geochemical pattern recognition through matrix decomposition abstract this study compares the use of joint singular value decomposition and semi discrete decomposition jss and non negative matrix factorisation with univariate analysis of raw data to detect multi element patterns in soils related to geochemical dispersion from mississippi valley type pb zn deposits in the irankuh area of central iran joint singular value decomposition and semi discrete decomposition clustering of the data identified a suite of mineralisation related variables and corresponding sample clusters that are spatially associated with mineralisation or variations in parent lithology non negative matrix factorisation generated three main factors and sample clusters that relate to the main zones of sulphide mineralisation variations in clay mineralogy and the composition of unaltered host rocks these two matrix decomposition techniques deliver similar results though jss delivers a significantly higher sample classification accuracy both methods result in delineation of a contiguous cluster of samples above an extensive zone of blind mineralisation at the tappe sorkh pb zn deposit and define new potentially mineralised targets between this deposit and the gushfil pb zn deposit more conventional univariate methods to detect anomalous populations of pb and zn in the soil geochemical data such as number size fractal analysis were less effective at defining these targets joint application of practical matrix decomposition techniques utilising noise removal and modelling of the underlying geochemical patterns associated with ore forming processes has led to more reliable prospectivity mapping of the pb zn deposits in irankuh

source finiteness of large earthquakes measured from long period rayleigh waves the source finiteness parameters of 11 large shallow earthquakes were determined from long period rayleigh waves recorded by the global digital seismograph network and international deployment of accelerometers networks the basic data sets are the seismic spectra of periods from 150 to 300 s in the determination of source process times we used furumoto s phase method and a linear inversion method in which we simultaneously inverted the spectra and determined the source process time that minimizes the error in the inversion these two methods yielded consistent results the source process times of the sumbawa indonesia colombia ecuador valparaiso chile and michoacan mexico earthquakes were estimated to be 79 118 69 and 77 s respectively from the linear inversion method the source process times determined from long period surface waves were in general longer than those obtained from body waves source finiteness of large shallow earthquakes with rupture on a fault plane with a large aspect ratio was modeled with the source finiteness function introduced by ben menahem the spectra were inverted to find the extent and direction of the rupture of the earthquake that minimize the error in the inversion for a rupture velocity of 2 5 km s 1 the estimated rupture was unilateral 100 km long and along the strike n26 w for the may 26 1983 akita oki japan earthquake 165 km and s57 e for the september 19 1985 michoacan mexico earthquake 256 km and n31 e for the december 12 1979 colombia ecuador earthquake and 149 km and s15 w for the march 3 1985 valparaiso chile earthquake the results for the august 19 1977 sumbawa indonesia earthquake showed that the rupture was bilateral and in the direction n60 e these results are in general consistent with the rupture extent inferred from the aftershock area of these earthquakes

sulfur isotope geochemistry of gypsiferous aridisols from central iran abstract gypsum accumulation is one of the prominent pedogenic processes occurring in many and regions of the world gypsiferous soils occur in large areas of the iranian central plateau the origin of gypsum in the aridisols of central iran and its distribution in different landscapes were studied using sulfur and oxygen isotopic composition of both solid and dissolved sulfates the results strongly support the hypothesis that the area was cut off from the tethys seaway at the end of the mesozoic era and as a result the lower cretaceous sulfate has controlled the s geochemistry of the younger sediments including the soils studied the mean values of 34 s and 18 o of the soil gypsum and of dissolved sulfate match with the average isotopic values of the marine sediments which are the most common soil parent materials the results also confirm that s and o in dissolved so 4 and so 4 in gypsum have not undergone any reduction and re oxidation reactions dissolution and reprecipitation appear to be the possible mechanisms responsible for the observed minimal isotope fractionation both 34 s and 18 o values of the soil gypsum decrease slightly with decreasing elevation in the study area these findings are important for understanding the landform evolution in this arid region

dispersion and attenuation of mantle waves through waveform inversion summary we propose a new approach to the determination of elastic and anelastic parameters of the earth s structure from seismic data instead of measuring such functionals of the medium response as the phase delay or spectral ratios we perturb parameters of the model to satisfy the observed waveforms the advantage of our waveform inversion technique wit is that it uses the properties of the earth as a smoothing filter also because the earth s structure is the common denominator the method allows simultaneous interpretation of different functionals of this structure for example the waveforms of rayleigh and love waves for the same source receiver pair following extensive testing of the method on synthetic and actual data we subject results of our analysis of 37 recordings for various sources and stations to pure path decomposition the period range of analysis extends from 160 to 630s we distinguish four types of regions stable continents areas tectonically active within the last 400myr ocean floors younger than 38 myr and old ocean floors older than 38 myr the results indicate significantly different responses of the oceanic and continental areas at long periods stable continental and tectonic regions have nearly the same dispersion for periods greater than 300 35os and then diverge rapidly with stable continents showing higher velocities the young and old oceans on the other hand become distinct at periods as long as 500 s the old oceans are faster in terms of shear velocity models the data are consistent with a difference of about 4 per cent between the young and old oceans in a depth range from 400 to 670 km while the continental regions are similar and close to the global average at shallower depths our structures are conceptually similar to those inferred from previous pure path analyses and short period surface wave studies while we cannot yet establish statistically significant differences in q for the four regions such differences are obtained if one distinguishes only between continents and oceans the q for the latter is 10 20 per cent lower in the period range of the analysis

