near end member magnesiochloritoid in prograde zoned pyrope dora maira massif western alps in the ultrahigh pressure metamorphic terrane of the dora maira massif western alps magnesiochloritoid up to 97 mol end member occurs along with ellenbergerite talc chlorite or kyanite as prograde inclusions in a few pyrope megablasts whereas most pyrope megablasts in this terrane are relatively homogeneous prp90 prp98 the magnesiochloritoid bearing megablasts commonly preserve a clear prograde fe mg zonation pattern from prp70 to prp98 the nearly homogeneous chloritoid inclusions also record this zonation pattern their xmg increasing from 0 70 to 0 96 from garnet core to garnet rim these zonations are shown to be prograde and to record increasing p and t conditions up to about 700 c 30 kbar the occurrence of magnesiochloritoid in some garnets simply reflects either a slightly more fe rich system general case or a more al rich and originally corundum bearing system one unzoned near end member pyrope megablast fe mg partitioning between chloritoid and zoned host garnet changes from normal to reverse i e xmgcld xmggrt from core to rim or from rim to core in other megablasts of yet similar composition in case of reverse partitioning a diffusion zone of a few tens of mu m wide exists in garnet around the inclusions toward which xmggrt decreases and reaches a normal partitioning value at the contact these features are interpreted in terms of disequilibrium and tentatively ascribed to slow diffusion in chloritoid with respect to garnet growth rate or to two competing garnet forming reactions with the metastable one which produces a more mg rich garnet being kinetically favoured the prograde inclusions of magnesiostaurolite show a consistent fe mg reversal with garnet i e xmgst xmggrt which is interpreted as an equilibrium feature at high pressure and high xmg magnesiochloritoid locally breaks down into symplectites of chlorite and an extremely low si magnesiostaurolite down to 7 0 si per formula unit which is probably metastable with respect to magnesiostaurolite corundum

radar observations of a 3 day kelvin wave in the equatorial mesosphere mesospheric radars are used to investigate the characteristics of a kelvin wave from two equatorial sites jakarta indonesia in the western pacific and christmas island in the central pacific our study focuses on the time span from mid january through mid october 1993 a kelvin wave with a period near 3 days was detected throughout this 9 month duration although it underwent deep amplitude modulations on a 20 day timescale a fitting procedure is applied to study the phase amplitude behavior of the wave the vertical wavenumber was measured by the radars and found to be small wandering around zero with only a weak bias toward downward phase progression the long vertical wavelength suggests that the wave was predominantly zonal wavenumber 1 the amplitude of the wave measured by the jakarta meteor scatter radar was much larger than the amplitude measured by the mf partial reflection radar at christmas island the smaller wave amplitude at christmas island could at least partially be due to a measurement bias associated with mf radars the radar at jakarta is a vhf meteor scatter radar and is not susceptible to this bias however the mean velocities and the amplitudes of the tidal and quasi 2 day wave components were in good agreement at the two sites the estimated 9 month averaged zonal acceleration was 0 67 ms 1 day 1 over jakarta at 94 98 km and only about half as large over christmas island the magnitude of the zonal acceleration occasionally showed large enhancements which suggest the importance of refractive effects associated with vertical and temporal variations in the mean winds the larger 3 day wave amplitudes and inferred acceleration at jakarta may reflect its location in the western pacific a region of high convection and hence an excitation region for equatorial waves the relative phase of the wave between the two radar sites gradually shifted over a timescale of weeks these smooth variations in relative phase are suggestive of a superposition of waves with different zonal wavenumbers perhaps radiating preferentially from one longitude the phase of the wave as a function of altitude and time was much more disordered at jakarta than at christmas island the conjecture can be made that the more chaotic phase structure observed over jakarta is due to higher order zonal wavenumber components which weaken as they propagate eastward

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

evolution and distribution of the conodonts sweetognathus and iranognathus and related genera during the permian and their implications for climate change abstract the conodont genus sweetognathus which is characterized by pustulose ornamentation on a wide flat topped carina originated in the earliest permian as s expansus from diplognathodus edentulus the asselian through artinskian part of the sweetognathus lineage is well represented in kansas by the successive evolution of s expansus s merrilli s aff s merrilli s whitei and s bucaramangus sweetognathus and iranognathus lineages were mainly confined to tropical areas from the kungurian onward the kungurian and guadalupian part of the sweetognathus lineage is well represented in south china by the successive evolution of s whitei artinskian s guizhouensis lower kungurian s subsymmetricus upper kungurian s iranicus hanzhongensis roadian and s fengshanensis capitanian an additional lineage in west texas is represented by the evolution of s sulcatus to s aff adjunctus to s adjunctus and to s bicarinum in the urals and northwestern pangea the late part of the sweetognathus lineage is represented by rare specimens of s bogoslovskajae upper artinskian lower kungurian during the late artinskian s whitei radiated into s toriyamai and s bucaramangus and also gave rise to neostreptognathodus pequopensis and probably pseudosweetognathus costatus neostreptognathodus exsculptus may have evolved from adetognathus paralautus through adetognathus telfordi sp nov iranognathus characterized by a narrow carina with poorly developed denticles and bearing subtle and smaller pustulose micro ornament replaced sweetognathus at or near the guadalupian lopingian boundary it probably also evolved from diplognathodus in the topmost guadalupian a lineage of iranognathus sp nov a to i erwini can be recognized for the guadalupian and lopingian boundary interval a lineage of iranognathus sp nov a to i movschovithschi to i sosioensis to i tarazi is found throughout the guadalupian and lopingian boundary interval and the wuchiapingian of south china sweetognathus and iranognathus tend to develop homeomorphic accessory nodes iteratively during lowstand periods of global sea level near the artinskian kungurian and guadalupian lopingian boundaries and in the late wuchiapingian sweetognathus and iranognathus seem to be equatorial warm water inhabitants distribution patterns reflect glaciation in gondwana during the asselian and sakmarian a warm climate during the artinskian cooling in north pangea during the kungurian and later permian slight amelioration during the guadalupian warming during the wuchiapingian and cooling during the changhsingian in the peri gondwana region definitions for most of the important sweetognathus species are refined three new species and subspecies iranognathus sp nov a adetognathus telfordi sp nov gullodus duani sp nov are described

the pyrope coesite rocks and their country rocks at parigi dora maira massif western alps detailed petrography mineral chemistry and pt path both the coarse and fine grained varieties of the partly coesite bearing pyrope quartzites their interlayered jadeite kyanite rocks and the biotite phengite gneiss country rock common to all of them were subjected to detailed petrographic and textural studies in order to determine the sequence of crystallisation of their mineral constituents which were also studied analytically by microprobe prior to pyrope and coesite growth the mg rich metapelites were talc kyanite chlorite rutile ellenbergerite schists which upon continued prograde metamorphism developed first pyrope megacrysts in silica deficient local environments at the expense of chlorite talc kyanite and subsequently the smaller pyrope crystals with coesite inclusions from reacting talc kyanite based on geobarometrically useful mineral inclusions as well as on experimentally determined phase relations a prograde pt path simplified for water activity 1 is constructed which passes through the approximate pt conditions 16 kbar and 560 c 29 kbar and 720 c and finally up to 37 kbar at about 800 c where the mg rich metapelite was a pyrope coesite rock with phengite kyanite and talc still present during the retrograde path pyrope was altered metasomatically either into phlogopite kyanite quartz or at a later stage to chlorite muscovite quartz both assemblages yield pt constraints the latter about 7 9 kbar 500 600 c the country rock gneisses have also endured high pressures of at least 15 kbar but they provide mostly constraints on the lowest portion of the uplift conditions within the greenschist facies about 5 kbar 450 c microprobe data are presented for the following minerals pyrope ellenbergerite dumortierite unusually mgti rich jadeite vermiculite formed after na phlogopite paragonite and for several generations of phengite chlorite talc phlogopite dravite and glaucophane in the high pressure rocks as well as for biotite chlorite phengites epidote garnet albite and k feldspar in the country rock gneisses an outstanding open problem identified in this study is the preservation of minerals as inclusions within kyanite and pyrope beyond their pt stability limits

stratigraphic versus environmental significance of permian serrated conodonts around the cisuralian guadalupian boundary new evidence from oman abstract conodonts from the cephalopod limestones of rustaq and ba ad oman have for many years been dated as wordian because of the presence of the ammonoid waagenoceras revised definitions for guadalupian stages and major differences of conodont morphology among apparently coeval faunas necessitate a review of this age assignment the lack of serration within the oman conodont faunas as well as from waagenoceras bearing limestone blocks in sicily differs markedly from conodonts in the guadalupian stratotype sections of west texas these differences have previously been interpreted to be the result of upwelling cold bottom water that may have restricted the distribution of serrated warm water jinogondolella species however our samples from oman are dominated by species with a carinal configuration that is comparable to gondolellids from the equatorial warm water province ewwp abundant species include mesogondolella siciliensis in the lower ammonoid beds and mesogondolella idahoensis lamberti in the upper ammonoid beds if cold bottom water currents were present at oman then these taxa must have been pelagic living in warm surficial water in contrast the north cool water province ncwp includes coeval conodonts that have a different carinal configuration and are dominated by long ranging mesogondolella idahoensis idahoensis these taxa and their morphologic variations represent a geographic cline between the ewwp and ncwp in addition early roadian serrated gondolellids have been recognized in temperate cool water settings in the jilin province ne china the phosphoria basin idaho usa and the sverdrup basin arctic canada these serrated forms extend above the lower roadian in only the phosphoria basin indicating a distribution into temperatures cooler than previously thought at least during the early guadalupian other conodonts from the deep water cephalopod limestones of oman include rare shallow warm water sweetognathids suggesting that these too must have been pelagic if true then cold bottom waters probably played little role in conodont distribution the identified conodont taxa at oman best correlate with the uppermost kungurian at the luodian section of south china and in the guadalupe mountains of west texas suggesting that the lack of serration is not a result of cold water but rather of a stratigraphic position prior to the evolution and expansion of serrated gondolellids in the roadian it is possible that other paleoecologic controls affected distribution and an alternative age assignment of early roadian is considered for these conodonts the ammonoids including advanced species of waagenoceras suggest that the best correlation is with the third limestone of the word formation willis ranch member which correlates with the upper roadian according to ratified global stage definitions there is still an apparent discrepancy between conodont and ammonoid ages but discounting previous wordian ages has considerably reduced this associated fusulinaceans cannot resolve this argument because of profound provincialism but they can contribute to correlation of the global stages with tethyan stages it is here suggested that the kungurian correlates with the upper bolorian to upper murgabian and that the roadian correlates with the lower midian or upper murgabian and lower midian

tectonics of western tibet between the tarim and the indus a tarim to indus traverse provides insight into the tectonics of western tibet the kunlun was the site of a mid paleozoic collision at least three phases of post paleozoic accretion have thickened the blanket of sediments that covers western tibet sizeable parts of western qiangtang have remained stable however since the mid mesozoic since the neogene deformation and volcanism have been localized near the edges of the plateau strike slip motion along the karakorum and altyn tagh faults has been coeval with overthrusting in the himalayas and kunlun such slip partitioning and the volcanism appear to result simply from northward subduction of india and southward subduction of the tarim as tibet is extruded eastwards by india s penetration into asia

first report of lower permian basalts in south tibet tholeiitic magmatism during break up and incipient opening of neotethys abstract the neo tethys ocean began to form at early permian times when continental flood basalts were emplaced in various areas of the newly formed indian passive margin exposed today in the so called tibetan sedimentary zone of the himalaya lower permian mafic volcanic rocks which have long been known from various himalayan localities from kashmir to arunachal pradesh are here for the first time reported to occur also in south tibet bhote kosi basalts of the gyirong county the basalts unconformably overlie lowermost permian diamictites with locally intervening black shales and debris flow deposits and are followed in turn by chert bearing quartzarenites and silty to phosphatic marls yielding brachiopods of roadian wordian age the age of the lavas can thus be bracketed as late early permian post sakmarian and pre roadian the geochemistry of these subalkalic tholeiites akin to morbs testifies to their similarity not only with the adjacent nar tsum spilites of central nepal but also with the panjal traps and abor volcanics of the western and eastern himalayas respectively the geochemical signature of lower permian volcanic rocks is in fact uniform all along the himalayan range and markedly different from that of basaltic rhyolitic alkalic products sporadically emplaced during the previous rifting stage rift volcanism in the tethys himalaya began in the early carboniferous and came to an end in sakmarian times in the early permian initial submergence of the rift shoulders and sediment starvation were followed by tholeiitic magmatism which is therefore interpreted as following break up and incipient sea floor spreading in the neotethys ocean roughly contemporaneous emplacement of continental flood basalts of similar geochemical signature along a 2000 km long rift axis would in fact suggest extensive mantle melting at the transition from continental rifting to break up and opening of the neotethys between northern gondwana and the peri gondwanian blocks

