vertical wind distribution in the polar thermosphere during horizontal e region experiment hex campaign 1 vertical winds in the thermosphere were measured with two fabry perot interferometers at the poker flat research range pfrr and eagle observatory alaska during the horizontal e region experiment hex campaign feburary and march 2003 since these two observatories have almost the same geomagnetic latitude we could deduce vertical wind distributions along the same auroral arc the oi557 7 nm and oi630 0 nm emissions were separated using a dichroic mirror which enabled us to estimate temporal variations in vertical winds in the e and f regions simultaneously to measure the optical auroral distribution we used all sky imagers at the pfrr we had 13 clear nights out of a total of 23 we obtained the following results from the observations 1 the temporal variations in vertical wind observed at oi557 7 nm at the two observatories had a high degree of correlation despite being 300 km apart the correlation coefficients exceeded 0 6 on six of the 13 nights the chance of exceeding a correlation coefficient of 0 6 on an individual night is about 0 1 2 the correlation was relatively low in the oi630 0 nm observation 3 some low correlation cases for both wavelengths indicated that the location of the auroral arc with respect to the observatory was different for the two sites namely whether the auroral arc was poleward or equatorward of the observational area these results suggest that the vertical wind structures along one auroral arc are uniform at least 300 km apart this wind distribution was consistent with previous works in most cases but some exceptions were also found

vorticity and divergence in the high latitude upper thermosphere measurements made from the dynamics explorer 2 satellite in november 1981 through january 1982 and november 1982 through january 1983 have been analyzed to determine the divergence and vertical component of vorticity of the high latitude neutral wind field in the upper thermosphere for quiet kp 3 and active 3 kp 6 geomagnetic conditions and for both northern winter and southern summer hemispheres this analysis provides the first experimental determination of the large scale vorticity and divergence patterns in the polar thermosphere and provides insight into the relative strengths of the different sources of momentum and energy responsible for driving the winds the principal findings from this work include the following the mean neutral wind pattern is dominated by rotational flow rather than by divergent flow with a typical vorticity divergence ratio of 2 1 for active conditions and 4 1 for quiet conditions comparison of the divergence and vorticity patterns for quiet and active conditions indicates that the divergent component of the neutral flow intensifies more significantly with increasing geomagnetic activity than does the rotational component

auroral zone thermospheric dynamics 2 individual nights ground based fabry perot spectrometer measurements of the o i 15867 k 630 0 nm 1 k 1 cm 1 emission line were obtained from college alaska during the winters of 1981 to 1983 averages of the temperatures and winds derived from these measurements show a general flow driven by ion drag due to magnetospheric convection this hypothesis was supported by results from a global thermospheric circulation model individual nights however show differences from the average flow pattern during the recovery phase of an auroral substorm when the westward electrojet is over the observing site the equatorward meridional wind decreases in magnitude the zonal wind is generally westward in the evening and eastward in the morning however the crossover from westward to eastward flow is a function of the location of the substorm onset and the arrival of the westward electrojet over college zenith winds can be very large 200 m s and show no systematic pattern perhaps due to a superposition of wave modes from the auroral zone source region an example of a night with little auroral activity highlights the effects of magnetospheric convection and the auroral electrojet on the normal auroral zone wind pattern temperature measurements occasionally show large enhancements usually associated with type a red aurora

thermospheric circulation temperature and compositional structure of the southern hemisphere polar cap during october november 1981 thermospheric temperature composition and winds at f region heights over the southern hemisphere polar cap have been measured by the dynamics explorer 2 de 2 satellite during october november 1981 perigee of the de 2 satellite during this period was over the southern hemisphere polar cap and measurements made along 0900 2100 local time polar passes are used to determine the average universal time dependence of thermospheric properties for this local time slice the f region wind vector is derived from the meridional wind component measured by the fabry perot interferometer fpi and the zonal wind component measured by the wind and temperature spectrometer wats instruments on board de 2 the neutral gas temperature is derived from fpi and wats measurements and the compositional structure is determined from the neutral atmosphere composition spectrometer instrument the measured temperature composition and winds along the 0900 2100 local time polar passes all display a universal time dependence that is due to the displacement between geomagnetic and geographic poles the temperature and molecular nitrogen densities are enhanced and the atomic oxygen density is reduced in the magnetic polar cap in comparison with lower latitude regions the neutral wind pattern follows the pattern of ion drift associated with magnetospheric convection the national center for atmospheric research thermospheric general circulation model tgcm is used to calculate the temperature composition and winds over the southern hemisphere polar cap region for conditions similar to those of october 1981 the tgcm includes displaced geomagnetic poles the temperature composition and winds are determined along the de 2 satellite track for various universal times the calculated winds are in general agreement with the observed winds both having a two cell pattern of magnetospheric convection the calculated and observed composition patterns are also in general agreement with predictions made by the mass spectrometer and incoherent scatter radar 1983 empirical model when models and observations are normalized to the same constant pressure surface the calculated and observed maximum compositional variations in the magnetic polar cap occur near 0900 ut when the dawn sector of the auroral oval passes over the south geographic pole the overall pattern of the calculated temperature variation is similar to that observed except for the period between 1300 and 1500 ut better agreement with temperature in this time range is obtained with the inclusion of auroral particle precipitation within the magnetospheric cusp

geochemistry and u pb detrital zircon dating of paleozoic graywackes in east junggar nw china insights into subduction accretion processes in the southern central asian orogenic belt abstract the southern central asian orogenic belt caob is characterized by multiple and linear accretionary orogenic collages including paleozoic arcs ophiolites and accretionay wedges a complex history of subduction accretion processes makes it difficult to distinguish the origin of these various terranes and reconstruct the tectonic evolution of the southern caob in order to provide constraints on the accretionary history we analyzed major and trace element compositions of paleozoic graywackes from the huangcaopo group hg and kubusu group kg in east junggar the hg graywackes have relatively low chemical index of alteration cia values 50 to 66 suggesting a source that underwent relatively weak chemical weathering the identical average index of compositional variability icv values 1 1 for both the kg and hg samples point to an immature source for the paleozoic graywackes in east junggar which is consistent with an andesitic felsic igneous source characterized by low la th ratios and relatively high hf contents these graywackes are geochemically similar to continental island arc sediments and therefore were probably deposited at an active continental margin u pb dating of detrital zircons from the lower subgroup of the hg yielded a young age peak at 440 ma indicating a post early silurian depositional age however the youngest populations of detrital zircons from the kg graywackes and the upper subgroup of the hg yielded 206 pb 238 u ages of 346 ma and 355 ma respectively which suggest a post early carboniferous depositional age because of similarities of rock assemblages these two units should be incorporated into the early carboniferous nanmingshui formation the detrital zircon age spectrum of the early paleozoic hg graywackes resembles that of the habahe sediments in the chinese altai which suggests that the ocean between east junggar and the chinese altai was closed before the deposition of the sediments and that the armantai ophiolite was emplaced prior to the early devonian the differences in age spectra for detrital zircons from the post early carboniferous graywackes in east junggar and the harlik arc indicate that the emplacement of the kalamaili ophiolite postdates the early carboniferous therefore a long lasting northward subduction accretion process is suggested for the formation of east junggar and the reconstruction of the early paleozoic evolution of the southern caob

zircon u pb ages of the metamorphic supracrustal rocks of the xinghuadukou group and granitic complexes in the argun massif of the northern great hinggan range ne china and their tectonic implications abstract the basement of the argun massif in the northern great hinggan range consists of the metamorphic supracrustal rocks of the xinghuadukou group and associated granitic complexes the metamorphic supracrustal rocks were previously interpreted as paleoproterozoic while the granitic complexes were considered mesoproterozoic in age this paper presents new zircon la mc icp ms u pb ages of biotite plagioclase leptynite and biotite schist from the xinghuadukou group in the lulin forest area heilongjiang province zircon shrimp u pb ages of biotite plagioclase gneiss from the xinghuadukou group in lulin forest and quartz diorite and monzogranite from the granitic complexes in mohe county heilongjiang province new geochronological data from the three metasedimentary rock samples of the xinghuadukou group can be preliminarily divided into five groups 1 2017 2765 ma 2 1736 1942 ma 3 1359 1610 ma 4 749 1239 ma and 5 448 716 ma except for the zircons of the 448 716 ma group belonging to a metamorphic origin the other age groups had the youngest age of 749 17 ma indicating that the xinghuadukou group formed during the neoproterozoic era at least

observations of thermospheric horizontal neutral winds at watson lake yukon territory λ 65 n fabry perot interferometer observations of the thermospheric o i 6300 a emission have been conducted from an airglow observatory at a dark field site in the southeastern yukon territory canada for the period november 1991 to april 1993 the experiment operated in an unattended remote fashion has resulted in a substantial data set from which mean neutral winds have been determined dependent upon geomagnetic activity the nocturnal location of the site is either equatorward of the auroral oval or within the oval boundaries the data set is rich enough to permit hourly binning of neutral winds based upon the kp geomagnetic disturbance index as well as the season for cases of low geomagnetic activity the averaged vector horizontal neutral wind exhibits the characteristics of a midlatitude site displaying antisunward pressure gradient driven winds as the geomagnetic activity rises the late afternoon and evening winds slowly rotate sunward in an anticlockwise direction initially remaining near 100 m s in speed but eventually increasing to 300 m s for kp 5 for the higher levels of activity the observed neutral wind flow pattern resembles a higher latitude polar cap pattern characterized by ion drag forcing of thermospheric neutral gases in addition rotational coriolis forcing on the dusk side enhances the ion drag forcing resulting in dusk winds which trace out the clockwise dusk cell plasma flow on the dawn side the neutral winds also rotate in an anticlockwise direction as the strength of geomagnetic disturbances increase since the site is located at a transition latitude between the midlatitude and the polar cap the data set provides a sensitive test for general circulation models which attempt to parameterize the contribution of magnetospheric processes a comparison with the vector spherical harmonic vsh model indicates several regions of poor correspondence for december solstice conditions but reasonable agreement for the vernal equinox

