the denver earthquakes of 1967 1968 abstract a detailed study of the earthquakes associated with the rocky mountain arsenal disposal well is presented long period surface wave studies are used together with p wave first motions to show that the 10 april 9 august and 27 november 1967 earthquakes occurred at depths of 3 to 5 km and were characterized by normal faulting along a northwest striking fault plane a joint hypocenter relocation of 103 microearthquakes of a data set of 279 recorded between 1967 and 1968 shows a hypocenter pattern striking n50 w with most of the events located about 5 km northwest of the disposal well at depths between 3 to 8 km a fault plane dipping southwest is tenuously suggested by those earthquakes with depths less than 5 km modeling of near field seismoscope observations lend support to the focal mechanisms derived

destruction of ancient lower crust through magma underplating beneath jiaodong peninsula north china craton u pb and hf isotopic evidence from granulite xenoliths abstract zircons from granulite xenoliths entrained in a late cretaceous mafic dike in the jiaodong peninsula north china craton ncc show three distinct u pb age populations part of the old zircon grains yield discordant data that project to ages of about 2 4 to 2 5 ga a few grains indicate growth at about 2 0 ga and a third group yield cretaceous ages with peaks at 120 and 90 ma the oldest zircons give hf t dm model ages of 2 6 2 8 ga these results demonstrate the existence of original archean lower crust in the jiaodong region zircons of 2 0 ga have similar hf t dm model ages as the neoarchean paleoproterozoic grains suggesting that these zircons were products of metamorphic recrystallization due to thermal event without juvenile input early cretaceous zircons yield ehf t values of 21 to 12 and late cretaceous zircons large variable ehf t from 4 to 50 these data suggest that magmatic underplating occurred in the neoarchean to earliest proterozoic lower crust of the ncc both in the early and late cretaceous it is suggested that the mesozoic magma underplating which also provided the heat source for the voluminous mesozoic magmatism in the ncc significantly modified the composition of the archean to paleoproterozoic lower crust of the ncc

scaling law and its applications to earthquake statistical relations abstract the spectra of the far field body wave displacement for earthquakes of various magnitudes have been obtained using a two dimensional faulting model on a rectangular fault there are three corner frequencies f c 1 f c 2 and f c 3 in the displacement spectra f c 1 and f c 2 relate to faulting times for the long and wide directions on the rectangular fault respectively and f c 3 corresponds to the rise time of the source time function according to these three corner frequency values four spectral regions are defined u u 0 f 0 f f c 1 in the first region u 1 f f c 1 f f c 2 in the second region u 1 f 2 f c 2 f f c 3 in the third region and u 1 f 3 f f c 3 in the fourth region this results in different source parameter relations for different magnitude ranges i e different seismic moment ranges because the attenuation rates depend on frequency it is supposed that earthquake faulting is satisfied by three conditions of geometrical similarity stress environment and dynamic similarity therefore seismic moment faulting time along the length and width of the fault and rise time can all be scaled with fault length the constants in the scaling relations can be determined from seismic moment data for about 800 earthquakes that occurred during 1981 1983 and are given by dziewonski and woodhouse 1983 and m s and m b data from the isc bulletin thus the source parameter relations between m s and m b m s and m l m b and m l log m o and log s fault area log s and m s log l fault length and m s and log d average dislocation and m s can be deduced from the scaling law rather than from pure statistical relations these relations are statistically consistent with the observed data the average rupture velocity of the fault can also be estimated from the scaling law it is 2 65 km s the total time of rupture is 0 35 s km l km which is close to that estimated by kanamori 1981 and the dislocation slip rate is 287 1143 cm s

uniquely extensive soft sediment deformation in the rhaetian of the uk evidence for earthquake or impact the lower part of the cotham member in the penarth group latest triassic rhaetian of the uk incorporates a uniquely extensive metre scale horizon of soft sediment deformation interpreted as a seismite it shows evidence for only a single seismic event even at its thickest development it is recorded from more than forty sites across at least eight discrete sedimentary basins covering n250 000 km 2 and originally must have covered a still larger area such a widespread horizon of soft sediment deformation unique for the uk phanerozoic and implying a seismic event of exceptional magnitude is difficult to account for by conventional terrestrial mechanisms contemporaneous volcanism in the central atlantic magmatic province camp was too far distant to cause the deformation and the tectonic setting of the region was not conducive to earthquakes on this scale slump fold long axes suggest an epicentre broadly in the southern irish sea or st george s channel impact of a km scale asteroid here potentially could produce the observed sedimentological effects across the uk but any late triassic impact structure would now be concealed by a km or more of younger strata at its thickest development in northern ireland the seismite is succeeded by a rip up breccia and hummocky and wave rippled cross stratification these facies and their position immediately above the seismite are consistent with the effects of a tsunami arising directly from the seismic event tentative evidence for a tsunamite of this age has also been reported from southern france the putative tsunamite in northern ireland is succeeded by a desiccation cracked hiatus which may correlate with a similar hiatus truncating the seismite at sites in southern england the hiatus in southern england correlates closely with a 13 c isotope excursion that has been traced from eastern europe across to western north america and is associated with significant biotic changes the ultimate cause of the seismite and associated tsunamite remains unclear no impact crater of appropriate age or location is currently known and other evidence for impact at this time is at best equivocal it is considered here that impact of a km scale asteroid may have caused the observed sedimentological effects in the lilstock formation across the uk area but was not necessarily a significant contributory factor in the generation of either the isotope excursion or of the biotic changes through the triassic jurassic boundary interval

source parameters from locally recorded aftershocks of the 9 january 1982 miramichi new brunswick earthquake abstract source parameters are derived from 111 locally recorded three component seismograms of 40 aftershocks magnitude 1 0 to 3 5 of the 9 january 1982 miramichi new brunswick earthquake this data set greatly expands the set of three component data recorded at small source to receiver distances in eastern north america preliminary analysis showed that some aftershock spectra were modified by strong site effects the need to understand and account for site effects when analyzing the aftershock data in terms of simple source models led to a two part data analysis first site effects were modeled as a seismic wave resonance in a thin layer 0 to 10 m of low seismic impedance glacial till over a high seismic impedance bedrock half space second we calculated source parameters from sh wave seismograms and amplitude spectra incorporating what had been learned about site resonances correcting for obvious site effects partially succeeded in reducing scatter in the source parameter determinations but some site dependent discrepancies remain seismic moments range from 1 10 18 to 5 10 20 dyne cm and corner frequencies from 5 to 45 hz brune model stress drops primarily range between 5 and 300 bars stress drop apparently increases with increasing seismic moment trends in apparent stress calculated from radiated energy and seismic moment parallel trends in stress drop corner frequencies from these locally recorded data are greater than those derived from regionally recorded l g waves for earthquakes of comparable moment this result contradicts a recently proposed m 0 4 constant source scaling law based primarily on l g data

geodynamics of heterogeneous gold mineralization in the north china craton and its relationship to lithospheric destruction abstract the north china craton ncc hosts some of the world class gold deposits on the globe which can be classified into distinct types as the jiaodong type explosive breccia type and skarn type the jiaodong type gold deposits were formed at ca 120 130 ma both in the margins and interior of the ncc two explosive breccia gold deposits formed at ac 180 ma and 120 ma and are located in the southern margin and the interior of the ncc important skarn gold deposits of ca 128 ma formed within the interior of the ncc although the formation and distribution of these gold deposits are temporally and spatially heterogeneous they are commonly related with the lithospheric destruction of the ncc the interplay of several factors such as basement architecture inhomogeneous decratonization crust mantle interaction mantle dynamics magmatic characteristics high heat flow and massive flux of deep derived ore forming fluids operated in generating the gold endowment all the three types of gold systems are closely related with granitoid plutons and different types of dykes the magmas for which were sourced from the lower crust near the moho discontinuity and involved the mixing and mingling of felsic and mafic magmas the ore forming fluids display prominent magmatic signature and were largely derived from deep domains with probable input from the asthenosphere mantle the heterogeneous distribution of the giant gold systems in the ncc was geodynamically controlled by the destruction of the craton the regions at the confluence of two or three precambrian micro continental blocks are generally characterized by thinned lithosphere and high heat flow constituting the potential sites of giant gold deposits the mantle beneath these regions shows em2 characteristics implying the involvement of subducted oceanic components the magmatic intrusions associated with the gold systems crystallized under high oxygen fugacity conditions and were rich in volatiles

