paleomagnetism of coastal california and baja california alternatives to large scale northward transport paleomagnetic data from the santa lucia orocopia sloa and baja borderland bba allochthons of coastal california and baja california have been interpreted to indicate up to 2500 km of post mid cretaceous northward transport of these regions with respect to interior north america however with neogene strike slip offsets taken into account geological interpretations correlate basement rocks of the coastal allochthons with continental basement rocks directly across the san andreas and related fault systems we have examined paleomagnetic data from sloa and bba and conclude that apparent discordances can be explained without large scale pre neogene tectonic transport three major observations are fundamental to this analysis 1 paleolatitudes derived from volcanic rocks of the jurassic eugenia formation of bba and coast range ophiolite of sloa are concordant when compared to revised jurassic reference paleomagnetic poles from interior north america 2 isotopic and paleobarometric data from the peninsula ranges batholith in southern california indicate that the batholith has been tilted northeast side up by an amount that can account for discordant paleomagnetic directions observed in plutonic rocks of the batholith without large scale northward transport 3 literal interpretation of the paleolatitudes determined from paleomagnetic directions in upper cretaceous and paleogene marine sedimentary rocks of sloa and bba requires north then south then north transport and a complex motion history between the two allochthons however concordant paleolatitudes are indicated by some sedimentary rocks while coeval or younger sedimentary rocks of the same allochthon have discordant paleolatitudes coupled with recent documentations of compaction shallowing of paleomagnetic inclination in other marine sedimentary rocks these inconsistencies suggest that paleolatitudes derived from most of the marine sedimentary rocks of sloa and bba are biased towards low paleolatitudes by compaction shallowing

tomographic images of the upper crust from the los angeles basin to the mojave desert california results from the los angeles region seismic experiment we apply inversion methods to first arriving p waves from explosive source seismic data collected along line 1 of the los angeles region seismic experiment larse extending northeastward from seal beach california to the mojave desert in order to determine a seismic model of the upper crust along the profile we use resolution information to quantify the extent of blurring in the larse images and to smooth a damped least squares dls image by postinversion filtering pif most of the original data fit is preserved while minimizing model artifacts we compare dls pif and smoothing constraint inversion images using both real and synthetic data a preferred pif image includes larger scale features in the smoothing constraint inversion image and finer scale features in the dls inversion image that are consistent with geologic information we interpret principal model features in terms of geology including faulting the maximum depth of low velocity sedimentary and volcanic rocks in the los angeles basin is 8 9 km and in the san gabriel valley is 4 5 5 km a horst like uplift of basement rocks occurs between these basins the northeastern boundary of the san gabriel valley is imaged as a tabular moderately north dipping low velocity zone that projects to the surface at the southernmost trace of the sierra madre fault system in the central and southern san gabriel mountains velocity depth profiles are consistent with intermediate velocity mylonites overlying lower velocity pelona schist along a shallowly southwest dipping vincent thrust fault tomography does not provide a definitive dip for the san andreas fault but combined with other larse results is consistent with a vertical to steep northeast dip

small scale heterogeneity of phanerozoic lower crust evidence from isotopic and geochemical systematics of mid cretaceous granulite gneisses san gabriel mountains southern california an elongate belt of mid cretaceous compositionally banded gneisses and granulites is exposed in cucamonga terrane in the southeastern foothills of the san gabriel mountains of southern california banded gneisses include mafic granulites of two geochemical types type 1 rocks are similar to high al arc basalts and andesites but have higher hfse high field strength element abundances and extremely variable lile largeion lithophile element abundances while type 2 rocks are relatively low in al and similar to alkali rich mor midocean ridge or intraplate basalts intercalated with mafic granulites are paragneisses which include felsic granulites aluminous gneisses marble and calc silicate gneisses type 1 mafic granulites and calcic trondhjemitic pegmatites also oceur as cross cutting synmetamorphic dikes or small plutons small scale heterogeneity of deep continental crust is indicated by the lithologic and isotopic diversity of intercalated ortho and paragneisses exposed in cucamonga terrane geochemical and isotopic data indicate that k rb and u depletion and sm nd fractionation were associated with biotite muscovite dehydration reactions in type 1 mafic granulites and aluminous gneisses during high grade metamorphism field relations and model initial isotopic ratios imply a wide range of protolith ages ranging from early proterozoic to phanerozoic

multi scale depositional successions in tectonic settings observations in sedimentary basins affected by deformation show that the fault induced depositional accommodation at various spatial and temporal scales is closely linked to basin kinematics the tectonically driven sediment infill displays the history of deepening and shoaling facies that are controlled by the activation of faults and changes in their offset rates simply stated this results in shifting sedimentary facies towards the source area or towards the basin centre in response to increasing or decreasing depositional space we propose a first principle conceptual model for tectonic successions controlled by the balance between the rates of creation of depositional space and sediment supply these sediment bodies are bounded by succession boundaries and comprise sourceward or basinward shifting facies tracts that are separated at a point of reversal due to the relatively steep slopes associated with the evolution of faults changes in sediment supply rates and mass wasting are common in these systems and may complicate the normal rhythm of the shifting facies tracts once tectonic quiescence is achieved and if the basin is connected to the open ocean eurybatic or eustatic base level changes may take over and play a greater role in sedimentary rhythm and cyclicity we illustrate the efficacy of the new concept with a review of examples from extensional contractional and strike slip basins we show that the basic tectonic succession model is applicable at all temporal and spatial scales and whether the tectonics cause subsidence or uplift and in all types of tectonic settings that determine the evolution of sedimentary basins

paleogene strata of the eastern los angeles basin california paleogeography and constraints on neogene structural evolution post paleogene dextral slip of 8 9 km is demonstrated for the southeastern part of the whittier fault zone in the eastern los angeles basin area of southern california a linear axis of greatest thickness for the combined upper paleocene and lower to lower middle eocene clastic formations intersects the fault zone and is offset by it to give the new measure fragmentary evidence hints that the whittier structural zone may have exerted control on bathymetric topographic relief and sedimentation even in latest paleocene ca 54 ma a clear topographic influence was exerted by 20 17 ma strike slip and present deformational style is younger than ca 8 ma our paleogene isopach map extends as far west as long 117 58 w and is a foundation for companion zonal maps of predominant lithology and depositional environments integration of new palynological data with published biostratigraphic results and both new and published lithologic and sedimentological interpretations support the zonal maps reconstruction of marine nonmarine facies and fragmented basin margins yields a model for the northeastern corner of a paleogene coastal basin palinspastic adjustment for the neogene quaternary whittier fault offset and a reasoned westerly extension of the northern edge of the basin model yield a reconstruction of paleogene paleogeography paleoceanography our reconstruction is based partly on the absence of both paleocene and eocene deposits beneath the unconformable base of the middle miocene topanga group in a region nowhere less than 15 km wide between the raymond sierra madre cucamonga fault zone and the northern edge of the paleocene basin thus paleogene strata of the santa monica mountains could not have been offset from the northern extension of the santa ana mountains by sinistral slip on those boundary faults structural rearrangements needed to accommodate the clockwise rotation of the western transverse ranges from the early miocene starting position are thereby fixed

