the unique geomorphology and physical properties of the vestalia terra plateau abstract we produced a geologic map of the av 9 numisia quadrangle of asteroid vesta using dawn spacecraft data to serve as a tool to understand the geologic relations of surface features in this region these features include the plateau vestalia terra a hill named brumalia tholus and an unusual dark ribbon material crossing the majority of the map area stratigraphic relations suggest that vestalia terra is one of the oldest features on vesta despite a model crater age date similar to that of much of the surface of the asteroid cornelia numisia and drusilla craters reveal bright and dark material in their walls and both cornelia and numisia have smooth and pitted terrains on their floors suggestive of the release of volatiles during or shortly after the impacts that formed these craters cornelia fabia and teia craters have extensive bright ejecta lobes while diogenitic material has been identified in association with the bright teia and fabia ejecta hydroxyl has been detected in the dark material within cornelia numisia and drusilla three large pit crater chains appear in the map area with an orientation similar to the equatorial troughs that cut the majority of vesta analysis of these features has led to several interpretations of the geological history of the region vestalia terra appears to be mechanically stronger than the rest of vesta brumalia tholus may be the surface representation of a dike fed laccolith the dark ribbon feature is proposed to represent a long runout ejecta flow from drusilla crater

fluid inclusion characteristics of intrusion related gold mineralization tombstone tungsten magmatic belt yukon territory canada intrusion hosted low sulfide sheeted vein systems are common within many plutons and stocks of the middle cretaceous tombstone tungsten magmatic belt yukon territory and host significant gold mineralization fluid inclusion characteristics of five such systems namely emerald lake dublin gulch scheelite dome mike lake and mactung constrain the vein forming fluid composition formation temperatures and pressures hydrothermal fluid processes and potential fluid sources the veins contain a wide range of fluid inclusion types ubiquitous type 1a and 1b inclusions are low salinity 1a xnacl 1 kbar at emerald lake and dublin gulch and 2 kbar at mactung and scheelite dome that potentially control fluid composition and evolution a variety of fluid processes may have been responsible for gold precipitation including immiscibility and or release of an evolving magmatic fluid

structural and mechanical controls on intrusion related deposits of the tombstone gold belt yukon canada with comparisons to other vein hosted ore deposit types abstract intrusion related gold deposits at the clear creek scheelite dome and dublin gulch properties of the tombstone gold belt tgb yukon territory have dominantly e striking steeply dipping auriferous quartz extension veins within intrusions in adjacent metasedimentary rocks gold is hosted in subvertical nw to nnw striking sinistral faults as veins and breccias in e striking extension veins and locally in e to ene striking fault veins these structural relationships indicate low magnitude broadly e w directed shortening and n s extension during stock emplacement and gold mineralisation at 92 ma the lack of any deviation or deflection of the extension vein orientations in the country rocks with respect to their orientation within the stocks indicates consistent stress trajectories in both rock types these tgb deposits formed at 5 8 km depth where mean and differential stresses may be greater in magnitude than in shallower porphyry environments many porphyry systems feature magmatic related stresses that dominated the local stress field with more variable vein orientations the result conversely orogenic gold systems usually exhibit strong dimensionality in vein orientations fault hosted mineralisation in metasedimentary rocks of the tgb deposits in this study is comparable in geometry but generally smaller in size than in many orogenic gold systems intrusion related systems of the tgb exhibit intermediate structural styles of mineralisation that provide a useful bridge in understanding the diversity of mechanically controlled structural styles in otherwise mostly unrelated gold deposit types

stable isotopic and fluid inclusion indications of large scale hydrothermal paleoflow boiling and fluid mixing in the keno hill ag pb zn district yukon territory canada the keno hill vein system of the central yukon is restricted predominantly to the highly fractured graphitic keno hill quartzite unit of mississippian age hydrothermal mineral zoning is related spatially to a cretaceous granitic pluton which intrudes the quartzite during mineralization the quartzite acted as a district scale aquifer subsequent erosion has exposed a 40 km long vein system from its plutonic roots outward to polymetallic ag pb zn veins and further to assemblages of epithermal character the 18oquartz values from veins near the pluton increase outwards from 10 6 to 20 1 as a result of cooling of the hydrothermal fluids and exchange with the quartzite contours of isotope values outline broad paths of fluid movement within the quartzite proceeding further from the pluton 18oquartz values decrease to 10 5 at the outer edge of the system the presence of meteoric water is indicated here where late stage quartz has 18osmow values as low as 7 l the outward decreasing trend appears to have been established by mixing of isotopically light meteoric water with exchanged fluids that were in isotopic equilibrium with the quartzite fluid inclusions from quartz in the orebodies demonstrate an evolving h2o co2 nacl ch4 system loss of co2 and ch4 during water vaporization coincides with increasing salinity and decreasing temperature resulting from high enthalpy steam loss depressurization during active faulting is the principal mechanism late stage fluids are represented by dilute aqueous inclusions with lower homogenization temperatures quartz from silver rich veins has been shifted to higher 18o values by up to 4 relative to adjacent silver poor veins the result of a minimum 10 25 adiabatic boiling and fractionation dominated by water vaporization and associated cooling graphite initially buffered the hydrothermal fluids to a high co2 content with variable ch4 involvement of organic carbon from the host rocks is indicated by the negative 13cpdb values for the carbonates from 4 0 to 12 9 variations in the carbon isotopes result from fluctuating co2ch4 ratios reflecting the contrasting volatility of the gas pair siderite formed as a late stage product of the boiling event and its formation coincides with a decreasing 18o trend in the water created by the equilibration of graphite and water in replacing exsolved co2 the formation of ch4 during this stage had a reducing effect on the fluid resulting in an increase in 13csiderite values in association with the decreasing 18osiderite values a closed system boiling model together with calculations of water consumption during post boiling co2 and ch4 formation indicates that greater than 50 of the original water in the ore fluid was removed relatively saline mineralizing fluids resulted

geology and geochemistry of the clear creek intrusion related gold occurrences tintina gold province yukon canada the clear creek gold occurrences lie within deformed lower greenschist facies rocks of the western selwyn basin they consist of auriferous sheeted quartz veins that cut six cretaceous stocks and their hornfels the veins contain 1 2 combined pyrite and arsenopyrite with lesser pyrrhotite bismuthinite and scheelite as well as 2 5 g t au new 40ar 39ar geochronology of hydrothermal micas indicates that the veins formed within 1 2 million years of granitoid emplacement fluid inclusion microthermometry defines a parent ore fluid of 81 mol h2o 14 mol co2 4 mol nacl kcl and 1 mol ch4 which unmixed into a low and high salinity immiscible pair this suggests a more saline parent fluid and a greater degree of fluid unmixing relative to the other occurrences in the eastern tintina gold province inclusions trapped in as and bi rich high gold grade veins have homogenization temperatures of 300 350 c whereas inclusions found in more ag and pb rich veins are characterized by temperatures of

