the galileo imaging team plan for observing the satellites of jupiter the galileo spacecraft carries a 1500 nm focal length camera with a 800 800 ccd detector that will provide images with a spatial resolution of 10 rad pixel the spacecraft will fly by io at the time of jupiter orbit insertion joi and subsequently while in jupiter s orbit will have a total of 10 close passes by europa ganymede and callisto these close passes together with more distant encounters will be used by the imaging experiment primarily to obtain high resolution coverage of selected targets to fill gaps left in the voyager coverage to extend global color coverage of each satellite and to follow changes in the volcanic activity of io the roughly 390 mbit allocated for imaging during the tour will be distributed among several hundred frames compressed by factors that range from 1 to possibly as high as 50 after obtaining high resolution samples during the initial io encounter at joi roughly 10 of imaging resources are devoted to near terminator mapping of io s topography at 2 to 10 km resolution monitoring color and albedo changes of the ionian surface and monitoring plume activity observations of europa range in resolution from several kilometers per pixel to 10 m pixel the objectives of europa are 1 to determine the nature origin and age of the tectonic features 2 to determine the nature rates and sequence of resurfacing events 3 to assess the satellite s cratering history and 4 to map variations in spectral and photometric properties europa was poorly imaged by voyager so the plan includes a mix of high and low resolution sequences to provide context the imaging objectives at ganymede are 1 to characterize any volcanism 2 to determine the nature and timing of any tectonic activity 3 to determine the history of formation and degradation of impact craters and 4 to determine the nature of the surface materials because ganymede was well imaged by voyager most of the resources at ganymede are devoted to high resolution observations the callisto observations will be directed mostly toward 1 filling voyager gaps 2 acquiring high resolution samples of typical cratered terrain and components of the valhalla and asgaard basins 3 acquiring global color and 4 determining the photometric properties of the surface a small number of frames will be used to better characterize the small inner satellites of jupiter thebe amalthea metis and adrastea

regional variations in deformation mechanisms and structural styles in the central appalachian orogenic belt orogenic belts such as the central appalachian fold and thrust belt consist of distinct tectonic provinces characterized by different structural styles as a result of deformation under different physical conditions a quantitative study of deformation mechanisms was undertaken for quartzites and sandstones of the central appalachian orogenic belt in order to understand the controls of different physical parameters on the relative importance of these mechanisms and on the geometry and mechanics of formation of structures in the different provinces in the blue ridge province the dominant deformation mechanisms are pressure solution dislocation creep and extension fracturing with some accompanying grain boundary sliding and recrystallization the proportion of dislocation creep to pressure solution strain increases both with temperature and deviatoric stress an axial plane slaty cleavage which contains the maximum and intermediate principal directions of the strain ellipsoid maintains a uniform orientation in both the blue ridge and the great valley provinces folds in the blue ridge province have a similar geometry formed by progressive flattening of parallel folds due to internal deformation ductile deformation zones on the overturned limbs of folds acted as precursors for the propagation of thrust faults in the late stages of folding in the valley and ridge and massanutten synclinorium important deformation mechanisms in the sandstone units include pressure solution plastic deformation cataclasis brecciation extension fracturing and slip along minor faults and bedding planes major folds are strongly disharmonic and show variations between concentric and angular geometries they are associated with thrust ramps that propagated through progressively developing folds in the late stages of folding brittle deformation zones characterized by high intensities of extension fractures and cataclastic bands formed on the steep forelimbs these features are interpreted to be the result of layer parallel extension and the propagation of splay faults through these limbs cleavage developed during layer parallel shortening prior to the onset of folding and was rotated to its present fanned geometry during folding on the basis of the results of this study the central appalachian orogenic belt can be subdivided into two deformational provinces dominated by different deformation mechanisms and characterized by different geometries and mechanics of formation of the structures for orthoquartzites the tectonite front which separates the tectonites of the hinterland from the non tectonites of the foreland is located along the blue ridge front for carbonates and argillaceous sandstones the tectonite front is located along the north mountain fault

retreat of glaciers on puncak jaya irian jaya determined from 2000 and 2002 ikonos satellite images puncak jaya irian jaya indonesia contains the only remaining tropical glaciers in east asia the extent of the ice masses on puncak jaya has been mapped from high resolution ikonos satellite images acquired on 8 june 2000 and 11 june 2002 exclusive of southwall hanging glacier the ice extent on puncak jaya was 2 326km 2 and 2 152km 2 in 2000 and 2002 respectively from 2000 to 2002 the puncak jaya glaciers lost a surface area of 0 174km 2 or 7 48 of their 2000 ice extent comparison of the ikonos based glacier extents with previous glacier extents demonstrates a continuing reduction of ice area on puncak jaya by 2000 ice extent on puncak jaya had reduced by 88 of its maximum neoglacial extent between 1992 and 2000 meren glacier disappeared entirely all remaining ice masses on puncak jaya continue their retreat from their neoglacial maxima comparison of 2000 2002 ice extents with previous extents suggests that these glaciers have not experienced accelerating rates of retreat during the last half of the 20th century if the recession rates observed from 2000 to 2002 continue the remaining ice masses on puncak jaya will melt within 50 years

patterns of fracture and tidal stresses due to nonsynchronous rotation implications for fracturing on europa this study considers the global patterns of fracture that would result from nonsynchronous rotation of a tidally distorted planetary body the incremental horizontal stresses in a thin elastic or viscous shell due to a small displacement of the axis of maximum tidal elongation are derived and the resulting stress distributions are applied to interpret the observed pattern of fracture lineaments on europa the observed pattern of lineaments can be explained by nonsynchronous rotation if these features formed by tension fracturing and dike emplacement tension fracturing can occur for a small displacement of the tidal axis so that the resulting lineaments may be consistent with other evidence suggesting a young age for the surface

tropical glaciers recorders and indicators of climate change are disappearing globally in this paper we review the interaction of el nino southern oscillation enso variability and warming trends recorded in ice core records from high altitude tropical glaciers discuss the implications of the warming trends for the glaciers and consider the societal implications of glacier retreat enso has strong impacts on meteorological phenomena that directly or indirectly affect most regions on the planet and their populations many tropical ice fields have provided continuous annually resolved proxy records of climatic and environmental variability preserved in measurable parameters especially oxygen and hydrogen isotopic ratios d 18 o dd and the net mass balance accumulation these records present an opportunity to examine the nature of tropical climate variability in greater detail and to extract new information on linkages between rising temperatures on tropical glaciers and equatorial pacific sea surface temperatures in critical enso indicator regions the long term climate records from a collection of high altitude tropical ice cores provide the longer term context essential for assessing the significance of the magnitude and rate of current climate changes that are in large measure driving glacier retreat the well documented ice loss on quelccaya in the peruvian andes naimona nyi in the himalaya kilimanjaro in eastern africa and the ice fields near puncak jaya in papua indonesia presents a grim future for low latitude glaciers the ongoing melting of these ice fields response is consistent with model predictions for a vertical amplification of temperature in the tropics driver and has serious implications for the people who live in these areas

brittle frictional mountain building 2 thermal structure and heat budget this paper describes a simple thermal model of an actively deforming critically tapered fold and thrust belt the model determines the steady state temperature distribution and heat flow as well as the pressure temperature time histories of rocks that outcrop at the surface the main parameters controlling the thermal structure are the accretion and erosion rates the undisturbed geothermal gradient at the toe and the amount of frictional heating both shear heating on the decollement fault and internal strain heating within the deforming brittle wedge are incorporated in a mechanically consistent manner and they dominate the effect of radiogenic heating except in fold and thrust belts with significantly overpressured pore fluids the mean stresses temperatures and surface heat flow all increase with an increase in the basal and internal coefficients of friction and this dependence is used to constrain the level of friction on the decollement fault beneath the steady state fold and thrust belt in taiwan rocks outcropping in the core of the central mountain range of taiwan experience maximum theoretical temperatures in excess of 400 c and maximum mean pressures in excess of 500 mpa if the coefficient of basal friction is b 0 5 qualitatively these conditions are in good agreement with the observed high greenschist facies metamorphism the theoretical surface heat flow which increases from 95 mw m2 at the front of the fold and thrust belt to 240 mw m2 at the rear is in excellent agreement with the results of a recent geothermal survey of taiwan and theoretical cooling histories are in good agreement with fission track and other geochronologic studies taken together these results provide strong evidence that sliding on the basal decollement fault beneath taiwan is governed by a coefficient of friction in the range of typical laboratory measurements b 0 5 0 2 approximately 35 of the total surface heat flux of 3 gw is heat conducted into the base of the wedge from the top of the basal decollement fault and somewhat more than 30 is heat advected into the toe by accretion the remaining heat is generated internally about 25 by internal strain heating and about 10 by radiogenic heating either an increase in the coefficient of basal friction b or a reduction in the pore fluid pressure ratio b leads to an increase in the surface heat flow because of the increased frictional heating within the wedge and on the basal decollement fault the overall balance of energy in a steady state fold and thrust belt is described by the equation e w g q where is the rate at which both mechanical and heat energy are added from external sources w g is the rate at which work is performed against gravitational body forces in a reference frame attached to the overriding plate and q is the rate at which waste heat flows out of both the upper and lower boundaries the total power input into the taiwan fold and thrust belt is approximately 4 2 gw the mechanical work being done on the base and front of the fold and thrust belt accounts for 3 of these 4 2 gw in addition 0 9 gw of heat are being advected from the subducting plate into the toe by accretion the remaining 0 3 gw are being supplied by in situ radiogenic heating the outgoing energy is dominated by the 3 gw of heat conducted out the top in the surface heat flow however another 0 8 gw are conducted down beneath the rear portion of the basal decollement fault to heat the underlying subducting slab only 0 4 of the incoming 4 2 gw do useful mechanical work against gravity within the wedge the efficiency of brittle frictional mountain building in taiwan is therefore 10

solar radiation maintained glacier recession on kilimanjaro drawn from combined ice radiation geometry modeling 1 in the context of investigating modern glacier recession on kilimanjaro which began around 1880 this study addresses the glacier regime of the vertical ice walls that typically form the margins of kilimanjaro s summit glaciers these walls have suffered a continuous lateral retreat during the twentieth century to evaluate the role of solar radiation in maintaining glacier recession on kilimanjaro a radiation model is applied to an idealized representation of the 1880 ice cap the combined process based model calculates the spatial extent and geometry of the ice cap for various points in time after 1880 support for input data and fundamental assumptions are provided by an automatic weather station that has operated on the summit s northern icefield since february 2000 even in a simple climatic scenario only forced with an annual cycle of clouds the basic evolution in spatial distribution of ice bodies on the summit is modeled well the northern and southern icefields form in characteristic east west orientation which verifies the basic idea behind the model forcing the model with further climate related phenomena improves the results it then additionally reproduces the eastern icefield the third big ice entity on the summit this study qualitatively demonstrates that solar radiation is the main climatic parameter maintaining modern glacier recession on kilimanjaro summit but also suggests that retreat on the inner ice cap margin might have been supported by a secondary energy source the need for additional field measurements is emphasized in order to better understand the complex processes of glacier climate interaction on kilimanjaro index terms 1620 global change climate dynamics 3309 1827 hydrology glaciology 1863 3309 meteorology and atmospheric dynamics climatology 1620 3359 meteorology and atmospheric dynamics radiative processes 9305 information related to geographic region africa keywords tropical glaciers kilimanjaro climate change glacier retreat solar radiation modeling

