevada seismic zone cnsz the principal strain rates in the walker lane belt are 29 6 5 3 nstrain yr 1 n88 4 e 5 4 and 12 8 6 0 nanostrain yr 1 n01 6 w 5 4 extension reckoned positive and the clockwise as seen from above the earth rotation rate about a vertical axis is 13 6 4 0 nrad yr 1 the quoted uncertainties are standard deviations the motion in the walker lane belt can then be represented by a zone striking n35 w subject to 16 8 4 9 nstrain yr 1 extension perpendicular to it and 19 5 4 0 nstrain yr 1 right lateral simple shear across it the n35 w strike of the zone is the same as the direction of the local tangent to the small circle drawn about the pacific north america pole of rotation the principal strain rates for the cnsz are 46 2 11 0 nstrain yr 1 n49 9 w 6 0 and 13 6 6 1 nstrain yr 1 n40 1 e 6 0 and the clockwise rotation rate about a vertical axis is 20 3 6 3 nrad yr 1 the motion across the cnsz can then be represented by a zone striking n12 e subject to 32 6 11 0 nstrain yr 1 extension perpendicular to it and 25 1 6 3 nstrain yr 1 right lateral simple shear across it the n12 e strike of the zone is similar to the strikes of the faults rainbow mountain fairview peak and dixie valley within it

petrographic geochemical and fluid inclusion evidence for the origin of siliceous cap rocks above volcanic hosted massive sulfide deposits at myra falls vancouver island british columbia canada massive sulfides at the myra falls volcanic hosted massive sulfide vhms camp vancouver island british columbia canada are overlain by white chert black chert argillite and siltstone white chert is best developed above the battle orebody where it forms a siliceous caprock 3 5 m thick above the massive sulfides there is a gradational lateral change from white chert above massive sulfides to black chert and unaltered argillite 100 to 150 m south of the battle orebody chert horizons are also located above the ridge and extension ore zones but only minor chert lies above the hw orebody which is instead overlain by a thick argillite sequence the chert and argillite share similar sedimentologic and petrologic features including abundant parallel laminations interbedded turbidites radiolarian rich layers soft sediment deformation scours flame structures and small phosphatic concretions these features indicate that white and black chert formed as a replacement of mudstone rather than as exhalative or biogenic deposits silicification occurred early in the depositional history of the fine grained sediments and was contemporaneous with some ore formation early syndepositional features are still visible in the chert with primary pore spaces such as radiolarian tests filled by silica rutile apatite and minor sulfides displaying open space crystal growth the presence of minor ore clast breccias above the orebody indicates that at least parts of the battle orebody were exposed on the sea floor metal zoning is observed in the cap rock horizon above the battle orebody with higher cu zn and cd contentrations in chert directly above massive sulfides higher pb sb and ag contentrations in black chert at the edge of the siliceous cap rocks and lower metal concentrations in the distal argillite primary fluid inclusions in spherical quartz patches in chert above the battle orebody indicate that hydrothermal fluids passing through sediment were between 135 to 250c and had salinities ranging from 3 0 to 12 1 wt percent nacl equiv these data are similar to those for fluid inclusions measured in quartz interstitial to sulfides in the underlying battle orebody which have temperatures of homogenization ranging from 140 to 250c and salinities from 3 0 to 12 4 wt percent nacl equiv fluid inclusions in the battle orebody display a slight increase in salinity and homogenization temperature with depth which may reflect the overprinting of earlier high temperature stages by cooler fluids as the hydrothermal system waned or varying degrees of mixing between hydrothermal fluids and seawater a minimum depth for deposition of the cap rocks 200 m is estimated based on sedimentologic features such as fine parallel laminations and interbedded sandstone turbidites which indicate deposition below storm wave base greater water depths 1 000 1 500 m are suggested by the lack of evidence of boiling in fluid inclusions low o2 concentrations in the bottom water of the battle basin are suggested by the absence of bioturbation lack of fossils of benthic fauna degree of pyritization values 0 90 elevated zn pb cu cd as sb ag ba and v low fe and mn and v v ni 0 8 in the unaltered argillite paleosea floor reconstructions indicate that the battle and hw orebodies formed in small basins along a northwest trending ridge the finegrained sediments were deposited in depocenters within paleotopographic lows hydrothermal fluid densities estimated from fluid inclusions at myra falls range from 0 88 to 1 05 g cm3 and are higher than for many other vhms deposits however they are close to the density of seawater at 2c and a 2 000 m depth 1 028 g cm3 replacement textures in the siliceous cap rocks above the battle deposit the sheetlike morphology of the siliceous cap rocks and lateral metal zonation indicates that diffuse lateral flow of hydrothermal fluids through the porous sea floor sediments was more important than the buoyant rise of hydrothermal fluids into the water column however buoyant venting during formation of the battle deposit is indicated by positive eu anomalies and elevated metal values in argillite of the battle basin reflecting the wide dispersal of plume particulates the range of fluid densities indicate that the hydrothermal fluids emerging onto the sea floor and flowing laterally through porous sea floor sediments would have varied from buoyant to neutrally buoyant to negatively buoyant