improved resolution of earthquake source parameters from long period surface wave inversions abstract source centroid location optimization moment tensor inversions of long period fundamental mode surface wave spectra joint inversions of rayleigh and love wave spectra are used to find source moment tensors for the 18 october 1989 loma prieta california earthquake m w 6 9 and the 22 april 1991 valle de la estrella costa rica earthquake m w 7 6 for the loma prieta event the focal mechanism at the optimal centroid location is consistent with that at the epicenter and both agree with independent information for the costa rica event the solution at the optimal centroid location is consistent with geodetic and body wave observations whereas the solution found for the epicenter is not we conclude that optimizing for centroid location in spectral inversions is possible and improves the determination of long period surface wave source parameters

numerical simulation and a geochemical model of supergene carbonate hosted non sulphide zinc deposits abstract the proposed metallogenetic model presented in this paper is based on observations from the iranian non sulphide zinc deposits mehdi abad iran kuh and kuh e surmeh the emplacement of non sulphide ore can be generally subdivided into an oxidation stage followed by a post oxidation stage the formation of carbonate hosted non sulphide zinc deposits is primarily controlled by three factors climate protore composition and geology lithology and structure of the wall rocks the climate controls the oxidation and metal transport predominantly through the amount of meteoric water and the availability of oxygen which indirectly is controlled through the thickness of the soil cover and biogenic oxygen consumption favourable conditions for oxidation are an arid climate with minimal biogenic activity within the soil as a consequence oxygen can reach the sulphides easily resulting in higher metal concentrations of the supergene aqueous solutions dry climates are associated with a low water table preventing descending zn bearing fluids from contact with the aquifer and thus from dilution dispersion and removal of metals commonly non sulphide zinc deposits consist of two types of ore red zinc ore rich in zn 20 fe 7 pb as and white zinc ore typically with very high zinc grades up to 40 but low concentrations of iron 4 2 ions during the oxidation stage leads to the precipitation of highly insoluble anglesite which results in low pb 2 concentration within the fluid most of the zinc up to 80 at ph 6 or 97 at ph 5 leaves the oxidation zone and precipitates as zinc carbonates in adjacent parts of the carbonate host rock the neutralisation processes of the sulphuric acid with the carbonates of the host rock during the oxidation stage lead to the formation of co 2 g consequently the co 2 partial pressure p co2 g increases drastically and forms a co 2 g halo around the active oxidation zone thus most of the zinc precipitates as smithsonite which is stable and occurs exclusively in a high p co2 g environment the p co2 g decreases during the post oxidation stage and reaches the level of atmospheric p co2 g under these conditions hydrozincite becomes stable and starts to replace smithsonite most of the stage i smithsonite becomes corroded and is altered to stage ii hydrozincite the post oxidation stage is also associated with the successive formation of local zinc hydro silicates depending on the availability of sio 2 within the solution generally arid climates provide the best conditions for the preservation of non sulphide deposits the limited availability of meteoric water and deep to very deep water tables protect the non sulphide ore from subsequent dissolution

centroid moment tensor solutions for october december 1992 abstract centroid moment tensor solutions are presented for 205 earthquakes that occurred during the fourth quarter of 1992 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward

vertical lithogeochemical halos and zoning vectors at goushfil zn pb deposit irankuh district southwestern isfahan iran implications for concealed ore exploration and genetic models abstract the vertical lithogeochemical halos of indicator elements in host rocks over a blind zn pb deposit are developed by upward migration of geochemical halos this may prove to be a useful exploration guide for targeting undiscovered zn pb mineral systems the main objective of this investigation is to assess the vertical distribution patterns of the composite lithogeochemical halos for detecting possible exploration guides as well as a possible genetic model of zn pb sulfide mineralization the goushfil zn pb deposit is one of the most important lower cretaceous carbonate and shale hosted deposit in the irankuh district west central iran the deposit contains about 4 3 million tonnes of sphalerite galena barite ore with an average grade of 8 zn and 2 4 pb in order to examine the exploration significance of the vertical lithogeochemical halos about 274 rock samples from 26 boreholes were sampled and analyzed by icp ms for a multi element package the results demonstrate that the highly anomalous values for ag 0 1 120 ppm as 3 1165 ppm ba 9 2820 ppm ca 0 07 25 cd 0 005 210 ppm hg 0 9 24 ppm mg 0 03 11 75 pb 15 15 000 ppm zn 65 15 000 ppm and sb 1 305 ppm are developed in faulted or fracture controlled hydrothermally dolomitized and jasperoid carbonates and shales the newly proposed multiphase composite geochemical halos defined by ratios of ag cd pb zn ag as pb zn ca mg pb zn sb as pb zn hg sb pb zn sb ba pb zn and ba ca pb zn correlate with three exploration zones at the average depth of 10 200 and 310 m above and below the main ore zone all the composite lithogeochemical halos in particular ag cd pb zn in both rock and soil samples tend to increase toward the shallow depths but decrease as they approach the main zn pb ore toward the deeper parts of the ore zone this geochemical response of the composite halos could be used for targeting undiscovered zn pb sulfide mineralization the low contents of cu and fe in the mineralized rocks indicate a low modal content of chalcopyrite and pyrite in the precursor sulfide ore which correlate with those of the mississippi valley type mvt zn pb deposits this is also highlighted on the log pb zn pb pb zn cu pb zn cu and homogenization temperature salinity variodiagrams on which the goushfil data plot close to the mvt type zn pb mineralization