late paleozoic paleomagnetism of south mongolia exploring relationships between siberia mongolia and north china abstract the tectonic evolution of a large region that includes south siberia mongolia and north china is still a matter of fierce debate this is due at least in part to the contentious proposals detailing the kinematics of the major tectonic units in that area one solution to the problem is the acquisition of better defined paleomagnetic data for the various players in the system we carried out a paleomagnetic study of early carboniferous subduction related volcanic rocks of the trans altai zone in south mongolia and successfully isolated a pre folding and presumably primary component from 22 sites a critical analysis of late paleozoic paleomagnetic data from mongolia revealed several problematic data sets while the paleolatitudes derived from more reliable studies agreed well with the expected values for siberia and were consistently different from those for the north china block we also found that late paleozoic declinations from mongolia are rotated counterclockwise through various angles with respect to siberia in addition those rotations are widespread in both inner mongolia and the north china block in this paper we put forward some testable hypotheses and propose a preliminary paleogeographic scheme of the region 1 consistent difference in late paleozoic paleolatitudes between siberia and mongolia on the one hand and the north china block on the other is largely due to strong inclination shallowing in paleomagnetic data for the latter area where most data are from sedimentary rocks 2 widespread counterclockwise rotations in mongolia inner mongolia and north china may be accounted for by a wide zone of sinistral transpression that was active in the early mesozoic 3 in the early mesozoic the mongol okhotsk ocean was much narrower than is usually assumed 4 there was no large scale oroclinal bending between siberia and north china in the permian early mesozoic

zircon u pb and hf isotopic study of gneissic rocks from the chinese altai progressive accretionary history in the early to middle palaeozoic abstract gneissic rocks in the chinese altai mountains have been interpreted as either paleozoic metasedimentary rocks or precambrian basement this study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a ne sw traverse in the northwestern chinese altai petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from i type granites formed in a subduction environment three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 ma some give neoproterozoic ages and a few yield discordant paleoproterozoic to archean ages zircon hf isotopic compositions indicate that both juvenile mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived in contrast zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids and define single populations for each sample with mean ages between 380 and 453 ma the general absence of precambrian inheritance and positive zircon hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas our data can be interpreted in terms of a progressive accretionary history in early to middle palaeozoic times and the chinese altai may possibly represent a magmatic arc built on a continental margin dominated by neoproterozoic rocks

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

precambrian basement provenance implication and tectonic evolution of the gargan block of the tuva mongolia terranes central asian orogenic belt abstract although the phanerozoic geology of the central asian orogenic belt is extensively studied there is still much to reveal about the initiation and early stages of tectonism the gargan block of the tuva mongolia terranes at the mongolian russian border is one of the archean proterozoic continental crustal fragments that record the earliest evolutionary history of the belt to better constrain the age of its basement extent and provenance in regional tectonic framework we present new zircon u pb geochronologic data from previously undated basement gneisses and the overlying neoproterozoic meta sedimentary rocks of southern part of the gargan block comparison of available basement ages and precambrian detrital zircon spectra from nearby archean proterozoic continental crustal fragments show complex relationship amongst them we propose that the gargan block travelled by itself in most of the proterozoic or was derived from an unknown continental block obtained age confirms the existence of neoarchean neoproterozoic basement in the region however for the first time the 2749 814 ma salig complex reveals multiple stages of neoproterozoic metamorphic events within the central asian orogenic belt older of which at 1 ga may relate to an assembly of several of the pre existing continental crustal fragments in mongolia

slip rate estimate and past earthquakes on the doruneh fault eastern iran summary the doruneh fault with a length of 600 km is one of the longest and most prominent faults in iran it performs an important role in the regional tectonics but has no record of large earthquakes the geomorphology of the doruneh fault contains numerous indications of cumulative left lateral slip over various scales we describe three sites where late quaternary landforms are displaced by the fault a an incised alluvial fan near the village of uch palang is displaced by 800 850 m b the kuh e teagh ahmad fold is composed of folded quaternary gravels and is displaced by 200 400 m c a sequence of three terraces of the shesh taraz river are displaced left laterally by a maximum of 25 m infrared stimulated luminescence irsl dating of the uppermost shesh taraz river terrace gives a deposition age of 10 ka which correlates with changes in global climate 10 12 ka ago and provides a provisional slip rate estimate of 2 4 0 3 mm yr 1 no major recent or historical earthquakes are recorded on the doruneh fault relatively fresh scarps and partially infilled fractures appear to be the preserved surface ruptures from an earthquake event of unknown age a series of small streams showing left lateral displacements of 3 to 5 5 m with an average slip of 4 7 m record the possible magnitude of slip during this earthquake which from scaling relationships would have had an m w of 7 5 and ruptured the fault over a length of 100 km at the estimated slip rate of 2 5 mm yr 1 the average recurrence time between large magnitude earthquakes on the doruneh fault is 2000 yr

initiation of subduction and the generation of slab melts in western and eastern mindanao philippines adakite found in both the eastern and western parts of mindanao island philippines is a rare rock type characterized by low heavy rare earth elements and y contents together with high sr y ratios and is considered to be the result of the melting of young subducted oceanic crust which leaves an eclogite residue pliocene quaternary adakites from western mindanao zamboanga peninsula are probably derived from the melting of the young miocene sulu sea crust which is currently subducting beneath zamboanga associated nb enriched basalts are thought to come from mantle metasomatized through interaction with adakitic melts in eastern mindanao pliocene quaternary cones and plugs of typical adakitic composition mark the trace of the philippine fault in surigao and north davao the underlying philippine sea crust is of eocene age and therefore cannot melt under normal subduction thermal conditions thermal models indicate that melting at the start of subduction can occur subduction of the philippine sea plate began 3 to 4 ma beneath eastern mindanao and probably accounts for the presence of adakites along the philippine fault

stratigraphic and tectonic implications of a newly discovered glacial diamictite cap carbonate couplet in southwestern mongolia we report here the discovery of a new end cryogenian glacial diamictite and an overlying basal ediacaran cap carbonate within the tsagaan oloom formation of southwestern mongolia the identifi cation of the cryogenian ediacaran boundary coupled with new 13 c chemostratigraphic profi les facilitates the integration of the neoproterozoic stratigraphy of mongolia with records elsewhere these correlations indicate that a previously unrecognized 16 cryogenian 13 c anomaly is present in the newly defi ned tayshir member informal of the tsagaan oloom formation furthermore chemostratigraphic and lithostratigraphic relationships suggest an 35 m y depositional hiatus below the phosphorite bearing zunne arts member informal of the upper tsagaan oloom formation and that subsidence renewed in the latest ediacaran early cambrian we propose that the lower 1500 m of the tsagaan oloom formation was deposited on a thermally subsiding passive margin after rodiniaage rifting whereas the zunne arts member and the overlying 1600 m of early cambrian strata were deposited in a foredeep basin that formed as the southern margin of the dzabkhan terrane was subducted beneath the khantayshir dariv arc

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

isotope provinces mechanisms of generation and sources of the continental crust in the central asian mobile belt geological and isotopic evidence abstract the available geological geochronological and isotopic data on the felsic magmatic and related rocks from south siberia transbaikalia and mongolia are summarized to improve our understanding of the mechanisms and processes of the phanerozoic crustal growth in the central asian mobile belt camb the following isotope provinces have been recognised precambrian t dm 3 3 2 9 and 2 5 0 9 ga at the microcontinental blocks caledonian t dm 1 1 0 55 ga hercynian t dm 0 8 0 5 ma and indosinian t dm 0 3 ga that coincide with coeval tectonic zones and formed at 570 475 420 320 and 310 220 ma continental crust of the microcontinents is underlain by or intermixed with juvenile crust as evidenced by its isotopic heterogeneity the continental crust of the caledonian hercynian and indosinian provinces is isotopically homogeneous and was produced from respective juvenile sources with addition of old crustal material in the island arcs or active continental margin environments the crustal growth in the camb had episodic character and important crust forming events took place in the phanerozoic formation of the camb was connected with break up of the rodinia supercontinent in consequence of creation of the south pacific hot superplume intraplate magmatism preceding and accompanying permanently other magmatic activity in the camb was caused by influence of the long term south pacific plume or the asian plume damping since the devonian

precambrian ophiolite belts of southern siberia russia and their metallogeny abstract greenstone and ophiolite belts of different ages in southern siberia are compared the archaean olondo greenstone belt 3 0 2 9 ga within the aldan shield is different from younger ophiolite belts the early proterozoic baikal muya ophiolite belt 1 9 ga containing both komatiites and a complete ophiolitic sequence of the tholeiite series and the late proterozoic early cambrian 0 6 0 52 ga kurtushibin and ilchir ophiolite belts in western and eastern sayan are fairly comparable with young ophiolites and modern crust of oceanic type in the olondo greenstone belt there are komatiite and tholeiite series that are represented by both volcanic rocks and differentiated sills but no dyke complex is present in the baikal muya ophiolite belt there are metavolcanic rocks including komatiites and komatiitic basalts a dyke complex upper cumulate gabbros and lower metaperidotites ophiolites of the kurtushibin belt in the western sayan and ilchir belt in eastern sayan are examples of complete ophiolitic sequences with long and complicated evolution histories including development of a marianite boninite series of primitive island arc type asbestos chromite fe ti oxide polymetallic and gold deposits occurring precambrian ophiolites are briefly described when ophiolites appeared about 2 0 1 9 ga ago cr ni cu and asbestos were concentrated within them the composition of ophiolites and associated ores changed significantly with time a change in upper mantle convection may be the key to the magmatic and metallogenic evolution

