the vertical profile of winds on titan the huygens probe landed on titan on 14 january this year and seven papers published in this issue record the encounter they describe a world that resembles a primitive earth complete with weather systems and geological activity the huygens on titan section opens with an overview of the descent and landing and a news and views piece tomasko et al describe the dry riverbed and drainage channels seen during huygens descent evidence that liquid methane falls as rain or erupts from cryovolcanoes periodically flooding the surface this paper includes the images used on the cover to the huygens section niemann et al measured the abundances of isotopes of argon nitrogen and carbon in the atmosphere and conclude that there is no evidence that titan s methane comes from biological activity fulchignoni et al obtained precise measurements of temperature and pressure from the upper atmosphere right down to the surface on the way down huygens recorded evidence for lightning zarnecki et al report that the probe landed on a relatively smooth surface of icy grains with the consistency of wet clay or sand isral et al report that the aerosols in titan s clouds have solid cores made from complex organic molecules containing carbon and nitrogen and bird et al found that on average titan s winds blow in the same direction as the moon rotates and that close to the surface these winds are very weak travelling at around walking speed one of titan s most intriguing attributes is its copious but featureless atmosphere the voyager 1 fly by and occultation in 1980 provided the first radial survey of titan s atmospheric pressure and temperature1 2 and evidence for the presence of strong zonal winds3 it was realized that the motion of an atmospheric probe could be used to study the winds which led to the inclusion of the doppler wind experiment4 on the huygens probe5 here we report a high resolution vertical profile of titan s winds with an estimated accuracy of better than 1 m s 1 the zonal winds were prograde during most of the atmospheric descent providing in situ confirmation of superrotation on titan a layer with surprisingly slow wind where the velocity decreased to near zero was detected at altitudes between 60 and 100 km generally weak winds 1 m s 1 were seen in the lowest 5 km of descent

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

fluid flow patterns in fast spreading east pacific rise crust exposed at hess deep tectonic exposures of a volcanic sequence and sheeted dike complex over a 4 km wide region at hess deep equatorial pacific reveal significant spatial heterogeneity 10 103 m in the extent and nature of hydrothermal alteration in young fast spreading east pacific rise crust the volcanic sequence is fairly uniformly altered with only minor oxidation and alteration to clay minerals sheeted dikes in the eastern part of the field area are highly fractured with narrow intervals of intact dikes that dip up to 60 their alteration characteristics show a simple depth trend such that with increasing depth the dominant secondary mafic mineral changes from chlorite to amphibole clinopyroxene replacement increases 40 whole rock 18o values decreases 4 4 5 5 to 3 5 4 5 and calculated peak metamorphic temperatures increase 250 c to 450 700 c within the deepest dikes localized zones up to 400 m wide are chlorite rich and have low 18o 2 9 4 1 and low peak metamorphic temperatures 345 c these alteration patterns likely formed within broad recharge zones whereby the low 18o zones developed in the regions with the highest fluid flux in the west massive slightly rotated sheeted dikes near the volcanic sheeted dike transition are 18o and cu depleted and display higher peak temperatures 345 c than elsewhere in the shallow dikes these characteristics are consistent with formation within a high temperature hydrothermal discharge zone we propose that the spreading history of a fast spreading ridge segment can create significant spatial heterogeneity in fluid flow and alteration patterns within sheeted dike complexes similar to those preserved in many ophiolites

helium isotopes in ferromanganese crusts from the central pacific ocean abstract helium isotopes have been measured in samples of two ferromanganese crusts va13 2 and cd29 2 from the central pacific ocean with the exception of the deepest part of crust cd29 2 the data can be explained by a mixture of implanted solar and galactic cosmic ray produced gcr he in extraterrestrial grains and radiogenic he in wind borne continental dust grains 4he concentrations are invariant and require retention of less than 12 of the in situ he produced since crust formation loss has occurred by recoil and diffusion high 4he in cd29 2 samples older than 42 ma are correlated with phosphatization and can be explained by retention of up to 12 of the in situ produced 4he 3he 4he of va13 2 samples varies from 18 5 to 1852 ra due almost entirely to variation in the extraterrestrial he contribution the highest 3he 4he is comparable to the highest values measured in interplanetary dust particles idps and micrometeorites mms helium concentrations are orders of magnitude lower than in oceanic sediments reflecting the low trapping efficiency for in falling terrestrial and extraterrestrial grains of fe mn crusts the extraterrestrial 3he concentration of the crusts rules out whole undegassed 4 40 m diameter idps as the host instead it requires that the extraterrestrial he inventory is carried by numerous particles with significantly lower he concentrations and occasional high concentration gcr he bearing particles

