io heat flow from dark volcanic fields abstract dark flow fields on the jovian satellite io are evidence of current or recent volcanic activity we have examined the darkest volcanic fields and quantified their thermal emission in order to assess their contribution to io s total heat flow loki patera the largest single source of heat flow on io is a convenient point of reference we find that dark volcanic fields are more common in the hemisphere opposite loki patera and this large scale concentration is manifested as a maximum in the longitudinal distribution near 200 w consistent with usgs global geologic mapping results in spite of their relatively cool temperatures dark volcanic fields contribute almost as much to io s heat flow as loki patera itself because of their larger areal extent as a group dark volcanic fields provide an asymmetric component of 5 of io s global heat flow or 5 1012 w

introduction to the special section geology and geophysics of io io is about the size and density of earth s moon but it has a dramatically different thermal state and geologic history tidal heating leads to intense volcanic and tectonic activity so io is an accelerated experiment in planetary geology and geophysics here we can witness volcanic activity on very large scales and at very high temperatures perhaps providing insights into the early histories of the terrestrial planets io has always been a high priority objective of galileo but her proximity to jupiter s intense radiation belt has meant saving the best for last an io flyby occurred during jupiter orbit insertion in december 1995 but a tape recorder anomaly led to cancellation of remote sensing observations no further close flybys of io were planned until the final two orbits i24 and i25 of the galileo europa mission gem late in 1999 in order to minimize radiation damage to spacecraft and instrument electronics i24 was an exciting encounter with a spacecraft safing event and recovery just hours before io closest approach most of the io data were acquired but not without problems the majority of images from the solid state imager ssi were acquired in a mode that failed due to the cumulative radiation damage producing garbled images although reconstruction has produced some useful pictures keszthelyi et al this issue also the grating of the near infrared mapping spectrometer nims became stuck leading to loss of spectral sampling lopes et al this issue these instrument problems were mitigated by the use of different observation modes or strategies in subsequent orbits the 125 polar pass included another safing event this time eliminating the recording of the highest resolution observations however the medium resolution observations were of excellent quality and provided a surprise look at a new fissure eruption at tvashtar catena gem was followed by the galileo millennium mission gmm including another close io flyby in orbit i27 a fully successful encounter three additional io flybys are anticipated in august 2001 i31 october 2001 i32 and january 2002 i33 the groundtracks for all six io encounters are shown in plate 1

global distribution of volcanic centers and mountains on io control by asthenospheric heating and implications for mountain formation abstract jupiter s moon io possesses numerous tectonic mountains in addition to its ubiquitous volcanoes and volcanic features remarkably a distinct global anticorrelation exists between the spatial distribution of mountains and volcanic centers on io this relationship indicates an explicit connection between volcanism and mountain formation even though the mountains are tectonic in origin predominantly upthrusted crustal blocks spherical harmonic analysis shows the distribution of mountains and volcanic centers have statistically significant power at degree 2 this result is especially striking for the volcanic center distribution and directly implicates models of asthenospheric tidal heating the latter predict enhanced heat flux along the equator in a degree two pattern that matches observations mountain formation on io appears to be a form of dominantly vertical tectonism unique in the modern solar system continual burial by widespread volcanism drives the crust inward which leads to strong compression and at discrete locations mountains correlation coefficients between the volcanic and mountain distributions indicate statistically meaningful anticorrelation at low spectral degrees l 1 2 4 and 6 the anticorrelation is especially significant between the longitudinal sectorial l 2 components when considered on their own we compare this anticorrelation with published models that link volcano and mountain formation while consistent in part with l 2 convection models which predict such an anticorrelation in principle such low degree anticorrelations are also if not more compatible with mountain formation due to or influenced by thermal expansion of io s crust and deep compression and thrust faulting in regions of lower than average volcanic heat piping positive correlations between mountain and volcanic center distributions at high spectral degree may reflect structural links between a good fraction of mountain blocks and adjacent volcanic paterae whereas the anticorrelation at low degree implies that most volcanic features which are far more numerous overall form independently of mountains

representational bias in phytoliths from modern soils of central north america implications for paleovegetation reconstructions abstract understanding localized patterns and community compositions of vegetation in an environment is critical to the reconstruction of climatic and ecological conditions across all spatiotemporal scales one of the most accurate and useful ways to characterize vegetation and therefore to describe the climatic and ecological conditions of a location is through the plant fossil record phytoliths plant silica microfossils are often preserved in the absence of other paleobotanical data and are becoming more widely used for deep time vegetation reconstructions significant work has been done to standardize the analytical methodology of phytolith extraction statistical analysis and interpretation but more detailed investigations are needed to understand how well a given soil assemblage represents the actual aboveground plant biomass for a given ecosystem we present results from paired soil phytolith assemblages and local vegetation assemblages across the central united states including temperate forest grassland and rangeland scrubland ecosystems phytolith assemblages obtained via extractions from soil a horizons were compared to percent cover of species and plant biomass estimates obtained via in situ field observations and aerial estimates of tree cover to analyze differences in the relative abundance of forest woody vegetation vs grasses soil phytolith assemblages from all sites average a 29 bias toward the grass morphotypes as compared to actual aboveground biomass observations and comparisons to percent cover yielded broadly comparable bias figures percent bias estimates do not show significant correlations to most environmental factors temperature precipitation local elevation however an extremely strong correlation p

magma transport of heat on io a mechanism allowing a thick lithosphere models indicate that the high heat flow from io would result in a very thin approximately 5 km silicate lithosphere overlying a molten interior if all heat was transported through the lithosphere via conduction however the presence of mountains with relief in excess of 10 km would seem to demand a thick lithosphere at least locally a significant fraction of io s heat flow may be transported via advection through volcanoes advective heat transfer permits a thicker lithosphere than does pure conduction possibly reconciling io s high heat flow with the rugged topography

the origin and spread of grass dominated ecosystems in the late tertiary of north america preliminary results concerning the evolution of hypsodonty abstract sediment samples were collected in northwestern nebraska from the following lithologic units 1 the upper oligocene monroe creek formation the lower miocene harrison formation and upper harrison beds of the arikaree group and 2 the lower miocene runningwater formation and the dawes clay member box butte formation of the ogallala group the samples were processed using heavy liquid extraction and analyzed for siliceous plant microfossils phytoliths all samples yielded well preserved and diverse assemblages dominated by grass phytoliths but included phytoliths produced by woody and herbaceous dicotyledons palms and sedges the abundance of woody dicotyledons and palms decreased up section the grass assemblages consisted mainly of festucoid c3 phytolith morphotypes an index assessing the amount of tree cover d p the ratio of dicotyledon phytoliths to grass phytoliths was employed to interpret the data according to this analysis there was open c3 dominated grassland in the study area between 25 and 17 ma at least 7 ma before supposed adaptations to grasslands in ungulates hypsodonty originate

volcanic eruptions on io nine eruption plumes were observed over a period of 6 1 2 days during the voyager 1 encounter with io during the voyager 2 encounter 4 months later eight of these eruptions were still active the largest plume viewed by voyager 1 became inactive sometime between the two encounters however a major eruption occurred at surt sometime between the two encounters and deposited an ejecta blanket comparable in size to those associated with the largest plumes the plumes range in height from about 60 to over 300 km with corresponding ejection velocities of about 0 5 to 1 0 km s where topographic information exists plumes 1 and 8 the plume source is located on level plains rather than topographic highs and consists of either fissures or calderas with the exception of plume 1 pele the brightness distribution monotonically decreases from the core to the top of the plume the shape and brightness distribution together with the pattern of the surface deposit of at least plume 3 prometheus can be simulated by a ballistic model in which the ejection velocity is constant 0 5 km s and ejection angles vary from vertical 0 to 55 the brightness distribution of plume 1 is probably better explained by a shock front near the top of the plume numerous surface deposits similar to those associated with active plumes probably mark the sites of recent eruptions the distribution of active and recent eruptions appears to be concentrated in the equatorial regions and indicates the volcanic activity is more frequent and intense in the equatorial regions than the polar regions this suggests that the depositional rate is greater and the surface age younger in the equatorial regions which may account for the darker polar regions the geologic setting of certain plume sources and the very large reservoirs of volatiles required for the active eruptions suggests that sulphur volcanism rather than silicate volcanism is the most likely driving mechanism for the eruption plumes

chaos on io a model for formation of mountain blocks by crustal heating melting and tilting mountains are distributed across the surface of io the fiercely tidally heated moon of jupiter the large crustal thicknesses implied by their great heights can be reconciled with io s high heat flow if most of the heat escapes directly via volcanic eruptions the heat pipe model but the origin of the mountains has remained obscure recent images show that many of io s mountains are tilted blocks undergoing tectonic collapse and we propose here that the volcanic heat pipe and continuous terrain burial model naturally leads to such unstable topography that is burial 1 generates horizontal tensile stresses as the volcanic crustal stack is loaded 2 creates large horizontal compressive confining stresses as io s crust subsides moves to a smaller effective radius and importantly 3 allows for potentially large horizontal compressive thermal stresses as the base of the crust reheats owing to fluctuations in the efficiency of the volcanic heat piping faulting associated with these stresses may raise mountain scarps directly or in concert with thermal uplift due to the crustal reheating continued crustal heating and melting then lead to mountain collapse all over 1 m y to a few million years our model predicts that regions of active mountain formation and volcanic activity on io should be anticorrelated which is observed moreover substantial tidal heating and disruption of planetary crust are seen elsewhere in the jupiter system in the chaos terrains of europa there may be stronger commonalities between the two inner jovian moons and early earth than previously realized

magma ascent pathways associated with large mountains on io abstract while jupiter s moon io is the most volcanically active body in the solar system the largest mountains seen on io are created by tectonic forces rather than volcanic construction pervasive compression primarily brought about by subsidence induced by sustained volcanic resurfacing creates the mountains but at the same time inhibits magma ascent in vertical conduits dikes we superpose stress solutions for subsidence along with thermal stress both from the crustal conveyor belt process of resurfacing in io s lithosphere with stresses from io mountain sized loads in a shallow spherical shell solution in order to evaluate magma ascent pathways we use stress orientation least compressive stress horizontal and stress gradient compression decreasing upwards criteria to identify ascent pathways through the lithosphere there are several configurations for which viable ascent paths transit nearly the entire lithosphere arriving at the base of the mountain where magma can be transported through thrust faults or perhaps thermally eroded flank sections the latter is consistent with observations of some io paterae in close contact with mountains