source and tectonic implications of tonalite trondhjemite magmatism in the klamath mountains in the klamath mountains voluminous tonalite trondhjemite magmatism was characteristic of a short period of time from about 144 to 136 ma early cretaceous it occurred about 5 to 10 m y after the 165 to 159 ma josephine ophiolite was thrust beneath older parts of the province during the nevadan orogeny thrusting from 155 to 148 ma the magmatism also corresponds to a period of slow or no subduction most of the plutons crop out in the south central klamath mountains in california but one occurs in oregon at the northern end of the province compositionally extended members of the suite consist of precursor gabbroic to dioritic rocks followed by later more voluminous tonalitic and trondhjemitic intrusions most plutons consist almost entirely of tonalite and trondhjemite poorly defined concentric zoning is common tonalitic rocks are typically of the low al type but trondhjemites are generally of the high al type even those that occur in the same pluton as low al tonalite the suite is characterized by low abundances of k2o rb zr and heavy rare earth elements sr contents are generally moderate 450 ppm by comparison with sr rich arc lavas interpreted to be slab melts up to 2000 ppm initial 87sr 86sr 18o and nd are typical of mantle derived magmas or of crustally derived magmas with a metabasic source compositional variation within plutons can be modeled by variable degrees of partial melting of a heterogeneous metabasaltic source transitional mid ocean ridge to island arc basalt but not by fractional crystallyzation of a basaltic parent melting models require a residual assemblage of clinopyroxene garnet plagioclase amphibole residual plagioclase suggests a deep crustal origin rather than melting of a subducted slab such models are consistent with the metabasic part of the josephine ophiolite as the source because the josephine ophiolite was at low t during nevadan thrusting an external heat source was probably necessary to achieve significant degrees of melting heat was probably extracted from mantle derived basaltic melts which were parental to the mafic precursors of the tonalite trondhjemite suite thus under appropriate tectonic and thermal conditions heterogeneous mafic crustal rocks can melt to form both low and high al tonalitic and trondhjemitic magmas slab melting is not necessary

shrimp zircon u pb ages and tectonic implications of igneous events in the ereendavaa metamorphic terrane in ne mongolia abstract the ereendavaa metamorphic terrane in ne mongolia has long been considered as a pre altaid block or a precambrian cratonic terrane with a paleoproterozoic basement overlain by neoproterozoic cambrian rocks but the idea has not been supported by any isotopic dating sensitive high resolution ion microprobe shrimp zircon u pb dating on gneisses amphibolite and schists mylonites of the ereendavaa terrane suggests that the terrane mainly formed during early paleozoic 495 464 ma and late paleozoic early mesozoic 295 172 ma a minor amount of precambrian rocks might have been involved in the formation of the protoliths of these rocks as shown by precambrian inherited zircons 1796 794 ma the new age data also suggest that the ereendavaa terrane experienced at least two periods of magmatism 1 early paleozoic 495 464 ma and 2 late paleozoic early mesozoic 295 172 ma which are probably produced by the subduction of the paleo asian ocean in the south and the subduction of the mongol okhotsk ocean in the north respectively the mylonitized granite 172 ma and undeformed pegmatite 163 ma are interpreted to be syn and post kinematic products the new age data constrain the closure of the mongol okhotsk ocean at mid jurassic

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

spatial evolution of frictional heating and the predicted thermospheric wind effects in the vicinity of an auroral arc measured with the sondrestrom incoherent scatter radar and the reimei satellite 1 simultaneous observation with the sondrestrom incoherent scatter is radar and the reimei satellite was conducted on 3 october 2007 the objective was to measure horizontal patterns of the ionospheric structure in the vicinity of an auroral arc the is radar was scanned azimuthally with a fixed elevation angle and the satellite narrow view camera 557 7 nm was directed downward taking pictures every 0 12 s a stationary auroral arc was captured at 05 17 ut 02 54 mlt with both instruments simultaneously gross ionospheric features measured with the is radar around the arc were in good agreement with the expected magnetosphere ionosphere current system of particular interest was the horizontal pattern in the ion speed and temperature in the f region the ion speed within the arc was close to zero by contrast the larger ion speed 350 400 m s 1 on the poleward side was parallel to the arc and almost no horizontal shear within about 20 km width perpendicular to the arc this area was separated into two parts by the ion temperature one was associated with clear enhancements in excess of 1200 k and another was with more moderate enhancements less than 1000 k the widths of the two areas were approximately 10 km each the horizontal shear seen in the ion temperature suggested the presence of a narrow thermospheric wind shear of about 10 km width this paper suggests that the possible cause for the thermospheric wind shear was ion drag associated with localized soft particle precipitation or f region ionization

mapping thermospheric winds in the auroral zone a new all sky imaging fabry perot asifp spectrometer has been developed for ground based mapping of upper atmospheric wind and temperature fields in the auroral zone although several other asifp spectrometers exist for atmospheric studies rees et al 1984 sekar et al 1993 biondi et al 1995 these instruments have all operated with etalons of fixed optical gap a method potentially subject to errors in the presence of auroral intensity gradients in this instrument the etalon plate spacing is scanned periodically over one order of interference and each photon detected is assigned to a wavelength interval which is determined from both its arrival location on the detector and the etalon plate spacing prevailing at the detection time spectra accumulated this way are not distorted by spatial intensity gradients preliminary 630 nm observations were made during the winter of 1994 95 from poker flat research range alaska to illustrate some of the features we have observed in this study we present line of sight wind estimates derived for the night of december 7 1994 the background wind matches averages presented previously by sica et al 1986 and is consistent with winds driven principally by momentum deposition from ionospheric plasma convection through ion drag smaller scale curvature and divergence features are also discernable and are discussed

geochemical study of the cambrian ordovician meta sedimentary rocks from the northern altai mongolian terrane northwestern central asian orogenic belt implications on the provenance and tectonic setting abstract the altai mongolian terrane am is a key component of the central asian orogenic belt caob but its tectonic nature has been poorly constrained this paper reports geochemical compositions of cambrian ordovician meta sedimentary rocks from the northern am to trace their source nature and depositional setting which in turn place constraints on the geodynamic evolution of the am the cambrian ordovician meta sedimentary rocks from the northern am show variable major element compositions with negative correlation between sio2 and tio2 al2o3 fe2o3t mgo and k2o their high icv values 1 18 2 53 and relatively low cia values 37 9 76 3 indicate that the sediments were immature and probably underwent mild to moderate chemical weathering the low sio2 samples are characterized by relatively restricted sio2 al2o3 mostly 2 60 6 07 and low rb sr ratios 0 02 1 89 implying their proximal deposition without obvious sedimentary sorting and recycling in contrast the high sio2 samples show much higher sio2 al2o3 ratios 15 4 19 9 possibly due to sedimentary sorting and or silicification all these samples yield relatively high al2o3 tio2 ratios 15 6 22 8 strong lrees hrees differentiation la yb n 4 86 10 7 and obvious negative eu anomalies eu 0 61 0 83 combined with their th sc zr sc la th and co th ratios comparable with intermediate acidic magmatic rocks we infer that these kinds of magmatic rocks served as a major source for the investigated meta sedimentary rocks the tio2 al2o3 and fe2o3t mgo concentrations are mostly higher than typical sediments from passive margin and the th u la sc th sc eu eu zr hf zr th and la th ratios are quite similar to sediments from continental arcs these data suggest that the cambrian ordovician meta sedimentary rocks from the northern am were most likely deposited in an environment related to a continental arc setting rather than a passive regime these rocks show strong similarities to their counterparts in the chinese altai ca southern am and tseel terrane southeastern extension of the ca in western mongolia in terms of geochemical compositions and depositional setting with combination of recent isotopic studies for detrital zircons our data suggest that the am probably represented a coherent accretionary prism along a continental arc in the early paleozoic

generation of sodium rich magmas from newly underplated basaltic crust sodium rich rocks of trondhjemite tonalite dacite ttd or granodiorite ttg suites form much of precambrian continental crust1 they are thought to have formed by partial melting of subducted oceanic crust2 3 a process that would have been much more widespread early in earth history than at present owing to the higher thermal gradients prevailing at that time4 phanerozoic ttd suites do exist however and seem also to relate to subduction zones5 defant and drummond6 proposed that these suites form where young 25 myr hot oceanic lithosphere is subducted and melts thus locally simulating the conditions that led to widespread crustal growth in the archaean here we describe plutonic and volcanic rocks from the cordillera blanca complex in peru which have characteristics of the high al ttd suite but which were produced above a subduction zone containing a 60 myr old slab we present evidence that the complex formed by partial melting of newly underplated basaltic crust and argue that this mechanism should be considered more generally as an additional way of generating sodium rich arc magmas

intra oceanic arcs of the paleo asian ocean abstract the paper reviews and integrates geological geochronological geochemical and isotope data from 21 intra oceanic arcs ioa of the paleo asian ocean pao which have been identified in the central asian orogenic belt the world largest accretionary orogeny the data we discuss structural position of intra oceanic arc volcanic rocks in association with back arc terranes and accretionary complexes major periods of intra oceanic arc magmatism and related juvenile crustal growth lithologies of island arc terranes geochemical features and typical ranges of nd isotope values of volcanic rocks four groups of ioas have been recognized neoproterozoic early cambrian early paleozoic middle paleozoic and late paleozoic the neoproterozoic early cambrian or siberian group includes eleven intra oceanic arcs of eastern and western tuva sayan southern siberia russia northern and southwestern mongolia and russian altai the early paleozoic or kazakhstan group includes selety urumbai bozshakol chingiz and baydaulet aqastau arc terranes of the kazakh orocline the middle paleozoic or southern group includes six arc terranes in the tienshan orogen chinese altai east kazakhstan west junggar and southern mongoia only one late paleozoic intra oceanic arc has been reliably identified in the caob bogda in the chinese tienshan probably due to pao shrinking and termination the lithologies of the modern and fossil arcs are similar although the fossil arcs contain more calc alkaline varieties suggesting either their more evolved character or different conditions of magma generation of special importance is identification of back arc basins in old accretionary orogens because boninites may be absent in both modern and fossil ioas the three typical scenarios of back arc formation active margin rifting intra oceanic arc rifting and fore arc rifting were reconstructed in fossil intra oceanic arcs some arcs might be tectonically eroded and or directly subducted into the deep mantle therefore the structural and compositional records of fossil intra oceanic arcs in intracontinental orogens allow us to make only minimal estimations of their geometric length life span and crust thickness