the tectonic history of the southwestern united states and sonora mexico during the past 100 m y the area between the colorado plateau on the north new mexico and chihuahua to the east and southern and baja california to the southwest has undergone a complicated thermal and tectonic history climaxing in medial cretaceous time and manifested in a sequence of events which continue to the present time independent of plate boundary transform faulting this sustained sequence of events was initiated by subduction related magmatic emplacement largely between 120 and 50 ma beginning in the west and sweeping eastward across the region the emplacement of these rocks generated a large isostatic welt which began to elevate in late medial cretaceous time in the west central portion of the area and spread outward until in oligocene time the west coast of southern california was emergent almost to the continental escarpment both erosional and tectonic unloading accompanied elevation with the axis of the welt achieving its maximum elevation in earliest cenozoic time when north central sonora may have had elevations of the order of 5000 m body forces caused the welt to relax laterally producing thrust and nappe structures which were westward vergent in the west and eastward vergent in the east to the east these structures are included in what is called the larimide orogeny to the west they include such features as the santa rosa mylonite belt and related structures as with the magmatic emplacement the gravitational spreading began in the west during the eocene additional rebound in response to deep erosion and tectonic unroofing began to expose midcrustal rocks within the core area of the welt and subhorizontal detachment began along the brittle ductile boundary during oligocene and early miocene time renewed isostatic uplift resulted from rising magma and continued erosional and tectonic denudation spawned both brittle and ductile extension hydrothermal alteration and mineral deposition from mid miocene to the present time the central portion of the area has subsided while the marginal mountain ranges have elevated

possibility of spatial variation of high frequency seismic motions due to random velocity fluctuation of sediments considering the possibility that random velocity fluctuation of sediments may affect spatial variation of high frequency seismic motions in small areas a few hundred meters in diameter we examine this possibility experimentally and numerically by comparing seismic array data obtained at three geologically different sites rock stiff sediment and soft sediment sites we make two observations related to the effect of random velocity fluctuation of sediments the first observation is that above 3 hz waveform spatial variation evaluated in terms of the cross correlation is larger at the stiff sediment site than at the rock site the second is that above 2 hz the amplitude spatial variation evaluated by the spectral ratio shows more observation station specific behavior at the soft sediment site than at the stiff sediment site we try to explain these two observations by modeling the sediments as random media two dimensional finite difference simulations for plane sh and sv wave incidences demonstrate that the sediments may affect the seismic waveform variation above 3 hz if the autocorrelation functions of the velocity fluctuations are in the range derived from well log velocity data the velocity structure at the soft sediment site is modeled as a two layered random media having a low velocity surface layer the finite difference simulations for this sediment model demonstrate that it is also possible that amplitude variation above 2 hz is caused by random velocity fluctuations in the low velocity surface layer

tectonics of the san gabriel basin and surroundings southern california the sangabriel basin is a pliocene pleistocene transverse ranges structure bounded by the san gabriel mountains on the north the san jose and puente hills on the east and the repetto and montebello hills on the west a basement boundary between gneissoid rocks of san gabriel mountains aspect and peninsular ranges rocks strikes east across the basin and connects with the san jose fault this boundary may represent the eastward continuation of the canton fault a middle miocene precursor of the san gabriel fault system with up to 30 km of right slip canton fault displacement is largely canceled by 22 5 km of left slip on a precursor to the raymond fault such that an oligocene dacite in the san jose hills and clasts derived from it show little evidence of large horizontal displacement between the san gabriel mountains and puente hills clockwise rotation in the middle miocene probably influenced the distribution of lateral slip the fill in the northeast trending pliocene pleistocene san gabriel basin is a basal shallow marine sequence overlain by the nonmarine duarte conglomerate in contrast to the deep water fernando formation of the los angeles basin the paleoslope trends south in the direction of the repetto and puente hills evidence that uplift of these hills postdated deposition the triangular san gabriel basin is currently a stable block bounded by the right slip northwest striking east montebello fault on the west and the left slip northeast striking walnut creek fault on the east farther east the san jose and puente hills are underlain by an east trending active fold belt including the san jose reverse fault and anticline the walnut anticline and the puente hills anticline adjacent to the right lateral whittier fault the east montebello fault is bounded on the west by the elysian park anticlinorium a fold belt in downtown los angeles the left slip holocene raymond fault joins the sierra madre reverse fault at its segment boundary marked by the clamshell sawpit fault the triangular stable block between east trending fold belts is bounded on the south by the puente hills blind thrust and on the north by the sierra madre fault documenting north south quaternary convergence east west extension is also indicated although not confirmed by geodetic measurements

mineralogy and pressure temperature time path of cretaceous granulite gneisses south eastern san gabriel mountains southern california mid cretaceous granulite gneisses crop out in a narrow belt in the cucamonga region of the south eastern foothills of the san gabriel mountains southern california interlayered mafic granulites and pelitic carbonate calc silicate and quartzofeldspathic metasediments record hornblende granulite subfacies metamorphism at approximately 8 kbar and 700 800 c regional deformation and formation of banded gneisses ceased by c 108 ma although mafic intermediate magmatism and high grade metamorphism continued locally as late as c 88 ma garnet zoning in metapelitic gneisses suggests that peak metamorphism was followed locally by a period of near isobaric cooling but this interpretation requires diachronous cooling of the granulite belt which cannot be demonstrated without detailed thermo chronological data it is more likely that the entire terrane remained at granulite facies p t conditions until 88 ma followed by rapid uplift associated with juxtaposition against adjacent middle and upper crustal arc terranes uplift occurred between c 88 and 78 ma at rates of approximately 1 2 km ma 1 the geotectonic evolution of the cucamonga granulites is similar to mid cretaceous high p granulites in the sierra nevada and salinian block of central california late cretaceous uplift common to these granulites may provide an important tectonic link between dismembered mesozoic batholithic terranes in the california cordillera

platinum group elements co ni fe sulfarsenides and mineral paragenesis in cu ni platinum group element deposits copper cliff north area sudbury canada three deposits the offset sublayer 100 and 120 orebodies and contact sublayer lady violet deposit in the copper cliff north mine area sudbury were sampled with the aim of defining the mineral assemblages the ores are composed of pyrrhotite pentlandite chalcopyrite with minor titanomagnetite ilmenite accessory sulfarsenides bi te minerals and sperrylite sulfarsenides which are prominent accessory minerals contain the platinum group elements pge rh ru ir os and pt in decreasing order of abundance in solid solution some zoned sulfarsenide crystals have pge concentrated in the centers decreasing toward the edges nickeliferous cobaltite the common sulfarsenide contains as much as 16 at percent pge hollingworthite rh ru ass which occurs as cores or distinct crystals enclosed in cobaltite is a newly recognized occurrence in the 100 120 and lady violet deposits in the sudbury south range formation of primary pge bearing sulfarsenides is related to exsolution from monosulfide solid solution at about 550 to 600 c during late crystallization aqueous fluids interacted with the rocks resulting in precipitation of hydrous silicates epidote biotite chlorite and remobilization of pge bearing sulfarsenides

