wrinkle ridge assemblages on the terrestrial planets the wrinkle ridge assemblage is a group of associated features that have been observed on the moon mars and mercury members of the wrinkle ridge assemblage are classified as either arches or ridges based on morphology and ridges are subdivided into first second or third order ridges on the basis of dimensions the ridge assemblages described in this study are known to occur in mare basalts on the moon and smooth plains units that may be volcanic in origin on mars and mercury the structures that occur in the continental flood basalts of the columbia plateau in the northwestern united states are morphologically and dimensionally similar to features in the ridge assemblages on the terrestrial planets the anticlinal ridges of the columbia plateau and many first order ridges on the moon mars and mercury are interpreted to be folds with reverse or thrust faulting developed as a result of buckling flexure fracture or buckling as a consequence of reverse or thrust faulting fracture flexure estimates of the unit shortening across first order ridges using simple geometric forms to approximate the ridge morphology are lower than those determined for the anticlines of the columbia plateau where displacements are the results of folding and reverse to thrust faulting evidence of layer parallel extension that often accompanies folds developed by fracture flexure mechanisms i e drape or fault bend folds is not found in the anticlinal ridges of the columbia plateau and has only been observed in one ridge on the moon a kinematic model involving buckling followed by reverse to thrust faulting flexure fracture is favored for the origin of the anticlinal ridges of the columbia plateau and many of the first order ridges on the moon mars and mercury

structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

late quaternary deformation of the toppenish ridge uplift in south central washington mapping of quaternary sedimentary rocks and miocene basalts on toppenish ridge a fold in south central washington reveals a 32 km long zone of nearly 100 surface ruptures the ruptures indicate renewed movement on miocene structures in latest quaternary time the ruptures probably formed in response to regional compressive stress between 500 and 13 000 yr ago these ruptures are interpreted to represent the most recent surface deformation in central washington

syrtis major a low relief volcanic shield viking orbiter images and earth based radar elevation data have been used to document the volcanic geology of syrtis major and to reevaluate its physiographic setting these data indicate that syrtis major is actually a very low relief simple shield with a central caldera complex arcuate segments of concentric grabens at the shield summit define the limits of a 280 km diameter depression that is thought to have been created by foundering of a magma chamber lava flows with well defined scarps are associated with two summit calderas fissures and lava tubes are recognized on the shield flanks the lava flows were deposited on volcanic ridged plains that do not display flow scarps compressional stresses acting on the shield were apparently greatest following the deposition of the ridged plains unit but continued at a somewhat reduced rate after deposition of the younger lavas the extremely low relief shield of the syrtis major as well as other volcanic plains of intermediate age in the eastern hemisphere of mars is in striking contrast to the giant shields of tharsis montes such different types of volcanic landforms may result from changes with times in the composition differentiation history eruption rates and eruption temperatures of surface igneous rocks thus directly reflecting the thermal and chemical evolution of the interior the low relief on the shields may also reflect a substantially thinner crust in these regions relative to tharsis the physiographic evidence and radar elevation data confirm the fact that syrtis major is a planum plateau rather than a planitia low plain as published maps of mars now portray the feature in addition present evidence does not support an earlier suggestion that an impact basin predated volcanism at syrtis major

relations between surface deformation fault geometry seismicity and rupture characteristics during the el asnam algeria earthquake of 10 october 1980 abstract the el asnam earthquake of october 10 1980 ms 7 3 produced surface faulting on a northeast trending thrust fault of 30 km length with displacements of up to 6 5 m though average displacements were about 3 m in addition widespread tensional features were formed some in clear association with folding above the thrust and others in an area beyond the exposure of the thrust at the surface which may be related to buried reverse faults the observed thrust fault is split into southern central and northern segments local and teleseismic data are examined to show that the main shock nucleated at the southwest end of the fault and propagated 12 km northeast where a second rupture of approximately equal moment occurred continuing the faulting a further 12 km northeast along the central segment both ruptures nucleated at about 8 10 km depth displacements were largest on the central segment where they were probably enlarged by aftershocks including one of mb 6 1 three hours after the main shock the northern segment was much shorter than the other two and showed smaller displacement the junctions between fault segments are marked by distinct geomorphological characteristics and a change in strike of the faulting as well as a sudden drop in the observed displacement it appears that the rupture development is influenced by the changes in fault geometry between segments and that such junctions or barriers have persisted through much of the late quaternary