spatial structure in the thermospheric horizontal wind above poker flat alaska during solar minimum a new all sky imaging wavelength scanning fabry perot spectrometer was used to record high resolution r 200 000 spectra of the 630 nm thermospheric optical emission above poker flat alaska these spectra were used to derive spatially resolved maps of the horizontal wind vector at approximately 250 km altitude we describe the procedure used to infer vector winds from line of sight doppler shifts along with its limitations we present the time evolution of the vector wind fields obtained from this method for 6 nights of observation five of the 6 nights contained periods when we inferred the existence of significant curvature divergence or shear in the thermospheric wind across our instrument s 1000 km diameter field of view the sixth night exhibited little spatial structure and is shown for comparison we compare these results with a generic solar minimum winter time run of the national center for atmospheric research s thermosphere ionosphere and electrodynamics general circulation model while agreement was good at the start and end of the night considerable differences were found in the late evening and midnight sectors some possible origins for these discrepancies are proposed in particular we suggest that the f region horizontal wind may be deflected by upwelling vertical winds which are in turn driven by e region heating in the auroral zone we note that both the instrument used and our high latitude implementation of the analysis procedure are new experimental techniques thus the data presented here should be regarded as preliminary and if possible be validated by comparison with results from other techniques

massive granitoid production without massive continental crust growth in the chinese altay insight into the source rock of granitoids using integrated zircon u pb age hf nd sr isotopes and geochemistry this study integrates new and extant zircon u pb age and hf isotope data whole rock nd sr isotope data and geochemistry data from the chinese altay ca and adjacent areas in an attempt to identify the source rocks of granitoids and acidic intermediate volcanic rocks and hence continental crust growth in the ca the protolith of the gneisses includes the earliest products of erosion from the surface rocks of the island arc volcanics and the syn and post collisional granitoids of the caledonian orogenic mountain system whereas the provenance of metasedimentary rocks was exposed from increasingly deeper levels or from an expanded region that evolved from the axis to the flank of the mountain system as it was denuded until planation such that eroded material from the tuva mongol microcontinental block to the east could be delivered to the ca the ca tends to be more mafic and isotopically more primitive with depth because material eroded early constitutes the lower section and material eroded late constitutes the upper section of the early paleozoic sedimentary pile source rocks for the granitoids and acidic intermediate volcanic rocks of the ca include the eroded material from the microcontinental block the eroded material from the syn and post collisional granitoids of the caledonian province morb type mafic rocks and a minor component from the metasomatized lithospheric mantle eroded material from the terrains north of the ca was first deposited as an early paleozoic sedimentary pile in the ca the top section of this pile was again eroded and transported to the trench at the ca continental margin and these second round sediments were subducted beneath the ca accretionary wedge the un eroded lower section of the early paleozoic sedimentary pile lay at bottom of the ca accretionary wedge that was underplated by morb type mafic rocks the ca granitoids can be divided into orogenic 460 360 ma and post orogenic 320 260 ma the orogenic granitoids can be subdivided into groups 1 nd t integrated isotope and geochemistry data further constrain the source compositions of granitoids the granitoids in the northwest chinese altay were mainly derived from subducted sediment that was eroded from the top section of the early paleozoic sedimentary pile whereas those in the east chinese altay were derived dominantly from the lower section of the pile the source rock of the granitoids in the northeast of the middle chinese altay consists of the lower section of the early paleozoic sedimentary pile and sediment quartz keratophyre and keratophyre that were subducted or thrust beneath the northern chinese altay the main source rock of the granitoids in the southwest of the middle chinese altay varies between the subducted sediment in the westernmost segment and the lower section of the early paleozoic sedimentary pile and the mafic underplate to the east a geophysical sounding profile across the ca and east junggar reveals a three layer structure of the ca accretionary wedge underplated by an oceanic lithosphere that was detached from the downgoing oceanic spreading center from the silurian to the mid late devonian the active spreading center was repeatedly subducted beneath the ca along a southwestward retreating subduction zone as represented successively by four ne dipping thrust faults that converge to a low angle decollement at depth asthenospheric upwelling heated and melted the subducted sediment and the lower section of the early paleozoic sedimentary pile along with the mafic underplate and generated the acidic intermediate volcanic rocks and granitoids that culminated at 400 ma during the mid devonian shallow dipping decollement like subduction changed to a steeply dipping subduction beneath the lithospheric mantle wedge the mantle wedge shielded the ca crust from heating from the subducting spreading center which resulted in waning granitoid magmatism from 400 ma to 360 ma in conclusion there was massive granitoid production but not massive continental crust growth in the ca at 400 ma

juvenile versus recycled crust in the central asian orogenic belt implications from ocean plate stratigraphy blueschist belts and intra oceanic arcs abstract new or juvenile crust forms and grows mainly through mafic to andesitic magmatism at pacific type or accretionary type convergent margins as well as via tectonic accretion of oceanic and island arc terranes and translation of continental terranes during the last decades the juvenile or recycled nature of crust has been commonly evaluated using whole rock isotope and hf in zircon isotope methods however evidence for the accretionary or pacific type nature of an orogenic belt comes from geological data for example from the presence of accretionary complexes ac intra oceanic arcs ioa oceanic plate stratigraphy units ops and morb oib derived blueschist belts bsb the central asian orogenic belt caob represents the world s largest province of phanerozoic juvenile crustal growth during ca 800 m y between the east european siberian north china and tarim cratons from geological point of view the caob is a typical pacific type belt as it hosts numerous occurrences of accretionary complexes intra oceanic arcs ops units and morb oib derived blueschist belts in spite of its accretionary nature supported by positive whole rock nd isotope characteristics in caob granitoids the hf in zircon isotope data reveal a big portion of recycled crust such a controversy can be explained by presence of accreted microcontinents isotopically mixed igneous reservoirs and by the tectonic erosion of juvenile crust the most probable localities of tectonic erosion in the caob are the middle and southern tienshan and southern transbaikalia because these regions comprise a predominantly recycled crust based on isotope data but the geological data show the presence of intra oceanic arcs blueschist belts and accreted ops with oceanic island basalts oib and tectonically juxtaposed coeval arc granitoids and accretionary units this warrants combination of detailed geological studies with isotopic results as on their own they may not reflect such processes as tectonic erosion of juvenile crust and or arc subduction

storm time penetration to low latitudes of magnetospheric ionospheric convection and convection driven thermospheric winds from de 2 satellite measurements during two magnetic storms we show that i the magnetospheric convection driven east west ion flows of high velocities 1400 m s penetrate to magnetic latitudes as low as 30 with larger velocities 2000 3000 m s appearing at 45 50 latitudes and ii high velocity 300 640 m s thermospheric winds appear in association with the above ion flows the similarity of the latitude structures and time evolutions of the ion and neutral motions indicates that the zonal winds are driven by magnetospheric ionospheric convection through ion drag these velocities of the convection driven ion flows and winds at such low latitudes are much larger than those reported from observations or predicted by current models

neoproterozoic 800 ma orogeny in the tuva mongolia massif siberia island arc continent collision at the northeast rodinia margin abstract the tuva mongolia massif is a composite precambrian terrane incorporated into the palaeozoic sayany baikalian belt its neoproterozoic amalgamation history involves early 800 ma and late baikalian 600 550 ma orogenic phases two palaeogeographic elements are identified in the early baikalian stage the gargan microcontinent and the dunzhugur oceanic arc they are represented by the gargan glyba block and the island arc ophiolites overthrusting it the gargan glyba is a two layer platform comprising an early precambrian crystalline basement and a neoproterozoic passive margin sedimentary cover the upper part comprises olistostromes deposited in a foreland basin during the early baikalian orogeny the dunzhugur arc ophiolite form klippen fringing the gargan glyba and show a comprehensive oceanic arc ophiolite succession the dunzhugur arc faced the microcontinent as shown by the occurrence of forearc complexes the arc continent collision followed a pattern similar to phanerozoic collisions when the marginal basin lithosphere had been completely subducted the microcontinental edge partially underthrust the arc and the forearc ophiolite overrode it continued convergence caused a break of the arc lithosphere resulting in the uplift of the submerged microcontinental margin with the overthrust forearc ophiolites sliding into the foreland basin owing to the lithospheric break a new subduction zone inclined beneath the gargan microcontinent emerged initial melts of the newly formed continental arc are represented by tonalites intruded into the gargan microcontinent basement and its cover and into the ophiolite nappe the tonalite rb sr mineral isochron age is 812 18 ma which is similar to a u pb zircon age of 785 11 ma a period of tonalite magmatism in meso cenozoic orogenic belts is recognized some 1 10 m y after the collision accordingly the dunzhugur island arc gargan microcontinent collision is conventionally dated at around 800 ma it is highly probable that in the early neoproterozoic the gargan continental block was part of the southern in modern coordinates margin of the siberia craton it is suggested that a chain of precambrian massifs represents an elongate block separated from siberia in the late neoproterozoic the tuva mongolia massif is situated in the northwest part of this chain these events occurred on the ne neoproterozoic margin of rodinia facing the world ocean