role of horizontal thermal conduction and finite time thrust emplacement in simulation of pressure temperature time paths abstract comparison of metamorphic thermal histories produced by 1 one vs two dimensional conductive models and 2 instantaneous vs finite emplacement time thrusting indicates that the simple 1d or instantaneous models applied by many petrologists generally produce pressure temperature pt paths with topologies similiar to those generated by 2d time transitive models however maximum temperatures attained by footwall rocks are significantly lower in 1d than in 2d conductive models leading us to recommend that 2d thermal effects be incorporated into models whenever possible pt paths produced by instantaneous and finite duration thrust emplacement differ significantly during the synthrusting period but the peak metamorphic conditions t max and pressure at t max eventually attained by footwall rocks during erosional unroofing are the same within minimum analytical uncertainties 50 k 100 mpa on geothermobarometric data thus if erosion begins only after the end of the thrusting event instantaneous thrusting is a reasonable simplifying assumption that introduces relatively little inaccuracy into pt models devised to examine peak metamorphic conditions

strained craters on ganymede high resolution images of jupiter s satellite ganymede obtained by the galileo spacecraft reveal several elliptical craters that are transected by sets of subparallel ridges and troughs oriented roughly orthogonal to the long axis of the crater implying that these craters have been extensionally strained we analyze five such craters four in the ancient dark terrain and one in bright grooved terrain inferring their strain histories by assuming each crater was originally circular these strained craters have been elongated by amounts ranging from 5 to 50 all are deformed by extension near perpendicular to subparallel ridges and troughs and some are also deformed by distributed simple shear parallel to these tectonic structures the rift zones that deform these craters show extensions of 5 up to 180 for a well defined fault zone that rifts saltu crater within dark terrain of nicholson regio extensional fault zones consisting of domino style normal faults and representing strains of several tens of percent may be common on ganymede and strains of this order can alter pre existing surface features beyond recognition through the process of tectonic resurfacing

dark halo craters and the thickness of grooved terrain on ganymede dark halo craters in grooved terrain on ganymede represent potential probes of the subsurface geology these craters are surrounded by a broad diffuse low albedo annulus or halo halo radius is linearly proportional to crater radius indicating that the halo is related to the continuous ejecta deposit of the crater and is not removed by natural aging processes such as regolith development and exposure to the space environment the halos have orange violet albedo ratios that are intermediate between ratios associated with grooved terrain and cratered terrain we propose that halos result from the incorporation of cratered terrain material into crater ejecta in uruk sulcus only craters greater than 12 km in diameter have halos indicating that the cratered terrain material there forms a stratigraphic horizon buried at depth in the grooved terrain into which only larger craters can excavate this depth can be calculated from the transition diameter by reconstructing the transient crater we calculate a depth of excavation corresponding to the depth of burial of cratered terrain of 1 0 to 1 6 km this shallow burial is inconsistent with deep subsidence and burial stoping into the interior or lateral spreading apart of ancient cratered terrain units but is consistent with a filled graben model for grooved terrain where relatively clean ice has been emplaced over downdropped blocks of cratered terrain

understanding kinematic data from the moine thrust zone in terms of a kinematics based mathematical model of deforming thrust wedges abstract a salient recess pair along the moine thrust zone exhibits significant lateral kinematic variations specifically the more steeply dipping portion of the thrust surface associated with the recess shows evidence for greater strain magnitudes and more out of the plane motion than the adjoining salient additionally a subset of the grain shape data has grain shape approximations with their long axes oriented perpendicular to the regional transport direction to more fully understand these kinematic features we developed a kinematics based mathematical model of thrust wedge deformation our numerical model predicts an increase in strain magnitude as well as non plane strain flattening in the region of a thrust ramp consistent with the strain patterns observed within the recess along the moine thrust zone furthermore in the absence of a lateral confining boundary condition much of the model thrust wedge experiences transport perpendicular maximum extension except for the region closest to the thrust where simple shear deformation is dominant using our numerical model we predict the amount of lateral confining strain needed to induce plane strain deformation ps as well as the amount of lateral confining strain necessary to make the long axis of the strain ellipsoid parallel with the transport direction parallel we have found that the incremental parallel can be as much as 42 of the incremental strain magnitude thus we consider transport perpendicular lineations like those seen along the moine thrust zone to be the result of lateral confining boundary conditions that are weak enough to allow transport perpendicular maximum extension

a geometric analysis of surface deformation implications for the tectonic evolution of ganymede abstract a visual nonalignment of the furrows and the circularity of impact craters are used to study surface deformation on ganymede the furrow system is examined to test the hypothesis that lateral motion has taken place between areas of dark terrain results show that while lateral motion cannot be ruled out it may not be required to explain the geometry of the system initial nonconcentricity of the furrows or an early period of penetrative deformation shortly after furrow formation could also account for the present configuration centers of curvature of the furrows in galileo and marius regiones are numerically determined and it is shown that if lateral movement did occur it is not possible to determine the amount of displacement the axial ratios of impact craters in the uruk sulcus region which separates galileo and marius regiones are determined and show that large scale shear deformation has not occured in that area since bright terrain was emplaced deformation of impact craters within galileo regio suggests that ganymede s lithosphere has behaved rigidly throughout most of the satellite s evolution the shapes and orientations of impact craters in dark terrain around wedges of bright terrain are used to place an upper limit on the amount of extension associated with bright terrain formation

constraints on the expansion of ganymede and the thickness of the lithosphere grooves and furrows have been interpreted as grabens resulting from extension of ganymede s lithosphere geologically reasonable estimates of the dip 90 60 and displacement less than 1 km to a few hundred meters of faults bounding grooves on ganymede allow calculation of the extension and surface area increase 0 04 2 required for the formation of all grooved terrain the implied radius increase is thus limited between 0 02 and 1 1 planetary expansion is the maximum possible since formation of the grooved terrain began similar estimates for faults bounding furrows the oldest preserved tectonic features on ganymede indicate a maximum surface area increase of 0 5 for the best developed furrow system which is located in galileo regio if equivalent furrow systems existed on all of the cratered terrain then a maximum of 0 5 increase in surface area of ganymede is possible after the formation of the lithosphere and prior to the formation of grooved terrain faults bounding simple graben originate at a subsurface mechanical discontinuity and propagate upwards resulting in grabens with similar widths and similar spacings between members of a set the depth to this mechanical discontinuity for furrows and grooves on ganymede must give at least a minimum lithosphere thickness because it is impossible for faults to originate and propagate upwards from a point below the lithosphere therefore the minimum lithosphere thickness on ganymede is 5 km and 9 km in marius and galileo regiones respectively at the time of furrow formation and 4 km at the time of groove formation

global geological mapping of ganymede abstract we have compiled a global geological map of ganymede that represents the most recent understanding of the satellite based on galileo mission results this contribution builds on important previous accomplishments in the study of ganymede utilizing voyager data and incorporates the many new discoveries that were brought about by examination of galileo data we discuss the material properties of geological units defined utilizing a global mosaic of the surface with a nominal resolution of 1 km pixel assembled by the usgs with the best available voyager and galileo regional coverage and high resolution imagery 100 200 m pixel of characteristic features and terrain types obtained by the galileo spacecraft we also use crater density measurements obtained from our mapping efforts to examine age relationships amongst the various defined units these efforts have resulted in a more complete understanding of the major geological processes operating on ganymede especially the roles of cryovolcanic and tectonic processes in the formation of might materials they have also clarified the characteristics of the geological units that comprise the satellite s surface the stratigraphic relationships of those geological units and structures and the geological history inferred from those relationships for instance the characteristics and stratigraphic relationships of dark lineated material and reticulate material suggest they represent an intermediate stage between dark cratered material and light material units

late cretaceous paleocene synorogenic sedimentation and kinematic history of the sevier thrust belt northeast utah and southwest wyoming integration of cross cutting structural relationships overlapping sedimentary units new conglomerate provenance data and radiometric and palynological dates provides a basis for reinterpretation of the distribution and timing of late cretaceous through paleocene thrust faulting in the northeast utah southwest wyoming part of the sevier thrust belt these data indicate a general eastward progression of deformation that was punctuated by local out of sequence and hinterlandward verging events provenance data delimit a sequential restoration of a regional cross section the principal thrust systems in northeast utah and southwest wyoming are the willard ogden crawford absaroka and hogsback thrusts the willard is the westernmost structurally highest and oldest of the thrusts it carries a unique section of thick proterozoic sedimentary rocks as well as paleozoic rocks and was folded during displacement on younger thrust systems the next youngest thrust system is the ogden which comprises several basement rooted imbricate thrusts that together form a large antiformal stack with a structural culmination in the wasatch range growth of the wasatch culmination took place during coniacian through paleocene time contemporaneous with sequential displacement on the frontal crawford absaroka and hogsback thrusts total shortening in this part of the thrust belt was 100 km and structural relief of 25 km developed in the area of the wasatch culmination during coniacian through paleocene time thrusting followed an overall eastward progression that was interrupted by local out of sequence and hinterlandward verging events several episodes of synchronous displacement on two or more thrusts can be demonstrated shortening occurred in three main episodes the first episode 89 84 ma involved 33 km of shortening on the crawford thrust and its footwall imbricates approximately 19 km of structural relief on the basement cover contact developed in the area of the wasatch culmination the second episode 84 62 ma with a break between 75 69 ma involved 30 km of shortening mainly on the absaroka thrust and development of an additional 6 km of structural relief in the culmination the third episode of shortening 56 50 ma took place on the hogsback thrust involved 21 km of horizontal shortening and produced no significant increase in structural relief in the culmination long term rates of shortening ranged between 3 0 mm yr and 6 6 mm yr these three episodes of shortening produced three large accumulations of synorogenic conglomerate totaling 3 km in thickness the henefer formation and echo canyon and weber canyon conglomerates were deposited during crawford thrusting the evanston formation was deposited during and after absaroka thrusting and the lower conglomeratic part of the wasatch formation was deposited during and after hogsback thrusting most of the sediment in these synorogenic units however was derived from repeated uplift of the willard thrust sheet and from the eastern flank of the wasatch culmination in the rear part of the thrust belt only local minor accumulations were derived from the frontal ramp anticlines sediment accumulation and structural deformation were generally out of phase periods of regional shortening and uplift were marked by development of unconformities and sediment bypassing to distal parts of the foreland basin periods of structural inactivity were marked by accumulation of aerially widespread braided river conglomerate on top of the thrust belt one exception to this pattern is the henefer echo canyon weber canyon conglomerate deposit which contains evidence of progressive deformation in close proximity to the tip of the crawford thrust comparison of the sequential restoration with the late cretaceous subsidence history and isopach patterns in the distal foreland basin of western wyoming demonstrates that the principal controls on regional subsidence and sediment supply were the growth and erosion of the wasatch culmination growth of the duplex beneath the culmination may have been a means of maintaining critical taper in the thrust wedge

