primary platinum mineralization in the nizhny tagil and kachkanar ultramafic complexes urals russia a genetic model for pge concentration in chromite rich zones the nizhny tagil uralian alaskan type ultramafic complex is composed of a dunite core with a rim of wehrlite and pyroxenite the dunite unit which has a uniform mineral composition olivine fo 89 8 92 1 avg 0 25 wt cao represents an accumulation of olivine and minor chromite from a mafic magma in an open system magma chamber after solidification of the dunite differentiation began with the formation of the wehrlite olivine fo 77 9 88 8 and pyroxenite corresponding to the closure of the magmatic system two main types of chromitite occurrence are observed in the dunite body small 100 5 cm scattered schlieren of chromite crystals within the ultramafic unit and much larger up to 100 5 m concentrations the chromite composition in both types is similar and uniform cr cr al fe 3 66 02 mg mg fe 2 49 05 and cr cr al fe 3 69 14 mg mg fe 2 49 81 respectively the larger concentrations of chromite include brecciated and net textured ore or massive veins that reflect the dynamic accumulation of chromite crystals in cavities along magma conduits inside the dunite body these cavities are analogous to small magma chambers within the consolidated part of the dunite body and similar to podiform chromitites in ophiolites were created by continuous feeding of magma to the system the platinum group element pge content of the chromite free facies of the dunite is relatively low pt being the only significant pge typically between 0 3 35 ppb but as much as 98 ppb in one sample in contrast both types of chromite occurrence are enriched in pge two pge mineralizing episodes are distinguished an ir ru rh os rich pt pd poor episode in which the platinum group minerals pgm are mainly ir alloys and a pt pd rich episode in which the pgm are mainly pt alloys i e pt 2 fe ni cu ptfeni 2 and tetraferroplatinum and tulameenite like compositions along with rare hollingworthite and an unidentified rhnias mineral the primary pgm have been affected locally by a serpentinization related low temperature alteration that is characterized by addition of copper with alteration to complex pt fe ni cu alloys of varied stoichiometry including tulameenite and platinian copper placer concentrations derived from the nizhny tagil complex have a slightly different assemblage of pgm with abundant isoferroplatinum the presence of gold commonly aggregating the pgm and unusual au sn and au pb alloys the kachkanar complex situated 120 km north of the nizhny tagil complex has essentially the same characteristics apart from a slightly different composition of the ultramafic cumulates suggesting that they were derived from a magma of different composition the pgm distribution also differs in that it contains more abundant isoferroplatinum than other pgm the high pt concentrations are the result of the affinity of platinum minerals for chromite and the mode of chromite deposit formation in the cavities in which chromite crystallized pgm tended to be incorporated in chromite or remained attached to chromite crystals to explain the very high concentrations of chromite associated pgm we define a cr factor which is the ratio of the mass of silicate magma to the mass of chromite in contact with the ascending magma where the cr is high i e a relatively low proportion of chromite in contact with a large amount of magma crystallizing the pt minerals the efficiency of the mechanical collection of pt minerals is at a maximum and the pt concentration i e amount of pt minerals will be high possible variations due to the collection of pge by a sulfide liquid have not been established a model is proposed whereby the observed chromite and associated pt mineralization can result from the normal magmatic evolution of the complex provided that a structural hydrodynamic trap is available to concentrate the chromite

how many oceans meliata vardar and pindos oceans in mesozoic alpine paleogeography the timing of rifting and subduction in the meliata vardar and pindos zones of the hellenic dinaric carpathian region indicates that they cannot be considered remnants of a single ocean basin in contrast to several recently published mesozoic paleogeographies sea floor spreading in the meliata zone culminated in middle triassic ladinian time and ceased in the late triassic and subduction occurred from this time until late jurassic closure in contrast sea floor spreading in the vardar zone began in early jurassic time and culminated in the middle jurassic and subduction occurred from latest jurassic time in the pindos zone sea floor spreading was initiated in the early triassic with late jurassic and early tertiary subduction

observation of coherent echoes with narrow spectra near 150 km altitude during daytime away from the dip equator 1 we present the rare observation of backscatter echoes perpendicular to the geomagnetic field from the 150 km altitude vicinity over a region situated away from the dip equator namely at gadanki 13 5 n 79 2 e 6 4 dip latitude a layer of weak echoes having signal to noise ratio snr of the order of 12 to 3 db was seen drifting downward from 157 km at 0930 lt to about 148 km at 1028 lt on july 12 1997 the doppler velocity as well as doppler width was in the range 10 20 ms 1 while there was no quasi periodicity as such in terms of echo occurrence the echo properties were in other respects very similar to 150 km echoes seen in equatorial regions this included the descending phase with time during the morning hours these constitute the first observations of daytime 150 km echoes away from the dip equator and only add to the mystery regarding the origin of these structures

