the southern caspian a compressional depression floored by a trapped modified oceanic crust the south caspian intracontinental depression floored by oceanic basement is a relatively stable block with minor deformation surrounded by active fold thrust belts of arcuate form talesh alborz and kopeh dagh mountains which have undergone intense late cainozoic crustal shortening the basin is interpreted as a neogene quaternary compressional depression bounded by multi role mountain bordering reverse faults and apparently floored by a late paleozoic triassic or late mesozoic early tertiary modified oceanic crust trapped along an old geosuture it may be a relic of an old paleozoic triassic ocean or else a marginal sea developed behind a mesozoic paleogene ocean and analysis of geological and geophysical data enables a scheme to be suggested the general arcuate shape of the alborz and the talesh bordering mountain belts follows the pattern of the supposed rigid and thickened ocean crust of south caspian depression a tectono sedimentary study of the south caspian region coupled w

double vein ore bearing vs ore free structures in the xitian ore field south china implications for fluid evolution and mineral exploration abstract two types of spatially and temporally associated hydrothermal veins ore bearing and ore free occur as double vein structures in the xitian ore field south china here we investigated the genetic relationship material provenance fluid properties and prospecting significance of the co developed veins in the granite related fault controlled vein type xiangdong w goudanlan w chaling pb zn and xinggao fluorite deposits of the xitian ore field focusing on two common minerals quartz and zircon petrographic cl microthermometric and h o isotopic analyses of stage i and stage ii quartz in both the ore bearing and ore free veins of these deposits document two episodes of hydrothermal activity the first episode involved a high temperature up to 370 high salinity up to 28 nacl equiv high 18o 2 1 to 7 2 and high 2h 82 to 54 mean 68 n 13 fluid that corresponds to the main magmatic hydrothermal stage of the deposits and the second episode involved a low temperature down to 90 low salinity down to 1 nacl equiv low 18o 8 8 to 5 3 and low 2h 83 to 60 mean 73 n 6 fluid that represents an accessary mineralization stage variations in fluid inclusion types and compositions indicate that the processes of fluid mixing boiling cooling and degassing played important roles in mineralization and that magmatic fluid became less important than meteoric water along during the formation of ore free veins la icpms u pb dating reveals totally different age populations for these veins zircons from the ore bearing quartz veins yield older and more variable ages pre devonian 400 ma n 68 that are similar to that of the local basement sedimentary rocks whereas zircons from the ore free quartz veins yield younger and less variable ages triassic 250 200 ma n 31 and jurassic 170 140 ma n 13 that are identical to those of the host granite zircons in addition the ore free veins show lower temperatures salinities and total rees as recorded by quartz but greater alteration as reflected by cl and trace element features of hydrothermally altered zircons and wider vein size than the ore bearing veins we propose a mineral water separation model to explain the formation of the double vein structures in this model ore bearing veins and ore free veins formed in succession during faulting events ore bearing veins formed first in the smaller fractures and were the dominant sites of mineralization whereas the ore free veins served as dissipating passageways for residual water and silica in larger fractures we suggest that the mineral water separation model has good application prospects in mineral exploration and that zircons can be applied as an indicative mineral to differentiate the mineralization potential of different types of quartz veins

late eocene oligocene post collisional monzonitic intrusions from the alborz magmatic belt nw iran an example of monzonite magma generation from a metasomatized mantle source abstract a potassic magmatic association in the zagros hinterland of the tethyan orogen in iran is identified and characterized for relevant geochronologic and petrologic features new data including a combination of field relations u pb zircon geochronology and rock geochemistry come from seven plutons khankandi shaivar dagh yuseflu mizan saheb divan roudbar and abhar that form the arasbaran taroum batholith atb which forms part of the alborz magmatic belt amb of nw iran zircon shrimp ages range from 38 32 0 17 ma 38 94 0 42 ma and 37 78 0 28 ma for magma pulses of the abhar pluton at the east of the batholith to 24 51 0 27 ma and 23 55 0 47 ma for pulses of the mizan pluton at the west considering these ages and the previously published ones together emplacement of the batholith took place during late eocene and oligocene from 38 to 23 ma with an age progression from se to nw at a rate of 2 cm year the whole batholith is characterized by potassic rocks with k2o 2 wt in gabbros and diorites sio2 6 wt are normally found in rocks with intermediate silica contents of about 60 wt sio2 these intermediate silica rocks are truly monzonites and are the most abundant in each pluton with regard to trace elements the monzonitic rocks of the atb show some of the typical signatures of arc magmatism depletion in nb and ti most samples contain moderate contents of sr 500 800 ppm close to similar potassic magmas forming cenozoic complexes in central iran the relatively moderate sr y and la yb ratios suggest that atb magmas retain some adakitic signatures from the source region geochemical modeling is performed by using melt compositions and phase relations calculated with melts software combined with experimental data and trace element signatures we conclude that monzonitic and shoshonitic magmas of some plutons of the atb shaivar dagh kahnkandi and yuseflu have an adakitic signature inherited from early melts that metasomatized the peridotite mantle decompression melting at a relatively low pressure of a metasomatized mantle source is the most plausible explanation for the generation of potassic magmas of the atb the lack of adakitic signature in three plutons supports the hypothesis that trace element features are related to processes in the source the tectonic implications are straightforward first subduction is needed to cook a metasomatized mantle source by fluxing of calc alkaline melts adakitic or not from the subduction zone second lithosphere extension is needed to carry metasomatized mantle to melt and to generate the potassic magmatism that formed the arasbaran taroum batholith as well as other cenozoic potassic magmas of the alborz magmatic belt in nw iran

post collisional polycyclic plutonism from the zagros hinterland the shaivar dagh plutonic complex alborz belt iran the petrological and geochronological study of the cenozoic shaivar dagh composite intrusion in the alborz mountain belt nw iran reveals important clues to decipher complex relations between magmatic and tectonic processes in the central sectors of the tethyan alpine himalayan orogenic belt this pluton is formed by intrusion at different times of two main magmatic cycles the older cycle 1 is formed by calc alkaline silicic rocks which range in composition from diorites to granodiorites and biotite granites with abundant mafic microgranular enclaves the younger cycle cycle 2 is formed by k rich monzodiorite and monzonite of marked shoshonitic affinity the latter form the larger volumes of the exposed plutonic rocks in the studied complex zircon geochronology laser ablation icp ms analyses gives a concordia age of 30 8 2 1 ma for the calc alkaline rocks cycle 1 and a range from 23 3 0 5 to 25 1 0 9 ma for the shoshonitic association cycle 2 major and trace element relations strongly support distinct origins for each magmatic cycle rocks of cycle 1 have all the characteristic features of active continental margins shoshonitic rocks cycle 2 define two continuous fractionation trends one departing from a k rich basaltic composition and the other from an intermediate k rich composition a metasomatized mantle origin for the two shoshonitic series of cycle 2 is proposed on the basis of comparisons with experimental data the origin of the calc alkaline series is more controversial but it can be attributed to processes in the suprasubduction mantle wedge related to the incorporation of subducted melanges in the form of silicic cold plumes a time sequence can be established for the processes responsible of the generation of the two magmatic cycles first a calc alkaline cycle typical of active continental margins and second a k rich cycle formed by monzonites and monzodiorites this sequence precludes the younger potassic magmas as precursors of the older calc alkaline series by contrast the older calc alkaline magmas may represent the metasomatic agents that modified the mantle wedge during the last stages of subduction and cooked a fertile mantle region for late potassic magmatism after continental collision