validation of regional and teleseismic travel time models by relocating ground truth events recently developed 3d global seismic velocity models have demon strated location improvements through independent regional and teleseismic travel time calibration concurrently a large set of high quality ground truth gt events with location accuracies 10 km or better gt0 gt10 has been collected for europe the mediterranean north africa the middle east and western eurasia in this study we demonstrate event location improvements using this new data set by applying the regional and teleseismic model based travel time calibrations independently and jointly besides relocating events using all arrivals a subset of the gt events was also relocated using controlled station geometries generated from a constrained boot strapping technique this approach simulates sparse networks and reduces the effect of correlated errors to ensure valid 90 error ellipse coverage statistics with respect to the gt events we compared event relocations with and without travel time cal ibrations considering statistics of mislocation error ellipse area 90 coverage or igin time bias origin time errors and misfit relocations of over 1200 gt events show that pn and or p calibration reduced mislocation for 60 70 of the events joint regional pn and teleseismic p travel time calibration provided the largest lo cation improvements and achieved approximately gt5 accuracy levels due to cor related errors event locations using large numbers of stations have deficient 90 error ellipse coverage however the coverages derived from the model errors are appropriate for the simulated sparse regional and teleseismic networks our valida tion effort demonstrates that the global model based calibrations of pn and teleseis mic p travel times reduce both location bias and uncertainty over wide areas

use of empirical green s functions spectral ratios and kinematic source models for simulating strong ground motion abstract ground motions for large and moderately large earthquakes at short and moderate distances are particularly important for seismic hazard estimation in eastern north america ena very few direct observations of such ground motions have been obtained however because of the sparsity of recording sites and the relatively low rates of occurrence of large earthquakes inside the region estimation of strong ground motion must therefore rely heavily on theoretical models to extend empirical results obtained from small earthquakes and from the few larger ones for which reliable data are available because of the generally large distances between recording stations the main source of useful data comes from lg wave trains observed at relatively large distances for the two largest earthquakes to have occurred near populated regions of southeastern canada during the past decade spectral ratios of the lg wave trains of the mainshocks with respect to those of their aftershocks are found to depend almost entirely upon the source radiation characteristics of the sources alone this result is utilized to derive elastodynamically based kinematic rupture models that are consistent with the empirical spectral ratio data such models provide a firm physical basis from which to infer the most probable spectral characteristics for future large earthquakes in the region in converse application it is shown that spectral ratios obtained from such models along with empirical seismograms from small earthquakes can be used to accurately simulate strong ground motions at short and moderate as well as large distances as such small event seismograms are relatively plentiful the problem of reliable strong ground motion estimation is therefore reduced to that of obtaining reliable representative source spectral models the solution of this latter problem must continue to depend upon whatever empirical data are available and upon appropriately detailed theoretical modeling

four seismogenic environments in eastern canada abstract although the seismogenic environments in eastern canada have some common features the respective seismotectonic environments are influenced by local features the seismotectonic environment in four seismogenic regions are described in order to illustrate how local features are reacting with the ambient plate tectonic stress a common feature to modify the nature of the seismic activity the charlevoix earthquakes are occurring along steeply dipping planes formed during the opening of lapetus ocean in the proterozoic perturbed by a meteor impact during the paleozoic and reactivated by the opening of the present day atlantic ocean in the mesozoic theoretical curves of maximum shear stress versus depth based on a wet upper crust and a wet quartz rheology in the lower crust for which the heat flow is 1 0 hfu 42 mw m2 can account for the depth distribution of earthquakes in this region potential trigger mechanisms are gravitationally induced stress water infiltration and vertical shear strain changes approximately 3 10 8 yr due to post glacial rebound the unusually deep focus 29 km of the m 5 9 saguenay earthquake of 1988 could be due in part to the lower heat flow in this region as compared with that in the charlevoix region which is about 70 km to the east the miramichi earthquake sequence is occurring on conjugate faults within an intrusion at depths shallower than 10 km theoretical curves of maximum shear stress versus depth based on a wet quartz rheology in the lower crust for which the heat flow is 1 5 hfu can account for this depth distribution the steep gradient in the vertical ground movement rate 5 10 8 yr in the epicentral area which is probably due to post glacial rebound is a potential trigger mechanism for favorably oriented faults the normal fault seismic regime along northeastern baffin island can be explained by a combination of topography and post glacial rebound which can generate horizontal extensional stresses capable of overcoming the ambient compressional plate tectonic stress post glacial rebound stress can act as a trigger mechanism for the ne dipping faults in this region in the grand banks region there is seismic evidence indicating that the slump that caused the destructive tsunami also generated the strong seismic m 7 2 signals but double couple solutions that satisfy certain criteria are not ruled out the absence of surface faulting especially in the epicentral regions of large earthquakes is not properly understood but several possibilities are near surface layering that could mask the underlying fault offsets and a spatiotemporal variation in the ambient plate tectonic stress field as knowledge of the causative factors of eastern canada earthquakes and also the data base for empirical earthquake scaling relations increase an overview of the seismotectonics of these mid plate earthquakes should be enhanced

rb sr sm nd and pb isotope systematics of pyrite implications for the age and genesis of lode gold deposits lode gold deposits commonly consist of pyrite and lesser amounts of lead and zinc sulfides accompanied by quartz and calcite their exact origin remains controversial mainly because of the scarcity of reliable geochronological data here we present direct rb sr dating of pyrite from a lode gold deposit and propose the method as a useful geochronological technique for gold mineralization for which age data are poor a positive correlation between present day 87 sr 86 sr and 87 rb 86 sr ratios of pyrite fes 2 subsamples from the linglong gold mine of china corresponds to an age of 122 123 ma which dates the age of gold mineralization the sr nd and pb isotopic compositions of pyrites and the associated rocks suggest that the hydrothermal fluids responsible for the pyrite and gold mineralization were probably derived from a mixed source i e degassing of mafic magmas and meteoric water that had leached the country rocks

nature age and tectonic setting of granitoid hosted orogenic gold deposits of the jiaodong peninsula eastern north china craton china the jiaodong gold province along the southeastern margin of the north china craton has combined production and resources of 900 tonnes of gold more than 95 of the gold in this province is hosted in mesozoic granitoids which intruded late archean metamorphic basement rocks episodically at ca 160 150 and 130 126 ma the deposits of the jiaodong peninsula form one of the largest provinces of granitoid hosted lode gold deposits in the world the jiaodong gold deposits occur as massive auriferous quartz veins hosted in subsidiary second or third order faults and as disseminated and stockwork style mineralization hosted in alteration zones along major regional scale faults mineralization took place during brittle reactivation d3 of pre existing d2 ductile shear zones wall rock alteration is dominated by k feldspar and sericite with also sulfide minerals and extensive silicification closest to the orebodies the alteration was accompanied by the introduction of volatiles fe mg k rb ag as au bi and sb enrichment of base metals in the gold lodes is generally low although locally significant gold deposition took place at temperatures of 250 to 350 c for most gold deposits and the ore fluids are co2 bearing and have calculated salinities of 6 13 wt nacl equiv deposits from the zhao ye xixia and muping rushan belts have similar if not identical structural controls alteration patterns ore mineral assemblages and stable isotope signatures lead isotope data indicate that the ore stage leads were buffered by their host rocks the granitoid hosted gold deposits in the zhao ye belt are most radiogenic the greenstone hosted deposits in the xixia belt is the least radiogenic and the granitoid hosted deposits in the muping rushan belt have intermediate compositions gold mineralization in the zhao ye xixia and muping rushan belts in the jiaodong gold province appears to be broadly contemporaneously at ca 130 120 ma as constrained by shrimp u pb zircon dating on host rocks and a post gold dike as well as by ar ar rb sr and k ar dating of hydrothermal alteration minerals and ores this early cretaceous age is about 100 million years younger than the peak of ultra high pressure metamorphism in the qinling dabie sulu orogen between the north china and yangtze cratons and about 500 km south of the gold province however it overlaps with the extension and exhumation stage of the collisional orogeny and the subduction of the pacific plate beneath the eurasian continental crust whereas the majority of the jiaodong gold deposits occur on the margin of the north china craton some also occur in the suture zone between the two cratons they are significantly landward relative to the subduction zone of the pacific plate compared with typical orogenic lode gold deposits globally lode gold deposits of ca 130 120 ma occurred on both sides of the tan lu fault zone available data favor a temporal link of gold mineralization with pacific plate subduction

source scaling and moment estimation for the pacific northwest seismograph network using s coda amplitudes earthquake coda waves can be used for investigating both source and medium parameters in this investigation we introduce a method for estimating the scalar seismic moment of local earthquakes using s coda amplitudes recorded by regional network stations assuming a single scattering coda model more than 8000 coda amplitude measurements from 78 local western washington earthquakes with coda duration magnitudes from 2 4 to 5 0 are used to estimate source spectra in the narrow frequency band 2 to 12 hz using a transmission model based on previous studies we find that our source modeling best supports an omega square constant stress drop far field scaling model an average stress drop of 32 bars is inferred for the earthquakes studied to calibrate the moment estimation procedure a reference event with known moment and corner frequency is required using a suitable reference event we estimate moments for the remaining 77 events in the data set the moment values range from 5 1 1019 to 4 4 1023 dyne cm

