modeling the role of sodic alteration in the genesis of iron oxide copper gold deposits eastern mount isa block australia liberation of iron and potassium by widespread postmetamorphic albitization of country rocks was one of the likely contributing processes in the formation of both barren and mineralized magnetite chalcopyrite biotite gold hematite clinopyroxene actinolite apatite ironstones in the cloncurry district of the proterozoic mount isa block whole rock geochemical data indicate nearly immobile al ga ti zr during transformation of a variety of least altered rocks toward albitite the data indicate that the addition of na from a brine to the rock accompanied the loss of fe k ba rb ca sr co v mn pb and zn from those altered rocks and enrichment in the brine but that cu was not systematically stripped from a variety of wall rocks during albitization conversely the formation of metasomatic ironstones the immediate hosts to some cu au ores involves addition of most of the same elements that were lost during albitization the correlation between intensity of alteration its distribution and timing e g in breccias cored by ca 1530 1500 ma granitoids and convergence of all rock types toward magmatic stable isotope values provides strong evidence for a substantial component of igneous derived fluid simulations of the albitization process were carried out isothermally at 550 c and 350 mpa and polythermally from these conditions down to 400 c and 200 mpa using the gibbs minimization method with hch software and the unitherm database both simple fluid rock mixing models and more complicated reactor style algorithms used a range of input fluids from fluids equilibrated fluid with two feldspar granite through to na k ratios consistent with fluid inclusion results and geochemical data for initially unaltered wall rocks the apparent paradox of widespread albitization resulting from fluid released by two feldspar granites can be explained by relatively small shifts away from the k feldspar albite equilibrium curve and even isothermal model fluids derived from two feldspar granites produce albitites in calc silicate rocks outboard of granite proximal k feldspar clinopyroxene skarns matching field patterns those models with fluid na k ratios similar to those of fluid inclusions produced the most realistic alteration assemblages dominated by albite for both isothermal conditions and decreasing temperature which approximate those observed in the field pixe and microthermometric data on fluid inclusions from quartz in two feldspar quartz monzonite and pegmatite at the top of the mount angelay pluton indicate bulk na k molar ratios in the fluid of between 10 and 20 considerably higher than our thermodynamically calculated values for fluid in equilibrium with two feldspar granite of around 3 at 550 c 350 mpa such shifts may have been attained by admixture of magmatic hydrothermal fluid with small amounts of nacl brines trapped along grain boundaries in scapolite bearing calc silicate wall rocks by fluid immiscibility due to high initial co2 contents in the felsic intrusions by contributions from mafic magmas or from dissolution of salt rich layers into the intrusions prior to crystallization and fluid release with increasing amounts of fluid rock interaction in the models the fluids were enriched in k fe and ca approaching compositions observed in fluid inclusions in the ore deposits these fluids reacted with pelitic rocks which are common ore hosts would produce magnetite clinopyroxene biotite actinolite alteration at high temperature similar to the proximal alteration around ore deposits we infer that precipitation of sulfides in the cu au deposits was the result of mixing of cu bearing brine of ultimately magmatic origin but modified extensively via albitization with sulfur bearing fluids or reaction of the brine with sulfur bearing rocks when cu was absent from the initial magmatic fluid barren ironstones may have been the result

active fault motion in a coastal wetland matagorda texas abstract active growth faults contribute to the subsidence of deltaic basins around the world and can significantly augment local rates of relative sea level rise which can inundate and drown wetlands little information exists on the temporal frequency and spatial magnitude of motion along these faults our objective was to quantify fault activity and displacement at multiple time scales in a salt marsh wetland on the east matagorda peninsula texas we present evidence of this activity that includes remotely sensed aerial imagery lidar data ground penetrating radar data shallow seismic data lithostratigraphic and biostratigraphic evidence from core data and sub centimeter gps and survey monitoring the results support the interpretation that the matagorda fault is currently active and has been active in the past subsurface data to depths of 150 m displays evidence of disrupted strata at the fault plane as well as thicker strata on the downthrown side of the fault in the shallow subsurface down to 3 m of depth vertical displacement in stratigraphic markers and surface deformation exhibits a sinusoidal pattern that runs perpendicular to the fault plane which we interpret to represent fault propagation folding maximum throw on this fault is estimated at 0 75 m over the last 40 50 years we also recorded a vertical drop of 0 208 m in the span of a single year at a location close to the fault on its downthrown side records of yearly elevation change also show evidence of ongoing fault propagation folding we conclude that whereas the surface at the matagorda fault moves intermittently up and down at the yearly time scale fault displacement manifests as a sinusoidal pattern of displacement and deformation which has been integrated into the stratigraphic record at decadal to millennial time scales this study presents a rare look into active motion and details its effects on the modern evolution of unconsolidated sedimentary surfaces

gold remobilisation and formation of high grade ore shoots driven by dissolution reprecipitation replacement and ni substitution into auriferous arsenopyrite abstract both gold rich sulphides and ultra high grade native gold oreshoots are common but poorly understood phenomenon in orogenic type mineral systems partly because fluids in these systems are considered to have relatively low gold solubilities and are unlikely to generate high gold concentrations the world class obuasi gold deposit ghana has gold rich arsenopyrite spatially associated with quartz veins which have extremely high localised concentrations of native gold contained in microcrack networks within the quartz veins where they are folded here we examine selected samples from obuasi using a novel combination of quantitative electron backscatter diffraction analysis ion microprobe imaging synchrotron xfm mapping and geochemical modelling to investigate the origin of the unusually high gold concentrations the auriferous arsenopyrites are shown to have undergone partial replacement 15 by au poor nickeliferous arsenopyrite during localised crystal plastic deformation intragranular microfracture and metamorphism 340 460 c 2 kbars our results show the dominant replacement mechanism was pseudomorphic dissolution reprecipitation driven by small volumes of an infiltrating fluid that had relatively low s 2 and carried aqueous nicl 2 we find that arsenopyrite replacement produced strong chemical gradients at crystal fluid interfaces due to an increase in s 2 during reaction which enabled efficient removal of gold to the fluid phase and development of anomalously gold rich fluid potentially 10 ppm or more depending on sulphur concentration this process was facilitated by precipitation of ankerite which removed co 2 from the fluid increasing the relative proportion of sulphur for gold complexation and inhibited additional quartz precipitation gold re precipitation occurred over distances of 10 m to several tens of metres and was likely a result of sulphur activity reduction through precipitation of pyrite and other sulphides we suggest this late remobilisation process may be relatively common in orogenic belts containing abundant mafic ultramafic rocks which act as a source of ni and co scavenged by chloride bearing fluids both the preference of the arsenopyrite crystal structure for ni and co rather than gold and the release of sulphur during reaction can drive gold remobilisation in many deposits across broad regions

ribbon cliff landslide washington and the earthquake of 14 december 1872 abstract estimates of the epicentral location and maximum intensity of the earthquake of 14 december 1872 the largest and oldest historic earthquake documented in the pacific northwest are controversial largely because the estimates are based on ground effects the ribbon cliff landslide is one of the more critical ground effects used to argue that the epicenter was in the vicinity of lake chelan in central washington sketchy historical accounts link the ribbon cliff landslide to the 1872 earthquake but a subsequent study disputed the historical accounts and on the basis of dendrochronology concluded that the landslide occurred more than 100 yr prior to the earthquake however quaternary stratigraphic relations and the results of multiple dating techniques reported here indicate that the main ribbon cliff landslide probably occurred within a 14 yr period that includes the time of the 1872 earthquake although our study supports the historical accounts that link the landslide to the december 1872 earthquake it does not prove that seismic shaking triggered the landslide geomorphic and stratigraphic relations show that ribbon cliff has a long and complex history and that the landslide was not primarily a rockfall rockslide that originated from the cliff itself as some believe but rather that the main failure occurred in colluvium that had accumulated beneath the cliff four colluvial units and two volcanic ash deposits the mazama ash bed erupted about 6 8 ka and the mount st helens set w erupted about 1480 a d underlie the slopes below ribbon cliff most of the colluvium involved in the landslide accumulated after deposition of the mazama ash bed loss of support at the foot of the colluvial wedge because of undercutting by the columbia river probably was an important contributing factor to slope failure