igneous garnet and amphibole fractionation in the roots of island arcs experimental constraints on andesitic liquids to evaluate the role of garnet and amphibole fractionation at conditions relevant for the crystallization of magmas in the roots of island arcs a series of experiments were performed on a synthetic andesite at conditions ranging from 0 8 to 1 2 gpa 800 1 000 c and variable h2o contents at water undersaturated conditions and fo2 established around qfm garnet has a wide stability field at 1 2 gpa garnet amphibole are the high temperature liquidus phases followed by plagioclase at lower temperature clinopyroxene reaches its maximal stability at h2o contents 9 wt at 950 c and is replaced by amphibole at lower temperature the slopes of the plagioclase in boundaries are moderately negative in text t text x text h 2 text o space at 0 8 gpa garnet is stable at magmatic h2o contents exceeding 8 wt and is replaced by spinel at decreasing dissolved h2o the liquids formed by crystallization evolve through continuous silica increase from andesite to dacite and rhyolite for the 1 2 gpa series but show substantial enrichment in feo mgo for the 0 8 gpa series related to the contrasting roles of garnet and amphibole in fractionating fe mg in derivative liquids our experiments indicate that the stability of igneous garnet increases with increasing dissolved h2o in silicate liquids and is thus likely to affect trace element compositions of h2o rich derivative arc volcanic rocks by fractionation garnet controlled trace element ratios cannot be used as a proxy for slab melting or dehydration melting in the deep arc garnet fractionation either in the deep crust via formation of garnet gabbros or in the upper mantle via formation of garnet pyroxenites remains an important alternative despite the rare occurrence of magmatic garnet in volcanic rocks

post eocene volcanics of the abazar district qazvin iran mineralogical and geochemical evidence for a complex magmatic evolution abstract the style of volcanism of post eocene volcanism in the alborz zone of northern iran is different to that of eocene volcanism karaj formation indeed the volcanic succession of the abazar district located in a narrow volcanic strip within the alborz magmatic assemblage is characterized by distinct mineralogical and chemical compositions linked to a complex magmatic evolution the succession was produced by explosive eruptions followed by effusive eruptions two main volcanic events are recognized 1 a thin rhyolitic ignimbritic sheet underlain by a thicker lithic breccia and 2 lava flows including shoshonite latite and andesite that overlie the first event across a reddish soil horizon plagioclase in shoshonite an48 92 shows normal zoning whereas plagioclase in latite and andesite an48 75 has a similar composition but shows reverse and oscillatory zoning quilf temperature calculations for shoshonites and andesites yield temperatures of 1035 c and 1029 c respectively the geothermometers proposed by ridolfi et al 2010 and holland and blundy 1994 yield temperatures of 960 c and 944 c for latitic lava respectively the samples of volcanic rock show a typical geochemical signature of the continental arc regime but the andesites clearly differ from the shoshonites the latites and the rhyolites the mineralogical and chemical characteristics of these rocks are explained by the following petrogenesis 1 intrusion of a hot mantle depth mafic shoshonitic magma which differentiated in the magma chamber to produce a latitic and then a rhyolitic liquid 2 rhyolitic ignimbritic eruptions from the top of the magma chamber following by shoshonitic and then latitic extrusions 3 magma mingling between the latitic and andesitic magmas as indicated by the occurrence of andesite clasts within the latite and 4 andesitic effusions the youngest volcanic events in the alborz zone show a close chemical relationship with continental arc rocks indicating that they formed in a continental collision setting

cenozoic evolution of neotethys and implications for the causes of plate motions africa north america eurasia plate circuit rotations combined with red sea rotations and new estimates of crustal shortening in iran define the cenozoic history of the neotethyan ocean between arabia and eurasia the new constraints indicate that arabia eurasia convergence has been fairly constant at 2 to 3 cm yr since 56 ma with slowing of africa eurasia motion to 1 cm yr near 25 ma coeval with the opening of the red sea ocean closure occurred no later than 10 ma and could have occurred prior to this time only if a large amount of continental lithosphere was subducted suggesting that slowing of africa significantly predated the arabia eurasia collision these kinematics imply that africa s disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern eurasia slowed its motion the slow steady rate of northward subduction since 56 ma contrasts with strongly variable rates of magma production in the urumieh dokhtar arc implying magma production rate in continental arcs is not linked to subduction rate

physical chemical conditions of the teide volcanic system tenerife canary islands the teide volcano 3717 m is the central structure of the island of tenerife and at present its morphology is that of a stratovolcano which has grown on a large caldera with a collapse 17 km in diameter which was generated some 0 6 million years ago the different studies that have been carried out seem to indicate that in a oversimplified model there is an intermediate magma chamber with an approximate volume of 30 km3 and located 2 3 km below the actual base of the caldera i e almost at sea level with a temperature of 430 50 c and a pressure of 400 100 bar the summit fumarole emissions are 85 c and are formed mainly of co2 with small amounts of sulphur species h2 ch4 and he the water vapor 68 82 emitted with the gases comes from the vaporization of a perched aquifer in the upper cone as shown by the isotopic analyses

magmatic gases in well fluids aid the mapping of the flow pattern in a geothermal system abstract gas composition and silica concentrations of well fluids are used in conjunction with pressure temperature and enthalpy data to obtain a model of the drilled part of the krafla geothermal field northeast iceland a magma chamber is located at 3 8 km depth under the field magmatic gases emanate from the chamber and travel via a channel reaching the surface at the hveragil eruptive fissure the composition of the gases is apparently modified on the way in that sulphur which presumably is in the form of sulphur dioxide to begin with is removed on the way and what remains is in the form of hydrogen sulphide at the end it is suggested that the major removal mechanism is the deposition of pyrite and pyrrhotite during the passage of the gases through the hydrothermal system the hydrothermal system is divided into a lower part whose temperature exceeds 300 c and whose fluids are to a varying extent affected by the magmatic gases and an upper part whose temperature is ca 200 c this upper part is a run off from the lower part but the magmatic effects have mostly disappeared there

