formation of willemite in hydrothermal environments willemite zinc silicate is the main zinc mineral in some carbonate hosted ore deposits e g franklin new jersey vazante brazil beltana south australia kabwe zambia recent interest in these unconventional zinc deposits has increased because of high zinc grades that exceed 40 wt percent relatively low environmental impact of ore processing owing to the lack of acid generating sulfides in the waste and advances in ore processing technologies in the past most metallogenic studies proposed formation of willemite deposits by supergene or hypogene alteration of preexisting sulfide deposits however recent data on the vazante beltana and kabwe deposits indicate willemite crystallization at temperatures in excess of 150 c raising the possibility of primary precipitation from hydrothermal fluids we use numerical geochemical modeling to examine the formation of willemite under hydrothermal conditions activity activity diagrams reveal that in the presence of dissolved sulfur and quartz willemite instead of sphalerite will precipitate under oxidizing e g hematite stable sulfate predominant and alkaline ph higher than k feldspar muscovite quartz conditions willemite also becomes more stable relative to sphalerite at high temperature and willemite can coexist with magnetite at 300 c the stabilities and solubilities of sphalerite willemite smithsonite hydrozincite and zincite were calculated for wide ranges of temperature 25 300 c chloride concentration dissolved sulfur and carbon concentrations ph quartz saturation and oxidation potential plots of the solubility of the different minerals as a function of two variables e g temperature and redox state ph and redox state allow us to predict the effects of changing chemical conditions which in turn permits an estimate of the efficiency of particular precipitation processes cooling is an effective process for precipitating sphalerite but not willemite whereas ph increase e g by acidic fluids reacting with carbonates is effective for precipitating willemite but not sphalerite dynamic geochemical models that simulate physicochemical processes are used to understand the formation of the beltana willemite deposit in the adelaide geosyncline of south australia this small high grade deposit 850 000 t at 36 zn is hosted in dolomite of the cambrian ajax limestone next to a tectonic contact with the diapiric halite bearing clastic sediments of the callanna group the orebody is associated with hematite alteration and is characterized by the total absence of sulfides willemite is the only zinc ore mineral and the arsenate hedyphane ca 2 pb 3 aso 4 3 cl is the main lead mineral the model results show that willemite will precipitate in response to water rock interaction and fluid mixing processes at temperatures above 120 c the presence of arsenate in the hydrothermal fluid is likely to have been important at beltana in arsenate absent models sulfate is reduced to sulfide by the precipitation of ferrous iron as hematite resulting in the precipitation of sphalerite and galena in contrast in models including arsenate the reduction of sulfate to sulfide is inhibited and willemite is predicted to precipitate

carbonate hosted base metal deposits lead isotope data bearing on their genesis and exploration lead isotope analyses from four australian carbonate hosted pb zn deposits coxco sorby hills pillara and wagon pass demonstrate that these deposits have different lead isotope properties whereas lead isotope compositions for coxco and wagon pass exhibit linear trends leads from sorby hills and pillara are isotopically homogeneous although they have an excess of radiogenic lead when compared to massive sulfide ores at coxco the dispersion of the data is limited and most lead is identical to that of the nearby hyc deposit the leads from wagon pass however are more radiogenic than the other deposits 206 pb 204 pb 20 and there are measurable isotopic differences between galenas occurring only a few centimeters apart both pillara and wagon pass occur on the lennard shelf and this is one of the rare cases where homogeneous and heterogeneous leads occur within one carbonate province data from the ores and their weathered surface expressions demonstrate that the lead isotope compositions of the ores are maintained during oxidation these results suggest that lead isotope analyses of a limited number of either surface or drill core samples can be of considerable assistance in assessing the exploration potential of suspected base metal prospects in carbonate environments comparison of the australian results with published lead isotope data for a number of carbonate hosted deposits in different geologic settings allows two main groups to be distinguished one group is characterized by lead isotope compositions that are homogeneous within each deposit and the data are either normal e g pine point silesia eastern alps or radiogenic sorby hills pillara in the other group the data are generally radiogenic and form linear arrays viburnum trend wagon pass there is a lithological and isotopic transition between the carbonate hosted deposits with homogeneous normal isotope ratios and shale hosted massive sulfides which have a large component of carbonate in their host rocks e g hyc mount isa of the isotopically homogeneous deposits the central european ores occurring in mesozoic sediments on a paleozoic basement exhibit lead compositions conforming to average global lead evolution on the other hand sorby hills and pillara which occur in paleozoic host rocks on middle to lower proterozoic basements have a distinct excess of radiogenic lead of the deposits with heterogeneous lead coxco occurs over an only slightly older basement and exhibits the least radiogenic lead conforming to average lead evolution in contrast in the viburnum trend where ores occur in paleozoic hosts immediately above a middle proterozoic basement even the least radiogenic leads are anomalous in as much as they do not fit standard lead evolution models it thus seems that the radiogeneity of the leads in carbonate hosted deposits varies as a function of the age differences between the crystalline basement and the time of ore deposition the homogeneity of the leads from carbonate hosted deposits seems to depend on the proximity of the ores to deep sedimentary basins this is exemplified by the difference between data from pillara and wagon pass both of which occur on but different sides of the lennard shelf the isotopically heterogeneous wagon pass deposit lies only a few kilometers from the proterozoic kimberley basin whereas the homogeneous pillara prospect is on the edge of the fitzroy trough which contains a 5 km thick pile of phanerozoic sediments the homogeneity of the lead can be accounted for by the combined effects of sedimentation diagenesis and prolonged brine circulation on geologic and isotopic grounds we favor a lateral secretion origin for carbonate hosted deposits

advection of the equatorial anomaly over arecibo by small storm related disturbance dynamo electric fields during highly disturbed geomagnetic periods both the arecibo radar and the ramey ionosonde have recorded impressive nighttime ionospheric enhancements in which the peak electron density exceeded 1 1012 m 3 and the f2 peak height went above 400 km in the past it has been suggested that these events could be caused by either a downward plasmaspheric flux that increases the density in the f region or by an eastward electric field that pushes the equatorial anomaly poleward to the caribbean sector on february 17 18 1999 the arecibo radar made observations during an event in which the electron density again rose to daytime values near midnight for this event the peaks in density were observed predominantly southeast of arecibo while the ions sustained a northward eastward motion due to an eastward southward storm dynamo electric field tec maps from gps for this night confirmed that the density enhancements were due to a poleward expansion of the equatorial anomaly