zircon fission track ages from the gasherbrum diorite karakoram range northern pakistan the gasherbrum peaks in the himalaya of pakistan reach elevations of 8000 m the relief between the peaks and the adjacent valley baltoro glacier is in excess of 3000 m eight samples of the early cretaceous gasherbrum diorite at elevations between 4880 and 7165 m on gasherbrum iv were collected for fission track dating zircon fission track ages from the gasherbrum diorite vary from early cretaceous to middle tertiary in age there is no consistent pattern between age and elevation the cretaceous ages indicate that these rocks were never deeply buried i e heated to temperatures in excess of 175 c to reset the zircons during cenozoic time these results also indicate that the uplift of this part of the himalaya has been either very rapid and recent or very slow since early cretaceous time this latter possibility is not consistent with the high relief at gasherbrum and what is known about regional tectonics gasherbrum iv zircons currently at approximately 4880 m have never been at depths greater than 6 km and less than 3 km of material has been removed from the top of the range by erosion since the early cretaceous rapid uplift has occurred very recently and erosion rates have notmore been able to keep pace with this uplift less

evidence of a role for modulated atmospheric tides in the dependence of sporadic e layers on planetary waves 1 a large amplitude 7 day period westward propagating s 1 planetary wave pw of global response has been reported from ground radar and satellite wind measurements in the mesosphere lower thermosphere mlt during the second half of august and well into september 1993 following recent suggestions that pw might play a role in the formation of midlatitude sporadic e layers es haldoupis and pancheva 2002 found a strong 7 day periodicity present in all stations concurrently with the 7 day planetary wave reported elsewhere by analyzing sporadic e critical frequency foes time series from eight midlatitude ionosonde stations covering a longitudinal zone from about 58 e to 157 w this study provided the first direct proof in favor of a pw role on es formation in the present paper we further investigate this role by considering the same pw event and correlating the 7 day periodicity in foes directly with concurrent variations in the mesospheric neutral wind measured with atmospheric radars in saskatoon canada and in sheffield united kingdom although our analysis cannot exclude a direct pw role on es formation it shows clearly that es is affected indirectly by the pw through the action of the diurnal and semidiurnal tides which are strongly modulated by the same pw apparently through a nonlinear interaction process at altitudes below 100 km this 7 day pw modulation was found to be clearly present simultaneously in the amplitude of the zonal 12 hour tidal wind the meridional 24 hour tidal wind and in both the 12 hour and 24 hour periodicities which existed in the foes time series the results here provide a new physical explanation for the observed relation between sporadic e layers and planetary waves

early paleozoic s type granites as the basement of southern qiantang terrane tibet abstract identifying basement rocks is critical to understanding the continent formation and evolution during orogenesis despite two decades of research the age and composition of the basement rocks of the southern qiangtang terrane microcontinent sqt central tibet are still unclear in this study zircon u pb ages and hf o isotopes as well as whole rock nd isotopes are presented for the oldest known igneous rocks in the sqt precise sims zircon u pb dating of these rocks reveals that these early paleozoic granites were crystallized at ca 480 465 ma they exhibit a wide range of isotopic values with unradiogenic whole rock end t and zircon ehf t values ranging between 8 3 7 7 and 8 2 2 3 respectively and by high 18ozircon values of 8 1 11 4 these results reveal that the early paleozoic granites were crystallized from magmas that were almost entirely sediment derived when viewed in concert with regional data and constraints on the tectonic evolution of northern gondwana the sources for the early paleozoic granites are herein proposed to have been deposited in an extensional basin implying that these early paleozoic granites were generated in an extensional setting within an accretionary orogen thus the early paleozoic granites are considered to represent the basement of the sqt after a long period of attachment to northern gondwana the sqt became a small microcontinent when it was rifted and detached from northern gondwana during early permian after this time it drifted northwards to asia and collided with the northern qiangtang terrane to form a unified qiangtang terrane in the late triassic thus the sqt records a complete wilson cycle from construction rifting and departure drifting to collision

ultradeep metamorphic rocks the retrospective viewpoint ultradeep or ultra high pressure uhp metamorphic rocks formed from crustal protoliths within the stability field of coesite at pressures 2 5 3 0 gpa corresponding to depths 80 120 km occur locally though regionally distributed in at least five continental areas their recognition is solely based on characteristic minerals and mineral assemblages calibrated by experimental high pressure studies detailed petrographic and microprobe work especially on mineral inclusions in favorable cases allows the derivation of prograde pt paths during subduction and of retrograde ones during exhumation commonly the gneisses adjacent to the uhp rocks do not exhibit signs of ultradeep metamorphism apparently because the kinetics of their mineral reactions are sufficiently fast to allow complete reequilibration to shallower pt conditions during the retrograde path it is also possible however that uhp equilibria were not attained throughout the rock volumes subducted but only along zones of shearing and fluid introduction if it is true that not all uhp metamorphic rocks return to the crustal orogenic belts but some continue to be subducted to greater mantle depths the classical geochemical pattern of a one way mass transfer from mantle to crust throughout the earth s history is at stake the assumed gradual growth of continents may have had a counterpart of continent destruction during collision events most recent experimental studies at high pressures and relatively low temperatures show that at least three new hydrous mg a1 silicates exist that were not found in nature thus far but may be characteristic minerals in the cold portions of old subduction zones thus extending the water retentivity of subducting slabs to greater and hitherto unexpected depths

phase relationships of ellenbergerite a new high pressure mg al ti silicate in pyrope coesite quartzite from the western alps

permian coral faunas of the eastern cimmerian continent and their biogeographical implications abstract because of a depositional hiatus late carboniferous corals are unknown from the eastern cimmerian continent early permian asselian to artinskian corals are characterized by non dissepimented solitary forms and the absence of kepingophyllidae and waagenophyllidae forms common in the cathaysian biotic province roadian faunas in most areas of the eastern cimmerian continent are dominated by small solitary corals these faunas are quite different from those of the cathaysian area where abundant large solitary and compound corals occur by the wordian and into the capitanian large solitary and massive waagenophyllidae with a cathaysian aspect were well developed and widespread in the cimmerian continent however some endemic taxa like thomasiphyllum also occur late permian corals consist only of cathaysian elements therefore paleobiogeographically the coral faunas in the eastern cimmerian continent reveal the following changes 1 a peri gondwanan affinity during the early permian to early middle permian 2 an endemic cimmerian cathaysian affinity during the late middle permian and 3 a true cathaysian fauna during the late permian these changes may be related to the rifting of the cimmerian continent from gondwanaland in the late early permian and its subsequent northward drift

variability of equatorial counter electrojet signatures in the indian region 1 the limited longitudinal extent of equatorial counter electrojet cej has been inferred by several workers based on the analysis of ground data however the scale length of cej characteristics at 2 hours or less has not been estimated so far the present study seeks to characterize the longitudinal variability of cej phenomena at a longitudinal separation of 15 using hourly averaged variations at two equatorial electrojet eej pairs of stations hyderabad vencode at 77 e and port blair campbell bay at 93 e the nature of cej events are classified by time of occurrence and studied using 12 months of concurrent data at the two longitudes from examination of 323 cej events at ven vencode and 239 at cby campbell bay over a period of 346 days the observations are i the occurrence of cej is not simultaneous at ven and cby for about 40 of events ii the amplitude and occurrence frequency of cej events is greater at ven than cby during both kp 2 and kp 2 iii the influence of westward currents on the eej peak was evidenced by early or late peak occurrences comprising about 175 days at ven and 89 days at cby it is established here that considerable variability of cej signatures is observed between the two longitudes at 15 separation revealing the impact of local electrodynamics these local processes therefore significantly influence the characteristics of eej

fluid melt rock interaction in mafic eclogites and coesite bearing metasediments constraints on volatile recycling during subduction the question as to whether the metasomatizing slab agent needed to form island arc magmas is an aqueous fluid or a hydrous melt requires a knowledge of fluid melt rock interaction during high pressure low temperature metamorphism in the western alps typical anhydrous mafic eclogites monviso massif and coesite bearing metasediments dora maira massif have experienced a prograde p t path characteristic of a mature cold subduction zone microstructural petrologic geochemical and fluid inclusion studies show that fluid flow was limited during eclogite and high grade blueschist facies metamorphism most of the fluids were driven off the rocks at pressures lower than 1 and 1 6 gpa respectively with increasing pressure and temperature the remaining fluid phase was released during crystal plastic flow processes or devolatilisation reactions but retain the host rocks to form veins partial melts or dense hydrous silicates tectonic erosion at modern convergent margins delivers large amounts of terrigenous sediments kmash system in subduction zones in contrast to the basalt and peridotite systems the kmash system is characterized by a wide range of pressure sensitive reactions which allow the reconstruction of dehydration hydration depths in the subducted slab independently of the thermal structure of subduction zones terrigenous sediments will begin to melt at pressures 2 gpa the melt phase can absorb tremendeous quantities of water and represent major sinks for devolatilisation fluids dense hydrous silicates will form in any subducted sediments at all depths these silicates can store significant amount of water in their structure in the subducted oceanic crust and upper mantle heterogeneous distribution of fluids inherited from hydrothermal alteration at mid ocean ridges will cause contemporaneous dehydration and hydration reactions on a local scale rather than large scale fluid infiltration in the overlying mantle wedge the situation where a cold competent and fluid rich subducted slab is bounded above by a hot relatively weak and anhydrous material is likely to act against buoyant rise of devolatilisation fluids by forcing the fluids to flow downwards at sub arc depths 50 10 to 80150 km and for any geothermal gradient continuous internal buffering of volatile activities will retain the fluid phase in the slab this is in contrast with shallow sub forearc depths 20 to 50 10 km where tectonic vein arrays localized thrust faults serpentine diapirs mud volcanoes and boninite magmas attest to the release of large volume of fluids into the overriding mantle wedge

origin and tectonic setting of the giant duolong cu au deposit south qiangtang terrane tibet evidence from geochronology and geochemistry of early cretaceous intrusive rocks abstract we constrain the origin and tectonic setting of the giant duolong porphyry epithermal cu au deposit in the south qiangtang terrane of northern tibet based on new zircon u pb ages and hf isotopic data as well as whole rock major and trace element data from poorly studied ore associated intrusions in the duolong area the la icp ms zircon u pb dating indicates that the ore associated rocks formed between 121 and 126 ma these ore associated rocks are geochemically similar to low k tholeiitic m type granitoids and to mid to high k calc alkaline i type granitoids they have variable and predominantly positive zircon e hf t values 1 4 to 15 6 and variable crustal model ages t c dm hf 176 1122 ma taking into account previous data and the regional geology of the study area we propose that the ore associated rocks originated from fractional crystallization of mantle derived mafic melts and magma mixing of mantle derived mafic and hybrid lower crust derived felsic melts and the hybrid lower crust included a mix of juvenile and older continental material the duolong porphyry epithermal cu au deposit formed within an ensialic forearc of an active continental margin as a result of the northwards subduction of the bangong nujiang ocean crust beneath the south qiangtang terrane