first measurements of jupiter s zonal winds with visible imaging spectroscopy abstract we present the first measurements of jupiter s wind profile ever obtained with doppler velocity measurements in the visible hitherto knowledge about atmospheric dynamics has been obtained with cloud tracking techniques which consist of tracking visible features from images taken at different dates however cloud tracking indicates the motion of large cloud structures which is an indication of the speed of iso pressure regions rather than the speed of the actual atmospheric particles doppler imaging is as challenging motions are usually less than 100 m s 1 as appealing because it measures the speed of cloud particles instead of large cloud structures significant difference could appear in the case of atmospheric waves interfering with cloud structures here we present the first scientific results of a doppler imaging spectrometer that is dedicated to giant planet seismology and atmospheric dynamics by providing instantaneous line of sight velocity maps of the planets of the solar system the instrument has been developed in the framework of the projects jovial jovian oscillations through velocity images at several longitudes and jive in nm jovian interiors from velocimetry experiment in new mexico it is a fourier transform spectrometer with a fixed optical path difference working in the mid visible domain which monitors the position of solar fraunhofer lines that are reflected in the planets upper atmospheres after describing the instrument principle and the different steps of data reduction we report measurement of the average zonal wind speed of jupiter as a function of latitude from datasets obtained in 2015 and 2016 with two different telescopes when the planet was close to its opposition our results are consistent between the two years we compare the results with wind profiles obtained by cloud tracking on hst hubble space telescope images taken at the same epoch and identify a significant discrepancy in the north equatorial belt and northern part of the equatorial zone

1 ma east pacific rise oceanic crust and uppermost mantle exposed by rifting in hess deep equatorial pacific ocean abstract a series of dives with the french submersible nautile has been conducted in the region of the galapagos triple junction at the tip of the cocos nazca propagator most of the dives were devoted to the study of hess deep a rift valley produced by rifting of oceanic crust created at the axis of the very fast spreading east pacific rise the dives have enabled the structures and lithologies to be assessed and confirmed earlier dredging evidence for abundant basal crust and mantle rocks on an intra rift ridge located to the north of the axis of hess deep this shows that this situation is not specific not slow spreading ridges a nearly complete and unique log of young 1 ma crust and uppermost mantle representative of very fast accretion can be reconstructed even though the section is discontinuous and highly dismembered we propose two models that can explain the exposure on the ocean floor of the deep foundation of the oceanic crust one model stresses symmetry and vertical tectonics through isostasy diapirism of serpentinized mantle another model requires a larger amount of extension and emphasizes asymmetry with denudation of the upper crust through low angle detachment faulting in both models which differ mainly in the structure at depth amagmatic extension of east pacific rise crust by the cocos nazca propagator tip results in uplift and denudation of lower crust and upper mantle

magma chamber profiles from the bay of islands ophiolite complex models of the oceanic lithosphere derived from constraints imposed by the geology of ophiolite complexes require a magma chamber to produce the cumulate and other plutonic portions of the oceanic crust and upper mantle evidence from the bay of islands ophiolite complex indicates that layered plutonic rocks have not formed solely due to differential crystal settling to the horizontal floor of a magma chamber but have formed largely by heterogeneous nucleation and in situ crystallization along gently inclined as well as steeply inclined bounding surfaces of a large magma reservoir coherent well defined and systematically oriented large scale arcuate patterns described by mesoscopic igneous layering have been identified in the plutonic sections of two ophiolite massifs in the bay of islands complex these layering patterns seem to outline the shape of a large continuously evolving steady state magma chamber that extended along a ridge axis and ended at a transform fault intersection

stratospheric global winds on titan at the time of huygens descent 1 measurements of stratospheric zonal winds on titan were made in preparation for and during the time of the descent of the huygens probe into titan s atmosphere on 14 january 2005 fully resolved emission lines from ethane near 11 7 m were measured on the east center and west positions on titan using the nasa gsfc heterodyne instrument for planetary wind and composition hipwac mounted on the national astronomical observatory of japan 8 2 m subaru telescope on mauna kea hawaii analysis of the doppler shifts of the emission line shapes yielded mean prograde gas velocity 60 65 m s at altitudes below 120 km 5 mbar this result is consistent with retrievals from the huygens doppler wind experiment and from other observations near this altitude range current spectral line shapes however differed significantly from those obtained in similar measurements on subaru in 2004 and on the nasa irtf in 1993 1996 which retrieved prograde zonal winds 190 90 m s at 230 km 0 4 mbar the cores of the emission lines which probe the high altitude region could not be fitted as before to retrieve wind directly using the accepted atmospheric model for titan they imply an approximately tenfold increase in ethane mole fraction 1 2 10 4 with strong wind shear above the stratopause providing a potential probe of the lower mesosphere and possible evidence of temporal and spatial variability results contribute to coordinated measurements of winds by various techniques providing information on the altitude distribution of wind velocity in titan s atmosphere from near the surface to the lower mesosphere