high sr y and la yb ratios the meaning of the adakitic signature abstract the name of adakite is used to describe a far too large group of rocks whose sole common feature is high sr y and la yb ratios however such a signature can be achieved via different processes melting of a high sr y and la yb source deep melting with abundant residual garnet fractional crystallization or afc or interactions of felsic melts with the mantle causing selective enrichment in lree and sr over hree a database of the compositions of adakitic rocks including high silica and low silica adakites martin h smithies r h rapp r p moyen j f champion d c 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 2 1 24 continental adakites and archaean adakites was assembled geochemical modeling of the potential processes is used to interpret it and reveals that 1 the classical model of slab melting provides the best explanation for the genesis of high silica adakites 2 low silica adakites are explained by garnet present melting of an adakite metasomatized mantle i e at depths greater than 2 5 gpa 3 continental adakites is a term encompassing a huge range of rocks with a corresponding diversity of petrogenetic processes and most of them are different from both low and high silica adakites 4 archaean adakites show a bimodal composition range with some very high sr y examples similar to part of the ttg suite reflecting deep melting 2 0 gpa of a basaltic source with a relatively high sr y while lower sr y rocks formed by shallower 1 0 gpa melting of similar sources comparison with the archaean ttg suite highlights the heterogeneity of the ttgs whose composition spreads the whole combined range of hsa and archaean adakites pointing to a diversity of sources and processes contributing to the ttg suite

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

sr isotope diversity of hot spring and volcanic lake waters from zao volcano japan abstract the ratio of 87 sr 86 sr was measured from different water samples of thermal mineral hot spring as well as crater lake and meteoric origins in order to specify the location and to verify the detailed model of a volcano hydrothermal system beneath zao volcano the ratio showed a trimodal distribution for the case of thermal mineral water 0 7052 0 7053 type a zao hot spring 0 7039 0 7043 type b okama crater lake and shin funkiko hot spring and 0 7070 0 7073 type c gaga aone and togatta hot springs respectively however in comparison the ratio was found to be higher for meteoric waters 0 7077 0 7079 the water from the central volcanic edifice type b was found to be similar to that of nearby volcanic rocks in their sr isotopic ratio this indicates that the sr in water was derived from shallow volcanic rocks the 87 sr 86 sr ratio for water from the zao hot spring type a was intermediate between those of the pre tertiary granitic and the quaternary volcanic rocks thus suggesting that the water had reacted with both volcanic and granitic rocks the location of the vapor liquid separation was determined as the boundary of the pre tertiary granitic and the quaternary volcanic rocks by comparing the results of this strontium isotopic study with those of kiyosu and kurahashi kiyosu y kurahashi m 1984 isotopic geochemistry of acid thermal waters and volcanic gases from zao volcano in japan j volcanol geotherm res 21 313 331

isotopic variation of the hydrothermal system on vulcano island italy the isotopic and chemical composition of thermal waters and the isotopic composition of high temperature fumarolic steam at vulcano island indicate an evolution of the hydrothermal system from its magmatic origin through interaction with rocks and mixing with meteoric water seawater is not a component in this system the isotopic values of the fumaroles indicate a local magmatic composition of 7 to 8 18o and 5 to 15 d the high d values of this vapor may reflect contamination of the magma by connate water the isotopic and chemical composition of water from well w2 indicates the existence of geothermal fluid formed by mixing of hcl and so2 bearing condensates of volcanic origin with groundwater with subsequent evolution via water rock interaction the estimated isotopic composition of the geothermal water is 18o 1 and d 5 local shallow seismic events result in a temporary increase in fracture permeability enabling the mixing of magmatic vapor with groundwater or geothermal water tectonic activity associated with deep structures appears to increase the contribution of magmatic vapor to the fumaroles

arabia eurasia continental collision insights from late tertiary foreland basin evolution in the alborz mountains northern iran a poorly understood lag time of 15 20 m y exists between the initial arabia eurasia continental collision in late eocene to early oligocene time and the acceleration of tectonic and sedimentary processes across the collision zone in the early to late miocene the late eocene to miocene pliocene clastic and shallow marine sedimentary rocks of the kond eyvanekey and semnan basins in the alborz mountains northern iran offer the possibility to track the evolution of this orogen in the framework of collision processes a transition from volcaniclastic submarine deposits to shallow marine evaporites and terrestrial sediments occurred shortly after 36 ma in association with reversals in sediment provenance strata tilting and erosional unroofing these events followed the termination of subduction arc magmatism and marked a changeover from an extensional to a contractional regime in response to initiation of continental collision with the subduction of stretched arabian lithosphere this early stage of collision produced topographic relief associated with shallow foreland basins suggesting that shortening and tectonic loading occurred at low rates starting from the early miocene 17 5 ma flexural subsidence in response to foreland basin initiation occurred fast sediment accumulation rates and erosional unroofing trends point to acceleration of shortening by the early miocene we suggest that the lag time between the initiation of continental collision 36 ma and the acceleration of regional deformation 20 17 5 ma reflects a two stage collision process involving the soft collision of stretched lithosphere at first and hard collision following the arrival of unstretched arabian continental lithosphere in the subduction zone

quaternary syn collision magmatism from the iran turkey borderlands quaternary basaltic and andesitic lavas from the nw iran eastern turkey border area are related to the active arabia eurasia collision the lavas occur within the turkish iranian plateau which ceased crustal thickening before the establishment of a number of volcanic centres within iran and eastern turkey beginning at 10 ma models for generating syn collision magmatism in eastern anatolia have invoked slab break off beneath the thick crust and thin mantle lithosphere of the cenozoic east anatolia accretionary complex and or partial loss of the lower lithosphere here we report geochemical and sm nd rb sr data from a 200 km long n s traverse that samples volcanic flows in nw iran many of which originate from centres in turkey such as ararat and tendurek samples are transitional alkali tholeiitic basalts and andesites ararat samples have lower nb lower large ion lithophile element lile concentrations with 143nd 144nd 0 51290 other volumetrically smaller centres have higher nb higher lile with 143nd 144nd 0 51265 abundances of lile and nb increase from north to south the presumed degree of partial melting increases in the opposite direction away from the arabia eurasia suture melting is inferred to have taken place in the spinel lherzolite field largely from a continental lithosphere source influenced by mesozoic and early cenozoic neo tethyan subduction but a separate source with long term enrichment is needed to explain the high nb lower 143nd 144nd compositions

