holocene climatic and environmental changes inferred from midge records diptera chironomidae chaoboridae ceratopogonidae at lake berkut southern kola peninsula russia a radiocarbon dated sediment sequence from lake berkut in the southern part of the kola peninsula northwest russia was investigated by means of midge analysis in order to reconstruct the holocene climatic and environmental history of the region past mean july air temperatures at the study site and hypolimnetic oxygen contents of the lake water were inferred from chironomid based transfer functions the early holocene c 10 100 8400 cal yr bp is characterized by summer temperatures and hypolimnetic oxygen concentrations broadly similar to present day conditions the midge records give evidence of a lake level fall at c 7000 cal yr bp resulting in weakened thermal stratification of the lake water and improvement of the hypolimnetic oxygen conditions after c 4000 cal yr bp midge assemblages suggest a lake level rise related to increased effective moisture a secondary mid holocene climatic optimum with inferred mean july air temperatures of c 12 1 degrees c was recorded between 6000 and 4400 cal yr bp followed by minimum values c 11 3 degrees c between 3500 and 1500 cal yr bp accompanied by the onset of natural acidification of the lake the late holocene midge assemblages suggest weakly acidic conditions low hypolimnetic oxygen contents and a general warming trend during the last c 1500 years although paludification and natural acidification may have influenced the temperature reconstruction at this stage however the modern chironomid inferred mean july air temperature 12 5 degrees c is consistent with meteorological data from a nearby station in general the midge records reflect relatively warm and moist conditions at lake berkut before c 7000 cal yr bp a relatively warm and dry climate at c 7000 4000 cal yr bp and a shift to cooler and wetter climatic conditions in the region after c 4000 cal yr bp less

application of thermochronology to hydrothermal ore deposits thermochronology finds many applications in economic geology utilizing temperature sensitive radiometric dating techniques to reveal low temperature upper crustal processes can elucidate many aspects of deposit genesis including timing and duration of mineralization processes rate of exhumation and erosion of intrusive ore deposits and comparative preservation potential the tools are utilized to best advantage when combined with other thermochronometry techniques that provide complementary information in addition when thermochronometers are combined with geochronometers e g zircon u pb over 800 c of thermal history is revealed from emplacement to erosion fig 1 with the advent of computational algorithms that provide more accurate and detailed models of thermochronology results the economic geologist has a powerful tool to use when assessing economic favorability of a region or prospect this chapter summarizes the various ways that low temperature thermochronometers have been utilized in studies of economic mineralization and primarily focuses on studies of porphyry ore deposits these deposits are well characterized and provide a good platform from which to demonstrate the extended understanding of ore formation processes that is provided by thermochronology studies in this section we review the fundamental application of u th he fission track and 40ar 39ar thermochronometry methods to mineralized systems we then present a synopsis of how these techniques can be used in thermal history analysis either alone or in combination with other chronometers in order to provide more information on deposit genesis the discussion is presented from low through to higher temperature thermochronometers corresponding to their presentation on figure 1 u th he thermochronology as documented earlier in the volume u th he thermochronology is based on measuring the accumulation of radiogenic 4he produced from u and th decay the daughter helium is retained until the mineral is heated to a temperature at which its structure and helium retentivity change this closure temperature varies from

geochemistry and zircon geochronology of the permian a type hasanrobat granite sanandaj sirjan belt a new record of the gondwana break up in iran the sanandaj sirjan metamorphic plutonic belt ssb in west central iran is a polyphase metamorphic terrain composed of dominantly greenschist grade metasedimentary and metavolcanic rocks and felsic to mafic plutons of neoproterozoic phanerozoic ages the hasanrobat granite in central ssb occurs as a single pluton 20 km 2 surface area with relatively consistent mineralogy and chemistry quartz alkali feldspars microcline and perthite sodic plagioclases and biotite are the main constituents commonly associated with minor amphibole accessory phases include zircon allanite apatite and magnetite the country rocks are upper carboniferous lower permian sandstones and dolomitic limestones scattered patches of skarn type assemblages dominated by tremolite and talc occur in the dolomitic limestones and sandstones are recrystallized to a coarse grained quartzite at contact with the granite the granite is metaluminous to slightly peraluminous and is distinguished by high feo t mgo ratios typical of ferroan a type granites the a type affinity is also reflected by high na 2o k 2o high ga al ratios high contents of large ion lithophile elements lile high field strength elements hfse and rare earth elements ree as well as low contents of sr and distinct negative eu anomalies the biotites are aluminous fe rich and plot near the siderophyllite corner in the quadrilateral biotite diagram they are further distinguished by high fluorine contents 0 61 to 1 33 wt amphibole is ferrohastingsite in composition ion microprobe analyses of zircon grains separated from a representative granite sample yielded concordant u pb ages with weighted mean 206 pb 238 u age of 288 3 3 6 ma the granite and the country rocks are cut by a set of mafic dykes with asthenosphere like geochemical signatures such association suggests anorogenic intraplate magmatism in lower permian in the region this provides further evidence for and significantly constrains timing of a major extension in upper paleozoic in iran previously inferred from the rock record the extension led to the gondwana break up and the opening of neotethys ocean between sanandaj sirjan and zagros in permian

frictional resistance of faults during accelerating and decelerating earthquake slip the dynamic friction along faults controls earthquake ruptures in the crust but many previous studies have quantified this value only for constant slip rates experiments accounting for the more realistic condition of changing slip rates suggest that faults undergo a sequence of strengthening weakening and healing during acceleration and deceleration of slip the dynamic friction of faults during earthquake slip is a critical control on earthquake ruptures in the crust extrapolation of brittle crack theories to natural earthquakes1 2 3 has led to the commonly held view that fault friction reduces during rapid earthquake slip a process known as slip weakening1 high velocity gouge experiments4 5 and recent analyses of thermal pressurization6 7 and frictional melting8 support such a notion however these studies dealt with constant rates of slip along faults here we present the results of experiments aimed at understanding the frictional behaviour of fault zone materials under variable slip rates conditions that are more representative of natural earthquakes our results show that faults undergo a sequence of strengthening weakening and healing during acceleration and deceleration of slip such a sequence may be explained by the extrapolation of rate and state frictional behaviour9 10 at low slip velocities to more realistic slip rates but involving different physical mechanisms and a different scale the initial strengthening should impose a barrier for rupture growth into large earthquakes the healing on decelerating fault motion may lead to pulse like earthquake ruptures11 12 13 14 and static stress drops that are low in comparison with the dynamic stress changes15

effects of slip slip rate and shear heating on the friction of granite the stability of fault slip is sensitive to the way in which frictional strength responds to changes in slip rate and in particular to the effective velocity dependence of steady state friction ss ln v this quantity can vary substantially with displacement temperature and slip rate to investigate the physical basis for this behavior and the possible influence of shear heating we slid initially bare granite surfaces in unconfined rotary shear to displacements of hundreds of millimeters at normal stresses n of 10 and 25 mpa and at room temperature we imposed step changes in slip rate within the range 10 2 to 103 5 m s and also monitored frictional heating with thermistors embedded in the granite the transient response of to slip rate steps was fit to a rate and state dependent friction law using two state variables to estimate the values of several parameters in the constitutive law the first 20 mm of slip shows rising friction and falling ss ln v further slip shows roughly constant friction ss ln v and parameter values suggesting that a steady state condition is reached on the fault surface at v 10 m s ss ln v 0 004 0 001 at higher rates the response is sensitive to normal stress at n 25 mpa granite shows a transition to effective velocity strengthening ss ln v 0 008 0 004 at the highest slip rates tested at 10 mpa granite shows a less dramatic change to ss ln v 0 at the highest rates the maximum temperature measured in the granite is 60 c at 25 mpa and 103 5 m s temperatures are in general agreement with a numerical model of heat conduction which assumes spatially homogeneous frictional heating over the sliding surface the simplest interpretation of our measurements of ss ln v is that the granite is inherently velocity weakening ss ln v 0 mimics velocity strengthening these results have implications for the frictional behavior of faults during earthquakes high slip rates may cause a switch to effective velocity strengthening which could limit peak coseismic slip rate and stress drop for fluid saturated faults strengthening by this mechanism may be partly or fully offset by weakening due to thermal pressurization of a poorly drained pore fluid

