oblique convergence during the cimmerian collision evidence from the triassic aghdarband basin ne iran abstract the lower middle triassic aghdarband basin ne iran consists of a strongly deformed arc related marine succession deposited along the southern margin of eurasia in a highly mobile tectonic context this basin is a key area for the study of the cimmerian events as the triassic units show severe deformations which occurred short time after the collision of iran with eurasia and were sealed by the middle jurassic succession in this work we document the structural setting and evolution of this area based on detailed mesoscopic structural analyses of faults and folds paleostress reconstruction and revision of the triassic stratigraphy the triassic sequences are deeply involved in a n verging thrust stack interacting with an important left lateral transpressional fault zone characterized by strike slip faults vertical folds and high angle reverse faults generating intricate positive flowers systematic folds asymmetry indicates that they developed in a left lateral transpressional zone coeval to thrust imbrication to the south due to a marked strain partitioning the extent of the transpressional zone shows that important left lateral movements developed parallel to the belt during the cimmerian collision in response to oblique convergence between iran and eurasia inversion of triassic syn sedimentary faults possibly inherited from palaeozoic structures of the kopeh dagh basement and favouring strain partitioning is suggested by unconformities significant differences in the sedimentary successions repeated olistoliths scarp related coarse breccias and rapid tectonic drowning occurring especially along the northern tectonic boundary of the basin paleostress analyses point to a complex stress pattern showing a 45 rotation of the stress field along the left lateral fault system related to a complete deformation partitioning in two domains respectively characterized by pure reverse dip slip and strike slip motions the main direction of compression possibly oriented ne sw in present days coordinates favoured the development of large shear zones disrupting the eastern portion of the cimmerian orogen

element and isotope geochemical investigations of the kupferschiefer in the vicinity of rote faule indicating copper mineralization sangerhausen basin g d r abstract based upon extensive data on the elemental and isotopic compositions of kupferschiefer of the sangerhausen basin and according to results of trace element and structural investigations of bitumen extracts trends of lateral and vertical distribution of various elements and genetic assertions are presented irregular positions of f v se au and u in the correlation diagram peculiarities of the lateral distribution of these elements abnormally high elemental concentrations in the rocks and in the bituminous extracts as well as alterations discovered in the composition of hydrocarbon groups and their structures support the idea of an influx of oxidizing metalrich waters moving through the rote faule from the rotliegendes basin into the kupferschiefer sediment isotope geochemical investigations carbon nitrogen and oxygen of organic carbonate and silicate fractions were carried out in order to characterize more precisely the conditions of sedimentation and the regime of diagenesis the contrary 13 c curves of pb zn facies and rote faule facies and the 13 c enrichment in the organic matter of rote faule can be explained by different redox conditions during sedimentation and or diagenesis furthermore the decreasing 18 o values of carbonates of the rote faule also suggest an influx of meteoric waters the results oppose a final syngenetic to early diagenetic fixation of the metal contents in kupferschiefer areas in the vicinity of rote faule the established model of influx of metalliferous fluids which arose from the rotliegendes is of local interest for element input and element redistribution

rock physics transforms and scale of investigation abstractrock physics velocity porosity transforms are usually established on sets of laboratory and or well data with the latter data source being dominant in recent practice the purpose of establishing such transforms is to 1 conduct forward modeling of the seismic response for various geologically plausible what if scenarios in the subsurface and 2 interpret seismic data for petrophysical properties and conditions such as porosity clay content and pore fluid because the scale of investigation in the well is considerably smaller than that in reflection seismology an important question is whether the rock physics model established in the well can be used at the seismic scale we use synthetic examples and well data to show that a rock physics model established at the well approximately holds at the seismic scale suggest a reason for this scale independence and explore where it may be violated the same question can be addressed as an inverse problem assume that we have a rock physics tran

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

the anarak jandaq and posht e badam metamorphic complexes in central iran new geological data relationships and tectonic implications abstract the anarak jandaq and posht e badam metamorphic complexes occupy the nw part of the central east iranian microcontinent and are juxtaposed with the great kavir block and sanandaj sirjan zone our recent findings redefine the origin of these complexes so far attributed to the precambrian early paleozoic orogenic episodes and now directly related to the tectonic evolution of the paleo tethys ocean this tectonic evolution was initiated by late ordovician early devonian rifting events and terminated in the triassic by the eocimmerian collision event due to the docking of the cimmerian blocks with the asiatic turan block the variscan accretionary complex is a new name we proposed for the most widely distributed metamorphic rocks connected to the anarak and jandaq complexes this accretionary complex exposed from sw of jandaq to the anarak and kabudan areas is a thick and fine grain siliciclastic sequence accompanied by marginal sea ophiolitic remnants including gabbro basalts with a supra subduction geochemical signature new 40ar 39ar ages are obtained as 333 320 ma for the metamorphism of this sequence under greenschist to amphibolite facies moreover the limy intercalations in the volcano sedimentary part of this complex in godar e siah yielded upper devonian tournaisian conodonts the northeastern part of this complex in the jandaq area was intruded by 215 15 ma arc to collisional granite and pegmatites dated by id tims and its metamorphic rocks are characterized by some 40ar 39ar radiometric ages of 163 156 ma the variscan accretionary complex was northwardly accreted to the airekan granitic terrane dated at 549 15 ma later from the late carboniferous to triassic huge amounts of oceanic material were accreted to its southern side and penetrated by several seamounts such as the anarak and kabudan this new period of accretion is supported by the 280 230 ma 40ar 39ar ages for the anarak mild high pressure metamorphic rocks and a 262 ma u pb age for the trondhjemite rhyolite association of that area the triassic bayazeh flysch filled the foreland basin during the final closure of the paleo tethys ocean and was partly deposited and or thrusted onto the cimmerian yazd block the paleo tethys magmatic arc products have been well preserved in the late devonian carboniferous godar e siah intra arc deposits and the triassic nakhlak fore arc succession on the passive margin of the cimmerian block in the yazd region the nearly continuous upper paleozoic platform type deposition was totally interrupted during the middle to late triassic local erosion down to lower paleozoic levels may be related to flexural bulge erosion the platform was finally unconformably covered by liassic continental molassic deposits of the shemshak one of the extensional periods related to neo tethyan back arc rifting in late cretaceous time finally separated parts of the eocimmerian collisional domain from the eurasian turan domain the opening and closing of this new ocean characterized by the nain and sabzevar ophiolitic melanges finally transported the anarak jandaq composite terrane to central iran accompanied by large scale rotation of the central east iranian microcontinent ceim due to many similarities between the posht e badam metamorphic complex and the anarak jandaq composite terrane the former could be part of the latter if it was transported further south during tertiary time

the eo cimmerian late triassic orogeny in north iran the eo cimmerian orogen results from the late triassic collision of iran a microplate of gondwanan affinity with the southern margin of eurasia the orogen is discontinuously exposed along the northern side of the alborz mountains of north iran below the siliciclastic deposits of the shemshak group late triassic jurassic a preserved section of the external part of the belt crops out in the neka valley eastern alborz south of gorgan here the mesozoic successions shemshak group upper cretaceous limestones overlay a pre jurassic eo cimmerian thrust stack with a sharp unconformity the stack includes the gorgan schists an upper ordovician lower silurian low grade metamorphic complex overthrusted southward above a strongly deformed late palaeozoic middle triassic succession belonging to north iran in the talesh mountains western alborz the shanderman complex previously interpreted as an ophiolitic remnant isolated along the eo cimmerian suture is considered an allochthonous nappe of deeply subducted continental crust the new evidence for this is the occurrence of previously unknown eclogites dating to the carboniferous and probably related to the variscan history of transcaucasia south of the shanderman complex upper palaeozoic slates and carbonates occurring below the lower jurassic shemshak group also record the occurrence of an eo cimmerian metamorphic event based on our new data the eo cimmerian structures exposed in the alborz appear to be remnants of a collisional orogen consisting mainly of deformed continental crust where no ophiolites are preserved

quantitative seismic interpretation integrated with well test analysis in turbidite and presalt reservoirs abstract advances in acquisition techniques and in processing workflows have made seismic amplitude more reliable and consequently the quantitative information has become more trustworthy rock physics and seismic inversion are essential tools for reservoir characterization rock physics improves our knowledge about how the variations of reservoir properties affect the seismic response seismic inversion is a tool to obtain 3d volume of elastic properties combining the static information from seismic and well data is the first approach for reservoir characterization data from core well log and laboratory tests help to mitigate the risk associated with seismic interpretation additionally geophysicists may rely on dynamic data such as pressure production rates saturation temperature and fluid properties whenever available the pressure transient analysis obtained from well tests brings deeper reservoir insights estimations of the permeability profile flow barrier character and hydraulic comp

the role of organic matter in the metallogeny of the bohemian massif formations rich in organic matter occurred throughout most of the geologic history of the bohemian massif accumulation of organic matter was connected with basic submarine volcanic activity with transgressive sedimentary regimes and with limnic and paralic environments the largest carbon rich marine sediment accumulation occurred in late proterozoic and early paleozoic time in these periods substantial concentrations of trace elements and sulfur accumulated in black claystones where the metal associations were determined mostly by synchronous volcanicity in spite of the substantial amount of accumulated trace elements only subeconomic concentrations of pyrite pyrrhotite and u v sb au mineralizations were formed in association with proterozoic stromatolites subsequently cadomian and variscan metamorphic processes caused substantial remobilization of metals and sulfur in black claystones and produced disseminated gold and uranium deposits during the emplacement of postkinematic variscan granitoids organic matter and some metals were leached from the surrounding low metamorphic carbon rich sediments by hydrothermal solutions of deep crustal origin a typical feature of these deposits is the presence of isotopically light bitumens delta 13 c pdb 40 8 to 56 5ppm and the biological tracers phytane and pristane indicating a biogenic origin as a reducing agent organic carbon graphite controlled the localization of variscan hydrothermal uranium mineralization which occurs in graphitized shear zones in the highly metamorphosed basement of the bohemian massif the crystallinity of the graphitized organic matter decreases sharply in these zones probably due to hydrothermal decomposition of the graphite lattice the low crystallinity of graphite and anomalously light isotopic composition of the hydrothermal carbonates in this type of deposit delta 13 c pdb 6 to ppm indicate that graphitized organic matter was involved in the reduction of uranium bearing hydrothermal solutions during the formation of sandstone type uranium deposits in the carbon rich platform sediments of the bohemian massif the organic matter of host rocks became oxidized by the action of oxygen dissolved in ore bearing solutions this process gave rise to organic polymers similar to humic acids which reacted with uo super 2 2 to form insoluble uranium organic compounds

