an energy dispersive miniprobe multielement analyzer emma for direct analysis of trace elements and chemical age dating of single mineral grains abstract an energy dispersive miniprobe multielement analyzer emma was designed and constructed for the analysis of trace elements as cr cu fe ga ge hf mn ni pb rb se sr th y u zn in small individual mineral grains such as apatite garnet monazite sphene zircon and other accessory minerals the instrument is sensitive ppm for most elements rapid 3 6 min per analysis non destructive and essentially no sample preparation is required with respect to single zircon grains as small as 50 m with mass as low as a few g for example the detection limits for u th and pb are on the order of 10 ppm 5 10 times better than the electron microprobe here the emma is used to illustrate the variation in hf and y concentrations in single zircon grains from pegmatites granites basalts carbonatites and kimberlites also the instrument is used for chemical age dating u th total pb of 1 single zircon grains from the berdyshevsky intrusive complex ukraine and 2 single monazite grains from a small placer deposit within the transition zone between the saxothuringikum and moldanubikum bavaria germany the average age of the single zircon grains from berdyshevsky granite determined using emma 2 19 0 17 ga 1 is consistent with the u pb zircon intrusion age of this complex 2 14 0 07 ga and monazite data ranging from 1 95 to 2 48 ga with respect to the pegmatite from this complex the average age of 1 93 0 09 ga found with emma is geologically consistent with zircon and monazite ages ranging from 1 90 to 2 29 ga regarding the monazite grains from the placer the age dates obtained using emma 328 28 ma are comparable to the isotopic ages conventional u pb and pb pb step leaching which yielded ages of 312 3 and 324 12 ma respectively

3 d lithospheric structure and regional residual bouguer anomalies in the arabia eurasia collision iran this research has been partly funded by projectsatiza cgl2009 09662 bte and tecla cgl2011 26670 and consolider ingenio 2010 topo iberia csd2006 00041

lithospheric structure beneath the zagros collision zone resolved by non linear teleseismic tomography the upper mantle structure across the zagros collision zone in southwest iran is investigated using a non linear weighted damped least squares teleseismic tomography approach the resolution of the structures transitions in the upper mantle is enhanced significantly by correcting the teleseismic relative arrival time residuals for an a priori crustal velocity model and then performing the inversion with fixed crustal blocks to investigate whether or not the lithospheric blocks and major transitions in the resulting model are required by the data or are artefacts of the inversion the data were inverted using two different inverse methods singular value decomposition and a quadratic programming method new high quality seismic velocity models show apparent correlation between surface geological features and seismic velocity structures at lithospheric depth across the zagros collision zone the image shows a sharp lithospheric boundary at the main zagros thrust between 100 km and 250 km depth with p wave velocity about 3 per cent faster within the arabian shield to the south a step like increase in lithospheric thickness across the zagros collision zone is assumed to separate two different mantle structures namely the arabian to the south and the eurasian to the north domains the most striking feature resolved is a north dipping slab like positive velocity anomaly

upper mantle s velocity structure and moho depth variations across zagros belt arabian eurasian plate boundary the collision of the arabian and eurasian plates in the early miocene after the subduction of neo tethys ocean beneath eurasia formed the zagros belt a seismically active continental continental plate boundary in southwest iran the zagros suture zone is an important seismotectonic boundary indicating an abrupt cutoff between the intense seismicity of the zagros and the almost aseismic central iran plateau compared with other more evolved plate boundaries little is known about the deep lithospheric structure of the zagros belt such as the fate of subducted neo tethys plate and ambiguity in the presence of intermediate and deep earthquakes under the zagros suture zone in this study we use the partitioned waveform inversion pwi method to image the upper mantle s velocity structure and moho depth variations across zagros collisional zone the resulting moho depth along the profile shows the average moho depth value of order of 40 45 km for most parts of the profile with abrupt crustal thickening in the middle of the profile up to about 65 km as expected the derived models show that the relatively old and cold arabian plate has higher velocity at depth than the younger lithosphere farther north in central iran a sharp and steep subcrustal boundary is found roughly coincident with the surficial expression of the main zagros thrust mzt separating two different mantle domains a high velocity anomaly possibly representing a fragment of subducted lithosphere has been imaged beneath central iran at a depth between 350 and 600 km which is quite similar to the case of indo asian collision in qinghai tibetan plateau these observations as well as the sudden changes of shallow velocities along the cross section with a sharp boundary under the zagros suture zone support the idea that subducted oceanic lithosphere has broken off under the region of maximum moho depth a relatively low velocity region beneath the arabian plate is also imaged in our high resolution tomography model which is interpreted as an indication of lithospheric delamination within the arabian lithosphere

tectonics of the central zagros iran deduced from microearthquake seismicity summary microearthquakes in central zagros recorded for 7 weeks in 1997 lie in a 6 8 km zone that is likely located beneath 11 km of sediments they are not located on an active decollement between the sediments and the crystalline crust but rather define a pattern of nnw sse trending lineaments parallel to the fold axes observed at the surface the spacing between the seismic lineaments is 15 20 km and therefore different from that between the folds 10 15 km which suggests that there is not a simple relationship between the two focal mechanisms and precise relative locations are consistent with nw se striking reverse faulting connected by nnw sse striking right lateral strike slip faults the dip of the reverse faults is not certain but is likely ne for the northernmost faults the strain pattern deduced from the p axes is remarkably similar to the shortening deduced from gps based geodesy suggesting that microearthquakes are the response of the prefractured brittle crust to strain rather than localized on single active faults

upper cretaceous exhumation of the western rhodope metamorphic province chalkidiki peninsula northern greece the vertiskos unit of northern greece is an elongated basement belt with a complex poly metamorphic history it extends from greece chalkidiki peninsula to the south up to serbia in the north and arguably represents the westernmost part of the rhodope metamorphic province northern greece to southern bulgaria the vertiskos unit experienced a medium pressure lower amphibolite facies metamorphic overprint during the alpine orogeny the available medium temperature geochronology implies that it remained at temperature of approximately 300 c or slightly higher during lower cretaceous in order to constrain its post lower cretaceous thermal history until near surface exposure we applied apatite fission track analysis the central ages obtained range from 68 5 3 8 to 46 6 3 6 ma uppermost cretaceous to middle eocene and mean track lengths between 13 and 13 5 m we applied two inverse thermal modeling approaches using either each sample independently high degree of freedomin the thermal history better data fit or all samples together interpreting them as a vertical profile simpler thermal history worse data fit irrespective of the modeling approach we conclude that the bulk thermal history of the vertiskos unit crosses the high temperature limit of the apatite partial annealing zone by the uppermost cretaceous and reaches near surface conditions as early as lower middle eocene these results contrast with the thermal history of the other domains of the rhodope metamorphic province further east namely the southern rhodope core complex and the northern rhodope complex and establish the vertiskos basement complex as the oldest exhumed coherent basement fragment of the rhodope metamorphic province and greece

geology of the sari gunay epithermal gold deposit northwest iran the sari gunay epithermal gold deposit is located within a mildly alkaline latitic to trachytic volcanic complex in central northwest iran intrusive and volcanic rocks that host the deposit have been dated at between 11 7 and 11 0 ma with one younger sample at 8 0 ma 40ar 39ar dating of igneous biotite and hornblende whereas sericitic alteration associated with an early stage of hydrothermal activity occurred between 10 8 and 10 3 ma the best age estimate is 10 7 ma obtained by 40ar 39ar dating of sericite the main hydrothermal system was structurally localized by a diatreme breccia complex centered on the sari gunay hill earliest hydrothermal activity only encountered at depth 300 m below surface produced weak potassic alteration and quartz sulfide magnetite veining with low grades of cu and au mineralization reminiscent of shallow level 1 5 km depth porphyry gold systems paragenetically later quartz tourmaline breccias and veins followed the south southwest north northeast trend of the diatreme breccias and produced strong sericitic alteration and silicification in igneous clasts and wall rocks fluid inclusions indicate temperatures of 246 to 360 c and salinities of 34 4 to 46 1 wt percent nacl equiv in hypersaline inclusions coexisting with low density co2 bearing vapor phase inclusions these fluids do not appear to have deposited gold but the breccias provided further structural permeability for flow of later mineralizing epithermal fluids invisible gold occurs in solid solution in fine grained arsenical pyrite and minor arsenopyrite deposited in the early stages of quartz adularia pyrite stibnite veins late stage minerals in these veins include realgar orpiment cinnabar and extremely rare wire gold liquid rich fluid inclusions in these veins have an average homogenization temperature trapping temperature of 199 24 c salinities of 3 6 1 1 wt percent nacl equiv and coexist with low density co2 bearing vapor phase inclusions suggesting low pressure conditions phase separation may have been a contributory cause of gold deposition but precipitation of sulfides in response to rapid cooling of the system may have been the main control on deposition of pyrite hosted gold the sari gunay gold deposit and its host volcanic system form part of the takab belt of structurally controlled middle miocene mildly alkaline volcano plutonic complexes the sediment hosted zarshuran gold deposit located 190 km to the north northwest along the belt is also related to middle miocene magmatism the takab belt is marginally younger than and displaced to the southwest of the extensive eocene miocene urumieh dokhtar calk alkaline volcanic arc which hosts several large porphyry cu deposits e g sar cheshmeh meiduk rocks of the takab belt are also distinctly more alkaline than the urumieh dokhtar rocks viewed in the context of plate tectonic models for neogene closure of a neo tethys ocean between the afro arabian and eurasian plates these differences may reflect a normal subduction zone origin for the urumieh dokhtar arc and contained porphyry cu deposits but a collisional origin for the slightly younger takab belt volcanic rocks and epithermal gold deposits the sari gunay deposit may thus be classified as a collision related alkalic type epithermal system although it is less alkaline than classic deposits of this group such as porgera emperor or cripple creek the latter apparently being related to postcollisional or back arc extensional rather than syncollisional processes

