palaeomagnetism petrology and geochronology of tertiary magmatic and sedimentary units from iran abstract an amount of 160 samples from igneous and sedimentary formations of palaeocene or eocene age was collected in iran northeast of the zagros belt palaeomagnetic analyses petrological studies and k ar dating indicate palaeocene and eocene palaeomagnetic directions in the zabol baluch region east iranian range and show that the area remained approximately stable with respect to the eurasian and african plates from the beginning of the cainozoic era conversely large post eocene deformations occurred in central iran these large rotations are both clockwise and anti clockwise they might have resulted from lateral shears between arabia and northeast iran the central elburz underwent a large clockwise rotation which is probably late oligocene in age as a whole our results show that the so called persian plate did not exist during the cainozoic era

metallogeny of the precambrian in iran abstract precambrian complexes are exposed in northern and central iran on the basis of the degree of metamorphism and lithology three major units can be distinguished the oldest complex consists of high grade metamorphosed and partly granitized gneisses followed by a low grade metamorphic series including amphibolites quartzitic schists and marbles these rocks are overlain by series of greenschist facies or slightly higher grade flyschoid rocks alkalic granites which have in places invaded the above series have produced skarn type magnetite fe ore and vein type au mineralization the third known complex consists of intracontinental rift type sediments evaporites pyroclastics and magmatic rocks the precambrian basement in iran is a part of the afro arabian platform consolidated by the kibaro pan african orogeny this tectonic event ended with tensional intracontinental rifting and the development of taphrogenic rift structures with bimodal alkaline and carbonatite type magmatism this magmatism and related alteration produced metasomatic rocks and associated mineralizations about 750 500 ma in age mineralizations of u th v mn mo ti ba apatite rare earth elements ree stratiform pb zn massive sulphides and different types of fe ore are found within these taphrogenic belts

the carbonate rock hosted epithermal gold deposit of agdarreh takab geothermal field nw iran hydrothermal alteration and mineralisation the disseminated gold deposit of agdarreh 24 5 t at 3 7 g t au is hosted in hydrothermally leached miocene reefal limestone in the takab geothermal field which is part of the cenozoic urumieh dokhtar volcanic arc of nw iran alteration and mineralisation are largely bedding controlled blanket like and include 1 pre ore decalcification 2 first stage silicification associated with pyrite early pyrite with 3 4 wt as late pyrite with 1 3 wt as and sphalerite 3 second stage silicification with precipitation of galena pb sb as sulphides sulphosalts tellurides and native bismuth 4 late stage cinnabar and barite in vugs 5 oxide ore stage and carbonate alteration complex mn fe rich oxyhydroxides arsenates sulphates aps minerals and rutile in residual leached rock and infill of karstic cavities gold occurs invisibly in the jasperoids and is enriched in the mn fe oxyhydroxide surface cap of the jasperoids gold mineralisation is associated with the hydrothermal metal suite of as sb hg te se tl ba zn ag cd bi and pb and is characterised by very low cu contents arsenian pyrite probably carried most of the primary invisible gold native gold occurs in association with the late stage cinnabar and the oxide ore

denitrification in the recharge area and discharge area of a transient agricultural nitrate plume in a glacial outwash sand aquifer minnesota 1 recharge rates of nitrate no3 to groundwater beneath agricultural land commonly are greater than discharge rates of no3 in nearby streams but local controls of no3 distribution in the subsurface generally are poorly known groundwater dating cfc 3h was combined with chemical ions and gases and stable isotope n s and c analyses to resolve the effects of land use changes flow patterns and water aquifer reactions on the distributions of o2 no3 so4 and other constituents in a two dimensional vertical section leading from upland cultivated fields to a riparian wetland and stream in a glacial outwash sand aquifer near princeton minnesota within this section a plume of oxic no3 rich groundwater was present at shallow depths beneath the fields and part of the wetland but terminated before reaching the stream or the wetland surface groundwater dating and hydraulic measurements indicate travel times in the local flow system of 0 to 40 years with stratified recharge beneath the fields downward diversion of the shallow no3 bearing plume by semiconfining organic rich valley filling sediments under the wetland and upward discharge across the valley and stream bottom the concentrations and 15n values of no3 and n2 indicate that the no3 plume section was bounded in three directions by a curvilinear zone of active denitrification that limited its progress however when recalculated to remove the effects of denitrification the data also indicate changes in both the concentrations and 15n values of no3 that was recharged in the past isotope data and mass balance calculations indicate that fes2 and other ferrous fe phases were the major electron donors for denitrification in at least two settings 1 within the glacial fluvial aquifer sediments beneath the recharge and discharge areas and 2 along the bottom of the valley filling sediments in the discharge area combined results indicate that the shape and progress of the oxic no3 plume termination were controlled by a combination of 1 historical and spatial variations in land use practices 2 contrast in groundwater flow patterns between the agricultural recharge area and riparian wetland discharge area and 3 distribution and abundance of electron donors in both the sand aquifer and valley filling sediments the data are consistent with slow migration of redox zones through the aquifer in response to recharging oxic groundwater during holocene time then an order of magnitude increase in the flux of electron acceptors as a result of agricultural no3 contamination in the late twentieth century to which the redox zone configuration still may be adjusting the importance of denitrification for no3 movement through formerly glaciated terrains should depend on the source areas and depositional environments of the glacial sediments as well as geomorphology and recent stream valley sediment history