mechanical and geological effects of impact cratering on ida asteroids respond to impact stresses differently from either laboratory specimens or large planets gravity is typically so small that seismic disturbances of a few cm s 1can devastate unconsolidated topography yet the presence of regolith and the likelihood that many asteroids are gravitational assemblages tell us that gravity cannot generally be ignored we use numerical models for impact fracture in solids to examine the initial stage of crater formation on asteroid 243 ida up to the cessation of fracture and the establishment of the cratering flow at this stage we can infer final crater diameters but not profiles we find that a modified strength scaling applies for craters up to a few 100 m in diameter forming in rock subject to ida s gravity and that gravity controls all craters larger than 1 km bright annuli around a number of intermediate craters may be the result of low velocity surface disturbances rather than bright proximal ejecta deposits we also consider large impactors to which ida presents a curved finite target surface with irregular gravity these can excavate asymmetrical concavities stresses from large events can refocus and cause fracture far from the crater using the shape of ida as a basis for 3d hydrocode simulations we show that impact genesis of the vienna regio concavity can cause fracture in pola regio where grooves are observed in spacecraft images other simulations indicate that the formation of the 10 km crater azzurra might have reopened these fractures which may account for their fresh appearance this mechanism of groove formation requires an interior which coherently transmits elastic stress while this precludes a classic rubble pile asteroid it does allow well joined fault planes and welded blocks or pores smaller than the stress pulse

subsurface failure in spherical bodies a formation scenario for linear troughs on vesta s surface abstract many asteroids in the solar system exhibit unusual linear features on their surface the dawn mission recently observed two sets of linear features on the surface of the asteroid 4 vesta geologic observations indicate that these features are related to the two large impact basins at the south pole of vesta though no specific mechanism of origin has been determined further the orientation of the features is offset from the center of the basins experimental and numerical results reveal that the offset angle is a natural consequence of oblique impacts into a spherical target here we demonstrate that a set of shear planes develops in the subsurface of the body opposite to the point of first contact these subsurface failure zones then propagate to the surface under combined tensile shear stress fields after the impact to create sets of approximately linear faults on the surface comparison between the orientation of damage structures in the laboratory and failure regions within vesta can be used to constrain impact parameters e g the approximate impact point and likely impact trajectory

eclogite occurrences in the southern tianshan high pressure belt xinjiang western china abstract eclogite pods and layers of eclogites in mafic blueschists are the most prominent witnesses of eclogite facies metamorphism in the southern tianshan high pressure belt of western china the p t evolution was deciphered in order to understand the geotectonic framework of these rocks geothermobarometric evaluation for matrix assemblages reveals peak metamorphic condition between 14 and 21 kbar at 500 to 600 c prograde growth zoning and mineral inclusions in garnet are evidence for a clockwise p t path the presence of intimate eclogite metabasic blueschist interlayering and the high p t estimates suggest that the eclogite facies rocks from the southern tianshan high pressure belt formed in a tectonic regime similar to the franciscan type therefore the southern tianshan high pressure belt is most important in order to resolve the paleozoic tectonic evolution of central asia

global structure of asteroid 433 eros 1 models of asteroid formation and evolution suggest a variety of internal structures ranging from gravitationally bound accumulations of debris to fully rigid monolithic bodies the near shoemaker spacecraft has provided detailed imaging and gravity data relevant to the characteristics of structural features and global mass properties a long ridge coplanar with a degraded trough ridge system and an approximately parallel surface facet suggest exploitation of a nearly global fabric by both compressive and extensional failure at significantly different times

detailed structural analysis of the rim of a large complex impact crater bosumtwi crater ghana the 1 ma bosumtwi crater in ghana is an 11 km diameter presumably complex well preserved impact structure that is associated with the ivory coast tektite strewnfield detailed structural geologic studies along a complete traverse through the northwestern rim section indicated four zones characterized by distinct deformation styles from just outside of the crater rim to near the crater floor zone 1 is dominated by thick deposits of lithic impact breccia intercalated in places with products of local mass wasting zone 2 contains inward dipping thrust planes conjugate radial fractures isoclinal folding and overturned stratigraphic sequences zone 3 represents a megabreccia zone in which block size decreases upward and outward toward the rim crest the innermost zone 4 is dominated by intense thrust faulting of multiple orientations resulting in complex duplex and lens shaped bodies these deformation styles generally correspond to those previously reported from the rims of simple bowl shaped meteorite impact craters and appear to be characteristic of impact structures in general

the influence of recent major crater impacts on the surrounding surfaces of 21 lutetia we present 3 d simulations of impacts into asteroid 21 lutetia the subject of a fly by by the european space agency s rosetta mission to comet 67p churyumov gerasimenko using a 3 d shape model of the asteroid impacts of sizes sufficient to reproduce the observed craters in lutetia s north polar crater cluster npcc as observed by the osiris experiment have been simulated using the smoothed particle hydrodynamics technique the asteroid itself has been modelled both as a homogeneous body and as a body with an iron core crater erasure in the vicinity of the npcc has been observed by osiris the results show that this erasure has most probably been caused by ejecta deposition following the impact of a 2 3 km diameter projectile impacting at a velocity of 5 km s 1 or an impact with similar energy this would produce a crater of roughly 34 km in diameter comparable to the largest and oldest member of the npcc erasure of craters via the shock associated with such an impact is shown to be less significant and does not reproduce the observed spatial distribution of erased craters or ghost craters time series of the surface velocity fields resulting from the simulated impacts are also presented it is suggested that the surface velocity field and velocity shear may play a role in the generation of lineaments our model calculations show that the velocity field lines around 50 s after impact exhibit a reasonable qualitative correlation with the orientation of lineaments observed on the entire visible surface of lutetia it is also shown that incorporation of a core of 25 30 km in diameter does not modify the velocity field evolution with time and as such the presence or otherwise of such a core cannot be inferred from lineament observations if this concept for their formation is valid

thermally induced lineations on the asteroid eros evidence of orbit transfer 1 several systems of tectonic lineations have been observed on the surface of the asteroid 433 eros we suggest that many of these lineations may have resulted from thermal stresses associated with a secular change in surface temperature due to orbit migration we demonstrate how thermal diffusion can lead to tectonic features and how such features should be oriented with respect to eros complex geometry comparison to observed lineations suggests that some may be explained by thermal stresses such stresses represent a largely unexplored tectonic process on asteroids and could be used to gain rare insight into chaotic orbital dynamics if correct our results imply a gross orbital history over the last 100 myr involving slow several myr inward migration followed by more rapid outward migration to its present orbit

the geology of the occator quadrangle of dwarf planet ceres floor fractured craters and other geomorphic evidence of cryomagmatism abstract the dawn science team is conducting a geological mapping campaign at ceres during the nominal mission including iterative mapping using data obtained during each orbital phase we are using geological mapping as a method to identify the geologic processes that have modified the surface of dwarf planet ceres we here present the geology of the ac 9 occator quadrangle located between 22 s 22 n and 216 288 e the ac 9 map area is within the topographically high region named hanami planum features of note within the profile include impact craters occator azacca lociyo nepen and kirnis four of these craters have fractured shallow floors morphometrically comparable to floor fractured craters ffcs on the moon similar to models for the formation of the lunar ffcs we suggest that these ceres ffcs are a result of cryomagmatic uplift under the crater floors a set of regional linear structures called the samhain catenae do not have any obvious relationship to impact craters many of the catenae are comprised of smaller structures that have linked together suggestive of en echelon fractures it has been suggested that these fractures formed due to the uplift of hanami planum due to cryromagmatic plumes

