heat flow strong near fault seismic waves and near fault tectonics on the central san andreas fault the main san andreas fault strikes subparallel to compressional folds and thrust faults its fault normal traction is on average a factor of 1 2 thr 1 thr2 thr where thr is the coefficient of friction for thrust faults times the effective lithostatic pressure a useful upper limit for thr of 0 6 where is 3 12 is obtained from the lack of heat flow anomalies by considering off fault convergence at a rate of 1 mm yr for 10 km across strike if the fault normal traction is in fact this high the well known heat flow constraint of average stresses of 10 20 mpa during strike slip on the main fault becomes more severe only a few percent of the total slip during earthquakes can occur at the peak stress before dynamic mechanisms weaken the fault the spatial dimension of the high stress rupture tip zone is 10 m for 3 12 and for comparison 100 m for 1 high dynamic stresses during shaking occur within these distances of the fault plane in terms of scalars fine scale tectonic stresses cannot exceed the difference between failure stress and dynamic stress plate scale slip causes stresses to build up near geometrical irregularities of the fault plane strong dynamic stresses near the rupture tip facilitate anelastic deformation with the net effects of relaxing the local deviatoric tectonic stress and accommodating deformation around the irregularities there also is a mild tendency for near fault material to extrude upward slip on minor thrust faults causes the normal traction on the main fault to be spatially variable

lithology and internal structure of the san andreas fault at depth based on characterization of phase 3 whole rock core in the san andreas fault observatory at depth safod borehole abstract we characterize the lithology and structure of the spot core obtained in 2007 during phase 3 drilling of the san andreas fault observatory at depth safod in order to determine the composition structure and deformation processes of the fault zone at 3 km depth where creep and microseismicity occur a total of approximately 41 m of spot core was taken from three separate sections of the borehole the core samples consist of fractured arkosic sandstones and shale west of the saf zone pacific plate and sheared fine grained sedimentary rocks ultrafine black fault related rocks and phyllosilicate rich fault gouge within the fault zone north american plate the fault zone at safod consists of a broad zone of variably damaged rock containing localized zones of highly concentrated shear that often juxtapose distinct protoliths two zones of serpentinite bearing clay gouge each meters thick occur at the two locations of aseismic creep identified in the borehole on the basis of casing deformation the gouge primarily is comprised of mg rich clays serpentinite lizardite chrysotile with notable increases in magnetite and ni cr oxides hydroxides relative to the surrounding host rock the rocks surrounding the two creeping gouge zones display a range of deformation including fractured protolith block in matrix and foliated cataclasite structure the blocks and clasts predominately consist of sandstone and siltstone embedded in a clay rich matrix that displays a penetrative scaly fabric mineral alteration veins and fracture surface coatings are present throughout the core and reflect a long history of syn deformation fluid rock reaction that contributes to the low strength and creep in the meters thick gouge zones

parkfield earthquakes characteristic or complementary we model the two most recent mw 6 parkfield california earthquakes which occurred in 1966 and 2004 from a nonlinear global inversion of near fault strong motion seismograms our rupture models are characterized by spatially variable slip amplitude and rake rupture velocity and risetime the rupture models indicate that the two earthquakes generated slip in regions of the fault that are not identical as earlier suggested given the sparse seismic data set available for the 1966 earthquake we conduct a series of tests to verify our results 1 we perform synthetic tests in order to study the resolution of the 1966 seismic data set 2 we perform an inversion of the 2004 earthquake using a data set equivalent to the 1966 earthquake and 3 we model the 1966 data set under the a priori assumption that it was similar to the 2004 earthquake all of the tests as well as independent observations indicate that slip during the 1966 and 2004 parkfield earthquakes occurred in different regions of the fault this result implies that regions of a fault that are frictionally locked may remain locked even during a main shock moderate size earthquake in this scenario large earthquakes occur when all the locked regions of a fault are synchronized and ready to slip at the same time

some key features of the strong motion data from the m 6 0 parkfield california earthquake of 28 september 2004 the 2004 parkfield california earthquake was recorded by an extensive set of strong motion instruments well positioned to record details of the motion in the near fault region where there has previously been very little recorded data the strong motion measurements obtained are highly varied with significant variations occurring over only a few kilometers the peak accelerations in the near fault region range from 0 13 g to over 1 8 g one of the highest acceleration recorded to date exceeding the capacity of the recording instrument the largest accelerations occurred near the northwest end of the inferred rupture zone these motions are consistent with directivity for a fault rupturing from the hypocenter near gold hill toward the northwest however accelerations up to 0 8 g were also observed in the opposite direction at the south end of the cholame valley near highway 41 consistent with bilateral rupture with rupture southeast of the hypocenter several stations near and over the rupturing fault recorded relatively weak motions consistent with seemingly paradoxical observations of low shaking damage near strike slip faults this event had more ground motion observations within 10 km of the fault than many other earthquakes combined at moderate distances peak horizontal ground acceleration pga values dropped off more rapidly with distance than standard relationships at close in distance the wide variation of pga suggests a distance dependent sigma may be important to consider the near fault ground motion variation is greater than that assumed in shakemap interpolations based on the existing set of observed data higher density of stations near faults may be the only means in the near future to reduce uncertainty in the interpolations outside of the near fault zone the variance is closer to that assumed this set of data provides the first case where near fault radiation has been observed at an adequate number of stations around the fault to allow detailed study of the fault normal and fault parallel motion and the near field s wave radiation the fault normal motions are significant but they are not large at the central part of the fault away from the ends the fault normal and fault parallel motions drop off quite rapidly with distance from the fault analysis of directivity indicates increased values of peak velocity in the rupture direction no such dependence is observed in the peak acceleration except for stations close to the strike of the fault near and beyond the ends of the faulting

geologic exploration of a molybdenum rich porphyry copper deposit at mocoa colombia concealed porphyry copper molybdenum target high grade mineralization drilling to date has delineated 260 million metric tons of hypogene ore averaging a little more than 1 percent cu equivalent the deposit is associated with a partly unroofed stock of biotite dacite porphyry which was emplaced into broadly cogenetic andesitic and dacitic volcanic rocks during the jurassic a composite batholith of intermediate composition is located only 1 7 km from the deposit but was emplaced 30 to 40 m y earlier the cylindrical orebody contains chalcopyrite molybdenite and local traces of bornite the orebody is largely overlain by an essentially barren quartz sericite pyrite lithocap up to several hundred meters thick high grade copper molybdenum ore is hosted by multiple hydrothermal breccias although the mocoa porphyry system is overlain by a jarositic zone of partial leaching up to 260 m thick rapid erosion during the late cenozoic precluded generation of a significant zone of supergene chalcocite enrichment the high precipitation caused nearly complete removal of abundant hypogene anhydrite and supergene gypsum to depths of at least 900 m modified journal abstract

tomographic vp and vs structure of the california central coast ranges in the vicinity of safod from controlled source seismic data summary a seismic reflection refraction survey across the san andreas fault near parkfield california has refined our knowledge of the upper crustal structure of the central california coast ranges at the san andreas fault observatory at depth safod the survey consisted of a 46 km long line of seismographs 25 50 m spacing and 63 explosions 25 200 kg nominal spacing of 500 m with some gaps the traveltimes of refracted p and s waves from the explosions constitute independent data sets of relatively high quality that were inverted to produce p and s wave velocity models vp vs along the profile extending to as much as 5 km depth the vp and vs models show a prominent lateral drop in velocities a few hundred metres northeast of safod between the drill hole and the san andreas fault the vp model shows particularly well a southwest dipping velocity inversion beneath safod the top of which correlates with a fault penetrated by the drill hole that separates granitic rocks above from sedimentary rocks below in addition to vp and vs models a vp vs model was derived a vp vs ratio lower than 1 73 is seen only at depth in a narrow zone beginning at the target earthquakes for safod and extending downward and northeastward into the north america plate clusters in the parameter space spanned by vp vs ratios and vp can be identified by two different methods one more intuitive analytical method and one more abstract method based on neural network techniques these clusters are correlated to different rock types based on laboratory and in situ data these clusters are remapped back into x z plane along the profile prominent features mapped this way include salinian granitic rocks beneath and west of safod and a body of sedimentary rocks faulted beneath these granitic rocks along what we and others interpret to be a branch of the buzzard canyon fault bcf system these sedimentary rocks extend from this fault to the san andreas fault system unfortunately our cluster analysis shows no significant discontinuity at the san andreas fault owing presumably to the fact that the san andreas fault is located within sedimentary rocks having similar elastic properties this paper is an attempt to downward continue a geological map by geophysical means based on elastic properties of rock samples from the region

lead isotopic signatures of porphyry copper deposits in oceanic and continental settings colombian andes abstract three discrete sub belts of porphyry copper type mineralization are recognized in the colombian andes a western eocene sub belt an eastern jurassic to early cretaceous sub belt and between them a central miocene sub belt the western sub belt is part of an oceanic domain constituted by oceanic crust and overlying immature island arc rocks the eastern sub belt is within a continental domain underlain by the leading edge of the guayana shield and the central sub belt spans the faulted boundary between them the thicker continental crust includes important granulitic rocks which crop out locally as in the vicinity of the mocoa porphyry copper deposit pb isotopic ratios were determined for pyrite samples collected from 6 porphyry copper centers 3 in the western sub belt 2 in the eastern sub belt and one in the central sub belt ratios fall into 3 discrete populations the most radiogenic values represent the western sub belt the least radiogenic represent the eastern sub belt and an intermediate value corresponds to the central sub belt ratios therefore become progressively less radiogenic from the western oceanic domain to the eastern cratonic domain comparison of the pb isotopic ratios with those given in the literature for possible source materials for colombian porphyry copper leads enables the subcontinental mantle wedge subducted oceanic crust and subducted metalliferous sediments to be discounted as principal sources the relatively radiogenic signatures of 5 of the porphyry copper centers appear to be broadly compatible with either a subducted pelagic sediment source or an upper continental crust source whereas the sixth center mocoa is characterized by a distinctly less radiogenic 206 pb 204 pb ratio an admixture of a relatively small percentage of non radiogenic pb from granulitic material in the upper crust with the more radiogenic pb typical of the western sub belt centers could account for the mocoa data because much of the upper crustal section in the region of mocoa is thought to be dominated by granulitic material the radiogenic pb component could be best derived from subducted pelagic sediments if this is the case then a subducted pelagic sediment source could dominate the pb isotopic signatures of all colombian porphyry copper mineralization with some of the pb isotopic differences being produced by selective contamination with upper crustal leads of variable character if this conclusion is correct then the fundamental metal budgets of colombian porphyry copper systems are probably largely independent of upper crustal influences

constraining earthquake source inversions with gps data 2 a two step approach to combine seismic and geodetic data sets 1 we present a new method to combine static and wavefield data to image earthquake ruptures our combined inversion is a two step procedure following the work of hernandez et al 1999 and takes into account the differences between the resolutions of the two data sets the first step consists of an inversion of the static field which yields a map of slip amplitude this inversion exploits a special irregular grid that takes into account the resolution of the static data the second step is an inversion of the radiated wavefield it results in the determination of the time evolution of slip on the fault in the second step the slip amplitude is constrained to resemble the static slip amplitude map inferred from the gps inversion using this combined inversion we study the source process of the 2004 m6 parkfield california earthquake we conclude that slip occurred in two main regions of the fault each of which displayed distinct rupture behaviors slip initiated at the hypocenter with a very strong bilateral burst of energy here slip was localized in a narrow area approximately 10 km long the rupture velocity was very fast 3 5 km s and slip only lasted a short period of time 1 s then the rupture proceeded to a wider region 12 20 km northwest of the hypocenter here the earthquake developed in a more moderated way the rupture velocity slowed to 3 0 km s and slip lasted longer 1 2 s the maximum slip amplitude was 0 45 m

