ground based observations of volcanism on io in 1999 and early 2000 ground based observations of volcanism on io during the period of the 1999 and early 2000 galileo close flybys have detected several types of activity providing information which complements the spacecraft observations at loki a brightening began between august 25 and september 9 and continued through february on august 2 a major outburst was observed near 14 n 74 w whose brightness corresponds to an area of approximately 350 km 2 at a temperature of 1100 k observations of eruptions in late june 9906a and in late november 9911a at tvashtar provide temporal and photometric constraints on activity also seen by galileo high resolution adaptive optics images provide further information on the fainter sources distributed across the surface

two classes of volcanic plumes on io abstract comparison of voyager 1 and voyager 2 images of the south polar region of io has revealed that a major volcanic eruption occured there during the period between the two spacecraft encounters an annular deposit 1400 km in diameter formed around the aten patera caldera 311 w 48 s the floor of which changed from orange to red black the characteristics of this eruption are remarkably similar to those described earlier for an eruption centered on surt caldera 338 w 45 n that occured during the same period also at high latitude but in the north both volcanic centers were evidently inactive during the voyager 1 and 2 encounters but were active sometime between the two the geometric and colorimetric characteristics as well as scale of the two annular deposits are virtually identical both resemble the surface features formed by the eruption of pele 255 w 18 s these three very large plume eruptions suggest a class of eruption distinct from that of six smaller plumes observed to be continously active by both voyagers 1 and 2 the smaller plumes of which prometheus is the type example are longer lived deposit bright whitish material erupt at velocities of 0 5 km sec 1 and are concentrated at low latitudes in an equatorial belt around the satellite the very large pele type plumes on the other hand are relatively short lived deposit darker red materials erupt at 1 0 km sec 1 and rather than restricted to a latitudinal band are restricted in longitude from 240 to 360 w both direct thermal infrared temperature measurements and the implied color temperatures for quenched liquid sulfur suggest that hot spot temperatures of 650 k are associated with the large plumes and temperatures 2 in their annuli whereas the large plumes apparently do not two other plumes that occur at either end of the linear feature loki may be intermediate or hybrid between the two classes exhibiting attributes of both additionally loki occurs in the area of overlap in the regional distributions of the two plume classes two distinct volcanic systems involving different volatiles may be responsible for the two classes we propose that the discrete temperatures associated with the two classes are a direct reflection of sulfur s peculiar variation in viscosity with temperature over two temperature ranges 400 to 430 k and 650 k sulfur is a low viscosity fluid orange and black respectively at other temperatures it is either solid or has a high viscosity as a result there will be two zones in io s crust in which liquid sulfur will flow freely a shallow zone of orange sulfur and a deeper zone of black sulfur a low temperature system driven by so 2 heated to 400 to 400 k by the orange sulfur zone seems the best model for the small plumes a system driven by sulfur heated to 650 k by hot or even molten silicates in the black sulfur zone seems the best explanation for the large plume class the large pele type plumes are apparently concentrated in a region of the satellite in which a thinner sulfur rich crust overlies the tidally heated silicate lithosphere so the black sulfur zone may be fairly shallow in this region the prometheus type plumes are possibly confined to the equatorial belt by some process that concentrates so 2 fluid in the equatorial crust

contrasting geochemical features of the central iberian zone shales iberian massif spain implications for the evolution of neoproterozoic lower cambrian sediments and their sources in other peri gondwanan areas abstract more than 90 samples of shales have been collected for geochemical purposes from neoproterozoic and lower cambrian sedimentary series in an extensive area of the central iberian zone ciz for similar sio2 and al2o3 abundances the neoproterozoic shales ns are characterized by relatively higher tio2 and zr abundances and by higher cr th and ti nb ratios by contrast the lower cambrian shales lcs have higher al2o3 tio2 rb zr la yb cn and th yb ratios diagrams such as al2o3 tio2 al2o3 tio2 ti nb tio2 zr tio2 zr nb and ti nb rb zr are useful to define two distinct fields that discriminate the neoproterozoic from the lower cambrian compositions these and other geochemical features suggest that these rocks were derived from different source compositions and that the lower cambrian shales lcs were chemically more fractionated than those of the neoproterozoic these distinctive chemical features are also recorded by neoproterozoic and cambrian fine grained rocks in other areas in the central iberian zone and in other zones within iberia published neodymium isotopic results consistently distinguish both compositions and together with the geochemical data support a relatively fractionated nature for the lower cambrian sediments compared to the neoproterozoic ones it is proposed that continental deposits derived from the interior orogens in north gondwana would have been the sources for neoproterozoic sediments in the iberian zones whereas the lower cambrian sediments in these zones would have been derived from older crust beneath those continental deposits thus the neoproterozoic lower cambrian stratigraphic succession in iberia reflects an inverse stratigraphy of the source area and contrasts with zones of central and western europe where equivalent sedimentary series record important coeval igneous contributions and show less fractionated geochemical characteristics finally the possible connection between the central iberian zone and the meguma zone mz in canada is discussed on the basis of certain sedimentological and geochemical features it is proposed that the sedimentary series of the central iberian zone and of the meguma zone represent respectively proximal and distal north gondwana derived sediments

retrograde evolution in the central vosges mountains northeastern france implications for the metamorphic history of high grade rocks during the variscan orogeny abstract metamorphism in the vosges massif is characterized by rocks formed under a wide range of pressures and temperatures high pressure rocks garnet peridotites and eclogites facies rocks are found together with low pressure rocks garnetcordierite stability field hitherto metamorphism has been interpreted within the framework of an identical p t evolution for all rock types corresponding to either two separate geotectonic events or a unique p t evolution from high pressure to low pressure conditions we studied gneisses from the vosges massif in order to constrain the p t t path they followed p t estimation indicates that gneisses equilibrated between 5 and 7 kbar during peak metamorphism time rocks later experienced cooling from temperatures above 650 c down to 550 c it is possible that the entire p t evolution of the gneisses took place within the lower part of the amphibolite facies which is inconsistent with the p t evolution of the high pressure rocks the noteworthy absence of muscovite staurolite assemblages is attributed to conditions of low h2o and low o2 activity the consequences for the geodynamics in the vosges massif are that at least two separate geotectonic events are required in order to explain the juxtaposition of high pressure rocks with low pressure amphibolite facies rocks

upper neoproterozoic lower cambrian sedimentary successions in the central iberian zone spain sequence stratigraphy petrology and chemostratigraphy implications for other european zones o3 tio2 zr and nb abundances in shales from all the units strongly suggest a gradual compositional change within this sedimentary succession together with the petrological data the chemical results do not reveal any obvious coeval volcanic contribution to the sediments on the basis of the chemical data a comparison is made with other european zones containing detrital sediments composed of reworked crustal components