exsolution of chalcopyrite from bornite digenite solid solution an example of a fluid driven back replacement reaction sulfide minerals host most of the world s supplies of metals such as cu ni co zn pb or mo and understanding their crystallization dissolution and textural evolution is key to understanding the formation of mineral deposits metal recovery via metallurgy and their environmental impact despite the prominence of hydrothermally formed sulfide minerals the interpretation of textures in sulfide petrology relies mainly on comparison with results from experiments conducted under dry conditions here we show experimentally that the exsolution of chalcopyrite cufes2 lamellae from a bornite cu5fes4 digenite cu9s5 solid solution bdss is a back reaction which occurred during low temperature annealing 150 c following initial replacement of parent chalcopyrite by bdss at 300 c the back reaction is rapid days and its progress is catalyzed by small amounts of fluid present in the porosity within the bdss this porosity initially results from the formation of bdss via the replacement of parent chalcopyrite by an interface coupled dissolution reprecipitation mechanism during annealing bdss first breaks down into bornite and digenite via solid state exsolution the bornite digenite assemblage then exsolves chalcopyrite in local patches we discovered strikingly similar textures in iron oxide copper gold iocg deposits from south australia in these samples the fluid driven nature of the exsolution reaction is reflected by the fact that the chalcopyrite lamellae propagate around cracks and fractures within bornite as in our experiments most of this natural bornite formed via replacement of chalcopyrite these reactions are controlled by kinetic factors e g relative nucleation rates of cu fe sulfides presence of porosity rather than equilibrium thermodynamics but result in final assemblages and textures that may not be distinguishable from those evolving from equilibrium processes under dry conditions

ore minerals down to the nanoscale cu fe sulphides from the iron oxide copper gold deposit at olympic dam south australia abstract cu fe sulphide mineral assemblages from the olympic dam od fe oxide cu u au ag deposit south australia are studied down to the nanoscale to explore the potential these minerals have for understanding genetic processes such as primary deposit zonation cu fe sulphide pairs brown bornite associated with chalcopyrite bornite chalcopyrite zone and symplectites of purple bornite with species from the chalcocite group cu2 xs bornite chalcocite zone co define an upwards and inwards deposit scale zonation at od in the bornite chalcocite zone there is also an increase in the proportion of chalcocite relative to bornite within the symplectites towards upper levels in this case two phase cu2 xs assemblages are also present as anisotropic hexagonal chalcocite cch with lamellar exsolutions of digenite distinguishable at the m scale using compositional data electron microprobe combined with transmission electron microscopy tem study of foils prepared in situ via focused ion beam fib sem we show that cu fe sulphides from different ore zones feature nanoscale intergrowths lattice defects superstructure domains na and antiphase boundary domains apbs that can be interpreted as due to exsolution coarsening and phase transformation during cooling from high t solid solutions in the system cu fe s and sub systems according to published phase diagrams brown bornite cu fe s 5 contains pervasive lamellae of chalcopyrite which extend down to the nanoscale such specimens appear homogeneous at the m scale purple bornite cu fe s 300 c high t phases cu poor digenite followed by cooling along distinct paths down to

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

complex mineral zoning patterns caused by ultra local equilibrium at reaction interfaces chemically zoned minerals are useful records of temporal variations in ambient conditions and bulk chemical composition of the fl uid from which the minerals precipitate in fl buffered systems zoning of mineral compositions is expected to refl ect directly the evolution of fl composition here we show that during rapid fl uid rock reactions ultra local equilibrium can form complex mineral zoning patterns even when the overall system is highly fl uid buffered we reacted cleaved calcite single crystals with aqueous arsenate phosphate solutions with molar ratios of as as p between 0 01 and 0 15 at 250 c and water saturated pressure we fithat complex zoning patterns and solid solution between hydroxylapatiteand arsenate bearing hydroxylapatite that pseudomorphically replaced calcite formed within hours and these zoning patterns were destroyed within days during secondary reactions we propose a two stage reaction process in the formation of the fi nal reaction product 1 on an hour time scale calcite is dissolved and replaced by compositionally heterogeneous apatite the thin reaction interface fllayer becomes extremely enriched in arsenic at an ultra local scale as the reaction removes phosphate faster than the interface fl uid can re equilibrate with the bulk fl uid 2 the heterogeneous apatite is replaced by homogeneous apatite that refl ects the bulk fl uid composition over a longer days time scale through interface coupled dissolution precipitation this paper highlights the complexity that can arise from ultra local fl uid composition variations due to rapid fl uid rock interaction in a short lived fl uid fl ow event for example during a seismic cycle subsequent interpretation of complex zoning patterns as refl ecting the evolution of bulk fl uid would be erroneous

quantified multi scale x ray fluorescence element mapping using the maia detector array application to mineral deposit studies the maia large solid angle detector array and imaging system is capable of collecting high resolution images of up to 100 m pixels in size with dwell times of less than 0 2 ms per pixel and thus it is possible to document variation in textures associated with trace element chemistry by collecting quantified elemental maps of geological samples on the scale of entire thin sections in a short time frame 6 8 hr the analysis is nondestructive and allows variation to be recognised on a centimetre scale while also recognising zonations at the micron scale

significance of active growth faulting on marsh accretion processes in the lower pearl river louisiana abstract neotectonic processes influence marsh accretion in the lower pearl river valley active growth faults are suggested by groupings of ponded river channel sections transverse and linear river channel sections and down and across valley contrasts in channel sinuosity seismic profiles identified several likely fault induced structural anomalies two of which parallel the axes of surface distributary networks lithostratigraphy and biostratigraphy of six cores from across a suspected fault in the west middle river combined with 14 c based age control yielded evidence of vertical offsets indicating that this river section is on the plane of a growth fault these data were used to estimate fault slip rates over two time intervals 1 2 mm y over the last 1300 yr and 0 2 mm yr 1 over the last 3700 yr and delineated a sinusoidal pattern of deformation moving distally from the fault which we interpret as resulting from fault propagation folding higher rates of sediment accumulation of the order of cm yr 1 from 210 pb xs and 137 cs activity data on the down thrown side are consistent with sedimentary response to increased accommodation space and mass based sediment accumulation rates g cm 2 yr 1 exhibit a pattern inverse of that shown by fault driven sinusoidal deformation we contend that near surface growth faults are critically important to driving accretion rates and marsh response to sea level rise

subsidence of the texas coast inferences from historical and late pleistocene sea levels abstract changes in sea level observed at tide gauges are caused by actual changes in water level and by changes in elevation at the observing station recent research has focused on the relationship between climatic change and sea level but vertical land movement can be just as important particularly in subsiding sedimentary basins the purpose of this study is to compare long term rates of subsidence estimated from upper pleistocene strata along the central texas coast with historical subsidence rates from the same area obtained from geodetic surveys and tide gauge data this comparison shows that historical subsidence rates are much greater than long term averages and are equal or greater than actual sea level change along the texas coast south of galveston bay long term 10 5 yr subsidence rates were estimated by establishing the extent of marine marine influenced and nonmarine strata within the upper pleistocene beaumont formation in the copano bay area of the central texas coast and comparing the maximum elevation of in place marine influenced deposits with published maximum sea level estimates of 5 8 m above mean sea level msl from correlative well dated coral terraces from stable and uplifted areas in place shell bearing horizons deposited at or below sea level occur no higher than 2 m msl in the copano bay area suggesting that there has been no more than 6 m of subsidence since the probable time of deposition during the sangamon interglacial at 120 ka the long term average subsidence rate for this part of the texas coast is thus 0 05 mm yr or less historical subsidence rates were obtained by 1 1 calculating relative elevation changes between national geodetic survey first order leveling surveys conducted in the early 1950s with those conducted in the late 1970s to early 1980s 2 2 normalizing the relative elevation differences between surveys to annual rates of change relative to an arbitrarily chosen benchmark 3 3 referencing these lines to sea level at three tide gauges and 4 4 comparing calculated rates of relative sea level rsl rise along the lines with estimates of eustatic sea level esl rise rates of rsl rise for the texas coast south of galveston bay were generally 4 8 mm yr locally rates were as high as 23 mm yr these rates are significantly higher than global averages of 1 mm yr much of the difference is probably caused by subsidence of the texas coastal zone at rates of 1 22 mm yr or 20 440 times the long term average of 0 05 mm yr the highest subsidence rates were found locally where there has been historical water level decline in shallow aquifers lower subsidence rates of 3 7 mm yr occur regionally where groundwater decline is minimal or nonexistent increased subsidence over the long term average in these areas may be caused by pressure decline in underlying oil and gas reseivoirs