nakhlak carbonate hosted pb ag deposit isfahan province iran a geological mineralogical geochemical fluid inclusion and sulfur isotope study abstract the upper cretaceous nakhlak epigenetic vein type pb ag deposit is located 55 km northeast of the town of anarak in isfahan province iran the deposit contains 7 mt of galena barite ore with an average grade of 8 33 pb 0 38 zn and 72 ppm ag the ore mineralization occurs as stratabound epigenetic steeply dipping east west trending veins in faulted or fracture controlled upper cretaceous sadar carbonates galena and barite are the primary minerals minor sphalerite tennantite tetrahedrite pyrite and chalcopyrite occur as inclusions in galena cerussite with minor amounts of anglesite and plattnerite formed in the oxidized supergene zone the ore and ore related minerals were deposited in the hydrothermally dolomitized carbonate host rock containing saddle shaped dolomite geochemically the dolomitized carbonate host rocks are enriched in mgo fe 2 o 3 mno pb zn and ba but depleted in cao the galena concentrate contains high values of ag 932 ppm sb 342 ppm cu 422 ppm as 91 ppm and zn 296 ppm the presence of these trace elements indicates a low temperature type of galena mineralization this interpretation is corroborated by fluid inclusions containing 12 98 wt nacl equivalent salinity the inclusions homogenize at the low temperature of about 152 1 c the similarity between 34 s v cdt values in nakhlak barite and permian triassic 34 s marine sulfate values indicates that the nakhlak sulfur was probably provided from evaporates of permian triassic age the 34 s v cdt values of galena and barite samples occupy the ranges of 1 04 to 8 62 and 10 95 to 13 71 respectively and are similar to mississippi valley type mvt deposits the low temperature basinal fluids evaporate originated sulfur and fault or fracture controlled galena rich veins in the nakhlak deposit resemble the type of geological features documented in pb rich mvt deposits

fluid inclusions s isotopes and pb isotopes characteristics of the kuh e surmeh carbonate hosted zn pb deposit in the zagros fold belt southwest iran implications for the source of metals and sulfur and mvt genetic model abstract the kuh e surmeh zn pb deposit is hosted by upper permian carbonate platform in the zagros fold belt of southwestern iran the orebody is characterized by massive vein and banded textures it is mostly composed of sphalerite galena and pyrite accompanied with minor barite homogenization temperatures of fluid inclusions in sphalerite and barite range from 94 7 to 200 0 c and 93 6 to 198 0 c respectively fluid salinities of sphalerite and barite hosted inclusions vary from 8 1 to 21 3 wt nacl equiv and 10 5 to 22 6 wt nacl equiv respectively the 34s values of barite range from 11 2 to 11 9 similar to those of gypsum of the nar member 10 9 to 11 7 in the upper permian sedimentary strata and different from the 34s values of jahani salt dome gypsum 29 1 to 30 5 indicating that sulfur was derived from the upper permian evaporites the 34s values of galena and sphalerite range from 1 7 to 15 4 compatible with bacterial sulfate reduction bsr of the upper permian evaporites the pb isotopic compositions of galena yield 206pb 204pb ratios from 17 942 to 18 340 207pb 204pb ratios from 15 649 to 15 744 and 208pb 204pb ratios from 38 186 to 38 458 indicating an upper crustal lead source based on ore textures fluid inclusions isotope data and geochemical compositions of sulfide minerals the kuh e surmeh sulfide mineralization is believed to have precipitated from low temperature sedimentary basin brines and should be classified as a mississippi valley type deposit in a salt diapir environment mineralization is the result of mixing of hypogene metalliferous fluids with more dilute h2s rich fluids during miocene pliocene compression associated with the zagros orogeny