central anomaly magnetization high constraints on the volcanic construction and architecture of seismic layer 2a at a fast spreading mid ocean ridge the epr at 9 30 50 n abstract the central anomaly magnetization high camh is a zone of high crustal magnetization centered on the axis of the east pacific rise epr and many other segments of the global mid ocean ridge mor the camh is thought to reflect the presence of recently emplaced and highly magnetic lavas forward models show that the complicated character of the near bottom camh can be successfully reproduced by the convolution of a lava deposition distribution with a lava magnetization function that describes the variation in lava magnetization intensity with age this lava magnetization function is the product of geomagnetic paleofield intensity which has increased by a factor of 2 over the last 40 kyr and low temperature alteration which decreases the remanence of lava with exposure to seawater the success of the forward modeling justifies the inverse approach deconvolution of the magnetic data for lava distribution and integration of that distribution for magnetic layer thickness this approach is tested on two near bottom magnetic profiles al2767 and al2771 collected using alvin across the epr axis at 9 31 n and 9 50 n our analysis of these data produces an estimate of the relative thickness of the magnetic lava layer which is remarkably consistent with existing multichannel estimates of layer 2a thickness from lines cdp31 and cdp27 the similarity between magnetic layer and seismic layer 2a at the 9 10 n segment of the epr crest provides independent support to the notion that seismic layer 2a in young oceanic crust represents the highly magnetic lava layer and that the velocity gradient at the base of layer 2a is related to the increasing number of higher velocity dikes with depth in the lava dike transition zone the near bottom magnetic anomaly character of the camh is a powerful indicator of the emplacement history of upper crust at mors which allows prediction of the relative thickness and architecture of the extrusive lavas independent of other constraints

modes of extension at oceanic spreading centers evidence from the solea graben troodos ophiolite cyprus abstract the solea graben in the troodos ophiolite cyprus represents a preserved cretaceous age axial valley formed during a brief period of amagmatic seafloor spreading structural analysis of all crustal levels of the graben reveals two periods of deformation an extensive early phase of extensional deformation associated with seafloor spreading and a later phase of minor deformation associated with obduction and doming of the complex during the tertiary recent amagmatic extensional deformation produced networks of normal faults that dip toward the graben axis and sole into a regional detachment fault located at the sheeted dike plutonic contact and oriented subparallel to ophiolite pseudostratigraphy individual fault segments are essentially planar but link to approximate listric geometries locally bulk structural rotation of fault blocks bounding the graben occurred about a nnw trending axis parallel to the present graben trend average dips in the sheeted complex within the central portions of the graben suggest 40 50 of structural rotation although this is a minimum figure because present dike dips are not a simple function of rotation magnitude tensor analysis of fault populations associated with extensional deformation shows that 3 was oriented approximately perpendicular to the graben axis late near axis extensional deformation segmented the detachment fault along nnw trending normal faults obduction related uplift and doming of the troodos ophiolite is expressed in the solea graben by minor thrust reverse and strike slip faults principally developed during reactivation of pre existing low angle fault zones formed during seafloor deformation tensor analysis of this later phase of faulting shows that 1 was oriented approximately n s and that 2 and 3 alternated position during the deformation the style of deformation documented in the solea graben supports recent speculation for basin and range style detachment faulting at slow spreading ridge crests with low magma budgets such as parts of the mid atlantic ridge near large offset transform faults natural cross sectional exposure of the solea graben shows how extensional structures might link at depth beneath such slow spreading ridge segments and demonstrates the importance of extensive brittle deformation of the crust prior to establishment of large scale ore forming hydrothermal circulation cells