petrology of the motaghairat mafic ultramafic complex eastern desert egypt a high mg post collisional extension related layered intrusion abstract the geodynamic settings of the precambrian mafic ultramafic complexes in the eastern desert of egypt have important bearing on understanding the geotectonic evolution of the arabian nubian shield we present a detailed petrological study on a layered mafic ultramafic intrusion that is located at the contact between the precambrian continental crust and the miocene red sea oceanic crust the motaghairat layered intrusion consists of basal lherzolite orthopyroxenite troctolite olivine gabbro and anorthosite on the top variations in modal mineralogy and mineral chemistry along with the chemical composition of these units suggest their derivation from a common high mg tholeiitic parent melt through fractional crystallization processes the parental magma was derived from a metasomatised mantle source the primitive mantle normalized patterns of the calculated melts exhibit enrichment in u relative to th and ba relative lree which indicate that the enriched lithospheric mantle source was metasomatised by fluids derived from a subducted oceanic crust rather than by a sediment melt geological and petrological evidences suggest that the layered motaghairat intrusion was emplaced during post orogenic extension following subduction break off and lithospheric delamination after the collision between the amalgamated island arc terranes and the saharan metacraton the heat source required to melt the metasomatised lithospheric mantle was derived from the upwelling of hot asthenosphere after the subduction break off

upper cenomanian lower turonian sea level rise and its consequences on the adriatic dinaric carbonate platform the adriatic carbonate platform existed throughout most of the mesozoic as an isolated intraoceanic carbonate platform it is characterized by what has been traditionally labelled a continuous shallow marine carbonate sedimentation without terrigenous influences however global sea level changes left unequivocal imprints in the continuous carbonate record thus proving that the carbonate platform sensitively responded to sea level fluctuations this paper focuses on the relatively short cenomanian turonian drowning event which temporarily submerged the platform below the euphotic zone and which is related here to the well known global cenomanian turonian sea level highstand this drowning episode is characterized by the abrupt disappearance of numerous shallow water benthic invertebrate taxa and by an abundant occurrence of planktonic organisms including calcispheres and primitive planktonic foraminifera near the middle of the turonian the platform regime was re established correlating with the global fall in sea level the situation is different only at the south west margin of the platform where pelagic sedimentation initiated near the end of the cenomanian continues into the santonian and probably marks the adriatic trough the drowning began earlier in the middle cenomanian in those areas nearer to the north east margin of the platform the area of what is today central croatia and then progressed gradually towards the more interior areas of the platform the middle dalmatian islands which were drowned near the end of the cenomanian

geodynamic evolution of the northern dinarides and the southern part of the pannonian basin abstract most of the recent geodynamic interpretations of the pannonian basin focus on its relation to the formation of the carpathians and the alpine orogeny however also the dinarides were severely affected by neogene tectonics related to the formation of the pannonian basin especially in the northernmost dinarides neogene deformation played a very important role in the evolution of this mountain chain geological records clearly show evidence of two phases of plate convergence along the northern and eastern margins of the present day dinarides at the end of the jurassic the dinaridic parts of the tethys ophiolites were obducted onto the northeastern margins of the apulian microplate the second phase is documented in the central part of the northernmost dinarides it is genetically related to an ancient volcanic arc as indicated by late cretaceous palaeogene trench sediments with blueschist olistolithes which are interlayered by basalt rhyolites pyroclastics medium pressure metamorphosed trench sediments and associated synkinematic granitoids in the northern part of the dinarides subduction processes terminated with the eocene compressional event which caused the uplift of the dinarides numerous intramontane basins with shallow marine fluviatile and lacustrine deposits were generated during the oligocene penecontemporaneous andesites which are found along the drava and sava depressions of the south pannonian neogene basin can be correlated with the easternmost periadriatic tonalites however observations do not indicate strike slip faulting at that time in this area the neogene rift stage initiated the evolution of the pannonian basin it is marked by extruded submarine trachyandesites of karpathian age badenian basalts andesites dacites and rhyolites and pannonian alkali basalts which are interlayered by coeval sedimentary rocks main evidence for the large scale tectonic transport of large dinaridic blocks into the pannonian basin area are the periadriatic sava and zagreb zemplen fault systems and subparallel faults the late sarmatian global sea level drop which coincided with a compressional phase is regionally marked by an unconformity throughout the pannonian basin as reported by horvath horvath f 1995 phases of compression during the evolution of the pannonian basin and its bearing on hydrocarbon exploration mar pet geol 12 8 837 844 due to thermal subsidence during the pliocene more than 2000 m of lacustrine freshwater sediments were deposited in the south pannonian basin the pliocene compression phase can be observed in the transdanubian zone and also south of the mura and drava rivers by south and southwest dipping reverse fault systems