variations of the velocity contrast and rupture properties of m6 earthquakes along the parkfield section of the san andreas fault summary we investigate the seismic velocity contrast across the san andreas fault saf in the parkfield area using fault zone head waves fzhw that propagate along the bimaterial fault interface and direct p waves we systematically analyse large data sets of near fault waveforms recorded by several seismic networks over the period 1984 2005 clear fzhw are observed at many stations on the ne side of the fault in the creeping section of the saf north of middle mountain mm this indicates the presence of a sharp bimaterial interface and that the ne side of the fault has lower seismic velocities in that region the obtained p wave velocity contrast is about 5 10 per cent north of mm and it systematically decreases to 0 2 per cent near gold hill gh the along strike variations of the velocity contrast are consistent with geological observations of a sliver of high velocity rock immediately to the ne of the saf near gh associated with the gh fault and existing 3 d seismic tomography results the obtained imaging results offer an explanation for the mixed rupture directions of the m6 type parkfield earthquakes the strong velocity contrast around mm is expected to produce a preferred propagation direction to the se for earthquakes that nucleate near mm e g the 1934 and 1966 parkfield earthquakes in contrast the near zero velocity contrast and multiple fault branches near gh imply that earthquakes that nucleate near gh e g the 2004 parkfield earthquake are not expected to have a preferred propagation direction to the se and are likely to propagate in directions that are controlled by other factors such as structural and stress heterogeneities the observed systematic reduction of the velocity contrast along the saf from nw of mm to se of gh provides a dynamic arrest mechanism for earthquakes that nucleate in the northern part of the parkfield section and propagate to the se and a dynamic arrest mechanism for earthquakes that nucleate in the southern section and propagate to the nw

the source of lead in the osen sandstone lead deposit on the baltic shield norway the sandstone hosted lead deposits on the baltic shield occur in marine late precambrian to early cambrian sedimentary rocks a ground water model in which the basement is postulated as the metal source has been proposed for these deposits to test this model the osen deposit was selected because it lies directly on a homogeneous granite basement on the basis of u th pb whole rock isotopic analyses for three samples of unweathered basement granite trysil granite a basement age of 1 598 m y was established the lead isotopic compositions of four out of five specimens of galena from the osen deposit plot between isochrons calculated for the granite at 500 m y and 540 m y this is strong support for the hypothesis that the lead source was basement granite and suggests that mineralization took place soon after sedimentation a basement source for the lead is further substantiated by the regional pattern of lead isotopic compositions of sandstone lead deposits which reflects the character of adjacent basement terranes

a double magmatic heat pump at the core mantle boundary gigantic silicate magma chambers have been postulated to account for seismically inferred ultra low velocity zones at the base of the mantle acting to modulate heat transport out of the core and into plumes in the core rising plumes of liquid metal and light elements pump the latent heat outward from the inner core boundary by compositional convection the outer core thus pumps heat to the core mantle boundary cmb and the giant magma chamber pumps heat into the mantle to act as a plume source magmatic action at the cmb depends critically on the balance between melt composition compressibility and temperature a stably resident magma above the cmb must be denser than the mantle crystals mostly silicate perovskite pv and magnesiowustite mw dense melts should form at the cmb where they must be saturated with fe and feo from the core given normal mg fe partitioning mw will be denser than pv and melts from pv mw iron liq should also be intrinsically dense relative to the bulk crystal assemblage such melts may become superheated to overcome the compositional density and rise upward in the magma chamber assisted by turbulent mixing cooled melt sheds dense metal and metal oxide crystals and growth of these crystals releases light solute that quickly transports heat upward toward the chamber roof where it melts the mantle near the roof dense melt grows from the heat transported upward by compositional convection and sinks excess heat and occasionally some melt escapes to feed plumes in the mantle cmb magmas must be among the most fe rich in the earth

source and possible leaching process of ore metals in the uragen sandstone hosted zn pb deposit xinjiang china constraints from lead isotopes and rare earth elements geochemistry abstract the uragen world class zn pb deposit is located in the ulugqat basin in xinjiang china the deposit is characterized by low grade zn pb 3 wt and large tonnage of 4 84 mt metals in the southern ore zone and potentially 10 mt metals for the whole deposit the deposit is mainly hosted in sandstone and conglomerate of the fifth member of the lower cretaceous kezilesu group to provide better constraints on the source of ore metals systematic analyses of the pb isotopes and ree were conducted on sulfides and possible source terranes the sulfides have homogeneous pb isotopic ratios for 206pb 204pb of 18 528 18 690 for 207pb 204pb of 15 545 15 743 and for 208pb 204pb of 38 429 39 082 these ratios are different from those of the upper silurian upper devonian tangaitaer and paleocene aertashi formations the fourth member of the lower cretaceous kezilesu group and the permian granite despite partly overlapping with the values of sulfides the ratios of the proterozoic aksu metamorphic rocks are different in extent and variability however the clastic rocks of the fifth member of the lower cretaceous kezilesu group have almost the same pb isotopic compositions as the sulfides if the preferential leaching of radiogenic pb is taken into account the sulfides in the disseminated ores show lree enriched patterns with high lree hree ratios 3 50 12 06 variable changes of ce anomalies 0 67 1 22 and eu anomalies 0 52 1 33 that are also similar to those of the clastic rocks of the fifth member of the lower cretaceous kezilesu group but are significantly different from those of the basement rocks of the proterozoic aksu group and the evaporite sequences of the paleocene aertashi formation in the ce and eu anomalies petrographic observations indicate that the clastic rocks of the fifth member of the lower cretaceous kezilesu group have undergone sedimentation diagenetic reddening and bleaching reddening is related to the in situ oxidation of mafic minerals such as biotite to produce ferric iron oxide and hydroxide ioh that accompanied the liberation of ore metals from the silicate phase during subsequent crystallization of ioh to hematite preferential adsorption onto hematite could have been the main mechanism for separating zn pb from cu bleaching resulted from the dissolution of ioh during the oil gas infilling stage and based on mass balance calculations substantial amounts of leachable fe zn pb were extracted from the red clastic rocks by the ore forming fluid therefore we propose that the red clastic rocks of the fifth member of the lower cretaceous kezilesu group may be the predominant source of ore metals in the uragen deposit and that the leaching may be possibly related to the bleaching process

sediments at the top of earth s core unusual physical properties at the core mantle boundary have been inferred from seismic and geodetic observations in recent years we show how both types of observations can be explained by a layer of silicate sediments which accumulate at the top of the core as earth cools compaction of the sediments expels most of the liquid iron but leaves behind a small amount of core material which is entrained in mantle convection and may account for the isotopic signatures of core material in some hot spot plumes extraction of light elements from the liquid core also enhances the vigor of convection in the core and may increase the power available to the geodynamo

correlation of clayey gouge in a surface exposure of serpentinite in the san andreas fault with gouge from the san andreas fault observatory at depth safod abstract magnesium rich clayey gouge similar to that comprising the two actively creeping strands of the san andreas fault in drill core from the san andreas fault observatory at depth safod has been identified in a nearby outcrop of serpentinite within the fault zone at nelson creek each occurrence of the gouge consists of porphyroclasts of serpentinite and sedimentary rocks dispersed in a fine grained foliated matrix of mg rich smectitic clays the clay minerals in all three gouges are interpreted to be the product of fluid assisted shear enhanced reactions between quartzofeldspathic wall rocks and serpentinite that was tectonically entrained in the fault from a source in the coast range ophiolite we infer that the gouge at nelson creek connects to one or both of the gouge zones in the safod core and that similar gouge may occur at depths in between the special significance of the outcrop is that it preserves the early stages of mineral reactions that are greatly advanced at depth and it confirms the involvement of serpentinite and the mg rich phyllosilicate minerals that replace it in promoting creep along the central san andreas fault

galena lead isotopic variations in a mesozoic cenozoic andean arc antarctic peninsula the antarctic peninsula magmatic arc was the site of andean type subduction from at least silurian times to the late cenozoic hydrothermal galenas from eight localities in accretionary complex arc volcanic sequences and plutonic rocks along a strike length of 1100 km have restricted 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb compositions 18 628 18 734 15 599 15 673 and 38 441 38 689 respectively plotting on crustal average growth curves the local geological setting and comparison with andean leads suggest that the major source reservoir was isotopically homogeneous sedimentary rocks forming the late palaeozoic triassic accretionary complex the lead data suggest that old continental basement is absent at least as far south as 65 s galenas from a large 13 2 km epithermal vein system on hurd peninsula fall in three populations a main isotopically homogenous array 18 643 15 647 and 38 503 2 0 020 0 020 and 0 050 n 33 interpreted as a large hydrothermal system that extracted homogenous leads from early triassic turbidites two smaller sub populations with more radiogenic 206 pb 204 pb are associated with mid to late cretaceous intrusive rocks and may represent either local contributions of magmatic lead or younger hydrothermal episodes in western graham land two localities associated with mantle derived mafic intrusions of cenozoic age have low 207 pb 204 pb and 208 pb 204 pb ratios indicating addition of some mantle type lead

coseismic and postseismic slip of the 2004 parkfield earthquake from space geodetic data we invert interferometric synthetic aperture radar insar data jointly with campaign and continuous global positioning system gps data for slip in the coseismic and postseismic periods of the 2004 parkfield earthquake the insar dataset consists of eight interferograms from data collected by the envisat and radarsat satellites spanning the time of the earthquake and variable amounts of the postseismic period the two datasets complement each other with the insar providing dense sampling of motion in the range direction of the satellite and the gps providing more sparse but three dimensional measurements of ground motion the model assumes exponential decay of the postseismic slip with a decay time constant of 0 087 years determined from time series modeling of continuous gps and creepmeter data we find a geodetic moment magnitude of m 6 2 for a 1 day coseismic model and m w 6 1 for the entire postseismic period the coseismic rupture occurred mainly in two slip asperities one near the hypocenter and the other 15 20 km north postseismic slip occurred on the shallow portions of the fault and near the rupture areas of two m 5 0 aftershocks a comparison of the geodetic slip models with seismic moment estimates suggests that the coseismic moment release of the parkfield earthquake is as little as 25 of the total this underlines the importance of aseismic slip in the slip budget for the parkfield segment online material complete data tables and supplemental tables

paleotemperature analysis by authigenic minerals and its application to petroleum exploration paleotemperature analysis in sedimentary basins is very important to petroleum exploration because generation of petroleum from kerogen is controlled mainly by temperature vitrinite reflectance generally is used for this analysis a new technique of paleotemperature analysis depends on the relationship between transformation temperatures of authigenic minerals in diagenetically altered argillaceous sediments and their depth of first appearance in any specific well study of both the paleogeothermal gradient and porosity depth relationships in a basin make possible predictions of hydrocarbon pools in the exploration area for example primary migration of oil in neogene rocks of the niigata basin in central honshu japan has occurred at burial depths between 2 260 and 3 50 m 7 410 and 12 960 ft this corresponds to the analyzed paleogeothermal gradients of exploited oil and gas fields in the basin 3 0 to 4 0 c 100 m 1 6 to 2 2 f 100 ft

persistent fine scale fault structure and rupture development a new twist in the parkfield california story abstract we investigate the fine scale geometry and structure of the san andreas fault near parkfield ca and their role in the development of the 1966 and 2004 m6 earthquakes long term surface fault traces indicate that structural heterogeneities associated with secondary reverse and normal fault structures are present at both rupture tips near middle mountain and gold hill detailed analysis of almost 50 years of high resolution seismicity reveals a fault plane that has been twisted into a helicoid between middle mountain and gold hill numerical models support our conclusion that this shape is the result of long term torqueing of a strong stuck patch surrounded by a weak creeping region the changes in fault friction behavior and related geometric discontinuities act as barriers to rupture propagation of moderate size earthquakes at parkfield and as areas of concentrations where rupture initiates our study demonstrates also that smooth strike slip faults with large cumulative offset can form new fault segments at a late stage in their evolution

avalanches at the core mantle boundary 1 the partial collapse of topographic structure at the core mantle boundary cmb in avalanches slumps or turbidity flows would cause sudden temperature changes in both the upper core and the lower mantle although such collapses are hypothetical it is interesting to investigate the potential consequences downwelling from such events could disrupt core convection cells and trigger geomagnetic excursions and reversals buoyant sediment from the freezing of the inner core is hypothesized to rebuild the avalanched structures large avalanches could trigger mantle plumes oblique extraterrestrial impacts impart high shear to the cmb and can trigger one or more simultaneous avalanches yielding observed coincidences between craters tektite fields and reversals a triggered avalanche can explain the coincidence between the formation of the largest known volcanic province the ontong java plateau the start of the 35 myr cretaceous geomagnetic quiet period and reported coincidences between large flood basalts and extinctions

