late cenozoic structure and tectonics of the northern mojave desert in the fort irwin region of the northern mojave desert late cenozoic east striking sinistral faults predominate over northwest striking dextral faults of the same age kinematic indicators and offset marker units indicate dominantly sinistral strike slip on the east striking portions of the faults and sinistral thrust slip on northwest striking moderately dipping segments at the east ends of the blocks crustal blocks 7 10 km wide by 50 km long are bounded by complex fault zones up to 2 km wide at the edges and ends of each block faulting initiated after 11 ma and quaternary deposits are faulted and folded we document a minimum of 13 km cumulative sinistral offset in a north south transect from south of the bicycle lake fault to north of the drinkwater lake fault paleomagnetic results from 50 sites reveal two direction groups in early and middle miocene rocks the north to northwest declinations of the first group are close to the middle miocene reference pole however rock magnetic studies suggest that both primary and remagnetized directions are present in this group the northeast declinations of the second group are interpreted as primary and 63 5 7 6 clockwise from the reference pole and suggest net post middle miocene clockwise rotation of several of the east trending blocks in the northeast mojave domain the jurassic independence dike swarm in fort irwin may be rotated 25 80 clockwise relative to the swarm north of the garlock fault thus supporting the inference of clockwise rotation using a simple shear model that combines sinistral slip and clockwise rotation of elongate crustal blocks we predict 23 clockwise rotation using the observed fault slip or one third that inferred from the paleomagnetic results the discrepancy between slip and rotation may reflect clockwise bending at the ends of fault blocks where most of our paleomagnetic sites are located however at least 25 40 of clockwise tectonic rotation is consistent with the observed slip on faults within the domain plus possible rigid body rotation of the region evidenced by clockwise bending of northwest striking domain bounding faults our estimates of sinistral shear and clockwise rotation suggest that approximately half of the 65 km of dextral shear in the eastern california shear zone over the last 10 m y occurred within the northeast mojave domain the remainder must be accommodated in adjacent structural domains e g east of the avawatz mountains and west of the goldstone lake fault supporting appendices 1 and 2 are available on diskette or via anonymous ftp from kosmos agu org directory apend username anonymous password guest diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 or by phone at 800 966 2481 15 00 payment must accompany order

temporal changes in fault strike to 90 and extension directions during multiple episodes of extension an example from eastern nevada in areas with prolonged extensional histories or multiple episodes of extension temporally distinct extensional fault systems including dip slip normal oblique slip and or strike slip faults may form these fault systems may be spatially distinct overlapped or completely superimposed and different fault systems may have different fault strikes and extension directions although fault strike is not a very sensitive indicator of principal stress directions changes through time in fault strike of as much as 90 exceed the uncertainty overprinted extensional fault systems of different ages with significantly different to 90 fault strikes and extension directions provide strong evidence of changes in the regional stress field with time tens of millions of years of extension occurred in the basin and range province of the united states and many temporally distinct fault sets formed through that time we document at least four extensional episodes and the fault kinematics of each where possible in the central hiko range eastern nevada the four cenozoic extensional events are prevolcanic synvolcanic postvolcanic miocene pliocene and postvolcanic pliocene quaternary the prevolcanic faults strike north south and are interpreted as footwall faults to the regional eocene oligocene snake stampede extensional system which caused approximately east west extension the synvolcanic faults are late oligocene miocene age and strike east west although they are rare and have minor offset they accommodated north south directed extension postvolcanic faults part of the timpahute lineament are approximately east west striking normal and northeast striking oblique slip faults they also accommodated approximately north south extension during miocene time the northeast striking left normal oblique slip fault set formed as new faults and records a change between north south and east west extension in miocene time later east west extension occurred along the pliocene to quaternary hiko fault zone these four overprinted extensional systems show two separate changes in normal fault strike of 90 from north south to east west and from east west back to north south consequently the extension direction similarly changed through time we suggest that causes for the changes in direction of upper crustal extension include a change from stresses created by 1 plate interactions which generated approximately east west extension to 2 mantle motions which generated approximately north south extension and 3 back again the extension related to mantle motions is associated with a band of volcanism that passed across the northern basin and range province moving generally from north to south during the protracted period of extension therefore a change from plate boundary or interaction derived stresses to mantle or volcanism related stresses and back again is possible

sequence age and source of silicic fallout tuffs in middle to late miocene basins of the northern basin and range province the latest cenozoic 6 ma ash beds in the western united states have been intensively studied for several decades the more widespread of these ash beds are well documented event horizons that are of great value in studies of the timing and pace of geological climatological and biological events throughout the region because explosive volcanism was not restricted to latest neogene time in this region many older ash beds are likely to prove as useful as younger beds as event horizons once they are located characterized and dated as a first step in developing a useful chronology of older cenozoic ash beds in the western united states we have sampled and analyzed silicic fallout tuffs in middle to late miocene sedimentary basins across the northern basin and range province the northern basin and range basins ideally situated in the vicinity of major coeval silicic volcanic centers contain numerous relatively unaltered silicic fallout tuffs we have correlated tuffs between all sampled sections on the basis of glass shard composition the composite stratigraphic sequence established by the correlations contains more than 200 individual tuffs including 59 widely distributed tuffs termed correlative tuffs the tuffs vary widely in composition but most are in one of two compositional groups gray metaluminous vitric tuffs gm tuffs or white metaluminous vitric tuffs wm tuffs distribution patterns compositional characteristics and correlation with ash flow tuffs show that the source for most gm tuffs was the snake river plain volcanic province along the northern edge of the northern basin and range and the source for most wm tuffs was the southwestern nevada volcanic field in the southern part of the northern basin and range the northern basin and range tuffs range in age from ca 16 6 ma the ages of individual tuffs are determined variously by direct isotopic dating by correlation to previously dated fallout and ash flow tuffs or by interpolation age estimation ages for most tuffs are known to within 0 25 m y 1 or less and for many tuffs to within 0 1 m y or less the sequence and ages of tuffs established in this study provide insights into the evolution of the northern basin and range basins and patterns of explosive volcanism in coeval volcanic centers and contribute to the development of a high resolution stratigraphy and chronology of coeval sedimentary deposits throughout the western united states

geometry mechanisms and significance of extensional folds from examples in the rocky mountain basin and range province u s a abstract geologic mapping and structural analysis in paleogene half graben of idaho and montana have revealed over 70 extensional folds that form orthogonal sets with mostly ne and se trending axes on a regional scale they parallel or lie perpendicular to the strikes of the largest normal faults transverse folds at a high angle to the fault and folds oblique to the fault comprise more than half of the folds and reflect the highly three dimensional nature of the bulk strain detailed geometric analysis of 15 folds in the salmon horse prairie and medicine lodge basins shows that they typically have an upright to steeply inclined bisecting surface an interlimb angle of 141 and a plunge of 19 based on our synthesis of the eight common mechanisms of extensional folding and their distinguishing characteristics we were able to determine how some of the investigated folds formed fault bend folding above both fault parallel and fault perpendicular bends in the underlying normal fault produced most of the folds in the study area but displacement gradients along normal faults fault drag isostatic adjustments and transtension were also factors in the deformation most of the compound folds which result from more than one mechanism of folding are oblique to all adjacent normal faults recognition of such extensional folds is critical because they might be misinterpreted as contractional structures they influence sediment thickness patterns and dispersal in rift basins and may control the migration and trapping of petroleum and groundwater resources