using melt inclusions to determine parent magma compositions of layered intrusions application to the greenhills complex new zealand a platinum group minerals bearing island arc intrusion the permian greenhills complex of southland new zealand is a small ultramafic to mafic layered intrusion that hosts primary magmatic platinum group minerals pgms as inclusions in cumulus chromian spinel grains we have determined the major and trace element chemistry of the parent magmas of the complex using the composition of rehomogenized melt inclusions trapped in cumulus spinel grains from dunite these melt inclusions have compositions similar to those of primitive ankaramite dikes that cut the complex verifying that our data are representative of the parent melt chemistry these magmas have high mgo and cao and are enriched in pb sr and large ion lithophile elements compared to high field strength and rare earth elements we suggest that the parent magmas to the complex were primitive low k island arc tholeiite basalts that formed by high degrees of melting of a spinel peridotite source the platinum group element contents of such magmas are expected to be very high therefore the primary pgms at greenhills are suggested to have precipitated directly from the melt following differentiation and cooling in a shallow magma chamber

high resolution observations of 150 km echoes at jicamarca high resolution soundings of equatorial upper e region echoes at jicamarca exhibit gravity wave modulated signal intensity distributions and doppler velocities corresponding to vertical plasma drifts a gravity wave wind driven interchange instability is suggested as a possible generation mechanism of the field aligned plasma irregularities responsible for the echoes the echoes may be utilized in gravity wave studies and in zonal electric field measurements by radars with modest sensitivities

geological constraints on the alpine evolution of the mediterranean tethys abstract the geological data on the mediterranean chains and basins are used to point out the constraints that they put on the location through time of oceanic versus continental lithosphere and on the successive relations between them emphasis is put on the rules and conventions which enable us to interpret the geological data in terms of plate tectonics and on the major disputed points for which a solution must be chosen in the first part the location of oceanic versus continental lithosphere is dealt with using the data on the present day basins the ophiolites and the subduction processes a neogene age is retained for the western mediterranean and the surrounding continental blocks are considered to have been previously a part of iberia a cretaceous age is retained for the eastern mediterranean apulia is considered as a part of the african plate except for this period the black sea is considered as a back arc basin formed mostly during the upper cretaceous the ophiolites are used to locate the mesozoic oceans for the double ophiolitic belts of the dinaro hellenides and the taurides the tectonic interpretations which minimise the number of oceanic basins have been retained for the kirsehir block of turkey the chosen solution locates a jurassic ocean to the north and makes it disappear when a cretaceous ocean opens to the south data on the subduction processes added to the information on these basins and led us to consider as oceanic the unknown basements of the carpathian flysch and the maghrebian flysch basins the second part deals with the organisation of basins and platforms emphasising the chronology of their formation and subsequent crushing it furnished step by step constraints on the tectonic history of the system which is related to plate displacement the general pattern derived from these data shows a wedge shaped tethyan ocean which disappeared mostly through repeated subduction below the eastern part of its northern margin the jurassic stage shows westward extension of the ocean between the eurasian and african plates and ends with the dinaro hellenic obduction the cretaceous stage shows a complete reorganisation including individual displacement of the iberian apulian and kirsehir sub plates the tertiary stage shows the general collision between the renewed eurasian and african plates and neogene subduction of the basins which avoided collision

the ferguson lake deposit an example of ni cu co pge mineralization emplaced in a back arc basin setting the world s largest ni cu platinum group element pge deposits are dominantly hosted by ultramafic rocks within continental extensional settings e g raglan voisey s bay resulting in a focus

triassic magmatism of the dinarides in yugoslavia abstract the triassic magmatism of the dinarides had a polyphase character it took place during a period of about 50 ma during the initial stages of the mesozoic wilson cycle their earliest phases might have been connected with rifting processes and the subsequent ones preceeded directly the opening of the dinaridic part of the tethys and the formation of a spreading ridge the triassic magmatism is represented by basic and more commonly by intermediate and acid plutonic and volcanic rocks with calc alkaline affinity the triassic magmatic rock association can be correlated on major element evidence with calc alkaline rocks of recent convergent plate margins however field relationships and the data on immobile trace elements indicate that lavas poured out over triassic sediments on a carbonate platform which was underlain by rocks of the continental crust the basic diversity of the triassic magmatism of the dinarides was influenced by partial melting other processes crystallization contamination and others must have played a secondary role