petrology geochemistry and tectonics of the sabzevar ophiolite north central iran abstract the sabzevar ophiolite is a highly dismembered ophiolite complex located along the northern boundary of the central iranian microcontinent cim and is one of the internal iranian group of ophiolites and colored melanges the igneous rocks of this complex consist of peridotites harzburgite dunite and lherzolite serpentinite minor pyroxenite gabbros and a volcanic sequence that exhibits a wide range of composition from basalts and basaltic andesites to rhyodacite dacites rhyolites and basanites sedimentary rocks include a variety of upper triassic to lower cretaceous deep and shallow marine rocks these include pelagic fossiliferous carbonates that are mixed with the pillow basalt and basaltic andesite as interlayers or exotic blocks ranging in size from 10 to 100 m also present are extensive units of radiolarian chert which are interbedded within the basalts and basaltic andesites a combination of petrographic observations and analyses of incompatible trace elements and rare earth elements indicates the presence of at least four different types of extrusive rocks in the sabzevar ophiolite the geochemical data clearly identifies some of the extrusive rocks to have formed from three distinct types of basaltic melts i the group 1 basaltic rocks which formed from an initial melt with n morb like lree depleted chemical signatures and are petrogenetically related to the gabbros ii group 2 basaltic rocks which have e morb chemical signatures and iii group 3 basaltic rocks with lree enriched signatures and incompatible trace element patterns that suggest an island arc affinity the data also suggest that the gabbros and the group 1 basaltic rocks are petrogenetically related and produced by fractionation of plagioclase and to a lesser extent clinopyroxene and hornblende similar to other studied iranian ophiolites e g khoy band e zeyarat dar anar neyriz kermanshah and baft the results from the sabzevar ophiolite demonstrate the presence of relics of mid ocean ridge basalt morb like signatures in the extrusive units of neo tethyan ophiolites and suggests that the fossil oceanic lithosphere preserved in these ophiolites developed at an oceanic spreading center in addition the sabzevar ophiolite contains other volcanic rocks that have non morb like geochemical signatures e g within plate island arc the differences between these geochemical signatures could be a result of a differing upper mantle composition or different degrees of partial melting of the same upper mantle the presence of sizable nb anomalies in the extended rare earth element ree patterns for andesites and the group 3 basalts is characteristic of volcanic arc magmas or possibly are products of the ascending magma that was modified by crustal contamination the presences of the basanites and the silica undersaturated rocks could be attributed to extrusive activity following ophiolite emplacement plate reconstructions suggest that rocks of the sabzevar ophiolite were part of the tethyan oceanic crust that was formed during rifting of a narrow but deep seaway that separated the cim from the eurasian plate the ophiolite was emplaced during northeast dipping subduction i e closure of this segment of the tethyan seaway sabzevar ocean

discussion of results presented by hhndorf and dill some aspects of lead lead model ages of ore mineralizations from the western edge of the bohemian massif f r germany mineral deposita 21 329 336 1986

structures in southwest asia and evolution of the eastern tethys abstract southwest asia comprises the following 1 a two major orogenic belts a northern belt derived from the paleo tethys and a southern belt derived from the neo tethys 2 b minor orogenic belts derived from neo tethyan marginal basins 3 c continental blocks that originated from gondwana by splitting and stripping and subsequently drifted and collided with continental asia in its process of construction and 4 d residual oceanic basins which are assumed as being not yet closed neo tethyan marginal basins the entire region appears as the product of tethyan evolution

lead isotope and pb pb model age determinations of ores from central europe and their metallogenetic interpretation the paper presents lead isotope data from 211 samples from phanerozoic lead bearing ore occurrences in central europe particularly from the southern part of the former german democratic republic the data are interpreted in terms of amov s dynamic model of continuous lead isotope evolution the relationships between thoro genic and urano genic model ages and the source of lead in different regional units are discussed we observed differences in lead isotope evolution in the hercynian internides and externides within the moldanubian and saxothuringian zones we distinguish five main lead bearing ore associations 1 cambrian stratiform base metal hermsdorf waldsassen 206pb 204pb 17 50 17 70 2 devonian vein type sb bearing metamorphogene neumuhle hartmannsdorf 17 80 18 00 3 upper carboniferous permian polymetallic including tin vein type kutna hora freiberg altenberg 18 00 18 20 4 triassic jurassic pb ba vein type st ibro halsbrucke 18 20 18 60 5 cenozoic polymetallic vein type riftogene roztoky banska stiavnica 18 80 19 10 pb isotope characteristics from ores of the montagne noire and the brioude massiac district correspond to this subdivision ore associations from the rheno hercynian zone display higher 207pb 204pb ratios which can be explained by more evolved and less metamorphosed source rocks mineralizations of the eastern harz strasberg neudorf belong to the permian association those from the western harz clausthal bad grund to the triassic jurassic because of pb isotope agreement the stratabound rammelsberg and the vein bound ramsbeck i mineralization are presumed to be isogenetic pb isotope identity of distinct mineralizations in the basement zone halsbrucke bad grund and in the triassic sediments gorny slask mechernich bleiglanzbanke suggests a strong genetic coherence pb isotope conformity between the upper carboniferous permian triassic ore associations and hercynian postkinematic granitoids and lamprophyric rocks also favours a close relationship pb isotope and other data indicate crustal sources as the age of the ore associations decreases crustal influences generally increase apart from the roztoky mineralization

230th 238u radioactive disequilibria in tholeiites from the famous zone mid atlantic ridge 36 50 n th and sr isotopic geochemistry we analyzed u th and230th 232th activity ratios for a few tholeiites from the mid atlantic ridge famous zone at 36 50 n the results show a fairly wide scatter for both th u and 230th 232th ratios seawater contamination appears to be responsible for this scatter and for the uranium produces an increase in content yielding a 234u 238u ratio greater than 1 and for the th an increase of the 230th 232th ratio which is a very sensitive indicator for contamination also the latter often is selective u th and sr are not affected in the same manner when discarding all data for contaminated samples the famous zone appears to be very homogeneous with ath u ratio value of 3 05 and a 230th 232th ratio value of 1 24 comparison with other active volcanic areas reveals a negative correlation between 230th 232th and87sr 86sr ratios for present lavas which is indicative of a consistency in th u and rb sr fractionation in the source regions of these magmas the th isotopic geochemistry can thus provide useful information for the study of present volcanism information as valuable as that from sr pb or nd isotopes

seismic scale petrophysical interpretation and gas volume estimation from simultaneous impedance inversion abstract simultaneous impedance inversion was performed to obtain the seismic scale p and s wave impedances as well as the bulk density volumes from seismic angle stacks at a siliciclastic turbidite offshore gas reservoir to translate these variables into seismic scale total porosity clay content and water saturation sw we used a deterministic rock physics model established at the well a crucial input into this model is the bulk modulus kf of the brine gas system we need to link it to sw at the seismic scale this link can be one of simple mixing laws such as harmonic and arithmetic alternately it can be derived at the well by using upscaled variables and ensuring that they obey the well data driven rock physics model these different kf sw relations produce different interpretations for and sw thus allowing one to assess the variability in the estimates of the gas volume in place that is proportional to the product of and 1 sw

critical taper model of fold and thrust belts and accretionary wedges the fold and thrust belts and submarine accretionary wedges that lie along compressive plate boundaries are one of the best understood deformational features of the earth s upper crust although there is considerable natural variation among the many fold and thrust belts and accretionary wedges that have been recognized and explored several features appear to be universal in cross section fold and thrust belts and accretionary wedges occupy a wedge shaped deformed region overlying a basal detachment or decollement fault the rocks or sediments beneath this fault show very little deformation the decollement fault characteristically dips toward the interior of the mountain belt or in the case of a submarine wedge toward the island arc the topography in contrast slopes toward the toe or deformation front of the wedge deformation within the wedge is generally dominated by imbricate thrust faults verging toward the toe and related fault bend folding two north american fold and thrust belts that exhibit these features are shown in figure 1 neither of these two examples is tectonically active today the southern canadian fold and thrust belt was active during the late jurassic and cretaceous 150 100 ma whereas the southern appa lachians were deformed during the late carboniferous to permian alle ghenian orogeny 300 250 ma figure 2 shows two examples that are currently active the taiwan fold and thrust belt produced by the sub duction of the eurasian plate beneath the philippine sea plate suppe 1981 1987 and the barbados accretionary wedge produced by the sub

sedimentary record of late paleozoic to recent tectonism in central asia analysis of subsurface data from the turan and south kazak domains abstract the turan and south kazak domains tsk are in central asia between the caspian sea and the tien shan the area is covered by sediments deposited since the late permian during a series of tectonic events closely related to the history of two oceanic domains paleotethys and neotethys sedimentary basins on the tsk therefore provide constraints on the tectonic development of the southern margin of eurasia since the late permian our study is based on structure contour maps and isopach maps of five key stratigraphic markers of late permian to tertiary age isopach maps help locate major faults and delimit sedimentary basins providing information on vertical motions and in some instances horizontal motions subsidence associated with extension appears to have dominated the tsk from the late permian to the eocene the extension may have been of back arc type in southern eurasia next to the active margin where the paleotethys and neotethys successively subducted toward the north here sedimentary basins are both wide and deep up to 15 km during the mesozoic two compressional events of regional significance occurred in association with accretion of continental blocks at the southern margin of eurasia the first one at the end of the triassic led to strong selective inversion of basins over the turan domain the second one during the late jurassic early cretaceous had weaker effects since the oligocene following collision of both india and arabia with eurasia inversion has become more generalized and compressional basins have formed on the tsk throughout the entire history of development of the tsk from the late permian to the tertiary structures of paleozoic and early mesozoic age have exerted a strong control on sedimentation and especially on the location of depocenters the south kazak domain has registered little subsidence in comparison with the turan domain where some basins have become very deep