response of deep groundwater to land use change in desert basins of the trans pecos region texas usa effects on infiltration recharge and nitrogen fluxes quantifying the effects of anthropogenic processes on groundwater in arid regions can be complicated by thick unsaturated zones with long transit times human activities can alter water and nutrient fluxes but their impact on groundwater is not always clear this study of basins in the trans pecos region of texas links anthropogenic land use and vegetation change with alterations to unsaturated zone fluxes and regional increases in basin groundwater no3 concentrations median increases in groundwater no3 by 0 7 0 9 mg n l over periods ranging from 10 to 50 years occurred despite low precipitation 220 360 mm year high potential evapotranspiration 1570 mm year and thick unsaturated zones 10 150 m recent model simulations indicate net infiltration and groundwater recharge can occur beneath trans pecos basin floors and may have increased due to irrigation and vegetation change these processes were investigated further with chemical and isotopic data from groundwater and unsaturated zone cores some unsaturated zone solute profiles indicate flushing of natural salt accumulations has occurred results are consistent with human influenced flushing of naturally accumulated unsaturated zone nitrogen as an important source of no3 to the groundwater regional mass balance calculations indicate the mass of natural unsaturated zone no3 122 910 kg n ha was sufficient to cause the observed groundwater no3 increases especially if augmented locally with the addition of fertilizer n groundwater no3 trends can be explained by small volumes of high no3 modern recharge mixed with larger volumes of older groundwater in wells this study illustrates the importance of combining long term monitoring and targeted process studies to improve understanding of human impacts on recharge and nutrient cycling in arid regions which are vulnerable to the effects of climate change and increasing human reliance on dryland ecosystems

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

geologic and metallogenic significance of the isotopic composition of lead in galenas of the chilean andes eighty galena samples from different mineral deposits within the chilean andes from the mesozoic and cenozoic eras were analyzed for lead isotopes the results show a restricted dispersion between 18 65 to 18 28 15 68 to 15 56 and 38 72 to 38 11 on 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios respectively galenas from deposits hosted by pre jurassic to jurassic rocks are relatively enriched in radiogenic pb reflecting the involvement of old crustal pb galenas from lower cretaceous hosted deposits are less radiogenic and may reflect a mantlelike component those from tertiary rocks are isotopically more variable reflecting the influence of a more evolved crust there is no obvious correlation between the isotopic composition of the galena leads and the age of the hydrothermal event that gave rise to the particular mineral deposit when such ages can be determined from independent geologic evidence it is concluded that the galena leads were derived from a mixture of different lead reservoirs as defined in zartman and doe 1981 the correlation of isotopic composition with age of host rocks suggests either that the concentration of lead to form galena was more or less contemporaneous with the formation of the host rock or that the galena lead was essentially derived from the country rocks and inherited their original isotopic signature other workers have reported an overall similarity between the isotopic composition of galena leads and whole rock leads from the chilean andes however the isotopic compositions of galena leads from the argentinian andes show different characteristics from those of the chilean andes but the data are insufficient to allow firm conclusions