the permian fusulinoidean faunas of the sibumasu and baoshan blocks their implications for the paleogeographic and paleoclimatologic reconstruction of the cimmerian continent abstract permian fusulinoidean faunas occur in mainly four stratigraphic levels in the baoshan block of west yunnan and the sibumasu block of southeast asia which constituted part of the eastern cimmerian continent the oldest fauna from the upper part of the dingjiazhai formation in the baoshan block consists of pseudofusulina eoparafusulina and a new boultoniid genus and is assignable to the yakhtashian artinskian the second one which occurs in the basal part of the ratburi limestone and its equivalent strata in the sibumasu block is represented by monodiexodina and is probably referable to the bolorian kungurian the third fauna composed of eopolydiexodina rugososchwagerina yangchienia chusenella jinzhangia and several other genera is dated to the murgabian wordian and occurs in the lower part of the shazipo and daaozi formations in the baoshan block and the main part of the ratburi limestone in the sibumasu block the youngest fauna of probably dzhulfian wuchiapingian age is found in the upper part of the ratburi limestone and contains nanlingella reichelina codonofusiella and a few staffellid genera a smaller foraminiferal genus shanita found from the upper part of the ratburi limestone and the upper part of the shazipo formation is also an important element of the foraminiferal assemblage near the midian dzhulfian capitanian wuchiapingian boundary in the baoshan and sibumasu blocks in the eastern cimmerian continent low generic diversity throughout the permian and the paucity of tethys characterizing neoschwagerinid and verbeekinid genera during middle permian time are two remarkable features of the permian fusulinoidean faunas in the cimmerian continent the generic diversity of permian fusulinoidean faunas in space and time gradually increases from the early permian to late middle permian as well as from the eastern cimmerian areas to western ones the temporal increase of the generic diversity can be explained by the northward drift of the cimmerian continent during permian time in contrast the lower generic diversity of the eastern cimmerian permian fusulinoidean faunas against western ones is possibly due to an oblique arrangement of the continent to paleolatitude thus the western cimmerian continent was more proximal to the tropical tethyan domain than its eastern part in addition the middle permian cimmerian paleobiogeographic region is likely to be subdivided into two subregions the western tethyan cimmerian and the eastern gondwanan cimmerian based on the distribution pattern of verbeekinid and neoschwagerinid fusulinoideans and overall generic diversity the scarce occurrence or total absence of these essentially tethys indicating fusulinoideans in the baoshan and sibumasu blocks suggests that the eastern cimmerian continent was still far from the equatoro tropical cathaysian domain and was probably in a warm temperate or subtropical zone until the end of the permian the eastern cimmerian areas finally migrated into a tropical zone by the late triassic judging from well developed carnian sponge coral buildups in the chaiburi formation in the sibumasu block

early cretaceous exhumation of the qiangtang terrane during collision with the lhasa terrane central tibet the timing of the closure of the bangong ocean between the lhasa and south qiangtang terranes in central tibet and the resulting crustal thickening are still under debate we integrate published apatite fission track and u th he thermochronometer data with new zircon u th he ages from eight samples and with structural profiles to document that the south qiangtang terrane experienced slow exhumation between 200 and 150 ma associated with the opening of the bangong ocean accelerated exhumation around 0 2 0 3 mm a of the south qiangtang terrane was initiated at around 150 ma this exhumation event is interpreted to reflect collision between the lhasa and south qiangtang terranes after closure of the bangong ocean associated with crustal thickening via thick skinned folding and thrusting within the south qiangtang terrane the amalgamation of the lhasa and south qiangtang terranes recorded here may represent the first stage of crustal thickening in the central tibetan plateau this article is protected by copyright all rights reserved

late permian to late triassic palaeomagnetic data from iran constraints on the migration of the iranian block through the tethyan ocean and initial destruction of pangaea summary a palaeomagnetic study of late permian to early jurassic rocks from the alborz and sanandaj sirjan zones in iran and a compilation of selected palaeopoles from the carboniferous to the present provide an updated history of the motion of the iranian block within the tethys ocean the iran assemblage part of gondwana during the palaeozoic rifted away by the end of the permian we ascertain the southernhemisphere palaeoposition of iran at that time using magnetostratigraphy and show that it was situated close to arabia near to its relative position today a northward transit of this block during the triassic is shown with an estimated expansion rate of the neotethyan ridge of 100 140 km myr 1 the northward convergence with respect to eurasia ended during the ladinian middle triassic and is marked by a collision in the northern hemisphere with the turan platform which was the southern margin of the eurasian continent at that time no north south component of shortening is evidenced north of iran afterwards an analysis of the declinations from the late permian to the present shows diverent large rotations emphasizing the important tectonic phases suvered since the triassic finally we propose palaeomagnetic reconstructions of the tethys area during the late permian and the late triassic showing that the palaeotethys ocean was narrower than previously thought and did not widen its gate to the panthalassa before the triassic period

a traverse through the western kunlun xinjiang china tentative geodynamic implications for the paleozoic and mesozoic the northern part of the western kunlun southern margin of the tarim basin represents a sinian rifted margin to the south of this margin the sinian to paleozoic proto tethys ocean formed south directed subduction of this ocean beneath the continental southern kunlun block during the paleozoic resulted in the collision between the northern and southern kunlun blocks during the devonian the northern part of the paleo tethys ocean located to the south of the southern kunlun was subducted to the north beneath the southern kunlun during the late paleozoic to early mesozoic this caused the formation of a subduction accretion complex including a sizeable accretionary wedge to the south of the southern kunlun a microcontinent or oceanic plateau which we refer to as uygur terrane collided with the subduction complex during the late triassic both elements together represent the kara kunlun final closure of the paleo tethys ocean took place during the early jurassic when the next southerly located continental block collided with the kara kunlun area from at least the late paleozoic to the early jurassic the tarim basin must be considered a back arc region the kengxiwar lineament which connects the karakorum fault in the west and the ruogiang xingxingxia altyn tagh fault zone in the east shows signs of a polyphase strike slip fault along which dextral and sinistral shearing occurred

signatures of ultra fast kelvin waves in the equatorial middle atmosphere and ionosphere 1 in the equatorial atmosphere oscillations with periods of 3 to 4 days have been observed in the meteor radar zonal wind at cariri 7 4 s 36 5 w in the ionospheric minimum virtual height h f and the maximum critical frequency fof2 at fortaleza 3 9 s 38 4 w and in the timed saber satellite temperature data in the stratosphere mesosphere wavelet analyses of these time series reveal that the 3 4 day oscillation was observed for all of these data during the period from march 1 to 11 2005 from the characteristics of the downward phase propagation wavelength of 40 km longitudinal and latitudinal extension we conclude that this oscillation must be a 3 5 day ultra fast kelvin ufk wave this is the first report of clear evidence of propagation of a ufk wave from the stratosphere to the ionosphere the ufk wave could have an important role in the day to day variability of the equatorial ionosphere evening uplift

gondwanan deglaciation and opening of neotethys the al khlata and saiwan formations of interior oman abstract new stratigraphic petrographic and paleontological data from the lower permian of southeastern arabia help to elucidate the still debated timing of neotethys rifting and the climatic evolution following the gondwanan glaciation the transition from the al khlata to the saiwan formation here described in detail is interpreted to record continental break up and onset of neotethyan spreading between northern gondwana and the cimmerian terranes at mid sakmarian times as constrained by brachiopod assemblages the eastern oman arm of the neotethyan rift system instead failed and sea floor spreading of the indo madagascar trough was delayed until final fragmentation of gondwana in the late jurassic petrographic composition of lower permian sandstones documents a distinct change from transitional to dissected rift shoulder provenance and widespread exposure of granitoid basement rocks at a late syn rift to early post rift stage very abundant pore filling celestite at the al khlata saiwan transition may have precipitated from circulating brines related to remobilization of proterozoic salt due to rift tectonics the sharp base of the saiwan formation records a major transgression related to the onset of neotethyan spreading final deglaciation and consequent global sea level rise as indicated by ravinement surfaces associated with lag deposits with tree trunks reworked ferruginous pedogenic concretions and phosphate and by paleoecological analyses the basal bed of the saiwan formation is characterized by the pioneer pachycyrtella paleocommunity with pachycyrtella omanensis 85 suspension feeding rapid rates of reproduction and growth r strategy early maturity high mortality rates in the juveniles the more mature secondary ecological succession developed higher in the saiwan formation records maximum flooding and significant climatic amelioration the saiwan formation at the beginning of the late sakmarian finally sutures the irregular rift related topography in the rim basin of interior oman and records a shift towards warmer temperate conditions after the end of the gondwanan glaciation

a biogeographically mixed late guadalupian late middle permian brachiopod fauna from an exotic limestone block at xiukang in lhaze county tibet a total of 17 brachiopod species belonging to 15 genera are recorded from a limestone block of about 3 4 km2 in the indus tsangbo suture zone at xiukang in lhaze county of tibet the brachiopod fauna generally indicates a late guadalupian age late wordian capitanian late middle permian based on its association with the timorites bearing ammonoid fauna and the presence of the brachiopod urushtenoidea crenulata palaeobiogeographically the fauna exhibits transitional mixed characters between the warm water cathaysian and cold to temperate gondwanan faunas and may have developed on a carbonate build up or seamount on the oceanic crust

permian climatic and paleogeographic changes in northern gondwana the khuff formation of interior oman abstract detailed stratigraphic paleontologic and petrographic data from the middle permian khuff formation exposed in the haushi huqf area of interior oman provide new insight into the permian climatic evolution of the northern gondwana margin and on the still debated timing of neotethys opening between gondwana and the cimmerian blocks the khuff formation is interpreted to record a major transgression of neotethyan waters in wordian times middle permian at a stage of full oceanization and tectonic quiescence when thermal subsidence caused final drowning of rift shoulders and deposition of marine carbonates onto vast portions of stable arabia the petrographic composition of middle permian sandstones indicates a post rift stage and documents a long term increase in mineralogic stability ascribed to a shift toward warm humid climatic conditions coupled with reduced relief and longer transit times of detritus from source to basin raising temperatures and northward latitudinal drift towards lower tropic latitudes throughout the permian are fully documented by rich transitional marine faunas and available paleomagnetic evidence

u pb zircon rb sr and sm nd geochronology of high to very high pressure meta acidic rocks from the western alps three meta acidic rocks from the western italian alps a magnesiochloritoid bearing metapelite from the monte rosa massif a coesite pyrope quartzite from the dora maira massif and the monte mucrone granite in the sesia zone have been studied by u pb zircon rb sr on whole rock apatite and phengite and sm nd wholerock methods the mineral parageneses of the investigated rocks indicate high to very high pressure and medium to high temperature metamorphism this combined isotopic study has enabled us to constrain the ages of magmatic and metamorphic events and also to compare the behaviour of u pb zircon systems in three intensely metamorphosed areas of the pennine domain the u pb zircon data have yielded a magmatic age for the monte mucrone granite at 286 2 ma this result confirms the occurence of late hercynian magmatism in the sesia zone as in other austro alpine units and in other areas of the european crystalline basement in the monte rosa massif a geologically meaningless lower intercept age of 192 2 ma has been interpreted as an artefact due to a complex evolution of the u pb zircon system the magmatic shape of the zircons implies a magmatic or volcano sedimentary protolith for this rock originally considered as a metasediment the very high pressure metamorphism in the dora maira quartzite has produced an opening of the u pb zircon system at 121 12 29 ma the rb sr data support the occurence of high grade metamorphism during cretaceous times phengites model ages are slightly younger than the u pb zircon lower intercept ages due to cooling phenomena or possible response of the phengites to a later deformation the nd model ages from the whole rock samples as well as the u pb upper intercept ages from zircons of all three investigated rocks indicate the presence of proterozoic crustal components inherited from the precursors of these meta acidic rocks the studied zircon populations and their u pb systems apparently showed open system behaviour only when affected by extreme metamorphic conditions 700 750 c 28 kbar whereas eclogite facies conditions of 500 550 c and 14 16 kbar were not enough to disturb significantly the u pb zircon evolution it is also probable that the sedimentary or magmatic origin of the protoliths of these meta acidic rocks which involved different characteristics such as grain size and fluid phase concentration and composition could be another important factor controlling the u pb zircon system behaviour during metamorphic events