global color variations on io abstract visible and near infrared images of io from the galileo spacecraft reveal a surface more colorful than previously thought red yellow green white and black hues decorate the satellite presumably caused by a varied composition of sulfur compounds and silicates almost a third of io is covered by red and orange materials particularly at polar latitudes above 30 these red regions were scarcely distinguishable in the shorter wavelength voyager observations bright red pyroclastic deposits mark the locations of many hot spots plumes and visible surface changes providing a prominent flag of recent volcanic activity io s equatorial regions are dominated by yellow materials which occupy about 40 of the satellite s surface white and gray materials cover about 27 of io primarily in equatorial areas and in localized deposits at high latitudes these are identified with moderate to coarse grained so2 as mapped by the nims instrument on galileo r w carlson et al 1997 geophys res lett 24 2479 2482 greenish yellow materials in small isolated spots on io s anti jupiter hemisphere were recently discovered in 3 km pixel color imaging from orbit 14 unlike other ionian terrains these regions have a negative near infrared spectral slope suggesting contamination by a nonsulfur component only about 1 4 of io s surface is occupied by dark materials which display a variety of visible colors ranging from black to red and green most dark spots have a shallow spectral absorption feature at 0 9 m suggesting magnesium rich silicates rather than black sulfur little large scale alteration in the global color and albedo pattern has occurred between the voyager and galileo eras 90 of the surface appears unchanged despite the vigorous volcanic activity which must have taken place in the intervening 17 years this suggests that over a time scale of decades the bulk of io s resurfacing is restricted to a few small but persistently active areas

tidal dissipation surface heat flow and figure of viscoelastic models of io abstract the distribution of hot spots on io s surface and io s figure constrain models of io s interior voyager observations indicate that most hot spots and volcanic plumes are close to the equator recently however it has been proposed that a large low albedo feature in the south polar region may be the source of 40 of the surface heat flow we calculate spatial distributions of the dissipation rate surface heat flow and the figures of three and four layer maxwell rheology models of io by using the correspondence principle the models are required to satisfy the observed surface heat flow constraint and are consistent with the composition of a dehydrated c2 chondrite they consist of an inviscid fe fes core and viscoelastic silicate mantle and lithosphere layers a comparison of the calculated equilibrium figure with the observed figure of io supports the chosen core radius of 980 km in addition the four layer model has a partially molten asthenosphere a few tens of kilometers thick the preferred three layer model has a mantle shear modulus of 10 10 pa and a viscosity of 2 10 16 pa s consistent with rock properties the tidal dissipation rate for this model is largest along the polar axis integration of the dissipation rate over radius gives a surface heat flow with maxima at the poles and minima near the sub jovian and anti jovian points in contrast the dissipation rate in a molten or partially molten incompressible asthenosphere has maxima near the equator and is close to zero at the poles the asthenosphere dissipation rate is mainly a function of asthenosphere viscosity and thickness the thinner the asthenosphere the smaller is the required viscosity a 50 km thick asthenosphere requires a viscosity of about 10 8 pa s a strong south polar hot spot if it can be confirmed by infrared observation favors dissipation in the mantle but does not exclude dissipation in a partially molten asthenosphere equatorial hot spots and the concentration of prometheus type plumes near the equator favor asthenosphere heating but do not rule out deep mantle dissipation both asthenosphere and deep mantle heating may contribute to io s surface heat flow the properties of magma transport through the lithosphere and the planform of mantle convection might exert a control on the surface expression of heating at greater depth

a history of high temperature io volcanism february 1995 to may 1997 ground based observations of io s infrared thermal emission between february 1995 and may 1997 show several discrete brightenings for which we can constrain locations fluxes and durations several of these were brief high temperature events with temperatures up to at least 1500 k similar to but often smaller than the rare outbursts seen previously loki io s most powerful volcano was relatively active before and probably during galileo s december 1995 io flyby was faint during most of 1996 and began a major long lived brightening between february 20 and march 12 1997 thermal emission was not seen from ra patera site of an active plume in galileo images major outbursts were seen on march 2nd and september 27 1995

a survey of io s volcanism by adaptive optics observations in the 3 8 μm thermal band 1996 1999 in this study we analyze a series of images of io obtained with the european southern observatory adaptive optics system adaptive optics near infrared system adonis at 3 8 m from 1996 to 1999 with particular emphasis on the observations carried out in late 1999 in support of the galileo flybys of io use of a new myopic deconvolution method myopic iterative step preserving algorithm mistral especially designed for planetary objects significantly improves the quality and the reliability of the reconstructed images using a simulation of artificial images of io we estimate the extent to which this algorithm is able to prevent noise amplification to better restore sharp edges and to preserve the initial photometry once this algorithm has been applied to our data and the solar reflected background has been subtracted we have 89 images of io available for search and temporal survey of the hot spots over 4 years in most cases the data acquired during two consecutive nights provide an almost global view of the surface of io we identify 20 hot spots for which we determine the coordinates and the brightness at 3 8 m as a function of time more than half of the hot spots were detected on all the images and were considered as persistent particular emphasis has been put on the brightest two hot spots loki and pele for which we obtain a center to limb variation curve a cosine curve for loki and a curve decreasing slightly faster than a cosine law for pele with possible physical interpretations the temporal variations of their activity have been derived over these 4 years and for loki compared with the results of other ground based surveys the variability of the other fainter sources has also been derived but with less accuracy we have also identified a few new hot spots some of which are transient such as a diffuse emission seen in september and november 1999 at the location of the upcoming tvashtar outburst the data are based on observations 58 f 1003 63 s 0260 and 64 s 0661 collected at the european southern observatory in la silla chile

u pb investigations on zircons from pre variscan gneisses i a study from the schwarzwald west germany abstract field observations in the schwarzwald indicate that pre variscan rocks were formed by the following events 1 1 intrusion of granitic to granodioritic magma into sediments 2 2 a sequence of two anatectic events with an intervening regional metamorphism and development of a gneissic schistosity the absolute chronology of these older gneisses and migmatites has not yet been satisfactorily resolved we collected several samples of a coarse grained homogeneous orthogneiss of granodioritic composition and one sample of a metasedimentary source rock related to this orthogneiss body in the einetwald forest north of steinach kinzig valley the metasedimentary rock corresponds to the biotitepoor paragneisses in the schwarzwald the zircons in the latter sample are detrital and only very small specimens 45 m are euhedral the zircons from the orthogneiss samples are euhedral some are zoned and some have dark inclusions analyses of the three coarser fractions of the paragneiss form a linear array on a concordia diagram with upper and lower intercepts of about 2000 myr and 524 20 myr respectively the 2000 myr value is interpreted as the average age of the sedimentary source rocks for this material the 524 myr intercept defines an event responsible for most of the lead loss in the zircons as well as new zircon growth analyses of the zircons from the orthogneiss samples do not show a linear array on the concordia diagram because of inclusions of older inherited zircons stepwise leaching of two zircon fractions shows newly grown u rich zircon rims around old cores a 207 pb 206 pb age of 517 15 myr was found for the first dissolution steps about 50 of the zircons dissolved in subsequent steps with progressive dissolution of the residue 207 pb 206 pb age increased to 950 myr the u pb zircon data for the paragneiss and the orthogneiss establish an age of 520 15 myr for the magma intrusion