40ar 39ar thermochronology of the southern gawler craton australia implications for mesoproterozoic and neoproterozoic tectonics of east gondwana and rodinia 40ar 39ar thermochronology of the southern gawler craton australia reveals a protracted history of slow cooling with local crustal heating rapid cooling and fault reactivation between 1700 and 700 ma hornblendes from most of the southern part of the craton including the kalinjala mylonite zone yield ages 1580 1610 ma with younger more discordant samples showing evidence of retrogression these results indicate that the region cooled below 500 c 100 m y after the kimban orogeny and coincident with the gawler range hiltaba suite magmatism to the north perhaps associated with postorogenic extension biotite and k feldspar data indicate that regional cooling after this time was more gradual with a few exceptions locally in the southeastern eyre peninsula rapid cooling at 1425 ma is indicated by nearly concordant hornblende and biotite ages and may record a phase of regional extension other exceptions include areas of lower grade archean rocks that cooled to 350 c by 1700 1640 ma greenschist facies reactivation of shear zones occurred at 1100 ma during the musgravian orogeny on the basis of biotite single grain data and retrogressed amphiboles k feldspar age spectra record cooling at 700 800 ma following regional intrusion of the gairdner dike swarm and or denudation during rifting along the pacific margin of east gondwana and breakup of rodinia tectonothermal events revealed by these results previous geochronological and geological studies and available paleomagnetic data are comparable to other cratons and mobile belts in australia east gondwana and laurentia providing evidence that southeastern australia and north america were adjacent during much of proterozoic time

investigations of thermospheric ionospheric dynamics with 6300 a images from the arecibo observatory pilot observations were conducted at arecibo puerto rico using an all sky image intensified ccd camera system in conjunction with radar ionosonde and global positioning system gps diagnostic systems during the periods january 19 28 1993 and february 21 to august 22 1995 these represent the first use of campaign mode operations of an imager at arecibo for extended periods of f region observations the january 1993 period the so called 10 day run yielded a rich data set of gravity wave signatures perhaps the first case of direct imaging of thermospheric wave train properties in the f region the 6 month 1995 campaign revealed two additional optical signatures of f region dynamics a brightness wave in 6300 a passing rapidly through the field of view fov has been linked to meridional winds driven by the midnight temperature maximum mtm pressure bulge on may 3 1995 during a period of geomagnetic activity a 6300 a airglow depletion pattern entered the arecibo fov such effects represent the optical signatures of equatorial spread f instabilities that rise above the equator to heights near 2500 km thereby affecting arecibo s l 1 4 flux tube

high resolution oi 630 nm image measurements of f region depletion drifts during the guara campaign a high performance all sky imaging system has provided data on the evolution and drift motions of f region depletions above the magnetic dip equator at alc ntara brazil 2 3 s 44 5 w monochromatic images of depletions in the oi 630 nm nightglow were recorded on eight nights during 1 16 october 1994 as part of the guara campaign the drift motions of the depletions were typically 80 100 m s eastward prior to local midnight and reduced to a minimum of 30 50 m s in the morning hours in accord with previous observations however on october 2 3 and 12 13 the depletions were observed to reverse direction for 60 90 min achieving westward speeds of 30 m s before the motion reverted to eastward around 0100 lt and accelerated to 35 45 m s near dawn magnetic activity and other evidence suggests that these reversals in the motion of the airglow depletions probably result from reversals in the f region dynamo rather than from shifts in the altitude of the shear in the nighttime f region plasma drift

a discussion on the lead isotope geochemistry of galenas from the bambui group minas gerais brazil lead isotope data on galenas from the bambui group minas gerais have been assembled and discussed the isotope data when plotted on the single stage model iii lead isotope development curve of cumming and richards 1975 yield 207 206 ages of 650 50 m y and a linear array of data points with negative model ages which intercept the growth curve at 650 60 m y and 1850 150 m y the radiometric dates coincide with the two major orogenic episodes the brazilian and the transamazonian the data are interpreted in terms of a two stage model where the source of lead for galenas formed during brazilian orogeny is the basement rocks of transamazonian age the calculated th u value for the source rock is 2 9 0 3 the geographical distribution of lead isotope ratios shows a zonation in vazante paracatu region an area containing large deposits of zinc the implication of the distribution on the ore formation is discussed

the night when the auroral and equatorial ionospheres converged an all sky imaging system at the mcdonald observatory 30 67 n 104 02 w 40 magnetic latitude showed dramatic ionospheric effects during a moderate geomagnetic storm on 1 june 2013 the auroral zone expanded leading to the observation of a stable auroral red sar arc airglow depletions associated with equatorial spread f esf were also seen for the first time at such high magnetic latitude total electron content measurements from a global positioning system gps receiver exhibited ionospheric irregularities typically associated with esf we explore why this moderate geomagnetic disturbance leads to such dramatic ionospheric perturbations at midlatitudes a corotating interaction region like driver and a highly contracted plasmasphere caused the sar arc to occur at l shell 2 3 for esf at l 2 1 timing of the storm intensification alignment of the sunset terminator with the central magnetic meridian and sudden variations in the westward auroral electrojet all combined to trigger equatorial irregularities that reached altitudes of 7000 km the sar arc and esf signatures at the ionospheric foot points of inner magnetosphere l shells l 2 represent a dramatic convergence of pole to equator equator to pole coupling at midlatitudes

equatorial spread f related airglow depletions at arecibo and conjugate observations 1 we present evidence of the incursion into the caribbean region of airglow depletions associated with the equatorial rayleigh taylor instability data from the boston university all sky imager located at arecibo puerto rico 18 3 n 66 7 w 28 n magnetic latitude have been used to identify several nights with 630 0 nm airglow patterns that are typical signatures of equatorial spread f and distinctly different from the more common airglow bands frequently observed there two case studies 2 november 2002 and 26 february 2003 show the occurrence of simultaneous airglow depletions observed with another all sky imager located at el leoncito argentina 31 8 s 69 3 w 18 s magnetic latitude relatively close to the arecibo conjugate point supporting information is obtained from defense meteorological satellite program rocsat 1 and gps data all of them showing the presence of strong ionospheric irregularities collocated with the airglow depletions mapping the circular field of view from arecibo into the southern hemisphere reveals a distorted pattern due to the differences in the magnetic field characteristics in both hemispheres this adds an interesting spatial complexity to the formulation of conjugate point observing programs in the latin american longitude sector

vlf emission bursts in the terrestrial and venusian nightside troughs the existence of very low frequency 100 hz electric field bursts in the nightside venus ionosphere has been commonly assumed to be evidence for lightning by analogy to the earth where some of the whistler mode radiations above the ionosphere originate from lightning1 3 non lightning sources for venus whistler mode waves have been ignored vlf emission bursts not associated with lightning are frequently observed over the terrestrial polar ionosphere4 6 one type saucers are whistler mode wave emissions that propagate upwards along magnetic field lines5 6 here we show that the 100 hz emission bursts in the venusian nightside ionosphere are remarkably similar to those of the terrestrial vlf saucer emissions in terms of their spatial and temporal characteristics and the properties of their magnetoplasma environment we therefore propose that the generation mechanism for such vlf saucers6 7 should be considered as a viable alternative to lightning as a source of venusian ionospheric whistler mode emissions