improved estimates of glacier change rates at nevado coropuna ice cap peru accurate quantification of rates of glacier mass loss is critical for managing water resources and for assessing hazards at ice clad volcanoes especially in arid regions like southern peru in these regions glacier and snow melt are crucial dry season water resources in order to verify previously reported rates of ice area decline at nevado coropuna in peru which are anomalously rapid for tropical glaciers we measured changes in ice cap area using 259 landsat images acquired from 1980 to 2014 we find that coropuna ice cap is presently the most extensive ice mass in the tropics with an area of 44 1 km 2 and has been shrinking at an average area loss rate of 0 409 km 2 a 1 0 71 a 1 since 1980 our estimated rate of change is considerably lower than previous studies 1 4 km 2 a 1 or 2 43 a 1 but is consistent with other tropical regions such as the cordillera blanca located 850 km to the nw 0 68 a 1 thus if glacier recession continues at its present rate our results suggest that coropuna ice cap will likely continue to contribute to water supply for agricultural and domestic uses until 2120 which is nearly 100 years longer than previously predicted

topographic wavelengths of ganymede groove lanes from fourier analysis of galileo images galileo images have shown that grooved terrain on ganymede consists of pervasive ridges and grooves at a variety of spatial scales which complicates visual interpretation we use fourier analysis to separate complex surface deformation into its component dominant wavelengths closely correlated to topographic wavelengths to determine spatial relationships within and among grooved terrain units we analyze groove lanes in four galileo target sites uruk sulcus byblus sulcus tiamat sulcus and nicholson regio spanning a range of resolutions and lighting geometries and we find multiple dominant wavelengths in each fourier analysis of the complexly deformed uruk sulcus shows both similarities and differences in wavelength distribution among its tectono stratigraphic subunits a range of 0 5 to 6 km with a concentration at 1 2 km favorable comparison is made to a stereo derived topographic model of the dominant wavelengths displayed by byblus sulcus 1 3 3 and 10 km the longest wavelength is revealed by profiles across both high and low resolution images with very different lighting geometries tiamat sulcus displays different dominant wavelengths north 5 to 10 km and south 3 to 5 km of the orthogonally trending kishar sulcus groove lanes in nicholson regio are significantly different from the other sites because they are isolated within dark terrain fourier analysis of these dark terrain groove lanes shows dominant wavelengths 2 1 3 2 and 8 0 km that are similar to those in lanes of more typical grooved terrain this suggests that the tectonic style and lithospheric characteristics in this portion of ganymede s dark terrain were similar to those in bright grooved terrain at the time of deformation our results support the hypothesis that longer topographic wavelengths in ganymede s groove lanes formed by means of extensional necking of the lithosphere while multiple shorter wavelengths formed by normal faulting of the brittle lithosphere in both bright and dark terrains the similar wavelengths of deformation seen in several groove lanes in both bright and dark terrain suggest similarity in lithospheric thickness composition and mechanical structure at these disparate sites a global process such as differentiation could be responsible for creating a similar planet wide strain and thermal regime during the time of grooved terrain formation

relationship of spaced cleavage to folds and thrusts in the idaho utah wyoming thrust belt the idaho utah wyoming thrust belt of the rocky mountain cordillera preserves structures that developed at very shallow levels of the crust t 200 c the geometry of major structures is well documented and synorogenic conglomerates record the timing of movement on major thrusts spaced cleavage and pencil fracturing are developed within micrites of the jurassic twin creek formation the cleavage developed dominantly by pressure solution early in the deformation history of each thrust sheet aided by elevated temperatures and pressures in areas where increased overburden resulted from emplacement of earlier overriding sheets cleavage within any sheet is well developed in the area covered by the pre erosional extent of the previous sheet forelandward from this area cleavage intensity decreases drastically thermal modelling of the sheets agrees well with temperature estimates from illite crystallinity studies on material from the cleavage planes cleavage is axial planar to small folds and formed concurrently with small scale buckle folds and contraction faults during the early history of movement on each thrust however cleavage strongly fans about large scale folds formed later during movement suggesting passive rotation of cleavage with bedding during the later stages of thrust history the rotated cleavage may also be folded and overprinted by a second weaker cleavage during a second ramping or during movement on a later lower thrust cross folding may also develop as a result of lateral ramping thus complex patterns of interfering folds multiple cleavages and associated fiber filled fractures may be produced during motion on a single thrust fault and so magnify the problem of correlating cleavages and deciphering multiple deformations

cleavage development within a foreland fold and thrust belt southern pyrenees spain abstract in the southern pyrenees lithologically distinct cleavage fronts are each parallel to bedding and dip 20 towards the foreland pressure solution was the dominant mechanism of cleavage development the mudstone cleavage front is coincident with the 195 c paleoisotherm and is associated with a pressure solution strain of 5 a mechanical twin strain of 4 and a deviatoric stress magnitude of 65 mpa illite crystallinity measurements define a geothermal gradient of 15 c km 1 and indicate that the paleoisotherms are bedding parallel deviatoric stress magnitudes from calcite twins were regionally constant at 65 mpa and principal stress axes were perpendicular to cleavage temperature was the primary control on deformation micromechanisms and the position and orientation of the cleavage front within the foreland thrust wedge deformation below the cleavage front occurs predominantly by pressure solution which in conjunction with mechanical twinning and microfracturing produces a quasi plastic rheology stress magnitudes determined from mechanical twinning of carbonate grains and long term 10 6 10 76 y strain rates determined for regional folds and faults suggest an apparent macroscopic viscosity of 9 8 10 18 to 7 2 10 19 pa s for the lower thrust wedge above the cleavage front temperature pressure solution strain total strain and mesoscale deformation diminish the region of the thrust wedge above the 100 c paleoisotherm is characterized by large brittle faults with cataclastic fault zones and negligible grain scale deformation indicating an elastico frictional rheology

paleomagnetism and crustal rotations along a shear zone las vegas range southern nevada in southern nevada paleozoic isopachs mesozoic structures and mountain ranges trend north south but as they approach the right lateral west northwest trending las vegas valley shear zone lvvsz they are bent clockwise up to 90 in oroflexes 30 km long in the las vegas range the declination of the characteristic magnetization of the cambrian bonanza king formation has likewise been rotated clockwise more than 50 for samples from eight sites 13 23 samples per site in the las vegas range and in its extension south of the lvvsz stepwise thermal demagnetization to 600 c removed recent and tertiary overprints revealing a nearly horizontal late paleozoic viscous partial thermoremanent magnetization vptrm which predates both the tertiary oroflexural bending and the sevier thrusting in the area the declination of the characteristic magnetization after correcting for the dip of bedding varies from 133 2 at a site 24 km north of the shear zone to 196 4 13 km north of it and 204 4 11 km south of the shear zone this parallels a similar change in the structural trend the paleomagnetic data indicate that the las vegas range is broken into rather small blocks 5 km which rotate in response to more continuous deformation at depth this deformation of the upper crust can be modelled using a thin non newtonian viscous plate model which when applied to the las vegas valley shear zone predicts rotations similar to those seen in the las vegas range

small glaciers disappearing in the tropical andes a case study in bolivia glaciar chacaltaya 16 o s glaciar chacaltaya is an easily accessible glacier located close to la paz bolivia since 1991 information has been collected about the evolution of this glacier since the little ice age with a focus on the last six decades the data considered in this study are monthly mass balance measurements yearly mappings of the surface topography and a map of the glacier bed given by ground penetrating radar survey a drastic shrinkage of ice has been observed since the early 1980s with a mean deficit about 1 m a 1 w e from 1992 to 1998 the glacier lost 40 of its average thickness and two thirds of its total volume and the surface area was reduced by 40 with a mean estimated equilibrium line altitude lying above its upper reach the glacier has been continuously exposed to a dominant ablation on the whole surface area if the recent climatic conditions continue a complete extinction of this glacier in the next 15 years can be expected glaciar chacaltaya is representative of the glaciers of the bolivian eastern cordilleras 80 of which are small glaciers 0 5 km2 a probable extinction of these glaciers in the near future could seriously affect the hydrological regime and the water resources of the high elevation basins

deformation within foreland thrust sheets by populations of minor faults the dominant deformation mechanism within foreland thrust sheets is the displacement of blocks of weakly deformed rock on discrete mineral coated minor faults in highly deformed layers at the bases of three southern appalachian foreland sheets such minor faults are members of families or populations of consistently oriented structures the deformation style is similar in all three sheets rock nearest each thrust was shortened in the direction of sheet transport and thickened by a family of faults oriented at low angles to the thrusts rock further above each thrust experienced only the first of these two deformation stages statistical analyses of fault populations from these three sheets demonstrate that their deformation is quantitatively as well as qualitatively similar deformation due to movement on minor faults is statistically homogeneous at the scale of an outcrop in one of these sheets strain due to minor faults can be measured in that sheet a strain profile across this sheet is similar to strain profiles across continuously deformed sheets from internal portions of mountain belts suggesting that their responses to emplacement are similar

geologic evolution of galileo regio ganymede the geology of galileo regio is characterized by 1 two principal morphologic terrain units rough and smooth terrains 2 craters in various states of preservation and 3 a tectonic framework consisting of three furrow systems of different ages the three furrow systems transect the rough terrain but predate all other terrains as well as the oldest craters larger than about 10 km diameter a broadly arcuate nw se furrow system dominates the tectonic pattern and is intermediate in age between widely spaced ne sw and n s furrow systems the furrow systems were probably produced by extensional stresses that occurred during crustal solidification but before large craters could be retained smooth terrain is concentrated in the southern part of galileo regio and probably resulted from fluid extrusions along fractures associated with the dominant furrow system the distribution of smooth terrain on galileo regio suggests that the ancient crust of ganymede was relatively thin in the equatorial region and thickened poleward in this area the origin of the furrow systems is very uncertain the age relationships morphology and geometry of the furrow systems do not favor an origin by impact or tidal stressing a possible but speculative origin is crustal uplift caused by a plume like convection cell in a fluid mantle underlying a thin crust stratigraphic and morphologic relationships among furrows and crater palimpsests suggest that palimpsest morphology is largely the result of impact into a rheologically weak crust rather than viscous relaxation