surface slip associated with the 2004 parkfield california earthquake measured on alinement arrays although still continuing surface slip from the 2004 parkfield earth quake as measured on alinement arrays appears to be approaching about 30 35 cm between parkfield and gold hill this includes slip along the main trace and the southwest fracture zone swfz slip here was higher in 1966 at about 40 cm the distribution of 2004 slip appears to have a shape similar to that of the 1966 event but final slip is expected to be lower in 2004 by about 3 15 cm even when continuing slip is accounted for proportionately this difference is most notable at the south end at highway 46 where the 1966 event slip was 13 cm compared to the 2004 slip of 4 cm continuous global positioning system and creepmeters suggest that significant surface coseismic slip apparently occurred mainly on the swfz and perhaps on middle mountain the latter possibly caused by shaking langbein et al 2005 creepmeters indicate only minor 0 2 cm surface coseismic slip occurred on the main trace between parkfield and gold hill we infer that 3 6 cm slip accumulated across our arrays in the first 24 hr at highway 46 slip appears complete whereas the remaining sites are expected to take 2 6 years to reach their background creep rates following the 1966 event afterslip at one site persisted as much as 5 10 years the much longer recurrence intervals between the past two parkfield earthquakes and the decreasing slip per event may suggest that larger slip deficits are now growing along the parkfield segment

cenozoic plate kinematics subduction and magmatism south american andes revised plate reconstructions and enlarged isotopic age data sets strongly support three mechanisms for controlling the configuration and associated volcanism and tectonism of the andean subduction zone these include age of subducted plate convergence rate and interaction with hotspot traces from 50 to 25 ma in the andes the age of oceanic plate subducted progressively decreased apparently resulting in a9gradual decrease in subduction angle and consequent eastward shift in the loci of magmatic activity a major reorganization of plate motions at 25 ma resulted in an increased convergence rate normal to the chilean andes and was accompanied by subsequent broadening of the locus of magmatic activity into adjacent portions of bolivia and argentina convergence rates changed only slightly across the peruvian margin and no clear effect on subsequent magmatism is indicated interaction of the andean subduction zone with the juan fernandez and easter nazca hotspot traces apparently resulted in lower angle subduction and consequent gaps in magmatic activity as predicted continuations of the traces correspond with regions lacking dated volcanic rocks the current gaps in igneous activity correspond with contemporary subduction of the two traces and this association apparently occurred in the past as well

kinematic inversion of the 2004 m 6 0 parkfield earthquake including an approximation to site effects the 2004 m 6 0 parkfield earthquake yielded one of the largest amounts of near source strong ground motion seismic data ever we invert strong motion seismograms to obtain a model for the space time distribution of coseismic slip on the fault to reduce noise in the inversion we take into account local amplifications that affect each station by using records of the 1983 m 6 5 coalinga earthquake site amplification correlates well with large peak ground velocities registered during the 2004 parkfield mainshock the inversion for a kinematic rupture model yields a nonunique solution we therefore analyze various rupture models that explain the data equally well our preferred rupture model identifies a primary zone of high slip surrounding the hypocenter where the maximum slip is 57 cm a secondary slip area over which contours are not well resolved is located northwest of the hypo center the rupture speed is highly heterogeneous we infer an average rupture ve locity of 2 8 km sec close to the hypocenter and of 3 3 km sec in the secondary region of large slip to the northwest of the hypocenter by correlation of our rupture model with both microseismicity and velocity structure we identify six patches on the fault plane that behave in seismically distinct ways online material kinematic rupture model parameters

three dimensional modeling of near fault ground motions with nonplanar rupture models and topography case of the 2004 parkfield earthquake 1 we study the applicability of deterministic strong ground motion simulations at very near fault distances for a subvertical strike slip fault model corresponding to the 2004 m6 parkfield california earthquake in the frequency range up to 1 hz theoretical modeling under the assumptions of a planar rupture and 1 d medium shows that as a consequence of the s wave radiation pattern the particle motion for such close stations should be almost linear in the fault normal fn direction having fault parallel fp and vertical v components of almost zero however as shown on the parkfield earthquake recordings observed particle motions are rather circular with peak velocities at fp and v components comparable to those at fn components we investigate several realistic features that could explain this controversy namely nonplanar fault realistic three dimensional 3 d medium and the topography of the area we test and quantify these hypotheses using discrete wave number and discontinuous galerkin modeling methods applying 1 d and 3 d velocity structures respectively and two nonplanar rupture models we compare the synthetic and observed particle motions and peak velocity ratios and conclude that deviations from a planar rupture geometry in reasonable bounds for the parkfield fault and the influence of topography only partially explain the behavior of the observed seismograms on the contrary the heterogeneous 3 d velocity structure significantly reduces the synthetic peak ratios to values closer to 1 and provides rather circular particle motions therefore the 3 d velocity model is crucial to obtain realistic estimates of ground motions at near fault distances and is more important than the detailed fault geometry or topography in the parkfield area

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

coseismic and initial postseismic deformation from the 2004 parkfield california earthquake observed by global positioning system electronic distance meter creepmeters and borehole strainmeters global positioning system gps electronic distance meter creepmeter and strainmeter measurements spanning the m 6 0 parkfield california earthquake are examined using these data from 100 sec through 9 months following the mainshock the omori s law with rate inversely related to time 1 t p and p ranging between 0 7 and 1 3 characterizes the time dependent deformation during the postseismic period these results are consistent with creep models for elastic solids with an accurate function of postseismic response the coseismic displacements can be estimated from the high rate 1 min sampling gps and the coseismic displacements are approximately 75 of those estimated from the daily solutions consequently fault slip models using daily solutions overestimate coseismic slip in addition at 2 months and at 8 months following the mainshock postseismic displacements are modeled as slip on the san andreas fault with a lower bound on the moment exceeding that of the coseismic moment online material data description and supplementary figures tables and data used in models and time series analysis

estimation of the breakdown slip from strong motion seismograms insights from numerical experiments fukuyama and mikumo 2007 presented a method to extract informa tion about the friction controlling earthquake rupture directly from near field seismo grams recorded out to several kilometers from a fault this method computes a parameter d 00 approximating the breakdown slip dc from the rake parallel dis placement at the time of the peak particle velocity the validation of the method was based on simple 2d steady state green s functions an approach lacking sufficient physics of the rupture process to support their conclusions here we use 3d simula tions of subshear strike slip spontaneous rupture propagation to demonstrate that d 00 is almost always controlled by rupture and wave propagation effects rather than the fault friction process only if rupture reaches the earth s surface and within a short distance from the fault rc is it possible to extract information about dc from strong motion data due to the fast decay with distance from the fault of the seismic energy related to the stress breakdown process beyond rc d 00 is controlled by the dynamic stress drop from the earthquake rupture without information about dc rc is comparable to the length of the fault cohesive zone where the breakdown process takes place during rupture and approximately equal to 80 of the wavelength associated with the break down frequency defined as the reciprocal of the time span required by the stress to drop to the dynamic level our findings suggest that the dc estimate by fukuyama and mikumo 2007 for the 2000 mw 6 6 tottori earthquake is unrelated to the breakdown slip moreover the very narrow widths for rc obtained from our simulations are in agreement with previous studies challenging the resolution of bandlimited strong motion data to estimate dc from kinematic rupture models guatteri and spudich 2000 spudich and guatteri 2004

remobilization and mineralization of selenium tellurium in metamorphosed red beds evidence from the munster basin ireland abstract selenium and tellurium are vital elements for the ongoing development of carbon free energy generation but are only recovered in small volumes as by products of base and precious metal processing security of supply of these commodities is of high importance as their demand is forecast to increase in the near future thus more research is required on the varying mineralization systems where their occurrence and behavior are poorly understood such as sedimentary basins and metasedimentary terranes the munster basin of southern ireland is a good study area for sedimentary se te in such environments as it has a regionally high soil selenium anomaly and is characterized by devonian terrestrial red beds which were metamorphosed during the hercynian variscan orogeny the area also contains ore grade biogenic sediment hosted copper and remobilized vein hosted copper sulfides which are prospective for chalcophile selenium and tellurium quartz vein hosted se te mineralization was identified across the munster basin accompanied by trace gold silver mercury accessory phases new sulfur isotope data reinforces the model of sulfur and selenium remobilized from a biogenic red bed source which reflects a wider association of selenium deposits with oxidizing environments the co occurrence of tellurium mineralization suggests that it too may be concentrated in oxidizing environments associated traces of gold add to a growing body of evidence that gold is also transported and precipitated in oxidizing conditions in continental basins

rupture propagation of the 2004 parkfield california earthquake from observations at the upsar using a short baseline seismic array u s geological survey parkfield dense seismograph array upsar about 12 km west of the rupture initiation of the 28 september 2004 m 6 0 parkfield california earthquake we have observed the movement of the rupture front of this earthquake on the san andreas fault the sources of high frequency arrivals at upsar which we use to identify the rupture front are mapped onto the san andreas fault using their apparent velocity and back azimuth measurements of apparent velocity and back azimuth are calibrated using aftershocks which have a compact source and known location aftershock back azimuths show considerable lateral refraction consistent with a high velocity ridge on the southwest side of the fault we infer that the initial mainshock rupture velocity was approximately the rayleigh speed with respect to slower side of the fault and the rupture then slowed to about 0 66 near the town of parkfield after 2 sec the last well correlated pulse 4 sec after s is the largest at upsar and its source is near the region of large accelerations recorded by strong motion accelerographs and close to northern extent of continuous surface fractures on the southwest fracture zone coincidence of sources with preshock and aftershock distributions suggests fault material properties control rupture behavior high frequency sources approximately correlate with the edges of asperities identified as regions of high slip derived from inversion of strong motion waveforms

lead isotopic data from sulfide minerals from the cascade range oregon and washington abstract lead isotopic studies of mineral deposits associated with tertiary plutons found in the cascade range of oregon and washington demonstrate a rather uniform isotopic composition in various sulfide minerals 206 pb 204 pb 18 84 to 19 05 207 pb 204 pb 15 57 to 15 62 208 pb 204 pb 38 49 to 38 74 show less variation than data from the volcanic rocks of the cascade range and fall within the mixing array defined by the morb regression line and continental sediments an evaluation of the role of crustal assimilation by hydrothermal convection during emplacement was made on five sulfide deposits associated with a single composite batholith the cloudy pass pluton the pb isotopic data and mass balance calculations suggest that only minor amounts of the lead were derived from the overlying precambrian swakane biotite gneiss during emplacement the bulk of the metal that occurs in sulfide deposits in the cascade mineral belt appears to have been derived from subducted continental detritus the variation of the pb isotopic signature of sulfides from specific districts or deposits suggests that there is a correlation with age and structure of the crust 206 pb 204 pb is greater than 18 92 in northern washington and southern oregon where deposits have intruded mesozoic or older crust however the ore deposits between the northern oregon border and central oregon south of eugene have intruded younger crust composed largely of mafic and andesitic volcanic rocks and 206 pb 204 pb lies between 18 84 and 18 92 this region previously called the columbia embayment appears to be underlain by tertiary volcanic rocks lead isotopic data may be used to define the boundaries between discontinuous blocks of mesozoic crust and tertiary volcanic cover

introduction to the special issue on the 2004 parkfield earthquake and the parkfield earthquake prediction experiment the 28 september 2004 m 6 0 parkfield earthquake a long anticipated event on the san andreas fault is the world s best recorded earthquake to date with state of the art data obtained from geologic geodetic seismic magnetic and electrical field networks this has allowed the preearthquake and postearthquake states of the san andreas fault in this region to be analyzed in detail analyses of these data provide views into the san andreas fault that show a complex geologic history fault geometry rheology and response of the nearby region to the earthquake induced ground movement although aspects of san andreas fault zone behavior in the parkfield region can be modeled simply over geological time frames the parkfield earthquake prediction experiment and the 2004 parkfield earthquake indicate that predicting the fine details of future earthquakes is still a challenge instead of a deterministic approach forecasting future damaging behavior such as that caused by strong ground motions will likely continue to require probabilistic methods however the parkfield earthquake prediction experiment and the 2004 parkfield earthquake have provided ample data to understand most of what did occur in 2004 culminating in significant scientific advances