a multidiagnostic investigation of the mesospheric bore phenomenon 1 imaging measurements of a bright wave event in the nighttime mesosphere were made on 14 november 1999 at two sites separated by over 500 km in the southwestern united states the event was characterized by a sharp onset of a series of extensive wavefronts that propagated across the entire sky the waves were easily visible to the naked eye and the entire event was observed for at least 5 hours the event was observed using three wide angle imaging systems located at the boston university field station at mcdonald observatory mdo fort davis texas and the starfire optical range sor albuquerque new mexico the spaced imaging measurements provided a unique opportunity to estimate the physical extent and time history of the disturbance simultaneous radar neutral wind measurements in the 82 to 98 km altitude region were also made at the sor which indicated that a strong vertical wind shear of 19 5 ms 1km 1 occurred between 80 and 95 km just prior to the appearance of the disturbance simultaneous lidar temperature and density measurements made at fort collins colorado 1100 km north of mdo show the presence of a large 50 k temperature inversion layer at the time of the wave event the observations indicated that the event was most probably due to an undular mesospheric bore a relatively uncommon disturbance which has only recently been reported taylor et al 1995a evidence is also shown to suggest that a large east west tropospheric frontal system lying over the northern united states was the origin of the disturbance

lightning measurements from the pioneer venus orbiter the plasma wave instrument on the pioneer venus orbiter frequently detects strong and impulsive low frequency signals when the spacecraft traverses the nightside ionosphere near periapsis these particular noise bursts appear only when the local magnetic field is strong and steady and when the field is oriented to point down to the ionosphere thus the signals have all characteristics of lightning whistlers we have tried to identify lightning sources between the cloud layers and the planet itself by tracing rays along the b field from the orbiter down toward the surface an extensive data set consisting of measurements through orbit 1185 strongly indicates a clustering of lightning sources near the beta and phoebe regios with an additional significant cluster near the atla regio at the eastern edge of aphrodite terra these results suggest that there are localized lightning sources at or near the planetary surface

concurrent observations at the magnetic equator of small scale irregularities and large scale depletions associated with equatorial spread f in 2014 an all sky imager asi and an advanced modular incoherent scatter radar consisting of 14 panels amisr 14 system were installed at the jicamarca radio observatory the asi measures airglow depletions associated with large scale equatorial spread f irregularities 10 500 km while amisr 14 detects small scale irregularities 0 34 m this study presents simultaneous observations of equatorial spread f esf irregularities at 50 200 km scale sizes using the all sky imager at 3 m scale sizes using the julia jicamarca unattended long term investigations of the ionosphere and atmosphere radar and at 0 34 m scales using the amisr 14 radar we compare data from the three instruments on the night of 20 21 august 2014 by locating the radar scattering volume in the optical images during this night no topside plumes were observed and we only compare with bottomside esf amisr 14 had five beams perpendicular to the magnetic field covering 200 km in the east west direction at 250 km altitude comparing the radar data with zenith asi measurements we found that most of the echoes occur on the western wall of the depletions with fewer echoes observed the eastern wall and center contrary to previous comparisons of topside plumes that showed most of the echoes in the center of depleted regions we attribute these differences to the occurrence of irregularities produced at submeter scales by the lower hybrid drift instability comparisons of the asi observations with julia images show similar results to those found in the amisr 14 and asi comparison

venus volcanism and rift formation in beta regio a new high resolution radar image of beta regio a venus highland area confirms the presence of a major tectonic rift system and associated volcanic activity the lack of identifiable impact craters together with the apparent superposition of the theia mons volcanic structure on the rift system suggest that at least some of the volcanic activity occurred in relatively recent geologic time the presence of topographically similar highland areas elsewhere on venus aphrodite terra dali chasma and diana chasma suggests that rifting and volcanism are significant processes on venus

geometry of depleted plasma regions in the equatorial ionosphere an image intensified all sky 6300 a airglow imaging system operating on ascension island is early 1981 has been used to assemble a photographic data base of several hundred airglow depletion patterns by mapping the airglow depletion features along geomagnetic field lines to the equatorial plane the geometrical characteristics of plasma depleted regions may be described over the 400 to 1200 km altitude region above the equator such an analysis revealed that single or linear depletions tilted toward the west with an average skewness of 0 6 longitude west 100 km altitude corresponding to a zenith angle tilt of 40 at a height of 800 km the tilts increased with local time during the evening hours showing that an effective velocity shear of 0 05 m s km is required to account for the observed evolution in several cases the depletion geometry showed a wishbone or bifurcated pattern such features had a mean height of bifurcation of 740 km and tilt factors very similar to those found for linear depletions observed during the same local time periods

a dayside plasma depletion observed at midlatitudes during quiet geomagnetic conditions in this study we investigate a dayside midlatitude plasma depletion dmlpd encountered on 22 may 2014 by the swarm and grace satellites as well as ground based instruments the dmlpd was observed near puerto rico by swarm near 10 lt under quiet geomagnetic conditions at altitudes of 475 520 km and magnetic latitudes of 25 30 the dmlpd was also revealed in total electron content observations by the saint croix station and by the grace satellites 430 km near 16 lt and near the same geographic location the unique swarm constellation enables the horizontal tilt of the dmlpd to be measured 35 clockwise from the geomagnetic east west direction ground based airglow images at arecibo showed no evidence for plasma density depletions during the night prior to this dayside event the c nofs equatorial satellite showed evidence for very modest plasma density depletions that had rotated into the morningside from nightside however the equatorial depletions do not appear related to the dmlpd for which the magnetic apex height is about 2500 km the origins of the dmlpd are unknown but may be related to gravity waves

gas transport model for the magmatic system at mount pinatubo philippines insights from 210pb 226ra abstract measurements of 226ra 210pb disequilibria in eruptive products have the potential to track the accumulation or loss of volatiles in magmatic systems on timescales of decades because the intermediate nuclide 222rn follows the gas phase we present measurements of 210pb 226ra disequilibria for whole rock samples representing a time sequence of tephra through the june 15 1991 cataclysmic eruption of mount pinatubo volcano philippines mount pinatubo volcano is a dacitic system that did not significantly vent gases at the surface prior to eruption and we can therefore isolate the 210pb 226ra disequilibria due to gas accumulation without complications due to 222rn loss during degassing pyroclastic samples have 210pb 226ra 0 ranging from 1 01 to 1 10 averaging 1 06 a sample of the post climactic dome has 210pb 226ra 0 1 12 previous uranium series degassing studies have suggested that 210pb excesses are created by rapid volatile transport carrying the intermediate daughter 222rn and subsequent volatile accumulation and decay of 222rn to 210pb however bubbles in viscous dacite magma cannot rise at speeds needed to provide a flux of 222rn large enough to cause measurable disequilibria in the 210pb 226ra system in addition there is little evidence for magmatic sources large enough to supply a rapid flux of 222rn therefore we present a model in which 210pb 226ra disequilibria is established during basaltic recharge of the pinatubo reservoir the relatively low viscosity of basaltic magma allows for differential gas motion and the production of 210pb excess in localized basaltic melt transport of volatiles and 210pb rich basalt through a crystal matrix and the formation of bubble plumes in the dacitic reservoir produces a mixed magma with 210pb excess through this mechanism the timescale of gas transport and accumulation is constrained not by the half life of 222rn 3 8 days but rather by the half life of 210pb 22 6 years bubble plume motion preserves disequilibria and creates a zone of eruptable dacite with 210pb excess alleviating the need for gas transport on very short time scales using the rate of decay of 210pb coupled with published trace element data we present a quantitative investigation of this new conceptual model and propose that changes in 210pb values with time may suggest changing conditions of magma supply at volcanoes

