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

pumpellyites and coexisting minerals in different low grade metamorphic facies of liguria italy pumpellyite from four phase assemblages pumpellyite epidote prehnite chlorite pumpellyite epidote actinolite chlorite pumpellyite epidote na amphibole chlorite together with common excess phases considered to be low variance in a cao mgo feo al2o3 fe2o3 na2o sio2 h2o system have been examined in areas which underwent metamorphism in the prehnite pumpellyite pumpellyite actinolite and low temperature blueschist facies respectively the analysed mineral assemblages are compared for nearly constant basaltic chemical composition at varying metamorphic grade and for varying chemical composition basic intermediate acidic at constant metamorphic conditions low temperature blueschist facies in the studied mineral assemblages coexisting phases approached near chemical equilibrium at constant basaltic bulk rock composition the mgo content of pumpellyite increases and the xfe3 of both pumpellyite and epidote decreases with increasing metamorphic grade the fe3 being preferentially concentrated in epidote both pumpellyite and epidote compositions vary with the bulk rock composition at isofacial conditions pumpellyite becomes progressively enriched in fe and depleted in mg from basic to intermediate and acidic bulk rock compositions the compositional comparison of pumpellyites from high variance 1 3 phases assemblages in various bulk rock compositions basic intermediate acidic rocks greywackes gabbros shows that the compositional fields of both pumpellyite and epidote are wide and variable broadly overlapping the compositional effects observed at varying metamorphic grade in low variance assemblages the intrinsic stability of both fe and al rich pumpellyites extends across the complete range of the considered metamorphic conditions element partitioning between coexisting phases is the main control on the mineral composition at different p t conditions

cold climate modification of martian landscapes a case study of a spatulate debris landform in the hellas montes region mars 1 we use spaceborne image and topographic data of mars for a geomorphological study of the origin development and postemplacement modification of a 30 km long spatulate landform in the hellas montes area east of hellas planitia the area is characterized by an abundance of lobate debris aprons all of which have been interpreted as a result of creep and viscous deformation of rock and ice mixtures that make the eastern hellas planitia assemblages a type location for possible martian rock glaciers the spatulate landform has been discussed controversially in the past explanations range from a rock glacier to a wet debris avalanche or debris flow origin this work scrutinizes arguments provided in earlier works and presents evidence that a landslide origin of the spatulate landform connected with a sector collapse of a volcanic construct is conceivable we also find extensive observational evidence that the landslide has recently undergone or is still undergoing significant postemplacement modifications which are characteristic of rock glaciers in periglacial environments creep deformation as well as disintegration of the original surface by thermokarstic degradation is considered to have obliterated impact craters and in consequence create a seemingly younger age similar processes are considered to be common on mars under current climatic conditions our results imply that the strong and possible long term modification of landforms on mars by cold climate processes often hinders the identification of their original nature and complicates the assessment of true ages

watershed modeling in the tyrrhena terra region of mars 1 watershed analyses from high resolution image viking mars orbiter camera and thermal emission imaging system and topographic mars orbiter laser altimeter mola data are used to qualitatively and quantitatively characterize highland fluvial systems and analyze the role of water in the evolution of tyrrhena terra 13 s 30 s 265 w 280 w mars in this study geographical information system software is used in conjunction with mola digital elevation models to delineate drainage basin divides extract valley networks and derive basin and network morphometric parameters e g drainage density stream order bifurcation ratio and relief morphometry useful in characterizing the geologic and climatic conditions of watershed formation as well as for evaluating basin maturity and processes of watershed development model predicted valley networks and watershed boundaries which are dependent on the degree to which pixel sinks are filled in the topographic data set and a channelization threshold are evaluated against image and topographic data slope maps and detailed maps of valley segments from photogeologic analyses valley morphologies crater valley relationships and impact crater distributions show that valleys in tyrrhena terra are ancient based on geologic properties of the incised materials valley and network morphologies morphometric parameters and the presence of many gullies heading at or near crater rim crests surface runoff derived from rainfall or snowmelt was the dominant erosional process sapping may have only played a secondary role in valley formation in tyrrhena terra furthermore spatial and temporal relationships of dissected highland materials and impact craters suggests widespread but relatively short lived erosion by runoff with most activity in the noachian period