the karakorum block in central asia from ordovician to cretaceous abstract the karakorum block records a predominantly marine ordovician to cretaceous sedimentary history six major sedimentary cycles are recognised the oldest sediments early ordovician transgress over a crystalline basement the 1 km thick ordovician silurian mostly shaly succession contains rare carbonate intercalations in the early devonian a wide peritidal platform spread over the craton sedimentation rates were low 10 20 m ma and upper devonian probable lower carboniferous carbonates and clastics rest unconformably on the early devonian carbonates no evidence has been found for either late carboniferous or glaciogenic deposits sedimentation rates increased during the permian up to 50 m ma with thicknesses between 1 and 2 5 km three steps are identified 1 a huge alluvial to marginal marine terrigenous prism aggraded during the asselian sakmarian 2 the artinskian murgabian is characterised by local emergence and erosion linked to extension with block rotations 3 greater differentiation occurred from late permian to middle triassic when a peritidal carbonate flat developed in the southwest facing a deeper basin to the northeast carbonate sediments prevailed throughout the carnian norian the permo triassic evolution is interpreted as the passive margin stage of the karakorum block which previously belonged to the perigondwanian fringe when like mega lhasa it drifted northward on the tethyan transit plate mega lhasa is considered as a collage of blocks possibly separated by thinned crust or short lived seas with ocean crust quartzo lithic sandstones with grains of mafic volcanics and serpentinite overlain with gentle unconformity by pliensbachian toarcian red sandstones with sedimentary and metasedimentary clasts record the eo cimmerian deformation in the karakorum this orogenic episode was over by the aalenian when a shallow water carbonate ramp aggraded onto the previously emergent area the pre barremian upper jurassic and lower cretaceous are poorly documented in post barremian times the sedimentary succession of n karakorum was severely deformed in huge thrust sheets including slabs of crystalline basement a coarse conglomerate of mid cretaceous age sealed the thrust sheet edifice finally isolated campanian pelagic mudstones are recorded anticlockwise rotation of mega lhasa followed the late triassic docking of the iranian spur using the latter as pivot the rotation was completed during the middle jurassic when se pamir shaksgam and karakorum joined the qiangtang more closely assembling mega lhasa as it approached the asian margin

distribution and characteristics of mixed transitional mid permian late artinskian ufimian marine faunas in asia and their palaeogeographical implications abstract the permian marine biogeography of the asian region is characterised by the development of three broad realms boreal tethyan and gondwanan in the early early permian asselian to early artinskian there seems to have existed sharp biogeographical boundaries with no transitional zones between the realms presumably due to the effect of gondwanan glaciation and sharp climatic zonation the mid permian late artinskian to ufimian of the asian region is distinguished by the rise of two broad transitional zones in which mixed marine faunas flourished the northern transitional zone north and northeast china sikhote alin central and northeast japan is characterised by an admixture of both warm water cathaysian and cold temperate boreal genera the southern transitional zone arabian peninsula iran afghanistan the karakorum southeast and central pamir salt range central and northwest tibet shan thai terrane timor and western irian jaya on the other hand is distinguished by incorporating faunal elements of both gondwanan and cathaysian origin the mixed faunas of both transitional zones share several antitropically distributed genera e g monodiexodina lytvolasma and spiriferella and are succeeded by palaeotropical tethyan faunas of late permian age it has been postulated that the mixed mid permian fauna of the northern transitional zone was probably formed in an epicontinental sea which was connected to both the asian tethys and the arctic which facilitated the migration of cathaysian and boreal forms into the epicontinental sea and subsequent faunal mixing the formation of the mixed faunas of the southern transitional zone on the other hand is probably related to the breaking off of the cimmerian blocks from northern gondwana and subsequent drifting into a lower latitudinal zone with geographical proximity to both gondwana and cathaysia during the mid permian

the 2 day wave in the middle atmosphere observations and theory a recurrent global scale 2 day oscillation in the middle atmosphere is well documented in a variety of data sources meteor wind partial reflection satellite and rocketsonde the observed period is almost invariably near 2 1 days and the zonal structure has been established as a westward propagating wave number 3 mode observations also indicate that the meridional wind component maximizes near the equator and dominates the wind field at low latitudes these features suggest the disturbance s identification with the wave number 3 rossby gravity normal mode of a windless isothermal atmosphere such modes are found to exist largely independent of the mean fields the eigenperiods are only modestly altered by mean wind variations on the lowest three scale heights and the influence on the mode structure is local the vertical growth of amplitude is enhanced in regions of weak westerly wind relative to the wave and equatorward temperature gradient while the vertical growth rate is retarded and amplitudes may even decay in regions of strong westerlies or poleward temperature gradient in realistic mean fields the third rossby gravity mode has magnified responses very near 2 25 days in both equinox and solstice conditions the horizontal structure remains largely intact in the lowest levels however considerable asymmetry is introduced in the solstice upper stratosphere and mesosphere by the magnified vertical growth of amplitude in the summer hemisphere the latter results from the moderate easterlies and equatorward temperature gradient characteristic of the region as for the simple eigenstructure the meridional wind component in this region maximizes near the equator and dominates the wind field up to mid latitudes

pb sr nd isotopic behavior of deeply subducted crustal rocks from the dora maira massif western alps italy abstract pb nd and sr isotope data are reported on mineral separates and whole rock samples of mg rich metapelites and associated rocks that have been subducted to depths of ca 100 km in the mantle within the last 100 ma and returned to the surface and for which metamorphic conditions were estimated to be 700 800 c at 28 kilobars pressure three rock types fine and coarse grained pyrope quartzites and nafe rich jadeite kyanite quartz layers were collected from a single outcrop in the coesite bearing portion of the dora maira massif samples analyzed include pyrope pseudomorphs after pyrope phengite zircon the new mineral ellenbergerite and whole rocks isotope data from all three decay systems indicate minimal if any isotopic exchange with mantle rocks isotope ratios from minerals with low parent daughter ratios cluster around 143 nd 144 nd 0 51225 nd 7 6 87 sr 87 sr 0 7 15 75 15 80 with 206 pb 204 pb 19 4 20 7 these compare closely with ratios from precambrian granitic rocks or their derived sediments from the pb isotope data and the sm nd whole rock model ages we estimate a mean age of 2000 500 ma for the sediment protoliths pyrope mineral separates record approximate ages for alpine metamorphism of 34 38 ma by the sm nd method the u pb method applied to zircon and ellenbergerite yields possible additional metamorphic ages of 50 55 ma these data illustrate a possible mechanism for creating isotopically enriched mantle had these rocks yielded their isotopes to the mantle enriched mantle could have resulted the magnitude of the enrichment depending upon the total volume attained by the mixing process similarly the metasediments could also provide the high potassium abundances and appropriate pb sr and nd isotope ratios that are postulated to accompany mantle metasomatic processes

a crystal chemical basis for pb retention and fission track annealing systematics in u bearing minerals with implications for geochronology this study develops an empirical crystal chemical framework for systematizing the kinetics of pb loss and fission track annealing in u bearing minerals ionic porosity z the fraction of a mineral s unit cell volume not occupied by ions potentially accounts for kinetic behavior by monitoring mean metal oxygen bond length strength various tests of a general kinetics porosity relationship are presented based upon diverse mineral data including 1 pb diffusion parameters 2 measured closure temperatures tc for fission track annealing and 3 retentivities of both pb and fission tracks from apparent age data every kinetic parameter including tc and mineral age for both the u pb and fission track systems is inversely correlated with z within the sub assemblage zircon z 29 titanite 34 and apatite 38 assuming a diffusional closure model pb isotopic transport phenomena are described by a tc z scale calibrated with field based tc data for titanite 680 20 c and apatite 500 c extrapolation of this scale yields tc estimates for the following minerals staurolite tc 1060 c z 25 garnet 1010 c 26 5 zircon 900 c monazite xenotime and epidote 750 c 32 and ca clinopyroxene 670 30 c 34 1 depending on composition these empirical results imply that a u pb pb date for staurolite or garnet records the time of mineral growth not post growth isotopic closure as also concluded in recent field studies because z systematizes fission track annealing this recrystallization process like volume diffusion must also be rate limited by the strength of chemical bonds the extent to which other recrystallization processes are likewise rate limited is important to u pb geochronology because they potentially compete with diffusion as mechanisms for pb isotopic resetting in nature

reply to the comments on middle cretaceous back arc formation and arc evolution along the asian margin the shyok suture zone on northern ladakh nw himalaya by weinberg and dunlap

syn kinematic emplacement of the pangong metamorphic and magmatic complex along the karakorum fault n ladakh this paper investigates the age p t conditions and kinematics of karakorum fault kf zone rocks in the nw part of the himalaya karakorum belt granulite to greenschist facies assemblages were developed within the kf zone during strike slip shearing the granulites were formed at high temperature 800 c 5 5 kbar were subsequently retromorphosed into the amphibolite facies 700 750 c 4 5 kbar and the greenschist facies 350 400 c 3 4 kbar the tangtse granite emplaced syn kinematically at the contact between a lt and the ht granulite facies intrusion occurred during the juxtaposition of the two units under amphibolite conditions microstructures observed within the tangtse granite exhibit a syn magmatic dextral s c fabric compiled u pb and ar ar data show that in the central kf segment granulite facies metamorphism occurred at a minimum age of 32 ma subsequent amphibolite facies metamorphism at 20 18 ma further shearing under amphibolite facies 650 500 c was recorded at 13 6 0 9 ma and greenschist facies mica growth at 11 ma these data give further constrains to the age of initiation and depth of the karakorum fault the granulite facies conditions suggest that the kf accommodating the lateral extrusion of tibet could be at least a crustal or even a lithosphere scale shear zone comparable to other peri himalayan faults

structures and timing of permian rifting in the central oman mountains saih hatat abstract we investigated remnants of permian rifting sequences in the saih hatat metamorphic window central oman mountains part of the former arabian continental margin which has been overthrust by the semail ophiolite in the less deformed northwestern part of the saih hatat well preserved or inverted syn sedimentary normal faults indicate ene wsw permian extension we propose new stratigraphic correlations with the more deformed and metamorphosed parts of the saih hatat based on lithostratigraphy and large scale structures unfolding which indicate that breakup of the permian platform resulted in sediment thickening and deepening towards the ene this rift event was coeval with within plate volcanism that was widespread in all compartments of the margin but marked by a single event in the stratigraphic record of the platform in this part of the arabian margin rifting was restricted to a short time interval less than 5 my during the murghabian and volcanism can be correlated with the panjal traps event we propose that this part of the neotethyan margin formed as a volcanic rifted margin in a triple junction setting

tectonic evolution of the qiangtang block northern tibet during the late cisuralian late early permian evidence from fusuline fossil records abstract the tectonic evolution of the qiangtang block in the qinghai tibetan plateau has been a controversial subject for a long time in this paper the discovery of new stratigraphic and fusuline fossil evidence from the permian sequences qudi and lugu formations of the qiangtang block is reported and the palaeogeographical position and tectonic history of this block during the late cisuralian late early permian are discussed the qudi formation is typified by thick turbidite deposits and contains artinskian fusulines such as pseudofusulina and chalaroschwagerina the fusulines were deposited as grains involved in debris flow deposits suggesting a synchronicity with the depositional time of the turbidites the subsequent lugu formation is dominated by seamount type carbonates with an irregular basalt base fusulines cancellina pseudodoliolina and parafusulina in the base of the carbonates confirm its age as middle kungurian the transition from the turbidite qudi formation to the seamount lugu formation is here interpreted to be a continuous depositional process recording the qiangtang block s separation from the indian plate this separation signaled the opening of the neotethys ocean between the qiangtang block and the indian plate palaeogeographically the qiangtang block s separation is comparable with the baoshan block s separation in the east and central pamir s separation in the west by contrast the ultimate opening of the neotethys ocean by the separation of india pakistan and northern oman is apparently much later than this event recorded in the qiangtang block consequently it is interpreted that the opening of the neotethys ocean in the whole northern gondwanan margin is a diachronous series of events

mesospheric planetary wave signatures in the equatorial electrojet 1 using five years 1994 1998 of simultaneous and collocated measurements of horizontal winds associated with mesosphere and lower thermosphere mlt region and geomagnetic field measurements in the indian geomagnetic dip equatorial region an extensive experimental study has been made on the influences of mesospheric planetary waves on the equatorial electrojet eej the winds are measured using medium frequency mf radar 1 98 mhz located at tirunelveli the eej strength is determined by measuring the geomagnetic field strength at both the geomagnetic dip and off dip equatorial stations trivandrum and alibag india by noting the simultaneous time evolution of spectral signal morlet wavelet analysis in both the eej strength and mesospheric winds at 88 km it is found that mesospheric planetary waves with periodicities of 2 25 days often do propagate up to the ionospheric dynamo region and have their influences on eej strength sometimes only one of the parameters shows strong spectral signal in this periodicity range it is also observed that often the diurnal oscillation in eej strength and mesospheric winds exhibits coherent variations in amplitude when the signature of mesospheric planetary scale oscillations is found in the eej strength also it is found that variations in high energy solar radiations f10 7 is used as a proxy can influence the eej strength at planetary timescales this leads to an interesting question what actually causes the vertical coupling between ionosphere and atmosphere through upward propagating planetary waves to be operative only during some and not all of the episodes

