thermal structure of the venus atmosphere in the middle cloud layer thermal structure measurements obtained by the two vega balloons show the venus middle cloud layer to be generally adiabatic temperatures measured by the two balloons at locations roughly symmetric about the equator differed by about 6 5 kelvins at a given pressure the vega 2 temperatures were about 2 5 kelvins cooler and those of vega 1 about 4 kelvins warmer than temperatures measured by the pioneer venus large probe at these levels data taken by the vega 2 lander as it passed through the middle cloud agreed with those of the vega 2 balloon study of individual frames of the balloon data suggests the presence of multiple discrete air masses that are internally adiabatic but lie on slightly different adiabats these adiabats for a given balloon can differ in temperature by as much as 1 kelvin at a given pressure

hot dry rock geothermal energy in the jemez volcanic field new mexico abstract large young calderas possess immense geothermal potential due to the size of shallow magma bodies that underlie them through the example of the valles and toledo calderas new mexico and older more deeply eroded and exposed calderas it is possible to reconstruct a general view of geothermal environments associated with such magmatic systems although a zone of anomalous heat flow extends well beyond caldera margins high to moderate temperature hydrothermal systems appear to be restricted to zones along intracaldera faults and may account for only about five percent of the thermal energy available from the magmatic system much of the remaining thermal energy resides within caldera fill and basement rocks under and along the flanks of the caldera and can only be extracted by manmade geothermal systems depending upon the age and cooling history considerable thermal energy may still reside in crystallizing magma

new aspects of rhomb structures abstract the acute angles of 48 rhombic trapezoidal and triangular grabens horsts and upthrusts throughout the world were determined the results indicate an angular spread of 7 73 in most structures the two acute angles differ considerably most rhomb structures are grabens which show affinities to seismic faults and only a few are horsts and upthrusts in this connection modes of static crustal fracture propagation are compared to dynamic propagation rhomb structures occur along strike slip faults and in rifts these results question the universality of the pull apart model as a mechanism for rhomb structure development the two mechanisms that can lead to the formation of rhomb structures are 1 interaction of en echelon or non coplanar fractures by shear and extensional modes and 2 fracture bifurcation in an extensional mode the two mechanisms may result in faults of different shapes characterized by curved and straight boundaries respectively the grabens and horsts in extensional regions are the consequence of early fracture and later vertical displacements

tectonic and geologic evolution of the espanola basin rio grande rift structure rate of extension and relation to the state of stress in the western united states abstract the espanola basin of the rio grande rift began as a broad crustal downwarp in latest oligocene time most of the basin is 2 3 km deep but localized faulting allowed accumulation of up to 5 km of sedimentary fill in a central sub basin the localized early faulting ended before filling of the central espanola basin was completed about 10 m y ago movement on faults that define the present western margin of the espanola basin began 10 m y ago jemez mountain volcanism in the western espanola basin also began at about this same time west tilting of up to 30 occurred due to movement along pervasive n trending intrabasin faults about 7 5 m y ago in conjunction with continued movement along the western border faults volcanism continued after this tilting forming many of the large volcanic constructs of the jemez mountains regional uplift of the entire northern rio grande rift began 7 m y ago movement on the pajarito fault zone began about 5 m y ago and continues to the present this fault zone defines the western margin of the velarde graben a narrow central sub basin where recent movement has been concentrated some volcanism also has occurred within the southern velarde graben total extension across the espanola basin since 26 m y ago is estimated to have been 5 5 km roughly 10 or between 3 5 and 8 km assuming high angle planar faulting the 0 2 mm yr averaged long term rate of extension has been separated into three periods of activity 1 1 0 14 mm yr from 26 to 10 m y ago 2 2 0 5 mm yr from 10 to 5 m y ago 3 3 0 14 mm yr from 5 m y ago to present a change in least principal stress direction from wsw ene to wnw ese that occurred throughout the western united states about 10 m y ago coincides with a roughly 3 5 times increase in the rate of extension preferential development and movement of n to ne trending normal faults and a few degrees of clockwise rotation of rocks in the western espanola basin similar to the espanola basin initial basins of the southern rio grande rift were broad downwarps and rifting was greatly accelerated after 10 m y ago accelerated uplift of the northern rio grande rift also occurred at about this time indicating that activity in the entire rio grande rift was modulated by this change in extension direction 10 m y ago that appears related to pacific north american plate interactions this modulation coupled with major faulting 10 m y ago preceding uplift 7 m y ago in the espanola basin suggest a passive rifting process for the rio grande rift whereby stresses due to plate interactions elsewhere cause faulting in the lithosphere which leads to the development of a passive asthenospheric uplift furthermore the roughly 20 m y pre uplift history of sediment accumulation in basins of the central and southern rift and the inherited character trend and geometry of the rio grande rift as a whole are also more consistent with a passive rifting process