cenozoic metallogeny of greece and potential for precious critical and rare metals exploration abstract the cenozoic metallogeny in greece includes numerous major and minor hydrothermal mineral deposits associated with the closure of the western tethyan ocean and the collision with the eurasian continental plate in the aegean sea which started in the cretaceous and is still ongoing mineral deposits formed in four main periods oligocene 33 25 ma early miocene 22 19 ma middle to late miocene 14 7 ma and pliocene pleistocene 3 1 5 ma these metallogenic periods occurred in response to slab rollback and migration of post collisional calc alkaline to shoshonitic magmatism in a back arc extensional regime from the rhodopes through the cyclades and to arc related magmatism along the active south aegean volcanic arc invasion of asthenospheric melts into the lower crust occurred due to slab retreat and were responsible for partial melting of metasomatized lithosphere and lower crustal cumulates these geodynamic events took place during the collapse of the hellenic orogen along large detachment faults which exhumed extensive metamorphic core complexes in mainly two regions the rhodopes and the cyclades the detachment faults and supra detachment basins controlled magma emplacement fluid circulation and mineralization the most significant mineralization styles comprise porphyry epithermal carbonate replacement reduced intrusion related gold intrusion related mo w and polymetallic veins porphyry and epithermal deposits are commonly associated with extensive hydrothermal alteration halos whereas in other cases alteration is of restricted development and mainly structurally controlled porphyry deposits include cu au cu mo au re mo re and mo w variants epithermal deposits include mostly high and intermediate sulfidation hs and is types hosted in volcanic rocks although sedimentary and metamorphic rock hosted mineralized veins breccias and disseminations are also present the main metal associations are cu au ag te and pb zn au ag te in hs and is epithermal deposits respectively major carbonate replacement deposits in the kassandra and lavrion mining districts are rich in au and ag and together with reduced intrusion related gold systems played a critical role in ancient economies finally hundreds of polymetallic veins hosted by metamorphic rocks in the rhodopes and cyclades significantly add to the metal endowment of greece

tectonomagmatic characteristics of the back arc portion of the calama olacapato el toro fault zone central andes 1 post 20 ma magmatism in the central andes is either localized in the magmatic arc or distributed east of it on the altiplano puna plateau here there is a distinct concentration of magmatic centers on nw se trending lineaments such as the calama olacapato el toro cot that extends into the eastern cordillera to the east of the puna understanding the possible genetic relationship between prominent structures and magmatic centers on these lineaments is important to elucidate the tectonomagmatic evolution of the central andes we investigated the back arc area of the cot using remote sensing geological structural and petrochemical data our study demonstrates that this portion of the cot consists of nw se striking faults formed under overall left lateral transtension that decreases in activity toward the cot termini deformation on the cot occurred during and after activity of prominent n s striking transpressive fault systems and is coeval with magmatism which is focused on the central cot the most evolved magmatic rocks with an upper crustal imprint are exposed on the central cot whereas more primitive mantle derived mafic to moderately evolved magmatic rocks are found toward the cot termini this points to a genetic relationship between upper crustal deformation and magmatic activity that led to enhanced magma storage in the central cot cot magmas may result either from slab steepening or episodic delamination of the asthenospheric mantle

lithospheric structure beneath the south eastern zagros mountains iran recent slab break off integrated lithospheric modelling based on the combined interpretation of gravity geoid and topography data sets highlights a previously undocumented lithospheric thinning beneath the zagros collisional belt iran which we propose to relate to recent slab break off at the continent ocean transitional lithosphere recent published data on the distribution of seismicity at depth support this interpretation in agreement with other published models for the zagros mountains the overlying crust exhibits by contrast a noticeable thickening reaching a maximum of 52 km the consequent thermal uplift expected from slab break off is suggested to have modified the zagros wedge taper and triggered the recently documented switch from thin skinned to thick skinned deformation in the zagros fold thrust belt

deep crustal structure and flexure of the arabian plate beneath the zagros collisional mountain belt as inferred from gravity observations the zagros mountain belt region a neogene continental collisional zone between arabia and iran that is characterized by a suture a folded belt and a foreland basin is unusual among active mountain belts in that its 6 12 km thick sedimentary cover is shortening predominantly by folding while the basement is apparently thickening along numerous high angle reverse faults we have used over 9000 gravity measurements in the region in conjunction with limited seismological observations and geological cross sections of the uppermost 10 km of crust to infer the deeper crustal structure beneath the region crustal models constrained by the bouguer anomalies and other seismological and geological data are characterized by a moho that dips about 1 to the northeast beneath the folded belt and increases in dip to about 5 near the main zagros thrust mzt the moho depth increases from 40 km beneath the leading edge of the foreland basin the mesopotamian foredeep and persian gulf to as much as 65 km beneath the mzt alternative models that incorporate a subducted oceanic crust that is attached to the underthrusting arabian crust deviate little in their moho configurations from the above simpler models negative isostatic residual anomalies are interpreted to indicate local overcompensation beneath the foreland basin and near the folded belt and beneath the mzt we show that underthrust sedimentary rocks of the converging margins along the suture zone may account for the negative isostatic residual anomalies near the mzt however to explain the rest of the isostatic anomalies requires other forces to be acting on this collisional plate boundary for example elastic flexure models required a combination of topography and subsurface loads or downward force the origin of which is not clear to approximate the bouguer or isostatic residual anomalies associated with the foreland basin and the folded belt the topography load of the zagros mountain belt is insufficient to cause the required deflection of the underthrusting arabian plate a combination of isostatic elastic flexure and horizontal compression forces acting on the edge of the arabian craton and the transitional lithosphere of central iran appears to best model the crust of the zagros region we propose a model in which the lower crust of the converging arabian plate located beneath the zagros is being shortened and thickened plastically between the seismogenic rigid upper crust and a rigid uppermost mantle lid the mantle lid probably decoupled from the lowermost crust un der thrusts the iranian crustal blocks thus confined from below the horizontally compressed plastic lower crust hydraulically depresses the moho and raises the faulted and folded brittle upper crust in isostatic equilibrium

porphyry and epithermal deposits in greece an overview new discoveries and mineralogical constraints on their genesis abstract greece hosts a variety of magmatic hydrothermal ore deposits prospects with porphyry and epithermal styles playing a major role in its total gold endowment these deposit types are mainly clustered in two areas the rhodope and attico cycladic massifs and formed from about 33 ma to the pleistocene as a result of back arc extension in the aegean sea metamorphic core complex formation and contemporaneous post subduction and arc magmatism in the serbo macedonian massif porphyry cu au deposits include skouries fisoka tsikara vathi and gerakario causative intrusives are oligocene to miocene granodiorites to monzonites gold and pge mineralization is associated with potassic alteration of the intrusives in the eastern rhodope massif and the ne aegean islands porphyry prospects occur at pagoni rachi konos hill myli melitena west thrace fakos sardes and kaspakas limnos island and stypsi lesvos island mineralization is associated with oligocene to miocene subvolcanics of calc alkaline to shoshonitic affinity feature of these prospects which they share in common with several porphyry au only systems is their shallow depth of emplacement the presence of potassic sodic calcic and or phyllic alteration a strong epithermal overprint their low cu content an extreme re enrichment the multistage introduction of au the presence of banded quartz veinlets and the local presence of tourmaline new discoveries of porphyry style mineralization at king arthur st philippos and aisymi increases the gold potential in west thrace high intermediate sulfidation epithermal au ag polymetallic deposits prospects overprint and or occur laterally from porphyry style mineralization where they are spatially associated with lithocaps of advanced argillic alteration high intermediate sulfidation au ag epithermal mineralization at perama hill mavrokoryfi and pefka in west thrace and at pterounda mesotopos and megala therma on lesvos island is controlled by steeply dipping extensional faults within volcanic rocks without any obvious genetic relationship to spatially related porphyry style mineralization polymetallic epithermal deposits and prospects contain critical and energy critical metals e g te se bi sb in ge and ga which may be considered as by products in the attico cycladic area porphyry mo w mineralization occurs as sheeted quartz veins and stockworks cutting a potassic to sericitic altered miocene granodiorite stock in the lavrion district bonanza grade au and or ag rich veins with epithermal affinities crosscut metamorphic rocks at lavrion and on syros tinos antiparos and anafi islands milos island is characterized by shallow submarine volcanic hosted is hs epithermal au ag te and base metal deposits antimony as ag au deposits prospects on chios samos and kos islands in the eastern aegean sea indicate the potential for carlin style mineralization in greece several factors played a role to the metal endowment of the aegean porphyry epithermal systems magma fertility in the source regions depth of emplacement of causative intrusives relative contribution of mantle versus crustal material redox state of subduction related magmas and physico chemical fluid conditions at the site of ore deposition