hypogene zn carbonate ores in the angouran deposit nw iran the world class angouran nonsulfide zn pb deposit is one of the major zn producers in iran with resources estimated at about 18 mt at 28 zn mainly in the form of the zn carbonate smithsonite this study aims to characterize these carbonate ores by means of their mineralogy and geochemistry which has also been extended to the host rocks of mineralization and other local carbonate rock types including the prominent travertines in the angouran district as well as to the local spring waters petrographical chemical and stable isotope o h c sr data indicate that the genesis of the zn carbonate ores at angouran is fairly distinct from that of other classical nonsulfide zn deposits that formed entirely by supergene processes mineralization occurred during two successive stages with the zinc being derived from a preexisting sulfide ore body a first main stage of zn carbonates stage i carbonate ore is associated with both preexisting and subordinate newly formed sulfides whereas a second stage is characterized by supergene carbonates zn and minor pb coexisting with oxides and hydroxides stage ii carbonate ore the coprecipitation of smithsonite with galena pyrite and arsenopyrite as well as the absence of fe and mn oxides hydroxides and of any discernible oxidation or dissolution of the sphalerite rich primary sulfide ore shows that the fluids responsible for the main stage i carbonate ores were relatively reduced and close to neutral to slightly basic ph with high fco2 smithsonite 18ovsmow values from stage i carbonate ore range from 18 3 to 23 6 while those of stage ii carbonate ore show a much smaller range between 24 3 and 24 9 the 13c values are fairly constant in smithsonite of stage i carbonate ore 3 2 6 0 but show a considerable spread towards lower 13cvpdb values 4 6 to 11 2 in stage ii carbonate ore this suggests a hypogene formation of stage i carbonate ore at angouran from low temperature hydrothermal fluids probably mobilized during the waning stages of tertiary quaternary volcanic activity in an environment characterized by abundant travertine systems throughout the whole region conversely stage ii carbonate ore is unambiguously related to supergene weathering as evidenced by the absence of sulfides the presence of fe mn oxides and arsenates and by high 18o values found in smithsonite ii the variable but still relatively heavy carbon isotope values of supergene smithsonite ii suggests only a very minor contribution by organic soil carbon as is generally the case in supergene nonsulfide deposits

rapid estimation of rupture directivity application to the 1992 landers ms 7 4 and cape mendocino ms 7 2 california earthquakes using empirical green functions with regional and teleseismic surface waves it is possible to resolve fault finiteness effects in many cases uniquely defining the fault plane for relatively large earthquakes the technique requires very little data processing and can be applied in near real time with the current distribution of seismic stations the landers strike slip earthquake was dominated by two sub events with predominantly north northwestward rupture the second sub event was 1 5 times larger and rotated in strike by 12 counterclockwise relative to the first the cape mendocino thrust event had a relatively smooth rupture that propagated to the southwest on a shallow dipping fault

modeling the seismic source and tsunami generation of the december 12 1992 flores island indonesia earthquake on december 12 1992 a large earthquake m s 7 5 occurred just north of flores island indonesia which along with the tsunami it generated killed more than 2 000 people in this study teleseismicp andsh waves as well aspp waves from distances up to 123 are inverted for the orientations and time histories of multiple point sources by repeating the inversion for reasonable values of depth time separation and spatial separation a 2 fault model is developed next the vertical deformation of the seafloor is estimated from this fault model using a detailed bathymetric model linear and nonlinear tsunami propagation models are tested the data consist of a single tide gauge record at palopo 650 km to the north as well as tsunami runup height measurements from flores island and nearby islands assuming a tsunami runup amplification factor of two the two fault model explains the tide gauge record and the tsunami runup heights on most of flores island it cannot however explain the large tsunami runup heights observed near leworahang on hading bay and riangkroko on the northeast peninsula massive coastal slumping was observed at both of these locations a final model which in addition to the two faults includes point sources of large vertical displacement at these two locations explains the observations quite well

centroid moment tensor solutions for april june 1993 abstract centroid moment tensor solutions are presented for 196 earthquakes that occurred during the second quarter of 1993 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward

marble hosted sulfide ores in the angouran zn pb ag deposit nw iran interaction of sedimentary brines with a metamorphic core complex the angouran zn pb ag deposit zanjan province nw iran is located within the central sanandaj sirjan zone of the zagros orogenic belt the deposit has proven and estimated resources of 4 7 mt of sulfide ore at 27 7 zn 2 4 pb and 110 g t ag and 14 6 mt of oxidized carbonate ores at 22 zn and 4 6 pb it is hosted by a metamorphic core complex that is unconformably overlain by a neogene volcanic and evaporite bearing marine to continental sedimentary sequence the sulfide orebody precursor to the significant nonsulfide ores is located at the crest of an open anticline at the contact between neoproterozoic to cambrian footwall micaschists and hanging wall marbles 40ar 39ar data on muscovite from mineralized and unaltered footwall micaschists suggest a rapid mid miocene exhumation of the metamorphic basement 20 ma and yield an upper age constraint for mineralization the fine grained sulfide ore is massive replacive often brecciated clearly postmetamorphic and dominated by fe poor sphalerite with minor galena pyrite anhydrite quartz muscovite dolomite and rare calcite sphalerite contains na ca cl brine inclusions 23 25 mass total dissolved solids with homogenization temperatures of 180 70 c fluid inclusion chemistry na k li ca mg cl br ore geochemistry s and pb isotope data suggest that the angouran sulfide ore formed by the interaction of modified strongly evaporated miocene seawater and the lithotypes of an exhumed metamorphic core complex minor contributions of metals from miocene igneous rocks cannot be excluded mineralization occurred in a collisional intra arc setting with high heat flow probably during the transition from an extensional to a compressional regime the angouran deposit may represent a new type of low temperature carbonate hosted zn pb ore that is distinct from mississippi valley type and sedimentary exhalative deposits

