low to medium pressure variscan metamorphism in galicia nw spain evolution of a kyanite bearing synform and associated bounding antiformal domains

microseismicity in the region of tehran we record and analyze small earthquakes around tehran iran using the permanent seismological network of the institute of geophysics of the university of tehran and two temporary dense seismological networks installed for several weeks during 1999 and 2000 regional seismicity is distributed throughout central alborz extending from the caspian sea to the iran plain with the highest level of activity east of tehran related to the mosha and to the garmsar faults which both dip northward and have had strong historical earthquakes our focal mechanisms the first for these faults confirm a left lateral strike slip motion

ground surface response to continuous compaction of aquifer system in tehran iran results from a long term multi sensor insar analysis abstract most of the developed groundwater basins in iran are subject to land subsidence hazards resulting from the over extraction of groundwater several areas in tehran the capital city and a provincial center in north central iran have been reported to be subsiding at different rates in this study we present the results of an interferometric synthetic aperture radar insar time series analysis of tehran using different sar data between 2003 and 2017 by constructing more than 400 interferograms derived from 39 envisat asar c band 10 alos palsar l band 48 terrasar x x band and 64 sentinel 1 c band sar datasets we compile displacement time series from interferometric observations using the small baseline sb technique our analysis identifies 3 distinct subsidence features in tehran with rates exceeding 25 cm yr in the western tehran plain approximately 5 cm yr in the immediate vicinity of tehran international airport and 22 cm yr in the varamin plain to the southeast of tehran city the temporal pattern of land subsidence which is dominated by a decreasing trend generally follows the regional decline in groundwater level which suggests that anthropogenic processes caused by excessive groundwater extraction are the primary cause of land subsidence integrating a decadal time series of subsidence constructed from multi sensor insar with in situ observations suggests that inelastic and permanent compaction dominates the main deformation regime of the tehran aquifer and the ratio between elastic and inelastic deformation is approximately 0 4 a geological analysis indicates that the shape of the subsidence bowl in the western tehran plain does not follow the trend of major mapped faults in the region in contrast the subsidence bowl in varamin is controlled by the pishva fault which suggests that either this fault acts as a hydrologic barrier to the groundwater flow in this region or that the differences in sediment thickness causes the discontinuity in land subsidence

evidence for distributed active strike slip faulting in nw iran the maragheh and salmas fault zones abstract the study area is located in the northwestern iranian plateau and exhibits ongoing convergence between the arabian and eurasian plates not absorbed by the zagros orogenic belt in this paper we provide our geological observations made along the maragheh and salmas strike slip fault zones that affect the southern portion of northwest iran to the south of the north tabriz fault we use a combined methodology to characterize active faulting along these fault zones that included remote sensing analysis of high resolution satellite imagery and aerial photographs digital elevation models dems tectonic geomorphology investigations and geological field surveys active transtension is a common feature along the maragheh and salmas faults and our observations suggested that the onset of active transtension and related local extension along the faults in pleistocene occurred no earlier than 2 ma the maragheh and salmas fault zones contribute to the accommodation of dextral strike slip faulting in the region between the main recent fault to the south and the north tabriz fault to the north the spatial pattern of strike slip faulting over the northwest iranian region including the north tabriz fault the ahar fault salmas and maragheh fault zones favors a distributed deformation model which could help to advance our understanding of geodynamic processes and the level of seismic hazard in this part of the iranian plateau

active faulting within a megacity the geometry and slip rate of the pardisan thrust in central tehran iran geological survey of iran christ church college oxford natural environment research council economic and social research council

paleoearthquakes of the past 30 000 years along the north tehran fault iran the north tehran fault ntf is located at the southernmost piedmont of central alborz and crosses the northern suburbs of the tehran metropolis and adjacent cities where 15 million people live extending over a length of about 110 km the ntf stands out as a major active fault and represents an important seismic hazard for the iranian capital after historical seismicity in order to characterize the activity of the ntf in terms of kinematics magnitude and recurrence intervals of earthquakes we carried out a first paleoseismological study of the fault within its central part between tehran and karaj cities we opened a trench across a 3 m high fault scarp affecting quaternary deposits our study shows that the scarp is the result of repeated events along a main n115 e trending shallow dipping thrust fault associated with secondary ruptures from the trench analysis and infrared stimulated luminescence irsl dating of fault related sediments we interpreted between 6 and 7 surface rupturing events that occurred during the past 30 kyrs their magnitudes estimated from the displacements along the faults are comprised between 6 1 and 7 2 the two last events the largest occurred during the past 7 9 1 2 ka which yields a holocene slip rate of 0 3 mm yr the 7 earthquakes scenario suggests a regular periodicity with a mean recurrence interval of 3 8 kyrs however the two most recent events could correspond to the two largest historical earthquakes recorded in the area in 312 280 b c and 1177 a d and therefore suggest that the ntf activity is not regular

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

palaeoseismicity and pottery investigating earthquake and archaeological chronologies on the hajiarab alluvial fan iran for millennia humans have lived in locations that are highly vulnerable to large earthquakes often out of strategic or cultural necessity and or the proximity of these locations to resources necessary for survival despite the often catastrophic effects when large earthquakes occur recent history reveals that human nature is to rebuild rather than relocate implying that seismic activity is not a sufficient deterrent of population growth in tectonically vulnerable areas in order to investigate whether this was the case for ancient civilisations and thus perhaps a fundamental tenet of human behaviour a palaeo earthquake history was developed for the active cheskin and ipak faults in northwestern iran and compared with the well resolved archaeological history of the nearby sagzabad cluster settlements of zagheh 7170 6300 bp ghabristan 6215 4950 bp and sagzabad 4050 2350 bp combining new geologic geomorphic and chronologic datasets revealed the presence of a fault propagated anticline formed by large mw 6 5 7 0 earthquakes on a blind thrust fault that projects to seismogenic depth directly beneath the sagzabad cluster settlement sites large earthquakes with a return period of 90 probability under most faulting scenarios that the energy release from these earthquakes would have been of sufficient magnitude to generate peak horizontal acceleration pha values at the sagzabad cluster in excess of likely threshold values for complete settlement destruction poisson modelling assuming a time displacement repeating model for earthquake recurrence indicates a 66 42 probability of one two earthquakes that would generate pha 0 25 g occurring during occupation of zagheh a 79 55 probability for ghabristan and an 88 65 probability for sagzabad despite the near certainty that the residents of these holocene settlements experienced large destructive earthquakes the near continuous history of occupation at this area suggests that early humans were not apt to relocate in response to earthquake activity environmental e g alluviation stream channel avulsion climate change cultural and or political factors may have been more important drivers of settlement shifts and abandonment at the sagzabad cluster of iran

geoarchaeology and the value of multidisciplinary palaeoenvironmental approaches a case study from the tehran plain iran geoarchaeology and the value of multidisciplinary palaeoenvironmental approaches a case study from the tehran plain iran