rb sr systematics of fault gouges from the north anatolian fault zone turkey a combined mineralogical and rb sr isotopic investigation was conducted on fault gouges from two locations at eastern part of the north anatolian fault zone nafz the fault gouge samples contain no 2 m mica and consist chiefly of cryptocrystalline material which is extensively altered to illitic clays mixed layered illite smectite and some carbonate minerals the rb sr isochrones of leachate residue and untreated aliquots from various size fractions of samples yielded two different illite generations the oldest illite authigenesis which started at about 35 6 ma might be inherited from pre existing faults along the tethyan suture zone the authigenic illites from finer fractions correspond to an isochron age of 8 3 ma which is in agreement with the findings of previous works that may suggest a middle miocene age for the initiation of the nafz our sr isotope data indicate that the metamorphic fluids contain some mantle components and mobilised during fault movement

modeling the influence of sinking anhydrite blocks on salt diapirs targeted for hazardous waste disposal due to the low permeability and high ductility of rock salt many salt diapirs such as those in germany and the netherlands are targeted as long term repositories for disposal of high level radioactive and chemical wastes geophysical and subsurface data show that the gorleben salt diapir which is one of the most extensively investigated diapirs in the world and other salt diapirs of the zechstein formation in germany contain large blocks 80 m thick of high density anhydrite inclusions these blocks which were carried upward by the rising salt are considered to be detached segments of intercalated layers that initially were deposited with the salt results of physical and numerical models presented here show that such detached high density blocks which were entrained and carried upward by the diapir at an earlier stage tend to sink in the late stages of diapiric evolution when the rate of diapiric rise slows down during their descent these high density competent blocks deform by folding and create shear zones at the immediate contact with the less competent salt the descending blocks initiate a secondary internal flow within the salt diapirs they descend and they may deform any repository built within such diapirs which would otherwise be considered as tectonically inactive

the deep structure of the iranian plateau high resolution structures of the lithosphere asthenosphere system beneath a seismic profile in iran are obtained by the simultaneous inversion of data from receiver functions and fundamental mode rayleigh wave group velocity and validated by modeling bouguer gravity anomaly data the seismic data are gathered over a profile extending across zagros sanandaj sirjan zone ssz urumieh dokhtar magmatic arc udma central iran alborz binalud mountain ranges and kopeh dagh mountain ranges the results confirm the presence of crustal roots at the north and south of iranian plateau where it meets the arabian plate and eurasia the high velocity lithosphere of the arabian plate gently plunges nne ward beneath central iran supporting the subduction of the continental lithosphere responsible for the seismicity of the area the crust and lithosphere are thinner beneath central iran where two low velocity structures are very likely related to magma sources of the udma and in east of iran around lut block where the volcanism shows calcalkaline subduction related geochemistry the crustal lithospheric root to the north of the iranian plateau may represent the relict of a previous cimmeric subduction zone therefore the iranian lithosphere asthenosphere system could be the result of the coalescence of two separate subduction zones

application of 3d magnetic amplitude inversion to iron oxide copper gold deposits at low magnetic latitudes a case study from carajas mineral province brazil abstractstrong hydrothermal alteration modifies rock physical properties in iron oxide copper gold deposits iocgs and may result in characteristic signatures detectable in geophysical surveys magnetic data are commonly used in characterizing orebodies and 3d inversions are often used to assist in interpretations in areas with strong remanence and self demagnetization the total magnetization can have directions different from the inducing field direction this deviation precludes the use of traditional inversion methods magnetic amplitude inversion offers one solution to this challenge because the amplitude data are weakly dependent on the magnetization direction in addition the low magnetic latitude also imposes difficulty in amplitude data calculation due to the instability in the component conversion in the wavenumber domain to formulate a practical approach we present a case study on applying the magnetic amplitude inversion to the furnas southeast iocg deposit at the low magnetic latitude i

fluid inclusion evidence for the physicochemical conditions of sulfide deposition in the olympias carbonate hosted pb zn au ag sulfide ore deposit e chalkidiki peninsula n greece the olympias pb zn au ag sulfide ore deposit e chalkidiki n greece is hosted by marbles of the polymetamorphic kerdilia formation of paleozoic or older age the geologic environment of the ore also comprises biotite hornblende gneisses and amphibolites intruded by tertiary pegmatite aplite dikes lamprophyre dikes the 30 ma stratoni granodiorite and porphyritic stocks only limited parts of the deposit display shear folding and brecciation most of it is undeformed microthermometry of fluid inclusions in gangue syn ore quartz indicates three types of primary and pseudosecondary inclusions 1 h2o rich 1 18 wt nacl equivalent 3 6 mol co2 2 h2o co2 inclusions 4wt nacl equivalent with variable co2 contents coexisting in both undeformed and deformed ore 3 aqueous highsalinity 28 32 wt nacl equivalent inclusions found only in undeformed ore type 2 inclusions are differentiated into two sub types 2a relatively constant co2 content in the narrow range of 8 15 mol and homogenization to the liquid phase 2b variable co2 content between 18 and 50 mol and homogenization to the vapor phase type 1 and 2b inclusions are consistent with trapping of two fluids by unmixing of a high temperature saline aqueous co2 bearing fluid of possible magmatic origin probably trapped in type 2a inclusions fluid unmixing and concomitant ore mineralization took place at temperatures of 350 30 c and fluctuating pressures of less than 500 bar for both undeformed and deformed ores the wide salinity range of type 1 inclusions probably represents a complex effect of salinity increase due to fluid unmixing and volatile loss and dilution due to mixing with low salinity meteoric waters high solute enrichment of the residual liquid due to extreme volatile loss during unmixing may account for high salinity type 3 inclusions the olympias fluid inclusion salinity temperature gradients bear similarities to analogous gradients related to pb zn ores formed in granite hosted low t distalskarn skarn free carbonate replacement and epithermal environments

geochemistry of magnetite from the giant paleoproterozoic dahongshan fe cu deposit sw china constraints on nature of ore forming fluids and depositional setting abstract the dahongshan fe cu ore deposit hosted in the paleoproterozoic meta volcanic and meta sedimentary sequences is a giant deposit in the fe cu metallogenic province of southwestern china two ore types have been identified 1 massive and disseminated fe ores hosted dominantly in meta volcanic rocks and 2 disseminated and banded fe cu ores in meta sedimentary rocks magnetite presents in all orebodies and is dominant in the fe ores chemistry of magnetite suggest that the fluids for iron mineralization in the fe and fe cu orebodies are likely chemically similar and cogenetic minor sulfides e g molybdenite occur at the end of iron mineralization stage indicating the gradually decrease in oxygen fugacity for the mineralizing fluids with magnetite precipitation along with evolution mineralizing fluids generate magnetite with depletions in cr ni ga and v but enrichments in mn sn and co which are primarily reflective of the temperature decrease of fluids we have discovered some magnetite grains that are extremely rich in v 10000 ppm but low in ti and cr geochemical patterns suggest that they were formed by fluids similar to those of ordinary ores available knowledge about the unique high v magnetite indicates highly reduced marine environments for its generation ore bulk ree patterns showing remarkable positive eu anomalies and absence of obvious ce anomalies suggest a bif like marine environment consistent with the morphology of both fe and fe cu orebodies our results provide independent evidence for submarine environment in the formation of the giant precambrian stratiform fe cu ore deposit

seismic tomographic imaging of p and s waves velocity perturbations in the upper mantle beneath iran summary the inverse tomography method has been used to study the p and s waves velocity structure of the crust and upper mantle underneath iran the method based on the principle of source receiver reciprocity allows for tomographic studies of regions with sparse distribution of seismic stations if the region has sufficient seismicity the arrival times of body waves from earthquakes in the study area as reported in the isc catalogue 1964 1996 at all available epicentral distances are used for calculation of residual arrival times prior to inversion we have relocated hypocentres based on a 1 d spherical earth s model taking into account variable crustal thickness and surface topography during the inversion seismic sources are further relocated simultaneously with the calculation of velocity perturbations with a series of synthetic tests we demonstrate the power of the algorithm and the data to reconstruct introduced anomalies using the ray paths of the real data set and taking into account the measurement errors and outliers the velocity anomalies show that the crust and upper mantle beneath the iranian plateau comprises a low velocity domain between the arabian plate and the caspian block this is in agreement with global tomographic models and also tectonic models in which active iranian plateau is trapped between the stable turan plate in the north and the arabian shield in the south our results show clear evidence of the mainly aseismic subduction of the oceanic crust of the oman sea underneath the iranian plateau however along the zagros suture zone the subduction pattern is more complex than at makran where the collision of the two plates is highly seismic