zircon geochemical constraints on the protolith nature and metasomatic process of the mg rich whiteschist from the western alps abstract the mg rich silicic crustal rocks characterized by high sio2 and mgo contents are widespread in the alps providing rare targets to investigate the origin of mg rich fluids in the continental subduction zone however it is a prerequisite to elucidate the protolith nature of such mg rich rocks including the possible alteration process experienced before the alpine metamorphism for this purpose we carried out a detailed study of trace elements o hf isotopes and u pb ages for zircons from the coesite bearing whiteschist and its country rock metagranite at dora maria in western alps the whiteschist is characterized by much higher mgo contents than the adjacent metagranite relict magmatic zircons from the two types of rocks give essentially the same u pb ages of 262 ma similar ree contents and patterns the same range of ehf t1 values from 6 4 to 2 8 and 18o values from mostly 9 to 11 these features provide compelling evidence that the whiteschist and metagranite share the same protolith i e the permian granite all the above geochemical compositions are consistent with the argument that the high mgo content of the whiteschist was acquired from high mg fluids from dehydration of the serpentinized peridotite at the slab mantle interface in the continental subduction channel the hypothesis of a pre alpine hydrothermal alteration of the granitic protolith to cause the mgo enrichment is not favorable zircon in the metagranite does not show any metamorphic overgrowth during the alpine orogeny in contrast to the extensive overgrowth of metamorphic rims at 35 ma in the whiteschist the metamorphic rims show relatively low ree contents with variably flattened hree patterns different from the relict magmatic zircons that exhibit relative high ree contents with steep hree patterns this difference suggests that the breakdown of hydrous minerals plays a crucial role in dictating mineral reactions for zircon growth during the continental subduction zone metamorphism this interpretation is also consistent with the local occurrence of garnet coronae along the grain margins of biotite in the metagranite therefore this study provides not only the constraints on the protolith nature and metasomatic process of mg rich whiteschist from the western alps but also insights into the role of metamorphic fluids in controlling mineral reactions for the metamorphic growth of both zircon and garnet in the continental subduction zone

shoshonitic and ultrapotassic post collisional dykes from northern karakorum sinkiang china abstract high k calc alkaline shoshonitic and ultrapotassic post collisional dykes of neogene age have been found in the remote and little known region of northern karakorum located around the shaksgam valley north of the k2 gasherbrum range china the dykes derive from more or less comparable basic magma s and display rather unusual petrographic and geochemical characters with respect to the other k rich rocks the geochemical data are consistent with derivation of the basic magma s from small degrees of partial melting of garnet lherzolites previously enriched in incompatible elements of crustal origin possibly during the subduction of the indian plate beneath karakorum the spectrum of compositions reflects fractional crystallization governed by an early removal of clinopyroxene phlogopite plagioclase garnet amphibole followed by the precipitation of abundant alkali feldspar amphibole apatite quartz additionally assimilation of crustal rocks during magma ascent contributed to the unusual compositional characteristics and is suggested by the abundance of corroded quartz plagioclase xenocrysts and by the occasional presence of granitic xenoliths an apparent connection exists between magmatism and tectonism in the complex karakorum fault zone kfz it is suggested that during the neogene the strike slip kfz and some adjacent post metamorphic faults transiently behaved as extensional fault systems down to deep levels triggering ascent and emplacement of the k rich magma the subsequent re activation of a compressive and transcurrent regime determined the rapid and recent uplift of the more primitive lamprophyres occurring in the plutonites and metamorphites of the upper baltoro glacier and k2 gasherbrum range relative to the more fractionated and contaminated lamprophyres injecting the shallower rocks of the shaksgam valley area

new record of bathonian callovian calcareous nannofossils in the eastern karakoram block a possible clue to understanding the dextral offset along the karakoram fault we report the first record of bathonian callovian calcareous nannofossils from a marine sedimentary sequence of the eastern karakoram block in northern india the calcareous mudstones and packstones occasionally bearing red chert nodules yielded calcareous nanofossils and middle jurassic choffatia furcula ammonoids middle to upper jurassic nannofossil assemblage is dominated by representatives of the genus watznaueria the occurrence of ansulasphaera helvetica whose range is upper bathonian upper callovian indicates a correlation with nannofossil zones nj12 13 the occurrence of cyclagelosphaera wiedmannii further infer an upper bathonian callovian age these specimens show affinities with those found in a similar sedimentary formation exposed in north karakoram this suggests the existence of a narrow and elongated sedimentary basin oriented in a nw se direction at a latitude of c 25 30 n at that time the karakoram block was situated near the already welded qiangtang block of asia the northern and eastern karakoram blocks were connected during middle jurassic the activity and dextral offset of the karakoram fault separated the jurassic sedimentary formations of the northern and eastern karakoram blocks by c 150 km

a geological transect from kun lun to karakorum sinkiang china the western termination of the tibetan plateau preliminary note a geological geophysical expedition ev k2 cnr 1988 visited the area from west kun lun to karakorum k2 gasherbrum seven tectonic units including sedimentary magmatic and metamorphic rocks were distinguished in this area the northernmost are suggested to belong to the kun lun and qiangtang microplates the sedimentary sequence of shaksgam is proved to extend from the permian to the jurassic with carboniferous and cretaceous ages more doubtful this sequence shows intermediate affinities between the karakorum and the qiangtang the two southernmost units belong to the karakorum microplate the karakorum fault zone comprises a complex pattern of faults and thrusts with brittle deformation and uplifting of granitoid bodies

paleomagnetic analysis of eastern tibet implications for the collisional and amalgamation history of the three rivers region sw china abstract a comparative analysis of paleolatitudes and latitudinal displacements was undertaken for the south china simao baoshan shan thai indochina qiangtang lhasa and himalayan blocks by using available paleomagnetic data to determine the collisional and amalgamation history of the main blocks in the three rivers region western yunnan the results show that 1 the simao block is a south china derived block 2 the baoshan and shan thai blocks were subjected to rapid northward drift during the period from late carboniferous to late permian 3 the baoshan block collided with the simao block in the late permian and continued to drift rapidly northwards together with the south china and shan thai blocks until the late triassic 4 the paleo tethys separating the baoshan and simao blocks was possibly opened in the early silurian 5 the meso tethys ranged in age from early permian time to early cretaceous time and reached its greatest width of about 42 latitude in the late triassic

co2 forced climate and vegetation instability during late paleozoic deglaciation the late paleozoic deglaciation is the vegetated earth9s only recorded icehouse to greenhouse transition yet the climate dynamics remain enigmatic by using the stable isotopic compositions of soil formed minerals fossil plant matter and shallow water brachiopods we estimated atmospheric partial pressure of carbon dioxide pco2 and tropical marine surface temperatures during this climate transition comparison to southern gondwanan glacial records documents covariance between inferred shifts in pco2 temperature and ice volume consistent with greenhouse gas forcing of climate major restructuring of paleotropical flora in western euramerica occurred in step with climate and pco2 shifts illustrating the biotic impact associated with past co2 forced turnover to a permanent ice free world

characterization of seasonal and longitudinal variability of eej in the indian region this paper presents the seasonal and longitudinal variability of the equatorial electrojet eej based on geomagnetic variation data from two electrojet stations in the northern indian ocean at a longitudinal separation of 15 i e at 77 e and at 93 e one complete year of data is used i e from november 2011 to october 2012 at the two longitudes and compared with the climatological model of the equatorial electrojet eejm 2 0 the results of our analysis show that i the monthly averaged hourly values of eej strength at 77 e and 93 e are overall in agreement with global characteristics of eej with significant departures over the year of study ii the monthly average hourly daytime values at campbell bay and vencode show poor correlation r 10 nt 20 nt for 30 of quiet days sorted by planetary index kp 1 and 2 this variability is reflected in monthly average values v mechanisms for persistent differences in eej on day to day basis are sought from perturbation of westward ion drifts by neutral winds caused by the upward propagation of gravity waves from troposphere stratosphere into the mesosphere these mechanisms have been identified theoretically and experimentally the four wave structure of ionospheric current densities obtained by eejm 2 0 and other contemporary models closely resembles atmospheric tidal signatures and has a common origin the magnitude and persistence of these differences at short spatial scales 15 are significant observation these effects are reflected in the monthly and seasonal signatures of eej and contribute to the contemporary models

multicyclic history of the northern india continental margin northwestern himalaya 1 the geologic evolution of northern india is best recorded in the stratigraphic succession of the zanskar range northwestern himalaya which represents the most complete transect through this ancient continental margin sedimentary history began in the late proterozoic and recorded a late pan african orogenic event around the cambrian ordovician boundary when the gondwana supercontinent was eventually assembled the following long period of epicontinental deposition in shallow seas linked to palaeo tethys lasted until the early permian when a neo tethyan rift began to open between paleo india and the cimmerian microcontinents neo tethyan history can be subdivided into two sedimentary megasequences both recording a major tectonic and magmatic event in the lower part the first one began with breakup in the late permian and lasted until the end of the jurassic the second one started in the early cretaceous with the final detachment of india from gondwana and the opening of the indian ocean and ended with the india eurasia collision in the early eocene the two megasequences can be in turn subdivided into six transgressive regressive supersequences bounded by tectonically enhanced unconformities basal sandstone units of early permian late permian norian callovian early cretaceous and paleocene age are invariably associated with oolitic ironstones or reworked glauco phosphorites and mark the transgre sive part of each supersequence next condensed nodular carbonates or shales with pelagic fauna are typically overlain by thick shallowing upward marly units capped by regressive platformal carbonates the six tectono eustatic supercycles reflect successive rifting episodes which punctuated the progressive separation of india from the rest of gondwana and document the combination of plate microplate reorganizations and eustatic climatic and oceanographic changes in the tethyan domain after the onset of collision between india and asia close to the paleocene eocene boundary obduction of the remnants of the neo tethys ocean floor onto the indian margin began and the latter underwent multiphase deformation with fold thrust shortening followed by heating and extension after the main metamorphic event ophiolitic nappes were re thrusted and finally emplaced with their sedimentary sole on top of the passive margin succession

phase relations in the mgo p2o5 h2o system and the stability of phosphoellenbergerite petrological implications the polymorphic relations for mg3 po4 2 and mg2po4oh have been determined by reversed experiments in the temperature pressure t p range 500 1100 c 2 30 kbar the phase transition between the low pressure phase farringtonite and mg3 po4 2 ii the mg analogue of sarcopside is very pressure dependent and was tightly bracketed between 625 c 7 kbar and 850 c 9 kbar the high temperature high pressure polymorph mg3 po4 2 iii is stable above 1050 c at 10 kbar and above 900 c at 30 kbar the low pressure stability of farringtonite is in keeping with its occurrence in meteorites the presence of iron stabilizes the sarcopside type phase towards lower p from the five mg2po4oh polymorphs only althausite holtedahlite mg2po4oh the hydroxyl analogue of wagnerite and mg2po4oh were encountered relatively speaking holtedahlite is the low temperature phase 600 c mg2po4oh the high temperature low pressure phase and mg2po4oh the high temperature high pressure phase with an intervening stability field for althausite which extends from about 3 kbar at 500 c to about 12 kbar at 800 c althausite and holtedahlite are to be expected in f free natural systems under most geological conditions however wagnerite is the most common mg phosphate mineral implying that fluorine has a major effect in stabilizing the wagnerite structure coexisting althausite and holtedahlite from modum s norway show that minor fluorine is strongly partitioned into althausite kdf oh 4 and that holtedahlite may incorporate up to 4 wt sio2 synthetic phosphoellenbergerite has a composition close to mg0 9 0 1 2mg12p8o38h8 4 it is a high pressure phase which breaks down to mg2po4oh mg3 po4 2 h2o below 8 5 kbar at 650 c 22 5 kbar at 900 c and 30 kbar at 975 c the stability field of the phosphate end member of the ellenbergerite series extends therefore to much lower p and higher t than that of the silicate end members stable above 27 kbar and below ca 725 c thus the si p ratio of intermediate members of the series has a great barometric potential especially in the si buffering assemblage with clinochlore talc kyanite rutile h2o application to zoned ellenbergerite crystals included in the dora maira pyrope megablasts western alps reveals that growth zoning is preserved at t as high as 700 725 c however the record of attainment of the highest t and or of decreasing p through p rich rims 1 to 2 si pfu is only possible in the presence of an additional phosphate phase oh bearing or even oh dominant wagnerite in these rocks otherwise the trace amounts of p in the system remain sequestered in the core of si rich crystals 5 to 8 si pfu and can no longer react