tropical climate and glacier hydrology a case study in bolivia runoff from intertropical glaciers is highly variable indicating that they are greatly affected by climatic changes peculiar to tropical climates the 3 km2 basin presented in this case study lies in the cordillera real of bolivia and is 77 covered by glacier ice ranging in elevation from 6000 to 4830 m a s l a comparison of 2 years of study demonstrates the peculiar feature of intertropical glaciers that accumulation and melting periods coincide during the rainy season during the first hydrological year 1991 1992 runoff was 1793 mm for an average precipitation on the glacier of approximately 916 mm during the second year 1992 1993 runoff was 1080 mm for a precipitation of 1060 mm solar radiation and daily mean duration with positive temperature on the ablation zone are the parameters best explaining variation in monthly runoff gauge readings taken downstream enable discharge from the glacier to be established over a period of nearly 20 years the most prominent events coincide with significantly negative values of the southern oscillation index often linked to el nino southern oscillation enso phenomena in conclusion results show that these intertropical glaciers are receding rapidly as precipitation does not compensate for loss from melting

fault geometries on uranus satellite miranda implications for internal structure and heat flow abstract miranda a 470 km diameter uranian icy satellite has a surface that exhibits evidence of a complex tectonic history tectonic structures are mostly localized in three regions termed coronae but also form a rift system inferred to be global in extent ridges within the boundary of arden corona and those that make up the 340 chasma part of the global rift system have been interpreted as normal fault blocks using voyager data we test the hypothesis that these arden corona faults as well as those at the northern edge of the 340 chasma are listric in geometry for this testing we use four geometric criteria for listric faults 1 progressive down dip decrease in fault scarp dip 2 progressive down dip increase in back tilted face slope 3 concavity of the exposed scarp surface and 4 presence of a rollover structure results of this analysis support the hypothesis that the faults within the arden corona boundary are listric in geometry but do not strongly support the hypothesis for the faults within the 340 chasma by analogy with terrestrial structures the listric character of faults within the arden corona boundary suggests the presence of a subsurface detachment this detachment likely occurred at miranda s brittle ductile transition zone at the time of faulting measurements of the arden corona fault system geometry are used to estimate depths to the proposed brittle ductile transition zone at the time of faulting resulting in values of 6 7 9 0 km those depths in turn are used to estimate a thermal gradient of 6 25 k km 1 and a surface heat flux of 31 112 mw m 2 the weaker evidence of a listric geometry for the faults of the 340 chasma suggests that those faults did not interact with a brittle ductile transition at the time of their formation our estimated thermal gradient of the arden corona region is consistent with a previous heating event on miranda that was as significant as europa s current resonance induced tidal heating this heating event may be associated with a hypothesized previous tidal resonance of miranda with umbriel and or ariel

formation of ganymede grooved terrain by sequential extensional episodes implications of galileo observations for regional stratigraphy abstract high resolution galileo images of grooved terrain on ganymede have revealed details of the morphology of grooves and their stratigraphic relationships based on lower resolution voyager images complex areas of grooved terrain in uruk sulcus were interpreted in the context of structurally isolated grooved polygons which were resurfaced by cryovolcanism and individually deformed by local processes in galileo images of grooved polygon boundaries the faults comprising the groove lanes between the polygons are observed to truncate features within the polygons and incipient fractures from these groove lanes modify the edges of the polygons indicating that these groove lanes are younger than the polygons in the uruk sulcus region tectonic resurfacing by the formation of younger sets of grooves appears to be obscuring older patterns of deformation the grooved polygons are thus remnants of terrain affected by older episodes of deformation isolated from each other by areas of more recent deformation the stratigraphy of grooves can be determined for small areas covered by high resolution galileo images 100 m pixel and then generalized to larger areas imaged by voyager at lower resolution 1 km pixel this method has been applied to the regions around uruk sulcus and nippur sulcus resulting in two preliminary conclusions about the nature of grooved terrain deformation 1 the style of deformation has changed through time and 2 the orientation of least compressive stress has changed through time throughout the mapped region the stratigraphically oldest grooves are closely spaced subdued structures which indicate least compressive stress oriented nw se while the youngest grooves exhibit morphology consistent with tilt block normal faulting with least compressive stress oriented ne sw these observations are consistent over an area of 1 6 million square kilometers and therefore do not favor highly localized or low strain mechanisms for grooved terrain formation such as the cooling of cryovolcanic flows or the surface expression of diapirs instead the formation of grooved terrain on ganymede may be dominated by global expansion due to tidal heating and or differentiation possibly organized into coherent regional patterns by transient low order convection or changes in the satellite s figure

global reorientation and its effect on tectonic patterns on ganymede the basins of ganymede are studied in order to examine the effects of global reorientation on the grooves and furrows of the satellite an impact basin and the global reorientation of ganymede were modeled the damping time the time for relaxation of tidal bulge and the time for isostatic adjustment of craters are significant in calculating the duration and amount of global reorientation the regional global control of groove orientation is examined the data reveal that the tidal despinning and furrow formation created the reactivated zones of weakness in which the groove sets were formed it is observed that the grooved terrain emplacement caused a 15 deg shift in the paleopole

stresses in an overthrust sheet and propagation of thrusting an airy stress function solution an airy stress function solution is derived for the stress field in an elastic wedge shaped overthrust sheet subject to horizontal forces at the rear and at the front from this stress solution the state of stress on the basal thrust lower boundary of the sheet is obtained both normal and shear stresses on the basal thrust are affected by the rear pushing and front buttressing forces and by the slopes of the upper and lower boundaries of the wedge shaped block for 1 nonlinear components of external horizontal forces exerted on the vertical edges of the block and or 2 nonzero slopes of the upper and lower boundaries the normal and shear stresses vary systematically with position along the basal thrust the ratio of shear and normal stresses along this plane the frictional function of the thrust can be compared with the friction coefficient to determine where slippage is likely to occur since the frictional function is a function of position the strength is exceeded only on part of the thrust near the rear for most values of the parameters the assumption of simultaneous displacement of the whole thrust sheet on the basal plane is therefore not realistic even simple static models such as the present one indicate that the motion on thrust faults must be envisaged in terms of progressive consecutive dislocation type slippage

tectonic and volcanic evolution of dark terrain and its implications for the internal structure and evolution of ganymede furrows in ancient dark terrain on ganymede form three systems that are each hemispheric or greater in scale the oldest of the systems designated system iii is dominated by approximately concentric troughs centered on about 60 n 50 w system i in the anti jovian hemisphere contains concentric and subradial furrows arrayed around a large degraded palimpsest centered at 15 s 165 w furrows in each system formed on and locally are buried by dark volcanic materials that embay and infill preexisting topographic features they crosscut extremely few well preserved older craters and they occur on surfaces having significantly different relative crater ages system ii also in the anti jovian hemisphere contains widely spaced radially arrayed furrows commonly 500 2000 km in length which are organized around a large area of dark smooth resurfacing material intense dark terrain fracturing and some of the globally oldest light material the total thickness of dark terrain resurfacing estimated using the stratigraphy of different dark material deposits and the rim heights of the largest crater size class whose density was depleted by each deposit is probably in the range of 3 8 km multiple models of the origin of each furrow system were tested using observed geologic features and patterns systems i and iii were found to be most consistent with reactivation of impact generated multiringed structures by endogenic global extension during a period of widespread dark material volcanism that obliterated a dense ancient crater population system ii was found to be most consistent with fracturing of a single circular isostatic uplift covering an entire hemisphere on the basis of geologic observations and interpretations and theoretical models of convection in spheres it is hypothesized that the uplift developed by long term warming of the upwelling current of a single axisymmetric convection cell in an initially cooler undifferentiated interior such wanning would also have created global expansion and supplied the tensional stress inferred to have formed systems i and iii this hypothesis is supported by the concentration around the center of system ii of intense fracturing and relatively young dark volcanic deposits suggestive of high lithospheric heat flow lithospheric thinning and stress concentration an observed long term decrease in the width of extensional tectonic features interpreted to be of endogenic origin is also consistent with lithospheric thinning due to warming of a cool interior

fold thrust belt evolution expressed in an internal thrust sheet sevier orogen the role of cataclastic flow large hinterland thrust sheets are the dominant structures in retroarc fold thrust belt ftb wedges these internal sheets remain active throughout the history of an ftb and strongly influence the kinematics of the external portions of the ftb and the overall behavior of the entire tectonic wedge their emplacement and deformation account for a significant portion of the total mechanical energy budget in ftb evolution based on estimates using deformation features preserved within such sheets moreover the deformation within dominant internal sheets can be used as a means to evaluate the tectonic history of the wedge as a whole the principal deformation mechanisms in different parts of an ftb wedge are strongly controlled by variations in the geothermal gradient retroarc ftbs typically show a steeper geothermal gradient in the hinterland than in the foreland resulting in a foreland ward slope of the brittl ductile transition therefore a change from plastic to elastico frictional ef mechanisms is expected not only with decreasing depth but also across strike as a dominant internal thrust sheet is transported toward the foreland and undergoes exhumation by synorogenic erosion however evidence for cataclasis overprinting early plastic deformation features is often not preserved in ancient ftbs because of extensive erosion of the wedge top even where evidence for lat stage cataclastic behavior exists in either ancient or modern i e active orogens it is often not recognized or studied our work in the canyon range central utah segment of the sevier ftb shows that unraveling the ef mechanisms such as lat stage cataclastic flow is critical to understanding the total deformation history of an internal thrust sheet after initial emplacement under plastic deformation conditions the cr thrust sheet was continuously reactivated under ef conditions thereby helping to maintain critical taper of the ftb wedge during its development structures preserved in the cr thrust sheet therefore record a significant portion of the deformation history of the ftb as a whole the canyon range cr syncline part of the cr sheet underwent fold tightening within the ef regime and the cataclasized rocks are well preserved the geometry and progressive deformation patterns of the cr syncline reveal four distinct to partly overlapping deformation stages the history of the rocks in the cr thrust sheet has been tracked by incrementally retro deforming the ftb and by unraveling details of the deformation within the cr syncline at various scales for each stage we use the cr syncline as a type example to show that unraveling ef mechanisms is critical to 1 understanding the state of a ftb wedge during its evolution 2 calculating the energy involved in ftb emplacement and 3 developing accurate restorations placing constraints on the depth of the rocks for successive stages of deformation is essential for developing retrodeformable balanced cross sections and in turn geometric and kinematic models for wedge evolution