assimilated observations of thermospheric winds the aurora and ionospheric currents over alaska we present simultaneous measurements of thermospheric winds auroral emissions and ionospheric currents over alaska obtained from four separate instruments thermospheric f region wind maps were recorded by an all sky imaging fabry perot spectrometer located at poker flat and observing at 630 0 nm auroral images at 557 7 nm were obtained from the low resolution visible imager on board the polar satellite white light all sky auroral images were recorded by ground based all sky cameras located in alaska at poker flat 65 07 n 212 34 e and at kaktovik 70 06 n 217 24 e finally the east west component of the ionospheric f region plasma convection was inferred using the alaskan meridian chain of magnetometers montage images of these four data sets are presented projected onto a geographic map of the alaskan region we examine a 10 hour period during the alaskan local nighttime of february 10 1997 these montages illustrate a close relationship between spatial structures occurring in the aurora in the ionospheric plasma convection and in the f region wind field latitudinal shear of the geomagnetic zonal wind often observed in the premidnight time sector was seen to be associated with both the equatorward and poleward boundaries of the discrete aurora we focus particularly on a period commencing just after 0900 ut when a strong shear in the zonal wind was observed to sweep southward across alaska after magnetic midnight the wind field was dominated by the emergence of the cross polar jet from the polar cap this overwhelmed any wind features associated with local auroral processes

source parameters of earthquakes along the coastal margin of west africa and comparisons with earthquakes in other coastal margin settings abstract the coastal margins of western africa and most of the eastern americas are considered to be stable continental interiors where large earthquakes occur infrequently since these regions have similar geologic and tectonic histories it might seem reasonable to expect similarities between their large earthquakes on the other hand current plate forces acting on these regions differ and may lead to regional differences in earthquakes to examine the similarities of coastal margin earthquakes we first determined the source parameters for six earthquakes of m 5 5 occurring along the coastal margin of west africa a region that has not previously been studied in detail results of this analysis indicate that the earthquakes are shallow 8 15 km strike slip events along high angle faults dips generally 80 with nodal planes having orientations similar to those of faults mapped in the exposed precambrian basement five out of seven events show complexities in their source time functions east of the cameroon line most p axes trend northeast southwest to east west earthquakes west of the cameroon line show less coherency of stress field with p axes for onshore events trending northwest southeast and for offshore events north south to northeast southwest in contrast m 5 5 earthquakes of the eastern coastal margin of north and south america have reverse mechanisms with more moderate dips on nodal planes 45 70 and over 50 have east west oriented p axes which reflect stresses caused by the motion of north and south america relative to europe and africa in north america earthquakes appear to occur on faults that cannot be associated with surficial geology occur shallower or deeper than west african events and have shorter rupture lengths for the equivalent moment these differences suggest that west african events may not serve as useful analogs for events expected along the american coastal margin

holocene slip rate on the sabzevar thrust fault ne iran determined using optically stimulated luminescence osl abstract fault slip rates and the recurrence interval between earthquakes can be determined from reliable dating of deformed sediments we report optically stimulated luminescence osl ages of alluvial gravels fine grained sediments and colluvial deposits associated with the sabzevar thrust fault in northeastern iran six samples of the late quaternary deposits were dated by osl using the single aliquot regenerative dose sar protocol the osl ages indicate deposition of alluvial gravels in the study region between 30 and 9 13 ka followed by a period of fluvial incision which is ongoing at the present day the alluvial deposits have been uplifted by 9 5 m relative to the river level indicating a holocene slip rate of 1 mm yr and a rate of convergence across the fault of 0 4 0 6 mm yr assuming a maximum fault dip of 60 the average interval between large earthquakes on the sabzevar fault will be 3000 years if the fault dips 60 and less if the fault dip is less the last earthquake to destroy sabzevar was in 1052 a d

10be dating of alluvial deposits from southeastern iran the hormoz strait area abstract a key area for the understanding of the southeastern iran geodynamics the hormoz strait area was investigated tectonically active it provides useful sequences of quaternary deposits whose deposition may have ended either when the climate dried or when the tectonic activity uplifted the riverbed in situ produced cosmogenic 10be provides surface abandonment ages at 5 6 0 6 8 4 1 0 12 8 1 0 20 1 1 5 and 44 0 3 4 10be kyr located at the transition between the mediterranean winter rain and the indian monsoon domains and south of the northernmost position of the itcz intertropical convergence zone the studied area is very sensitive to climate changes some of the calculated 10be abandonment ages are within the entire investigated area coincidental with large scale climate shifts the offset of the mid holocene humid period 5 6 0 6 10be kyr the onset of the dry younger dryas cold and dry episode 12 8 1 010be kyr and the end of the last glacial maximum lgm 21 2 kyr at 20 1 1 5 10be kyr these events correspond to large scale changes in atmospheric circulation linked to global climate changes and or to sea level fluctuations in the persian gulf which was totally dry during the lgm locally observed abandonment ages at 8 4 1 0 and 44 0 3 4 10be kyr may likely be related to enhanced tectonic activity without regional impact

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

partial melting of subducting oceanic crust the conditions under which partial melting of subducting oceanic crust occurs can be determined by combining a partial melting model for basaltic compositions with two dimensional thermal models of subduction zones for porosities of 1 containing h20 the amount of partial melt generated at the wet basaltic solidus is limited to 100 mpa can be maintained by rocks close to or above their melting temperatures in the absence of high shear stresses substantial melting of the oceanic crust will only occur during subduction of very young 5 ma oceanic lithosphere partial melting of hydrated basalt amphibolites derived from the mid ocean ridge has been proposed e g 1 3 as being responsible for the generation of certain recent high al andesitic to dacitic volcanic rocks adakites three of these volcanic suites mount st helens southern chile and panama occur in volcanic arcs where oceanic crust 25 ma is being subducted at rates of 1 3 cm yr and the calculated thermal regime is several hundreds of degrees hotter than more typical subduction zone environments however oceanic lithosphere is not currently being subducted beneath baja and new guinea where recent adakites are also present suggesting that some adakite magmas may form by water undersaturated partial melting of underplated mafic lower crust or previously subducted oceanic crust further experimental work on compositions representative of oceanic crust is required to define the depth of possible adakite source regions more accurately

zircon u pb ages and geochemistry of newly discovered neoproterozoic orthogneisses in the mishan region ne china constraints on the high grade metamorphism and tectonic affinity of the jiamusi khanka block abstract the jiamusi khanka block located in the easternmost segment of the central asian orogenic belt caob is one of the least understood blocks in northeastern china the age of its basement the timing of the high grade metamorphism and the tectonic affinity of this block have all been subjects of controversy here we describe newly discovered neoproterozoic orthogneisses from the mishan region in the central jiamusi khanka block sims and la icp ms u pb dating of the magmatic cores of zircons from three of these high grade orthogneisses yielded weighted mean ages that range from 898 4 to 891 13 ma indicating that early neoproterozoic magmatism did occur in the jiamusi khanka block twenty two analyses of metamorphic zircons rims as well as some grains gave two groups of concordant ages one at ca 563 ma interpreted as the timing of the high grade metamorphism and the other around 518 496 ma interpreted as representing a subsequent retrograde metamorphism the orthogneisses represent metamorphosed peraluminous syn collisional syenogranites with sio2 71 29 78 08 wt a cnk 1 06 1 99 and na2o k2o 0 03 1 49 and they belong chemically to the high potassium calc alkaline series they have low sr 32 134 ppm contents and sr y ratios 1 6 16 9 and display strongly fractionated to nearly flat ree patterns with negative eu anomalies eu 0 22 0 95 and depletions in nb ta these geochemical characteristics suggest that the syenogranitic rocks were derived under low pressures from a crustal source with a high proportion of sedimentary rocks perhaps in a subduction related setting that was undergoing transition from compression to extension in the context of the reconstruction of gondwana the ca 898 891 ma magmatic activity and the ca 563 ma high grade metamorphism in the mishan region provide constraints on the possible linkages between the jiamusi khanka block and east gondwana during the neoproterozoic to early paleozoic

nighttime thermospheric winds over sondre stromfjord greenland observations of nighttime thermospheric neutral winds made at sondre stromfjord greenland with optical and radar instrumentation showed an occasional abatement in the equatorward meridional wind at a magnetic local time corresponding to the nighttime division between the evening and morning convection cells this abatement appeared primarily in the poleward observations in contrast however the characteristic midnight surge was usually seen in the equatorward set of observations the apparent acceleration of about 250 m s or greater within 4 6 latitude we attribute in part to a merging of neutral jet streams generated by polar cap ion drag adjacent to the auroral zone boundary and in part to the higher electron densities and plasma convection speeds adjacent to the auroral zone comparison of these results with those from ncar tgcm computations that assumed an analytical plasma convection model showed reasonable agreement except for the abatement feature

nighttime variation of thermospheric winds and temperatures over fritz peak observatory during the geomagnetic storm of march 2 1983 nighttime thermospheric winds and temperatures have been measured over fritz peak observatory colorado 39 9 n 105 5 w with a high resolution fabry perot spectrometer during the march 2 1983 geomagnetic storm the winds and temperatures are obtained from the doppler shifts and line profiles of the o i 15 867 k 630 nm line emission the planetary geomagnetic index kp increased abruptly from 4 to 7 during the beginning of the measuring period near 0000 ut on march 2 and remained at nearly that level throughout the night during the early evening hours near 1900 lt 0200 ut the zonal winds measured in both the east and west directions from fritz peak observatory were westward at a speed of about 100 m s 1 the westward winds increased in magnitude during the next 2 hours with the wind speed east of the station reaching 400 m s 1 and the winds to the west of the station reaching 300 m s 1 the westward winds remained at roughly these speeds until about local midnight 0700 ut when they gradually decreased to about 50 m s 1 in the east and the winds to the west of the station shifted to eastward at about 50 m s 1 the meridional winds measured in the early evening hours both to the north and south of the station were poleward at speeds ranging between 50 and 10 m s 1 near local midnight the wind measured north of the station gradually shifted to equatorward reaching a maximum speed of about 300 m s 1 near 0200 lt 0900 ut and then decreasing to about 100 m s 1 near dawn the wind measured south of the station remained poleward throughout the night at speeds ranging between 25 and 100 m s 1 the neutral gas temperature over fritz peak observatory increased throughout the night from about 1300 to 1600 k calculations made with the national center for atmospheric research thermospheric general circulation model suggest that the observed winds over fritz peak observatory l 3 are under the influence of an expanded magnetospheric convection pattern during the storm enhanced magnetospheric convection at mid latitudes characteristically produces westward winds during the early evening hours and a strong equatorward surge in the postmidnight winds