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

anisotropic models of the upper mantle long period rayleigh wave and love wave dispersion data particularly for oceanic areas have not been simultaneously satisfied by an isotropic structure in this paper available phase and group velocity data are inverted by a procedure which includes the effects of transverse anisotropy anelastic dispersion sphericity and gravity we assume that the surface wave data represents an azimuthal average of actual velocities thus we can treat the mantle as transversely isotropic the resulting models for average earth average ocean and oceanic regions divided according to the age of the ocean floor are quite different from previous results which ignore the above effects the models show a low velocity zone with age dependent anisotropy and velocities higher than derived in previous surface wave studies the correspondence between the anisotropy variation with age and a physical model based on flow aligned olivine is suggestive for most of the earth sh sv in the vicinity of the low velocity zone neat the east pacific rise however sv sh at depth consistent with ascending flow anisotropy is as important as temperature in causing radial and lateral variations in velocity the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age this layer defines the lid or seismic lithosphere in the pacific the lid thickens with age to a maximum thickness of 50 km this thickness is comparable to the thickness of the elastic lithosphere the lid thickness is thinner than derived using isotropic or pseudo isotropic procedures a new model for average earth is obtained which includes a thin lid this model extends the fit of a prem type model to shorter period surface waves

genesis of sediment hosted zn pb ba deposits in the irankuh district esfahan area west central iran the results of isotopic studies on carbonates and sulfur bearing minerals of the irankuh deposit occurring in lower cretaceous carbonate strata provide information concerning the nature of the fluids responsible for zn pb ba mineralization and associated dolomitization an epigenetic model for the irankuh deposits is supported by their discordant nature emplacement along the irankuh fault progressive depletion in stable carbon isotope ratios of the host dolostones as mineralization is approached and isotopic characteristics of the ore stage dolomites and barites the host rock dolostones show extensive depletion in 18 o delta 18 o 4 9 to 12 7ppm due to diagenetic modification and or recrystallization at increased temperatures based on isotopic and fluid inclusion data the ore stage dolomites in the deposits are interpreted as having formed from warm approximately 100 degrees c saline 87 sr enriched fluids similar to oil field brines the overlap in delta 18 o values and 87 sr 86 sr ratios between host dolostones and sucrosic and saddle dolomites implies that these rocks have been isotopically modified and precipitated by similar fluids the delta 34 s values of metal sulfides range from 3 6 to 9 6 per mil whereas barite values ranging from 14 3 to 18 9 per mil fall within the range of cretaceous age sulfate values it is inferred that seawater sulfate acted as the source of the sulfides and barite mineralization the reduced sulfur was generated by partial reduction of seawater sulfate by organic matter under hydrothermal conditions the presence of a hydrocarbon i e traces of bitumen and saddle and fracture filling dolomite with low delta 13 c values ranging to 6 4ppm in conjunction with the temperature of ore deposition provides evidence for thermochemical sulfate reduction carbonates and barites show 87 sr 86 sr ratios enriched in 87 sr which is atypical of derivation from normal seawater the enrichment of 87 sr is explained by extensive interaction of fluids with the underlying siliciclastic rock evolving toward more radiogenic compositions the release of the overpressurized fluids appears to have been due to dehydration reactions and regional tectonism the metal bearing fluids responsible for mineralization migrated along the major irankuh fault and mixed with sulfate bearing fluids at the ore depositional site hydrologic considerations demonstrate that the proposed model is feasible

moment tensor solutions estimated using optimal filter theory global seismicity 1992 abstract moment tensor solutions estimated using optimal filter theory are listed for 133 moderate to large earthquakes occurring during 1992

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

very broadband seismic analysis of the 1992 flores indonesia earthquake mw 7 9 the december 12 1992 flores island earthquake m w 7 9 which caused a destructive tsunami is located in the back arc of the transition zone between the sunda and banda arcs a region in active collision with the australian continental margin we study the earthquake using four seismological techniques spanning a period range of 1 1000 s and infer that the flores event may be characterized as a shallow back arc thrust with fault plane strike 70 30 dip 28 10 and rake 80 to 140 linear trade off with strike a rupture consisting of three discrete pulses with a total duration of 70 s centroid time 26 3 s and an estimated moment release between 7 5x10 20 and 8 0x10 20 n m from the slip vector we infer that compressional forces play an important role in the deformation mechanism of the back arc north of flores island body waves constrain the hypocentral depth to be 16 km with rupture mainly propagating updip to shallow depth and bilaterally along strike with most subevents located toward the northeast evidence for rupture directivity from surface wave deconvolutions is inconclusive but the overall source function is consistent with body wave results our body wave finite fault model is in rough agreement with two models proposed to explain tsunami run up observations normal mode modeling of w phase observations at periods longer than 70 s shows that slow slip is negligible from this and the slip distribution determined from the body wave analysis we infer that the seismic source is an unlikely candidate to explain anomalously high tsunami run ups measured on northeastern flores island