structural evidence for northeastward movement on the chocolate mountains thrust southeasternmost california the late cretaceous chocolate mountains thrust of southeastern california and southwestern arizona places a block of proterozoic and mesozoic continental crust over the late mesozoic continental margin oceanic sedimentary and volcanic rocks of the regionally distinctive orocopia schist the chocolate mountains thrust is interpreted as a thrust burial subduction fault rather than a low angle normal exhumation unroofing uplift fault an important parameter required to understand the tectonic significance of the chocolate mountains and related thrusts is their sense of movement the chocolate mountains thrust zone contains sparse to locally abundant mesoscopic asymmetric folds fabric relations supported by regional geologic evidence indicate that these folds are an integral part of and coeval with the thrust zone on a lower hemisphere equal area plot representing the orientation and sense of asymmetry of 80 thrust zone folds from 36 localities spread over an area 60 by 10 km z folds plot northwest of and s folds plot southeast of a northeast southwest striking vertical plane of overall monoclinic symmetry the only sense of movement consistent with the collective asymmetry of the thrust zone folds is top to the northeast asymmetric microstructures studied at several localities also indicate top to the northeast movement paleomagnetic data suggest that the original sense of thrusting prior to neogene vertical axis tectonic rotation related to the san andreas fault system was northward the essential point is that movement of the upper plate of the chocolate mountains thrust evidently was continentward continentward thrusting suggests a tectonic scenario in which an insular or peninsular microcontinental fragment collided with mainland southern california the suture predicted by this model is elusive but the chocolate mountains thrust and underlying orocopia schist themselves may represent the suture at the present level of exposure alternative tectonic models involving subduction of the orocopia schist eastward beneath continental southern california circumvent the suture problem but are presently not supported by any direct structural evidence

compositional variations within and between five sudbury ore deposits recent work on the platinum group element pge content in ni sulfide ores has shown that those associated with komatiite magmas generally have low pt pd ru ir os ratios 13 the levack west and little stobie 1 and 2 deposits conform with this generalization having ratios of 18 6 19 2 and 13 2 respectively hoffman et al 1979 pt and pd are present in roughly equal proportions in these deposits ranging between 1 000 and 3 000 ppm in massive sulfides new data from the strathcona deposit indicate values of close to 400 ppm for both pt and pd approximately one third of the levels at the nearby levack west deposit both strathcona and levack west are strongly zoned with respect to platinum group elements au and base metals cu ni zn pt pd and au increase away from the irruptive hanging wall into the footwall and co rh ru ir and os increase in the reverse direction at strathcona this zoning results in a decrease of the pt pd ru ir os ratio from 132 in the footwall to 2 2 in the hanging wall ore relevant phase equilibria data indicate that cu ni zn pt and pd are likely to become enriched in the residual liquid of a fractionating sulfide melt whereas co rh and ru will concentrate in the early crystallizing monosulfide solid solution the correspondence between the experimental data and natural observations is strong evidence that the zoning is the consequence of the fractionation of a sulfide melt with the residual liquid being expelled progressively into the footwall average data obtained for the falconbridge depost resemble those of the hanging wall at strathcona both in the low pt pd ru ir os ratio of 2 3 and in a low cu ni ratio suggesting that the ore sampled represents an early crystallizing fraction and that a late crystallizing pt rich fraction equivalent to the footwall ore at strathcona and amounting to perhaps twice the present volume of ore was not included in the sampling and may well not be within the present orebody the deposit is located largely within a vertical fault zone it is possible that the sulfide melt was introduced up the fault crystallizing as it moved upward and that the pt rich portion crystallized farthest up the fault and has been removed by erosion however sampling over a 1 600 m vertical interval of the ore zone has failed to reveal any progressive variation in the pt pd ru ir os ratio within the fault zone an alternative and preferred hypothesis is that the deposit was originally zoned as at strathcona with the pt rich portion forming away from the irruptive within the footwall this portion may have been faulted off leaving the early crystallizing portion behind to become remobilized into the fault zone if true the present location of the pt rich portion is intriguing in addition to having lower concentrations of platinum group elements than levack west the strathcona deposit also has lower concentrations of ni and cu these compositional differences can be modeled in terms of a larger amount of sulfide equilibrating with a given amount of the host silicate magma at the former deposit than at the latter sequences of similar magmatic events coupled with a proposed fractionation of olivine can account for many of the compositional variations between different sudbury deposits

intrusion of horizontal dikes tectonic significance of middle proterozoic diabase sheets widespread in the upper crust of the southwestern united states initially horizontal sheet intrusions of middle proterozoic diabase are abundant in a region 650 by 300 km across in arizona and california the diabase forms discordant sheets in basement granite and gneiss and sills in overlying shelf sedimentary sequences massive granite is the most common basement host for the sheets probably because it fractured more easily than foliated hosts during sheet emplacement steep feeder dikes are rare compared to the sheets the diabase in many places is exposed in fault blocks that were tilted during tertiary tectonic extension structure sections restored from the map patterns of upended blocks show that the sheets were intruded at levels throughout the upper crust to depths of at least 13 km sheet intrusion implies a vertical orientation of the least compressive stress so i conclude that the crust was under tectonic compression or in an isotropic state of stress at the time of diabase intrusion about 1 1 ga magma overpressures water encountered by rising magma vertical changes in the crustal stress regime and flotation of low density granite all may be important factors for sheet intrusion the stress conditions suggested by the presence of the sheets argue against an extensional tectonic regime earlier proposed for the diabase event the diabase province contrasts structurally with similar age provinces of basaltic magmatism elsewhere in north america that show evidence of tectonic extension such as the midcontinent rift the consistent orientations of the sheets commonly allow them to be used as structural markers for postdiabase deformation of basement blocks sheet intrusions in the geologic record may be seriously underreported their recognition is important for the interpretation of seismic reflection profiles of continental crust sheets in arizona may be responsible for the bagdad reflection sequence which extends to depths of at least 15 km