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

denitrification and mixing in a stream aquifer system effects on nitrate loading to surface water ground water in terrace deposits of the south platte river alluvial aquifer near greeley colorado usa had a median nitrate concentration of 1857 mol l 1 median nitrate concentrations in ground water from adjacent floodplain deposits 468 mol l 1 and riverbed sediments 461 mol l 1 both of which are downgradient from the terrace deposits were lower than the median concentration in the terrace deposits the concentrations and 15n values of nitrate and n2 in ground water indicated that denitrifying activity in the floodplain deposits and riverbed sediments accounted for 15 30 of the difference in nitrate concentrations concentrations of cl and sio2 indicated that mixing between river water and ground water in the floodplain deposits and riverbed sediments accounted for the remainder of the difference in nitrate concentrations river flux measurements indicated that ground water discharge in a 7 5 km segment of river had a nitrate load of 1718 kg n day and accounted for about 18 of the total nitrate load in the river at the downstream end of that segment this nitrate load was 70 less than the load predicted on the basis of the median nitrate concentration in the terrace deposits and assuming no denitrification or mixing in the aquifer water exchange between the river and aquifer caused ground water that originally discharged to the river to reenter denitrifying sediments in the riverbed and floodplain thereby further decreasing the nitrate load in this stream aquifer system results from this study indicated that denitrification and mixing within akluvial aquifer sediments may substantially decrease the nitrate load added to rivers by discharging ground water

effects of human induced alteration of groundwater flow on concentrations of naturally occurring trace elements at water supply wells the effects of human induced alteration of groundwater flow patterns on concentrations of naturallyoccurring trace elements were examined in five hydrologically distinct aquifer systems in the usa although naturally occurring these trace elements can exceed concentrations that are considered harmful to human health the results show that pumping induced hydraulic gradient changes and artificial connection of aquifers by well screens can mix chemically distinct groundwater chemical reactions between these mixed groundwaters and solid aquifer materials can result in the mobilization of trace elements such as u as and ra with subsequent transport to water supply wells for example in the high plains aquifer near york nebraska mixing of shallow oxygenated lower ph water from an unconfined aquifer with deeper confined anoxic higher ph water is facilitated by wells screened across both aquifers the resulting higher o2 lower ph mixed groundwater facilitated the mobilization of u from solid aquifer materials and dissolved u concentrations were observed to increase significantly in nearby supply wells similar instances of trace element mobilization due to human induced mixing of groundwaters were documented in 1 the floridan aquifer system near tampa florida as and u 2 paleozoic sedimentary aquifers in eastern wisconsin as 3 the basin fill aquifer underlying the california central valley near modesto u and 4 coastal plain aquifers of new jersey ra adverse water quality impacts attributed to human activities are commonly assumed to be related solely to the release of the various anthropogenic contaminants to the environment the results show that human activities including various land uses well drilling and pumping rates and volumes can adversely impact the quality of water in supply wells when associated with naturally occurring trace elements in aquifer materials this occurs by causing subtle but significant changes in geochemistry and associated trace element mobilization as well as enhancing advective transport processes published by elsevier ltd

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

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

determination of groundwater recharge regime and flowpath in the lower heihe river basin in an arid area of northwest china by using environmental tracers implications for vegetation degradation in the ejina oasis abstract environmental tracers cfcs stable isotopes 18o 2h and 3h and major ions were employed to study river infiltration and groundwater recharge in the aquifer system in the basin of the lower heihe river northwest china three groups of waters have been recognized 1 young groundwater connected to the river with large variation of cfc apparent ages ranging from 40 a and being depleted in 18o and 2h compared with the river water and 3 groundwater in gurinai a grassland located about 100 km from the river in which the predominant discharge is from the badain jaran desert with cfc apparent ages ranging from 25 to 50 a and being enriched in 18o and 2h compared to the river water the groundwater along the river contains cfcs and 3h down to depths of about 120 m and the shallow groundwater exhibits cfc apparent ages in a wide range which are not dependent on the well depth groundwaters along the river show a similar trend of enrichment in 18o and 2h as the river water whereas groundwaters in depression cones are depleted in heavier isotopes and have low cfc and 3h concentrations the cfc apparent age of the groundwater increases with increasing distance downstream indicating that the dominant part of the groundwater is from infiltration of river water in the upper reaches modifications of groundwater recharge are reflected in variations of stable isotope compositions as well as cfc and 3h concentrations in the groundwater that was recharged from the river over the last decades despite recharging from river water groundwater abstraction has induced a water balance deficit the riparian ecosystem in the ejina oasis is constrained by both decreased river flow and increased groundwater abstraction the vegetation degradation in the ejina oasis is controlled not only by natural aridification but also worsened by heavy groundwater abstraction and decreased river flow