active volcanism on io global distribution and variations in activity abstract io s volcanic activity has been monitored by instruments aboard the galileo spacecraft since june 28 1996 we present results from observations by the near infrared mapping spectrometer nims for the first 10 orbits of galileo correlate them with results from the solid state imaging system ssi and from groundbased observations and compare them to what was known about io s volcanic activity from observations made during the two voyager flybys in 1979 a total of 61 active volcanic centers have been identified from voyager groundbased and galileo observations of these 41 are hot spots detected by nims and or ssi another 25 locations were identified as possible active volcanic centers mostly on the basis of observed surface changes hot spots are correlated with surface colors particularly dark and red deposits and generally anti correlated with white so 2 rich areas surface features corresponding to the hot spots mostly calderas or flows were identified from galileo and voyager images hot spot temperatures obtained from both nims and ssi are consistent with silicate volcanism which appears to be widespread on io two types of hot spot activity are present persistent type activity lasting from months to years and sporadic events which may represent either short lived activity or low level activity that occasionally flares up sporadic events are not often detected but may make an important contribution to io s heat flow and resurfacing the distribution of active volcanic centers on the surface does not show any clear correlation with latitude longitude voyager derived global topography or heat flow patterns predicted by the asthenosphere and deep mantle tidal dissipation models however persistent hot spots and active plumes are concentrated toward lower latitudes and this distribution favors the asthenosphere rather than the deep mantle tidal dissipation model

the upper neoproterozoic lower cambrian of the central iberian zone spain chemical and isotopic sm nd evidence that the sedimentary succession records an inverted stratigraphy of its source the upper neoproterozoic lower cambrian sedimentary succession in the central iberian zone has recently been divided into 12 sedimentary units i to xii units i to iv are of late neoproterozoic age and units v to xii are early cambrian throughout the stratigraphic section shales with similar ranges of sio2 and al2o3 have tio2 and zr contents that are coupled and vary gradually from the bottom unit i tio2 1 0 1 1 zr 245 287 ppm to the top unit xii tio2 0 74 0 86 zr 141 192 ppm these two parameters clearly distinguish upper neoproterozoic from lower cambrian compositions as do certain elemental ratios al2o3 tio2 rb zr nb ti which vary from low values at the bottom of the section to high at the top however other elements the rare earth elements rees y do not fit this general trend with heavy rees and y showing extreme concentrations in some lower cambrian units which also have negative ce anomalies units i to iii and units xi to xii have uniform tdm neodymium model ages 1 1 and 1 7 ga respectively but the units between these two groups have erratic values between 1 4 ga unit vii and 3 4 ga unit viii thus the bottom and top units have neodymium isotope ratios that indicate the presence of two source compositions a composition that records a juvenile contribution younger than 1 1 ga and a composition mainly derived from an old basement some samples from lower cambrian units have disturbed ree abundances and neodymium isotope ratios that are attributed to extensive chemical alteration that resulted in ree and y redistribution this alteration probably affected the material now preserved as unit iv during a period of relative sea level fall at the end of the late neoproterozoic both elemental and isotopic results support the suggestion that the upper neoproterozoic lower cambrian stratigraphic section records an inverse stratigraphy of a source hinterland composed of a cover sequence of relatively juvenile crustal materials underlain by an older basement through time the deeper crust gradually increased its contribution to the sediments in the basin from late neoproterozoic to lower cambrian times these results are compatible with data from many other european zones

palaeozoic evolution of the variscan vosges mountains a geological synthesis of the palaeozoic vosges mountains ne france is presented using existing observations and new data the geodynamic evolution involves 1 early palaeozoic sedimentation and magmatism 2 late devonian subduction triggering back arc spreading 3 early lower carboniferous continental subduction continent continent collision and polyphase deformation and metamorphism of the orogenic root and 4 late lower carboniferous orogenic collapse driven by thermal weakening of the middle crust the evolution is integrated within the framework of the european variscan belt the northern vosges comprise sediments of rhenohercynian affinity separated from tepla barrandian metasediments by a lower carboniferous magmatic arc the latter is correlated with the mid german crystalline rise and is ascribed to the south directed subduction of the rhenohercynian basin the saxothuringian moldanubian suture is thought to be obliterated by the magmatic arc while the lalaye lubine fault is interpreted as the tepla barrandian moldanubian boundary the central vosges are paralleled with the moldanubian domain of the bohemian massif where identical lithologies record the devonian carboniferous se directed subduction of the saxothuringian passive margin below the moldanubian upper plate the southern vosges represent the upper moldanubian crust and are linked to the southern black forest the presence of an oceanic domain to the south of the vosges black forest remains unclear

observations and initial modeling of lava so2 interactions at prometheus io we present observations and initial modeling of the lava so2 interactions at the flow fronts in the prometheus region of io recent high resolution observations of prometheus reveal a compound flow field with many active flow lobes many of the flow lobes are associated with bright streaks of what is interpreted to be volatilized and recondensed so2 radiating away from the hot lava lower resolution color data show diffuse blue to violet areas also near the active flow front perhaps from active venting of so2 not clearly visible in any of the images is a single source vent for the active plume while the size of the proposed vent is probably near the limit of the resolution we expected to see radial or concentric albedo patterns or other evidence for gas and entrained particles above the flow field the lack of an obvious plume vent earlier suggestions that the prometheus type plumes may originate from the advancing flow lobes and the high resolution images showing evidence for large scale volatilization of the so2 rich substrate at prometheus encouraged us to develop a model to quantify the heat transfer between a basaltic lava flow and a substrate of so2 snow we calculate that the vaporization rate of so2 snow is 2 5 10 6 m s 1 per unit area using an estimated 5 m2 s 1 lava coverage rate from change detection images we show that the gas production rate of so2 at the flow fronts is enough to produce a resurfacing rate of 0 24 cm yr 1 at the annulus of prometheus this is much less than other estimates of resurfacing by the prometheus plume while not easily explaining the main prometheus plume our model readily accounts for the bright streaks

rb sr and u pb isotope studies on migmatites from the schwarzwald germany constraints on isotopic resetting during variscan high temperature metamorphism mineral and isotope studies were undertaken on migmatites from the schwarzwald moldanubian zone of the variscan belt the aims of the study were to date the migmatite formation and to determine the processes involved in migmatization in order to evaluate their influence on isotopic resetting textural evidence and the comparison of mineral compositions from leucosomes and mesosomes of two centimetre scale migmatite profiles respectively suggest that migmatitic textures and mineral assemblages were formed by metamorphic segregation deformation enhanced mass transport rather than by partial melting anatexis the results of rb sr thin slab dating on these profiles indicate that sr isotopes were not completely reset during migmatization no true isochron ages but ages of approximate isotopic homogenization were obtained on the thin slabs by calculating 87sr 86sr ratios back to various stages in their evolution the coincidence of these rb sr data with u pb ages of monazites from migmatites and non migmatitic gneisses shows that gneisses and migmatites were formed during the same high temperature event in the carboniferous 330 335 ma the observation that high temperature metamorphism failed to equilibrate sr isotopes on the centimetre scale imposes limitations on the use of conventional whole rock isochron techniques in dating migmatites