hydrothermal upflow zones in the oceanic crust abstract breccias recovered from the mid atlantic ridge south of the kane fracture zone mark and the east pacific rise at hess deep record distinct alteration signatures associated with the upwelling of hydrothermal fluids in the shallow oceanic crust two breccia types have been defined based on the mineralogy of the matrix type i breccias have a matrix characterized by fe rich chlorite quartz pyrite and anatase type ii breccias exhibit a matrix consisting of mg rich chlorite epidote quartz pyrite and titanite fluid inclusion analyses indicate a similar range in homogenization temperatures for the two breccia types 150 375 c but distinct ranges in salinity type i breccias have salinities greater than that of seawater 3 3 10 wt nacl whereas type ii breccias display much lower salinities mineral stability relationships coupled with the fluid inclusion data suggest that the type i breccias were produced by hydrothermal fluids relatively enriched in cl and depleted in h2s whereas the type ii breccias were associated with hydrothermal fluids relatively depleted in cl and enriched in h2s these chemical trends are consistent with those displayed by hydrothermal fluids actively venting on the seafloor thus we propose that the observed variability in the chemistry of modern submarine vent fluids is paralleled by distinct alteration assemblages in the upflow zones below the seafloor as defined by the type i and type ii breccia suites based on these results we predict that the relatively h2s depleted vent systems at tag southern juan de fuca and 11 13 n along the east pacific rise should be characterized by upflow zones with a mineralogy similar to the type i breccias conversely the relatively h2s enriched vent systems at 21 n and 11 13 n along the east pacific rise are likely associated with upflow zones that have a mineralogy similar to the type ii breccias as more fossil upflow zones in the oceanic crust are identified these results could be used to define temporal variability of upwelling fluid chemistry at specific ridge sites on a geologic time scale

implications for crustal accretion at fast spreading ridges from observations in jurassic oceanic crust in the western pacific 1 downhole logging data and basement stratigraphy interpretations are used to determine the spreading environment and crustal accretion history of the ocean basement cored at odp hole 801c located in the jurassic magnetic quiet zone of the western pacific high resolution microresistivity data obtained with the formation microscanner are used to measure the dip of the extrusive layers and indicate a 10 30 increase in dip down the drill hole with lava flow contacts dipping back toward the original ridge axis this structural pattern and the high proportion of massive flows relative to pillow units are consistent with prevailing crustal accretion models proposed for faster spreading ridges e g 60 km m y full rate a detailed analysis of the age data basement lithology related geochemistry and structural attitudes suggest the shallowest 100 m of the drilled section e g sequences i iii were emplaced just off the ridge sequence iii or significantly farther off axis up to 5 15 m y later sequences i and ii the remainder of the drilled section e g sequences iv viii has geochemical lithological and physical trends that are assumed to be representative of crust created at faster spreading ridges the pattern of dipping lava flow contacts from this deeper section of the drill hole suggests lava flows emanating from the ridge axis are limited to 1 2 km off axis our results suggest ocean crust drilled at hole 801c was created at faster spreading rates however caution should be used when incorporating sequences i iii into geochemical reference sections for faster spreading ridges

structure and variability of oceanic crust on the flanks of the east pacific rise between 11 and 13 n we use over 500 seismograms collected by five ocean bottom seismometers to examine the structure and variability of 0 5 m y old crust in the rivera ocean seismic experiment rose area of the east pacific rise between 11 and 13 n there are no significant differences among the first arrival travel times for 10 independent refraction line segments along the isochron amplitude patterns recorded on the individual lines however suggest that structural boundaries within the upper crust vary by hundreds of meters in depth over lateral distances of tens of kilometers within this 200 km segment of lithosphere on the basis of the modeling of amplitude patterns at ranges of 5 10 km and of comparisons with the upper crust sampled at deep sea drilling project hole 504b and in ophiolite complexes layer 2 can be divided into three units 2a corresponds to extrusive volcanics with a steep velocity gradient 2b to extrusives with a near zero velocity gradient and 2c to a complex region of transition from extrusives to sheeted dikes the total thickness of layer 2 varies by about 0 7 km over the length of the line another amplitude peak which varies in range between 14 and 21 km may be related to the downward transition from sheeted dikes to isotropic gabbros within layer 3 the variability of these two amplitude patterns provides direct evidence that the along strike structure of oceanic crust in the rose area is definably heterogeneous and that the process of crustal accretion is likewise variable on the scale resolved by amplitude and travel time information

contribution of volcanism and tectonism to axial and flank morphology of the southern east pacific rise 17 10 17 40 s from a study of layer 2a geometry multichannel seismic images from the east pacific rise 17 10 17 40 s are used to study the geometry of seismic layer 2a in the near axis region wave equation datuming is applied to stacked common midpoint data to remove the distorting effects of seafloor topography on the layer 2a event processed stacks are compared with seafloor morphology and tectonic fabric imaged in side scan sonar data assuming layer 2a corresponds with the extrusive crust these data are used to study the relationship between volcanism and tectonism in the accumulation of the extrusive layer and to assess the contribution of extrusives to ridge crest and ridge flank morphology we find variations in axial thickening of layer 2a which imply twofold variation in the width of the extrusive layer accumulation zone as well as systematic changes in the pattern of accumulation of this layer on the ridge flanks the layer 2a horizon mimics abyssal hill relief consistent with a horst and graben origin for this topography short wavelength variations in the thickness of layer 2a are superimposed on this relief which we attribute to volcanic modification of tectonic topography at the edge of the neovolcanic zone the integrated off axis thickness of layer 2a is correlated with ridge cross sectional area and indicates persistent 100 000 years spatial gradients in extrusive layer thickness systematic changes in the cross axis shape of the ridge observed over distances of 5 10 km cannot be attributed to the extrusive layer and it appears that axial structure beneath the volcanics governs the cross axis morphology of the ridge