interannual variations of the quasi 16 day oscillation in the polar summer mesospheric temperature nighttime measurements of the hydroxyl meinel 4 2 rotational band have been used to infer the mesospheric temperature over scandinavia from june to august during the years 1992 1995 while the nightly averaged temperatures show a statistically significant quasi 16 day oscillation in the 1992 and 1994 summer data none is observed during 1993 and 1995 when present the period amplitude and temporal behavior of this oscillation agree with both model predictions and previous wind measurements of the 1 3 rossby normal mode in the summer mesosphere thus this temperature oscillation appears to correspond to the thermal signature of the 16 day rossby mode its appearance in the summer mesosphere is shown to occur when the oscillating zonal flows in the upper stratosphere near the equator are in an eastward phase while it appears to be blocked during the westward phases this correspondence of the 16 day wave in the summer mesosphere with the eastward equatorial wind would favor the explanation that it is generated in the winter hemisphere and propagates vertically and toward the summer pole following the westerly mean winds

capitanian late guadalupian permian global brachiopod palaeobiogeography and latitudinal diversity pattern a global database containing 3365 occurrences 821 species and 251 genera of the capitanian late guadalupian permian brachiopod faunas from 24 stations has been analyzed by cluster analysis using the jaccard and otsuka coefficients and the probabilistic index of similarity nonmetric multidimensional scaling and minimum spanning tree two supergroups three groups and six subgroups are revealed and interpreted as representing respectively two biotic realms the palaeoequatorial and gondwanan realms two regions and six provinces an additional realm the boreal realm based on the fauna from spitsbergen also appears recognizable although it also shows considerable similarities with southwestern north america and the northern margin of gondwana as revealed by the statistical analysis the palaeoequatorial realm can be further subdivided into the north america region and the asian tethyan region the six biotic provinces are the cathaysian province in the palaeotethys and mesotethys the greenland svalbard province in the arctic region the austrazean province in eastern australia and new zealand the grandian province in western north america and the two transitional zones the himalayan province in the southern temperate zone and the sino mongolian japanese province in the northern temperate zone polynomial regression analysis and rarefaction analysis indicate that the generic diversities of brachiopod faunas during the capitanian peaked in the palaeoequatorial cathaysian province and the two transitional zones himalayan province and sino mongolian japanese province but fell dramatically in the polar regions the generic diversity of the palaeoequatorial grandian province is apparently lower than in the two transitional zones of temperate palaeolatitudes suggesting that the generic diversity of capitanian brachiopod faunas does not exhibit a strict negative correlation with palaeolatitudes this in turn would suggest that biogeographical determinants such as geographical barriers inhabitable area and ocean currents other than latitude related temperature control may also have played an important role in the dispersal of some brachiopods and the characterization of some local provinces and high diversities the capitanian global brachiopod palaeobiogeography is generally comparable with those in the wuchiapingian and changhsingian but with some notable differences these include 1 that the grandian province of the capitanian in western north america vanished after the end guadalupian regression 2 that the western tethyan province of the lopingian could not be distinguished in the capitanian and 3 that the austrazean province was larger in area than either in the wuchiapingian or in the changhsingian

variability of the equatorial electrojet its relations to the sq current system and semidiurnal tides average diurnal and seasonal variations of the horizontal geomagnetic element delta h are examined the semiannual variation in equatorial electrojet strength is found to disappear in afternoon hours this may be related to changes in the latitude of the sq current system focus during the day this in turn may be caused by a superposed semidiurnal tide and may also explain delta h variations at stations near the focus

middle permian foraminifers from the zhabuye and xiadong areas in the central lhasa block and their paleobiogeographic implications abstract two new middle permian foraminifer faunas are described from the xiala formation in the zhabuye and xiadong sections in the central lhasa block the presence of some significant taxa in paleobiogeography such as shanita lysites biconcavus hemigordiopsis subglobosa indicates that the lhasa block was in the cimmerian province in paleobiogeography during the middle permian furthermore the nankinella chusenella fusuline assemblage that occurs in the upper part of the xiala formation in the xiadong section resembles contemporaneous fusuline faunas from the xainza and bashor areas in the lhasa block and the northern part of the tengchong block the endemism of the nankinella chusenella assemblage in the lhasa and tengchong blocks indicates that these two blocks were isolated from both the south qiangtang block and the northern gondwanan margin during the middle permian it further suggests that both the bangong nujiang ocean and the neotethys ocean would have opened before the middle permian a new species chusenella tsochenensis sp nov was described

discovery of an eclogite belt in the lhasa block tibet a new border for paleo tethys abstract a newly discovered eclogite belt in the eastern part of the lhasa block tibet is about 500 1000 m wide and at least 60 km long in an e w direction the eclogites occur as tectonic slices in garnet bearing mica quartz schist they are generally fresh and form thick massive layers that consist chiefly of garnet grt omphacite omp phengite phe rutile rut quartz qtz p t calculations based on the grt omp phe mineral assemblage yielded peak metamorphic conditions of 2 7 gpa and 730 c close to the phase boundary between coesite and quartz and thus the eclogites can be regarded as part of a very high pressure metamorphic belt petrochemical data suggest that the eclogite protoliths were typical morb basalts derived from depleted mantle shrimp u pb dating of zircons from the eclogite yielded metamorphic ages ranging from 242 15 to 292 13 ma with an average value of 262 5 ma the morb eclogites are interpreted to be remnants of paleo tethyan oceanic lithosphere the eclogites along with permian island arc volcanic rocks to the north are believed to mark a carboniferous permian suture zone dividing the lhasa block into a northern and southern segment this newly identified suture zone suggests that the border of the paleo tethyan ocean jumped southward from north of the bangong nujiang suture to within what is now the lhasa block

evidence for equatorial kelvin modes in nimbus 7 lims abstract eastward propagating disturbances over the equator are diagnosed in two independent nimbus 7 lims limb infrared monitor of the stratosphere data sets they are evident consistently at several pressure levels throughout the stratosphere and account for much of the temperature variance in the tropics the disturbances which can be seen in wavenumbers 1 3 are in phase and symmetric about the equator latitudinally evanescent and have short moderate vertical phase structure 10 40 km which progresses downward wavenumber 1 has spectral components which propagate eastward at periods of 6 7 8 6 days 54 69 m s 1 and 3 5 4 0 days 115 135 m s 1 wavenumber 2 exhibits eastward propagating variance at periods of 6 0 7 5 days 31 39 m s 1 and 3 8 4 3 days 55 62 m s 1 the faster waves appear principally in the upper stratosphere these features are in reasonable agreement with the structure and dispersion characteristics of simple quasi separable kelvin modes with the exception of the slower w

temporal and spatial variations of late mesozoic granitoids in the sw qiangtang tibet implications for crustal architecture meso tethyan evolution and regional mineralization abstract the western segment of the south qiangtang terrane w sqt is an ideal place to investigate the late mesozoic crustal architecture tectonomagmatic evolution and regional mineralization of this terrane where the emplacement of voluminous late mesozoic granitoids provides favorable conditions to form some world class porphyry cu au mineral deposits as well as a series of fe pb zn and w mineral deposits or occurrences here we synthesize the spatial distribution geological geochronological geochemical and isotopic data of the late mesozoic granitoids and associated mineral deposits or occurrences in w sqt these data suggest that the granitoid magmatism in w sqt lasted from ca 170 ma to ca 110 ma with two magmatic flare ups at ca 170 150 ma and ca 130 110 ma in particular the granitoids formed between ca 170 ma and ca 120 ma are generally younger from north to south indicating a southward migration of magmatism during this period the compositions of the granitoids vary considerably across w sqt becoming more reduced and evolved from the ancient coastal area i e the area close to the bangong nujiang suture zone to the continental interior area moreover the zircon ehf t values of the granitoids also gradually decrease from the ancient coastal area to the interior area indicating the ancient crustal components in the source of the granitoids increase continentward we therefore concluded that an ancient crustal basement with archean to paleoproterozoic ages must exist beneath the interior of the south qiangtang terrane i e the south qiangtang terrane has been an older microcontinent based on this conclusion a comprehensive model involving the flat subduction break off rollback and complete detachment of the bangong nujiang oceanic slab was proposed for the late mesozoic tectonomagmatic and metallogenic evolution of w sqt in particular the thickening of w sqt crust during late jurassic and the occurrence of magmatic gap ca 140 130 ma were interpreted to be associated with the flat subduction of bangong nujiang oceanic slab the development of regional extension recorded by early cretaceous 127 122 ma mafic dikes and bimodal volcanic rocks and the southward migration of granitoid magmatism were attributed to the break off and rollback of bangong nujiang oceanic slab our study also shows that the early cretaceous mantle derived juvenile crust derived highly oxidized and less evolved granitoids are most favourable for the generation of significant porphyry cu au deposits while the middle late jurassic mature crust derived relatively reduced and highly evolved granitoids are highly prospective for pb zn and w mineralisations in addition the granitoids generated by a mixture of mantle derived and mature crust derived components have high potential for skarn fe cu deposits for the w sqt magmatic belt as a whole cu au prospective granitoids fe cu prospective granitoids and pb zn w prospective granitoids exist in the south the middle and the north respectively

two day wave coupling of the low latitude atmosphere ionosphere system 1 vertical coupling in the low latitude atmosphere ionosphere system driven by the 2 day wave in the tropical mlt region has been investigated the problem is studied from an observational point of view three different types of data were analyzed in order to detect and extract the 2 day wave signals the 2 day wave event during the period from 1 december 2002 to 28 february 2003 was identified in the neutral winds by radar measurements located at four tropical stations the 2 day variations in the ionospheric electric currents registered by perturbations in the geomagnetic field and in the f region electron densities were detected in the data from 23 magnetometer and seven ionosonde stations situated at low latitudes two features for each kind of wave were investigated in detail the variation with time of the wave amplitude and the zonal wave number the results show that the westward propagating global 2 day wave with zonal wave number 2 seen in the ionospheric currents and in f region plasma is forced by the simultaneous 2 day wave activity in the mlt region the main forcing agent in this atmosphere ionosphere coupling seems to be the modulated tides particularly the semidiurnal tide this tide has a larger vertical wavelength than the diurnal tide and propagates well into the thermosphere the parameter that appears to be affected and thus drives the observed 2 day wave response of the ionosphere is the dynamo electric field

quasi 16 day oscillation in the mesosphere and lower thermosphere a quasi 16 day wave in the mesosphere and lower thermosphere is investigated through analyses of radar data during january february 1979 and through numerical simulations for various background wind conditions previous workers have examined about 19 days of tropospheric and stratospheric data during january 10 28 1979 and present conflicting evidence as to whether a large westward propagating wavenumber 1 oscillation observed during this period can be identified in terms of the second symmetric rossby normal mode of zonal wavenumber 1 commonly referred to as the 16 day wave in the present work we have applied spectral analysis techniques to meridional and zonal winds near 95 km altitude obtained from radar measurements over obninsk russia 54 n 38 e and saskatoon canada 52 n 107 w these data reveal oscillations of the order of 10 m s 1 with a period near 16 days as well as waves with periods near 5 and 10 days these periodicities all correspond to expected resonant frequencies of atmospheric disturbances associated with westward propagating free rossby modes of zonal wavenumber 1 numerical simulations are performed which demonstrate that the 95 km measurements of the 16 day wave are consistent with upward extension of the oscillation determined from the tropospheric and stratospheric data noteworthy features of the model in terms of its applicability in the mesosphere lower thermosphere regime are explicit inclusion of eddy and molecular diffusion of heat and momentum and realistic distributions of mean winds especially between 80 and 100 km the latter include a westerly wind regime above the summer easterly mesospheric jet thus providing a ducting channel enabling interhemispheric penetration of the winter planetary wave disturbance this serves to explain the appearance of a quasi 16 day wave recently reported in the high latitude summer mesopause williams and avery 1992 however the efficiency of this interhemispheric coupling may be reduced by gravity wave stress no significant penetration of the 16 day oscillation above about 100 km is predicted by the model reported signatures of a 16 day periodicity in ionospheric data therefore require modulation of tidal or gravity wave accessibility to the thermosphere or perhaps in situ excitation