the rand granite in the southern schwarzwald and its geodynamic significance in the variscan belt of sw germany the rand granite is a heterogeneous metamorphosed granitoid rock complex with numerous wallrock inclusions situated in the moldanubian zone at the southern margin of the central schwarzwald gneiss complex it is a largely mylonitized elongated body and is thrust over the badenweiler lenzkirch zone forming a nappe with shear zones along its northern and southern boundaries it comprises meta granites meta trondhjemites and biotite augen gneisses derived from monzogranites to granodiorites mineral behaviour indicates that the magmatic body has been deformed under upper greenschist facies conditions nappe thrusting which also affected the south schwarzwald gneiss complex occurred in visean time during high temperature low pressure metamorphism kinematic indicators in the mylonites document e to ese directed nappe transport highly transpressive relative to the trend of the nappe boundaries and the foliation the trondhjemites formed at 351 5 4 ma predating the variscan ht metamorphism they have initial end values of 6 6 to 6 7 and relatively low initial 87sr 86sr ratios 0 7042 to 0 7063 indicating a predominant mantle origin the granites and protoliths of the biotite augen gneisses probably crystallised between 436 and 377 ma suggested by u pb zircon model ages they are different from the trondhjemites with low initial end values 4 7 to 3 3 and higher initial 87sr 86sr ratios 0 7068 0 7077 indicating that large part of the rand granite originated from anatexis of continental crust internal structure of zircons from the rand granite reveals mixing of magmas derived from both mantle and crust sources these new data support an interpretation that the rand granite developed along an active continental margin and therefore represents a possible root of a variscan magmatic arc

upper neoproterozoic series in the central iberian cantabrian and west asturian leonese zones spain geochemical data and statistical results as evidence for a shared homogenised source area abstract analyses 100 of six groups of upper neoproterozoic shales from different areas in central and northern spain covering an extension of over 60 000 km2 reveal relatively uniform major and trace element abundances and values of relevant ratios such as al2o3 tio2 k2o al2o3 mol ti zr ti nb rb zr rb th sm nd eu eu la yb n la nb zr y zr nb th nb th yb th u and cr zr the six groups of shales define indistinguishable chondrite normalised and upper continental crust normalised patterns for rare earth and trace elements respectively and show relatively low fractionated geochemical features compared with those of the continental upper crust statistical calculations demonstrate a normal distribution of the abundances of major and trace elements and element ratios they suggest a remarkable geochemical homogeneity for the upper neoproterozoic series studied and they separate this series from the lower cambrian one in the central iberian zone on the basis of 15 element ratios the extension of the upper neoproterozoic detrital series and the similar geochemical features of shales in all the studied areas suggest an extensive and homogenised source region thus the mean of the 100 analyses neoproterozoic iberian average shale nibas is proposed as a standard of comparison to identify the specific recycled and homogenised source for detrital upper neoproterozoic sediments in central and northern iberia and probably also in other european peri gondwanan areas the ranges of statistically distinctive geochemical parameters separating the upper neoproterozoic from the lower cambrian series are given as possible criteria to help in the studies of areas where no other data provide conclusive information about the series ages

internal structure of io and the global distribution of its topography abstract the distribution of equatorial long wavelength topography on io consists of alternating basins and swells similar to the pattern expected if tidal heating in a thin asthenosphere controls the elevation of the surface through a conductive lithosphere in isostatic equilibrium the equatorial basin swell pattern is shifted in longitude with respect to theoretical tidal heating patterns however making the correlation between theoretical heat flow and elevation unclear we calculate global topography for multilayer io models with dissipation occurring in a viscous asthenosphere and a solid mantle two models are considered a thermal swell model in which topography and heat flow are positively correlated and a differentiated lithosphere model in which topography and heat flow are negatively correlated both models match the observed pattern of alternating basins and swells along the equator and moderate polar topography if about two thirds of the tidal heating occurs in the asthenosphere and about one third occurs in the underlying solid mantle the mean thicknesses of the model lithospheres are 35 km in the differentiated model and 150 km in the thermal swell model polar topography and the hypsometric distribution of elevations in the differentiated lithosphere model match the observations better than the thermal swell model in a differentiated lithosphere model consistent with the topography the asthenosphere is at least 50 km thick with viscosity about 100 mpa sec and is about 7 more dense than the lithosphere the mantle density exceeds the asthenosphere density by at least 10 the shift of the equatorial basin swell pattern suggests that io s lithosphere has recently undergone a zonal rotation of about 25

determining sedimentation ages of high grade metamorphic gneisses by their palynological record a case study in the northern schwarzwald variscan belt germany in the northern schwarzwald moldanubian zone of the variscan belt paragneisses drilled from approximately 2500 m depth at the buhl 1 drilling site have experienced amphibolite facies metamorphism and were later partly transformed to mylonites under greenschist facies conditions completely graphitised acritarchs and chitinozoans were recovered from these paragneisses and mylonitic gneisses whereas both groups of palynomorphs give evidence of a marine depositional environment only the chitinozoans are stratigraphically useful in this case and indicate a paleozoic age previous findings of acritarchs in a different high grade metamorphic gneiss unit within the schwarzwald indicate an upper proterozoic marine sedimentation age the spectrum of palynomorphs found thus far in the schwarzwald in combination with petrological data suggests that within the moldanubian domain of the armorican microplate rocks with different sedimentary records later experienced diverging prograde metamorphic histories in general the results reveal that palynological studies in combination with petrological data are a promising tool for reconstructing pre orogenic settings in collisional belts

mountains on io high resolution galileo observations initial interpretations and formation models during three close flybys in late 1999 and early 2000 the galileo spacecraft acquired new observations of the mountains that tower above io s surface these images have revealed surprising variety in the mountains morphologies they range from jagged peaks several kilometers high to lower rounded structures some are very smooth others are covered by numerous parallel ridges many mountains have margins that are collapsing outward in large landslides or series of slump blocks but a few have steep scalloped scarps from these observations we can gain insight into the structure and material properties of io s crust as well as into the erosional processes acting on io we have also investigated formation mechanisms proposed for these structures using finite element analysis mountain formation might be initiated by global compression due to the high rate of global subsidence associated with io s high resurfacing rate however our models demonstrate that this hypothesis lacks a mechanism for isolating the mountains the large fraction 40 of mountains that are associated with paterae suggests that in some cases these features are tectonically related therefore we have also simulated the stresses induced in io s crust by a combination of a thermal upwelling in the mantle with global lithospheric compression and have shown that this can focus compressional stresses if this mechanism is responsible for some of io s mountains it could also explain the common association of mountains with paterae