coupling between mineral replacement reactions and co precipitation of trace elements an example from the giant olympic dam deposit abstract the mechanisms of scavenging of minor elements in reactive fluid dominated systems control the distribution nature concentration and reactivity of economically valuable or deleterious elements in many environments ranging from hydrothermal ore deposits to sedimentary basins here we show that in a high grade cu u ore from the super giant olympic dam ore deposit remobilized u was scavenged during the fluid driven replacement of chalcopyrite cufes2 by bornite cu5fes4 hydrothermal experiments show that the pseudomorphic replacement of chalcopyrite by bornite proceeded via an interfaced coupled dissolution reprecipitation icdr reaction mechanism with further bornite growing via overgrowth addition of u vi to the experimental fluid resulted in scavenging of u in the form of nano to micro particles of uraninite uraninite precipitation occurred concurrently with replacement resulting in abundant uraninite decorating the initial surface of the parent chalcopyrite grain as well as the coarse porosity that developed within overgrowth bornite our results highlight the importance of disequilibrium or local equilibrium in controlling the endowment of u in complex ores under far from equilibrium fluid dominated conditions e g during seismic or eruptive events fast fluid movements associated with brecciation and or faulting can lead to fast mineral reactions the resulting ultra local conditions e g surface of reacting mineral reaction induced porosity play an important role in controlling the precipitation of minor elements u in this case and interpretation of precipitation mechanisms as reflecting the evolution of bulk fluid may be erroneous

uraninite from the olympic dam iocg u ag deposit linking textural and compositional variation to temporal evolution the olympic dam iocg u ag deposit south australia the world s largest known uranium u resource contains three main u minerals uraninite coffinite and brannerite four main classes of uraninite have been identified uraninite occurring as single grains is characterized by high pb and ree y rey but based on textures can be classified into three of these classes typically present in the same sample primary uraninite class 1 is smallest 10 50 m displays a cubic euhedral habit and both oscillatory and sectorial zoning zoned uraninite class 2 is coarser sub euhedral and combines different styles of zonation in the same grain cobweb uraninite class 3 is coarser still up to several hundred micrometers has variable hexagonal octagonal morphologies varying degrees of rounding and features rhythmic intergrowths with sulfide minerals in contrast the highest grade u in the deposit is found as micrometer sized grains to aphanitic varieties of uraninite that form larger aggregates up to millimeter and vein fillings massive class 4 and have lower pb and rey but higher ca nanoscale characterization of primary and cobweb uraninite shows these have defect free fluorite structure both contain lattice bound pb rey which for primary uraninite is concentrated within zones and for cobweb uraninite is within high pb rey domains micro fractured low pb rey domains sometimes with different crystal orientation to the high pb rey domains in the same cobweb grain contain nanoscale inclusions of galena cu fe sulfides and rey minerals the observed pb zonation and presence of inclusions indicates solid state trace element mobility during the healing of radiogenic damage and subsequent inclusion nucleation recrystallization during formula 1 driven percolation of cu bearing fluid tetravalent lattice bound radiogenic pb is proposed based on analogous evidence for u bearing zircon calculating the crystal chemical formula to uo2 stoichiometry the sum of cations m is 1 for most classes but the presence of mono di and trivalent elements rey ca etc drive stoichiometry toward hypostoichiometric m o2 x in the absence of measured o and constraints of hypostoichiometric fluorite structure charge balance calculations showing o deficit in the range 0 15 0 36 apfu is compensated by assumption of mixed u oxidation states crystal structural formulas show up to 0 20 apfu pb and 0 25 apfu rey in classes 1 3 while for class 4 these are an order of magnitude less low pb and rey subcategories of classes 2 and 3 are similar to massive uraninite with 0 2 apfu ca other elements si na mn as nb etc show two distinct geochemical trends 1 across classes 1 3 and 2 class 4 whereby low pb rey sub populations of classes 2 and 3 are part of trend 2 for certain elements plots of alteration factor cao sio2 fe2o3 vs pb u suggest two uraninite generations early high pb rey classes 1 3 and late massive class 4 there is evidence of pb loss from diffusion leaching and or recrystallization for classes 2 3 low pb rey domains micro analytical data and petrographic observations reported here including nanoscale characterization of individual uraninite grains support the hypothesis for at least two main uraninite mineralizing events at olympic dam and multiple stages of u dissolution and reprecipitation early crystalline uraninite is only sparsely preserved with the majority of uraninite represented by the massive aphanitic products of post 1590 ma dissolution reprecipitation and possibly addition of uranium into the system coupled dissolution reprecipitation reactions are suggested for early uraninite evolution across classes 1 to 3 the calculated oxidation state u6 u4 u6 of the early and late populations point to different conditions at the time of formation charge compensation for rey rich early fluids rather than auto oxidation of uraninite late uraninites may have formed hydrothermally at lower temperatures t 250 c 1 embed mml math 1 gif

ore petrography using megapixel x ray imaging rapid insights into element distribution and mobilization in complex pt and u ge cu ores geologic samples are extremely diverse and share a tendency for both heterogeneity and complexity this is especially true for ores which commonly result from a complex interplay of processes in highly dynamic environments in recent years a number of tools allowing the chemical mapping of major e g mineral liberation analysis mla minor e g electron microprobe epma and trace e g laser ablation inductively coupled plasma mass spectrometry la icp ms elements in geologic samples at 1 to 50 m resolution and over mm2 areas have seen rapid development and have become readily available to date the application of synchrotron based x ray fluorescence sxrf mapping has been limited to addressing key questions because of low availability and high cost this paper demonstrates how recent advances in x ray fluorescence detector technology are bringing new possibilities to ore petrology millisecond dwell times allow collection of thin section size maps at resolutions of a few m in hours while improvements in data analysis software simplify the production of quantitative elemental maps based on the imaging of six samples representative of different commodities pt u cu ge and different geologic contexts pge deposit sandstone hosted u deposit vein type polymetallic hydrothermal deposit iron oxide copper gold iocg deposit we demonstrate that megapixel sxrf msxrf can efficiently provide the information necessary to understand metal speciation in the context of thin section scale textural complexity image analysis revealed a number of new results for the studied deposits for example 1 the distribution of micrometer sized pt rich grains and ti mobility during the formation of schistosity at the fifield point prospect new south wales australia 2 the presence of ge contained in organic matter and of hg minerals associated within quartzite clasts in the lake frome u ores south australia 3 confirmation of the two stage ge enrichment in the barrigao deposit with demonstration of the presence of ge in solid solution in the early chalcopyrite portuguese iberian pyrite belt and 4 the enrichment of u during late dissolution reprecipitation reactions in the bornite ores of the moonta and wallaroo iocg deposits south australia these results illustrate that msxrf is a powerful technique for locating nano to microparticles of precious metals pt and trace contaminants e g hg that form distinct micro minerals in addition it is a powerful tool for understanding commodities with relatively low ore grades and complex distribution 100 1 000 ppm e g u ge

the role of deep processes in late 20th century subsidence of new orleans and coastal areas of southern louisiana and mississippi 1 geodetic leveling observations from biloxi ms to new orleans la and water level gauge measurements in the new orleans lake pontchartrain area were analyzed to infer late 20th century vertical motions these data were used to test the validity of previous subsidence rate measurements and the models that predict the location and causes of subsidence water gauges attached to bridge foundations and benchmarks affixed to deep rods that penetrate holocene strata subsided as much as 0 8 m locally between 1955 and 1995 the observed deep seated subsidence far exceeds model predictions and demonstrates that shallow processes such as compaction and consolidation of holocene sediments are inadequate by themselves to explain late 20th century subsidence deep seated subsidence occurring east and north of the normal faults marking the gulf of mexico basin margin can be explained by local groundwater withdrawal and regional tectonic loading of the lithosphere by the modern mississippi river delta mrd sharp changes in subsidence coincide with strands of the basin margin normal faults displacements are consistent with activity and show motions consonant with fault creep deep subsidence of the region to the south including new orleans can be explained by a combination of groundwater withdrawal from shallow upper pleistocene aquifers the aforementioned lithospheric loading and perhaps nongroundwater related faulting subsidence due to groundwater extraction from aquifers 160 to 200 m deep dominated urbanized areas and is likely responsible for helping to lower local flood protection structures and bridges by as much as 0 8 m

omak rock and the 1872 pacific northwest earthquake abstract omak rock is an about 40 ton granite boulder balanced on a narrow support the rock is located in northern washington state in the general vicinity of the 1872 pacific northwest m 7 earthquake the survival of the balanced rock has in the past been used to place limits on peak acceleration and intensity at its location and thus possibly on the epicenter of the earthquake using dynamical analysis i find that the rock could have survived far greater peak ground motion than previously concluded and might well have survived within a few kilometers of the epicenter thus invalidating the earlier conclusions