dynamics of the equatorial mesosphere first results with a new generation partial reflection radar the first observations of mesospheric winds made between january august 1990 with an mf partial reflection radar located on christmas island 2 n 157 w in the central pacific are described the mean zonal winds are in general westward but show clear evidence for a wave driven circulation power spectral studies indicate that waves are present over a wide range of periods ultra fast kelvin waves are especially evident in january march with peak amplitudes 20 ms 1 and intrinsic phase speeds of 150 ms 1 indicated the kelvin waves are estimated to contribute an eastward acceleration of up to 10 ms 1 day 1 gravity wave amplitudes are also found to be almost as large as those observed at mid latitude sites which suggests that convection is a major source of gravity wave activity

phosphoran pyroxene and olivine in silicate inclusions in natural iron carbon alloy disko island greenland a survey of literature data on the p contents of olivine pyroxene and garnet in mantle xenoliths and the bulk p contents of mantle xenoliths shows that available data is ambiguous as to whether mantle p is primarily contained in silicates or in phosphates even though phosphates are rarely observed in mantle xenoliths garnet probably contains more of the mantle s p than olivine or pyroxene bulk p contents of mantle xenoliths vary significantly estimation of the primitive mantle p content from xenoliths requires interpretation of the partial melting and contamination histories of the xenoliths

carboniferous triassic subduction and accretion in the western kunlun china implications for the collisional and accretionary tectonics of the northern tibetan plateau a newly defined 250 km by 500 km carboniferous triassic subduction accretion complex the mazar accretionary prism in the western kunlun comprises two subduction complexes and a forearc basin succession 1 the bazar dara subduction complex contains imbricated blocks of sandstone arenite limestone and metavolcanic rocks in a matrix of weakly metamorphosed triassic deep sea turbidites the metavolcanic rocks include basalt diabase spilite and andesitic porphyry trace element geochemistry shows that pillow and amygdaloidal basalts are oceanic island tholeiites this zone has ordovician to permian fossils and is situated on the older more highly deformed and metamorphosed side of the prism adjacent to the sailiyak magmatic arc 2 the heweitan subduction complex is composed of blocks of limestone turbidite and radiolarite in a slate phyllite matrix intercalated with calc alkalic volcanic rocks this complex has permian to triassic fossils and is situated on the younger less deformed and metamorphosed side of the prism adjacent to the suture zone 3 the qitai forearc basins are infilled with turbidites late triassic intercalated with carbonates these rocks overlie the accretionary prism the accretion related structure is dominated by large scale northeast dipping thrusts and subvertical cleavage stitched by 215 190 ma granites there is an overall decrease in metamorphic grade and deformation intensity from the arc to the suture zone across the bazar dara and heweitan subduction complexes the mazar accretionary prism formed by subduction accretion processes during closure of the paleotethyan ocean and the final docking of the gondwanan karakoram qiangtang block to the cathaysian eurasian kunlun block

late palaeozoic global changes affecting high latitude environments and biotas an introduction abstract the late palaeozoic ice age lpia spanning approximately from 320 ma serpukhovian late mississippian to 290 ma mid sakmarian early permian represents the vegetated earth s largest and most long lasting regime of severe and multiple glaciations involving processes and patterns probably comparable to those of the last ice age accompanying the lpia occurred a number of broadly synchronous global environmental and biotic changes these global changes as briefly reviewed and summarized in this introductory paper comprised but are not limited to the following massive continental reorganization in the lead up to the final assembly of pangea resulting in profound changes in global palaeogeography palaeoceanography and palaeobiogeogarphy substantially lowered global atmospheric carbon dioxide concentrations p co 2 coupled with an unprecedented increase in atmospheric oxygen concentrations reaching earth s all time high in its last 600 million year history sharp global temperature and sea level drops albeit with considerable spatial and temporal variability throughout the ice age and apparently a prolonged period of global sluggish macro evolution with both low extinction and origination rates compared to other times in the aftermath of the lpia the world s climate entered into a transitional climate phase through the late early to middle permian before its transformation into a greenhouse state towards the end permian in recent years considerable amount of data and interpretations have been published concerning the physical evidence in support of the lpia its broad timeframe and eustatic and ecosystem responses from the lower latitudes but relatively less attention has been drawn to the impact of the ice age on late palaeozoic high latitude environments and biotas it is with this mission in mind that we have organized this special issue with the central focus on late palaeozoic high latitude regions of both hemispheres that is gondwana and northern eurasia our aim is to gather a set of papers that not only document the physical environmental changes that had occurred in the polar regions of gondwana and northern eurasia during the lpia but also review on the biotic responses at different taxonomic ecological and spatial scales to these physical changes in a refined chronological timeframe this introductory paper is designed to provide a global context for the special issue with a brief review of key late palaeozoic global environmental changes including changes in global land sea configurations atmospheric chemistry global climate regimes global ocean circulation patterns and sea levels and large scale biotic biogeographic and evolutionary responses followed by a summary of what we see as unresolved scientific issues and various working hypotheses concerning late palaeozoic global changes and in particular the lpia as a possible reference to future research

some seasonal hemispheric similarities in ƒ o f2 quasi 2 day oscillations the annual variations of the amplitude period and probability of existence of of2 quasi 2 day oscillations at middle latitudes in both northern and southern hemispheres are investigated the of2 hourly data for the period 1977 1982 for stations kiev 50 5 n 30 5 e and wakkanai 45 39 n 141 69 e for the northern hemisphere and kerguelen 49 35 s 70 24 e and campbell island 52 6 s 169 1 e for the southern hemisphere are used for analysis it is found that there is a strong tendency for hemispheric similarities in the seasonal variations of oscillation amplitude period and probability of existence the annual variations of the oscillation amplitude are modulated by the 12 month hemispheric and semiannual geomagnetic waves the dominant period of oscillation is maximum in summer 50 51 hours and minimum in winter 47 49 hours and the probability of existence has a maximum in the summer half year and minimum in the winter half year the seasonal similarities in the annual variations of the oscillation period and the probability of existence show the possible influence of the planetary 2 day wave in the middle neutral atmosphere on the electron density variations in the f region

zircon u pb dating and in situ hf isotopic analysis of permian peraluminous granite in the lhasa terrane southern tibet implications for permian collisional orogeny and paleogeography article i nfo the lhasa terrane has long been interpreted as a simple tectonic block rifted from gondwana during the late paleozoic and then drifted northward before finally amalgamating with the qiangtang terrane during the early cretaceous in this paper we document permian peraluminous granites near pikang in the southern margin of the central lhasa terrane close to the recently documented songdo eclogite of permian age zircon shrimp and la icpms u pb dating for a pikang granite sample gives an identical crystallization age of about 263 ma and a wide age range of inherited zircons 283 2141 ma in situ hf isotopic analyses for 20 zircons of 263 ma yielded ehf t values of 4 5 to 1 9 the pikang granites have high a cnk values 1 08 and high normative corundum 1 3 2 0 indicative of peraluminous s type granite they are characterized by moderately negative eu anomalies eu eu 0 48 0 61 and strongly negative ba nb sr p and ti anomalies the granites have high end t values 6 4 to 6 0 and low initial 87 sr 86 sr ratios 0 7082 0 7096 relative to melts derived from mature continental crust these rocks are interpreted to have been generated by mixing between mantle melts and their induced melting of mature crustal materials we interpret the pikang peraluminous granite magmatism the regional angular unconformity between the middle and the upper permian and the eclogite of the same metamorphic age 262 ma from the same geotectonic location to represent different products of a common event in time and space we tentatively term this common event as syncollisional orogeny i e the permian gangdese orogeny we further hypothesize that the orogeny may be genetically associated with the collision between the lhasa terrane and the northern margin of australia following the closure of the paleo tethyan ocean south of the lhasa terrane

origin and pre cenozoic evolution of the south qiangtang basement central tibet abstract the qiangtang terrane in central tibet with its high pressure rocks is a key area to unravel the evolution of the paleo tethys we present a new 1 50 000 map of the rongma area in the central qiangtang terrane of which relatively little is known so far we show that the qiangtang metamorphic belt can be separated in a paleozoic autochthonous basement and an overlying allochthonous thrust stack of subduction melange that contains high pressure rocks and permian sediments detrital zircon ages youngest peak at 591 ma and an 470 ma granite intrusion age constrain the age of the qiangtang basement to be between the late precambrian to middle ordovician this is in agreement with the observed unconformity between basement and overlying mid late ordovician strata this unconformity and the zircon age spectra are comparable to the himalaya area the qiangtang terrane must thus have been part of the gondwana supercontinent during the early paleozoic the occurrence of the late triassic eclogite and glaucophane bearing schists in the central qiangtang terrane indicates the existence of a suture zone between the north and south qiangtang terranes before the late triassic this suture zone resulted from closure of the paleo tethys between the north and south qiangtang terranes late triassic syn collisional granites and rapidly exhumed high pressure rocks resulted from the closure of this ocean and final amalgamation of the re united qiangtang terranes with eurasia collision of the lhasa and qiangtang terranes is correlated with north dipping reverse faults in the south qiangtang terrane which were probably related to exhumation of the qiangtang basement and formation of the qiangtang culmination

the break up of east gondwana along the northeast coast of oman evidence from the batain basin recent detailed studies on the batain nappes northeast coast of oman which represent a special part of the so called oman exotics have led to a better understanding of the neotethyan geodynamic evolution the batain exotics bear witness to volcanic activity sea level changes tectonic instability rifting and oceanization along the eastern oman margin during late palaeozoic and mesozoic times they allow definition of the batain basin as an aborted permian branch of neotethys this marine basin was created in early permian times extending southward to the east african madagascar region and was linked to the karoo rift system the presented revised classification of the batain nappes considers the batain basin to be no longer a part of the hawasina basin and the neotethyan margin proper we attribute the batain basin to a mozambique somali masirah rift system somoma this system started in early permian times creating a marine basin between arabia and india madagascar rifting in the late triassic and oceanization during late jurassic times led to the separation of east gondwana

granites of western karakorum and northern kohistan pakistan a composite mid cretaceous to upper cenozoic magmatism abstract the petrography the chemical mineralogical typology and the ages of six plutonic units four from the karakorum axial batholith darkot pass ghamu bar batura and hunza units and two of northern kohistan gindai and nomal plutons are defined and compared based on field data and analyses of up to 78 samples major elements ree rb s sbnd sr and k ar isotopes the karakorum axial batholith is a composite body three major intrusive stages occurred 1 around mid cretaceous times ca 110 95 ma with the emplacement of subalkaline i e monzonitic darkot pass and calc alkaline hunza ghamu bar units 2 during palaeogene maybe up to 43 ma batura subalkaline unit a strong tectonommetamorphic event recorded in the gneissification of the cretaceous intrusives occurred between these two stages it may be of palaeocene age p t estimates of the highest metamorphic grade rocks of the hunza unit have yielded values of 580 640 c and 5 0 5 kbar and 3 during upper miocene ca 9 ma baltoro subalkaline unit debon et al 1986c in addition a conspicuous network of aplo pegmatitic dykes emplaced into the hunza area possibly from the eocene up to the upper cenozoic with a maximum during the middle miocene ca 15 ma most of these major magmatic stages are met again among the acidic intrusives and dykes of northern kohistan the first one as blastomylonitic tholeiitic plutons nomal ca 102 ma petterson and windley 1985 the second one as subalkaline plutons gindai ca 59 ma and a third one as leucocratic dykes of oligocene age ca 30 ma petterson and windley 1985 these data may be related to the geodynamic evolution of the nw part of the india eurasia suture zone thus allowing better constraints on the major steps of this evolution the partly synchronous closures by n dipping subduction of the two tethys branches which are assumed to have encircled the kohistan arc in upper mesozoic times may have generated both the karakorum and the kohistan intrusives of cretaceous and palaeogene ages the northern branch very likely closed before the southern one at the time of the second intrusive stage palaeogene a kohistan and karakorum had already collided were welded and had suffered the same major tectonometamorphic event b subduction of the southern tethys floor beneath the welded kohistan karakorum was still active c however collision between india and kohistan karakorum may have already begun particularly at the level of the nanga parbat promontory finally it is emphasized that the intrusive processes continued in the karakorum long after the collision e g baltoro granite