intense silicification of footwall sedimentary rocks in the stockwork alteration zone beneath the brunswick no 12 massive sulphide deposit bathurst new brunswick intensely silicified volcaniclastic mudstones that underlie the brunswick no 12 massive sulphide deposit in northern new brunswick resemble silicified rocks described in the immediate footwall of many ancient and modern massive sulphide deposits the white to grey cryptocrystalline silica in the silicified rocks becomes more common with proximity to the vent and is most abundant immediately below the massive sulphide zone mass balance analysis of altered footwall sedimentary rocks on the 850 m level of the mine shows that sio2 increases up to 300 the high silica enrichment in the feeder zone is consistent with the presence of cherty silica in the massive sulphides and in associated exhalative iron formation coincident with silicification are enrichments in s feot mgo mno cao p2o5 f cl y cu co cr and ni as well as light rare earth elements and eu oxygen isotope analyses of chloritized and silicified footwall sedimentary rocks suggest that the hydrothermal fluid had a 18o composition o

reactive flow models of the anarraaq zn pb ag deposit red dog district alaska the red dog ore deposit district in the brooks range of northern alaska is host to several high grade shale hosted zn pb deposits due to the complex history and deformation of these ore deposits the geological and hydrological conditions at the time of formation are poorly understood using geological observations and fluid inclusion data as constraints numerical heat and fluid flow simulations of the anarraaq ore deposit environment and coupled reactive flow simulations of a section of the ore body were conducted to gain more insight into the conditions of ore body formation results suggest that the ore body and associated base metal zonation may have formed by the mixing of oxidized saline metal bearing hydrothermal fluids 200 c with reducing hs rich pore fluids within radiolarite rich host rocks sphalerite and galena concentrations and base metal sulfide distribution are primarily controlled by the nature of the pore fluids i e the extent and duration of the hs source forward modeling results also predict the distribution of pyrite and quartz in agreement with field observations and indicate a reaction front moving from the initial mixing interface into the radiolarite rocks heuristic mass calculations suggest that ore grades and base metal accumulation comparable to those found in the field 18 zn 5 pb are predicted to be reached after about 0 3 my for initial conditions 30 ppm zn 3 ppm pb 20 deposition efficiency

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

geologic setting petrology and geochemistry of stratiform sphalerite galena barite deposits red dog creek and drenchwater creek areas northwestern brooks range alaska similar stratiform sphalerite galena barite deposits occur in the red dog creek area de long mountains quadrangle and in the drenchwater creek area howard pass quadrangle northwestern brooks range alaska the deposits located approximately 180 km apart are hosted by mississippian and pennsylvanian strata of the kagvik structural sequence of late paleozoic and early mesozoic age this sequence is situated in the lowermost structural plate of a series of predominantly east striking shallow dipping thrust plates that characterize the regional structure the deposits occur in shale tuff tuffaceous sandstone altered chert and quartz exhalite these units are in places interlayered with or adjacent to bedded or nodular barite or submarine keratophyre flows chert and shale commonly contain abundant highly altered fine grained feldspar pumice lapilli and mafic volcanic rock fragments the main types of occurrences at red dog creek are 1 disseminated and stratiform sulfides thinly bedded in organic rich mississippian and pennsylvanian shale and chert 2 massive sulfide veins and breccia fillings in silicified mississippian and pennsylvanian shale and 3 stratiform sulfide bearing lenses subdivided into 3a quartz exhalite with up to several percent sulfides and barite 3b massive sulfide quartz lenses with up to several percent barite and 3c barite quartz lenses with up to several percent sulfides at drenchwater creek sulfides and barite occur as 1 disseminations in shale chert tuff and tuffaceous sandstone 2 disseminations to aggregates in quartz exhalite and 3 occurrences in veins crosscutting cleavages in brecciated chert and shale the stratiform sulfides occur in zones up to several thousand meters long and several tens of meters thick preliminary grades at red dog creek are 17 1 percent zinc 5 0 percent lead and 2 4 oz silver per ton contained in at least 85 million tons the range of sulfide sulfur isotope values at red dog creek is 16 6 per mil to 3 6 per mil sphalerite averages 0 8 per mil pyrite is isotopically lighter than coexisting sphalerite in quartz exhalite and massive sulfide lenses this isotopic relationship is compatible with paragenetic relationships which show pyrite crystallized both earlier and later than other sulfides galena is isotopically lighter than coexisting sphalerite three groups of geologically and isotopically distinct barites exist including isotopic values appropriate for derivation from late paleozoic seawater sulfate early in the depositional sequence isotopically light pyrite formed from organically reduced seawater sulfate sphalerite galena late pyrite and some barite precipitated from two sulfur bearing solutions that mixed at the mineralization site isotopically light barite associated with sulfides precipitated from oxidized h 2 s without seawater sulfate contribution lead isotope data from red dog and drenchwater creeks are compatible with generation of lead in a phanerozoic mature island arc setting a typical orogene or possibly a back arc type intracratonic basin the stratiform sphalerite galena barite deposits probably formed in an incipient island arc environment near a continental margin containing magmas of keratophyric and andesitic composition where metal laden hydrothermal fluids discharged into a deep water low energy environment later intense deformation associated with plate docking and thrusting disrupted and partly remobilized and stratiform deposits