comparison of seafloor tectonic fabric at intermediate fast and super fast spreading ridges influence of spreading rate plate motions and ridge segmentation on fault patterns we have conducted a comparative study of the tectonic morphology of young seafloor using seamarc ii side scan sonar surveys of the intermediate spreading ecuador rift the fast spreading east pacific rise epr 8 30 10 n and the super fast spreading epr 18 19 s we find that characteristics of fault populations are not only a function of spreading rate but also vary along axis within individual ridge segments i e with proximity to large and short offset discontinuities we also find that fault azimuths can be used to examine plate kinematics on a finer scale than can be obtained using magnetic data alone most of the variation in fault populations with spreading rate can be explained by an inverse relationship between spreading rate and thickness of the brittle layer for example regions of super fast spreading are characterized by the largest numbers of short faults the smallest average fault spacing and throw and the highest fault density in addition clusters of short closely spaced antithetic faults subsidiary to long master inward dipping faults are common within the super fast spreading area presumably the result of a thinner weaker brittle layer faults facing away from the ridge axis occur in increasing numbers with increasing spreading rate such that few outward facing faults are found at slow to intermediate rates and approximately equal numbers of inward and outward facing faults are observed at the fastest rates rapid thickening of the brittle layer with distance from the ridge may account for the predominance of inward facing faults at slower spreading rates outward facing faults at all spreading rates have shorter mean lengths and lower vertical offsets these differences may reflect the shorter time outward facing faults are active owing to increasing strength of the lithosphere with distance from the ridge fault lengths and spacings in all areas approximate exponential distributions the extensional strain represented by fault populations is calculated from the displacement and length distributions of faults and strain estimates of 4 are obtained for each area assuming that fault spacing reflects fracture depth extent where faults initiate we infer a brittle layer thickness of 1 km when faulting begins fault populations are examined for ridge segment scale variations in amagmatic extension we see evidence for greater amagmatic extension associated with long term reduced magma supply along the eastern third of the ecuador rift evidence for local increased brittle extension is also found within 15 km of transform faults discordant zones left by overlapping spreading centers oscs are characterized by low fault abundances at oscs discrete events of ridge tip propagation may accommodate extension taken up elsewhere along the ridge by normal faulting fault azimuths do appear to be useful indicators of plate motion within the epr 8 30 10 n area fault trends record a recent change in pacific cocos plate motion 3 6 at 1 m y consistent with magnetic anomaly and fault lineation data from elsewhere along the northern epr within the ecuador rift fault azimuths scatter within 3 of predicted trends and are consistent with constant spreading about one pole for the past 1 5 m y

overview of the coordinated ground based observations of titan during the huygens mission coordinated ground based observations of titan were performed around or during the huygens atmospheric probe mission at titan on 14 january 2005 connecting the momentary in situ observations by the probe with the synoptic coverage provided by continuing ground based programs these observations consisted of three different categories 1 radio telescope tracking of the huygens signal at 2040 mhz 2 observations of the atmosphere and surface of titan and 3 attempts to observe radiation emitted during the huygens probe entry into titan s atmosphere the probe radio signal was successfully acquired by a network of terrestrial telescopes recovering a vertical profile of wind speed in titan s atmosphere from 140 km altitude down to the surface ground based observations brought new information on atmosphere and surface properties of the largest saturnian moon no positive detection of phenomena associated with the probe entry was reported this paper reviews all these measurements and highlights the achieved results the ground based observations both radio and optical are of fundamental importance for the interpretation of results from the huygens mission

a mechanism for decoupling within the oceanic lithosphere revealed in the troodos ophiolite contrasting kinematic histories recorded in the sheeted dykes and underlying plutonic rocks of the troodos ophiolite provide a new perspective on the mechanical evolution of oceanic spreading centres the kinematic framework of the decoupling zone that partitions deformation between the sheeted dykes and plutonics contrasts with low angle detachment models for slow spreading ridges based on continental rift analogues a model for the generation of multiple horizontal decoupling horizons linked by planar normal faults demonstrates new possibilities for the kinematic and rheological significance of seismic reflectors in oceanic lithosphere