cenozoic thermal mechanical and tectonic evolution of the rio grande rift careful documentation of the cenozoic geologic history of the rio grande rift in new mexico reveals a complex sequence of events at least two phases of extension have been identified an early phase of extension began in the mid oligocene about 30 ma and may have continued to the early miocene about 18 ma this phase of extension was characterized by local high strain extension events locally 50 100 regionally 30 50 low angle faulting and the development of broad relatively shallow basins all indicating an approximately ne sw 25 extension direction consistent with the regional stress field at that time extension events were not synchronous during early phase extension and were often temporally and spatially associated with major magmatism a late phase of extension occurred primarily in the late miocene 10 5 ma with minor extension continuing to the present it was characterized by apparently synchronous high angle faulting giving large vertical strains with relatively minor lateral strain 5 20 which produced the modern rio grande rift morphology extension direction was approximately e w consistent with the contemporary regional stress field late phase graben or half graben basins cut and often obscure early phase broad basins early phase extensional style and basin formation indicate a ductile lithosphere and this extension occurred during the climax of paleogene magmatic activity in this zone late phase extensional style indicates a more brittle lithosphere and this extension followed a middle miocene lull in volcanism regional uplift of about 1 km appears to have accompanied late phase extension and relatively minor volcanism has continued to the present we have estimated geotherms and calculated lithospheric strength curves for the two phases of extension using geologic data to constrain earlier events and geophysical data to constrain the modern geotherm and crustal structure a high geotherm was deduced for early phase extension resulting in a shallow crustal brittle ductile transition and negligible mantle strength the lithosphere cooled after early phase extension resulting in a deeper crustal brittle ductile transition and perhaps more significantly a considerable zone of mantle strength immediately beneath the moho these results indicate that early phase extensional style was controlled by a crustal decollement near the brittle ductile transition which was prevented during late phase extension by significant strength in the uppermost mantle late cenozoic uplift of the rift zone cannot be explained by crustal thinning during extension and geotherm evolution predicted from simple cooling however this uplift does not appear to be restricted to the rift zone and pliocene to recent volcanism and heat flow data suggest that uplift may be caused by magmatic thickening of the crust perhaps unrelated to rifting the complex interrelationship among regional and local prerifting synrifting and postrifting events in the rio grande rift suggests that rifting at least in this region should not be considered in isolation of other geologic events

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

denudation vertical crustal movements and sedimentary basin infill denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass recent empirical results from a wide range of sources are presented on the rates of these processes denudation alone can cause non tectonic isostatic surface uplift of the right magnitude predicted by theory a case is made following ahnert for a single linear relationship although with much scatter between denudation rate and mean drainage basin relief for large basins some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one dimensionality and neglect of suspended and washload contributions basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland but problems arise in the apportionment of the various hinterland fluxes that occur in real world three dimensional basins sediment yields in smaller half graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields examples are given from extensional basins in the western usa and greece the length of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed through the fractal form of hack s law and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands

aerial seismology using balloon based barometers seismology on venus has long eluded planetary scientists due to extreme temperature and pressure conditions on its surface which most electronics cannot withstand for mission durations required for ground based seismic studies we show that infrasonic low frequency pressure fluctuations generated as a result of ground motion produced by an artificial seismic source known as a seismic hammer and recorded using sensitive microbarometers deployed on a tethered balloon are able to replicate the frequency content of ground motion we also show that weak artificial seismic activity thus produced may be geolocated by using multiple airborne barometers the success of this technique paves the way for balloon based aero seismology leading to a potentially revolutionary method to perform seismic studies from a remote airborne station on the earth and solar system objects with substantial atmospheres such as venus and titan

fracture interaction in the gregory rift east africa abstract vertical fracture is important and fracture interaction is quite intensive in the central gregory rift crack branching and non coplanar crack interactions in the rift are characterized for major and minor faults these two manifestations follow theoretical and experimental angular relationships of fracture reasonably well mantle diapirism seems to have been responsible for both tensile probably unstable fracture and block tilting ultimately resulting in fault dips deviating from the vertical