petrogenesis of post collisional a type granitoids from the urumieh dokhtar magmatic assemblage southwestern kerman iran constraints on the arabian eurasian continental collision abstract three plutons deh siahan bande bagh and baghe khoshk sharghi collectively referred to as the dbb hereafter in southwestern kerman in the southeastern part of the urumieh dokhtar magmatic assemblage udma of the zagros orogenic belt differ from the typical calc alkaline metaluminous i type intrusions of the region the dbb intrusions have a distinct lithological assemblage varying from diorite through monzogranite and monzonite to alkali feldspar syenite and alkali granite the dbb granitoids are metaluminous to slightly peraluminous alkaline to shoshonitic in composition and have high total alkali contents with k2o na2o high feot mgo values and low cao and mgo contents they are enriched in some liles such as rb and th and hfses such as zr y and rees except eu and depleted in sr and ba relative to primordial mantle and have low concentrations of transitional metals these features along with various geochemical discriminant diagrams suggest that the dbb granitoids are post collisional a type granitoids which had not been recognized previously in the udma the chondrite normalized ree patterns of the dbb granitoids show slightly enriched light rees la sm n 2 26 4 13 negative eu anomalies eu eu n 0 19 0 74 and flat heavy ree patterns gd yb n 0 80 1 87 the negative eu anomaly indicates an important role for plagioclase and or k feldspar during fractional crystallization whole rock rb sr isotope analysis yields an isochron age of 33 1 ma with an initial 87sr 86sr value of 0 7049 0 0001 whole rock sm nd isotope analysis gives endt values from 2 56 to 3 62 at 33 ma the positive endt and low isr values of the dbb granitoids together with their tdm of 0 6 0 7 ga suggest their formation from partial melting of a lithospheric mantle source modified by fluids or melts from earlier subduction processes melting of lithospheric mantle occurred via a dehydration melting process at pressures below the garnet stability field as a consequence of lithospheric mantle delamination or break off of a subducted slab and melting of the lithospheric mantle by upwelling of hot asthenosphere on the basis of rb sr age dating and the post collisional geochemical signatures of the dbb granitoids along with extensive pre collisional volcanic eruptions in middle eocene we suggest late eocene for the time of collision between the arabian and central iranian plates this also implies that the calc alkaline i type intrusions in the southwestern kerman and in other parts of the udma may have formed in a post collisional context

geochemistry and zircon u pb geochronology of aligoodarz granitoid complex sanandaj sirjan zone iran the aligoodarz granitoid complex agc is located in the sanandaj sirjan zone ssz western iran and consists of quartz diorites granodiorites and subordinate granites whole rock major and trace element data mostly define linear trends on harker diagrams suggesting a cogenetic origin of the different rock types 87 sr 86 sr i and endt ratios are in the ranges 0 7074 0 7110 and 3 56 to 5 50 respectively the trace elements and sr nd isotopic composition suggest that the granitoids from the agc are similar to crustal derived i type granitoids of continental arcs the whole rock suite was produced by assimilation and fractional crystallization starting from a melt with intermediate composition likely possessing a mantle component in situ zircon u pb data on the granites with la icp ms yield a crystallization age of 165 ma inherited grains spanning in age from 180 ma up to 2027 ma were also found and confirm that assimilation of country rock has occurred chemical and chronological data on the agc were compared with those available for other granitoid complexes of the central ssz e g dehno boroujerd and alvand the comparison reveals that in spite of the different origins that have been proposed all these granitoid complexes are likely genetically related they share many chemical features and are derived from crustal melts with minor differences alvand granites have the most peculiar compositions most likely related to the presence of abundant pelitic component all these intrusions are coeval and reveal the presence of an extensive magmatic activity in the central sector of the ssz during middle jurassic

regional fire history based on charcoal analysis of sediments from nine lakes in western mongolia fires are common in grassland regions of the world and the frequency and severity of fire is linked to climate driven changes in fuel loads western mongolia is dominated by grasslands but the fire history of this region is largely unknown we reconstructed modern fire 48 lakes and historical fires 9 lakes using sediment charcoal modern fuel loads were estimated using a combination of clipped plots satellite based estimates of annual aboveground net primary productivity npp and npp modeled from annual temperature and precipitation loss on ignition and environmental magnetics of lake sediments were analyzed as proxies for climate we found little evidence for modern or historical fire in the landscape as charcoal was absent from the surface sediments of 34 of 48 lakes charcoal influxes were uniformly low averaging from 0 002 to 0 028 mm2 cm2 per yr over the past 1200 years at nine lakes and the past 6000 5000 years at two of the lakes with longer sediment records in the modern landscape li

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

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

new tectonic configuration in ne iran active strike slip faulting between the kopeh dagh and binalud mountains in this paper a combined approach of geomorphic analyses detailed geological mapping on spot 5 satellite images and field surveys complemented by radiometric dating ar 40 ar 39 allows proposing a new and consistent tectonic configuration for the northeastern arabia eurasia collision zone it favors a simple strike slip faulting mechanism in ne iran accommodating the northward motion of central iran with respect to eurasia between the binalud and kopeh dagh mountains our results demonstrate that similar to 2 mm a similar to 25 of this northward motion has been transferred from the binalud to the kopeh dagh through the meshkan transfer zone since similar to 5 ma the modern state of stress deduced from fault kinematics analyses shows n30 degrees e trending maximum stress axis and confirms a dominant strike slip faulting mechanism combining our geological data with other available data we conclude that kinematics of deformation can be appropriately described by rigid block faulting in ne iran instead the continuous deformation as it has been thought during the last 3 decades

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

u pb dating and emplacement history of granitoid plutons in the northern sanandaj sirjan zone iran abstract the sanandaj sirjan zone ssz which runs parallel to the zagros fold and thrust belt of iran underwent a multistage evolution starting with neotethys initiation its subsequent subduction below the iranian continental crust and eventual closure during convergence of arabia towards central iran plutonic complexes are well developed in the northern part of the ssz and we have dated a number of them by id tims u pb on zircon the new data record the following events a mid jurassic period that formed the boroujerd plutonic complex 169 ma the astaneh pluton 168 ma and the alvand pluton 165 ma late jurassic emplacement of the gorveh pluton 157 149 ma mid cretaceous 109 ma formation of a i type phase in the hasan salary pluton near saqqez followed by early paleocene 60 ma intrusion of a type granite in the same pluton and the youngest intrusive event recorded so far in the ssz with the intrusion of granite in the gosheh tavandasht complex near boroujerd at 34 9 ma these different events reflect specific stages of subduction related magmatism prior to the eventual miocene collision between the two continental blocks

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

1300 years of climatic history for western central asia inferred from tree rings more than 200 000 ring width measurements from 384 trees were obtained for 20 individual sites ranging from the lower to upper local timber lines in the northwest karakorum of pakistan and the southern tien shan of kirghizia samples were obtained predominantly from juniper species juniperus and were analysed to reconstruct regional climatic variation patterns in western central asia since ad 618 site distri bution represents diverse ecological conditions e g combinations of temperature and moisture stress within the karakorum and tien shan mountains permitting both intra montane and inter montane comparisons of chronologies three different types of chronologies ree ecting interannual decadal and centennial scale ring width variations were calculated a statistic skeleton plotting technique was used to identify ring width pointer years interannual a 101 year kernel e lter was used to identify decadal scale variations and for a subset of long lived trees the mean ring width of the entire single series was used to identify centennial trends after extracting and calibrating each of these three distinct wavelengths in ring width variation the results were combined into a comprehensive reconstruction ree ecting primarily temperature e uctuations in western central asia since ad 618 the nature and the temporally changing strength of the climatic signals of this reconstruction are discussed in detail a maximum latewood density record of pinus tienschanica from central tien shan was used as a predictor series to calibrate and validate tree ring width variation in so doing we link our results to the circumpolar maximum latewood density network briffa et al 1998a 1998b schweingruber and briffa 1996

holocene changes in seasonal precipitation highlighted by fire incidence in eastern canada postglacial fire history has been reconstructed for eastern canada from charcoal influx anomalies from 30 sites taken from a lacustrine charcoal database the reconstruction exhibits coherent patterns of fire occurrence in space and time the early holocene is characterised by high fire incidence there is a major change to much lower occurrence slightly after 8 ka bp a return to more fire appears after 3 ka bp this sequence does not fit with the hydro climatic reconstruction deduced from lake level reconstructions for northeastern north america which indicates a dry early and mid holocene and a wet late holocene fire occurrence however closely matches summer relative humidity inferred from 18o the differences between fire frequency and lake level history are due to changes in the seasonality of precipitation and drought frequency lake levels are essentially controlled by winter precipitation while summer precipitation controls fire occurrence the early holocene before 8 7 5 ka bp experienced dry summers due to higher solar radiation and dry adiabatic winds from the residual laurentide ice sheet the middle holocene was dominated by wet summers due to stability of the atlantic air mass over eastern canada after 2 5 ka bp summers became drier albeit not as fire conducive as during the early holocene late holocene summers conducive to fire are explained by more frequent incursions of dry cool pacific or cold arctic air masses over eastern canada