morphological dating of cumulative reverse fault scarps examples from the gurvan bogd fault system mongolia summary we relate reverse fault scarp morphology formed by several earthquake dislocations to the average deformation rate using a morphological dating model based on a diffusion analogue of erosion our scarp degradation model includes diffusive erosion during the interseismic period the gravitational collapse of the coseismic fault scarp just after formation and the variation of the surface rupture location interactions between thrusting and geomorphic processes acting on scarp morphology are analysed along the gurvan bogd range in mongolia four main processes acting on scarp morphology were distinguished i gravitational collapse of the frontal scarp resetting the diffusive scarp if fault offsets are big and faulting is localized 2 progressive erosion of the fault scarp during the interseismic period 3 folding associated with the frontal thrust and backthrusts 4 competing alluvial deposition on mountain piedmont slopes and abrasion of the fault scarp by wash processes the growth of cumulative reverse fault scarps is suppressed when they are located in the outwash of major drainage basins they can grow higher in distance from major catchment discharges the modelling suggests that the morphology of the scarp and its apparent degradation stage depend on the parameters controlling the amount of frontal collapse the magnitude of coseismic offsets the dip of the fault near the surface and the step distance between faults folding associated with thrusting creates a convexity on the upper part of the scarp and increases its height the comparison of different scarp profiles suggests that folding leads to an overestimate of the morphological age we estimate a diffusion coefficient at 3 3 1 7 m 2 ka l morphological ages calculated with our model confirm that slip rate along reverse faults of the gurvan bogd range has not been constant over the last 100 ka

kinematic links between the eastern mosha fault and the north tehran fault alborz range northern iran kinematic interaction of faults is an important issue for detailed seismic hazard assessments in seismically active regions the eastern mosha fault emf and the north tehran fault ntf are two major active faults of the southern central alborz mountains located in proximity of tehran population similar to 9 million we used field geomorphological and paleoseismological data to explore the kinematic transition between the faults and compare their short term and long term history of activity we introduce the niknamdeh segment of the ntf along which the strike slip kinematics of emf is transferred onto the ntf and which is also responsible for the development of a pull apart basin between the eastern segments of the ntf the ira trench site at the linkage zone between the two faults reveals the history of interaction between rock avalanches active faulting and sag pond development the kinematic continuity between the emf and ntf requires updating of seismic hazard models for the ntf the most active fault adjacent to the tehran metropolis study of offsets of large scale morphological features along the emf and comparison with estimated slip rates along the fault indicates that the emf has started its left lateral kinematics between 3 2 and 4 7 ma according to our paleoseismological data and the morphology of the nearby emf and ntf we suggest minimum and maximum values of about 1 8 and 3 0 mm year for the left lateral kinematics on the two faults in their linkage zone averaged over holocene time scales our study provides a partial interpretation based on available data for the fault activity in northeastern tehran region which may be completed with studies of other active faults of the region to evaluate a more realistic seismic hazard analysis for this heavily populated major city c 2014 elsevier b v all rights reserved

implications of earthquake focal mechanism data for the active tectonics of the south caspian basin and surrounding regions summary the south caspian basin is a relatively aseismic block within the alpine himalayan belt but is surrounded by zones of high seismicity we used the focal mechanisms of 16 earthquakes whose source parameters we determined from inversion of body waves and the mechanisms of 15 other earthquakes to determine the style of faulting in the seismic belts surrounding the south caspian basin earthquakes beneath the talesh mountains of north west iran and immediately off shore in the south west caspian sea have shallow thrust mechanisms showing that the continental crust of north west iran is overthrusting the oceanic like crust of the south caspian basin earthquakes south of the caspian sea in northern iran show a mixture of focal mechanisms both high angle reverse faulting and left lateral strike slip faulting mechanisms are observed in the high alborz mountains farther south on the edge of the central iran plateau oblique left lateral reverse mechanisms are observed it appears that the ne direction of shortening between central iran and the south caspian basin is partitioned into pure left lateral strike slip and thrusting in the wnw trending high alborz but is accommodated by oblique faulting in lower elevations earthquakes in the kopet dag mountains east of the caspian sea also show a mixture of high angle reverse and strike slip faulting mechanisms and may be another example of the partitioning of oblique slip into strike slip and thrust motion normal faulting mechanisms at centroid depths of 35 50 km dominate in the belt of seismicity that extends across the central caspian sea the significance of the normal faulting earthquakes is enigmatic it is improbable that these events represent the motion between the southern caspian basin and eurasia for they imply a sense of motion that is incompatible with the observed topography and folding in the sediments two shallow earthquakes at about 12 km depth in this belt one a small event and the other a large second subevent of a multiple earthquake have thrusting mechanisms suggesting that shortening occurs as the continental crust of the northern caspian sea is thrust over the oceanic like crust of the southern caspian basin shortening is also suggested by the orientations of folds in the sedimentary cover south of the central caspian sea seismic belt we suggest that this shortening does indeed represent a nne motion of the caspian sea relative to eurasia but that the motion is slow and has not produced many earthquakes the deeper normal faulting events may be related to bending or down dip extension of the incipient subducted slab if the motion of the caspian sea relative to eurasia is indeed slow then the motion in the alborz between central iran and the south caspian basin will be almost the same as that between iran and eurasia as has previously been assumed the combined effect of the overthrusting of the south caspian basin by the talesh alborz mountains in the south and by the continental crust of the northern caspian sea in the north will lead to the eventual destruction of the south caspian basin and the possible formation of an intermediate depth dipping seismic zone within the continental interior similar to that presently observed in the hindu kush

sr z sbnd nd isotopic record of multi stage interactions between mantle derived magmas and crustal components in a collision context the ultramafic granitoid association from vivero hercynian belt nw spain late stage epizonal calc alkaline granitoids of the hercynian belt are often associated with coeval more basic rocks such granitoids have been the focus of special attention when studying the role of mantle derived magmas in granitoid genesis these studies conclude that basic magmas are involved in granitoid production but their contribution to the chemical composition of granitoids is often controversial the vivero massif nw spain includes calc alkaline granitoids and coeval ultramafic and mafic rocks but these granitoids are syntectonic and intruded into middle crustal levels during an early stage scattered major and trace element chemistry together with heterogeneous sr nd isotopic results preclude an origin of this ultramafic to granitoid association by any closed system fractionation process ultramafic rocks include peridotites pyroxenites and homblendites with endi from 3 5 to 1 3 and 87sr86sr i ratio from 0 7059 to 0 7080 they are interpreted as cumulates formed by in situ fractional crystallization from contaminated basaltic magmas particularly by interaction with 87sr enriched fluids mafic rocks comprise biotite amphibole diorites quartz diorites and tonalites with ndi from 3 8 to 0 0 and 87sr86sr i ratio from 0 7058 to 0 7073 they represent either cumulates or more evolved magmas of calc alkaline affinity these rocks display an inverse correlation between the degree of differentiation and the degree of contamination inferred from isotope data this points to wall rock assimilation by thermal erosion during ascent of basic magmas up to the middle crust and supports the participation of mantle sources with positive end and 87sr86sr i 0 7058 granitoids range from amphibole biotite tonalites through biotite granodiorites to monzonitic granites they show an isotopic trend which diverges from that of ultramafic and mafic rocks endi 6 0 to 1 9 decreases while 87sr86sr i ratio 0 7061 to 0 7082 increases from tonalites to monzonitic granites reflecting an increasing contribution of crustal components in more differentiated rocks assimilation and fractional crystallization mixing included account for such an evolution contamination of basic magmas by this process occurring at deeper crustal level produced hybrid tonalites and related mafic magmatic enclaves only monzonitic granites are interpreted as pure crustal melts their hree fractionated patterns gd yb 4 5 suggest equilibrium with a garnet rich residuum partial melting of moderate time integrated rb sr protolith such as greywackes and or meta igneous rocks of intermediate acid composition could account for the isotopic composition of these monozogranites this example shows that at least some calc alkaline granitoids of collisional setting are not produced by pure intra crustal melting they are formed through a complex multi stage hybridization process involving mantle derived magmas crustal components and several concomitant magmatic processes