mountains and calderas on io possible implications for lithosphere structure and magma generation abstract the combination of voyager images and newly acquired galileo images with low illumination and resolutions ranging from 2 to 6 km pixel now allows determination of the global distribution of mountains and volcanic centers on io the mountains generally do not have characteristics typical of terrestrial volcanic landforms they are evenly distributed across the surface and show no obvious correlation with known hot spots or plumes relative elevations determined by shadow measurements and stereoscopy indicate that mountains in the newly imaged area range in elevation up to at least 7 6 km the origin of the mountains remains uncertain some appear to be multitiered volcanic constructs others enclosing the partial remains of large circular depressions appear to be remnants of old volcanoes yet others show extensive tectonic disruption volcanic centers also appear to be distributed evenly across the surface except for an apparently somewhat lower density at high latitudes the low latitudes have one volcanic center per 7 10 4 km 2 and on average the centers are spaced roughly 250 km apart the global distribution of high mountains suggests that the lithosphere over most of io is thick although the thickness cannot be calculated the previously suggested 30 km appears reasonable as a lower limit the high rates of resurfacing combined with the likely dissipation of most of the tidal energy in the asthenosphere and underlying mantle implies a very low temperature gradient in the upper part of the lithosphere and steep gradients in the lower lithosphere the slow rate of separation of melt from host rock in the magma source regions as a consequence of the low gravity on io coupled with the high rate of magma production will likely result in larger melt fractions than is typical for source regions on earth the variety of volcanic landforms suggests that volcanic products with a range of compositions are deposited on the surface this mixture will be carried downward through the lithosphere as a consequence of the 0 5 1 5 cm yr resurfacing rates during descent the more volatile components will tend to be driven off early but complete or near complete melting at the base of the lithosphere may result in rehomogenization of the silicate mixture that remains

landform degradation and slope processes on io the galileo view the galileo mission has revealed remarkable evidence of mass movement and landform degradation on io we recognize four major slope types observed on a number of intermediate resolution 250 m pixel 1 images and several additional textures on very high resolution 10 m pixel 1 images slopes and scarps on io often show evidence of erosion seen in the simplest form as alcove carving slumps and slides at all scales many of the mass movement deposits on io are probably mostly the consequence of block release and brittle slope failure sputtering plays no significant role sapping as envisioned by mccauley et al 1979 remains viable we speculate that alcove lined canyons seen in one observation and lobed deposits seen along the bases of scarps in several locations may reflect the plastic deformation and glacial flow of interstitial volatiles e g so2 heated by locally high geothermal energy to mobilize the volatile the appearance of some slopes and near slope surface textures seen in very high resolution images is consistent with erosion from sublimation degradation however a suitable volatile e g h2s that can sublimate fast enough to alter io s youthful surface has not been identified disaggregation from chemical decomposition of solid s2o and other polysulfur oxides may conceivably operate on io this mechanism could degrade landforms in a manner that resembles degradation from sublimation and at a rate that can compete with resurfacing

volcanic resurfacing of io post repair hst imaging abstract in march 1994 we used the newly refurbished hubble space telescope hst to obtain global imaging of io at five wavelengths between 0 34 and 1 02 m with a spatial resolution of 160 km the images provided the clearest view of io since voyager and the first systematic observations in the wavelength range 0 7 1 0 m we have produced absolutely calibrated global mosaics of io s reflectance in all our five wavelengths the near infrared images reveal that the 0 55 to 0 7 m absorption edge seen in io s disk integrated spectrum has a very different spatial distribution from the better known 0 40 to 0 50 m absorption edge studied by voyager and must be generated by a different chemical species the 0 55 to 0 7 m absorption edge is strongly concentrated in the pyroclastic ejecta blanket of the volcano pele at a few much smaller discrete spots and probably also in the polar regions the pele ejecta spectrum is consistent with the idea that s 2 o partially decomposed to s 4 and probably s 3 may be the species responsible for the 0 55 to 0 7 m absorption edge at pele and elsewhere on io though s 4 generated by other processes may also be a possibility s 2 o can be produced by high temperature decomposition of so 2 gas and the high temperature of the pele volcano may account for its concentration there spectral anomalies of comparable size and prominence are not seen around the other pele type volcanos surt and aten a s mcewen and l a soderblom 1983 icarus 55 191 217 suggesting that these volcanos if chemically similar to pele are much less active the spectrum of high latitude regions is similar to that of quenched red sulfur glass and if this similarity is not coincidental the glass may be preserved here by the low polar surface temperatures alternatively the low polar temperatures may preserve sulfur that has been reddened by radiation there are many changes in albedo patterns in the 15 years between voyager and these hst observations but these are generally subtle at hst resolution and are not strongly concentrated in longitude however there was a major brightening of a 400 km diameter region centered on ra patera between march 1994 and repeat hst observations in july 1995 which was a larger albedo change than any seen in the previous 15 years this was presumably due to a large eruption at ra patera as confirmed by galileo images long exposure eclipse images of io at 1 02 m on march 6 1994 place strong limits on the area of exposed silicate magma on io at the time of the observations

a komatiite analog to potential ultramafic materials on io ultramafic volcanism is one model which fits currently available data for some eruptions on jupiter s moon io assuming that such activity does occur it is possible to apply komatiitic analogs and terrestrial ultramafic flow models to io we have used such analogs and models along with galileo data to investigate the nature of ultramafic materials that are assumed to occur at high temperature hotspots on io the unusual komatiites of the commondale greenstone belt south africa are consistent with available galileo data on the temperatures and composition of potential ionian ultramafic materials these komatiites had high sio2 50 wt and mgo 31 wt contents which are inferred to result in high liquidus temperatures 1610 c low dynamic viscosities 0 2 pa s and low densities 2680 kg m and in the crystallization of orthopyroxene phenocrysts not found in other komatiites we used the commondale composition and the model of williams et al 1998 to investigate potential ultramafic flow behavior on io compared to their terrestrial counterparts ionian ultramafic lava flows would have less potential for turbulent flow lower maximum emplacement distances and lower thermal erosion rates because of the lower ionian gravity and their more silicic composition shallow 10 m thermal erosion channels seem less likely on io unless 1 lavas are superheated 2 lavas are more ultramafic 31 mgo 3 eruption rates eruption durations or flow volumes are high or 4 substrates are unconsolidated partly consolidated or volatile rich and thus more erodable if volatiles are present in the lava as vesicles then increasing lava vesicularity results in decreasing maximum emplacement distances decreasing thermal erosion rates and decreasing erosion channel depths for given eruption durations