constraints on magnetic energy and mantle conductivity from the forced nutations of the earth observations of the earth s nutations are used to explore the possible presence of a conducting layer at the base of the mantle the existence of such a layer is suggested by recent experiments on iron and silicate mixtures at high pressures and temperatures knittle and jeanloz 1986 1989 which indicate that iron may react with silicate minerals to produce metallic compounds nutations provide an ideal tool for investigating the existence of such a layer because they are sensitive to the electrical properties within a thin magnetic boundary layer along the core mantle boundary cmb evidence in favor of a conducting layer is found in the effects of ohmic dissipation which cause the amplitude of the earth s nutation to be out of phase with tidal forcings although out of phase components in the earth s nutations are conventionally attributed to the dissipative influences of ocean tides and mantle anelasticity these effects appear incapable of explaining nutation amplitudes determined from very long baseline interferometry vlbi observations the additional effects of ohmic dissipation enhanced by the presence of a thin conducting layer at the cmb are sufficient to reconcile theory and observation the largest mismatch between observations and theory taking account of ocean tides and mantle anelasticity is a discrepancy of 0 39 0 04 milliarcseconds in the out of phase component of the retrograde annual nutation this discrepancy can be eliminated if the lowermost 200 m of the mantle has a conductivity of 5 105s m 1 and the magnetic energy in the spherical harmonic components of the field at the cmb in degrees l 12 is approximately 4 times greater than the energy inferred in degrees l 12 from surface observations unfortunately the vlbi observations do not uniquely resolve the mantle conductivity and magnetic energy so that trade offs exist between these two parameters nevertheless a high mantle conductivity is favored on the grounds that the alternative involving high levels of magnetic energy yields an excessive amount of ohmic heating other interpretations of the vlbi discrepancy are also discussed one such alternative involves viscous dissipation at the cmb requiring a kinematic viscosity of 0 1m2s 1

no mushy zones in the earth s core abstract mushy zones assemblages of crystals and their pore space liquids have been invoked for both the upper and lower boundaries of the liquid outer core the timescale of very slow accumulation compared with solidification at either of these interfaces militates against such zones where instead hard ground should be expected to form by solidification at the interface such adcumulus growth involves isothermal isocompositional solidification by successful exchange of evolving solute with fresh melt from an infinite reservoir at both boundaries of the outer core the removal of rejected material is significantly aided by compositional convection the accumulation rates at the outer core boundaries are orders of magnitude slower than required for adcumulus growth as calibrated both by field and experimental evidence in silicate melts a conceptual phase diagram for the core mantle boundary helps to visualize the relevant equilibria capture of core metal into the mantle has been suggested to occur via a mushy zone to explain a high electrical conductivity there as plausibly required by the secular behavior of the earth s nutation one conjecture is that the rejected light elements from the freezing of the inner core might be able to congregate as a porous flotation sediment at the top of the core the idea of porosity in such a mushy zone must be rejected from experience with solidification of cumulates from magmas a high electrical conductivity might instead be caused by solution of core metal by mantle followed by exsolution the hottest part of the mantle lies in contact with the molten outer core where the maximum solubility of fe must occur in the major mantle phases on leaving the core mantle boundary the mantle must cool and may exsolve metal on the metal silicate solvus if the iron rich metal resides chiefly in the rheologically weaker metal oxide phase which coats the deforming perovskite grains it may furnish a short circuit for mantle conductivity in the basal mantle at still cooler and higher levels the mantle encounters more normal mantle redox conditions and any exsolved fe metal should oxidize to feo in the metal oxide and perovskite phases ceasing to be a conductor

lead isotope signatures of the igneous rocks and porphyry copper deposits from the kerman cenozoic magmatic arc se iran and their magmatic metallogenetic implications abstract copper deposits in the kerman cenozoic magmatic arc kcma of iran are genetically related to miocene porphyries the porphyries and their associated cu deposits were intruded and emplaced into eocene volcanic sedimentary successions lead isotope compositions of the eocene volcanic rocks exhibit homogeneous non radiogenic values 206 pb 204 pb 18 40 to 18 49 207 pb 204 pb 15 41 to 15 48 and 208 pb 204 pb 38 15 to 38 36 in contrast the miocene ore hosting porphyries and associated sulfide minerals also show a relatively radiogenic and homogenous pb isotopic values with orogen character 206 pb 204 pb 18 52 to18 60 207 pb 204 pb 15 58 to 15 64 and 208 pb 204 pb 38 57 to 38 80 the shift in the pb isotopic composition of igneous rocks with time towards higher pb isotopic values precludes derivation of the ore hosting porphyries from a reservoir of similar composition to those in the eocene volcanic rocks the non radiogenic pb isotope signature of the eocene volcanic rocks indicates an origin from subduction related mantle derived magmas whereas the higher pb isotopic values of the miocene ore hosting porphyries suggest an increasing involvement of crustal materials with lower u pb ratios than the upper crust in the source region of these rocks combining the pb isotope data with petrogenetic considerations suggests derivation of the middle miocene ore hosting porphyries from a mixed reservoir with slightly radiogenic pb values such as a hybridized lower continental crustal source this source probably formed because of the involvement of cretaceous oligocene subduction related mantle derived mafic magmas at the base of arc crust the contribution of the miocene collision related mantle derived mafic magma in melting of the hybridized lower continental crust caused generation of the middle miocene porphyries hosting large copper deposits with the least 206 pb 204 pb ratios among other porphyries the higher 206 pb 204 pb ratios of the late miocene pliocene porphyries hosting small copper deposits as well as barren porphyries may reflect a decreasing involvement of collision related mantle derived mafic magma in the source of the late miocene pliocene porphyries the overall similarity in pb isotope values between sulfide minerals and ore hosting porphyries suggests a magmatic source for most of the pb and possibly other metals the more radiogenic isotopic ratios of some late sulfide minerals suggest an insignificant metal contribution from an external source such as local country rocks during hydrothermal circulation

the 2004 parkfield earthquake the 1985 prediction and characteristic earthquakes lessons for the future the 1985 prediction of a characteristic magnitude 6 parkfield earth quake was unsuccessful since no significant event occurred in the 95 time window 1985 1993 anywhere near parkfield the magnitude 6 earthquake near parkfield in 2004 failed to satisfy the prediction not just because it was late it also differed in character from the 1985 prediction and was expectable according to a simple null hypothesis furthermore the prediction was too vague in several important respects to meet the accepted definition of an earthquake prediction an event occurring by chance and meeting the general description of the predicted one was reasonably probable the original characteristic earthquake model has failed in comprehensive tests yet it is still widely used modified versions employed in recent official seismic hazard calculations allow for interactions between segments and uncertainties in the parameters with more adjustable parameters the modified versions are harder to falsify the characteristic model as applied at parkfield and elsewhere rests largely on selected data that may be biased because they were taken out of context we discuss implications of the 2004 event for earthquake prediction the characteristic earthquake hypothesis and earthquake occurrence in general

fault zone controls on the spatial distribution of slow moving landslides slow moving landslides earthflows can dominate hillslope sediment flux and landscape erosion in hilly terrain with mechanically weak fine grained rock controls on the occurrence of slow moving landslides are poorly constrained and need to be understood for landscape evolution models sediment budgets and infrastructure and hazards planning here we use airborne interferometric synthetic aperture radar insar and aerial photographs to document 150 previously unidentified active earthflows along the central creeping portion of the san andreas fault california the earthflows move seasonally in response to winter rainfall occur on hillslopes at 20 40 gradients less than typically associated with rapid catastrophic landslides and have similar morphological characteristics to earthflows in different climatic and tectonic settings although our data extend up to 10 km from the fault trace 75 of detected landslides occur within 2 km of the active fault topographic precipitation and rock type metrics alone are not enough to explain the observed spatial distribution of earthflows instead we hypothesize that earthflows cluster near the creeping san andreas fault because of a fault induced zone of reduced bulk rock strength that increases hillslope susceptibility to failure in addition similar lithology topography and climate exist north of the creeping section of the fault yet earthflows there are rare this may be due to large magnitude earthquakes episodically triggering coseismic rapid landslides which preferentially remove weak rock from the fault damage zone our analysis suggests that the necessary conditions for earthflow formation in central california include some combination of reduced rock strength fine grained sedimentary rock threshold precipitation and relief and possibly the absence of large magnitude earthquakes these conditions likely hold for earthflow development in other areas and our work suggests that local variations in rock strength and seismicity such as those associated with fault zones need to be taken into account in order to accurately predict earthflow occurrence

space time distribution of afterslip following the 2009 l aquila earthquake 1 the inversion of multitemporal dinsar and gps measurements unravels the coseismic and postseismic afterslip slip distributions associated with the 2009 mw 6 3 l aquila earthquake and provides insights into the rheological properties and long term behavior of the responsible structure the paganica fault well resolved patches of high postseismic slip 10 20 cm appear to surround the main coseismic patch maximum slip 1 m through the entire seismogenic layer above the hypocenter without any obvious depth dependent control time series of postseismic displacement are well reproduced by an exponential function with best fit decay constants in the range of 20 40 days a sudden discontinuity in the evolution of released postseismic moment at 130 days after the main shock does not correlate with independent seismological and geodetic data and is attributed to residual noise in the insar time series the data are unable to resolve migration of afterslip along the fault probably because of the time interval six days between the main shock and the first radar acquisition surface fractures observed along the paganica fault follow the steepest gradients of postseismic line of sight satellite displacements and are consistent with a sudden and delayed failure of the shallow layer in response to upward tapering of slip the occurrence of afterslip at various levels through the entire seismogenic layer argues against exclusive depth dependent variations of frictional properties on the fault supporting the hypothesis of significant horizontal frictional heterogeneities and or geometrical complexities we support the hypothesis that such heterogeneities and complexities may be at the origin of the long term variable behavior suggested by the paleoseismological studies rupture of fault patches with dimensions similar to that activated in 2009 appears to have a 500 year recurrence time interval documented by paleoseismic and historical studies in addition to that paleoseismological evidence of large 0 5 m coseismic offsets seems to require seismic events recurring every 1000 2000 years characterized by 1 multisegment linkage 2 surface ruptures larger than in 2009 and 3 complete failure of the 2009 coseismic and postseismic patches

lead isotope data from the sar cheshmeh porphyry copper deposit iran lead isotope compositions of nine sulfide concentrates from ore samples from the sar cheshmeh deposit are reported they range from virtually unaltered granodiorite through varying degrees of potassic alteration to ores showing strong phyllic alteration sericite veins the samples without strong phyllic alteration have fairly uniform lead isotope compositions around 206pb 204pb 18 6 207pb 204pb 15 6 and 208pb 204pb 38 7 two samples with sericite veins have markedly more radiogenic lead it is concluded that the fluid responsible for the potassic alteration and the associated mineralization was essentially magmatic whereas convecting meteoric water from the country rock acted as a mineralizing solution during phyllic alteration in the context of the plumbotectonics model the deposit has a typical orogen signature intermediate between primitive and mature island arc settings

sedimentary and diagenetic controls on red bed ore genesis the middle tertiary san bartolo copper deposit antofagasta province chile the middle tertiary pacencia group of antofagasta province northern chile consists of over 2 km of continental sediments these include alluvial fan playa and lacustrine facies representing deposition in an arid closed basin copper mineralization is hosted by sheet and ribbon sandstone bodies which were deposited in a high energy playa marginal sandflat environment ore minerals occur dominantly as a matrix to these lithic arkoses replacing earlier carbonate and sulfate cements the main ore minerals are native copper cuprite and atacamite although there is an along strike passage into copper sulfide cements in a structurally complex zone copper iron and copper sulfides were deposited in crosscutting fractures commonly replacing evaporite veins primary chalcopyrite and bornite exhibit progressive oxidation to anilite digenite and djurleite chalcocite is not found much of this material has oxidized further to covellite of normal and blaubleibender varieties galena and native silver are present in uneconomic amounts atacamite has a complex paragenesis representing at least locally the earliest copper bearing phase provenance studies of the host sediments and lead isotope data for the sulfides indicate that both the sandstones and the metals were derived from a calc alkaline volcano plutonic complex to the east of the basin an area now obscured by the recent volcanic andes sulfur isotope results for copper sulfides show very light delta 34 s values 33ppm indicative of biogenic sulfate reduction under conditions of unrestricted sulfate supply