dynamics and evolution of so2 gas condensation around prometheus like volcanic plumes on io as seen by the near infrared mapping spectrometer abstract we analyze a series of spectral image cubes acquired by the galileo near infrared mapping spectrometer nims over the prometheus region of io we use so2 frost a volatile compound ubiquitous on the surface as a tracer to understand various thermodynamic and volcanic processes acting in this equatorial region here we develop a new method to derive from the 12 wavelength nims products the distribution and physical properties of solid so2 this method is based on the inversion of a bidirectional reflectance model on two observed spectral ratios sensitive to 1 the areal abundance of so2 and 2 its mean grain size as a result reliable and consistent maps of so2 abundance and granularity are obtained which can be correlated to distinguish four different physical units the distribution of these so2 units indicates zones of condensation metamorphism and sublimation linked with the thermodynamic and volcanic processes of interest our maps depict equatorial plains undisturbed by any kind of vigorous volcanic activity over 35 40 of their surface elsewhere 10 20 of the equatorial plains display abnormally low frost coverage which may imply the recent presence of positive thermal anomalies with temperatures in the range 110 200 k hot spots such as prometheus culann surya and tupan to mention the most persistent emit a great variety of gases some of which will condense at io s surface near their source regions associated fields of freshly condensed so2 are easily observed and deposits of more refractory compounds with higher e g s8 or lower e g nacl molecular weight must also be present although their exact nature is unknown three different mechanisms of emission are proposed for the volatile compounds and supported by the distribution maps these are a the interaction between flowing lava and preexisting volatile deposits on the surface b direct degassing from the lava an d c the eruption of a liquid aquifer from underground the geometric elongation of the prometheus so2 deposition ring being related to the development of a 95 km long lava field is the best illustration of mechanism a details of the progressive emplacement of the so2 ring by the associated plume are examined by the development of a semiempirical model of material deposition based on a ballistic transfer from the sources to the surface this model shows that lava emission may have been occuring at prometheus at a fairly constant rate since voyager mechanism b may operate at the hot spot surya which presents a noticeable field of fresh so2 frost but no extended lava flow finally we have noted on the northwestern flank of the volcanic edifice emakong the existence of an extremely deep 1 3 so2 absorption which is indicative of abundant pure and perhaps icy so2 deposits these could be the result of the eruption of an so2 liquid aquifer mechanism c

ridges and tidal stress on io abstract sets of ridges of uncertain origin are seen in twenty nine high resolution galileo images which sample seven locales on io these ridges are on the order of a few kilometers in length with a spacing of about a kilometer within each locale the ridges have a consistent orientation but the orientations vary from place to place we investigate whether these ridges could be a result of tidal flexing of io by comparing their orientations with the peak tidal stress orientations at the same locations we find that ridges grouped near the equator are aligned either north south or east west as are the predicted principal stress orientations there it is not clear why particular groups run north south and others east west the one set of ridges observed far from the equator 52 s has an oblique azimuth as do the tidal stresses at those latitudes therefore all observed ridges have similar orientations to the tidal stress in their region this correlation is consistent with the hypothesis that tidal flexing of io plays an important role in ridge formation

a post galileo view of io s interior abstract we present a self consistent model for the interior of io taking the recent galileo data into account in this model io has a completely molten core substantially molten mantle and a very cold lithosphere heat from magmatic activity can mobilize volatile compounds such as so 2 in the lithosphere and the movement of such cryogenic fluids may be important in the formation of surface features including sapping scarps and paterae

a high resolution stable isotopic record from the junggar basin nw china implications for the paleotopographic evolution of the tianshan mountains this study presents high resolution oxygen and carbon isotopic records of paleosol carbonates from fluvial sediments and lacustrine carbonates sampled from the jingou he and kuitun he stratigraphic sections located in the northern tianshan piedmont these sections expose remarkable outcrops of junggar foreland basin sediments that have been previously dated by high resolution magnetostratigraphy to between 23 6 and 1 ma and 10 5 and 3 1 ma a total of 216 samples of fluvio lacustrine sediments were collected from which isotopic analyses yield 18o smow values that range from 13 7 to 29 9 in the jingou he section and 16 3 to 21 0 in the kuitun he section 13c pdb values range from 12 9 to 3 0 in the jingou he section and from 7 8 to 4 0 in the kuitun he section 18o values decrease between 25 and 23 ma and then remain relatively steady with the exception of one period that contains samples with higher oxygen isotope values at 16 ma during the periods when there are samples that overlap in time from the kuitun he and jingou he sections we observe a difference of 1 7 between values from the two locales the 13c values also decrease between 25 and 23 ma and then remain relatively steady until 10 ma with again one short period of higher values at 16 ma then between 10 and 3 1 ma carbon isotope values progressively increase we interpret that 18o and 13c isotopic values during lacustrine periods 25 23 ma and 16 ma as largely controlled by evaporation and opening closing of the lake to external inputs we interpret the 18o values of paleosol carbonate in the junggar basin to be influenced by the hypsometry of the high tianshan range while the 13c values may record the uplift history of the depositional area in the foreland basin itself as well as the isotopic composition of plants consequently we conclude that the jingou he and kuitun he drainage basins in the central tianshan have remained at relatively unchanged elevations for the past 20 ma we also suggest that the elevation of the southern part of the foreland basin increased between 10 and 3 1 ma probably as a result of tectonic deformation in the piedmont and sedimentary filling of the sedimentary basin the carbon isotope record remains relatively stable through time and isotopic values suggest that there was little or no expansion of c4 plants in this region in the late miocene

mapping of the culann tohil region of io from galileo imaging data abstract we have used galileo spacecraft data to produce a geomorphologic map of the culann tohil region of io s antijovian hemisphere this region includes a newly discovered shield volcano ts i goab tholus and a neighboring bright flow field ts i goab fluctus the active culann patera and the enigmatic tohil mons radegast patera tohil patera complex analysis of voyager global color and galileo solid state imaging ssi high resolution regional 50 330 m pixel and global color 1 4 km pixel images along with available galileo near infrared mapping spectrometer nims data suggests that 16 distinct geologic units can be defined and characterized in this region including 5 types of diffuse deposits ts i goab fluctus is the center of a low temperature hotspot detected by nims late during the galileo mission and could represent the best case for active effusive sulfur volcanism detected by galileo the culann volcanic center has produced a range of explosive and effusive deposits including an outer yellowish ring of enhanced sulfur dioxide so2 an inner red ring of so2 with short chain sulfur s3 s4 contaminants and two irregular green diffuse deposits one in tohil patera apparently produced by the interaction of dark silicate lava flows with sulfurous contaminants ballistically emplaced from culann s eruption plume s fresh and red mantled dark lava flows west of the culann vent can be contrasted with unusual red brown flows east of the vent these red brown flows have a distinct color that is suggestive of a compositional difference although whether this is due to surface alteration or distinct lava compositions cannot be determined the main massif of tohil mons is covered with ridges and grooves defining a unit of tectonically disrupted crustal materials tohil mons also contains a younger unit of mottled crustal materials that were displaced by mass wasting processes neighboring radegast patera contains a nims hotspot and a young lava lake of dark silicate flows whereas the southwest portion of tohil patera contains white flow like units perhaps consisting of ponds of effusively emplaced so2 from 0 15 s the hummocky bright plains unit away from volcanic centers contains scarps grooves pits graben and channel like features some of which have been modified by erosion although the most active volcanic centers appear to be found in structural lows as indicated by mapping of scarps dems derived from stereo images show that with the exception of tohil mons there is less than 1 km of relief in the culann tohil region there is no discernable correlation between centers of active volcanism and topography

galileo at io results from high resolution imaging during late 1999 early 2000 the solid state imaging experiment on the galileo spacecraft returned more than 100 high resolution 5 to 500 meters per pixel images of volcanically active io we observed an active lava lake an active curtain of lava active lava flows calderas mountains plateaus and plains several of the sulfur dioxide rich plumes are erupting from distal flows rather than from the source of silicate lava caldera or fissure often with red pyroclastic deposits most of the active flows in equatorial regions are being emplaced slowly beneath insulated crust but rapidly emplaced channelized flows are also found at all latitudes there is no evidence for high viscosity lava but some bright flows may consist of sulfur rather than mafic silicates the mountains plateaus and calderas are strongly influenced by tectonics and gravitational collapse sapping channels and scarps suggest that many portions of the upper 1 kilometer are rich in volatiles

imaging of volcanic activity on jupiter s moon io by galileo during the galileo europa mission and the galileo millennium mission the solid state imaging ssi instrument provided the first high and medium resolution views of io as the galileo spacecraft closed in on the volcanic body in late 1999 and early 2000 while each volcanic center has many unique features the majority can be placed into one of two broad categories the promethean eruptions typified by the volcanic center prometheus are characterized by long lived steady eruptions producing a compound flow field emplaced in an insulating manner over a period of years of decades in contrast pillanian eruptions are characterized by large pyroclastic deposits and short lived but high effusion rate eruptions from fissures feeding open channel or open sheet flows both types of eruptions commonly have 100 km tall bright so2 rich plumes forming near the flow fronts and smaller deposits of red material that mark the vent for the silicate lavas