multiple hydrothermal processes in footwall units of the north range sudbury igneous complex canada and implications for the genesis of vein type cu ni pge deposits systematic regional sampling along the contact zone of the 1 85 ga age sudbury igneous complex with the archean levack gneiss footwall in the north range of the sudbury structure revealed textural mineralogical and fluid inclusion systematics of post sudbury igneous complex hydrothermal processes that affected the various lithologies at late stages of emplacement of the sudbury igneous complex and formation of magmatic fe ni cu sulfide deposits a partial melt from the levack gneiss invaded the contact zone this partial melt is revealed by small microdikes and irregular bodies of granophyric quartz plagioclase with megacrysts of hornblende clinopyroxene and titanite plagioclase hornblende equilibrium was established at 750 to 800 c and 1 10 to 1 55 kbars pressure corresponding to about a 4 to 6 km depth under lithostatic conditions f cl wt percent ratios around 15 for accessory apatite and hornblende indicate that a cl rich fluid phase separated during the crystallization of the footwall granophyre this is expressed as miarolites the cl rich fluid 50 wt nacl equiv salinity was trapped as primary fluid inclusions in quartz at around 480 c minimum temperature and around 1 1 kbars minimum pressure during supercooling these inclusions are rich in ca fe mn and k as well as na chloride this fluid may have interacted with earlier primary magmatic sulfide causing remobilization and reprecipitation of cu ni platinum group elements pge in veins and disseminations in the footwall these veins are parallel to the sudbury igneous complex footwall contact and are characterized by chalcopyrite pentlandite millerite magnetite stilpnomelane ferropyrosmalite epidote and chlorite michenerite moncheite merenskyite froodite insizwaite sobolevskite gold and bi ni sulfides are associated with sulfides epidote quartz actinolite and chlorite are common in the alteration selvages of the veins compositions and assemblages of platinum group minerals pgm indicate their precipitation below 575 to 485 c primary highly saline fluid inclusions about 40 wt nacl equiv in quartz indicate crystallization at 400 to 480 c and around 1 6 kbars minimum t and p respectively late carbonate epidote actinolite chlorite veins and alteration overprinted the earlier assemblages at about 300 to 400 c with some bornite millerite native silver and other bi sulfides the second stage of hydrothermal activity is characterized by regional carbonic aqueous nacl co 2 ch 4 h 2 o type immiscible fluids that were trapped as secondary inclusions in quartz from various lithologies no mineralization is related to this stage along the north range boiling of these fluids took place during a pressure drop from lithostatic to hydrostatic conditions during uplift from about a 5 to 6 to a 3 to 4 km depth at 300 to 350 c high 20 26 wt nacl equiv and low salinity 6 12 wt nacl equiv fluids coexisted with different carbonic species contents the predominant north south and northwest southeast orientations of fluid inclusion planes reveal that mobilization of carbonic aqueous solutions may be related to the northwesterly oriented thrusting in the sudbury structure during the late stages 1 8 1 7 ga of the penokean orogeny and to predominantly north south faulting in the north range the third stage of fluid mobilization also took place mostly along northerly and northwesterly oriented fractures aqueous fluids were ca rich brines 20 40 wt salinity with temperatures between 150 and 250 c some of these fluids also circulated in fractures parallel to the sudbury igneous complex footwall contact ne sw thus they locally may have interacted with the earlier sulfide assemblages and are also responsible for formation of late veinlets with chalcopyrite epidote quartz chlorite assemblages mobilization of these fluids took place under litho and hydrostatic conditions at about a 4 to 6 km depth this hydrothermal activity is related to a regional tectonothermal event during emplacement of northwesterly oriented sudbury dikes 1 24 ga regional scale fluid inclusion studies along the north range highlight the role of multiple hydrothermal processes in the metallogenic evolution of the sudbury igneous complex and especially in the distribution of copper and precious metals in the footwall units

a deterministic and stochastic velocity model for the salton trough basin and range transition zone and constraints on magmatism during rifting as a high resolution addition to the 1992 pacific to arizona crustal experiment pace a 45 km long deep crustal seismic reflection profile was acquired across the chocolate mountains in southeastern california to illuminate crustal structure in the transition between the salton trough and the basin and range province the complex seismic data are analyzed for both large scale deterministic and fine scale stochastic crustal features a low fold near offset common midpoint cmp stacked section shows the northeastward lateral extent of a high velocity lower crustal body which is centered beneath the salton trough off end shots record a high amplitude diffraction from the point where the high velocity lower crust pinches out at the moho above the high velocity lower crust moderate amplitude reflections occur at midcrustal levels these reflections display the coherency and frequency characteristics of reflections backscattered from a heterogeneous velocity field which we model as horizontal intrusions with a von karman fractal distribution the effects of upper crustal scattering are included by combining the mapped surface geology and laboratory measurements of exposed rocks within the chocolate mountains to reproduce the upper crustal velocity heterogeneity in our crustal velocity model viscoelastic finite difference simulations indicate that the volume of mafic material within the reflective zone necessary to produce the observed backscatter is about 5 the presence of wavelength scale heterogeneity within the near surface upper and middle crust also produces a 0 5 s thick zone of discontinuous reflections from a crust mantle interface which is actually a first order discontinuity

empirical tests of carbon isotope thermometry in granulites from southern california abstract peak metamorphic carbon isotope fractionations between calcite and graphite cal gr in marbles and calc silicates from the cucamonga granulite terrane san gabriel mountains california range from 3 48 to 2 90 the data are used to test three previously published calibrations of the calcite graphite carbon isotope thermometer an empirical calibration of the calcite graphite carbon isotope thermometer gives temperatures of 700 750 c a theoretical experimental calibration of the system gives temperatures of 760 870 c an experimental calibration gives temperatures of 870 1300 c temperatures calculated using the empirical calibration are in agreement with those calculated from garnet based cation exchange thermometry when uncertainty is considered temperatures calculated using the theoretical experimental calibration overlap the upper range of cation exchange thermometry temperatures and range to 50 c higher the experimental calibration yields temperatures from 50 to 480 c higher than those from cation exchange thermometry moreover temperatures from the experimental calibration are also inconsistent with mineral and melt equilibria in the granulite phase assemblage despite the better agreement between cation exchange thermometry and the empirical calibration of the calcite graphite system temperatures calculated using the theoretical experimental calibration may be real peak metamorphic temperatures if retrograde diffusion partially reset garnet based cation exchange thermometers by c 50 c then the cation exchange temperatures are consistent with those from the theoretical empirical calibration thermometric evidence from biotite dehydration melting equilibria is consistent with either the empirical calibration if melting was fluid present or the theoretical experimental calibration if melting was fluid absent