an analysis of morphologic variation in simple lunar craters previous photogeologic classification of lunar craters have differentiated them into various morphologic types in an attempt to identify the physical factors responsible for these morphologic variations this study examined 44 fresh simple lunar craters between 1 1 and 14 km in diameter on the maria photogeologic analysis was performed using apollo stereo panoramic photography while a quantitative analysis of cross sectional shape was done using fourier analysis these analyses showed that the sample could not be split into two distinct types flat and round floored as had been done previously the two crater types at best represent end members of a distribution of morphologies some correlation was found between the degree of relative degradation and floor roundness implying that flat floors are primary and round floors are degradational features no difference was found between the average depth to diameter ratio of flat and round floored craters indicating that the factor of two variation in depth to diameter ratio in this sample of fresh craters is a primary morphologic feature and that minor degradation of fresh craters has no significant effect on average crater depth

venus tectonics an overview of magellan observations the nearly global radar imaging and altimetry measurements of the surface of venus obtained by the magellan spacecraft have revealed that deformational features of a wide variety of styles and spatial scales are nearly ubiquitous on the planet many areas of venus record a superposition of different episodes of deformation and volcanism this deformation is manifested both in areally distributed strain of modest magnitude such as families of graben and wrinkle ridges at a few to a few tens of kilometers spacing in many plains regions as well as in zones of concentrated lithospheric extension and shortening the common coherence of strain patterns over hundreds of kilometers implies that even many local features reflect a crustal response to mantle dynamic processes ridge belts and mountain belts which have characteristic widths and spacings of hundreds of kilometers represent successive degrees of lithospheric shortening and crustal thickening the mountain belts of venus as on earth show widespread evidence for lateral extension both during and following active crustal compression venus displays two principal geometrical variations on lithospheric extension the quasi circular coronae 75 2600 km diameter and broad rises with linear rift zones having dimensions of hundreds to thousands of kilometers both are sites of significant volcanic flux but horizontal displacements may be limited to only a few tens of kilometers few large offset strike slip faults have been observed but limited local horizontal shear is accommodated across many zones of crustal stretching or shortening several large scale tectonic features have extremely steep topographic slopes in excess of 20 30 over a 10 km horizontal scale because of the tendency for such slopes to relax by ductile flow in the middle to lower crust such regions are likely to be tectonically active in general the preserved record of global tectonics of venus does not resemble oceanic plate tectonics on earth wherein large rigid plates are separated by narrow zones of deformation along plate boundaries rather tectonic strain on venus typically involves deformation distributed across broad zones tens to a few hundred kilometers wide separated by comparatively undeformed blocks having dimensions of hundreds of kilometers these characteristics are shared with actively deforming continental regions on earth the styles and scales of tectonic deformation on venus may be consequences of three differences from the earth 1 the absence of a hydrological cycle and significant erosion dictates that multiple episodes of deformation are typically well preserved 2 a high surface temperature and thus a significantly shallower onset of ductile behavior in the middle to lower crust gives rise to a rich spectrum of smaller scale deformational features 3 a strong coupling of mantle convection to the upper mantle portion of the lithosphere probably because venus lacks a mantle low viscosity zone leads to crustal stress fields that are coherent over large distances the lack of a global system of tectonic plates on venus is likely a combined consequence of a generally lesser strength and more limited horizontal mobility of the lithosphere than on earth

