rare earth element signatures of economic and sub economic porphyry copper systems in urumieh dokhtar magmatic arc udma iran abstract a wide variety of porphyry copper deposits have been reported along the cenozoic urumieh dokhtar magmatic arc in iran the formation of these deposits is attributed to closure of neo tethys and the subsequent collisional tectonic regime during the tertiary this study presents whole rock rare earth element ree data for the giant to small sarcheshmeh meiduk sungun darreh zerreshk dalli iju parkam and ali abad with sub economic daraloo and reagan porphyry copper systems the data indicate a temporal and geochemical evolution from sub economic porphyry systems to economic deposits all the economic and sub economic porphyry copper systems exhibit lree enrichment relative to hree whereas the economic deposits exhibit a relatively steep downward lree to hree profile reflecting higher lree abundance the eu anomalies vary from distinct negative in sub economic deposits eu eu 0 28 0 70 to either markedly less negative or positive anomalies eu eu 0 45 1 67 in economic deposit the economic porphyry deposits are characterized by relatively high la sm and sm yb values representing high crustal assimilation in a relatively thickened crust and provide insight into fractionation of hornblende with minor garnet in deep crustal parts mash zone compared with sub economic deposits the steep downward lree to mree and flatter to slightly upward mree to hree in economic deposits indicate hornblende involvement magma evolution toward more volatile content it seems that in an ongoing process of closure of neo tethys during compression and crustal shortening the early eocene oligocene sub economic intrusions are followed by adakite like hydrous miocene and younger economic cu bearing intrusions

diagenetic cycling of arsenic in amazon shelf sediments in order to help elucidate major natural controls on the diagenetic behavior of as vertical profiles of total dissolved and solid phase as were measured in amazon shelf deposits a deltaic region little influenced by human activity arsenic distributions are typically characterized by subsurface porewater maxima and surficial solid phase enrichment maximum porewater as concentrations 2 4 m are an order of magnitude greater than levels reported in most other coastal marine environments and elevated concentrations extend several meters below the sediment surface dissolved as varies inversely with easily leachable as 40 140 nmol g 1 in the solid phase and directly with increases in solid phase fe ii these patterns reflect a strong redox coupling with fe whereby oxidized as is associated with fe oxyhydroxides in surface sediments then subsequently reduced and released upon burial in the extensive suboxic zone upward diffusion and intense physical reworking of sediments presumably releases the dissolved arsenic fraction to the water column or allows for re adsorption in surface sediments arsenic porewater concentrations generally increase away from the river in some cases regular seasonal variations are evident apparently corresponding to nonsteady state ingrowth of diagenetic profiles following extensive sediment reworking during rising river flow the massive cycling of as in amazon shelf sediments is likely due to the combined effects of intense chemical weathering in regions of the drainage basin production of oxides and a turbulent physical regime present on the shelf both of which promote sedimentary cycling of fe and coupled elements during early diagenesis

seismotectonic and seismicity of makran a bimodal subduction zone se iran abstract the present study combined spatial distribution and mechanism of seismicity seismicity parameters geomorphology in satellite imagery and tectonic features in makran inland to show that the makran low angle thrust fault is divided into two separate segments depth dispersal of earthquakes especially relocated events shows that the sinking plate is steeper in the west than in the east of makran significant facts were identified from the variation of moho depth between west and east slip rates of the inland faults and crustal shortenings in the north of makran the sistan suture zone plays a significant role in dividing the overriding plate into a non deforming helmand block and a less deforming lut block these blocks have different resistances against the northward subduction large and great events such as the 1989 chabahar mw 5 5 and 1945 gwadur mw 8 1 occurred in the south of subduction fronts of the western and eastern makran respectively they occurred in shallow depth and were the pieces of evidence of weak and strong coupling between the oceanic and continental crusts on a low angle and a very low angle reverse faults respectively spectral analysis and depth determination of the instrumental and pre instrumental earthquakes respectively helped to separate some plate boundary and intraplate events this separation geometry and non characteristic behavior of the subduction zone revealed from spatial and temporal distribution of the earthquakes probably dedicate a mature aleutian type for the subduction zone in the east missing great m 6 1 earthquakes less slip rate of the continental faults and steeper dipping of the sinking plate in the west probably indicate a kurile type for the iranian part of subduction makran is a bimodal subduction because geomorphological and seismic pieces of evidence indicate a nnw surficial and right lateral fracture zone in the continental crust and a nw deep and left lateral fracture zone in the oceanic crust respectively the fractures and geometry of subductions showed that the eastern makran has seismotectonically a wider area for potential coupling of a larger earthquake than the western makran

dispersal and deposition of eolian and fluvial sediments off peru and northern chile relative abundances of quartz and feldspar in fine grained terrigenous sediments have been used to recognize specific continental sediment sources along northwestern south america and to trace the dispersal of specific grain size fractions from these sources to adjacent continental margin and deep sea sedimentary environments quartz feldspar ratios are low 0 6 for all fractions of sediments derived from southern peru and northern chile but such ratios increase systematically in central and northern peru as the importance of granitic and related intrusives increases relative to more basaltic extrusives and gabbroic equivalents limited published analyses of dusts collected offshore prospero and bonatti 1969 are also consistent with a latitudinally varying continental sediment source we find that clay

quantitative finite strain and kinematic flow analyses along the zagros transpression zone iran abstract the ghouri area in southwest iran exposes a cross section through the zagros orogenic belt the area provides an opportunity to investigate quantitative finite strain rs kinematic vorticity number wk proportions of pure shear and simple shear components sense of shear indicators steeply plunging lineations and other moderate to steeply plunging stretching lineations in a transpressional zone based on a classical strain analysis of deformed microfossils with oblate strain ellipsoid shape the zagros orogenic belt is classified as a pure shear dominated zone of transpression but asymmetry of shear sense indicators suggests that a significant component of simple shear was involved along the deformation zone boundaries the long axes of the microfossils and stretched pebbles of a deformed conglomerate were used to indicate the stretching direction in this zone the stretching lineations have a steep to moderate plunge but a constant strain magnitude characteristics of dextral inclined transpressional kinematics in the zagros continental collision zone were quantified and indicate an estimated k value

arsenic distribution in the environment the effects of scale abstract the distribution of as in a variety of sample materials was studied at different scales from continental to local combining published data sets with the aim of delineating the impact and relative importance of geogenic vs anthropogenic as sources geochemical mapping of as with a variety of sample materials demonstrates that variation is high at all scales local to continental from sample densities of 400 sites per km2 to 1 site per 5000 km2 different processes govern the as distribution at different scales a high sample density is needed to reliably detect mineralisation or contamination in soil samples in both cases the impact on the much larger geochemical background variation is limited to a local scale distribution patterns in geochemical maps on the sub continental to continental scale are dominated by natural variation given that the geochemical background is characterised by a high variation at all scales it appears impossible to establish a reliable single value for good soil quality or a natural background concentration for as for any sizeable area e g for europe for such a differentiation geochemical maps at a variety of scales are needed different sample materials can pick up dissimilar geochemical sources and processes even when collected from the same survey area weathering soil formation leads to an as increase in soils when compared to rocks soils and stream sediments return very comparable median as concentrations plants are usually well protected against as uptake there are however plant species that can accumulate unusually high as concentrations the marine environment is generally enriched in as several geochemical mapping projects deliver indications for crustal as degassing as an important process leading to as enrichment in the surface environment

sandy beaches contamination by arsenic a result of nearshore sediment diagenesis and transport brazilian coastline abstract we studied the distribution of as fe ca and al in beach sands and near shore surface sediments along the brazilian coast from the equatorial zone to rio de janeiro state high concentrations of as up to 120 mg kg 1 exceeding the environmentally acceptable thresholds were found in the beach sands and near shore surface sediment in several segments of the studied coast that increased from north to south the significant positive correlation r 2 0 58 between as and calcium carbonate in the beach sands corroborated the hypothesis that calcareous bioclasts participate in metalloid retention and its accumulation in beach sediments most likely enrichment of as occurs in the oxic horizon of sediments caused by the diagenetic redistribution of various elements enrichment of as in beach sands occurs in the coast of bahia and espirito santo states that is facilitated by clastic material of calcareous algae