temperature fields generated by the elastodynamic propagation of shear cracks in the earth w 1 the temperature maximum shifts toward the crack tip for faults having slip zone thickness of the order of centimeters or less the onset of thermally induced phenomena e g frictional melting thermal pressurization etc may occur at any point along the rupture depending on the degree of slip localization and rupture duration in the absence of significant increases in the pore fluid pressure localized fault slip may raise temperature by several hundred degrees sufficient to cause melting the onset of frictional melting may give rise to substantial increases in the effective fault strength due to an increase in the effective fault contact area and high viscosity of silicate melts near solidus the inferred transient increases in the dynamic friction viscous braking are consistent with results of high speed rock sliding experiments and might explain field observations of the fault wall rip out structures associated with pseudotachylites possible effects of viscous braking on the earthquake rupture dynamics include 1 delocalization of slip and increases in the effective fracture energy 2 transition from a crack like to a pulse like rupture propagation or 3 ultimate rupture arrest assuming that the pulse like ruptures heal by incipient fusion the seismologic observations can be used to place a lower bound on the dynamic fault friction this bound is found to be of the order of several megapascals essentially independent of the earthquake size further experimental and theoretical studies of melt rheology at high strain rates are needed to quantify the effects of melting on the dynamic fault strength index terms 3210 mathematical geophysics modeling 5104 physical properties of rocks fracture and flow 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling 8010 structural geology fractures and faults

magma generation by slab steepening and breakoff beneath a subduction accretion complex an alternative model for collision related volcanism in eastern anatolia turkey 1 eastern anatolia is regarded as one of the best examples of continental collision represented by a 2 km high plateau it displays shallow and diffuse seismicity indicating that the crust is still being actively deformed perhaps the most striking aspect of eastern anatolia is the volume and compositional variability of collision related volcanic products erupted during the neogene and quaternary time a number of models have been proposed for the genesis of this volcanism in the region however recent geophysical studies have revealed that a mantle lithosphere is almost completely absent beneath a greater portion of the region which makes us question the validity of the previous models in this paper we propose a new model for magma genesis slab steepening and breakoff beneath a large subduction accretion complex this model holds that a northward subducting oceanic lithosphere beneath the eastern anatolia accretionary prism gets steepened and eventually detached from the continental lithosphere of the bitlis poturge massif following the continent accretionary complex collision this brings the asthenospheric mantle in contact with the accretionary complex at shallow depths e g around 50 km resulting in rapid regional uplift and extensive melting which leads to collisional volcanism

petrology and geochemistry of the granitoid complex of boroujerd sanandaj sirjan zone western iran abstract the middle jurassic boroujerd granitoid complex of the sanandaj sirjan zone with a u pb zircon age of 169 172 ma was emplaced in an active continental margin setting this complex consists of three main units an elongate nw se extending granodioritic unit sio2 58 71 wt which is widespread throughout the area a quartz dioritic unit sio2 52 63 wt exposed as small stocks within the granodioritic body and a monzogranitic unit sio2 70 75 wt widely scattered as separate small outcrops through the southern part of the area a series of nw trending aplites and pegmatites are present in the granodioritic unit and its aureole geochemically this complex is metaluminous to slightly peraluminous typical of i type granites it belongs to high k calc alkaline series and displays the geochemical characteristics typical of volcanic arc granites related to an active continental margin e g significant nb ti p and sr depletion isotopic data sri 0 7062 0 7074 and endt 3 02 to 3 62 are consistent with a crustal protolith in addition fractional crystallization may have played an important role in the formation of the whole spectrum of the granitoid types that occur in the boroujerd area

pseudotachylytes rarely generated rarely preserved or rarely reported pseudotachylyte is the only fault rock that is known to form exclusively at seismic slip rates so it is unique in preserving direct evidence of the dynamic processes in action during earthquakes it is commonly assumed that pseudotachylyte is rare and debate has centered on whether it is rarely generated or commonly generated but rarely preserved we present field and electron microscope observations of eight new pseudotachylytes from faults in the sierra nevada that have previously been the focus of many detailed studies of fault growth and mechanics these pseudotachylytes range from being abundant and easy to recognize in outcrop to being impossible to identify without microscope observations our data show that pseudotachylytes are much more common in the sierra nevada than has previously been reported we suggest that pseudotachylytes may be present within many fault zones but remain unreported primarily due to difficulty in identifying very thin or reworked pseudotachylytes in the field and therefore the use of these fault rocks to interpret dynamic earthquake processes must be revisited

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

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

strong velocity weakening and powder lubrication of simulated carbonate faults at seismic slip rates 1 high velocity friction tests were conducted on solid and hollow cylinders of carrara calcite marble dolomite marble silicate bearing calcite marble and calcite gouge to investigate the strength of carbonate faults during seismic slip the experiments performed at normal stresses of 0 6 14 7 mpa slip rates of 0 03 1 60 m s and room temperature in a rotary shear friction testing machine yielded an extraordinarily low steady state friction coefficient 0 1 at slip rates of 1 1 1 2 m s the slip weakening distance of 4 28 m became shorter at higher normal stress or frictional work rate strong velocity weakening was observed not only in steady state but also in nonsteady state friction while the slip rate was changing thus slip deceleration was accompanied by fault strength recovery large rapid temperature rises in narrow shear localization zones less than a few micrometers induced carbonate decomposition such as the breakdown of calcite into aggregates of cao nanograins and co2 in carrara marble scanning electron microscope observation revealed that the shear localization zone in the highly porous decomposition product was a layer of scattered small grains mostly 1 m in diameter these microstructures and the measured high permeability 10 14 m2 of the decomposed marble indicate that the dominant weakening mechanism in our experiments was possibly powder lubrication powder rheology at high slip rates is not yet well understood but the frictional behavior of nanograins appears to be strongly velocity dependent if decarbonation occurs during seismic slip in natural carbonate faults powder lubrication may make the faults slippery even under fluid drained conditions

vegetation change in the eastern pamir mountains tajikistan inferred from lake karakul pollen spectra of the last 28 kyr abstract we present a pollen record for last 28 cal kyr bp from the eastern basin of lake karakul the largest lake in tajikistan located in the eastern pamir mountains at 3915 m asl a geographically complex region the pollen record is dominated by artemisia and chenopodiaceae while other taxa apart from poaceae are present in low quantities and rarely exceed 5 in total arboreal pollen occur predominantly from 28 to 13 cal kyr bp but as likely no trees occurred in the high mountain regions of the eastern pamir during this time due to the high altitude and cold climate arboreal taxa are attributed to long distance transport probably by the westerlies the dominant atmospheric circulation tree pollen influx decreases strongly after 13 cal kyr bp allowing the pollen spectra to be interpreted as a regional vegetation signal we infer that from 27 6 to 19 4 cal kyr bp the eastern pamir was dominated by dry mountain steppe with low vegetation cover while from 19 0 to 13 6 cal kyr bp artemisia values increase and chenopodiaceae most herb taxa and inferred far distant input from arboreal taxa decrease between 12 9 and 6 7 cal kyr bp open steppe vegetation dominated with maximum values in ephedra and while steppe taxa still dominated the spectra from 5 4 to 1 cal kyr bp meadow taxa start to increase during the last millennium alpine steppe and alpine meadows expanded and a weak human influence can be ascertained from the increase of asteraceae and the occurrence of plantago pollen in the spectra

on the deterministic description of earthquakes 1 the quantitative estimate of earthquake damage due to ground shaking is of pivotal importance in geosciences and its knowledge should hopefully lead to the formulation of improved strategies for seismic hazard assessment numerical models of the processes occurring during seismogenic faulting represent a powerful tool to explore realistic scenarios that are often far from being fully reproduced in laboratory experiments because of intrinsic technical limitations in this paper we discuss the prominent role of the fault governing model which describes the behavior of the fault traction during a dynamic slip failure and accounts for the different and potentially competing chemical and physical dissipative mechanisms we show in a comprehensive sketch the large number of constitutive models adopted in dynamic modeling of seismic events and we emphasize their prominent features limitations and specific advantages in a quantitative comparison we show through numerical simulations that spontaneous dynamic ruptures obeying the idealized linear slip weakening sw equation and a more elaborated rate and state dependent friction law produce very similar results in terms of rupture times peaks slip velocity developed slip and stress drops provided that the frictional parameters are adequately comparable and more importantly that the fracture energy density is the same our numerical experiments also illustrate that the different models predict fault slip velocity time histories characterized by a similar frequency content a feeble predominance of high frequencies in the sw case emerges in the frequency ranges 0 3 1 and 11 50 hz these simulations clearly indicate that even forgiving the frequency band limitation it would be very difficult virtually impossible to discriminate between two different but energetically identical constitutive models on the basis of the seismograms recorded after a natural earthquake

geochemistry and u pb zircon geochronology of the alvand plutonic complex in sanandaj sirjan zone iran new evidence for jurassic magmatism abstract this paper presents geochemical sr nd isotopic and u pb zircon geochronological data on the alvand plutonic complex in sanandaj sirjan zone ssz western iran the gabbroic rocks show a trend of a calc alkaline magma suite and are characterized by low initial 87 sr 86 sr ratios 0 7023 0 7037 and positive e nd t values 2 9 3 3 which suggest derivation from a moderately depleted mantle source geochemical features of the granites illustrate a high k calc alkaline magma series whereas the leucocratic granitoids form part of a low k series granites have intermediate 87 sr 86 sr ratios 0 707 0 719 and negative e nd t values 1 0 to 3 4 while leucocratic granitoids have higher initial 87 sr 86 sr ratio 0 713 0 714 and more negative e nd t values 3 5 to 4 5 potential basement source lithologies for the granites are proterozoic granites and orthogneisses and those for the leucocratic granites are plagioclase rich sources such as meta arkoses or tonalites the u pb dating results demonstrate that all granitoids were exclusively emplaced during the jurassic instead of being cretaceous or younger in age as suggested previously the pluton was assembled incrementally over c 10 ma gabbros formed at 166 5 1 8 ma granites between 163 9 0 9 ma and 161 7 0 6 ma and leucocratic granitoids between 154 4 1 3 and 153 3 2 7 ma granites and leucocratic granitoids show some a type affinity it is concluded that the alvand plutonic complex was generated in a continental arc related extensional regime during subduction of neo tethyan oceanic crust beneath the ssz the u pb zircon age data recently corroborated by similar results in the central and southern ssz indicate that jurassic granitoids are more areally extensive in this belt than previously thought