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

palinspastic reconstruction of southeastern california and southwestern arizona for the middle miocene a paleogeographic reconstruction of southeastern california and southwestern arizona at 10 ma has been made based on available geologic and geophysical data clockwise rotation of 39 has been reconstructed in the eastern transverse ranges consistent with paleomagnetic data from late miocene volcanic rocks and with slip estimates for left lateral faults within the eastern transverse ranges and nw trending right lateral faults in the mojave desert this domain of rotated rocks is bounded by the pinto mountain fault on the north the model requires that the western part of the late miocene pinto mountain fault was a thrust fault which gained displacement to the west because of the absence of evidence for rotation of the san bernardino mountains or for significant right slip faults within the san bernardino mountains the squaw peak thrust system of meisling and weldon 1989 may be a western continuation of this fault system the sheep hole fault bounds the rotating domain on the east east of this fault an array of nw trending right slip faults and south trending extensional transfer zones has produced a basin and range physiography while accumulating up to 16 km of right slip this maximum is significantly less than the 37 5 km of right slip required in this region by a recent reconstruction of the central mojave desert dokka and travis 1990a geologic relations along the southern boundary of the rotating domain are poorly known but this boundary is interpreted to involve a series of curved strike slip faults and linking normal faults that accommodated noncoaxial extension quaternary movement on the pinto mountain and nearby faults is unrelated to the rotation of the eastern transverse ranges and a hiatus during part of pliocene time followed the deformation which produced the rotation the reconstructed clemens well fault in the orocopia mountains proposed as a major early miocene strand of the san andreas fault projects eastward towards arizona where early miocene rocks and structures are continuous across its trace making large displacements on this structure unlikely the model predicts a 14 clockwise rotation and 32 extension during late miocene and early pliocene time along a nw trending line parallel to the present trace of the san andreas fault palinspastic reconstructions of the san andreas system based on this proposed reconstruction may be significantly modified from current models

el chichon volcanic debris in an arctic tropopause fold a research flight with the noaa wp 3d aircraft revealed evidence for stratospheric tropospheric exchange within the arctic through tropopause folding on the flank of the polar vortex observations showed descent of the tropopause and of stratospheric ozone to 700 mb along the west coast of greenland measurements of condensation nuclei and analysis of high volume impactor samples documented the presence of volcanic debris probably from the 1982 el chichon eruption including h2so4 droplets within the polar vortex and associated tropopause fold

evolution of magmatic vapor to gold rich epithermal liquid the porphyry to epithermal transition at nevados de famatina northwest argentina fluid inclusions in the subeconomic porphyry cu mo au system at nevados de famatina and closely associated high sulfidation epithermal cu au ag as sb te veins at la mejicana northwest argentina were studied to reconstruct the evolution of hydrothermal fluids from their deep magmatic source to the shallow epithermal environment field geology vein petrography fluid inclusion microthermometry and single inclusion microanalysis by laser ablation inductively coupled plasma mass spectrometry la icp ms were combined to determine the evolution of pressure temperature and ore metal concentrations in the fluids cathodoluminescence imaging complements transmitted light petrography to constrain the successive stages of quartz formation and the entrapment sequence of the fluid inclusion populations aqueous liquid inclusions of 5 wt percent nacl equiv salinity trapped in quartz sericite pyrite qsp veins between 360 and 325 c contain unusually high concentrations of cu 400 5 000 ppm as 200 ppm sb and te both up to 100 ppm and au several ppm along with other ore forming elements these veins are paragenetically transitional between subeconomic porphyry copper mineralization exposed in the valley floor and high sulfidation epithermal veins with high au grades which are preserved along a high ridge adjacent to the porphyry stock low density vapor and hypersaline liquid i e brine inclusions were trapped in early formed quartz of the porphyry stockwork veins between 450 and 600 c the brine contains lower cu and au concentrations than coexisting vapor inclusions and texturally even earlier inclusions of intermediate density that are trapped in phenocrysts and some stockwork veins the latter may be equivalent to a parental fluid the low and intermediate density fluids compositionally overlap in salinity with the aqueous liquids recorded by the later transitional quartz sericite pyrite veins fluid inclusions and geologic time relations indicate that the transitional quartz sericite pyrite veins were the channelways for metal rich aqueous liquids that generated the high sulfidation epithermal cu au deposit these mineralizing liquids are interpreted to have evolved by continuous density increase contraction from a low salinity s rich magmatic fluid of low to intermediate density this vaporlike fluid was produced by exsolution from a magma that existed at greater depth during the late stages of cooling of the magmatic hydrothermal complex and probably underwent minor brine separation prior to reaching the present level of exposure epithermal mineral precipitation occurred upon dilution of the low salinity magmatic fluid with meteoric water which entered the hydrothermal system as it was cooled and successively eroded during continued magmatic fluid ascent

chlorine 36 fallout in the summit greenland ice core project ice core the natural cosmogenic radioisotope 36cl has been measured in the greenland ice core project ice core from summit greenland generally a good correlation between 36cl and 18o was found even in glacial periods with strong 18o oscillations the 36cl flux is calculated assuming an exponential relationship between accumulation rate and 18o a prominent excursion is detected between 35 and 40 kyr b p which coincides with a similar 10be peak measured in the same samples this sheds light on possible causes of this excursion in the lowest part of the ice core the flux decreases smoothly this can be interpreted as radioactive decay of 36cl t1 2 300 kyr

fault tectonics and deformation a method of quantification using field data abstract a new method for analysing fault populations in terms of infinitesimal strain is discussed a fractured rock volume taken as a whole can be considered to be affected by continuous deformation provided fault offsets are small compared to its size each fault then acts as a penetrative simple shear we combinen simple shears to define an average deformation ellipsoid for the given faulted volume the method has been tested using accurate fault slip data collected in two superposed levels of coal mines of the lorraine basin the studied rock volume has been affected by extensional phenomena during permo triassic results show that within a major tilted block the average deformation corresponds to e w extension with a total factor of extension of 1 03 this result is in good agreement with independent estimates