geochemistry of metasediments in the hercynian and pre hercynian crust of the schwarzwald the vosges and northern switzerland abstract several units in the pre hercynian gneiss basement and hercynian schists of the schwarzwald southwestern germany and northern switzerland and the vosges france were characterized geochemically the samples are attributed to possible sedimentary protoliths by means of their main constituents groups of analyses belonging to the defined protoliths are then compared by means of statistical procedures the mann whitney test and multiple discriminant analysis which reveal significant differences so that every area is characterized by a specific pattern of major and trace elements furthermore correlations between some units of the schwarzwald and the vosges are possible the gneisses of ste marie aux mines vosges can be closely correlated with those of the central schwarzwald whereas there is a distinct contrast between gneisses of the central schwarzwald and gneisses of the southern schwarzwald the schists of baden baden schwarzwald most probably have their counterpart in the schists of ville in the vosges

global scale sea surface variability from combined altimetric and tide gauge measurements by correcting geosat altimetric data for a set of line frequencies and then doing a heavy average in space and time a set of global maps of sea surface variability is produced over time intervals ranging from three months to two years these maps are demonstrated to be consistent with the global network of tide gauges and sets of maps incorporating those data into the altimetric estimates are also produced tide gauge records too fragmentary for computation of a two year mean are employed by time differencing them an estimate of the global difference of sea level change over one year on very large space scales shows the effects of the 1987 el nino the spherical harmonic coefficients employed in the computations are then used to estimate the full three dimensional frequency wavenumber spectrum of surface circulation variability

violent silicate volcanism on io in 1996 we monitored io s volcanic thermal emission from 1 7 to 4 8 m in 1995 96 the data reveal a number of brightenings when io s thermal emission increased several fold we use a model of emission from lava flows to understand observations of two brightenings in 1996 the brightenings were caused by eruptions 3km in extent with eruptive rates of 104 106 m s 1 and with maximum lava temperatures 1400 k these events were probably lava lakes and or fire fountains

shrimp dating of zircons from high grade metasediments of the schwarzwald sw germany and implications for the evolution of the moldanubian basement four metasedimentary zircon populations from different tectonometamorphic units of the central and the northern schwarzwald variscan belt sw germany were investigated using sem cathodoluminescence and shrimp dating despite partially strong modifications of primary internal morphologies during variscan metamorphism at amphibolite 750 c 0 4 0 6 gpa and granulite facies conditions 950 1 000 c 1 4 1 8 gpa many grains show well preserved protolith ages the detritus indicates a northern gondwana origin and different palaeozoic episodes of sediment deposition and consolidation two of the studied sediments were deposited in cambrian early ordovician times and consolidated in positions close to northern gondwana late ordovician and rare devonian detritus from sediments of two other tectonometamorphic units indicates much later sedimentation close to the leading edge of gondwana or a terrane assemblage during northern drift towards laurussia subsolidus growth of new zircon due to variscan granulite facies metamorphism of one of the tectonometamorphic units is precisely dated at 335 2 ma

magmatic differentiation of io abstract if io has been volcanically active through much of its history it must be highly differentiated we present an initial attempt to quantify the differentiation of the silicate portion of io we suggest that on average each part of io has undergone about 400 episodes of partial melting we employ a widely used thermodynamic model of silicate melts to examine the effect of such repeated differentiation despite many caveats including a grossly oversimplistic model of the differentiation process uncertainties in the initial composition of the mantle and the failure to model more than four episodes of partial melting we are able to make some robust conclusions io should have a roughly 50 km thick low density 2600 2900 kg m 3 alkali rich siliceous crust composed primarily of feldspars and nepheline the crustal magmas should have relatively low melting temperatures

volcanic activity on io during the galileo era abstract galileo s explorations have revealed a remarkable variety of eruptive styles among io s diverse volcanoes activity at hundreds of volcanic centers ranges from dormant through sporadic to continuous over the 20 year period of spacecraft observation high temperature volcanism is common on io suggesting that the lavas are made up of mafic to ultramafic silicates rather than sulfur compounds io s largest plumes are driven by so2 and sulfur rich gasses vented from the silicate interior that produce prominent red pyroclastic deposits red deposits flag the source regions of many other ongoing or very recent eruptions smaller plumes are produced near the margins of active lava flows by explosive volatilization of the underlying or surrounding so2 these plumes produce so2 snowflakes that mantle existing topography io s volcanism drives significant variations in the atmosphere and plasma torus yet most of the heat loss occurs through lava flows and by the quiet overturning of lava lakes without

active volcanism on io as seen by galileo ssi abstract active volcanism on io has been monitored during the nominal galileo satellite tour from mid 1996 through late 1997 the solid state imaging ssi experiment was able to observe many manifestations of this active volcanism including 1 changes in the color and albedo of the surface 2 active airborne plumes and 3 glowing vents seen in eclipse about 30 large scale tens of kilometers surface changes are obvious from comparison of the ssi images to those acquired by voyager in 1979 these include new pyroclastic deposits of several colors bright and dark flows and caldera floor materials there have also been significant surface changes on io during the galileo mission itself such as a new 400 km diameter dark pyroclastic deposit around pillan patera while these surface changes are impressive the number of large scale changes observed in the four months between the voyager 1 and voyager 2 flybys in 1979 suggested that over 17 years the cumulative changes would have been much more impressive there are two reasons why this was not actually the case first it appears that the most widespread plume deposits are ephemeral and seem to disappear within a few years second it appears that a large fraction of the volcanic activity is confined to repeated resurfacing of dark calderas and flow fields that cover only a few percent of io s surface the plume monitoring has revealed 10 active plumes comparable to the 9 plumes observed by voyager one of these plumes was visible only in the first orbit and three became active in the later orbits only the prometheus plume has been consistently active and easy to detect observations of the pele plume have been particularly intriguing since it was detected only once by ssi despite repeated attempts but has been detected several times by the hubble space telescope at 255 nm pele s plume is much taller 460 km than during voyager 1 300 km and much fainter at visible wavelengths prometheus type plumes 50 150 km high long lived associated with high temperature hot spots may result from silicate lava flows or shallow intrusions interacting with near surface so2 a major and surprising result is that 30 of io s volcanic vents glow in the dark at the short wavelengths of ssi these are probably due to thermal emission from surfaces hotter than 700 k with most hotter than 1000 k well above the temperature of pure sulfur volcanism active silicate volcanism appears ubiquitous there are also widespread diffuse glows seen in eclipse related to the interaction of energetic particles with the atmosphere these diffuse glows are closely associated with the most active volcanic vents supporting suggestions that io s atmopshere is dominated by volcanic outgassing globally volcanic centers are rather evenly distributed however 14 of the 15 active plumes seen by voyager and or galileo are within 30 of the equator and there are concentrations of glows seen in eclipse at both the sub and antijovian points these patterns might be related to asthenospheric tidal heating or tidal stresses io will continue to be observed during the galileo europa mission which will climax with two close flybys of io in late 1999