orientation relative age and extent of the tharsis plateau ridge system the tharsis ridge system is roughly circumferential to the regional topographic high of northern syria planum and the major tharsis volcanoes however many of the ridges have orientations that deviate from the regional trends normals to vector means of ridge orientations calculated in 10 boxes of latitude and longitude show that the tharsis ridges are not purely circumferential intersections of vector mean orientations plotted as great circles on a stereographic net show that the ridges are not concentric to a single point but to three broad zones these data indicate either that the tharsis ridge system did not form in response to a single regional compressional event with a single stress center or that the majority of the ridge system did form in a single event but with locally controlled deflections in the generally radially oriented stress field superposition relationships and relative ages suggest that the compressional stresses that produced the ridges occurred after the emplacement of the ridged plains volcanic units early in the hesperian period but did not extend beyond the time of emplacement of the syria planum formation units or the basal units of the tharsis montes formation during the latter half of the hesperian period comparison of topographic data with the locations of ridges demonstrates a good correlation between the topographic edge of the tharsis rise and outer extent of ridge occurrence compressional deformation related to tharsis is present out to about 5100 km from the regional topographic center located near northern syria planum the innermost extent cannot be determined because the ridged plains units have been buried by more recent volcanic units although ridge formation appears to have extended farther inward than is presently observed models involving a combination of isostatic stresses and stresses resulting from flexural loading appear to explain best the observed tensional features topography gravity and to a first approximation the locations and orientations of the compressional ridges

post 12 million year clockwise rotation in the central columbia plateau washington the pomona flow 12 m y b p of the columbia river basalt group was sampled for paleomagnetic analysis at 32 sites in the yakima fold belt of the central columbia plateau to assess the pattern of deformation field directions from anticlinal ridges are found to be rotated clockwise relative to sites from synclinal areas two geographic patterns of rotation are present the primary pattern is one in which the greatest amount of rotation occurs in the crest hinge area of the anticlines and decreases into synclines a secondary pattern in which the amount of rotation is consistent within a geometric segment but varies among them is superimposed on the primary pattern the pattern of clockwise rotation is interpreted to be the result of local tectonic rotation occurring along a closely spaced north northwest trending primary shear system and northeast trending secondary shear system the shear system and concurrent rotation are interpreted to have developed during the growth of the yakima folds the relationship between the paleomagnetic data and the geologic structures can be used to constrain tectonic models for the columbia plateau the data reported in this study indicate that clockwise rotation can not be attributed to rigid block or microplate rotation but support models that predict localized dextral shear furthermore it is postulated that this mechanism may contribute to clockwise rotation observed in other parts of the western united states

wrinkle ridges of arcadia planitia mars wrinkle ridges of arcadia planitia were examined to determine their morphology spatial distribution and the amount of crustal shortening and strain they accommodate ridges trend generally northward but their orientation and distribution are strongly controlled by the relief of the underlying knobby material ridges begin or end at inselbergs of older terrain and are associated with buried craters arcadia planitia ridges have an average width of 3425 m and accommodate an average folding shortening of 3 m and a faulting shortening of 55 m mean total shortening is 57 m three east west transects were constructed at 20 25 and 28 n to estimate regional shortening and strain average total shortening across the transects is about 900 m corresponding to a regional compressive strain of 0 06 the total shortening and compression across arcadia planitia are less than in lunae planum faults associated with the arcadia ridges are inferred to have a westward dip compared with an eastward dip for lunae planum ridges the generally levels of compression and symmetric orientation of the ridges suggest a regionally organized stress system differences in the shortening and strain between lunae planum and arcadia planitia may reflect the effects of local lithology or azimuthal variations in the stress field