tracing crustal evolution in the nw iberian peninsula through the rbsr and upb systematics of palaeozoic granitoids a review abstract the abundant granitoids in the palaeozoic basement of the northwestern iberian peninsula include 470 440 ma old suites early middle ordovician now present as orthogneisses and several variscan suites the age data presently available suggest that the latter have been generated in three separate time intervals 330 320 ma ago late visean early namurian 310 300 ma ago westphalian and 290 280 ma ago late stephanian autunian rb sr whole rock and u pb zircon systematics along with field and chemical evidence testify to the generation of the early and late palaeozoic granitoids from lower palaeozoic and precambrian maximum age 1 7 1 6 ga sedimentary sequences respectively the source rocks contained zircons derived from a late archaean early proterozoic continental crust that probably underlies the whole of western europe although for the greater part modified beyond recognition by younger crustal reworking

geochemical studies in the drainage basin of the rio vouga portugal abstract the hydrothermal waters in the vouzela region portugal have a temperature of 68 c and are characterized by a high content of f li b bicarbonate sulphate and silica ninety three water samples including two hydrothermal waters were analyzed for major and trace elements in order to investigate the genesis of the hydrothermal water in the vouzela region two older hercynian granites are exposed the abas granite and the sao pedro do sul granite the abas granite is intersected by the ribama fault albitization is ubiquitous other alteration effects are tourmalinization k feldspathization and muscovitization these processes and the associated sn w deposits were induced by the intrusion of the younger viseu granite in the present situation rainwater penetrates into the abas granite especially via the ribama fault and the greisenization zone it becomes part of a hydrothermal system leaches li f b and silica and rises via the termas fault in the hydrothermal springs of termas de sao pedro do sul geothermal equilibrium calculations yield a temperature of 205 10 c for the thermal reservoir the percentage of mixing with cold groundwater near the surface in the circulation system is estimated at 73 the circulation system is possibly maintained by the heat generated by the decay of u th k and their daughter products elements which are encountered in extremely high concentrations in the sao pedro do sul granite

deciphering oblique shortening of central alborz in iran using geodetic data the alborz is a narrow 100 km and elevated 3000 m mountain belt which accommodates the differential motion between the sanandaj sirjan zone in central iran and the south caspian basin gps measurements of 12 geodetic sites in central alborz between 2000 and 2002 allow to constrain the motion of the belt with respect to western eurasia one site velocity on the caspian shoreline suggests that the south caspian basin moves northwest at a rate of 6 2 mm year with respect to western eurasia north south shortening across the alborz occurs at 5 2 mm year to the south deformation seems to extend beyond the piedmont area probably due to active thrusting on the pishva fault we also observe a left lateral shear of the overall belt at a rate of 4 2 mm year consistent with the geological motion observed along e w active strike slip faults inside the belt e g the mosha fault

faulting and folding in quaternary deposits of tehran s piedmont iran abstract tehran lies on the southern flank of the central alborz an active mountain belt characterized by many historical earthquakes some of which have affected tehran itself the border between the alborz mountain and the tehran s piedmont northern part of tehran city is marked by the north tehran fault ntf dividing the eocene rock formation from the alluvial units of different ages early pleistocene to the recent alluvium a detail mapping of the piedmont combined with structural study reveal that two active thrust faults situated south of the ntf are of importance for hazard assessment of the city the geomorphological evidences along the ntf are not in agreement with an active fault indicating that the fault activity may have been shifted southward furthermore differentiation of newly recognized alluvial units and their inferred ages together with the mapped fault pattern permit us to characterize the quaternary deformation the late pleistocene alluvial deposits consist of three alluvial fans among them the youngest one together with the modern alluvial fan defines the holocene deposit the present deformation in the piedmont is accommodated along vertically left lateral strike slip faults and low angle thrust faults trending in range from n070 to n110e

late archaean early proterozoic source ages of zircons in rocks from the paleozoic orogen of western galicia nw spain abstract u pb data are reported for nine suites of zircons and three monazites from the paleozoic orogen in western galicia nw spain one paragneiss and six orthogneisses from the early paleozoic basement and two carboniferous ca 310 ma old intrusions of two mica granite new whole rock rb sr analyses along with earlier data indicate an age of ca 470 440 ma ordovician for the emplacement of the granitic precursors of the orthogneisses monazite from the paragneiss also yields an u pb age of ca 470 ma for all nine investigated suites of zircons the u pb systematics signal the presence of a minor proportion of precambrian zircon the zircon data from two orthogneisses and the paragneiss display roughly linear arrays with upper intercepts between about 3 0 ga and 2 0 ga and lower intercepts between ca 480 and 460 ma the former are interpreted as approaching the age of the old zircon component and the latter as reflecting either the time of crystallization of new zircons from the magma orthogneisses or the time of radiogenic lead loss from the old zircons paragneiss the suites of zircons from all other investigated orthogneisses suffered isotopic disturbance posterior to the granite emplacement 470 440 ma ago in most cases leading to false discordias without geochronological significance similarly the zircons of the two investigated two mica granites do not produce meaningful discordias because of post paleozoic disturbance the monazite u pb systems of the latter granites indicate sub recent lead loss from the high initial 87 sr 86 sr ratios an involvement of precambrian continental crust material is evident in the generation of the early paleozoic suite of granites while the zircon u pb data give evidence of the presence of about 3 0 2 0 ga old late archaean early proterozoic components in the source material zircons from the oldest sedimentary rocks in the area now present as catazonal paragneisses and a likely source for the granites likewise reveal a provenance age of 3 0 2 0 ga the late archaean early proterozoic source rocks in western galicia probably formed part of an archaean continental crust underlying much of western europe but mostly modified beyond recognition by younger events

post neogene right lateral strike slip tectonics at the north western edge of the lut block kuh e sarhangi fault central iran abstract late cenozoic strike slip tectonics and active faulting in central iran have been extensively described in the last decades this study presents results of integrated structural and geomorphological analyses along the kuh e sarhangi fault a major ne sw striking brittle deformation zone that cuts across the basement and neogene quaternary cover successions at the north western edge of the lut block structural investigations document post neogene ne sw dextral transpressive tectonics and geomorphic evidence support a late quaternary age for the faulted alluvial fan deposits along the bedrock range fronts northward the nearly parallel great kavir doruneh fault is known to have active left lateral strike slip kinematics and its easternmost segment was considered as the northern margin of the lut block the new findings impose reconsideration of the current regional kinematic models with implications on the seismogenic fault networks of central iran