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

early cretaceous migmatitic mafic granulites from the sabzevar range ne iran implications for the closure of the mesozoic peri tethyan oceans in central iran terra nova 22 26 34 2010 abstract the ophiolitic melange of the sabzevar range northern iran is a remnant of the mesozoic oceanic basins on the northern margin of the neotethys that were consumed during the arabia eurasia convergence history occurrence of km scale dismembered mafic hp granulitic slices is reported in this study granulites record an episode of amphibole dehydratation melting and felsic tonalite throndhjemite melt segregation at c 1 1 gpa and 800 c in situ u th pb geochronology of zircon and titanite grains hosted in melt segregations points to an early cretaceous albian age for the metamorphic climax results of this study i impose reconsideration of the current palaeotectonic models of the neothetyan convergent margin during the early cretaceous and ii argue that punctuated events of subduction of short lived back arc oceanic basins accompanied the long lasting history of the neotethyan subduction in the region

a continuous late glacial and holocene record of vegetation changes in kazakhstan the late glacial and holocene vegetation history of northern kazakhstan is reconstructed using a well dated continuous pollen record from ozerki swamp 50 degrees 24 n 80 degrees 28 e altitude 210 m near semipalatinsk a montane steppe taiga community chenopodiaceae artemisia picea larix and betula dominated in this area between 13 000 and 10 100 yr b p at the beginning of the holocene poaceae and artemisia dominated the steppe and picea and larix disappeared from 7800 to 7250 yr b p a sharp increase in betula pollen percentages suggests afforestation after 5800 yr b p pinus sylvestris spread through the steppe zone of kazakhstan these changes in vegetation distribution are interpreted in terms of changing absolute winter temperatures due to orbitally induced insolation changes the absence of boreal conifers during the early holocene can be explained by absolute minimum temperatures below 60 degrees c or 8 degrees c colder than today c 1997 elsevier science b v

petrochemistry of the siah kuh granitoid stock southwest of kerman iran implications for initiation of neotethys subduction abstract the upper triassic siah kuh granitoid stock is part of a series of triassic cretaceous intrusions in the phanerozoic sanandaj sirjan zone in the zagros orogenic belt south central iran the siah kuh stock intrudes lower paleozoic amphibolites of the abshur metamorphic complex and upper devonian lower carboniferous greenschists of the sargaz metamorphic complex the siah kuh granitoid stock consists mainly of coarse to medium grained leucogranodiorite leucomonzogranite and alkali granite with subordinate syenite it also contains a number of mafic enclaves of different sizes and is intruded by alkali granite and granophyre dikes along with monzonitic and a few dioritic dikes the siah kuh granitoid rocks are characterized by enrichment in large ion lithophile elements lile such as rb ba k ce and depletion in high field strength elements hfse such as y nb and zr the chondrite normalized ree patterns are characterized by moderate lree enrichment la yb n 1 31 4 82 and unfractionated hree gd yb n 0 50 to 1 33 granodiorites with the least fractionated hree and a general absence of eu anomalies suggest the involvement of plagioclase and absence of garnet during the melting processes alkali granites with the highest la yb n values and pronounced negative eu anomalies are more differentiated products nd isotope analyses of the siah kuh granitoids yield an errorchron age of 199 30 ma mswd 1 30 consistent with the field relationships and give nd model ages tdm from 0 81 to 1 64 ga and end t values from 1 81 to 2 45 at 200 ma these geochemical data suggest that the siah kuh granitoid stock has characterisitics of metaluminous to slightly peraluminous calc alkaline i type granite formed in a volcanic arc setting the onset of subduction of the neotethys oceanic crust beneath the central iranian microcontinent in triassic time could have accounted for the continental arc volcanism dehydration of subducted oceanic crust and partial melting of mantle wedge caused partial melting of subcontinental lithosphere which resulted in the formation of metasomatised and enriched mafic arc magmas at variable water fugacity and led to the formation of the siah kuh granitoid rocks

the holocene paleolimnology of lake issyk kul kyrgyzstan trace element and stable isotope composition of ostracodes the stable isotope and trace element geochemistry of ostracode shells from lake issyk kul kyrgyzstan provide an important new paleoclimate record for central asia the n 18 o n 13 c sr ca mg ca and u ca composition of shells from the species candona neglecta found in two piston cores constrains the paleohydrology of the lake from 8700 to 1000 calendar yr before present these data combined with robust chronologies based on 16 ams 14 c dates suggest that the region went from a relatively moist climate in the early holocene to a more arid climate in the late holocene intense freshwater input presumably glacial runoff flowed into the lake from 8700 to 8300 cal yr bp as evident from the n 18 o and n 13 c values from 8300 to 6900 cal yr bp n 18 o and sr ca values indicate that the lake was relatively fresh and an open basin and u ca values suggest that the lake was well mixed with well oxygenated bottom waters there is a transition zone between 6900 and 4900 cal yr bp when n 18 o and sr ca values rapidly increase and mg ca and u ca values rapidly decrease during this period the lake evolved from an open freshwater well mixed lake to a closed more saline less well mixed lake for the remainder of the record n 18 o sr ca mg ca and u ca are relatively constant implying conditions similar to modern conditions although the slight increasing trend in sr ca may suggest an increase in salinity over this period the n 13 c values were approximately in equilibrium with atmospheric co2 in the early part of the record but became relatively negative in the later part of the record this indicates that the dominant mechanism controlling the isotopic composition of dissolved inorganic carbon shifted from exchange with the atmosphere to variations in biological productivity fl 2001 elsevier science b v all rights reserved

what can physical source models tell us about the recurrence time of earthquakes abstract earthquake prediction no matter what the timescale has been and continues to be a contentious subject and it is indubitably a prominent challenge for modern seismology and earthquake physics indeed few natural events can have the catastrophic consequences of earthquakes earthquakes today account for about 60 of natural fatalities a physical description of an earthquake represents an amenable approach to the prediction but it suffers of some limitations basically due to the notorious ignorance about the initial state of a given fault and about the physical law controlling its traction evolution independent on those intrinsic epistemic limitations the concept of the earthquake recurrence based upon the idea of the cyclic or characteristic earthquake has been often invoked to describe and thus to predict subsequent instability events on a seismogenic structure in this paper by using the simplest analog fault model the one degree of freedom mass spring system we quantitatively show that the concepts of the recurrence time and the earthquake cycle have limitations even making them meaningless we will discuss in a compendious synopsis all the possible physical mechanisms which can dramatically affect the recurrence time our conclusions emphasize again that the competing mechanisms potentially occurring during faulting even in the simplest and idealized condition of an isolated fault can significantly complicate the regular cyclicity of earthquakes predicted by the analog fault system these conclusions can contribute to the debate about the role of the physical modeling of earthquakes in the contest of seismic hazard assessment