on the common solar signal in different cosmogenic isotope data sets 1 in this article we aim to determine frequency ranges and intervals of time in which the solar signal dominates in different cosmogenic isotope data from a 14c based reconstruction of cosmic ray intensity over the last millennia we computed expected 10be variations in two antarctic sites dom fuji and south pole and two greenland sites dye 3 and gisp 2 and compared them with the actually measured 10be abundance at the sites by applying different methods of analysis such as bivariate correlation conventional fft coherence and wavelet coherence we found the following 1 the modeled series on the basis of 14c data are in good agreement with the measured 10be data sets on different timescales and at different locations confirming the existence of a common solar signal in both isotope data 2 the 10be data are driven by the solar signal on timescales from about 100 years up to 1000 years or even to multimillennial scales at the longer scales paleomagnetism plays an increasingly important role 3 the local climate dominates the 10be data mostly on short 100 years timescales but the solar signal becomes important even at short scales during periods of grand minima of solar activity 4 there is an indication of a possible systematic uncertainty in the early holocene likely due to a not perfectly stable thermohaline circulation which requires additional studies we have shown that both 14c and 10be based records are consistent with each other over a wide range of timescales and time intervals they form a robust basis for quantitative reconstructions of solar activity variations in the past

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

patterns and timing of late quaternary faulting in the great basin province and relation to some regional tectonic features large scale surface faulting events each tens of kilometers long and involving more than a meter of displacement of late quaternary age have not been uniformly distributed but have been concentrated in subprovincial and smaller belts and areas within the great basin province furthermore faulting apparently has not been uniformly distributed over time the average recurrence interval of large scale faulting events on individual faults in the province is measured in thousands or tens of thousands of years in contrast to such long recurrence intervals in the central nevada and eastern california seismic belts large scale faulting events have occurred during the last 111 years in an apparently coherent sequential belt filling pulse of activity in which events were separated by only a few years or a few decades the questions are where are other pulses of large scale faulting likely to occur and what controls the localization of such belts and areas characterized by higher rates of faulting two examples of tectonic subprovinces that may play a role in delimiting smaller zones of faulting are the black rock carson sink zone of extension and the central nevada downwarp the central nevada seismic belt lies along the dividing line between these two subprovinces and the northwest margin of the black rock carson sink zone of extension coincides with the margin of a fingerlike belt of dense faulting in northwestern nevada

contemporaneous formation of adjacent porphyry and epithermal cu au deposits over 300 ka in northern luzon philippines there is commonly a close spatial relation between porphyry cu au and high sulfidation epithermal cu au deposits throughout the world although a genetic association has not been proven nowhere is this spatial association better seen than in northern luzon philippines where the lepanto epithermal cu au deposit overlies the far southeast fse porphyry cu au deposit both world class orebodies fresh rock and hydrothermal mineral separates yield k ar ages indicating that premineralization and postmineralization volcanism occurred at 2 2 1 8 ma and 1 2 0 9 ma respectively and that the hydrothermal system was active from 1 5 to 1 2 ma k ar ages of alunite from lepanto have the same range as those of hydrothermal biotite and illite from the fse deposit indicating that both epithermal and porphyry mineralization formed from an evolving magmatic hydrothermal system that was active for about 300 ka this temporal relation strengthens the argument for a genetic link between these two styles of ore deposit and has implications for exploration where one style of mineralization is found there is potential for the other nearby

apatite u th he thermochronometry as an innovative geothermal exploration tool a case study from the southern wassuk range nevada abstract extensional type geothermal systems are complicated by the interrelation between footwall advection during exhumation and the subsequent redistribution of heat by migrating hydrothermal fluids in the hanging wall the southern wassuk range wr hanging wall hosts a moderate temperature extensional type geothermal system and is ideal for studying this duality by analyzing a suite of apatite ahe and zircon zhe helium samples from the footwall and hanging wall of the southern wr young 3 4 ma ahe ages along the wr front are concentrated along the se corners of segmented footwall blocks marking the location of focused mio pliocene transtension fracture dilation and advection hydrothermally reset ahe ages along the footwall range front suggest that the hawthorne geothermal system 85 135 c is long lived and has resided at a prominent structural boundary in the wr footwall marked by localized advection and range front deformation in contrast the presence of both hydrothermally reset and non reset ahe ages from a 1 4 km deep borehole in the hanging wall basin probably indicate that the geothermal plumbing system and current manifestation as a thermal anomaly 113 c are juvenile and are controlled by the generation of newly formed faults in the hanging wall ahe ages have been shown here to greatly enhance the focusing of regional scale geothermal exploration efforts and for the first time have been used to identify and estimate the temperature of unseen hydrothermal fluids

recycling of cosmogenic nuclides after their removal from the atmosphere special case of appreciable transport of 10be to polar regions by aeolian dust abstract in this paper we discuss the general problem of recirculation of atmospheric cosmogenic isotopes after their initial removal from the atmosphere practically all nuclides are recycled after their removal from the atmosphere the noble gas radio nuclides re circulate between the atmosphere and the hydrosphere the fraction of time spent in these reservoirs depends on their solubility and half lives radiocarbon atoms spend most of their life time in the oceans before being removed to the sediments all cosmogenic nuclides which are removed from the atmosphere by wet precipitations spend most of their life time in the hydrosphere or in sediments a special exception arises in the case of nuclides such as 10 be and 26 al which are particle active and adhere to aerosols and top soils in the lithosphere strong winds dislodge surface particles and transport the smaller particles to great distances we discuss the special case of the transport of particle reactive 10 be via aeolian dust which can result in appreciable 10 be fluxes in polar regions in cold climates vis a vis its direct deposition from the atmosphere we compare estimated concentrations of dust transported 10 be with the measured total 10 be concentrations in antarctica in the vostok and taylor dome ice cores and atmospheric 10 be concentrations in greenland in the gisp and grip ice cores during certain epochs high aeolian dust concentrations contribute significantly to 10 be fluxes in greenland comparable to or greater than atmospheric 10 be fluxes in the antarctica however even during epochs of high dust fluxes the aeolian 10 be contributions are 10 be fluxes these results imply that great care should be taken in analyzing 10 be concentrations in greenland especially