impact of the lateral blast on the spatial pattern and grain size characteristics of the 18 may 1980 mount st helens fallout deposit the 18 may 1980 eruption of mount st helens started with a lateral blast that fed a pyroclastic surge which then uplifted to form a co blast plume thirty minutes later plinian activity started at the vent and fluctuated in intensity for 9 h the resulting fallout deposit documented to 600 km from vent presents some striking features 1 displacement of the overall deposit to the north of the vent 2 a secondary thickness and mass maximum at 300 km from vent 3 a total grain size distribution dominated by fine ash 62 wt of the deposit 63 m and 4 individual grain size distributions that vary dramatically in the crosswind direction from strongly bimodal in the south to skewed unimodal in the north results from a new deconvolution of the individual grain size distributions show that they are a combination of a coarse subpopulation that decreases in size with distance from vent and a constant fine subpopulation with a mean of 15 m relative proportions of each subpopulation vary asymmetrically in the crosswind directions with the fine subpopulation preponderant toward the north and the coarse one dominating the south of the deposit both reach their absolute maxima in mass on the deposit axis componentry analyses of selected samples show that blast derived material is greatly enriched toward the north of the deposit these results indicate that the co blast plume dispersed fine grained material over great distances and dominated the fine subpopulation comparison with reanalysis data of atmospheric wind fields and satellite images of the spreading ash cloud suggests contrasting ash transport and depositional processes for the early co blast plume and the later vent derived plinian plumes the co blast plume is displaced to the north it had a high overshoot height and eastward dispersion via strong winds low in the stratosphere 10 15 km the plinian plumes were lower and dispersed most of the material to the southeast as the direction of high velocity winds shifted just before the late climactic plinian eruptive phase fine ash fine subpopulation was deposited continuously throughout the deposit with an increase of sedimentation rate 300 km from the vent where there is a secondary maximum in the deposit mass and thickness fine ash probably settled by a combination of enhanced sedimentation mechanisms including not only aggregation but also gravitational convective instabilities of cloud base hydrometeor formation and destruction and entrainment of small particles by larger ones finally we show that half of the deposit by mass in the medial area was deposited by the co blast plume and that a significant proportion of the mount st helens fallout deposit is nonjuvenile which has implications for the magmatic budget of this eruption

geological setting and timing of the chah zard breccia hosted epithermal gold silver deposit in the tethyan belt of iran the breccia hosted epithermal gold silver deposit of chah zard is located within a high k calc alkaline andesitic to rhyolitic volcanic complex in the central part of the urumieh dokhtar magmatic arc udma west central iran the total measured resource for chah zard is 2 5 million tonnes of ore at 12 7 g t ag and 1 7 g t au 28 6 t ag 3 8 t au making it one of the largest epithermal gold deposits in iran magmatic and hydrothermal activity was associated with local extensional tectonics in a strike slip regime formed in transtensional structures of the dehshir baft strike slip fault system the host rocks of the volcanic complex consist of eocene sedimentary and volcanic rocks covered by miocene sedimentary rocks la icp ms u pb zircon geochronology yields a mean age of 6 2 0 2 ma for magmatic activity at chah zard this age represents the maximum age of mineralization and may indicate a previously unrecognized mineralization event in the udma breccias and veins formed during and after the waning stages of explosive brecciation events due to shallow emplacement of rhyolite porphyry detailed systematic mapping leads to the recognition of three distinct breccia bodies volcaniclastic breccia with a dominantly clastic matrix gray polymict breccia with a greater proportion of hydrothermal cement and mixed monomict to polymict breccia with clay matrix the polymictic breccias generated bulk mineable ore whereas the volcaniclastic breccia is relatively impermeable and largely barren precious metals occur with sulfide and sulfosalt minerals as disseminations as well as in the veins and breccia cements there is a progression from pyrite dominated stage 1 to pyrite base metal sulfide and sulfosalt dominated stages 2 and 3 to base metal sulfide dominated stage 4 breccias and veins hydrothermal alteration and deposition of gangue minerals progressed from illite quartz to quartz adularia carbonate and finally gypsum dominated assemblages free gold occurs in stages 2 and 4 principally intergrown with pyrite quartz chalcopyrite galena sphalerite and ag rich tennantite tetrahedrite and also as inclusions in pyrite high rb sr ratios in ore grade zones are closely related to sericite and adularia alteration positive correlations of au and ag with cu as pb zn sb and cd in epithermal veins and breccias suggest that all these elements are related to the same mineralization event

groundmass crystallization of mount st helens dacite 1980 1986 a tool for interpreting shallow magmatic processes the 1980 1986 eruption of mount st helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale groundmass plagioclase size measurements are coupled with measured changes in matrix glass plagioclase and fe ti oxide chemistry to document increasing groundmass crystallinity and thus to better constrain proposed physical models of the post may 18 1980 magmatic reservoir measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth approximately 10 9 cm s of groundmass plagioclase occurred immediately subsequent to may 18 relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10 11 cm s plagioclase growth rates then decreased to 1x10 11 cm s through 1986 changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst rim chemistry although the matrix glass composition appears to have remained approximately constant from 1981 1986 after a rapid compositional change from may 18 until the end of 1980 plagioclase microphenocrysts show increasingly more complex zoning patterns with time microphenocryst core compositions are commonly positively correlated with crystal size both of these observations indicate continuous groundmass plagioclase growth through 1986 magmatic temperatures estimated from fe ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930 c and at log fo2 of 10 8 by 1985 1986 oxide temperatures decreased to 870 c chemical and textural changes can be explained by 1 rapid degassing and crystallization in response to the intrusion of magma into a shallow 4 5 km reservoir toward the end of the may 18 1980 eruption 2 continued crystallization at a much reduced rate through 1986 due to slow cooling of the shallow magma reservoir growth rates and consequent chemical changes appear to decrease at the end of 1980 this is coincident with the change in eruption style from explosive eruptions sometimes followed by dome growth to solely extrusive dome building events and can be explained by the expected viscosity increase of both degassing and increasing crystallinity the model of twostage crystallization of magma in a shallow reservoir is consistent with conclusions from gas studies casadevall et al 1983 gerlach and casadevall 1986 a b patterns of crater deformation chadwkck et al 1988 and post 1980 seismicity endo et al 1990 although it does not explain the experimental data of hill and rutherford 1989 on the growth rate of amphibole reaction rims textural measurements on mount st helens dacite can also be used to evaluate crystallization kinetics in silicic magmas systems for which experimental data is almost non existent plagioclase growth rates are 5 10 times slower than estimated plagioclase growth rates in basaltic systems a result consistent with the higher viscosity of a more silicic melt furthermore patterns of textural change both average crystal size and number density are similar to those observed during the 1984 mauna loa eruption by lipman and banks 1987 suggesting that the only modification to the crystallization behavior of plagioclase required in extrapolation from basaltic systems is a moderate decrease in rates such that the rate of crystallization scales with the melt viscosity