the global surface roughness of 433 eros from the near laser rangefinder abstract we performed the first global surface roughness assessment of the asteroid 433 eros at baselines horizontal distances of 4 200 m we measured surface roughness using the root mean square rms deviation over a variety of baselines after first detrending the height to remove long wavelength slope effects the global surface roughness of eros is found to be self affine at all baselines investigated the surface roughness is statistically correlated with crater density at baselines of 100 200 m and boulders at a baseline of 5 m no global spatial statistical correlation was found for baselines of 4 200 and mapped tectonic lineaments ponds slope or geopotential elevation the surface roughness of the crater shoemaker charlois regio is controlled by the interplay of a high boulder density producing higher surface roughness values at small baselines and low crater density lowering surface roughness values at long baselines we estimated the mobile regolith thickness regolith that moves around and infills topography to be 0 2 6 2 m from the difference in the surface roughness values at the baseline of 4 m furthermore we find that the change in rms deviation as a function of baseline compares favorably with the moon and differs significantly from existing results for rubble pile asteroid itokawa

phobos grooves and impact craters a stereographic analysis abstract phobos parallel grooves were first observed on viking images 38 years ago and since then they have been greatly debated leading to several formation hypotheses nevertheless none of them have been favoured and widely accepted in this work we provide a different approach assuming that phobos grooves can be the expression of fracture planes and deriving their spatial distribution and orientation on 3d reconstructions we point out that any origin related only to craters at phobos surface should be ruled out since the majority of the grooves is unrelated to any craters now present at its surface this raises the intriguing possibility that such grooves if expression of fracture planes are remnant features of an ancient parent body from which phobos could have originated such scenario has never been considered for phobos though this origin was already proposed for the formation of 433 eros grooves buczkowski d l barnouin jha o s prockter l m 2008 icarus 193 39 if this idea holds true the observed groove distribution could be explained as the result of possible major impacts on the larger parent body which were inherited by the phobos shard

the small inner satellites of saturn shapes structures and some implications abstract properties of the small inner satellites of saturn are updated using final cassini image data the equatorial ridges on pan and atlas are morphologically structurally and gravitationally distinct from their cores and represent distinct additions to rather than modifications of the precursor bodies exposures of lineated substrates on pandora and epimetheus show a relationship between regolith grooves and structures in underlying bedrock structures exposed on epimetheus suggest formation at depth including filling or annealing of fractures these structures and sharp bedrock regolith boundaries indicate a history far more complex than simple rubble pile assembly these exposures of bedrock also indicate past removal of the expected regolith from large fractions of these object s surfaces late in their cratering records

regolith transport in craters on eros abstract images of eros from the near shoemaker spacecraft reveal bright and dark albedo features on steep crater walls unlike markings previously observed on asteroids these features have been attributed to the downslope movement of space weathered regolith exposing less weathered material science 292 2001 484 meteor planet sci 36 2001 1617 icarus 155 2002 145 here we present observations of the interiors of large craters 1 km in diameter to test this hypothesis and constrain the origin of the features we find that bright regions in these craters correspond to steep slopes consistent with previous work the geographic distribution of craters with albedo variations shows no pattern and does not resemble the distribution of ponds another phenomenon on eros attributed to regolith movement shadows and other indications of topography are not observed at feature boundaries implying that the transported layer is 1 m thick the presence of multiple bright and dark units on long slopes with sharp boundaries between them suggests that mobilized regolith may be halted by frictional or other effects before reaching the foot of the slope features on crater walls should darken at the same rate as bright ejecta deposits from crater formation the lack of observed morphologically fresh craters with bright interiors or ejecta suggests that the albedo patterns are younger than the most recently formed craters greater than about 100 m in diameter smaller or micrometeorite impacts which would not necessarily leave evident deposits of bright ejecta remain possible causes of albedo patterns although their effectiveness is difficult to assess electrostatic processes and thermal creep are also candidates

impact fracture patterns on phobos ellipsoids abstract phobos ellipsoid models made of clay were fragmented by the impact of high velocity projectiles to examine the idea proposed by p thomas j veverka and t duxbury 1978 nature 273 282 284 that the grooves on phobos are the manifestation of fractures produced by the stickney forming impact the fracture lines on the models consist of two sets one is concentric around the impact site and along e lines which are defined as the intersecting lines of the ellipsoid surface and a set of spherical surfaces with the center of the spheres at the impact site the other runs radially from the impact site and along p lines which are defined as the lines crossing e lines perpendicularly on the ellipsoid surface some patterns of the grooves originating radially from the crater stickney on phobos are very similar to the p lines the gridded topography hummocky groove sections and smooth topography on phobos could have been formed by the fracture or associated surface disturbances due to the wave induced by the stickney forming impact because they are distributed along the e lines surrounding the converging point of the p lines all the models except one showed that the density of the fractures east of the impact site is greater than that of those to the west fracture patterns similar to one of the most prominent groove sets which converge and diminish into the region of about 270 0 were not produced by the impact on the ellipsoid of uniform constituent these grooves would have been produced by the opening of preexisting cracks by the stickney forming impact other grooves also seem to be affected by such latent cracks

a unified nomenclature for tectonic structures on the surface of enceladus abstract enceladus has experienced widespread and diverse tectonic deformation the diversity and nonuniform distribution of structures visible on the surface attests to a complicated and perhaps long lived tectonic history currently no fundamental classification scheme based on morphology exists for the tectonic structures on enceladus which limits analysis and discussion of tectonic structures and regional and global tectonic histories characterization and classification of structures on enceladus is an important first step in understanding its tectonic history here we propose a global morphologic i e nongenetic classification scheme for tectonic structures on enceladus five classes of tectonic structures on enceladus have been identified based on images and limited topographic data troughs scarps chasmata ridges and bands morphological variation of structures exists within these classes reinforcing the complicated tectonic history of this small body

cadmium isotope fractionation in the fule mississippi valley type deposit southwest china high precision cadmium cd isotope compositions are reported for sphalerite galena and smithsonite from the fule zn pb cd deposit a typical mississippi valley type deposit in southwest china dark sphalerite has lighter 114 110cd values 0 06 to 0 46 than light sphalerite 0 43 to 0 70 and the cd in galena is primarily in the form of sphalerite micro inclusions with 114 110cd of 0 35 to 0 39 from early to late stages 114 110cd values of smithsonite regularly increase from 0 19 to 0 42 whereas cd zn ratios decrease from 252 to 136 the 114 110cd variation pattern of supergene smithsonite reflects kinetic rayleigh fractionation during low temperature processes from the bottom to the top of the orebody the dark sphalerite has different patterns in 114 110cd values cd zn ratios 34s values and fe concentrations compared to the light sphalerite indicating that dark and light sphalerite formed by different processes the varying patterns of 144 110cd values and cd zn ratios within light sphalerite are similar to those of layered smithsonite and the 144 110cd values have a positive correlation with 34s values indicating that cd isotope fractionation in the light sphalerite was due to kinetic rayleigh fractionation instead in dark sphalerite the 144 110cd values have a negative correlation with 34s values and a positive correlation with the cd zn ratio thus it can be concluded that dark sphalerite could be modeled in terms of two component mixing basement fluid and host rock fluid which is in agreement with previous explanations for the negative correlation between 66zn and 34s in some typical zn pb deposits we propose that the significant variation in cd isotope composition observed in the fule zn pb cd deposit confirms that cd isotopes can be used for tracing fluid evolution and ore formation