tearing and breaking off of subducted slabs as the result of collision of the panama arc indenter with northwestern south america we present two regional lithospheric cross sections that illustrate eastward and southeastward dipping subducted slabs to depths of 315 km beneath the surface of colombia in northwestern south america these cross sectional interpretations are based on relocated earthquake hypocentral solutions models supported on gravity and magnetic regional data and coda q q c tomography the method of tomographic imaging based on spatial inversion of the coda wave has advantages of providing information on the lateral variations of the anelastic properties and thermal structure of the lithospheric system mapping of earthquake defined benioff zones combined with tomographic imaging reveals the presence of an 240 km long east west striking slab tear named here the caldas tear the proposed caldas tear separates a zone of shallow 20 30 dipping southeastward subduction in the area of colombia adjacent to panama and the caribbean sea which is not associated with subduction related volcanism from an area of steeper 30 40 dipping slab adjacent to the eastern pacific ocean that is associated with an active north south chain of active arc volcanoes we propose that the caldas slab tear separating these two distinct subducted slabs originally formed as the southern boundary of the panama indenter an extinct island arc that began subducting beneath northwestern south america about 12 ma the area south of the panama indenter is miocene oceanic crust of the nazca plate which subducts eastward beneath northwestern south america at normal angles and melts to form a north south trending active volcanic arc in addition to the formation of the caldas tear we propose that impedance of the thicker crustal area of the panama arc indenter over the past 12 ma may have led to down dip break off of previously subducted oceanic crust that is marked by an extremely concentrated and active earthquake swarm of intermediate depth earthquakes beneath east central colombia

geodynamic evolution of the central dinarides abstract the central part of the dinarides unlike the northwestern and southeastern dinarides shows a consistent pattern in the distribution of the large tectonostratigraphic units from southwest apulia to northeast the following five main units originating in different parts of the mesozoic tethys can be distinguished 1 adriatic dinaridic carbonate platform formations 2 carbonate clastic units flysch bosniaque of the passive continental margin 3 ophiolite bearing formations of the dinaridic ophiolite zone also containing radiolarites greywackes and shales including melange formations and overstepped late jurassic to cretaceous cover sequences 4 active continental margin units represented by upper cretaceous palaeogene trench sediments with blueschists tectonized ophiolite melange alpine medium pressure metamorphic rocks originated from upper cretaceous palaeogene sediments and alpine synkinematic granitoids 5 a nappe consisting of allochthonous palaeozoic triassic formations which is thrust onto the ophiolites and genetically related sedimentary formations the frontal parts of this nappe directly overlie the northeastern margin of the adriatic dinaridic carbonate platform i e the external dinarides the evolution of the central dinarides was controlled by a sequence of tectonic events which took place within the alpine cycle 1 rifting processes lasting some 40 50 ma which started in the late permian and ended in the norian 2 opening of the oceanic dinaridic tethys commenced in the late triassic and persisted for some 70 80 ma until the end of the jurassic 3 subduction processes and emplacement of ophiolites started in late jurassic early cretaceous times during the closing phase of the dinaridic ocean or dinaridic tethys the palaeozoic triassic nappe was emplaced on the ophiolites the thrusting was accompanied by alpine metamorphism 120 100 ma 4 the main alpine deformational event and medium pressure metamorphism with synkinematic granite plutonism took place in late eocene early oligocene times when the ophiolite and palaeozoic triassic nappes were emplaced on the adriatic dinaridic carbonate platform which at the same time was deformed resulting in the development of the external dinarides fold and thrust belt

silver base metal epithermal vein and listwaenite types of deposit crnac rogozna mts kosovo part i ore mineral geochemistry and sulfur isotope study abstract pb zn ag vein and listwaenite types of mineralization in crnac deposit western vardar zone were deposited within several stages i the pre ore stage comprises pyrite arsenopyrite pyrrhotite quartz kaolinite and is followed by magnetite pyrite ii the syn ore stage is composed of galena sphalerite tetrahedrite and stefanite and iii the post ore stage is composed of carbonates pyrite arsenopyrite and minor galena the vein type mineralization is hosted by jurassic amphibolites and veins terminate within overlying serpentinites mineralized listwaenites are developed along the serpentinite amphibolite interface the reserves are estimated to 1 7 mt of ore containing in average 7 6 lead 2 9 zinc and 102 g t silver sulfides from the pre and syn mineralization assemblage of the vein and listwaenite types of mineralization from the crnac pb zn ag deposit have been analyzed using microprobe crush leachates and sulfur isotopes the pre ore assemblage precipitated under high sulfur fugacities f s 2 10 8 10 6 bar from temperatures ranging between 350 c and 380 c most likely water rock reactions boiling and or increase of ph caused an increase of 34 s of pyrite toward upper levels within the deposit the decomposition of pre ore pyrrhotite to a pyrite magnetite mixture occurred at a fugacity of sulfur from f s 2 8 7 10 10 to 9 6 10 9 bar and fugacity of oxygen from f o 2 2 4 10 30 to 3 1 10 28 bars indicating a contribution of an oxidizing fluid i e meteoric water during pre ore stages of hydrothermal activity the crystallization temperatures obtained by the sphalerite galena isotope geothermometer range from 230 to 310 c the 34 s values of pre and syn ore sulfides pyrite galena sphalerite 34 s 0 3 5 9 point to magmatic sulfur values of 34 s of galena and sphalerite are decreasing upwards due to precipitation of early formed sulfide minerals post ore assemblage precipitated at temperature below 190 c based on data presented above we assume two fluid sources i a magmatic source supported by sulfur isotopic compositions within pre and syn ore minerals and a high mol of fluorine found within pre and syn ore leachates and ii a meteoric source deduced by coincident pyrite magnetite intergrowth sulfur isotopic trends within syn ore minerals and decrease of crystallization temperatures from the pre ore stage 380 350 c towards the syn ore 310 215 c and post ore stages