constraining earthquake source inversions with gps data 1 resolution based removal of artifacts 1 we present a resolution analysis of an inversion of gps data from the 2004 mw 6 0 parkfield earthquake this earthquake was recorded at thirteen 1 hz gps receivers which provides for a truly coseismic data set that can be used to infer the static slip field we find that the resolution of our inverted slip model is poor at depth and near the edges of the modeled fault plane that are far from gps receivers the spatial heterogeneity of the model resolution in the static field inversion leads to artifacts in poorly resolved areas of the fault plane these artifacts look qualitatively similar to asperities commonly seen in the final slip models of earthquake source inversions but in this inversion they are caused by a surplus of free parameters the location of the artifacts depends on the station geometry and the assumed velocity structure we demonstrate that a nonuniform gridding of model parameters on the fault can remove these artifacts from the inversion we generate a nonuniform grid with a grid spacing that matches the local resolution length on the fault and show that it outperforms uniform grids which either generate spurious structure in poorly resolved regions or lose recoverable information in well resolved areas of the fault in a synthetic test the nonuniform grid correctly averages slip in poorly resolved areas of the fault while recovering small scale structure near the surface finally we present an inversion of the parkfield gps data set on the nonuniform grid and analyze the errors in the final model

san andreas fault geometry in the parkfield california region in map view aftershocks of the 2004 parkfield earthquake lie along a line that forms a straighter connection between san andreas fault segments north and south of the parkfield reach than does the mapped trace of the fault itself a straightedge laid on a geologic map of central california reveals a 50 km long asymmetric northeastward warp in the parkfield reach of the fault the warp tapers gradually as it joins the straight creeping segment of the san andreas to the northwest but bends abruptly across cholame valley at its southeast end to join the straight locked segment that last ruptured in 1857 we speculate that the san andreas fault surface near parkfield has been deflected in its upper 6 km by nonelastic behavior of upper crustal rock units these units and the fault surface itself are warped during periods between large 1857 type earthquakes by the presence of the 1857 locked segment to the south which buttresses intermittent coseismic and continuous aseismic slip on the parkfield reach because of nonelastic behavior the warping is not completely undone when an 1857 type event occurs and the upper portion of the three dimensional fault surface is slowly ratcheted into an increasingly prominent bulge ultimately the fault surface probably becomes too deformed for strike slip motion and a new more vertical connection to the earth s surface takes over perhaps along the southwest fracture zone when this happens a wedge of material currently west of the main trace will be stranded on the east side of the new main trace

examining tendencies of in plane rupture to migrate to material interfaces summary we perform a numerical parameter space study of 2 d in plane ruptures in a model consisting of two different half spaces separated by a low velocity layer and possible simultaneous slip along multiple faults ruptures are nucleated by a bilateral expanding stress drop in a limited source region and may continue to propagate spontaneously or not along one or several faults most calculations are done for purely elastic media and faults governed by coulomb friction but some simulations employ prakash clifton friction and kelvin voigt viscosity the faults two of which are material interfaces are situated equidistant and parallel to each other using different nucleation locations different initial stress different velocity contrasts different frictional fault separations different widths of a low velocity zone and different number of faults we examine the range of conditions for which ruptures migrate to other faults and continue to propagate in a self sustaining manner the model produces diverse migration and propagation phenomena represented by several phase diagrams however a general result of the study is that ruptures tend to migrate to the material interfaces and become self sustained wrinkle like pulses for wide ranges of conditions the wrinkle like pulses propagate along each material interface unilaterally in the direction of motion on the more compliant side of the interface referred to as the positive direction the existence of a large number of faults produces like viscosity distributed deformation that reduces the divergent behaviour of the wrinkle like pulses in many cases ruptures migrate to the interface with the stronger contrast and propagate unilaterally in the positive direction associated with that interface and the overall contrast across the fault zone in smaller number of cases ruptures migrate to the interface with the weaker contrast and propagate unilaterally in the opposite positive direction associated with that interface for various parameter combinations self sustained unilateral pulses travel simultaneously in the two opposite positive directions along the interfaces on the opposite sides of the low velocity layer a low resolution imaging of these ruptures would lead to an inference on bilateral propagation the m6 2004 september parkfield california earthquake may provide a natural example of such a case

the control of basin evolution on patterns of sedimentation and diagenesis an example from the mississippian great orme north wales the mississippian north wales platform is located on the margins of the east irish sea basin and has been little studied over the last 30 years the exposed visean limestones provide new insights into the deposition porosity evolution distribution of dolomitization and pb zn and cu mineralization on the north wales carbonate platform this is of relevance to the characterization of fault related dolomite hydrocarbon reservoirs and age equivalent mississippi valley type mineral deposits in particular the study demonstrates the intimate relationship between sedimentation basin scale tectonism and post depositional fluid flux depositional cyclicity is marked with metre scale upward shallowing cycles in which pervasive marine and meteoric calcite cements occlude matrix porosity and syndepositional fractures consequently subsequent burial diagenetic replacive dolomitization is matrix selective and cements are primarily restricted to fractures seven phases of dolomite are defined based on texture and cathodoluminescence petrography with phases d1 d3 as the most volumetrically significant dolomite phases d0 d2 are matrix replacive cross cutting stratigraphy and locally fingering along beds for several metres dolomite phases d3 d7 are hosted by faults and fractures and also line vugs evidence of telogenesis is recorded where burial diagenetic products are post dated by calcite cements precipitated from meteoric fluids dolomitization probably occurred during the mississippian and continued into the pennsylvanian pb zn mineralization is also interpreted to have occurred during the pennsylvanian associated with variscan tectonism overall the north wales platform displays a more complex paragenesis than age equivalent platforms in the pennine basin owing to multiple phases of burial and exhumation the study demonstrates the importance of linking burial history to detailed field and petrographical data to understand and predict the spatial and temporal controls on diagenetic processes and products within syn and post rift sequences

recordings of the 2004 parkfield earthquake on the general earthquake observation system array implications for earthquake precursors fault rupture and coseismic strain changes the 2004 parkfield earthquake generated a unique set of near field high resolution colocated measurements of acceleration volumetric strain and ve locity at 11 stations in the general earthquake observation system geos array the recordings indicate no precursory strain or displacement was discernable at sen sitivities of 10 11 strain and 5 10 8 m 25 sec prior to the earthquake at distances of 0 5 to 12 km of fault rupture coherent fault parallel and fault normal displacement pulses observed along the fault north of the epicenter are consistent with model predictions for fling directivity and displacement for right lateral strike slip fault rupture the fault parallel and fault normal pulses imply apparent rupture velocities of 2 86 0 15 and 3 03 0 24 km sec respectively unprecedented high resolution volumetric strain recordings on opposite sides of the fault show that dynamic strains radiated from ruptured segments of the fault are more than an order of magnitude larger than final coseismic strain offsets associated with fault slip suggesting that dynamic radiated strain may have contributed to the triggering of failure on unrup tured segments high resolution recordings show that coseismic strain offsets occur abruptly over time intervals of less than 10 sec near the time of arrival of the dominant radiated fault parallel and fault normal displacements subsequent measurements show that the strain offsets continue to increase by as much as 69 in 5 min and 300 in 24 hr over that measured during initial fault slip at depth estimates of local material parameters from simultaneous measurements of volumetric strain and ac celeration confirm seismic calibration factors previously measurable in situ only at tidal periods

origin of the ore forming fluids and metals of the bangpu porphyry mo cu deposit of tibet china constraints from he ar h o s and pb isotopes abstract the bangpu porphyry mo cu deposit is a representative mo dominated deposit besides the sharang porphyry mo deposit in the gangdese metallogenic belt the mo cu mineralization has a close relationship with the monzogranite porphyry and diorite porphyrite we identify three stages during the ore formation a pre ore stage a main ore stage with mo cu deposited dominantly and a post ore stage in this study he ar h o s and pb isotopic compositions of the bangpu deposit were determined based on these determinations integrated isotope geochemistry studies were performed to constrain the possible sources of the ore forming fluids and metals the 3 he 4 he and 40 ar 36 ar ratios of fluid inclusions exhibit a range of 0 12209 0 36370 ra and 275 6 346 1 respectively the 4 he and 40 ar concentrations vary from 1 51 to 3 57 10 7 cm 3 stp g 1 and 0 49 to 9 31 10 7 cm 3 stp g 1 respectively he ar isotopic compositions suggest dominantly crustal derived fluid with minor amount of meteoric water in the main ore stage the 18 o fluid and d fluid values vary from 1 3 to 3 9 and 140 5 to 73 7 respectively indicating that magma fluids mixed with meteoric water the average 34 s value of the sulfides 0 3 in the main ore stage is close to the ore forming porphyries indicating a magmatic source the lead isotopic components of ore sulfides exhibit restricted ranges with 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 18 450 18 728 15 602 5 672 and 38 715 39 211 respectively and values in the range of and 9 46 9 58 indicating ore forming metals of primarily an upper crust source with a small amount of mantle materials compared to the bangpu deposit the ore metals derived from mantle are even greater in the jiama and qulong deposits which leads to cu being the dominant mineralization in the jiama and qulong deposit

diagenesis of tertiary playa sandstones of northern chile implications for andean uplift and metallogeny the oligo miocene pacencia group of antofagasta province northern chile consists of over 2 km of molassic sediments deposited in a series of alluvial fan and playa sub environments sandstones of the artolla member exposed around san bartolo represent playa marginal sandflat deposits and locally host stratiform copper mineralization a detailed study of these sediments has revealed a complex sequence of diagenetic modifications to the arkosic detrital mineral assemblage early dissolution of unstable ferro magnesian minerals and calcic feldspar resulted in the release of ions into intra stratal solution and the subsequent formation of a suite of eogenetic authigenic minerals these include early hematite coatings on framework grains pore lining zeolite and pore filling calcite gypsum and celestite cements syntaxial overgrowths of albite quartz and less common k feldspar are well developed following early oxidative intrastratal conditions the influx of acidic fluids derived from mudrocks during mesogenesis resulted in an important secondary porosity generation and the establishment of an acidic reducing intrastratal environment this facilitated the subsequent introduction of low temperature mineralizing solutions and formation of the san bartolo copper deposit a return to oxidative diagenetic conditions is recorded by late stage overgrowths of k feldspar and quartz and the oxidation of native copper chalcopyrite cements to cuprite tenorite and chalcocite covellite assemblages this final telogenetic modification to the mineral assemblage is related to flushing by meteoric waters and provides independent evidence for an important phase of andean deformation and uplift in the middle to upper miocene

reassessment of a slip budget along the parkfield segment of the san andreas fault historically the parkfield segment has represented a transition in fault behavior along the san andreas fault saf despite a 33 mm yr long term slip rate along the saf slip has not been observed on the cholame segment since the great 1857 fort tejon earthquake during that time the parkfield segment has experienced slip from at least six m 6 0 earthquakes aseismic fault creep and from minor earthquakes data from aseismic slip rate studies and historical earthquake studies allow us to estimate the total slip released along this portion of the saf since 1857 assuming the saf should slip at the long term slip rate a slip deficit of 5 m exists along the cholame segment since 1857 the slip deficit is approximately equivalent to 1857 offsets measured on the cholame and the southeast portion of the parkfield segment thus the slip deficit in southeast parkfield and cholame may be as great as the slip accommodated along these segments in 1857 the slip deficit abruptly decreases to the northwest across the parkfield segment it is 2 m near the town of parkfield and 0 m northwest of middle mountain an m 7 event rupturing all or part of the cholame segment and the southeastern parkfield segment slip decreasing to the northwest would release the accumulated slip and is plausible importantly this study also shows that the change in the pattern of strain release occurs in the middle of the parkfield segment rather than at its ends online material tables showing aseismic and coseismic slip estimations and calculations