geology re os age s and o isotopic composition of the lar porphyry cu mo deposit southeast iran abstract the lar porphyry cu mo deposit is located 20 km northeast of zahedan in the sistan suture zone ssz in the southeastern part of iran lar is a sub economic porphyry cu mo deposit with average grades of 0 16 cu 0 01 mo and 0 66 ppb au the cu mo mineralization developed in post collisional shoshonitic syenitic to monzonitic intrusions in an oligocene igneous complex known as the lar igneous complex lic the host and country rocks have undergone variable degrees of supergene and hypogene alteration including silicic potassic propylitic phyllic and argillic alteration the cu mo mineralization is mainly controlled by nnw striking faults and fractures and occurs as quartz veins and veinlets disseminated sulfides and stockworks the mineralization can be divided into two types hypogene and supergene hypogene mineralization is characterized by chalcopyrite pyrite bornite molybdenite and magnetite whereas supergene mineralization is characterized by enargite covellite chalcocite digenite malachite azurite and iron hydroxides sulfur isotope values for hypogene sulfides range from 0 28 to 1 76 and suggest an igneous source or mantle derived origin for sulfur the 18o values for quartz in mineralized quartz veins range from 9 6 to 11 5 these values would be in equilibrium with waters having calculated 18oh2o values of 9 3 11 2 suggesting magmatic water re os dating of two molybdenite samples from two different drill holes yields dates of 29 72 0 11 and 31 95 0 11 suggesting that the system was active for at least 2 0 m y

high magmatic flux during alpine himalayan collision constraints from the kal e kafi complex central iran voluminous eocene gabbros to granites of the kal e kafi backarc composite intrusion were emplaced prior to the alpine himalayan collision in the central iranian backarc but the reasons for precollisional high arc and backarc magmatic productivity 60 53 ma are unclear diagnostic geochemical signatures are high k2o sr contents and successively depleted middle rare earth element ree patterns reflecting a highly metasomatized source and an increasing role for amphibole and garnet 0 10 in the relatively younger granites release of concealed k sr rich fluids from oceanic fractures and faults during buckling and bulging of a precollisional choking oceanic slab and melting of phlogopite bearing lithosphere with subsequent interaction of the melt with lower crustal garnet amphibolite of a 40 km thick crust can explain the kal e kafi geochemical and isotopic signatures gravimetric data indicating a 39 km present day backarc crustal thickness are consistent with geochemical results but also imply little if any collisional crustal thickening of the central iranian plateau high eocene arc backarc melt flux prior to collision in this region reflects vigorous thermal convection which may in fact be diagnostic of collisional magmatism explaining the presence of postcollisional shoshonitic melts in this and other collisional orogenic settings

on the motion of hawaii and other mantle plumes abstract the hawaiian hotspot and its prominent bend at 47 ma have figured prominently in the development of ideas on the nature of mantle plumes and plate motion here i review paleomagnetic analyses associated with ocean drilling program odp leg 197 which together with studies of plate circuits and geodynamic modeling results indicate southward motion of the hawaiian hotspot during formation of the emperor seamounts these analyses confirm the long posited idea that mantle plumes should be influenced by mantle flow moreover these results indicate that late cretaceous early paleogene hotspot motion was the dominant factor in forming the emperor track and thus the famous bend morphology an important corollary of this finding on hotspot motion is that long term polar wander of earth which has been inaccurately assessed by viewing paleomagnetic data in a fixed hotspot reference frame has been far less than previously thought salient points for future research raised by the odp leg 197 paleomagnetic results include the scale of mantle flow recorded by hotspot track segments and the underlying processes that cause track segments to be dominated by mantle flow rather than plate motion for given time intervals

phase relationships in the system kalsio 4 mg 2 sio 4 sio 2 h 2 o as a model for hybridization between hydrous siliceous melts and peridotite the system kalsio4 mg2sio4 sio2 h2o includes model representatives of 1 hydrous siliceous magma from subducted oceanic crust the eutectic liquid in kalsi3o8 sio2 h2o and 2 the overlying mantle peridotite the assemblage forsterite enstatite fo en in a series of partly schematic isobaric isothermal sections the products of hybridization between the model materials at pressures between 20 and 30 kbar have been determined the liquid dissolves peridotite components with little change in composition hybridization is not a simple mixing process because of the incongruent melting of peridotitic assemblages with phlogopite ph hybridization causes solidification of the liquid with products a sequence of three mineral assemblages ph ph quartz qz and ph en the products represent an absolute geochemical separation and local concentration of all potassium from the liquid hybridization is accompanied by h2o saturation of melts and evolution of aqueous fluid although there are significant differences between the melt composition and that of the magma rising from subducted oceanic slab and between fo en and the mantle rock extrapolation of the results suggests that the conclusions can probably be extended to mantle conditions with sodium in the melt and jadeitic clinopyroxene included in the hybrid products

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

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

zagros orogeny a subduction dominated process this paper presents a synthetic view of the geodynamic evolution of the zagros orogen within the frame of the arabia eurasia collision the zagros orogen and the iranian plateau preserve a record of the long standing convergence history between eurasia and arabia across the neo tethys from subduction obduction processes to present day collision from 150 to 0 ma we herein combine the results obtained on several geodynamic issues namely the location of the oceanic suture zone the age of oceanic closure and collision the magmatic and geochemical evolution of the eurasian upper plate during convergence as testified by the successive sanandaj sirjan kermanshah and urumieh dokhtar magmatic arcs the p t t history of the few zagros blueschists the convergence characteristics across the neo tethys kinematic velocities tomographic constraints subduction zones and obduction processes together with a survey of recent results gathered by others we provide lithospheric scale reconstructions of the zagros orogen from 150 to 0 ma across two sw ne transects the evolution of the zagros orogen is also compared to those of the nearby turkish and himalayan orogens in our geotectonic scenario for the zagros convergence we outline three main periods regimes 1 the mid to late cretaceous 115 85 ma corresponds to a distinctive period of perturbation of subduction processes and interplate mechanical coupling marked by blueschist exhumation and upper plate fragmentation 2 the paleocene eocene 60 40 ma witnesses slab break off major shifts in arc magmatism and distributed extension within the upper plate and 3 from the oligocene onwards 30 0 ma collision develops with a progressive sw migration of deformation and topographic build up sanandaj sirjan zone 20 15 ma high zagros 12 8 ma simply folded belt 5 0 ma and with partial slab tear at depths 10 ma to present our reconstructions underline the key role played by subduction throughout the whole convergence history we finally stress that such a long lasting subduction system with changing boundary conditions also makes the zagros orogen an ideal natural laboratory for subduction processes