magma ascent rates from amphibole breakdown an experimental study applied to the 1980 1986 mount st helens eruptions recent 1980 1986 mount st helens dacites contain the phenocryst assemblage plagioclase amphibole low ca pyroxene magnetite ilmenite and rare high ca pyroxene which indicates that they all originated from an 8 km deep reservoir at 900 20 c with xh2o 0 67 in fluid according to experimental data iron titanium oxide phenocryst compositions indicate that all post may 18 dacitic magmas erupted at 900 20 c except for the final lava extrusion in october 1986 the magma reservoir may have cooled to 866 c by october 1986 amphiboles in the post may 18 1980 magma contain one or more amphibole populations characterized by reaction rims of different thicknesses the development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir constant p and t and isothermal decompression experiments show that during a 900 c constant rate decompression from 8 km to the surface no reaction rim develops on amphibole in 4 days a 10 m rim develops in 10 days and a 35 m rim develops in 20 days these experimental data and histograms of rim widths in 1980 1986 mount st helens dacites show that post may 18 eruptions are composed in large part of magma represented by a population of thin rimmed amphiboles magma which ascended from the deep 8 km reservoir in 6 to 10 days the remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 m magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly millimeter scale into the erupting magma the mixing in a viscous slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population the experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post may 18 dacites of about 15 30 m h for magma represented by the thick rimmed amphiboles and from 35 to 50 m hr for magma represented by the thin rimmed crystals an ascent rate of 66 m h is indicated for the may 18 1980 eruption which contains amphiboles with no reaction rims the volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath mount st helens in 1981 1982 was equivalent to a cylinder 8 km long and 8 9 m in radius

adakite differentiation and emplacement in a subduction channel the late paleocene sabzevar magmatism ne iran this study describes the structural setting petrogenesis and geochronology of a suite of acidic magmatic rocks that are intruded in the metamorphic core of the tertiary ophiolitic suture zone of the sabzevar range ne central iran these intrusive bodies show tabular geometries with solid state fabrics documenting syntectonic emplacement during crustal shortening in the total alkalis silica tas diagram their compositions define a medium k calc alkaline suite spanning from basaltic andesite to the dacite and rhyolite fields they show characteristic low mgo 0 15 0 60 wt and ni 40 ar 39 ar white mica and amphibole geochronology constrains the sabzevar magmatism to the late paleocene at ca 58 ma genesis of the sabzevar magmatic suite is interpreted in terms of prograde wet amphibolite melting during oceanic subduction within a pressure temperature range between a plagioclase out and a hornblende out boundary magma differentiation and high pressure amphibole fractionation of pristine slab melts are proposed as the dominant factors that imparted the adakite signature in the sabzevar structural zone implications in terms of the regional tectonic scenario are discussed and framed within the advancing and retreating evolution of the neotethyan subduction during the mesozoic tertiary time span

correlation of lineaments and groundwater quality in dasht e arjan fars sw of iran the ne oriented dasht e arjan graben is located 65 km west of shiraz and has resulted from the active kare e bas fault segmentations this extensional graben bounded by two fault system east arjan and west arjan to the shahneshin and salamati anticline in these study using landsat 7 etm images with resolution 2 5 m and directional filtering in the four azimuths and semi automatic technique for linear structure in the study area using the obtained data from extracted lineaments the rose diagrams of the main strike lineaments are well confirm with field measurements of faults with n56 4 e direction the structural lineaments of the study area show that the dasht e arjan area is underlain by the limestone sandstone and marl landsat imagery of the area has been analyzed and interpreted in order to determine the lineament and groundwater quality across the area the fracture is structurally controlled and mostly influences both the groundwater and surface water pollution and flow directions in the dasht e arjan using visual interpretation determining the lineaments on the satellite image is very difficult and subjective and it requires an experienced interpreter in this study the lineament analysis is undertaken to examine the orientation of the lineament the relationship between lineaments and tectonic features and groundwater quality lineament density maps show that the lineament density is high around areas areas having high lineament density represent areas with relatively high groundwater pollution field observations agreed with the results from the analysis of the imagery

magnetostratigraphy of miocene pliocene zagros foreland deposits in the front of the push e kush arc lurestan province iran abstract the timing of the deformation in the zagros simply folded belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences the foreland basin infill at the front of the push e kush arc is composed of fine grained fluvial plain deposits agha jari fm and coarse conglomerates at the top of the section bakhtyari fm a magnetostratigraphic study was carried out in a composite section spanning about 2800 m in order to date growth strata and to constrain the timing of the deformation in the mountain front flexure mff magnetostratigraphic correlation of the base of the agha jari fm with chron c5a yields an age of 12 8 to 12 3 ma for this base the transition to the conglomerates of the bakhtyari fm correlates with the upper gauss chron c2an at approximately 3 ma the deposition age of the top of the preserved bakhtyari fm is extrapolated around the pliocene pleistocene boundary the base of the agha jari fm growth strata and thus the beginning of the deformation in the front of the push e kush arc is dated at 8 1 7 2 ma the topmost preserved bakhtyari is folded in the ne flank of the changuleh anticline and is unconformably overlying the sw flank of the anaran anticline this indicates that the tectonic deformation in the front of the push e kush arc was active at least during 5 my the mff is a relatively long lived structure active from 8 1 to 7 2 ma to about the pliocene pleistocene boundary partly synchronous with the changuleh anticline to the foreland after mff tectonic cessation only the changuleh anticline remained active

a magmatic geohygrometer application to mount st helens and other dacitic magmas compositions of andesitic to dacitic melts in equilibrium with plagioclase orthopyroxene and clinopyroxene have been experimentally calibrated as a geohygrometer application to melson s data on melt inclusions and matrix glasses from the 1980 1982 cycle of eruptions of mount st helens reveals systematic dewatering trends ca 4 1980 to 1 1982 h 20 in subliquidus intratelluric melt in pyroclastics and 2 3 1980 to 1 1982 in subliquidus melt in dome building dacites before each pyroclastic event intratelluric crystallization achieved melt h 20 contents of ca 6 at a depth of at least 8 km a necessary condition for crystallization of amphibole dewatering trends indicate that individual magma blobs or ribbons then ascended to successively higher levels over the 3 yr cycle from a minimum depth of 4 km in 1980 to 0 35 km in 1982 and pyroclastically erupted comparison of mount st helens compositions to worldwide andesites and dacites suggests that near liquidus arc magmas that crystallize plagioclase and pyroxenes contain l 2 h 2 0 on average whereas magmas in continental margins contain appreciably more h2o

a magnetotelluric survey of ophiolites in the neyriz area of southwestern iran a wide band magnetotelluric study of the ophiolitic zone of the zagros orogenic belt was conducted in the neyriz area of southwestern iran the purpose of the study was to image subsurface structures electrically and relocate the main zagros thrust fault in the region the thrust fault has a complex structure with obscure behavior and is believed to be located within a zone of ongoing continental plate convergence the fault zone with a nw se geological trend is parallel to the zagros orogenic belt and separates the neyriz ophiolite assemblage from the adjacent sanandaj sirjan metamorphic zone magnetotelluric data were collected along a sw ne profile across the geologic strike the study included 18 stations and modeling was performed using a 2 d inversion scheme analysis of both modes of magnetotelluric data te and tm clarifies the signatures of large resistivity variation in the study area due to the presence of a high contrast in resistivity between the ophiolites and neighboring rocks we are able to discern two sharp boundaries as faulting planes and borders of the ophiolite radiolarite zone in the north eastern and southwestern parts of the 2 d resistivity models respectively

geochemical fluid inclusion and o h s isotope studies of the milajerd au polymetallic prospect central iran implications for ore genesis abstract the milajerd pb zn au polymetallic prospect in naein qom magmatic zone is a favorable target for exploration geological and geochemical characteristics such as setting alteration assemblages fluid inclusion microthermometry and stable isotopes are consistent with the milajerd pb zn au polymetallic prospect being a typical low sulfidation ls epithermal deposits the au polymetallic mineralization occurs mainly as structurally controlled veins and brecciated dikes hosted by calc alkaline volcanic rocks mineralization at the milajerd prospect is controlled by an annular fault system the sulfide mineralogy of the deposit includes sphalerite galena pyrite arsenopyrite and marcasite the principal gangue minerals are quartz calcite sericite and adularia the alteration assemblages include quartz pyrite quartz sericite pyrite and chlorite calcite epidote fluid inclusions in quartz sulfide veins have homogenization temperatures th of 158 255 c and salinities of 4 7 7 7 wt nacl equiv whereas those in barren quartz carbonate veins yield th values of 135 176 c and salinities of 1 1 4 3 wt nacl equiv the h and o isotopic composition dwater 120 to 92 inferred 18owater 6 2 to 3 5 of fluid inclusions in quartz veins imply that cooling a mixed magmatic and meteoric waters was the main mechanisms of ore deposition at milajerd deposit the 34s values of ore sulfides are mostly close to zero avg 0 1 indicating a magmatic source of sulfur which could have emanated directly from magmatic activity or have been leached from the surrounding volcanic rocks