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

soil altitudinal sequence on base poor parent material in a montane cloud forest in sierra juarez southern mexico the soils of montane cloud forests mcf are still insufficiently studied a number of researchers report podzols to be the main soil group for mcf ecosystems however a great deal of contradictory data exists we studied an altitudinal sequence of soils formed on ferrous chlorite shale under natural mcf vegetation in sierra juarez southern mexico from 1500 to 2500 m asl the soils of the upper part of the toposequence were folic stagnic podzols with inclusions of folic stagnosols in local depressions while the soils of the lower part of the toposequence were folic cambisols humic hyperdystric all the soils in the toposequence were extremely acid and had thick organic surface horizon mineral horizons of all soils were poor both in exchangeable and total reserves of bases the bases were concentrated mainly in organic topsoil with decreasing altitude both the thickness of albic horizons the depth of the maximum acid oxalate extractable fe and al concentrations and the difference in clay content between the eluvial and illuvial horizons decreased in the upper part of the toposequence the composition of soil clays was similar to that of parent material chlorite and mica with some mixed layered 2 1 minerals however gibbsite and kaolinite were also present in the soils of the other site within the same upper mcf belt the phenomenon was ascribed to parent material heterogenity in the medium and lower parts of the toposequence gibbsite and kaolinite were the dominant minerals we consider that the main pedogenic processes in the study area are raw humus accumulation weathering in situ podzolization and iron reduction due to water stagnation in mineral topsoil the intensity of weathering decreases while the extent of water stagnation increases with altitude to a great extent the genesis and altitudinal distribution of the soils in the mcf depends on parent material

uranium isotopes in the platte river drainage basin of the north american high plains region abstract the north and south platte rivers contribute sigficant concentrations of dissolved uranium to the platte river system from the weathering of uraniferous rocks at their headwaters in colorado and wyoming uranium isotopes measured in three groups of samples collected from the platte river and its major tributaries exhibted a wide range of concentrations 0 27 31 7 g l and activity ratios 1 03 1 72 reflecting variations in the contributions of different sources under differing flow conditions locally elevated uranium concentrations and higher activity ratios were associated with groundwater sources during low flow periods uranium concentrations in surface runoff were lower than in baseflow and correlated significantly with dissolved solids uranium activity ratios in runoff were closer to equilibrium values than those in baseflow suggesting that dissolved uranium in runoff is less affected by disequilibrium processes mixing calculations using uranium concentrations and activity ratios indicate considerable variations in longitudinal and transverse mixing of tributary water with plate river water and temporal variations of groundwater contributions baseflow and irrigation return flow in the plate river system

the kuh e surmeh mineralization a carbonate hosted zn pb deposit in the simply folded belt of the zagros mountains sw iran the kuh e surmeh carbonate hosted zinc lead deposit located within the simply folded belt of the zagros mountains in southwestern iran is an orogen related mississippi valley type deposit originally formed in the foreland thrust belt of the zagros mountains structural and textural observations indicate that ore deposition took place as open space fillings in brecciated carbonate rock and as internal sediments consisting of fine grained ore minerals interlayered with carbonates the preferred genetic model for the concentration of the ore metals is that of dewatering of the zard kuh basin due to regional tectonic compaction tectonism and expulsion of basin derived fluids into the highly porous and brecciated dolomitized rocks of the dalan formation the metals precipitated from dense basinal brine 15 wt equiv nacl at low temperatures less than 200 c typically within strata of a late paleozoic carbonate platform

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

a new tectonic scenario for the sanandaj sirjan zone iran abstract recent geochemical studies of volcanic rocks forming part of the ophiolites within the zagros and naien baft orogen indicate that most of them were developed as supra subduction ophiolites in intra oceanic island arc environments intra oceanic island arcs and ophiolites now forming the naien baft zone were emplaced southwestward onto the northeastern margin of the south sanandaj sirjan zone while those now in the high zagros were emplaced southwestward onto the northern margin of arabia thereafter subduction continued on opposite sides of the remnant oceans the floor of neo tethys ocean was subducted at a low angle beneath the entire sanandaj sirjan zone and the floor of the naien baft ocean was subducted beneath the central iranian micro continent the naien baft ocean extended into north west iran only temporarily this failed ocean arm between the urumieh dokhtar magmatic assemblage and the main zagros thrust was filled by thick upper triassic upper jurassic sediments the naien baft ocean finally closed in the paleocene and neo tethys closed in the early to middle eocene after arabia was sutured to iran the urumieh dokhtar magmatic assemblage recorded slab break off in the middle eocene