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

pb isotope evidence for the origin of lead in strata bound pb zn deposits in triassic carbonates of the eastern and southern alps a comparison of ore lead isotope ratios of pb zn deposits hosted in triassic carbonates of the eastern and southern alps with the isotopic composition of trace leads of their host rocks of triassic volcanics and of the underlying clastic sediments shows that these rocks could have supplied only part of the ore lead the isotopic signature of feldspar lead from crystalline basement rocks however reveals that they must have contributed a significant amount of metal to these deposits the presence of barite and of thallium is also indicative that feldspars were the main source of lead arsenic is one of the few important trace elements in these deposits and is known to occur in some areas of lower paleozoic metasediments in unusually high concentrations any model explaining the origin of these deposits must consider the extensive leaching of the basement and to some extent of the overlying clastic sediments as well how the metal bearing solutions entered the lagoonal back reef areas is still open to question as feeder channels have not yet been positively identified the results further demonstrate that the basement also acted as a metal source for galena bearing deposits hosted in permian sediments vein type deposits in permian volcanics and probably the barite fluorite polymetallic deposits along a devonian erosional surface in the carnic alps as well

siderite mineralization of the gemericum superunit western carpathians slovakia review and a revised genetic model abstract the gemericum is a segment of the variscan orogen subsequently deformed by the alpine carpathian orogeny the unit contains abundant siderite sulphide and quartz antimony veins together with stratabound siderite replacement deposits in limestones and stratiform sulphide mineralization in volcano sedimentary sequences the siderite sulphide veins and siderite replacement deposits of the gemericum represent one of the largest accumulations of siderite in the world with about 160 million tonnes of mineable feco 3 more than 1200 steeply dipping hydrothermal veins are arranged in a regional tectonic and compositional pattern reflecting the distribution of regional metamorphic zones siderite sulphide veins are typically contained in low grade chlorite zone sedimentary volcano sedimentary or volcanic lower and upper paleozoic rocks quartz antimony veins are hosted by higher grade units biotite zone siderite sulphide veins are dominated by early siderite followed by a complex set of stages including quartz sulphide chalcopyrite tetrahedrite barite tourmaline quartz and sulphide remobilization stages the temporal evolution of these stages is difficult to study because of the widespread and repeated tectonic processes within vein replacement and recrystallization siderite sulphide veins show considerable vertical up to 1200 m and lateral up to 15 km extent and a thickness typically reaching several metres carbonate replacement siderite deposits of the gemericum are hosted by a silurian limestone belt and are similar to stratabound siderite deposits of the eastern alps e g erzberg austria based on a review of geological petrological and geochronological data for the gemericum and extensive stable and radiogenic isotope data and fluid inclusion data on hydrothermal minerals the siderite sulphide veins and siderite replacement deposits are classified as metamorphogenic in a broad sense the deposits were formed during several stages of regional crustal scale fluid flow isotope s c sr pb fingerprinting identifies the metamorphosed rock complexes of the gemericum as a source of most components of hydrothermal fluids fluid inclusion and stable isotope data evidence the participation of several contrasting fluid types and the existence of contrasting p t conditions during vein evolution a high 1 8 o medium to high salinity h 2 o type fluid is the most important component during siderite deposition whereas h 2 o co 2 type fluid inclusion containing dense liquid co 2 and corresponding to minimal pressures between 1 and 3 kbar were found in a younger tourmaline quartz stage younger quartz ankerite siderite sulphide stages are characterized by high salinity 17 to 35 wt nacl equivalent and low temperature t h 90 to 180 c h 2 o type fluids the vein deposits are interpreted as a result of multistage hydrothermal circulation with variscan and alpine mineralization phases based on available indirect data the most important mineralization phase was related to regional fluid flow during the uplift of a variscan metamorphic core complex producing siderite sulphide barite mineralization while tourmaline quartz stage and sulphide remobilization stages are related to alpine processes two phases of vein evolution are evident from two groups of 87 sr 86 sr isotope ratios of sr rich rb poor hydrothermal minerals 0 71042 0 71541 in older barite and 0 7190 0 7220 in late stage celestine and strontianite

geochemical characteristics 40ar 39ar ages and original tectonic setting of the band e zeyarat dar anar ophiolite makran accretionary prism s e iran abstract the makran accretionary prism in southeastern iran contains extensive mesozoic zones of melange and large intact ophiolites representing remnants of the tethys oceanic crust that was subducted beneath eurasia to the north of the makran accretionary prism lies the jaz murian depression which is a subduction related back arc basin the band e zeyarat dar anar ophiolite is one of the ophiolite complexes it is located on the west side of the makran accretionary prism and jaz murian depression and is bounded by two major fault systems the principal rock units of this complex are a gabbro sequence which includes low and high level gabbros an extensive sheeted diabase dike sequence late intrusive rocks which consist largely of trondhjemites and diorites and volcanic rocks which are largely pillow basalts interbedded with pelagic sedimentary rocks including radiolarian chert chondrite and primitive mantle normalized incompatible trace element data and age corrected nd pb and sr isotopic data indicate that the band e zeyarat dar anar ophiolite was derived from a midocean ridge basalt like mantle source the isotopic data also reveal that the source for basalts was indian ocean type mantle based on the rare earth element ree data and small isotopic range all the rocks from the band e zeyarat dar anar ophiolite are cogenetic and were derived by fractionation from melts with a composition similar to average e morb fractionation was controlled by the removal of clinopyroxene hornblende and plagioclase three 40ar 39ar plateau ages of 140 7 2 2 142 9 3 5 and 141 7 1 0 ma and five previously published k ar ages ranging from 121 4 to 146 5 ma for the hornblende gabbros suggest that rocks from this ophiolite were formed during the late jurassic early cretaceous plate reconstructions suggest that the rocks of this complex appear to be approximately contemporaneous with the masirah ophiolite which has crystallization age of 150 ma like masirah the rocks from the band e zeyarat dar anar ophiolite complex represent southern tethyan ocean crust that was formed distinctly earlier than crust preserved in the 90 100 ma bitlis zagros ophiolites including the samail ophiolite

the margins of laurussia in central and southeast europe and southwest asia the continuation of the laurussian margin into central and southeast europe and southwest asia is defined by the rheic suture which becomes harder to trace to the southeast because of complex post variscan strike slip displacements and tectonic stacking linked to the cimmerian and alpine cycles the uncertain extent of the neoproterozoic baikalian orogeny fringing baltica ambiguous early paleozoic paleobiogeographic data and strike slip activity complicate the distinction of the tornquist suture from the transeuropean suture zone there is growing evidence for the incorporation of the brunovistulian malopolska and west moesian terranes into the late neoproterozoic cambrian baltican margin the istanbul zonguldak terrane along with the bitesh and east moesia terranes may have been part of the avalonian terrane assemblage although an arabian nubian shield or baltica provenance cannot be excluded the terranes of the armorica terrane assemblage bordering the rheic suture include the outer carpathian tatra getic and balkan terranes in southeast europe and sakarya and the anatolide tauride terrane in turkey further east the rheic suture may be present in the caucasus in all probability between the greater caucasus and the scythian platform or alternatively between the greater caucasus and transcaucasia alborz in northern iran is interpreted as a distal part of transcaucasia the location of the rheic suture in the southeast part of the turan domain of central asia is poorly constrained

biostratigraphic zonation and 40ar 39ar ages for the neotethyan khoy ophiolite of nw iran abstract the khoy ophiolite in northwestern iran represents a piece of oceanic lithosphere formed in the mesozoic neotethys this ophiolite consists from bottom to top of well defined basal metamorphic rocks peridotites gabbros and a variety of upper to lower cretaceous deep marine rocks these include pelagic fossiliferous carbonates and basalts as interlayers or exotic blocks four hornblende separates from gabbros and amphibolites give values from 108 to 111 ma the results from microfossil studies show the presence of late cretaceous e g marginotruncana globotruncana and middle to late eocene e g globorotalia orbulonoides planktonic foraminifera the data suggest that although the initial rifting and crystallization of the oceanic crust of the khoy ophiolite began in the late albian the volcanic activities continued through to the late eocene time another possibility for such variation of lithofacies and biofacies and disturbances in the fossil record may be the result of bioturbation and transportation and rapid changes of depositional conditions during eruption of the basaltic lava flows pelagic sediments alone have been listed and of the foraminiferas the first three are planktonic as would be expected only orbulonoides is a benthic form and aberrant the third possibility is that the khoy ophiolite may represent a classic supra subduction type ophiolite where volcanic members of the different parts of oceanic environment e g morb volcanic arc ocean island are now juxtaposed

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

estimating p and s wave inverse quality factors from observed seismic data using an attenuative elastic impedance p and s wave inverse quality factors quantify seismic wave attenuation which are related to several key reservoir parameters porosity saturation viscosity etc estimating the inverse quality factors from observed seismic data provides additional and useful information during gas bearing reservoir prediction we first propose an approximate reflection coefficient and attenuative elastic impedance in terms of the inverse quality factors and then we establish an approach to estimate elastic properties p and s wave impedances and density and attenuation p and s wave inverse quality factors from seismic data at different incidence angles and frequencies the approach is implemented as a two step inversion a model based and damped least squares inversion for attenuative elastic impedance and a bayesian markov chain monte carlo inversion for the inverse quality factors synthetic data tests confirm that p and s wave impedances and inverse quality factors are reasonably estimated in the case of

lead isotopic composition of hercynian granitic k feldspars constrains continental genesis lead isotope compositions have been determined in many k feldspars from granitic rocks emplaced during the variscan hercynian orogeny sensu lato around 300 myr in various parts of europe and the eastern us the ratios show a regular geographical pattern with contours arched around southern france and parallel to the atlantic coast of the us this distribution parallels predriftpalaeogeographical zones during the palaeozoic the lead isotope pattern of variscan granitic rocks is similar to that of some orogenic volcanic suites but is better explained by crustal melting than by an hercynian mantle crust material mixing the continental crust from these areas must be older than 3 000 myr large scale fluid circulation in the crust during orogenic processes apparently explains the observed geographical patterns of lead isotopes

space time patterns of magmatism along the tethysides a preliminary study five maps showing spatio temporal evolution of magmatism along the tethysides for the following time intervals late carboniferous and permian 320 248 ma triassic and early jurassic 247 188 ma