recognition of the regional lineaments of iran using geospatial data and their implications for exploration of metallic ore deposits abstract the relationship between major structural lineaments and locations of ore deposits in iran has been investigated using geospatial data in the course of lineament extraction satellite images aeromagnetic data digital elevation model dem and structural maps were processed and the lineaments and large scale faults were identified the extracted lineaments based on subjective assessment from each dataset were imported into gis software and the lineament map of iran was prepared by data integration the analysis for selecting significant lineament was mainly based on fault correlated lineament and lineament with field map fractures which was sets as benchmarks for compiling a final output map four major regional lineament trends of n s e w nw se and ne sw were identified in the data of all images which are corresponded to the structural zones and the major fault systems of iran the mineral deposits active and abandoned and mineral indications database compiled are based on the published maps papers reports and the ore deposits data files of geological survey of iran integrating the output of these two datasets by gis software resulted in the combined map of lineaments and gold copper lead zinc and iron deposits of iran the number and distance of ore deposits toward the lineaments were processed by the counting and cumulative methods in the gis software s approximately over 90 of the ore deposits of iran are located in the central part of the lineaments 15 km on each side which are concordant with a definition of large lineament about 50 of these mineral deposits are closer than 5 km to the lineaments there are significant correlations between lineament density and intersections with ore deposits occurrences the observed associations at this scale are informative in establishing exploration strategy and decreasing exploration risks for detailed work on ore deposit scale

the april 22 1991 valle de la estrella costa rica mw 7 7 earthquake and its tectonic implications a broadband seismic study the rapture process of a large back arc thrusting earthquake the april 22 1991 valle de la estrella costa rica mw 7 7 earthquake is investigated using broadband body waves and long period surface waves we find the source process to be relatively simple with the source models separately obtained from body and surface waves being very consistent the event occurred on a shallow southwest dipping rapture plane on which most energy is released updip of the hypocentral location 10 20 km deep high frequency radiation appears to have been released over a relatively small source area our preferred model has a focal mechanism with strike 102 10 dip 17 14 and rake 63 17 a seismic moment of 3 8 1 5 1020 n m and a total rupture duration of 40 6 s the earthquake appears to be associated with the north panama deformed belt npdb a thrust and fold complex that has accommodated the oroclinal deformation of panama this event along with previous large events north of panama in 1882 and 1916 indicates that there is substantial convergence along the npdb marking the npdb as a probable emerging plate boundary it remains difficult to gauge the earthquake hazard in the region because of the tectonic complexity

geology isotope geochemistry and fluid inclusion investigation of the robat zn pb ba deposit malayer esfahan metallogenic belt southwestern iran abstract the robat zn pb ba deposit in the arak mining district in the malayer esfahan metallogenic belt memb has an estimated reserve of 5 million tonnes mt ore grading 2 1 wt zn and 1 4 wt pb and 4 mt barite ore this deposit hosted by early cretaceous carbonate rocks formed in an extensional back arc environment between the sanandaj sirjan zone and central iranian microcontinent sulfide and barite ores display a strong lithological control and form stratabound stacked ore lenses which are hosted in two horizons by silicified and dolomitized limestone they are generally best developed below marl layers within intercalated shale marl and limestone the textural and mineralogical data indicate two main stages of sulfide and barite mineralization at the robat deposit the first stage comprised deposition of volumetrically minor early fine grained disseminated sulfides and barite near the seafloor in unconsolidated sediments subsequently sub seafloor replacement of barite carbonate and early sulfide laminae bands occurred by precipitation of late sulfides and other hydrothermal minerals within the early cretaceous limestone dominant sequence the minerals in this later stage were deposited in a close relationship with quartz veins electron microprobe analyses revealed that sphalerite has a very high fe content averaging about 1 23 wt and is relatively enriched in as ga ge cd ag and bi which is similar to irish type carbonate hosted deposits in addition the ag content of galena is comparatively low although concentrations of ga ge cd zn and sb are fairly high fluid inclusion microthermometric study of hydrothermal quartz revealed two types of primary two phase l v fluid inclusions in hydrothermal quartz type i fluid inclusions with irregular shapes were recorded along crystal growth zones whereas type ii inclusions are observed as isolated inclusions with relatively regular shapes that are less common than type i type i and ii inclusions exhibit homogenization temperatures of 140 239 c and 233 290 c with salinities of 2 2 11 8 and 5 5 11 5 wt nacl equiv respectively fluid inclusions extracted from quartz displayed dsmow between 67 and 56 and measurements of hydrothermal quartz yielded 18ofluid smow of 12 9 to 23 5 the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of galena samples fell in the ranges of 18 412 18 427 15 642 15 647 and 38 556 38 580 respectively the different ratios for the pb isotopes suggest a dominant continental crust origin for pb in the ores geological textural mineralogical and isotopic data may be cumulatively interpreted to indicate that the robat carbonate hosted deposit formed from sub seafloor replacement like commonly observed for irish type base metal deposits