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

a theoretical study of thermospheric composition perturbations during an impulsive geomagnetic storm the compositional response of the neutral thermosphere to an impulsive geomagnetic storm has been investigated using a numerical simulation made with the national center for atmospheric research thermospheric general circulation model ncar tgcm calculated time dependent changes in neutral thermospheric composition have been studied together with detailed neutral parcel trajectories and other diagnostic information from the model to gain a greater understanding of the physical mechanisms responsible for composition variability during geomagnetic storms and in particular to investigate the causes of the positive and negative ionospheric storm effects the following principal results were obtained from this study 1 calculated perturbations in thermospheric composition following the onset of an impulsive geomagnetic storm were found to be in good qualitative agreement with the previous experimental statistical study of storm time thermospheric morphology by prolss 1981 2 during the initial onset phase of the simulated storm upward vertical winds occurred in the auroral zone and downward winds occurred in the central magnetic polar cap 3 the largest perturbations in mass mixing ratio of nitrogen n2 at f region altitudes were found to be associated with parcels of neutral gas that travelled through the cusp region and with parcels that were trapped within the auroral zone for a long time 4 storm time enhancements in n2 were found to occur in the midnight and early morning sectors both within and equatorward of the auroral zone and these were determined to be associated with the advective effects of the large antisunward polar cap neutral winds the physical size of the region of enhanced n2 values was determined to be related to the time taken for individual parcels of air to corotate out of the large day to night thermospheric wind jet and thus to the magnitudes of the antisunward polar cap winds 5 decreases in n2 were found to occur in regions of downward vertical winds and in regions into which relatively nitrogen poor air was advected by the horizontal wind 6 calculated compositional perturbations following the onset of the storm were found to propagate to mid latitudes due to the advective effects of equatorward winds leading to the mid latitude positive ionospheric storm effects this last result is in disagreement with the earlier study of rishbeth et al 1985 who found the compositional disturbance to be largely restricted to the auroral zone on a constant pressure surface however it is consistent with the more recent study undertaken by fuller rowell et al 1991 who demonstrated that composition changes were seen well beyond the auroral oval

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

contribution of archaeological data to studies of earthquake history in the iranian plateau we use archaeological evidence to identify ancient earthquakes in the vicinity of large 20th century events in the iranian plateau two large earthquakes on the zagros main recent fault were preceded by historical earthquakes in ad 1008 and ad 1107 and by earthquakes in the intervals ad 224 459 and 1650 1600 bc giving return times of 1800 2100 500 800 and 850 950 years the ad 1962 ms 7 2 bo in zahra earthquake on the ipak fault in north central iran was preceded by an earthquake in 2000 1500 bc recorded at the sagzabad mound a return time of 3500 4000 years if there are no missing events the ad 1990 ms 7 3 rudbar tarom earthquake in the western alborz mountains was preceded by an earthquake in 1000 800 bc recorded at the marlik mound a return time of 2800 3000 years the ad 1948 ms 7 2 kopeh dagh earthquake that destroyed ashkabad capital of turkmenistan was preceded by an earthquake in 10 bc ad 10 recorded at mithradatkert nesa mound and by an earthquake in 2000 bc recorded at ak tapeh mound assuming no missing earthquakes this region has an earthquake return time of about 2000 years in khorasan province which was struck by a sequence of large earthquakes from ad 1936 to 1997 a mosque at qa en was destroyed in the mid 11th century ad probably the historical earthquake of ad1066 in the absence of palaeoseismic investigations archaeology offers the promise of recording earthquakes through more than one seismic cycle in different regions of iran q 2001 elsevier science ltd all rights reserved

the hex experiment determination of the neutral wind field from 120 to 185 km altitude near a stable premidnight auroral arc by triangulating the drift of rocket deployed chemical trails 1 on 25 march 2003 horizontal e region experiment hex released trimethyl aluminum trails from two rockets launched northward from poker flat research range near fairbanks to map the vertical wind field near a stable premidnight auroral arc system they deployed three trails of trimethyl aluminum chemical puffs whose subsequent motion traced the prevailing wind field this motion was determined using triangulation from four ground observation sites position and speed accuracies were estimated to be 1 km and a few meters per second respectively the first rocket followed a novel flat trajectory it released a nearly horizontal trail of length 200 km at an average altitude of 145 km the second rocket was launched 19 min later and released two trails between 125 and 175 km altitude along a conventional steep trajectory all puffs between 130 and 175 km altitude drifted geomagnetic westward almost exactly parallel to the aurora from prior observations and modeling we had expected to observe convective upwelling near the arcs we did not vertical winds were essentially downward throughout the horizontal trail with speeds between 0 and 20 m s 1 although an abatement of downward flow was observed 40 km equatorward of the arcs these data alone do not establish a causal relationship between the abatement and the arcs vertical speeds of 20 m s 1 are relatively modest however because the observed wind field would entrain air parcels in flow parallel to the arc system even vertical speeds around 15 m s 1 could displace individual air parcels by several scale heights if they occurred all along the arcs

winds in the high latitude lower thermosphere dependence on the interplanetary magnetic field 1 wind observations in the summertime lower thermosphere at high southern latitudes measured by the wind imaging interferometer windii on the upper atmosphere research satellite are statistically analyzed in magnetic coordinates and correlated with the interplanetary magnetic field imf to determine influences of imf dependent ionospheric convection on the winds effects are clearly detectable down to 105 km altitude above 125 km the wind patterns show considerable similarity with ionospheric convection patterns and the speed of the averaged neutral wind in the polar cap often exceeds 300 m s the correlation between the imf bz component and the diurnal harmonic of the winds is generally best when the imf is averaged over the preceding 1 4 5 hours the magnetic zonal mean zonal wind below 120 km correlates best with the imf by component when the latter is averaged over approximately the preceding 20 hours the wind has a significantly stronger rotational than divergent component around and above 120 km a dusk side anticyclonic wind vortex is prominent consistent with earlier findings around 140 km and higher the dusk side vortex intensifies for negative bz but around 120 km it is the dawn side cyclonic vortex that responds more strongly to bz variations the dependence of the wind on the imf is nonlinear especially with respect to imf bz for positive bz the difference winds are largely confined to the polar cap while for negative bz the difference winds extend to subauroral latitudes a significant correlation between the diurnal bz dependent neutral and convection velocity components exists above 108 km when the convection velocity is suitably rotated in magnetic local time mlt with respect to the wind the rotation that maximizes the correlation ranges from 1 5 hours at 130 km wind preceding convection to nearly 6 hours at 108 km wind lagging convection the rotated diurnal bz dependent wind pattern projects onto the diurnal bz dependent ionospheric convection pattern with about 60 the amplitude of the latter above 125 km decreasing to about 17 at 108 km on timescales of 20 hours a by dependent magnetic zonal mean zonal wind generally exists with maximum wind speeds at 80 magnetic latitude typically 10 m s at 105 km increasing to about 60 m s at 123 km and 80 m s at 200 km in the southern hemisphere the wind is cyclonic when the time averaged by is positive and anticyclonic when by is negative the wind direction is expected to be opposite in the northern hemisphere

slab melting as an explanation of quaternary volcanism and aseismicity in southwest japan two volcanoes on the quaternary volcanic front in southwest japan have erupted medium k andesite and dacite which are chemically similar to adakites i e high al 2 o 3 sr y low y and steep rare earth element ree patterns with no negative eu anomalies unlike other subduction related volcanoes in japan earthquake data and the extrapolated position of the philippine sea plate from its near trench position indicate that the leading edge of the plate is 75 100 km deep beneath these volcanoes melting of the plate at this depth would leave a garnet eclogite residual accounting for the y and heavy ree depletion the lack of seismic data and active volcanism in southwest japan can be attributed to the attenuated seismic response of the plate due to melting and to the atypical nature of magma generation

the neoproterozoic lower cambrian in northern govi altay western mongolia regional setting lithostratigraphy and biostratigraphy this paper provides a framework for the stratigraphy and correlation of key sections through the neoproterozoic lower cambrian of the govi altay area western mongolia studied by members of igcp project 303 dzabkhan formation volcanic rocks at the base of the succession are suggested to have formed during rifting of the baydrik tarbagatay microcontinent in the baykalian interval c 850 650 ma pre vendian accretion transformed this rift and adjacent microcontinental fragments into a marginal marine back arc basin in which accumulated relatively uninterrupted neoproterozoic and earliest palaeozoic sediments lithostratigraphy for the latter is defined with detailed maps at five sections bayan gol northern and southern blocks tsagaan gol salaany gol and tayshir the tsagaan oloom formation lower member contains two diamictites of possible sturtian age middle and upper carbonates are compared with the yudomian vendian of siberia the former ending with a unit of boxonia grumulosa stromatolites in the upper member phosphorite shale is followed mainly by limestones with the earliest skeletal fauna the bayan gol formation comprises siliciclastic limestone intercalations with increasingly diverse invertebrate biota correlation of lithological marker beds across the study area produces a composite stratigraphic section to which the earliest skeletal fossil occurrences are tied the anabarites trisulcatus zone of the nemakit daldynian stage begins near the base of the tsagaan oloom formation upper member unit 11 the purella antiqua zone begins near the base of the bayan gol formation unit 18 assemblages typical of the nochoroicyathus sunnaginicus zone base of the tommotian stage range through units 19 to 23 elements typical of the dokidocyathus regularis zone middle tommotian appear in unit 24 near the top of the bayan gol formation