platinum group minerals in the o toole ni cu co deposit brazil the o toole deposit is a cu ni co sulfide lens hosted by ultrabasic rocks the orebody has undergone postdeformational metamorphism and shearing the main sulfides of the o toole deposit are pyrrhotite po pentlandite pn and chalcopyrite cp in average proportions of 65po 30pn 5cp cobaltite gersdorffite and sphalerite are the most frequent accessories minerals assay data indicated the presence of platinum group elements pge platinum group minerals pgm were identified during microscopy on ore from the o toole deposit mineral identifications were made and confirmed by electron microprobe kotulskite melonite followed by irarsite and sperrylite are the most abundant pgm other identified phases include osas 2 osass osrhass ruteas osruas osas 5 and a complex os re as te fe y rh mineral platinum group minerals occur frequently as inclusions in cobaltite gersdorffite suggesting that the pgm formed first since pyrrhotite replaces cobaltite gersdorffite indicating its later crystallization it can be deduced that the pgm formed during the first stages of magma crystallization before sulfides and arsenides routine microprobe analysis identified a rhenium sulfide res 2 the second reported global occurrence

a third issue devoted to platinum deposits preface studies of magmatic deposits and the processes which produced concentrations of platinum group elements continue to dominate the platinum group element literature since the last special issue economic geology 1982 v 77 no 6 development of ideas on the fluid dynamics of mafic magma chambers to explain the layering mcbirney and noyes 1979 huppert and sparks 1980 campbell et al 1983 irvine et al 1983 huppert et al 1984 sparks and huppert 1984 have significantly contributed to our current understanding of these deposits the challenge facing us now is a detailed petrogenetic explanation of the significance of certain other phenomena such as fluid inclusions and cl bearing minerals papers on the bushveld complex are an important component of this special issue but they are not as predominant as in the last of particular interest are the first papers representing results of the current worldwide search for new bushveld type platinum group element deposits another feature of this special issue is an increased focus on chromitites both from the bushveld and elsewhere

seismic mapping of shallow fault zones in the san gabriel mountains from the los angeles region seismic experiment southern california during the los angeles region seismic experiment larse a reflection refraction survey was conducted along a profile line 1 extending from seal beach california northeastward to the mojave desert and crossing the los angeles and san gabriel valley basins and san gabriel mountains in most shot gathers from the southern and central san gabriel mountains clear secondary arrivals are seen that merge or appear to merge with first arrivals at three locations including the location of the vincent thrust fault an exposed late mesozoic early cenozoic megathrust these secondary arrivals are interpretable as reflections in the shallow crust 5 km depth from a concave upward interface that projects to the surface in the north near the vincent thrust fault is offset in its central part at the san gabriel fault an old branch of the san andreas fault and terminates in the south at 1 to 2 km depth at the southern mountain front the velocity structure above and below this interface strongly suggests it is the vincent thrust fault intermediate velocities 6 2 km s consistent with mylonites overlying the vincent thrust fault are observed above it lower velocities 5 8 km s consistent with the pelona schist underlying the vincent thrust fault are observed below it problems arise however in attempting to match this reflector to the exposed vincent thrust fault which is seen in outcrops east of line 1 the vincent thrust fault is shallower than the reflector in most places an unmapped structure steep fault monocline or thrust fault is required between line 1 and the outcrops that either drops the vincent thrust fault down to the depths of the reflector or repeats the vincent thrust fault beneath line 1 in the footwall of another thrust fault an alternative interpretation of the reflector is a deep greenstone horizon within the pelona schist although this alternative is not favored by the velocity structure

thermobarometric constraints on the depth of exposure and conditions of plutonism and metamorphism at deep levels of the sierra nevada batholith tehachapi mountains california we present thermodynamic estimates of pressures temperatures and volatile activities in variably deformed gabbroic to granitic cretaceous 115 100 ma batholithic and framework rocks of the tehachapi mountains southernmost sierra nevada california al contents of hornblende in granitoids imply igneous emplacement at 8 kbar in the southernmost tehachapi mountains with lower pressures 3 7 kbar to the north metamorphic pressures and temperatures for garnet bearing paragneisses and metaigneous rocks were estimated on the basis of garnet hornblende plagioclase quartz and garnet biotite plagioclase quartz thermobarometers disparate results for the metaigneous rocks from the latter system point to the difficulty of applying pelite based thermobarometers to rocks of contrasting composition and mineralogy preferred pressures cluster at 7 1 9 4 and 3 6 4 3 kbar incomplete knowledge of reaction histories however limits our interpretation of the lower pressures because they are minimum estimates the 4 kbar samples are all from a small area and if our interpretation is correct they imply a local more shallow event superimposed on crust once residing at deeper structural levels garnet hornblende and garnet biotite temperatures are less coherent likely owing to retrograde fe mg exchange and range from 570 to 790 c the majority of the rocks are igneous and affected by recrystallization and metamorphism during subsolidus cooling they are not granulites country rock paragneisses are typically migmatized at peak metamorphic conditions near that of the wet granite solidus 690 c veinlike paragenesis of garnet in the metaigneous rocks suggests formation related to the presence of a fluid phase thermodynamic estimates of volatile activities in these garnet bearing assemblages suggest variable mostly co 2 rich fluid compositions in the absence of any pervasive fluid flux the igneous rocks of the tehachapi mountains were thus intruded at depths of 30 km making them the deepest known exposed components of the cretaceous sierra nevada batholith metamorphism occurred at these great depths and perhaps locally after 15 km of uplift before 87 ma implying an uplift rate of 1 2 mm yr a minimum uplift rate is 0 6 mm yr this original uplift and possible subsequent uplift events may have been related to underthrusting of a block of rand schist from what is now the southeast with concomitant widespread ductile deformation the deduced pressure temperature and uplift history is similar to those of high pressure high temperature cretaceous batholithic rocks in salinia and the san gabriel mountains but direct correlation is not wan anted when compared with higher level intrusive rocks from analogous portions of the sierra nevada batholith to the north the tehachapi rocks reveal a deep batholith that is more heterogeneous and somewhat more mafic on average but displaying a similar level of isotopic hybridization involving mantle and crustal sources the batholith is quartz rich at these levels suggestive of a weak ductile middle crust susceptible to prolonged deformation and possible delamination

late cretaceous intra arc thrusting in southern california thick zones of mylonitic rock are exposed in or between a number of the suspect crystalline terranes in the transverse ranges and eastern peninsular ranges of southern california after palinspastic reconstruction of strike slip displacements along neogene faults in the region the mylonite zones appear in a semicontinuous belt several hundred kilometers long mylonitic deformation in these areas is of a similar style and age lineation trends in the mylonitic rocks are closely aligned when palinspastic reconstruction takes into account the block rotations in the region and the sense of shear is consistently west directed the mylonite zones appear to have formed concurrently in a major midcrustal thrust system that juxtaposed the basement terranes during the late cretaceous a kinematic model is proposed in which a west directed ductile thrust zone along the eastern side of the peninsular ranges is offset by a sinistral tear fault or lateral thrust ramp along the southern margin of the san gabriel mountains from a ductile thrust underlying crystalline basement terranes to the north this model requires the suspect basement rocks of the peninsular and transverse ranges to be linked tectonically by the latest cretaceous this late cretaceous thrust system also appears to continue directly into autochthonous basement rocks in the san bernardino mountains the late cretaceous westward displacement of basement rocks in the transverse ranges relative to the northern end of the peninsular ranges batholith is mirrored by similar tectonic movement around the southern end of the sierra nevada batholith it is argued here that a formerly continuous batholithic belt was breached by ductile west directed thrusting during the late cretaceous between the two still recognizable batholiths the salinia terrane represents the westernmost portion of this westward escaping arc segment and would have been established as a crustal salient by the latest cretaceous this model implies that the basement terranes involved in this thrusting episode are parautochthonous fragments of a cretaceous continental arc and refutes suggestions that they have been accreted in the cenozoic