tsunami earthquakes slow thrust faulting events in the accretionary wedge the november 20 1960 peru october 20 1963 kurile and june 10 1975 kurile earthquakes are classified as tsunami earthquakes based on anomalously large tsunami excitation relative to earthquake magnitude long period surface wave analysis indicates double couple faulting mechanisms for all three events rather than single force mechanisms indicative of submarine landslides the earthquakes have shallow depths 15 km and are located near the trench axis and seaward of most other thrust zone events beneath the accretionary prism body waveform inversion indicates very shallowly dipping thrust faulting mechanisms for the three events with dip angles of 6 8 surface wave spectral amplitudes and deconvolution of sh waveforms suggests anomalously long source durations and large seismic moments relative to ms specifically the 1963 kurile event ms 7 2 shows a duration of 85 s and a moment of 6 0 1027 dyn cm mw 7 8 the 1975 kurile event ms 7 0 shows a duration of 60 s and a moment of 2 0 1027 dyn cm mw 7 5 and the 1960 peru event ms 6 75 shows a time function consisting of four subevents with a total duration of 110 130 s and a seismic moment of 3 4 1027 dyn cm mw 7 6 estimated rupture velocities are about 1 km s or less but there is no evidence of unusually low stress drops the august 1 1968 philippines event previously classified as a tsunami earthquake shows none of the anomalous source properties and teleseismic tsunami height measurements are sparse we do not consider this event a tsunami earthquake most of the anomalous tsunami excitation results from underestimation of earthquake size by ms due to the long source duration the tsunami heights are not significantly anomalous relative to seismic moment the slow nature of these events may result from rupture through the sedimentary rock along the basal decollement of the accretionary prism standard scaling laws when adjusted for the slow seismic velocity in the source region show an mw ms relationship similar to that observed for the tsunami earthquakes and predict ms saturation at about 7 3 rather than 8 0 for typical events

stable isotope geochemistry of sulfur bearing minerals and clay mineralogy of some soils and sediments in loot desert central iran abstract stable isotope geochemistry is a unique technique to study the source of salts in soils and sediments in the present research sources of gypsum and other sulfur bearing minerals using stable isotope technique and clay mineralogy were studied in different landforms in loot desert central iran four geomorphic surfaces including neogene conglomeratic formations reg surfaces yardangs and kaleshoor playa surfaces were observed the 34 s values in these geomorphic surfaces ranged between 10 1 12 6 11 2 14 3 11 8 13 8 and 12 1 13 0 respectively the sequential extraction by hcl and hno 3 br 2 was used to find if metal sulfides could have played a role in gypsum formation and is a controlling sulfur source the mean value of 12 9 for 34 s showed that sulfate in the lower cretaceous formation is controlling the s geochemistry decrease of 34 s values during sequential extraction showed some anomalies that could be attributed to the mixing of some soluble sulfate remains by metal insoluble sulfides data on gypsum crystallization water showed a similar trend with isfahan and rafsanjan areas central iran but likely with a cooler temperature at the time of gypsum formation as the 18 o and d were much lighter in the area studied association of large amounts of palygorskite crystals with gypsum and or anhydrite supports that palygorskite was probably formed after the precipitation of gypsum under a high ph and mg ca ratio presence of large amounts of palygorskite in different layers of yardangs showed that the old large loot plain is formed under conditions of post tethyan shallow hyper saline water conditions

multibeam study of the flores backarc thrust belt indonesia using the seamarc ii seafloor mapping tool in conjunction with closely spaced seismic reflection profiles we have mapped a segment of the flores back arc thrust zone structural irregularities along the deformation front of the thrust zone result from changing stratigraphy and basement structure of the lower plate ne trending faults cutting the outer slope of the flores basin are easily mapped because they truncate dense drainage patterns obliquely mud diapirs probably indicating elevated fluid pressures have formed throughout the accretionary wedge but appear to be concentrated as do back arc thrust earthquakes at the ends of thrust faults the overall orientation of the deformation front of the accretionary wedge is 100 suggesting a nne sense of thrust motion and supporting an origin of the thrust zone by collision of the arc with australia rather than by magmatic forcing or gravitational sliding or spreading orientations of faults and folds close to the arc are not consistent with the trends of the frontal thrusts however and the difference may be due to either different initial orientations or to later rotations of structural features as the accretionary wedge grew

evidence for a predominantly non solar origin of nitrogen in the lunar regolith revealed by single grain analyses we measured the amounts of 14n and 36ar in single mineral and glass grains from a lunar soil by laser extraction with the goal of studying the controversial origin of trapped nitrogen in the lunar regolith the average 14n 36ar ratio of 29 ilmenite grains is 379 similar to the value determined previously on a large ilmenite separate from the same soil and 10 times larger than the solar ratio of 37 however the 14n 36ar ratios in the individual grains vary between 1 and 440 times the solar ratio 36ar amounts in the ilmenite grains scatter by more than two orders of magnitude n amounts by less than a factor of 6 the variability of the 14n 36ar ratio forms a striking contrast to the very uniform relative abundances of ar kr and xe trapped from the solar corpuscular radiation observed earlier in ilmenite and other mineral grains from the same soil this strongly suggests that on average some 90 of the n in the grains has a non solar source contrary to the often expressed view that essentially all n in the lunar regolith has been trapped from the solar wind the conclusion that the lunar regolith testifies to a secular variation of the n isotopic composition in the solar wind of 30 becomes thus highly questionable the origin of the bulk of trapped lunar nitrogen remains unknown