morphologic and topographic analyses of debris aprons in the eastern hellas region mars this paper presents new detailed analyses of small scale morphologic and topographic characteristics of martian debris aprons that support viking based interpretations of debris aprons as ice rich flow features derived from local uplands fifty four debris apron complexes in the eastern hellas region of mars were examined using mars global surveyor data sets including mars orbiter camera images and mars orbiter laser altimeter topographic profiles consistent patterns in a suite of small scale surface textures and geomorphic features observed throughout the population reflect a history of viscous flow and surface degradation through wind ablation and loss of contained ice a wide variety of shapes seen in topographic profile reveal variations in distribution of contained ice and different stages of apron development and degradation the results of this study provide new evidence consistent with multiple models of apron formation including rock glacier debris covered glacier and ice rich landslide models typical eastern hellas debris aprons formed from a series of large scale events emplacing debris that was enriched initially or later by ground ice complemented by small scale mass wasting of multiple styles and postemplacement flow of apron masses

ice and debris in the fretted terrain mars viking moderate and high resolution images along the northern highland margin were studied monoscopically and stereoscopically to contribute to an understanding of the development of fretted terrain results suport the hypothesis that the fretting process involved flow facilitated by interstitial ice the process apparently continued for a long period of time and debris apron formation shaped the fretted terrain in the past as well as the present interstitial ice in debris aprons is most likely derived from ground ice obtained by sapping or scarp collapse debris aprons could have been removed by sublimation if they consisted mostly of ice or by deflation if they consisted mostly of debris to remove the debris wind erosion was either very intense early in martian history or was intermittent perhaps owing to climatic cycles the location of debris aprons in two midlatitudinal belts can be attributed to atmospheric conditions that permit ice to remain in the ground at moderate depth in those latitudes and climatic factors that permit temperatures to be warm enough for ice to flow channels have minimum gradients of 5 8 m km which permits flowing ice to deform by dislocation creep at exceedingly low strain rates alternately ice charged debris may have been buoyed by brines by analogy with the fretted channels ice could have flowed through the outflow channels if the atmospheric pressure was somewhat higher in the past and permitted ice to exist in the equatorial area

evolution of the navua valles region implications for mars paleoclimatic history abstract the navua valles are comprised of a system of channels and valleys on the inner northeastern rim of hellas basin which is a 1500 km long sloping terrain drainage systems and regional geology in this unique setting were not previously mapped in detail we mapped this region using ctx 6 m px as the base map and assessed surface unit ages resulting from our crater counting we found that the timing of the deposit forming episodes in this region during the hesperian and early to middle amazonian largely correlated to active phases of the hadriacus mons volcanic center we found evidence for several episodes of fluvial activity hesperian to the amazonian with declining intensity and transitioning to ice dominated processes the channels in the navua valles region erode into deposits dating from the noachian to early amazonian including the noachian highlands noachian to early amazonian crater ejecta and likely volcanic plains formed from the hesperian to the hesperian amazonian transition channels directly originating from hadriacus mons are younger while precipitation fed channels at larger distance from the volcanic center are older indicating different triggers for fluvial activity crater counting results indicate that almost all channel floors were at least partially resurfaced during the amazonian and that several channel deposits formed during the last 0 5 gyr water pathways likely included surface channels lakes and subsurface flow the navua valles channel system is discontinuous and the number of terminal deposits sink locations is almost as high as the number of channel sources which is unusual for valley networks elsewhere on mars interior channels formed only in the major navua channels they are even more fragmented than their parent channels but occur along their entire length channels and valley systems within the navua valles are potential targets for in situ astrobiological studies as they could have provided potential habitats at least periodically from the late hesperian to the late amazonian