source spectral scaling inversion for two earthquake sequences offshore western norway abstract short period and high frequency noress observations from two after shock sequences offshore western norway with epicentral distances of 424 and 405 km respectively have been used in testing a new hedgehog inversion procedure for determination of source spectral scaling characteristics based on a previously developed spectral ratio method this inversion procedure provides insight into resolution properties uncertainties and trade off considerations between source parameters the two main events analyzed have m l magnitudes of about 5 while the smallest aftershocks are about 1 5 with seismic moments in the range 10 17 to 10 12 nm the observed spectral ratios support 2 source models for both of the earthquake sequences but only if certain constraints are imposed on the scaling parameter that determines the stress drop sensitivity with respect to seismic moment in that case stress drop is found to be almost independent of seismic moment of 3 24 for one of the sequences and increasing with moment of 3 80 for the other without such constraints which may not be justifiable in the case of earthquake sequences equally good solutions are found for 3 models in which case attains values around 5 to 6 indicating strongly increasing stress drop external constraints on the source spectral slope and or corner frequency will similarly help in resolving the method which also simultaneously determines corner frequencies or stress drop if adopting some model relating this to corner frequency for all of the events albeit with a poorer resolution can either use independently determined seismic moments or it can determine these as part of the inversion quite similar results are obtained in those two cases reflecting essentially the quality of the initial moment determinations the observed variations in stress drop sensitivity between two earthquake sequences only 84 km apart and occurring in similar tectonic environments are consistent with the considerable variations that have been observed on a larger scale caution is therefore needed if the scaling relations derived in this study are applied to other events larger ones and or series of main events or to different seismic regions

epicentre accuracy based on seismic network criteria summary we establish reliable and conservative estimates for epicentre location accuracy using data that are readily available in published seismic bulletins a large variety of seismic studies rely on catalogues of event locations making proper assessment of location uncertainty critical event location and uncertainty parameters in most global regional and national earthquake catalogues are obtained from traditional linearized inversion methods using a 1 d earth model to predict traveltimes reported catalogue uncertainties are based on the assumption that error processes are gaussian zero mean and uncorrelated unfortunately these assumptions are commonly violated leading to the underestimation of true location uncertainty especially at high confidence levels we find that catalogue location accuracy is most reliably estimated by station geometry we make use of two explosions with exactly known epicentres to develop local network location 0 2 5 accuracy criteria using monte carlo simulations of network geometry we find that local network locations are accurate to within 5 km with a 95 per cent confidence level when the network meets the following criteria 1 there are 10 or more stations all within 250 km 2 an azimuthal gap of less than 110 3 a secondary azimuthal gap of less than 160 and 4 at least one station within 30 km to derive location accuracy criteria for near regional 2 5 10 regional 2 5 20 and teleseismic 28 91 networks we use a large data set of exceptionally well located earthquakes and nuclear explosions beyond local distances we find that the secondary azimuthal gap is sufficient to constrain epicentre accuracy and location error increases when the secondary azimuthal gap exceeds 120 when station coverage meets the criterion of a secondary azimuth gap of less than 120 near regional networks provide 20 km accuracy at the 90 per cent confidence level while regional and teleseismic networks provide 25 km accuracy at the 90 per cent confidence level

phase relations among tellurides sulfides and oxides pt ii applications to telluride bearing ore deposits data on telluride bearing mineral assemblages from various types of ore deposits are compiled and interpreted in terms of the prevailing fugacities of te 2 s 2 and the temperature during deposition in the majority of hydrothermal deposits the appearance of tellurides after initial deposition of sulfides reflects an increase in the f sub te 2 f sub s 2 ratio most likely due to input of h 2 te from a magmatic source in some vein deposits such as boulder county colorado initial deposition of native tellurium is followed by deposition of minerals with progressively lower tellurium content indicating a decrease in f sub te 2 over the course of telluride deposition this trend may reflect local isolation of early formed minerals from the hydrothermal fluids and or progressive depletion of tellurium at the source ore minerals in other deposits such as mahd adh dhahab saudi arabia reveal systematic temporal or spatial variations in mineralogy that are attributed to introduction of a tellurium rich fluid into a preexisting sulfide assemblage and subsequent buffering of f sub te 2 and f sub s 2 by reactions such as 2pbs te 2 2pbte s 2 this buffering may exert considerable control on vein minerals such as the presence and relative abundance of gold and calaverite and the presence or absence of native tellurium

the magmatic metamorphic and tectonic evolution of the northern marginal zone of the limpopo belt in zimbabwe the northern marginal zone of the limpopo belt in southern africa comprises a plutonic assemblage of granitoids including a distinctive suite of porphyroclastic granites and a much less abundant supracrustal assemblage of metabasites and iron formations these rocks are at granulite facies above a normal thickness of continental crust most of the plutonic assemblage are intrusive rocks that crystallized from dry melts from 2800 to 2600 ma with a relatively simple thermal history they may have been derived from partial melting of a mafic source some supracrustal rocks have experienced two thermal events at granulite facies a reverse sense shear zone forms the boundary of the northern marginal zone with the zimbabwe craton the southern boundary is the triangle shear zone which is proven as a continuous structure along a much greater strike length than previously documented a widespread sub vertical foliation in the northern marginal zone and the reverse shear zone formed during progressive nnw sse shortening crustal thickening occurred both magmatically and tectonically in the late archaean and was accompanied by synchronous uplift protracted magmatism provides a mechanism to incorporate supracrustal rocks into the lower crust and can explain the occurrence of more than a single thermal event

origin and evolution of ore fluid and gold deposition processes at the giant taishang gold deposit jiaodong peninsula eastern china abstract the early cretaceous taishang gold deposit is the largest deposit in the linglong goldfield jiaodong peninsula with a pre mining endowment of 326 t of gold it is hosted in the 165 150 ma linglong biotite granite and controlled by the nee to ne trending potouqing fault near the northern end of the regional zhaoping fault system hydrothermal alteration is well developed in the footwall of the potouqing fault and is characterized by a narrow zone of sericitization followed by a wider zone of silicification and an even wider zone of potassic alteration the main orebodies no i orebody comprise disseminated and stockwork veinlet systems although about 5 of the resources are in larger quartz veins no ii orebody four stages have been identified for both styles of mineralization on the basis of cross cutting relationships and mineralogical and textural characteristics pyrite quartz sericite stage 1 quartz pyrite stage 2 quartz pyrite base metal sulfide stage 3 and quartz carbonate stage 4 gold was mainly deposited in stages 2 and 3 with minor amounts in stage 1 petrographical microthermometric and laser raman spectroscopic studies on fluid inclusion assemblages in quartz and calcite from the four stages reveal three types of primary fluid inclusions type 1 h 2 o rich aqueous carbonic type 2 co 2 rich aqueous carbonic and rare type 3 carbonic inclusions stage 1 quartz primary inclusions are only type 1 inclusions with an estimated composition of 88 h 2 o 10 co 2 4 5 wt nacl equiv and 0 5 ch 4 with trapping at 336 c and 1 7 kbars the gold rich stages 2 and 3 from both orebodies typically contain primary fluid inclusion assemblages with both type 1 and 2 inclusions which show similar phase transition temperatures and were trapped between 246 and 294 c the stage 4 quartz and calcite contain only primary type 1 inclusions which are estimated to have a composition of 93 h 2 o 6 0 co 2 3 6 wt nacl equiv and trace amount of ch 4 and were trapped at temperatures of 236 c the 34 s values of hydrothermal pyrite from the four stages have a narrow range from 4 5 to 8 0 and are within the ranges for whole rock sulfides from the archean jiaodong group and magmatic pyrite from mesozoic granitoid and intermediate basic dikes the 18 o values of hydrothermal quartz range mainly from 10 9 to 12 5 and remain constant for all four stages calculated fluid 18 o values are 1 3 10 0 the d water values calculated from hydrothermal sericite range from 60 to 45 considering the fluid inclusion compositions 18 o and d compositions of ore forming fluids and regional geological events the most likely ultimate potential fluid and metal reservoirs would be the paleo pacific oceanic slab and its overlying sediments which were thrust below the high grade metamorphic rocks of the jiaodong peninsula the initial ore forming fluids were medium high temperature co 2 rich and low salinity h 2 o co 2 nacl ch 4 homogeneous fluids over the duration of the hydrothermal system the fluid remained fairly consistent in p t x although becoming slightly more water rich during final post ore activity fluid immiscibility occurred during stages 2 and 3 ore deposition at pressures that fluctuated strongly from 1700 to 580 bars during hydrofracturing the hs 2 ion was the most probable gold transporting complex at taishang wall rock sulfidation and episodic pressure drops with associated fluid unmixing and other chemical changes were the two main mechanisms of ore deposition

uniquely extensive seismite from the latest triassic of the united kingdom evidence for bolide impact a 2 4 m thick seismite in places overlain by a previously unreported tsunamite can be traced across 250 000 km 2 of the outcrop and subcrop of the latest triassic rhaetian cotham member of the penarth group united kingdom an extent unique for the british phanerozoic its consistent thickness intensity of deformation and preferred orientations of slump fold axes indicate a seismic event of m 10 with an epicenter 600 km w or nw of central britain the magnitude of the event is incompatible with known terrestrial mechanisms fault volcano but is consistent with a major bolide impact a short but unknown interval separates the top of the cotham member seismite from major geochemical and biotic perturbations associated with the end triassic extinction although a direct link between the seismite and these other events remains equivocal the exceptional extent of mega seismites such as this may prove a useful indicator of previously undocumented bolide impacts