highly structured tropical airglow and tec signatures during strong geomagnetic activity a remarkable set of all sky images using the 630 nm airglow emission has been taken over the arecibo observatory in puerto rico wave like structures at a height of about 250 km are commonly found to travel in the southwest direction at speeds ranging from 20 120 m s most surprising is that geomagnetic activity seems to greatly amplify them forming very intricate patterns of light and dark simultaneous observations using gps satellite transmissions on one night reveal that dark regions are severely plasma depleted while bright regions have nighttime content as large as the full noontime ionosphere this unexpected geomagnetic effect at mid latitudes has implications for trans ionospheric radiowave propagation and space weather

comment on venus nightside ionospheric troughs implications for evidence of lightning and volcanism by h a taylor jr j m grebowsky and p a cloutier

geology of the beltana willemite deposit flinders ranges south australia beltana is a high grade hypogene willemite deposit hosted in lower cambrian carbonate rocks in the arrowie basin northern flinders ranges south australia it is situated adjacent to a major growth fault on the basin margin ooid grainstone units of the woodendinna dolomite and units of archaeocyathid rich wilkawillina limestone are the main host lithologies lead minerals in subeconomic quantities are also present in karstic collapse breccias surrounding the willemite orebodies mineralization is structurally controlled and associated with brecciation and extensive hematite rich hydrothermal zincian dolomitization ore minerals include willemite and coronadite with lesser mimetite hedyphane and smithsonite late stage gangue minerals include manganocalcite dolomite and minor quartz the texture of willemite is heterogeneous resulting from various depositional mechanisms such as partial to massive replacement of the carbonate host rock internal sedimentation fracture fill brecciation and vein fill on the periphery of the deposit smithsonite formed by weathering of willemite beltana is centered on a karstic collapse breccia that extends at least 100 m vertically formed in part through corrosion by acidic ore solutions the geochemical signature of the orebody includes high levels of zn pb cd as and mn notably silver is absent from the deposit and sulfur concentrations are low 20 ppm fluid inclusion studies yield a low minimum temperature range of ore deposition between 50 and 170 c k ar dating of coronadite associated with the willemite orebody indicates an age of formation of 435 5 ma premining resources of willemite ore were 850 000 t at 36 percent zn and an associated body of subeconomic lead contained more than 800 000 t at 8 9 percent pb 3 9 percent zn and 1 percent as the deposit has some similarities with mississippi valley type deposits but differs in ore and alteration mineral assemblages

venus summary and review of science research activities 1983 87 in the past four years the first high resolution synoptic images of the surface of venus have been obtained and we have learned more about the nature of its surface and atmosphere the major accomplishments of the u s s r in venus exploration have been observed with great interest by u s investigators some of whom have begun joint research efforts with soviet scientists venera 15 and 16 radar imaging experiments and new data obtained at the arecibo observatory have provided answers to some important questions conjectured volcanic features have been resolved into unmistakable calderas or distinct lava flow morphologies the question of whether venus like the earth may have high erosion rates is answered and from the observed number of presumed impact craters it appears that resurfacing rates on venus are much smaller than on earth no evidence of water or wind activity has been seen

comment on further evidence for lightning at venus in contradiction to the findings of singh and russell 1986 the pioneer venus orbiter pvo electric field data are not found to provide evidence for either lightning or volcanism at venus it is suggested that the noise considered by singh and russell to be clustered at low altitudes actually appears frequently at high altitudes the frequent appearance of the broadband noise in the upper ionosphere indicates that this noise like that attributed to lightning by scarf et al 1980 is actually generated within the ionosphere near the pvo by the solar wind interaction with the ionosphere

shrinking equatorial plasma bubbles the formation of equatorial plasma bubbles epbs associated with spread f irregularities are fairly common phenomenon in the postsunset equatorial ionosphere these bubbles grow as a result of eastward polarization electric field resulting in upward e b drift over the dip equator as they grow they are also mapped to low latitudes along magnetic field lines the epbs are often observed as airglow depletions in the images of oi 630 nm emission on occasions the growth of the features over the dip equator is observed as poleward extensions of the depletions in all sky images obtained from low latitudes herein we present interesting observations of decrease in the latitudinal extent of the epbs corresponding to a reduction in their apex altitudes over the dip equator such observations indicate that these bubbles not only grow but also shrink on occasions these are the first observations of shrinking epbs the observations discussed in this work are based on all sky airglow imaging observations of oi 630 0 nm emission made from panhala 11 1 n dip latitude in addition ionosonde observations made from dip equatorial site tirunelveli 1 1 n dip latitude are used to understand the phenomenon better the analysis indicates that the speed of shrinking occurring in the topside is different from the bottomside vertical drifts when the epbs shrink they might decay before sunrise hours

venus nightside ionospheric troughs implications for evidence of lightning and volcanism ionization troughs are frequently observed in the venus nightside ionosphere by the orbiter ion mass spectrometer oims on the pioneer venus orbiter pvo these events typically exhibit density depletions which may range from a factor of 2 to an order of magnitude or more often feature sharp density gradients and frequently are associated with superthermal ion fluxes although their full spatial extent cannot be determined the ion trough dimensions as perceived along the pvo orbit track extend from 1 to more than 10 in latitude and longitude troughs have been encountered at altitudes ranging from more than 1000 to less than 250 kilometers the nightside trough boundaries are similar to both the ionization gradients which mark the venus dayside ionopause and the ionization gradients which define the high latitude ionization trough in the earth ionosphere in each of these venus and earth phenomena there is a close association between sharp gradients in thermal ion distributions and energetic and dynamic processes stimulated by the interaction between the solar wind interplanetary magnetic field imf and the thermal ionosphere a close correlation is identified between ion trough events and prominent published examples of 100 hz plasma waves detected by the orbiter electric field detector oefd which have been interpreted by scarf and russell 1983 and by ksanfomaliti et al 1983 as whistler mode propagation stimulated by lightning in the lower atmosphere and frequently occurring over mountains while the occasional coincidence between the detection of whistler waves and the overflight of venus mountain ranges is also observed for the ion troughs neither phenomenon is seen to exhibit convincing evidence of an association with the mountains overall these findings lead us to believe that many of the 100 hz noise bursts previously attributed to lightning are like the ion troughs actually the result of the interaction between the ionosphere and the combined effects of the solar wind and the draped imf if this interpretation is correct there may be little evidence for lightning from the pvo measurements similarly a supporting argument for active volcanism as a possible source for the deduced lightning events would also be discounted