evidence for multiple ice deposits on the northeastern rim of hellas basin mars abstract four prominent fluvial systems dao niger and harmakhis valles and a system of smaller channels between niger and harmakhis valles characterize a wide topographic trough that connects hesperia planum and hellas planitia hesperia hellas trough hht the source depressions of the canyons of dao and harmakhis valles are at the lowermost level about 5 4 km and lower the system of niger vallis is at medium elevation about 3 to 4 km and the small channels occur at the highest topographic levels about 2 5 to 3 2 km all systems are among the youngest features in the region they formed due to the release of subsurface water and apparently have their sources at different topographic levels below or within the layered suite of volcanic deposits in hht two scenarios can explain the subsurface nature of their sources 1 flow of liquid ground water from extensive watershed toward the source areas and accumulation of water there and 2 deposition of ice bearing materials in and around the sources the first scenario requires the existence of extensive confining layers at different topographic levels corresponding to the levels of the floors of the canyons channels because the presence of such confining layers on mars is problematic we consider the first scenario to be less likely we believe that the deposition of ice bearing materials at different levels during the growth of the lava plateau in hht can better explain the key features of the fluvial systems the subsurface nature of the sources and the relatively young age in this scenario the higher topographic position of the ice bearing deposits corresponds to the younger age of deposition the possible accumulations of ice were buried by successive volcanic deposits including lava flows in hht and later were heated from below by magmatic intrusions that caused melting of the icy deposits release of water and formation of the fluvial structures

evidence of liquid water in recent debris avalanche on mars 1 the identification of landforms associated to liquid water on mars is a major goal for the understanding of the geologic and climatic evolution of this planet in the region of reull vallis near hellas basin lobate debris aprons are recent landforms due to the creep of water ice mixed with rocks among these landforms one unusually long debris apron has a tongue shape and gross morphology that indicates a different mechanism of deposition this study demonstrates using topographic data from viking dem and mola mars observer laser altimeter that the geometric parameters of this feature support the presence of liquid water during its flow this landform is therefore comparable in size to the most developed wet debris avalanches on earth its late amazonian age questions the presence of near surface liquid water in the recent geological past of mars

the results of deep geomagnetic soundings in the west carpathians summary the results of geomagnetic soundings in the west carpathians are presented the number of observation sites in this region was approximately 90 the data treatment included the calculation of single station transfer functions and the separation of the fields into external and internal parts on some profiles the interpretation was based on the construction of two dimensional models explaining the observed features the observed distribution of geomagnetic induction vectors is very regular and the axis of the anomaly runs in the contact region between the outer and inner carpathians the thickness of the well conducting rock complex exceeds 10 km the well conducting rocks seem to be the sediments which accumulated in the contact region of the platform the asymmetry in the distribution of induction vector amplitudes on some profiles can be accounted for by asymmetrical geometry which is characteristic of the underthrusting of rocks

comprehensive analysis of glaciated martian crater greg abstract the 66 km diameter martian crater greg east of hellas hosts various distinctive features including dendritic valleys filled with chevron textured masses south wall and lobate tongues a few kilometers long north wall we analyze these features by various quantitative techniques to illuminate martian geologic and climatic history crater retention model ages indicate that greg is at least 1 3 gy old but surface layers of mantles and glacial features are orders of magnitude younger properties of the dendritic valleys combined with climate models suggest that fluvial activity began under a thicker warmer atmosphere soon after the crater s formation the oldest exposed fluvial systems have surface crater retention ages of a few hundred my indicating runoff in recent geologic time much of greg is covered by ice rich mantle deposits for which we infer gradual accumulation and depths of order 30 85 m they mask pre existing landforms the lobate tongues are interpreted as glaciers with mean slope of 10 2 2 3 and average thickness of 33 19 m our calculations and data suggest that these glaciers were originally ice rich and that their surface layers have been depleted by volatile loss the glaciers probably formed when ice rich mantle deposits reached critical thickness and flowed downhill the top 5 10 m of the mantle and glaciers show crater survival times of order a few my to 15 my which remarkably is the time since the last 1 4 episodes of obliquity 45 global climate models affirm that greg lies in one of two non polar areas with extremes of ice deposition during high obliquity epochs this match with observations supports the use of such models in studies of planetary climate change

global and regional ridge patterns on mars abstract over 16 000 wrinkle ridges on mars have been classified mapped and digitized to provide a large computer accessible data base for analyzing regions subjected to possible compressive stresses the survey has revealed major compressive structures that occur well beyond the tharsis dominated hemisphere the large variety of affected geologic terrains indicate stresses not simply localized in the intercrater plains one major area of inferred compression occurs in the southern cratered highlands near longitude 180 w where major ridges and scarps extend over 3000 km the occurrence and orientation of many ridges are locally controlled by ancient impact basins the chryse basin in particular has an important effect on ridges in northern lunae planum the removal of all basin concentric ridges reveals however a complex global pattern although such patterns may yet be controlled by heavily degraded impact basins major regional trends also emerge that appear to require broader scale global stresses most ridges in the western hemisphere are shown to be orthogonal to three centers corresponding to tharsis 1 n 122 w syria 12 s 104 w and chryse 19 n 47 w ridges not included in these three sets are generally more random and highly localized most but by no means all ridges in the eastern hemisphere are controlled by the hellas and isidis basins a simple global grid is not yet identifiable and may not be recognizable owing to the large number of regional patterns