venus atmospheric structure and dynamics from the vega lander and balloons new results and pds archive abstract the longest lived in situ measurement platforms at venus have been the soviet vega balloons in 1985 and the only high quality pressure temperature profile in the lowest 10 km of the atmosphere is that from the vega 2 lander here we review the mission and the resultant literature and report the archival of numerical data from these investigations on the nasa planetary data system atmospheres node to facilitate their access to the community we additionally report some new results including the striking absence of a signature of the planetary boundary layer in the near surface potential temperature profile from the vega 2 lander in contrast to the well defined boundaries seen in a comparable profile at titan

ground based near infrared imaging observations of venus during the galileo encounter near infrared images of venus obtained from a global network of ground based observatories during january and february 1990 document the morphology and motions of the night side near infrared markings before during and after the galileo venus encounter a dark cloud extended halfway around the planet at low latitudes 40 and persisted throughout the observing program it had a rotation period of 5 5 0 15 days the remainder of this latitude band was characterized by small scale 400 to 1000 kilometers dark and bright markings with rotation periods of 7 4 1 days the different rotation periods for the large dark cloud and the smaller markings suggests that they are produced at different altitudes mid latitudes 40 to 60 were usually occupied by bright east west bands the highest observable latitudes 60 to 70 were always dark and featureless indicating greater cloud opacity maps of the water vapor distribution show no evidence for large horizontal gradients in the lower atmosphere of venus

tectonic rotations within the rio grande rift evidence from paleomagnetic studies paleomagnetic studies on miocene pliocene volcanic rocks from the espanola basin of the rio grande rift new mexico reveal directions discordant from the expected mean direction for north america the paliza canyon formation tschicoma formation and lobato basalt all sampled in the jemez mountains west of the pajarito fault zone have mean declinations east of the expected mean the cerros del rio volcanics lying east of the pajarito fault zone have a westerly declination combined with published data on the santa fe group sediments east of the fault zone and the valles rhyolite west of the fault zone distinct rotations of the two areas are evident the western block has rotated clockwise 12 while the eastern block shows 16 of counter clockwise motion differential rotations of 25 30 are calculated between the two blocks 4 m y is the minimum differential rotation for the past 5 m y geologic explanations for these rotations include the opening of the rio grande rift in response to clockwise rotation of the colorado plateau and significant left slip along the rio grande rift

effusive eruptions from a large silicic magma chamber the bearhead rhyolite jemez volcanic field nm abstract large continental silicic magma systems commonly produce voluminous ignimbrites and associated caldera collapse events less conspicuous and relatively poorly documented are cases in which silicic magma chambers of similar size to those associated with caldera forming events produce dominantly effusive eruptions of small volume rhyolite domes and flows the bearhead rhyolite and associated peralta tuff member in the jemez volcanic field new mexico represent small volume eruptions from a large silicic magma system in which no caldera forming event occurred and thus may have implications for the genesis and eruption of large volumes of silicic magma and the long term evolution of continental silicic magma systems 40ar 39ar dating reveals that most units mapped as bearhead rhyolite and peralta tuff the main group were erupted during an 540 ka interval between 7 06 and 6 52 ma these rocks define a chemically coherent group of high silica rhyolites that can be related by simple fractional crystallization models preceding the main group minor amounts of unrelated trachydacite and low silica rhyolite were erupted at 11 9 and 8 ma respectively whereas subsequent to the main group minor amounts of unrelated rhyolites were erupted at 6 1 and 1 5 ma the chemical coherency apparent fractional crystallization derived geochemical trends large areal distribution of rhyolite domes 200 km2 and presence of a major hydrothermal system support the hypothesis that main group magmas were derived from a single large shallow magma chamber the 540 ka eruptive interval demands input of heat into the system by replenishment with silicic melts or basaltic underplating to maintain the bearhead rhyolite magma chamber although the volatile content of main group magmas was within the range of rhyolites from major caldera forming eruptions such as the bandelier and bishop tuffs eruptions were smaller volume and dominantly effusive bearhead rhyolite domes occur at the intersection of faults and are cut by faults suggesting that the magma chamber was structurally vented preventing volatiles from accumulating to levels high enough to trigger a caldera forming eruption

a kinematic model of southern california we propose a kinematic model for southern california based on late quaternary slip rates and orientations of major faults in the region internally consistent motions are determined assuming that these faults bound rigid blocks relative to north america most of california west of the san andreas fault is moving parallel to the san andreas fault through the transverse ranges and not parallel to the motion of the pacific plate this is accomplished by counterclockwise rotation of california south of the san andreas fault and by the westward movement of central california north of the gar lock fault the velocities of the blocks are calculated along several paths in southern california that begin in the mojave desert and end off the california coast a path that crosses the western transverse ranges accumulates the accepted relative north america pacific plate velocity whereas paths to the north and south result in a significant missing component of motion this implies the existence of a zone of active deformation in southern california that is interpreted to include the western transverse ranges and northwest trending predominately strike slip faults close to the coast both north and south of the transverse ranges strain on this system accounts for about a third of the total north america pacific plate motion