testing the utility of paleonutrient proxies cd ca and zn ca in benthic foraminifera from thermocline waters 1 reconstruction of oceanic nutrient concentrations in the past provides information about nutrient cycling and physical circulation and the role these processes have played in past climate changes the cd ca and zn ca of benthic foraminifera have been used successfully to reconstruct past deep ocean nutrient concentrations in this study we test the ability of benthic foraminiferal cd ca and zn ca to detect changes in thermocline nutrient concentrations using a set of 31 multicores collected in the florida straits multicore sites span depths of 173 751 m estimated seawater cd concentrations of 0 02 0 42 nmol kg 1 and estimated seawater zn concentrations of 0 3 3 1 nmol kg 1 cd ca in several taxa of benthic foraminifera captures the regional differences and general shape of the nutricline on either side of the florida straits indicating that it is capable of resolving small changes in upper ocean nutrient concentrations in the past we estimate that the upper ocean partition coefficient for calcitic cd ca may be slightly higher than the established value low seawater zn concentrations combined with low partition coefficients and slight laboratory contamination severely complicated the evaluation of benthic foraminiferal zn ca however at least one species c pachyderma incorporates zn with a relatively high partition coefficient 22 minimizing these complications c pachyderma zn ca reflects the regional differences and general shape of the nutricline on either side of the florida straits and demonstrates potential for thermocline paleoceanography

stratigraphy and structural evolution of southern mare serenitatis a reinterpretation based on apollo lunar sounder experiment data the apollo lunar sounder experiment alse detected two subsurface reflecting horizons in southern mare serenitatis these horizons appear to be regolith layers 2 m thick which correlate with major stratigraphic boundaries in southeastern mare serenitatis our analysis differs from previous interpretations and implies that the lower horizon represents the interface between the earliest mare unit unit i 3 8 b y and the modified serenitatis basin material below the upper horizon represents the regolith developed by sustained impact bombardment of the unit i surface prior to the emplacement of the intermediate basalts unit ii 3 5 b y the latest volcanic episode unit iii 3 2 b y resulted in a very thin infilling 400 m deep in the southern portion of the basin and was undetected by alse profiles of the stratigraphic surfaces represented by the alse reflecting horizons are reconstructed for three stages in the basin filling history these reconstructions permit the timing and magnitude of various volcanic and tectonic events within the serenitatis basin to be assessed on the basis of comparison with orientale ring topography the large subsurface arch is interpreted to be the peak ring related topography of the serenitatis basin the thickness of mare basalts across the alse ground track is highly variable basalts are 400 m thick above the peak ring while they reach a maximum thickness of 2 5 km in the depression between the first and second basin rings comparison with orientale topography suggests that a major increase in basalt thickness of 6 km may occur 50 km inside the peak ring this region was unsampled by the alse traverse extensive load induced deformation occurred after the emplacement of unit i 1 2 km thick maximum this loading of the lithosphere resulted in graben formation along the margins of the basin major downwarping and tilting of the unit i surface and production of discrete zones of faulting buckling and subsidence pre mare topography exerted a strong control over the tectonic patterns in the basin topographic highs such as ring structures underwent 400 m of subsidence whereas intraring depressions underwent as much as 1 4 km of downwarping although the lithosphere was tectonically most active between the emplacement of units i and iii it continued to respond to the load of units i and ii after the emplacement of unit iii as evidenced by 600 m of postunit iii structural relief the association of all mare ridges transected by the alse ground track with distinct offsets or depth changes in the subsurface layering indicates that these surface features are tectonic in origin

new early triassic bryozoa trepostomata from spitsbergen with some remarks on the stratigraphy of the investigated horizons new trepostomatous bryozoan species paralioclema winsnesi sp nov paralioclema mariaholmensis sp nov and paralioclema sp cf mariaholmensis are described from the lower triassic succession of spitsbergen the investigated bryozoan faunas are associated with coarse sandstones calcareous siltstones and shelly limestones the bryozoan colonies are mostly well preserved in situ and show limited evidence of transportation some zoarial fragments show bioerosion the conodont species neogondolella elongata ellisonia triassica neospathodus dieneri and neospathodus svalbardensis extracted from the investigated horizons are dienerian smithian in age