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

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

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

new insights on late quaternary asian palaeomonsoon variability and the timing of the last glacial maximum in southwestern china abstract a 6 35 m core 06sd was retrieved from lake shudu yunnan province china the sediments spanning the period 22 6 10 5 kcal yr bp 6 35 1 44 m were analysed using a combination of variables including pollen charcoal particle size magnetic susceptibility and loss on ignition the resulting palaeorecord provides a high resolution reconstruction of late pleistocene to early holocene climatic and environmental changes in southwestern china our findings indicate that from c 22 6 to 17 7 kcal yr bp vegetation assemblages were primarily aligned to sparse xerophytic grassland tundra or cold tolerant boreal pinus forest indicating that climatic conditions in southwestern china were cold and dry however from c 17 7 to 17 4 kcal yr bp the lake shudu record is punctuated by marked environmental changes these include the establishment of denser vegetation cover a marked expansion of boreal pinus forest and enhanced hydrological activity in the catchment over centennial timescales perhaps suggesting that stepwise variations in the asian monsoon were triggering fundamental environmental changes over sub millennial timescales thereafter the pollen record captures a period of environmental instability reflected in fluctuations across all of the variables which persists until c 17 1 kcal yr bp after c 17 1 kcal yr bp the expansion of steppe vegetation cover and cold cool mixed forest consisting of mesophilous vegetation such as tsuga and picea thermophilous trees including ulmus and deciduous quercus inferred from the lake shudu pollen record point to the establishment of warmer wetter and perhaps more seasonal conditions associated with a strengthening asian summer monsoon during the shift from pleistocene to holocene climatic conditions

stratigraphic charcoal analysis on petrographic thin sections application to fire history in northwestern minnesota results of stratigraphic charcoal analysis from thin sections of varved lake sediments have been compared with fire scars on red pine trees in northwestern minnesota to determine if charcoal data accurately reflect fire regimes pollen and opaque spherule analyses were completed from a short core to confirm that laminations were annual over the last 350 yr a good correspondence was found between fossil charcoal and fire scar data individual fires could be identified as specific peaks in the charcoal curves and times of reduced fire frequency were reflected in the charcoal data charcoal was absent during the fire suppression era from 1920 a d to the present distinct charcoal maxima from 1864 to 1920 occurred at times of fire within the lake catchment fire was less frequent during the 19th century and charcoal was substantially less abundant fire was frequent from 1760 to 1815 and charcoal was abundant continuously fire scars and fossil charcoal indicate that fires did not occur during 1730 1750 and 1670 1700 several fires occurred from 1640 to 1670 and 1700 to 1730 charcoal counted from pollen preparations in the area generally do not show this changing fire regime simulated sampling of the thin section data in a fashion comparable to pollen slide methods suggests that sampling alone is not sufficient to account for differences between the two methods integrating annual charcoal values in this fashion still produced much higher resolution than the pollen slide method and the postfire suppression decline of charcoal characteristic of my method but not of pollen slides is still evident consideration of the differences in size of fragments counted by the two methods is necessary to explain charcoal representation in lake sediments

vegetation history fire history and lake development recorded for 6300 years by pollen charcoal loss on ignition and chironomids at a small lake in southern kyrgyzstan alay range central asia analyses of pollen microscopic charcoal loss on ignition loi and chironomids in the sediment of the small sub alpine lake kichikol 2541 m a s l 39 59 n 73 33 e alay range kyrgyzstan provide new data to reconstruct the vegetational and lacustrine history during the past 6300 years from 6300 5100 calibrated 14c years bp cal yr bp semi deserts with chenopodiaceae and ephedra and rather open juniperus stands persisted around the lake at 5100 4000 cal yr bp dense juniperus forest established around 4000 cal yr bp the forest retreated and was probably restricted to north facing slopes as is the case today changes in the hydrology of kichikol are inferred from lithological properties pollen of aquatic plants and remains of aquatic invertebrates the lacustrine development of kichikol suggests a step wise increase in humidity during the mid and late holocene with major shifts recorded at 5000 and 4000 cal yr bp at the beginning of the record kichikol was a very shallow possibly temporary pond an initial rise in water table is registered at c 5000 cal yr bp followed by a second rise to near present levels at c 4000 cal yr bp these hydrological shifts could be related to an increase of westerly moisture transport from the mediterranean region as a consequence of a late holocene weakening of the central asian high and indian monsoon systems moderate human impact in the region is recorded after 2100 cal yr bp as indicated by pollen of plantago lanceolata type and a slight increase of charcoal accumulation rates considering the general course of climate as well as human impact we conclude that the present forest composition is natural or quasi natural

is the initial thermal state of a fault relevant to its dynamic behavior the prediction ofimpending earthquakes undoubtedly remains one of the most pursued goals of modern seismology within the framework of a deterministic description of earthquake faulting the initial state of the fault system and the choice of the governing model describing its rheological behavior play a fundamental role in the description of the earthquake recurrence in classical models of faulting this initial stateisbasicallydescribedbytheinitialshear stressdistribution priortothenextearth quakeevent andbytheinitialslidingvelocity inthispaper byassumingarate state andtemperature dependent rheology weinvestigatewhether theinitialthermalstate of the fault can also have a significant role in earthquake dynamics our numerical results clearly demonstrate that the initial temperature greatly influences the cosesimic slip and thus the earthquake magnitude the released stress and thus the radiated energy andtheintereventtime i e theearthquakerecurrence despitetheremainingissueson theconceptofearthquakecyclicity ourresultscancontributetothelivelydebateonthe deterministic hazard assessment illuminating that the temperature field also plays a fundamental role in earthquake dynamics not only because it controls possible phase changes and the chemical environment of the fault zone but also because it affects the response of a brittle fault and earthquake cycles

zircon u pb age constraints from iran on the magmatic evolution related to neotethyan subduction and zagros orogeny abstract this study reports zircon la icpms u pb ages of 50 igneous rock samples from the urumieh dokhtar magmatic arc udma and sanandaj sirjan structural zone ssz in iran these results together with literatures and our unpublished age data better delineate the magmatic evolution related to the neotethyan subduction and subsequent zagros orogeny that resulted from the arabia eurasia collision subduction related magmatism was active during jurassic time as evidenced by the presence of widespread i type granitoids from the middle to late jurassic 176 144 ma in the ssz after a protracted magmatic quiescence in the early cretaceous igneous activity renewed inland in the udma from which we identify late cretaceous granitoids 81 72 ma in jiroft and bazman areas the southeastern segment of the udma the udma volcanism was most active and widespread during the eocene and oligocene 55 25 ma much longer lasting than previously thought as just an eocene pulse such a prolonged igneous flare up event in the udma can be correlated to armenia where coeval calc alkaline rocks are common the udma magmatism ceased progressively from northwest to southeast with magmatic activities ending the early miocene ca 22 ma in meghri the middle miocene ca 16 ma in kashan and the late miocene ca 10 6 ma in anar respectively the southeastward magmatic cessation is consistent with the notion of oblique and diachronous collision between arabia and eurasia post collisional volcanism started ca 11 ma in saray east off the urumieh lake which along with later eruptions in sahand 6 5 4 2 ma and sabalan 0 4 ma volcanoes forms a compositionally unique component of the vast volcanic field covering much of the lesser caucasus nw iran and eastern anatolia regions

asynchronous evolution of the indian and east asian summer monsoon indicated by holocene moisture patterns in monsoonal central asia abstract the numerical meta analysis of 92 proxy records 72 sites of moisture and or temperature change confirms earlier findings that the dominant trends of climatic evolution in monsoonal central asia since the last glacial roughly parallel changes in northern hemisphere summer insolation i e the period following the last glacial maximum was characterized by dry and cold conditions until 15 cal kyr bp followed by a warm wet period coincident with the bolling allerod warm period and terminated by a cold dry reversal during the younger dryas period after an abrupt increase at the start of the holocene warm and wet conditions prevailed until ca 4 cal kyr bp when moisture levels and temperatures started to decrease ordination of moisture records reveals strong spatial heterogeneity in moisture evolution during the last 10 cal kyr the indian summer monsoon ism areas northern india tibetan plateau and southwest china exhibit maximum wet conditions during the early holocene while many records from the area of the east asian summer monsoon indicate relatively dry conditions especially in north central china where the maximum moisture levels occurred during the mid holocene we assign such phenomena to strengthened hadley circulation centered over the tibetan plateau during the early holocene which resulted in subsidence in the east asian monsoonal regions leading to relatively dry conditions our observations of the asynchronous nature of the two asian monsoon subsystems on millennial time scales have also been observed on annual time scales as well as implied through the spatial analysis of vertical air motion patterns after strong ascending airflows over the tibetan plateau area that were calculated from ncep ncar reanalysis data for the last 30 years analogous with the early holocene the enhancement of the ism in a future warming world will result in an increase in the asynchronous nature of the monsoon subsystems this trend is already observed in the meteorological data from the last 15 years