spatiotemporal patterns of fault slip rates across the central sierra nevada frontal fault zone abstract patterns in fault slip rates through time and space are examined across the transition from the sierra nevada to the eastern california shear zone walker lane belt at each of four sites along the eastern sierra nevada frontal fault zone between 38 and 39 n latitude geomorphic markers such as glacial moraines and outwash terraces are displaced by a suite of range front normal faults using geomorphic mapping surveying and 10 be surface exposure dating mean fault slip rates are defined and by utilizing markers of different ages generally 20 ka and 150 ka rates through time and interactions among multiple faults are examined over 10 4 10 5 year timescales at each site for which data are available for the last 150 ky mean slip rates across the sierra nevada frontal fault zone have probably not varied by more than a factor of two over time spans equal to half of the total time interval 20 ky and 150 ky timescales 0 3 0 1 mm year 1 mode and 95 ci at both buckeye creek in the bridgeport basin and sonora junction and 0 4 0 3 0 1 mm year 1 along the west fork of the carson river at woodfords data permit rates that are relatively constant over the time scales examined in contrast slip rates are highly variable in space over the last 20 ky slip rates decrease by a factor of 3 5 northward over a distance of 20 km between the northern mono basin 1 3 0 6 0 3 mm year 1 at lundy canyon site to the bridgeport basin 0 3 0 1 mm year 1 the 3 fold decrease in the slip rate on the sierra nevada frontal fault zone northward from mono basin is indicative of a change in the character of faulting north of the mina deflection as extension is transferred eastward onto normal faults between the sierra nevada and walker lane belt a compilation of regional deformation rates reveals that the spatial pattern of extension rates changes along strike of the eastern california shear zone walker lane belt south of the mina deflection extension is accommodated within a diffuse zone of normal and oblique faults with extension rates increasing northward on the fish lake valley fault where faults of the eastern california shear zone terminate northward into the mina deflection extension rates increase northward along the sierra nevada frontal fault zone to 0 7 mm year 1 in northern mono basin this spatial pattern suggests that extension is transferred from more easterly fault systems e g fish lake valley fault and localized on the sierra nevada frontal fault zone as the eastern california shear zone walker lane belt faulting is transferred through the mina deflection

two phase westward encroachment of basin and range extension into the northern sierra nevada 1 structural geophysical and thermochronological data from the transition zone between the sierra nevada and the basin and range province at latitude 39 n suggest 100 km westward encroachment of basin and range extensional deformation since the middle miocene extension accommodated primarily by east dipping normal faults that bound west tilted range forming fault blocks varies in magnitude from 150 in the wassuk and singatse ranges to the east geological and apatite fission track data from exhumed upper crustal sections in the wassuk and singatse ranges point to rapid footwall cooling related to large magnitude extension starting at 14 15 ma farther to the west geological and thermochronological data indicate a younger period of extension in the previously unextended pine nut mountains the carson range and the tahoe truckee depression initiated between 10 ma and 3 ma and incipient post 0 5 ma faulting to the west of the tahoe truckee area these data imply the presence of an extensional breakaway zone between the singatse range and the pine nut mountains at 14 15 ma forming the boundary between the sierra nevada and basin and range at that time in addition fission track data imply a miocene preextensional geothermal gradient of 27 5 c km 1 in the central wassuk range and 20 5 c km 1 in the singatse range much higher than the estimated early tertiary gradient of 10 5 c km 1 for the sierra nevada batholith this might point to a significant increase in geothermal gradients coupled with a likely decrease in crustal strength enabling the initiation of extensional faulting apatite fission track geophysical and geological constraints across the sierra nevada basin and range transition zone indicate a two stage coupled structural and thermal westward encroachment of the basin and range province into the sierra nevada since the middle miocene