multimode rayleigh wave attenuation and qβ in the crust of the barents shelf the multimode method of cheng and mitchell 1981 is used to study the attenuation properties of the crust throughout the barents shelf the sensitivity of the spectra to various source factors and to propagation factors which might characterize a shelf region are thoroughly studied for plane layered models the method is very sensitive to q in the upper crust and to q of sedimentary layers if those layers are thick and highly attenuating it is far less sensitive to q in the lower crust and to q the spectra for shallow strike slip earthquakes are very insensitive to changes in strike slip and dip angles of the fault throughout the entire period range of interest but are very sensitive to variations in focal depth except in the long period range of the fundamental mode and the short period range of the higher modes the fundamental mode but not the higher mode spectra for one path across the barents shelf are apparently distorted at short periods by lateral heterogeneities along the travel path simple two layer trial and error inversions yield a model of the barents shelf with an upper crustal q value of about 80 three layer inversions with a sedimentary layer however yield an upper crustal q of about 250 if the sediments are 1 km thick and are characterized by q values of 40 shear velocity models for the barents shelf show variations between about 3 0 and 3 6 km s in the upper crust along different paths the lower crust shows smaller regional differences but velocities vary between 3 5 and 4 0 km s through the depth range 25 35 km the variation of shear velocities in the upper mantle may correlate with those of the upper crust and vary regionally between about 4 3 and 4 8 km s

fluid immiscibility in natural processes use and misuse of fluid inclusion data ii interpretation of fluid inclusion data in terms of immiscibility abstract phase equilibrium analysis of the relevant systems together with the application of the principles of chemical equilibrium put severe constraints on the interpretation of fluid inclusion data in terms of immiscibility in part i following from that point the major limits on the accuracy and even the validity of fluid inclusion quantitative data and their interpretation in terms of fluid composition and density are briefly discussed the practical implications of the general constraints temperature pressure topology of the fluid systems are envisaged emphasis is laid on some important consequences such as the use of isochore intercepts and the possible resulting interpretation of fluid mixing rather than unmixing the case of highly saline inclusions the identification and interpretation of heterogeneous trapping the composition and density constraints on coexisting fluids are presented and illustrated by natural examples taking into account all the measurable parameters in fluid inclusions volume temperature and nature of phase transitions more or less complete individual spectroscopic analyses all the available experimental data and all the theoretical constraints may be long and difficult however it is most generally very informative and productive although part of these data is often sufficient to deny unmixing nevertheless a final example on metamorphic fluids demonstrates how such an approach can prove and also characterize a fluid unmixing during a geologic process

hydrothermal alteration in the core of the yaxcopoil 1 borehole chicxulub impact structure mexico petrographic electron microprobe and raman spectrometric analyses of yaxcopoil 1 core samples from the chicxulub crater indicate that the impact generated a hydrothermal system relative textural and vein crosscutting relations and systematic distribution of alteration products reveal a progression of the hydrothermal event in space and time and provide constraints on the nature of the fluids the earliest calcite halite and gaylussite suggest that the impactite sequence was initially permeated by a low temperature saline brine subsequent development of a higher temperature hydrothermal regime is indicated by thermal metamorphic diopside hedenbergite aeg3fs 18 33 en32 11wo 47 53 after primary augite and widespread na k for ca metasomatic alkali exchange in plagioclase hydrothermal sphene apatite magnetite bornite as well as early calcite combined 3 to 8 vol were introduced with metasomatic feldspar a lower temperature regime characterized by smectite after probable primary glass secondary chlorite and other pre existing mafic minerals as well as very abundant calcite veins and open space fillings extensively overprinted the early hydrothermal stage the composition of early and late hydrothermal minerals show that the solution was chlorine rich cl f 10 and that its fe mg ratio and oxidation state increased substantially 4 to 5 logo2 units as temperature decreased through time the most altered zone in the impactite sequence occurs 30 m above the impact melt the lack of mineralogical zoning about the impact melt and convective modeling constraints suggest that this unit was too thin at yaxcopoil 1 to provide the necessary heat to drive fluids and implies that the hydrothermal system resulted from the combined effects of a pre existing saline brine and heat that traveled to the yaxcopoil 1 site from adjacent areas where the melt sheet was thicker limonite after iron oxides is more common toward the top of the sequence and suggests that the impactite section was subjected to weathering before deposition of the tertiary marine cover in addition scarce latest anatase stringers chalcopyrite and barite in vugs francolite after apatite and recrystallized halite are the likely products of limited post ydrothermal ambient temperature diagenesis or ocean and or meteoric water circulation

stochastic prediction of ground motion and spectral response parameters at hard rock sites in eastern north america empirical predictions of ground motions from large eastern north american earthquakes are hampered by a lack of data for such events for this reason most prediction techniques have been based at least in part on data from the seismically active and well instrumented western north america concentrating on the prediction of response spectra on hard rock sites we have used a relatively new theoretical technique that does not require western data to make ground motion predictions for eastern north america this method often referred to as the stochastic model has its origins in the work of hanks and mcguire who treat high frequency motions as filtered random gaussian noise for which the filter parameters are determined by a seismological model of both the source and the wave propagation the model has been successfully applied to the predictions of ground motions in the western united states and to short period magnitudes from large to great earthquakes worldwide for our application the essential parameters of the model are estimated by using existing data from small to moderate eastern north american earthquakes a crucial part of the model is the relation between seismic moment and corner frequency the relation proposed in 1983 by nuttli for mid plate earthquakes leads to predictions of ground motions that are lower than available data by a factor of about 4 on the other hand a constant stress parameter of 100 bars gives model predictions in good accord with the data to aid in applications the ground motion predictions are given in the form of regression equations for earthquakes of magnitude 4 5 to 7 5 at distances within 100 km of the source the explanatory variables are hypocentral distance and moment magnitude m because predictions are often required in terms of m g rather than m we have used the theoretical model to establish a relation between the two magnitudes the predicted relation agrees with the sparse data available although the large uncertainties in the observed magnitudes for the larger events as well as the sensitivity of the theoretical magnitude to the attenuation model make it difficult to discriminate between various source scaling models

high frequency spectral scaling of a main shock aftershock sequence near the norwegian coast a high frequency seismic element was recently added to the noress regional array in norway this system can monitor seismic signals at frequencies up to 50 hz in february 1986 the high frequency seismic element recorded an mblg 4 7 main shock and several aftershocks which occurred 420 km northwest of noress off norway s western coast these events produced high frequency signals which were well above the background noise at the station p wave spectra of these events scale in a manner consistent with the square constant stress drop source model the data do not require any change in this scaling to magnitudes mblg below 2 in contrast to previous reports that constant stress drop scaling breaks down at smaller magnitudes

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

average seismic source parameter relations for plate margin earthquakes abstract empirical mb ms and mo data are used to develop an average spectral scaling relation for plate margin earthquakes using equations based upon a rectangular bilateral dislocation model with uniform rupture velocity the spectra give values of fault rupture length and width static stress drop and average fault displacement as a function of mb ms and mo compared to mid plate earthquakes of the same seismic moment the large average plate margin earthquake has a bigger rupture length rupture area and average fault displacement and a smaller rupture width and static stress drop

a terrane interpretation of the archaean limpopo belt the limpopo belt is a zone of thickened archaean crust whose origin is currently explained by a late archaean continent continent collision between the kaapvaal and zimbabwe cratons this review shows that the two cratons have fundamentally different geological histories and that the zimbabwe craton was unlikely to have behaved as a stable cratonic block at the time of the limpopo belt collision the geological histories of the zimbabwe craton the north marginal central and south marginal zones of the limpopo belt and the kaapvaal craton are shown to be sufficiently different from one another to warrant their consideration as discrete terranes the boundaries between the five units outlined above are all major shear zones further supporting a terrane model for the limpopo belt the five units were all intruded by late to syn tectonic granites c 2 6 ga constraining the accretion event to c 2 6 ga

partitioning of trace elements in co crystallized sphalerite galena chalcopyrite hydrothermal ores abstract there is an abundance of published trace element data for sphalerite galena and chalcopyrite in natural systems yet for a co crystallized assemblage comprising these base metal sulphides there is no detailed understanding of the preferred host of many trace elements laser ablation inductively coupled plasma mass spectrometry trace element maps and spot analyses were generated on 17 assemblages containing co crystallized sphalerite and or galena and or chalcopyrite from 9 different ore deposits these deposits are representative of different ore types geologic environments and physiochemical conditions of ore formation as well as superimposed syn metamorphic remobilisation and recrystallization the primary factors that control the preferred base metal sulphide host of mn fe co cu zn ga as se ag cd in sb te tl and bi are element oxidation state ionic radius of the substituting element element availability and the maximum trace element budget that a given sulphide mineral can accommodate temperature pressure redox conditions at time of crystallization and metal source do not generally appear to influence the preferred base metal sulphide host of all the trace elements exceptions are ga in and sn recrystallized at high metamorphic grades when the preferred host of ga and sn usually becomes chalcopyrite in more typical lower temperature ores the preferred host of ga is sphalerite indium concentrations also increase in chalcopyrite during recrystallization at lower temperatures the partitioning behaviour of sn remains poorly constrained and shows little predictable pattern among the data here the results obtained may be used as a tool to assess co crystallization if trace element distributions in a given base metal sulphide assemblage match those reported here and assuming those distributions have not been significantly altered post re crystallization then it may be suggestive of a co crystallized assemblage such information provides a foundation for novel attempts to develop trace element in sulphide geothermometers