zircon u pb ages and emplacement history of the nodoushan plutonic complex in the central urumieh dokhtar magmatic belt central iran product of neotethyan subduction during the paleogene abstract the nodoushan plutonic complex is composed of a wide range of felsic and mafic rocks straddling several of the major orogenic zones in iran diorite porphyry diorite granodiorite and granite intrusives belong to the central part of the urumieh dokhtar magmatic belt which is part of the alpine himalayan orogenic belt monzogabbroic members of the complex are instead located within the bordering sanandaj sirjan magmatic metamorphic zone these plutons were emplaced into permian and lower cretaceous sedimentary units and eocene calc alkaline volcanic and subvolcanic rocks new u pb zircon ages reveal that the plutonic complex was assembled incrementally over ca 15 m y during three main episodes at 40 487 0 063 ma near the middle late eocene boundary at 30 52 0 11 ma and 30 06 0 10 ma in the early oligocene middle rupelian and at 24 994 0 037 and 24 13 0 19 ma in the late oligocene latest chattian the activity recorded in the nodoushan plutonic complex represents the final stages of subduction related magmatism prior to the eventual miocene collision between the arabian and eurasian blocks

crystalline rocks of the spinatizha area pakistan abstract during the cretaceous an andesitic arc developed across south asia facing the tethys ocean remnants of this arc are preserved in iran afghanistan and the chagai hills and kohistan pakistan west of the chaman fault near spinatizha pakistan 33 33 n 66 23 e a terrain of crystalline rocks is exposed that links the chagai hills portion of this arc with the kandahar portion of it in afghanistan four units are present 1 the spinatizha metamorphic complex includes orthogneiss greenschist amphibolite metavolcanics marble and foliated muscovite granite extreme variation in rock type and degree of metamorphism characterises the entire complex it is the oldest unit west of the chaman fault in pakistan 2 the bazai ghar volcanics consist of weakly deformed tuffs flow breccias and other coarse grained pyroclastics of andesitic arc type andesite flows and at least one silicic welded tuff are also present the bazai ghar volcanics are everywhere separated from the spinatizha metamorphic unit by granitic intrusions and a major fault 3 both the above units are intruded by a series of calc alkaline granitic plutons ranging from diorite to granite the silicic plutons generally intrude the more mafic ones the bazai ghar volcanics and related intrusions are probably equivalent to the cretaceous sinjrani volcanics and the cretaceous and younger intrusions of the chagai hills 4 along the fault zone between the volcanic and metamorphic rocks is a small area of previously unknown clastic sedimentary rocks conglomerates and slates the unit is of palaeogene age but cannot yet be correlated with known units the spinatizha crystalline terrain extends south along the chaman fault into afghanistan and is covered by the helmund desert to the west it is the eastern continuation of the calc alkaline arc terrain of the chagai hills dragged by oroclinal flexing into the chaman transform zone to the north it connects with the kandahar volcanic arc the metamorphic complex may represent the basement on which the arc terrain rests only exposed due to strong vertical uplift near the chaman fault

late cretaceous and early miocene andean type plutonic activity in northern makran and central iran two calc alkaline plutonic complexes bazman and natanz intruded through the south eastern active and south western ancient continental margins of central iran have been dated by the rb sr whole rock isochron method at 74 2 and 24 4 5 ma respectively detailed trace element studies together with low 87 sr 86 sr initial ratios 87 sr 86 sr ratios and the gabbros at least were intruded some 10 ma earlier

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

a combined magnetometry and gravity study across zagros orogeny in iran abstract in this work the structural geology and the tectonic conditions of the zagros orogeny along the route of qom to kermanshah cities were investigated using the combined geophysical methods of the airborne magnetometry and the ground based gravity data airborne magnetometry data of iran with a line space of survey 7 5 km were used to model the magnetic susceptibility property along the route at first the airborne magnetic data were stably 500 m downward continued to the ground surface in order to enhance minor changes of the earth s magnetic field over the studied region afterward 3d inverse modeling of the magnetic data was implemented to the downward continued data and subsequently the section of magnetic susceptibility variation along the desired route was extracted and imaged at depth the acquired model could appropriately predict the observed magnetic data showing low misfit values between the observation and the predicted data the analytic signal filter was applied to the reduced to pole rtp magnetic data leading to the determination of the active and probable hidden faults in the structural zones of the zagros such as sanandaj sirjan central domain cd and urumieh dokhtar based upon the generated peaks along the profile of analytic signal filter in addition the density variations of the subsurface geological layers were determined by 3d inverting of the ground based gravity data over the whole study area and extracting this property along the route the joint models of magnetic susceptibility and density variation could appropriately localize the traces of faults along with the geologically and tectonically structural boundaries in the region the locations of faults correspond well to the variation of geophysical parameters on the inverted sections probable direction slope and extension at depth of these faults were also determined on the sections indicating a high tectonized zone of the sanandaj sirjan zone ssz parallel to the zone of the urumieh dokhtar magmatic assemblage udma the udma zone increases the magnetic and the bouguer anomalies by intruding into the cd zone as well

the behaviour of arsenic in muddy sediments of the bay of biscay france abstract we have studied particulate and dissolved arsenic species in sediment and porewaters at sites in the bay of biscay france ranging in depths from 150 to 2 800 m at all stations major redox species oxygen nitrate ammonia total and reactive iron and manganese sulphate and sulphur reflect early diagenetic depth sequences of redox reactions comparable to other marine environments vertical distributions of dissolved and particulate as species and major redox species are related to changes in redox conditions and their major carrier phases such as fe and mn oxides arsenic diagenesis appears strongly dependent on fe cycling a subsurface maximum of dissolved as and surface enrichment of particulate as correspond to dissolution and precipitation of fe iii phases except for the shallowest and most bioturbated site flux calculations show three different vertical diffusive as fluxes two upwards and one downwards phase changes of recycled as result in local accumulations of reactive as at different redox fronts mass balance calculations indicate that the upward as flux toward the oxidized layer can explain the enrichment of hcl extractable particulate as in this layer a portion of the upward diffusing as can escape the sediment and may be fixed onto settling fe oxides by adsorption or co precipitation and contribute to reactive particulate as input i e as is recycled across the water sediment interface

adakite like signature of porphyry granitoid stocks in the meiduk and parkam porphyry copper deposits ne of shahr e babak kerman iran constrains on geochemistry abstract the middle miocene porphyry granitoid stocks of meiduk and parkam porphyry copper deposits are intruded in the north western part of the dehaj sarduiyeh volcano sedimentary belt in the south eastern extension of the urumieh dukhtar magmatic arc udma in iran the porphyritic to microgranular granitoids are mainly consist of quartz diorite granodiorite and diorite the whole rock geochemical analyses of these rocks reveals sub alkaline calc alkaline meta peraluminous and i type characteristics their geochemical characteristics such as al 2 o 3 content of 13 51 17 05 wt high sr concentration mostly 400 ppm low yb an average of 0 74 ppm and y an average of 9 02 ppm contents strongly differentiated ree patterns la yb 20 lack of eu anomaly eu eu 1 are indicative of adakitic signature their enrichment in low field strength elements lfse and conspicuous negative anomalies for nb ta and ti are typical of subduction related magmas detailed petrological studies and geochemical data indicated that meiduk and parkam porphyry granitoids were derived from amphibole fractionation of hydrous melts at a depth of 40 km in a post collisional tectonic setting