eocene gold ore formation at muteh sanandaj sirjan tectonic zone western iran a result of late stage extension and exhumation of metamorphic basement rocks within the zagros orogen a multidisciplinary study including field geology microstructure analysis 40ar 39ar dating and fluid inclusion microthermometry and raman spectrometry has been carried out on the muteh gold deposit located in a greenschist to amphibolite facies metamorphic rock complex of the sanandaj sirjan tectonic zone zagros orogen iran the muteh gold deposit has been previously interpreted as genetically related to precambrian granitic intrusions as an exhalative hot spring deposit related to paleozoic rhyolitic acidic tuffs and to local metamorphic processes host rocks of the gold deposit are predominantly schist and gneiss and subsidiary amphibolite and quartzite and are intruded by leucogranites in the vicinity of the gold deposit the metamorphic and granitic rocks display a subhorizontal mylonitic foliation containing a northeast oriented stretching lineation field investigations in one of the producing open pits show that the gold orebodies are controlled by northwest oriented normal faults and joints dipping to the northeast and the southwest and crosscutting the ductile fabric of the host rocks both the ductile fabric of the host rocks and the gold ore controlling brittle structures are interpreted to have formed within a single continuous extensional event which started with ductile deformation and gradually changed into brittle deformation hydrothermal alteration associated with ore formation consists of quartz muscovite pyrite dolomite ankerite and albite which crosscuts the ductile fabric and overprints the metamorphic minerals of the host rocks pyrite is the dominant opaque mineral and is the major phase associated with gold chalcopyrite marcasite bismuth galena sphalerite and pyrrhotite are subsidiary to rare phases 40ar 39ar incremental heating and in situ laser ablation age data reveal a coherent sequence of cooling and hydrothermal events in the metamorphic complex hosting the muteh gold deposit muscovite samples from the alteration zone and from one quartz vein from the orebodies yield 40ar 39ar ages between 55 7 and 38 5 ma and show that gold mineralization is the youngest among the different dated events this eocene age is consistent with the young structural setting of the gold orebodies revealing an emplacement along northwestoriented normal faults which can be correlated with tertiary extensional tectonic events reported by previous field investigations the data also indicate that gold ore formation is coeval with magmatism in the adjacent tertiary urumieh dokhtar magmatic belt and with intrusive activity within the sanandaj sirjan zone with a 40ar 39ar age of 54 ma near muteh according to our study the remaining 40ar 39ar data reveal a cretaceous to early tertiary metamorphic magmatic and deformation history of the complex hosting the muteh gold deposit the fluid inclusion study showed that distinct fluids were present during the regional geologic evolution predating ore formation and later eocene gold ore formation early regional fluids consist of an h2o co2 nacl fluid with subsidiary n2 and ch4 that underwent local unmixing the salinities of the liquid rich inclusions resulting from unmixing range between 2 2 and 17 5 wt percent nacl equiv and those of the co2 rich vaporrich inclusions range between 2 8 and 7 2 wt percent nacl equiv the high salinity of the regional liquid rich fluids is attributed to metamorphism of evaporite bearing sedimentary rocks magmatic intrusions retrograde hydration reactions metamorphism of impure marbles and migmatization the fluid inclusions spatially associated with the gold veins postdating regional metamorphism and ductile deformation of the host rocks contain a low salinity aqueous fluid with a dilute low density co2 component and maximum salinities between 2 6 and 5 8 wt percent nacl equiv gold deposition at muteh occurred during or after late stages of eocene brittle extension as a result of exhumation of the host metamorphic complex possibly during magmatic activity in the sanandaj sirjam zone it is most likely linked to the introduction of a distinct low salinity low co2 content aqueous fluid during crustal extension these fluids are younger than and therefore unrelated to the highly saline and co2 rich regional metamorphic magmatic fluids our results refute previous models advocating precambrian to paleozoic ages of the muteh gold deposit

southern borderland of triassic laurasia in north east iran results obtained by iranian and european geoscientists in the critical area to the north east of the north iran suture east of mashhad are desribed and discussed a slightly metamorphosed ophiolite belt outcropping as the south easterly continuation of the previously known ophiolites of mashhad along the north eastern perimeter of the fariman torbat e jam depression proved to be either the remnant of a permian ocean floor or more likely the remnant of a narrow ocean trough there is as yet no proof of a triassic age for this ophiolitic belt to the north of this ophiolitic belt an epicontinental triassic sequence is exposed at the southern edge of laurasia in the erosional window of aghdarband this is the result of intermittent sedimentation in a pull apart basin along sinistral strike slip faults the triassic of aghdarband has much in common with other deposits of the triassic tethys however it shows a few unique features e g the early anisiannicomedites fauna of a palaeobiogeographic north tethyan subprovince or volcanogenic sedimentation during the late anisian and the entire ladinian

isotopic and trace element arguments for the lower crustal origin of hercynian granitoids and pre hercynian orthogneisses massif central france abstract the cadomian hercynian basement of the massif central france contains both pre metamorphic orthogneisses 600 410 ma and post metamorphic undeformed granitoids 360 275 ma major trace element and sr nd isotopic analyses of these intrusions indicate slight differences in source material for orthogneisses and two types of underformed granitoid a granodiorite monzogranites and leucogranites orthogneisses have moderately enriched ree patterns la yb 5 3 13 3 variable hree contents ybn 4 2 25 and strong negative eu anomalies eu eu 0 23 0 36 their tnd values are low 5 8 to 1 7 indicating a strong crustal component in the source but tsr values are also generally low 25 to 100 and overlap the field of age corrected isotopic values for lower crustal granulite xenoliths from the massif central the source of the orthogneisses is therefore considered to be dominated by a lower crustal meta igneous component with additional input from a lower crustal metasedimentary source granodiorites monzogranites tend to show strong lree enrichment la yb 11 26 with small eu anomalies eu eu 0 54 0 75 and ybn values between 6 and 8 5 these granitoids form the least evolved end members of a series trending to highly evolved leucogranites with similar la yb ratios 11 36 but with generally larger eu anomalies eu eu 0 24 0 62 and lower ybn values 3 8 initial isotopic ratios of the leucogranites tnd 7 9 to 4 5 and tsr usually 100 mostly fall within the field of age corrected lower crustal metasedimentary granulite xenoliths from the region and it is proposed that these leucogranites were formed by partial melting of lower crustal metasediments granodiorites and monzogranites have tnd between 6 5 and 3 4 and tsr values

structure and stratigraphy of the tepla barrandian neoproterozoic bohemian massif a new plate tectonic reinterpretation abstract the tepla barrandian unit tbu of the bohemian massif exposes a section across the once extensive avalonian cadomian belt which bordered the northern active margin of gondwana during late neoproterozoic this paper synthesizes the state of the art knowledge on the cadomian basement of the tbu to redefine its principal component units to revise an outdated stratigraphic scheme and to interpret this scheme in terms of a recent plate tectonic model for the cadomian orogeny in the bohemian massif the main emphasis of this paper is on an area between two newly defined fronts of the variscan pervasive deformation to the nw and se of the barrandian lower paleozoic overlap successions this area has escaped the pervasive variscan late devonian to early carboniferous ductile reworking and a section through the cadomian orogen is here superbly preserved the nw segment of the tbu consists of three juxtaposed allochthonous belts of unknown stratigraphic relation the kralovice rakovnik radnice kralupy and zbiroh sarka belts differing in lithology complex internal strain patterns and containing sedimentary and tectonic melanges with blocks of diverse ocean floor meta basalts we summarize these three belts under a new term the blovice complex which we believe represents a part of an accretionary wedge of the cadomian orogen the se segment of the tbu exposes the narrow picin belt which is probably a continuation of the blovice complex from beneath the barrandian lower paleozoic and a volcanic arc sequence the davle group their stratigraphic relation is unknown flysch units the st chovice group and svrchnice formation overlay the arc volcanics and both units contain material derived from volcanic arc the former was also sourced from the nw segment whereas the latter contains an increased amount of passive margin continental material in contrast to the blovice complex the flysch experienced only weak cadomian deformation the new lithotectonic zonation fits the following tectonic scenario for the cadomian evolution of the tbu well the s to se directed cadomian subduction beneath the tbu led to the involvement of turbidites chaotic deposits and 605 39 ma ocean floor in the accretionary wedge represented by the blovice complex the accretionary wedge formation mostly overlapped temporally with the growth of the volcanic arc the davle group at 620 560 ma upon cessation of the arc igneous activity the rear of the wedge and some elevated portions of the arc were eroded to supply the deep water flysch sequences of the st chovice group whereas the comparable svrchnice formation 560 to

rock physics diagnostic of north sea sands link between microstructure and seismic properties velocity in high porosity sands strongly depends on the position and amount of intergranular material velocity is high if the original grains are cemented at their contacts it is low if the pore filling material is placed away from the contacts the amount and type of intergranular material can be theoretically determined from velocity and porosity data by adjusting an effective medium theoretical model curve to a trend in the data and then assuming that the microstructure of the sediment is such as used in the model we apply this diagnostic method to clean sands in the heimdal formation the north sea the results show that the reservoir zone sand in one well under examination has slight contact cementation while it is completely uncemented and friable in another well this conclusion is supported by microscopic grain images the rock physics diagnostic is important for establishing a velocity porosity trend consistent with local geology such trends can improve the accuracy of porosity prediction from seismic data

comparison of seismic upscaling methods from sonic to seismic the term upscaling used here means a prediction of elastic wave velocities at lower frequencies from the velocities at higher frequencies three different methods of upscaling are considered including the simple averaging backus averaging and pair correlation function methods these methods are applied to upscale the elastic wave velocities measured at sonic frequencies 2 khz logging data available for a well penetrating layers of gas bearing shales and carbonates as a result a velocity distribution over depth for vp and vs is found in the frequency range of 50 500 hz the difference in the results obtained for a particular depth by the three theoretical methods in the surface seismic frequency bandwidth 50 100 hz is 600 m s for p wave and 260 m s for s wave velocity this difference is attributed to different theoretical backgrounds underlying these methods

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

lead isotope systematics of epigenetic lead zinc mineralization in the western part of the rheinisches schiefergebirge germany in the western part of the rheinisches schiefergebirge three different types of epigenetic lead zinc vein mineralization in paleozoic rocks can be distinguished 1 syntectonic variscan veins 2 post variscan saxonian veins mainly in paleozoic siliceous clastic rocks 3 post variscan carbonate hosted mineralization in the aachen stolberg area ore impregnations occur in the triassic buntsandstein bunter sandstone and muschelkalk of the maubach mechernich triangular depression covering the paleozoic rocks data points define two distinct populations in both lead isotope diagrams and thus indicate two major variscan and post variscan mineralization events the lead isotope pattern of the paleozoic sedimentary rocks bears good evidence that this thick rock sequence may be the main source of metals for the mineralization the metals were mobilized at deeper levels by saline fluids at different times there are no direct indications for remobilization of the older variscan vein ore deposits the sandstone and carbonate hosted ore impregnations of maubach mechernich have a similar lead isotope pattern to the post variscan mineralization in the paleozoic sedimentary basement