comparative elemental and oxygen isotope geochemistry of jasperoid in the northern great basin evidence for distinctive fluid evolution in gold producing hydrothermal systems this comparative geochemical study of jasperoid in the northern great basin is based on 65 samples from 10 carlin type gold deposits and 22 similar but apparently barren hydrothermal systems multielement geochemistry coupled with oxygen isotope data indicate that hydrothermal fluids in barren and mineralized systems evolved in different ways and that there are fundamental geochemical differences among the various gold producing deposits of the area much of the variation in the jasperoid geochemical data can be explained in terms of seven abstract end member components obtained through factor analysis three of these components factors dominate the results and are related to common products of alteration and mineralization in epithermal systems of the northern great basin element associations for these factors are factor 1 tio 2 al 2 o 3 la k 2 o sr fe 2 o 3 th factor 2 au ag sb sio 2 as pb and factor 3 w b v zn co au cao ni mn cu samples from barren systems are predominantly associated with high factor 1 loadings whereas samples from mineralized systems are generally characterized by high loadings of factor 2 and or factor 3 factor 1 is related to residual argillically altered noncarbonate constituents in original host rocks factor 2 is related to hydrothermal silica jasperoid and is characterized by many of the so called pathfinder elements used in great basin exploration factor 3 although characterized by a transition metal assemblage is related to syngenetic inclusions of hydrothermal calcite within jasperoidal silica high factor 2 loadings are associated with samples from the windfall and northumberland deposits but not with samples from other gold producing systems in the study factor 3 on the other hand is the dominant component in most samples from the carlin gold quarry maggie creek pinson and preble deposits it therefore appears that there are at least two geochemically discernible types of gold deposits in the northern great basin these types are represented in this study by the windfall deposit factor 2 at one extreme and by the gold quarry deposit factor 3 at the other other deposits including alligator ridge and tonkin springs are intermediate between these extremes in this study the hydrothermal geochemistry of the jerritt canyon samples is obscured by a chert related compositional factor jasperoid samples from gold producing ore deposits have delta 18 o values ranging from 3 to 20 per mil whereas jasperoid samples from analogous barren systems have delta 18 o values ranging from 3 to 11 per mil this indicates that at least some fluids in ore related hydrothermal systems were relatively 18 o rich compared to those in barren systems jasperoid samples having high delta 18 o values invariably have high factor 3 loadings the elemental and isotopic geochemistry of jasperoid samples indicates that hydrothermal fluids in individual gold producing systems of the northern great basin evolved in different ways it appears that high co 2 contents were a critical distinguishing feature of deeply circulating fluids in the hydrothermal systems associated with high factor 3 loadings within the scope of this study it therefore appears that the systems located on the carlin and getchell trends mineral belts must have been relatively co 2 rich fluids in these systems would have been relatively reactive and perhaps more efficient at extracting gold and other metals from rocks in fluid exchange reservoirs moreover the generally high 18 o character of ore stage fluids in these systems as inferred from jasperoid compositions is indicative of extensive water rock exchange the largest gold deposits in the jasperoid study area appear to have been high co 2 high 18 o systems the primary source of co 2 in these systems is uncertain it does appear however that deep crustal structure rather than the lithologic character of fluid exchange reservoirs was probably a dominant factor governing the distribution of high co 2 systems in the northern great basin

ordovician aleman ribbon cherts an example of silicification prior to carbonate lithification abstract the ordovician aleman formation southwestern new mexico is primarily composed of dolomite with ribbons of chert the presence of stromatolites relict evaporite nodules and other features indicates an intertidal to shallow subtidal depositional environment the stromatolitic layers are preferentially silicified with dissolution of opaline sponge spicules providing the main if not sole source of silica silicification occurred in both the vadose and phreatic realms essentially penecontemporaneous with accumulation of the sediment and concomitant with dolomitization this is indicated by the preservation in silicified form of original anhydrite lath morphology central cavities in chert nodules partially filled with geopetal matrix dolomite and matrix dolomite immediately adjacent to conchoidal fractures of silicified carbonate grainstones the latter relationship indicates that the chert was rigid and fractured before the carbonate host sediments were lithified