hydrogen isotopic compositions of hydrogen and methane from some volcanic areas in northeastern japan abstract d h ratios of volcanic condensates hydrogen and methane collected from hachimantai zao azuma nasu and kusatsu shirane volcanic areas in northeastern japan were determined together with chemical components on the basis of the isotopic ratios for volcanic condensates it is concluded that most of the water vapor is essentially local surface water which has been heated and slightly enriched in18o by exchange with silicates d values of hydrogen and methane range from 220 to 515 smow and from 180 to 487 smow respectively the d h ratio in volcanic hydrogen indicates that hydrogen may have isotopically equilibrated with water vapor at temperatures between 200 and 400 c the d value of methane also suggests that volcanic methane has been in isotopic disequilibrium with the water vapor and hydrogen and that most of the methanes may be thermogenic methanes produced by pyrolysis of carbonaceous materials

subduction history of the tethyan region derived from seismic tomography and tectonic reconstructions 1 in the mantle underneath the tethyan suture zone large volumes of positive velocity anomalies have been imaged by seismic tomography and interpreted as the present day signature of subducted tethyan lithosphere we investigate the mesozoic cenozoic subduction history of the region by integrating independent information from mantle tomography and tectonic reconstructions three different subduction scenarios for the tethyan oceanic lithosphere representative for the available tectonic reconstructions are used to predict the present thermally anomalous volumes associated with the lithospheric surface subducted since the late mesozoic next these predicted thermal volumes and their expected positions are compared to the relevant anomalous volumes derived from seismic tomographic images in this analysis we include among others the possible effects of ridge subduction and slab detachment after the cenozoic continental collisions absolute plate motion and slab thickening in the mantle our preferred subduction model comprises the opening of large back arc oceanic basins within the eurasian margin the model points to slab thickening by a factor of 3 in the mantle in which case the estimated volumes allow for active oceanic spreading 1 2 5 cm yr in the tethyan lithosphere during convergence our results further indicate the occurrence of early oligocene slab detachment underneath the northern zagros suture zone followed by both westward and eastward propagation of the slab tear and diachronous eocene to miocene slab detachment below the eastern to western himalayas free sinking rates of the detached material of 2 cm yr in the lower mantle provide the best fit between the tomographic mantle structure and our tethyan subduction model

the gabbro shoshonitic monzonite granodiorite association of khankandi pluton alborz mountains nw iran abstract the khankandi pluton forms part of a group of gabbro granodiorite intrusions in the alborz mountains of nw iran a petrographical and geochemical study of this plutonic association reveals the existence of several magmatic cycles with different origins and slight differences in age the oldest cycle c1 is represented by granodiorites a second cycle c2 is formed by a gabbro monzonite association with a clear shoshonitic affinity that dominates most of the intrusive volume gabbros and monzonites form a co magmatic association zircons from the monzonites were analyzed by la icp ms for u pb dating an average age of 28 9 ma ranging from 23 7 to 33 6 ma was obtained gabbros monzonites and granodiorites share a nearly common isotopic ratio for sr and nd both initial sr and nd ratios are clustered within a narrow range from 0 7045 to 0 7047 for the 87sr 86sr ratio and end from 1 46 to 1 89 comparison with experimental studies together with mantle like isotopic ratios and comparisons of ree patterns points to an origin by variable melting rates from a common metasomatised mantle source for gabbros and monzonites melting of a subducted melange is suggested for the granodiorite magmas predating the gabbro monzonite intrusion the two sources a metasomatised mantle and ascending silicic plumes are direct consequence of subduction

isotopic composition of acid sulfate chloride waters and volcanic steam from some volcanoes in northeastern japan abstract acid sulfate chloride water and volcanic steam samples collected from andesitic volcanoes in northeastern japan have been examined for chemical and isotopic compositions the acid thermal waters and fumarolic condensates are significantly enriched in d as well as 18 o compared to the respective local surface waters although their compositions are variable the chemical and isotopic evidence suggests that these waters may be mixtures of magmatic and meteoric waters this fact is also supported by the n 2 ar and he ar ratios of fumarolic gases and 34 s values of sulfur species in the acid thermal waters

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

the caucasus an actual example of the initial stages of continental collision abstract a field study of the neotectonics of the georgian caucasus is combined with geophysical geodetic and geological information in order to obtain a mechanical model of actual deformation the analysis of satellite photos together with topographical and geological maps shows that the great caucasus is bisected by a nne trending sinistral strike slip fault zone the western great caucasus is thrusted to the south over the rioni basin while on the other hand its northern flank is a monocline that descends gently into the russian platform active volcanism is present from elbruz to kazbeg the eastern great caucasus is limited by thrusts to the north and to the south and intermediate structures are disposed in a fan like shape no recent volcanism is observed the eastern limit of the chain is a nnw trending dextral strike slip fault zone seismicity from a local network illustrates the activity of the thrusts and gives evidence for the strike slip faults microtectonic data confirm the recent activity and the sinistral character of the borjomi kazbeg strike slip fault the strike slip faults bordering the eastern caucasus may be seen as the limits of a plastic wedge in front of the arabian plate at an early stage of continental collision

fluid inclusion and stable isotope constraints on ore genesis of the zajkan epithermal base metal deposit tarom hashtjin metallogenic belt nw iran in the zajkan pb zn cu au ag deposit of the tarom hashtjin metallogenic belt thmb northwest iran mineralization occurs as quartz base metal sulfide veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation four stages of ore formation are identified at zajkan 1 quartz chalcopyrite pyrite veins 2 quartz galena sphalerite chalcopyrite pyrite veins and breccias 3 quartz hematite veins and breccias and 4 barren quartz carbonate veinlets the primary metallic minerals are pyrite chalcopyrite sphalerite galena and trace amounts of hematite gangue minerals are mainly quartz sericite chlorite and calcite the main wall rock alteration is silicification and intermediate argillic and propylitic alteration the coexistence of different types of fluid inclusions lv vl and v in individual fluid inclusion assemblages in quartz and sphalerite suggests boiling and heterogeneous trapping excluding the heterogeneously entrapped fluid inclusions the microthermometric measurements of primary lv fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273 degrees c from fluids with salinities between 1 7 and 6 4 wt nacl equiv the oxygen isotopic compositions delta o 18 water vsmow of 3 7 to 1 1 parts per thousand indicate that the ore forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore stages sulfur isotopic values of sulfide minerals vary over a narrow range from 5 0 to 0 9 parts per thousand vcdt averaging 2 2 parts per thousand vcdt suggesting that sulfur was derived from a homogeneous magmatic source the fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at zajkan our data suggest that the zajkan deposit is an intermediate sulficiation style epithermal mineralization the estimated ore formation depth of zajkan indicates minor denudation in the region and may imply a great prospecting potential for other epithermal mineralization in the thmb