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

thermal histories from the central alborz mountains northern iran implications for the spatial and temporal distribution of deformation in northern iran we integrate new and existing thermochronological geochronological and geologic data from the western and central alborz mountains of iran to better constrain the late cenozoic tectonic evolution of northern iran in the context of the arabia eurasia collision new data are presented for two granitic plutons north of the alborz range crest additional new apatite u th he data are also presented for volcanic intrusive and detrital apatite grains from two transects south of the range crest our most definitive results include zircon and apatite u th he and limited k feldspar 40 ar 39 ar thermal history data from the cretaceous ca 98 ma nusha pluton that reveal that the alborz basement underwent generally slow denudation 0 1 km m y as late as 12 ma with more accelerated exhumation 0 45 km m y that likely began shortly after 12 ma the lahijan pluton a late neoproterozoic cambrian basement exposure near the caspian shore records apatite u th he closure at 17 13 ma additional u th he results from detrital apatites sampled along two separate horizontal transects all consistently yielded latest miocene to pliocene apparent ages that imply that even supracrustal cover rocks within the alborz have undergone significant regionally extensive exhumation overall our data are consistent with 5 km of regionally extensive denudation since ca 12 ma the onset of rapid exhumation in the alborz at ca 12 ma appears to be consistent with other timing estimates that place the onset of the arabia eurasia collision between 14 and 10 ma

active tectonics and late cenozoic strain distribution in central and eastern iran 1 right lateral shear between central iran and afghanistan is accommodated on n s right lateral strike slip faults surrounding the aseismic dasht e lut north of 34 n the right lateral shear is accommodated on left lateral faults that rotate clockwise about vertical axes little is known of the late tertiary and younger offsets and slip rates on the active fault systems results that are important for understanding the regional tectonics we use observations from satellite imagery to identify displaced geological and geomorphological markers which we use in conjunction with the overall morphology and orientation of the active fault systems to estimate the total cumulative right lateral shear estimates of cumulative fault movements from offset features and inferred vertical axis rotation of fault bounded blocks suggest that the late cenozoic strain is concentrated toward the eastern margin of iran along the sistan shear zone where bedrock offsets of at least 70 km are observed across the active faults the geomorphology of the deh shir anar and great kavir strike slip faults in central iran suggest that although little shortening is accommodated across this region they might still be active and hence capable of producing earthquakes present day activity on these faults in central iran would not be expected from distributions of instrumental and historical earthquakes although speculative the late tertiary strain distribution described in this paper is consistent with what we know of the present day rates of shear in eastern iran and provides a framework to which later more detailed work can be added

early eocene crustal thickening in southern tibet new age and geochemical constraints from the gangdese batholith abstract the lhasa terrane southern tibet is where the thickest part of the earth s crust occurs as a result of the india asia collision this paper reports zircon u pb age and geochemical data of samples collected from the gangdese batholith southern lhasa terrane a subset of which has already been dated at 65 41 ma using zircon u pb geochronology ji w q wu f y chung s l li j x liu c z 2009a zircon u pb chronology and hf isotopic constraints on the petrogenesis of gangdese batholiths southern tibet chemical geology 262 229 245 to constrain the timing and mechanism s responsible for crustal thickening beneath southern tibet our new data indicate that the gangdese magmatism lasted continuously from ca 65 to 34 ma during which geochemical evidence for crustal thickening is observed crustal thickening is best illustrated by the progressive increase in la yb and sr y of the early to latest eocene magmatic rocks associated with the decrease in hf isotopic ratios of paleocene to eocene magmatic zircons we also identify in this study the oldest ca 51 ma post collisional adakitic granitoids in the gangdese batholith interpreted as products from partial melting of underplated basaltic lower crust therefore a thickened crust likely existed by that time at least locally in the southern lhasa terrane tibet

the eocene bimodal piranshahr massif of the sanandaj sirjan zone nw iran a marker of the end of the collision in the zagros orogen abstract the bimodal piranshahr massif is composed of coeval but geochemically unrelated mafic 40 7 0 2 ma zircon u pb sensitive high resolution ion microprobe shrimp age and a type felsic rocks 41 0 5 ma rb sr and 41 3 0 8 ma zircon u pb shrimp age the mafic rocks consist of two geochemical types of gabbros that derived from different magmas the more abundant gabbros are moderately alkaline have ratios of large ion lithophile elements to ree and high field strength elements to ree similar to those of intraplate mantle magmas 87 sr 86 sr 41 ma 0 7036 and e nd 41 ma 7 2 the less abundant gabbros have calc alkaline affinities 87 sr 86 sr 41 ma 0 7043 and e nd 41 ma 4 78 felsic rocks are metaluminous a2 type annite fayalite hedenbergite hypersolvus leucocratic coarse grained agpaitic syenites pulaskites and granites with 87 sr 86 sr 41 ma 0 7048 and e nd 41 ma 3 6 4 5 syenites pulaskites and granites are genetically related pulaskites probably represent alkali enriched water rich residual melts from which an f rich vapour phase was later separated granites were probably generated during open system processes in which f rich hydrous alkaline fluids released from the syenites acted upon pre existing felsic rocks the c 41 ma age of the post collisional piranshahr massif indicates that the related collision probably occurred at 50 60 ma i e late palaeocene or early eocene thus resolving a much debated question

dynamic seismic ruptures on melting fault zones 1 we present a physical model that describes the behavior of spontaneous earthquake ruptures dynamically propagating on a fault zone and that accounts for the presence of frictional melt produced by the sliding surfaces first we analytically derive the solution for the temperature evolution inside the melt layer which generalizes previous approximations then we incorporate such a solution into a numerical code for the solution of the elastodynamic problem when a melt layer is formed the linear slip weakening law initially governing the fault and relying on the coulomb friction is no longer valid therefore we introduce on the fault a linearly viscous rheology with a temperature dependent dynamic viscosity we explore through numerical simulations the resulting behavior of the traction evolution in the cohesive zone before and after the transition from coulomb friction and viscous rheology the predictions of our model are in general agreement with the data from exhumed faults we also find that the fault after undergoing the breakdown stress drop controlled by the slip weakening constitutive equation experiences a second traction drop controlled by the exponential weakening of fault resistance due to the viscous rheology this further drop enhances the instability of the fault increasing the rupture speeds the peaks in fault slip velocity and the fracture energy density

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

magmatic and metamorphic history of the deh salm metamorphic complex eastern lut block eastern iran from u pb geochronology the deh salm metamorphic complex dmc of the lut block in east iran consists of metapelites amphibolites marbles and metasandstones intruded by granite and pegmatites u pb dating of zircon monazite xenotime and titanite by id tims show that the granitic rocks were emplaced at 166 163 ma confirming that the high temperature metamorphism was synchronous with the intrusive activity and that the region cooled rapidly thereafter late to post magmatic hydrothermal activity was probably responsible for the late crystallization at 159 5 ma of zircon and titanite in an amphibolite and of monazite in granite xenocrystic zircons yield indications for a carboniferous component in the source together with a variety of precambrian ages which indicate a provenance of the sedimentary protolith from mature continental crust the timing and rapidity of the events are consistent with evolution of the dmc in a back arc environment during the jurassic subduction of the neotethys ocean

a 5000 yr record of climate change in varved sediments from the oxygen minimum zone off pakistan northeastern arabian sea the upper holocene marine section from a kasten core taken from the oxygen minimum zone off karachi pakistan at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1 2 mm yr and a unique record of monsoonal climatic variability covering the past 5000 years our chronostratigraphy is based on varve counts verified by conventional and ams 14 c dating individual hemipelagic varve couplets are about 0 8 1 5 mm thick with light colored terrigenous laminae a deposited mainly during the winter monsoon alternating with dark colored laminae b rich in marine organic matter coccoliths and fish debris that reflect deposition during the high productivity season of the late summer monsoon august october precipitation and river runoff appear to control varve thickness and turbidite frequency we infer that precipitation decreased in the river watershed indicated by thinning varves after 3500 4000 yr b p this is about the time of increasing aridification in the near east and middle east as documented by decreasing nile river runoff data and lake level lowstands between turkey and northwestern india this precipitation pattern continued until today with precipitation minima about 2200 1900 yr b p 1000 yr b p and in the late middle ages 700 400 yr b p and precipitation maxima in the intervening periods as documented by spectral analysis the thickness of varve couplets responds to the average length of a 250 yr cycle a 125 yr cycle the gleissberg cycle of solar activity 95 yr and a 56 yr cycle of unknown origin higher frequency cycles are also present at 45 39 29 31 and 14 yr the sedimentary gray value also shows strong variability in the 55 yr band plus a 31 yr cycle because high frequency cyclicity in the enso band ca 3 5 and 5 yr is only weakly expressed our data do not support a straightforward interaction of the pacific enso with the monsoon driven climate system of the arabian sea

mid to late holocene climate driven regime shifts inferred from diatom ostracod and stable isotope records from lake son kol central tian shan kyrgyzstan abstract arid central asia represents a key region for understanding climate variability and interactions in the northern hemisphere patterns and mechanisms of holocene climate change in arid central asia are however only partially understood multi proxy data combining diatom ostracod sedimentological geochemical and stable isotope analyses from a ca 6000 year old lake sediment core from son kol central kyrgyzstan show distinct and repeated changes in species assemblages diatom and ostracod inferred conductivity shifts between meso euhaline and freshwater conditions suggest water balance and regime shifts organism derived data are corroborated by stable isotope mineralogical and geochemical records underlining that son kol was affected by strong lake level fluctuations of several meters the 13ccarb 18ocarb correlation shows repeated switchovers from a closed to an open lake system from 6000 to 3800 and 3250 to 1950 cal yr bp son kol was a closed basin lake with higher conductivities increased nutrient availability and a water level located below the modern outflow son kol became again a hydrologically open lake at 3800 and 1950 cal yr bp comparisons to other local and regional paleoclimate records indicate that these regime shifts were largely controlled by changing intensity and position of the westerlies and the siberian anticyclone that triggered changes in the amount of winter precipitation a strong influence of the westerlies ca 5000 4400 3800 3250 and since 1950 cal yr bp enhanced the amount of precipitation during spring autumn and winter whereas cold and dry winters prevailed during phases with a strong siberian anticyclone and southward shifted westerlies at ca 6000 5000 4400 3800 and 3250 1950 cal yr bp similarities between variations in winter precipitation at son kol and records of the predominant nao mode further suggest a teleconnection between wet dry winter climate in central asia and a positive negative nao mode thus this study identifies climate fluctuations as the main driver for hydrological regime shifts in son kol controlling physicochemical conditions and consequently causing abrupt species assemblage changes this emphasizes the importance of multi proxy approaches to identify triggers thresholds and cascades of aquatic ecosystem transformations