crosscutting relations and relative ages of ridges and faults in the tharsis region of mars abstract observations of ridge fault crosscutting relationships on the ridged plains units surrounding the tharsis region of mars have led to the development of a classification scheme involving three distinct types of intersections ridges crosscut by faults are designated type c and account for 81 of the observed intersections ridges terminated at one end by a fault type t as well as those superposed on grabens type s are less numerous interpretation of the morphology of these intersections and the angles of intersection between ridges and faults with radial trends to major topographic features in the tharsis region have led to the following conclusions 1 the major ridge forming events in the tharsis region were roughly coincident with and in some cases possibly prior to the extensional events that produced the faulting of the tempe and mareotis regions the coprates and memnonia regions and the rifting of valles marinrris 2 the compressional events that formed most of the ridges are restricted in time both by the irrelationship to regional extensional events and by the age of the units on which they formed the suggestion that compressional ridges are a result of a single long term viscoelastic response of the lithosphere to loading of the crust is not supported by this study a model involving one or more isostatically compensated uplifts and subsequent relaxation of the crust after the emplacement of the ridged plains volcanic units is favored

the huntzinger flow evidence of surface mixing of the columbia river basalt and its petrogenetic implications variation in chemical composition within flows of the columbia river basalt group crbg is typically small but one flow the huntzinger flow exhibits a large intraflow compositional range the composition varies both vertically and laterally but mass balance calculations for both major minor oxides and trace elements show that the variation can be explained by simple binary mixing between two end members these end member compositions are identical to two saddle mountains basalt flows the basalt of lapwai wilbur creek member and the asotin member primary intraflow features of the huntzinger flow are highly variable which is atypical for most crbg flows in addition to common features such as a scoriaceous flow top an entablature and a colonnade the flow exhibits evidence of invasion into sediments pillow hyaloclastic zones ophimottling and veins ophimottling and veins can be directly related to compositional variations veins occur in zones of mixing between the two end members and ophimottling is confined to zones dominated by the asotin composition the huntzinger flow is dominated by clinopyroxene and plagioclase with lesser amounts of olivine and variable amounts of glass the mineralogies of the two end member compositions are similar to those of the asotin and lapwai flows from the clear water embayment the intermediate compositions of the huntzinger flow contain characteristics of both flows suggesting mixing of the two the compositional variation indicates that mixing increases from the eastern part of the pasco basin where the asotin composition occurs in the center of the flow and is surrounded by lapwai to the western side where there is almost complete mixing of the lapwai and asotin this pattern is analogous to that produced when two flows mix by free turbulent flow from a free jet based upon this analogy a flow emplacement model is proposed in which the basalt of lapwai is initially emplaced in the pasco basin and prior to solidification is invaded by and mixed with the asotin lava this model places several petrogenetic constraints on this interval of the saddle mountains basalt the close spatial and temporal association of the asotin member and basalt of lapwai with yet a third flow the wahluke flow wilbur creek member allows the rate of eruption to be estimated and constrains the rate of magma recharge to a storage chamber the role of crustal contamination can also be evaluated from this model the conditions required for surface mixing suggest that this may not have been a unique occurrence and that other crbg flows may be composite flows resulting from mixing

reconciling channel formation processes with the nature of elevated outflow systems at ophir and aurorae plana mars 1 many hesperian outflow channels head at elevations compatible with aquifer recharge beneath the martian south polar cap and such channels are widely interpreted as the products of this recharge some outflow channels head at greater elevations that are inconsistent with southern recharge including three systems located in aurorae planum and eastern ophir planum these three systems have previously been interpreted as having formed through aqueous outbursts from local aquifers recharged by the meltwaters of ancient upland glaciers to the west however the viability of this interpretation is weakened by the lack of a geomorphic record supportive of past meltwater flow from western uplands inconsistencies between hypothesized processes and the nature of regional topography and mineralogy and the absence of satisfactory analog processes for catastrophic aqueous flow from the subsurface in contrast a volcanic origin for the ophir and aurorae systems appears to be in accord with the basic characteristics of constituent channels and associated landforms the volcanotectonic nature of the valles marineris system and adjacent upland plains and the nature of available analog landforms and processes though numerous uncertainties remain a volcanic interpretation of these outflow systems can more simply account for the existence of component channels the attributes of other elevated outflow systems on mars similarly appear to be most consistent with volcanic origins if the ophir and aurorae systems formed volcanically thermal considerations imply minimum erupted lava volumes of 6 4 103 km3 for allegheny vallis and 6 2 104 km3 for elaver vallis