the pieniny klippen belt in the western carpathians of northeastern slovakia structural evidence for transpression abstract the pieniny klippen belt represents a 600 km long but only a few kilometers wide suture zone in the carpathian orogenic belt based on a quantitative analysis along a part of its nw trending segment in northeastern slovakia we present structural data supporting transpression the continuous interaction of strike slip shearing horizontal shortening and vertical lengthening as a major deformation style in its polyphase deformation history dextral transpression is expressed in the map scale and outcrop fault pattern the oblique orientation of fold axes to the faults bounding the klippen belt and extension parallel to the fold axes the transpression related strain field is described and quantified by the analysis of 1 orientation of rotated fold axes displaying an acute angle to the margins of the klippen belt 2 orientation and geometry of paleostress derived from mesoscale fault striae analysis e trend of 3 trajectories and flattening geometry and 3 the deformation history indicated by extension veins non coaxial regime different techniques using fault striae data quantify paleostress and subdivide heterogeneous data sets mathematically into homogeneous subsets the observed deformation history is modelled as a homogeneous transpression deformation the best fitting model requires a nw trending present day orientation external contraction direction e g plate slip vector and predicts 16 fold axes parallel extension and 23 axial plane normal shortening

volcanism on mars more than 15 years of planetary exploration of mars have given insight into the geologic processes that have shaped its surface the newly acquired viking data have shown that volcanism is one of the most important geologic processes operating on mars throughout its history in situ chemical analyses of martian soil by the viking lander spacecraft indicate mafic to ultramafic source rocks this is consistent both with available remote sensing data which indicate the presence of mafic minerals such as pyroxene and olivine and with petrologic modeling based on available geophysical data which suggest that martian lavas are probably iron rich and ultramafic these data strongly suggest that basaltic volcanism is widespread on mars and much of the photogeological data may be studied in this context photogeological analysis of the martian surface has shown two main types of volcanic morphologies the first type is central volcanoes which are volcanic landforms developed by continued and prolonged eruption from a point source vent this category includes 1 shields the classic low profile volcanic mountains of which olympus mons is the most spectacular example 2 domes steep sided constructs such as tharsis tholus that may represent lower rates of eruption than the shields or possibly more silicic lava compositions 3 highland patera radially textured low profile volcanoes that occur in the cratered terrain and are interpreted as ash shields 4 alba patera an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree and 5 various small features such as cinder cones the second major category is volcanic plains which are units recognized by several criteria of which the presence of mare ridges and flow lobes are the most useful volcanic plains are subdivided into four main groups 1 simple flows broad smooth to rolling plains that contain numerous mare type ridges but no flow lobes interpreted as being composed of thick single cooling units 2 complex flows displaying multiple overlapping flow lobes interpreted to be indicative of thin multiple cooling units 3 undifierentiated flows plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers and 4 questionable plains volcanic units heavily modified by other processes erosion tectonism etc so that their origins are uncertain when these categories of volcanic morphologies are combined with relative age data provided by crater statistics a volcanic history for mars can be derived as follows early heavy bombardment of mars was accompanied and followed by small scale fluvial channeling extensive flood volcanism the plateau plains and ash shield volcanism in the cratered terrain shortly after this time less extensive flood volcanism continued to resurface the planet during formation of the northern southern hemisphere dichotomy central volcanism became more prominent with the development of the alba patera center as well as the older shields and domes of the northern hemisphere early tharsis and elysium regions the development of the tharsis and elysium uplifts may have triggered the release of large scale catastrophic floods producing large channels continued uplift and lithospheric thinning concentrated volcanic activity in the tharsis region producing large shield volcanoes and extensive lava plains both central vent and plains volcanism have been active throughout martian history but the volumes of extrusion have gradually decreased with time this is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time gradually turning off the volcanism although many questions remain regarding martian volcanism the viking data have provided a remarkable detailed overview of the probable nature of the volcanic history of mars