relation between regional lineament systems and structural zones in nevada analysis of diverse geologic geophysical and geochemical data shows that six of eight extensive lineament systems delineated in landsat images of nevada are morphologic and tonal expressions of three broad structural zones the lineament systems defined in this report are the walker lane rye patch midas pancake range warm springs timpahute pahranagat and northern nevada rift the three structural zones are the walker lane structural zone the humboldt structural zone and the southern nevada structural zone the northwest trending walker lane structural zone which includes the walker lane lineament system is 150 to 200 km wide and is marked by northwest oriented faults a broad belt of high frequency aeromagnetic anomalies and concentrations of volcanic rocks 34 to 6 m y old the northwest trending rye patch lineament system may mark the northeast boundary of this structural zone and is characterized by stratigraphic discontinuities alignment of aeromagnetic anomalies and contrasting aeromagnetic anomaly patterns on opposing sides northern nevada is dominated by the northeast trending 150 to 200 km wide humboldt structural zone which is marked by the midas lineament system northeast oriented faults broad gravity anomalies and the battle mountain heat flow high this zone appears to extend into central montana the humboldt structural zone is transected by the northern nevada rift lineament system which is partly defined by a relatively narrow belt of north northwest trending basaltic dikes that produce a series of pronounced aeromagnetic highs the east trending 150 to 175 km wide southern nevada structural zone includes the pancake range warm springs and timpahute lineament systems this zone is marked by disruption and termination of ranges stratigraphic discontinuities east to east northeast trending faults and an easterly grain in the aeromagnetic and gravity patterns the other lineament system in southern nevada the northeast trending pahranagat may lie within a poorly defined southward extension of a broad structural zone defined in utah by a belt of volcanic rocks 34 to 0 m y old stratigraphic discontinuities coincidence with three extensive gravity lineaments and a belt of aeromagnetic anomalies this paper proposes that the lineament systems except for the northern nevada rift lineament system are conjugate shears formed during and after middle miocene extension of the great basin these lineament systems probably reflect only the most recent movement along broad crustal zones which may be of pre miocene age the three documented structural zones and possibly one including the pahranagat lineament system may reflect transition zones between the central great basin where 30 extension has been documented and the adjacent regions that responded differently to spreading since middle miocene time the humboldt structural zone appears to be especially important for geothermal and mineral exploration in nevada because of the presence of the battle mountain heat flow high and a high concentration of metal districts within this zone in nevada

early fimiston and late oroya au te ore paringa south mine golden mile kalgoorlie 4 mineralogical and thermodynamic constraints on gold deposition by magmatic fluids at 420 300 c and 300 mpa the golden mile deposit 1767 t au in the archean yilgarn craton western australia is controlled by d2 strike slip and d3 reverse faults displacing folded tholeiitic greenstones granodiorite and monzodiorite dykes emplaced into the faults predate and are synchronous with propylitic and sericite ankerite alteration overprinted by the ore arsenopyrite and chlorite thermometry and fluid inclusion data indicate ore formation at 420 30 c and 300 mpa and cooling to the ambient temperature at 10 km depth 250 300 c fimiston refractory ore 7 g t au in propylitic golden mile dolerite is zoned from inner albite ankerite to outer ankerite phengite quartz replacement pyrite magnetite is overprinted by pyrite hematite anhydrite arsenical pyrite encloses chalcopyrite tennantite gold and tellurides gold thio sulfide complexes buffered by magmatic so2 and h2s in the fluid were destabilised during the ankerite pyrite replacement of propylitic chlorite a reaction releasing hydrogen ions for the hydrolitic alteration of adjacent albite gold deposition was assisted by declining gold silver tellurium and sulfur solubility as the fluid cooled dissolved sulfate is recorded in pyrite by negative 34s 10 to 5 at magmatic 33s 0 0 2 oroya ore bodies are subdivided into oxidised pyrite lodes 5 g t au in propylitic gmd and reduced lodes 30 120 g t au characterised by stage 1 silica pyrite and siderite chlorite replacement in ankerite rich wall rocks rapid cooling an acidic fluid and the retrograde solubility of ankerite facilitated replacement and the deposition of minor arsenopyrite pyrrhotite chalcopyrite sphalerite and gold locally the h2s rich fluid log fs2 5 8 0 5 bar at 420 c was reduced by organic methane oroya stage 2 ore fills crosscutting veins and cements breccia quartz chalcedony dolomite ankerite calcite v muscovite v chlorite and v tourmaline form the gangue of pyrite telluride magnetite ore altaite tellurium myrmekites were deposited at 400 c as melt droplets together with tellurantimony altaite calaverite montbrayite and petzite as fluid temperature and tellurium fugacity declined free gold krennerite coloradoite and melonite also crystallised joined by sylvanite and hessite below 350 c finally trace covellite and digenite precipitated at high fluid sulfidation states

response of the tropical tropopause to el chichon and the el nino of 1982 1983 we present time series of anomalies of tropopause height tropopause potential temperature and lower stratospheric potential temperature over the tropical western pacific for the period 1980 1982 these observations show a decrease in tropopause height as anticipated following the lower stratospheric warming associated with el chichon however the magnitude of the decrease in tropopause height is considerably less than expected analysis reveals however that the tropospheric warming associated with the el nino can account for this discrepancy

geomagnetic and atmospheric effects upon the cosmogenic 10be observed in polar ice analytical tools are developed that allow the 10 be measured in ice cores to be inverted to yield quantitative information about the long term time dependence of the cosmic ray flux outside the earth s magnetic field it is concluded that the historic changes in both the magnitude and direction of the geomagnetic dipole and the inter latitudinal mixing in the atmosphere produce effects that can be large compared to the standard deviation of 22 year average 10 be data and appropriate procedures are developed to compensate for them the 10 be response function is shown to have peaked near 1 8 gev nucleon since 1950 while during the maunder minimum it approximated 0 8 gev nucleon this shows that the 10 be data are approximately a factor of two more sensitive to cosmic ray modulation than are high latitude sea level neutron monitors the z 2 cosmic radiation contributes 30 to 49 of the observed 10 be introducing a substantial rigidity dependence into the temporal variations a mathematical model is developed that computes the 10 be flux arriving at points in the polar cap taking into account polar wander changes in the geomagnetic moment and various degrees of atmospheric mixing it is shown that polar wander introduces variations into the observed flux that may be approximately three times the standard deviation of 22 year average 10 be data and that there may be significant differences between the northern and southern hemispheres the mathematical model together with the temporal changes in the nitrate concentration observed in ice cores indicate that the secular changes in 10 be due to climate driven changes in atmospheric circulation were 4 during the little ice ages two methods are outlined that allow independent determinations of the characteristics of the region of the atmosphere that contributes to the 10 be observed in the polar caps for the antarctic this has approximated the region south of 40 s for the past millennium frequently 10 be measurements are made using 4 8 year ice samples and it is shown that the unresolved 11 year variations of the cosmic radiation are the dominant source of statistical variation in these data and a procedure developed to largely eliminate them failure to eliminate these unresolved 11 year variation greatly diminishes the value of the 10 be data in the study of the long term changes in the galactic cosmic radiation