stable isotope constraints on the origin of kaolin deposits from variscan granitoids of galicia nw spain abstract kaolinite rich fractions of 18 o from 16 5 to 22 4 and in d from 99 to 40 these widely spread values question a single crystallization process as no statistically significant overall correlation between 18 o and d can be obtained the analytical spread is such that 11 of the 43 analyzed separates plot below the kaolinite weathering line and one at the line separating the supergene from hypogene evolution field noteworthy for this wide scatter is the fact that some separated size fractions especially from ramon fazouro deposit contain also up to 65 halloysite as well as varied amounts of contaminating minerals generally considered as relicts from parental igneous rocks such as quartz illite muscovite and feldspars however the addition of these minerals does not appear to significantly bias the isotopic data of the 18 o and d values with a best fit line d 8 75 18 o 248 r 0 896 n 5 95 rather similar to the kaolinite weathering line of d 7 5 18 o 220 however the overall spread of values and particularly those for coarser material together with occurrences of halloysite strongly suggest that higher temperature process es also occurred kaolinite and also likely halloysite crystallized from waters whose 18 o values were of meteoric signature from about 5 to 1 at temperatures ranging from about 20 c to 50 c the higher crystallization temperatures especially at the sedimentary lendo deposit imply fluids at higher temperatures than during a climatic controlled weathering process probably of a low temperate hydrothermal character with a fluid isotopically close to meteoric origin however interaction with fluids at higher temperatures and with higher 18 o cannot be ruled out because the relatively wide ranges of kaolin 18 o and d values are difficult to reconcile with a narrow range of 18 o and d for the interacting parental fluids the most likely scenario for the kaolinite and halloysite precipitation is then a two stage process of interaction with meteoric waters at close earth surface temperature but with one of the two episodes occurring at temperatures slightly above those of weathering processes even under tropical conditions there is no compelling evidence for an episode of significantly high temperature such as in most hydrothermal fluid rock interactions but a low temperature episode of about 50 c cannot be ruled out unequivocally especially for the

evaluation of relative tectonic activity in the tehran basin central alborz northern iran abstract recent deformations in the area studied control structural expansions influenced by tectonic activities causing transformations of geologic features and morphological landforms the tehran basin is located at the southern edge of the central alborz and is the result of the arabian eurasian convergence and clockwise rotation of the south caspian basin with respect to eurasia hence assessment of the drainage pattern permutations and mountain fronts appears necessary we used six significant morphometric indices for this evaluation stream length gradient sl drainage basin asymmetry af hypsometric integral hi ratio of valley floor width to valley height vf drainage basin shape bs and mountain front sinuosity smf the combined analyzed indices represented the relative active tectonics iat the study area was divided into four regions according to the values of iat these classes include class 1 very high activity class 2 high class 3 moderate and class 4 low the regions with high relative tectonic activity mostly correspond with the active structures in the basin the tectonic activity classes 1 and 2 coincide with the fault mountain fronts in the southern edge of the central alborz especially the north tehran fault the parts of the central mosha fault and the regions in the east the southeast and the west of the basin indicate the moderate class of tectonic activity class 3 the low elevation plain in the south and southwest of the area shows the lowest relative tectonic activity class 4

plio quaternary stress states in ne iran kopeh dagh and allah dagh binalud mountain ranges abstract ne iran including the kopeh dagh and allah dagh binalud deformation domains comprises the northeastern boundary of the arabia eurasia collision zone this study focuses on the evolution of the plio quaternary tectonic regimes of northeast iran we present evidence for drastic temporal changes in the stress state by inversion of both geologically and seismically determined fault slip vectors the inversions of fault kinematics data reveal distinct temporal changes in states of stress during the plio quaternary since 5 ma the paleostress state is characterized by a regional transpressional tectonic regime with a mean n140 10 e trending horizontal maximum stress axis 1 the youngest modern state of stress shows two distinct strike slip and compressional tectonic regimes with a regional mean of n030 15 e trending horizontal 1 the change from the paleostress to modern stress states has occurred through an intermediate stress field characterized by a mean regional n trending 1 the inversion analysis of earthquake focal mechanisms reveals a homogeneous transpressional tectonic regime with a regional n023 5 e trending 1 the modern stress state deduced from the youngest fault kinematics data is in close agreement with the present day stress state given by the inversions of earthquake focal mechanisms according to our data and the deduced results in northeast iran the arabia eurasia convergence is taken up by strike slip faulting along ne trending left lateral and nnw trending right lateral faults as well as reverse to oblique slip reverse faulting along nw trending faults such a structural assemblage is involved in a mechanically compatible and homogeneous modern stress field this implies that no strain and or stress partitioning or systematic block rotations have occurred in the kopeh dagh and allah dagh binalud deformation domains the plio quaternary stress changes documented in this paper call into question the extrapolation of the present day seismic and gps derived deformation rates over geological time intervals encompassing tens of millions of years

rb sr evidence for the presence of ordovician gsranites in the deformed basement of the badajoz cordoba belt sw spain a rb sr whole rock investigation of suites of samples from two orthogneiss bodies in the almendralejo area of the oporto portalegre badajoz cordoba belt points to an ordovician age for the granitic magmatism about 470 ma for the almendralejo gneiss peralkaline metagranite and about 425 ma for the ribera del fresno gneiss leucocratic subaluminous metagranite both with high initial87sr 86sr ratios this points to a post ordovician hercynian age for the metamorphism and tectonic deformation that affected the area including the gneisses and rules out the alleged cadomian or even older age

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

patterns of historical earthquake rupture in the iranian plateau the iranian plateau accommodates the 35 mrn yr convergence rate be tween the eurasian and arabian plates by strike slip and reverse faults with relatively low slip rates in a zone 1000 km across although these faults have only locally been the subject of paleoseismological studies a rich historical and archeological record spans several thousand years long enough to establish recurrence intervals of 1000 to 5000 yr on individual fault segments several clusters of earthquakes provide evidence of interaction among reverse and strike slip faults probably due to adjacent faults being loaded by individual earthquakes the dasht e bayaz sequence of 1936 to 1997 includes earthquakes on left lateral right lateral and reverse faults the neyshabur sequence of four earthquakes between 1209 and 1405 respected the seg ment boundary between the neyshabur and binalud reverse fault systems the two pairs of earthquakes may have ruptured different faults in each segment similar to the 1971 and 1994 san fernando california earthquakes the 1978 tabas reverse fault earthquake was preceded by the 1968 ferdows earthquake part of the dasht e bayaz sequence the north tabriz fault system ruptured from southeast to north west in three earthquakes from 1721 to 1786 a previous cluster may have struck this region in 855 to 958 the mosha fault north of tehran ruptured in three earthquakes in 958 1665 and 1830 five large earthquakes struck the tehran region from 743 to 1177 but only two that large have struck the area since 1177 other earthquakes occurred in pairs in the talesh mountains near the caspian sea 1863 1896 the iran turkey border 1840 1843 and the nayband gowk fault system both 1981 other historical events did not occur as parts of sequences the historic seismic moment release in iran accounts for only a small part of the plate convergence rate which may be due to aseismic slip or to the iranian historical record long as it is being too short to sample long term deformation across the plateau no historic earthquakes of m 8 have struck iran however several long straight strike slip faults doruneh west neh east neh and nayband have not sustained large historical earthquakes raising the possibility that these long faults could produce earthquakes of m 8 thereby removing at least part of the apparent slip deficit an increased understanding of iran s seismic hazard could be obtained by an extensive paleoseismology program and space geodetic arrays supplementing the abundant historical and archaeological record

the nilpena ureilite an unusual polymict breccia implications for origin nilpena 173 g a new ureilite find from the parachilna area of south australia is an unusual polymict breccia containing polymineralic aggregates mineral fragments and achondritic and chondritic lithic enclaves in a dark c rich matrix the polymineralic aggregates consist of equigranular textured olivine fa20 and pigeonite en75wo9fs16 and exhibit evidence of shock in the form of undulose extinction and kink banding monomineralic fragments consist of olivine fa19 24 with highly forsteritic rims up to fa3 and pigeonite and appear to be derived by brecciation of the polymineralic aggregates the enclave material consists of lithic granular olivine fragments porphyritic enstatite fragments either enstatite chondrite or aubrite olivine clinobronzite fragments resembling an h3 chondrite and eucritelike lithic fragments composed of plagioclase an98 salitic clinopyroxene wo48 5en31 4fs20 1 and olivine fa49 53 the matrix contains kamacite generally rich in p schreibersite and troilite the texture of nilpena suggests formation by disruption of a olivine pigeonite granular aggregate while the presence of the diverse chondritic and achondritic enclave material suggests an origin as a surface or near surface breccia like other ureilites nilpena is strongly differentiated with respect to cosmic abundances but is significantly enriched in ba and lree a lack of correlation of lithophile elements with fe fe mg ratio among ureilites suggests that the differentiation was not caused by varying degrees of partial melting of a homogeneous source a cumulate origin therefore seems more plausible