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

late permian to late triassic palaeomagnetic data from iran constraints on the migration of the iranian block through the tethyan ocean and initial destruction of pangaea summary a palaeomagnetic study of late permian to early jurassic rocks from the alborz and sanandaj sirjan zones in iran and a compilation of selected palaeopoles from the carboniferous to the present provide an updated history of the motion of the iranian block within the tethys ocean the iran assemblage part of gondwana during the palaeozoic rifted away by the end of the permian we ascertain the southernhemisphere palaeoposition of iran at that time using magnetostratigraphy and show that it was situated close to arabia near to its relative position today a northward transit of this block during the triassic is shown with an estimated expansion rate of the neotethyan ridge of 100 140 km myr 1 the northward convergence with respect to eurasia ended during the ladinian middle triassic and is marked by a collision in the northern hemisphere with the turan platform which was the southern margin of the eurasian continent at that time no north south component of shortening is evidenced north of iran afterwards an analysis of the declinations from the late permian to the present shows diverent large rotations emphasizing the important tectonic phases suvered since the triassic finally we propose palaeomagnetic reconstructions of the tethys area during the late permian and the late triassic showing that the palaeotethys ocean was narrower than previously thought and did not widen its gate to the panthalassa before the triassic period

potential field signatures along the zagros collision zone in iran abstract the zagros orogenic belt known as an active fold thrust belt was formed in southwestern iran due to the convergence of the arabian and eurasian plates in this study potential field data are inverted in 3d to image the variations of magnetic susceptibility and density contrast along the collision zone resulting in better tectonic understanding of the studied region geophysical data measured by airborne magnetic and ground based gravity systems are used to construct an integrated model that facilitates the interpretations of various tectonic zones across a 450 km line this line intersects the main structural units from the sw portion of the zagros belt the constructed model reveals a contrast that indicates the transition between the two continental plates coinciding with the western boundaries of the sanandaj sirjan zone ssz at the main zagros thrust mzt fault the subduction of the arabian continental crust below the iranian one is evident because of its lower susceptibility property and alternating sequence of high and low density regions higher susceptibility magnetic remanence and density are the mainstays of the urumieh dokhtar magmatic assemblage udma zone at the ne of the studied route whereas lower values of these properties correspond to 1 the thin massive tertiary neogene and quaternary sediments of the central domain cd zone and 2 the thick sedimentary and salt intrusion cover over the zagros fold and thrust belt zftb higher density of regions in the arabian crust below the zftb implies that fault activities have caused significant vertical displacement of the basement finally a simplified geological model is presented based upon the inversions of the geophysical data in which the main geological units are divided along the studied route

fluid migration through thrust faults in the helvetic nappes western swiss alps the 18o 13c and 87sr 86sr values of calcite and organic matter were measured for carbonate mylonites from numerous thrusts in the helvetic alps carbonate mylonites in most of the thrusts retain essentially unaltered protolith 18o and 13c values consistent with there having been little to no advection of isotopically distinct fluid through these faults only carbonate mylonites from the basal thrusts of the largest nappes have 18o and or 13c values that differ from those of their protoliths the zone of isotopic alteration exchange is confined to c 10 to 20 meters of these fault contacts we propose the fluids that migrated through these faults contained variable amounts of organically derived carbon and radiogenic strontium and were probably derived from dewatering of the sedimentary rocks and prograde metamorphic reactions in the nappes root zones apart from the basal thrusts of the largest nappes that behaved as narrow laterally extensive conduits for fluids there is little isotopic evidence that large quantities of fluids passed through most of the carbonate hosted thrusts in the helvetic alps

exhumation of limpopo central zone granulites and dextral continent scale transcurrent movement at 2 0 ga along the palala shear zone northern province south africa abstract the palala shear zone is part of a major tectonic lineament in southern africa which extends over 1000 km from central botswana to the soutpansberg in south africa the lineament is situated between the central zone of the limpopo belt and the kaapvaal craton at its main exposure in the koedoesrand window 50 km e of ellisras northern province the palala shear zone comprises a c 15 km wide mylonite zone which can be subdivided into a northern central and southern domain this study addresses the tectono metamorphic history of the palala shear zone in the koedoesrand window and its role in the tectonics of the limpopo belt in order to do this structural and petrographical work was combined with geochronology age data from relic mineral parageneses show that metapelites from the central domain underwent granulite facies metamorphism around 2 6 ga however because of an intense proterozoic overprint field relationships of the archean event are largely disrupted during a second high grade event at c 2 0 ga granulite facies metamorphism was reached in the northern domain and the adjacent limpopo central zone charnockites were emplaced in the northern domain after 2 1 ga and were affected by retrograde amphibolite and greenschist facies metamorphism around 1 97 ga post orogenic transcurrent faulting under sub greenschist facies conditions characterizes the central and southern domains field observations and microstructural investigations indicate a dextral shear sense for the retrograde mylonitisation these findings document that the palala shear zone played an important role during the exhumation of the proterozoic granulites in the limpopo central zone associated with a transpressive orogeny between 2 05 and 1 95 ga low grade post orogenic transcurrent faulting in the palala shear zone at c 1 9 ga may be associated with the transtensional opening of the soutpansberg and palapye grabens on the basis of the tectono metamorphic history in the koedoesrand window and regional geophysical geochemical and sequence stratigraphic data the palala shear zone is interpreted as a proterozoic suture zone along which the archean kaapvaal and zimbabwe provinces were juxtaposed

multiple stages of hydrothermal ree remobilization recorded in fluorapatite in the paleoproterozoic yinachang fe cu ree deposit southwest china abstract the yinachang deposit in the kangdian region southwest china contains large amounts of fe cu and ree and formed at 1700 ma in this deposit there are three stages of alteration and mineralization including pre ore na fe alteration fe ree mineralization and cu ree mineralization in the fe ree mineralization stage ree rich fluorapatite with total ree concentrations ranging from 10 700 to 34 000 ppm formed together with magnetite in the following cu ree mineralization stage large amounts of ree especially lree were leached out of the ree rich fluorapatite due to the interaction between fluorapatite and cl f co2 and ca rich but ree unsaturated fluids the leaching of ree was associated with the removal of si na th u pb and ba and modification of the oxygen isotope signature in the fluorapatite during a 840 ma tectonothermal event ree rich fluorapatite underwent the second interaction with oxidized f co2 and possibly cl rich but na and ca deficient fluids due to fluid fluorapatite interaction ree were removed from the fluorapatite but were immediately reincorporated into new phases within the fluorapatite thus the altered fluorapatite contains abundant ree mineral inclusions including bastnasite ce monazite ce and minor xenotime y a very small portion of the lree were transported out of the fluorapatite and formed bastnasite ce and monazite ce grains in the vicinity of the altered fluorapatite in addition to the metasomatism of fluorapatite allanite and primary synchysite ce from the cu ree mineralization stage were also altered with variable replacement of allanite by an assemblage of synchysite ce chlorite bastnasite ce and primary synchysite ce by bastnasite ce these styles of alteration were possibly synchronous with the second alteration phase of the fluorapatite this study demonstrates that ree can be mobilized during multiple stages of hydrothermal activities and highlights the significant controls fluid compositions have on ree transportation and deposition in hydrothermal system

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

kinematics of cretaceous subduction and exhumation in the western rhodope chalkidiki block in the chalkidiki peninsula of northern greece a thrust complex made of a basement vertiskos unit a cover circum rhodope belt and arc back arc units chortiatis magmatic suite and eastern vardar ophiolites is exposed in the chalkidiki peninsula of northern greece the complex forms the western part of the rhodope metamorphic province and lies on the hanging wall of the kerdylion detachment the structure responsible for the exhumation of the southern rhodope core complex and the most prominent and visible ductile structure related to the tertiary aegean extension the chalkidiki thrust complex arguably preserves a complete record of cretaceous deformation and related fabrics in this contribution we describe the geometry of foliation stretching lineation and shear sense s on a regional scale the regional foliation strikes nw se and displays different patterns in the three studied units i dominantly dipping at low angle in the vertiskos unit ii affected by upright folding in the circum rhodope belt and iii systematically steeply dipping to the ne in the chortiatis magmatic suite stretching lineation trend dominantly sw ne in the three mentioned units on the basis of new mapping neglecting local perturbations and deformation related to tertiary extension we infer the regional kinematics of cretaceous syn metamorphic thrusting and subsequent exhumation of the metamorphic units thrusting took place toward the sw in present day coordination and the related fabrics are recorded throughout the metamorphic pile on the contrary exhumation related fabrics are related to shear toward the ne and are preferentially recorded in the uppermost part of the metamorphic pile suggesting that extension was more localised and of less finite intensity compared to thrusting

magnetotelluric signature for the zagros collision zagros is a relatively young and active fold thrust belt which has formed due to convergence between the eurasian and arabian plates magnetotelluric mt soundings along a transect were carried o

alleghenian age of the upper mississippi valley zinc lead deposit determined by rb sr dating of sphalerite mississippi valley type mvt ore deposits in north america are generally thought to have formed from warm brines which migrated from sedimentary basins to sites of deposition in sedimentary strata of the neighbouring craton long after unification of the sediments1 3 when and how these migrations occurred is not well understood but recent geological evidence suggests that continental scale brine migration can be triggered by tectonic collisions4 6 indirect evidence7 9has suggested an association of north american mvt mineralization with the late palaeozoic alleghenian ouachita orogeny recently however nakai et al 10obtained a rb sr age of 377 29myr for sphalerites from the east tennessee mvt district which they linked to the middle palaeozoic acadian orogeny here we report rb sr dates for sphalerites from the mvt type section the upper mississippi valley umv zinc lead district rb sr data from two distinct sphalerite bands from the west hayden ore body yield two independent but indistinguishable isochrons of permian age 269 6 myr and 270 4 myr consistent with a brine migration episode initiated by the alleghenian ouachita orogeny in conjunction with the previous data indicating a link to the acadian orogeny10 11 our results indicate that north american mvt deposits formed in at least two distinct tectonic episodes