hydrothermal biogenic and seawater components in metalliferous black shales of the brooks range alaska synsedimentary metal enrichment in a carbonate ramp setting trace element and os isotope data for lisburne group metalliferous black shales of middle mississippian early chesterian age in the brooks range of northern alaska suggest that metals were sourced chiefly from local seawater including biogenic detritus but also from externally derived hydrothermal fluids these black shales are interbedded with phosphorites and limestones in sequences 3 to 35 m thick deposition occurred mainly on a carbonate ramp during intermittent upwelling under varying redox conditions from suboxic to anoxic to sulfidic deposition of the black shales at 335 ma was broadly contemporaneous with sulfide mineralization in the red dog and drenchwater zn pb ag deposits which formed in a distal marginal basin relative to the composition of average black shale the metalliferous black shales n 29 display large average enrichment factors 10 for zn 10 1 cd 11 0 and ag 20 1 small enrichments 2 10 are shown by v cr ni cu mo pd pt u se y and all rare earth elements except ce nd and sm a detailed stratigraphic profile over 23 m in the skimo creek area central brooks range indicates that samples from at and near the top of the section which accumulated during a period of major upwelling and is broadly correlative with the stratigraphic levels of the red dog and drenchwater zn pb ag deposits have the highest zn toc total organic carbon cu toc and tl toc ratios for calculated marine fractions no detrital component of these three metals average authigenic detrital free contents of mo v u ni cu cd pb ge re se as sb tl pd and au show enrichment factors of 4 3 103 to 1 2 106 relative to modern seawater such moderate enrichments which are common in other metalliferous black shales suggest wholly marine sources seawater and biogenic material for these metals given similar trends for enrichment factors in organic rich sediments of modern upwelling zones on the namibian peruvian and chilean shelves the largest enrichment factors for zn and ag are much higher 1 4 107 and 2 9 107 respectively consistent with an appreciable hydrothermal component other metals such as cu pb and tl that are concentrated in several black shale samples and are locally abundant in the red dog and drenchwater zn pb ag deposits may have a partly hydrothermal origin but this cannot be fully established with the available data enrichments in cr up to 7 8 106 are attributed to marine and not hydrothermal processes the presence in some samples of large enrichments in eu up to 6 1 107 relative to modern seawater and of small positive eu anomalies eu eu up to 1 12 are considered unrelated to hydrothermal activity instead being linked to early diagenetic processes within sulfidic pore fluids initial os isotope ratios 187os 188os calculated for a paleontologically based depositional age of 335 ma reveal moderately unradiogenic values of 0 24 to 0 88 for four samples of metalliferous black shale a proxy for the ratio of coeval early chesterian seawater is provided by initial 187os 188os 335 ma ratios of four unaltered black shales of the coeval kuna formation that average 1 08 nearly identical to the initial ratio of 1 06 for modern seawater evaluation of possible sources of unradiogenic os in the metalliferous black shales suggests that the most likely source was mafic igneous rocks that were leached by externally derived hydrothermal fluids this unradiogenic os is interpreted to have been leached by deeply circulating hydrothermal fluids in the kuna basin followed by venting of the fluids into overlying seawater we propose that metal bearing hydrothermal fluids that formed zn pb ag deposits such as red dog or drenchwater vented into seawater in a marginal basin were carried by upwelling currents onto the margins of a shallow water carbonate platform and were then deposited in organic rich muds together with seawater and biogenically derived components by syngenetic sedimentary processes metal concentration in the black shales was promoted by high biologic productivity sorption onto organic matter diffusion across redox boundaries a low sedimentation rate and availability of h2s in bottom waters and pore fluids

geochronology of the western and central brooks range alaska implications for the geologic evolution of the anarraaq and red dog zn pb ag deposits a compilation of published geochronology of rocks and minerals from the western and central brooks range provides a framework for understanding the complex history of the brooks range and northern alaska a simplified timeline of events comprises 1 devonian extension 2 mississippian extension and zn pb ag mineralization 3 a passive interval 4 pre brooks range orogeny rock formation and thermal event 5 inception of brooks range orogeny 6 exhumation and the end of main stage deformation and 7 subsequent episodic deformation this compilation is supplemented by new 40ar 39ar dates of white mica from the anarraaq and red dog zn pb ag barite deposits from the western brooks range the deposits are hosted in black shale and carbonate rocks of the late mississippian early pennsylvanian kuna formation quartz pyrite white mica grains in sedimentary rocks above the anarraaq deposit yield an age of 195 0 2 0 ma and paragenetically late quartz pyrite white mica from the main orebody at the red dog deposit has an age of 126 1 0 7 ma these white micas are much younger than the age of zn pb ag mineralization at red dog 338 5 8 ma re os age of pyrite the date for white mica from anarraaq 195 ma appears to be related to a large scale thermal event in the region immediately before the inception of the brooks range orogeny the white mica from the red dog deposit 126 ma correlates with the later stages of the orogeny a period of blueschist metamorphism extension and rapid exhumation which varied with geographic location these dates suggest that the red dog deposits underwent significant hydrothermal overprinting during multiple episodes of the brooks range orogeny

synlithification deformation processes of the cretaceous sediments of the ivory coast ghana transform margin a way to detail the margin history the ivory coast ghana margin is a typical transform margin along which large scale tectonism has been well documented the cretaceous sediments of the ivory coast ghana transform margin were subjected to numerous tectonic gravitational and hydrothermal forces during lithification in this paper we infer the order of occurrence of deformation regimes from characteristic deformations observed in samples of ocean drilling program odp leg 159 three main types of minor scale deformation are identified and characterized in terms of geometry rheology and kinematics 1 extensional structures such as normal faults and irregular veins with angular indented walls that are widely recorded at all odp sites 2 compressional structures that are confined to the marginal ridge of the ivory coast ghana transform margin and include reverse faults folds and vertical crenulation cleavage and 3 various types of shear zone at low angles with respect to bedding which are continuous throughout the cretaceous succession of the ridge structural analysis combined with thin section observation shows that most of these deformations occurred in water rich sediments the extensional minor scale structures are related to the early cretaceous rifting stage of the margin as characterized at regional scale by half grabens and tilted blocks the compressional structures observed in the samples are attributed to turonian santonian positive inversion tectonics and related to the occurrence of large scale flower structures and inverted extensional blocks in contrast the shear zones at low angles with respect to bedding observed throughout the cretaceous series are linked to local gravity induced tectonics