the tiger deposit a carbonate hosted magmatic hydrothermal gold deposit central yukon canada the tiger gold deposit located in central yukon canada has an inferred resource of 8 28 mt containing 289 400 ounces gold at an average grade of 1 09 g t and an indicated resource of 7 15 mt containing 509 000 ounces gold at an average grade of 2 21 g t a detailed paragenetic and geochemical study of the carbonate hosted replacement style deposit provides constraints on the fluid history and genesis of the gold mineralizing system the deposit is hosted in silurian devonian unmetamorphosed carbonate rocks of the mackenzie platform and occurs 7 km northeast of the dawson thrust which broadly marks the northeast boundary of the selwyn basin a nearby paleocene intrusion the rackla pluton subcrops 3 km from the tiger deposit no other deposits of this kind have been described within the mackenzie platform the tiger deposit consists of strata bound replacement style mineralization adjacent to an interpreted local feeder fault mineralization occurs in two distinct assemblages 1 hydrothermal dolomite gold bearing arsenopyrite and minor pyrite and 2 fractures hosting native gold associated with bismuth antimony silver tungsten and minor base metals carbon oxygen and strontium isotope values suggest magmatic water originating from the rackla pluton as the source of mineralizing fluids for the tiger deposit microthermometric data from gold bearing dolomites quartz and sphalerite document the presence of hot 350 c aqueous carbonic fluids for the duration of gold mineralization overprinted by cooler 150 c aqueous meteoric fluids late in the paragenesis during the waning of the mineralizing system the tiger deposit is thus interpreted to represent a distal expression of paleocene magmatic activity hosted in carbonates northeast of the selwyn basin central yukon

the geomorphology of ceres introduction observations of ceres the largest object in the asteroid belt have suggested that the dwarf planet is a geologically differentiated body with a silicate core and an ice rich mantle data acquired by the dawn spacecraft were used to perform a three dimensional characterization of the surface to determine if the geomorphology of ceres is consistent with the models of an icy interior rationale instruments on dawn have collected data at a variety of resolutions including both clear filter and color images digital terrain models have been derived from stereo images a preliminary 1 10 m scale geologic map of ceres was constructed using images obtained during the approach and survey orbital phases of the mission we used the map along with higher resolution imagery to assess the geology of ceres at the global scale to identify geomorphic and structural features and to determine the geologic processes that have affected ceres globally results impact craters are the most prevalent geomorphic feature on ceres and several of the craters have fractured floors geomorphic analysis of the fracture patterns shows that they are similar to lunar floor fractured craters ffcs and an analysis of the depth to diameter ratios shows that they are anomalously shallow compared with average ceres craters both of these factors are consistent with ffc floors being uplifted due to an intrusion of cryomagma kilometer scale linear structures cross much of ceres some of these structures are oriented radially to large craters and most likely formed due to impact processes however a set of linear structures present only on a topographically high region do not have any obvious relationship to impact craters geomorphic analysis suggests that they represent subsurface faults and might have formed due to crustal uplift by cryomagmatic intrusion domes identified across the ceres surface present a wide range of sizes 100 km basal shapes and profiles whether a single formation mechanism is responsible for their formation is still an open question cryovolcanic extrusion is one plausible process for the larger domes although most small mounds 10 km diameter are more likely to be impact debris differences in lobate flow morphology suggest that multiple emplacement processes have operated on ceres where three types of flows have been identified type 1 flows are morphologically similar to ice cored flows on earth and mars type 2 flows are comparable to long runout landslides type 3 flows morphologically resemble the fluidized ejecta blankets of rampart craters which are hypothesized to form by impact into ice rich ground conclusion the global trend of lobate flows suggests that differences in their geomorphology could be explained by variations in ice content and temperature at the near surface geomorphic and topographic analyses of the ffcs suggest that cryomagmatism is active on ceres whereas the large domes are possibly formed by extrusions of cryolava although spectroscopic analysis to date has identified water ice in only one location on ceres the identification of these potentially ice related features suggests that there may be more ice within localized regions of ceres crust figure 1 dawn high altitude mapping orbit imagery 140 meters per pixel of example morphologic features a occator crater arrows point to floor fractures b linear structures denoted by arrows c a large dome at 42 n 10 e visible in the elevation map d a small mound at 45 5 s 295 7 e e type 1 lobate flow arrows point to the flow front analysis of dawn spacecraft framing camera image data allows evaluation of the topography and geomorphology of features on the surface of ceres the dwarf planet is dominated by numerous craters but other features are also common linear structures include both those associated with impact craters and those that do not appear to have any correlation to an impact event abundant lobate flows are identified and numerous domical features are found at a range of scales features suggestive of near surface ice cryomagmatism and cryovolcanism have been identified although spectroscopic analysis has currently detected surface water ice at only one location on ceres the identification of these potentially ice related features suggests that there may be at least some ice in localized regions in the crust 1 pending yes

drainage pits in cohesionless materials implications for the surface of phobos viking orbiter images show grooves and chains of pits crossing the surface of phobos many of which converge toward the large crater stickney or its antipode although it has been proposed that the pits and grooves are chains of secondary craters their morphology and geometric relations suggest that they are the surface traces of fractures in the underlying solid body of phobos several models have been proposed to explain the pits of which the most plausible are gas venting and drainage of regolith into open fractures the latter mechanism is best supported by the image data and is the mechanism studied in this investigation drainage pits and fissures are modeled experimentally by using two rigid substrate plates placed edge to edge and covered by uniform thicknesses of dry fragmental debris simulated regolith fracture extension is simulated by drawing the plates apart allowing drainage of regolith into the newly created void a typical drainage experiment begins with a shallow depression on the surface of the regolith above the open fissure increased drainage causes local drainage pits to form continued drainage causes the pits to coalesce forming a cuspate groove the resulting experimental patterns of pits and grooves have pronounced similarities to those observed on phobos characteristics such as lack of raised rims linearity of grooves and chains of pits uniform spacing of pits and progression from discrete pits to cuspate grooves are the same in the experiments and on phobos in contrast gas venting pits occur in irregular chains and have raised rims these experiments thus indicate that the phobos grooves and pits formed as drainage structures the pit spacing in an experiment is measured at the time that the maximum number of pits forms prior to groove development the average pit spacing is compared to the regolith thickness for each material regression line fits indicate that the average spacing of drainage pits in unconsolidated noncohesive regolith is nearly equal to the thickness of regolith and appears to gbe independent of the angle of repose within the resolution of our experiments this provides a simple means of estimating regolith thickness where drainage pits are present on phobos two locations differing by 90 degrees in longitude have average pit spacings that suggest regolith thicknesses of 290 and 300 m suggesting that large areas of phobos have a nearly uniform regolith thickness of approximately 300 m