volcanic belts as markers of the mesozoic cenozoic active margin of eurasia abstract from the triassic to the present linear belts of calc alkaline volcanism developed along the southern margin of eurasia in the triassic the calc alkaline belt can be traced in turan fore caucasus crimea and dobrogea its development is related to the closure of the paleo tethys when fragments of gondwana iran afghanistan etc were approaching eurasia since the early jurassic calc alkaline volcanism has been related to subduction of the oceanic crust of the mesozoic tethys five stages of calc alkaline volcanic activity can be distinguished early jurassic middle jurassic early cretaceous late cretaceous paleogene and late miocene quaternary the configuration of the volcanic belts the intensity of the volcanism and the chemistry of the erupted products change considerably from stage to stage mesozoic belts were most pronounced in the pontian transcaucasian segment of the margin starting from the late cretaceous and especially in the cenozoic the volcanic belts can be continuously traced from the balkans to afghanistan most of the belts were actually island arcs formed on the fragments of the hercynian of baikalian basement and in this respect similar to the island arc of japan only the incipient island arcs of senonian age formed close to the passive margin of gondwana are the exceptions they were built on oceanic crust and are geochemically close to the mariana arc at certain times early jurassic eocene parallel chains of island arcs existed in general the situation resembled the present day convergent boundary in the western pacific as closure of the tethys proceeded island arcs gave way to marginal continental volcanic belts with wide spread development of high potassium particularly shoshonitic series peaks of volcanic activity in the bajocian late cretaceous eocene and late miocene present alternated with quiet periods and corresponded to the times when the convergence rate between africa and eurasia increased the opening of the back arc basins is reflected in outbursts of basaltic rift type volcanism these outbursts occurred in the toarcian aalenian bathonian late jurassic aptian turonian and early middle eocene

tectonic reversal of the western doruneh fault system implications for central asian tectonics the left lateral doruneh fault system dfs bounds the north margin of the central iranian microplate cim and has played an important role in the structural evolution of the turkish iranian plateau the western termination of the dfs is a sinistral synthetic branch fault array that shows clear kinematic evidence of having undergone recent slip sense inversion from a dextral array to a sinistral array in the latest neogene or earliest quaternary similarly kinematic evidence from the anarak metamorphic complex suggests that this complex initially developed at a transpressive left stepping termination of the dfs and that it was inverted in the latest neogene to a transtensional fault termination the recognition that the dfs and other faults in ne iran were inverted from dextral to sinistral strike slip in the latest neogene and the likely connection between the dfs and the herat fault of afghanistan suggests that prior to the latest miocene all of the north iranian and northern afghan ranges were part of a distributed dextral fault network that extended from the west himalayan syntaxes to the western alborz also the recognition that regional slip sense inversion occurred across northern and northeastern iran after the latest miocene invalidates tectonic models that extrapolate pleistocene to recent fault slip kinematics and rates back beyond this time

copper zinc chromium and osmium isotopic compositions of the tepla barrandian unit black shales and implications for the composition and oxygenation of the neoproterozoic cambrian ocean abstract two neoproterozoic cambrian shale suites that consist of normal nbs and metal rich hmbs black shales from the tepla barrandian unit bohemian massif czech republic are studied in terms of their cu zn cr and re os isotopic compositions to improve our knowledge of elemental and isotopic mass balance of these elements in earth s oceans in the past and the extent of surface oxygenation at the neoproterozoic cambrian boundary the rock compositions indicate that the inputs of cu and zn have been controlled by variable proportions of metal rich authigenic and low metal terrigenous sources the latter having exceptionally low 65cu and partially 66zn in this respect our data confirm previous studies conclusions that organic rich sediments with high a terrigenous flux play an important role in the sinking of light zn in the oceans and provide new evidence that these types of rocks also represent the currently unidentified burial of very light cu in the ocean the chromium isotopic composition reveals a complex history of cr uptake and fractionation through the dominant cr input from different terrigenous sources with variable 53cr followed by cr fractionation that was controlled by redox states nbs on the other hand mixing and or continuous equilibrium isotopic exchange between seawater and hydrothermal cr was the dominant process for the hmbs the re os contents of the nbs were controlled by hydrogenous components which yield a poorly defined re os age for the least disturbed samples of 555 60 ma indicating an open system behavior while the hmbs re os composition was largely influenced by hydrothermal fluids during deposition the calculated authigenic 65cu which is similar to that in the present day ocean and highly positive 53cr values of the hmbs suggest high levels of surface oxygenation during the neoproterozoic cambrian transition furthermore the authigenic 66zn which is indistinguishable from that in the present day ocean may imply a constant zn isotopic composition of the oceans from the neoproterozoic because of the well balanced cycle of phosphates which were strongly adsorbed by fe hydroxides the radiogenic nature of the initial 187os 188os 0 6 although with a high associated error seems to not confirm previous indications of an abrupt increase of seawater 187os 188os during the late neoproterozoic due to the large scale radiogenic os flux into the ocean

evolution of uranogenic and thorogenic lead 1 a dynamic model of continuous isotopic evolution a dynamic model of the continuous isotopic evolution of uranogenic and thorogenic lead based on the minimum possible number of assumptions is proposed here the model is based on the simple assumption that the rate of change of the ratios 238 u 204 pb and w 232 th 204 pb present day values increased initially and after attaining a maximum started decreasing because of surface cooling of the earth the time t m when the and w rates of change attained their maximums is a model parameter depending on the age of formation of the different layers of the crust or in mixing processes on the participation of materials from the older or younger crust and mantle mathematically this is suitably described by a two parameter function which is the product of a linear and an exponential function the deduced equations of the model are calibrated according to the isotopic data on ore lead from the isotopic ratios of a lead sample it is possible to determine the two model ages uranogenic and thorogenic and the model parameter t m or another parameter t related to t m the values of the model parameters t m or t indicate the time of the enrichment ancient or younger in u pb which is an extremely important index for identifying the pb source type the use of these model parameters provide the possibility of a better theoretical description of the pb isotopic characteristics in the different types of sources

thrust tectonics of the binalood region ne iran the binalood region in ne iran which is an eastern segment of the alborz mountains is affected by thin skinned tectonics lower paleozoic jurassic cretaceous and cenozoic rock sequences as well as remnants of the paleo tethys oceanic realm are transported in a southwestward direction by several thrust faults which are of two generations 1 cimmerian and 2 alpine structural units in this region form either single thrust sheets or duplexes they have been displaced sequentially in a piggyback style from the hinterland ne to foreland sw under ductile brittle ductile and brittle conditions geometrically they constitute an antiformal stack breached on its southwestern side by major and minor out of sequence thrusts

sequence stratigraphic significance of sedimentary cycles and shell concentrations in the aitamir formation albian cenomanian kopet dagh basin northeastern iran abstract albian cenomanian siliciclastic shallow marine sediments of the aitamir formation kopet dagh basin northeastern iran form strongly asymmetric fining coarsening upward cycles which are interpreted as recording changes in relative sea level deepening shallowing cycles these cycles correspond to depositional sequences in which deposits of the lowstand systems tract are not present the sequence boundary coinciding with the transgressive surface shell concentrations are found in distinct positions within the depositional sequence as transgressive lags at the base of the transgressive systems tract tst in the maximum flooding zone mfz and at or close to the top of the highstand systems tract hst they are dominated by bivalves mainly oysters and or ammonites and differ from each other in a number of stratigraphic sedimentologic palaeoecological and taphonomic features such as species diversity preservation quality orientation percentage of disarticulation and degree of biogenic alteration characteristic features of concentrations at the base of the tsts are moderate time averaging distinct basal erosional surface sorting a chaotic to preferred convex up orientation and nearly total disarticulation of shells they are suggestive of an environment in which reworking and local transport was frequent events similar features are shown by concentrations near the tops of the hsts except that the shells were largely concentrated in lenses rather than in beds as in the transgressive lags associated sedimentary structures indicate deposition above fair weather wave base in a high energy environment concentrations occurring in the mfz in contrast are autochthonous and highly time averaged having accumulated during times of low rates of sedimentation below storm wave base this is supported by their high preservation quality comparatively high percentage of articulated shells shells of infaunal organisms commonly preserved in life position high glauconite content and biogenic alteration being the most important taphonomic features

structures of the zagros fold thrust belt in iran the zagros fold thrust belt in iran forms the external part of the zagros active orogenic wedge it includes a sequence of heterogeneous latest neoproterozoic phanerozoic sedimentary cover strata 7 to 12 km thick and composed of alternating incompetent and competent layers overlying precambrian crystalline basement with a complex pre zagros structural fabric balancing structures of the cover statigraphic units in the zagros fold thrust belt requires in sequence and out of sequence involvement of the precambrian basement in the deformation six detailed balanced and retrodeformable cross sections which are constructed based on geological and geophysical data across various sectors of the belt show fault bend and fault propagation folds interpreted to have formed by slip on their subjacent thrusts out of sequence basement rooted thrusts as the interpretations in the constructed cross sections suggest have breached the cover basement interface and using incompetent cover strata for propagation cut across the cover structures and have created associated new folds superimposed upon the pre existing structures this style of deformation which has resulted in structural complexity of the belt characterizes a 200 to 300 km wide zone of distributed partly synchronous deformation with along strike and across strike variations it also implies that the zagros fold thrust belt as the external part of the orogenic wedge is still in its subcritical condition with internal deformation to achieve a critical taper in creating structural complexity in addition to out of sequence thrusting mechanically weak layers evaporites and mudstones of the cover strata have played a significant role by providing several detachment horizons shortening estimates across the belt are variable based on the constructed cross sections and their restorations minimum shortening estimates range from 16 percent to 30 percent in different sectors of the belt

approximate fluid substitution for vertical velocities in weakly anisotropic vti rocks despite the prevalence of elastic anisotropy in rocks most models used routinely for wave propagation imaging and rock physics assume an isotropic earth the main reason for using isotropic approximations is that we seldom measure enough parameters to characterize the stiffness tensor of a rock completely fluid substitution is an important example because of an incomplete knowledge of the stiffness tensor often we choose isotropic equations over their anisotropic form assuming weak anisotropy we derive an approximate form of the anisotropic fluid substitution equation for seismic waves propagating along the symmetry axis of a transversely isotropic medium the approximation takes the form of the usual isotropic calculation with a simple first order correction proportional to the thomsen anisotropic parameter thus requiring only three elastic constants because can be either greater than or less than zero in a vti medium we can explain why isotropic fluid substitution sometimes overpredicts

palaeobiogeographic implications of late bajocian late callovian middle jurassic dinoflagellate cysts from the central alborz mountains northern iran abstract the dalichai formation with an age of late bajocian late callovian was sampled in central alborz mountains of northern iran and studied for palynological palaeobiogeographical and palynocorrelation purposes palynological studies revealed diverse and well preserved dinoflagellate cyst assemblages and lead to identification of three zones i e cribroperidinium crispum late bajocian dichadogonyaulax sellwoodii bathonian to early callovian and ctenidodinium continuum early to middle callovian zones subzone a of the d sellwoodii zone early to middle bathonian was also differentiated this biozonation corresponds to those recognised in northwest europe furthermore the ammonoid families recorded including phylloceratidae oppeliidae reineckeiidae perisphinctidae haploceratidae parkinsoniidae and sphaeroceratidae which confirm the late bajocian to late callovian age are quite similar to those of northwest europe and the northwestern tethys the close similarities of the dinoflagellate cyst assemblages and ammonite fauna of northern iran with those of northwest europe and the northwestern tethys during the middle jurassic indicate direct but episodic marine connection and faunal exchange between the two areas