kinematics of the northern walker lane an incipient transform fault along the pacific north american plate boundary in the western great basin of north america a system of dextral faults accommodates 15 25 of the pacific north american plate motion the northern walker lane in northwest nevada and northeast california occupies the northern terminus of this system this young evolving part of the plate boundary offers insight into how strike slip fault systems develop and may reflect the birth of a transform fault a belt of overlapping left stepping dextral faults dominates the northern walker lane offset segments of a w trending oligocene paleovalley suggest 20 30 km of cumulative dextral slip beginning ca 9 3 ma the inferred long term slip rate of 2 10 mm yr is compatible with global positioning system observations of the current strain field we interpret the left stepping faults as macroscopic riedel shears developing above a nascent lithospheric scale transform fault the strike slip faults end in arrays of n striking normal faults suggesting that dextral shear diffuses into extension in the great basin coeval extension and dextral shear have induced slight counterclockwise fault block rotations which may ultimately rotate riedel shears toward the main shear zone at depth thus facilitating development of a throughgoing strike slip fault

the importance of siliceous radiolarian bearing mudstones in the formation of sediment hosted zn pb ba mineralization in the selwyn basin yukon canada sediment hosted massive sulfide shms mineralization occurred in three main episodes during the evolution of the selwyn basin yukon and northwest territories canada in the macmillan pass district tom and jason deposits the upper devonian strata of the earn group host the youngest least deformed examples of shms mineralization the earn group comprises gray to black homogeneous mudstones which have been deformed in the cordilleran fold and thrust belt are weathered and poorly exposed this makes stratigraphic correlations and the recognition of prospective units very challenging the host rock siliceous mudstone and mineralized intervals at the tom and jason zn pb ba deposits have been sampled from drill core major element chemistry and total organic carbon toc data are presented for the host rock samples from two drill holes tyk 5 n 18 76 17 n 19 all mudstones contain between 2 and 5 wt toc and 67 to 83 wt sio2 subtle alteration marked by potassium loss k2o al2o3 50 radiolarians by volume within the mineralized horizons and in barren time equivalent strata and therefore are a useful stratigraphic marker unit in otherwise homogeneous featureless fine grained mudstones the presence of highly siliceous carbonaceous mudstone units with preserved radiolarians suggests that in the late devonian there is a link between biological productivity in the water column the resultant sedimentation and the shms deposits these biosiliceous lithologies may be particularly favorable host rocks to shms mineralization for the following reasons 1 high porosities during early diagenesis preserve volume and enhance permeabilities in partially lithified sediments which are important parameters for subseafloor replacement mineralization 2 these units are rich in organic materials due to their deposition in productive settings and have a high capacity for the generation of sulfide via sulfate reduction therefore we suggest there is a link between times of high biological activity and productivity in oceans sediments derived from those processes and shms deposits

large magnitude late holocene earthquakes on the genoa fault west central nevada and eastern california the genoa fault a principal normal fault of the transition zone between the basin and range province and the northern sierra nevada displays a large and conspicuous prehistoric scarp three trenches excavated across this scarp exposed two large displacement late holocene events two of the trenches contained multiple layers of stratified charcoal yielding radiocarbon ages suggesting the most recent and penultimate events on the main part of the fault occurred 500 600 cal b p and 2000 2200 cal b p respectively normal slip offsets of 3 5 5 m per event along much of the rupture length are comparable to the largest historical basin and range province earthquakes suggesting these paleoearthquakes were on the order of magnitude 7 2 7 5 the apparent late holocene slip rate 2 3 mm yr is one of the highest in the basin and range province based on structural and behavioral differences the genoa fault is here divided into four principal sections the sierra diamond valley carson valley and jacks valley sections and is distinguished from three northeast striking faults in the carson city area the kings canyon carson city and indian hill faults the conspicuous scarp extends for nearly 25 km the combined length of the carson valley and jacks valley sections the diamond valley section lacks the conspicuous scarp and older alluvial fans and bedrock outcrops on the downthrown side of the fault indicate a lower activity rate activity further decreases to the south along the sierra section which consists of numerous distributed faults all three northeast striking faults in the carson city area ruptured within the past few thousand years and one or more may have ruptured during recent events on the genoa fault

mineralogical and chemical variations castellanos shale hosted zn pb ba deposit northwestern cuba the shale hosted castellanos sedimentary exhalative zn pb ba deposit of jurassic age in northwestern cuba consists of pyrite sphalerite and galena in a hydrothermal quartz carbonate barite matrix with very little clastic or shale matrix the northeastern end of the zn pb ba lens overlies a transgressive cu stringer zone which is interpreted as the vent or feeder channel for the exhalative mineralization abundance patterns in the sulfide assemblage define layering within the deposit in the southwestern part of the deposit sphalerite and galena increase and pyrite decreases stratigraphically upward within individual layers to the northeast near the vent sphalerite and galena decrease upward parallel to pyrite in the area of the vent the basal carbonate is exclusively dolomite however calcite abundance increases rapidly upward remote from the vent dolomite is the dominant carbonate from the base to the top of the deposit carbonate and barite are the main gangue minerals near the discharge site quartz is the major gangue mineral in the southwestern section these and other variations result from differences in a ca super 2 f oh2 temperature and sigma s relative to sulfide forming cations especially fe super 2 at the discharge site and in the depositional basin some distance from the vent