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

ceres ezinu quadrangle a heavily cratered region with evidence for localized subsurface water ice and the context of occator crater abstract dawn is the first spacecraft to visit and orbit ceres the largest object in the asteroid belt and the only dwarf planet in the inner solar system the dawn science team undertook a systematic geologic mapping campaign of ceres entire surface here we present our contribution to this mapping campaign a geologic map and geologic history of the ezinu quadrangle located in the northern mid latitudes from 21 66 n and 180 270 e from our map we reconstruct the geologic history of ezinu quadrangle which is dominated by impact cratering large impact craters that formed a few hundreds to tens of millions of years ago such as datan messor ninsar and occator are surrounded by ejecta and contain the products of mass wasting hummocky crater floor material and talus material and crater wall collapse terrace material two of these large impact craters are the sources of lobate flows which we interpret as melt flows emplaced after the ballistically deposited ejecta morphological evidence suggests these lobate flows are rich in water ice bearing material that was excavated during the formation of the impact craters there are only a few localized occurrences of lobate flows suggesting that the water ice bearing source materials have restricted extents and or are deeply buried within ceres subsurface the quadrangle also contains a variety of linear features secondary crater chains are formed by the impact of locally and globally sourced material and pit chains and grooves are formed by the collapse of surficial materials into sub surface fractures the ezinu quadrangle contains the northern portion of occator crater which is the host crater of prominent bright regions called faculae our geologic analysis therefore also provides context for the future investigation of occator and its intriguing faculae

the a type mount scott granite sheet importance of crystal magma traps the presence of rapakivi feldspar and of distinctive porphyritic texture of mount scott granite indicates a period of crystallization prior to final emplacement beneath an extensive penecontemporaneous rhyolite volcanic pile final crystallization conditions are interpreted to have been 50 mpa at depths 1 4 km based on stratigraphic constraints however geobarometry based on the al content of amphibole phenocrysts and comparison of granite compositions with phase relations in the sio2 naalsi3o8 kalsi3o8 ternary system both yield pressure estimates of 200 mpa these pressure estimates are interpreted as plumbing the depth of a temporary storage chamber at 7 8 km this depth coincides in this case both with the probable proterozoic basement cover contact and with the calculated brittle ductile transition at time of ascent of mount scott magma although rising magma that fed the preceeding voluminous carlton rhyolite apparently rose unimpeded past these horizontal anisotropies rising magma that formed mount scott granite temporarily paused at this depth based on magmastatic calculations we suggest that horizontal anisotropies e g brittle ductile transition become crustal magma traps where the magma driving pressure exceeds the lithostatic load when the anisotropy is encountered during rifting initial large influxes of magma may proceed passed crustal anisotropies but have the effect of increasing the relative magma driving pressure through reducing horizontal stress thus magma driving pressure may eventually exceed the lithostatic load at the depth of the brittle ductile transition thereby activating this crustal magma trap ponding of magma at the brittle ductile transition chokes the eruption such a pause in magma supply rate may permit a return to initial stress conditions and deactivate the crustal magma trap once again magma will rise to the surface initiating a new magmatic cycle

petrogenesis of the cretaceous cassiar batholith yukon british columbia canada implications for magmatism in the north american cordilleran interior the ca 100 ma cassiar batholith is the single largest plutonic body in the hinterland of the canadian cordillera and is part of widespread middle cretaceous to eocene magmatism that occurred in the omineca crystalline belt the cassiar batholith is dominated by muscovite biotite granite and biotite muscovite granodiorite along with subordinate biotite hornblende granodiorite quartz monzodiorite and quartz monzonite the batholith has a wide range of strontium neodymium and oxygen isotope compositions 87 sr 86 sr i 0 706 to 0 734 nd 2 7 to 17 1 t dm 2000 to 980 ma 18 o 7 6 to 11 6 but the batholith9s lead isotope compositions are limited 206 pb 204 pb 19 14 to 19 24 207 pb 204 pb 15 70 to 15 72 208 pb 204 pb 39 14 to 39 26 these data require that the cassiar magmas have been generated from at least two distinct sources an isotopically evolved felsic source and an isotopically more primitive source of mafic to intermediate composition we propose that the felsic source comprised mesoproterozoic to neoproterozoic metasedimentary rocks and paleoproterozoic basement rocks of the north american cratonic margin determining the mafic source is more problematic but most likely it was proterozoic basement rocks of mafic to intermediate composition such as have been reported from various parts of the omineca crystalline belt the cassiar batholith is lithologically geochemically and isotopically similar to other major batholiths in the cordilleran interior including the batholiths of southeastern british columbia and the idaho batholith we interpret these similarities to reflect melting of common crustal source materials namely proterozoic basement and cover rocks of western laurentia the cassiar batholith and other cordilleran interior granitoids are distinct from granitoids generated in known subduction zone environments in terms of their mineralogical geochemical and isotopic characteristics these differences reflect a predominantly or exclusively crustal source region for the cordilleran interior granitoids in contrast subduction zone magmatism contains a significant mantle input even in cases where subduction takes place beneath thick continental crust these results strongly suggest that cordilleran interior granitoids did not form directly from a subduction setting rather an intracontinental collisional setting seems more appropriate in which magma generation occurred in response to crustal thickening followed in some cases by extension

geologic map of the northern hemisphere of vesta based on dawn framing camera fc images abstract the dawn framing camera fc has imaged the northern hemisphere of the asteroid 4 vesta at high spatial resolution and coverage this study represents the first investigation of the overall geology of the northern hemisphere 22 90 n quadrangles av 1 2 3 4 and 5 using these unique dawn mission observations we have compiled a morphologic map and performed crater size frequency distribution csfd measurements to date the geologic units the hemisphere is characterized by a heavily cratered surface with a few highly subdued basins up to 200 km in diameter the most widespread unit is a plateau cratered highland unit similar to although of lower elevation than the equatorial vestalia terra plateau large scale troughs and ridges have regionally affected the surface between 180 e and 270 e these tectonic features are well developed and related to the south pole veneneia impact saturnalia fossae trough unit elsewhere on the hemisphere they are rare and subdued saturnalia fossae cratered unit in these pre rheasilvia units we observed an unexpectedly high frequency of impact craters up to 10 km in diameter whose formation could in part be related to the rheasilvia basin forming event the rheasilvia impact has potentially affected the northern hemisphere also with s n small scale lineations but without covering it with an ejecta blanket post rheasilvia impact craters are small