early diagenesis of arsenic in sediments of the kalix river estuary northern sweden solid phase as fe mn s and al and pore water total as fe mn and s have been determined for two cores from the kalix river estuary at the same station the depositional flux of arsenic was measured sediment traps fe iii oxides persist in the anoxic zone of the sediment and act as a carrier for arsenic down to depths of 10 15 cm the release of arsenic into the pore water is controlled by the reduction dissolution of these oxides as a result internal cycling of arsenic i e upward diffusion in pore water re adsorption onto fe iii oxides in the oxidized surface layer and reburial occurs in the uppermost 10 15 cm at the base of the arsenic cycling zone solid phase arsenic maxima 160 170 g g 1 of probable diagenetic origin occur the quantity of arsenic diffusing back towards the oxidized surface layer 2 2 g cm 2 yr 1 as is close to 75 of the quantity of arsenic being deposited due to sedimentation 2 9 g cm 2 yr 1 as however a mass balance for the surface layer indicates that re adsorption of arsenic onto fe iii oxides may effectively prevent diffusion of dissolved arsenic back into the overlying water column it is concluded that the interpretation of sedimentary arsenic profiles may be severely complicated due to post depositional migration of arsenic

spatial analysis of mount st helens tephra leachate compositions implications for future sampling strategies tephra particles in physically and chemically evolving volcanic plumes and clouds carry soluble sulphate and halide salts to the earth s surface ultimately depositing volcanogenic compounds into terrestrial or aquatic environments upon leaching of tephra in water these salts dissolve rapidly previous studies have investigated the spatial and temporal variability of tephra leachate compositions during an eruption in order to gain insight into the mechanisms of gas tephra interaction which emplace those salts however the leachate datasets analysed are typically small and may poorly represent the natural variability and complexity of tephra deposits here we have conducted a retrospective analysis of published leachate analyses from the 18 may 1980 eruption of mount st helens washington analysing the spatial structure of the concentrations and relative abundances of soluble ca cl na and s across the deposits we have identified two spatial features 1 concentrated tephra leachate compositions in blast deposits to the north of the volcano and 2 low s cl and na cl ratios around the washington idaho border by reference to the bulk chemistry and granulometry of the deposit and to current knowledge of gas tephra interactions we suggest that the proximal enrichments are the product of pre eruptive gas uptake during cryptodome emplacement we speculate that the low s cl and na cl ratios reflect a combination of compositional dependences on high temperature so2 uptake and preferential hcl uptake by hydrometeor tephra aggregates manifested in terrestrial deposits by tephra sedimentation and fallout patterns however despite our interrogation of the most exhaustive tephra leachate dataset available it has become clear in this effort that more detailed insights into gas tephra interaction mechanisms are prevented by the prevalent poor temporal and spatial representativeness of the collated data and the limited characterisation of the tephra deposits future leachate studies should aim to extensively sample across tephra deposit limits whilst simultaneously characterising deposit stratigraphy and tephra chemistry mineralogy and granulometry taking steps to ensure the quality and comparability of collected leachate datasets

island arc affinity of the central iranian volcanic belt abstract three types of tectonic settings are proposed for the central iranian volcanic belt civb namely rift continental margin and post collision settings however geochemical tectonic stratigraphic and metallogenic evidence favor an ensialic island arc setting the discrimination diagrams that have been used in this study are useful for making a distinction between ensialic island arcs and continental margin arcs from which the ensialic island arcs were derived

geomorphological analysis of the drainage system on the growing makran accretionary wedge abstract the morphology of six adjacent major catchments draining the onshore makran accretionary wedge in southeast iran and southwest pakistan was studied to examine how the channel pattern and the length profiles may reflect the recent and active growth of the wedge qualitative field surveys were combined with the quantitative analysis of channel steepness and concavity measured from digital elevation models these profiles were compared with modelled profiles using a stream power approach assuming homogeneously uplifting uniform rock substratum results show a distinct difference between the studied western and eastern catchments the three western rivers are in morphological equilibrium whereas the two eastern rivers exhibit profiles with prominent convexities and knickpoints thus notably diverging from equilibrium concave up shapes all the studied catchments share the same base level flow on similar lithologies and developed under uniform climate conditions therefore we interpret the morphometric differences in terms of differential rock uplift rate as a response to local tectonic activity this interpretation is consistent with both uplift rates of marine terraces along the coast of makran and the recorded seismicity the geomorphological analysis presented here extends coastal information to wide inland areas and documents longer term tectonic behaviour than the seismotectonic record hence the steeper surface slope and faster surface uplift rates recorded by the eastern catchments compared to equilibrium of the western catchments are regional long term signals relevant for a wide part of the makran accretionary wedge we attribute the regional geomorphic difference to quaternary variations in tectonic regimes that forced differential uplift rates of the wedge surface we hypothesize that the different tectonic regimes are related to different subduction rates

compositional heterogeneity of tephras from the 1980 eruptions of mount st helens samples collected at hourly intervals on may 18 19 1980 at three sites 200 km downwind from mount st helens have made possible a detailed reconstruction of the conditions that contribute to the compositional heterogeneity of mineral and glass components observed in distal tephra layers the air fall tephra deposited at the sites during the first 7 hours of the may 18 eruption is mostly coarse grained microlite rich nonjuvenile glass and feldspar grain size maxima in this initial tephra can be related to the cataclysmic blast at 0832 and a subsequent pulse of the eruption at 1200 juvenile microlite free glass increases in relative abundance at the sampling sites beginning at about 1900 such a change between nonjuvenile and juvenile tephra can be related to a 5 km increase in column height associated with the last major pulse of the eruption which occurred at 1700 at the volcano electron microprobe study of both microlite rich and microlite free pumice in the time series samples reveals significant compositional differences interstitial glass in nonjuvenile pumice deposited during the first few hours at the sampling sites is enriched in sio2 and k2o and depleted in tio2 feo and mgo relative to juvenile glass by comparison major element composition of the least evolved juvenile glass sampled during the last several hours of the eruption displays a slight trend toward less evolved composition least squares calculations suggest that the more evolved character of the nonjuvenile glass can be explained by greater fractional crystallization brought about by enhanced cooling in a cryptodome prior to eruption whereas the temporal changes observed in juvenile glass composition during the last several hours of the eruption suggest the presence of a small slightly zoned magma chamber at depth electron microprobe study of glass coated ilmenites magnetites and plagioclases provides the following estimates of the physical conditions in this reservoir 865 50 c ph2o 2 2 kbar and log o2 11 7 analyses of bulk pumice glass and selected mineral phases from may 25 june 12 july 22 and october 16 18 pumices erupted from mount st helens indicate that the bulk pumice magma compositions have become slightly more andesitic with time while mineral and co existing glass compositions have changed significantly in post may 18 eruptions with both being more highly evolved than those associated with the may 18 eruption an application of the magnetite ilmenite geothermometer to june 12 and july 22 samples indicates temperatures of 919 30 c and 930 50 c respectively least squares calculations suggest that such evolved post may 18 glass and mineral phases can be derived by fractional crystallization of a magma composition like bulk may 18 pumice into approximately 50 crystals and 50 residual liquid such partitioning between crystals and residual liquid appears to have occurred on the scale of centimeters and is interpreted as a consequence of accelerated crystallization under reduced water pressure

heavy mineral distribution as related to environmental conditions for modern beach sediments from the susanoglu atakent mersin turkey geochemical works were conducted on anthropogenically effective lithologic unit exposing along the susanoglu coast in mersin turkey for this purpose beach sand sediments from 33 stations were collected and heavy metal and oxide concentrations were analyzed to determine the source of heavy metals natural and anthropogenic simple and multivariate statistical analyses were applied according to factor analysis three factors were determined the first factor consists of sio2 al2o3 na2o k2o tio2 cr ni cu and mo and total variance is explained with 27 502 and expressed as natural process factor these elements cr ni cu mo are closely associated with geogenic materials and came from same sources of ultrabasic rocks ophiolite the second factor consists of cao mgo tio2 mno ni pb zn and w and total variance is explained with 21 505 and expressed as anthropogenic factor these elements pb zn cd v w are anthropogenic and are mainly due to the effluent or industrial input activities and came from different sources of pollution in the study area the third factor consists of pb cd and sb and total variance is explained with 9 748 and expressed as intermediate factor the factor analysis and the cluster analysis are in support of each other cr ni co cd hg and mo concentrations are greater than turkish acceptable values and they show toxic effect al cu pb cd and mo concentrations in beach sand deposits in the susanoglu coast are found as 1 44 1 26 1 21 1 02 and 1 04 mg kg and higher than those in kizkalesi beach sands however all other heavy metal contents are determined in low concentrations