flood lavas on earth io and mars flood lavas are major geological features on all the major rocky planetary bodies they provide important insight into the dynamics and chemistry of the interior of these bodies on the earth they appear to be associated with major and mass extinction events it is therefore not surprising that there has been significant research on flood lavas in recent years initial models suggested eruption durations of days and volumetric fluxes of order 10 7 m 3 s 1 with flows moving as turbulent floods however our understanding of how lava flows can be emplaced under an insulating crust was revolutionized by the observations of actively inflating pahoehoe flows in hawaii these new ideas led to the hypothesis that flood lavas were emplaced over many years with eruption rates of the order of 10 4 m 3 s 1 the field evidence indicates that flood lava flows in the columbia river basalts deccan traps etendeka lavas and the kerguelen plateau were emplaced as inflated pahoehoe sheet flows this was reinforced by the observation of active lava flows of 100 km length on io being formed as tube fed flows fed by moderate eruption rates 10 2 10 3 m 3 s 1 more recently it has been found that some flood lavas are also emplaced in a more rapid manner new high resolution images from mars revealed platy ridged flood lava flows named after the large rafted plates and ridges formed by compression of the flow top a search for appropriate terrestrial analogues found an excellent example in iceland the 1783 1784 laki flow field the brecciated laki flow top consists of pieces of pahoehoe not aa clinker leading us to call this rubbly pahoehoe similar flows have been found in the columbia river basalts and the kerguelen plateau we hypothesize that these flows form with a thick insulating but mobile crust which is disrupted when surges in the erupted flux are too large to maintain the normal pahoehoe mode of emplacement flood lavas emplaced in this manner could have intermittently reached effusion rates of the order of 10 6 m 3 s 1

keck ao observations of io in and out of eclipse abstract we present adaptive optics ao observations of io taken with the w m keck ii telescope on 18 december 2001 ut before the satellite went into eclipse and while it was in jupiter s shadow making these kind of io in eclipse observations as well as the associated data reduction and analysis are challenging hence one focus of the paper is to explain the methods and tools used for these data sets for the sunlit images io itself was used as the wavefront reference source while nearby ganymede was used as reference star when io was in eclipse observations were obtained in k l and m bands the sunlit images have been deconvolved using mistral the io in eclipse data were deconvolved with idac and mistral the former gives better results both in absolute photometry and in matching the original images we determined the flux densities of the hot spots from the original io in eclipse data with starfinder as well as from the deconvolved images by integrating the intensity over the relevant areas we determined the highly anisoplanatic psf via a fft method from the original data and used this in starfinder and as a starting psf for idac and mistral we derived temperatures and areal coverage of all 19 spots detected in both k and l band images of io in eclipse we also determined temperatures and areal coverage of the hot spots visible on the l and m band images of sunlit io most volcanoes contain a compact hot core 10 km2 at 600 800 k within a larger area at lower temperatures e g 102 104 km2 at 300 500 k the total heat flow contributed by these active volcanoes is 0 2 w m 2 8 of the average global heat flow measured at 5 20 m by veeder et al j geophys res 99 1994 17095

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

lava lakes on io observations of io s volcanic activity from galileo nims during the 2001 fly bys abstract galileo s near infrared mapping spectrometer nims obtained its final observations of io during the spacecraft s fly bys in august i31 and october 2001 i32 we present a summary of the observations and results from these last two fly bys focusing on the distribution of thermal emission from io s many volcanic regions that give insights into the eruption styles of individual hot spots we include a compilation of hot spot data obtained from galileo voyager and ground based observations at least 152 active volcanic centers are now known on io 104 of which were discovered or confirmed by galileo observations including 23 from the i31 and i32 io fly by observations presented here we modify the classification scheme of keszthelyi et al 2001 j geophys res 106 e12 33 025 33 052 of io eruption styles to include three primary types promethean lava flow fields emplaced as compound pahoehoe flows with small plumes 200 km high plumes and rapidly emplaced flow fields and a new style we call lokian that includes all eruptions confined within paterae with or without associated plume eruptions thermal maps of active paterae from nims data reveal hot edges that are characteristic of lava lakes comparisons with terrestrial analogs show that io s lava lakes have thermal properties consistent with relatively inactive lava lakes the majority of activity on io based on locations and longevity of hot spots appears to be of this third type this finding has implications for how io is being resurfaced as our results imply that eruptions of lava are predominantly confined within paterae thus making it unlikely that resurfacing is done primarily by extensive lava flows our conclusion is consistent with the findings of geissler et al 2004 icarus this issue that plume eruptions and deposits rather than the eruption of copious amounts of effusive lavas are responsible for io s high resurfacing rates the origin and longevity of islands within ionian lava lakes remains enigmatic

volcanic activity at tvashtar catena io abstract galileo s solid state imager ssi observed tvashtar catena four times between november 1999 and october 2001 providing a unique look at a distinctive high latitude volcanic complex on io the first observation orbit i25 november 1999 resolved for the first time an active extraterrestrial fissure eruption the brightness temperature was at least 1300 k the second observation orbit i27 february 2000 showed a large 500 km 2 region with many small hot regions of active lava the third observation was taken in conjunction with cassini imaging in december 2000 and showed a pele like annular plume deposit the cassini images revealed an 400 km high pele type plume above tvashtar catena the final galileo ssi observation of tvashtar orbit i32 october 2001 revealed that obvious to ssi activity had ceased although data from galileo s near infrared mapping spectrometer nims indicated that there was still significant thermal emission from the tvashtar region in this paper we primarily analyze the style of eruption during orbit i27 february 2000 comparison with a lava flow cooling model indicates that the behavior of the tvashtar eruption during i27 does not match that of simple advancing lava flows instead it may be an active lava lake or a complex set of lava flows with episodic overlapping eruptions the highest reliable color temperature is 1300 k although higher temperatures cannot be ruled out they do not need to be invoked to fit the observed data the total power output from the active lavas in february 2000 was at least 10 11 w

high resolution isotopic record of c4 photosynthesis in a miocene grassland abstract the origin and spread of grasslands is one of the key evolutionary events in the cenozoic which is characterized by long term cooling and drying climatic conditions one way to examine the relationship between vegetation and climate is to study the isotopic composition of organic carbon preserved in paleosols paleosols that preserve organic matter in the form of carbonaceous root traces provide direct evidence of the proportion of c3 to c4 biomass that grew in the soil in contrast with pedogenic carbonate 13c values which may also reflect complicating factors including mixing from atmospheric 13c in low productivity ecosystems a high temporal and spatial resolution reconstruction of past ecosystems was derived from thirty five paleosols in a thirty four meter section of the sixmile creek formation at timber hills montana usa that was deposited during the miocene 10 2 8 9 ma ago phytoliths were extracted from paleosol samples to compare vegetation assemblages to inferences based on isotopic compositions with both proxies giving similar results isotopic results from organic matter indicate both a small component of c4 photosynthetic plants locally prior to their regional expansion to dominance in the late miocene through the early pleistocene and large variation in the abundance of c4 plants 0 25 in this ecosystem both laterally and on a 100 kyr timescale in contrast pedogenic carbonate 13c values from this site indicate a high proportion of c4 photosynthesis that is at odds with both phytolith and 13corg results suggesting that the carbonate values are biased by diagenesis or diffusion of atmospheric co2 and that a similar issue may impact previous paleovegetation reconstructions based on pedogenic carbonates quantitative reconstructions of mean annual temperature and mean annual precipitation indicate little local variability through time and that the fluctuations in c4 proportion were not climatically driven instead the variable proportion of c4 photosynthesis is best explained by ecosystem scale variables such as succession fluvial avulsion and fire regime

orogenic tectonism on io 1 we catalog 143 ionian mountains montes and mountain like features mensae tholi plana and small peaks in order to investigate orogenic tectonism on io from this comprehensive list we select 96 mountains for which there are sufficient coverage and resolution to discern spatial relationships with surrounding geologic features three of the 96 mountains are probably volcanoes 92 appear to be tectonic massifs and 1 is ambiguous of the 92 tectonic mountains 38 abut paterae volcanic or volcano tectonic craters with irregular or scalloped margins this juxtaposition is unlikely to be a coincidence as the probability of it occurring by chance is 0 1 we propose instead that orogenic faults may act as conduits for magma ascent thus fueling patera formation near mountains as resurfacing buries a shell of material from io s surface to the base of the lithosphere its effective radius is reduced and it heats up we calculate the lithospheric volume change due to subsidence and thermal expansion as a function of lithospheric thickness conservation of volume dictates that this material must be uplifted at io s surface by estimating the total volume of the mountains we are able to place a lower limit of 12 km on io s lithospheric thickness we hypothesize that in some cases mountain formation may be facilitated by asthenospheric diapirs impinging on the base of the lithosphere the resulting lithospheric swell could focus the compressive stresses that drive orogenic tectonism this model is one of several possible mechanisms for uplifting isolated mountains such as are observed on io

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

reconnaissance of upper jurassic morrison formation ichnofossils rocky mountain region usa paleoenvironmental stratigraphic and paleoclimatic significance of terrestrial and freshwater ichnocoenoses seventy five types of ichnofossils documented during a four year reconnaissance study in the upper jurassic morrison formation demonstrate that highly diverse and abundant plants invertebrates and vertebrates occur throughout most of the morrison or equivalent strata invertebrate ichnofossils preserving the most environmentally and climatically sensitive in situ behavior of morrison organisms are in nearly all outcrops terrestrial ichnofossils record biotic processes in soil formation indicating soil moisture and water table levels freshwater ichnofossils preserve evidence of water depth salinity and seasonality of water bodies ichnofossils categorized as epiterraphilic terraphilic hygrophilic and hydrophilic new terms reflect the moisture regime where they were constructed the ichnofossils are vertically zoned with respect to physical chemical and biological factors in the environment that controlled their distribution and abundance and are expressed as surficial shallow intermediate and deep the sedimentologic stratigraphic and geographic distribution of morrison ichnofossils reflects the environmental and climatic variations across the basin through time marginal marine tidal to brackish water ichnofossils are mainly restricted to the windy hill member very large to small termite nests dominate the salt wash member similar size ranges of ant nests dominate the brushy basin member soil bee nests dominate in the salt wash decreasing in abundance through the brushy basin deeper and larger insect nests indicate more seasonal distribution of precipitation and rainfall shallower and smaller insect nests indicate either dry or wet substrate conditions depending on the nest architecture and paleopedogenic and sedimentologic character of the substrate trace fossil indicators of flowing or standing water conditions are dominant in the tidwell member and in fluvial sandstones of the salt wash and brushy basin members large communities of perennial freshwater bivalve traces are abundant in the tidwell and brushy basin members but to a lesser extent in the salt wash member shallow crayfish burrows indicating a water table level close to the surface 1 m are restricted to channel bank and proximal alluvial deposits in the salt wash recapture and brushy basin members sauropod theropod pterosaur and other vertebrate tracks occur throughout the morrison formation associated with alluvial lacustrine and transitional marine shoreline deposits ichnofossils and co occurring paleosols in the morrison reflect the local and regional paleohydrologic settings which record the annual soil moisture budget and were largely controlled by the climate in the basin contributions to near surface biologic systems by groundwater from distant sources were minor except where the water table perennially seasonally or ephemerally intersected the ground surface the jurassic morrison formation in the southern portion of the basin experienced a mosaic of seasonal climates that varied from a drier tidwell windy hill deposition to a wetter lower and middle salt wash deposition and slightly drier upper salt wash deposition tropical wet dry climate returning to a wetter tropical wet dry climate near the end of morrison deposition brushy basin deposition the northern part of the basin experienced similar trends across a mosaic of mediterranean climate types the range and mosaic pattern of wet dry morrison climates is analogous to the range of climates and their seasonal variability that dominates the african savanna today