stable isotopic composition of precipitation in the semi arid north central portion of the us great plains abstract where data are available hydrologic studies may use stable oxygen and hydrogen isotopes to investigate groundwater surface water interaction groundwater recharge and advective diffusive transport to estimate groundwater ages or to unravel paleohydrology such studies require that the isotopic composition of precipitation be known as precipitation is a major input to groundwater and surface water systems oxygen 18 18 o and deuterium 2 h data for precipitation are lacking for the semi arid portion of the north central great plains of the us and thus there is need to establish additional meteoric water lines as isotope input functions across the region as well as to develop better understanding of the isotopic climate linkages that control oxygen and hydrogen isotope ratios in precipitation this study examines the 18 o and 2 h composition of precipitation for a representative site near north platte nebraska in the semi arid north central great plains during the years 1989 through 1994 oxygen 18 values range from 30 5 to 1 7 deuterium values range from 228 to 11 yearly arithmetic mean values for the north platte station are 9 8 and 71 respectively weighted yearly means for 18 o and 2 h over the 6 year period were 9 6 and 69 respectively north platte values show a strong isotopic enrichment between winter and summer precipitation and a strong 18 o t correlation r 2 0 845 for mean monthly values of 0 54 per degree celsius the local meteoric water line for the site is 2 h 7 66 18 o 4 96

pb isotopic compositions of some zn pb deposits and occurrences from urumieh dokhtar and sanandaj sirjan zones in iran abstract this study reports pb isotope ratios of galena pbs sampled from some zn pb deposits and occurrences n 18 within two major structural provinces of iran the sanandaj sirjan zone ssz and urumieh dokhtar zone udz regardless of the nature of the host rock and ore type the pb isotopic data plot in distinct isotopic fields according to their geographic situation which suggest that the structural terranes had an important control on the lead isotope compositions the zn pb deposits in the udz record distinctly higher 206pb 204pb and 208pb 204pb ratios compared to those within the ssz both zones however have radiogenic 207pb 204pb ratios 15 55 suggesting a dominant input of pb from crustal sources in thorogenic 208pb 204pb vs 206pb 204pb and uranogenic 207pb 204pb vs 206pb 204pb plots the pb isotope data define two linear arrays which may be attributed to mixing between mantle like end members and at least two distinct crustal sources characterized by high u pb and th u ratios in plumbotectonic discrimination diagrams the samples plot proximal to the orogenic curve which again supports interaction between crustal and mantle reservoirs however both neo tethys subduction and in particular mesozoic and tertiary orogenic activities seem to have played important roles in remobilizing pb and forming zn pb deposits in ssz and udz respectively the similarity of pb isotopic compositions between udz deposits and those for previously reported eocene volcanics demonstrates that long lived and widespread hydrothermal activity promoted remobilization of lead from the crust the latter occurred subsequent to neo tethys lithosphere subduction in the tertiary and continued subsequent the collision of the iranian and arabian plates in the miocene

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

the urumieh plutonic complex nw iran a record of the geodynamic evolution of the sanandaj sirjan zone during cretaceous times part i petrogenesis and k ar dating the urumieh plutonic complex is located in the northwestern part of the sanandaj sirjan zone iran the urumieh plutonic complex comprises three components i e a dioritic suite a granitic suite consisting of biotite bearing granites and younger stocks i e an alkaline suite alkali syenite and alkali granite and a muscovite bearing granite based on k ar chronology of separated minerals amphibole biotite muscovite and feldspar and field observations the urumieh complex was built during two distinct episodes the diorite and granite suites were emplaced between 100 and 92 ma whereas the younger suites were emplaced between 82 and 80 ma the dioritic suite has sio2 contents in between 56 59 wt and major and trace elements characteristic of mafic i type granitoids a ckn molar ratio 0 81 0 88 this suite is characterized by relatively high mg 49 low na2o content 3 5 wt and a relatively high abundance of lile incompatible elements their chondrite normalized ree patterns are relatively flat la yb n 7 in average and show small or no negative eu anomalies eu eu 0 9 in average some diorites show mingling and mixing textures that may support local crustal contamination of the dioritic melt geochemical features suggest that diorites formed in a subduction setting by partial melting of metasomatized mantle the coeval granites are peraluminous 1 04 molar a ckn 1 37 with sio2 contents between 66 69 wt their chondrite normalized ree patterns are slightly enriched in lree relative to hree la yb n 11 in average with negative eu anomalies eu eu 0 4 in average these granites have biotite as the main mafic mineral and locally contain restitic xenoliths they originated by partial melting of metasediments the younger alkaline syenite and granite are only slightly peraluminous molar a cnk 1 04 in average they show enrichment in hfse high contents of ree and relatively high feo mgo and ga al ratios typical of a type magmas the other younger granite pluton dourbeh granite has peculiar mineralogical and geochemical features none of these late syenite and granites were intruded by mafic dikes and they do not contain any comagmatic mafic enclaves they seem to have been derived only from crustal melting changing of magmatic sources during the 100 80 ma time interval is discussed with respect to the geodynamic context the first magmatic episode 100 92 ma is regarded as subduction related whereas the second one at ca 80 ma likely ocurred during the collision between the arabian margin and the sanandaj sirjan zone