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 strong seismic velocity contrast in the shallow mantle across the zagros collision zone iran summary surface wave dispersion measurements are interpreted jointly with the inversion of teleseismic p wave traveltime residuals along a dense 620 km long temporary seismic profile across the zagros to investigate its upper mantle structure the s wave model determined from rayleigh wave dispersion in the zagros fold and thrust belt has high velocities from 4 5 0 2 km s 1 below the moho to 4 9 0 25 km s 1 at 200 km depth which are comparable to a shield like structure beneath the suture region from the main zagros thrust mzt to the urumiehdokhtar volcanic arc s wave velocities are lower than beneath the zagros in the top 50 km of the upper mantle with a minimum of 4 4 0 2 km s 1 at 80 km depth from 150 km and deeper s velocities are as high as beneath the zagros we suggest that part of the velocity difference at shallow depth is due to higher mantle temperatures and or higher fluid content beneath the northern half of the profile but that velocities are too high to support the hypothesis of mantle lid delamination under the suture zone teleseismic p traveltime relative residuals display a long wavelength variation along the transect with a difference of 1 1 s between negative residuals in the zagros simple folded belt and positive residuals in central iran this difference backprojects into a 6 7 per cent lateral variation of p wave velocity in the shallow upper mantle with higher vp beneath zagros and lower vp beneath central iran the main short wavelength variation of the residual is located in the suture region with late p arrivals in the region of the mzt and early arrivals in the sanandaj sirjan zone ssz using synthetic models of vp perturbations we show that the high velocities of the arabian platform have to extend laterally at least to the ssz to fit the observed p delays this model also predicts rayleigh wave phase velocities which are within the error bars of the observed dispersion it supports the model of crustal scale overthrusting at the mzt

active deformation and seismic potential in the serbomacedonian zone northern greece abstract the seismic potential in the central part of the serbomacedonian geological zone n greece is examined for 1 the lateral distribution of the rupture zones of the 1902 1932 and 1978 large shocks and 2 the potential stress drop stored in the area of these three shocks the distribution of rupture zones defines an area trending sse nnw and the whole length of the area examined has been ruptured since 1902 in the area of the 1902 and 1932 large earthquakes the slip accumulated is enough to generate more large shocks

rb sr dating of sphalerites from tennessee and the genesis of mississippi valley type ore deposits mississippi valley type mvt ore deposits commonly consist of some combination of lead zinc and iron sulphides accompanied by barite fluorite dolomite and calcite they are thought to form by fluid expulsion from sedimentary successions1 3 but their exact origin has remained controversial because of the scarcity of reliable geochronological data in a recent and widely quoted model the mvt deposits of the central and eastern united states formed as a result of large scale lateral fluid flow driven by the tectonic squeezing of sedimentary successions during the late palaeozoic alleghenian orogeny 330 250 myr 4 here we report the first direct rb sr dating of sphalerites from an mvt deposit and propose this as a useful geochronological technique for sulphide mineralization with poor age control rb sr data for sphalerites from coy mine east tennessee define an isochron age of 377 29 myr ruling out any genetic connection with the alleghenian orogeny instead mvt mineralization in the eastern united states was apparently generated from fluids expelled during thrusting associated with the older acadian orogeny 380 350 myr

geochemical and geochronological constraints on the formation of shear zone hosted cu au bi te mineralization in the stanos area chalkidiki northern greece abstract copper gold bismuth tellurium mineralization in the stanos area chalkidiki peninsula greece occurs in the proterozoic to silurian aged serbomacedonian massif which tectonically borders the mesozoic circum rhodope metamorphic belt to the west and crystalline rocks of the rhodope massif to the east this area contains the paliomylos chalkoma and karambogia prospects which are spatially related to regional nw se trending shear zones and hosted by marble amphibolite gneiss metagabbro and various muscovite biotite chlorite actinolite feldspar quartz schists of the silurian vertiskos unit metallic minerals occur as disseminated to massive aggregates along foliation planes and in boudinaged quartz veins iron bearing sulfides pyrite arsenopyrite and pyrrhotite formed prior to a copper bearing stage that contains chalcopyrite along with galena sphalerite molybdenite and various minerals in the system bi cu pb au ag te fluid inclusion homogenization temperatures of primary aqueous liquid vapor inclusions in stage i quartz veins range from 170 1 c to 349 6 c peak at 230 c with salinities of 4 5 to 13 1 wt nacl equiv calculated isochores intersect p t conditions associated with the upper greenschist facies caused by local overpressures during late stage tectonic movement along the shear zone in the eocene which produced stretching and unroofing of rocks in the region values of 34 s for sulfides in the stanos shear zone range from 2 42 to 10 19 and suggest a magmatic sulfur source with a partially reduced seawater contribution for fluids in equilibrium with quartz 18 o at 480 c varies from 5 76 to 9 21 but does not allow for a distinction between a metamorphic and a magmatic fluid a 187 re 187 os isochron of 19 2 2 1 ma for pyrite in the paliomylos prospect overlaps ages obtained previously from intrusive rocks spatially related to the skouries porphyry cu au the asimotrypes au and the intrusion related palea kavala bi te pb sb au deposits in northern greece as well as alteration minerals in the carbonate replacement madem lakkos pb zn deposit ore forming components of deposits in the stanos area were likely derived from magmatic rocks at shallow depth that intruded an extensional shear environment at 19 ma

seismological constraints on the crustal structure beneath the zagros mountain belt iran summary the zagros mountain belt of western iran results from the collision of the arabian and central iran continental blocks the stage of the collision is unclear and the crustal structure of the zagros is rather poorly known in this study we investigate the velocity structure of the crust and upper mantle beneath the ghir region located in the central zagros using data collected by a temporary local seismological network including a broad band instrument the structures of the sedimentary cover and the upper crystalline crust are estimated from the inversion of p and s traveltimes of local earthquakes recorded on a dense seismological network the upper crust consists of an 11 km thick sedimentary layer v p 4 70 km s 1 above a 8 km thick upper crystalline crust v p 5 85 km s 1 the velocity of the lower crust and the depth of the moho are found using receiver function analysis of teleseismic earthquakes the lower crystalline crust is unusually slow v p 6 5 km s 1 and 27 km thick the upper bound for the total crustal thickness beneath the ghir region is 46 2 km a comparison of the thickness of the crystalline crust of the zagros with available information for the thickness of the crystalline crust of the arabian platform shows that at present the zagros has a thinner crust the current crustal thickness beneath the zagros is comparable to the pre collision crustal thickness of the arabian platform suggesting that the zagros is now in a very early stage of continental collision

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

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

structural characteristics of the transitional zone from internal to external parts of the zagros orogen iran abstract mapping and detail field investigations integrated with geophysical data in bakhtyari area across the transitional zone of the zagros orogen shows a number of sw verging thrust sheets kinematic analysis of these sheets using deformed structures at the basal thrust zone as well as geophysical data from basement top allow us to recognize internal and external thrust sheets the former show duplex thrust system with ductile brittle deformation conditions while the latter have imbricate fan thrust system with brittle deformation condition only the internal thrust sheets along which the basement is also involved converge downward to form a crustal scale ductile thrust referred here as the root zone to the zagros orogen this root zone proposed as a suture to the zagros orogen and the boundary between the afro arabian plate and the eurasia plate the time for initiation of thrusting based on the late miocene age of syn tectonic bakhtyari conglomerate is compatible with the time of continent continent collision between the afro arabian plate and the eurasia plate determined by the plate reconstructions

constraints in 3d gravity inversion a three dimensional 3d inversion program is developed to interpret gravity data using a selection of constraints this selection includes minimum distance flatness smoothness and compactness constraints which can be combined using a lagrangian formulation a multigrid technique is also implemented to resolve separately large and short gravity wavelengths the subsurface in the survey area is divided into rectangular prismatic blocks and the problem is solved by calculating the model parameters i e the densities of each block weights are given to each block depending on depth a priori information on density and the density range allowed for the region under investigation the present computer code is tested on modelled data for a dipping dike and multiple bodies results combining different constraints and a weight depending on depth are shown for the dipping dike the advantages and behaviour of each method are compared in the 3d reconstruction recovery of geometry depth size and density distribution of the original model is dependent on the set of constraints used from experimentation the best combination of constraints for multiple bodies seems to be flatness and a minimum volume for the multiple bodies the inversion method is tested on real gravity data from the rouyn noranda quebec mining camp the 3d inversion model for the first 10 km is in agreement with the known major lithological contacts at the surface it enables the determination of the geometry of plutons and intrusive rocks at depth