layered convection in io implications for short wavelength surface topography and heat flow abstract io one of the four galilean moons of jupiter is remarkable for its extensive volcanism and extreme interior tidal heating the tidal heating likely yields a very low viscosity asthenosphere and consequently a very high rayleigh number of o 10 12 for convection in the interior in a state of quasi steady balance the internally generated heat must be transported from the interior to the base of the io lithosphere and exhausted to space the mechanisms whereby the convective radial heat transfer is evacuated involve both conduction and volcanism despite io s ubiquitous volcanism only 4 of its mountains montes appear to have a volcanic origin and most of the mountainous regions seem to be related to tectonic processes by employing an original control volume based numerical model we investigate the style of convection in the interior of io and the correlation of the scale of convection with the ionian surface heat flux and topography our control volume results support the existence of significant asthenospheric heating and demonstrate that short wavelength features of the surface heat flux are well correlated in scale to an expected layered intra lithospheric style small scale convection these numerical analyses suggest that the amplitude of the short wavelength topography of io is expected to be on the order of a few hundreds of meters the model results also demonstrate that the ionian highs cannot be produced by a lithospheric flexure process above the hot upwellings and therefore other tectonic events such as have previously been suggested must be responsible for the formation of the high ionian mountains that reach in excess of 17 km in elevation

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

volcanic eruptions on io heat flow resurfacing and lava composition abstract we model an infrared outburst on io as being due to a large erupting lava flow which increased its area at a rate of 1 5 10 5 m 2 sec 1 and cooled from 1225 to 555 k over the 2 583 hr period of observation the inferred effusion rate of 3 10 5 m 3 sec 1 for this eruption is very high but is not unprecedented on the earth and is similar to the high eruption rates suggested for early lunar volcanism eruptions occur 6 of the time on io these eruptions provide ample resurfacing to explain io s lack of impact craters we suggest that the large total radiometric heat flow 10 14 w and the size and temperature distribution of the thermal anomalies mcewen et al 1992 bull am astron soc 24 935 veeder et al 1994 j geophys res 99 17 095 17 162 can be accounted for by a series of silicate lava flows in various stages of cooling we propose that the whole suite of io s currently observed thermal anomalies was produced by multiple high eruptive rate silicate flows within the past century

three dimensional simulations of mantle convection in io io has very high surface heat flow and an abundance of volcanic activity which are thought to be driven by nonuniform tidal heating in its interior this nonuniform heat is transported to the base of the lithosphere by very vigorous convection in io s silicate mantle the form of which is presumably responsible for the distribution of surface features such as volcanoes and mountains we here present three dimensional spherical calculations of mantle convection in io in order to ascertain the likely form of this convection and the resulting distribution of heat flow at the surface and core mantle boundary different models of tidal dissipation are considered the endmember scenarios identified by m n ross and g schubert 1985 icarus64 391 400 of dissipation in the entire mantle or dissipation in a thin 100 km thick asthenosphere as well as the preferred distribution of m n ross et al 1990 icarus85 309 325 comprising 1 3 mantle and 2 3 asthenosphere heating the thermal structure of io s mantle and asthenosphere is found to be strongly dependent on tidal heating mode as well as whether the mantle asthenosphere boundary is permeable or impermeable results indicate a large scale flow pattern dominated by the distribution of tidal heating with superimposed small scale asthenospheric instabilities that become more pronounced with increasing rayleigh number these small scale instabilities spread out the surface heat flux resulting in smaller heat flux variations with increasing rayleigh number scaled to io s rayleigh number of o 1012 variations of order a few percent are expected this small but significant variation in surface heat flux may be compatible with the observed distributions of volcanic centers and mountains which appear fairly uniform at first sight but display a discernible distribution when suitably processed the observed distribution of volcanic centers is similar to the asthenosphere heating distribution implying that most of the tidal heating in io occurs in an asthenosphere

subsidence of topography on io topographic features on io tend to subside because their underlying roots are softened and eroded by contact with hot mantle this can be offset by crustal thickening due primarily to ongoing volcanism but observations suggest that this is 1 cm year 1 at current topographic highs since crustal thinning occurs at 50 cm year 1 if the underlying material is a pure magma ocean we conclude that io has no global magma ocean viscosities in excess of 10 10 p are implied for io s interior

a new stereo topographic map of io implications for geology from global to local scales we use voyager and galileo stereo pairs to construct the most complete stereo digital elevation model dem of io assembled to date controlled using galileo limb profiles given the difficulty of applying these two techniques to io due to its anomalous surface albedo properties we have experimented extensively with the relevant procedures in order to generate what we consider to be the most reliable dems our final stereo dem covers 75 of the globe and we have identified a partial system of longitudinally arranged alternating basins and swells that correlates well to the distribution of mountain and volcano concentrations we consider the correlation of swells to volcano concentrations and basins to mountain concentrations to imply a heat flow distribution across io that is consistent with the asthenospheric tidal heating model of tackley et al 2001 the stereo dem reveals topographic signatures of regional scale features including loki patera ra patera and the tvashtar paterae complex in addition to previously unrecognized features including an 1000 km diameter depression and a 2000 km long topographic arc comprising mountainous and layered plains material

rayleigh distillation and the depth profile of 13c 12c ratios of soil organic carbon from soils of disparate texture in iron range national park far north queensland australia a depth and particle size specific analysis of soil organic carbon soc and its isotopic composition was undertaken to investigate the effects of soil texture or particle size on the depth profile of stable carbon isotopic composition of soc 13csoc in two tropical soils depth specific samples from two soil profiles of markedly different texture coarse grained and fine grained were separated into particle size classes and analyzed for the mass mass concentration of soc c and 13csoc within 1 m of the soil surface 13csoc in the coarse textured soil increases by 1 3 to 1 6 while 13csoc from the fine textured soil increase by as much as 3 8 to 5 5 this increasing depth trend in the coarse textured soil is approximately linear with respect to normalized c while the increase in the fine textured soil follows a logarithmic function with respect to normalized c a model of rayleigh distillation describing isotope fractionation during decomposition of soil organic matter som accounts for the depth profile of 13csoc in the fine textured soil but does not account for the depth profile observed in the coarse textured soil despite their similar climate vegetation and topographic position these results suggest that kinetic fractionation during humification of som leads to preferential accumulation of 13c in association with fine mineral particles or aggregates of fine mineral particles in fine textured soils in contrast the coarse textured soil shows very little applicability of the rayleigh distillation model rather the depth profile of 13csoc in the coarse textured soil can be accounted for by mixing of soil carbon with different isotopic ratios

surface changes on io during the galileo mission abstract a careful survey of galileo ssi global monitoring images revealed more than 80 apparent surface changes that took place on io during the 5 year period of observation ranging from giant plume deposits to subtle changes in the color or albedo of patera surfaces explosive volcanic activity was discovered at four previously unrecognized centers an unnamed patera to the south of karei that produced a pele sized red ring a patera to the west of zal that produced a small circular bright deposit a large orange ring detected near the north pole of io and a small bright ring near io s south pole only a handful of io s many active volcanoes produced large scale explosive eruptions and several of these erupted repeatedly leaving at least 83 of io s surface unaltered throughout the galileo mission most of the hot spots detected from ssi nims and ground based thermal observations caused no noticeable surface changes greater than 10 km in extent over the five year period surface changes were found at every location where active plumes were identified including acala which was never seen in sunlight and was only detected through auroral emissions during eclipse two types of plumes are distinguished on the basis of the size and color of their deposits confirming post voyager suggestions by mcewen and soderblom icarus 55 1983 191 smaller plumes produce near circular rings typically 150 200 km in radius that are white or yellow in color unless contaminated with silicates and frequently coat their surroundings with frosts of fine grained so2 the larger plumes are much less numerous limited to a half dozen examples and produce oval orange or red sulfur rich rings with maximum radii in the north south direction that are typically in the range from 500 to 550 km both types of plumes can be either episodic or quasi continuous over a five year period repeated eruptions of the smaller so2 rich plumes likely contribute significantly to io s resurfacing rate whereas dust ejection is likely dominated by the tenuous giant plumes both types of plume deposits fade on time scales of months to years through burial and alteration episodic seepages of so2 at haemus montes zal montes dorian montes and the plateau to the north of pillan patera may have been triggered by activity at nearby volcanic centers

carbon isotope ratio of cenozoic co2 a comparative evaluation of available geochemical proxies 1 the carbon isotope ratio 13c of plant material is commonly used to reconstruct the relative distribution of c3 and c4 plants in ancient ecosystems however such estimates depend on the 13c of atmospheric co2 13cco2 at the time which likely varied throughout earth history for this study we use benthic and planktonic 13c and 18o records to reconstruct a long term record of cenozoic 13cco2 confidence intervals for 13cco2 values are assigned after careful consideration of equilibrium and non equilibrium isotope effects and processes as well as resolution of the data we find that benthic foraminifera better constrain 13cco2 compared to planktonic foraminiferal records which are influenced by photosymbiotes depth of production seasonal variability and preservation furthermore sensitivity analyses designed to quantify the effects of temperature uncertainty and diagenesis on benthic foraminifera 13c and 18o values indicate that these factors act to offset one another our reconstruction suggests that cenozoic 13cco2 averaged 6 1 0 6 1 while only 11 2 million of the last 65 5 million years correspond to the pre industrial value of 6 5 with 90 confidence here 13cco2 also displays significant variations throughout the record at times departing from the pre industrial value by more than 2 thus the observed variability in 13cco2 should be considered in isotopic reconstructions of ancient terrestrial plant ecosystems especially during the late and middle miocene times of presumed c4 grassland expansion