rb sr and sm nd isotopic study of the glen mountains layered complex initiation of rifting within the southern oklahoma aulacogen rb sr and sm nd isotopic data for rocks and minerals of the glen mountains layered complex gmlc a midcontinent mafic layered intrusion in the wichita mountains of southwestern oklahoma constrain the time of initiation of rifting within the southern oklahoma aulacogen and provide information on the chemistry of the early paleozoic mantle four whole rock samples define a rb sr isochron corresponding to a maximum crystallization age of 577 165 ma and an initial sr isotopic composition of 0 70359 2 these whole rock analyses do not define a sm nd isochron rather they display a significant range in initial nd isotopic composition end 3 63 5 35 a three point sm nd mineral whole rock internal isochron for an anorthositic gabbro provides a crystallization age of 528 29 ma these data suggest that the gmlc was emplaced into the southern oklahoma aulacogen during the initial phase of rifting along the southern margin of the north american craton in the early paleozoic this sm nd internal isochron age is within analytical uncertainty of u pb zircon ages for granites and rhyolites from the wichita mountains therefore mafic and felsic magmatism may have been contemporaneous within the rift during the early stages of development hybrid rocks and composite dikes in the wichita mountains provide field evidence for contemporaneous mafic and felsic magmas initial sr and nd isotopic data suggest that magmas parental to the gmlc were derived from a depleted mantle source however nd isotopic data for the gmlc plot distinctly below data for the depleted mantle source cited by depaolo and thus suggest that the parental magmas of the gmlc were either contaminated by proterozoic crust of the southern midcontinent or were derived from a heterogeneous mantle source region that had variable initial nd isotopic compositions

mineralogical and spectral analysis of vesta s gegania and lucaria quadrangles and comparative analysis of their key features abstract this work is aimed at developing and interpreting infrared albedo pyroxene and oh band depths and pyroxene band center maps of vesta s gegania and lucaria quadrangles obtained from data provided by the visible and infrared vir mapper spectrometer on board nasa s dawn spacecraft the gegania and lucaria quadrangles span latitudes from 22 s to 22 n and longitudes from 0 e to 144 e the mineralogical and spectral maps identify two large scale units on this area of vesta which extend eastwards and westward of about 60 e respectively the two regions are not associated to large scale geological units which have a latitudinal distribution rather than longitudinal but are defined by different contents of carbonaceous chondrites cc the eastern region poor in ccs is brighter and oh depleted whereas the western one rich in ccs is darker and oh enriched a detailed analysis of the small scale units in these quadrangles is also performed almost all the units show the typical correspondence between high albedo deep pyroxene bands short band centers and absence of oh and vice versa only a few exceptions occur such as the ejecta from the aelia crater where dark and bright materials are intimately mixed the most characteristic features of these quadrangles are the equatorial troughs and the lucaria tholus the equatorial troughs consist of graben i e a depression limited by two conjugate faults the graben do not present their own spectral signatures but spectral parameters similar to their surroundings in agreement to their structural origin this is observed also in graben outside the gegania and lucaria quadrangles however it is possible to observe other structural features such as tectonic grooves characterized by a changing composition and hence an albedo variation this result is confirmed not only by mineralogical maps of vesta but also by analyzing the virtis rosetta observations of lutetia the albedo change is instead a typical behavior of geomorphic grooves finally ridges are characterized by a bluer color and in some cases shorter band centers than their surroundings suggesting that they are composed of fresher materials we also performed a comparative analysis between the three tholi of vesta i e lucaria which gives the name to its quadrangle aricia in the marcia quadrangle and brumalia numisia quadrangle whereas brumalia tholus is a young magmatic intrusion the absence of diogenites the low albedo and the orientation of aricia and lucaria tholi suggest that they are older features which are covered by dark materials and therefore experienced a different geological history than brumalia

plasticity and diffusion creep of dolomite abstract natural and synthetic dolomites have been shortened in triaxial compression experiments at temperatures of 400 850 c equilibrium co2 pore pressures effective confining pressures of 50 400 mpa and strain rates of 10 4 to 10 7 s 1 at low temperatures t 600 mpa both for coarse grained 240 m and fine grained 2 m and 12 m samples differential stresses vary little with strain rate or temperature and microstructures of coarse grained samples are dominated by f twins and undulatory extinction an exponential relation o exp 1 3 between strain rate and differential stress 1 3 describes the crystal plasticity of dolomite at a fixed pe and t with 0 079 0 01 mpa 1 and 0 023 07 03 mpa 1 for coarse and fine grained materials respectively however measured values of 1 3 increase with increasing temperature a trend that has been observed for dolomite single crystals but cannot be described by an arrhenius relation at high temperatures t 800 c for coarse t 700 c for fine dolomite strengths are reduced with increasing temperature and decreasing strain rate but the mechanisms of deformation differ depending on grain size high temperature flow strengths of coarse grained dolomite can be described by a power law o 1 3 nexp h rt with a large value of n 5 and a ratio of parameters h n 60 6 kj mol microstructures of coarse grained samples deformed at t 800 c show evidence of dislocation creep with little mechanical twinning high temperature flow strengths of fine grained synthetic dolomite fit a thermally activated newtonian law where the effective n 1 28 0 15 and h 280 45 kj mol consistent with diffusion creep the change in mechanical response of coarse grained natural dolomite with increasing temperature represents a transition from twinning and slip with little or no recovery to dislocation creep while the change in response of fine grained synthetic dolomite represents a transition from crystal plasticity to diffusion creep the combined results for coarse and fine grained dolomites define a deformation mechanism map with fields of crystal plasticity dislocation creep and diffusion creep strengths of coarse grained dolomite in the crystal plastic and dislocation creep fields are much larger than strengths of calcite rocks deformed by similar mechanisms in contrast strengths of fine grained dolomite deformed by diffusion creep are more comparable to those of fine grained calcite suggesting little contrast in rheology

the dublin gulch intrusion hosted gold deposit tombstone plutonic suite yukon territory canada the dublin gulch intrusion is a member of the tombstone plutonic suite a linear belt of middle cretaceous intrusions that extend across the yukon territory like many of the intrusions in this suite the dublin gulch intrusion is associated with several different zones of gold and tungsten mineralization within and immediately adjacent to the intrusion the eagle zone 50 3 mt 0 93 g t gold located in the southwestern part of the dublin gulch intrusion hosts the most significant concentration of gold in the area the gold occurs in a broadly east west striking steeply south dipping series of sheeted veins the veins consist of early quartz scheelite pyrrhotite pyrite arsenopyrite and are associated with k feldspar albite alteration envelopes these grade out to and are overprinted by sericite carbonate chlorite alteration the same assemblage also occurs in veinlets that refracture sheeted quartz veins and contain the majority of the gold the gold occurs with molybdenite lead bismuth antimony sulfosalts galena and bismuthinite gold correlates strongly with bismuth r 2 0 9 a relationship common to several intrusion related gold deposits but has a poor correlation with all other elements tungsten and molybdenum have a weak inter element correlation r 2 0 55 and paragenetically pre date the majority of gold precipitation lead zinc copper silver antimony and arsenic have moderate to strong inter element correlations 0 58 to 0 93 the change from tungsten bearing mineralization through to gold bismuth rich ores with elevated syn to post ore lead zinc copper silver antimony and arsenic can be grossly correlated with a change in hydrothermal fluid composition early scheelite bearing quartz contains primary co2 rich fluid inclusions which are post dated by secondary inclusions with higher salinities up to 15 wt nacl equiv and less co2 these latter inclusions are interpreted to coincide with the later gold bismuth and base metal mineralization the favored genetic model is one in which early co2 rich fluids exsolved from a magma with an initially high co2 content but progressively became more saline and h2o rich as the system evolved