degradation of mid latitude craters on mars abstract recent geomorphic remote sensing and atmospheric modeling studies have shown evidence for abundant ground ice deposits in the martian mid latitudes numerous potential water ice rich flow features have been identified in craters in these regions including arcuate ridges gullies and small flow lobes previous studies such as in newton basin have shown that arcuate ridges and gullies are mainly found in small craters 2 30 km in diameter these features are located on both pole facing and equator facing crater walls and their orientations have been found to be dependent on latitude we have conducted surveys of craters 20 km in diameter in two mid latitude regions one in the northern hemisphere in arabia terra and one in the southern hemisphere east of hellas basin in these regions prominent lobes potentially ice rich are commonly found on the walls of craters with diameters between 20 100 km additional water ice rich features such as channels valleys alcoves and debris aprons have also been found in association with crater walls in the eastern hellas study region channels were found to be located primarily on pole facing walls whereas valleys and alcoves were found primarily on equator facing walls in the arabia terra study region these preferences are less distinct in both study regions lobate flows gullies and arcuate ridges were found to have pole facing orientation preferences at latitudes below 45 and equator facing orientation preferences above 45 similar to preferences previously found for gullies and arcuate ridges in smaller craters interrelations between the features suggest they all formed from the mobilization of accumulated ice rich materials the dependencies of orientations on latitude suggest a relationship to differences in total solar insolation along the crater walls differences in slope of the crater wall differences in total solar insolation with respect to wall orientation and variations in topography along the crater rim can explain the variability in morphology of the features studied the formation and evolution of these landforms may best be explained by multiple cycles of deposition of ice rich material during periods of high obliquity and subsequent modification and transport of these materials down crater walls

towards a mechanical model for the formation of the pannonian basin abstract new maps showing crustal and lithospheric thickness variations in the pannonian basin and the surrounding east alpine carpathian and dinaric mountains have been prepared on the basis of recent seismic seismologic and electromagnetic data a map presenting miocene faults of regional significance has been also constructed for the same region by using a wealth of recently available national and or more local studies it is suggested that observed crustal and lithospheric structural contrasts have been controlled primarily by neogene kinematic history of the region kinematic history is characterized by the following main patterns 1 1 indentation by adria and large scale backthrusting in the southern alps 2 2 eastward escape and extension of the eastern alps 3 3 extensional collapse in the pannonian basin area 4 4 formation of broad wrench fault systems along strike in the dinarides and southern carpathians and the western carpathians with dextral and sinistral shear respectively 5 5 compression and accretion of the external thrust and fold belt in the eastern carpathians these kinematic patterns are thought to be interrelated and all are manifestations of the late stage evolution of an overthickened orogenic wedge in order to arrive at a better understanding of the mechanism of extension which formed the pannonian basin deep crustal seismic profiles hydrocarbon exploration reflection lines and borehole data have been analyzed in the little hungarian plain this plain represents the transition zone between the alps and the pannonian lowlands and the results are illustrated by eight interpreted cross sections one result of regional importance is the clear recognition that the transdanubian central range at the southeastern flank of the little hungarian plain is composed of alpine pre senonian thrust sheets this finding marks the end of a century of debate the allochthony of the substrata of the pannonian basin can be now considered proven another result of more general interest is that these cross sections document the mode of lithospheric extension preexisting compressional detachment planes reactivate as low angle normal faults and lead to tectonic unroofing of deeply buried metamorphic terranes characterized by ductile flow along subhorizontal lineation