the final galileo ssi observations of io orbits g28 i33 abstract we present the observations of io acquired by the solid state imaging ssi experiment during the galileo millennium mission gmm and the strategy we used to plan the exploration of io despite galileo s tight restrictions on data volume and downlink capability and several spacecraft and camera anomalies due to the intense radiation close to jupiter there were many successful ssi observations during gmm four giant high latitude plumes including the largest plume ever observed on io were documented over a period of eight months only faint evidence of such plumes had been seen since the voyager 2 encounter despite monitoring by galileo during the previous five years moreover the source of one of the plumes was tvashtar catena demonstrating that a single site can exhibit remarkably diverse eruption styles from a curtain of lava fountains to extensive surface flows and finally a 400 km high plume over a relatively short period of time 13 months between orbits i25 and g29 despite this substantial activity no evidence of any truly new volcanic center was seen during the six years of galileo observations the recent observations also revealed details of mass wasting processes acting on io slumping and landsliding dominate and occur in close proximity to each other demonstrating spatial variation in material properties over distances of several kilometers however despite the ubiquitous evidence for mass wasting the rate of volcanic resurfacing seems to dominate the floors of paterae in proximity to mountains are generally free of debris finally the highest resolution observations obtained during galileo s final encounters with io provided further evidence for a wide diversity of surface processes at work on io

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

large scale hydrological change drove the late miocene c4 plant expansion in the himalayan foreland and arabian peninsula carbon isotope changes in paleosols from siwalik pakistan and marine sediments from the bengal fan indicate a major c 4 plant expansion in the himalayan foreland during the late miocene however the timing and mechanisms behind the c 4 plant expansion remain enigmatic here we present high resolution 60 k y biomarker and compound specific isotope data spanning the past 11 m y from ocean drilling program site 722 in the arabian sea an 5 6 increase in leaf wax 13 c values indicates a marked rise of c 4 plants from 10 to 5 5 ma with accelerated expansion from 7 9 to 5 5 ma a concurrent 50 rise in leaf wax d values is attributed to a combined effect of changes in precipitation amount and evaporation indicating that source regions for the plant waxes became progressively drier from 10 to 5 5 ma in contrast to earlier reports our isotope records biomarker abundances alkenone u k 37 and globigerina bulloides abundance data do not suggest enhanced summer monsoon circulation during this time interval rather our results suggest that large scale hydrological changes drove the late miocene expansion of c 4 plants in the himalayan foreland and arabian peninsula

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

regional scale variability in the spread of grasslands in the late miocene abstract a new paleovegetation reconstruction based on both phytolith and paleosol carbon isotopic data is presented for the middle late miocene 11 2 9 5 ma of southwestern montana both sources of data indicate an open habitat c3 grassland ecosystem with a small c4 component

a quantitative weathering classification system for yellow travertines weathering can cause adverse effects on the physico mechanical properties of rocks although the processes and outcomes of weathering have been investigated for many rock types the travertine weathering was not paid enough attention as much as the others however the unfavorable effects of weathering may arise rapidly due to travertine s calcium carbonate composition and highly porous texture travertine is an important rock type in building stone market and is generally preferred as an exterior facade material this rock type was also used in many historical buildings and sculptures in the past and the signs of extensive weathering can be recognized on some of these travertine made structures in this study it was aimed to characterize the effect of weathering on travertine s structural properties the yellow travertine from eskipazar karabuk turkey was selected as the study material and the samples with different weathering degrees were collected from site the chemical physical and mechanical properties of those samples were determined in laboratory the physico mechanical variations with progressive weathering grades were statistically evaluated and a weathering classification based on a rating system was proposed for yellow travertine in rock material scale the newly developed system may assist in characterizing the degree of weathering for historical structures built by yellow travertine additionally the classification may also guide to further researches on the weathering of different types of travertine

active volcanism on io io one of jupiter9s moons has hundreds of active volcanoes many of which are erupting high temperature silicate lavas in his perspective mcewen reviews how data returned by the galileo spacecraft have helped to resolve some questions regarding io9s volcanism but have raised others especially regarding the moon9s internal structure

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

stable isotopic results from paleosol carbonate in south asia paleoenvironmental reconstructions and selective alteration article i nfo we measured 18 o and 13 c values of paleosol carbonate nodules from a variety of sedimentary units in southern asia in order to reconstruct paleoenvironmental conditions and to evaluate for possible diagenetic alteration paleosol carbonate nodules were collected from lower to upper cretaceous strata exposed in two locations in southern tibet and from lower to middle miocene strata in northern india and nepal additional samples were collected from stratigraphically adjacent marine carbonate units to test for possible resetting of stable isotope values based on the implausibly low 18 o values 13 of most of the marine carbonate samples we interpret the 18 o values of the associated paleosol carbonate nodules as being reset and therefore unreliable for paleoenvironmental or paleoelevation reconstruction importantly the 18 o values of 13 c values of marine carbonate rocks fall within the expected primary

sequence stratigraphy of cenozoic continental rocks southwestern montana because the presently used bozeman group lithostratigraphy is difficult to apply to cenozoic basin fill rocks in the jefferson beaverhead melrose and divide valleys southwestern montana we advocate the use of sequence stratigraphy surface sequence boundaries are in many cases marked by calcic paleosol zones these zones can be projected into the subsurface and tied to seismic reflection data density velocity contrasts between calcic paleosol zones and overlying nonpedogenic rocks generate bright reflectors that define sequence boundaries sequence boundary delineation is further enhanced by reflection termination patterns similar to those found in marine strata sequence age calibration is based upon vertebrate fossil and radiometric age data five sequences separated by basin wide unconformities are recognized most sequence bounding unconformities are marked by paleosols an occurrence not previously reported for cenozoic strata of southwestern montana the sequences and their age ranges are 1 bridgerian uintan approximately 50 to 44 ma calc alkaline volcanic flows and interstratified sedimentary rocks 2 duchesnian to whitneyan approximately 42 to 30 ma terrestrial sedimentary and volcanic rocks 3 arikareean approximately 27 to 21 ma terrestrial sedimentary and volcanic rocks 4 barstovian to blancan approximately 16 to 4 ma terrestrial sedimentary and volcanic rocks and 5 early quaternary approximately 1 8 ma to holocene terrestrial sedimentary and volcanic rocks

tectonics of mascon loading resolution of the strike slip faulting paradox subsidence of lunar mascon maria impact basins partly filled with mare basalt and sites of prominent positive gravity anomalies typically led to the formation of concentric graben arcuate rilles around the flanks of the basin while compressive features mare ridges formed in interior regions although previous numerical models of the response of the lunar lithosphere to mascon loading predict that an annulus of strike slip faulting should also have formed around mascon maria no such faults have been observed this strike slip faulting paradox however arises from an oversimplification of the earlier models viscoelastic finite element models of lunar mascon basins that include the effects of lunar curvature heterogeneous crustal strength initial stress conditions and multistage load histories show that the width of a predicted annulus of strike slip faulting may be small the use of anderson s criterion for predicting fault styles may also overpredict the width of strike slip faulting a faulting style criterion that takes into account transitional faulting in which both strike slip and dip slip components are present predicts zones of pure strike slip faulting that are about half of the width predicted by the anderson criterion furthermore strike slip faulting should be observed only in regions in which flexural stresses are sufficient to induce rock failure however since stress patterns consistent with strike slip faulting around mascon loads represent a transition between compressional and extensional provinces differential stresses tend to be low in these regions and for at least part of this region are not sufficient to induce rock failure a mix of concentric and radial thrust faulting is observed in some mascon maria at odds with previous models that predict only radial orientations away from the basin center this apparent discrepancy may be partly explained by the multistage emplacement of mare basalt units a scenario that leads to a stress pattern where concentric and radial orientations of thrust faults are equally preferred detailed models of the serenitatis basin indicate a 25 km thick lunar lithosphere at the time of rille formation and a 75 km thick lithosphere at the time of late stage mare ridge formation the extent of observed mare ridges and the inferred cessation of rille formation around serenitatis prior to the time of emplacement of the youngest mare basalt units is consistent with the superposition of a global horizontal compressive stress field generated by the cooling and contraction of the lunar interior with the local stresses associated with lithospheric loading

environmental change in the great plains an isotopic record from fossil horses abstract carbon and oxygen isotope ratios of fossil horse tooth enamel from nebraska and texas show evidence for late neogene environmental changes in the great plains the earliest unambiguous c4 dietary signal among texas equids coincides with the age of the classic late hemphillian age coffee ranch fauna which we suggest is 6 6 ma based on volcanic ash correlations c4 vegetation was present in the diets of a small fraction of late hemphillian equids in nebraska and was thereafter ordinary in the diets of both nebraska and texas equids there is no unequivocal evidence for abundant c4 vegetation in the diets of pre late hemphillian equids and we suggest that the ensuing dietary change reflects c4 biomass expansion in the latest miocene carbon isotope ratios of post hemphillian horses in nebraska can be divided into two statistically distinct populations on the basis of whether tortoise remains co occur with horse remains indicating that the two proxies carbon isotopes and presence absence of tort