oxygen boron chromium and niobium enrichment in native au and ag grains a case study from the linglong gold deposit jiaodong eastern china quartz vein type gold mineralization in the linglong deposit constitutes one of the important sources of gold in china here we report the first finding of anomalous enrichment of boron b oxygen o chromium cr and niobium nb in native gold and ag te grains from the linglong deposit the oxygen content of gold and silver grains ranges up to 75 83 at boron up to 97 85 at chromium up to 26 23 at and tellurium up to 33 4 at the au precipitation is mainly linked to pyrite precipitation under reducing conditions the hfse enrichment including chromium cr and niobium nb in the gold and silver grains indicate that the ore forming fluids were derived from high temperature magmas sourced from depth the enrichment of low temperature te in the native gold and silver grains combined with the typical features of fluid boiling as inferred from fluid inclusion studies indicate that the ore fluids derived from depth upwelled rapidly and metal precipitation occurred through decompression at shallower levels our results suggest good prospect for gold and silver at depth in linglong

seismic gaps and recurrence periods of large earthquakes along the mexican subduction zone a reexamination abstract seismic gaps and recurrence periods of large shallow interplate earthquakes along the mexican subduction zone are reexamined after combining information from a catalog of nineteenth century9s earthquakes some relocated epicenters of the early part of this century source parameters of recent large earthquakes and redetermined magnitudes of great shallow earthquakes of this century tehuantepec and michoacan gaps have not experienced a large shock in this century and perhaps none in the past century they are either aseismic or have anomalously large repeat times guerrero jalisco and ometepec regions presently appear to have a high seismic potential observed average repeat times of large earthquakes m s 7 4 in six regions east central and west oaxaca san marcos petatlan and colima are between 32 to 56 yr data of this century indicate that the strain is released mostly in large events m s 7 4 a simple dislocation model with parameters obtained from the studies of recent earthquakes explains the observed recurrence periods quite well the b value for this zone is not meaningful an observation which is of significance for seismic risk estimation most of seismic moment or equivalently seismic energy release since 1800 appears to occur for 15 yr followed by relative quiescence in the next 15 yr

regional travel time uncertainty and seismic location improvement using a three dimensional a priori velocity model we demonstrate our ability to improve regional travel time prediction and seismic event location accuracy using an a priori 3d velocity model of western eurasia and north africa wena1 0 travel time residuals are assessed relative to the iasp91 model for approximately 6000 pg pn and p arrivals from seismic events having 2 epicenter accuracy between 1 km and 25 km ground truth 1 gt1 and gt25 respectively recorded at 39 stations throughout the model region ray paths range in length between 0 and 40 local regional and near teleseismic providing depth sounding that spans the crust and upper mantle the dataset also provides representative geographic sampling across eurasia and north africa including aseismic areas the wena1 0 model markedly improves travel time predictions for most stations with an average variance reduction of 29 for all ray paths from the gt25 events when we consider gt5 and better events alone the variance reduction is 49 for location tests we use 196 geographically distributed gt5 and better events in 134 cases 68 of the events locations are improved and average mislocation is reduced from 24 9 km to 17 7 km we develop a travel time uncertainty model that is used to calculate location coverage ellipses the coverage ellipses for wena1 0 are validated to be representative of epicenter error and are smaller than those for iasp91 by 37 we conclude that a priori models are directly applicable where data coverage limits tomographic and empirical approaches and the development of the uncertainty model enables merging of a priori and data driven approaches using bayesian techniques online material correction surfaces and histograms of travel time residuals for 40 stations

inhomogeneous lithospheric thinning in the central north china craton zircon u pb and s he ar isotopic record from magmatism and metallogeny in the taihang mountains abstract the large scale mesozoic magmatism and related metallogeny in the taihang mountains tm provide important clues for the lithospheric thinning of the north china craton ncc among the ore deposits the vein gold mineralization of shihu in the fuping region and the skarn ore deposit of xishimen in the wu an region represent typical mesozoic metallogeny in the tm in the shihu gold mine the mapeng batholith is dominantly composed of monzogranite and granodiorite whereas the wu an pluton in the xishimen iron mine mainly comprises monzonite and diorite here we present zircon la icp ms u pb data from 8 samples which reveal the timing of magmatism in the tm as ca 130 ma which is contemporaneous with the large scale metallogeny in the margins of the ncc the 34s values recorded in the sulfide minerals from the shihu gold deposit and the xishimen skarn iron deposit show a range of 2 2 5 0 and 11 6 18 7 respectively helium isotopic compositions of fluid inclusions in pyrite from the shihu gold deposit vary from 0 12 to 1 98 ra where ra is the 3he 4he ratio of air 1 39 10 6 with calculated mantle helium values of 1 4 25 whereas those of the xishimen skarn iron deposit range from 0 06 to 0 19 ra with calculated mantle helium of 0 7 2 2 the s he ar isotopic data suggest a lower crustal origin for the ore forming components with variable inputs of mantle source the large population of inherited zircons in our samples with 207pb 206pb ages ranging between 2500 ma and 1800 ma also supports crustal participation our data reveal that the shihu gold deposit witnessed greater mantle input than the xishimen skarn iron deposit suggesting that the continental lithosphere is markedly thinner under the fuping region than that under the wu an region our interpretation is also supported by published data from two ultra broadband high precision magnetotelluric sounding profiles across the tm region showing a variation in the lithosphere thickness from 155 km to 70 km while moving from the south wu an region to the north fuping region our study suggests that inhomogeneous lithospheric thinning in the central ncc occurred at least as early as ca 130 ma ago

tectonics and distribution of gold deposits in china an overview gold exploration in china has expanded rapidly during the last two decades since a modern approach to economic development has become a national priority china currently produces 180 tonnes t of gold annually which is still significantly less than south africa usa and australia however china is now recognized as possessing significant gold resources in a wide range of mineral deposit types present estimates of gold resources in china exceed 4 500 t which comprise 60 in gold only deposits more than 25 in base metal rich skarn porphyry and vein deposits and more than 10 in placer accumulations the major gold provinces in china formed during the main episodes of phanerozoic tectonism such tectonism involved interaction of china s three major precambrian cratons north china tarim and yangtze or south china when combined with cathaysia block with the angara or siberian kazakhstan kyrgyzstan and indian cratons resulting collisions included deformation of accreted oceanic sequences between the cratonic blocks the most important ore forming orogenies were 1 the late paleozoic variscan 405 270 ma which led to amalgamation of the angara north china and yangtze cratons 2 the indosinian 270 208 ma which led to the collision of north china and south china cratons 3 the yanshanian 208 90 ma which was largely influenced by the subduction of the izanagi pacific plates beneath eastern china and 4 the himalayan 90 ma indentation of the indian continent into eurasia no important precambrian gold systems are recognized in china mainly because of reworking of exposed precambrian rocks by these younger orogenies but there are a few caledonian 600 405 ma gold bearing systems in northern xinjiang most of china s orogenic epithermal and carlin like gold deposits are in the reworked margins of major cratonic blocks and in metasedimentary rock dominated fold belts adjacent to these margins accordingly the major gold provinces are present along the northern southeastern and southern margins of the north china craton along the southwestern and northwestern margins of the yangtze craton in the tianshan and altayshan orogenic belts in northern xinjiang and throughout the southeastern china fold belt gold placer deposits derived from these primary deposits are concentrated in the northernmost part of northeastern china and along the northwestern margin of the yangtze craton the major provinces with significant gold in porphyry related copper systems and base metal skarns are present in the yangtze river area along the northeastern and southeastern margin of the yangtze craton in the fold belt in southwestern china and scattered through northern china three quarters of the chinese gold only deposits occur within the north china craton margins half are located in the uplifted precambrian metamorphic rocks and most of the remainder are hosted in the phanerozoic granitoids that intruded the reworked precambrian terranes the abundance of granite hosted gold contrasts the north china craton with other precambrian cratons such as those in western australia central canada and zimbabwe where gold is mainly hosted in the archean greenstone belts this difference may be explained by the multiple episodes of phanerozoic tectonism along the north china craton margins resulting from the collision of the angara north china and south china cratons and from subduction of the izanagi pacific oceanic plates underneath the eastern china continent