support of long wavelength loads on venus and implications for internal structure a thin shell formulation for computing stress distributions on the surfaces of one plate planets is developed the lithospheric model includes laterally varying density anomalies at two depths corresponding to undulations on a crust mantle boundary and variations in upper mantle density for a given set of model parameters values for the vertical displacement crustal thickness anomaly and mantle density anomaly required to satisfy the topographic and gravitational boundary conditions are computed along with the resulting stress field the computed stresses can then be compared to stress directions inferred from observed tectonic features this formulation is used to study loads on venus s lithosphere and it is found that most highland areas appear to have been formed in a state of isostasy or by uplift with a significant portion of their support probably derived from dynamic processes in the mantle a possible exception is ishtar terra whose circumferential mountain belts are most consistent with a radially compressive stress regime generated by flexural loading reasonable lithospheric models predict low density mantle beneath atla beta eisila thetis and tethus regiones and thick crust accompanied by higher density mantle under ishtar terra and ovda regio thus western aphrodite terra appears to be more closely related to ishtar than to the rest of the equatorial highlands these results favor a hot spot model of venus tectonics in which beta eastern aphrodite eisila and tethus are expected to be relatively young and thermally active while ovda and ishtar should be older and less active

reply to comment on venus nightside ionospheric troughs implications for evidence of lightning and volcanism by h a taylor jr j m grebowsky and p a cloutier

lead isotope constraints on the origin of nonsulfide zinc and sulfide zinc lead deposits in the flinders ranges south australia hypogene nonsulfide zinc deposits represent a mode of zinc enrichment in the earth s crust that until recently has largely been overlooked relative to supergene nonsulfide zinc and sulfide zinc lead deposits the flinders ranges a deformed and uplifted portion of the northern adelaide geosyncline in south australia host numerous prominent examples of hypogene nonsulfide zinc mineralization and thus provide an excellent setting in which to investigate the origin of this deposit type the flinders ranges also host numerous syngenetic and mississippi valley type sulfide zinc lead deposits allowing a possible genetic relationship between sulfide and nonsulfide mineralization to be examined in the present study lead isotope compositions of zinc and lead minerals from nonsulfide zinc and sulfide zinc lead deposits from throughout the flinders ranges were analyzed to investigate these issues all the lead isotope compositions measured are anomalous with respect to the holmes houtermans and stacey kramers models compositions range from 18 332 to 21 125 for 206pb 204pb from 15 729 to 16 022 for 207pb 204pb and from 38 264 to 40 967 for 208pb 204pb the anomalous highly radiogenic lead isotope compositions probably reflect input from the highly uranium and thorium enriched basement rocks in the region the data also form a linear trend in both 207pb 204pb versus 206pb 204pb and 208pb 204pb versus 206pb 204pb space indicating that the data either define an isochron from one of multiple possible stages of lead evolution or that the deposits all contain varying mixtures of the same two end member leads in either case implying that the deposits are genetically related for a mixing scenario the present data provide little further constraint on the origin of a hypothetical less radiogenic end member however further constraints on the origin of the more radiogenic end member can be obtained by considering the slope of the regression line through the data based on an instantaneous model of lead growth the maximum age of formation of the more radiogenic lead component would be between 910 and 1036 ma these ages fall within a period of tectonic quiescence in the region but allow for the possibility that the lead may be associated with a younger event such as the 850 to 600 ma rifting event that led to the opening of the adelaide geosyncline based on a continuous model of lead growth the more radiogenic lead component could have evolved in a source with an age between 1313 and 1523 ma before it was sequestered in the mineral deposits at about 435 ma these 1313 to 1523 ma dates correspond with the age of much of the younger igneous rocks e g the hiltaba suite granites in the gawler craton that flank the adelaide geosyncline on the west and may comprise part of the basement of the adelaide geosyncline the lead isotope data also show a strong regional pattern consisting of two distinct centers of radiogenic lead one located in the southeast corner of the study area and a second broader zone lying near the west central part of the study area this pattern may in part be a function of depth to the basement in which the more radiogenic lead occurs in deposits located near the edges of the basin where sediment thicknesses are lower although heterogeneity in basement composition and proximity to sources of less radiogenic lead may also have affected the pattern finally the lead isotope compositions also show some correlation with deposit size in which the largest deposits in the flinders ranges also contain the most radiogenic lead

climatology of postsunset equatorial spread f over jicamarca 1 we use radar observations from 1996 to 2006 to study the climatology of postsunset equatorial 3 m spread f irregularities over jicamarca during all seasons we show that the spread f onset times do not change with solar flux and that their onset heights which occur near the altitude of the evening f region velocity vortex increase linearly from about 260 to 400 km from solar minimum to solar maximum higher onset heights generally lead to stronger radar echoes during the equinox spread f onset occurs near vertical drift evening reversal times while during the december solstice they occur near the drift reversal times close to solar minimum and near the time of the prereversal velocity peak for high solar flux conditions on average radar plume onset occurs earlier with increasing solar flux in all seasons plume onset and peak altitudes increase with solar activity and the peak heights are generally highest during the equinox the f region upward drift velocities that precede spread f onset increase from solar minimum to solar maximum and are approximately proportional to the maximum prereversal drift peak velocities

planetographic clustering of low altitude impulsive electric signals in the night ionosphere of venus the possible occurrence of lightning in the venus atmosphere has long been a subject of speculation1 2 so the initial reports of impulsive electromagnetic signals deep in the venus atmosphere3 and in the night ionosphere4 generated much interest the results of optical experiments however were mixed the infrared spectrometer on venera 9 observed one sequence of lightning like activity5 the star sensor of the pvo orbiter6 saw none and the vega balloon photometers7 obtained negative but ambiguous results evidence for the lightning generation of the electromagnetic signals includes their impulsive nature their occurrence patterns8 9 their altitude dependences8 10 and their electromagnetic polarization11 although only signals below several hundred hertz can directly propagate to the pvo spacecraft higher frequency signals could scatter in the inhomogeneities of the night ionosphere12 as these higher frequencies cannot propagate far into the ionosphere and are seldom observed at altitudes of above 400 km ref 13 they mark the location of the generating region in this paper we map the locations of the observations made at 730 hz during the first three night time observing seasons of pioneer venus when the spacecraft reached altitudes low enough to detect these leakage signals these maps show that there are specific active regions of enhanced signal occurrence and that at least some of these active regions appear to remain fixed in planeto graphic coordinates from year to year