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

geodetic constraints on present day motion of the arabian plate implications for red sea and gulf of aden rifting 1 five years of continuously recording gps observations in the kingdom of saudi arabia together with new continuous and survey mode gps observations broadly distributed across the arabian peninsula provide the basis for substantially improved estimates of present day motion and internal deformation of the arabian plate we derive the following relative geodetic euler vectors latitude n longitude e rate myr counterclockwise for arabia nubia 31 7 0 2 24 6 0 3 0 37 0 01 arabia somalia 22 0 0 5 26 2 0 5 0 40 0 01 arabia india 18 0 3 8 87 6 3 3 0 07 0 01 arabia sinai 35 7 0 8 17 1 5 0 0 15 0 04 and arabia eurasia 27 5 0 1 17 6 0 3 0 404 0 004 we use these euler vectors to estimate present day stability of the arabian plate the rate and direction of extension across the red sea and gulf of aden and slip rates along the southern dead sea fault south of the lebanon restraining bend 4 5 4 7 0 2 mm yr left lateral 0 8 1 1 0 3 mm yr extension and the owens fracture zone 3 2 2 5 0 5 mm yr right lateral increasing from north to south 1 2 mm yr extension on a broad scale the arabian plate has no resolvable internal deformation weighted root mean square of residual motions for arabia equals 0 6 mm yr although there is marginally significant evidence for n s shortening in the palmyride mountains syria at 1 5 mm yr we show that present day arabia plate motion with respect to eurasia is consistent within uncertainties i e 10 with plate tectonic estimates since the early miocene when arabia separated from nubia we estimate the time of red sea and gulf of aden rifting from present day arabia motion plate tectonic evidence for a 70 increase in arabia nubia relative motion at 13 ma and the width of the red sea and gulf of aden and find that rifting initiated roughly simultaneously 2 2 myr along the strike of the red sea from the gulf of suez to the afar triple junction as well as along the west gulf of aden at 24 2 2 ma based on the present kinematics we hypothesize that the negative buoyancy of the subducted ocean lithosphere beneath the makran and the zagros fold thrust belt is the principle driver of arabia eurasia convergence and that resisting forces associated with arabia eurasia continental collision have had little impact on plate motion

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

zircon u pb and hf isotopic constraints from eastern transhimalayan batholiths on the precollisional magmatic and tectonic evolution in southern tibet abstract before the indian collision with asia northward subduction of the neo tethyan oceanic lithosphere produced an andean type convergent margin in south asia characterized by arc magmatism starting from the early jurassic and lasting until the eocene the magmatic arc is now represented by widespread intrusive bodies or the so called transhimalayan batholiths in the lhasa terrane of southern tibet that have been divided into two main magmatic suites i e the northern plutonic belt and the southern gangdese batholith their temporal distribution concerning how exactly the magmatic suites correlate eastwards and then southeastwards around the eastern himalayan syntaxis however remains poorly constrained here we report the first combined zircon u pb and hf isotopic study of the transhimalayan batholiths from the eastern part of the lhasa terrane 95 97 5 e and 28 5 30 n se tibet zircon u pb dating results of 24 granitoids indicate that the rocks were emplaced principally in the early cretaceous 133 110 ma and subordinately in the paleocene 66 57 ma long after an older granite intrusion in the earliest jurassic 198 ma the zircon ehf t values range from 5 to 20 yielding hf crustal model ages tdmc between 0 8 and 2 4 ga that peak at 1 7 ga suggesting a major episode of crustal growth in the proterozoic and a predominantly or even exclusively crustal source for the granitoid petrogenesis these zircon u pb and hf isotopic constraints together with whole rock geochemical characteristics allow us to correlate them to s type granitoids in the northern plutonic belt rather than to the i type gangdese batholith from the central part of the southern lhasa terrane in contrast to the gangdese magmatism that formed with a significant juvenile mantle input related to the neo tethyan subduction these s type granitoids show geochemical similarities to the north american cordilleran interior batholiths that did not form directly from a subduction setting thus we attribute the petrogenesis of the widespread early cretaceous granitoids in the northern belt and eastern himalayan batholiths to a postcollisional regime due to the late jurassic early cretaceous continental collision between the lhasa and qiangtang terranes under this framework the s type magmatism was generated in response to collision induced crustal thickening which may have capabilities of causing crustal anatexis by itself in the region however continued interplay with the neo tethyan subduction zone processes such as back arc extension could also have played a crucial and long lasting role in the magma generation

an efficient mechanism to avert frictional melts during seismic ruptures abstract we consider the spatio temporal evolution of temperature due to frictional heating caused by the spontaneous propagation of 3 d dynamic seismic ruptures on planar faults in our numerical experiments which characterize typical crustal earthquakes we assume that fault friction is controlled by different linear and nonlinear slip dependent friction laws in this paper we confirm that a necessary condition to prevent melting is to have a nearly complete breakdown stress drop our simulations which employ a nonlinear slip dependent governing equation recently inferred from laboratory experiments by sone and shimamoto 2009 reproduce such a dramatic fault weakening and represent a plausible explanation for the prevention of melting during earthquake ruptures we also demonstrate that low friction alone although necessary is not a sufficient condition to avert melts the linear or classical slip weakening sw law would produce melting even assuming the same lengthscales and frictional levels to avoid melting with linear sw law we have to impose a specific value of the sw distance this reveals the prominent role of the time evolution of traction within the cohesive zone where the stress release is realized and of the value of the fracture energy density

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

temperature sensitive tien shan tree ring chronologies show multi centennial growth trends two millennia length juniper ring width chronologies processed to preserve multi centennial growth trends are presented for the alai range of the western tien shan in kirghizia the chronologies average the information from seven near timberline sampling sites and likely reflect summer temperature variation for comparison chronologies are also built using standard dendrochronological techniques we briefly discuss some qualities of these inter decadal records and show the low frequency components removed by the standardization process include a long term negative trend in the first half of the last millennium and a long term positive trend since about ad 1800 the multi centennial scale alai range chronologies where these trends are retained are both systematically biased but in an opposite sense in their low frequency domains nevertheless they represent the best constraints and estimates of long term summer temperature variation and reflect the medieval warm period the little ice age and a period of warming since about the middle of the nineteenth century

petrology geochemistry and geochronology of trondhjemites from the qori complex neyriz iran metamorphism magmatism and thrusting were the result of subduction of neotethys beneath the continental margin arc of the sanandaj sirjan shear zone sssz during the mesozoic the qori metamorphic complex is a part of the southern sssz leuco granitic trondhjemitic rocks crop out in the qori metamorphic complex and are rare rock types in the sssz these rocks have intruded into the marbles and garnet amphibolites the highest grade metamorphic rocks of the qori metamorphic complex and in some outcrops a transitional boundary between the amphibolites and the granitoids can be distinguished the granitoids are granular in texture and consist of plagioclase albite oligoclase quartz k feldspar muscovite and subordinate garnet spinel rutile and apatite which primarily occur as inclusions in the main phases the peraluminous trondhjemitic rocks are enriched in na2o and sio2 and depleted in feo mgo and cao similarities with some trondhjemitic liquids produced through partial melting of amphibolites or hydrous basalts i e low al2o3 content less than 15 wt low ba sr tio2 and eu content all with negative anomalies moderately enriched lrees and y and flat hree patterns suggest that the evolution of the parental magma was controlled by residual plagioclases during partial melting of a garnet amphibolite source concentrations of ferromagnesian elements mg fe and mn are low suggesting that the granitic rocks were not produced by high degrees of partial melting furthermore they display low amounts of ferromagnesian components from the protolith garnet amphibolite this is supported by consideration of compatible elements especially cr ni and ti and the less robust hree which respectively show very high and high bulk partition coefficients for relatively small degrees 20 of partial melting of the source the partial melting of the garnet amphibolites occurred at pressures and temperatures between 7 5 and 9 5 kbar at a depth of 25 to 32 km and 680 and 720 degrees c respectively based on the grt hbl and hbl pl thermometers and a grt hbl pl qtz barometer precise u th zircon shrimp ages of the trondhjemite show magmatic ages of 147 4 0 76 ma volgian late jurassic and suggest that neotethys began to subduct beneath the continental margin arc of the sssz as a result of this process an arc related metamorphism occurred leading to the development of the garnet amphibolites in the qori metamorphic complex c 2009 elsevier b v all rights reserved