mapping so2 frost on io by the modeling of nims hyperspectral images abstract we analyze a collection of hyperspectral images of io acquired by the near infrared mapping spectrometer nims of galileo during the g2 to e16 orbits of jupiter this analysis leads to the geographical distribution and physical characterization of so 2 frost deposits over about three fourths of io s surface these deposits are excellent tracers of various phenomena including volcanic production and emission atmospheric transportation condensation metamorphism irradiation and sublimation that occur throughout the so 2 cycle we assume that the deposits of solid so 2 are optically thick and are geographically mixed with other sulfur bearing compounds we first assess the mean moderate backscattering behavior of the so 2 frost henyey greenstein phase function parameter g 0 27 0 05 using a sequence of spectra at two different locations over a large range of phase angles this behavior may indicate a granular texture with many defects or a fluffy texture second a more systematic inversion of the hyperspectral images is achieved based on a linear spectral model of pure so 2 with variable grain size mixed with a spectrally neutral unit as a result we produce two global mosaics that map so 2 frost coverage and mean grain size so 2 deposits are omnipresent on io s surface at the spatial scale of this study 200 km but the so 2 frost is concentrated within several large areas centered at medium latitudes these so 2 rich regions surface coverage higher than 60 show a longitudinal correlation with plumes located lower in latitude suggesting that these plumes are the principal sources of so 2 gas after a possible dynamic condensation around the plumes or at the equator the gas is remobilized by the solar or thermal fluxes and flows mostly latitudinally toward the coldest and nearest regions devoid of hot spots third the correlation of the distribution and grain size mosaics distinguishes four different so 2 physical units that indicate relative regional variations of condensation metamorphism and sublimation finally comparisons with voyager ultraviolet a s mcewen t v johnson d l matson and l a soderblom 1988 icarus vol 75 pp 450 478 and galileo visible p geissler a s mcewen l keszthelyi r m c lopes gautier j granahan and d p simonelli 1999 icarus vol 140 pp 256 282 observations demonstrate molecular contamination of so 2 at medium and high latitudes and that these contaminated so 2 deposits may be optically thin

origin of mountains on io by thrust faulting and large scale mass movements voyager stereoimages of euboea montes io indicate that this mountain formed when a large crustal block was uplifted 10 5 kilometers and tilted by approximately 6 degrees uplift triggered a massive slope failure on the northwest flank forming one of the largest debris aprons in the solar system this slope failure probably involved relatively unconsolidated layers totaling approximately 2 kilometers in thickness overlying a rigid crust or lithosphere at least 11 kilometers thick mountain formation on io may involve localized deep rooted thrust faulting and block rotation due to compression at depth induced during vertical recycling of io s crust

stealth plumes on io we suggest that io s eruptive activity may include a class of previously undetected so2 geysers the thermodynamic models for the eruptive plumes discovered by voyager involve low to moderate entropy so2 eruptions the resulting plumes are a mixture of solid and gas which emerge from the vent and follow essentially ballistic trajectories we show that intrusion of silicate magma into buried so2 deposits can create the required conditions for high entropy eruptions which proceed entirely in the vapor phase these purely gaseous plumes would have been invisible to voyager s instruments hence we call them stealth plumes such eruptions could explain the patchy so2 atmosphere inferred from recent uv and microwave spectral observations the magma intrusion rate required to support the required gas production for these plumes is a negligible fraction of estimated global magma intrusion rates

revisiting the hypothesis of a mushy global magma ocean in io abstract the recent data from io lend new support to the hypothesis of a mushy global magma ocean persisting to this day on io

io s thermal emission from the galileo photopolarimeter radiometer galileo s photopolarimeter radiometer instrument mapped io s thermal emission during the i24 i25 and i27 flybys with a spatial resolution of 2 2 to 300 kilometers mapping of loki in i24 shows uniform temperatures for most of loki patera and high temperatures in the southwest corner probably resulting from an eruption that began 1 month before the observation most of loki patera was resurfaced before i27 pele s caldera floor has a low temperature of 160 kelvin whereas flows at pillan and zamama have temperatures of up to 200 kelvin global maps of nighttime temperatures provide a means for estimating global heat flow

prometheus io s wandering plume unlike any volcanic behavior ever observed on earth the plume from prometheus on io has wandered 75 to 95 kilometers west over the last 20 years since it was first discovered by voyager and more recently observed by galileo despite the source motion the geometric and optical properties of the plume have remained constant we propose that this can be explained by vaporization of a sulfur dioxide and or sulfur snowfield over which a lava flow is moving eruption of a boundary layer slurry through a rootless conduit with sonic conditions at the intake of the melted snow can account for the constancy of plume properties

io in the near infrared near infrared mapping spectrometer nims results from the galileo flybys in 1999 and 2000 galileo s near infrared mapping spectrometer nims observed io during the spacecraft s three flybys in october 1999 november 1999 and february 2000 the observations which are summarized here were used to map the detailed thermal structure of active volcanic regions and the surface distribution of so2 and to investigate the origin of a yet unidentified compound showing an absorption feature at 1 m we present a summary of the observations and results focusing on the distribution of thermal emission and of so2 deposits we find high eruption temperatures consistent with ultramafic volcanism at pele such temperatures may be present at other hot spots but the hottest areas may be too small for those temperatures to be detected at the spatial resolution of our observations loki is the site of frequent eruptions and the low thermal emission may represent lavas cooling on the caldera s surface or the cooling crust of a lava lake high resolution spectral observations of emakong caldera show thermal emission and so2 within the same pixels implying that patches of so2 frost and patches of cooling lavas or sulfur flows are present within a few kilometers from one another thermal maps of prometheus and amirani show that these two hot spots are characterized by long lava flows the thermal profiles of flows at both locations are consistent with insulated flows with the amirani flow field having more breakouts of fresh lava along its length prometheus and amirani each show a white ring at visible wavelengths while so2 distribution maps show that the highest concentration of so2 in both ring deposits lies outside the white portion visible measurements at high phase angles show that the white deposit around prometheus extends into the so2 ring this suggests that the deposits are thin and that compositional or grain size variations may occur in the radial direction so2 mapping of the chaac region shows that the interior of a caldera adjacent to chaac has almost pure so2 the deposit appears to be topographically controlled suggesting a possible origin by liquid flow

paterae on io a new type of volcanic caldera paterae defined by the international astronomical union as irregular crater s or complex one s with scalloped edges are some of the most prominent topographic features on io paterae on io are unique yet in some aspects they resemble calderas known and studied on earth mars and venus they have steep walls flat floors and arcuate margins and sometimes exhibit nesting all typical of terrestrial and martian basalt shield calderas however they are much larger many are irregular in shape and they typically lack shields their great sizes some 200 km diameter and lack of associated volcanic edifices beg comparison with terrestrial ash flow calderas however there is no convincing evidence on io for the high silica erupted products or dome resurgence associated with this type of caldera ionian paterae seem to be linked with the eruption of large amounts of mafic to ultramafic lavas and colorful sulfur rich materials that cover the floors and sometimes flow great distances away from patera margins they are often angular in shape or are found adjacent to mountains or plateaus indicating tectonic influences on their formation a database of 417 paterae on io measured from images with 3 2 km pixel 1 resolution 80 of its surface reveals that their mean diameter of 41 0 km is close to that for calderas of mars 47 7 km is smaller than that for venus 68 km but dwarfs those for terrestrial basalt shield calderas 6 6 km and ash flow calderas 18 7 km thirteen percent of all paterae are found adjacent to mountains 42 have straight or irregular margins and 8 are found atop low shields abundant smaller paterae with more continuously active lava eruptions are found between 25 s and 25 n latitude whereas fewer and larger paterae are found poleward of these latitudes patera distribution shows peaks at 330 w and 150 w longitude likely related to the direction of greatest tidal massaging by jupiter ionian patera formation may be explained by portions or combinations of models considered for formation of terrestrial calderas yet their unusual characteristics may require new models with a greater role for tectonic processes