time calibration of a pt path from the western tauern window eastern alps the problem of closure temperatures new hornblende k ar and 39ar 40ar and mica rb sr and k ar ages are used to place specific timemarks on a well constrained pressure temperature path for the late alpine metamorphism in the western tauern window after identification of excess 40ar the closure behavior of ar in hornblende is compared with that of sr and ar in phengite and biotite samples were collected in three locations whose maximum temperatures were 570 c zemmgrund 550 c pfitscher joch and 500 540 c landshuter hutte

relationships between a porphyry cu mo deposit base and precious metal veins and laramide intrusions mineral park arizona in the wallapai mining district porphyry style copper molybdenum mineralization occurs within and near laramide granitoid stocks at the center of an elongate zone of polymetallic quartz veins the principal mineralized veins form a well defined paragenetic sequence with a simplified mineralogy progressing through 1 anhydrite molybdenite am veins of quartz k feldspar anhydrite pyrite biotite molybdenite 2 quartz molybdenite qm veins with quartz molybdenite pyrite 3 anhydrite chalcopyrite ac veins containing quartz k feldspar anhydrite pyrite magnetite chalcopyrite chlorite rutile 4 quartz pyrite qp veins of quartz sericite pyrite and quartz pyrite chalcopyrite epidote chlorite and 5 polymetallic quartz pmq veins with a gangue assemblage of quartz sericite calcite kaolinite epidote chlorite and a variety of base and precious metal minerals the coexistence of vapor and liquid rich fluid inclusions in vein quartz shows that the molybdenite bearing anhydrite and quartz veins formed at 360 degrees to 410 degrees c from boiling low salinity brines chalcopyrite deposition in the anhydrite chalcopyrite veins was at 380 degrees to 420 degrees c from nonboiling brines averaging 20 equiv wt percent nacl and 25 equiv wt percent kcl the quartz pyrite veins formed at 320 degrees to 350 degrees c from brines of 1 to 13 equiv wt percent nacl the polymetallic quartz veins formed from dilute brines of 1 to 7 equiv wt percent nacl temperatures in the first stage of mineralization of the polymetallic quartz veins abruptly increased to 400 degrees to 450 degrees c in and near mineral park but declined outward to less than 300 degrees c on the district periphery in subsequent stages fluid temperatures decreased across the district to less than 200 degrees c pressures were 250 to 300 bars probably in a hydrostatic pressure regime during boiling related to molybdenite mineralization but they may have increased to about 1 100 bars lithostatic pressure during chalcopyrite deposition in the anhydrite chalcopyrite veins a depth during mineralization of 3 to 4 km is suggested copper and molybdenum mineralization occurred in a lithocap environment above a progenitor intrusion but was not directly related to the exposed ithaca peak stocks the evolution from hypersaline fluids in the anhydrite chalcopyrite veins to low salinity lower temperature fluids in the quartz pyrite veins suggests an influx of meteoric water into the waning porphyry style hydrothermal system brines up to 100 degrees c hotter appeared during the formation of the paragenetically later polymetallic quartz veins and constituted a new and much larger hydrothermal system the heat source presumably an unexposed intrusion was much larger than the porphyry style system the zonation in base metal ratios of polymetallic quartz veins is symmetrical with respect to the proposed heat source

geology and geochronology of the arnea sithonia and ouranopolis intrusions chalkidiki peninsula northern greece abstract the chalkidiki peninsula comprises the greek geotectonic units of the vardar axios zone and the serbo macedonian massif several granitic bodies of various ages intrude this area and many of them are of unknown or disputed age the ages of the arnea sithonia and ouranopolis granitoids are investigated using 40 ar 39 ar stepheated mineral and rb sr whole rock analyses the arnea granite has experienced intense but variable deformation recrystallization and retrogression in general it lacks easily datable minerals because of it s highly evolved silica rich composition however coarse grained phlogopitic mica separated from a minor less evolved porphyritic part of the intrusion yields an excellent 40 ar 39 ar plateau age of 136 1 ma rb sr whole rock samples give a regression line of age 155 11ma and an initial 87 sr 86 sr ratio of 0 7174 0 0017 mswd 280 the scatter may reflect the widespread recrystallization and deformation of the arnea granite the arnea granite is at least late jurassic in age and has undergone regional greenschist metamorphism during the early cretaceous biotite from the sithonia granitoid yields a plateau age of 43 0 6 ma muscovites from crosscutting pegmatites within the granitoid give slightly saddle shaped age spectra with minimum ages of 49 ma and 50 ma suggesting argon 40 excess biotite and muscovite from the ouranopolis granitoid yield plateau ages of 44 1 1 ma and 47 0 7 ma respectively it is suggested that this granitoid is coeval and cogenetic with the sithonia granitoid both intrusions are eocene in age rb sr whole rock samples from the sithonia and ouranopolis granitoids failed to provide any isochrons this is interpreted to be due to inhomogeneities in these young intrusions the age data strongly suggest that the sithonia and ouranopolis granitoids are unrelated to the arnea granite coupled with geochemical and petrographic data these results clarify the relationships between some of the granitic intrusions and have important regional implications

chronology of magmatism and mineralization in the kassandra mining area greece the potentials and limitations of dating hydrothermal illites abstract various geochronological methods u pb rb sr and k ar have been applied to constrain the timing of magmatism and polymetallic mineralization in the kassandra mining district northern greece these data provide the first geochronological evidence that porphyry copper mineralization proximal copper skarns and distal high temperature carbonate hosted pb zn ag au replacement ores formed contemporaneously and probably within less than 2 million years polymetallic mineralization is temporally related to the emplacement of granodioritic to quartz dioritic porphyries 24 25 ma that postdate the largest post tectonic intrusion of the area the stratoni granodiorite 27 9 1 2 ma andesite porphyry dikes which crosscut the pb zn ag au ores and associated alterations represent the last magmatic phase in the area 19 1 0 6 ma and did not contribute to metal concentration the combination of k ar rb sr and oxygen isotope studies of hydrothermal illite rich clays and careful granulometric analysis constrains the reliability of these geochronological methods and emphasizes the importance of characterizing the post formational history of the sample we identify various processes which partly disturbed the k ar and rb sr system of some clays such as retrograde alteration by heated meteoric waters superimposed supergene illitization and resetting of both isotopic systems due to a hydrothermal overprint related to the intrusion of the andesite porphyry our data however suggest that diffusive ar loss from the finest clay fractions k ar system conventional k ar ages of 200 c therefore do not give reliable formation ages the loss of ar may be used to model the cooling history of the hydrothermal system applying the concept of closure temperatures dodson 1973 40k 40arrad isochrons of natural coarser grained 0 6 m size fractions of illites from single samples even when slightly contaminated with feldspars may yield meaningful ages either of the formation or of a reheating event the rb sr dating of hydrothermal clays is sensitive to contamination by adsorbed strontium which may not be cogenetic with the clay as well as feldspars which may not have been homogenized isotopically by the illitization process

seismological evidence for crustal scale thrusting in the zagros mountain belt iran summary crustal receiver functions rfs computed from the records of 45 temporary seismological stations installed on a 620 km long profile across central zagros provide the first direct evidence for crustal thickening in this mountain belt due to a rather short 14 km average station spacing the migrated section computed from radial rfs displays the moho depth variations across the belt with good spatial resolution from the coast of the persian gulf to 25 km southwest of the main zagros thrust mzt the moho is almost horizontal with slight depth variations around 45 km crustal thickness then increases abruptly to a maximum of 70 km beneath the sanandaj sirjan metamorphic zone between 50 and 90 km northeast of the surface exposure of the mzt further northeast the moho depth decreases to 42 km beneath the urumiehdokhtar magmatic assemblage and the southern part of the central iranian microcontinent the region of thickest crust is located 75 km to the northeast of the bouguer anomaly low at 220 mgals gravity modelling shows that the measured moho depth variations can be reconciled with gravity observations by assuming that the crust of zagros underthrusts the crust of central iran along the mzt considered as a crustal scale structure this hypothesis is compatible with shortening estimates by balanced cross sections of the zagros folded belt as well as with structural and petrological studies of the metamorphic sanandaj sirjan zone

new constraints on upper mantle s velocity structure and crustal thickness of the iranian plateau using partitioned waveform inversion summary the continental collision between the african and eurasian plates resulted in a tectonically young and complex deformation in the iranian plateau the present day iranian plateau is characterized by diverse tectonic domains including the continental collisions e g zagros and alborz and the oceanic plate subduction e g makran partitioned waveform inversion method is used here to image the s velocity structure of the upper mantle and moho depth variations in the iranian plateau of nearly 3000 waveforms originally selected for the analysis we have fitted 974 waveforms from 101 events and 39 stations which result in 11 688 linear constraints on the upper mantle s velocity structure and moho depth for the region our new seismic images show seismically faster upper mantle beneath the zagros and the arabian plate compared to the central iran and alborz this high velocity anomaly has descended beneath the central iran along the main zagros thrust across the zagros collision zone the tomographic images show a slab stagnation in the transition zone at about 410 km depth in the form of a horizontal high velocity zone which does not penetrate the deeper parts of the mantle the lowest s velocities are concentrated beneath the central iran and alborz according to our velocity models a strong high velocity anomaly is resolved beneath the trapped south caspian basin with clear indication of westward underthrusting beneath the talesh and western alborz in makran southeast iran there is a clear evidence of subduction of oceanic crust of the arabian plate beneath the makran belt which is correlated with seismicity pattern across the makran zone also the inverted moho map using a priori information of crustal thickness constraints shows the large crustal thickness beneath the zagros suture zone in some places to a maximum depth of 65 km which indicates the influence of crustal thickening and shortening beneath arabian eurasian plate boundary a significantly crustal thinning is observable across the south caspian basin compared to its margins