transferability of strong ground motion coherency between the smart1 and smart2 arrays abstract seismic wave coherency in strong ground shaking is modeled in synthetic accelerograms to provide realistic input for engineering analysis of multi supported structures at present there is only a small number of available measured coherency functions a seminal set coming from earthquake recordings by the smart1 array in taiwan a comparison of coherency functions for both vertical and horizontal motions from a magnitude 5 5 earthquake recorded by the new smart2 indicates no significant difference in the range 1 to 10 hz for separation distances of 400 800 and 1500 m

fluid inclusion evidence for hydrothermal enrichment of magmatic ore at the contact zone of the ni cu platinum group element 4b deposit lindsley mine sudbury canada most ni cu platinum group element pge deposits of the sudbury igneous complex 1 85 ga have massive or disseminated magmatic segregational characteristics however stringers and disseminations of chalcopyrite rich platinum group mineral pgm bearing fe ni cu sulfides at the contact of the lindsley 4b orebody with the enclosing murray granite 2 4 ga contain quartz k feldspar biotite epidote stilpnomelane amphibole garnet and other hydrous silicates associated with pgm sphalerite galena native au pyrite and mackinawite these assemblages in fracture controlled veins and disseminations are compatible with hydrothermal processes being responsible for the enriched grade near the contact fluid inclusion petrography and microthermometry reveal that hydrothermal activity took place in five stages early nacl cacl 2 h 2 o type fluids were trapped in k feldspar of the metasomatically altered murray granite at temperatures of about 370 degrees to 410 degrees c and 270 degrees c later quartz intergrown with sulfides contains fluid inclusions with nacl kcl cacl 2 h 2 o type solutions trapped between 200 degrees to 380 degrees c and 130 degrees to 230 degrees c sem eds analyses of chlorides in inclusions reveal that these fluids were also enriched in ba pb fe and mn later fluids trapped in secondary inclusions 200 degrees 240 degrees c were cacl 2 nacl h 2 o type temperature calculations assume 2 kbars lithostatic pressure all aqueous inclusions are characterized by high salinity 23 43 wt low temperature secondary inclusions contain co 2 ch 4 fluids carbonic fluids are related to metamorphism accompanying deformation during the penokean orogeny the higher temperature fluids were heated by the sudbury igneous complex the observations support the hypothesis that very saline hot fluids interacted with igneous minerals and primary magmatic ores and remobilized base and precious metals and precipitated them along permeable fractured and brecciated zones to produce cu pge au concentration disseminated sulfides and veins

effects of progressive mylonitization on ar retention in biotites from the santa rosa mylonite zone california and thermochronologic implications the santa rosa mylonite zone developed predominantly from a granodiorite protolith in the eastern margin of the peninsular ranges batholith a wide variation in k ar biotite dates within the zone is shown to reflect the times of cooling through closure temperatures whose variability is chiefly a result of deformation induced reduction in grain size we suggest that such variation generally may be exploited to place constraints on the timing of deformation episodes previous workers have shown that deformation in the santa rosa mylonite zone involved the formation of mylonites and an imbricate series of low angle faults which divide the area into structural units field work petrographic studies and tem analysis of deformation mechanisms in biotite show that the granodiorite mylonite the lowermost structural unit formed below the granodiorite solidus the granodiorite mylonite varies from protomylonite to ultramylonite with regions of high strain distributed heterogeneously within the zone previously reported biotite and hornblende k ar dates from the granodiorite protolith below 82 89 ma and the asbestos mountain granodiorite above 61 68 ma the mylonite zone indicate dramatically dissimilar thermal histories for the lowermost and uppermost structural units other workers fission track dates on sphene zircon and apatite from the granodiorite mylonite and the asbestos mountain granodiorite suggest thermal homogenization and rapid cooling to 100 c by ca 60 ma within and adjacent to the mylonite zone k ar dates on 5 samples of biotite from variably deformed granodiorite range from 62 76 ma dates are not correlated with structural depth but clearly decrease with degree of deformation and concomitant grain size reduction 40ar 39ar incremental heating analyses of biotite from the granodiorite protolith reveals no evidence of excess argon and produces a relatively flat age spectrum 40ar 39ar incremental heating analysis of biotite from the granodiorite mylonite discloses discordance consistent with 39ar recoil loss k analysis of samples allowing k ar dates to be calculated is therefore recommended as an adjunct to 40ar 39ar step heating analysis in rocks that have experienced similar deformation during mylonitization biotite grain size reduction through intracrystalline cataclasis results in estimated grain dimensions as small as 0 05 m locally within porphyroclasts as large as 1 mm because biotite compositions are relatively uniform fe fe mg mn ti alvi 0 47 0 52 and show no systematic variation with grain size compositional dependence of activation energy and diffusivity can be eliminated as sources of variation in ar retention ar closure temperatures calculated with appropriate diffusion parameters for the observed grain sizes are in the range 220 280 c and define a cooling curve consistent with a thermal history intermediate between those of the granodiorite protolith below and the asbestos mountain granodiorite above the mylonite zone changes in the slope of the cooling curve indicate that the main deformation episode initiated at or above ca 330 c 80 ma above the closure temperature for thermally activated diffusion of argon in biotite and continued to a minimum of ca 220 260 c 62 ma

mineralogy of melonite group and other tellurides from the ivrea verbano basic complex western italian alps melonite merenskyite and moncheite occur as minute grains 40 to less than 5 mu m dispersed within the main sulfides pyrrhotite pentlandite and chalcopyrite in sulfide concentrations of the ivrea verbano layered basic complex electron microprobe analyses indicate that melonite and merenskyite cover the whole range of ni pd substitution confirming the sofar inferred existence of a complete solid solution between these phases moncheite is much less abundant and always contains significant amounts of pd and ni substitution of bi for te is only occasional melonite is frequently found in paragenetic association with hessite altaite bi tellurides ni co sulfarsenides au ag alloys electrum and irarsite