timing and significance of late glacial and holocene cirque glaciation in the sierra nevada california mapping and radiocarbon dates of cirque moraines in the sierra nevada demonstrate that the last significant pre little ice age glacier advance in the range the recess peak resulted from snowline lowering roughly twice that of the matthes little ice age advance and that the recess peak advance is late pleistocene in age we mapped recess peak and matthes deposits in 64 cirques along a profile of the main sierran crest that spans the north south limits of neoglacial deposits in the range equilibrium line altitudes for the reconstructed recess peak glaciers vary greatly but coherently with those of the matthes advance the variability of both sets of deposits reflects strong topographic influences on snow accumulation and ablation patterns in their deep cirques tephrochronology and radiocarbon dates from lake sediment cores provide limits on the timing of the two advances previous work documenting the absence of a young regionally extensive tephra on matthes moraines in the central sierra demonstrates that they formed after 700 14c years bp 650 cal years bp the age of the recess peak advance has been less certain we therefore collected and dated sediment cores from lakes dammed behind terminal moraines correlating to the recess peak advance in four widely separated drainages along the sierran crest north to south south fork american river lee vining creek middle fork san joaquin river and bishop creek twenty three high precision ams radiocarbon dates on gyttja peat and macrofossils from the cores are internally consistent and demonstrate that the recess peak advance previously thought to be of late holocene age 2500 years bp ended before 11 190 70 14c years bp 13 100 85 cal years bp recess peak is therefore late pleistocene in age and probably predates the north atlantic younger dryas climatic reversal the absence of any glacial deposits on the bedrock between the recess peak and matthes deposits indicates that 1 any advance related to the younger dryas event in central california was smaller than the matthes advance 2 the matthes advance was the most extensive and possibly the only neoglacial event in the range and 3 climate in the sierra between 13 000 cal years bp and 650 cal years bp was apparently too warm and or dry to support glaciers larger than those of the little ice age other mapping indicates that the recess peak is the first significant glacier advance after retreat of tioga local late wisconsin maximum glaciers these results suggest a regionally variable climate in western north america during the younger dryas event because glaciers appear to have expanded in the canadian rockies at that time the new recess peak age limits combined with other dated lake cores indicate that the sierra was essentially deglaciated by 14 000 15 000 cal years bp 12 000 13 000 14c years bp substantially earlier than previously estimated this finding indicates that current production rates of some in situ cosmogenic nuclides calibrated on an assumed deglaciation of the range at 11 000 cal years bp 10 000 14c years bp may be systematically too high by as much as 20

morphology and processes in lake tahoe california nevada lake tahoe was surveyed using a state of the art high resolution multibeam mapping system to provide an accurate base map for the myriad of ongoing environmental studies in and around the lake the newly defined basin morphology shows steep basin margins on the northern eastern and western sides and a gentle margin on the southern side two large flat plateaus several kilometers wide extend from the shore to about 40 m water depth in the northern and northwestern sections of the basin a series of ridges in the west and north are presumed traces of faults some of which border the lake basin and some of which traverse across the northern section of the lake and converge in mckinney bay mckinney bay is a large reentrant in the western margin that was created by a failure of the western margin that occurred about 300 ka the failure generated a major debris avalanche that carried large blocks some more than 1000 m long and 80 m high across the basin apparently the debris avalanche was deflected by the eastern margin of the basin and flowed to the north and south small debris flows and slides have continued to occur in this area small debris aprons occur along the northern western and eastern margins some apparently the remnants of collapsed terminal moraines formed in the basin from the 160 ka tahoe glaciation which reached the edge of the basin eroded plateaus and ridges occur on a glacial outwash plain that covers the gentle southern margin the plateaus and ridges are inferred to be remnants of another large terminal moraine of the tahoe glaciation