emplacement and tectonic deformation of smooth plains in the caloris basin mercury abstract messenger s first flyby of mercury provided the first complete view of the caloris basin and its interior smooth plains multispectral imaging shows that the interior plains are spectrally distinct from surrounding terrain with a reflectance about 15 20 higher and a steeper spectral slope than the global average the caloris basin rim massifs and hummocky material in contrast have lower reflectance and a shallower spectral slope than the global average and extend around the entire basin isolated relatively red patches along the margins of caloris each surround irregularly shaped scalloped edged rimless depressions that are interpreted to be volcanic vents some with associated pyroclastic deposits a nearly continuous annulus of smooth plains exterior to the basin displays spectral characteristics that contrast sharply with those of the basin interior smooth plains the exterior smooth plains are lower in reflectance and spectrally similar to the caloris rim massifs and the hummocky materials the rims and floors of larger impact craters in the interior plains expose low reflectance material there is widespread evidence of contractional and extensional tectonic deformation of the caloris interior smooth plains a set of linear radial graben pantheon fossae radiates outward from a zone near the basin center and some of these graben extend to and intersect a set of generally basin concentric graben distributed along the outer margin of the caloris basin floor the average areal extensional strain expressed by the mapped system of graben is 0 08 wrinkle ridges also deform the interior smooth plains and predate both basin radial and basin concentric graben the average areal contractional strain expressed by the mapped wrinkle ridges is 0 07 the density of wrinkle ridges on the western interior smooth plains is less than on the eastern interior plains in contrast to the more even distribution of graben a similar difference is seen between the density of wrinkle ridges on the western and eastern exterior smooth plains with far fewer wrinkle ridges per unit area on the western annular plains superposition relations spectral contrast and the occurrence of volcanic vents and possible pyroclastic deposits all support a volcanic origin for the caloris interior plains crater counts indicate that the caloris exterior plains and hummocky material are younger than the caloris rim and interior plains and are therefore also likely volcanic in origin the contrast in spectral properties between the interior and exterior plains indicates a difference in the composition of the two expanses of volcanic material models for extensional tectonic deformation of the caloris basin interior inferred from the distribution of graben viewed by mariner 10 must be reevaluated to account for the discovery of pantheon fossae

formation and erosion of layered materials geologic and dust cycle history of eastern arabia terra mars 1 eastern arabia terra is mantled in a layer of dust a few centimeters to a meter thick yet contains morphologic features that suggest a history of multiple events of deposition and consolidation of fine grained material and a significant amount of erosion early in martian history this region was affected by volcanic and fluvial activity but has since been dominated by aeolian processes five craters in this region contain interior mound material that ranges in height from 1600 to 2100 m above the crater floor the fluted erosional pattern and the thermal inertia are suggestive of a weakly indurated material and the extensive layering implies that these mounds were formed by a repeated process or processes although these materials primarily occur within craters there are materials outside craters that have similar erosional features and fine laminations suggesting a more extensive deposit the most likely process to form this material is the deposition and cementation of air fall dust and is potentially related to martian obliquity changes the significant amount of erosion of the intracrater mounds unit indicates a dramatic change from a depositional environment to an erosional regime over the past 106 108 years currently dust is accumulating in this region in years with planet encircling dust events but global circulation model results indicate that dust devils may be removing slight amounts of dust from arabia terra these observations suggest that the thickness of the dust mantle may not be currently increasing and may instead be in equilibrium

origin of planetary wrinkle ridges based on the study of terrestrial analogs wrinkle ridges linear asymmetric topographic highs are common physiographic features on the moon mars and mercury we describe here some terrestrial features of similar morphology and scale that have formed under compressional stress systems similar to planetary wrinkle ridges all of the terrestrial analogs are produced by the anticlinal folding of rocks above reverse faults that shallow and typically break the surface characteristics common to both terrestrial and planetary ridges include 1 a linear asymmetric antiformal shape 2 tension cracks and grabens along the hinges of the antiform 3 overlapping en echelon lobes 4 reversals of the sense of asymmetry along strike 5 occurrence in compressional environments and 6 similarity to features produced during compression of various materials in laboratory scale models these similarities strongly suggest that planetary wrinkle ridges result from deformation associated with shallow thrust faults that either break or come close to the surface kinematic models capable of explaining the development of wrinkle ridges include 1 anticlinal folding of rocks over a buried thrust fault that may subsequently propagate to the surface and 2 fault bend folding of upper plate rocks over the surface flattening bend of a thrust fault