seismic imaging of oceanic layer 2a between 9 30 n and 10 n on the east pacific rise from two ship wide aperture profiles we analyze two ship multichannel seismic wide aperture profiles wap acquired on the east pacific rise epr between 9 30 c and 10 n in may and june 1985 for offsets between 2 and 5 km most of the wap common depth point cdp gathers exhibit a strong retrograde reflection like seismic arrival that corresponds to rays turned within a very strong velocity gradient zone underlying the uppermost crustal layer 2a stacking of this postcritical arrival for hundreds of cdp gathers along the wap lines yields remarkably clear and virtually continuous images of the bottom of layer 2a for several tens of kilometers along and across the epr an innovative combination of this image with others of the seafloor sf and of the axial magma chamber amc provides an unusually clear composite picture of young upper crust we combine these images with detailed seismic velocity information also obtained from the cdp gathers to achieve an accurate determination of the layer 2a thickness in the area along the epr axis between 9 30 n and 10 n layer 2a shows a relatively constant thickness between 100 and 150 m 80 120 ms two way travel time across the axis however a line near 9 30 n indicates that layer 2a thickness rapidly increases by approximately a factor of 2 within 2 4 km of the axis and remains nearly constant afterwards thus the final thickness of layer 2a is attained before the development of large scale tectonic faulting strongly suggesting that the thickening of layer 2a away from the axis is due to successive episodes of volcanic activity increasing the thickness of the uppermost crustal section from the top rather than tectonic fracturing lowering the uppermost crustal seismic velocities and pushing the bottom of layer 2a downwards as the crust moves away from the axis

the thermal structure of the venus atmosphere intercomparison of venus express and ground based observations of vertical temperature and density profiles the venus international reference atmosphere vira model contains tabulated values of temperature and number densities obtained by the experiments on the venera entry probes pioneer venus orbiter and multi probe missions in the 1980s the instruments on the recent venus express orbiter mission generated a significant amount of new observational data on the vertical and horizontal structure of the venus atmosphere from 40 km to about 180 km altitude from april 2006 to november 2014 many ground based experiments have provided data on the upper atmosphere 90 130 km temperature structure since the publication of vira in 1985 the thermal structure of the venus atmosphere team was supported by the international space studies institute issi bern switzerland from 2013 to 2015 in order to combine and compare the ground based observations and the vex observations of the thermal structure as a first step towards generating an updated vira model results of this comparison are presented in five latitude bins and three local time bins by assuming hemispheric symmetry the intercomparison of the ground based and vex results provides for the first time a consistent picture of the temperature and density structure in the 40 km 180 km altitude range the venus express observations have considerably increased our knowledge of the venus atmospheric thermal structure above 40 km and provided new information above 100 km there are however still observational gaps in latitude and local time above certain regions considerable variability in the temperatures and densities is seen above 100 km but certain features appear to be systematically present such as a succession of warm and cool layers preliminary modeling studies support the existence of such layers in agreement with a global scale circulation the intercomparison focuses on average profiles but some vex experiments provide sufficient global coverage to identify solar thermal tidal components the differences between the vex temperature profiles and the vira below 0 1 mbar 95 km are small there is however a clear discrepancy at high latitudes in the 10 30 mbar 70 80 km range the vex observations will also allow the improvement of the empirical models vts3 by hedin et al 1983 and vira by keating et al 1985 above 0 03 mbar 100 km in particular the 100 150 km region where a sufficient observational coverage was previously missing the next steps in order to define the updated vira temperature structure up to 150 km altitude are 1 define the grid on which this database may be provided 2 fill what is possible with the results of the data intercomparison and 3 fill the observational gaps an interpolation between the datasets may be performed by using available general circulation models as guidelines an improved spatial coverage of observations is still necessary at all altitudes in latitude longitude and at all local solar times for a complete description of the atmospheric thermal structure in particular on the dayside above 100 km new in situ observations in the atmosphere below 40 km are missing an altitude region that cannot be accessed by occultation experiments all these questions need to be addressed by future missions

titan s stratospheric zonal wind temperature and ethane abundance a year prior to huygens insertion 1 saturn s satellite titan may have stratospheric winds up to 210 m s circling titan in 1 terrestrial day compared to its 16 day rotation theoretical models explaining such super rotating winds are not well constrained by observations of titan or a similar slow rotator venus we report measurements taken in december 2003 of zonal wind near titan s equatorial region including the cassini huygens probe entry latitude super rotating prograde zonal winds of 190 90 m s near 220 km altitude are found from doppler shifted c2h6 gas emission near 12 m confirming high wind velocity even near the equator stratospheric temperature constraints and ethane abundance 8 3 ppm also are retrieved results are not inconsistent with earlier measurements and with recent cassini cirs results but indicate possible variations between titan s hemispheres differences in east and west c2h6 spectral line shapes can be accounted for by different vertical distributions of either c2h6 abundance or temperature or by unidentified dynamical effects