characterization of porosity in sulfide ore minerals a usans sans study porosity plays a key role in the formation and alteration of sulfide ore minerals yet our knowledge of the nature and formation of the residual pores is very limited herein we report the application of ultra small angle neutron scattering and small angle neutron scattering usans sans to assess the porosity in five natural sulfide minerals violarite marcasite pyrite chalcopyrite and bornite possibly formed by hydrothermal mineral replacement reactions and two synthetic sulfide minerals violarite and marcasite prepared experimentally by mimicking natural hydrothermal conditions usans sans data showed very different pore size distributions for these minerals natural violarite and marcasite tend to possess less pores in the small size range 100 nm compared with their synthetic counterparts this phenomenon is consistent with a higher degree of pore healing or diagenetic compaction experienced by the natural violarite and marcasite surprisingly nanometer sized 20 nm pores were revealed for a natural pyrite cube from la rioga spain and the sample has a pore volume fraction of 7 7 both chalcopyrite and bornite from the massive sulfide assemblage of the olympic dam deposit in roxby downs south australia were found to be porous with a similar pore volume fraction 15 but chalcopyrite tends to have a higher proportion of nanometer size pores centered at 4 nm while bornite tends to have a broader pore size distribution the specific surface area is generally low for these minerals ranging from 0 94 to 6 28 m2 g and the surfaces are generally rough as surface fractal behavior was observed for all these minerals this investigation has demonstrated that usans sans is a very useful tool for analyzing porosity in ore minerals we believe that with this quantified porosity information a deeper understanding of the complex fluid flow behavior within the porous minerals can be expected

active near surface growth faulting and late holocene history of motion matagorda peninsula texas abstract the structural framework of the northern gulf of mexico coastal zone includes numerous growth fault systems neotectonic processes in coastal environments here have been shown to be important contributors to subsidence and relative sea level rise as well as having significant influences on sedimentary accretion processes one active growth fault at east matagorda peninsula texas was subjected to detailed study to address the hypotheses that 1 this fault was present and active before the peak of regional hydrocarbon recovery in the mid 20th century and that 2 slip along this fault has been episodic over the resolved period of record to characterize the late holocene behavior of this fault three core transects were established normal to the surface fault trace and stratigraphic analysis was conducted with the use of radiocarbon 14c for chronological control correlation of time equivalent stratigraphic boundaries reveals a maximum total late holocene offset of 0 7 m the matagorda fault was in place long before the peak of regional oil and gas extraction but experienced a late holocene rejuvenation initiated between 2500 and 1500 years bp the kinematic behavior of the fault expressed as temporally and spatially variable measures of expanded stratigraphic thicknesses on the downthrown extent suggest that sediment loading from the transgressive matagorda barrier complex may have contributed to this rejuvenation and that slip along the fault persists to the present radiocarbon chronology also revealed clear differences in the magnitude of fault throw during the late holocene with maximum displacement 0 7 m occurring at the southwestern most transect and minimum throw at the northeastern most transect 0 2 m

variations in shoreface progradation and ravinement along the texas coast gulf of mexico shoreface architecture evolution mid holocene to present and depths of transgressive ravinement were examined from sabine pass at the texas louisiana border to south padre island near the texas mexico border using 30 shoreface transects shoreface transects extend out to 16 m water depth each created from an echo sounding profile and on average seven sediment cores the shoreface is composed of three broad sedimentological facies the upper shoreface composed almost entirely of sand the proximal lower shoreface composed of sand with thickly to medium bedded 50 10 cm mud and the distal lower shoreface composed dominantly of mud with medium to thinly bedded 20 3 cm sand shoreface architecture and evolution is extremely variable along the texas coast shoreface gradients increase from 2 25 m km 1 in east texas to 3 50 m km 1 in south texas shoreface sands coarsen towards south texas east and south texas shoreface deposits are thin and retrograding whereas central texas shoreface deposits are thicker and prograding central texas is characterized by stacked shoreface successions whereas in east texas lower shoreface sands are preserved only in offshore banks preservation of shoreface deposits is low in south texas although eustatic fluctuations and accommodation space have a strong impact on overall mid holocene to present shoreface evolution and preservation potential along strike variations in sediment supply and wave energy are the main factors controlling shoreface architecture the transgressive ravinement surface varies from 6 to 15 m along the texas coast

development of microporosity diffusion channels and deuteric coarsening in perthitic alkali feldspars turbidity is an almost universal feature of alkali feldspars in plutonic rocks and has been investigated by us in alkali feldspars from the klokken syenite using sem and tem it is caused by the presence of myriads of tubular micro inclusions either fluid filled micropores or sites of previous fluid inclusions and is associated with coarsening of microperthite and development of sub grains micropores are abundant in coarsened areas in which porosities may reach 4 5 but are almost absent from uncoarsened pristine braind microperthite areas the coarsening is patchy and involves a scale increase of up to 103 without change in the composition of the phases low albite and low microcline or in the bulk composition of the crystal it occurs abruptly along an irregular front within individual crystals which retain their original shapes the coherent braid microperthite gives way across the front to an irregular semi coherent film perthite over a few m and then to a highly coarsened irregular patch perthite containing numerous small sub grains on scales of a few hundred nm in both phases the coarsening and micropore formation occured at a t 400 450 c and it is inferred to have been driven by the release of coherent strain energy low angle grain boundary migration being favoured by a fluid the patchy nature of the coarsening and the absence of a relationship with initial grain boundaries suggest that the fluid was of local origin possibly arising in part through exsolution of water from the feldspar the sub grain texture and microporosity modify profoundly the permeability of the rock and greatly enhance the subsequent reactivity of the feldspars

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

experimental study of the formation of chalcopyrite and bornite via the sulfidation of hematite mineral replacements with a large volume increase chalcopyrite cufes2 and bornite cu5fes4 are the most abundant cu bearing minerals in hydrothermal cu deposits forming under a wide range of conditions from moderate temperature sedimentary exhalative deposits to high temperature porphyry cu and skarn deposits we report the hydrothermal synthesis of both chalcopyrite and bornite at 200 300 c under hydrothermal conditions both minerals formed via the sulfidation of hematite in solutions containing cu i as a chloride complex and hydrosulfide at ph near the pka of h2s aq over the whole temperature range polycrystalline chalcopyrite formed first followed by bornite assuming that fe behaves conservatively the transformation of hematite to chalcopyrite involves a large increase in volume 290 the reaction proceeds both via direct replacement of the existing hematite and via overgrowth around the grain chemical exchanges between bulk solution and hematite are enabled by a network of micrometer size pores however in some cases the chalcopyrite overgrowth develops large grain sizes with few apparent pores and in these cases fluid transport may have been via a network of fractures similarly to the replacement of hematite by chalcopyrite bornite forms via the replacement of chalcopyrite the reaction has a large positive volume 230 and proceeds both via chalcopyrite replacement and via overgrowth this study shows that replacement reactions can proceed via coupled dissolution reprecipitation even where there is a large volume increase between parent and product mineral this study also provides further evidence about the controls of reaction pathways onto the final mineral assemblage in this case the host initial fluid was undersaturated with respect to fe bearing minerals upon slow release of fe at the surface of hematite a mineral assemblage of chalcocite bornite and finally chalcopyrite is expected however in practice chalcocite did not nucleate on the surface of hematite rather relatively slow nucleation of bornite enabled high concentrations of fe to build up near the dissolving hematite so that chalcopyrite high sulfidation experiments or chalcopyrite pyrite low sulfidation crystallized first

reaction induced fracturing during replacement processes replacement processes are common transformation mechanisms in minerals and rocks at a variety of conditions and scales the underlying mechanisms are in general poorly understood but both mechanical and chemical processes are thought to be important replacement of leucite kalsi2o6 by analcime naalsi2o6 h2o is common in silica poor igneous rocks a 10 increase in volume is associated with the replacement process and this generates stresses that eventually cause fracturing of the reacting leucite experimentally reacted leucite samples display characteristic fracturing patterns that include both spalling of concentric onion skin like layers near the reacting interface and the formation of cross cutting often hierarchically arranged sets of fractures that divide the remaining leucite into progressively smaller domains these structures may explain the patchy alteration patterns observed in natural leucite samples and similar so called mesh textures associated with the serpentinization of olivine grains during hydration of mafic or ultramafic rocks they are also strikingly similar to larger scale patterns formed during spheroidal weathering processes a simple discrete element model illustrates the mechanics that control the formation of such systems and shows how these replacement processes may be accelerated due to the generation of new reactive surface area by hierarchical fracturing processes