emarat carbonate hosted zn pb deposit markazi province iran a geological mineralogical and isotopic s pb study abstract the emarat deposit with a total proved reserve of 10 mt ore grading 6 zn and 2 26 pb is one of the largest zn pb deposits in the malayer esfahan belt the mineralization is stratabound and restricted to early cretaceous limestones and dolomites the ore consists mainly of sphalerite and galena with small amounts of pyrite chalcopyrite calcite quartz and dolomite textural evidence shows that the ore has replaced the host rocks and thus is epigenetic sulfur isotopes indicate that the sulfur in sphalerite and galena has been derived from cretaceous seawater through thermochemical sulfate reduction sulfur isotope compositions of four apparently coprecipitated sphalerite galena pairs suggest their precipitation was under equilibrium conditions the sulfur isotopic fractionation observed for the sphalerite galena pairs corresponds to formation temperatures between 77 c and 168 c which agree with homogenization temperatures of fluid inclusions lead isotope studies indicate that the lead in galena has been derived from heterogeneous sources including orogenic and crustal reservoirs with high 238 u 204 pb and 232 th 204 pb ratios ages derived from the pb isotope model give meaningless ages ranging from early carboniferous to future it is probable that the pb isotope model ages that point to an earlier origin than the early cretaceous host rocks are derived from older reservoirs in the underlying carboniferous or jurassic units either from the host rocks or from earlier formed ore deposits within these units this research and other available data show that the emarat zn pb deposit has many important features of mississippi valley type mvt lead zinc deposits and thus we argue that it is an mvt type ore deposit

back arc thrusting in the eastern sunda arc indonesia a consequence of arc continent collision the structure of the eastern sunda back arc region is dominated by two large north directed thrusts the wetar and flores thrusts and one or more minor thrusts which may represent early stages of subduction polarity reversal of the arc the relationships between thrusting and magmatic activity surface slopes cross arc faulting uplift forearc structure and collision by the australian continental margin provide constraints on the likely driving mechanisms of thrust formation driving mechanisms are considered in two broad categories one set of possible mechanisms originates within the upper plate and includes gravity sliding gravity spreading and magmatic intrusion the other set focuses on stress propagation between the upper and lower plates and for this arc system the major mechanism is that of continental collision while no one mechanism explains the range of observations we see in the back arc region all of these aspects play some role in the development of the thrusts we can eliminate upper plate mechanisms as primary driving forces because slope effects are similar in areas of both thrusting and nonthrusting in addition the wetar thrust shows a negative relation between thrusting and volcanism and side looking airborn radar images show no evidence of postvolcanic rifting that could accompany intrusion without volcanism collision between the arc and the australian continent provides the clearest driving mechanism but it does not explain the discontinuous nature or the particular location of the thrusts we suggest a sequence that appears to account for the data and to provide insight into the controversies often associated with other such thrust belts thrusting was initiated in those areas where the crust of the forearc region was thick a factor that facilitated stress propagation across the arc and where the crust of the back arc was thin which facilitated back arc thrusting thrusting concentrated at the base of the slope where the slope stress is maximum the early thrusting may have been helped also by thermal weakening of the crust due to volcanism as convergence proceeded volcanism waned then ceased in the eastern part of the arc the crust then strengthened and thrusting required higher stress to maintain and propagate this later stage should show higher seismic energy release which appears to be the case for the wetar thrust region displacement on the flores thrust appears to be matched by deflection of the volcanic arc we have estimated shortening in the back arc from interpretation of reflection profiles and for the flores thrust the value of approximately 30 km is consistent with that estimated for deflection of the arc compressional deformation continues west of the collision zone across the bali basin and into java it is reported in ne sumatra as well this deformation involves much less convergence than the eastern sunda thrusts and it may be related to magmatic processes to subduction of oceanic plateaus such as the roo rise or in the case of the bali basin to efficient lateral propagation of the flores thrust

long period surface wave inversion for source parameters of the 18 october 1989 loma prieta earthquake abstract we performed simultaneous seismic moment tensor inversions of long period 157 288 s fundamental mode rayleigh and love waves from the 1989 loma prieta earthquake to further constrain the source process of the event utilizing a two step spectral inversion technique we explored the model dependence and centroid location sensitivity of the long period surface wave analysis to assess the confidence bounds on the results we found that estimates of the source duration and depth are highly dependent on the choice of propagation attenuation and source velocity structure models including centroid location parameters in the inversion stabilizes moment tensor estimates but yields a biased location away from the epicenter due to model inaccuracies our source duration estimate is 11 5 s using a recent velocity model mpa with the centroid time of 6 s being significantly less than earlier surface wave studies centroids of 10 22 s and hence more compatible with both body wave and strong motion duration estimates an unconstrained moment tensor inversion at the optimum centroid location yields a stable major double couple solution strike 124 6 dip 67 6 rake 126 7 and a seismic moment estimate 3 0 0 2 1019 nm mw 6 9 similar to earlier long period studies and body wave and geodetic results the surface wave centroid depth estimate is 22 11 km which overlaps the body wave estimates 13 5 km thus surface wave source parameters for the loma prieta event allowing for plausible model dependence are fully compatible with body wave determinations and there is no evidence for any anomalous coseismic long period source process