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

isotopic evolution of the mantle the role of magma mixing trace element and isotopic data for magmas from the two major mantle reservoirs appear to be inconsistent the incompatible elements and sr and nd isotopes show that abyssal tholeiities morb are form a reservoir that has current and time integrated depletions of the elements that are fractionated into a melt morb however have206pb 204pb and207pb 204pb ratios suggesting long term enrichment in u pb i e future single stage ages alkali basalts and tholeiities from continents and oceanic islands are derived from lile and u pb enriched reservoirs sr and nd isotopic ratios however appear to indicate that some of these basalts are derived from unfractionated reservoirs and others from reservoirs with time integrated depletions the apparent stages of the mantle reservoirs are much younger than the ages of continental shields these inconsistencies can be reconciled by assuming that oceanic and continental basalts are mixtures of magmas from depleted and enriched reservoirs morb are slightly contaminated depleted magmas while ocean island and continental basalts are mixtures of morb or a depleted picritic parent magma and an enriched end member having trace element patterns similar to high k magmas such as kimberlites or nephelinites the mixing relations are such that mixtures can be enriched in u pb rb sr nd sm 206pb 204pb relative to primitive mantle yet appear to have time integrated depletions in143nd 144nd and87sr 86sr a small amount of contamination by material from an enriched reservoir can explain the pb results for morb depleted basalts are more sensitive to pb than to rb or nd contamination the238u 204pb of uncontaminated morb may be about 7 compared to 7 9 for the primary growth curve and 10 for the enriched reservoirs similarly continental and ocean island basalts may represent mixtures of enriched and depleted magmas if so the ages of mantle reservoirs have been underestimated we propose that both of the major mantle magmas source are in the upper mantle and that both are global in extent the shallower one 200 km depth is inhomogenous having been enriched metasomatised at various time by fluids from the depleting layer it may also be the sink of subducted sediments and hydrothermally altered oceanic crust the deeper source 220 670 km depth is more homogenous more garnet rich and provides depleted magmas which however become contaminated as they rise through the shallow encriched layer partial melting and diapiric ascent originated in the thermal boundary layer between the two chemically distinct layers magma mixing prior to eruption is an inevitable consequence of a chemically layered mantle with depleted magmas rising through an enriched uppermost mantle this allows quantification of the heretofore nebolous concept of mantle metasomatism

the triassic and associated rocks of the nakhlak and aghdarband areas in central and northeastern iran as remnants of the southern turanian active continental margin abstract the triassic succession of the nakhlak area in central iran consists of 1 the lithologicallalam formation which is a sequence of shallowing and coarsening upward marine turbidites deposited equon the forearc side of an accretionary prism 2 the baqoroq formation a resentatsequence of coarse to fine polymictic fluvial conglomerates and 3 the ashin for mation which comprises alternating distal marine shales and sand stones that have turbiditic characteristics these rocks are wnot litholog ically similar to time equivalent lithostratigraphic units of late permian triassic age of the aghdarband area of northeastern iran which are interpreted to be forearc deposits but they may have formed in close association with them in a single tectonic and sedimen tary framework accepting the 135 counterclockwise rotation of the central east iranian microcontinent authorwith respect to the turan plate since triassic time and assuming that the triassic rocks of the nakhlak and the late permian to triassic rocks of the aghdarband formed in a single tectonosedimentary framework on the no rthern side of the paleo tethyan oceanic realm we present here a sequential develop ment in this scheme rocks of the bnakhlak and aghdarband areas are considered deposits of a forearc basin ridge slope centralenvironment the separation of the nakhlak succession from the rest of the turan plate and its transportation to central iran might have occurred as 1 a lithospheric segmen t of the turan plate first detached from turan and then attached to the iranian plate and finally rotated with it in a coun terclockwise direction to successionits present site or 2 as a thin thrust slice first obducted over th e iranian continental shelf and then displaced to cen tral iran by its counterclockwise rotation introduction

advances in research of asian geology a summary of 1 5m international geological map of asia project abstract the international geological map of asia at a 1 5 000 000 scale igma5000 is the first digital asian geological map under the standard of the commission for the geological map of the world cgmw major advances that have been achieved in compiling the map are manifested in the following understandings 1 large amounts of mesozoic volcanic rocks occurring in the eastern asian coastal area are mainly cretaceous instead of upper jurassic lower cretaceous most of the carboniferous permian volcanic rocks in central asia seem not to be arc volcanics but the product of an extensional stage the basal boundary of the meso neoproterozoic jixian section in china is not dated at 1 8 ga as defined previously but less than 1 68 ga 2 the most significant neoarchean tectono thermal events in the sino korean craton and the indian craton took place at 2 5 ga rather than at 2 7 ga the basement of the yangtze craton was finally formed at 0 75 0 8 ga which is 0 2 0 3 ga later than the greenville orogenic cycle geologically south china is identified to be an early paleozoic caledonian foldbelt the qinling belt where no oceanic basin was developed in triassic times is not an indosinian collisional orogen but a continental crust subduction one when pangea was formed indo australian gondwana had been joined to paleo asia and between them there was no oceanic basin i e no paleo tethys which continued from paleozoic to mesozoic a huge indosinian orogenic belt existed on the southern margin of paleo asia to the north of the zagros himalayas 3 asia is a composite continent consisting of three major cratons the siberian indian and arabian and three huge orogenic belts with a number of minor cratons and numerous microcontinents included the main body of the asian continent took its shape during the mesozoic the orogenic belts belong respectively to three global tectonic domains the paleo asian tethyan and pacific the small cratons such as sino korea yangtze tarim and sibumasu are thought to be affiliated to the tectonic transform zone between gondwana and siberia they had been situated on the northern margin of gondwana before the disappearance of the paleo asian ocean and were lying on the southern margin of paleo asia after the closing of the paleo asian ocean and then the opening of the tethys the fact that ophiolites in asia appear to get progressively younger in age from north to south throws light on the phanerozoic evolutionary process of the dispersion of gondwana and the accretion of asia accompanied by a southward migration of its orogenic belts

paleozoic to triassic ocean opening and closure preserved in central iran constraints from the geochemistry of meta igneous rocks of the anarak area the anarak area belongs to an ophiolitic belt along the northern border of the central east iranian microcontinent and is thought to contain fragments of the former paleotethys and neotethys oceans a wide range of meta igneous rocks from the late paleozoic to triassic anarak metamorphic complex amc and nearby meraji area have been studied to constrain the origins and modes of emplacement of oceanic remnants in central iran our samples occur as layers and lenses embedded in extensive sequences of deformed meta sediments and smaller bodies of serpentinized ultramafic rocks petrographical and geochemical data combined with field and satellite observations allow recognition of seven types of meta igneous rocks preserved from low grade to blueschist facies conditions their origins based on relative abundances of immobile trace elements include subduction zone mid ocean ridge ocean intraplate and continental rift settings these data and existing geochronological constraints show the amc formed an accretionary complex formed exhumed incrementally during the carboniferous permo triassic and triassic igneous rocks from meraji formed in the early devonian due to opening of the paleotethys and belong to a rift sequence extending over 300 km along the edge of the central east iranian microcontinent the amc and nearby rock associations record the evolution of the paleotethys during a complete wilson cycle between ca 450 and 225 ma with implications for 1 continental rifting 2 ocean opening 3 subduction initiation 4 ocean intraplate and continued mid ocean volcanism 5 ridge subduction and 6 final closure of the ocean during continent continent collision alternate interpretations of the anarak metabasites are possible but require radical departures from the widely accepted model for tectonic evolution of the paleotethys with the existence of paleotethyan backarc basin s and permian or earlier collision of continental blocks in central iran in any case our results show accretionary complexes preserved along suture zones contain an important record of the evolution of oceanic crust from ancient ocean basins

neoproterozoic to early cambrian franciscan type melanges in the tepla barrandian unit bohemian massif evidence of modern style accretionary processes along the cadomian active margin of gondwana abstract melanges have been reported from a variety of modern tectonic settings and are a hallmark of the franciscan type subduction accretion complexes in the precambrian however well documented examples of melanges become extremely scarce this paper describes in detail neoproterozoic to early cambrian melanges recently recognized in the cadomian basement of the tepla barrandian unit bohemian massif the melanges are of sedimentary and tectonic origin and include voluminous successions of graywackes interpreted to represent mass transport deposits presumably along the upper slope of an accretionary wedge the clast compositions indicate multiple episodes of mixing of terrigenous arc derived and deep water pelagic material moreover abundant bodies of meta basalts interpreted as dismembered seamounts or pillow volcanoes were emplaced tectonically into various structural levels of this sedimentary melange by two different mechanisms at an upper level the irregular to elongated bodies of basalts were offscraped only weakly strained and incorporated in the sedimentary matrix that exhibits steep cleavage indicating horizontal pure shear shortening and oblate strain in contrast at a lower level disc shaped and closely spaced basalt bodies are ductilely sheared and reworked into a flat lying prolate to plane strain fabric suggesting horizontal ductile flow presumably along the base of the accretionary wedge during flat slab oceanic subduction our new u pb ages also reveal that the melange formation continued until the early cambrian

scale of experiment and rock physics trends because rock is heterogeneous at all scales it is often invalid to assign a single porosity permeability resistivity or velocity to a volume in the subsurface well data demonstrate that these properties can vary appreciably between two points just a foot apart the same happens at the pore scale consider for example a ct scan of a 1 3 mm berea sandstone cube figure 1 the porosity of this sample as calculated by counting the blue pore space pixels is 0 164

evolution of uranogenic and thorogenic lead 2 some differences in the variations of the206pb 204pb and208pb 204pb ratios abstract on the basis of a dynamic model of a continuous pb isotope evolution the variations in the isotopic ratios of uranogenic and thorogenic pb in a number of young ore deposits ocean sediments and volcanic rocks from mid ocean ridges oceanic islands island arcs and continents are evaluated the deviations in the th u ratio from its model values are calculated a model parameter t which indicates a more ancient enrichment in u pb crustal type pb sources or younger enrichment in u pb mantle type pb sources is also calculated the relative change in the th u ratio is close to 1 for mantle type pb sources lower t values and decreases for crustal type pb sources higher t values an interpretation of these changes could be connected with the differences in the u and th geochemical behaviours in metamorphic processes under the conditions of a deeper mantle or crustal source owing to the differences in their valence states in some cases they have similar u 4 and th 4 migration abilities in others u 6 and th 4 considerably different