cumulative right lateral fault slip rate across the zagros makran transfer zone role of the minab zendan fault system in accommodating arabia eurasia convergence in southeast iran the zendan minab zone is the transition zone between the zagros collision to the west and makran subduction to the east it is also linked to the north with the nayband gowk fault system that bounds the lut block to the east the total convergence rate between arabia and eurasia is estimated to range between 23 and 35 mm yr 1 in a nne trending direction the deformation through the minab zendan system is accommodated within two fault systems the western n160 e trending minab zendan fault system and the eastern north south sabzevaran jiroft fault system the study area is characterized by a well defined succession of quaternary deposit levels the age of these deposits was estimated by archaeological data regional palaeoclimate correlations and constrained by additional in situ10be dating in another paper in this study these deposits exhibit offsets both lateral and vertical that are evaluated by satellite image analysis and gps profiles thanks to offsets and ages the strike slip rates associated with the minab zendan and the sabzevaran jiroft fault systems are calculated to be 5 1 1 3 or 6 6 1 5 and 6 2 0 7 mm yr 1 respectively these results allow an evaluation of the velocity vector of the musandam peninsula oman with respect to the lut block of 11 4 2 0 or 12 9 2 2 mm yr 1 in a n10 15 e direction close to the gps estimates this study also constrains the in plane slip rates for each fault previous works indicate that the zagros accommodates only 10 mm yr 1 of shortening while 10 mm yr 1 should be accommodated by the alborz mountains in northern iran this last 10 mm yr 1 may be accommodated through the nayband gowk system and the east iranian ranges implying that the two fault systems constituting the zagros makran transfer zone have different geodynamic roles the western minab zendan fault system links the makran and zagros deforming zones whereas the northwestern jiroft sabzevaran fault system is transmitting the deformation to the nayband gowk system and then to the alborz ranges the presence of another such strike slip zone within the makran seems to indicate that the accommodation zone between the zagros and makran is wide of the order of 400 km we interpret this deformation pattern that accompanies the genesis of the immature transform zone by a flexure of the slab under the zagros makran transfer zone instead of a tear in the slab that may be expected to induce a sharper transition zone

evolution of a kyanite bearing belt within a ht lp orogen the case of nw variscan iberia kyanite replaces andalusite in a belt of ordovician and silurian pelitic rocks that form a narrow synform pinched between high grade antiforms in nw variscan iberia kyanite occurs across the belt in al rich black pelites in assemblages i kyanite chloritoid chlorite muscovite and ii kyanite staurolite chlorite muscovite in i kyanite occurs in the matrix and in kyanite muscovite aggregates that pseudomorph earlier andalusite porphyroblasts the aggregates are found across the belt and can still be recognized in assemblage ii and even in iii andalusite staurolite biotite muscovite this latter being a hornfelsic silurian schist where kyanite is relic and staurolite occurs in the matrix and is resorbed inside new massive pleochroic andalusite kfmash and mnkfmash pseudosections have been constructed using thermocalc for al rich and al poorer compositions from the belt chloritoid zoning in al rich rocks containing assemblage i plus chloritoid chlorite thermometry complemented with garnet chlorite thermometry in al poorer lithologies mean that the path is one of increasing pressure and temperature conditions prior to assemblage i with earlier andalusite stable are those of the andalusite chloritoid chlorite field as testified by chloritoid enclosed in andalusite porphyroblast rims the passage from assemblage i to ii implies a prograde path within the kyanite field assemblage iii represents peak conditions indicating a prograde staurolite consuming reaction across a kfmash field leading eventually to a locally found andalusite biotite muscovite hornfels the lowest pressure stages are recorded by cordierite biotite in al poor pelites garnet bearing mnkfmash assemblages in al poorer pelites record conditions similar to assemblages ii and iii the replacement of andalusite by kyanite in assemblage i is attributed to downdragging of andalusite bearing rocks into a synform as testified by the strained andalusite porphyroblasts affected by a subvertical crenulation cleavage prograde metamorphism in the eastern contact of the belt is due to heat transferred to the belt from the ascending high grade antiform across the vivero fault

block rotation induced by the change from the collision to subduction implications for active deformations within the areas surrounding south caspian basin abstract northern of iran is experiencing a complex deformation due to the northward convergence of arabian plate since late cenozoic the majority of this complexity is due to the presence of a rigid old thickened oceanic crust of the south caspian basin scb this rigid block trapping between eurasia and central iran makes an inhomogeneous body in the context of deforming zone composed by alborz talesh apsheron balkhan caucasus and kopeh dagh located in south west northwest north and east of the scb respectively among them the formation and evolution of the alborz orocline are under debates the presence of sinistral strike slip faults with normal separation initially understood by nw motion of northern alborz inferred by gps measurements raised long debates in the latest proposition it is assumed that the scb is rotating clockwise this study however shows that the model of scb s rotation and or nw ward motion of scb is not kinematically consistent therefore it aims at constraining the alborz northern central iran and nw iran as a sliver block are rotating around the scb the block rotation is facilitated by geo sutures inherited since paleozoic therefore this article specifically pays attention to the active extensional tectonic regime as a signal for the area that is under rotational movement the block rotation induced by the change from the collision in kopeh dagh to subduction scb and kura basin beneath alborz talesh apsheron balkhan and great caucasus respectively and consequently the reactivation of ancient geo sutures in northern iran led to a rapid rotation of microcontinents this assumption may account for the ongoing deformational pattern in alborz and nw iran the disharmonic arabian plate convergence and scb s retreating induce forces by the block rotation and cause episodic tectonic activities that are responsible for current tectonic complexity in the north of iran if the climax of the collision was 5 ma then the block rotation and related deformation are younger events with respect to the collision and subduction

plio quaternary tectonic regime changes in the transition zone between alborz and kopeh dagh mountain ranges ne iran abstract this paper is concerned with the changes in the plio quaternary stress states in ne iran and provides evidence for regional active deformation across a wide transition zone between the alborz and kopeh dagh mountains the arabia eurasia convergence is involved in the strike slip faulting along ne trending left lateral faults in the eastern alborz as well as nw trending right lateral faults in the western kopeh dagh the inversion result of fault kinematic data slip vector measurement of fault plane and focal mechanisms strongly indicates an active transpressional tectonic regime in the study area we provide evidence for drastic temporal changes in the stress state during the plio quaternary based on the inversions of fault kinematic data a regional transpressional tectonic regime with a mean n036 20 e trending horizontal 1 is representative for the modern stress state the older state reveals compressional to transpressional tectonic regimes comprising a n135 20 e trending horizontal 1 the modern transpressional tectonic regime characterized by a regional ne trending 1 is consistent with the inversion of earthquake focal mechanisms that yield a n47 e trending 1 for the present day stress state the kinematic results are significantly homogeneous and mechanically compatible with the active geological structures in the way that reverse and strike slip faulting are coherent with a single 1 direction