origin of gneisses in the aureole of the san gabriel anorthosite complex and implications for the proterozoic crustal evolution of southern california granulite facies gneisses along the southwestern margin of the san gabriel anorthosite complex include compositionally banded locally migmatitic felsic gneisses and mafic granulites with rare interlayered augen gneiss and garnet hypersthene spinel aluminous gneiss previous workers accepted a 1 4 ga age for these granulites and a 1 2 ga age for the adjacent anorthosite complex and hence that this proterozoic basement is allochthonous with respect to the southwestern united states part of the north american craton solvus geothermometry in felsic and mafic granulites yields minimum metamorphic temperatures of 900 950 c and new u pb zircon data yield a minimum metamorphic age of 1186 ma coincident with that of the adjacent anorthosite we reinterpret these rocks as a 1190 ma anorthosite complex and its granulite grade thermal aureole geochemical data suggest that the anorthosite complex intruded early proterozoic rocks correlative with the mojave crustal province representing the north american craton exposed to the northeast we conclude that these proterozoic basement rocks represent the southwestern margin of the north american craton and not an exotic terrane accreted in mesozoic or tertiary time

implications of volcanism in coastal california for the neogene deformation history of western north america 1 the geologic record of coastal california includes evidence of numerous volcanic centers younger than 30 ma that do not appear to have erupted in an arc setting by correlating these volcanic centers with specific slab windows predicted from analysis of magnetic anomalies on the pacific plate we add new constraints to tectonic reconstructions since 30 ma our correlations such as erupting the morro rock islay hill complex south of the pioneer fracture zone and the iversen basalt south of the mendocino fracture zone require larger displacements within western north america than advocated by most previous authors specifically we infer at least 315 km of motion between the sierra nevada and rigid north america at an azimuth of about n60 w and at least 515 km between baja california and rigid north america in a similar direction a consequence of inferring a large displacement of baja california is that the pacific north american plate boundary must have developed most of its current form prior to 10 ma we interpret a slab window developing between cocos and monterey plates after 19 ma that reconstructs under nearly all of the southern california volcanic centers dated at 18 14 ma most of the sedimentary basins associated with volcanic rocks show brief periods of rapid subsidence synchronous with volcanism followed by slow subsidence of variable but often extended duration consistent with rapid extension of cold lithosphere over recently introduced hot asthenosphere

late cretaceous juxtaposition of metamorphic terranes in the southeastern san gabriel mountains california new structural petrological and geochronological data from the southeastern san gabriel mountains define the amalgamation history of suspect terranes in this region four metamorphic terranes constitute the area the cucamonga san antonio san gabriel and baldy terranes and were juxtaposed in two discrete episodes during the late cretaceous the cucamonga san antonio and san gabriel terranes were juxtaposed along subparallel east west trending left lateral mylonitic fault zones during the first episode the cucamonga terrane consists of lower cretaceous granulite facies gneissic rocks these rocks were intruded in the late cretaceous by granitic rocks as the cucamonga terrane was faulted ductilely against the southern margin of the san antonio terrane mylonitized units were subjected concurrently to retrograde amphibolite facies metamorphism metasedimentary pendants in the san antonio terrane were metamorphosed under upper amphibolite facies conditions as plutonic rocks were emplaced syntectonically along its northern boundary the san antonio terrane was juxtaposed concurrently against the san gabriel terrane a terrane consisting of precambrian gneiss and precambrian and mesozoic intrusive rocks the boundary is represented by middle fork complex a ductile zone intermingling rocks of the two terranes after palinspastic restoration of local cenozoic fault displacements the left lateral mylonitic fault zones separating the terranes appear as parts of a major sinistral transform system along the southern margin of the san gabriel mountains displacement for each of the mylonitic fault zones was approximately several tens of kilometers and was part of a broad left lateral shear system this system is modeled as a lateral ramp or tear fault to a west directed synplutonic ductile thrust system underlying the san gabriel terrane crosscutting syn and post tectonic intrusives indicate that most of the displacement occurred between 88 and 78 m y ago no lithologic isotopic or structural data support previous assertions that these terranes were accreted to north america during the tertiary the late cretaceous synplutonic juxtaposition of the cucamonga san antonio and san gabriel terranes was followed by underthrusting of oceanic rocks of the baldy terrane that is pelona schist along the vincent thrust precise timing of this episode is as yet uncertain

fluid inclusion characteristics of hydrothermal cu ni pge veins in granitic and metavolcanic rocks at the contact of the little stobie deposit sudbury canada abstract cu and precious metal enriched massive ore and veins occur at contacts of two fe ni cu sulfide orebodies of the little stobie mine sudbury with metavolcanic rocks of the elsie mountain formation and the murray granite veins contain chalcopyrite pyrrhotite pentlandite platinum group minerals quartz carbonate chlorite amphibole and other minerals a granitic dike resulting from partial re melting of the murray granite cuts back into the sudbury igneous complex near little stobie mine and contains barren veinlets with similar mineralogy but no sulfides quartz from ore veins contains fluid inclusions that were trapped during several stages early high temperature fluids at least 180 270 c in orebody 1 and 280 350 c in orebody 2 were extremely saline and occur as polyphase isolated and fracture controlled inclusions with halite sylvite fe mn as well as pb ba chloride daughter minerals and other unknown solids late secondary aqueous inclusions are not chloride saturated they were trapped at a minimum of 80 150 c their microthermometric behavior may be modeled in the cacl 2 nacl h 2 o system with salinity of 21 27 cacl 2 equiv wt very late secondary inclusions have either ca rich saline or very dilute about 1 equiv wt nacl compositions and homogenization temperatures of 200 300 c with the exception of these very late secondary inclusions the association of co 2 ch 4 rich inclusions with aqueous ones was usually observed the density of these carbonic fluids decreased from early to late stages microthermometric data from barren veins are fundamentally different from those of early inclusions from orebodies this implies that these heavy metal rich fluids were responsible for ore deposition in veins the minimum pressure of entrapment for early fluids was 1800 2200 bars late ca rich brines were trapped at lower minimum pressure 200 900 bars high pressure data are in agreement with the estimated minimum paleodepth of crystallization of south range ores later fluids were probably trapped during the uplift of orebodies and their host rocks comparison of data to other cu pge au rich ore of the sudbury structure suggests that the presence of co 2 rich fluids in south range deposits and their absence in north range deposits may be related to different metamorphic histories the high temperature hydrothermal fluids were driven by the heat of the sudbury igneous complex these very saline fluids interacted with primary magmatic ores remobilized metals and redeposited them along convenient structures such as fracture zones and breccias in and along various units near the footwall contact the identification of such highly saline fluid inclusions with high heavy metal content may be useful in the exploration for cu pge au enriched footwall vein type ores in the sudbury structure