oxide mineralization at the radomiro tomic porphyry copper deposit northern chile the main copper oxide minerals in the radomiro tomic deposit are atacamite copper clays chrysocolla and copper wad their relative abundance provides the basis for dividing the oxide zone into two major geologic units the upper oxide unit and the lower oxide unit furthermore the study of mineral abundances in the oxide zones allowed the definition of an oxide mineral zonation that consists of five mineral assemblages based on the relative proportion of the three main copper oxide components atacamite copper clays and chrysocolla these classifications allow both an understanding of the distribution of copper minerals throughout the zone and an interpretation of the supergene processes that formed it the upper oxide unit is mineralogically heterogeneous the copper content is furnished on average by 40 vol percent atacamite 31 vol percent copper clays with minor chysocolla and copper wad the lower oxide unit is more homogeneous atacamite accounts for 70 vol percent of the copper ore minerals with minor amounts of copper clays and chrysocolla copper and chlorine concentrations and porosity are greater in the upper oxide unit whereas hematite chalcocite and molybdenite concentrations and specific gravity are greater in the lower oxide unit the vertical distribution of the cl cu ratio shows a chlorine deficient zone located between elevations of 2 780 and 2 870 m between these elevations the proportion of atacamite is lower and the proportion of copper clays chrysocolla and copper wad is higher than in other portions of either the upper oxide or lower oxide units the oxide zone at radomiro tomic was originated through the in situ oxidation of a preexisting secondary sulfide enrichment blanket oxidation produced an extensive zone of atacamite accompanied by weakly developed argillic alteration the upper part of the deposit was further enriched by lateral migration of copper rich solutions to the north and east where copper precipitated as chrysocolla copper wad and copper in clays in these areas strong argillic alteration characterized by the presence of montmorillonite was developed this second alteration phase impacted only the uppermost portion of the oxide zone and the base of overlying gravels

long term afterslip of the 2004 m 6 0 parkfield california earthquake implications for forecasting amount and duration of afterslip on other major creeping faults abstract we present the longest record of surface afterslip on a continental strike slip fault for the 2004 m 6 0 parkfield california earthquake from which we can derive critical information about the duration and predictability of afterslip relevant to urban displacement hazard applications surface slip associated with this event occurred entirely postseismically along the interseismically creeping 0 6 1 5 cm yr main trace of the san andreas fault using the first year of afterslip data the program after correctly predicted the cumulative surface afterslip maximum 35 cm eventually attained by 1 yr postearthquake observed afterslip had accumulated to only 74 of its modeled final value u f in units of length the 6 yr data suggested final slip would be reached everywhere by 6 12 yrs parkfield s afterslip lasted much longer 6 12 yrs than afterslip following a 2014 m 6 0 event in napa california where no interseismic creep was known and its afterslip neared completion 97 of u f by 1 yr the uncertainty in u f for the napa event fell to 2 cm in only three months versus in 2 yrs for the parkfield event mostly because duration of the power law stage of afterslip at parkfield is much longer 1000 493 1666 days versus 100 35 421 days for napa because the urban hayward fault near san francisco california like the parkfield section exhibits interseismic creep in a similar geological regime significant afterslip might last for up to a decade following an anticipated m 6 7 earthquake potentially delaying postearthquake recovery electronic supplement tables of afterslip observations and coefficients for computing afterslip

oil shales evaporites and ore deposits abstract the relationships between oil shales evaporites and sedimentary ore deposits can be classified in terms of stratigraphic and geochemical coherence oil shale and black shale deposition commonly follows continental red beds and is in turn followed by evaporite deposition this transgressive regressive sequence represents an orderly succession of depositional environments in space and time and results in stratigraphic coherence the amount of organic carbon of a sediment depends on productivity and preservation both of which are enhanced by saline environments work on great salt lake utah allows us to estimate that only 5 of toc originally deposited is preserved inorganic carbonate production is similar to toc production but preservation is much higher oil shales and black shales commonly are enriched in heavy metals through scavenging by biogenic particles and complexation by organic matter ore deposits are formed from such rocks through secondary enrichment processes establishing a geochemical coherence between oil shales and ore deposits the permian kupferschiefer of n europe is used as an example to define a kupferschiefer type kst deposit here oxygenated brines in contact with red beds become acidified through mineral precipitation and acquire metals by dissolving oxide coatings oxidation of the black shale leads to further acid production and metal acquisition and eventually to sulfide deposition along a reducing front in order to form ore bodies the stratigraphic coherence of the red bed black shale evaporite succession must be joined by the geochemical coherence of the ore body evaporite black shale association the cretaceous cu zn deposits of angola the zambian copperbelt as well as the creta oklahoma deposits are other kst examples in the zambian copperbelt evaporites are indicated by the carbonate lenticles thought to be pseudomorphs after gypsum anhydrite nodules mvt deposits are also deposited by acid brines but at more elevated temperatures and with carbonates as principal host rocks the pine point deposits are cited for their close association with evaporites alkaline metal rich brines are postulated for the hyc deposit of mcarthur river australia such brines are known from the green river formation and deposits formed from such brines constitute the grt class they can be recognized by the presence of magadi type cherts and zeolite analcime k spar tuffs the cu co ore bodies of outokumpu finland might also belong to this type a new classification of sedimentary ore deposits is proposed based on their geochemical environment kst and mvt are formed from acid ore fluids while grt and ct creede type are derived from basic ore fluids ph of the fluids is best evaluated not from the ores themselves but from their effect on the host rocks

diversity of fault zone damage and trapping structures in the parkfield section of the san andreas fault from comprehensive analysis of near fault seismograms summary we perform comprehensive analyses of trapped waves and signals of damaged fault zone rocks associated with time delays of body waves along the parkfield section of the san andreas fault saf waveforms generated by thousands of earthquakes and recorded by near fault stations in several permanent and temporary deployments are examined with attention to the possible influence of a lithology contrast across the fault on signals of the low velocity damage zone clear candidate trapped waves are identified at only three stations mmnb and two of the other near fault stations flip and pies further to the nw clear candidate trapped waves are not seen at any of the near fault stations to the se of mmnb the locations of the events generating good candidate trapped waves at mmnb and the other two stations are not distributed broadly in space but clustered in a small number of locations moreover events that generate clear candidate trapped waves at one station do not typically generate trapped waves at the other two stations these observations imply that the damage zone is highly variable along strike and that a coherent connected waveguide does not exist for distances along strike larger than at most 3 5 km the distance between stations synthetic waveform fits for observed trapped waves at stations mmnb and flip indicate that the most likely parameters of the trapping structures at these locations are widths of about 150 m depths of about 3 km velocity reductions of 30 40 per cent and q values of 10 40 synthetic calculations of trapped waves demonstrate that if there is a contrast of seismic velocity across the fault the trapped waves are delayed relative to the s wave arrival trapped waves at station mmnb and to a lesser extent also at stations flip and pies in the nw section show this characteristic this suggests a lithology contrast in the top few km at these locations in agreement with results from tomography and studies of head waves in the parkfield area at several mini across fault arrays where trapped waves are not observed a low velocity damage zone is detected from the delay in the arrival time of body wave phases relative to a nearby off fault station the observed delay of the s wave is greater than the p wave delay consistent with the existence of a damage zone with poisson ratio of about 0 33 the observations of time delays without trapped waves indicate that parts of the damage zone are insufficiently coherent to generate trapped waves a broader damage zone may exist in the region between the saf and the south west fracture zone the results highlight the diversity of damage structures along the 40 km of the saf examined in this study and imply that fault imaging based on data at single sites does not necessarily apply to a larger section

diagenetic processes and the mineralization in the triassic of central england continental red beds are the host rocks of a characteristic style of mineralization which suggests a genetic link between red bed formation and ore formation samples of unmineralized and mineralized triassic sediments from central england have been studied sedimentologically petrographically and geochemically with the aim of clarifying this link which may provide valuable guides for exploration on the basis of sedimentological and petrographic observations it is suggested that these red beds were formed as a result of diagenetic alteration whereby detrital silicates and oxides are progressively dissolved and the iron released is deposited as hematite a model for mineralization is proposed involving the release of trace metals from detrital minerals during diagenesis their retention in saline interstitial solutions migration to suitable sites of precipitation and deposition by reaction with trapped hydrocarbons or reduced sulphur

scaling properties of the parkfield aftershock sequence aftershock sequences present a unique opportunity to study the physics of earthquakes important questions concern the fundamental origin of three widely applicable scaling laws 1 gutenberg richter frequency magnitude scaling 2 omori s law for aftershock decay rates and 3 bath s law for the difference between the magnitude of the largest aftershock and a mainshock the high resolution parkfield seismic network provided the opportunity for detailed studies of the aftershock sequence following the 28 september 2004 m 6 0 parkfield earthquake in this article it is shown that aftershocks satisfy the gutenberg richter scaling relation only for relatively large times after the mainshock there is a systematic time delay for the establishment of this scaling law the temporal evolution of the rates of occurrence of aftershocks is quantified using the generalized omori s law this scaling law contains two characteristic times c and the analysis suggests that the parameter c plays the role of a characteristic time for the establishment of gutenberg richter scaling this time increases systematically with a decreasing lower magnitude cutoff the systematic time delay is attributed to a cascade of energy from long wavelengths to short wavelengths the parameter is a measure of the average time until the first aftershock occurs we find that slightly varies with the lower magnitude cutoff of the sequence we also note that the largest aftershock inferred from an extrapolation of gutenberg richter scaling m 5 0 is equal to the largest observed aftershock this scaling associated with the universal applicability of bath s law is attributed to a constant partitioning of energy between a mainshock and its associated aftershock sequence we also give in this article the distribution of interoccurrence times between successive aftershocks we show that this distribution is well approximated by a nonhomogeneous poissons process driven by the modified omori s law the self consistency between interoccurrence statistics and decay rates is taken as further evidence for the applicability of our studies

pb and sr isotopic systematics of some basalts and sulfides from the east pacific rise at 21 n project rita abstract tholeiitic basalts and sulfide deposits from the cyana and alvin diving programs rita project on the east pacific rise were analyzed for pb and sr isotopes the basalt data plot within the field defined previously by other east pacific rise basalts 206 pb 204 pb 18 35 18 58 207 pb 204 pb 15 48 15 53 208 pb 204 pb 37 8 38 1 87 sr 86 sr 0 7022 0 7025 pb u and sr contents 0 5 0 05 and 110 ppm respectively and values 6 are typical of morb whereas th u ratios 3 5 are significantly higher the pb isotopic ratios of the sulfide samples are very homogeneous 206 pb 204 pb 18 47 207 pb 204 pb 15 49 208 pb 204 pb 37 90 and plot in the middle of the basalt field this indicates that 1 the sulfide pb was derived from the basaltic crust without any significant contribution from either seawater or hemipelagic sediments and 2 the solutions from which the sulfides were deposited had uniform pb isotopic composition the pb contents of three sulfide samples is relatively high 170 1310 ppm the sr contents of five sulfide samples are widely scattered from 12 to 210 ppm with 87 sr 86 sr ratios intermediate between basaltic and seawater values 0 70554 0 00005 to0 70795 0 00011 leaching experiments show that both basalt derived sr and seawater sr were present in the solutions which deposited the sulfides in some cases sr was also adsorbed from seawater onto the sulfides following their deposition basalt derived sr and seawater sr are also present in associated non sulfide phases

paleoseismic and postseismic observations of surface slip along the parkfield segment of the san andreas fault parkfield is considered a transitional segment along the san andreas fault saf between continuous fault creep to the northwest and segments to the southeast that last slipped in the great 1857 fort tejon earthquake historically creep and recurring m 6 0 earthquakes have been observed at parkfield california but the segment s relevance in great saf earthquakes has remained uncertain this paleoseismic study of the central parkfield segment provides a 2000 year record of tectonically deformed fluvial and sag stratigraphy two fault perpendicular excavations across a pressure ridge and a sag pond 200 m north of carr hill exposed five primary fault zones displaying apparent vertical offsets upward splaying clay shear bands and warped stratigraphy four of five fault zones extended into the uppermost stratigraphy suggesting recent surface offset and fault creep several antithetic fault splays and one primary fault zone displayed upward terminations but strong indicators of large magnitude earthquakes with meter scale surface offset and rupture such as filled fissures and colluvial scarp deposits were not observed the absence of evidence for large magnitude earthquakes does not preclude the possibility of 1857 style earthquakes extending into the parkfield segment however all deformation exposed within these trenches is consistent with repeated small ground rupture and fault creep the 2004 m 6 0 parkfield earthquake ruptured through the site and activated at least three of the five fault zones exposed in our excavations comparison between 2004 vertical offset and vertical offsets within the exposed stratigraphy suggests a recurrence interval between 8 and 188 years for m 6 0 earthquakes at parkfield online material supplemental unit descriptions unanalyzed radiocarbon samples and trench logs and photos