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

lithogeochemical studies of aureoles around the panasqueira tin tungsten deposit portugal multi element lithogeochemical surveys of aureoles surrounding tin tungsten bearing quartz vein systems have been utilized infrequently in exploring for these deposits at panasqueira beira beixa portugal a wrich quartz vein mineralization occurs in the beira schists surrounding a greisenized cupola and offers a suitable test case for such lithogeochemical studies therefore shale samples were collected at a density of about 6 samples per km2 pronounced anomalies of tin and tungsten have been detected in these samples together with those of other elements coeval with the mineralizing processes

active couple indentation in geodynamics of nnw iran evidence from synchronous left and right lateral co linear seismogenic faults in western alborz and iranian azerbaijan domains abstract situated within the central portion of the arabia eurasia collision zone nnw iran exhibits an interesting active tectonic context characterized by synchronous left and right lateral co linear seismogenic faults along the adjacent wnw striking west central alborz e g the rudbar earthquake fault and iranian azerbaijan e g the north tabriz seismogenic fault these structural domains are deforming as a single deformable geomechanical territory between the nearly rigid central iran and south caspian domains to the ssw and nne respectively in this paper we analyze tectonic interactions of these active structural domains and their influence on the geodynamics of nnw iran based on morphotectonic and seismological investigations indentation tectonics is suggested to play an important role in the geodynamics of this territory at a plate tectonic scale the rigid arabian plate acts as the main indenter which bulldozes the less rigid crustal domains ahead into folded belts within zagros and caucasus to the north and pushes other blocks aside in this deformation system the south caspian domain acts as a backstop against southern and western deformation zones the structural domains of alborz to the east and iranian azerbaijan caucasus to the west are separated by the nnw striking astara talesh dextral transpressional zone analysis of morphotectonic features and focal mechanisms conducted in this central portion of nnw iran confirms dextral faulting localized along the nnw striking deformation zone which is in agreement with the observed reverse earthquake faulting on west dipping planes we also discuss the contraction trajectories derived from kinematics and geometry of active folding and faulting features observed within nnw iran our study highlights two prominent sets of fan shaped trajectories dominating in the west and east sides of the n s zone in the astara zanjan direction we propose a couple indentation geodynamic model to explain the fan shaped pattern of these two laterally convergent sets of trajectories within the talesh azerbaijan and alborz domains

evolution and paragenetic context of low δd hydrothermal fluids from the panasqueira w sn deposit portugal new evidence from microthermometric stable isotope noble gas and halogen analyses of primary fluid inclusions abstract the evolution paragenetic context and origin of remarkably low d hydrothermal fluids from the hercynian panasqueira w sn cu ag deposit have been investigated through a combined microthermometric stable isotope halogen and noble gas fluid inclusion study large variations in d between 60 and 134 have been observed in primary fluid inclusions from growth zones in a quartz crystal pa66 paragenetically constrained to the main sulfide stage mss of ore formation the same fluids exhibited relatively constant fluid inclusion homogenisation temperatures 254 to 260 c salinities 7 4 to 8 7 wt nacl equivalent and calculated fluid 18o 3 8 to 4 4 all the fluids exhibited 40ar excesses mean molar br cl and i cl ratios varied from 2 3 10 3 4 2 10 3 and 8 10 4 10 10 4 respectively with the more br rich fluids being associated with the more deuterium depleted fluids the low palaeolatitude of panasqueira throughout the main stages of ore formation and the overwhelming predominance of meteoric fluids in the main late and post ore mineralising fluids with d of 40 to 65 lends little support for any models involving low d palaeometeoric water the limited range of 40ar cl ratios 1 1 10 5 1 6 10 5 also precludes boiling during the mss or mixing of meteoric water with highly fractionated deuterium depleted magmatic waters as viable mechanisms for producing the low d fluids the high br cl and i cl of the mss fluids indicate significant fluid interactions with organic rich sediments or metasediments in particular regionally abundant carboniferous coals or coaly sediments that are inferred to be depleted in deuterium by around 85 compared to palaeometeoric water the large range of d observed in the mss fluids may be explained by isotopic exchange of palaeometeoric water with these coals at varying water rock wt wt ratios between 0 02 and 0 002 with fluid oxygen isotopic compositions controlled by exchange with the beira schists such a model is consistent with the requirements that any satisfactory model must take into account viz i the relative constancy of temperature salinity 40ar and fluid 18o during excursions to low d ii the high i cl and br cl ratios observed and iii the coincidence of these low d fluids with the onset of precipitation of polymetallic sulfides and phosphates under reducing conditions the model indicates that meta sedimentary sources of ore forming components became increasingly important during the evolution of the panasqueira sn w deposit and accounts in part for the observed progression from oxide dominated to base metal sulfide dominated parageneses

structural and kinematic analysis of the corredoiras detachment evidence for early variscan synconvergent extension in the ordenes complex nw spain an important detachment is described in the allochthonous ordenes complex in the nw iberian massif and its meaning is related to the kinematics of contemporaneous convergent structures the corredoiras detachment cd separates a hangingwall unit characterised by a medium pressure metamorphic gradient from a footwall high pressure and high temperature unit and an underlying ophiolitic unit an associated ductile shear zone nearly 2000 m thick developed in the lower part of the hangingwall unit where the corredoiras orthogneiss a lower ordovician metagranite was progressively transformed into augengneisses mylonitic and ultramylonitic gneisses the attitude of the stretching and mineral lineation in the mylonites varies due to late refolding at map scale but the sense of movement can be estimated being roughly top to the se according to crosscutting relationships the cd developed subsequent to the thrusting of the high pressure high temperature unit onto the ophiolitic unit and prior to younger extensional detachments upright folding and strike slip tectonics the geometric relationships of the cd with the previous structures in the footwall unit the subtractive character of the metamorphic gap between its hangingwall and footwall and the available isotopic data suggest that the cd is an early variscan ductile extensional detachment the movement of which was roughly simultaneous with the onset of thrusting of the allochthonous complexes over their relative autochthon

present day crustal deformation and plate kinematics in the middle east constrained by gps measurements in iran and northern oman summary a network of 27 gps sites was implemented in iran and northern oman to measure displacements in this part of the alpine himalayan mountain belt we present and interpret the results of two surveys performed in 1999 september and 2001 october gps sites in oman show northward motion of the arabian plate relative to eurasia slower than the nuvel 1a estimates e g 22 2m m yr 1 at n8 5 e instead of 30 5 mm yr 1 at n6 e at bahrain longitude we define a gps arabia eurasia euler vector of 27 9 0 5 n 19 5 1 4 e 0 41 0 1 myr 1 the arabia eurasia convergence is accommodated differently in eastern and western iran east of 58 e most of the shortening is accommodated by the makran subduction zone 19 5 2m m yr 1 and less by the kopet dag 6 5 2m m yr 1 west of 58 e the deformation is distributed in separate fold and thrust belts at the longitude of tehran the zagros and the alborz mountain ranges accommodate 6 5 2m m yr 1 and 8 2m m yr 1 respectively the right lateral displacement along the main recent fault in the northern zagros is about 3 2m m yr 1 smaller than what was generally expected by contrast large rightlateral displacement takes place in northwestern iran up to 8 mm yr 1 the central iranian block is characterized by coherent plate motion internal deformation 2m m yr 1 sites east of 61 e show very low displacements relative to eurasia the kinematic contrast between eastern and western iran is accommodated by strike slip motions along the lut block to the south the transition zone between zagros and makran is under transpression with right lateral displacements of 11 2m m yr 1