a review of permian stratigraphy palaeobiogeography and palaeogeography of the qinghai tibet plateau the permian marine lithostratigraphy biostratigraphy and faunal compositions among all the major tectonic blocks in the qinghai tibet plateau are synthesised based on published literature authors unpublished data and field observations palaeobiogeographically the permian marine faunas in the qinghai tibet plateau can be assigned to four biotic provinces cathaysian indoralian cimmerian and himalayan provinces as well as a broad south transitional zone for parts of the permian the qamdo block clearly belongs to the cathaysian province as it is characterised by a lack of glacial deposits and a dominance of warm water faunas during the whole permian the qiangtang block lhasa block and the himalaya tethys zone in southern tibet can be grouped into the south transitional zone during the cisuralian which is characterised by the combination of the bivalve eurydesma the brachiopods cimmeriella bandoproductus and the fusuline monodiexodina the south transitional zone gave birth to the cimmerian province as shown in the qiangtang and lhasa blocks from roadian to capitanian during which its faunas were characterised by an admixture of cold and warm water elements supplemented by a limited number of endemic taxa such as the fusuline eopolydiexodina the non fusuline foraminifer shanita hemigordiopsis assemblage and the coral thomasiphyllum the formation and development of the south transitional zone and the cimmerian province is interpreted to be closely linked to and driven by the northward drift of the cimmerian continent superimposed with a gradual global warming in the wake of gondwanan deglaciation the consequently combined effects of these events forced the climate of the drifting peri gondwana blocks to ameliorate and its marine faunas to transform from an essentially cold water gondwanan type in the early cisuralian through a transitional stage to a predominantly warm water cathaysian type by the lopingian the himayala tethys zone in southern tibet is assigned to the himalayan province from late guadalupian to lopingian and identified by persistent occurrences and dominance of cold water brachiopods and corals both the permian sedimentary sequences and faunal successions are strongly different between the qamdo block and the qiangtang block this is taken to suggest that the longmu co shuanghu lancangjiang suture between the two blocks most likely represents the main branch of the palaeotethys suture in tibet a comparison and correlation of permian sequences and faunas between tibetan blocks and adjacent blocks in western yunnan indicates that the qiangtang block should be aligned with the baoshan block whereas the lhasa block more closely related to the tengchong block further comparison and correlations of permian stratigraphy and faunas of all major peri gondwana blocks suggest that they probably constituted three different continental slices rather than one as perceived in some previous literature the first slice is composed of central pamir the qiangtang block and the baoshan block the second slice consists of south pamir karakorum south afghanistan central iran and turkey these two continental slices are both characterised by a continuously active rifting event from artinskian to guadalupian by contrast the third slice is interpreted to consist of the lhasa block the tengchong block and the sibumasu block none of which has late cisuralian rift related basalts the baoshan block and the lhasa block are thought to have initially early cisuralian intersected probably at a triple junction point close to western australia and were then rifted off from gondwana at different times during the permian

35 ma old ultrahigh pressure metamorphism and evidence for very rapid exhumation in the dora maira massif western alps abstract ion microprobe shrimp data on zircons from various rock types of an ultrahigh pressure uhp metamorphic whiteschist type pyrope quartzite lens of the dora maira massif dmm consistently show domains giving a late eocene age of 35 4 1 0 ma which is taken as the age of uhp metamorphism these domains partially replace the older oscillatory zoning pattern of the zircons formed during primary magmatic crystallization at about 275 ma zircons of a metagranitic country rock next to the uhp metamorphic lens have these primary features best preserved all zircons measured also yield intermediate ages between 275 and 35 ma with a statistical concentration between 260 and 210 ma thus the uniformity of the initial zircon population both in the lens and the country rock evidences a common protolith that is a granite intruded during the late herynian while the intermediate ages are at least partly due to incomplete resetting of the zircons during uhp metamorphism those in the 260 210 ma range may be related to rifting episodes in the permotriassic the mg rich chemistry of the whiteschist lenses is due to local metasomatic alterations of the granite perhaps by fluids derived from evaporitic sediments dating as early as the permotriassic as well the more pervasive resetting of zircon ages during uhp metamorphism in the pyrope quartzite lenses is explained by the ubiquity of fluids and or melts produced during subduction by a series of dehydration reactions that occurred only in the more hydrous mg rich protoliths and not in their drier granitic neighborhood fission track ages determined partly on the same zircon samples yielding 29 9 1 4 ma mark the time when the uhpm unit had reached about 290 c at a shallow location within the crust thus exhumation over a vertical distance of about 120 km must have occurred within about 5 6 ma indicating an average uplift rate of about 20 24 km ma and an average cooling rate of about 85 100 c ma the radiometric data obtained do not lend any support to an eo alpine cretaceous subduction event so that deep subduction and immediately following exhumation all took place during early to mid tertiary time this scenario seems to apply to large portions of the western and central alps as well calling for drastic geodynamic reinterpretations of these parts of the alps

pb sr nd isotopic behavior of deeply subducted crustal rocks from the dora maira massif western alps italy ii what is the age of the ultrahigh pressure metamorphism pb nd and sr isotope data are reported from two localities on mineral separates from mg rich metapelites and associated rocks that have been subducted to depths of at least 100 km for which metamorphic conditions are estimated at 28 33 kilobars pressure and 700 800 c and then returned to the surface initial isotope ratio data from the granitoid country rock are similar to those found in the metapelites the initial ratios indicate predominantly recycled aged granitic crustal materials for the sources of all of the samples five zircon samples 4 from pyrope megacrysts and 1 from fine grained pyrope quartzite lenses in the metapelites accurately define a chord yielding intercept ages of 304 10 and 38 0 1 4 ma in a concordia diagram zircon from the country rock also plots along the chord the zircon data together with initial nd and sr data indicate that the sedimentary sources of the rocks were derived mainly or entirely from sialic hercynian rocks ellenbergerite from pyrope megacrysts and monazite from the fine grained ground mass yield slightly younger ages of 30 34 ma apparently reflecting lower blocking temperatures than that of zircon sm nd data from a pyrope megacryst give an errorchron corresponding to an age of 38 ma in agreement with the zircon date a major question concerns the timing of the ultrahigh pressure metamorphism experimental data suggest that pyrope and quartz coesite as well as ellenbergerite formed by various metamorphic reactions if as generally assumed the ultrahigh pressure metamorphism occurred ca 100 ma ago our data require that the zircon did not experience measurable lead loss at that time but lost major amounts of lead 38 ma ago during late alpine metamorphism estimates of diffusion rates for nd in pyrope further suggest that the apparent sm nd age of 38 ma for the megacryst is not consistent with that model those problems are resolved if the ultrahigh pressure metamorphism occurred 38 40 ma ago but problems remain from ar ar dates of 100 ma on phengite an inferred 120 ma age for zircon lead loss from another study and possibly by the very rapid uplift required if the metamorphism is that young

rift related sedimentation and volcanism of the north indian margin inferred from a permian triassic exotic block at lamayuru indus suture zone ladakh himalaya and regional comparisons abstract stratigraphical petrographical and geochemical work on an important limestone exotic within the indus suture zone near lamayuru reveals the following history of events i late permian deposition on a shallow water carbonate platform open to the neotethys ocean ii late permian early triassic break up tilting fissuring and subsidence iii early triassic mantling by ammonite bearing pink pelagic carbonate and chlorite rich volcaniclastic sediment iv deposition of fe mn and or mn rich oxide sediments as crusts and fissure fills the metal rich oxides were precipitated from hydrothermal solutions related to nearby volcanism v late triassic eruption of pillowed and massive basalts of within plate type on an irregular seafloor taking account of evidence from similar exotic units associated with upper cretaceous melange beneath the spontang ophiolite further south in the zanskar mountains e g photoskar unit the lamayuru exotic is interpreted as part of a small carbonate platform formed somewhere between the zanskar lamayuru passive continental margin and a permian triassic neotethyan spreading axis to the north the carbonates probably capped a volcanic seamount that later collapsed and was covered by pelagic sediments and basic extrusives the lamayuru exotic was later detached from its igneous basement and tectonically emplaced probably in the latest cretaceous and was also influenced by early tertiary suturing of neotethys and mid late tertiary backthrusting

ellenbergerite a new high pressure mg al ti zr silicate with a novel structure based on face sharing octahedra ellenbergerite occurs as purple millimetre size grains associated with talc kyanite clinochlore rutile and zircon in composite inclusions within decimetre large pyrope crystals 90 98 mole percent end member in the quartzite layer of the dora maira massif western alps from which coesite has been recently reported chopin 1984 it is hexagonal a 12 255 8 c 4 932 4 a z 1 space group p63 mohs hardness 6 5 dmes 3 15 dcal 3 10 no cleavage uniaxial negative and vividly pleochroic colourless e colourless to deep lilac with colour zoning the intensely coloured variety has 1 6789 5 e 1 670 1 microprobe analysis yields sio2 39 1 p2o5 0 45 al2o3 25 1 tio2 4 0 mgo 22 2 feo 0 20 sum 99 05 wt including h2o 8 0 coulometrically the formula calculated on a o28 oh 10 basis implying 7 5 wt h2o is mg6 71 fe0 03 ti0 61 al6 00 si7 92 p0 08 o28 oh 10 the colour zoning is due to nearly complete ti zr substitution in addition ellenbergerite may contain more than 8 wt p2o5 with strictly correlated changes of si mg al and ti zr contents over 80 of which represent the sial pmg substitution

sedimentology palaeoecology and palaeoenvironmental evolution of the 1985 lhasa to golmud geotraverse vertical and horizontal measurements of almost 30 km of sections were made along the geotraverse route at 113 localities ranging in age from ordovician to tertiary over 280 palaeocurrent measurements were taken and 200 thin sections were studied ordovician strata occur only in the kunlun terrane w here thick metamorphosed sequences of elastics and carbonates occur these are tentatively interpreted as platform margin and slope deposits during carboniferous times in the kunlun terrane transgressive late dinantian marine limestones with tropical to subtropical eurasian reefoidal faunas overlie fluviatile redbeds derived from an unroofed orogenic belt the lhasa terrane contains shelf basin elastics with low diversity faunas succeeded by thick late carboniferous early permian glacio marine mixtites deposited by iceberg meltout permian carbonate ramp and shelf facies with reefoidal developments occur over both the lhasa and qiangtang terranes with coal bearing elastics and fluviatile redbeds also occurring in the latter

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

magmatic expression of tectonic transition from oceanic subduction to continental collision insights from the middle triassic rhyolites of the north qiangtang block abstract the tectonic transition from subduction to collision is a fundamental process during orogenesis yet the magmatic expression of this transition and related deep geodynamic processes remain unclear this study focuses on a newly identified volcanic belt within the moyun zaduo sulu area of the north qiangtang block and presents new zircon u pb data that indicate that this belt formed during the middle triassic 247 241 ma a time characterized by a regional transition from subduction to collisional tectonism the volcanic belt is located to the south of a permian to early triassic arc and is dominated by high k calc alkaline and peraluminous rhyolites these rhyolites have low mg nb ta and eu values contain low contents of sr have high rb sr and whole rock end t values and show positive zircon ehf t values all of which suggest that they formed from magmas generated by the dehydration melting of juvenile crustal material the migration of middle triassic volcanism in this region was most likely caused by rollback of the subducting longmucuo shuanghu tethyan oceanic slab combining our new data with previously published results of numerical modeling of subduction collisional processes and regional data from north central tibet yields insights into the magmatic expressions and related deep geodynamics of the transition from oceanic subduction to continental collision this combination of data also suggests that variations in oxygen fugacity can be used as a proxy for the discrimination of magmatism related to subduction the transition from subduction to collision and collisional tectonism