klippen belt flysch belt and inner western carpathian paleogene basin relations in the northern slovakia by magnetotelluric imaging the paper presents the interpretation of magnetotelluric measurements along the sw ne profile near stara ubov a northern slovakia the profile passes through the outer carpathian flysch belt klippen belt and ends in the inner western carpathians paleogene nw from ru bachy horst structure the interpretation of the older measurements from profile mt4 was utilized and moreover the 3 d geoelectrical model of studied region was constructed the magnetotelluric data interpretations verified the northern inclination of flysch belt structures and their smaller thickness out of klippen belt in direction to the carpathian electrical conductivity zone axis we consider this as a consequence of the flower structure more precisely the southern branch of the suture zone related to mentioned conductivity zone northerly from this zone the thickness of the outer carpathian flysch belt increases and the structures have inclination to the south i e to the subduction zone the contact of flysch belt with klippen belt has a fault character and it is subvertical slightly inclined to the north the southern boundary between klippen belt and inner western carpathians has also fault character and is very steep we detect the continuation of the ru bachy horst to the ne in the basement of inner western carpathian paleogene the structural discordance between this horst and klippen belt direction is a result of younger tectonic processes according to our results the depth distribution of the pre tertiary basement below the inner western carpathian units is non uniform the basement is broken to a number of partial blocks horsts and grabens

late cretaceous deformation of the pieniny klippen belt west carpathians abstract the late cretaceous position and dynamics of the pieniny klippen belt of the west carpathians which lies behind the palaeogene flysch accretionary prism are reconstructed as shown by the reconstruction based on structural sedimentological and palaeomagnetic data the pieniny klippen belt occupied a wnw ese to nw se trending zone during the late cretaceous which acted as an oblique convergent boundary between the ancestral west carpathians and the oceanic lithosphere attached to the north european platform sediments of the pieniny klippen belt were part of both the mountain belt and foredeep at that time known change from pelagic micritic limestone to a flysch sequence is progressively younger seawards in the thrust slice stack forming the pieniny klippen belt the syn sedimentary record includes flysch olistostrome and wildflysch sediments both the nw se thrusting along the ne sw striking faults and dextral strike slip faulting along the wnw ese to nw se striking faults were active in the late cretaceous in the area of the current pieniny klippen belt

from the variscan to the alpine orogeny crustal structure of the bohemian massif and the western carpathians in the light of the sudetes 2003 seismic data summary the variscan orogeny is the major middle to late palaeozoic tectonometamorphic event in central europe and the bohemian massif is the largest exposure of rocks deformed during this orogeny the bohemian massif consists of the saxothuringian barrandian and moldanubian units adjacent to this massif in the southeast the western carpathians form an arc shaped mountain range related to the alpine orogeny during the cretaceous to tertiary the complex crustal scale geological structure of the variscan bohemian massif and the western carpathians and especially their contact were analysed in this study employing the data of the sudetes 2003 international seismic refraction experiment the analysed seismic data were acquired along the 740 km long nw se oriented s04 profile that crossed the bohemian massif and the western carpathians before terminating in the pannonian basin the data were interpreted by 2 d trial and error forward modelling of p waves and additional constraints on crustal structure were provided by gravity modelling the complex velocity structure derived in our analysis included low velocities of 5 85 km s 1 at the contact of the saxothuringian and barrandian units that reflect the presence of low density granites there are distinct lateral variations in deep crustal structure in the transition between the bohemian massif and the western carpathians the abrupt change of the crustal thickness in this transition zone may be associated with the pieniny klippen belt a deep seated boundary between the colliding palaeozoic lithospheric plate to the north and the alcapa microplate to the south in the upper crust of this transition low velocities of 4 km s 1 extend to 6 km and represent the sedimentary fill of the carpathian flysch and foredeep that thins towards the foreland this basin is also expressed as a pronounced gravity low the moho in the carpathians reaches a depth of 32 33 km in contrast in the pannonian basin the moho rises to a depth of 25 km which corresponds to the pannonian gravity high

sedimentology and hydrocarbon habitat of the submarine fan deposits of the central carpathian paleogene basin ne slovakia abstract the central carpathian paleogene basin accommodates a subsiding area of the destructive plate margin the basin history comprises marginal faulting and alluvial fan accumulation e 2 transgressive onlap by shoreface sediments and carbonate platform deposits e 2 glacio eustatic regression induced by cooling terminal eocene event forced regression tectonic subsidence and growth fault accumulation of basin floor and slope fans e 3 decelerating subsidence aggradation and sea level rising during the mud rich deposition o 1 high magnitude drop in sea level mid oligocene event retroarc backstep of depocenters and lowstand accumulation of sand rich fans and suprafans o 2 m 1 subduction related shortening and basin inversion along the northern margins affected by backthrusting and transpressional deformation o 2 m 1 the basin fill sequence has poor toc 0 5 to fair toc