post collisional miocene adakitic volcanism in nw iran geochemical and geodynamic implications abstract in nw iran about 30 subvolcanic porphyritic dacitic to rhyodacitic domes 1 5 km2 are intruded into a variety of rock sequences from permian to early miocene in age these subvolcanic domes occur along the north tabriz north misho and darediz dextral faults in the northern part of the urumieh dokhtar magmatic arc udma of iran the udma contains intrusive and extrusive rocks of eocene quaternary age geochemical data indicate that the subalkalic dacitic to rhyodacitic rocks have an adakitic composition with na2o k2o 1 high sr 346 737 ppm mg 0 48 and low y 10 20 ppm and hree fractionated ree patterns ce yb n 9 76 absence of negative eu anomaly low content of y nb ti and high sr y 20 58 and ce yb n ratios suggest that the source was probably amphibole eclogite or garnet eclogite possibly generated during subduction of the neo tethyan oceanic slab beneath the central iran microplate the adakitic volcanism was followed by eruption of alkaline magmas including ultrapotassic shoshonitic and lamprophyric volcanic rocks slab melting occurred after cessation of subduction possibility from the detached slab transtensional tectonics accompanied by a locally extensional stress regime may account for magma genesis and ascent

intermediate sulfidation type base metal mineralization at aliabad khanchy tarom hashtjin metallogenic belt nw iran abstract the aliabad khanchy epithermal base metal deposit is located in the tarom hashtjin metallogenic belt thmb of northwest iran the mineralization occurs as cu bearing brecciated quartz veins hosted by eocene volcanic and volcaniclastic rocks of the karaj formation ore formation can be divided into five stages with most ore minerals such as pyrite and chalcopyrite being formed in the early stages the main wall rock alteration is silicification and chlorite argillic and propylitic alteration microthermometric measurements of fluid inclusion assemblages show that the ore forming fluids have eutectic temperatures between 30 and 52 c trapping temperatures of 150 290 c and salinities of 6 6 12 4 wt nacl equiv these data demonstrate that the ore forming fluids were medium to high temperature medium to low salinity and low density h2o nacl cacl2 fluids calculated 18o values indicate that ore forming hydrothermal fluids had 18owater ranging from 3 6 to 0 8 confirming that the ore fluid system evolved from dominantly magmatic to dominantly meteoric the calculated 34sh2s values range from 8 1 to 5 0 consistent with derivation of the sulfur from either magma or possibly from local volcanic wall rock combined the fluid inclusion and stable isotope data indicate that the aliabad khanchy deposit formed from magmatic hydrothermal fluids after rising to a depth of between 790 and 500 m the fluid boiled and subsequent hydraulic fracturing may have led to inflow and or mixing of early magmatic fluids with circulating groundwater causing deposition of base metals due to dilution and or cooling the aliabad khanchy deposit is interpreted as an intermediate sulfidation style of epithermal mineralization our data suggest that the mineralization at aliabad khanchy and other epithermal deposits of the thmb formed by hydrothermal activity related to shallow late eocene magmatism the altered eocene volcanic and volcaniclastic rocks especially at the intersection of subvolcanic stocks with faults were the most favorable sites for epithermal ore bodies in the thmb

alkaline character of eocene volcanism in the middle part of central iran and its geodynamic situation alkaline volcanic rocks sometimes feldspathoid bearing appear in variable stratigraphic positions within the eocene of the middle part of central iran no magmatic zonation and no k2o enrichment in both time and space can be found in this volcanic sequence these facts together with other geochemical and geological features of the iranian eocene provinces do not agree with a volcanism related to a subduction zone model

exhumation of the west central alborz mountains iran caspian subsidence and collision related tectonics crystallization and thermal histories of two plutons in the west central alborz also elburz elburs mountains northern iran are combined with crosscutting relations and kinematic data from nearby faults to determine the cenozoic tectonic evolution of this segment of the youthful euro arabian collision zone u pb 40 ar 39 ar and u th he data were obtained from zircon biotite k feldspar and apatite the akapol pluton intruded at 56 2 ma cooled to 150 c by ca 40 ma and stayed near that temperature until at least 25 ma the nearby alam kuh granite intruded at 6 8 0 1 ma and cooled rapidly to 70 c by ca 6 ma these results imply tectonic stability of the west central alborz from late eocene to late miocene time consistent with miocene sedimentation patterns in central iran elevation correlated u th he ages from the akapol suite indicate 0 7 km m y exhumation between 6 and 4 ma and imply 10 km of alborz uplift that was nearly synchronous with rapid south caspian subsidence suggesting a causal relation uplift south caspian subsidence and subsequent folding reversal of alborz strike slip from dextral to sinistral and eastward extrusion of central iran coarse zagros molasse deposition dead sea transform reorganization red sea oceanic spreading and north and east anatolian fault slip all apparently began ca 5 2 ma suggesting a widespread tectonic event that we infer was a response to buoyant arabian lithosphere choking the neo tethyan subduction zone

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

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

acid sulfate chloride volcanic waters formation and potential for monitoring of volcanic activity abstract this paper deals mainly with acidic sulphate chloride asc waters that are discharged at volcanic edifices generally not associated with crater lakes geographically the largest number of such manifestations were found on japanese and kuril islands these waters are formed by 1 condensation of magmatic vapor under shallow conditions and or 2 dissolution of magmatic gases in underground waters 3 near surface mixing of steam heated sulphate waters with sodium chloride waters of deeper formation 4 interaction of sodium chloride waters with the rocks undergone by argillic and advanced argillic alteration including hydrolysis of elemental sulfur 5 a combination of several of the listed processes criteria to assess the nature of such waters using their chemical and isotopic composition are based on the relative abundances of major species and trends in isotopic compositions generally controlling by mixing of magmatic host rock meteoric endmembers an overview of available data on temporal chemical variations of such waters shows that usually volcanic activity is marked by an increase in the so4 cl ratio during or after the eruptive event the response on the volcanic activity depends on hydrogeological conditions that control the appearance of the asc springs