bi melt formation and gold scavenging from hydrothermal fluids an experimental study abstract the role of polymetallic melts in scavenging ore components has recently been highlighted in the context of fluid poor metamorphosed ore deposits in contrast the role of polymetallic melts in systems dominated by hydrothermal fluids remains poorly understood using a simple au bi model system we explored experimentally whether such polymetallic melts can precipitate directly from a hydrothermal fluid and investigated the ability of these melts to scavenge au from the solution the experiments were conducted in custom built flow through reactors designed to reproduce a hydrothermal system where melt components are dissolved at one stage along the flow path e g bi was dissolved by placing bi minerals along the fluid path whereas melt precipitation was caused further along the flow path by fluid rock interaction bi rich melts were readily obtained by reaction with pyrrhotite graphite or amorphous fes when au was added to the system bi au melts with compositions consistent with the au bi phase diagram were obtained in the case of fluid reaction with pyrrhotite epitaxial replacement of pyrrhotite by magnetite was observed with textures consistent with an interface coupled dissolution reprecipitation reaction icdrr in this case the metallic melt precipitated as blebs that were localized at the replacement front or within the porous magnetite direct fractionation of bi au melts from a hydrothermal fluid or precipitation of a bi melt followed by partitioning of au from ambient fluid offer new pathways to the enrichment of minor ore components such as au without requiring fluid saturation with respect to a au mineral this mechanism can explain the strong geochemical affinity recognized between au and low melting point chalcophile elements such as bi in many gold deposits examples of deposits where such a model may be applicable include orogenic gold deposits and gold skarns contrary to models involving migration of polymetallic melts to explain element remobilization only small quantities ppm of polymetallic melts are required to affect the au endowment of a deposit via interaction with a hydrothermal fluid the experiments also show that micro environments can play a critical role in controlling melt occurrences for example reaction fronts developing via icdr reactions can promote melt formation as observed during the replacement of pyrrhotite by magnetite the associated transient porosity creates space for the melt and promotes melt fluid exchanges whereas the reaction front provides local geochemical conditions favorable to melt precipitation e g reduced low ah2s aq and catalytic surface

influence of growth faults on coastal fluvial systems examples from the late miocene to recent mississippi river delta abstract the details of how fluvial systems respond to spatial changes in land surface subsidence produced by active faulting remain incompletely understood here we examine the degree to which the positioning of individual channels and channel belts is affected by local maxima in subsidence associated with the hanging walls of growth faults the channel forms and faults are imaged using a seismic volume covering 1400 km2 of breton sound and barataria bay in southern louisiana usa we look at the consequences of interactions between channels channel belts and faults in late miocene to recent strata more than fifty individual channels that crossed the traces of active growth faults were examined of these channels only three appear to have been redirected by the faults there also appeared to be no systematic change in the cross sectional geometries of channels or channel belts associated with crossing a fault though the orientation of the channel belts appears to be more influenced by faulting than the orientation of individual channels seven out of ten mapped channel belts appear to have been steered by growth faults we propose that channel belts are more likely to be influenced by faults than individual channels because channel belts are longer lived features unlikely to shift their overall position before experiencing a discrete faulting event in addition the style of influence in the few cases where an individual channel is affected by a fault is different from that of larger systems while downstream of a fault channel belts generally become oriented perpendicular to fault strike the individual channels are directed along the hanging wall of the fault running parallel to the fault trace we relate this to the ratio of the length scale of fault rollover relative to the channel or channel belt width fluvial fault interactions with higher values for this ratio are more likely to be carried parallel to the fault trace than systems with lower ratio values

evidence of regional subsidence and associated interior wetland loss induced by hydrocarbon production gulf coast region usa analysis of remote images elevation surveys stratigraphic cross sections and hydrocarbon production data demonstrates that extensive areas of wetland loss in the northern gulf coast region of the united states were associated with large volume fluid production from mature petroleum fields interior wetland losses at many sites in coastal louisiana and texas are attributed largely to accelerated land subsidence and fault reactivation induced by decreased reservoir pressures as a result of rapid or prolonged extraction of gas oil and associated brines evidence that moderately deep hydrocarbon production has induced land surface subsidence and reactivated faults that intersect the surface include 1 close temporal and spatial correlation of fluid production with surficial changes including rapid subsidence of wetland sediments near producing fields 2 measurable offsets of shallow strata across the zones of wetland loss 3 large reductions in subsurface pressures where subsidence rates are high 4 coincidence of orientation and direction of displacement between surface fault traces and faults that bound the reservoirs and 5 accelerated subsidence rates near producing fields compared to subsidence rates in surrounding areas or compared to geological rates of subsidence based on historical trends subsidence rates in the gulf coast region near producing fields most likely will decrease in the future because most petroleum fields are nearly depleted alternatively continued extraction of conventional energy resources as well as potential production of alternative energy resources geopressured geothermal fluids in the gulf coast region could increase subsidence and land losses and also contribute to inundation of areas of higher elevation

a comparison of factors controlling sedimentation rates and wetland loss in fluvial deltaic systems texas gulf coast abstract submergence of coastal marshes in areas where rates of relative sea level rise exceed rates of marsh sedimentation or vertical accretion is a global problem that requires detailed examination of the principal processes that establish maintain and degrade these biologically productive environments using a simple 210 pb dating model we measured sedimentation rates in cores from the trinity lavaca navidad and nueces bayhead fluvial deltaic systems in texas where more than 2000 ha of wetlands have been lost since the 1950s long term average rates of fluvial deltaic aggradation decrease southwestward from 0 514 0 008 cm year 1 in the trinity 0 328 0 022 cm year 1 in the lavaca navidad to 0 262 0 034 cm year 1 in the nueces the relative magnitudes of sedimentation and wetland loss correlate with several parameters that define the differing fluvial deltaic settings including size of coastal drainage basin average annual rainfall suspended sediment load thickness of holocene mud in the valley fill and rates of relative sea level rise there is some evidence that upstream reservoirs have reduced wetland sedimentation rates which are now about one half the local rates of relative sea level rise the extant conditions indicate that fluvial deltaic marshes in these valleys will continue to be lost as a result of submergence and erosion

an equilibrium profile model for retreating marsh shorelines in southeast louisiana abstract louisiana s coastal marshes are experiencing the highest wetland loss rates in the u s in part due to subsidence driven relative sea level rise these marshes are also vulnerable to the erosive power of wave attack 1 on the marsh edge adjacent to open water bodies and 2 after the marsh platform is submerged marsh shorelines in barataria bay breton sound and the active balize delta of southeastern louisiana were examined in areas where the subaerial marsh platform had disappeared since 1932 vibracore transects of marsh and adjacent bay surface sediments to 2 m depth were analyzed using geotechnical stratigraphic and radiochemical 137 cs and 210 pb methods and the subaerial to subaqueous transition of the marsh was mapped for elevation using standard stadia rod transit and fathometer measurements results indicate that marsh edge erosion of the platform takes place subaqueously until water depths of 1 5 m are reached this is observed even in interior pond regions but the shoreface elevation profiles are a function of fetch exposed open bay sites display greater incision depth and rate of the marsh platform than protected interior bay or pond sites core stratigraphy reveals that the outer part of the subaqueous platform switches from erosional to depositional as retreat proceeds covering the incised marsh deposits unconformably with estuarine shelly muds 137 cs and excess 210 pb activity indicates that these muds are deposited within a few decades of subaerial marsh loss the consistency of the cross shore profile results suggests that a single profile of equilibrium can approximate the morphology of eroding marsh edges in southeast louisiana platform stratigraphy and resistance to erosion have a limited effect on profile shape this equilibrium profile and remote sensing images of shoreline change are used to estimate the sediment yield to adjacent estuarine areas by this process on average 1 5 m3 of sediment are yielded per m shoreline length annually from both barataria bay and breton sound due to the highly organic nature of the eroded sediment 30 this supply of organic rich material could significantly impact estuarine productivity and hypoxia on the louisiana continental shelf

a global earthquake discrimination scheme to optimize ground motion prediction equation selection we present a new automatic earthquake discrimination procedure to determine in near real time the tectonic regime and seismotectonic domain of an earth quake its most likely source type and the corresponding ground motion prediction equation gmpe class to be used in the u s geological survey usgs global shakemap system this method makes use of the flinn engdahl regionalization scheme seismotectonic information plate boundaries global geology seismicity cat alogs and regional and local studies and the source parameters available from the usgs national earthquake information center in the minutes following an earthquake to give the best estimation of the setting and mechanism of the event depending on the tectonic setting additional criteria based on hypocentral depth style of faulting and regional seismicity may be applied for subduction zones these criteria include the use of focal mechanism information and detailed interface models to discriminate among outer rise upper plate interface and intraslab seismicity the scheme is validated against a large database of recent historical earthquakes though developed to assess gmpe selection in global shakemap operations we anticipate a variety of uses for this strategy from real time processing systems to any analysis involving tectonic classification of sources from seismic catalogs