on a summer maximum in the occurrence frequency of 150 km f1 radar echoes over pohnpei 1 using three and a half years of 50 mhz radar data collected from pohnpei federated states of micronesia 6 96 n 158 19 e geographic 0 3 magnetic dip latitude we show for the first time that the occurrence frequency of 150 km or f1 echoes has a broad but conspicuous maximum during northern summer in this longitude sector with minimal activity in other months given a seasonal similarity to sporadic e es we suggest that an es layer instability cosgrove and tsunoda 2002 generates a polarization electric field which maps along geomagnetic field lines to the f1 region there forms thin plasma sheets that provide gradients to excite 3 m scale plasma waves via an interchange process

first vhf radar observations of tropical latitude e region field aligned irregularities indian mst radar at gadanki 13 5 n 79 2 e 12 5 dip was operated during july august 1994 to observe the 3 m scale size field aligned irregularities associated with the lower e region irregularity structure was studied by using height time variation of the echo intensity and weighted mean doppler velocity in this paper results of three diurnal cycles of observation are presented field perpendicular echoes were observed both during daytime and nighttime a layered irregularity structure extending down to altitude below 86 km was seen during the nighttime the daytime structure showed a narrow echoing region with significant downward slope doppler velocity was in the range of 20 50 ms 1 both during day and night and was in general consistent with the slope of scattering structure observed in the height time intensity plots

further investigations on 150 km echoing riddle using simultaneous observations of 150 km and e region echoes from off electrojet location gadanki 1 in this paper we present a detailed study of the off electrojet daytime 150 km echoes based on simultaneous observations of daytime 150 km and e region echoes made on a few days per month during july 2005 to august 2006 using the gadanki radar daytime 150 km echoes are found to occur in all seasons over gadanki although echo occurrence is found to be maximum in equinoxes and minimum in summer no clear seasonal preference over gadanki has been observed in contrast e region echo occurrence made simultaneously shows a strong seasonal dependence with remarkably low occurrence in winter as compared to other seasons interestingly the 150 km echoes show a distinctly different morphology in winter as compared to other seasons echoes are observed in two distinct height regions in winter as compared to one broad region in other seasons also the strongest echo and the lowest altitude of echo occurrence are found to be associated with winter further a significant share of doppler velocities is found to be downward in winter as compared to predominantly upward velocities observed in other seasons no seasonal dependence in the spectral width of 150 km echoes however has been observed seasonally averaged doppler velocities are quite similar to those of the f region drifts reported from jicamarca again seasonally averaged drifts are found to be downward in winter afternoon as compared to upward velocities observed in other seasons notwithstanding the seasonal differences observed in the 150 km echoes echo occurrence is found to have a common feature of strong forenoon afternoon asymmetry with forenoon occurrence being greater these observations are discussed in the light of present understanding on the daytime 150 km echoing phenomenon

platinum group elements as petrological indicators in mafic ultramafic complexes of the central and southern urals preliminary results abstract platinum group elements pge and gold were analyzed by icp ms after the ni sulphide fire assay pre concentration step in 44 rocks from 5 orogenic mafic ultramafic massifs of the central and southern urals they comprise a ring zoned ural alaskan type bodies of the pt bearing belt kachkanar tagil uktus and b lherzolite harzburgite complexes overlain by layered wehrlite gabbro and diorite nurali mindyak supposed to be ophiolite type suites total pge and au contents are generally higher in ural alaskan type complexes compared with lherzolite harzburgite complexes mantle normalized pge patterns range from nearly unfractionated in the dunites pd ir 0 57 3 68 to mildly and strongly fractionated in wehrlite clinopyroxenite and gabbro pd ir 9 1 187 exceptionally high values of pd ir 761 2622 are observed in amphibole rich lithologies at kachkanar possibly indicating a relationship between fractionation of the less refractory pd and increased fluid activity in the parental magma pronounced positive pt anomalies up to 20 times the mantle estimate distinguishes the ural alaskan type dunites and progressively reduces in pyroxenites and gabbros in the lherzolite harzburgite complexes of mindyak and nurali layered wehrlites and pyroxenites as well as rocks from the gabbro diorite units have fractionated pge patterns pd ir 2 94 92 39 and positive pt anomaly as in the ural alaskan complexes conversely the pt anomaly is negative in the peridotites and increases from lherzolites and harzburgites to dunites similarly to residual mantle from alpine type orogenic massifs the pd ir 0 71 3 7 is higher than in ophiolites and resembles that of lherzolite massifs of the western mediterranean representing sub continental mantle variation of the pt anomaly versus pd ir in ural alaskan type complexes and in the layered sequences overlaying lherzolite harzburgite mantle suites is consistent with magmatic fractionation in which pt behaves as a compatible element it reflects a progressive depletion by partial melting in mantle peridotites the pt becoming incompatible in the last stage of melting in which pt poor residual dunites are formed the positive pt anomaly in ural alaskan type complexes is striking and would appear as a distinctive feature of the parent magma probably inherited from its mantle source