accommodation of transpressional strain in the arabia eurasia collision zone new constraints from u th he thermochronology in the alborz mountains north iran the alborz range of n iran provides key information on the spatiotemporal evolution and characteristics of the arabia eurasia continental collision zone the southwestern alborz range constitutes a transpressional duplex which accommodates oblique shortening between central iran and the south caspian basin the duplex comprises nw striking frontal ramps that are kinematically linked to inherited e w striking right stepping lateral to obliquely oriented ramps new zircon and apatite u th he data provide a high resolution framework to unravel the evolution of collisional tectonics in this region our data record two pulses of fast cooling associated with sw directed thrusting across the frontal ramps at 18 14 and 9 5 7 5 ma resulting in the tectonic repetition of a fossil zircon partial retention zone and a cooling pattern with a half u shaped geometry uniform cooling ages of 7 6 ma along the southernmost e w striking oblique ramp and across its associated nw striking frontal ramps suggests that the ramp was reactivated as a master throughgoing n dipping thrust we interpret this major change in fault kinematics and deformation style to be related to a change in the shortening direction from ne to n nne the reduction in the obliquity of thrusting may indicate the termination of strike slip faulting and possibly thrusting across the iranian plateau which could have been triggered by an increase in elevation furthermore we suggest that 7 6 m y old s directed thrusting predated inception of the westward motion of the south caspian basin

characterization and timing of the different types of fluids present in the barren and ore veins of the w sn deposit of panasqueira central portugal the panasqueira w sn deposit is the largest quartz vein type deposit of the iberian peninsula and the most important wolframite deposit in western europe the ore veins are almost exclusively sub horizontal besides ore bearing sub horizontal veins the panasqueira mine also contains barren quartz veins there are essentially two generations of barren quartz quartz contemporaneous with the earliest regional metamorphism qi and recrystallized quartz contemporaneous with the thermal metamorphism related to the granite intrusion qii fluid inclusion studies microthermometry and raman were undertaken in order to distinguish fluids contemporaneous with the barren quartz from those contemporaneous with the ore bearing quartz qiii fluid inclusion data indicate that the barren and ore bearing quartz fluids are dominantly aqueous 93 to 98 mol h2o with a nearly constant bulk salinity 8 to 12 wt eq nacl with the quantity of volatile component determined by raman spectrometry higher in qiii but never greater than 5 mol however the co2 ch4 n2 ratio is different for each type of quartz volatiles are dominated by ch4 10 to 96 mol zch4 and or n2 3 to 87 mol zn2 in the barren quartz and by co2 60 to 73 mol zco2 in ore bearing quartz the bulk chemical composition of the fluids in qiii is comparable to that found commonly in hydrothermal fluids associated with wolframite mineralization where na k ca and hco3 cl so4 a dispersion in th 226 to 350 c found in qiii together with a variation in the degree of filling 0 5 to 0 7 and with the consequent variation of fluid densities 0 70 to 0 79 may result from changes in the fluid pressure regime below lithostatic pressure suggesting vein filling related to tectonic events

distinguishing between fault scarps and shorelines the question of the nature of the kahrizak north rey and south rey features in the tehran plain iran terra nova 22 227 237 2010 abstract tehran is one of the largest cities in the world 12 million people facing seismic hazard standing at the foothills of alborz mountains the capital of iran is exposed to potential earthquakes associated with several nearby active faults classically mentioned as active features the kahrizak the north rey and the south rey scarps cross the town itself and would be the sources of several destructive historical earthquakes however the nature of these topographic scarps remains uncertain to assess whether these features correspond to active faults we carried out a morphological and stratigraphic study our results show that the three scarps define horizontal scarp lines that follow contour lines matching ancient shorelines further east this point associated with other morphological characteristics such as the flatness of the upper and the lower surfaces the long and regular streams that incised the upslope upper surfaces and the fact that the deposits are horizontal and without deformations suggests in fact that the kahrizak the north rey and the south rey scarps correspond most likely to ancient shore lines and are not fault scarps

the kinematics of the dasht e bayaz earthquake fault during pliocene quaternary implications for the geodynamics of eastern central iran the arabia eurasia convergence is accommodated across the iranian plateau and surrounding mountain ranges strike slip faults play significant roles in the current deformation of the iranian plateau and were responsible for several moderate to large earthquakes especially in east of iran the sinistral dasht e bayaz fault shows conspicuous seismic and geological activities while the role of the fault in the accommodation of active convergence is still debated this paper focuses on the pliocene quaternary to present day states of stress in the region affected by the dasht e bayaz fault we applied the fault slip inversion technique to both kinds of seismologic and geological fault slip data the inversion results indicate a mean n045 5 e trending 1 in the modern stress field which agrees with the present day tectonic regime regional n050 05 e trending 1 deduced from the inversion of earthquake focal mechanism data the paleostress state is characterized by a n135 15 e trending regional mean 1 with a transpressional stress regime e w faults of the region such as the dasht e bayaz fault were reverse dextral in this paleostress field we show that the shift in fault kinematics during the pliocene quaternary times has not been restricted to northeastern parts of the iranian plateau the cross cutting relationship between active n s dextral and e w sinistral faults indicates a crosswise to conjugate fault arrangement in the middle and the eastern end of the dasht e bayaz fault integrating our results at a larger regional scale we present a kinematic model in which the region between lut and kopeh dagh is divided by the doruneh fault into two tectonic domains in the northern domain active convergence is taken up by the extrusion of fault bounded crustal blocks while in the southern domain the convergence is accommodated through crosswise strike slip faulting accompanied by reverse thrust faulting in confining wedges

left lateral active deformation along the mosha north tehran fault system iran morphotectonics and paleoseismological investigations abstract the mosha and north tehran faults correspond to the nearest seismic sources for the northern part of the tehran megacity the present day structural relationships and the kinematics of these two faults especially at their junction in lavasanat region is still a matter of debate in this paper we present the results of a morphotectonic analysis aerial photos and field investigations within the central part of the mosha and eastern part of the north tehran faults between the mosha valley and tehran city our investigations show that generally the traces of activity do not follow the older traces corresponding to previous long term dip slip thrusting movements the recent faulting mainly occurs on new traces trending e w to ene wsw affecting quaternary features streams ridges risers and young glacial markers and cutting straight through the topography often defining en echelon patterns right and left stepping these new traces correspond to steep faults with either north or south dipping directions along which clear evidences for left lateral strike slip motion are found at their junction zone the two sinistral faults display a left stepping en echelon pattern defining a positive flower structure system clearly visible near ira village further west the left lateral strike slip motion is transferred along the ene wsw trending niavaran fault and other faults the cumulative offsets associated with this left lateral deformation is small compared with the topography associated with the previous late tertiary thrusting motion showing that it corresponds to a recent change of kinematics

the accommodation of arabia eurasia plate convergence in iran continental convergence between arabia and eurasia is taken up by distributed deformation in iran at wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field the only quantitative source of information on the spatial distribution of strain rates within iran is the record of earthquakes we find that we can reproduce the style of deformation observed in the seismicity by simply minimizing the rate of work in a continuous viscous medium that has to accommodate the arabia eurasia plate motion between the defined shapes of iran s rigid borders when in addition we specify central iran azerbaijan and the southern caspian basin to be relatively rigid blocks within the deforming zone then the fit to the style of the observed strain rate distribution is even better we conclude that much of the pattern of deformation in iran is predetermined by the shape of its rigid borders and by the disposition of relatively rigid blocks within it this is likely also to have been a common occurrence in older orogenic belts we confirm earlier suggestions that earthquakes between 1909 and 1992 can account for only a small part 10 20 of the total deformation required by the convergence between the arabia and eurasia plates we then show that the whole plate motion can be accommodated by a velocity field with the same orientations and relative magnitudes of principal strain rates seen in the earthquakes but with larger absolute magnitudes there is therefore no requirement that the large proportion of aseismic deformation in iran is substantially different in style orientation or distribution from that released seismically in the earthquakes