stratigraphy and ammonite fauna of the upper shemshak formation toarcian aalenian at tazareh eastern alborz iran abstract with a thickness of 3900 m the tazareh section is one of the thickest developments of the shemshak formation in the alborz range it overlies with sharp and disconformable contact the limestones and dolomites of the lower middle triassic elikah formation and is topped again with a disconformable contact by the marls and limestones of the middle jurassic dalichai formation the nearly exclusively siliciclastic succession represents a range of environments from fluvial channels flood plains swamps and lake systems to storm dominated shelf and a comparatively deep marine and partly dysoxic basin the segment of the section between 2300 and 3500 m is exclusively marine and contains a moderately diverse ammonite fauna ranging from the middle toarcian to the upper aalenian the ammonite fauna comprises 21 taxa among them the new genus shahrudites with two new species shahrudites asseretoi and s stoecklini from the middle aalenian bradfordensis zone the other ammonites from the shemshak formation at tazareh as elsewhere in north and central iran are exclusively tethyan in character and closely related to faunas from western and central europe an ammonite based correlation of toarcian aalenian successions of the eastern alborz with time equivalent strata of the lut block part of the central east iranian microcontinent ca 500 km to the south suggests a strong influence of synsedimentary tectonics during the deposition of the upper shemshak formation

the cimmerian evolution of the nakhlak anarak area central iran and its bearing for the reconstruction of the history of the eurasian margin new structural sedimentological petrological and palaeomagnetic data collected in the region of nakhlak anarak provide important constraints on the cimmerian evolution of central iran the olenekian upper ladinian succession of nakhlak was deposited in a forearc setting and records the exhumation and erosion of an orogenic wedge possibly located in the present day anarak region the triassic succession was deformed after ladinian times and shows south vergent folds and thrusts unconformably covered by upper cretaceous limestones following the late jurassic neo cimmerian deformation palaeomagnetic data obtained in the olenekian succession suggest a palaeoposition of the region close to eurasia at a latitude around 208n in addition the palaeopoles do not support large anticlockwise rotations around ver tical axes for central iran with respect to eurasia since the middle triassic as previously suggested the anarak metamorphic complex amc includes blueschist facies metabasites associated with discontinuous slivers of serpentinized ultramafic rocks and carboniferous greenschist facies variscan metamorphic rocks including widespread metacarbonates the amc was formed at least partially in the triassic its erosion is recorded by the middle triassic baqoroq formation at nakhlak which consists of conglomerates and sandstones rich in meta morphic detritus the amc was repeatedly deformed during post triassic times giving origin to a complex structural setting characterized by strong tectonic fragmentation of previously formed tectonic units based on these data we suggest that the nakhlak anarak units represent an arc trench system developed during the eo cimmerian orogenic cycle different tectonic scenarios that can account for the evolution of the region and for the occurrence of this orogenic wedge in its present position within central iran are critically discussed as well as its relationships with a presumed variscan metamorphic event the cimmerian orogeny affecting the southern eurasian margin between turkey and thailand is related to the collision of several microplates most of which detached from northern gondwana in the early permian during the opening of the

the variscan belt in central europe main structures geodynamic implications open questions abstract the variscan belt of europe originated from the confrontation of northern europe and gondwana with intervening pre variscan blocks cadomian and older armorica tepla barrandean moravo silesian though a strike slip component cannot be excluded geological evidence suggests a subduction collision process newly discovered features include basaltic rocks with morb affinities high pressure metamorphic rocks trench deposits and large scale allochthonism which also affects the pre variscan basement and has often led to an inversion of the metamorphic isogrades large scale thrusting is evident at all crustal levels and is also observable by geophysical methods the structure of the variscan crust is best described as horizontal tectonic layering late ordovician through carboniferous convergence closed one rhenohercynian and one saxo thuringian basin to the north and at least one mediterranean basin to the south of the pre variscan blocks subduction occurred from the north as well as from the south down under the dorsal core region the exact timing and the driving mechanism of this bilateral activity remains a problem likewise uncertain are the exact limination of the pre variscan blocks and the existence and width of oceanic areas in the saxothuringian zone and in the south facing part of the moldanubian zone there is good evidence of early palaeozoic rifting and of late ordovician through carboniferous plate convergence palaeomagnetic and palaeoclimatic constraints however suggest only a limited extent of oceanic basins in these areas while they appear to allow a wider ocean at the rhenohercynian saxothuringian boundary which is relatively unobtrusive from the geological point of view research during the past decade has produced a wealth of information on the variscan fold belt in europe the resulting geodynamic models however are extremely diverging evidently it is not the time yet for definitive statements the present paper intends to review the state of knowledge to deduce such basic items of a geodynamic model as appear reasonably well documented and to point out the most urgent open questions stress will be laid on central europe which offers a complete cross section through the northern flank of the variscan belt and where we have carried out most of our studies during the last years

paleoenvironmental reconstruction using biological markers for the upper triassic middle jurassic sedimentary succession in tabas basin central iran abstract the upper triassic middle jurassic sedimentary succession in the tabas basin with a thickness of about 1600 m provides a case showing geochemical property changes through the triassic jurassic boundary the studied section kamarmacheh kuh is composed of the marine nayband formation norian rhaetian overlain by siliciclastic sediments of ab e haji formation lower jurassic aalenian detailed geochemical analyses were conducted on selected samples from both formations and the results were used to infer paleo depositional conditions most of the studied samples contain

the shanderman eclogites a late carboniferous high pressure event in the nw talesh mountains nw iran the shanderman metamorphic complex exposed along the caspian foothills of the talesh mountain western alborz iran has always been interpreted as an ophiolitic fragment of the palaeotethys ocean according to our new data this unit consists of metamorphic rocks mainly represented by garnet staurolite micaschists with large bodies of metabasites containing well preserved eclogitic phase assemblages the shanderman complex sc was later intruded at middle crustal levels by intermediate basic intrusive bodies new ar ar ages of paragonitic white micas in equilibrium with the high pressure assemblages have given a late carboniferous age 315 9 ma our new data suggest that the sc was equilibrated in high pressure conditions during an orogenic event that predates the eo cimmerian orogeny by more than 100 ma and that may be tentatively ascribed to the variscan orogeny sensu latu we suggest that the shanderman complex represents a fragment of the upper palaeozoic european continental crust the occurrence of eclogites in these regions can be explained by two different hypotheses 1 the sc high pressure rocks can be related to the accretion of gondwana related transcauscasian moesian microplate to the southern margin of eurasia or 2 the sc eclogites can represent a fragment of the late palaeozoic variscan belt sensu latu of central europe which has been translated eastwards during permian along a dextral megashear zone taking from a pangea b to a pangea a plate configuration this metamorphic unit was stacked southwards on the northern edge of the iran plate during the eo cimmerian events occurring at the end of the triassic the eclogite bearing basement of the sc was finally exhumed at the end of the eo cimmerian orogeny as suggested by the composition of the basal layers of the shemshak group dated here middle jurassic that cover the crystalline rocks of the sc along a regional non conformity the sc was probably displaced further southwards during the mesozoic opening of the south caspian basin and the tertiary thrust stacking and dextral shearing accompanying the formation of the alborz intracontinental belt

structural evolution of the kopeh dagh fold and thrust belt ne iran and interactions with the south caspian sea basin and amu darya basin abstract we present a detailed stratigraphic and structural study of the kopeh dagh fold and thrust belt in ne iran which is an investigation of the complex polyphased tectonic history of this belt and its links with the adjacent south caspian sea and amu darya basins based on numerous field surveys a large amount of 2d and 3d seismic data borehole data and more than 150 new biostratigaphic datings a new detailed biostratigraphic chart and 4 main regional cross sections illustrate the importance of lateral facies variations and structural inheritance in the present day structure of the belt after the cimmerian orogeny corresponding to the closure of the paleotethys ocean in late triassic early jurassic times a middle jurassic post collisional rifting event was associated with the deposition of one of the main source rocks of the kopeh dagh and the amu darya basin kashafrud formation following this rifting event over 7 km of sediments were accumulated until the tertiary above a regional post triassic unconformity the occurrence of local uplifts during the late cretaceous early paleocene is interpreted as a consequence of regional scale modification of plate slab coupling in the neotethys subduction zone the main inversion of the kopeh dagh occurred at late eocene times when the far field deformation developed in eurasia as a consequence of the locking of the neo tethys subduction this folding phase is sealed in the western part of the belt by a major eocene oligocene unconformity at the base of the thick sedimentary series belonging to the south caspian sea basin the bulk of sedimentary infill in the south caspian sea basin is oligocene and younger and it is probably related to syn compressional downward flexure of the resistant basement basin at the onset of the alpine phase in the eastern part of the kopeh dagh this deformation is characterized by middle jurassic graben inversion with evidence of forced folding short cuts and as well by larger scale basement uplifts in contrast the northwestern part of the belt shows thrust faults involving basement and fault propagation folds within the sedimentary sequence the kopeh dagh presents tectonic structures that are parallel to the paleotethys suture zone which emphasizes the importance of the structural inheritance and inversion processes during the structural evolution of the belt finally a change from a mostly dip slip to a mostly strike slip tectonics occurred during the pliocene within the kopeh dagh as a consequence of a major tectonic reorganization in north east iran