glacier climate interaction at low latitudes in the low latitudes there is an absence of major thermal seasonality yet there are three different climate regimes related to global circulation patterns and their seasonal oscillation the humid inner tropics the dry subtropics and intermediate between these two the outer tropics for the respective glacier regimes the vertical profiles of specific mass balance vbps are modeled considering vertical gradients of accumulation air temperature and albedo the duration of the ablation period and a factor for the ratio between melting and sublimation the model is first calibrated with data from hintereisferner austrian alps and is then applied to tropical conditions the simulated vbp matches well the measured profiles from irian jaya and mount kenya due to lack of field evidence the subtropical vbp cannot be verified directly however application of the respective model versions separately to the humid and dry seasons of the outer tropical glaciar uruashraju cordillera blanca peru provides reasonable results glaciers in the humid inner tropics are considered to be most sensitive to variations in air temperature while dry subtropical glaciers are most sensitive to changes in air humidity the two seasons of the outer tropics have to be viewed from these different perspectives

grooved terrain on ganymede first results from galileo high resolution imaging abstract high resolution galileo imaging has provided important insight into the origin and evolution of grooved terrain on ganymede the uruk sulcus target site was the first imaged at high resolution and considerations of resolution viewing geometry low image compression and complementary stereo imaging make this region extremely informative contrast variations in these low incidence angle images are extreme and give the visual impression of topographic shading however photometric analysis shows that the scene must owe its character to albedo variations a close correlation of albedo variations to topography is demonstrated by limited stereo coverage allowing extrapolation of the observed brightness and topographic relationships to the rest of the imaged area distinct geological units are apparent across the region and ridges and grooves are ubiquitous within these units the stratigraphically lowest and most heavily cratered units lineated grooved terrain generally show morphologies indicative of horst and graben style normal faulting the stratigraphically highest groove lanes parallel ridged terrain exhibit ridges of roughly triangular cross section suggesting that tilt block style normal faulting has shaped them these extensional tectonic models are supported by crosscutting relationships at the margins of groove lanes thus a change in tectonic style with time is suggested in the uruk sulcus region varying from horst and graben faulting for the oldest grooved terrain units to tilt block normal faulting for the latest units the morphologies and geometries of some stratigraphically high units indicate that a strike slip component of deformation has played an important role in shaping this region of grooved terrain the most recent tectonic episode is interpreted as right lateral transtension with its tectonic pattern of two contemporaneous structural orientations superimposed on older units of grooved terrain there is little direct evidence for cryovolcanic resurfacing in the uruk sulcus region instead tectonism appears to be the dominant geological process that has shaped the terrain a broad wavelength of deformation is indicated corresponding to the voyager observed topography and may be the result of ductile necking of the lithosphere while a finer scale of deformation probably reflects faulting of the brittle near surface the results here form a basis against which other galileo grooved terrain observations can be compared

evidence for europa like tectonic resurfacing styles on ganymede 1 very high resolution imaging and stereo topographic data obtained during the galileo g28 encounter with ganymede show 1 evidence for europa like crustal spreading and resurfacing to form portions of the bright terrain and 2 bright terrain that appears smooth at voyager resolution and thus a strong candidate for cryovolcanism but instead is tectonically deformed and lacks embayment relationships when viewed at high resolution in contrast to previous views these new data show that tectonism has been the dominant process in shaping some very smooth areas and that ganymede appears to have experienced europa like crustal spreading during its previous history

new model for evolution of fold and thrust belt curvature based on integrated structural and paleomagnetic results from the pennsylvania salient in a number of curved fold and thrust belts worldwide such as the cantabrian arc and the wyoming idaho salient paleomagnetic data indicate vertical axis rotations inconsistent with structural findings this apparent conflict is especially pronounced in the pennsylvania salient where the paleomagnetically defined vertical axis rotations are opposite of the rotation sense indicated by structural studies we resolve this apparent disparity by developing an integrated and kinematically admissible model that has implications for other curved mountain belts the curvature of the pennsylvania salient may be explained by deformation partitioning in an initially laterally tapered basin between the cambrian ordovician carbonates and the overlying siliciclastic rocks earliest deformation occurred in the lowest strata and progressed toward the foreland and up section with time lateral differences in initial layer parallel shortening in the cambrian ordovician carbonates caused differential translation and rotations about a vertical axis in the cover sequence because of initial basin geometry the orogenic wedge developed a lateral taper with further shortening in the wedge and involvement of the cover rocks in the fold and thrust deformation gravitational driving forces became more important and the paleostress trajectories diverged in opposite directions on the two arms of the salient in response to the lateral taper

monthly balance and water discharge of an inter tropical glacier zongo glacier cordillera real bolivia 16 s measurements of mass balance were performed every month on zongo glacier bolivia simultaneously water discharge temperature and precipita tion data were obtained the first year of the survey 1991 92 was marked by an enso el nino southern oscillation event with high temperature and low precipitation whilst the following year 1992 93 was normal results point to the early and late wet season october december and march may as playing a critical role in the determination of the annual mass balance the wet season is the warmest period of the year and consequently the duration of the wet season is a highly relevant variable in determining mass balance both glaciological and hydrological methods for the determination of the mass balance provide similar results our study confirms that enso events have a major influence on the rapid glacier retreat currently affecting this part of the andes

the evolution of tectonic features on ganymede the bands of bright resurfaced terrain on ganymede are probably broad grabens formed by global expansion and filled with deposits of ice grooves within the bands are thought to be extensional features formed during the same episode of expansion the crust of ganymede is modeled as a viscoelastic material subjected to extensional strain with sufficiently high strain rates and stresses deep normal faulting will occur creating broad grabens that may then be filled continuing deformation at high strain rates and stresses will cause propagation of deep faults up into the flood deposits and normal faulting at the surface while lower strain rates and stresses will cause formation of open extension fractures or if the crustal strength is very low grabens at the surface the spacing between adjacent fractures may reflect the geothermal gradient at the time of deformation surface topography resulting from fracturing and normal faulting will decay with time as a result of viscous relaxation and mass wasting

tectonic framework of grooved terrain on ganymede abstract an analysis of the tectonic features grooves and prominent troughs comprising grooved terrain on ganymede shows a global tectonic framework domains of grooves bordered by deep structural boundaries that controlled their extent and orientation developed along preferred orientations some of these directions are much more prominent than others and appear to coincide with at least two great circles with pole locations at 152 long 55 lat and 65 long and 50 lat the great circle hypothesis is in good agreement with several statistical tests of the data set several mechanisms for the emplacement of grooved areas along great circles are discussed a plausible mechanism is a pattern of equatorial symmetric rising and descending convection cells because the studied areas represent only a small portion of ganymede interpretations of global tectonic patterns and models of formation must remain tentative

palaeozoic arc growth deformation and migration across the lachlan fold belt southeastern australia abstract the palaeozoic lachlan fold belt lfb is a low pressure metamorphic belt characterized by greenschist facies rocks and infolded volcanic sequences which indicate that the belt has not undergone substantial uplift at any stage porphyroblast matrix relationships in one of the highest grade metamorphic zones of the lfb the omeo complex indicate that the thermal peak was reached before or was synchronous with the earliest deformation similar to that in high grade metamorphic zones of the northern arunta inlier central australia in both areas the metamorphism is of low p high t type centred on major granite intrusions as regional aureoles and characterized by anti clockwise p t t paths however in the outer lower grade parts of the aureoles peak metamorphic conditions post date the earliest deformation this diachronous relationship indicates that 1 outward migration of a thermal front was centred on major granitoid intrusions batholiths 2 deformation propagated outward more rapidly than migration of the thermal front and 3 plastic and ductile deformation began only after heating around the batholiths thus orogeny was initiated after and localized by heat focusing in the mid crust associated with batholith emplacement therefore the early deformation is a result of thermal softening it is typically subhorizontal ductile shear at mid crustal levels but is characterized by upright to inclined folds at upper crustal levels in the latter environment the typically discordant contact aureole plutons are often interpreted as post tectonic granitoids but they were part of the ongoing mid crustal thermal perturbation that induced regional greenschist facies metamorphism which overprinted the early formed upright folds as it migrated to upper crustal levels orogeny migrated generally eastward through the lfb it began with the early silurian benambran orogeny centred on the wagga metamorphic belt wmb and terminated with the carboniferous kanimblan orogeny which was most intense in the hill end trough eastward migration of orogeny across central victoria part of the west lfb began in the ballarat bendigo zone during the early devonian and terminated in the melbourne zone in the middle devonian orogeny was centred on the meridional batholiths of the lfb each of which are considered to represent the transitory axis of an ancient magmatic arc stepwise but generally eastward arc migration caused the eastward migration of orogeny a tectonic model based on the modern southwest pacific arc system can be applied to the lfb following cambrian intra oceanic arc growth associated with west dipping subduction an ordovician marginal sea developed partly on stretched cambrian crust and was flooded by an extensive turbiditic wedge closure of the eastern part the east lfb began in the early silurian after a magmatic arc developed over the wmb possibly associated with an east dipping subduction zone after re establishment of west dipping subduction in the middle silurian absolute motion retreat of the upper australian plate caused by oblique plate convergence resulted in dextral transtension and the generation of siluro devonian inter arc and back arc basins transient compression resulted in deformation along the magmatic arc and induced formation of a new outboard eastward arc system periodic compression within the evolving arc and back arc system resulted in a series of east younging east verging linear siluro devonian fold and thrust belts which were localized adjacent to elongate batholiths that represent the relict arc systems local westward jumps in deformation and plutonism occurred the most significant is the 600 km westward jump into the west lfb caused by closure of the remainder of the passive ordovician back arc basin melbourne and bendigo ballarat zones west dipping subduction beneath the basin produced a low pressure fold thrust belt similar to the east lfb though the granitoids have a more primitive isotopic character indicating closure of thin dominantly oceanic crust in the early to middle devonian localized deformation induced by thermal softening of the crust within magmatic arcs that have developed on earlier passive margins is likely to produce anticlockwise p 7 t paths and may be a typical feature of southwest pacific style tectonism

brittle to ductile transition due to large strains along the white rock thrust wind river mountains wyoming abstract the deformed foreland of the rocky mountain cordilleras is characterized by major reverse faults that bring precambrian basement rocks to the surface the white rock thrust in the wind river mountains of wyoming is one such fault that developed at fairly shallow levels in the crust detailed study of grain size variations and textures within the fault zone provide a framework for discussion of the mechanics of movement along the fault textural criteria are suggested for distinguishing between dominantly brittle and dominantly ductile deformation a transition from brittle fracturing to ductile deformation is seen with increasing strain and resultant decrease in grain size along the fault zone diffusional creep in the final stages of deformation leads to strain softening and may allow large strains to take place along narrow zones at low deviatoric stresses this may be one way of obtaining large displacements along major faults at shallow levels in the crust