u pb ages of zircons from meta igneous and meta sedimentary rocks of the sierra de guadarrama implications for the central iberian crustal evolution u pb data of zircons from various gneisses of the eastern sierra de guadarrama central spain make it possible to reconstruct the pre hercynian and hercynian history of this area 1 upper intercept ages 2400 ma for meta igneous and 2000 ma for meta sedimentary rocks of discordias defined by data of anhedral zircon fractions document the existence of early proterozoic crust 2 lower intercept minimum ages of anhedral zircon fractions show radiogenic lead loss at about 540 ma due to a thermal event leading to volcanism and emplacement of granitoid rocks into precambrian crust growth of euhedral zircons is possibly related to this event 3 lower intercept minimum ages of about 380 ma defined by anhedral zircon fractions in meta sedimentary rocks prove an early hercynian event according to present knowledge on the metamorphism in the sierra de guadarrama this event could be explained in terms of a barrow type medium pressure metamorphism the inferred cadomian igneous event relates the geological history of central spain with that of western africa to the south and brittany to the north furthermore similarities of the crustal evolution in the area studied and other internal zones of the hercynian belt moldanubian zone french central massiv are confirmed the early hercynian event for the first time affected all the rocks of the area together the pre hercynian evolution of the two complexes is different and the present association of the basement rocks may be explained by thrusting or in terms of early hercynian nappe transport

comparison of strain and stress tensor orientation application to iran and southern california strain and stress tensors along plate boundaries in iran and southern california are oriented coaxially if they are estimated based on small to moderate earthquakes if large earthquakes m 7 are included in the analysis the estimate of stress directions does not change but the orientation of the released strain rotates significantly thus the direction of the total released strain is different from the stress by about 20 in both iran and southern california and by about 45 in central california we interpret this observation to indicate that the smaller earthquakes occur on faults favorably oriented for failure in the prevailing stress field in which they are possibly generated the larger events rupture near vertical strike slip faults that are unfavorably oriented but weak this weakness causes failure under low ratio of shear to normal stress this view is supported by the fact that in the southern california data set the average angle between the fault planes and the greatest principal stress is about 40 whereas it forms an angle of 70 with the san andreas fault nearly 90 in central california for estimating the seismic strain release by kostrov s method along about a 10 km wide section of the san andreas fault zone we used the data set from which jones determined the stress directions for earthquakes in the range of 2 6 m 4 3 we estimated the directions of principal strain for iran based on 111 focal mechanisms and the scalar moment for earthquakes in the range of 4 4 m 8 we inverted regional subsets of these data for volumes with dimensions of a few hundred kilometers for the stress directions using the method of gephart and forsyth the average misfits for these inversions ranged from 2 to 5 based on test inversions of synthetic data with known misfits we found that these misfits can be attributed solely to inaccuracies of less than 10 in the fault plane solutions therefore the results for iran are most likely obtained for volumes with uniform stress directions we propose that stress inversions with misfits smaller than 6 can be accepted as meaningful as an approximate general guideline because our tests for iran agree with those for hawaiian data sets performed by wyss

meta igneous origin of hercynian peraluminous granites in n w french massif central implications for crustal history reconstructions seventy samples of hercynian peraluminous granites gueret millevaches and saint sylvestre massifs and metamorphic units of the limousin area were analysed for rb sr and sm nd the source rocks of the peraluminous granites can be found in the metamorphic rocks of limousin among them meta igneous rocks were largely predominent over meta sedimentary rocks in the source of the three granites millevaches and gueret granites were generated by the partial melting of rocks comprising meta volcanics and meta sediments whereas the saint sylvestre granite was produced exclusively by the melting of late precambrian granites this leads to confusing t dm nd values the confusion being amplified by the segregation of monazite during the petrogenetic evolution of the peraluminous granites which leads to dramatic fractionation in sm nd ratios the data of the present study tend to demonstrate that peraluminous granites do not give a good representation of isotopic mean crustal estimates late precambrian time seems however to have been a period of extensive crustal generation in western europe

field examples of strike slip fault terminations in mongolia and their tectonic significance deformation at the ends of large intracontinental strike slip faults that do not simply link other major structures often involves rotations about a vertical axis we use earthquake slip vectors surface rupture in earthquakes and geomorphology to examine the ends of three major strike slip faults in mongolia in these places a simple pattern is seen consisting of a thrust fault on one side with a displacement that decreases away from the strike slip fault consistent with local rotational deformation strike slip faults that terminate in this way allow the style of faulting to change spatially within a deforming area for example from dominantly strike slip to dominantly dip slip while still accommodating the overall deformation required by larger scale regional motions such a change in fault style should also be accompanied by a change in the rotation rate about a vertical axis which may be detected paleomagnetically the kind of strike slip fault termination described here may have consequences for how large strike slip fxaults evolve and grow and for the variation in displacement along their length

variscan collisional magmatism and deformation in nw iberia constraints from u pb geochronology of granitoids u pb geochronology of variscan granitoid rocks from the west asturian leonese zone of the nw iberian belt documents the episodic nature of magmatism in this section of the western european variscides each magmatic episode is characterized by granitoids with distinct features and has a duration on the scale of several millions of years the ages of these granitoids place new constraints on the age and duration of magmatic and tectonic events that are consistent with previous structural studies and proposed models for the tectonic evolution and migration of deformation in the nw iberian variscan belt granitoid rocks in this zone belong to two main magmatic episodes syn and post tectonic relative to the variscan orogeny and are broadly representative of the granitoid types found in the nw iberian variscan belt the syntectonic association is formed by i tonalite granodiorite monzogranite intrusions emplaced synchronously with the main phase of crustal deformation d 2 at c 325 ma and ii younger leucogranite intrusions emplaced synchronously with syn convergence extensional structures at c 320 310 ma the post tectonic association is composed of i volumetrically dominant tonalite granodiorite monzogranite intrusions and associated minor mafic intermediate rocks emplaced at c 295 290 ma and ii scarce leucogranite intrusions emplaced at c 290 285 ma

microseismicity and seismotectonics around the mosha fault central alborz iran abstract we present the results of a microearthquake study conducted during 5 months of 2006 with 44 portable seismological stations around the mosha fault the most prominent structure located east of tehran where several major earthquakes occurred during the historical time in the central alborz iran we recorded 538 earthquakes at more than 4 stations among these earthquakes 148 were located with statistical uncertainties erh and erz less than 3 km a gap less than 180 and rms less than 0 3 s we also present the seismicity recorded by the institute of geophysics of the university of tehran from may 1996 to july 2008 igtu recorded almost 13 000 events during this time 4428 were recorded in more than 4 stations and 599 with the same criteria as for the temporary network most earthquakes are located along the mosha fault at depths ranging between 0 km and 20 km with a maximum between 10 and 15 km as it does at most of the other faults in central alborz cross sections clearly show the mosha fault in its central part dipping northward at an angle of 70 we computed also 51 focal mechanisms most of them show left lateral strike slip motion associated with the mosha fault a few mechanisms located south of the mosha fault are consistent with normal faulting