present tectonic motion across the coast ranges and san andreas fault system in central california geodetic results from very long baseline interferometry vlbi satellite laser ranging slr and the global positioning system gps are used to estimate angular velocities between the sierran microplate pacific plate and north american plate the sierra pacific pole of rotation lies nearer to the san andreas fault than does the pacific north america pole of rotation and leads to different tectonic implications than if the latter is used the angular velocities show that the san andreas fault system and central california coast ranges accommodate motion of 39 2 mm yr mainly by strike slip faulting all confidence limits following signs in this paper are 95 confidence limits fault normal motion is small is mainly convergent at rates up to 3 3 1 0 mm yr and varies along the coast but is divergent at 2 6 1 2 mm yr across san pablo bay and associated topographic lows across which the sierran and central valley watershed drains to the pacific ocean the mountain ranges tend to be larger where the fault normal convergence rates are larger the low convergence rate 0 5 1 8 mm yr normal to the san andreas fault in the carrizo plain differs sharply from that previously inferred 8 2 1 2 mm yr and 4 9 1 6 mm yr by feigl et al 1993 the difference is due to differences between their and our elastic strain accumulation models and between how their and our pacific plate reference frames are defined the ranges in most places require a minimum of 4 2 1 m y of fault normal convergence at the present rate to attain their present cross sectional area if erosion is neglected more if it is not the amount of convergence previously estimated from a balanced cross section across the diablo range in central california requires 10 8 3 m y of convergence at the present rate the former is consistent with widely held views about the onset of the coast range orogeny but the latter is not both are consistent however with the recent plate reconstructions by s cande j stock and colleagues which indicate that pacific plate motion relative to north america changed to a more convergent direction 20 25 clockwise of its prior direction at ca 8 to 6 ma and not at 3 5 ma as had been previously inferred the inferred change in direction of plate motion is large compared with the present angle of convergence across the straight and narrow segment of the san andreas fault of 0 7 4 7 from which we infer that the sierran microplate changed motion relative to north america at the same time ca 8 to 6 ma as did the pacific plate we further infer that the motion accommodated across the great basin must also have changed at the same time we also examine the hypothesis that stable sliding occurs along the san andreas fault and other northwest striking strike slip faults in central california where the fault normal convergence rate is low or negative and that these faults are unstable where the fault normal convergence rate is high such a relationship appears to hold in general but fails in detail in particular there are substantial sections of fault with small inferred rates of fault normal convergence across which the san andreas fault is locked moreover the creeping section of the san andreas fault i e the section between parkfield and the calaveras junction is the locus of greater fault normal convergence 3 2 1 4 mm yr than is the locked part of the fault 0 5 1 8 mm yr south of parkfield thus this hypothesis is at best a partial explanation for the observed distribution of locked and nonlocked sections of the fault

san andreas fault rupture scenarios from multiple paleoseismic records stringing pearls we present a new method to objectively combine paleoseismic event data from multiple sites into rupture scenarios and apply it to the southern san andreas fault ssaf of california first a pool is constructed of all ruptures between sites allowed by fault geometry and available event age probability distribution functions pdfs scenarios constructed by drawing from this pool are evaluated by the average quality of agreement event dating evidence by the degree of misfit of cumulative displacement over all ruptures compared to a prediction from the fault slip rate and elapsed time and by the number of events in the scenario three slip rate models from the 2008 working group on california earthquake probabilities wgcep were considered scenarios with full fault length ruptures tend to be inconsistent with low slip rates through the san bernardino and san gorgonio sections of the ssaf favorable scenarios tend to include 1857 like ruptures for three of the most recent five prehistoric ruptures in the northern half of the ssaf from carrizo to approximately wrightwood they also include one to two ruptures that involve the southern half of the ssaf but most earthquakes there appear shorter and exhibit less consistency from event to event by combining paleoseismic data into ensembles of scenarios and selecting viable scenarios using external constraints our method provides rupture histories useful for seismic hazard assessment without having to first settle which event at a site correlates with those at adjoining sites this opens a way for paleoseismic data to be used with greater power to understand the seismic hazard posed by faults like the southern san andreas

kinematic modelling of extensional fault propagation folding abstract many studies have shown that in extensional basins discrete faulting at depth is commonly linked to more distributed deformation in particular folding at higher levels such extensional fault propagation folds are particularly common where there is a distinct mechanical contrast between faulted basement and sedimentary cover outcrop and analogue modelling studies indicate that such folds form as upward widening zones of distributed deformation monoclines above discrete faults at depth with increasing displacement strain the folds are cut by faults as they propagate upwards into the cover to date however there has been little investigation into the kinematics of linked basement faulting and extensional fault propagation folding here we present a two dimensional kinematic model of linked basement faulting and fault propagation folding which is based upon trishear the model allows investigation of the influence of shear zone geometry and the rate of fault propagation upon the style of folds and the strains associated with them the evolution of linked basement faulting and folding predicted by the model is compared in detail to that observed in an analogue model the kinematic model reproduces well many of the features seen both in the analogue model and reported from outcrop and seismic studies

a metamorphosed potassic alteration zone associated with the bleikvassli znpbcu orebody northern norway abstract the bleikvassli zn pb cu deposit is located in amphibolite facies schists and gneisses in the rodingsfjellet nappe complex north norwegian caledonides a microcline gneiss occurs as a lens shaped body up to 250 m thick in the footwall and as small irregular bodies in the hanging wall the microcline gneiss contains 40 75 microcline and is characterized by a spotty texture the footwall microcline gneiss is chemically zoned with highest k 2 o content 10 12 wt and highest alkali to alumina ratio 0 76 in the central part the mica and plagioclase contents increase towards the margins of the gneiss which grades laterally into the surrounding kyanite mica schist the field relations and the chemical composition of the gneiss indicate that the potassium rich protolith formed by addition of alkalies sio 2 and heat to a pelitic sediment the microcline gneiss has thus been interpreted as the central part of a hydrothermal alteration zone associated with the bleikvassli orebody