source characterization of nevada test site explosions and western u s earthquakes using lg waves implications for regional source discrimination an investigation is made of the lg waves from 15 nuclear tests at the nevada test site nts and 25 shallow western united states earthquakes to obtain a scheme for discriminating between possible source mechanisms the data were recorded at four broadband stations operated by lawrence livermore national laboratory llnl which encircle the nts the lg wave spectra are modeled through a genetic algorithm search to find optimal values for 1 the seismic moment m o 2 the corner frequency of the amplitude spectrum f c 3 the 1 hz attenuation quality factors q o for all of the paths and 4 the frequency dependence of attenuation along the paths because the inversion solves for the path attenuation characteristics little a priori information is needed for the analysis the resulting m o and f c values are used in conjunction with the m b values as seismic discriminants the populations of earthquakes and explosions have nearly identical relationships between their moments and corner frequencies for earthquakes the relationship is log m o 16 07 2 93 log f c for the set of nts explosions using an earthquake source model the relationship is log m o 15 87 2 76 log f c a source discriminant is found however through a comparison of the moments and m b values this gives a line log m o 10 20 1 16 m b which cleanly separates the earthquake and explosion populations with earthquakes falling above and explosions below the line reliability tests examine the inverse trade off between moments and q o values noise in the lg spectra has a limited effect on the scaling relations

reply to comment on improving sparse network seismic location with bayesian kriging and teleseismically constrained calibration events by stephen c myers and craig a schultz by a douglas we thank alan douglas douglas 2004 for his thoughtful comments on myers and schultz 2000 in myers and schultz 2000 we improve seismic location accuracy and uncertainty estimates for a sparse regional network by improving travel time predictions and better characterizing residual uncertainties station specific travel time corrections and associated uncertainty estimates are calculated using the bayesian kriging methodology of schultz et al 1998 the bayesian kriging methodology is an empirical approach that exploits the spatial correlation of travel time residuals to interpolate an empirical calibration set of travel time residuals into a minimum variance geographically continuous surface of travel time corrections and an associated uncertainty surface in myers and schultz 2000 we test the bayesian kriging approach by relocating events in the 1991 racha georgia earthquake sequence 42 n 43 e we compare uncalibrated locations based on p wave travel times for the ak135 model kennett et al 1995 and calibrated locations calibrated travel times and uncertainties to benchmark locations that are constrained with a dense local distance network the calibration data set consists of event locations that are constrained by a teleseismic network one goal of the study was to assess the utility of teleseismically constrained events for calibration we find that better travel time prediction for regional paths can be achieved by using the teleseismically constrained calibration events and the improved travel time prediction improves regional network location accuracy a major advantage of bayesian kriging over many other interpolation techniques is the propagation of uncertainty from the calibration data set into a travel time prediction uncertainty surface sources of data set uncertainty include calibration event locations phase observations for calibration events and calibration event spacing we find that coverage ellipses evernden 1969 are representative of observed epicenter accuracy i e confidence level of the coverage ellipse is indicative of the number of occurrences of the benchmark location within the ellipse when the

geologic and geochemical controls on the mineralogy and grain size of gold bearing phases eastern australian volcanic hosted massive sulfide deposits the mineralogy and occurrence of gold varies in a systematic manner in volcanic hosted massive sulfide deposits of eastern australia in deposits where it is concentrated with zinc at or near the top of the massive sulfide deposit gold occurs in auriferous arsenopyrite and pyrite in the center of the lens and electrum of variable fineness 300 900 in the baritic top of the lens the former occurrence results from precipitation of the gold into the lattice of arsenopyrite and coprecipitation of submicroscopic gold grains in arsenic poor pyrite the latter occurrence results from direct precipitation of electrum from thio complexes owing to the decrease in a sub h 2 s caused by dilution and oxidation as hydrothermal fluids mix with seawater in deposits where gold is concentrated with copper at the base of the sulfide lens and in the stringer zones the gold occurs as electrum of high fineness 750 1 000 or as gold tellurides that are commonly associated with chalcopyrite and or pyrite this occurrence is caused by the direct precipitation of gold from chloro complexes owing to an increase in ph or a decrease in temperature as the hydrothermal fluids move up through the sulfide body gold in auriferous pyrite is readily mobilized during deformation as the pyrite fractures gold migrates via solution precipitation mechanisms to cracks and grain boundaries to form electrum by combination with silver which is released from sulfide minerals in a similar manner with increasing stress the electrum is released from pyrite to recrystallize with other easily remobilized minerals such as galena during this process electrum grain size increases thermodynamic modeling of the variation in electrum fineness shows good agreement with variations measured in massive sulfide ores for gold transported as a thio complex the predicted fineness of 190 to 990 for temperatures of 200 degrees to 300 degrees c and typical volcanogenic fluids matches the observed variation in deposits of the zn au association the very high finenesses observed in deposits of the cu au association can be modeled assuming gold chloro complex transport and high ag au ratios in the hydrothermal fluids

the effects of sulfidation and oxidation during metamorphism on compositionally varied rocks adjacent to the bleikvassli zn pb cu deposit nordland norway petrographic electron microprobe and bulk rock geochemical analyses indicate that the distribution and composition of ferromagnesian silicates biotite garnet and staurolite in and adjacent to the metamorphosed bleikvassli zn pb cu volcanogenic massive sulfide deposit norway are dependent upon the competing effects of f o2 f s2 and host rock composition the enrichment in magnesium content of these silicates within the orebody and at distances of as much as 5 10 m away is due to the increased f o2 and f s2 conditions imposed on the silicates in zones subject to minor hydrothermal alteration during regional metamorphism alternatively within pelitic country rocks at distances 5 10 m from ore the host rock chemistry controls the composition of metamorphic silicate minerals also country rocks within a few meters of ore are distinguished by the common presence of zinc bearing staurolite up to 9 wt zno coexisting with biotite garnet rocks in the bleikvassli deposit were hydrothermally enriched in zinc and fluorine prior to metamorphism the fluorine resides mainly in biotite which is an additional contributing factor to the magnesium enrichment of that mineral due to fe2 f avoidance our inference that the sulfidation oxidation halo around the bleikvassli ore deposit is only meters in width contrasts with the view of maiga 1983 who proposed the effects of sulfidation could be identified at distances 159 m from ore it is evident that the delineation of a sulfidation oxidation halo bordering a metamorphosed massive sulfide deposit must be done carefully in order to discriminate between the effects due to variations in primary rock composition versus those resulting from a sulfur and oxygen fugacity gradient between the massive sulfides and the sulfur poor country rocks

average seismic source parameter relations for mid plate earthquakes mid plate earthquakes which are defined as having their epicenters at least 500 km from plate margins represent a small portion of the total global seismicity however because those occurring within continental interiors are characterized by anomalously large damage areas they are of particular interest empirical mb ms and m o data are used to develop scaling relations for mid plate earthquakes from them it is found that the corner period t o2 of their far field displacement spectra varies as the one fourth power of the seismic moment which indicates that average stress drop increases as seismic moment increases by use of savage s 1972 rectangular bilateral dislocation model the derived spectra of mid plate earthquakes yield estimates of fault rupture length and width average fault displacement and source rise time as a function of seismic moment these relations show that large mid plate earthquakes such as the 1886 south carolina and 1811 and 1812 new madrid events do not require large fault rupture length

the southeastern illinois earthquake of 10 june 1987 the later aftershocks the 10 june 1987 southeastern illinois earthquake mblg 5 2 was the seventh in a series of moderate magnitude 4 5 mmi vii shocks to occur in the wabash valley seismic zone of southeastern illinois and southwestern indiana since 1891 located about 200 km east of st louis missouri the shock caused minor damage in the epicentral area had a contiguous felt area of about 433 000 km2 and had a total felt area over 1 million km2 within 47 hours after the main shock a cooperative effort between the u s geological survey and memphis state university installed a 15 station aftershock monitoring network later expanded to 21 instruments that recorded more than 100 aftershocks in the following 4 day period results from the 56 aftershocks that were well located indicate a compact cylindrically shaped aftershock volume about 1 7 km long 0 8 km wide and with a vertical distribution between about 9 and 12 km in depth composite focal mechanism solutions of the aftershocks suggest that the predominant mode of faulting is reverse slip but some strike slip type motion occurred similar to the mechanism for the main shock as determined from teleseismic data the maximum principal compressive stress p axes is oriented easterly to east southeasterly and is subhorizontal in plunge these results combined with historical observations and the recent discovery of earthquake induced liquefaction features in the area imply that the seismic potential of the zone may be greater than generally perceived