solar and climate influences on ice core 10be records from antarctica and greenland during the neutron monitor era abstract cosmogenic 10be in polar ice cores is a primary proxy for past solar activity however interpretation of the 10be record is hindered by limited understanding of the physical processes governing its atmospheric transport and deposition to the ice sheets this issue is addressed by evaluating two accurately dated annually resolved ice core 10be records against modern solar activity observations and instrumental and reanalysis climate data the cores are sampled from the dss site on law dome east antarctica spanning 1936 2009 and the das2 site southeast greenland 1936 2002 permitting inter hemispheric comparisons concentrations at both dss and das2 are significantly correlated to the 11 yr solar cycle modulation of cosmic ray intensity r xy 0 54 with 95 ci 0 31 0 70 and r xy 0 45 with 95 ci 0 22 0 62 respectively for both sites if fluxes are used instead of concentrations then correlations with solar activity decrease the strength and spectral coherence of the solar activity signal in 10be is enhanced when ice core records are combined from both antarctica and greenland the amplitudes of the 11 yr solar cycles in the 10be data appear inconsistent with the view that the ice sheets receive only 10be produced at polar latitudes significant climate signals detected in the 10be series include the zonal wave three pattern of atmospheric circulation at dss r xy 0 36 with 95 ci 0 57 0 10 and the north atlantic oscillation at das2 r xy 0 42 with 95 ci 0 64 0 15 the sensitivity of 10be concentrations to modes of atmospheric circulation advises caution in the use of 10be records from single sites in solar forcing reconstructions

record of cosmogenic in situ produced 14c in vostok and taylor dome ice samples implications for strong role of wind ventilation processes we present results of studies of in situ cosmogenic 14 c in several ice samples from the vostok and taylor dome cores spanning the time intervals of 20 and 11 k y b p respectively the results are in variance with our findings for the greenland ice sheet project 2 gisp 2 samples where near quantitative 14 c retention was observed the partitioning of 14 c in the co and co 2 phases is however quite similar in the gisp and two antarctic ice samples noting that most of the in situ 14 c is produced in the ice during its accumulation to thicknesses of up to 10 m we interpret the observed 14 c deficiencies in antarctic ice samples as due to grain metamorphism recrystallization and sublimation or evaporation caused by wind ventilation simplified models for wind ventilation exhibit an interesting feature of the firnification processes they differently affect the concentrations of in situ 14 c and of the cosmogenic nuclides 10 be and 36 cl scavenged from the atmosphere in the accumulating firn by studying the concentrations of in situ cosmogenic 14 c and the atmospheric cosmogenic nuclides in the same ice samples one can hope to obtain fairly realistic models of the chemical impacts of firnification processes specifically relationships between precipitation and accumulation and the main processes contributing to modifications in the nuclide concentrations

mineralization of the northwest quartz pyrite gold veins implications for multiple mineralization events at lepanto mankayan mineral district northern luzon philippines

porphyry and epithermal deposits and 40ar 39ar geochronology of the baguio district philippines the baguio district is located in the central cordillera of northern luzon philippines it contains numerous mineralized porphyry copper gold epithermal gold silver and skarn gold lead zinc deposits the district is floored by cretaceous eocene metavolcanic and metasedimentary rocks which are overlain by marine to terrestrial sedimentary and volcanic rocks of early miocene to pliocene ages tertiary arc magmatism related to east directed subduction of the south china sea plate along the manila trench beneath northern luzon produced a major batholith the central cordillera intrusive complex which defines the eastern boundary of the baguio district the intrusive complex was emplaced in the early miocene based on 40ar 39ar age determinations for the lucbuban gabbro 22 6 0 5 ma and virac granodiorite 20 23 0 38 and 20 2 0 7 ma recent exploration has led to the discovery of several new porphyry copper gold and skarn prospects in the western baguio district mineralization was preceded by the intrusion of a suite of hornblende megacrystic andesite dikes in the central part of the district from 4 55 0 15 to 3 45 0 19 ma porphyry copper gold and skarn deposits at black mountain and mexico on the western side of the district formed between 3 09 0 15 and 2 81 0 24 ma the santo tomas ii cu au pd porphyry deposit was emplaced into the central southern part of the district at about 1 5 ma based on secondary biotite 40ar 39ar ages of 1 48 0 05 ma and 1 47 0 05 ma on the eastern side of the district porphyry style mineralization at the hartwell and ampucao porphyry cu au prospects returned 40ar 39ar ages of 1 09 0 10 and 0 51 0 26 ma respectively quartz carbonate base metal sulfide style epithermal gold silver veins are well developed on the eastern side of the baguio district and crosscut porphyry style mineralization at the acupan baguio gold and nugget hill deposits epithermal veining is inferred to have occurred in the past million years based on a reported k ar age determination of 0 65 0 07 ma from the acupan gold mine a large advanced argillic alteration zone the baguio lithocap crops out in the northwest part of the district and formed between 1 4 and 0 9 ma based on previous k ar dating pliocene pleistocene mineralization in the baguio district was triggered by the east directed subduction of the scarborough ridge ridge subduction caused the subduction angle along the manila trench beneath northern luzon to decrease which facilitated crustal thickening and exhumation ridge subduction also promoted the development of northwest trending faults in the upper plate that interacted with major arc parallel north and arc normal northeast trending fault sets associated with the philippine fault system fertile magmas were emplaced into transtensional strike slip relay basins resulting in the accumulation of more than 35 moz of gold and several million tonnes of copper over approximately 3 m y

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

beryllium 10 concentrations in the hyper arid soils in the atacama desert chile implications for arid soil formation rates and el nino driven changes in pliocene precipitation abstract meteoric 10be concentrations in soil were measured to understand the mechanism timescale and climatic dependence of soil formation in the hyper arid atacama desert the observed systematic decline of soil 10be concentrations with depth has been reproduced using a simple model that assumes soil matrix including 10be builds up as layers over time while 10be decays in situ this suggests a mechanism of soil accumulation via atmospheric deposition which is in agreement with stable isotopic evidence the model estimates an age of 6 6 0 4 ma for the total soil profile small discrepancies between the model and observations are likely mainly due to changes in precipitation rates that can impact 10be delivery rates and 10be movement within the profile interpreted in this way the 10be data suggest drying in the atacama after 4 7 ma and returning to an insignificant wet period at 1 ma which was possibly connected to el nino or la nina like climate change