the bajo de la alumbrera and agua rica cu au mo porphyry deposits of argentina genetic constraints on ore formation and sources based on isotope signatures abstract important copper gold molybdenum porphyry deposits occur in the northwest region of argentina part of the central andes this paper provides new isotope information on two of these deposits bajo de la alumbrera and agua rica the latter having an epithermal overprint event the two deposits are genetically associated with the miocene farallon negro volcanic complex whole rock and sulfide samples were analyzed for pb sr and nd isotopes to characterize the sources of magma and mineralization of both deposits sr and end data made it possible to divide the samples into three distinct groups most samples are slightly differentiated have oib ocean island basalts isotope characteristics and show some nd fractionation lead isotope also shows distinct groups with an enrichment trend in radiogenic lead in both deposits the sulfides are more radiogenic than the host rocks but are clearly related to them because all plot on a single trend a crustal contribution to the deposits is suggested on the basis of lead isotope signatures the similarity on the pb isotope signatures suggests the same magmatic fluid source although at agua rica the crustal component is more evident than at bajo de la alumbrera possibly because of the assimilation of paleozoic country rocks at agua rica

variations in fault slip and strain accumulation at parkfield california initial results using two color geodimeter measurements 1984 1988 repeated length measurements of several geodetic baselines near parkfield california have revealed significant variations in the local rates of shallow fault slip and strain this network of baselines surveyed several times each week straddles the san andreas fault in the transition zone between the creeping section to the northwest and the locked section to the southeast the length measurements characterized by a precision approaching 0 1 ppm reveal large fluctuations in the rates of baseline extension principal mode analysis of the length change data indicates that the two largest components of the signal are 1 secular extensions and contractions consistent with surface slip on the main strand of the san andreas fault and 2 a large seasonal oscillation with no obvious spatial coherence on most of these baselines the second component appears to be in phase with seasonal rainfall when data from the baselines with the largest amplitude of the seasonal signal are excluded the remaining data can be modeled in terms of both spatial and temporal variations in surface slip variations in the components of the changes in uniform strain and the possible displacement of the central monument in this radial network in parameterizing this model the spatial variation of slip beneath the near surface is reflected by changes in shear strain although the computed secular shear is highly dependent upon the specified parameterization of surface slip the data are consistent with the hypothesis that slip at intermediate depths lags behind the surface slip rate however the range in models that fit the data does not necessarily imply that there is a deficit in slip at depth relative to the surface comparison of the inferred values of surface slip from the model with the observed fault slip measured by very short baseline creep meters indicates close agreement in secular rates but the short term variations observed with the creep meters are either highly attenuated or nonexistent in the modeled slip since the modeled slip is a spatial average which smooths out possible short wavelength variations in the surface slip for which the creep instruments are most sensitive an interesting conclusion from the two color data is that surface slip on the san andreas fault appears to be spread over a 2 km wide zone on the south flank of middle mountain but is confined to a very narrow zone to the south as the fault passes through the center of the network this conclusion is dependent upon the assumption that a few critical monuments are stable and track tectonic displacements in the long term finally the largest observed strain change is an extensional strain coincident with the kettleman hills earthquake m5 5 in august 1985

source of lead in central american and caribbean mineralization ii lead isotope provinces abstract in an earlier study of mesozoic and cenozoic mineralization in central america and the caribbean region we found that lead isotopic compositions of deposits in northern central america which is underlain by a pre mesozoic craton ranged to higher 206 pb 204 pb and 207 pb 204 pb compositions than did deposits from elsewhere in the region where the basement is mesozoic oceanic material using 16 analyses for 12 new deposits as well as new analyses for 11 of the samples studied previously we have found that lead isotopic compositions correlate closely with crustal type but show little or no correlation with depth to the m discontinuity the deposits are divisible into three main groups including in order of increasing 207 pb 204 pb and 208 pb 204 pb ratio 1 deposits in southern central america and all deposits in the greater antilles except cuba 2 all deposits in northern central america and 3 the cuban deposits southern central american and caribbean lead is higher in 207 pb 204 pb and 208 pb 204 pb than most mid ocean ridge basalts but could have been derived directly or indirectly from undepleted mantle northern central america can be divided into the maya block which belongs to the americas plate and the chortis block which belongs to the caribbean plate maya block deposits fall along a linear array whereas those of the chortis block except the monte cristo deposit form a cluster these results suggest that the maya block is underlain by crust or mantle with a large range of u pb and th u ratios whereas the chortis block basement is more homogeneous two stage model calculations indicate an age of about 2280 310 m y for the maya block basement although no such rocks are known in the region comparison of the chortis block data to our recently published lead isotopic analyses of mexican deposits shows considerable similarities suggesting that the chortis block could have been derived from mexico

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

nonlinear ground response analysis of turkey flat shallow stiff soil site to strong ground motion blind predictions of ground response at the turkey flat vertical array site during the 2004 parkfield earthquake were performed using a series of nonlinear and equivalent linear ground response analysis codes in this article we report the out come of the blind predictions compare the predictions to measurements released after the predictions were made and provide discussion on residuals between the data and model predictions the prediction exercise considered various sources of material variability and model variability specifically these analyses utilized five dif ferent nonlinear analysis codes each exercised with a suite of small strain shear wave velocity profiles and modulus reduction damping curves that encompass the range of reported material properties below the site frequency of about 5 hz velocity profile variability dominates the computed response variability upon full release of strong motion data from the site the predictions were generally found to be biased towards underprediction at high frequencies sensitivity analyses and results of recent geophy sical testing at the site suggest this underprediction bias is most likely a result of in accuracies in prior estimates of near surface shear wave velocities analyses performed with the recent profile show no significant bias except at the site frequency where the response is overpredicted

slip on the san andreas fault at parkfield california over two earthquake cycles and the implications for seismic hazard parkfield california which experienced m 6 0 earthquakes in 1934 1966 and 2004 is one of the few locales for which geodetic observations span multiple earthquake cycles we undertake a comprehensive study of deformation over the most recent earthquake cycle and explore the results in the context of geodetic data collected prior to the 1966 event through joint inversion of the variety of parkfield geodetic measurements trilateration two color laser and global positioning system including previously unpublished two color data we estimate the spatial distribution of slip and slip rate along the san andreas using a fault geometry based on precisely relocated seismicity although the three most recent parkfield earthquakes appear complementary in their along strike distributions of slip they do not produce uniform strain release along strike over multiple seismic cycles since the 1934 earthquake more than 1 m of slip deficit has accumulated on portions of the fault that slipped in the 1966 and 2004 earthquakes and an average of 2 m of slip deficit exists on the 33 km of the fault southeast of gold hill to be released in a future perhaps larger earthquake it appears that the fault is capable of partially releasing stored strain in moderate earthquakes maintaining a disequilibrium through multiple earthquake cycles this complicates the application of simple earthquake recurrence models that assume only the strain accumulated since the most recent event is relevant to the size or timing of an upcoming earthquake our findings further emphasize that accumulated slip deficit is not sufficient for earthquake nucleation online material model fault geometry fit to the data for the inversions and model resolution

hydrochemistry of the saline groundwaters of the lower mersey basin permo triassic sandstone aquifer uk saline groundwater occurs at depth in the triassic sandstones of the northern end of the cheshire basin in northwest england major and minor ion data suggest that the origin of the salinity is dissolution of evaporite deposits the salinity probably developed in an interval following the tertiary inversion of the basin which would have allowed faulted contact between the sandstones and the overlying evaporite sequence of the mercia mudstone group isotope evidence suggests the saline waters to have been considerably diluted by presumably dispersive mixing with a meteoric water recharged under cool and therefore quaternary climatic conditions comparison with other uk permo triassic basin brines suggests the merseyside waters are not unusual except in terms of the importance of exchange reactions and dilution by quaternary recharge waters these factors are due to the shallow maximum burial depth of the aquifer and the preservation of smectites and also to the geometry of the aquifer and its low permeability faults in the light of the water chemistry data it is suggested in a slight modification of the proposal of naylor et al q geol soc lond 146 685 699 1988 that the cheshire basin mineralization resulted from mixing of the relatively oxidized so4 rich evaporite brines with the reduced so4 poor metal rich barich coal measures brines which were expelled through faults from the coal measures during basin inversion some degree of oxyhydroxide stripping of the sandstones by the coal measures brines would have enhanced metal concentrations the water resulting from the mixing of brines would have been far from equilibrium and the barite and sulphide precipitation followed along the faults

metal sources in mineral deposits and crustal rocks of ecuador 1 n 4 s a lead isotope synthesis ecuador consists of terranes having both continental chaucha tahuin loja terranes and oceanic macuchi alao salado terranes affinity which were accreted to the amazon craton from late jurassic to eocene four main magmatic arcs were formed by the subduction of the farallon nazca plate since the juras sic a jurassic continental arc on the western margin of the amazon craton a jurassic island arc alao terrane an early tertiary island arc macuchi terrane and a middle late tertiary continental arc encompassing the ter ranes of macuchi chaucha tahuin loja and alao after complete assembly of the ecuadorian crust mineral deposits formed during these magmatic arc activities include porphyry cu and gold skarn deposits in associa tion with the jurassic continental arc polymetallic volcanic hosted massive sulfide deposits vhms in associ ation with the jurassic island arc of alao au cu zn vhms deposits in association with the early tertiary is land arc of macuchi and porphyry cu and precious metal epithermal deposits in association with the middle late tertiary continental arc magmatism on the newly assembled crust of ecuador macuchi chaucha tahuin loja and alao terranes in this study we have compiled 148 new and 125 previously published lead isotope analyses on paleozoic to miocene metamorphic intrusive volcanic and volcanosedimentary rocks as well as on jurassic to miocene magmatic related ore deposits of ecuador lead isotope compositions of the magmatic rocks of the four main arc events derive from mixing of various sources including mantle variably enriched by pelagic sediments and or by a high 238u 204pb component and heterogeneous continental crust rocks lead isotope compositions of the ecuadorian ore deposits display a broad range of values 206pb 204pb 18 3 19 3 207pb 204pb 15 54 15 74 208pb 204pb 38 2 39 2 which is as large as the range previously re ported for all magmatic related ore deposits of the central andean provinces i and ii combined ore deposits formed before complete assembly of the ecuadorian crust through complete accretion of the several terranes i e pre eocene have lead isotope compositions overlapping those of the associated magmatic rocks sug gesting a largely magmatic origin for their lead in contrast post assembly ore deposits i e post eocene have lead isotope compositions that only partly overlap those of the coeval magmatic rocks of the continental arc in fact several ore deposits have lead isotope compositions shifted toward those of the basement rocks that host them suggesting that lead derives from a mixture of magmatic lead and basement rock lead leached by hy drothermal fluids most ecuadorian ores have high 207pb 204pb values 15 55 suggesting a dominant continental crust or pelagic sediment origin of the lead however we caution against concluding that chalcophile metals for ex ample cu and au also have a continental crust origin ore deposits of the different terranes of ecuador irrespective of their age plot in distinct isotopic fields which are internally homogeneous this suggests that lithologic factors had an important control on the lead isotope compositions ultimately lead isotope compositions of the ore deposits of ecuador mirror the isotopic compositions of the rocks of the host terranes and are consistent with the multiterrane nature of the ecuado rian crust