accommodation of late cenozoic oblique shortening in the alborz range northern iran abstract the alborz range northern iran deforms by strain partitioning of oblique shortening onto range parallel left lateral strike slip and thrust faults deformation is due to the north south arabia eurasia convergence and westward motion of the adjacent south caspian relative to iran roughly north south shortening occurs on thrusts that dip inwards from the range margins precambrian basement is not exposed because of detachment along upper proterozoic evaporites and the thickness of overlying strata 10 km other detachments occur within phanerozoic sediments active left lateral strike slip faults trend ene in the east of the range wnw in the west the eastern mosha fault has a left lateral offset of 30 35 km shortening across the range is 30 km 25 30 at the longitude of tehran this is hard to reconcile with the crustal thickness of 35 km which is similar to adjacent basins percentage shortening across the alborz is similar to the adjacent kopet dagh but because the latter is twice as wide finite shortening is roughly half the difference may be accommodated by subduction of the adjacent south caspian basin northwards under the middle caspian south caspian sediments began folding in the pliocene the present kinematics of the alborz may have begun at this time including a reversal from range parallel right lateral to left lateral strike slip faulting but the regional stratigraphy indicates uplift as early as the mid tertiary

across arc geochemical variations in the paleogene magmatic belt of iran abstract across arc geochemical variations between igneous rocks from the magmatic front mf to rear arc ra are commonly observed for convergent margins but the processes that are responsible for these variations are unclear to address these questions we studied a well exposed cenozoic continental arc the urumieh dokhtar magmatic belt udmb of iran and its rear arc counterpart to the north north iran ra magmatism is bimodal characterized by mafic to felsic igneous rocks of calc alkaline to shoshonitic affinity the new zircon u pb ages show that plutonic rocks are 42 38 ma whereas volcanic rocks are older at 52 ma 87sr 86sr t and end t values of udmb ra igneous rocks range from 0 70483 and 0 70783 and 2 5 and 3 6 respectively zircons from plutonic rocks show ehf t values ranging from 1 8 to 9 8 higher than volcanic rocks with ehf t between 2 6 and 9 2 isotopic data agrees with inferences from incompatible trace element ratios e g th yb zr nb and la yb that mafic plutonic rocks originated from an enriched mantle source whereas felsic volcanic rocks show more interaction with continental crust high magmatic fluxes did not occur at the same time in the mf and ra udmb mf flared up at 54 37 ma and 20 5 ma overlapping ra magmatic flare ups at 45 40 ma and 30 25 ma the available major and trace element data from the udmb show that most magmatic rocks experienced strong fractional crystallization and assimilation fractional crystallization processes making it difficult to identify across arc geochemical variations moreover the bulk rock end t and zircon ehf t values are highest at the mf but the across arc isotopic variability seems to be mainly controlled by crustal influence high flux magmatism in the udmb was related to protracted heating of the crust as a result of subduction of neotethys oceanic lithosphere this weakened the continental lithosphere leading to strong extension in paleogene time accompanied by decompression melting and magmatic flare ups

characterization of low temperature pyroclastic surges that occurred in the northeastern japan arc during the late 19th century abstract three eruption events occurring in the central part of the northeastern japan arc were investigated and compared adatara ad1900 zao ad1895 and bandai ad1888 producing low temperature lt pyroclastic surges these events are characterized by steam eruptions ejecting no juvenile material these eruptions well preserved eruptive deposits and facies facilitated granulometric analyses of the beds which revealed the transport and deposition mechanisms of lt surges combining these results with those of investigations of documents reporting the events we correlated each eruption to the relevant individual bed and reconstructed the lt surge development sequence important findings related to the transport and deposition modes are the following 1 bed sets consisting of thin laminated ash and its overlying thick massive tuff were recognized in the adatara 1900 proximal deposits the bed set was probably produced by a strong wind that discharged and propagated quickly from the vent leading wind and a gravitationally segregated highly concentrated flow originated from the eruption column within a discrete eruption episode a similar combination might have occurred during the first surge of the bandai 1888 event 2 comparison of the proximal and distal facies for the largest eruption of adatara 1900 event indicates that the initial turbulence of the eruption cloud decreased rapidly transforming into a density stratified surge with a highly concentrated part near the base similar surges occurred in the climatic stage of zao 1895 3 bandai 1888 ejecta indicate massive beds deposited preferentially at topographic lows co occurring planar beds showed no topographic affection as indicated by the topographic blocking of a stratified surge the observed facies massive tuffs crudely stratified tuffs and thin bedded tuffs are compatible with those for high temperature surges at bandai absence of dune bedded tuffs and commonly poorer sorting in the lt surge deposits might be attributable to poor thermally induced turbulence of eruption columns condensation of vapor in the surges might have contributed to the poor sorting the estimated explosion energies were 6 10 13 j for adatara ad1900 6 5 10 10 j for zao ad1895 and 6 5 10 15 j for bandai ad1888 implying that the three events were hydrothermal eruptions with distinctive eruptive mechanisms regarding eruption sources the adatara 1900 event was caused solely by thermal energy of the hydrothermal fluid although magma intrusion likely triggered evolution of hydrothermal systems at zao in 1895 steam eruptions in the bandai 1888 event occurred simultaneously with sudden exposure of the hydrothermal system whose triggers require no internal energy