timing of formation and tectonic nature of the purportedly neoproterozoic jiageda formation of the erguna massif ne china constraints from field geology and u pb geochronology of detrital and magmatic zircons abstract this paper reports new secondary ion mass spectrometry and laser ablation inductively coupled plasma mass spectrometry u pb age data for detrital and magmatic zircons from metasedimentary and igneous rocks from the jiageda formation jf of the erguna massif ne china these data constrain the timing of formation and tectonic nature of the jf as well as the tectonic affinity of the erguna massif the jf within the erguna massif is dominated by metasedimentary rocks and volcanics that have a gneissic or schistose structure the majority of zircons from metasedimentary volcanic and intrusive rocks in this area show striped absorption and fine scale oscillatory growth zone patterns and relatively high th u ratios 0 11 11 39 that are indicative of a magmatic origin four samples from the base of the type section of the jf in the village of jiageda yield detrital zircons with similar age populations that peak at 790 850 890 and 960 ma in addition to a few mesoproterozoic to paleoproterozoic and neoarchean zircons whereas a single sample from the upper part of the jf yields zircons that include a youngest age group of 764 ma zircons from granites and mafic dikes that intruded the type section of the jf yield weighted mean ages of 261 238 183 and 160 ma in comparison zircons from four volcanic samples collected 15 km northwest of the village of jiageda and one metasedimentary sample from the jf in the badaguan area all yield late mesozoic crystallization ages 158 132 126 and 128 ma for the four volcanic rocks and a youngest age of 178 2 ma for the metasedimentary rock combining these results with knowledge of the field relationships of the rocks in this area and previously published ages we infer that 1 the originally determined neoproterozoic jf does not represent a standard stratigraphic sequence but instead consists of neoproterozoic to mesozoic metasedimentary and volcanic rocks while the true neoproterozoic jf is exposed only in the village of jiageda and 2 nearly all of the sediments within the neoproterozoic jf were sourced directly from units that were exposed within the study area and adjacent regions our new data also provide precise geochronological evidence for the existence of a precambrian terrane within the erguna massif the ages of detrital zircons from neoproterozoic units within the erguna massif and precambrian geochronological data from adjacent cratons and massifs near the southern siberian craton indicate that the erguna massif and the massifs of the southern siberian craton e g the tuva mongolian and central mongolian massifs are not linked to the siberian and the north china cratons but instead most likely represent a fragmented precambrian terrane derived from the tarim craton

the geomagnetic quiet nighttime thermospheric wind pattern over fritz peak observatory during solar cycle minimum and maximum nighttime thermospheric winds and temperatures at f region heights have been measured over fritz peak observatory colorado 39 9 n 105 5 w with a high resolution fabry perot spectrometer from about november 1972 to the present the winds and temperatures are obtained from the doppler shifts and line profiles of the o i 15 867 k 630 nm line emission the data obtained during geomagnetic quiet conditions ap 20 have been separated into two groups representing solar cycle minimum conditions 1972 1977 and solar cycle maximum conditions 1978 1979 the monthly variation of the nighttime zonal and meridional winds are presented for both groups the results show that during solar cycle minimum the zonal winds are predominantly eastward during the winter months at speeds of 50 75 m s 1 and westward during the summer months at speeds of 50 100 m s 1 the meridional winds measured to the north and south of fritz peak observatory are equatorward throughout most of the night at nearly the same speed the equatorward winds in the summer peak near midnight at about 100 150 m s 1 the equatorward winds in the winter also peak near midnight but with smaller speeds 50 75 m s 1 during solar cycle maximum the zonal winds are again predominantly eastward during the winter months reaching peak speeds of 60 75 m s 1 in the early evening hours and decreasing afterward in the summer the winds are eastward during the early evening hours shifting to westward near midnight and increasing to a maximum speed of 75 100 m s 1 in the early morning hours the meridional winds are poleward at 20 m s 1 in the early evening hours shifting to equatorward near 2100 lt and then increasing in magnitude with maximum speeds near or after midnight there is a considerable difference in the speed of the winds measured to the north and south of fritz peak observatory during the summer the equatorward winds measured to the north are 150 175 m s 1 whereas the equatorward winds measured to the south are 50 75 m s 1 during the winter the speeds are smaller 50 75 m s 1 and 25 30 m s 1 to the north and south of the station respectively calculations made with the national center for atmospheric research thermospheric general circulation model for different seasons are in reasonable agreement with the observations during both solar minimum and solar maximum during solar cycle maximum the observed and calculated meridional wind differences to the north and south of fritz peak observatory are attributed to enhanced auroral heating and ion drag associated with magnetospheric convection north of the observatory the equatorward driven winds slow south of fritz peak observatory owing to the diminishing influence of high latitude forcings

vertical wind observations with two fabry perot interferometers at poker flat alaska characteristics of vertical winds in the polar thermospheric region were examined using data sets generated with two types of fabry perot interferometers at poker flat alaska 65 11 n 147 42 w the communications research laboratory fabry perot interferometer crlfpi simultaneously observed the o i 557 7 nm and o i 630 0 nm emissions whereas the geophysical institute scanning doppler imaging interferometer gi sdi observed the o i 630 0 nm emission the height of the o i 557 7 nm and o i 630 0 nm emissions were 100 140 and 200 240 km respectively the data were obtained from october 1998 to february 1999 and our findings were as follows 1 observations of the o i 630 0 nm emission showed that upward downward vertical winds were often present when bright aurora existed equatorward poleward of the observatory this is consistent with previous studies crickmore et al 1991 innis et al 1996 1997 2 comparison of vertical winds estimated from two different wavelengths 557 7 and 630 0 nm showed that vertical winds were often observed simultaneously at both wavelengths as reported by price et al 1995 however the vertical winds observed at different heights sometimes had different features when thin but bright aurora passed over the observatory a similar observation was reported by ishii et al 1999 3 vertical winds were often observed along with divergence and rotation of the horizontal wind field some vertical winds not associated with active aurora may be driven by the divergence in the horizontal wind

structure and composition of the aleutian island arc and implications for continental crustal growth we present results of a seismic reflection and refraction investigation of the aleutian island arc designed to test the hypothesis that volcanic arcs constitute the building blocks of continental crust the aleutian arc has the requisite thickness 30 km to build continental crust but it differs strongly from continental crust in its composition and reflectivity structure seismic velocities and the compositions of erupted lavas suggest that the aleutian crust has a mafic bulk composition in contrast to the andesitic bulk composition of continents the silicic upper crust and reflective lower crust that are characteristic of continental crust are conspicuously lacking in the aleutian intraoceanic arc therefore if island arcs form a significant source of continental crust the bulk properties of arc crust must be substantially modified during or after accretion to a continental margin the pervasive deformation intracrustal melting and delamination of mafic to ultramafic residuum necessary to transform arc crust into mature continental crust probably occur during arc continent collision or through subsequent establishment of a continental arc the volume of crust created along the arc exceeds that estimated by previous workers by about a factor of two

nd isotopic study of the neoproterozoic mara rosa arc central brazil implications for the evolution of the brasilia belt abstract the goias magmatic arc is a 0 9 0 64 ga island arc underlying large areas of the western part of the brasilia belt in central brazil it is exposed in two separate sections known as the arenopolis arc in the south and the mara rosa arc in the north it is made of island arc volcanic sedimentary sequences forming narrow nne to nnw belts separated from each other by tonalitic granodioritic granitic orthogneisses all rocks are metamorphosed under upper greenschist to amphibolite facies conditions but have kept major geochemical and isotopic features indicating the juvenile nature of the igneous protoliths the meta igneous and metasedimentary rocks are intruded by a number of late to post orogenic granites e nd 850 ranging from 1 5 to 4 6 with t dm values between 1 0 and 1 1 ga metasedimentary rocks in the mara rosa supracrustal belts display geochemical features suggesting that they represent first cycle immature sediments which preserve chemical characteristics of their igneous sources their nd isotopic characteristics support this interpretation t dm model ages for detrital metasediments are mostly in the interval between 0 9 and 1 2 ga indicating that they are a product of erosion of the arc rocks the absence of older contributions to these sediments seems to indicate an intraoceanic setting this is also suggested by the nd isotopic composition of the 0 8 ga old tholeiitic amphibolites which display positive initial e nd 4 9 indicating derivation from a depleted mantle source syn orogenic deformed granites forming small intrusions within the supracrustal belts have t dm ages ranging from 0 77 to 2 54 ga the older model age values indicate the presence of hidden fragments of ancient crust which were probably tectonically interleaved with younger rocks during accretion of the arc the post orogenic granites are moderately peraluminous and the nd model ages between 1 0 and 1 3 ga indicate that their parental magmas were predominantly re melts of the arc rocks their peraluminous nature reflects the incorporation of substantial amounts of arc sediments in the original magma garnet whole rock sm nd ages for the metasediments may be interpreted to refer to two metamorphic events an older event at 0 76 0 73 ga and a younger event at 604 610 ma mineral chemistry indicate that the older episode was characterized by higher p t and the younger by lower p t the older metamorphic event is interpreted preliminarily as the result of the accretion of island arc terranes to the western edge of the orogen and the younger event as a result of final ocean closure and continental collision between the amazon and sao francisco continents the goias arc formation and accretion is partially coeval with rodinia break up suggesting that the western margin of the sao francisco congo was peripheral in that supercontinent and faced a wide oceanic basin during most of the neoproterozoic