enhanced velocities and a shear in daytime esq over kwajalein and their relationship to 150 km echoes over the dip equator we present the first evidence of enhanced irregularity drift velocities and a velocity shear in the daytime e region at 4 3 n dip latitude these features found in radar measurements from kwajalein during q type sporadic e esq events are interpreted in terms of a polarization electric field that develops in response to the presence of latitudinal gradients in field line integrated conductivity caused by sporadic e layers because the e region over kwajalein connects directly to 150 km altitude over the magnetic dip equator we suggest that a similar polarization process is responsible for the so called 150 km echoes that have been observed routinely by the jicamarca radar

radar observations of daytime 150 km echoes from outside the equatorial electrojet belt over gadanki 1 we present systematic observations of daytime 150 km echoes from gadanki 13 5 n 79 2 e 6 3 dip latitude the echoing region is confined to 142 162 km altitude and show forenoon descent and afternoon ascent displaying a necklace shape quite similar to that of the equatorial 150 km echoes signal to noise ratio velocity and spectral width are as high as 13 db above noise 5 to 35 m s 1 and 2 to15 m s 1 respectively the observed necklace shape is first of its kind from gadanki and the present observations have almost all characteristics of equatorial daytime 150 km echoes the gadanki radar observations hence provide first experimental evidence on the occurrence of daytime 150 km echoes outside the equatorial electrojet belt

equatorial 150 km irregularities observed at pohnpei first observations of meter scale equatorial 150 km plasma irregularities outside the american longitude sector are reported the observations conducted at pohnpei western pacific with a wind profiling st radar demonstrate the feasibility of making ionospheric electric field measurements with low cost instruments and also reveal a potentially important anisotropy in the angular distribution of 150 km vhf radar echoes

characteristics of 150 km echoes linked with solar eclipse and their implications to the echoing phenomenon 1 this paper presents a study based on gadanki radar observations of 150 km echoes made during the solar eclipse of 15 january 2010 that occurred during 1122 1515 ist radar echoes were observed only during 1150 1215 ist and 1344 1356 ist linked with the entry and recovery phases of the eclipse respectively the most striking observation found is the unusual ascending and descending features of the echoing regions observed during these two time periods although these echoes occurred at higher altitudes than those of control days snr and spectral width of these echoes are similar to those of the lower echoing region observed on the control days further doppler velocities suggest the presence of westward electric field unlike those of the control days concurrent ionosonde observations showed ascent and descent of the f1 layer very similar to those observed in the 150 km echoes these observations and related analysis suggest that the observed echoes were due to the combined action of the electron density gradients and the reduced recombination rate linked with the solar eclipse effect these observations are first of its kind and elucidate the role of density gradient and recombination rate in the 150 km echoing process

platinum group element geochemistry of intraplate basalts from the aleppo plateau nw syria early middle miocene intraplate basalts from the aleppo plateau nw syria have been analysed for their platinum group elements pges they contain extremely low pge abundances comparable with most alkali basalts such as those from hawaii and mid ocean ridge basalts the low abundances together with high pd ir pt ir ni ir cu pd y pt and cu zr are consistent with sulphide fractionation which likely occurred during partial melting and melt extraction within the mantle some of the basalts are too depleted in pges to be explained solely by partial melting of a primitive mantle like source such ultra low pge abundances however are possible if the source contains some mafic lithologies many of the basalts also exhibit suprachondritic pd pt ratios of up to an order of magnitude higher than primitive mantle and chondrite an increase too high to be attributable to fractionation of spinel and silicate minerals alone the elevated pd pt associated with a decrease in pt but not ir and ru are also inconsistent with removal of pt bearing pge minerals or alloys which should have concurrently lowered pt ir and ru in contrast melting of a metasomatized source comprising sulphides whose pt and to a lesser extent rh were selectively mobilized through interaction with silicate melts may provide an explanation