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

sedimentary thickness variations and deformation intensity during basin inversion in the flinders ranges south australia abstract the central and northern parts of the adelaide fold belt in the flinders ranges south australia consist of a sequence of neo proterozoic cambrian sediments overlying a meso proterozoic basement complex both of which were mildly deformed in an intracratonic setting during the 500 ma delamerian orogeny the fold belt lies within a prominent heat flow anomaly average heat flows of 90 mwm 2 reflecting extraordinary enrichments in heat producing elements in the meso proterozoic basement suggesting that anomalous thermal regimes may have been significant in localising delamerian deformation however spatial variations in deformation intensity correlate more closely with variations in the thickness of the sedimentary sequence than with observed variations in heat flow suggesting that the thickness of the sedimentary blanket plays a crucial role in localising delamerian deformation during basin inversion we use simple numerical models of lithospheric strength to investigate the potential role of sedimentary thickness variations on the distribution and style of deformation focussing on the impact of a variable thickness sediment pile deposited above a radioactive basement we show that for thermal parameters appropriate to the flinders ranges moho temperatures may vary by 25 30 c for every additional kilometre of sediment for a brace goetze lithospheric rheology controlled by a combination of temperature dependent creep processes and frictional sliding the observed variations in thickness of the sedimentary pile are sufficient to cause dramatic reductions in the vertically integrated strength of the lithosphere by many orders of magnitude thereby providing a plausible explanation for observed correlation between sediment thickness and deformation intensity during basin inversion

the cadjebut deposit as an example of mississippi valley type mineralization on the lennard shelf western australia single episode or multiple events the cadjebut zn pb deposit is one of several mississippi valley type resources hosted in devonian carbonates of the lennard shelf western australia several dolomitization events and at least three pulses of mineralization are documented in the cadjebut area indicating multiple episodes of fluid expulsion during basin evolution the data contrast with previous models which propose a single dolomitization and mineralization event for the lennard shelf two major mineralization events are recorded in the cadjebut area the earlier more weakly developed mineralization event is characterized by finely crystalline sphalerite and marcasite laths disseminated in dolomite cements that occlude primary porosity in evaporitic sequences the later mineralizing event forming the cadjebut orebody is represented in terms of diagenesis either in cloudy calcites that replace evaporitic minerals or within blocky calcite cements in large secondary vugs and cavities timing relationships relative to diagenetic events in the area indicate that the first mineralization event occurred early in the diagenetic history prior to significant burial and is interpreted to be middle devonian late givetian early frasnian in age the later event occurred subsequent to significant chemical compaction and maximum burial and is dated as mid carboniferous late tournaisian westphalian anomalous values of zn and pb in early carboniferous sediments of the lennard shelf and the apparent absence of mineralization in late carboniferous to permian sediments support a shelfwide mid carboniferous event stratigraphic constraints suggest an absolute age for cadjebut of 325 or 25 ma this second mineralization event coincides with a period of reefal platform emergence second order cycle regression and minor uplift of the lennard shelf all temporally coinciding with the waning stages of the alice springs orogeny centered in central australia 700 km to the southeast of cadjebut the two main pulses of mississippi valley type mineralization on the lennard shelf have distinctive patterns of pb isotope compositions the early burial small resource mineralization has heterogeneous pb isotope compositions whereas later economic and subeconomic mineralization has more homogeneous signatures the pb isotope data and the overall intensity of mineralization suggest that large volumes of fluid were expelled during the later period of platform emergence sea level regression distal orogenic events and mineralization

observations and modeling of the coupled latitude altitude patterns of equatorial plasma depletions 1 the equatorial ionosphere is host to the most dramatic and enigmatic plasma instability mechanism in the geospace environment equatorial spread f esf was discovered in early ionosonde measurements and interpreted theoretically using rayleigh taylor theory subsequent diagnostic and modeling advances have improved substantially our understanding of esf onset and evolution and its associated effects on the ionosphere throughout the low latitude domain the degree to which esf mechanisms penetrate into the lower midlatitudes is a topic of current study a reverse of the familiar concept of high to low latitude coupling for space weather phenomena optical diagnostic systems first ground based and now space based reveal the presence of esf structures via images of airglow depletions that are aligned in the approximately north south direction spanning the geomagnetic equator ground based all sky camera systems used to capture the two dimensional horizontal patterns of airglow depletions are the main source of observations showing that esf processes intrude to midlatitudes in the l 1 5 domain in this paper we review the process of mapping airglow depletions along geomagnetic field lines to the equatorial plane hence defining the maximum apex heights achieved a case study comparison of simultaneous radar backscatter data from kwajalein with optical data from wake island sites that share common magnetic meridians in the pacific section confirms the utility of the approach and its applicability to sites at other longitudes modeling studies based on buoyancy arguments using flux tube integrated mean density values versus l shell apex heights show that instability induced plasma depletions starting at f layer bottomside heights easily reach altitudes above 2000 km in the equatorial plane implying that esf intrusions to lower midlatitudes should be a relatively frequent occurrence

brightening of 630 0 nm equatorial spread f airglow depletions 1 observations from the boston university all sky imaging system at arecibo puerto rico 18 3 n 66 7 w 28 n mag show an unusual behavior of nighttime 630 0 nm airglow depletions associated with equatorial spread f esf these structures move eastward before reversing their motion and become airglow enhancements few other cases have been found all during december solstices for the case study presented here data from the arecibo incoherent scatter radar and the republic of china scientific satellite rocsat 1 provide supporting information the radar shows that around local midnight the background zonal and meridional plasma motions reverse to westward and southward respectively rocsat 1 shows enhanced ion density i e a low latitude plasma blob above the bright feature recorded by the all sky imager indicating a possible connection between both phenomena drifts parallel to the magnetic field are observed only in the region where the enhancement occurs one possible interpretation of this change in the brightness of the depleted structure involves the influence of northward meridional winds and a reversal in the zonal drift motion most likely caused by a zonal wind reversal

observations of equatorial spread f from haleakala hawaii 1 since the 1920s it has been known that the equatorial ionosphere can become highly disturbed in the post sunset period we have placed a new array of instruments on top of the haleakala volcano in hawaii to study these disturbances from midlatitudes two airglow imagers provide two dimensional snapshots of the development of these disturbances during the night while two gps receivers can quantify their severity here we report on the spectacular february 16 17 2002 disturbance which reached an altitude of 1500 km over the magnetic equator and mapped magnetically to latitudes well north of hawaii the signals from every global positioning system satellite in the field of view from maui were severely disturbed whenever the corresponding look direction passed through one of the turbulent features we also present an example from march 19 2002 in which the spread f activity is not as severe to demonstrate that the instrumentation still provides valuable information

comment on the night when the auroral and equatorial ionospheres converged by martinis c j baumgardner m mendillo j wroten a coster and l paxton intense oi 630 0 nm emission depletions were detected over mexico by an all sky imager during the main phase of the geomagnetic storm on 1 june 2013 minimum dst index 119 nt those emission depletions were interpreted to be associated with equatorial plasma bubbles martinis et al 2015 if bubbles were responsible for those middle latitude emission depletions they would have been extreme bubbles which extended over 40 magnetic latitudes and 7000 km in altitude at the magnetic equator however a few factors challenge this interpretation first the emission depletions detected over mexico showed westward drift whereas the equatorial ionosphere including bubbles drifted eastward on that night second the middle latitude emission depletions were tilted westward with respect to the geographic meridian but the westward tilt of bubbles was not identified third the growth of bubbles was not evident when the middle latitude emission depletions grew the westward tilt and westward propagation of the middle latitude emission depletions are consistent with the characteristics of medium scale traveling ionospheric disturbances mstids observed over the united states on that night thus the emission depletions over mexico can be interpreted to be the signature of mstids