seismicity and stress tensor inversion in the central washington cascade mountains abstract tectonic stress in the pacific northwest washington is dominated by a n s major compressive axis 1 and a minor compressive axis 3 which varies from e w to near vertical some variations in this pattern occur in different parts of the region in this study we used 550 earthquakes in the central washington cascade mountains to study in detail the uniformity of the stress tensor in this volcanic arc earthquakes from the pacific northwest seismograph network pnsn catalog were divided into several subsets based on epicentral and depth groupings and stress tensor inversions using the gephart and forsyth technique were computed for each group as in previous similar studies the maximum compressive stress axis 1 is nearly horizontal and trending n s to nne ssw in all but one subset shallower events directly under mount rainier have a near vertical 1 for other subsets the minimum compressive stress axis 3 deviates from vertical to horizontal for different groups of events in particular events in the depth range of 10 to 14 km in the western rainier seismic zone wrsz have near vertical 3 direction whereas other depth ranges in this area show a near horizontal e w 3 orientation we hypothesize that the change in orientation of 3 in the 10 to 14 km depth range in the wrsz may be due to the influence of the nearby mount rainier magmatic system independent evidence for magma at this depth comes in the form of a few deep long period lp events

tectonic control of subsidence and southward displacement of southeast louisiana with respect to stable north america 1 gps data collected between 1995 and 2006 suggest that southeast louisiana including new orleans and the larger mississippi delta are both subsiding vertically and moving southward with respect to stable north america both motions are likely related due to their common tectonic setting subsidence in the new orleans area occurs in part because it is located in the hanging wall of a large listric normal fault system that forms the northern boundary of a 7 10 km thick allochthon that is detached from stable north america southward motion of this allochthon relative to stable north america occurs at 2 2 0 6 mm yr the average subsidence rate for gps sites located on the allochthon is 5 2 0 9 mm yr relative to earth s center of mass or 7 mm yr relative to mean sea level motion of the allochthon is likely due to the gravity instability created by rapid holocene sediment deposition in the delta following continental glacial retreat and is facilitated at depth by weak salt horizons because new orleans and other communities of southeastern louisiana lie atop this active allochthon future motion of this body should be considered during rebuilding of the region following hurricanes katrina and rita

modern day tectonic subsidence in coastal louisiana subsidence is leading to the slow inundation of communities and wetlands of louisiana mississippi texas and alabama united states by the gulf of mexico the prevailing paradigm considers subsidence to be the result of young sediment compaction and or consolidation and human activities this paper describes the results of a test of this theory based on an examination of historic motions of benchmark in the michoud area of orleans parish louisiana this methodology allowed for an assessment of vertical change at different levels over time relative to a precise vertical datum north american vertical datum of 1988 navd88 data do not support the current theory on the origins of subsidence they demonstrate that tectonic causes dominate in the study area during 1969 1971 and 1971 1977 tectonism was responsible for 16 9 mm yr and 7 1 mm yr of subsidence respectively these contributions account for 73 and 50 of the total subsidence during these intervals the change in deep subsidence is attributed to renewed motion along a large normal fault michoud fault over the same time intervals intermediate depth subsidence due to compaction of pleistocene to middle miocene strata was constant 4 6 mm yr similarly subsidence due to shallow processes i e sediment compaction and groundwater offtake was 1 5 mm yr and 2 5 mm yr subsidence associated with petroleum extraction was not a factor due to the lack of local production

field evidence of subsidence and faulting induced by hydrocarbon production in coastal southeast texas abstract three large mature hydrocarbon fields in coastal southeast texas were examined to evaluate competing hypotheses of wetland losses and to characterize subaerial and submerged surfaces near reactivated faults and zones of subsidence detailed topographic and bathymetric profiles and shallow cores at the port neches clam lake and caplen fields provide a basis for distinguishing between 1 extensive land surface subsidence without significant subaqueous erosion and 2 localized minor subsidence near faults accompanied by extensive subaqueous erosion subaqueous erosion results from submergence of wetlands current and wave excavation of surface sediments and organic detritus and exportation of the eroded sediments through adjacent water bodies with swift currents such as navigation channels responses to induced subsidence and fault reactivation are different at each field site detailed stratigraphic correlations of sediment cores show that at port neches subsidence of 35 to 90 cm and minor marsh erosion 20 to 35 cm created more than 15 million m3 of accommodation space in a nearly circular pattern over the field at caplen the marsh surface subsided only about 4 cm but the surface eroded 30 to 40 cm vertically creating about 3 5 million m3 of accommodation space the breakup of wetlands and their conversion to open water appears to be in an initial stage at the clam lake field where marsh plants are being submerged along a fault the different surficial responses and wetland losses at each field are related to the primary type of hydrocarbon produced and the rates of production although the absolute magnitude of induced subsidence may be less than 1 m even a minor reduction in land elevation is sufficient to cause major wetland losses

the december 1872 washington state earthquake the largest historical earthquake in eastern washington occurred on 15 december 1872 we used modified mercalli intensity mmi assignments for 12 twentieth century earthquakes to determine attenuation relations for different regions in the pacific northwest mmi attenuation for propagation paths east and west of the cascade mountains differs significantly only for epicentral distances greater than about 225 km we used these attenuation relations and the mmi assignments for the 15 december 1872 earthquake to conclude that its epicentral region was east of the cascade mountains near lake chelan washington and most probably near the south end of lake chelan the intensity magnitude m i is 6 8 and moment magnitude m is 6 5 7 0 at the 95 confidence level manuscript received 23 october 2001

evidence for distributed clockwise rotation of the crust in the northwestern united states from fault geometries and focal mechanisms paleomagnetic and gps data indicate that washington and oregon have rotated clockwise for the past 16 myr late cenozoic and quaternary fault geometries seismicity lineaments and focal mechanisms provide evidence that this rotation is accommodated by north directed thrusting and right lateral strike slip faulting in washington and sw to w directed normal faulting and right lateral strike slip faulting to the east several curvilinear nw to nnw trending high angle strike slip faults and seismicity lineaments in washington and nw oregon define a geologic pole 117 7 w 47 9 n of rotation relative to north america many faults and focal mechanisms throughout northwestern u s and southwestern british columbia have orientations consistent with this geologic pole as do gps surface velocities corrected for elastic cascadia subduction zone coupling large quaternary normal faults radial to the geologic pole which appear to accommodate crustal rotation via crustal extension are widespread and can be found along the lewis and clark zone in montana within the centennial fault system north of the snake river plain in idaho and montana to the west of the wasatch front in utah and within the northern basin and range in oregon and nevada distributed strike slip faults are most prominent in western washington and oregon and may serve to transfer slip between faults throughout the northwestern u s

low temperature alteration of monazite fluid mediated coupled dissolution precipitation irradiation damage and disturbance of the u pb and th pb chronometers abstract low temperature alteration of monazite is documented in three centimeter sized monazite crystals from norway arendal madagascar ambato and sri lanka the three crystals have different chemical compositions especially in their u th y and pb contents and have 208 pb 232 th ages ranging from 491 to 900 ma optical microscope om scanning electron microscope sem and transmission electron microscope tem images and electron microprobe analyses epma show that all three preserve a similar patchy texture this texture is interpreted as resulting from an alteration reaction in which unaltered monazite mnz1 reacts to form a secondary th u y depleted high th u monazite mnz2 accompanied by thorite huttonite thsio 4 thorianite tho 2 and xenotime ypo 4 the proportions of which are dependent upon the initial composition of the monazite mnz1 images reveal variably intense internal fracturing with cracks filled with th rich fe rich phases monazite xenotime thermometry demonstrates that the pristine monazites mnz1 interacted with a low temperature fluid the alteration process is interpreted to follow a mechanism of fluid mediated coupled dissolution precipitation chemical dating with the electron microprobe shows no th u pb age differences between primary and secondary monazites except in the case of the ambato monazite in which altered domains yield older 750 ma apparent ages than the pristine mnz1 domains u pb and th pb isotope dating using la icp ms yields ages consistent with electron probe dates for pristine mnz1 zones however disturbance of these systems in the altered monazite domains leads to variable age results for these depending on sample in the case of sri lanka and arendal only 208 pb 232 th dates provide a reasonable estimate of the age of alteration which are constrained to be 450 and 864 ma respectively u pb systems are disturbed due to common pb contamination up to 40 and u fractionation relative to th during alteration responsible for depletion of u in altered monazites and increase of th u in contrast for the ambato monazite both the u pb and th pb systems were affected and yield inconsistent older dates for altered zones this is attributed to significant common pb contamination up to 80 which affects all pb isotopes and explains why electron probe ages are erroneous th u silicate contamination during measurement resulting from the presence of a numerous nano phases and nano fractures filled with th u silicates that are visible only under tem also contributes to the anomalously old ages for these disturbed mnz2 domains these results demonstrate the important role of radiation damage effects in particular swelling induced fracturing and the essential role of porosity and cracks which allow fluid charged with elements migration through monazite during low temperature alteration