in situ evidence for the nature of the seismic layer 2 3 boundary in oceanic crust the igneous oceanic crust is typically thought of as comprising two layers an upper crust seismic layer 2 characterized by a rapid increase in seismic velocity with depth and a thicker lower crust seismic layer 3 which is distinguished from layer 2 by both a higher p wave velocity 6 69 0 26 km s l and a much smaller vertical velocity gradient 1 8 km continuous hole drilled into the oceanic crust11 13 and find that at this location the seismic layer 2 3 boundary lies within the sheeted dyke complex where it is associated with gradual downhole changes in crustal porosity and alteration not a litho logical transition from sheeted dykes to gabbro

structure of uppermost fast spread oceanic crust exposed at the hess deep rift implications for subaxial processes at the east pacific rise the uppermost 2 km of the oceanic crust created at the fast spreading 135 mm yr 1 full rate equatorial east pacific rise epr is exposed for tens of kilometers along escarpments bounding the hess deep rift mosaics of large scale digital images from the remotely operated vehicle rov argo ii and direct observations from the submersible alvin document a degree of geological complexity and variability that is not evident from most studies of ophiolites or prevailing models of seafloor spreading dramatic variations in the thickness and internal structure are documented in both the basaltic volcanic and sheeted dike rock units these rock units are characterized by extensive faulting fine scale fracturing and rotations of coherent crustal blocks meters to tens of meters across the uppermost basaltic lavas are essentially undeformed and have overall gently inclined flow surfaces through most of the basaltic lava unit however lava flow contacts dip 20 70 w toward the epr and generally increase in dip downward in the section dikes cutting the lavas and in the underlying sheeted dike unit generally dip 90 40 e away from the epr deeper level gabbroic rocks show little evidence of the intense fracturing typical of the overlying units we interpret this upper crustal structure as the result of subaxial subsidence within 1 2 km of the epr that accommodated the thickening of the basaltic lava unit to 500 m variations in the thickness of lava and dike units and spatially related structures along the rift escarpments suggest temporal fluctuations in magma supply these results indicate that substantial brittle deformation accompanied waxing and waning volcanism during the accretion of the crustal section exposed at the hess deep rift if this type of structure is typical of uppermost oceanic crust generated at the epr these processes may be common along fast spreading mid ocean ridges

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

characterization of zonal winds in the stratosphere of titan with uves 2 observations coordinated with the huygens probe entry 1 the huygens probe has successfully entered titan s atmosphere and landed on its surface on 14 january 2005 with the aim of characterizing the zonal wind flow in titan s stratosphere close to the time of entry coordinated observations were carried out at the very large telescope on the nights of 7 12 14 and 15 january as in our previous investigation luz et al 2005 we used the uves instrument mounted on the kueyen ut2 telescope simultaneously achieving high spectral resolving power and high spatial resolution the field has been derotated in order to align the 0 3 arcsec aperture perpendicularly to titan s rotation axis in this configuration spatial information in the east west direction is preserved in a set of spectra in the direction perpendicular to dispersion we present measurements of zonal winds obtained with the technique of absolute accelerometry the observations were made in the wavelength range 4200 6200 a probing between 115 and 280 km with peak contributions at 200 and 170 km for the lower and upper parts of the domain we detect prograde zonal winds with lower limits 46 and 53 ms 1 at these altitudes these values are close to our previous measurements

geologic structure of the uppermost oceanic crust created at fast to intermediate rate spreading centers abstract geological investigations of major fault scarps tectonic windows and dsdp odp drill holes provide direct views of the uppermost oceanic crust generated at fast to intermediate rate spreading centers these areas reveal a consistent upper crustal structural geometry with basaltic lava flows defining a pattern of downward increasing inward dip toward the spreading center at which they formed and dikes in the lavas and underlying sheeted dike complex showing a similar degree of outward dip widespread fracturing faulting and hydrothermal metamorphism accompanied magmatic construction these geological relationships can be interpreted in terms of dramatic asymmetrical subaxial subsidence of upper crustal rock units that diminishes across the very narrow few kilometers wide zone of lava accumulation and dike intrusion at the ridge axis this type of crustal structure is in accord with some existing models of spreading but augments these idealized views with more realistic geological