airglow characteristics of equatorial plasma depletions a new low light level all sky 6300 a airglow imaging system has been developed for ground based studies of the optical signatures of equatorial plasma depletions the system was designed for narrowband interference filters 6 a full width at half power with interchangeable all sky 180 and narrow field 60 lenses and records images photographically by using a standard 35 mm camera a field test of the apparatus was conducted on ascension island 8 0 s 14 4 w from january 24 to february 10 1981 the photographs were analyzed for broad morphological characteristics by using simple overlay techniques augmented by digital image processing methods to extract more quantitative detail the initial results to come from these observations show that airglow depletions occur most often during the 2030 2330 lt period often covering one fourth of the visible sky they extend from the magnetic equator to beyond the crest of the equatorial anomaly with east west cross sections of 100 km to several hundred kilometers they are usually not aligned with magnetic meridians showing a progressive skewness to the west at further distances from the equator several cases of apparently twisting overlapping and bifurcating depletions were observed the depletions drifted to the east with speeds that decreased from 190 m s at 2100 lt to 80 m s at 0100 lt the airglow intensities within depletions were typically 40 50 of the background levels and the western walls of the depletions usually had a steeper gradient than the corresponding eastern walls

a statistical analysis of equatorial plasma bubble structures based on an all sky airglow imager network in china this paper investigates the statistical features of equatorial plasma bubbles epbs using airglow images from 2012 to 2014 from a ground based network of four imagers in the equatorial region of china it is found that 1 epbs mainly occur during 21 00 00 00 local time lt in equinoxes there is an asymmetry in occurrence rates between march june and september equinoxes december solstices 2 most epbs occur in groups of two to six depletions the distance between adjacent epb depletions is 100 700 km and the average is 200 300 km the zonal extension of an epb group is usually less than 1500 km but can reach 3000 km 3 epbs usually have a maximum drift velocity near 100 m s at 21 00 22 00 lt in 9 5 1 5 geomagnetic latitude and then decrease to 50 70 m s toward sunrise 4 the averaged westward tilt angle of most epbs with respect to the geographic north south increased from 5 10 to 23 30 with lt between 20 00 and 03 00 lt then decreasing to 10 20 toward sunrise 5 when 90 140 the maximum pmle increases by 3 4 5 5 when f10 7 changes from 90 to 190 6 the epb occurrence patterns and zonal drift velocities are significantly different from those at kolhapur india which locates west to our stations by 20 0 32 0 in longitude

lead isotope constraints on the genesis of pb zn deposits in the neoproterozoic vazante group minas gerais brazil abstract the neoproterozoic vazante group at the western border of the sao francisco craton brazil hosts the largest zn pb district in south america several authors have classified this mineral district as mississippi valley type mvt based on the intimate association with carbonates and the epigenetic character of most ore bodies in this paper we present 47 new lead isotope data from four deposits located along the 300 km n s vazante paracatu unai linear trend pb isotope ratios indicate sources with relatively high u pb and th pb ratios considering the 206pb 204pb and 208pb 204pb ratios as indicative parameters for the source we suggest an upper crustal source for the metals the small variation on the pb isotope ratios compared to those observed in the classical mvt deposits and other geological fluid inclusion and sulphur isotopic data indicates a metallogenic event of long duration it was characterized by focused circulation of hydrothermal fluids carrying metals from the basement rocks and from the sedimentary pile the data obtained are more compatible with an evolution model similar to that of irish type deposits the existence of three pb isotopic populations could be the result of regional differences in composition of the source rocks and in the fluid rock interaction since the mineralization is a long term process

all sky imaging observations of conjugate medium scale traveling ionospheric disturbances in the american sector 1 all sky imaging systems at arecibo puerto rico 18 3 n 66 7 w 28 mag lat and mercedes argentina 34 6 s 59 4 w 24 6 mag lat are used to study ionospheric conjugate processes at lower midlatitudes for the first time in the american sector the simultaneous occurrence in both hemispheres of medium scale traveling ionospheric disturbances has been observed the first year of observations yielded 43 nights 40 with simultaneous occurrence of airglow bands supporting information from gps receivers indicate the presence of vertical total electron content variations that correlate with the airglow structures observed with the imagers weak phase fluctuations have been measured indicating that these structures do not produce severe large scale ionospheric irregularities

global radar units on venus derived from statistical analysis of pioneer venus orbiter radar data unsupervised linear discriminant cluster analysis of pioneer venus reflectivity and rms slope data has produced a classification of 15 radar units examination of four hypsometric provinces previously established for venus has been used to show that although the highland 6053 to 6055 5 km and mountainous greater than 6055 5 km provinces are distinctly different in their radar unit compositions from each other and from the lowlands less than 6051 km and rolling plains 6051 to 6053 km provinces the lowlands and rolling plains provinces are very nearly the same in their radar properties this observation indicates that hypsometry alone is not a reliable criterion for quantitative examination of the surface geology on venus a classification unit encompassment scheme has been developed that shows the presence of three distinct trends two toward elevations higher than the planetary mean elevation and the other toward elevations lower than the mean venera lander data and earth based radar images have been used to infer that seven units within the two higher elevation unit encompassment trends represent materials of mostly basaltic composition that differ only in their surface morphologies the physical characteristics of these materials indicate that they form terrains ranging from banded through rift valley to relatively flat and that the materials are composed of bedrock and soil in variable ratios three other radar classification units appear to be morphologically transitional forms between units of these two higher elevation unit encompassment trends the five remaining units are associated with the lower elevation unit encompassment trend their geologic significance cannot be determined with any certainty with the existing pioneer venus radar data the radar units that correspond to those of an existing radar unit map produced by supervised analysis display similar areal distributions on venus however our radar unit map shows more detail and is relatively unbiased in terms of unit definition this global radar classification image of the venusian surface provides a working data base from which more exacting geologic interpretations can be made when higherresolution imagery becomes available