plagioclase preferred orientation and induced seismic anisotropy in mafic igneous rocks fractional crystallization and crystal segregation controlled by settling or floating of minerals during the cooling of magma can lead to layered structures in mafic and ultramafic intrusions in continental and oceanic settings in the lower crust thus the seismic properties and fabrics of layered intrusions must be calibrated to gain insight into the origin of seismic reflections and anisotropy in the deep crust to this end we have measured p and s wave velocities and anisotropy in 17 plagioclase rich mafic igneous rocks such as anorthosite and gabbro at hydrostatic pressures up to 650 mpa anorthosites and gabbroic anorthosites containing 80 vol plagioclase and gabbros consisting of nearly equal modal contents of plagioclase and pyroxene display distinctive seismic anisotropy patterns vp z vp y 1 and vp z vp x 1 for anorthosites while 0 8 vp y than the gabbros laminated anorthosites with vp x vp y vp z display a strong crystal preferred orientation cpo of plagioclase whose 010 planes and 100 and 001 directions parallel to the foliation for the gabbros and amphibolites characterized by vp x vp y vp z and vp x vp y vp z respectively pyroxene and amphibole play a dominant role over plagioclase in the formation of seismic anisotropy the poisson s ratio calculated using the average p and s wave velocities from the three principal propagation polarization directions x y and z of a highly anisotropic anorthosite cannot represent the value of a true isotropic equivalent the cpo induced anisotropy enhances and decreases the foliation normal incidence reflectivity at gabbro peridotite and anorthosite peridotite interfaces respectively

surface expressions of structural features on eros abstract near shoemaker imaging of the asteroid eros has revealed a variety of surface forms that probably reflect underlying structures they range from global to local in scale the most prominent positive topographic feature is a long ridge rahe dorsum which extends over 18 km and has the morphology of a thrust fault two large ancient trough systems are also present grooves are ubiquitous commonly occur in suborthogonal sets and have linear or scalloped outlines the grooves on eros are similar in morphology and scale to those on other small bodies such as gaspra ida and phobos and are likely to have a similar mode of origin namely drainage of regolith into underlying fractures models that use groove dimensions as indicators of regolith thickness imply depths of up to several tens of meters many craters have been subjected to structural control resulting in squared outlines we find no evidence that specific groove sets are associated with individual impact events however evidence exists that preexisting structures have been reactivated by later impact activity the large scale of rahe dorsum and many grooves on eros s surface suggests that the asteroid is a largely coherent but fractured body

433 eros lineaments global mapping and analysis using images and laser ranging data from the near shoemaker mission we map lineaments on the surface of eros in order to investigate the relationship between surface morphology and interior structure several sets of lineations are clearly related to visible impact craters while others suggest that different parts of the asteroid may have undergone different stress histories some of these sets infer internal structure at least on a local level this structure may derive from eros parent body and suggest although largely coherent eros interior may have portions that have not undergone a common history

an estimate of eros s porosity and implications for internal structure abstract earth based spectral measurements and near shoemaker magnetometer x ray and near infrared spectrometer data are all consistent with eros having a bulk composition and mineralogy similar to ordinary chondrite meteorites oc by comparing the bulk density of 433 eros 2 67 0 03 g cm 3 with that of ocs 3 40 g cm 3 we estimate the total porosity of the asteroid to be 21 33 macro or structural porosity best estimated to be 20 is constrained to be between 6 and 33 we conclude that eros is a heavily fractured body but we find no evidence that it was ever catastrophically disrupted and reaccumulated into a rubble pile

gold copper bismuth mineralization in hedenbergitic skarn tombstone mountains yukon gold mineralization on the marn property yukon occurs in two pyroxene skarn bodies which are adjacent to the mount brenner stock in the ogilvie mountains the skarns are separated by a 600 m wid

geochemical constraints on the genesis of the scheelite dome intrusion related gold deposit tombstone gold belt yukon canada the scheelite dome intrusion related gold deposit western selwyn basin yukon is hosted in hornfelsed metasedimentary strata that lie adjacent to the exposed apices of a monzogranite to quartz monzonite plutonic complex of the mid cretaceous tombstone tungsten magmatic belt tintina gold province alaska and yukon a variety of mineralization styles occur throughout a 10 3 km east trending corridor and include reduced au and w rich skarns au w and ag pb zn sb rich quartz tension vein arrays and multiphase fault veins and isolated zones of au rich sericite carbonate altered rock integrated u pb shrimp data for magmatic zircon and ar ar data for magmatic and hydrothermal biotite indicate that gold mineralization occurred within 1 to 2 m y of magma emplacement fluid inclusion oxygen isotope and arsenopyrite geothermometry data indicate that hydrothermal minerals formed at depths of 6 to 9 km over a temperature range from 550 c high temperature au rich skarns formed at 400 c whereas vein hosted mineralization formed at 280 to 380 c in skarns au is strongly associated with enrichments of bi te w and as whereas a variety of au rich veins occur with as rich type 1 and te and w rich type 2 end members silver pb zn sb veins are typically au poor and represent the latest and lowest temperature phase in the hydrothermal paragenesis the fluid inclusion data indicate that all mineralization styles were formed from low salinity 4 wt nacl equiv aqueous carbonic fluids consistent with the composition of fluid inclusions within infilled miarolitic cavities in the intrusive rocks however the nonaqueous fluid was predominantly ch 4 in skarn co 2 in au te and au w veins and a fluid with roughly equal amounts of co 2 ch 4 and n 2 in au as and ag pb zn sb veins oxygen isotope data are consistent with a mineralizing fluid of predominantly magmatic origin that was variably modified to more positive 18 o values during interaction with 18 o enriched metasedimentary strata sulfur isotope data suggest two possible sources of sulfur a magmatic source characterized by 34 s values of approximately 5 to 0 per mil and sulfur from the metasedimentary country rocks characterized by more negative 34 s values of approximately 15 to 10 per mil collectively the data indicate that gold at scheelite dome was deposited from a magmatic hydrothermal system interaction of magmatic fluids with graphitic hornfels rocks resulted in reduction of the ore fluids higher ch 4 co 2 ratios and modification of the oxygen and sulfur isotope values of the ore fluids toward those of the metasedimentary hornfels progressive reduction and cooling of hydrothermal fluids in addition to phase separation in vein hosted mineralization were the mechanisms for gold deposition compared to other intrusion related gold deposits associated with the tombstone tungsten magmatic belt magmatism exposed mineralization at scheelite dome is predominantly hosted by hornfelsed metasedimentary rocks this results in more diverse mineralization styles and a greater spread of isotope and fluid inclusion data