geology and mapping of dark terrain on ganymede and implications for grooved terrain formation geological mapping of regional and high resolution galileo images reveals a variety of units and structures within ganymede s dark terrain we have made a detailed study of areas within galileo marius and nicholson regiones in order to investigate the style of tectonic deformation experienced by dark terrain adjacent to swaths of grooved terrain dark terrain appears to become fractured as a precursor to grooved terrain formation in places dark fractured swaths are recognized which have similar characteristics to brighter grooved terrain swaths tectonic deformation may be but is not always focused through preexisting weaknesses caused by impact craters and furrows a prominent groove lane anshar sulcus is inferred to have formed by the process of hanging wall rollover accompanied by a small amount of right lateral horizontal shear offset resulting from ne sw extension

possible breakup of dark terrain on ganymede by large scale shear faulting a system of arcuate furrows in galileo regio and marius regio two large blocks of ancient dark terrain has previously been proposed to be the remnant of an originally more concentric furrow set that was disrupted by shear estimates of the two regions poles of furrow concentricity indicate a considerable westward offset of the galileo regio pole these measurements suggest the possibility of about 500 km of left lateral offset of the two areas four additional independent structural indicators support this hypothesis there is evidence that shear deformation was concentrated along a major structural lineament which closely follows a small circle about 45 of arc of radius which encloses galileo regio and that a smaller amount of distributed shear occurred across an adjacent 500 to 1500 km wide band there is also morphologic evidence for zones of minor right lateral shear between central and southern marius regio and between barnard and nicholson regio and for a zone of minor left lateral shear in nun sulci stratigraphic relations indicate that any major shear offsets occurred before and during the earliest stages of grooved terrain formation before most grooves had formed and before virtually all light material had been emplaced however regionally dominant groove orientations are generally consistent with orientations expected for transtensional features either shear strain or the shear s driving mechanism may have had a long term effect on patterns of deformation of ganymede s lithosphere

the tectonics of ganymede the surface of ganymede the largest icy jovian satellite is composed of two distinct terrain types showing abundant evidence of global scale tectonics there is geological evidence consistent with the formation of younger bright terrain by the emplacement of relatively clean ice into rift zones developed in the more silicate rich dark terrain

ring geometry on ganymede and callisto abstract arguments have been made based on geometry for both an impact and an internal origin for the ancient partially preserved major furrow system of ganymede zuber and parmentier concluded that furrows are not concentric but could be impact related if multiringed structures on icy satellites are initially noncircular we examine the geometry of the valhalla ring structure on callisto in order to assess the circularity of an unmodified ring system despite prominent local meandering the only gross deviations from concentricity in the valhalla system are found in the outer northeast quadrant of the system here a number of ring segments intersect small circles about the center at angles up to 30 the ganymede furrow system was remapped to make use of improvements in coordinate control the least squares center of curvature determined using natural weighting for all furrows in marius and galileo regio is 20 7 1 1 s 179 2 1 1 w 2 uncertainty furrows in marius and galileo regio are reasonably concentric are much more circular than previously estimated and probably once covered at least an entire hemisphere of ganymede in addition at least three other multiring systems of varying size are identified on ganymede indicative of a projectile population thus we find furrow geometry and occurrence are consistent with an impact origin deviations of some furrows from concentricity about the center of curvature on the scale of those found at valhalla do exist as in the case of valhalla these variations are principally confined to outer regions of the structure and are interpreted as inherent properties of multiringed structures on icy satellites the cause s of this may be in the ring formation mechanism itself but are more likely due to variations in preexisting lithospheric mechanical properties the perceived present nonalignment of the assumed originally concentric furrows has been used to argue for large scale lateral motion of dark terrain blocks in ganymede s crust presumably in association with bright terrain formation the overall alignment of furrows as well as the inherent scatter in centers of curvature for subregions of galileo and marius regio do not support this hypothesis

terrain types and local scale stratigraphy of grooved terrain on ganymede grooved terrain is subdivided on the basis of pervasive morphology into 1 groove lanes elongate parallel groove bands 2 grooved polygons polygonal domains of parallel grooves 3 reticulate terrain polygonal domains of orthogonal grooves and 4 complex grooved terrain polygons with several complexly cross cutting groove sets detailed geologic mapping of select areas employing previously established conventions for determining relative age relations reveals a general three stage sequence of grooved terrain emplacement first dissection of the lithosphere by throughgoing grooves and pervasive deformation of intervening blocks second extensive flooding and continued deformation of the intervening blocks third repeated superposition of groove lanes concentrated at sites of initial throughgoing grooves this sequence is corroborated by crater density measurements dominant orientations of groove sets are parallel to relict zones of weakness that probably were reactivated during grooved terrain formation groove lane morphology and development consistent with that predicted for passive rifts suggests a major role of global expansion in grooved terrain formation

strain variation in thrust sheets across the sevier fold and thrust belt idaho utah wyoming implications for section restoration and wedge taper evolution abstract although strain in fold and thrust belts is typically inhomogeneous on the largest scale strain within thrust sheets shows regular patterns the strain which is a quantitative measure of the deformation of any thrust sheet is independent of the translation of the sheet the internal deformation can be represented by a deformation profile the change in shape during thrusting of a fault perpendicular line which can then be used to unstrain the sheet during restoration in cross section balancing deformation profiles in well studied thrust sheets show regular geometric patterns and compatibility constraints can be used to minimize the data needed to define the profiles in other sheets from the geometry of deformation profiles and direct field observations the most important component of internal deformation of thrust sheets in many fold and thrust belts is early layer parallel shortening lps this can be removed in a straightforward manner during restoration and significantly affects the geometry i e taper of the restored section original basin wedge taper may have important implications for the mechanical evolution of fold and thrust belts thus changes in original basin taper resulting from strain removal may affect significantly the way in which we interpret the evolution of a fold and thrust belt in an area

disappearance of the last tropical glaciers in the western pacific warm pool papua indonesia appears imminent the glaciers near puncak jaya in papua indonesia the highest peak between the himalayas and the andes are the last remaining tropical glaciers in the west pacific warm pool wpwp here we report the recent rapid retreat of the glaciers near puncak jaya by quantifying the loss of ice coverage and reduction of ice thickness over the last 8 y photographs and measurements of a 30 m accumulation stake anchored to bedrock on the summit of one of these glaciers document a rapid pace in the loss of ice cover and a 5 4 fold increase in the thinning rate which was augmented by the strong 2015 2016 el nino at the current rate of ice loss these glaciers will likely disappear within the next decade to further understand the mechanisms driving the observed retreat of these glaciers 2 32 m long ice cores to bedrock recovered in mid 2010 are used to reconstruct the tropical pacific climate variability over approximately the past half century on a quasi interannual timescale the ice core oxygen isotopic ratios show a significant positive linear trend since 1964 ce 0 018 0 008 per year p 0 03 and also suggest that the glaciers retreat is augmented by el nino southern oscillation processes such as convection and warming of the atmosphere and sea surface these papua glaciers provide the only tropical records of ice core derived climate variability for the wpwp

multiple scales of mechanical stratification and decollement fold kinematics sierra madre oriental foreland northeast mexico regional to outcrop scale stratigraphic relationships within mesozoic shallow marine carbonates and clastics at sierra del fraile anticlinorium in northeast mexico play an important role in controlling the deformation distribution strain history and kinematics during folding structural analyses of meso and microscopic deformation features from all stratigraphic and structural positions within the anticlinorium allow for the delineation of five regional scale lithotectonic units kilometer to decameter scale stacking patterns of the preorogenic succession and the meter scale stacking patterns of individual shallowing upward carbonate cycles are shown to influence deformation kinematics in predictable ways mesoscopic faults and cleavage patterns along with penetrative strain from anisotropy of magnetic susceptibility ams fabrics constrain fold kinematics as progressive limb rotation about pinned anticlinal and synclinal hinges with constant limb length and a mobile basal decollement horizon within the evaporites of the minas viejas formation that core the anticlinorium ams fabrics are shown to be a useful proxy for nascent penetrative strain orientations in sedimentary rocks macroscopic differences in strain suggest strong lithologic facies control responding to differences in bed thickness grain size and carbonate content at the regional scale variation in deformation between the lithotectonic units identifies decollement horizons coincident with lithotectonic boundaries in the minas viejas upper taraises and parras formations

history of the sevier orogenic wedge in terms of critical taper models northeast utah and southwest wyoming problems with applying critical taper models to ancient orogenic wedges are overcome in the late cretaceous late paleocene sevier orogenic wedge in utah and wyoming by a symptomatic approach in which wedge behavior is inferred from the time space distribution of thrust faulting erosion and synorogenic sediment accumulation in association with the orogenic wedge in turn the causes of wedge behavior are interpreted in terms of features that are known about the sevier wedge such as the locations of major decollements and the lithologic constituents of major thrust sheets from coniacian through late paleocene time 35 m y basement and cover rocks in the sevier wedge were shortened by 100 km in three major and one minor events an overall eastward progression of thrusting was punctuated by several episodes of out of sequence and hinterland vergent thrusting over the long term wedge taper was controlled by internal wedge strength initial taper and changes in the durability of the upper surface of the wedge and its internal lithostratigraphy critical taper was maintained by the offsetting effects of basement duplexing in the rear of the wedge and forward imbrication at the front of the wedge while the basal decollement was mainly in basement rocks the wedge was highly tapered and thrust spacing was relatively close 15 km beginning ca 75 ma the basal decollement ramped upward and eastward into weak cambrian shale and jurassic salt thrust spacing increased to 25 45 km and wedge taper decreased drastically the highly tapered rear part of the wedge carried strong basement rocks above moderately weak mylonitic and cataclastic decollements whereas the frontal lower taper part of the wedge carried sedimentary rocks above extremely weak salt and shale decollements through time internal strength of the wedge decreased as it incorporated an increasing proportion of sedimentary rocks the thrust belt was able to advance eastward in spite of its decreasing internal strength and decreasing taper because the basal decollement of the wedge also became weaker through time both by strain softening beneath the rear of the wedge and by propagating along extremely weak rocks beneath the front of the wedge provenance data from associated synorogenic conglomerates indicate that the durability of the upper surface of the wedge probably increased over the long term history of the sevier wedge as an increasing proportion of the erosional surface became occupied by resistant precambrian quartzite and basement rocks this would have had the effect of decreasing the rate of erosion through time and maintaining a steeper surface slope which would have helped the wedge to remain at critical to supercritical taper the sevier wedge also exhibits several shorter term 10 km and 3 was subjected to regional erosion marked by major unconformities that ultimately caught up with tectonic thickening and caused the wedge to stall this cyclicity is attributed to the need for wedges to become supercritical before they can propagate forward over large distances and a lag time between wedge thickening and uplift and wedge erosion erosion eventually catches up to the rate of uplift the wedge stalls and the locus of deformation shifts to the rear of the wedge in order to rebuild taper this analysis suggests that orogenic wedges continually deform and find a way to maintain taper sufficient to allow forward propagation as long as a sufficient push from the rear exists the actual taper value may change substantially through time as lithostratigraphy internal strength upper surface durability and presence absence of weak potential stress guides conspire to maintain a critical taper