errors in hypocenter location picking model and magnitude dependence abstract the location procedures of seismic events are influenced by two major classes of errors the error in picking individual seismic phases and modeling error due to the departure of the real earth from the reference model used in the location both classes of error influence the estimate of location and it is difficult to separate them the role of picking errors can be assessed by a nonlinear analysis using a monte carlo procedure arrivals times are perturbed with random numbers drawn from a normal distribution and the event is relocated using these perturbed arrival times by repeating the procedure many times a cluster of locations is obtained which can be used to investigate the effects of picking errors on the hypocenter this analysis is insensitive to velocity model errors as these are fixed for a given combination of stations and phases some care must be exercised when analysing multidimensional distributions in two dimensional slices because of a projection effect the modeling error due to the influence of lateral heterogeneity in the earth is examined by comparing the locations of the same event using different combinations of phases and network geometries which reinforces the need to use arrivals other than p for accurate depth resolution the sensitivity of p arrivals to changes in depth are swamped by model errors and inclusion of depth sensitive phases such as pp is highly recommended the effect of picking errors on location is found to be much smaller than the mislocation caused by neglecting lateral heterogeneity when only p arrivals are used consequently the monte carlo analysis which is primarily aimed at picking errors only is most appropriate when multiple phases have been used to more accurately constrain the hypocenter especially for the depth component altering the type of phase data used in the location plays a similar role in changing the network geometry in that both are mechanisms that influence the nature of the constraint on the hypocenter by relocating events with network geometries corresponding to the different magnitudes it is found that the location of the event can be affected significantly by the magnitude and when using robust statistics to describe earthquake residuals the mislocation can occur in a systematic manner the effect is marked in regions with significant lateral variations in seismic velocities for example low magnitude events in the flores sea are found to be dragged toward australia as a result of the fast paths to australian stations relative to the iasp 91 reference velocity model

native gold and native copper grains enclosed by olivine phenocrysts in a picrite lava of the emeishan large igneous province sw china a native gold bleb found in an olivine phenocryst in a picrite lava from the emeishan large igneous province elip may be the first documented case of the transport of gold as a distinct precious metal phase in a mantle derived magma four picrite layers have been recognized in the lower part of the volcanic succession in the lijiang area in the western part of the elip the native gold bleb was found enclosed in an olivine phenocryst in the second picritic layer of a basalt picrite succession in the elip the gold bleb is spheroidal about 30 m in diameter consists of pure gold and does not contain any other elements in addition native copper grains were also discovered in the serpentinized olivine phenocrysts and native zinc and moissanite sic were separated from an 20 kg sample of picrite the paragenesis of these minerals suggests that the primary magmas were s unsaturated the native gold and native copper grains are considered to be xenocrysts from the mantle transported to shallow depths by a rising plume and then captured by the picritic melts the discovery of native gold and native copper grains provides direct evidence that the gold in the hydrothermal gold deposits and the native copper deposits in the elip lavas ultimately may be derived from a mantle plume

comparison of source scaling relations of eastern and western north american earthquakes source scaling relations have been obtained for earthquakes in eastern north america and other continental interiors and compared with a relation obtained for earthquakes in western north america the scaling relation for eastern north american earthquakes was constructed from measurements of seismic moment and source duration obtained by the waveform modeling of seismic body waves the events used include nine events of m blg magnitude 4 7 to 5 8 that occurred after 1960 and four earlier events with magnitudes between 5 5 and 6 6 the scaling relation for events in other continental interiors was used for comparative purposes and to provide constraints for large magnitudes detailed analysis of the uncertainties in the scaling relations has allowed the resolution of two important issues concerning the source scaling of earthquakes in eastern north america first the source characteristics of earthquakes in eastern north america and other continental interiors are consistent with constant stress drop scaling and are inconsistent with nonconstant scaling models such as that of nuttli 1983 second the stress drops of earthquakes in eastern north america and other continental interiors are not significantly different from those of earthquakes in western north america and have median values of approximately 100 bars the source parameters of earthquakes in eastern north america are consistent with a single constant stress drop scaling relation whereas the source parameters of earthquakes in western north america are much more variable and show significant departures from an average scaling relation in which stress drop decreases slightly with seismic moment

the dependence of peak horizontal acceleration on magnitude distance and site effects for small magnitude earthquakes in california and eastern north america abstract one hundred and ninety free field accelerograms recorded on deep soil 10 m deep were used to study the near source scaling characteristics of peak horizontal acceleration for 91 earthquakes 2 5 m l 5 0 located primarily in california of the six attenuation relationships developed in this study the one considered most reliable is given by the expression ln p h a 2 5 0 1 0 6 2 3 m l 1 0 ln r 7 2 8 where pha is the mean of the two horizontal components of peak acceleration in g m l is local magnitude r is epicentral distance in kilometers and is a random error term with mean of zero and standard deviation of 0 506 an analysis of residuals based on an additional 171 near source accelerograms from 75 earthquakes indicated that accelerograms recorded in building basements sited on deep soil have 30 per cent lower accelerations and that free field accelerograms recorded on shallow soil 10 m deep have 82 per cent higher accelerations than free field accelerograms recorded on deep soil accelerations recorded on rock were found to be similar in amplitude to those recorded on deep soil a separate analysis of site effects for the imperial valley and oroville regions of california indicated that peak accelerations from individual sites can depart significantly from predictions based on broad site classifications an analysis of residuals based on 27 selected strong motion recordings from 19 earthquakes in eastern north america indicated that near source accelerations associated with frequencies less than about 25 hz are consistent with predictions based on attenuation relationships derived for california once site effects and differences in regional magnitude scales are taken into account

three recent larger earthquakes offshore norway three earthquakes of magnitude around 5 occurred offshore western norway on 5th february 1986 on 8th august 1988 and on 23rd january 1989 these earthquakes representing the highest seismic activity level in this area for at least 30 years were all felt by people over most of southern and central norway focal mechanism solutions for these earthquakes indicate thrust faulting along n s to nne ssw striking fault planes in response to nw se compressional stress most probably of plate tectonic origin a number of high quality digital recordings of the ground motions at various distances from these and other recent earthquakes in norway have shown that source spectral as well as wave attenuation characteristics in this area are reasonably consistent with what has been derived from other intraplate areas

improving sparse network seismic location with bayesian kriging and teleseismically constrained calibration events monitoring the comprehensive nuclear test ban treaty will require improved seismic location capability for small magnitude events the international monitoring system ims is well suited to locate events that are large enough to be recorded at teleseismic distances however small events are likely to be recorded on a sparse subset of ims stations at regional to upper mantle distances less than 30 and sparse network locations can be strongly effected by travel time errors that result from path specific velocity model inaccuracies in an effort to improve sparse network location capability we outline a procedure that applies empirical corrections to travel times determined with an appropriate velocity model more specifically bayesian kriging and calibration events constrained with a global network are used to estimate epicenter specific travel time corrections for a test sparse network of stations we calculate travel time residuals for the calibration events relative to the ak135 velocity model travel time residuals are assigned to the respective calibration epicenter forming a set of spatially varying travel time correction points the spatial set of correction points is declustered to reduce the dimension of the observations with minimal reduction in accuracy of the travel time corrections we then use the declustered set of calibration points and bayesian kriging to form continuous travel time correction surfaces for each station of the test network the effectiveness of travel time correction surfaces is evaluated by locating with and without corrections a subset of the 1991 racha earthquake sequence caucasus mountains for which we have accurate locations that were independently determined with a dense local network when no travel time correction is applied the mean horizontal distance between the local and test network locations is 42 km and there is a distinct bias in sparse network locations toward the north northwest the mean difference between local and sparse network locations is cut to 13 km when corrections are applied and the bias in location is significantly reduced when calibration events in the racha vicinity are not used to make the correction surfaces there is still a significant improvement in location with mean mislocations of 15 km when corrections are not applied only one of the locally determined locations lies within the associated 90 coverage ellipse determined with the test sparse network however by using travel time corrections and estimates of model uncertainty determined using kriging representative error ellipses are obtained this study demonstrates that kriging correction surfaces based on global network constrained calibration events can improve the ability to accurately locate lower magnitude events while providing representative coverage ellipses

empirical magnitude and spectral scaling relations for mid plate and plate margin earthquakes abstract published values of body wave magnitude m b surface wave magnitude m s and seismic moment m o for mid plate and plate margin earthquakes are analyzed to determine their inter relationship and to develop scaling laws for earthquake spectra all of the plate margin earthquakes used in the study occurred near the border of the pacific ocean the mid plate earthquakes occurred in both continental plate interiors and oceanic plate interiors for mid plate earthquakes the m b m s relation can be represented by two straight lines of slope one and two the intersection of the two lines corresponds to the body wave magnitude for which the corner period of the spectrum is at 1 sec the m b m s relation for plate margin earthquakes is more complicated because the derived spectra exhibit two corner periods a principal feature of the m b m o and m s m o relations is the fact that the large plate margin earthquakes have a higher m o value than the mid plate earthquakes for the same m b or m s because m b is a measure of the spectral amplitude for frequencies at which damaging ground motion occurs and m 0 is a measure of the spectrum at very long periods it follows that mb is a good estimator of strong ground motion whereas a moment derived magnitude is not the latter however is a good measure of fault rupture area the derived spectra of the mid plate earthquakes are flat at the long periods and have a slope of two at the short periods their seismic moment varies as the fourth power of the corner period implying that the stress drop increases as the moment increases for the large plate margin earthquakes the derived spectra are flat at the long periods have a slope of one at intermediate periods and a slope of two at short periods the stress drops are almost independent of moment for the larger plate margin earthquakes the moment magnitude relations for mid plate earthquakes indicate that an m s 8 7 event requires a fault rupture length of only 60 km for a fault width of 20 km a plate margin earthquake of m s 8 7 and fault width of 20 km would require a fault length of 6000 km obviously impossible assuming a fault width of 20 km an m s 8 2 earthquake has a rupture length of about 850 km which is as large as can be expected for strike slip faults such as the san andreas of california subduction zone earthquakes on the other hand if they have fault widths as great as 200 km can give rise to m s 8 7 earthquakes