major episodes of geologic history of isidis planitia on mars abstract we have mapped the area of isidis planitia 1 27 n 75 103 e in order to assess the geologic history of this region using modern data sets such as mola topography and the high resolution images provided by the hrsc ctx and hirise cameras results of our mapping show that the geologic history of isidis planitia consists of three principal episodes 1 impact dominated episode noachian until 3 8 ga during this time the oldest materials in the study area were formed mostly by impact reworking and mass wasting other processes e g volcanism and fluvial glacial activity likely operated at this time but played a subordinate role 2 an episode related to volcanic and fluvial glacial activities late noachian early amazonian 3 8 2 8 ga volcanism appears as the most important process at the beginning of this episode 3 8 3 5 ga and was responsible for the formation of a large circum isidis volcanic province by the early hesperian epoch volcanic materials covered large portions of the isidis rim almost completely buried the previous crater record on the floor of the isidis basin and probably were the major contributors to the filling of the basin fluvial glacial processes prevailed closer to the end of the episode early hesperian early amazonian 3 5 2 8 ga and were responsible for widespread resurfacing in the isidis planitia region mostly at 3 1 3 4 ga glaciers and or ice sheets probably resulted in a massive glaciation of the rim and the floor of the isidis basin the total volume of material eroded from the isidis rim by glacial and fluvial activity is estimated to be about 35 000 50 000 km 3 which is equivalent to a composite layer about 40 60 m thick on entire floor of the basin more important however is that the eroded materials were likely saturated with ice water and could form wet deposits on the floor 3 wind dominated episode since early amazonian 2 8 ga wind activity dominated the later geologic history of isidis planitia but resulted only in minor modification of the surface

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

the saddle mountains the evolution of an anticline in the yakima fold belt the saddle mountains uplift is an asymmetrical north vergent anticline with a length of about 110 km it varies from an open to tight fold and is divided into six segments based upon differences in geometry flows of the columbia river basalt group intercalated sedimentary deposits of the ellensburg formation and suprabasalt sediments thin over the uplift and thicken into the synclines variations in thickness are used to determine the timing of deformation and age of major and minor structures the close correlation of growth rate of the folds with rate of magma supply of the columbia river basalt group suggests that the yakima fold belt resulted from the same tectonic processes that produced eruption of the columbia river basalt modified journal abstract

orientation and origin of ridges in the lunae palus coprates region of mars numerous wrinkle ridges similar in appearance to lunar mare ridges occur on volcanic plains units surrounding the tharsis region of mars where they are oriented circumferential to the center of the plateau by analogy with lunar mare ridges and from morphologic evidence such as the smooth slopes of arches these features are interpreted to result primarily from compressional folding of the volcanic plains although the uppermost ridge may represent faulting of the near surface materials east of the tharsis region ridges are best developed in the lunae palus and coprates quadrangles where they can be used to indicate the degree of compressional stress occurring there comparison of ridge orientations in these quadrangles to a tharsis center at 1 n 122 w indicates that more than 60 of the total length of ridges is orthogonal to a normal from this center non orthogonal ridges are seen to have general northerly orientations after removal of the tharsis orthogonal population trends of graben in surrounding terrain indicate that non orthogonal ridges are not greatly affected by regional scale structures comparison of the frequency of orthogonal and non orthogonal ridges further suggests that loading due to the tharsis plateau was effective in producing compressional features as far as 4000 km from the center of the load additional sources for compressional stress are necessary to account for ridge systems at greater distances from the tharsis plateau