plate tectonic evolution of the mediterranean middle east region abstract an interpretive model for the mesozoic cenozoic plate tectonic evolution of the mediterranean and adjacent areas is illustrated by a series of paleoposition maps at selected intervals between the late triassic and recent this interval witnessed an important period of tensional development during the triassic and jurassic that fragmented pangea after its late paleozoic consolidation a number of oceanic areas evolved through jurassic time all of which have since been consumed during the alpine orogeny during the cretaceous and tertiary sea floor spreading geometry in the north and south atlantic resulted in convergence between africa and eurasia that controlled the evolution of the mediterranean and adjacent middle east areas from the late mesozoic to recent the interpretation departs from several previous ones in the following respects 1 1 the eastern mediterranean and adjacent middle east area are interpreted to have developed as two seaways with an intervening continental sliver derived from africa that now comprises central turkey and west iran these seaways persisted from the late triassic to late cretaceous by which time they were largely consumed by northward subduction 2 2 spreading that produced the present eastern mediterranean sea developed during the late cretaceous driving the tripolitza eratosthenes iskenderun continental fragments northward from africa to collision with central turkey as the preceding southern arm of the mesozoic tethys sea floor was entirely consumed initial block faulting in this zone occurred during the jurassic and early cretaceous but without subsidence reaching clearly bathyal depths until the cenomanian turonian this differs from the timing of events in the ionian sequence of the pindic nappe of crete which shows a change from shallow carbonate shelf in the triassic to deep basin in the liassic to the north of equivalent platform facies of the tripolitza nappe 3 3 moesia and rhodope are concluded to have been a single plate until a rifting event that started during the late jurassic the balkan mountains are interpreted to represent an alpine inversion of this mesozoic rift system that extended west from the black sea basin 4 4 the eastern carpathian microcontinental sliver is concluded as continuing southward as the serbo macedonian massif that separates rhodope from the vardar zone rather than as rhodope itself 5 5 the scutari pec lineament is considered as representing a major discontinuity between the apulia pannonian plate and adjacent greece and turkey ophiolites to the northwest of this lineament originated in a single oceanic area the vardar zone ophiolites to the southeast of this lineament evolved from two oceanic areas those of interior greece and northern anatolia and the associated ankara melange relating to the vardar zone the former north arm of tethys and the pindos southern anatolia zagros oman ophiolites relating to a former south arm of mesozoic tethys 6 6 based on the history of development of various elements of the alpine system there is a strong suggestion that important dextral movement took place along a major strike slip fault system reaching from the middle east to the central alps between late cretaceous and middle eocene times

the discrimination of pyroclastic deposits on the basis of the mossbauer spectra of their magnetites a preliminary test abstract magnetite fe3o4 has the spinel structure which has two cation sites which also contain vacancies the spinel structure is also stable over large deviations from stoichiometry fe3o4 has a phase transition at 120 k and physical properties at room temperature can be very different from those at liquid nitrogen temperature it is magnetic at room temperature and is thus easily separated magnetically from any mineral of which it is a component for these reasons it seems an ideal substance for fingerprinting minerals by mossbauer spectroscopy since it is capable of exhibiting large variations in its physical properties the room temperature mossbauer spectra of seven samples of magnetite extracted from volcanic ash were found to be sufficiently different that different sources could be distinguished by visual inspection a least squares analysis showed that the spectra could be composed of 3 relaxing six line patterns the ratios of the intensities of these patterns and ratios of their relaxation times gave 5 parameters which appear to characterize the different sources of the tephra one of these parameters appears to be a function of the temperature of crystallization of the magnetite

monitoring the 1980 1982 eruptions of mount st helens compositions and abundances of glass the mount st helens eruptive sequence of 1980 through 1982 reflects the tapping of successively less water rich more highly crystallized and more viscous highly phyric dacitic magmas these changes reflect both syn and preeruption processes the decreasing water content points to a continued decline in the volume and intensity of explosive pyroclastic activity this decreasing water content appears to be composed of a long term trend established during a long period of repose about 130 years imposed on short term trends established during short periods about 7 to 100 days of repose between eruptions in the present eruptive cycle the last two eruptive cycles of this volcano the t a d 1800 and w cycles about a d 1500 exhibited similar trends these changes are inferred from a combination of petrographic bulk chemical and electron and ion microprobe analyses of matrix and melt inclusion glasses

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

chronology and pyroclastic stratigraphy of the may 18 1980 eruption of mount st helens washington many timed observations make it possible to subdivide the 9 hour plinian eruption of mount st helens on may 18 1980 into six phases defined by eruption style the phases are correlated with stratigraphic subunits of ashfall tephra and pyroclastic flow deposits the suite of pyroclastic deposits indicates that the eruption became more pumice rich and compositionally diverse with time perhaps owing to concurrent eruption of less evolved gas poor parts of the magma body with the more evolved gas rich parts the paroxysmal phase i 0832 0900 consisted of landslides lithic pyroclastic flows of a lateral blast and other explosions and a weak pre plinian column phase i pyroclastic deposits include lithic ash flow deposits intercalated with and overlying the voluminous debris avalanche deposit and basal pumice lapilli tephra that underlies a pisolitic ash layer the early plinian phase ii 0900 1215 consisted of vertical ejection of tephra with an early pulse of small pyroclastic flows on the upper flanks 1010 1035 a brief period of lithic ash ejection 1035 1100 and a pumice rich pulse that accompanied growth in height of the eruption column 1100 1215 deposits include minor pyroclastic flows on the crater rim and a reversely graded sequence of proximal tephra that include the lower pumice lapilli layer the lower lithic ash layer and the middle pumice lapilli layer all of which consist of evolved white dacitic pumice 63 64 sio2 during the early ash flow phase iii 1215 1500 the height of the eruption column decreased vertical ejection of tephra ceased and pyroclastic flows were fed from intermittent fountains phase iii deposits consist of a poorly exposed sequence 12 m of ash flow tuff that consist of many thin flow units 2 m each containing pumiceous white dacite 63 64 sio2 and denser gray silicic andesite 61 62 sio2 and fine grained ash cloud deposits interbedded with a nongraded middle pumice ash layer the climactic phase iv 1500 1715 developed in two stages fountain fed pyroclastic flows followed by a short pulse 1625 1715 of vigorous vertical ejection of tephra these stages were accompanied by the peak seismic energy release and peak eruption column height respectively climactic deposits consist of a thick 35 m sequence of thick lapilli rich ash flow sheets 4 12 m each with white and gray pumice and streaky scoria bands 60 sio2 in pumice breccia clasts and the reversely graded upper pumice lapilli layer that is interbedded with fine grained ash cloud deposits during the late ash flow phase v 1715 1815 eruption intensity waned but included a brief episode of small pyroclastic flows 1745 1815 phase v deposits consist of small distributary lobes of ash flow tuff containing white and gray pumice and minor fine ash deposits phase vi activity 1815 to may 19 1980 consisted of a low energy ash plume with transient increases in intensity while seismicity continued at depth sustained vertical discharge of phase ii prodeced evolved dacitewith high s cl ratios ash flow activity of phase iii is attributed to decreases in gas content indicated by reduced s cl ratios and increased clast density of the less evolved gray pumice climactic events are attributed to vent clearing and exhaustion of the evolved dacite