magnetotelluric evidence for a deep crustal mineralizing system beneath the olympic dam iron oxide copper gold deposit southern australia the iron oxide copper gold olympic dam deposit situated along the margin of the proterozoic gawler craton south australia is the world s largest uranium deposit and sixth largest copper deposit it also contains significant reserves of gold silver and rare earth elements gaining a better understanding of the mechanisms for genesis of the economic liberalization is fundamental for defining exploration models in similar crustal settings to delineate crustal structures that may constrain mineral system fluid pathways coincident deep crustal seismic and magnetotelluric mt transects were obtained along a 220 km section that crosses olympic dam and the major crustal boundaries in this paper we present results from 58 long period 10 104 s mt sites with site spacing of 5 10 km a two dimensional inversion of mt data from 33 sites to a depth of 100 km shows four notable features 1 sedimentary cover sequences with low resistivity 1000 m archean crustal core from a more conductive crust and mantle to the north typically 500 m 3 to the north of olympic dam the upper middle crust to 20 km is quite resistive 1000 m but the lower crust is much more conductive 100 m and 4 beneath olympic dam we image a low resistivity region 100 m throughout the crust coincident with a seismically transparent region we argue that the cause of the low resistivity and low reflectivity region beneath olympic dam may be due to the upward movement of co2 bearing volatiles near the time of deposit formation that precipitated conductive graphite liberalization along grain boundaries simultaneously annihilating acoustic impedance boundaries the source of the volatiles may be from the mantle degassing or retrograde metamorphism of the lower crust associated with proterozoic crustal deformation

field aligned 777 4 nm composite airglow images of equatorial plasma depletions 1 we present a powerful tool to analyze two dimensional field aligned images of equatorial plasma depletions taken from mid latitudes by shifting each individual image by the sum of the longitudinal offsets obtained by performing a cross correlation between successive images a single composite image can be formed for the entire night it is shown that these field aligned composite images give information on the observation times of the depletions associated with spread f as they pass by hawaii in addition they can be used to estimate the formation time and location of the depletions to the west of the observing site this technique also yields estimates of the eastward velocity and velocity shear of the depletions we suggest that the information gained by using these images can be used to predict satellite scintillations at stations to the east of the observing station

telemetry interference incorrectly interpreted as evidence for lightning and present day volcanism at venus spike like responses to interruptions in the data recorded by the orbiter electric field detector oefd on the pioneer venus orbiter pvo have been incorrectly identified as broadband whistler noise and then interpreted as evidence of lightning and volcanism by singh and russell 1986 1987 we show that these spikes are non physical artifacts of the processing of interruptions in telemetry data and are readily distinguished from other non artificial noise appearing in the measurements we independently analyze the spikes and the non artificial noise to show that key portions of the results of singh and russell are compromised by the inclusion of the artificial data this conclusion is certified by the fact that a the distribution of the spikes only data matches the distribution of noise presented by singh and russell while b the number and distribution of all non spike noise is quite incompatible with their results this finding is consistent with our prior research and leads us to reiterate that the pvo electric field data set used by singh and russell provides no basis for inferring the presence of either lightning or present day volcanism at venus

lead isotope systematics of vein type antimony mineralization rheinisches schiefergebirge germany a case history of complex reaction and remobilization processes mesothermal vein type sb mineralization in the rheinisches schiefergebirge germany is characterized by two different mineralization styles which are 1 extensional quartz stibnite vein systems and 2 cu pb sb sulphosalt assemblages in overprinted pre existing pb zn veins a detailed pb isotope study of 52 representative samples from both mineralization types indicates distinct compositional patterns cu pb sb sulphosalts meneghinite boulangerite bournonite formed by reaction remobilization are characterized by pb isotope compositions 206pb 204pb 18 179 18 223 which are identical to the precursor galena 206pb 204pb 18 168 18 223 the pb isotope composition of sulphosalt minerals in these vein systems was controlled by lead inherited from pre existing galena stibnite and pb sulphosalts zinkenite semseyite plagionite formed in quartz stibnite vein systems display pb isotope ratios 206pb 204pb 18 250 18 354 which are more radiogenic than galenas from variscan pb zn ore veins 206pb 204pb 18 162 18 303 detailed small scale investigation of thrust zones hosting pb zn ores and crosscutting quartz ankerite fissure veins ramsbeck deposit indicates that the pb isotope compositions of recrystallized galena and remobilized phases boulangerite semseyite bournonite are arranged along a linear trend this is interpreted as mixing between primary galena with 206pb 204pb 18 206 and overprinting hydrothermal fluids with a more radiogenic composition 206pb 204pb 18 354 expressed by intermediate compositions 206pb 204pb 18 256 18 334 of newly formed sulphosalts the pb isotope systematics of the vein type sb mineralization is in accordance with a model of pb extraction from similar crustal sources palaeozoic sedimentary sequences at different times

first observation of interhemispheric asymmetry in the epbs during the st patrick s day geomagnetic storm of 2015 in this work we have studied the characteristics of epbs such as their zonal drift and tilt from the low latitude and dip equatorial region in the indian longitude sector during the main phase of the 17 march 2015 storm all sky airglow imaging observations from tirunelveli 8 7on 77 8oe geographic 1 7on dip latitude and kolhapur 16 7on 74 3oe geographic 11 5on dip latitude are utilized here on 17 march 2015 epbs were observed to drift eastward during 14 30 16 30 ut between 3os and 15on dip latitudes a westward drift presumably under the influence of the disturbance dynamo electric field ddef initially appeared at higher dip latitudes almost 10 hours after the storm onset and subsequently the same was observed at lower dip latitudes the epbs attained a peak westward drift at 17 00 ut followed by a gradual decrease in their speed till 18 30 ut after regaining their westward speed the epbs continued to drift westward till 22 00 ut moreover a latitudinal gradient in the drift motion of the epbs was also observed on this night another interesting observation made from the images obtained from tirunelveli was the presence of a large westward tilt of the epbs the most intriguing finding of this study however was the asymmetry in the tilt of the epbs at conjugate points during the pre midnight hours on 17 march 2015 in this study the possible mechanisms that can explain these observations are discussed in the light of the current understanding of the equatorial electrodynamics and epbs

optical interferometric measurements of nighttime equatorial thermospheric winds at arequipa peru we obtained nighttime measurements of equatorial thermospheric wind dynamics at arequipa peru with an automated field widened fabry perot interferometer between april 1983 and august 1983 and reduced data from 62 nights significant seasonal variations in both zonal and meridional components of the thermospheric neutral wind vector were observed near the equinox between 2000 and 2300 lt the zonal wind component is eastward with an amplitude between 100 and 150 m s that gradually ebbs to zero by dawn the meridional component is generally small throughout the night in the winter months may august and at the winter solstice the zonal wind persists eastward throughout the night with speeds between 50 and 150 m s the meridional component is directed poleward southward toward the winter hemisphere with a speed of 50 75 m s that decays to zero by midnight comparison with the predictions of the national center for atmospheric research thermospheric general circulation model for equinoctial and solstice conditions shows good agreement we conclude that the observed seasonal changes are caused by the changing nature of the solar forcing function the arequipa results found the day to day variability in the winter thermospheric winds to be less than that found for the summer equatorial observations obtained at kwajalein interferometric measurements of the 630 0 nm intensity at equinox showed a major reduction of the emission lasting 1 or 2 hours in all directions but south shortly after evening twilight this decrease was not observed during winter