effects of faulting on crustal stresses during mountain formation on io abstract the vast majority of mountains observed on io are tectonic upthrusted blocks a product of compressional forces the mechanism behind their formation is generally understood to be related to io s heat pipe volcanism and crustal subsidence compressional thermoelastic stresses from sustained local or regional shut down of io s heat pipe volcanism could be potentially important orogenic drivers as well kirchoff and mckinnon 2009 formation of mountains on io variable volcanism and thermal stresses icarus 201 598 614 at the same time extensional tectonic features rifts pull apart basins simple graben are found on io furthermore results from a two dimensional finite element model of thrust fault formation in the ionian environment show that natural kinematics of fault motion creates localized regions of near surface extension while compressional stresses at depth are greatly reduced bland and mckinnon 2016 mountain building on io driven by deep faulting nat geosci 9 429 432 in light of these observations and model results we refine our previous one dimensional advective heat pipe model of io s crustal stresses exploring another horizontal boundary strain end member which is the laterally unconfined or integral stress condition first suggested by turcotte 1974 are transform faults thermal contraction cracks j geophys res 79 2573 2577 we also explore the effects of directly incorporating brittle failure limits and liquid sulfur through pore pressure on these failure limits horizontally unconfined vertical boundaries serve as an end member representation for stress release on preexisting faults and in the context of io predict extensional failure in the upper crust in response to deeper compression of either subsidence and or thermal origin including these modifications greatly decreases the size of the region in compressional failure in the lower crust unless the effects of pore sulfur are included as in our previous work the most favorable condition for mountain formation on io is suggested to be a combination of subsidence stress thermal stress from a decrease in volcanic heat piping and crustal thinning due to basal melting

extraterrestrial lava lakes abstract active lava lakes are rare on earth with only ten documented examples all formed by lavas of basaltic composition and housed inside summit craters or calderas the existence of lava lakes on other planetary bodies may imply similarities in either composition or volcano tectonic settings and so has important implications for understanding the link between melt production and volcanism we review lava lakes on earth and other planets particularly active caldera like features interpreted to be currently containing active lava lakes on jupiter s moon io and features interpreted as remnants of lava lakes on venus and mars mercury and the moon do not boast the major calderas or shield volcanoes of their larger rocky neighbors partly due to a horizontally compressive tectonic regime arising from global contraction that makes it difficult to move melts through the upper crust we discuss the evidence for active lava lakes on io and show how modeling based on terrestrial lava lakes can reveal how these phenomena differ on both bodies the superficial similarities do not necessarily imply that the plumbing is similar observations of the largest lava lake on io loki patera provide insight into the nature of ionian lava lakes in general which may be more similar to eruptive episodes on the east pacific rise on earth which lead to temporary lava lakes although temporal data for io s lava lake activity are scarce studies of temporal variability of lava lakes on earth are useful for providing ground truth for comparisons future studies of earth by remote sensing and field observations and of io by both ground based observations and future missions are needed to answer many questions including why lava lakes rare on earth appear to be common on io

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

using phytolith assemblages to reconstruct the origin and spread of grass dominated habitats in the great plains of north america during the late eocene to early miocene abstract this paper outlines a general approach for analyzing siliceous microfossils from plants phytoliths in geologic sediments and uses this method to reconstruct the evolution of grasslands in the central great plains during the late tertiary phytolith assemblage analysis is widely employed for reconstructing vegetation types in pleistocene holocene paleoecology and archaeology but no standardized methodology is currently available published phytolith studies are often system specific and tailored after specific modern analogues as a result they vary in extraction technique classification scheme and method of inference for ancient phytolith assemblages whose modern analogues are not well understood a more general analytic approach is necessary this analytic approach includes studying all size fractions 2 250 mm using a classification scheme based on the available literature and a comprehensive modern phytolith reference collection and comparing relative frequencies through time of all diagnostic phytoliths to interpret changes in habitat structure this general method was applied to late eocene to early miocene sediment samples from northwestern nebraska to deduce vegetation history and the results were compared to those obtained using a more specific technique stromberg paleogeogr paleoclimatol paleoecol 177 2002 59 in both studies phytoliths were extracted by means of heavy liquid separation from the following lithostratigraphic units 1 the late eocene chadron formation and the early oligocene brule formation white river group 2 the late oligocene early miocene monroe creek formation the early miocene harrison formation and anderson ranch formation arikaree group and 3 the early miocene runningwater formation and box butte formation ogallala group the two techniques general vs specific produced results that differ markedly data from the general approach indicate the presence of relatively closed habitats in late eocene to early oligocene typified by the presence of phytoliths from bambusoid grasses woody and herbaceous dicotyledons and palms the introduction and spread of modern open habitat grasses such as pooids arundinoids and panicoids occurred between the late oligocene and early miocene this resulted in a savanna or woodland type habitat by the early miocene in contrast analysis using the specific method suggested the presence of open habitats in northwestern nebraska from the late eocene onward the difference in interpretation based on the two approaches is principally due to inclusion of phytoliths 50 mm and the use of an expanded reference collection in the current study general analytic approach these results point to the importance of methodological choices in phytolith analysis and emphasize the usefulness of phytoliths as paleoecological indicators in the fossil record

a proxy for humidity and floral province from paleosols abstractwe develop a proxy to infer humidity from the geochemistry of paleosols in order to enhance reconstructions of ancient paleoclimate beyond trends in mean annual precipitation geochemical transfer functions developed herein are used to estimate net primary production and evapotranspiration along three latitudinal transects of modern soils in the coterminous united states mean annual precipitation and the degree of chemical weathering are estimated from the major element concentrations in soils the ratio of evapotranspiration estimated from our proxy and mean annual precipitation provides a method of determining the humidity province of ancient climates that is more robust and meaningful than previous methods and our approach differs from existing methods since both the influx and efflux of moisture are explicitly determined the required input parameters for application of this proxy are 1 the soil morphology 2 accurate and complete major element concentration data for the active soil

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

ungulate diets reveal patterns of grassland evolution in north america abstract equids from the late miocene hemphillian north american land mammal age of texas evolved c4 dominated diets earlier than their nebraska counterparts leading researchers to hypothesize a northward expansion of c4 grasses between 8 and 6 ma however competing hypotheses from multiple paleoecological proxies support one of three hypotheses that northward c4 expansion occurred at the expense of c3 woodlands c3 grasslands or was not occurring during the hemphillian we test these alternative hypotheses by comparing the ecosystems of hemphillian texas and nebraska 6 3 7 5 ma using hoofed mammal dietary reconstruction hypsodonty and digestive strategy and by incorporating published tooth enamel isotopes paleosol isotopes and phytolith assemblage data we also use hypsodonty mesowear and microwear in a detailed comparison of two localities that are roughly contemporary cambridge nebraska at 7 ma and coffee ranch texas at 6 6 ma to rule out time averaging as an explanatory variable through analogy with modern african communities we reconstruct texas and nebraska ecosystems as bushland and woodland respectively using the proportions of hypsodont taxa we estimate mean annual precipitation values of 1217 mm year for nebraska and 1368 mm year for texas using rarefaction we also do not find differences in the richness of brachydont hypsodont and hindgut fermenting taxa we therefore conclude that both ecosystems were largely similar in hoofed mammal faunal structure during the late miocene when compared to published paleosol and phytolith data which show no differences in c3 c4 biomass among latitudes our results allow us to reject hypotheses of northward c4 expansion during the late miocene we therefore suggest that the equid enamel isotopes may have been biased by two potential factors the primary reliance on a single locality of appropriate age and possible behavioural lag in c4 feeding among nebraska equids these results suggest that the formation of a modern c3 c4 latitudinal gradient occurred later than is previously suggested by equid enamel carbon isotopes

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

formation of mountains on io variable volcanism and thermal stresses abstract thermal stresses are potentially important drivers of io s tectonics and mountain building it has been hypothesized that sustained local or regional shut down of heat pipe volcanism on io could lead to deep crustal heating and large compressive stresses mckinnon w b schenk p m dombard a j 2001 geology 29 103 106 such large stresses would then be relieved by thrust faulting and uplifting of crustal blocks producing mountains like those observed on io here we analyze the tectonic consequences of the heat pipe model in detail considering both the initial thermal stress state of a basalt or peridotite crust created by heat pipe volcanism and relative roles of subsidence stresses due to burial of preexisting layers and thermal stresses arising from variable volcanism and changes in crustal lithosphere thickness we limit the magnitude of the potential subsidence stresses in our study because the magnitude of subsidence stresses can be quite large if not dominant results indicate that for a fixed crustal thickness the region of failure and faulting moves closer to the surface as eruption rate decreases and time increases when the crust melts at its base as volcanism decreases as might occur under steady state tidal heating resulting in crustal thinning the region of failure is brought even closer to the surface naturally when compressive subsidence stresses are included the vertical extent of crust in brittle failure thickens to include most of the lithosphere in contrast increases in eruption rate cause the extent of the region in compressional failure to decrease and be driven very deep in the crust in the absence of sufficient subsidence stress therefore regions of declining volcanism are more likely to produce mountains whereas regions of extensive or increasing volcanism are less likely to do so this is consistent with the observation of a global anticorrelation between mountains and volcanic centers on io finally we find that the choice of crustal composition rheology dry basalt vs dry peridotite has little effect on our results implying that basalt peridotite and komatiite are all similarly stiff in the io environment

observations and temperatures of io s pele patera from cassini and galileo spacecraft images abstract pele has been the most intense high temperature hotspot on io to be continuously active during the galileo monitoring from 1996 2001 a suite of characteristics suggests that pele is an active lava lake inside a volcanic depression in 2000 2001 pele was observed by two spacecraft cassini and galileo the cassini observations revealed that pele is variable in activity over timescales of minutes typical of active lava lakes in hawaii and ethiopia these observations also revealed that the short wavelength thermal emission from pele decreases with rotation of io by a factor significantly greater than the cosine of the emission angle and that the color temperature becomes more variable and hotter at high emission angles this behavior suggests that a significant portion of the visible thermal emission from pele comes from lava fountains within a topographically confined lava body high spatial resolution nightside images from a galileo flyby in october 2001 revealed a large relatively cool

carbon isotope fractionation during decomposition of organic matter in soils and paleosols implications for paleoecological interpretations of paleosols abstract stable isotope ratios reported as 13c of organic carbon preserved in paleosols have potential utility as a valuable paleoecological indicator if the isotopic composition of paleobiomass is preserved in the paleosol organic carbon without fractionation however soil organic matter is in a constant state of decomposition in an open system and frequently decomposes further during alteration after burial of the paleosol during this decomposition kinetic fractionation of 13c 12c in an open system results in concentration of 13c in the residual organic matter preserved in the soil and paleosol this paper summarizes studies of modern soils which show that this 13c enrichment follows a rayleigh distillation process whereby the 13c 12c ratio is a function of the natural logarithm of the fraction of remaining soil organic carbon leaving soil organic carbon 13c enriched by up to 6 with respect to the original biomass if the fraction of original biomass carbon remaining during these decomposition processes deviates significantly from 1 the soil organic carbon can be 13c enriched by several per mil and thus not a good paleoecological indicator of the 13c value of the original biomass therefore effective paleoecological studies of 13c preserved in paleosol organic carbon must therefore demonstrate that the measured concentration of organic carbon in the paleosol is near its maximum concentration during soil formation or that the paleosol organic matter does not include the 13c enriched products of microbial decomposition suggestions are made for interpreting the effects of carbon isotope fractionation of organic matter and for materials and methods most useful for paleoecological studies from bulk paleosol organic carbon