the magmatic record in the arghash region northeast iran and tectonic implications the area of arghash in northeast iran promi nent for its gold mineralization was newly mapped on a scale of 1 20 000 with particular attention to the occurring generations of igneous rocks in addition geochronological and geochemical investigations were carried out the oldest geological unit is a late precambrian hornblende bearing diorite pluton with low k composition and primi tive isotope signatures this diorite u pb zircon age 554 6 ma is most likely a remnant from a peri gondwana island arc or back arc basin about one third of the map area is interpreted as an upper cretaceous mag matic arc consisting of a volcanic and a plutonic part the plutonic part is represented by a suite of hornblende bearing medium k i type granitoids minor diorite mainly quartz monzodiorite and granodiorite dated at 92 8 1 3 ma u pb zircon age the volcanic part comprises medium k andesite dacite and tuffitic rocks and must be at least slightly older because it is locally affected by contact metamorphism through the hornblende grani toids the upper cretaceous arc magmatism in the arg hash massif is probably related to the northward subduction of the sabzevar oceanic basin which holds a back arc position behind the main neotethys subduction front small occurrences of pillow basalts and sediments sandstone conglomerate limestone tectonically interca lated in the older volcanic series may be relics of earlier cretaceous or even pre cretaceous rocks in the early cenozoic the cretaceous magmatic arc was intruded by bodies of felsic weakly peraluminous granite u pb zircon age 55 4 2 3 ma another strong pulse of magmatism followed slightly later in the eocene producing large masses of andesitic to dacitic volcanic rocks the geo chemistry of this prominent eocene volcanism is very distinct with a high k signature and trace element contents similar to shoshonitic series high p zr cr sr and ba high sr y ratios feature affinities to adakite magmas the eocene magmatism in the arghash massif is interpreted as related to thermal anomalies in crust and mantle that developed when the sabzevar subduction system collapsed the youngest magmatic activities in the arghash massif are lamprophyres and small intrusions of quartz monzo diorite porphyries which cut through all other rocks including an oligocene miocene conglomerate cover series

variations of stable oxygen and hydrogen isotope ratios in the cold and thermal springs of the bazman volcanic area in the southeast of iran the bazman volcanic area which comprises thermal and cold water springs with different natural characteristics was selected as the case study of this research the cold springs can be divided into western and eastern groups in total 16 water samples were collected from the thermal and cold water springs for hydrochemical and stable isotope analyses in the study area the groundwater temperature ranged from 28 1 c in the cold water to 43 9 c in the hot springs the electrical conductivity ec values of the groundwater samples were 1102 10 250 s cm the highest ec values belonged to the thermal springs known to have brackish water in this area the 18o and 2h values in the springs ranged from 5 06 to 0 04 and 24 1 to 8 6 respectively the relationship between 2h and 18o values and physicochemical characteristics was investigated in the west of the area the isotopic composition of the cold springs was close to that of the lmwl while the eastern cold springs had an isotopic composition highly enriched in 2h and 18o in contrast the isotopic composition of the thermal springs was almost on that of the gmwl and their deuterium isotope was more depleted than that of cold springs the difference between the isotopic composition of the thermal springs and the lwml can be the result of hot water rock interaction and underground evaporation however magma was not effective on this difference the results showed that the groundwater of the western cold springs moved with faster velocity through the long and deep macro pores and preferential flow channels in carbonate and igneous rocks while in the eastern springs groundwater originated from fine fractures with a low depth in shale and sandstone rocks

arsenic from gold mining in marine and stream sediments in baja california sur mexico the environmental impacts associated with arsenic as from historical mining areas may persist for many years we evaluated the influence of as in smelter and tailing wastes from a historic gold mine near san antonio in the south east of the baja california mexico on fluvial and marine sediments in the san juan de los planes basin and la ventana bay respectively arsenic levels in the smelter and in the surrounding tailing wastes ranged from 82 000 to 208 000 mg kg 1 and from 4220 to 92 000 mg kg 1 respectively the as concentrations in fluvial sediments were much lower as these derived from wastes that had been scattered and had been subject to weathering for some time as concentrations in surface sediments in the san antonio stream close to the smelter and further downstream ranged from 477 to 1100 mg kg 1 and from 64 to 613 mg kg 1 respectively as concentrations were between 0 05 and 9 mg kg 1 in surface shelf sediments from the coast adjacent to la ventana bay the concentration was highest in sediment collected close to the outlet of the main stream la bocana of the los planes basin the as concentrations in all the solid waste samples from near san antonio exceeded the effect range medium erm of the sediment quality guidelines 70 mg kg 1 overall 71 and 43 of the stream samples exceeded the effect range low erl 8 2 mg kg 1 and the erm respectively indicating potential risks for biota and humans

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

geochemical characteristics of igneous host rocks of lubin zardeh au cu deposit nw iran abstract the lubin zardeh au cu pb zn deposit is located in the azerbaijan western alborz zone 45 km ne of zanjan iran it is situated within the eocene oligocene volcanic plutonic belt of the tarom subzone of the alborz mountains range quartz monzonite and tuffs are the main host rock of the lubin zardeh au cu pb zn deposit granitoid rocks are predominantly high k calc alkaline with shoshonitic affinities they are i type metaluminous magnesian and are characterized by lile lree and th enrichment relative to hfse depletion in nb ta ti and weak depletion in hree and y these granitoids show some affinities with adakites e g high sr y and la yb ratios coupled with low yb and y and enrichment in lree and lile with weak eu anomalies their relatively low to moderate initial 87sr 86sr values 0 7047 0 7051 positive nd t 36 ma values 0 39 2 1 and tdm ages of 0 69 to 1 06 ga with pb isotopic ratios of initial 206pb 204pb 18 49 18 68 initial 207pb 204pb 15 58 15 61 and initial 208pb 204pb 38 33 38 77 are consistent with a phlogopite bearing amphibole rich and enriched lithospheric mantle source metasomatized by earlier subducted sediments the geochemical and isotopic compositions of the granitoids are similar to the host rocks of porphyry and epithermal deposits in the urumieh dokhtar zone

an improved quantitative measure of the tendency for volcanic ash plumes to form in water implications for the deposition of marine ash beds laboratory experiments and numerical simulations have shown that volcanic ash particles immersed in water can either settle slowly and individually or rapidly and collectively as particle laden plumes the ratio of timescales for individual and collective settling in the form of analytical expressions provides a dimensionless quantitative measure of the tendency for such plumes to grow and persist which has important implications for determining particle residence times and deposition rates however existing measures in the literature assume that collective settling obeys stokes law and is therefore controlled by the balance between gravitational forces and viscous drag despite plume development actually being controlled by the balance between gravitational forces and inertial drag even in the absence of turbulence during early times this paper presents a new measure for plume onset which takes into account the inertial drag controlled rather than viscous drag controlled nature of plume growth and descent a parameter study comprising a set of numerical simulations of small scale volcanic ash particle settling experiments highlights the effectiveness of the new measure and by comparison with an existing measure in the literature also demonstrates that the timescale of collective settling is grossly under estimated when assuming that plume development is slowed by viscous drag furthermore the formulation of the new measure means that the tendency for plumes to form can be estimated from the thickness and concentration of the final deposit the magnitude and duration of particle flux across the water s surface do not need to be known the measure therefore permits the residence times of particles in a large body of water to be more accurately and practically determined and allows the improved interpretation of layers of volcaniclastic material deposited at the seabed