major episodes of the hydrologic history in the region of hesperia planum mars 1 the high resolution stereo color camera hrsc data over hesperia planum and its surroundings reveal important details of geologic episodes and water related processes in this region 1 the noachian fluvial events of hesperia planum depression included accumulation of water and formation of a water ice reservoir there later the reservoir was depleted in several phases reflecting diminishing amounts of water climate changes and or volcanism were important in these volatile releases 2 the massive 0 45 1 5 106 km3 erosion from the hesperia depression before the main lava eruption possibly resulted in thick 0 5 1 5 km deposits in hellas planitia 3 measurements of the flooded craters within hesperia planum provide the estimates of the thickness of lavas there about 250 500 m the final volume of lavas within hesperia planum 0 4 0 7 106 km3 is comparable with the range of some terrestrial igneous provinces such as columbia river basalts 4 extended magmatism possibly triggered formation of the outflow channel in a few locations after the lava emplacement during this episode about 0 04 106 km3 of material about 4 5 8 9 of the volume eroded in the episode of massive erosion were removed the thickness of the composite lava layer exposed on the walls of the outflow channels a few hundreds of meters corresponds well to the thickness estimates made by the measurements of the flooded craters 5 dispersed viscous flows debris aprons flow like deposits reflect the final fluvial events viscous flows from the subsurface sources in the southwestern trough associate with dao niger and harmakhis valles these flows represent the final volatile discharge from the hesperia reservoir that mostly was depleted by the earlier events of massive erosion and formation of the outflow channels viscous surface flows are mostly associated with reull vallis and probably reflect redistribution of volatiles related to the late episodes of evolution of this outflow channel

surface characteristics and degradational history of debris aprons in the tempe terra mareotis fossae region of mars abstract we have documented the surface characteristics and degradational history of a population of 65 lobate debris aprons in the tempe terra mareotis fossae region of mars these aprons were compared to other martian debris aprons to evaluate similarities and differences among different populations which can provide insight into the dominant controls on apron development tempe mareotis debris aprons found at the bases of isolated or clustered massifs escarpments and crater interior walls were studied using viking orbiter mars global surveyor and mars odyssey datasets in a gis database six textures related to degradation of apron surfaces are identified in moc images and they are divided into two groups an upper surface group and a lower surface group degradation occurs within an inferred smooth upper surface mantle of ice and debris producing a sequence of pitted ridge and valley and knobby textures of the upper surface group where upper surface materials have been removed smooth and ridged textures of the lower surface group are exposed degradation to various depths may expose lower surface materials which may consist of the main apron mass remnants of mantling deposits or both a combination of geologic processes may have caused the degradation including ice sublimation ice melt and eolian activity apron surfaces have lower maximum thermal inertias and mean surface temperatures than adjacent plains surfaces which may be explained by the trapping of unconsolidated materials in low lying pits and valleys formed by surface degradation or from the disruption of crusts on degraded portions of apron surfaces one feature observed only on tempe mareotis debris aprons are broad ridges which mimic the shape of massif bases for tens of kilometers we propose these to be constructional features that could have formed during cycles of increased debris production apron morphometric parameters including area volume slope thickness relief and h l were compiled and the results show that tempe mareotis aprons have average surface areas volumes and frontal thicknesses that are 2 3 times smaller than eastern hellas aprons within the tempe mareotis population escarpment related aprons are larger than massif related aprons suggesting that aprons with larger source areas have potentially greater volatile accumulation translating into longer apron travel distances and lower h l values

topographic and morphologic characteristics of reull vallis mars implications for the history of the reull vallis fluvial system 1 the eastern rim region of hellas basin is characterized by the four prominent and quite extensively researched cf crown et al 2005 and references therein outflow channels in this work we focus on the reull vallis on the basis of observations from available data sets we present a hypothesis for the evolution of reull vallis and its complimentary fluvial system we suggest that this system consists of parts that were formed during several phases rather than being a single continuous channel our results show that the fluvial system of reull vallis consists of two main parts and likely had independent formation phases and different sources of water our results also show that the upper portion of the reull vallis was formed by outflow from beneath hesperia planum as proposed already in earlier works but the suggested segments 1 and 2 mest and crown 2001 of the vallis are not directly linked there seems to have been an on surface source for the formation of the segment 2 in the form of a topographic depression that was filled before the subsequent draining and formation of segment 2 our interpretation of the evolution and formation implies a complex history for the reull vallis system