geometry and rate of extension across the pajarito fault zone espanola basin rio grande rift northern new mexico the central velarde graben is the active subbasin of the espanola basin section of the rio grande rift in north central new mexico the velarde graben is bounded on the west in the jemez volcanic field by the pajarito fault zone this fault zone has produced a steep fault scarp about 100 m high where it cuts the l l m y old tshirege member of the bandelier tuff detailed mapping along the north trending pajarito fault zone has revealed a fairly simple geometry in the tshirege member the faults follow numerous vertical joints below this member fault dips are 60 and not listric at shallow depths this simple geometry allows calculation of a mean rate of extension of 0 05 mm yr across the pajarito fault zone for the past 1 1 m y if extension is not perpendicular to the fault zone the extension rate could be as great as 0 07 mm yr lack of transverse tilt of the velarde graben wedge implies that the extension rate across the eastern margin is about the same as for the western margin comparison with a published extension rate for the northern albuquerque belen basin just to the south of the jemez mountains of 0 3 mm yr both sides since rifting began 26 m y ago indicates a slower opening for the velarde graben during the past 1 1 m y if extension is localized along the margins of the velarde graben with little activity along other fault zones in the espanola basin then both the mean rate of extension and the width of the actively extending region have decreased with time for this section of the rio grande rift

core mantle interactions abstract recent studies of the magnetic field at the core mantle boundary have revealed fixed sites of either static magnetic features or persistent secular variation this suggests part of the magnetic field behaviour is controlled by the mantle the most plausible mechanism for core mantle interaction is thermal coupling although topography may also be significant the magnetic sites coincide with anomalies in lower mantle seismic velocity as determined from tomography and density as determined by flow models of mantle convection constrained by tomography and the geoid some magnetic features coincide with subduction zones particularly those near indonesia they may be caused by bumps on the core mantle boundary beneath trenches paleomagnetic pole positions suggest the magnetic behaviour has persisted for at least 5 myr as would be expected if it were controlled from the mantle

investigation of air temperature on the nightside of venus derived from virtis h on board venus express abstract we present the spatial distribution of air temperature on venus night side as observed by the high spectral resolution channel of virtis visible and infrared thermal imaging spectrometer or virtis h on board the esa mission venus express the present work extends the investigation of the average thermal fields in the northern hemisphere of venus by including the virtis h data we show results in the pressure range of 100 4 mbar which corresponds to the altitude range of 65 80 km with these new retrievals we are able to compare the thermal structure of the venus mesosphere in both hemispheres the major thermal features reported in previous investigations i e the cold collar at about 65 70 s latitude 100 mbar pressure level and the asymmetry between the evening and morning sides are confirmed here by comparing the temperatures retrieved by the virtis spectrometer in the north and south we find that similarities exist between the two hemispheres solar thermal tides are clearly visible in the average temperature fields to interpret the thermal tide signals otherwise impossible without day site observations we apply model simulations using the venus global circulation model venus gcm lebonnois s hourdin f forget f eymet v fournier r 2010b international venus conference aussois 20 26 june 2010 of the laboratoire de meteorologie dynamique lmd we suggest that the signal detected at about 60 70 latitude and pressure of 100 mbar is a diurnal component while those located at equatorial latitudes are semi diurnal other tide related features are clearly identified in the upper levels of the atmosphere

a geological and geophysical appraisal of the baca geothermal field valles caldera new mexico abstract the baca location 1 geothermal field is located in north central new mexico within the western half of the plio pleistocene valles caldera steam and hot water are produced primarily from the northeast trending redondo creek graben where downhole temperatures exceed 260 c at depths of less than 2 km stratigraphically the reservoir region can be described as a five layer sequence that includes tertiary and quaternary volcanic rocks and mesozoic and tertiary sediments overlying precambrian granitic basement production is mainly controlled by fractures and faults that are ultimately related to activity in the rio grande rift system geophysically the caldera is characterized by a gravity minimum and a resistivity low in its western half a 40 mgal gravity minimum over the caldera is due mostly to the relatively low density volcanics and sediments that fill the caldera and probably bears no relation to deep seated magmatic sources two dimensional gravity modeling indicates that the depth to precambrian basement in redondo canyon is probably at least 3 km and may exceed 5 km in eastern parts of the caldera telluric and magnetotelluric surveys have shown that the reservoir region is associated with low resistivity and that a deep low resistivity zone correlates well with the depth of the primary reservoir inferred from well data telluric and magnetotelluric data have also identified possible fault zones in the eastern and western sections of the production region that may form boundaries to the redondo creek reservoir these data also suggest that the reservoir region is located at the intersection of lineaments that trend north south and northeast southwest magnetotelluric results indicate deep low resistivity at the western edge of the caldera which may be associated with deep hot fluids on the basis of geophysical and well data we make three estimates of reservoir dimensions the estimates of the areal extent of the reservoir range from 10 to 30 km 2 depending on whether the sulphur creek or the valle seco area is considered to contain deep geothermal resources