mineralogy of ni cu platinum group element sulfide ore in the 800 and 810 orebodies copper cliff south mine and p t x conditions during the formation of platinum group minerals the 800 and 810 orebodies are two major deposits in the copper cliff south mine located at opposite contacts between the quartz diorite of the copper cliff offset dike and metapelite of the mckim formation the copper cliff south mine is one of the richest cu ni platinum group elements pge deposits in the copper cliff offset dike the ore is composed of variable proportions of pyrrhotite chalcopyrite and pentlandite and occurs as massive sulfides semimassive sulfides with inclusions of quartz diorite and wall rocks net textured sulfides disseminated sulfides and veins sphalerite and magnetite are also present in minor amounts the primary magmatic minerals in the quartz diorite are plagioclase quartz amphibole and biotite the most common platinum group mineral pgm in the copper cliff south mine is sperrylite ptas 2 it occurs in every textural type of ore typically enclosed by chalcopyrite pyrrhotite pentlandite cobaltite and hydrous silicates such as chlorite amphibole and epidote sperrylite may be homogeneous zoned with sb rich cores and sb poor rims associated with hollingworthite rhass and cobaltite or it may contain inclusions the pd bearing minerals are froodite pdbi 2 and michenerite pdbite which are most commonly enclosed by silicates chlorite biotite quartz or chalcopyrite hollingworthite invariably occurs in the center of zoned cobaltite in veins or in disseminated sulfides argentian gold au 0 56 ag 0 44 occurs as small grains in chalcopyrite and in a veinlet with parkerite ni 2 bi 3 s 2 the most abundant ag mineral is hessite ag 2 te which is present in almost every sample with galena gersdorffite and locally pgm volynskite agbite 2 occurs as a zoned grain with tsumoite bite in the center the most common trace minerals spatially and genetically associated with pgm are tsumoite galena gersdorffite cobaltite hessite melonite and native te the copper cliff south mine area was affected by more than one hydrothermal event deformation and metamorphism all of which affected the primary igneous textures and mineralogy of the rocks the first hydrothermal event was responsible for the extensive remobilization of metals including some pge this is revealed by the presence of pgm in large veins in quartz diorite and metapelite and by chlorite amphibole epidote biotite and quartz that often enclose pgm the temperature at the time of this event was estimated in samples containing garnet and biotite in equilibrium to be 327 to 540 c pressure estimated using amphibole chemistry may have been as high as 3 to 4 kbars the fluid responsible for the transport of metals was very rich in cl and oxidizing the fluid composition temperature and or pressure changed with time suggested by the presence of zoned minerals including sperrylite gersdorffite and cobaltite based on the textural relationships sperrylite precipitated before tellurides and galena and after or at the same time as michenerite a second hydrothermal event produced calcite bearing veinlets that cut larger veins

petrology and crystallization history of multiphase sulfide droplets in a mafic dike from uruguay implications for the origin of cu ni pge sulfide deposits sulfide blebs in a mafic dike belonging to the uruguayan dike swarm replicate at a small scale many features observed in larger platinum group element enriched nickel copper sulfide deposits such as in sudbury and noril sk these blebs formed by the crystallization of droplets of immiscible sulfide liquid form 1 cm sized ovoid geopetal structures with pyrrhotite and pentlandite at the base chalcopyrite and cubanite at the top and titaniferous magnetite at the margins magnetite crystallized first followed by nickel and iron rich monosulfide solid solution which sank to the bottom of the droplets and from which pyrrhotite and pentlandite subsequently exsolved the remaining copper rich liquid in the upper part of the droplets crystallized to form an intermediate solid solution from which chalcopyrite and cubanite subsequently exsolved the final extremely evolved cu fe s rich pd sn pb mo ag bi te and sb bearing liquid crystallized as 10 to 20 sized veinlets filling fractures in the magnetite and adjacent silicate minerals the veinlets crossing the magnetite often terminate in 100 m sized subrounded globules at the contact of the magnetite and the surrounding silicate minerals indicating a direction of veinlet filling away from the center of the blebs textural evidence in the blebs illustrates that as crystallization proceeded and the immiscible sulfide liquid droplets within the dike sank a distance of less than 1 mm relative to the adjacent silicate onto already partially crystallized silicate minerals the sulfide liquid surrounded and resorbed the already solid magnetite grains at the top of the blebs magnetite grains were isolated above the sulfide liquid and partially surrounded by quartz plagioclase and amphibole an assemblage representing a late stage magma that had been drawn into the space created above the droplets as they sank and which is more evolved than that of the surrounding host dike the location of the blebs within the dike isolated from influences external to the dike indicates both that the fracture filling by evolved immiscible cu rich sulfide liquid is related to crystallization processes rather than later tectonic events and that the bismuth tellurium and antimony have a late magmatic origin associated with crystallization of the immiscible sulfide liquid

irarsite hollingworthite solid solution series and other associated ru os ir and rh bearing pgm s from the shetland ophiolite complex pure end and intermediate members of the irarsite hollingworthite solid solution series occur in the shetland ophiolite complex hollingworthite frequently rims irarsite their compositions are unusually pt poor compared with analyses of these minerals from elswhere suggesting the existence of a pt poor environment during their formation ir sb s and rh sb s have been identified as inclusions within irarsite ir sb s and rh sb s together with rh ni sb are thought to be new platinum group minerals pgm s in ophiolite complexes two types of laurite are present an os rich up to 22 os variety is entirely enclosed by chromite whereas an os free variety is located in the silicate matrix interstitial to the chromite laurites in the rims of chromite grains are os free but contain tiny inclusions of native osmium it is suggested that either the availability of os decreased during crystallisation of the laurites or that os has been removed from laurites not totally enclosed by chromite in a few cases laurite is surrounded by a ruthenian pentlandite containing up to 12 ru

hualien seismic downhole data analysis abstract the hualien taiwan large scale seismic test lsst was initiated in 1993 by a consortium of industrial and research enterprises from five countries japan usa taiwan france and korea this in situ lsst includes two five accelerometer free field downhole arrays that recorded site response during seven earthquakes 1993 1995 in this paper the seismic site response during two of these events is analyzed correlation analyses of the recorded downhole accelerations are performed to calculate an average shear wave velocity profile in addition the actual seismic shear stress strain histories are directly calculated from the recorded downhole lateral accelerations these histories are then used to estimate soil stiffness and material damping in the linear small strain range the estimated soil stiffness is found to be significantly different in the longitudinal and transverse directions which suggests a marked azimuthal variation of soil properties anisotropy in a recent study of seismic site response ueshima and okano further investigation of seismic response of soil and embedded structure in hualien lsst program proceedings of eleventh world conference on earthquake engineering acapulco mexico 1996 also arrive at this interesting conclusion in addition this anisotropic soil response appears to have been manifested during earlier in situ experimental studies of foundation impedance functions barros and luco 1995 identification of foundation impedance functions and soil properties from vibration tests of the hualien containment model soil dynamics and earthquake engineering 14 229 248 finally the identified linear soil properties are shown to represent adequately the recorded seismic site response at small strains