the moldanubian zone in the french massif central vosges schwarzwald and bohemian massif revisited differences and similarities in order to portray the main differences and similarities between the northeastern variscan segments french massif central fmc vosges black forest and bohemian massif bm we review their crustal scale architectures the specific rock associations and lithotectonic sequences as well as the ages of the main magmatic and metamorphic events this review demonstrates significant differences between the moldanubian domains in thebmand the fmc on this basis we propose distinguishing between the eastern and western moldanubian zones while the vosges black forest mountains are an intermediate section between the bm and the fmc the observed differences are the result of first the presence in the french segment of an early large scale accretionary system prior to the main variscan collision and second the duration of saxothuringian armorican subduction which generated long lived magmatic arc and back arc systems in the bohemian segment while the magmatic activity in the fmc was comparably short lived

evaluation of sulfur flow emplacement on io from galileo data and numerical modeling galileo images of bright lava flows surrounding emakong patera have been analyzed and numerical modeling has been performed to assess whether these flows could have resulted from the emplacement of sulfur lavas on io images from the solid state imaging ssi camera show that these bright white to yellow emakong flows are up to 370 km long and contain dark sinuous features that are interpreted to be lava conduits 300 500 m wide and 100 km long near infrared mapping spectrometer nims thermal emission data yield a color temperature estimate of 344 k 60 k 131 c within the emakong caldera we suggest that these bright flows likely resulted from either sulfur lavas or silicate lavas that have undergone extensive cooling pyroclastic mantling and or alteration with bright sulfurous materials the emakong bright flows have estimated volumes of 250 350 km3 similar to some of the smaller columbia river basalt flows if the emakong flows did result from effusive sulfur eruptions then they are orders of magnitude greater in volume than any terrestrial sulfur flows our numerical modeling results show that sulfur lavas on io could have been emplaced as turbulent flows which were capable of traveling tens to hundreds of kilometers consistent with the predictions of sagan 1979 and fink et al 1983 our modeled flow distances are also consistent with the measured lengths of the emakong channels and bright flows modeled thermal erosion rates are 1 4 m d 1 for flows erupted at 140 180 c which are consistent with the melting rates of kieffer et al 2000 the emakong channels could be thermal erosional in nature however the morphologic signatures of thermal erosion channels cannot be discerned from available images there are planned galileo flybys of io in 2001 which provide excellent opportunities to obtain high resolution morphologic and color data of emakong patera such observations could along with further modeling provide additional information to better constrain whether sulfur lavas produced the emakong flows

thermal signature eruption style and eruption evolution at pele and pillan on io the galileo spacecraft has been periodically monitoring volcanic activity on io since june 1996 making it possible to chart the evolution of individual eruptions we present results of coanalysis of near infrared mapping spectrometer nims and solid state imaging ssi data of eruptions at pele and pillan especially from a particularly illuminating data set consisting of mutually constraining near simultaneous nims and ssi observations obtained during orbit c9 in june 1997 the observed thermal signature from each hot spot and the way in which the thermal signature changes with time tightly constrains the possible styles of eruption pele and pillan have very different eruption styles from september 1996 through may 1999 pele demonstrates an almost constant total thermal output with thermal emission spectra indicative of a long lived active lava lake the nims pillan data exhibit the thermal signature of a pillanian eruption style a large vigorous eruption with associated open channel or sheet flows producing an extensive flow field by orbit c10 in september 1997 the high mass eruption rate high liquidus temperature at least 1870 k eruption at pillan is the best candidate so far for an active ultramafic magnesium rich komatiitic flow on io a style of eruption never before witnessed the thermal output per unit area from pillan is however consistent with the emplacement of large open channel flows magma temperature at pele is 1600 k if the magma temperature is 1600 k it suggests a komatiitic basalt composition the power output from pele is indicative of a magma volumetric eruption rate of 250 to 340 m3 s 1 although the pele lava lake is considerably larger than its terrestrial counterparts the power and mass fluxes per unit area are similar to active terrestrial lava lakes

the summer 1997 eruption at pillan patera on io implications for ultrabasic lava flow emplacement galileo data and numerical modeling were used to investigate the summer 1997 eruption at pillan patera on io this event now defined as pillanian eruption style keszthelyi et al this issue included a high temperature 1600 c possibly ultrabasic 140 km high plume eruption that deposited dark orthopyroxene rich pyroclastic material over 125 000 km2 followed by emplacement of dark flow like material over 3100 km2 to the north of the caldera we estimate that the high temperature energetic episode of this eruption had a duration of 52 167 days between may and september 1997 with peak eruption temperatures around june 28 1997 galileo 20 m pixel 1 images of part of the pillan flow field show a widespread rough pitted surface that is unlike any flow surface we have seen before we suggest that this surface may have resulted from 1 a fractured lava crust formed during rapid low viscosity lava surging perhaps including turbulent flow emplacement 2 disruption of the lava flow by explosive interaction with a volatile rich substrate or 3 a combination of 1 and 2 with or without accumulation of pyroclastic materials on the surface well developed flow lobes are observed suggesting that this is a relatively distal part of the flow field shadow measurements at flow margins indicate a thickness of 8 10 m we have modeled the emplacement of putative ultrabasic flows from the summer 1997 pillan eruption using constraints from new galileo data results suggest that either laminar sheet flows or turbulent channelized flows could have traveled 50 150 km on a flat unobstructed surface which is consistent with the estimated length of the pillan flow field 60 km our modeling suggests low thermal erosion rates 20 m erosion channels was unlikely especially distal to the source we calculate a volumetric flow rate of 2 7 103 m3 s 1 which is greater than those for typical mauna loa kilauea flows but comparable to those for the 1783 laki eruption and the inferred flow rates of the roza flows in the columbia river flood basalts the differences in ultrabasic eruption styles on earth and io appear to be controlled by the different eruption environments plumes at sites of ultrabasic eruptions on io suggest strong magma volatile interactions on a low gravity body lacking an atmosphere whereas the geology at sites of komatiite eruptions on earth suggest mostly submarine emplacement of thick flows with a pronounced lack of subaerial explosive activity