tectonic magmatic and metallogenic evolution of the tethyan orogen from subduction to collision abstract this paper reviews the tectonic magmatic and metallogenic history of the tethyan orogen from the carpathians to indochina focus is placed on the formation of porphyry cu mo au deposits as being the most characteristic mineral deposit type formed during both subduction and collisional processes in this region relatively little is known about the history of the paleotethys ocean which opened and closed between gondwana and eurasia in the paleozoic and few ore deposits are preserved from this period the neotethyan ocean opened in the permian early triassic as the cimmerian continental fragments the cores of turkey iran tibet and indochina rifted from the northern gondwana margin and drifted northwards these microcontinents docked with the eurasian margin at various points in the mesozoic and cenozoic and formed a complex archipelago involving several small back arc basins and remnants of the paleotethyan ocean the main neotethyan ocean and these smaller basins were largely eliminated by collision with india and africa arabia in the early eocene and early mid miocene respectively although neotethyan subduction continues beneath the hellenic arc and the makran the majority of porphyry type deposits are found in association with neotethyan subduction mainly in the mesozoic and paleogene and syn to post collisional events in the mid paleogene to neogene they are found throughout the orogen but some sections are particularly well endowed including the carpathians balkans rhodopes eastern turkey lesser caucasus nw iran se iran sw pakistan southern tibet and se tibet indochina other sections that appear barren may reflect deeper levels of erosion young sedimentary cover or lack of exploration although there may also be real reasons for low prospectivity in some areas such as minimal subduction e g the western mediterranean region or lithospheric underthrusting as proposed in western tibet over the last decade improved geochronological constraints on the timing of ore formation and key tectonic events have revealed that many porphyry deposits that were previously assumed to be subduction related are in fact broadly collision related some forming in back arc settings in advance of collision some during collision and others during post collisional processes such as orogenic collapse and or delamination of subcontinental mantle lithosphere while the formation of subduction related porphyries is quite well understood collisional metallogeny is more complex and may involve a number of different processes or sources these include melting of orogenically thickened crust previously subduction modified lithosphere including metasomatized mantle underplated mafic rocks or lower crustal arc plutons and cumulates or upwelling asthenosphere e g in response to delamination slab breakoff back arc extension or orogenic collapse the most fertile sources for syn and post collisional porphyry deposits appear to be subduction modified lithosphere because these hydrated lithologies melt at relatively low temperatures during later tectonomagmatic events and retain the oxidized and relatively metalliferous character of the original arc magmatism unusually metallically enriched lithospheric sources do not seem to be required but the amount of residual sulfide phases in these rocks may control metal ratios e g cu au in subsequent magmatic hydrothermal ore deposits relatively au rich deposits potentially form in these settings as observed in the carpathians e g rosia montan turkey kisladag copler and iran sari gunay dalli although the majority of syn and post collisional porphyries are cu mo rich and resemble normal subduction related deposits e g in the gangdese belt of southern tibet this similarity extends to the associated igneous rocks which being derived from subduction modified sources largely retain the geochemical and isotopic character of those original arc magmas while still retaining a broadly calc alkaline character these rocks may extend to mildly alkaline shoshonitic compositions and may display adakite like trace element signatures high sr y and la yb ratios reflecting melting of deep crustal garnet amphibolitic sources but they are otherwise hard to distinguish from normal subduction related magmas small post collisional mafic alkaline volcanic centers are common throughout the orogen but for the most part appear to be barren however similar rocks in other post subduction settings around the world are associated with important alkalic type porphyry and epithermal au cu deposits and the potential for discovery of such deposits in the tethyan orogen should not be overlooked

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

petrogenesis of mantle derived lile enriched archean monzodiorites and trachyandesites sanukitoids in southwestern superior province reply in southwestern superior province diorite monzodiorite and trachyandesite sanukitoids occurring within syn to post tectonic intrusive complexes and within greenstone belts have the following chemical characteristics 55 60 wt sio2 mgo 6 wt mg 0 60 ni and cr both 100 ppm na2o k2o 6 wt sr and ba both 600 1800 ppm and rare earth element ree patterns that are strongly light rare earth element lree enriched cen 80 250 ybn 4 10 and show no eu anomalies sanukitoids and their granodioritic derivatives constitute at least 5 of the exposed crust in the study area the sanukitoids cannot be derived by melting fractionation or crustal contamination of basalts or lamprophyres that are coeval with the sanukitoids crustal contamination of komatiites fails to explain the high large ion lithophile element lile contents of the sanukitoids rather we suggest that the sanukitoids were derived by hydrous melting of lile enriched mantle peridotite at pressures between 10 and

isotopic geochemistry of acid thermal waters and volcanic gases from zaō volcano in japan abstract the chemical composition and d h 18 o 16 o and 34 s 32 s ratios have been determined for the acid hot waters and volcanic gases discharging from za volcano in japan the thermal springs in za volcano issue acid sulfate chloride type waters za and acid sulfate type waters kamoshika gases emitted at kamoshika fumaroles are rich in co2 so2 and n2 exclusive of h2o chloride concentrations and oxygen isotope data indicate that the za thermal waters issue a fluid mixture from an acid thermal reservoir and meteoric waters from shallow aquifers the waters in the za volcanic system have slight isotopic shifts from the respective local meteoric values the isotopic evidence indicates that most of the water in the system is meteoric in origin sulfates in za acid sulfate chloride waters with 34s values of around 15 are enriched in 34s compared to za h2s while the acid sulfate waters at kamoshika contain supergene light sulfate 34 s 4 derived from volcanic sulfur dioxide from the volcanic exhalations the sulfur species in za acid waters are lighter in 34s than those of other volcanic areas reflecting the difference in total pressure

temporal spatial distribution and tectonic setting of porphyry copper deposits in iran constraints from zircon u pb and molybdenite re os geochronology abstract porphyry copper deposits pcds in iran are dominantly distributed in arasbaran nw iran the middle segment of the urumieh dokhtar magmatic arc udma and kerman central se iran with minor occurrences in eastern iran and the makran arc this paper provides a temporal spatial and geodynamic framework of the iranian porphyry cu mo au systems based on geochronologic data obtained from zircon u pb and molybdenite re os dating of host porphyritic rocks and molybdenites in 15 major pcds the dating results define a long metallogenic duration 39 6 ma and suggest a long history of tectonic evolution from the accretionary orogeny related to early cenozoic closure of the neo tethys ocean to subsequent collisional orogeny for the iranian porphyry copper systems the oldest porphyry mineralization occurred in the eastern part of iran after the closure of a branch of the neo tethyan sistan ocean between the lut and afghan blocks in the late eocene 39 37 ma this was followed by mineralization in the kerman porphyry copper belt over a time interval of about 20 m y where two metallogenic epochs have been recognized including late oligocene 29 27 ma and miocene 18 6 ma the bondar e hanza deposit formed in the late oligocene while and the remaining dated deposits belong to miocene epoch according to the deposits characteristics and their ages the miocene epoch can be divided into early middle and late stages the darreh zar bakh khoshk chah firouzeh and sar kuh deposits formed during the early middle miocene the largest porphyry deposits occur in the middle stage during the middle miocene 14 11 ma and include the sar cheshmeh meiduk dar alu and now chun deposits these deposits were formed during crustal thickening uplift and rapid exhumation of the belt the final stage of porphyry mineralization occurred during the late miocene 9 6 ma and formed the iju kerver kuh panj and abdar deposits there were two porphyry mineralization stages in the arasbaran porphyry copper belt in nw iran including an older late oligocene 29 27 ma and a younger early miocene 22 20 ma events the haft cheshmeh deposit belongs to the older stage and the world class sungun and masjed daghi deposits formed during the early miocene in the middle segment of the udma saveh yazd porphyry copper belt pcds formed during middle miocene time 17 15 ma the geochronological results reveal that the porphyry mineralization moved from the northwest to southeast of udma over the time our dating results combined with the possible late eocene oligocene timing for collision between the arabian and iranian plates support a model for iranian pcd formation by partial melting of previously subduction modified lithosphere in a post subduction and post collisional tectonic setting