high temperature carbonate hosted ag pb zn cu deposits of northern mexico the high temperature carbonate hosted ag pb zn cu deposits of northern mexico occur in thick carbonate dominant jurassic cretaceous basinal sedimentary sequences floored by paleozoic or older crust the districts lie within or on the margins of a major fold thrust zone structures parallel to the trends of this belt control mineralization in many districts altered and or mineralized volcanic and intrusive rocks of tertiary age are found in all but three of the districts mineralization apparently occurred during a restricted period 47 to 26 m y ago the deposits are characterized by irregular ore lenses that commonly reveal strong structural controls and are stratigraphically discordant orebodies are of three principal morphological types mantos chimneys and pods and are composed of massive sulfides and or calc silicate skarn sulfide mantos and chimneys are enclosed within carbonate rocks and are generally remote from intrusive bodies sulfide mantos commonly grade downward into sulfide chimneys which may in turn grade downward into skarn chimneys cored by dikes podiform skarn and sulfide orebodies principally occur along stock dike or sill contacts but they may also be developed at some distance from an intrusive contact the associated intrusions are not widely mineralized despite the variations between ore types major similarities are seen in structural controls host rock characteristics and sulfide mineralogy structural controls include intrusive contacts faults fold axes fractures fissures and cavern zones intrusive contacts and intrusion related faults are most important in the skarns whereas regional fault fold and fracture systems are dominant controls on mantos and chimneys mineralization commonly occurs below relatively impermeable shaly units sills or volcanic rocks but some extensive orebodies show remarkable restriction to specific horizons within apparently homogeneous carbonate successions studies of mineralized and unmineralized strata have found no consistent links between ore deposition and carbonate composition facies organic content or insoluble components however zones of secondarily enhanced porosity and permeability induced by recrystallization heating deformation or hydrothermal dolomitization are important mineralization controls geochemical data for the deposits are sparse but indicate strongly contrasting conditions among some of the major districts fluid inclusion data indicate temperatures in the range 200 degrees to 500 degrees c and salinities ranging from i to 60 equiv wt percent nacl the hotter more saline solutions are typically from skarn zones evidence for boiling has not been reported the skarn ores of naica concepcion del oro and velardefia show tight clustering of sulfide sulfur isotope values near 0 whereas the skarn and massive sulfide ores of santa eulalia show a wide range of values in most cases there is isotopic disequilibrium between galena and sphalerite pyrrhotite or pyrite calcite veinlet stockworks above mineralization and limestone wall rocks adjacent to mineralization show shifts of carbon and oxygen isotopes to lighter values the tightly clustered sulfur isotopes and high temperature high salinity fluid inclusions have been interpreted as indicating a strong magmatic component in the mineralizing fluids at naica concepcion del oro and velardena but santa eulalia and other districts show evidence suggesting extensive mixing between magmatic and meteoric fluids it appears that the spectrum of mineralization styles shown by these deposits represent differing responses to variations in intrusive associations depth of emplacement host rock characteristics and geochemical evolution of the individual systems

3d gravity inversion and thermodynamic modelling reveal properties of shallow silicic magma reservoir beneath laguna del maule chile abstract active large volume silicic magma systems are potentially the most hazardous form of volcanism on earth knowledge of the location size and physical properties of silicic magma reservoirs is therefore important for providing context in which to accurately interpret monitoring data and make informed hazard assessments accordingly we present the first geophysical image of the laguna del maule volcanic field magmatic system using a novel 3d inversion of gravity data constrained by thermodynamic modelling the joint analysis of gravity and thermodynamic data allows for a rich interpretation of the magma system and highlights the importance of considering the full thermodynamic effects on melt density when interpreting gravity models of active magmatic systems we image a 30 km 3 low density volatile rich magma reservoir at around 2 km depth containing at least 85 melt hosted within a broader 115 km 3 body interpreted as wholly or partially crystallised 70 crystal cumulate mush our model suggests a magmatic system with shallow crystal poor magma overlying deeper crystal rich magma even though a large density contrast 600 kg m 3 with the surrounding crust exists the lithostatic load is 50 greater than the magma buoyancy force suggesting buoyancy alone is insufficient to trigger an eruption the reservoir is adjacent to the inferred extension of the troncoso fault and overlies the location of an intruding sill driving present day deformation the reservoir is in close proximity to the 2 0 km 3 nieblas rln eruption at 2 3 ka which we calculate tapped approximately 7 of the magma reservoir however we suggest that the present day magma system is not large enough to have fed all post glacial eruptions and that the location or size of the system may have migrated or varied over time with each eruption tapping only a small aliquot of the available magma the presence of a shallow reservoir of volatile rich near liquidus magma in close proximity to regional scale faulting has important implications for volcano monitoring and hazard mitigation

seismic imaging of the lithospheric structure of the zagros mountain belt iran we present a synthesis and a comparison of the results of two temporary passive seismic experiments installed for a few months across central and northern zagros the receiver function analysis of teleseismic earthquake records gives a high resolution image of the moho beneath the seismic transects on both cross sections the crust has an average thickness of 43 2 km beneath the zagros fold and thrust belt and the central domain the crust is thicker beneath the hanging wall of the main zagros reverse fault mzrf with a larger maximum moho depth in central 69 2 km than in northern zagros 56 2 km the thickening affects a narrower region 170 km beneath the sanandaj sirjan zone of central zagros and a wider region 320 km in northern zagros we propose that this thickening is related to overthrusting of the crust of the arabian margin by the crust of central iran along the mzrf considered as a major thrust fault cross cutting the whole crust the fault is imaged as a lowvelocity layer in the receiver function data of the northern zagros profile moreover the crustal scale thrust model reconciles the imaged seismic moho with the bouguer anomaly data measured on the central zagros transect at upper mantle depth p wave tomography confirms the previously observed strong contrast between the faster velocities of the arabian margin and the lower velocities of the iranian micro blocks our higher resolution tomography combined with surface wave analysis locates the suture in the shallow mantle of the sanandaj sirjan zone beneath central zagros the arabian upper mantle has shield like shear wave velocities while the lower velocities of the iranian upper mantle are likely due to higher temperature but these velocities are not low enough and the low velocity layer not thick enough to conclude on a delamination of the lithospheric mantle lid beneath iran the lack of a high velocity anomaly in the mantle beneath central iran suggests that the neotethyan oceanic lithosphere is probably detached from the arabian margin

a geophysical potential field study to image the makran subduction zone in se of iran abstract the makran subduction wedge as one of the largest subduction complexes has been forming due to the arabian oceanic lithosphere subducting beneath the lut and the afghan rigid block microplates to better visualize the subducting oceanic crust in this region a geophysical model of magnetic susceptibility from an airborne magnetic survey line spacing about 7 5 km over the makran zone located at southeast of iran is created to image various structural units in iran plate the constructed geophysical model from the 3d inverse modeling of the airborne magnetic data indicates a thin subducting slab to the north of the makran structural zone it is demonstrated that the thickness of sedimentary units varies approximately at an interval of 7 5 11 km from north to south of this zone in the iranian plate meanwhile the curie depth is also estimated approximately

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

the evolution of illite to muscovite mineralogical and isotopic data from the glarus alps switzerland thirty five illite and muscovite concentrates were extracted from triassic and permian claystones shales slates and phyllites along a cross section from the diagenetic alpine foreland tabular jura and borehole samples beneath the molasse basin to the anchi and epimetamorphic helvetic zone of the central alps concentrates and thin sections were investigated by microscopic x ray infrared mossbauer thermal dta and tg wet chemical electron microprobe k ar rb sr 40ar 39ar and stable isotope methods with increasing metamorphic grade based on illite crystallinity data xrd and ir the following continuous changes are observed i the 1md 2m1 polymorph transformation is completed in the higher grade anchizone ii k2o increases from 6 8 wt diagenetic zone to 8 5 10 anchizone to 10 11 5 epizone reflecting an increase in the total negative layer charge from 1 2 to 2 0 iii a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone epizone boundary iv a shift of an endothermic peak in differential thermal curves from 500 to 750 c v k ar and rb sr apparent ages of the fraction 2 m decrease from the diagenetic zone to the epizone k ar ages being generally lower than rb sr ages the critical temperature for total ar resetting is estimated to be 260 30 c k ar and rb sr ages become concordant when the anchizone epizone boundary is approached the stable isotope data on the other hand show no change with metamorphic grade but are dependent on stratigraphic age these results suggest that the prograde evolution from 1 md illite to 2m1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals however this is not a recrystallization process this restructuration is completed approximately at the anchizone epizone boundary the isotopic data indicate significant diffusive loss of 40ar and 87sr prior to any observable lattice reorganization the restructuration progressively introduces a consistent repartition of ar and k in the mineral lattices and is outlined by the 40ar 39ar age spectra concordant k ar and rb sr ages of around 35 30 ma with concomitant concordant 40ar 39ar release spectra are representative for the main phase of alpine metamorphism calanda phase in the glarus alps a second age group between 25 and 20 ma can probably be attributed to movements along the glarus thrust ruchi phase while values down to 9 ma in regions with higher metamorphic conditions suggest thermal conditions persisting at least until the middle tortonian