emplacement depth and carbon dioxide rich fluid inclusions in intrusion related gold deposits phanerozoic intrusion related gold deposits have many consistent characteristics such as a spatial temporal and geochemical association with moderately reduced predominantly ilmenite series i type intrusions the deposits exhibit a range of characteristics that vary over a wide range of emplacement depths 7 km deposits in shallow crustal settings 5 km have characteristics of mesothermal environments and are hosted by plutons containing sheeted veins greissen and disseminated gold fluid characteristics also vary with depth deposits in shallow environments contain high temperature 350 c immiscible brine 30 wt nacl equiv and low salinity 5 wt nacl equiv vapor that commonly contains carbon dioxide deposits in deeper environments contain abundant low salinity carbon dioxide rich aqueous fluids 10 wt nacl equiv that in some deposits are postdated by moderate to high salinity brines 10 40 wt nacl equiv these contrasting fluid types are interpreted to be magmatic in origin and are the result of the complex interplay between exsolution of different volatiles carbon dioxide water and chlorine from felsic magmas emplaced at different crustal levels experimental studies have shown that carbon dioxide will exsolve from felsic magmas at much higher pressures than water and chlorine due to its lower solubility in the melt thus deposits formed from felsic magmas in deeper environments will contain abundant carbon dioxide rich fluids subsequent fluids released from the magma are likely to be water rich and more saline felsic magmas in shallow environments will contain lower concentrations of carbon dioxide that will partition into the vapor phase during phase separation between brine and vapor

shoemaker crater as the source of most ejecta blocks on the asteroid 433 eros the loose material regolith on the surfaces of asteroids is thought to represent ballistically emplaced ejecta from impacts but the identification of source craters and the detailed study of the regolith modification have been hampered by the limited spatial resolution and area coverage of the few asteroids imaged by spacecraft here we report the results of global mapping of the asteroid 433 eros from high resolution images obtained by the near shoemaker spacecraft based on the images and ejecta emplacement models we suggest that most large ejecta blocks on eros originate from a relatively young 7 6 km diameter crater a large fraction of the ejecta from impacts pre dating that crater has apparently been buried or eroded the images also show evidence for the action of a variety of sorting environments for regolith particles after they are deposited on the surface

impact produced seismic shaking and regolith growth on asteroids 433 eros 2867 steins and 25143 itokawa abstract of the several near earth and main belt asteroids visited by spacecraft to date three display a paucity of small craters and an enhanced number of smoothed and degraded craters 433 eros which has a deficit of craters 100 m in diameter 2867 steins which has a deficit of craters 500 m in diameter and 25143 itokawa which has a deficit of craters 100 m in diameter the purpose of this work was to investigate and model topographic modification and crater erasure due to impact induced seismic shaking as well as impact driven regolith production and loss on these asteroid surfaces to perform this study we utilized the numerical three dimensional cratered terrain evolution model ctem initially presented in j e richardson icarus 204 2009 which received a small body sb specific update for this work sbctem simulations of the surface of 433 eros correctly reproduce its observed cratering record for craters up to 3 km in diameter at a minimum main belt exposure age of 225 75 myr using a very weak rock target strength of 0 5 5 0 mpa and producing a mean regolith depth of 80 20 m which agrees with published estimates of an actual regolith layer tens of meters in depth sbctem simulations of the surface of 2867 steins correctly reproduce its heavily softened cratering record at a minimum main belt exposure age of 175 25 myr using a weak rock target strength of 2 5 5 0 mpa extending this simulation produces a mean regolith depth of 155 5 m at a minimum main belt exposure age of 475 25 myr in good agreement with the 145 35 m actual mean regolith depth estimated from two chains of drainage pit craters on the surface with both crater density and regolith depth in an equilibrium state sbctem simulations of the surface of 25143 itokawa correctly reproduce its extremely sparse cratering record at a minimum main belt exposure age of 20 5 myr using a soft soil target strength of 10 20 kpa and producing a mean regolith overturn depth of 5 0 1 0 m given that itokawa is composed entirely of regolith and boulders these simulations demonstrate the efficacy of impact induced seismic shaking to erase small craters on the surface of asteroids 25 km mean diameter correctly reproducing their observed cratering records while using a main belt impactor population and standard crater scaling relationships these simulations also show that the observed regolith layer on asteroids in the 5 50 km size range can be generated entirely through impact cratering processes and indicate that regolith depth can be used as a additional constraint on the surface age of a given asteroid

thrust faults and the near surface strength of asteroid 433 eros 1 near shoemaker images reveal widespread occurrence of tectonic landforms on asteroid 433 eros hinks dorsum is a ridge that extends for about 18 km around the asteroid and strongly resembles thrust fault structures on the terrestrial planets tectonic landforms can provide information on the mechanical properties of asteroids a subject of much controversy modeling constrained by topographic data shows that hinks dorsum can be accounted for by a shallow rooted thrust fault no greater than 250 m in depth with 90 m of cumulative slip strength envelopes based on frictional and rock mass strength criteria suggest the near surface shear strength of eros is from 1 to 6 mpa a spatial correlation is found between shoemaker crater a transition from low to high crater density and hinks dorsum this spatial relation along with the estimated strength of the asteroid suggests the thrust fault was formed by impact induced compression

intraplate magmatism related to opening of the southern iapetus ocean cambrian wichita igneous province in the southern oklahoma rift zone abstract southern oklahoma and adjacent parts of texas contain an extensive igneous province emplaced during early cambrian rifting within the southern oklahoma rift zone the rift zone was initiated in association with the opening of the southern iapetus ocean during rodinia supercontinent breakup and later became the site of a series of linked uplifts and basins as a result of late paleozoic inversion igneous rocks within the rift are referred to as the wichita province and are present mostly in the subsurface although critical exposures occur in the wichita and arbuckle mountains in southwestern and southern oklahoma wells drilled into basement in the region provide a wealth of information on the distribution and relations of the major igneous units in the upper crust and geophysical data provide important constraints on deeper levels of the rift zone the upper parts of the igneous rift fill comprise the carlton rhyolite group which has an estimated subsurface areal extent of 40 000 km 2 and the related wichita sheet granites which intrude the lower parts of the rhyolite succession these rocks have a type characteristics and were emplaced after intrusion tilting and uplift of a large tholeiitic layered mafic complex smaller bodies of gabbro also intruded the layered complex after it was tilted u pb zircon and 40 ar 39 ar geochronology indicates the felsic rocks and at least some of the mafic units were emplaced in a relatively narrow time frame at 539 530 ma basalts and intermediate lavas are present only in the subsurface our new work shows these lavas to have tholeiitic to mildly alkaline compositions and to be more extensive than previously realized forming thick successions that both underlie and are intercalated with the rhyolites diabase dikes were intruded into older crust during initial opening of the rift and a suite of late diabase intrusions also cuts the rhyolites and granites indicating that mafic magma was supplied to the rift throughout its igneous history geophysical data show that an enormous mass of mafic rock occupies deeper parts of the rift extending to depths of at least 10 km beneath the surface the total volume of igneous rock emplaced within the rift is estimated to be in excess of 250 000 km 3 detailed studies of carlton rhyolite exposures in the wichita mountains complemented by work on drill cuttings from basement wells indicate that lava flows up to 400 m thick make up major parts of the rhyolitic succession the generally limited exposures of these rhyolite lavas in the wichita mountains are interpreted to be remnants of laterally extensive flow units similar to those documented from other a type felsic provinces trace element abundances define three distinct geochemical groups of rhyolite suggesting derivation from three different sources or magma reservoirs flows belonging to the different geochemical groups are intercalated in the wichita mountains exposures which may indicate that laterally extensive flows from separate magma chambers came to rest on top of one another during accumulation of the rhyolitic volcanic pile