kilometric irregularities in the e and f regions of the daytime equatorial ionosphere observed by a high resolution hf radar during the international equatorial electrojet year high resolution vertical hf coherent radar experiments were performed in the ivory coast 9 24 62 n 5 37 38 w at frequencies in the range 1 8 mhz kilometric scale irregularities were observed in the e and f regions of the daytime equatorial ionosphere these irregularities constitute a large sporadic e layer within the altitude range 100 to 150 km larger than the width of the equatorial electrojet the higher part of this irregular region is detached in the morning and evening forming an intermediate region at 150 160 km these 150 km echoes overtakes the e region electrojet echoes at 100 120 km at noon the echolocation shows that the reflections arise from the vertical direction up to 150 km with a significant contribution of reflections from east west directions above 110 km the f1 region irregularities are characterized by time and height scales significantly larger than the e region irregularities scales as in the e region the f1 region reflections arise from the vertical and from east west directions when the reflection distance increases the variations of the doppler frequency versus the observation distance at several sounding frequencies are well explained by a horizontal motion of the irregular plasma flow both in the e and f regions with velocities of 100 m s and 130 m s respectively

neoarchean convergent margin ni cu mineralization axis lake and nickel king ni cu deposits in the south rae craton of the canadian shield abstract the southern portion of the rae craton in the canadian shield is host to multiple ca 2 63 ga ni cu rich metamorphosed mafic intrusions with noritic noritic anorthositic and pyroxenitic compositions including those hosting the undeveloped axis lake and nickel king deposits found in northern saskatchewan and southeast northwest territories in order to understand the setting of these intrusions and their concomitant mineralization we investigated their geochemical and isotopic characteristics mineralized intrusions at axis lake and nickel king are metamorphosed up to granulite facies with local partial melting the intrusions preserve whole rock major element geochemistry consistent with a sub alkaline basaltic composition e g sio2 46 54 wt tio2 the nd isotope values of the axis lake intrusion ndt2630 0 3 to 2 1 are more juvenile and closer to the depleted mantle value relative to those of the nickel king deposit ndt2630 2 4 to 0 4 this agrees with their also distinctive th yb and nb yb distributions suggesting oceanic and continental arc like settings respectively the axis lake and nickel king nd isotope compositions are indistinguishable from other arc like 2 61 to 2 58 ga mafic to felsic intrusions and volcanic rocks recognized in the rae craton and the neighboring chesterfield block the age spatial distribution and geochemistry of the studied intrusions coincide with the initial stages of a recently defined 2 63 2 60 ga continental arc the roots of which are found in the south rae craton our data indicate that neoarchean intrusions with an arc like geochemistry may be a significant exploration target in the rae craton this broadens possible host suites beyond the established paleoproterozoic rift related rocks most commonly considered as the prime target for ni cu pge mineralization

on the sheet like nature of 150 km f1 radar echoes 1 the so called 150 km or f1 echoes are shown to arise from field aligned irregularities fai that are embedded in a sheet like region using a 49 92 mhz radar on christmas island which has an antenna beam directed toward geographic east at a zenith angle of 29 5 high resolution doppler velocity variations within the radar scattering volume are used to infer that the sheet like region could have both tilt and curvature this finding is used to infer that plasma density n must be enhanced within the sheet like region and that fai could be generated by an interchange instability driven by a vertical electric field or a zonal neutral wind that acts on the horizontal component of the gradient in n how tilted sheet like structures could form in the f1 region is discussed

the role of subduction accretion processes in the tectonic evolution of the mesozoic tethys in serbia abstract ophiolitic rocks and melange occur in two belts in serbia to the northeast the vardar zone and to the southwest the dinaride ophiolite belt of the drina ivanjica belt which is interpreted as being a microcontinent rifted from apulia the tethys in the vardar zone has a long and complex palaeozoic early tertiary history that is still poorly understood ophiolitic rocks are known to have formed at least in the early late jurassic some of the extrusives apparently formed in a supra subduction zone setting based on immobile element geochemical evidence the mesozoic tethys in the vardar zone closed at least partly by the latest jurassic evidence from the apulian margin in the southwest and from the drina ivanjica belt further to the northeast shows that a small red sea type oceanic basin rifted in the late permian early triassic followed by spreading in the mid late triassic to early jurassic evidence from immobile trace elements shows that these extrusives are of mid ocean ridge and within plate type during the early late jurassic this southerly oceanic strand began to close creating melange as a classic subduction accretion complex morb and seamount type lavas channelised micaceous turbidites rare calciturbidites and large limestone masses capped by condensed successions were incorporated in the melange through tectonic processes many of these units originated at or near the southwestern margin of the drina ivanjica inferred microcontinent less deformed debris flows olistostromes reflect gravity reworking and or diapirism with accumulation mainly in perched basins above the subduction zone large overriding harzburgitic ophiolite thrust sheets may have developed in response to incipient spreading above a subduction zone dipping to the southwest these ophiolites were emplaced northeastwards complete with metamorphic soles in response to collision of the trench with the drina ivanjica belt southwest directed sliding of sediments into the foredeep took place prior to suturing in the tithonian and later transgression by clastic sediments