land subsidence in houston texas measured by radar interferometry and constrained by extensometers 1 we present results from a radar interferometry study over the houston galveston texas gulf coast region from the nearly 60 potential interferograms considered an atmospheric artifact assessment is performed and a tractable set of interferograms selected for detailed processing and error analysis the subsequent interferogram time series spanning 1996 1998 is constrained by coincident extensometer data with root mean square error less than 2 5 mm the interferogram time series confirms that historic subsidence in east houston has stopped consistent with current groundwater use patterns broad scale subsidence bowls are observed in west and northwest houston where maximum subsidence rates are in excess of 2 and 4 cm yr 1 respectively linear interferogram phase signatures associated with approximately 1 cm of differential subsidence across faults including the long point fault in northwest houston are observed near the seabrook extensometer a hereto unidentified subsidence bowl with a maximum subsidence rate in excess of 3 cm yr 1 is revealed this study demonstrates that when used in conjunction with a set of traditional geodetic measurements radar interferometry can measure the spatial and temporal evolution of urban land subsidence within even the most challenging of environments

the role of neo tectonics in the sedimentary infilling and geomorphological evolution of the guadalquivir estuary gulf of cadiz sw spain during the holocene abstract a multidisciplinary analysis of cores and geomorphic patterns in the marshes of donana national park sw spain has yielded new evidence regarding the sedimentary infilling and geomorphological evolution of the guadalquivir estuary during the holocene the sedimentation and geomorphological disposition have been strongly conditioned by neotectonic activity along a set of sw ne alignments interrupted by other alignments that follow e w and nw se directions the most conspicuous of the sw ne alignments is the torre carbonero marilopez fault tcmf south of this fault the estuary experienced a marked subsidence from about 4000 to 2000 cal yr bp through a series of sedimentary sequences of retrogradation and aggradation within the context of relative sea level rise from c 2000 cal yr bp to the present the subsidence has remained relatively dormant with progradation of the littoral systems and infilling of the marshland progressing within a context of sea level stability our results reveal that neotectonic activity is a critical factor that must also be reckoned with in any attempt to understand the holocene geomorphological evolution in the guadalquivir estuary

long aftershock sequences within continents and implications for earthquake hazard assessment one of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries plate tectonics gives no insight however into where and when earthquakes will occur within plates because the interiors of ideal plates should not deform as a result within plate interiors assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes here however we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago we present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries these predictions are in accord with observations so the common practice of treating continental earthquakes as steady state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere

fluid evolution and origins of iron oxide cu au prospects in the olympic dam district gawler craton south australia geologic observations suggest two stages of hydrothermal activity at a number of presently subeconomic iron oxide copper gold systems in the olympic dam district eastern gawler craton they contain high and moderate to low temperature fe oxide rich hydrothermal alteration the mineral assemblages include magnetite calc silicate alkali feldspar fe cu sulfides and hematite sericite chlorite carbonate fe cu sulfides u ree minerals in all documented prospects the minerals of the hematitic assemblages replace the minerals of the magnetite rich assemblages the bulk of the subeconomic cu au mineralization is associated with the hematitic alteration assemblages microanalysis by proton ion probe pixe of hypersaline fluid inclusions in magnetite rich assemblages however demonstrates that significant amounts of copper 500 ppm were transported by the early stage high temperature 400 c fluids responsible for the magnetite rich alteration these brine inclusions contain multiple solid phases liquid vapor multiple solids including chalcopyrite in some cases in comparison inclusions of the hematitic stage are relatively simple liquid vapor types with homogenization temperatures of 200 to 300 c and containing 1 to 8 wt percent nacl equiv the br cl ratios of the magnetite forming fluids measured by pixe lie beyond the range of typical magmatic and or mantle values allowing for the possibility that the fluids originated as brines from a sedimentary basin or the crystalline basement sulfur isotope compositions of chalcopyrite and pyrite demonstrate that sulfur in both alteration assemblages was derived either from cooling magmas and or crystalline igneous rocks carried by relatively oxidized fluids so42 h2s 34ssulfides from 5 to 2 or from crustal sedimentary rocks 34ssulfides from 5 to 10 oxygen and hydrogen isotope compositions of waters calculated for minerals of the magnetite rich assemblage have 18o values of 7 7 to 12 8 per mil and d values of 15 to 21 per mil the only available 18o and dfluid values for the hematitic assemblage are 4 7 and 9 per mil respectively the isotopic compositions of both fluids coupled with the available literature data can be explained in terms of fluid reequilibration with felsic gawler range volcanics or other felsic igneous rocks in the region and with metasedimentary rocks of the wallaroo group at low water to rock ratios prior to their arrival at the mineralization sites the lack of significant copper mineralization associated with magnetite forming fluids that carried copper suggests that there was no effective mechanism of saturation of copper minerals or the quantity of these fluids was not sufficient to produce appreciable copper mineralization association of the copper gold mineralization with the hematitic alteration in the subeconomic prospects can be explained by a two stage model in which preexisting hydrothermal magnetite with minor associated copper gold mineralization was flushed by late stage oxidized brines that had extensively reacted with sedimentary or metamorphic rocks the reduction of these brines driven by conversion of magnetite to hematite resulted in precipitation of copper and gold the oxidized brines may have contributed additional copper and gold to the system in addition to upgrading preexisting subeconomic cu au mineralization when compared to published models for the olympic dam deposit the new data for fluids in subeconomic fe oxide cu au prospects of the olympic dam district indicate the diversity of origins of iron oxide copper gold systems even within the same geologic region

how complete is the isc gem global earthquake catalog abstract the international seismological centre in collaboration with the global earthquake model effort has released a new global earthquake catalog covering the time period from 1900 through the end of 2009 in order to use this catalog for global earthquake studies i determined the magnitude of completeness m c as a function of time by dividing the earthquakes shallower than 60 km into seven time periods based on major changes in catalog processing and data availability and applying four objective methods to determine m c with uncertainties determined by nonparametric bootstrapping deeper events were divided into two time periods because of differences between the four methods the final m c was determined subjectively by examining the main features of each method in both the cumulative and binned magnitude frequency distributions the time periods and m c values for shallow events are 1900 1917 m c 7 7 1918 1939 m c 7 0 1940 1954 m c 6 8 1955 1963 m c 6 5 1964 1975 m c 6 0 1976 2003 m c 5 8 and 2004 2009 m c 5 7 using these m c values for the longest time periods for which they are valid e g 1918 2009 1940 2009 the shallow data fits a gutenberg richter distribution with b 1 05 and a 8 3 within 1 standard deviation and with no declustering the exception is for time periods that include 1900 1917 during which there are only 33 events with m m c and for those few data b 2 15 0 46 that result calls for further investigations for this time period ideally having a larger number of earthquakes for deep events the results are m c 7 1 for 1900 1963 although the early data are problematic and m c 5 7 for 1964 2009 for the later time period b 0 99 and a 7 3