the mechanical paradox of large overthrusts the mechanical paradox of large overthrusts originates with a fallacious assumption in the conceptual model upon which mechanical analyses of overthrust faulting have been based the notion that the maximum width of a sheet of rock that may be displaced along an overthrust fault can be determined by using the mohr coulomb failure criterion to compare the strength of the rocks with the stress required to overcome the total frictional resistance to slip and the total cohesion or adhesion over the entire fault surface tacitly assumes that slip is initiated and occurs simultaneously over the entire fault surface this unstated and untenable assumption which is incompatible with what is known about real faults is the real explanation for the mechanical paradox a realistic model for overthrust faulting must be compatible with the nature of real overthrust faults and particularly with the way in which displacements including earthquake displacements occur on real faults most large overthrusts are discrete shear surfaces within a coherent mass of rock that is physically continuous around their ends total displacement clearly varies from place to place over these discrete shear surfaces and moreover must be the cumulative result of many relatively small incremental displacements that also varied from place to place over the finite part of the fault surface on which they occurred each increment began as a local shear failure and propagated along the fault as a smeared out somigliana dislocation at a velocity that was small considering the time required for propagation over the total area of the fault during any individual displacement event whether a megathrust earthquake or a creep event only a small part of the fault surface was in relative motion at any one time fault displacements may appear to occur simultaneously across laboratory specimens that are very small relative to the velocity of propagation of displacement because the transit time is so short when the linear scale is expanded over six orders of magnitude to encompass an entire surface of a large overthrust fault however the transit time is much longer because the velocity of propagation is very small relative to the area of the fault surface and the displacement clearly involves only a very small part of the fault surface at any one time the shape and size of overthrust faults result from the propagation of dislocations and this process is controlled by the strength heterogeneity and anisotropy of the rock mass as well as by variations in the regional stress field but not by the frictional resistance to sliding integrated over the entire fault surface

morphological mapping of ganymede investigating the role of strike slip tectonics in the evolution of terrain types abstract the heavily fractured surface of ganymede displays many morphologically distinctive regions of inferred distributed shear and strike slip faulting that may be important to the structural development of its surface to better understand the role of strike slip tectonism in shaping this complex icy surface we perform detailed mapping at nine sites using galileo and voyager imagery noting key examples of strike slip morphologies where present these four morphological indicators are en echelon structures strike slip duplexes laterally offset pre existing features and possible strained craters we map sites of both light grooved terrain nun sulci dardanus sulcus tiamat sulcus uruk sulcus and arbela sulcus and terrains that are transitional from dark to light terrains nippur and philus sulci byblus sulcus anshar sulcus and the transitional terrain of northern marius regio at least one if not more of the four strike slip morphological indicators are observed at every site suggesting strike slip tectonism is indeed important to ganymede s evolutionary history byblus sulcus is the only mapped site where the presence of strike slip indicators is limited to only a few en echelon structures every other mapped site displays examples of at least two types with arbela sulcus containing candidate examples of all four in addition quantification of morphological characteristics suggests related rotation between sites as evidenced by the predominant nw se trend of mapped features within the light terrain present in five different sites nun tiamat uruk nippur philus byblus and anshar sulcus moreover incorporation of strike slip tectonism with pre existing observations of extensional behavior provides an improved synoptic representation of ganymede s tectonic history

lithospheric stresses due to radiogenic heating of an ice silicate planetary body implications for ganymede s tectonic evolution thermal evolution models of differentiated and undifferentiated ice silicate bodies containing longlived radiogenic heat sources are examined lithospheric stresses arise due to volume change of the interior and temperature change in the lithosphere for an undifferentiated body the surface stress peaks early in the evolution while in the differentiated case stresses peak later and continue to accumulate for longer periods of time the variation of near surface stress with depth shows that stresses for the undifferentiated body initially penetrate to great depths but rapidly concentrate within a few kilometers of the surface for the differentiated body elastic stresses never accumulate at a depth greater than a few kilometers these models are applied to consider long term radioactive heating as a possible mechanism of tectonic activity and bright terrain formation on ganymede

the age and timing of folding in the central appalachians from paleomagnetic results comparison of the paleomagnetic pole positions of late paleozoic secondary magnetizations with a time averaged reference apparent polar wander path for north america shows that sedimentary rocks within the central appalachians were remagnetized in the later half of the permian between ca 255 and 275 ma ages of remagnetization do not vary for sites distributed along or across strike of the central appalachian fold and thrust belt or across the appalachian plateau in new york nor do they vary with stratigraphic position of the host rocks however the pattern of folding relative to remagnetization across the valley and ridge and great valley in pennsylvania maryland and west virginia shows a distinct temporal variation individual fold tests yield postfolding magnetizations near the hinterland margin of the fold and thrust belt synfolding magnetizations in the central part of the belt and prefolding magnetizations near the foreland because of the similar age of the late paleozoic magnetization we conclude that rocks across the central appalachians were remagnetized in a relatively short period of time as folding and thrusting propagated more slowly toward the foreland we interpret this pattern to indicate that older folds near the hinterland grew prior to remagnetization folds in the central region grew during remagnetization and folds near the foreland grew after remagnetization rapid remagnetization relative to folding is also evident from the physical characteristics and magnetic properties of secondary hematite in remagnetized synfolding folds in such folds rocks were apparently remagnetized during an increment of fold growth in which there was partial and possibly negligible fold limb rotation collectively these results may constrain the mechanism for basinal fluid mobilization during deformation current models for remagnetization involve the migration of chemically active brines into the foreland during tectonism if realistic our results bear on this model by suggesting that brine migration was not directly related to the successive emplacement of individual thrust sheets as has been suggested for other fold and thrust belts

ramifications of four dimensional progressive deformation in contractional mountain belts abstract studies of progressive deformation aim to identify and establish temporal sequences of structural stages each characterized by a suite of structures which form under specific rock and environmental conditions because of the natural spatial variation in rock type and environmental parameters in an orogen several structural stages may operate concurrently in different parts of an orogenic wedge at any given instant in time rocks experiencing different stages of deformation are bounded by deformation fronts as intrinsic and extrinsic conditions of deformation vary through time spatial migration of deformation fronts causes rocks to record temporal overprinting of structural stages in convergent orogens deformation fronts as mapped in their finite state are typically forelandward dipping due to the regional orogenic wedge geometry and thermal structure depending on the competing deformation processes deformation rate changes on either side of the front may cause deformation fronts to change orientation relief and surface area with time differences in migration rates of different deformation fronts could cause rearrangement of the sequence of structural stages with depth and laterally across the same mountain belt

strain hardening and strain softening in fault zones from foreland thrusts the movement of thrust sheets is accomplished in part by deforming the rocks adjacent to thrust faults in foreland fold and thrust belts emplacement generates an array of mesoscopic faults in a thick layer along the base of a sheet ductile deformation of rocks in the layer occurs by displacing fault bounded blocks relative to one another in a kind of mesoscopic grain boundary sliding analyses of data from three southern appalachian thrust sheets indicate that this block sliding is first accompanied by strain hardening then by strain softening and it is accommodated by intra block fractures small faults and veins the density of accommodation features increases near thrusts and where these features become sufficiently numerous a layer of cataclastic rocks forms along the thrust we describe foliated cataclasites from two thrusts the microstructures of which indicate that the cataclasites exhibited extreme ductility interrupted occasionally by brittle processes deformation of the cataclasites was accompanied by strain softening strain softening deformation in fault arrays near thrusts is genetically related to strain softening deformation in cataclasites during the formation of the cataclasite rocks in the sheet are impelled to cross a strain energy hump after which they deform at either higher rates or lower stresses

multiply deformed terrains problems of correlation abstract the best tools available for carrying out a structural analysis in a complex area are overprinting style and patterns of orientation unfortunately all have limitations which are reviewed briefly and discussed in areas of continuous unfaulted outcrop the deformational history can be established purely on the basis of overprinting but even in such areas there can be problems since not all overprinting relationships are unambiguous most fold interference patterns are reliable overprinting relationships based on foliations however are commonly unreliable and various examples are cited and discussed even in areas where the sequence of deformational events can be established their temporal significance is unclear since the methods applied only determine local relative timing and absolute relationships must vary in space and time across an orogen

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

hydrothermal alteration in anthracite from eastern pennsylvania implications for mechanisms of anthracite formation orthogonal joint sets cleat in anthracite rank coal beds from eastern pennsylvania contain two mineralogically and chemically different authigenic clay mineral assemblages in localities from all four anthracite fields the systematic cleat contains significant quantities 20 to 95 wt of authigenic rectorite sudoite or tosudite which are clay minerals primarily associated with hydrothermal veins and ore deposits the strike of systematic cleat in this region roughly parallels the inferred direction of lateral compressive stress during the alleghany orogeny the opposing nonsystematic cleat contains mostly authigenic nh 4 illite a clay that also occurs in the coal matrix all of these authigenic clay minerals formed during anthracitization t 200 c by replacement of kaolinite and quartz both of which formed during an earlier stage of coalification and are present in the joints and matrix of nearly all coal samples these distinct mineralogical structural relations are observed throughout the anthracite region and suggest that 1 mineralogical variations in the coal joints are related primarily to permeability variations that were controlled by the orientation of alleghanian stress fields 2 hydrothermal fluids passed through the systematic cleat during anthracitization and 3 hydrothermal alteration influenced diagenesis in this region hydrothermal alteration may be related to basin wide fluid migrations that were driven by alleghanian age uplift basinal fluid flow concentrated along permeable joints and detachment zones could have efficiently transported heat from depth and thereby increased the rate of coalification and decreased the postulated minimum depths at which anthracitization occurred perhaps 5km vs 6 10 km

brine volcanism and the interior structures of asteroids and icy satellites abstract cryovolcanism is among the foremost processes responsible for modifying the surfaces of icy satellites volcanic brine petrogenesis in ammonia deficient satellites should mainly involve eutectic melting in relevant salt water systems carbonaceous chondrites provide useful insights into the compositions of salts and aqueously altered rock in icy satellites and asteroids c1 chondrites contain about one fifth by mass of salts in various states of hydration many aspects of the petrogenesis and physical volcanology of icy satellite brines should be well described in the system h2o mgso4 na2so4 minor components include sulfates of k ni mn and ca chondrites also contain abundant carbonates but these are probably not very important in brine magmatism due to their low solubilities under expected conditions chlorides are also unimportant under most circumstances because of the low cosmic abundance ratio of cl s soluble salts may have profound effects on the geology and structure of icy satellites and asteroids in some models late episodes of water volcanism are facilitated by high buoyant forces due to the relatively high densities of sulfate rich mantle and crustal layers in other models early hypersaline brine volcanism quickly yields to plutonic magmatism due to low crustal densities europa probably has a layered crust composed of anhydrous mg na sulfates near the base and a frozen or partially molten eutectic mixture of ice and hydrated mg and na sulfates near the surface ganymede may have a crust about 300 km thick composed of a 10 1 ratio of ice mirabilite and a mantle 500 km thick composed of 50 ice phases plus 50 hydrated mg and na sulfates