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

arabia eurasia collision and the forcing of mid cenozoic global cooling the end of the eocene greenhouse world was the most dramatic phase in the long term cooling trend of the cenozoic era here we show that the arabia eurasia collision and the closure of the tethys ocean gateway began in the late eocene at 35 ma up to 25 million years earlier than in many reconstructions we suggest that global cooling was forced by processes associated with the initial collision that reduced atmospheric co2 these are 1 waning volcanism across southwest asia 2 increased organic carbon storage in paratethyan basins e g black sea and south caspian 3 increased silicate weathering in the collision zone and 4 a shift towards modern patterns of ocean currents associated with increased vigour in circulation and organic productivity

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

the urumieh plutonic complex nw iran a record of the geodynamic evolution of the sanandaj sirjan zone during cretaceous times part i petrogenesis and k ar dating the urumieh plutonic complex is located in the northwestern part of the sanandaj sirjan zone iran the urumieh plutonic complex comprises three components i e a dioritic suite a granitic suite consisting of biotite bearing granites and younger stocks i e an alkaline suite alkali syenite and alkali granite and a muscovite bearing granite based on k ar chronology of separated minerals amphibole biotite muscovite and feldspar and field observations the urumieh complex was built during two distinct episodes the diorite and granite suites were emplaced between 100 and 92 ma whereas the younger suites were emplaced between 82 and 80 ma the dioritic suite has sio2 contents in between 56 59 wt and major and trace elements characteristic of mafic i type granitoids a ckn molar ratio 0 81 0 88 this suite is characterized by relatively high mg 49 low na2o content 3 5 wt and a relatively high abundance of lile incompatible elements their chondrite normalized ree patterns are relatively flat la yb n 7 in average and show small or no negative eu anomalies eu eu 0 9 in average some diorites show mingling and mixing textures that may support local crustal contamination of the dioritic melt geochemical features suggest that diorites formed in a subduction setting by partial melting of metasomatized mantle the coeval granites are peraluminous 1 04 molar a ckn 1 37 with sio2 contents between 66 69 wt their chondrite normalized ree patterns are slightly enriched in lree relative to hree la yb n 11 in average with negative eu anomalies eu eu 0 4 in average these granites have biotite as the main mafic mineral and locally contain restitic xenoliths they originated by partial melting of metasediments the younger alkaline syenite and granite are only slightly peraluminous molar a cnk 1 04 in average they show enrichment in hfse high contents of ree and relatively high feo mgo and ga al ratios typical of a type magmas the other younger granite pluton dourbeh granite has peculiar mineralogical and geochemical features none of these late syenite and granites were intruded by mafic dikes and they do not contain any comagmatic mafic enclaves they seem to have been derived only from crustal melting changing of magmatic sources during the 100 80 ma time interval is discussed with respect to the geodynamic context the first magmatic episode 100 92 ma is regarded as subduction related whereas the second one at ca 80 ma likely ocurred during the collision between the arabian margin and the sanandaj sirjan zone

effect of frictional heating on pre seismic sliding a numerical simulation using a rate state and temperature dependent friction law summary using a simple spring block model and a rate and state dependent friction law incorporating the effect of temperature variation i perform a numerical simulation of aseismic sliding prior to unstable seismic faulting i compare the simulation result of pre seismic sliding in the case where the temperature effect due to frictional heating on frictional strength is taken into consideration heated fault with the result in the case where the temperature effect is neglected unheated fault assuming model parameters appropriate for the nucleation site of a large interplate earthquake it is found that an earthquake occurrence time is a little earlier on the heated fault than on the unheated fault this is because the frictional strength is weakened by temperature rise due to frictional heating during pre seismic sliding the amplitude of precursory crustal deformation caused by pre seismic sliding on the heated fault is estimated to be about 20 per cent smaller than that on the unheated fault

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

temperature variations of constitutive parameters can significantly affect the fault dynamics abstract a rate and state dependent governing law with temperature dependent constitutive parameters is considered on the basis of laboratory inferences we model the whole seismic cycle of a homogeneous fault obeying to such a law by adopting a spring slider dashpot fault analog model we show that the variations of the parameter a accounting for the so called direct effect with the temperature cause the system to enter at high speeds in a conditionally stable regime and also in a velocity strengthening regime although we do not observe the complete cessation of slip we can see a severe reduction of the degree of the instability of the fault in particular the peaks of the sliding velocity are reduced as well as the developed temperature due to frictional sliding and the released stress during each instability event moreover the recurrence times are reduced of a factor of two with respect to a reference configuration where the canonical formulation of rate and state friction with temporally constant parameters is assumed the obtained results can help the interpretation of high velocities laboratory experiments and further illuminate the importance of the temperature in the context of seismic hazard assessment

thermochemical pressurization of faults during coseismic slip 1 during earthquakes frictional heating on the fault plane induces a temperature rise and thus a pore pressure rise which is known as thermal pressurization tp coseismic mineral dehydrations may occur because of this temperature increase and are included within the tp framework dehydrations are modeled as a source term for pore pressure because of the total volume change and as a sink term for temperature because they are endothermic the reaction occurs within the slipping zone when a threshold temperature ts is reached dehydration reaction kinetic is modeled using a first order reaction rate using energy and fluid mass conservation we derive analytically the equations of evolution of pore pressure temperature and reaction extent in the undrained adiabatic case using a constant reaction rate we investigate the values of the kinetic rate constant required to produce a significant effect which are much higher than laboratory data reported in the literature on clay serpentine and phyllosilicate dehydration we show however that such high values can be reached if the temperature dependency of the rate constant is taken into account next we include fluid and heat transport and use an arrhenius law to calculate the rate constant as a function of temperature the subsequent set of differential equations is then solved numerically the main effect of dehydration reactions is an increase of pore pressure and a stabilization of the temperature during slip we explore a wide range of parameters in order to determine in which cases dehydration can be considered as a nonnegligible process for high permeability rocks 10 18 m2 and when the amount of water that can be released is of the order of 10 dehydration is an important mechanism as it delays the onset of melting which would normally occur even within the tp framework if the onset temperature is low compared to the initial temperature t0 ts t0 150 c overpressure can occur if the reactions are highly endothermic and if their kinetic is fast enough frictional melting would not occur unless the dehydration reactions are completed within the slipping zone

two twentieth century mlh 7 5 earthquakes recorded in annually laminated lake sediments from sary chelek western tian shan kyrgyzstan central asia is highly vulnerable to large earthquakes yet existing records of past seismic activity in this area are still insufficient to reliably assess regional earthquake hazard on longer timescales within this study the sediments of sary chelek a mountain lake in the western kyrgyz tian shan were investigated to explore its potential as a natural paleoseismic archive the lacustrine deposits are characterized by a succession of annually laminated varved sediments overlying event deposits that consist of large scale turbidites and distorted lake sediments similar to earthquake related deposits described from other lake sediment records microscopic sediment analysis furthermore revealed distorted varves in the laminated sequence that closely resemble earthquake related soft sediment deformation structures varve counting and radiometric dating determine the formation of the distorted varves and the emplacement of the large scale event deposits to the early 1990s and mid 1940s respectively this is in good temporal agreement with the occurrence of two large earthquakes that struck western kyrgyzstan in ad 1992 and ad 1946 these results and particularly the precise age control of the sary chelek sediment record highlight its potential for establishing a long and precisely dated record of regional earthquake activity

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

insights from the talysh of azerbaijan into the paleogene evolution of the south caspian region the age and mode of formation of the south caspian basin are disputed an 10 km thick predominantly middle eocene clastic and volcanic succession is exposed in the talysh mountains of azerbaijan at its western margin here high k alkali basalts pass laterally to the east and southeast into volcanogenic sandstone dominated turbidity current and debris flow deposits these southeasterly directed depositional systems accumulated in water depths generally greater than 200 m and fed directly into the western south caspian basin new ar ar ages cluster around 39 ma with an upper 1400 m thick volcanic interval being deposited in 2 2 0 2 m y we interpret that this rapid deposition and magmatism records a major back arc extensional transtensional event in the talysh north of the north dipping neotethyan subduction zone this event is recognized across much of southwest asia and may indicate a period of significant basin formation within the adjacent south caspian basin a transition into upper eocene lower oligocene strata dominated by fine grained turbidity current and hemipelagic sediments with slope instability features is interpreted to mark the end of rifting and volcanism in the talysh and the start of the arabia eurasia collision overlying oligocene coarse clastic rocks are interpreted as the erosional products of localized topography created by the further propagation of compressional deformation into the talysh region