uranium and sm isotope studies of the supergiant olympic dam cu au u ag deposit south australia the olympic dam cu u au ag deposit in the archean proterozoic gawler craton south australia is a type example of the iron oxide copper gold iocg spectrum of deposits and one of the largest cu u au resources known mineralization is hosted in a lithologically and texturally diverse hematite rich breccia complex developed within a granite of the 1 59 ga gawler silicic province emerging evidence indicates that both the breccia complex and its metal content developed over 1000 ma responding to major tectonic events e g at 1300 1100 825 and 500 ma however metal sources and exact mechanism s of ore formation remain poorly known new high precision 238u 235u data for a set of 40 whole rock samples representing all major lithological facies of the breccia complex show a narrow range 238ucrm112a 0 56 to 0 04 at the scale of sampling there is no correlation of 238u with lithology degree of alteration or u mineralogy although ores with u 5 wt have subtly higher 238u values 0 20 to 0 00 than the majority of samples 0 7 wt u 0 56 to 0 23 the new u isotope data are consistent with published data for uraninites from olympic dam and with published results from high temperature u deposits they overlap completely with the range of 238u values in granitoids including the host granite 0 18 to 0 32 and with estimates of the upper continental crust in general this similarity suggests that olympic dam 238u values reflects the crustal sources of u which probably include felsic volcanic rocks and granitoids the isotopic homogeneity suggests depositional mechanisms that involve minimal isotopic fractionation of u alternatively primary fractionation signatures may have been erased during the long history of the u mineralization high grade u ores may record isotopic neutron capture effects related to fissionogenic neutrons high precision sm isotope data for five high u 5 wt u u sm 500 olympic dam ores define a neutron capture line with correlated depletions in 149sm up to 2e units and excesses in 150sm up to 4e units but fission fragment contributions to sm are below detection these observations provide evidence for small scale neutron capture effects with calculated neutron fluences of 1015 to 1016 n cm 2 similar to those observed in several proterozoic and phanerozoic u deposits the apparent lack of fission fragment contributions in olympic dam high grade ores can be explained with an age of u deposition or re deposition that is substantially younger than the initial 1 59 ga age of the oldest iocg style mineralization the results presented here thus i suggest uranium sources in common likely igneous upper crustal lithologies ii support geochronological evidence for gradual addition of u in several stages over 1000 ma at elevated temperatures of mineralization and iii do not show the high 238u signatures expected from low temperature reworking of older low 238u ores

m loga observations for recent large earthquakes abstract using a magnitude m log area a dataset augmented with seven large m 7 0 earthquakes occurring since wells and coppersmith 1994 this short note assesses the current validity of the bilinear m log a relations for continental strike slip earthquakes proposed by hanks and bakun 2002 in particular the l model scaling at m 7 the relations determined by hanks and bakun 2002 are only insignificantly altered leaving these bilinear m log a relations as valid now as when first proposed

timing and nature of fluid flow and alteration during mesoproterozoic shear zone formation olary domain south australia the development of shear zones at mid crustal levels in the proterozoic willyama supergroup was synchronous with widespread fluid flow resulting in albitization and calcsilicate alteration monazite dating of shear zone fabrics reveal that they formed at 1582 22 ma at the end of the olarian d3 deformational event and immediately prior to the emplacement of regional s type granites two stages of fluid flow are identified in the area first an albitizing event which involved the addition of na and loss of si k and fe and a second phase of calcsilicate alteration with additions of ca fe mg and si and removal of na fluid fluxes calculated for albitization and calcsilicate alteration were 5 56 109 to 1 02 1010 mol m 2 and 2 57 108 5 20 109 mol m 2 respectively these fluxes are consistent with estimates for fluid flow through mid crustal shear zones in other terranes the fluids associated with shearing and alteration are calculated to have 18o and d values ranging between 8 and 11 and 33 and 42 respectively and nd values between 2 24 and 8 11 our results indicate that fluids were derived from metamorphic dehydration of the willyama supergroup metasediments fluid generation occurred during prograde metamorphism of deeper crustal rocks at or near peak pressure conditions shear zones acted as conduits for major crustal fluid flow to shallow levels where peak metamorphic conditions had been attained earlier leading to the apparent retrograde fluid flow event thus the peak metamorphism conditions at upper and lower crustal levels were achieved at differing times prior to regional granite formation during the same orogenic cycle leading to the formation of retrograde mineral assemblages during shearing

coupled dissolution and precipitation at mineral fluid interfaces reactions occurring at mineral fluid interfaces are important in all geochemical processes and essential for the cycling of elements within the earth understanding the mechanism of the transformation of one solid phase to another and the role of fluids is fundamental to many natural and industrial processes problems such as the interaction of minerals with co2 saturated water the durability of nuclear waste materials the remediation of polluted water and mineral reactions that can destroy our stone based cultural heritage are related by the common feature that a mineral assemblage in contact with a fluid may be replaced by a more stable assemblage

partitioning of arsenic between hydrothermal fluid and pyrite during experimental siderite replacement abstract arsenian pyrite is the major host mineral of gold in carlin type gold deposit ctgd and forms during the interaction of h2s bearing hydrothermal fluids with fe bearing carbonates e g siderite ankerite fe rich dolomite in the wall rock experimental replacement of siderite at hydrothermal conditions i e 200 c psat was used to study the parameters that control the formation of ctgd pyrite i e ph time ah2s and the partitioning of as between the hydrothermal fluid and newly formed pyrite hydrothermal pyrite formed via replacement of siderite in experiments mainly occurs as two types 1 porous massive pyrite at alkaline ph conditions or 2 clusters of dense euhedral to anhedral pyrite grains at slightly acidic conditions ph concentration of as in newly formed pyrite depends strongly on the as concentration of the hydrothermal fluid used in the experiment calculated partition coefficients vary between 300 and 1700 with lowest d values at high as concentrations of the fluid in the studied system as 1 substitutes for s 2 as indicated by the correlation of high as with low s concentrations experimental findings agree well with previous studies in natural ctgd on as substitution and the partitioning of as between ore stage pyrite and hydrothermal fluids trapped as fluid inclusions the newly constrained partition coefficients for as help to explain the large heterogeneity in natural ctgd pyrite compositions which is caused by changes in the fluid composition due to the strong partitioning of as into the forming pyrite

the mississippi delta region past present and future the mississippi delta region of south louisiana houses a wealth of resources within a dynamic subsiding landscape foundations for the delta region reflect neogene evolution of the depocenter whereas details of the modern landscape reflect late pleistocene to holocene evolution of the alluvial deltaic plain the holocene delta plain was constructed by cyclical growth of deltaic headlands followed by avulsion and relocation of the fluvial sediment source abandoned headlands were then submerged and reworked while a new headland was created at the site of active fluvial sediment input historic period levees have decoupled the delta plain from its fluvial sediment source at the same time global sea level rise was accelerating which has accelerated delta plain submergence diversions of mississippi river water and sediment are necessary to achieve delta plain sustainability but upstream dams trap 50 of the total sediment load and there is not enough supply to keep pace with subsidence and accelerated

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

the replacement of plagioclase feldspars by albite observations from hydrothermal experiments oligoclase and labradorite crystals have been experimentally replaced by albite in an aqueous sodium silicate solution at 600 c and 2 kbars the replacement is pseudomorphic and is characterised by a sharp chemical interface which progresses through the feldspar while preserving the crystallographic orientation reaction rims of albite up to 50 m thick can be readily achieved within 14 days re equilibration of plagioclase in an 18o enriched sodium and silica bearing solution results in oxygen isotope redistribution within the feldspar framework structure the observed characteristics of the reaction products are similar to naturally albitised plagioclase and are indicative of an interface coupled dissolution reprecipitation mechanism chemical analyses demonstrate that the albitisation is accompanied by the mobilisation of major minor and trace elements also including elements such as al and ti which are commonly regarded as immobile during hydrothermal alteration the results contribute to developing our understanding of the close association between large scale albitisation and secondary ore mineralisation which is common in nature

three ingredients for improved global aftershock forecasts tectonic region time dependent catalog incompleteness and intersequence variability following a large earthquake seismic hazard can be orders of magnitude higher than the long term average as a result of aftershock triggering because of this heightened hazard emergency managers and the public demand rapid authoritative and reliable aftershock forecasts in the past u s geological survey usgs aftershock forecasts following large global earthquakes have been released on an ad hoc basis with inconsistent methods and in some cases aftershock parameters adapted from california to remedy this the usgs is currently developing an automated aftershock product based on the reasenberg and jones 1989 method that will generate more accurate forecasts to better capture spatial variations in aftershock productivity and decay we estimate regional aftershock parameters for sequences within the garcia et al 2012 tectonic regions we find that regional variations for mean aftershock productivity reach almost a factor of 10 we also develop a method to account for the time dependent magnitude of completeness following large events in the catalog in addition to estimating average sequence parameters within regions we develop an inverse method to estimate the intersequence parameter variability this allows for a more complete quantification of the forecast uncertainties and bayesian updating of the forecast as sequence specific information becomes available online material omori parameter confidence limits alternative omori fits taking into account b value variation larger tectonic regions and a longer temporal fitting window and synthetic test results