rb sr chronology and crystal chemistry of celadonites from the parana continental tholeiites brazil abstract celadonites from the parana flood basalts have been dated by internal rb sr isochrons using the ammonium acetate leaching technique previously used by hart and staudigel 1986 for celadonites from dsdp holes the residues after leaching have very high 87rb 86sr ratios 18 7 1900 and very radiogenic 87sr 86sr 0 73 2 96 electron microprobe analyses show that potassium and thus also presumably rubidium became enriched in these minerals during the transformation of a proto celadonite smectite phase into celadonite our leaching experiment suggests that radiogenic 17sr and rubidium are very resistant to chemical fractionation during leaching and thus may have remained in closed system for rb sr chronology ages varying from 107 1 to 81 1 ma have been obtained at two different sites one on high ti basalts in the northern parana basin and the other on low ti basalts in the southern basin these ages are significantly younger than the eruption of the flood basalts 127 137 ma and in this respect are in good agreement with results obtained on celadonites from oceanic ridges initial 87sr 86sr ratios are distinctly higher in the celadonites than in the host basalts probably due to contamination by radiogenic strontium transported by the hydrothermal fluids our results suggest that mineralogy and isotopic composition are different in celadonites from the northern and southern parana basins although this needs to be confirmed on a larger dataset

the south zagros suture zone in teleseismic images abstract the geometry of intra continental lithosphere boundaries along the zagros orogenic belt in the arabia eurasia collision is investigated by means of teleseismic data the data are gathered over a seismic linear profile extending across south zagros the sanandaj sirjan metamorphic zone the urumieh dokhtar magmatic arc central iran and the kopeh dagh binalud mountains we exploit the p and s receiver functions leading to map the geometry of the crustal and subcrustal interfaces the migrated depth sections reveal an abrupt crustal thickening and a gentle crustal thinning 60 km north and 30 km south of the zagros suture respectively associated to the buckled antiformal moho south of the suture a deeper synform in the lithospheric lid of the lower arabia plate is shown by migrated depth sections affecting the lithospheric mantle of the arabia plate beneath the suture zone this geometry implies an unexpected intra lid decoupling these features imply that the central iran lithosphere acts as a relatively strong backstop producing significant internal deformation expressed by shortening and thickening at the edge of the arabian lithosphere the 410 km and 660 km transition zones are imaged by p to s converted phases and showed lateral continuity implying an originally low dip angle subduction of the oceanic arabian plate beneath central iran

comprehensive approaches to 3d inversion of magnetic data affected by remanent magnetization three dimensional 3d inversion of magnetic data to recover a distribution of magnetic susceptibility has been successfullyusedformineralexplorationduringthelastdecade however the unknown direction of magnetization has limited the use of this technique when significant remanence is present we have developed a comprehensive methodology for solving this problem by examining two classes of approaches and have formulated a suite of methods of practical utility the first class focuses on estimating total magnetization direction and then incorporating the resultant direction into an inversion algorithm that assumes a known direction thesecondclassfocusesondirectinversionoftheamplitude of the magnetic anomaly vector amplitude data depend weaklyuponmagnetizationdirectionandareamenabletodirect inversion for the magnitude of magnetization vector in 3d subsurface two sets of high resolution aeromagnetic dataacquiredfordiamondexplorationinthecanadianarctic areusedtoillustratethemethods usefulness

rb sr and k ar ages on minerals at temperatures of 300 400 c from deep wells in the larderello geothermal field italy rb sr and k ar ages have been obtained on six biotites two muscovites and one hornblende from samples of micaschist gneiss and amphibolite of lower paleozoic to precambrian age at a depth exceeding 2 000 m in basement rocks of the larderello travale geothermal region most of the data cluster in the range 2 5 3 7 ma revealing the existence of a pliocene thermal event to which the origin of the field may be attributed the resulting duration of the larderello geothermal field is unexpectedly long in the basement levels of the two wells examined unstabilized minimum temperatures of 290 and 380 c were measured all the biotites show almost complete 40ar and 87sr retention at the measured well temperatures petrologic evidence stilpnomelane stability and experimental data activation energies and diffusion coefficients also favour a closure temperature above 400 c for rb sr and k ar in biotites in agreement with recent direct experimental determinations

kar ages of clay size concentrates from the mineralisation of the pedroches batholith spain and evidence for mesozoic hydrothermal activity associated with the break up of pangaea abstract the k ar ages of 32 clay concentrates extracted from samples of ore gangue and wallrock associated with mineralisation in the pedroches batholith lie in the range 119 285 ma although some of the mineralisation is of permian age more than half of the ages lie between 210 and 230 ma and indicate a hydrothermal event at this triassic time a comparison with age data for mineralisation and certain anorogenic magmatism in other areas of the north atlantic reveals a consistent pattern of a major event at ca 210 230 ma and a minor event at ca 160 ma with little cretaceous or tertiary activity it is proposed that the ca 210 230 ma event was related to an initial rapid fracturing of the crust associated with the break up of pangaea which was related with an increase in the geothermal gradient and penetration of the deep crust by surface waters which returned via both new and rejuvenated fissure systems

origin of au rich carbonate hosted replacement deposits of the kassandra mining district northern greece evidence for late oligocene structurally controlled and zoned hydrothermal systems

the structure and kinematics of the southeastern zagros fold thrust belt iran from thin skinned to thick skinned tectonics 1 we present the first complete balanced cross section across the southeastern zagros fold thrust belt zftb the following main structural features emerge from this section 1 in the south of the zftb the proterozoic to recent sedimentary sequence has been decoupled from its panafrican basement along the ductile basal evaporites and folded into a series of large detachment anticlines ongoing shortening of these structures has resulted in migration of the basal salt layers into the cores of the anticlines and propagation of forelimb thrusts 2 in the north of the zftb deep seated ramps have folded the hanging wall rocks and produced imbrications and duplex structures within the higher levels of the sedimentary sequence 3 out of sequence thrusts linked to major seismogenic basement faults have cut through the structures in the cover of the zftb a three step incremental restoration of the section shows that two main phases of deformation can be separated in the tectonic evolution of the zftb a mio pliocene thin skinned phase in the course of which most of the structures in the cover were generated followed by a pliocene to recent thick skinned phase expressed as out of sequence faulting in the cover which is currently underlined by the seismicity within the basement in plan view the initial structures of the southeastern zftb developed with a curved shape essentially controlled by the shape and thickness of the underlying proterozoic salt basin i e the jura style in the following basement involved phase out of sequence thrusts cut at oblique angles through the preexisting structures of the cover the total shortening absorbed in the cover amounts to at least 45 km corresponding to a ratio of 22

basement faulting and the focal depths of the larger earthquakes in the zagros mountains iran summary the present day seismicity of the zagros seems to occur on high angle reverse faults distributed across the whole width of the belt it does not indicate activity on a single inclined thrust surface and there do not seem to have been any well located events at intermediate depths modelling of the long period teleseismic body waves of seven large earthquakes presented here shows their focal depths to be in the range 8 15 km this is thought to indicate faulting in the uppermost basement beneath the sedimentary cover though the absence of published seismic refraction results renders the sediment thickness uncertain faulting of this type and depth may occur on inherited normal faults which have subsequently been reactivated as thrusts such reactivation allows considerable shortening to take place in the early stages of continental collision without the subduction or excessive thickening of continental crust

structure of the mountain front flexure along the anaran anticline in the pusht e kuh arc nw zagros iran insights from sand box models this is a contribution of the group of dynamics of the lithosphere gdl financed by a collaborative project between the institute of earth sciences jaume almera csic of barcelona spain and statoilhydro tehran and statoilhydro research centre with the partial support of project team consolider ingenio 2010 no csd 2006 00041

magma emplacement in a thrust ramp anticline the gavorrano granite northern apennines italy 1 magma emplacement in the upper crust is often associated with crustal extension whereby space for intrusions is made by dilation along transtensive and strike slip faults the lenticular shape of several intrusions indicates that a further mechanism for magma intrusion is laccolith emplacement with roof uplift of the overburden additionally melts exploit rheological discontinuities e g sedimentary layering during their ascent we present an emplacement model for intrusion of the shallow level gavorrano granite northern apennine italy which is located at the core of an open anticline the shape of the intrusion and structural features of the host rocks are indicative of a synkinematic emplacement in a growing thrust anticline space was provided by the opening of dilatation zones at the core of anticline as a consequence of different amounts of translation between hanging wall and footwall units which were separated by evaporitic rocks these evaporitic units acted as major decollement layers analog models provide results in good agreement with the structural setting of the anticline and emphasize the possibility that melts filled the dilatation zone with the decollement layers further facilitating intrusion