exploration tools for linked porphyry and epithermal deposits example from the mankayan intrusion centered cu au district luzon philippines the mankayan mineral district of northern luzon philippines hosts several significant ore deposits and prospects of various types within an area of similar to 25 km 2 including the far southeast porphyry cu au deposit the lepanto high sulfidation epithermal cu au deposit the victoria intermediate sulfidation epithermal au ag vein deposit the teresa epithermal au ag vein deposit the guinaoang porphyry cu au deposit and the buaki old palidan porphyry cu au prospects all having formed in a period of about 2 m y from similar to 3 ma the geologic units include 1 a basement composed of late cretaceous to middle miocene metavolcanic rocks volcaniclastic rocks 2 the miocene 12 to 13 ma tonalitic bagon intrusive complex 3 the pliocene similar to 2 2 to 1 8 ma imbanguila dacite porphyry and pyroclastic rocks and 4 postmineralization cover rocks including die similar to 1 2 to 1 0 ma bato dacite porphyry and pyroclastic rocks and the similar to 0 02 ma lapangan tuff extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the imbanguila dacite formation consists of quartz alunite pyrophyllite or diaspore with local zones of silicic alteration and a halo of dickite kaolinite the alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps the northwest striking portion is similar to 4 km long and hosts the lepanto enargite au ore deposit also controlled by the lepanto fault the lepanto epithermal deposit is related to the underlying far southeast porphyry the quartz alunite alteration halo of lepanto is contemporaneous with the similar to 1 4 ma potassic alteration of the porphyry there are also silicic advanced argillic alteration patches similar to 600 m above the far southeast orebody at the present surface these are interpreted to be perched alteration there is no systematic mineralogical or textural zoning in the lepanto lithocap that indicates direction to the intrusive source most surface samples of the lithocap contain less than 50 ppb au despite many being less than a few hundred meters from underground cu au ore this study found that several characteristics of the lepanto lithocap change systematically with distance from the causative intrusion the alunite absorption peak at similar to 1 480 nm in the short wavelength infrared swir spectrum shifts to higher wavelengths where the sample is closer to the intrusive center due to higher na and lower k content in the alunite published experimental studies indicate that high na na k is related to higher formation temperature high ca alunite including huangite also occurs at locations proximal to the intrusive center alunite mineral composition analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that the pb content decreases toward the intrusive center whereas sr la sr ph and la pb increase markedly whole rock compositions using only nonmineralized taken as cu similar to 350 m above the upper extent of the veins an airborne geophysics survey indicates that the far southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite destructive phyllic alteration such low magnetic anomalies on the margin of a large lithocap elsewhere may deserve attention the directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry epithermal districts

tectonic fabric of sierra leone west africa implications for mesozoic continental breakup a lineament map interpreted from landsat images has been integrated with available geological and geophysical data from both offshore and onshore regions of sierra leone the lineament patterns are related to intraplate and plate marginal reaction of pre existing structures during mesozoic rifting events that resulted in strong tectonic controls on magmatism of four main lineament trends the nnw sse to n s nne ssw and ene wsw trends are directly relatable to archaean fabric in the leo uplift a nw se trend reflects coast parallel late mesozoic dykes that follow the rokelide pan african fabric reactivated archaean nnw and n s trending structures nw se trending faults defining offshore basins are segmented and offset by ene wsw trending continental extensions of ocean fracture zones both the guinea and sierra leone fracture zones have nucleated on ene wsw trending sinistral archaean shear zones in the leo uplift the four lineament trends focused mesozoic magmatic events through protracted reactivation spatial and geometric relationships between the magmatic provinces and tectonic fabric indicate that intraplate deformation occurs far inland during rifting events the angular relationships between the permo triassic ne trending guinea belt the jurassic triassic nw se trending coast parallel dykes and the ene wsw trending ocean fracture zones centred on the eariy jurassic freetown basic igneous complex suggest that the sierra leone liberia continental margin evolved as an obliquely sheared rift rift transform passive margin during mesozoic continental breakup

microthermometry of enargite hosted fluid inclusions from the lepanto philippines high sulfidation cuau deposit abstract the spatial relation between porphyry and high sulfidation epithermal deposits is particularly well revealed in the mankayan mineral district of northern luzon philippines where the lepanto high sulfidation cu au deposit lies over and adjacent to the far southeast fse porphyry cu au deposit consequently a study was undertaken to characterize the fluids responsible for epithermal mineralization in this environment the ore stage at lepanto consists of enargite luzonite cu 3 ass 4 pyrite tennantite tetrahedrite and chalcopyrite infrared petrography of the enargite reveals variable transparency with growth banding and twinning visible in euhedral specimens two phase liquid vapor fluid inclusions occur as primary and secondary types ranging from t h of fluid inclusions in enargite were measured from within the lateral 3 0 km and vertical 0 5 km extent of the enargite mineralization these values show a cooling trend toward the northwest away from the area over the porphyry deposit with average t h ranging from 285 c proximal to 166 c distal ice melting temperatures t m were measured using a cycling technique as ice was usually not visible in frozen inclusions apparent salinities range from 4 5 to 0 2 eq wt nacl with samples from the margins of the deposit showing a general decrease in apparent salinity with lower t h secondary fluid inclusions in quartz phenocrysts tend to have a higher average t h and lower apparent salinities compared to enargite hosted inclusion fluids from the same locations several samples of pyrite are also transparent to ir radiation and show internal features such as growth banding and in one instance a two phase liquid vapor fluid inclusion this inclusion yielded a salinity of 1 2 eq wt nacl there is a large discrepancy in t h and apparent salinities between the enargite mineralization and the subjacent porphyry deposit despite contemporaneous formation suggesting that the hot 500 c hypersaline magmatic brines associated with porphyry mineralization did not directly ascend to the elevation of the enargite deposit however absorbtion of magmatic vapors into overlying meteoric water may have created the mineralizing fluid of the lepanto deposit as this liquid moved to the northwest along the lepanto fault it was cooled and diluted by mixing with groundwater resulting in enargite deposition

the tropical tropopause and the el nino of 1982 1983 an earlier study of the behavior of the tropical tropopause during 1982 is extended through 1984 the earlier study focused on the influence of the el chichon volcanic eruption but it also considered the influence of the 1982 1983 el nino event during its onset phase in the latter half of 1982 here we present anomalies of tropopause height tropopause potential temperature and lower stratospheric potential temperature through 1984 these anomalies clearly show a much warmer than normal tropopause potential temperature over the western tropical pacific associated with el nino the abnormally warm tropopause potential temperature which was evident in late 1982 reaches a peak in early 1983 and continues abnormally warm until about october 1983 during this period the tropopause is also abnormally high but the lower stratospheric potential temperature is near normal