daytime 150 km echoes observed with the equatorial atmosphere radar in indonesia first results 1 results of the daytime 150 km echoes from 10 36 s magnetic latitude observed using the equatorial atmosphere radar ear which are first of its kind from magnetic southern hemisphere are presented the echoing region of 145 165 km shows forenoon descent and afternoon ascent with signal intensity modulation with time resembling a necklace and the doppler spectra are narrow which are quite similar to those reported earlier from other locations westward and upward southward irregularity drifts are found to be consistent with daytime background electric fields providing a tool to investigate low latitude daytime electrodynamics detectability of these echoes suggests the absence of strong latitudinal dependence in contrast to the earlier belief suggesting a possibility of their detection at mid latitudes also the echoes show zonal anisotropy that is opposite to that observed over pohnpei the implications of these observations are discussed in the light of present understanding of 150 km echoing phenomenon

eoalpine to neoalpine magmatic and metamorphic processes in the northwestern vardar zone the easternmost periadriatic zone and the southwestern pannonian basin abstract the occurrence of eoalpine neoalpine genetically different granitoids and penecontemporaneous volcanics are characteristic for the vardar zone these rocks are mostly associated with late cretaceous paleogene basinal sedimentary rocks underlain by ophiolites the late cretaceous paleogene rocks were progressively metamorphosed under mediumpressure conditions and intruded by synkinematic mesoalpine granitoids the high pressure blueschist metamorphism was related to a pre maastrichtian eoalpine metamorphic event eoalpine and mesoalpine magmatism and the related metamorphism of the vardar zone may have taken place along a magmatic arc i e the subduction zone the easternmost parts of the periadriatic zone are characterized only by oligocene granitoids accompanied by penecontemporaneous volcanic rocks here younger alpine metamorphic phases only overprint and mylonitize older pre alpine formations most of the mesoalpine granite plutonism both of the vardar zone and the easternmost area of the periadriatic zone was related to subsequent extension the southwestern and southern parts of the pannonian basin contain the products of four pulses of mesoalpine and neoalpine synsedimentary volcanic activity egerian eggenburgian ottnangian carpathian badenian and post badenian represented by predominant basalt andesites trachyandesites and trachydacites this post subduction volcanism was closely connected with the cyclic marine ingressions in the pannonian basin

drift and aspect sensitivity of scattering irregularities in the upper equatorial e region recent observations at jicamarca peru of vhf radio signals coherently scattered from the upper equatorial e region during midday hours show that the corresponding irregularities in the electron density distribution are aligned along the earth s magnetic field vertical electron drift velocities in the altitude region between 120 km and 170 km show spatial and temporal variations of as much as 30 these variations are attributed to small scale varying electric fields which are generated by the dynamo action of gravity waves in the neutral atmosphere

coupled crust mantle response to slab tearing bending and rollback along the dinaride hellenide orogen we integrate structural geophysical and geodetic studies showing that the dinarides hellenides orogen along the adria europe plate boundary in the western balkan peninsula has experienced clockwise oroclinal bending since eocene oligocene time rotation of the hellenic segment of this orogen has accelerated since the middle miocene and is associated with a north to south increase in shortening along the orogenic front within the paleogene nappe pile bending was accommodated by orogen parallel extension clockwise block rotation and thrusting in the hanging wall of the skhoder peja normal fault spnf the spnf and related faults cut the older skhoder peja transfer zone with its pre neogene dextral offset of the west vardar ophiolite nappe rotation of the spnf hanging wall involved miocene to recent out of sequence thrusting that was transferred to the hellenic orogenic front via lateral ramps on dextral transfer zones along strike of the dinarides hellenides and coincident with the southward increase in neogene shortening the depth of the adriatic slab increases from 160 km north of the spnf to 200 km just to the south thereof to several hundreds of kilometers to the south of the kefalonia transfer zone the geodynamic driver of tectonics since the early miocene has been enhanced rollback of the hellenic segment of the adriatic slab in the aftermath of eocene oligocene slab tearing and breakoff beneath the dinarides which focused slab pull in the south the sw retreating hellenic slab segment induced clockwise bending of the southern dinarides and northern hellenides including their adriatic foreland about a rotation pole in the vicinity of the mid adriatic ridge

geochemistry of platinum group elements of the zoned ultramafic alto condoto complex northwest colombia the alto condoto complex dated at 20 ma is a zoned ultramafic intrusion with a magmatic rock sequence ranging from dunite to hornblendite the different petrographic units are cumulates formed by fractional crystallization processes parts of the central dunite are anomalously enriched in ptfe alloys and to a minor degree in iros alloys all other lithologic units of the complex display normal fractionation trends of platinum group elements pge with a general increase of total pge from wehrlite to horn blende clinopyroxenite and hornblendite this normal trend is best described by increasing pd and decreasing ir abundances the controlling factor for pge mineralization in zoned ultramafic complexes is probably an effective ptfe alloy precipitation during the crystallization of olivine this may be initiated by rapid tectonic movements causing pressure decrease and overheating of the magma with pge alloy formation as a result of the f sub o 2 shift during olivine crystallization