recycling of orogenic arc crust triggers porphyry cu mineralization in kerman cenozoic arc rocks southeastern iran pre collisional eocene oligocene arc diorites quartzdiorites granodiorites and volcanic equivalents in the kerman arc segment in central iran lack porphyry cu mineralization and ore deposits whereas collisional middle late miocene adakite like porphyritic granodiorites without volcanic equivalents host some of the world s largest cu ore deposits petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment ore hosting kuh panj porphyry intrusions exhibit high sr 400 ppm low y 20 no negative eu anomalies eu eu 1 and relatively non radiogenic sr isotope signatures 87sr 86sr 0 7042 0 7047 relative to eocene oligocene granitoids mainly sr 12 la yb 15 eu eu 1 87sr 86sr 0 7053 0 7068 trace element modeling indicates peridotite melting for the barren eocene oligocene intrusions and a hydrous garnet bearing amphibolite source for middle late miocene ore hosting intrusions the presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30 35 to 40 45 km or 12 kbar the changes in residual mineralogy in the source of eocene to miocene rocks in the kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel underplating of cu and sulfur rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust mantle boundary and dehydration melting under oxidizing conditions produced syn and post collisional ore hosting intrusions while the lack of post collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur rich and oxidized adakitic magmas

geology of the onshore makran accretionary wedge synthesis and tectonic interpretation abstract this contribution is a synthesis of studies carried out since 2004 in the makran accretionary wedge exposed in se iran these studies were intended to improve our understanding of the behaviour of accretionary wedges and of the significance of the makran wedge in the frame of tethys tectonics reassessing the stratigraphy and structure of the iranian makran has allowed distinguishing four main litho tectonic units the lithological content of these four units is briefly described to discuss the sedimentary environments which record the general filling of an oceanic basin with clastic sediments derived from the north the petrology of ophiolites exposed in the backstop region to the north of the accretionary wedge itself demonstrates the existence of an oceanic basin formed in the jurassic late cretaceous to the north of continental slivers which had separated from central iran there is petrological evidence for a subduction related magmatic arc during the late cretaceous which sourced much of the clastic material in the cretaceous lower miocene turbidites present throughout the wedge the literature survey shows that the late cretaceous to present evolution of the pakistan part of the makran fold and trust belt is in its major attributes similar to that of the iranian makran these observations and results are discussed in a tectonic model that integrates knowledge on the oman mountains on the other side of the current oman subduction

the eastern iranian orocline abstract the eastern iranian range is seen as a large scale india eurasia collisional event and the subsequent amalgamation of the afghan and lut micro continents including the neo tethyan accretionary complexes and associated island arcs revised examination of the nature of tectono stratigraphic units distributed in both sides of the n s elongated eastern iranian orogen reveals two remarkable facts first from a general perspective it is structurally a giant parallel antiform in profile view second lithologically the most time equivalent comparable tectonic units from both northern and southern domains comprising the eastern iranian orogen are connectable follow the strike of hinge and limbs zones of the antiform and a m shaped disharmonic pattern in its core these characters are thought to be formed in response to two principal deformational phases resulting from two perpendicular stress directions the first was n s associated with the north dipping subduction of the tethyan oceanic lithosphere beneath the roughly ribbon shaped cimmerian supercontinent including the afghan and lut blocks before late eocene afterward the second was e w shortening originated by the westward escape of the afghan block as a consequence of the indian plate indentation into eurasia this orogen parallel stress was correspondingly accommodated by tens of degrees counter clockwise rotation of the lut block around a vertical axis the result of such shortening was oroclinal buckling and concomitant retreating of the subduction zone and closure of the sistan ocean a remaining wedge shaped part of the neotethys ocean formed by the ribbon curvature the development of the eastern iranian orogen already included the sistan suture zone an enormous mass of folded eocene flysch deposits with a general n s axial surface and some cretaceous ophiolitic remnants the plate scale buckling which was formed by this late stage orogenic event is hereby considered as an orocline call eastern iranian orocline lithosphere buckling around a vertical axis caused a large scale crustal folding coeval with the bending of its mantle part increasing the lithospheric thickness of the orocline compared to adjacent regions the syn orocline deformation associated delamination and resulting magmatic events took place in eastern iran during a short period of about 10 to 20 ma in the late paleogene the orocline hinge zone is occupied by the khorasan outer arc and the birjand core while its limbs are composed of the baluch inner arc and the southwestern and southeastern terminations of the lut and afghan blocks the eastern iranian orocline seems to be the middle segment of a triple bending belt with n s two opposite facing bend including afghan lut and sanandaj sirjan blocks this large curvature is possibly an example of secondary oroclines which was formed by collision related escape tectonics although the limited available kinematic data show a kind of progressive orocline

the late jurassic panjeh submarine volcano in the northern sanandaj sirjan zone northwest iran mantle plume or active margin abstract the tectonic setting in which jurassic igneous rocks of the sanandaj sirjan zone sasz of iran formed is controversial sasz igneous rocks are mainly intrusive granodiorite to gabbroic bodies which intrude early to middle jurassic metamorphic basement jurassic volcanic rocks are rare here we report the age and petrology of volcanic rocks from the panjeh basaltic andesitic rocks complex in the northern sasz southwest of ghorveh city the panjeh magmatic complex consists of pillowed and massive basalts andesites and microdioritic dykes and is associated with intrusive gabbros the overall sequence and relations with surrounding sediments indicate that this is an unusually well preserved submarine volcanic complex igneous rocks belong to a metaluminous sub alkaline medium k to high k calc alkaline mafic suite characterized by moderate al2o3 13 7 17 6 wt and variable fe2o3 6 0 12 6 wt and mgo 0 9 11 1 wt contents zircon u pb ages 145 149 ma define a late jurassic tithonian age for magma crystallization and emplacement whole rock compositions are enriched in th u and light rare earth elements lrees and are slightly depleted in nb ta and ti the initial ratios of 87sr 86sr 0 7039 0 7076 and end t values 1 8 to 4 3 lie along the mantle array in the field of ocean island basalts and subcontinental metasomatized mantle immobile trace element ti v zr y nb yb th and co behavior suggests that the mantle source was enriched by fluids released from a subducting slab i e deep crustal recycling with some contribution from continental crust for andesitic rocks based the chemical composition of panjeh mafic and intermediate rocks in combination with data for other gabbroic to dioritic bodies in the ghorveh area we offer two interpretations for these and other jurassic igneous rocks of the sasz as reflecting melts from a subduction modified oib type source above a neo tethys subduction zone or b plume or rift tectonics involving upwelling metasomatized mantle mostly reflecting the 550 ma cadomian crust forming event

textures water content and degassing of silicic andesites from recent plinian and dome forming eruptions at mount pelee volcano martinique lesser antilles arc previous petrological and phase equilibrium experimental studies on recent silicic andesites from mount pelee volcano have evidenced comparable pre eruptive conditions for plinian and dome forming pelean herein eruptions implying that differences in eruptive style must be primarily controlled by differences in degassing behaviour of the mount pelee magmas during eruption to further investigate the degassing conditions of plinian and pelean magmas of mount pelee we study here the most recent mount pelee s products p1 at 650 years b p 1902 and 1929 eruptions which cover a range of plinian and pelean lithologies for bulk rock vesicularities glass water contents glass inclusions in phenocrysts and matrix glasses and microtextures water contents of glass inclusions are scattered in the plinian pumices but on average compare with the experimentally deduced pre eruptive melt water content i e 5 3 6 3 wt whereas they are much lower in the dominant pelean lithologies crystalline poorly vesicular lithics and dome samples this indicates that the glass inclusions of the pelean products have undergone strong leakage and do not represent pre eruptive water contents the water content of the pyroclast matrix glasses are thought to closely represent the residual water content in the melt at the time of fragmentation determination of the water contents of both the pre eruptive melt and matrix glasses allows the estimation of the amount of water exsolved upon syn eruptive degassing we find the amount of water exsolved during the eruptive process to be higher in the pelean products than in the plinian ones typically 90 100 and 65 70 of the initial water content respectively the vesicularities calculated from the amount of exsolved water compare with the measured vesicularities for the plinian pumices consistent with a closed system near equilibrium degassing up to fragmentation by contrast the low residual water contents low groundmass vesicularities and extensive groundmass crystallization of the pelean products are direct evidence of open system degassing microtextural features including silica bearing and silica free voids in the pelean lithologies may represent a two stage vesiculation