10be spikes in plio pleistocene cyclothems wanganui basin new zealand identification of the local flooding surface lfs marine shelf sediments of the wanganui basin castlecliff section spanning oxygen isotope stages 21 17 ca 920 680 ka contain spikes of enriched 10be concentrations and enhanced 10be 9be ratios up to 10 background values the 10be spikes do not coincide precisely with peaks in carbonate content and grainsize or with changes in bulk rock chemical composition rather they appear in the sequence a little above the base of each cyclothem at the presumed location of the local flooding surface lfs they therefore originated in response to seafloor sediment starvation during transgression and not from ice sheet melting biogenic scavenging or geomagnetic intensity changes as has been suggested previously for 10be spikes in some deep sea or continental margin sequences

increased production of cosmogenic 10be during the last glacial maximum beryllium 10 half life 1 5 myr is produced by spallation of nitrogen and oxygen atoms by cosmic rays in the upper atmosphere its production rate is proportional to the flux of cosmic rays which is modulated by solar activity and the strength of the earth s magnetic field1 2 weakening of the magnetic field allows more cosmic rays to impinge on the earth s atmosphere thereby increasing 10be production here we report that the ocean wide average accumulation rate of 10be in pacific sediments which reflects the global average production rate of 10be ref 3 was at least 25 greater during the height of the most recent ice age 24 000 16 000 yr ago than during the holocene the past 10 000 yr the higher production rate of 10be records the lower intensity of the geomagnetic field during that period and is consistent with the hypothesis developed to explain the younger 14c ages of fossil corals compared with ages obtained by u th dating4 these results also point to a more general need to consider variations in production rate in geochronological studies using other cosmogenic nuclides

shallow to near surface vein type epithermal gold mineralization at lalab in the sibutad gold deposit zamboanga del norte mindanao philippines abstract the sibutad vein type epithermal gold deposit is the most promising economically feasible gold mineralization found in recent years in zamboanga del norte province in zamboanga peninsula mindanao island the sibutad gold deposit occurs in pliocene to pleistocene volcanic rocks resting on a deformed island arc block to the east of the tectonically active sindangan cotabato daguma lineament the host rocks are the malindang volcanics composed of lower and upper members which are both intruded by andesite porphyry the lower member is made up of andesite flows dacite tuff and tuffite whereas volcanic breccia and tuff breccia characterize the upper member the sibutad gold deposit is subdivided into the larayan and lalab prospects in lalab which is the prospect studied hydrothermal activity and gold mineralization occur in the andesite flows the geology alteration and mineralization of the lalab orebody are of adularia sericite type that suggests the gold was precipitated from reduced near neutral ph solutions within a shallow to near surface environment the following events produced the lalab orebody 1 pre breccia wallrock alteration 2 hydrothermal brecciation 3 post breccia wallrock alteration and 4 gold mineralization gold precipitated in quartz veins was a response to boiling followed by fluid mixing prolific gold zones occur between 30 m below sea level and 200 m above sea level

structures that accommodated differential vertical axis rotation of the western transverse ranges california 1 new paleomagnetic and structural data from the northwestern transverse ranges of california define the location geometry and kinematics of structures that facilitated differential vertical axis rotation paleomagnetic declinations in the southern coast ranges indicate negligible amounts of vertical axis rotation which contrasts sharply with data from rocks of the same age in the western transverse ranges that record approximately 90 of clockwise rotation since early miocene time this change in paleomagnetic declinations occurs across an east west trending zone of reverse faults and folds that includes the western big pine pine mountain fault the santa ynez fault and the structures in between the structures in this zone exhibit increased amounts of shortening to the west such that the zone closed in a fan like fashion resulting in rotation of the southern edge with respect to the northern edge the new data and interpretations refine previous models of vertical axis rotation in southern california by describing the deformation present at rotation boundaries that allowed distinct areas to rotate relative to the surrounding crust

late cenozoic tectonics of the northwestern san bernardino mountains southern california the late cenozoic structural and stratigraphic history of the northwestern san bernardino mountains supports two distinct episodes of uplift in late miocene to earliest pliocene and quaternary time that we hypothesize are related to movements on low angle structures beneath the range in this paper we document the nature distribution and timing of late cenozoic deformation and deposition in the northwestern san bernardino mountains and we illustrate the neotectonic evolution of the area in a series of interpretive paleotectonic block diagrams in the first episode of deformation late miocene to earliest pliocene motion on the south southwest directed squaw peak thrust system disrupted drainage in pre existing miocene nonmarine basins and uplifted the western third of the present range to form the ancestral san bernardino mountains crystalline rocks of the san bernardino mountains were thrust southward across the present site of the san andreas fault between 9 5 and 4 1 ma at a time when the san gabriel fault was the active strand of the san andreas transform system we speculate that the liebre mountain crystalline block at the northern margin of the ridge basin may be the missing upper plate of the squaw peak thrust now offset along the san andreas fault the second episode of deformation began with uplift of the northern plateau of the modern san bernardino mountains on north directed range front thrusts in early pleistocene time between 2 0 and 1 5 ma synchronous uplift of the northern plateau recorded in early pleistocene fanglomerates on the northwestern margin of the range is interpreted to be the result of movement of a relatively coherent crustal block northward up a south dipping detachment ramp beneath the central range in middle pleistocene time activity on the northern range front began to wane and the locus of uplift shifted to a narrow zone of arching and northward tilting adjacent to the san andreas fault which subsequently migrated rapidly northwestward along the san andreas fault from the western san bernardino mountains into the northeastern san gabriel mountains we attribute this pattern of deformation to the passage of a bulge or strike slip ramp attached to the southwest side of the san andreas fault at depth

10be in polar ice data reflect changes in cosmic ray flux or polar meteorology we have theoretically estimated the expected changes in the global cosmic ray production of 10be in the atmosphere with changes in solar activity and the consequent variations in its fallout in the polar regions the global 10be production rate is found to be about 20 higher during periods of very low solar activity compared to the average solar modulation level observed during the past 3 solar cycles the stratospheric 10be fallout pattern has been derived using the fallout data for 90sr as an analog this fallout shows an amplitude attenuation by a factor of about three at 70 the higher the latitude the higher the attenuation the results have been compared with the long time series available for 10be in polar ice in greenland and in antarctica 70 78 latitude it is concluded that the observed variations in 10be concentrations in ice cores are primarily due to climatic changes for both short and long period variations thus 10be data can be used as a proxy for climate induced meteorological changes in the polar region

kinematic evolution of the olinghouse fault and the role of a major sinistral fault in the walker lane dextral shear zone nevada usa abstract the olinghouse fault is a highly oblique sinistral fault in the northern walker lane dextral shear zone in this study we use geologic mapping and structural analysis of 56 fault surfaces and several folds to constrain the evolution and kinematic role of the olinghouse fault within the walker lane we document a two stage development of the olinghouse fault with an early phase of extension between 12 and 10 ma followed by left lateral shear with a component of extension beginning at 8 to 5 ma the sinistral olinghouse fault has played a relatively complex kinematic role in the evolution of the walker lane including acting as a boundary for clockwise vertical axis block rotation a strain transfer zone between loci of extension and a structural domain boundary redistributing strain between the carson and pyramid lake domains the fault has accumulated 2 5 3 km of left lateral offset at an average rate of 0 3 0 6 mm yr the complexity of this sinistral normal fault zone within a broad zone of dextral shear was likely influenced by the propagation of walker lane dextral shear into a zone of pre existing crustal structure