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

dwm07 global empirical model of upper thermospheric storm induced disturbance winds 1 we present a global empirical disturbance wind model dwm07 that represents average geospace storm induced perturbations of upper thermospheric 200 600 km altitude neutral winds dwm07 depends on the following three parameters magnetic latitude magnetic local time and the 3 h kp geomagnetic activity index the latitude and local time dependences are represented by vector spherical harmonic functions up to degree 10 in latitude and order 3 in local time and the kp dependence is represented by quadratic b splines dwm07 is the storm time thermospheric component of the new horizontal wind model hwm07 which is described in a companion paper dwm07 is based on data from the wind imaging interferometer on board the upper atmosphere research satellite the wind and temperature spectrometer on board dynamics explorer 2 and seven ground based fabry perot interferometers the perturbation winds derived from the three data sets are in good mutual agreement under most conditions and the model captures most of the climatological variations evident in the data

auroral zone thermospheric dynamics 1 averages forty four nights of thermospheric neutral wind and temperature measurements were obtained with a ground based fabry perot spectrometer at college alaska 65 invariant latitude mostly during high to moderate levels of solar activity the spectrometer scanned the o i 15 867 k 6300 a emission line yielding line profile measurements that originate from an altitude range between 170 and 280 km the observed average wind direction is to the northwest in the early evening changing to the south near midnight and then to the southeast in the morning the overall wind pattern generally persists but the wind speed increases with increasing geomagnetic activity a change in the zonal wind direction occurs earlier in magnetic local time with increasing magnetic activity the meridional wind pattern also shifts equatorward with the auroral oval during increasing magnetic activity consequently the average wind pattern in the north during low geomagnetic activity is rather similar to the moderate activity average in the south and the moderate geomagnetic activity average wind pattern in the north is similar to the high geomagnetic activity average in the south the observed average thermospheric temperature is found to be governed by geomagnetic activity and the previous day s 10 7 cm solar flux

precambrian crystalline basement in southern mongolia as revealed by shrimp zircon dating single zircon ages determined by ion microprobe shrimp ii for granitoid gneisses from the southern slope of the baga bogd massif gobi altai southern mongolia reveal several episodes of zircon growth ranging from late palaeoproterozoic to late cambrian the oldest events are documented by a zircon crystallization age for a gneiss protolith at 1519 11 ma and by a xenocrystic zircon from a dark grey augen gneiss yielding an age of c 1701 ma discrete igneous events are recorded in granite gneisses with protolith emplacement ages of 983 6 956 3 and 954 8 ma these ages provide the first record of early neoproterozoic magmatic activity in this region a much younger and discrete magmatic event is recorded by several dioritic to granitic orthogneisses which are tectonically interlayered with the older gneisses and have protolith emplacement ages between 502 and 498 ma these late cambrian granitoids of calc alkaline affinity are likely to have been emplaced along an active continental margin and suggest that the baga bogd precambrian crustal fragment was either docked against the southward present day coordinates growing margin of the caob or was a large enough crustal entity to develop an arc along its margin we speculate that the precambrian gneisses of this massif may be part of a crustal fragment rifted off the tarim craton

u pb zircon ages of granites from the southern margin of the yangtze block timing of neoproterozoic jinning orogeny in se china and implications for rodinia assembly abstract neoproterozoic jinningian bendong granodiorite and sanfang and yuanbaoshan granites occurred in northern guangxi southern margin of the yangtze block se china and were generally considered to be of orogenic origin that is the collision between the yangtze and huanan blocks during the jinning orogeny these granites were intruded into the mesoproterozoic sibao metamorphic basement and covered unconformably by the neoproterozoic danzhou metasediments they are dominantly peraluminous asi 1 18 1 29 and have low initial end values of 4 8 to 7 6 indicating derivation from a supracrustal source with strong enrichment in rb k and th and relatively low zr hf and higher rare earth elements they are similar to post collision granites zircon u pb ages of 819 9 826 10 and 824 4 ma were obtained for the bendong granodiorite and the sanfang and yuanbaoshan granites respectively by both shrimp and conventional dating methods the age result precludes the existence of any late mesoproterozoic grenville age granitic magmatism in the southern margin of yangtze block together with previous age determinations of ophiolites along the southern margin of the yangtze block the jinning orogeny is referred to the neoproterozoic orogeny which took place between 1 0 and 0 80 ga and likely ended at 0 82 ga the granite formation age of 0 82 ga also supports the basal boundary age of 0 80 ga for the post orogenic sinian system which is probably stratigraphically correlated with the adeladean system in south australia as the link between australia east antarctica and laurentia in the configuration of the supercontinent rodinia the collision between the yangtze and huanan blocks during the neoproterozoic jinning orogeny probably marks the termination of the rodinia assembly

the most ancient ophiolite of the central asian fold belt u pb and pb pb zircon ages for the dunzhugur complex eastern sayan siberia and geodynamic implications abstract ophiolitic rocks with a zircon age of 1020 ma occur in the dunzhugur complex of east sayan siberia and are part of a neoproterozoic to early palaeozoic segment of the central asian fold belt the most spectacular suite is exposed along the oka and bokson rivers where a complete ophiolite sequence with mantle tectonites a layered sequence composed of dunite wehrlite and pyroxenite a gabbro section a sheeted diabase dyke complex and basaltic pillow lavas are exposed petrologic and geochemical data suggest that all members of the ophiolite originally belonged to the same cogenetic mafic ultramafic crustal section and support a supra subduction zone setting in a fore arc rifting environment for its origin two multigrain zircon size fractions from a plagiogranite are both slightly discordant but yielded a combined mean 207pb 206pb age of 1020 10 ma evaporation of three additional fractions of three to four grains each from the same sample produced a mean 207pb 207pb age of 1019 9 0 7 ma that we consider to most closely reflect the time of igneous crystallization of the plagiogranite this is the oldest ophiolite so far dated from the central asian fold belt the southern margin of the siberian craton and the palaeo asian ocean were established at the end of the mesoproterozoic at least 1000 ma ago during the time interval 1000 570 ma one or several large ocean basins existed between baltica siberia kazakhstan tarim and northern china and these blocks are therefore unlikely to have been part of the supercontinent rodinia rifting initiation of subduction and marginal basin formation began prior to 1000 ma and continued through 570 ma the dunzhugur ophiolite of eastern sayan provides evidence for the early opening of the palaeo asian ocean not later than 1000 ma ago

geomorphology and structure of the jid right lateral strike slip fault in the mongolian altay mountains abstract we describe the late cenozoic structure and evolution of the jid right lateral strike slip fault in the northern mongolian altay mountain chain parts of the jid fault have a vertical component of motion introduced by bending along the fault some locations show additional structural complexity at the earth s surface with parallel strands having strike slip normal and reverse faulting probably indicating a spatial separation of dip slip and strike slip components of motion in cross section the jid fault shows indications of recent movements at scales ranging from drainage re organisation at the kilometre scale to ground deformations likely to result from movements during the last earthquake which occurred 870 980 years ago based on osl dating of deposits exposed in trenching from the scale of the ruptures the earthquake would have had a magnitude of 7 5 with an estimated right lateral slip of 5 m numerous horizontal offsets of about 10 15 m and vertical scarps of 5 m in the youngest alluvial deposits show the likely cumulative movement over the last 15 000 years and suggest a maximum slip rate of roughly 1 mm yr the minimum cumulative right lateral slip on the jid fault is 1 km which would accumulate in 1 ma at present day rates of slip the relatively small vertical component of motion on the jid fault is not sufficient to generate topography in the adjacent kharkhiraa and turgen uul mountains with relief of over 2000 m the high mountains may therefore result from localised uplift on thrust faults rather than by oblique slip on the jid fault

thermospheric winds at high latitudes from chemical release observations wind measurements from 39 chemical release rockets launched from auroral belt and polar cap sites between 1967 and 1979 are summarized and interpreted multipoint measurements between 200 and 320 km altitude were obtained from all flights by tracking the neutral strontium clouds produced as by products of ba cuo releases these releases producing ba clouds also provided the simultaneous measurements of ion drift that are needed for wind analysis trail releases of trimethylaluminum and lithium provided measurements between 90 and 200 km from 19 rockets the wind measurements at different local times and latitudes are disorganized when presented in geographic and solar local time coordinates an organized wind system at altitudes above 160 km emerges when wind vectors are presented in magnetic local time and invariant latitude coordinates the dominant role of electric field ion drag as a driving force and the inertial characteristics of the wind system are clearly illustrated when the wind vectors are superposed on model patterns of the global high latitude ion convection at altitudes above the 110 km shear region and below a transitional zone in the 140 160 km range relationships between the observed winds and the causative mechanisms become less apparent as a consequence of the slower response to changing ion drag conditions a notable exception occurs in the polar cap where high velocity winds are observed at all altitudes under the influence of continuous antisolar ion flow a key factor affecting the wind pattern is the formation of a pressure ridge along the interface zone between the polar cap and the auroral belt in the evening hours back pressures from this ridge suppress the coriolis forces in the adjacent regions and contribute to the development of a dusk to dawn component in the antisolar polar cap flow the observations clearly indicate that the antisolar polar cap wind loses momentum and deposits energy in the early morning auroral belt at high altitudes i e 160 320 km there is directional continuity but a velocity loss as the polar cap wind inertially penetrates the morning auroral region at lower altitudes i e 140 km the observations are less definitive but indicate that the wind is discontinuous along the morning auroral belt interface in general the observations do not reveal wind characteristics that can be attributed to pressure gradients from joule heating or heating by precipitating particles a possible but speculative exception is that the perturbing effects of heating may explain why observed velocities tend to be lower than velocities calculated for model ion drag conditions other wind effects from high latitude heating apparently have less influence than the time space variability of the electric field and are thus obscured by these variations the existence of the classical day night flow from dayside euv heating is demonstrated by measurements from three rockets launched at subauroral latitudes on the dayside the influence of this flow at higher latitudes is similarly not identifiable in the presence of the ion drag winds a number of the gross characteristics of the observed high latitude wind pattern are simulated reasonably well by fuller rowell and rees recent model