implications of the vega balloon results for venus atmospheric dynamics both vega balloons encountered vertical winds with typical velocities of 1 to 2 meters per second these values are consistent with those estimated from mixing length theory of thermal convection however small scale temperature fluctuations for each balloon were sometimes larger than predicted the approximate 6 5 kelvin difference in temperature consistently seen between vega 1 and vega 2 is probably due to synoptic or planetary scale nonaxisymmetric disturbances that propagate westward with respect to the planet there is also evidence from doppler data for the existence of solar fixed nonaxisymmetric motions that may be thermal tides surface topography may influence atmospheric motions experienced by the vega 2 balloon

deformation across the western united states a local estimate of pacific north america transform deformation we obtain a locally based estimate of pacific north america relative motion and an uncertainty in this estimate by integrating deformation rate along three different paths leading west across southwestern north america from east of the rio grande rift to near the continental escarpment data are primarily quaternary geologic slip rate estimates and resulting deformation determinations therefore are instantaneous in a geologic sense but long term with respect to earthquake cycles we deduce a rate of motion of the pacific plate relative to north america that is 48 2 mm yr a rate indistinguishable from that predicted by the global kinematic models rm2 and nuvel 1 however we obtain an orientation that is 5 9 counterclockwise of these models a more westerly motion of the pacific plate with respect to north america is calculated from all three paths the relatively westerly motion of the pacific plate is accommodated by deformation in the north american continent that includes slip on relatively counterclockwise oriented strike slip faults including the san andreas fault which is especially relevant in and south of the transverse ranges and a margin normal component of net extension across the continent which is especially relevant north of the transverse ranges deformation of the sw united states occurs in regionally coherent domains within which the style of deformation is approximately uniform in the vicinity of the transverse ranges two important shear systems splay from the san andreas fault the eastern california shear zone trending nnw from the eastern transverse ranges and the trans peninsular faults trending sse from the western and central transverse ranges within the transverse ranges the right lateral san andreas fault steps left seemingly requiring large amounts of convergence there however most of this convergence is avoided through a funneling flow of the crust toward the western transverse ranges and into the relatively narrow central california coast ranges and the northern motion of the mojave the former process involves an alternation of rotation direction from counterclockwise in and south of the central transverse ranges to clockwise in the western transverse ranges

vega balloon dynamics and vertical winds in the venus middle cloud region the vega balloons provided a long term record of vertical wind fluctuations in a planetary atmosphere other than earth s the vertical winds were calculated from the observed displacement of the balloon relative to its equilibrium float altitude the winds were intermittent a large burst lasted several hours and the peak velocity was 3 meters per second

block rotations in the rio grande rift new mexico additional paleornagnetic data from the north central rio grande rift support previous suggestions for counterclockwise rotation of a large crustal block thirteen sites from intrusive and extrusive rocks associated with the oligocene espinaso formation in the area around the ortiz mountains central new mexico yield magnetic directions of i 42 1 and d 337 8 alpha 95 10 3 comparison with the expected direction for the oligocene indicates 17 8 11 4 of counterclockwise rotation this agrees with previous studies of miocene to pliocene rocks north of the study area that also show about 15 of counterclockwise rotation and corroborates the timing of this motion as post 5 ma the extent of the rotated block now includes areas in and adjacent to the espanola basin east of the pajarito fault zone from the san luis basin in the north to the albuquerque basin in the south extensive published geologic and structural information indicates that counterclockwise block rotation in the rio grande rift probably results from left slip along the rift the rotated block is diamond shaped and bounded by major fault zones embudo fault to the north pajarito fault zone to the west tijeras canoncito fault zone to the southeast and picuris pecos fault to the east structural consequences of the counterclockwise block rotation are uplift at the acute ends sandia and picuris uplifts and subsidence at the obtuse ends velarde graben and santa fe embayment