geothermal exploration with hymap hyperspectral data at brady desert peak nevada abstract we explore the use of hymap hyperspectral mapper to remotely map unique geothermal indicator minerals over the brady desert peak geothermal fields geothermal related minerals and rocks such as sinter tufa and sulfates display diagnostic characteristics in the visible and shortwave infrared their presence and distribution can be used to guide more detailed field work for geothermal exploration the brady desert peak geothermal fields are located about 80 km east of reno nevada in the hot springs mountains north northeast striking en echelon faults offset tertiary volcanic and lacustrine rocks two geothermal power plants produce electricity from two separate geothermal systems one with numerous fumaroles and mudpots the other showing no active surface expression of geothermal activity surface occurrences of gypsum calcium carbonate hematite and opaline silica were identified at both sites with the hyperspectral data these minerals when considered together are indicative of geothermal activity at both sites mapping results were synthesized with other spatial data in a geographic information systems gis database that was used to help draw structural interpretations of faulting and fault controls at the brady desert peak area the same processing methods can be applied to new hyperspectral data sets for future exploration in the great basin especially in areas that lack obvious thermal expressions

greenland ice10be concentrations and average precipitation rates north of 40 n to 45 n abstract a model of 10 be deposition within the subarctic and arctic is developed based on the behavior of 90 sr in the troposphere measured 10 be fluxes based on analyses of 10 be in one year s snow fall 1979 1980 from the dye 3 site in southwest greenland and on published data and predicted 10 be fluxes based on the 10 be deposition model agree these results indicate that with regard to 10 be the troposphere north of 40 n to 45 n presently behaves as if it is well mixed and that the average precipitation rate within that reservoir controls in large part the concentration of 10 be in greenland ice inversion of the greenland ice core 10 be concentration record with the aid of the model indicates 1 that the average precipitation rate in the subarctic and arctic was lower than the present rate during the maunder minimum of solar activity and higher than the present rate during the wolf and sporer solar activity minimums and 2 that during the wisconsin holocene transition the average precipitation rate in the subarctic and arctic was about one third the present precipitation rate

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

meteoric cosmogenic beryllium 10 adsorbed to river sediment and soil applications for earth surface dynamics abstract rainfall scavenges meteoric cosmogenic 10be from the atmosphere 10be falls to the earth s surface where it binds tightly to sediment particles in non acidic soils over the life span of those soils as such meteoric 10be has the potential to be an excellent geochemical tracer of erosion and stability of surfaces in a diverse range of natural settings meteoric 10be has great potential as a recorder of first order erosion rates and soil residence times even though this tracer was first developed in the late 1980s and showed great promise as a geomorphic tool it was sidelined in the past two decades with the rise of the sister nuclide in situ 10be which is produced at a known rate inside quartz minerals since these early days substantial progress has been made in several areas that now shed new light on the applicability of the meteoric variety of this cosmogenic nuclide here we revisit the potential of this tracer and we summarize the progress 1 the atmospheric production and fallout is now described by numeric models and agrees with present day measurements and paleo archives such as from rain and ice cores 2 short term fluctuations in solar modulation of cosmic rays or in the delivery of 10be are averaged out over the time scale soils accumulate 3 in many cases the delivery of 10be is not dependent on the amount of precipitation 4 we explore where 10be is retained in soils and sediment 5 we suggest a law to account for the strong grain size dependence that controls adsorption and the measured nuclide concentrations and 6 we present a set of algebraic expressions that allows calculation of both soil or sediment ages and erosion rates from the inventory of meteoric 10be distributed through a vertical soil column the mathematical description is greatly simplified if the accumulation of 10be is at a steady state with its export through erosion in this case a surface sample allows for the calculation of an erosion rate explored further this approach allows calculation of catchment wide erosion rates from river sediment similar to the approach using 10be produced in situ in contrast to the in situ 10be approach however these analyses can be performed on any sample of fine grained material even where no quartz minerals are present therefore this technique may serve as a tool to date sediment where no other chronometer is available to track particle sources and to measure earth surface process rates in soil suspended river sediment and fine grained sedimentary deposits

seismicity and fault kinematics through the eastern transverse ranges california block rotation strike slip faulting and low angle thrusts hypocentral locations and first motion data from the southern california seismic network are used to infer the present pattern of deformation along the southern san andreas fault the study area lies between the san jacinto fault and desert hot springs and includes the san bernardino mountains and san gorgonio pass this region has some of the deepest earthquakes observed anywhere along the entire san andreas system exhibits a complex surface geology characterized by both right and left lateral faults has high topographic relief as a result of recent uplift and is a potential site for the nucleation of a great earthquake although this area is unusually seismogenic little activity can be directly associated with major throughgoing faults seismicity is also generally absent in the upper 5 km the predominant style of faulting above 10 12 km is oblique slip with a large reverse component the spatial distribution of relocated hypocenters and first motion data suggests the presence of a system of left slip faults striking northeast this pattern of faulting in conjunction with an unusual set of normal and reverse focal mechanisms is interpreted as the clockwise rotation of a small set of crustal blocks subject to regional right lateral shear at depths greater than about 10 km seismicity defines a wedge shaped volume undergoing pervasive internal deformation on a combination of strike slip and low angle thrust faults velocity structures determined from earthquake arrival times suggest a low velocity zone at about 10 km below the san bernardino mountains but not below the san jacinto mountains this is nearly the same depth as the transition between the two layers of different kinematic behavior seen south of the mill creek mission creek branch of the san andreas fault and the maximum depth of seismicity seen north of that fault the low velocity zone and the transition between block rotations and the deeper deformation may thus correspond to a detachment under much of this region and would imply that the overthrust san bernardino mountains are allochthonous the present pattern of seismic deformation in shocks of small to moderate size may only characterize the interval between large earthquakes and may change systematically as the region prepares to accommodate large right lateral displacements

deformation along the yammuneh the restraining bend of the dead sea transform paleomagnetic data and kinematic implications a simple geometrical model shows that the plate margin along the restraining bend segment of the transform plate boundary be deformed in order to accommodate overlap of the crust this model predicts both the maximum width of the deformed zone and the magnitude of deformation when the general geometry of the plate margin is known as well as the plate slip vector and the amount of cumulative displacement this idea has been tested along the plate margin of the yammuneh restraining bend of the dead sea transform the plate margin has been deformed by nne folding parallel to the restraining bend and by east west trending right lateral strike slip faults paleomagnetic measurements yield counterclockwise rotation of r r 61 0 9 6 and f f 23 4 17 2 the paleomagnetic rotational data and fault kinematic suggest that the mechanism which accommodates regional left lateral shear is simultaneous right lateral strike slip faulting on secondary faults and block rotation the magnitude of deformation is the same as that predicted by the model which is 100 shortening in a direction parallel to the plate slip vector and negligible deformation in a direction parallel to the transform the large amount of rotation implies that probably more than one fault set is involved and present day seismic activity is the current manifestation of this crustal deformation process if this prediction is correct then the current deformation of the plate margin is accommodated by more favorable newly formed nnw right lateral strike slip faults