aeolian n alkane isotopic evidence from north pacific for a late miocene decline of c4 plant in the arid asian interior abstract aeolian deposition in the central north pacific has been well recognized to originate from arid asian interior while there is no doubt about the transport of organic matters along with the mineral dust from the source region little is known about the nature and changes of the terrestrial organic compounds preserved in the deep sea sediments in this study higher plant leaf wax n alkanes from odp site 1208 and site 886 in the north pacific since the middle miocene were analyzed to explore long term changes in vegetation and climate in the source region accumulation rates of leaf wax n alkanes show an increasing trend consistent with the documented climatic drying of the asian interior since the late miocene the records of carbon isotopic enrichment factors of c29 n alkane relative to atmospheric co2 ec29 co2 show a prominent decrease from 12 to 8 ma the average ec29 co2 value prior to 8 ma is 0 8 heavier than after 8 ma although almost all values of ec29 co2 25 3 to 21 3 are well within the range of c3 plants adjustment of isotope discrimination by c3 plants is not considered as the main cause of the observed variations instead changes in relative abundance of c3 vs c4 plants are invoked to interpret the ec29 co2 records higher c4 contribution 17 7 5 3 to the local vegetation is inferred for the period prior to 8 ma implying a slightly warmer climate in the source region a marked decline in c4 plants from 12 to 8 ma interpreted as a result of regional temperature drop coincides with the prominent growth of northern tibetan plateau around 8 ma along with the global cooling climate our results therefore point to apparently close links among plateau uplift development of drying and cooling climates and vegetation changes in the asian interior

volcanic history geologic analysis and map of the prometheus patera region on io data from jupiter s moon io returned by the galileo spacecraft have been used to create a geologic map of prometheus patera its associated flow field and nearby features we have identified the location of the vent that fed the prometheus flow field during the galileo epoch in the north eastern portion of the main prometheus flow field this vent is the probable source of a small sulphur rich plume previous studies suggested that the vent may be atop a tectonic fault but we find that the vent is offset from the putative fault it is plausible that in the past magma exploited the fault to reach the surface at prometheus patera but subsequent magma cooling in the conduit could have caused an obstruction preventing further eruptions from providing significant contributions to the prometheus flow field we also speculate on how a new prometheus plumbing system may be fed by mafic magmas after melt stalls in magma reservoirs during its ascent through the lithosphere from the mantle

the geothermal gradient of io consequences for lithosphere structure and volcanic eruptive activity we solve numerically the equations describing the transfer of heat through the lithosphere of io by a mixture of conduction and volcanic advection as proposed by o reilly and davies o reilly t c davies g f 1981 geophys res lett 8 313 316 removing the requirement that average material properties must be used as expected the dominance of advective heat transfer by volcanic eruptions means that io s geothermal gradient well away from volcanic centres is very small of order 1 k km 1 this result is independent of any reasonable assumptions about the radiogenic heating rate in the lithosphere the lithosphere temperature does not increase greatly above the surface temperature until the base of the lithosphere is approached except in limited areas around shallow magma bodies as a consequence solid volatile sulphur compounds mobilized by volcanic processes and re deposited on the surface of io commonly remain solid until they reach great depths as they are progressively buried by ongoing activity for current estimates of the volcanic heat transfer rate melting of so2 does not begin until a depth of 20 km and sulphur remains solid to a depth of 26 km in a 30 km thick lithosphere rising magmas can incorporate fluids from these deep sulphur compound aquifers and we quantify the major influence that this can have on the bulk density of the magma and hence the resulting possible intrusion and eruption styles

lava fountains from the 1999 tvashtar catena fissure eruption on io implications for dike emplacement mechanisms eruption rates and crustal structure the first direct evidence that patterns of basaltic eruptive activity may be very similar on io and earth was seen on november 26 1999 when the solid state imaging system on board the galileo spacecraft obtained high resolution images of a fissure eruption taking place in one of the calderas of the tvashtar catena complex we analyzed the dynamics of the fissure eruption from the morphology of the lava fountains and pyroclastic deposits and derived an estimate of the eruption rate our best estimate of the volume eruption rate per unit length of fissure lies in the range 0 7 to 7 m3 s 1 m 1 and multiplying this rate by the fissure length of 25 km yields a total volume eruption rate of magma of 2 104 to 2 105 m3 s 1 the upper end of the inferred eruption rate is very close to the upper end of the range of eruption rates observed or inferred for fissure eruptions on earth theoretical models of the possible dike systems feeding the fissure show that for eruptions of positively buoyant magma the elastic properties of rocks are such that a magma flux of 6 to 7 m3 s 1 m 1 is the largest value that can ever be realized in such eruptions this limiting value being independent of planetary gravity and thus the same on all silicate bodies the eruption rate inferred for tvashtar can also be achieved by a negatively buoyant magma but in that case the source depth cannot be much greater than a few tens of kilometers we find that some eruptive events are consistent with the effusion of magmas which are buoyant relative to the crust whereas others appear to involve magmas which are not this implies that the distribution of crustal volatiles is laterally very inhomogeneous our analyses suggest that the depths from which magmas make their final ascent to the surface of io are generally of order tens rather than hundreds of kilometers

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

geologic mapping of the amirani gish bar region of io implications for the global geologic mapping of io abstract we produced the first geologic map of the amirani gish bar region of io the last of four regional maps generated from galileo mission data the amirani gish bar region has five primary types of geologic materials plains mountains patera floors flows and diffuse deposits the flows and patera floors are thought to be compositionally similar but are subdivided based on interpretations regarding their emplacement environments and mechanisms our mapping shows that volcanic activity in the amirani gish bar region is dominated by the amirani eruptive center aec now recognized to be part of an extensive combined amirani maui flow field a mappable flow connects amirani and maui suggesting that maui is fed from amirani such that the post voyager designation maui eruptive center should be revised amirani contains at least four hot spots detected by galileo and is the source of widespread bright sulfur flows and active dark silicate flows being emplaced in the promethean style slowly emplaced compound flow fields the floor of gish bar patera has been partially resurfaced by dark lava flows although other parts of its floor are bright and appeared unchanged during the galileo mission this suggests that the floor did not undergo complete resurfacing as a lava lake as proposed for other ionian paterae there are several other hot spots in the region that are the sources of both active dark flows confined within paterae and so2 and s2 rich diffuse deposits mapped diffuse deposits around fractures on mountains and in the plains appear to serve as the source for gas venting without the release of magma an association previously unrecognized in this region the six mountains mapped in this region exhibit various states of degradation in addition to gaining insight into this region of io all four maps are studied to assess the best methodology to use to produce a new global geologic map of io based on the newly released combined galileo voyager global mosaics to convey the complexity of ionian surface geology we find that a new global geologic map of io should include a map sheet displaying the global abundances and types of surface features as well as a complementary gis database as a means to catalog the record of surface changes observed since the voyager flybys and during the galileo mission

the zamama thor region of io insights from a synthesis of mapping topography and galileo spacecraft data abstract we have studied data from the galileo spacecraft s three remote sensing instruments solid state imager ssi near infrared mapping spectrometer nims and photopolarimeter radiometer ppr covering the zamama thor region of io s antijovian hemisphere and produced a geomorphological map of this region this is the third of three regional maps we are producing from the galileo spacecraft data our goal is to assess the variety of volcanic and tectonic materials and their interrelationships on io using planetary mapping techniques supplemented with all available galileo remote sensing data based on the galileo data analysis and our mapping we have determined that the most recent geologic activity in the zamama thor region has been dominated by two sites of large scale volcanic surface changes the zamama eruptive center is a site of both explosive and effusive eruptions which emanate from two relatively steep edifices zamama tholi a and b that appear to be built by both silicate and sulfur volcanism a 100 km long flow field formed sometime after the 1979 voyager flybys which appears to be a site of promethean style compound flows flow front so2 plumes and adjacent sulfur flows larger possibly stealthy plumes have on at least one occasion during the galileo mission tapped a source that probably includes s and or cl to produce a red pyroclastic deposit from the same vent from which silicate lavas were erupted the thor eruptive center which may have been active prior to voyager became active again during the galileo mission between may and august 2001 a pillanian style eruption at thor included the tallest plume observed to date on io at least 500 km high and new dark lava flows the plume produced a central dark pyroclastic deposit probably silicate rich and an outlying white diffuse ring that is so2 rich mapping shows that several of the new dark lava flows around the plume vent have reoccupied sites of earlier flows unlike most of the other pillanian eruptions observed during the galileo mission the 2001 thor eruption did not produce a large red ring deposit indicating a relative lack of s and or cl gases interacting with the magma during that eruption between these two eruptive centers are two paterae thomagata and reshef thomagata patera is located on a large shield like mesa and shows no signs of activity in contrast reshef patera is located on a large irregular mesa that is apparently undergoing degradation through erosion perhaps from so2 sapping or chemical decomposition of sulfur rich material from multiple secondary volcanic centers