seismomagnetic effects from the long awaited 28 september 2004 m 6 0 parkfield earthquake precise measurements of local magnetic fields have been obtained with a differentially connected array of seven synchronized proton magnetometers located along 60 km of the locked to creeping transition region of the san andreas fault at parkfield california since 1976 the m 6 0 parkfield earthquake on 28 september 2004 occurred within this array and generated coseismic magnetic field changes of between 0 2 and 0 5 nt at five sites in the network no preseismic magnetic field changes exceeding background noise levels are apparent in the magnetic data during the month week and days before the earthquake or expected in light of the absence of measurable precursive deformation seismicity or pore pressure changes obser vations of electric and magnetic fields from 0 01 to 20 hz are also made at one site near the end of the earthquake rupture and corrected for common mode signals from the ionosphere magnetosphere using a second site some 115 km to the northwest along the fault these magnetic data show no indications of unusual noise before the earthquake in the ulf band 0 01 20 hz as suggested may have preceded the 1989 ml 7 1 loma prieta earthquake nor do we see electric field changes similar to those suggested to occur before earthquakes of this magnitude from data in greece uni form and variable slip piezomagnetic models of the earthquake derived from strain displacement and seismic data generate magnetic field perturbations that are con sistent with those observed by the magnetometer array a higher rate of longer term magnetic field change consistent with increased loading in the region is apparent since 1993 this accompanied an increased rate of secular shear strain observed on a two color edm network and a small network of borehole tensor strainmeters and increased seismicity dominated by three m 4 5 5 earthquakes roughly a year apart in 1992 1993 and 1994 models incorporating all of these data indicate increased slip at depth in the region and this may have played a role in the final occurrence of the 28 september 2004 m 6 0 parkfield earthquake the absence of electric and magnetic field precursors for this and other earthquakes with m 5 7 3 elsewhere in the san andreas fault system indicates useful prediction of damaging earthquakes seems unlikely using these electromagnetic data

comment on material contrast does not predict earthquake rupture propagation direction by r a harris and s m day 1 harris and day 2005 hereinafter referred to as hd concluded from some numerical simulations and low resolution analysis of 8 m4 m6 earthquakes near parkfield ca that material contrast in fault zone structures is not important for earthquake propagation direction the limited theoretical and observational results of hd do not justify such a general conclusion considerations of a larger body of results suggest that material contrast may produce a statistically preferred direction of earthquake ruptures the inferred diversity of the 8 discussed events is consistent with their small number and relatively small size in addition the behavior has a natural explanation in a structure with two material interfaces the san andreas fault saf and the southwest fracture zone sfz on the opposite sides of a deformation damage region large earthquakes propagating predominantly as mode ii ruptures and affected primarily by properties of the bounding crustal blocks rather than the local structure are likely to exhibit a smaller amount of diversity

anisotropy in the shallow crust observed around the san andreas fault before and after the 2004 m 6 0 parkfield earthquake local seismic arrays were deployed at two locations along the san an dreas fault saf near parkfield california before and after the 2004 m 6 0 parkfield earthquake using local earthquakes we determine the anisotropic field within 1 2 km of the main trace of the saf at the two array locations separated by 12 km the initial array near the safod site was deployed for six weeks in october and november 2003 and the second array located near the town of parkfield was de ployed for 3 months following the 28 september 2004 m 6 0 parkfield earthquake we find the fast shear wave polarization direction nearly fault parallel n40w for stations on the main fault trace and within 100 m to the southwest of the saf at both array locations these fault parallel measurements span the 100 to 150 m wide zone of pervasive cracking and damage interpreted from fault zone trapped waves associated with the main fault core li et al 2004 2006 outside of this zone the fast orientations are scattered with some preference for orientations near n10e roughly parallel to the regional maximum horizontal compressive stress direction rh in addition fast directions are preferentially oriented parallel to a northern branch of the saf recorded on stations in the 2004 parkfield deployment the measured anisotropy is likely due to a combination of stress aligned micro cracks away from the fault and shear fabric within the highly evolved fault core the majority of our measurements are taken outside of the main fault core and we es timate the density of microcracks from the measured delay times apparent crack densities are approximately 3 with large scatter the data suggest weak depth dependence to the measured delay times for source depths between 2 and 7 km below 7 km source depth the delay times do not correlate with depth suggesting higher confining pressure is forcing the microcracks to close no coseismic variation in the anisotropic parameters is observed suggesting little to no influence on measured splitting due to the 2004 m 6 0 parkfield earthquake however the premainshock and postmainshock data presented here are from arrays separated by 12 km limiting our sensitivity to small temporal changes in anisotropy

conglomerate hosted copper mineralization in cretaceous andean molasse the coloso formation of northern chile alluvial fan sediments of the lower cretaceous coloso formation of northern chile were deposited during the evolution of a half graben arid intra arc basin the sediments were derived from an andesitic volcanic arc and show compositional variation which can be interpreted as an unroofing sequence copper mineralization is stratigraphically restricted to the upper 150 m of the sequence in conglomerates of predominantly granodioritic composition the presence of mineralized clasts at this level indicates the erosion of bedrock mineralization lead isotopic signatures of ore sulphide support the sedimentological evidence for derivation of the sediments and metals from an island arc volcano plutonic complex to the west of the basin a genetic model is proposed in which uneconomic metal concentrations were transported into the basin as detrital phases and released by diagenetic reactions the precipitation of copper minerals followed authigenic formation of quartz feldspar analcime and calcite and also some secondary parosity generation copper minerals include the oxychloride atacamite and the suphides bornite digenite djurleite and covellite sulphur isotope values for the sulphides are relatively heavy isotope enriched 34 s 3 6 to 12 8 although these results could be interpreted in terms of closed system bacterial sulphide reduction there is no known occurrence of organic material within the coloso basin an alternative explanation involving the mixing of diagenetically derived copper rich brines and sulphur rich hydrothermal fluids is proposed to account for the coloso mineralization

migration of early aftershocks following the 2004 parkfield earthquake a significant number of the early aftershocks following large shallow earthquakes are missing in existing earthquake catalogues an analysis of the waveforms of 3 647 relocated earthquakes along the parkfield section of the san andreas fault reveals 11 times more aftershocks within three days of the 2004 parkfield earthquake than listed in a standard catalogue large shallow earthquakes are immediately followed by numerous aftershocks a significant portion of these events is missing in existing earthquake catalogues mainly because seismicity after the mainshock can be masked by overlapping arrivals of waves from the mainshock and aftershocks1 2 3 4 however recovery of the missing early aftershocks is important for understanding the physical mechanisms of earthquake triggering2 3 4 and for tracking postseismic deformation around the rupture zone associated with the mainshock5 6 7 here we use the waveforms of 3 647 relocated earthquakes8 along the parkfield section of the san andreas fault as templates9 10 to detect missing aftershocks within three days of the 2004 magnitude 6 0 parkfield earthquake we identify 11 times more aftershocks than listed in the standard catalogue of the northern california seismic network we find that the newly detected aftershocks migrate in both along strike and down dip directions with logarithmic time since the mainshock consistent with numerical simulations of the expansion of aftershocks caused by propagating afterslip11 12 the cumulative number of early aftershocks increases linearly with postseismic deformation in the first two days supporting the view that aftershocks are driven primarily by afterslip13 14

genesis of the ores of the zambian copperbelt abstract the theories for the origin of the ores of the copperbelt of zambia and zaire are reviewed following an account of the historical development of ideas from epigenetic through syngenetic to syngenetic diagenetic and ultimately to neohydrothermalist theories models for the genesis of these deposits are critically assessed in the light of the data currently available this examination is conducted with particular regard to the questions of the sources of copper and cobalt the timing of mineralizing events and the physicochemical conditions of metal sulphide precipitation although accepting that the origin of these ores remains controversial it is concluded that the most likely sources of both copper and cobalt are the rocks of the basement complex that metals were probably transported both in surface and ground waters and that the main mineralizing event took place during early diagenesis with sulphide precipitation occurring via bacterial reduction of seawater sulphate the precipitation of sulphides probably occurred at temperatures around 20 60 c and at near neutral ph with minor fluctuations in eh and variations in the solubilities of the metals involved causing mineral zonation the burial and compaction of these sediments probably resulted in the expulsion of metal rich fluids and formation of sulphides in the immediate footwall and hanging wall of the main ore horizon with continued burial resulting in the formation of sulphide bearing pods and veins of lateral secretion origin tectonic deformation and metamorphism in the lufilian orogeny although resulting in a set of cross cutting high temperature mineralized veins appears not to have resulted in significant remobilization of the sulphides

surface fault slip associated with the 2004 parkfield california earthquake surface fracturing occurred along the san andreas fault the subparallel southwest fracture zone and six secondary faults in association with the 28 september 2004 m 6 0 parkfield earthquake fractures formed discontinuous breaks along a 32 km long stretch of the san andreas fault sense of slip was right lateral only locally was there a minor 1 11 mm vertical component of slip right lateral slip in the first few weeks after the event early in its afterslip period ranged from 1 to 44 mm our observations in the weeks following the earthquake indicated that the highest slip values are in the middle mountain area northwest of the mainshock epicenter creepmeter measurements indicate a similar distribution of slip surface slip along the san andreas fault developed soon after the mainshock field checks in the area near parkfield and about 5 km to the southeast indicated that surface slip developed more than 1 hr but generally less than 1 day after the event slip along the southwest fracture zone developed coseismically and extended about 8 km sense of slip was right lateral locally there was a minor to moderate 1 29 mm vertical component of slip right lateral slip ranged from 1 to 41 mm surface slip along secondary faults was right lateral the right lateral component of slip ranged from 3 to 5 mm surface slip in the 1966 and 2004 events occurred along both the san andreas fault and the southwest fracture zone in 1966 the length of ground breakage along the san andreas fault extended 5 km longer than that mapped in 2004 in contrast the length of ground breakage along the southwest fracture zone was the same in both events yet the surface fractures were more continuous in 2004 surface slip on secondary faults in 2004 indicated previously unmapped structural connections between the san andreas fault and the southwest fracture zone further revealing aspects of the structural setting and fault interactions in the parkfield area

inference of coseismic slip via joint inversion of gps and aftershock data the 2004 parkfield example 1 in many coseismic slip inversions the number of model parameters is much larger than that of the independent observations and the problem is extremely underdetermined it is thus instructive to incorporate additional data sets into the slip inversion in this study i describe a new approach for coseismic slip inversion whereby both gps displacements and first day aftershock rate changes are used jointly to constrain the solution the joint inversion incorporates the dieterich s aftershock model which adopts a constitutive friction that depends logarithmically on the sliding rate the method is applied to the 2004 parkfield earthquake the joint inversion not only provides resolving power of slip at depths inaccessible to gps only inversions but it also helps to gain insight on the fault mechanical properties i show that the data are consistent with the adopted aftershock model being the dominant mechanism for aftershock production along the parkfield segment and i obtain an upper bound on the friction dependence on the log of rate of fault patches that have experienced aftershock activity a consequence of the irregular aftershock distribution is that the slip distribution is extremely nonsmooth with the aftershock zones acting as barriers

setting characteristics and age of the andean porphyry copper belt in colombia three distinct porphyry copper subbelts are defined in the colombian andes 1 a western subbelt emplaced during the early to middle eocene in an oceanic domain underlain by ophiolitic basement along the western side of the western cordillera 2 a composite eastern subbelt generated during the middle jurassic to earliest cretaceous in a continental domain underlain by elements of the guyana shield along the eastern side of the central cordillera and the western side of the eastern cordillera and between the two 3 a central subbelt formed in the early to late miocene at the contact of the oceanic and continental domains along the cauca patia depression and its flanks k ar geochronometry undertaken as part of this study provided preferred minimum ages of 54 7 or 1 3 m y for murindo 48 1 or 1 0 m y for acandi and 42 7 or 0 9 m y for pantanos pegadorcito in the western subbelt 166 or 4 m y for mocoa 166 or 4 m y for dolores 144 or 3 m y for california and 131 or 2 m y for infierno chili in the eastern subbelt and 17 4 or 0 4 m y for piedrasentada in the central subbelt the porphyry copper prospects are associated with dacite to tonalire porphyry stocks which in the western and eastern subbelts intruded batholiths emplaced perhaps 15 to 30 m y earlier but which in the central subbelt are isolated within metamorphic or sedimentary host rocks the porphyry copper systems exhibit a variety of alteration patterns with potassium silicate and sericitic alteration important in the highest grade prospects and propylitization predominant in low grade occurrences none of the prospects displays significant supergene enrichment although porphyry coppers in the continental domain tend to be more molybdenum rich than those in the oceanic domain gold rich prospects occur in both settings as do major lode gold deposits the jurassic and miocene subbelts are interpreted to have been emplaced during eastward subduction at andean type continental margins whereas the western eocene subbelt could have been generated in either a modified andean type setting or in an intraoceanic island arc prior to its accretion to the continental edge