a comparison of jiaojia and linglong type gold deposit ore forming fluids do they differ abstract the jiaodong peninsula contains the most important concentration of gold deposits in china which can be divided into jiaojia type and linglong type deposits based on mineralization style the former is characterized by disseminated and stockwork style mineralization hosted in first order regional faults with relatively larger tonnages and lower gold grades the latter is characterized by massive auriferous quartz veins commonly hosted in subsidiary second or third order faults with smaller tonnage but higher grade orebodies despite these differences both groups of deposits have the same alteration assemblages mineral paragenesis element concentrations and ore forming ages the mainly jiaojia type luoshan gold deposit and the mainly linglong type fushan gold deposit are characterized by h o s pb isotope data that indicate the ore forming fluids have a dominantly metamorphic source the fluids were derived during the yanshanian orogenic event and were most likely associated with dehydration and decarbonization processes near the top of the subducting paleo pacific plate the linglong type ores have relatively lighter calculated 18 o compositions 3 9 to 2 3 than the jiaojia type ores 0 3 8 0 possibly because of a greater degree of mixing with meteoric water petrographic cathodoluminescence microthermometric and laser raman spectroscopic analyses of fluid inclusion assemblages in quartz from the two types of ores indicate fluids were similar in both cases characterized by medium high homogenization temperatures 211 393 c significant co 2 15 mol minor ch 4 18 in the carbonic phase and low salinity 11 2 wt nacl eq the linglong type ores however have a wider range of co 2 and ch 4 concentration and salinity than the jiaojia type ores fluid immiscibility occurred in main ore stage of both ore types with the trapping conditions of 77 185 mpa and 284 328 c although the unmixing is more intense and widespread in the linglong type ores both fluid wallrock interaction and fluid immiscibility are important gold deposition processes in the two types but immiscibility is more important in the linglong type ores and that has led to the typical higher gold grade in general there is little geochemical differences between the ore forming fluids for jiaojia and linglong type gold deposits both jiaojia and linglong type ores can exist in a single deposit and form in the same metallogenic event the linglong type ores developed as more massive veins because of their location in zones of more extensive extension and they lack significant post ore cataclastic deformation

li rich zincostaurolite and its decompression related breakdown products in a diaspore bearing metabauxite from east samos greece an emp and sims study li h rich zincostaurolite locally formed at a metabauxite marble contact along the eastern coast of samos during early alpine high p low t metamorphism the staurolite which probably grew from gahnite cookeite kaolinite pyrophyllite diaspore and minor fe oxide occurs as prismatic crystals up to several mm long in a calcite matrix it has an unusual composition with 7 5 12 9 wt zno 1 0 4 9 wt feo 0 66 0 82 wt li 2 o up to 2 6 wt nio and 0 59 wt coo and 0 32 wt mgo calculated structural formulae point to high h 2 o contents 4 14 h atoms per 48 oxygen atoms during late alpine uplift of the samos rocks the staurolite was at greenschist facies conditions variably replaced by bluish cobaltoan gahnite x zn 0 82 white na ca li mica ni rich chlorite x ni 0 42 0 59 zincohogbomite x zn 0 68 0 80 diaspore and fe hydr oxide detailed emp work and determination of li in staurolite and mica by sims indicates systematic zn fe mg ni co li partitioning between staurolite and its decomposition products implying local scale chemical equilibrium balanced reaction equations based on mineral chemical data indicate that the breakdown of staurolite occurred largely isochemically with only introduction of water na and ca into the reacting system the breakdown of high p staurolite during uplift and decompression is thought to be related to the sensitivity of its complex crystal chemistry to changes in physico chemical conditions

ore forming fluids associated with granite hosted gold mineralization at the sanshandao deposit jiaodong gold province china the sanshandao gold deposit with total resources of more than 60 t of gold is located in the jiaodong gold province the most important gold province of china the deposit is a typical highly fractured and altered disseminated gold system with high grade quartz sulphide vein veinlet stockworks that cut mesozoic granodiorite there are four stages of veins that developed in the following sequence 1 quartz k feldspar sericite 2 quartz pyrite arsenopyrite 3 quartz base metal sulfide and 4 quartz carbonate fluid inclusions in quartz and calcite in vein veinlet stockworks contain c o h fluids of three main types the first type consists of dilute co2 h2o fluids coeval with the early vein stage molar volumes of these co2 h2o fluid inclusions ranging from 50 60 cm3 mol yield estimated minimum trapping pressures of 3 kbar homogenization temperatures obtained mainly from co2 h2o inclusions with lower co2 concentration range from 267 375 c the second inclusion type with a co2 h2o ch4 composition was trapped during the main mineralizing stages these fluids may reflect the co2 h2o fluids that were modified by fluid rock reactions with altered wallrocks isochores for co2 h2o ch4 inclusions with homogenization temperatures ranging from 204 325 c and molar volumes from 55 to 70 cm3 mol provide an estimated minimum trapping pressure of 1 2 kbar the third inclusion type aqueous inclusions trapped in cross cutting microfractures in quartz and randomly in calcite are post mineralization and have homogenization temperatures between 143 228 c and salinities from 0 71 7 86 wt nacl equiv stable isotope data show that the metamorphic fluid contribution is minimal and that ore fluids are of magmatic origin most likely sourced from 120 126 ma mafic to intermediate dikes this is consistent with the carbonic nature of the fluid and the cross cutting nature of those deposits relative to the host mesozoic granitoid

depth variation of seismic source scaling relations implications for earthquake hazard in southeastern australia abstract advances in earthquake data acquisition and processing techniques have allowed for improved quantification of source parameters for local australian earthquakes until recently only hypocentral locations and local magnitudes ml had been determined routinely with little attention given to the inversion of additional source parameters the present study uses these new source data e g seismic moment stress drop source dimensions to further extend our understanding of seismicity and the continental stress regime of the australian landmass and its peripheral regions earthquake activity within australia is typically low and the proportion of small to large events i e the b value is also low it is observed that average stress drops for southeastern australian earthquakes appear to increase with seismic moment to relatively high levels up to approximately 10 mpa for ml 5 0 earthquakes this is thought to be indicative of high compressive crustal stress coupled with strong rocks and fault asperities furthermore the data indicates that shallow focus earthquakes shallower than 6 km appear to produce lower than average stress drops than deeper earthquakes between 6 and 20 km with similar moment recurrence estimates were obtained for a discrete seismogenic zone in southeastern australia decreasing b values with increasing focal depth for this zone indicate that larger earthquakes with high stress drops tend to occur deeper in the crust this may offer an explanation for the apparent increase of stress drop with hypocentral depth consequently earthquake hazard estimates that assume a uniform gutenburg richter distribution with depth i e constant b value may be too conservative and therefore slightly overestimate seismic hazard for surface sites in southeastern australia

tectonics granitoids and mesozoic gold deposits in east shandong china abstract mesozoic granitoids in east shandong 1 contain some 30 moz gold making east shandong the largest granitoid hosted gold province in the world the gold province is located along the northern boundary of the suture zone between the north china and south china cratons according to their mineralogical geochemical and geochronological characteristics two groups of mesozoic granitoids are recognised in east shandong namely the middle yanshanian my ca 160 150 130 ma and the late yanshanian ly ca 117 85 ma granitoids the first group of granitoids only occur to the north of the suture zone whereas the second group of granitoids occur on both sides of the suture zone these characteristics suggest that the two groups of granitoids were associated with different tectonic events a tectonic analysis suggests that the my granitoids are the result of collision and suturing of the north and south china cratons during the triassic to jurassic whereas formation of the ly granitoids is attributed to the distal inland influence of subduction of the pacific izanagi plate underneath the eurasian continent during the cretaceous the major gold deposits are spatially associated with the my granitoids in east shandong most of the gold occurs either as quartz veins in the granitoids or disseminated in altered shear zones along the boundary of the granitoids and archaean metamorphic rocks the major gold mineralization and alteration generally display the characteristics of gold only provinces namely co 2 rich low salinity and reduced fluids and proximal mica and sulfide alteration these characteristics are different from those of phanerozoic granitoid related skarn porphyry systems accordingly the gold mineralization may be more tectonically and structurally controlled rather than have a direct genetic relationship with the granitoid itself according to the relationships between tectonics granitoids distribution of gold deposits and fluid geochemistry the major gold in east shandong may have been formed during the subsequent exhumation stage after the collision of the north and south china cratons