migration of deformation fronts during progressive deformation evidence from detailed structural studies in the pennsylvania anthracite region u s a abstract detailed study of selected outcrops in the pennsylvania anthracite region has resulted in identification of five at least partly continuous stages of alleghanian progressive deformation these structural stages are in sequence a layer parallel shortening and top to the foreland layer parallel shear b a second episode of layer parallel shortening c flexural slip and flexural flow folding d fold modification and late thrust faulting and e late veining and fracturing at each outcrop an average shortening direction was determined for each observed structural stage the mean regional shortening direction for each structural stage was calculated and maps showing the spatial distribution of the shortening directions for each stage were constructed the mean regional shortening directions for the five structural stages successively rotated 25 30 clockwise during the evolution of the fold and thrust belt shortening directions for structural stages b and c over the region show a systematic clockwise change in orientation from hinterland to foreland indicating that these structural stages of progressive deformation were time transgressive on a regional scale

sequential thrusting model for mountain building constraints from geology and heat flow of taiwan in this study we analyze the thermal evolution of the taiwan fold and thrust belt based on the available geological information a finite element program is used to simulate the complex kinematics of the observed sequential thrusting and the interplay of uplift erosion and sedimentation processes the discrete sequential thrusting model successfully reproduces the observed decrease in heat flow at the deformation front in northern taiwan this reveals that the heat flow drop may be due to the recent stacking of cold thrust sheets at the deformation front this inference is consistent with the high seismicity and dense quaternary fault distribution in western taiwan the model also successfully reproduces the observed high heat flow in the central ranges suggesting that the observed high heat flow may be a result of tectonic unroofing due to active underplating uplift and erosion these conclusions are insensitive to uncertainties in the frictional coefficient on the thrust plane

analysis and interpretation of composite foliations in areas of progressive deformation abstract in areas of progressive deformation where successive structures develop during a relatively continuous deformation within a geologically short time period traditional chronological notations of structural elements e g s 1 s 2 etc can give erroneous impressions of how large rock masses evolve in time and space we demonstrate from field examples that successive structures can develop which a are comparable in morphology and orientation but of different ages b are different in morphology but of comparable age and c show rapid morphological changes over short distances under such conditions correct identification of the relative age of structures is often difficult to impossible we consider the concepts of a composite foliation and of transposition cycles as vehicles to objectively evaluate the significance of different sets of structures in the evolution of larger rock masses we suggest that 1 structural elements be labeled using morphological notation adding numerical subscripts only when independent evidence is available 2 geologists more fully acknowledge and integrate the concept of deformation partitioning into their models and 3 when analyzing areas of multiple deformation more emphasis is placed on the relationship between domains of differing complexity integration of these three perspectives in the analysis will lead to a more realistic basis upon which to model the structural evolution of large rock masses

sequential development of grooved terrain and polygons on ganymede grooves on ganymede have been interpreted as fractures that result from extensional tectonics which accompanied by some type of resurfacing changed relatively low albedo heavily cratered terrain to higher albedo less cratered grooved terrain the formation of grooves involved initial fracturing of cratered terrain resurfacing confined within these fractures and subsequent fracturing of resurfacing material crosscutting and terminating or t structural relationships among grooves groove sets and cratered terrain indicate that grooved terrain developed in three stages the formation of primary grooves marks the initial breakup of cratered terrain secondary grooves generally terminate against primary grooves and complete the breakup of cratered terrain into polygons that are mechanically isolated from adjacent polygons in the final stage 3 polygons of cratered terrain are fractured resurfaced and the resurfacing material is subsequently fractured by a set of closely spaced parallel to subparallel grooves that terminate against the older primary and or secondary grooves in each of these stages the groove forming process occurs in the same sequence fracturing resurfacing and subsequent fracturing of resurfacing material but most of the area of grooved terrain is resurfaced during stage 3 the process may stop during any of the three stages yielding areas of fractured cratered terrain polygons of cratered terrain polygons which have been resurfaced but not subsequently fractured smooth terrain or completely grooved terrain regardless of place or time of development grooved terrain appears to have evolved according to the same sequential order of stages because the development of grooves within each stage created smaller isolated polygons out of larger areas this process has resulted in the break up of the surface of ganymede into progressively smaller and more equidimensional mechanical units

tectonic controls of metamorphic field gradients abstract we investigate the effects of horizontal variations in tectonic factors heat production and rate amount and duration of erosion on the magnitudes and gradients of pressure p temperature t and cooling ages observed in mountain belts horizontal gradients of p t and cooling ages are largely controlled by two dimensionless parameters 1 the horizontal length scale over which erosion erosion rate or erosion duration varies and 2 the peclet number pe which describes the relative rates of advection and diffusion of heat in contrast the magnitudes of observed p and t depend strongly on the degree of thickening and original burial depth as well as pe and since horizontal heat conduction can usually be ignored do not depend strongly on p and t gradients generally increase with decreasing and pe for calculations in which either but not both erosion rate or erosion duration is horizontally constant p and t gradients are moderate in magnitude and increase in the direction of increasing total erosion in contrast calculations with horizontally constant total erosion but varying erosion rate and erosion duration show small temperature and pressure gradients pressures and temperatures can increase in the same or in opposite directions depending on the magnitude of calculations with horizontally varying crustal heat production show small but non zero temperature gradients and negligible pressure gradients these results indicate that knowledge of temperature pressure and cooling age gradients in individual mountain belts can constrain fundamental quantities such as magnitude and horizontal gradient of the exhumation rate and the average shear strain rate occurring during exhumation on the basis of their metamorphic field gradients most mountain belts can be divided into one of three groups the first and largest group shows strongly positive p and t gradients precambrian orogenic areas comprise the second group and have small t gradients

evidence for non plane strain flattening along the moine thrust loch srath nan aisinnin north west scotland we report quartz c axis patterns grain shape fabrics and microstructures for 11 mylonitic quartzites and quartz phyllosilicate schists from a transect across the moine thrust at loch srath nan aisinnin north west scotland in the footwall samples collected more than 42 m normal distance from the thrust surface quartz c axis textures indicate a general flattening strain i e 0 k 1 samples within 19 m normal distance of the thrust are completely recrystallized and exhibit asymmetric c axis patterns recrystallized hanging wall fault rocks exhibit random c axis patterns on the scale of a standard thin section relict footwall grains provide the closest approximation of finite strain they have octahedral shear strains s between 1 10 and 1 47 and exhibit general flattening k values 0 0524 0 659 the long axis of the mean relict grain shape trends parallel to the regional transport direction and plunges gently to the ese in contrast recrystallized footwall grains have a mean grain shape with the longest axis oriented nearly perpendicular to the transport direction furthermore these samples have grain shape k value ranges from 0 157 to 0 295 recrystallized hanging wall grain shapes exhibit the lowest octahedral shear strains s 0 532 0 733 and largest mean k values 0 351 0 961 of this sample set the long axes of the mean recrystallized hanging wall grain shapes are parallel to transport similar to that of relict footwall grains unrecrystallized quartz overgrowths about opaque mineral grains suggest concurrent elongation in all directions within the mylonitic foliation and support the inference of general flattening deformation the mylonitic foliation and penetrative lineation are consistent with a wnw shearing direction however both were folded during later deformation increments recrystallized grains in footwall quartzites suggest a 305 320 azimuth for the shearing direction the best fit axis of the poles to the foliation is 18 145 close to the mean trend plunge of mesoscopic fold hinges at this site 18 151 both suggest a nnw azimuth for the shearing direction thus structural microstructural and fabric indicators suggest a change in the azimuth of the shearing direction from 286 to 331

crater densities and crater ages of different terrain types on ganymede abstract crater densities and size frequency distributions on ganymede were measured for separate areas of dark furrowed and dark smooth terrains reticulate terrain complex grooved terrain and groups of groved polygons and groove lanes having a variety of relative ages these measurements were used first together with results of previous studies to test alternate models of heliocentric and planetocentric crater forming bombardments of ganymede and callisto the spatial distribution of crater production functions on ganymede is consistent with a single impactor population having dominated cratering of that satellite s observed surface in addition relative crater ages of different ganymedean material deposits are better reconciled with the deposits stratigraphic relations if a heliocentric impactor population is assumed these results are consistent with results of previous studies interpreted here to indicate that the spatial distributions of most classes of craters on ganymede and younger craters on callisto are more consistent with heliocentric than with planetocentric bombardment the measurements were then used to infer the sequence and style of surface modification of ganymede bounds on absolute ages depend on the assumption of heliocentric bombardment dark terrain was emplaced during a prolonged period of volcanic resurfacing of older heavily cratered terrain probably at least 10 8 yrs in duration and at least 3 8 4 0 gyr ago furrows generally formed on blanket like deposits of dark material typically hundreds of meters or more in thickness soon after their emplacement furrow formation continued globally throughout the period of dark material deposition next dark terrain was deformed locally by reticulate terrain formation light terrain emplacement subsequently began at least regionally within complex grooved terrain it continued for an extended period perhaps several times 10 8 yrs in grooved lanes grooved polygons andsmooth terrain where a light material layer averaging several hundred meters or more in thickness was emplaced

strain partitioning in the helvetic thrust belt of eastern switzerland from the leading edge to the internal zone abstract the strain and strain partitioning in the helvetic thrust belt are analysed in order to determine their variation across the belt from the external thin skinned portion to the internal thick skinned portion and in order to begin the detailed mechanical analysis of the entire fold and thrust belt coarse grained limestones of jurassic and cretaceous age were chosen for analysis because they can be traced from the external to the internal zones the strain within a bed is partitioned into three components transgranular pressure solution microfaults veins twinning granular and intragranular exclusive of twinning crystal plasticity associated with recrystallization transgranular strain was very important in the early history of the helvetic nappes giving way to twinning at a later stage under tectonic burial twinning strain was early in the infrahelvetic complex giving way to intracrystalline deformation at the later stage of burial the transition from transgranular to intragranular dominated strain occurred at a vitrinite reflectance value of 3 5 significantly below the greenschist grade of metamorphism in a large scale fold at the leading edge of the helvetic nappes transgranular strains were associated with the buckling stage of the fold and twinning occurred during fold tightening in more internal parts of the helvetic nappes twinning strains are also late with regard to transgranular strains but here their pattern corresponds to the regional finite strain pattern in the internal zone the infrahelvetic complex twinning seems to have been an early event and records an initial layer parallel shortening followed by regional internal deformation with intragranular strains