the mountains of io global and geological perspectives from voyager and galileo to search for local and global scale geologic associations that may be related to the internal dynamics of lo we have completed a global catalog of all mountains and volcanic centers we have identified 115 mountain structures covering 3 of the surface and 541 volcanic centers including paterae calderas and dark spots and shield volcanoes the average length of an ionian mountain is 157 km with the longest being 570 km the mean height of ionian mountains is 6 3 km and the highest known mountain is boosaule montes 17 5 3 km five basic morphologic types of mountains have been identified mesa plateau peak ridge and massif very few mountains bear any physical similarity to classic volcanic landforms but many resemble flatiron mountains on earth and are interpreted as tilted crustal blocks this would be consistent with the hypothesis that most mountains are thrust blocks formed as a result of compressive stresses built up in the lower crust due to the global subsidence of volcanic layers as they are buried over time schenk and bulmer 1998 more than one mechanism may be responsible for all ionian mountains however the proximity of some mountains to paterae may indicate a direct link between some mountains and volcanism although it is not always clear which came first in contrast to earlier studies a pronounced bimodal pattern is observed in the global distribution of both mountains and volcanic centers the regions of highest areal densities of volcanic centers are near the sub and anti jovian regions but are offset roughly 90 in longitude from the two regions of greatest concentration of mountains this anticorrelation may indicate the overprinting of a second stress field on the global compressive stresses due to subsidence the bimodal distribution of volcanic centers and mountains is consistent with models of asthenospheric tidal heating and internal convection developed by tackley et al 2001 over regions of mantle upwelling compressive stresses in the lower crust induced by global subsidence might be reduced encouraging volcanism and discouraging mountain building in regions of mantle downwelling these compressive stresses in the lower crust might be increased discouraging volcanism and encouraging mountain building alternatively the global pattern may be related to possible but undocumented nonsynchronous rotation of lo which would produce two regions each of compression and extension in the crust evidence of layering and of mass wasting including landslides block sliding debris aprons and downslope creep on ionian mountains suggests that the crust of lo is essentially a layered stack of partially consolidated volcanic lavas and plume deposits becoming more consolidated with depth the lower crust especially may also be ductily deformed punctuated by volcanic intrusions and faulting at paterae and broken into blocks some of which have been uplifted to form mountains

geologic mapping of the hi iaka and shamshu regions of io abstract we produced regional geologic maps of the hi iaka and shamshu regions of io s antijovian hemisphere using galileo mission data to assess the geologic processes that are involved in the formation of io s mountains and volcanic centers observations reveal that these regions are characterized by several types of volcanic activity and features whose orientation and texture indicate tectonic activity among the volcanic features are multiple hotspots and volcanic vents detected by galileo one at each of the major paterae hi iaka shamshu and tawhaki we mapped four primary types of geologic units flows paterae floors plains and mountains the flows and patera floors are similar but are subdivided based upon emplacement environments and mechanisms the floors of hi iaka and shamshu paterae have been partially resurfaced by dark lava flows although portions of the paterae floors appear bright and unchanged during the galileo mission this suggests that the floors did not undergo complete resurfacing as flooding lava lakes however the paterae do contain compound lava flow fields and show the greatest activity near the paterae walls a characteristic of pele type lava lakes mountain materials are tilted crustal blocks that exhibit varied degrees of degradation lineated mountains have characteristic en echelon grooves that likely formed as a result of gravitational sliding undivided mountains are partially grooved but exhibit evidence of slumping and are generally lower elevation than the lineated units debris lobes and aprons are representative of mottled mountain materials we have explored the possibility that north and south hi iaka mons were originally one structure we propose that strike slip faulting and subsequent rifting separated the mountain units and created a depression which by further extension during the rifting event became hi iaka patera this type of rifting and depression formation is similar to the mechanism of formation of terrestrial pull apart basins with comparison to other regional maps of io and global studies of paterae and mountains this work provides insight into the general geologic evolution of io

lineations and structural mapping of io s paterae and mountains implications for internal stresses abstract the mountains of jupiter s volcanic moon io are tall steep and tectonic in origin yet their precise modes of formation and their associations with volcanic paterae are not fully understood global spatial statistics of paterae and mountains and their associated lineations reveal that both types of features are more common at low latitudes and tectonic lineations have preferred orientations whereas straight patera margins are randomly oriented additionally structurally controlled lineations tend to cluster with each other and in areas of high concentrations these tectonic lineations are shorter in length than their global average these results indicate that global scale rather than local or regional processes are involved in forming io s tectonic structures but that the diversity of mountain characteristics and the collapse of paterae adjacent to mountain complexes are more locally controlled regional structural mapping of the hi iaka shamshu tohil and zal regions reveals io s mountains reside in large fault bounded crustal blocks that have undergone modification through local responses of subsurface structures to variable stresses strike slip motion along reactivated faults led to the formation of transpressional and transtensional features creating tall peaks and low basins some of which are now occupied by paterae we propose io s mountains result from a combination of crustal stresses involving global and local scale processes dominantly volcanic loading and tidal flexing these stresses sometimes are oriented at oblique angles to pre existing faults reactivating them as reverse normal or strike slip faults modifying the large cohesive crustal blocks that many of io s mountains reside in further degradation of mountains and burial of faults has occurred from extensive volcanism mass wasting gravitational collapse and erosion by sublimation and sapping of sulfur rich layers this model of fault bounded blocks being modified by global stresses and local structural response accounts for the variation and patterns of mountain sizes shapes and orientations along with their isolation and interactions with other features it also provides a context for the operation and extent of global and regional stresses in shaping io s surface

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 heat flow from dark paterae abstract dark paterae on the jovian satellite io are evidence of recent volcanic activity some paterae appear to be entirely filled with dark volcanic material while others have only partially darkened floors dark paterae have area and heat flow longitudinal distributions that are bimodal as well as anti correlated with the longitudinal distribution of mountains on io at a global scale as part of our study of io s total heat flow we have examined the darkest paterae and quantified their thermal emission in order to assess their contribution this is the first time that the areas of the dark material in these paterae have been measured with such precision and correlated with their thermal emission dark paterae yield a significantly larger contribution to io s heat flow than dark volcanic fields dark paterae including loki patera yield at least 4 10 13 w or 40 of io s total heat flow in comparison dark flow fields yield 10 13 w or 10 of io s total heat flow of the total heat loss from dark paterae loki patera alone yields 10 13 w or 10 of io s total thermal emission

geologic mapping of the zal region of io abstract we produced a regional geologic map of the zal region of io s antijovian hemisphere using galileo mission data we discuss the geologic features summarize the map units and structures that are present discuss the nature of volcanic activity and present an analysis of the volcanic tectonic and gradational processes that affect the region the zal region consists of five primary types of geologic materials plains mountains paterae floors flows and diffuse deposits the flows and patera floors are similar but are subdivided based on uncertainties regarding emplacement environments and mechanisms the zal region includes two hotspots detected by galileo one along the western scarp of the zal patera volcano and one at the rustam patera volcano name submitted to iau a third hotspot at the nearby at am patera volcano name submitted to iau is the source of diffuse and pyroclastic materials that blanket north zal mons the western bounding scarp of zal patera is the location of a fissure vent that is the source of multiple silicate lava flows the floor of zal patera has been partially resurfaced by dark lava flows although portions of the patera floor appear bright and unchanged during the galileo mission this suggests that the floor did not undergo complete resurfacing as a flooding lava lake but does contain a compound flow field mountain materials exhibit stages of degradation lineated material degrades into mottled material we have explored the possibility that north and south zal mons were originally one structure we propose that strike slip faulting and subsequent rifting separated the mountain units opened a fissure which serves as a vent for lava flow and created a depression which by further extension during the rifting event became zal patera with comparison to other regional maps of io this work provides insight into the general geologic evolution of io

mountain building on io driven by deep faulting the high relief on jupiter s moon io has been linked to compression due to global subsidence simulations show that io s mountains may form along thrust faults that initiate at the lithosphere s base where the compressive stresses are highest jupiter s volcanic moon io possesses some of the highest relief in the solar system massive isolated mountain blocks that tower up to 17 km above the surrounding plains these mountains are likely to result from pervasive compressive stresses induced by subsidence of the surface beneath the near continual emplacement of volcanic material the stress state that results from subsidence and warming of io s lithosphere has been investigated in detail1 2 3 4 however the mechanism of orogenesis itself and its effect on regional tectonism and volcanism has not been firmly established here we present viscoelastic plastic finite element simulations demonstrating that io s mountains form along deep seated thrust faults that initiate at the base of the lithosphere and propagate upward we show that faulting fundamentally alters the stress state of io s lithosphere by relieving the large volcanism induced subsidence stresses notably in the upper portion of the lithosphere stresses become tensile near zero differential stress a number of processes are therefore altered post faulting including magma transport through the lithosphere interactions with tidal stresses and potentially the localization of mountain formation by thermoelastic stresses we conclude that io s mountains form by a unique orogenic mechanism compared with tectonic processes operating elsewhere in the solar system

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

pakistan mammal tooth stable isotopes show paleoclimatic and paleoenvironmental changes since the early oligocene abstract this research presents an isotopic study of three large mammal groups elephantoid proboscideans hyracodontid and rhinocerotid rhinocerotoids equids of the hipparion group from the bugti hills sequence eastern balochistan pakistan combined with published data from the miocene siwalik group northern central pakistan these two exceptional fossil records from pakistan provide an unambiguous source of biotic information from the early oligocene up to the late miocene the 13 c c and 18 o c results from the same herbivore groups show several significant variations in environmental and climatic conditions throughout the 30 to 7 5 myr period in this region first from 30 to 22 myr the environment is characterized by a relatively dry but dense forest existing under a temperate to subtropical climate with a more closed tropical environment at 23 myr oligocene 18 o of the terrestrial herbivore teeth agrees with the marine foraminifera 18 o and mg ca trends suggesting that the pakistan region was affected by global climate rather than regional conditions after 22 myr the 18 o c mammal enamel results show a long term decreasing trend until 15 myr toward a wetter environment with the appearance of tropical forests in response to the probable onset of the asian monsoon this is a period of high tectonic activity with the india asia collision leading to uplift of the tibetan plateau and shrinkage of the epicontinental paratethys sea this activity modified the land sea distribution and the thermal contrast between ocean and continent the driving force of the monsoon climate the middle miocene environment in pakistan experienced moist conditions under an intense monsoon system with relatively closed rainforest after 12 myr the 18 o c enamel values record a positive shift until 9 3 myr toward a drier environment with an increase of seasonality as suggested by higher 18 o c variability after 9 3 myr these late miocene drier climatic conditions and the asian monsoon intensification could potentially favour the c 4 photosynthetic pathway and hence the development of grassland to the detriment of subtropical forests resulting in the higher enamel 13 c values recorded after 9 3 myr