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

isotopic composition of lead in proterozoic anoxic metasedimentary and volcanogenic rocks from the bohemian massif czech republic with metallogenetic implications abstract the isotopic composition of lead in normal and metal rich black shales and associated volcanogenic rocks has been studied in the barrandian upper proterozoic of the bohemian massif which is a part of the central european variscan belt these rocks played an important role in the metallogeny of the bohemian massif the late proterozoic age of metamorphism is evidenced by the slope of the secondary isochron of the uranogenic lead corresponding to the age of 635 45 ma and by the model age of 540 590 ma of thorogenic lead in the samples with low th u ratios in most of the samples the leached pb is less radiogenic than the residual pb no correlation was established between the presence of more radiogenic samples and the distance towards variscan granitoids the samples are mostly associated with the upper proterozoic volcano sedimentary sequences far from variscan intrusions and only some occur in the exocontacts of variscan plutons this suggest that most of the uranium was introduced into rocks during cadomian metamorphism rather than variscan tectonomagmatic phases however a possible contribution of radiogenic lead in connection with the latter events as well as some heterogeneity in u pb and th pb ratios from the time between sedimentation and metamorphism cannot be excluded the comparatively low 208 pb 204 pb ratios indicate that thorium was not mobilized by the metamorphic fluids and testifies that th is less mobile under metamorphic conditions the 207 pb 204 pb values 15 57 15 63 of less radiogenic lead in the rocks are close to those of galenas from different variscan polymetallic mineralizations in the bohemian massif which suggests a common source from a well mixed reservoir as observed in ore leads in mature island arcs or at active boundaries between continental and oceanic plates

velocity dispersion and upscaling in a laboratory simulated vsp a laboratory and numerical study was conducted to investigate the impact of scale dependent seismic wave propagation in randomly layered media as applied to sonic logs surface seismic and vertical seismic profiles vsps analysis of the laboratory results 1 confirmed the wavelength dependence of velocities inferred from traveltimes 2 indicated that scale effects can introduce traveltime errors when upscaling from logs to surface seismic and vsps and 3 illustrated that erroneous vsp interval velocities can result when layer thicknesses are smaller than about one tenth of the wavelength a simple approximate recipe is presented for estimating these traveltimes by successively filtering the medium using a running backus average and ray theory the scale dependent dispersion was also predicted well using a more rigorous invariant imbedding formulation the predicted traveltimes using the approximate recipe compare well with the times observed in the laboratory stack of steel and plastic layers and in numerical studies of stratified media the dispersion curves predicted by the approximate method also show the overall behavior computed with the more rigorous invariant imbedding formulation

pre hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the schwarzwald crystalline sw germany lead isotopes of k feldspars from five granites of the se schwarzwald and from metamorphites are positively correlated in 207 204 as well as 208 204 vs 206 204 diagrams

tertiary and quaternary geodynamics of southern lut iran as deduced from palaeomagnetic isotopic and structural data abstract palaeomagnetic measurements and k ar age determinations carried out on lavas from dash e lut in southeast iran reveal an anticlockwise rotation of about 90 of the depression south of lut between paleocene and miocene time it is probably associated with the collision between india and asia

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

geohistory analysis and petroleum reservoir characteristics of lower cretaceous neocomian sandstones eastern kopet dagh basin northeastern iran the eastern part of the kopet dagh basin of northeastern iran contains over 4000 m of upper jurassic through tertiary strata deposited in a variety of shallow marine and terrestrial environments geohistory diagrams from well and outcrop data provide a useful mechanism with which to relate the stratigraphic framework of this part of the basin to the tectonic history of the region during some episodes of regional tectonic uplift e g episodes occurring 99 95 ma 74 70 ma and 63 54 ma sediment accommodation space continued to be created in the basin due to sediment loading and compaction of increased amounts of fine grained sediments in some cases concomitant with eustatic sea level rises much of the post jurassic subsidence in this part of the kopet dagh basin was aused by sediment loading rather than tectonism the effects of basin geohistory on petroleum reservoir properties were studied using the lower cretaceous neocomian shurijeh formation as an example detailed petrologic sedimentologic and geohistory analyses done on this formation show that the petroleum reservoir properties of shurijeh sandstones were affected by their depositional settings and the subsequent subsidence of these units through meteoric and compactional hydrogeologic regimes in this part of the kopet dagh basin these rocks consist mostly of sublitharenitic red beds deposited during a regressive phase of sedimentation dominated by rapid siliciclastic sediment supply the lower and middle parts of the interval studied were deposited in low sinuosity braided fluvial systems and the upper part was deposited in high inuosity meandering systems by relating the paragenetic sequence of the shurijeh sandstones to the geohistory of this formation we determined the timing of both porosity destroying and porosity enhancing diagenetic processes and related these processes to the timing of petroleum generation

organic matter and the concentration of metals in precambrian stratiform deposits of the bohemian massif abstract organic matter is preserved in unmetamorphosed and low grade metamorphic pyrite and or mn bearing black shales pyrite mn stratiform ores cherts and siliceous stromatolites of proterozoic age in the barrandian area of the bohemian massif this organic matter consists mostly of kerogen with an isotopic composition and relative concentration of free radicals which depend on the metamorphic grade of the host rock 13 c pdb 30 7 to 36 9 nrel 0 161 to 0 132 enrichment of the kerogen in the light isotope of carbon a marked isotopic shift towards more positive 13c values with increasing metamorphic grade and the very low crystallinity of the incipient graphite lattice reflect the original aliphatic alicyclic character and algal origin of the kerogen its composition is similar to that of shungite chiefly aliphatic and alicyclic hydrocarbons were identified in the solvent extracts of these proterozoic rocks alkane patterns differ according to host rock type indicating their possible syngenetic origin other identifiable organic compounds amino acids carboxylic acids phenols and aromatic aldehydes are probably a result of later contamination the concentrations of u th v cr sb ag au zn and cu in pyrite and pyrite mn ores are relatively low in contrast stratiform concentrations of u v and chiefly au ag sb and zn are confined to siliceous stromatolites rich in kerogen or to adjacent jaspilites from a palaeogeographic viewpoint the highest concentrations of metals occur at the boundary between the oxidic facies stromatolites jaspilites and intercalations of other rocks and the reduced facies black shales where a syndiagenetic geochemical barrier developed mineralization was significantly influenced by subalkaline volcanism stromatolites of an intertidal type apparently formed where volcanoes rose to sea level stromatolitic breccias are intruded by chromium rich green quartz veins and locally covered by tuffs

early permian pangea b to late permian pangea a the pre drift wegenerian model of pangea is almost universally accepted but debate exists on its pre jurassic configuration since tedirving introd ucedpangea b by placing gond wana farther to the east by v3000 km with respect to laurasia on the basis of paleomagnetic data new paleomagnetic data from radiometrically dated early permian volcanic rocks from parts of adria that are tectonically coherent with africa gondwana integrated with published coeval data from gondwana and laurasia again only from igneous rocks fully support a pangea b configuration in the early permian the use of paleomagnetic data strictly from igneous rocks excludes artifacts from sedimentary inclination error as a contributing explanation for pangea b the ultimate option to reject pangea b is to abandon the geocentric axial dipole hypothesis by introducing a significant non dipole zonal octupole component in the late paleozoic time averaged geomagnetic field we demonstrate however by using a dataset consisting entirely of paleomagnetic directions with low inclinations from sampling sites confined to one hemisphere from gondwana as well as laurasia that the effects of a zonal octupole field contribution would not explain away the paleomagnetic evidence for pangea b in the early permian we therefore regard the paleomagnetic evidence for an early permian pangea b as robust the transformation from pangea b to pangea a took place during the permian because late permian paleomagnetic data allow a pangea a configuration we therefore review geological evidence from the literature in support of an intra pangea dextral megashear system the transformation occurred after the cooling of the variscan mega suture andlasted v20 myr in this interval the neotethys ocean opened between india arabia and the cimmerian microcontinents in the east while widespread lithospheric wrenching and magmatism took place in the west around the adriatic promontory the general distribution of plate boundaries and resulting driving forces are qualitatively consistent with a right lateral shear couple between gondwana and laurasia during the permian transcurrent plate boundaries associated with the pangea transformation reactivated variscan shear zones andwere subsequently exploitedby the opening of western neotethyan seaways in the jurassic

the cimmerian orogeny in northern iran tectono stratigraphic evidence from the foreland from the permian onwards the gondwana derived iran plate drifted northward to collide with eurasia in the late triassic thereby closing the palaeotethys this eo cimmerian orogeny formed the cimmeride fold and thrust belt the upper triassic middle jurassic shemshak group of northern iran is commonly regarded as the cimmerian foreland molasse however our tectono stratigraphic analysis of the shemshak group resulted in a revised and precisely dated model for the triassic jurassic geodynamic evolution of the iran plate initial cimmerian collision started in the carnian with subsequent late triassic synorogenic peripheral foreland deposition flysch lower shemshak group subduction shifted south in the norian onset of neotethys subduction below iran and slab break off around the triassic jurassic boundary caused rapid uplift of the cimmerides followed by liassic post orogenic molasse middle shemshak group during the toarcian aalenian upper shemshak group neotethys back arc rifting formed a deep marine basin which developed into the oceanic south caspian basin during the late bajocian late jurassic

platform carbonates of the upper jurassic mozduran formation in the kopet dagh basin ne iran facies palaeoenvironments and sequences abstract the mozduran formation a thick carbonate succession over 1200 m of the upper jurassic callovian kimmeridgian in northeast iran has been studied to determine its palaeoenvironments and sequences detailed petrographic investigations have led to the recognition of several microfacies and microfacies groups which constitute four palaeoenvironmental associations tidal flat beach lagoonal platform margin and open marine most of the mozduran formation sediments were deposited on a rimmed carbonate platform adjacent to a deeper marine environment the mozduran carbonate succession consists of five thick shallowing upward sequences 3rd order cycles no major hiatus has been recognized between these cycles therefore the contacts are considered subtidal conformities drowning unconformities these 3rd order cycles can be correlated with those recognized in upper jurassic strata in other parts of the world thus they are considered largely eustatic mainly tectono eustatic in origin numerous small scale shallowing upward cycles parasequences are contained within the major shallowing upward cycles both subtidal and peritidal parasequences showing an abrupt deepening of microfacies have been recognized a combination of episodic subsidence and autocyclic processes could have been responsible for the formation of these small scale cycles rapid carbonate accumulation reflected in rare first generation marine cements including meteoric cements resulted in grain to grain pressure solution and sutured contacts during burial with late cements filling the remaining pores many of the platform margin grainstones packstones have been replaced by coarsely crystalline dolomite possibly through seawater pumping and kohout convection during the transgressive and highstand phases of sea level

rules of upscaling for rock physics transforms composites of randomly and independently drawn elements the tight trends transforms between two rock physical properties obtained in the physical or digital laboratory on cm or mm sized samples may hold for a composite constructed of these samples one requirement is that all the elements of the composite obey the same trend another requirement is that the composite is spatially uncorrelated and hence approximately isotropic the final requirement is that the underlying elemental transforms are approximately linear the methods we use to address this exportability of trends for the dynamic elastic moduli or the elastic wave impedance versus porosity permeability versus porosity and electrical resistivity versus porosity are respectively theoretical elastic bounding numerical reservoir scale fluid flow and electrical current simulations a practical implication is that if an elastic property of a large volume is determined from remote sensing be it seismic or cross well data its average porosity can be estimated using the transforms established at a much smaller scale then this average porosity can be translated into the hydraulic and electrical properties once again using the elemental transforms established in the physical or digital laboratory