the josephine ophiolite northwestern california the 157 m y old josephine ophiolite is a complete ophiolite consisting of the following units harzburgite tectonite cumulate ultramafics cumulate gabbro interlayered with cumulate ultramafics cumulate gabbro high level gabbro and diorite a 1 5 km thick sheeted dike complex and 0 4 km of pillow lava and breccia the ophiolite is conformably overlain by the galice formation consisting of a thin siliceous pelagic sequence overlain by a thick sequence of turbidites having both volcanic arc and continental margin sources the ophiolite and overlying galice formation were intruded by numerous 150 to 151 m y old calc alkaline dikes and sills followed shortly by deformation and regional metamorphism under conditions of prehnite pumpellyite to lower greenschist facies the josephine peridotite makes up the base of the ophiolite and covers 800 km2 it is an alpine type peridotite that represents upper mantle material and the residue of partial melting ultramafic rocks overlying the josephine peridotite are olivine spinel clinopyroxene cumulates that grade upward into clinopyroxene and orthopyroxene olivine plagioclase cumulates and finally to clinopyroxene plagioclase cumulates high level gabbros and diorites are characterized by highly variable textures complex intrusive relationships strongly zoned plagioclase and abundant mafic dikes plagiogranites occur at this level as dikes small intrusions and screens between mafic dikes but they are rare the sheeted dike complex consists of mafic dikes averaging 0 6 m in thickness chilled margins are locally well preserved and many of the dikes have been split and intruded by younger dikes resulting in half and marginless dikes the dike complex is composed of 100 sheeted dikes near the center but contains gabbro screens near the base and pillow lava and breccia screens in its upper parts the dikes are inclined at 40 to bedding after correcting for folding and are inferred to have been rotated shortly after formation the extrusive sequence consists predominantly of pillow lavas but contains abundant pillow breccias and some massive lavas some of the breccias formed as talus deposits whereas others are graded and matrix supported indicating transport and redeposition possibly in an area of rugged submarine topography the dikes and lavas have geochemical affinities to island arc tholeiites but are in some aspects transitional to mid ocean ridge basalts the dikes and lavas are cogenetic with the underlying plutonic sequence as indicated by similarity in crystallization sequence contradictory intrusive relationships between sheeted dikes and high level plutonic rocks and lack of diabase dikes in the lowermost cumulates and harzburgite the upper portions of the ophiolite were hydrothermally metamorphosed at the spreading center resulting in downward changes in mineralogy texture and 18o in addition metalliferous sediments and massive sulfides that occur overlying and within the pillow lavas probably were formed by precipitation from thermal springs a geothermal gradient of 250 350 c km is inferred from mineral assemblages on the basis primarily of its regional setting the ophiolite is inferred to have formed in a back arc basin in particular it is within a thrust sheet sandwiched between a coeval magmatic arc complex and a slightly older arc complex remnant arc this interpretation is consistent with abundant volcanic arc detritus in graywackes overlying the ophiolite the island arc magmatic affinities of the lavas and dikes may be the result of formation of the ophiolite during the earliest stages of back arc spreading

structure of young oceanic crust at 13 n on the east pacific rise from expanding spread profiles we present the results of the analysis of expanding spread profiles esps collected on and near the axis of the east pacific rise at 13 n these profiles were collected at 0 1 1 2 1 3 6 and 9 5 km from the rise axis and all but the most distant profile show a distinct low velocity zone lvz located within layer 3 of the oceanic crust at the ridge crest the top of the magma chamber is at the base of layer 2 while 3 6 km off axis the roof of the lvz is 1 1 km below the top of layer 3 the profile farthest from the ridge could possibly have a residual lvz confined to the lower 1 5 km of the crust the total width of the lvz as determined from the esp data is at least 6 km and possibly much greater this wide lvz apparently contradicts multichannel seismic data which show cross axis reflections from the magma chamber with a width of 5 km we suggest that a resolution of this apparent contradiction lies in a model of the rise axis with a small and transient central magma chamber of high partial melt fraction surrounded by a much larger and permanent region of hot rock with only isolated pockets of partial melt the esp data are sensitive to this larger region while the reflection data accurately map the presence or absence of the central magma chamber with its high impedance contrast we identify the presence of a layer at the top of the oceanic crust with initial p wave velocities between 2 35 and 2 6 km s while the s wave velocity is estimated as being 0 8 km s the layer thickness lies between 100 and 200 m these velocities are consistent with previous estimates for the pacific and recent results for the atlantic the thickness of this layer is consistent with that of layer 2a determined from geophysical measurements at deep sea drilling project hole 504b