cretaceous tertiary convergence and continental collision sanandaj sirjan zone western iran abstract the sanandaj sirjan zone contains the metamorphic core of the zagros continental collision zone in western iran the zone has been subdivided into the following from southwest to northeast an outer belt of imbricate thrust slices radiolarite bisotun ophiolite and marginal sub zones which consist of mesozoic deep marine sediments shallow marine carbonates oceanic crust and volcanic arc respectively and an inner complexly deformed sub zone late palaeozoic mesozoic passive margin succession rifting and sea floor spreading of tethys occurred in the permian to triassic but in the sanandaj sirjan zone extension related successions are mainly of late triassic age subduction of tethyan sea floor in the late jurassic to cretaceous produced deformation metamorphism and unconformities in the marginal and complexly deformed sub zones deformation climaxed in the late cretaceous when a major southwest vergent fold belt formed associated with greenschist facies metamorphism and post dated by abundant palaeogene granitic plutons in the southwest of the zone a late cretaceous island arc passive margin collision occurred with ophiolite emplacement onto the northern arabian margin similar to that in oman final closure of tethys was not completed until the miocene when central iran collided with the northeast arabian margin

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

effects of surface water irrigation on sources fluxes and residence times of water nitrate and uranium in an alluvial aquifer abstract effects of surface water irrigation on an alluvial aquifer were evaluated using chemical and isotopic data including 2 h 18 o 3 h 3 he ar ne n 2 15 n and 234 u 238 u activity ratios in a transect of nested wells in the north platte river valley in western nebraska usa the data were used to evaluate sources and fluxes of h 2 o no 3 and u all of which were strongly affected by irrigated agriculture combined results indicate that the alluvial aquifer was dominated by irrigation water that had distinctive chemical and isotopic features that were inherited from the north platte river or acquired from agricultural soils or recharge processes values of 2 h 18 o ar and ne indicate that most of the ground water in the alluvial aquifer was irrigation water that was derived from the north platte river and distributed during the growing season the irrigation water was identified by an evaporated isotopic signature that was acquired by the river in major upstream reservoirs in wyoming and by relatively warm gas equilibration temperatures related to warm season recharge apparent 3 h 3 he ages indicate that the ground water in the alluvium was stratified and mostly 3 0 m a age gradients and no 3 concentrations indicate that recharge occurred by a combination of focused leakage from irrigation canals rapid local recharge low no 3 and distributed infiltration beneath the irrigated agricultural fields lower recharge high no 3 large amounts of u with relatively low 234 u 238 u activity ratios were present in the alluvial aquifer as a result of irrigation with u bearing river water and minor amounts of u with higher 234 u 238 u activity ratios were added locally from basal and underlying volcanic rich sediments distributions of no 3 15 n no 3 dissolved gases and ground water ages indicate that no 3 concentrations increased and 15 n no 3 values decreased in distributed recharge in the last few decades possibly in relation to a documented increase in the agricultural use of artificial fertilizers canal leakage caused substantial dilution of no 3 within the alluvial aquifer whereas denitrification occurred mainly near the bottom of the alluvium the average residence time of the irrigation water within the aquifer was relatively short about 9 a and reactions such as respiration denitrification and u exchange in the saturated zone had relatively little effect on the overall composition of the alluvial ground water in comparison to what they might have had in the absence of irrigation recharge