zeolite to prehnite pumpellyite facies metamorphism of the late proterozoic zig zag dal basalt formation eastern north greenland abstract the zig zag dal basalt formation 1300 m maximum thickness of late proterozoic age exposed in eastern north greenland has been variably affected by low temperature metamorphism resulting in the development of calc silicate and mafic phyllosilicate bearing assemblages relatively fresh flows sometimes preserving primary olivine calcic plagioclase augite and pigeonite and showing randomly mixedlayer chlorite smectite are sandwiched between flows showing not only more extensive alteration but also higher temperature assemblages accordingly in these flows the primary igneous phases are replaced with the exception of augite and prehnite and pumpellyite along with rare zeolites are sporadically developed while regular mixed layer chlorite smectite and or true chlorite predominate temperatures have been estimated on the presence absence of various secondary minerals and also using the chlorite geothermometer and are indicative of progressive metamorphism in the range from below 125 c to approximately 200 c i e in the zeolite facies to lowermost prehnite pumpellyite facies range no depth dependent temperature related zonation of secondary mineral phases as seen in other thick altered basalt successions has been identified in the zig zag dal basalts however instead alteration appears to have been influenced by the physical character of the flows themselves including flow thickness degree of vesicularity and the presence or absence of jointing all of which appear to have exerted an influence over access of fluid this relation between flow character and intensity of alteration suggests that fluid flow through the zig zag dal basalts must have been predominantly lateral rather than vertical

low grade metamorphism and geotectonic setting of the macuchi formation western cordillera of ecuador the cretaceous eocene basic to intermediate marine volcanic rocks of the mucuchi formation constitute the western cordillera in northern ecuador their chemical features mostly correspond to those of tholeiitic basalts with some calc alkaline affinities and suggest an oceanic island arc setting the macuchi rocks are affected by low grade non deformative metamorphism characterized by zeolite prehnite pumpellyite and lower greenschist facies assemblages depth zonation is suggested by the downward mineral sequence i laumontite pistacitic epidote pumpellyite prehnite ii pumpellyite prehnite pistacitic epidote iii actinolite biotite pistacitic epidote chlorite this broad zonation and the chemistry of individual minerals point to an interaction between the volcanic rocks and sea water under a moderate to high thermal gradient 75 c km alteration appears to have been dependent primarily on fluid control volume pressure composition temperature and reaction kinetics which together partly overshadow the role of load pressure compositional variations of a mineral species at the scale of a contiguous flow or even at the scale of a thin section show that intensity of alteration was spatially uneven depending on rock permeability and consequently metastable equilibrium commonly exists however a progressive approximation to equilibrium as a result of p t control is shown by the mineralogy a high fo2 of the fluid phase is evident from the mineral chemistry the metamorphism of the macuchi volcanics is similar to the hydrothermal burial type produced during the development of a volcanic arc where lavas and volcanoclastics accumulated in a shallow marine environment however some of its characteristics point to a transition toward systems defined by a higher t p ratio such as those found in ocean floor metamorphism a model is proposed in which the macuchi volcanics are assigned to an oceanic island arc generated contemporaneously with a marginal basin which has opened as the outcome of progressive north south attenuation of the continental crust due to mantle diapirism

origin of periodically spaced wrinkle ridges on the tharsis plateau of mars ridged plains are a major geologic unit on mars and are a predominant unit on the tharsis plateau a region that has undergone uplift extension and extensive shield and flood volcanism these units probably flood volcanic in origin are characterized by landforms classed as wrinkle ridges wrinkle ridges are interpreted to be folds resulting from buckling followed by reverse to thrust faulting flexure fracture a prominent characteristic of many of the wrinkle ridges on mars particularly those in the tharsis ridge system is the periodic nature of their spacing the periodic spacing has been evaluated in six major provinces on the tharsis plateau with regions further divided into domains based largely on variation in ridge orientation the average spacing of the tharsis ridges based on 2934 measurements is 30 km in an effort to account for the periodic nature of the wrinkle ridges the ridged plains material is modeled as both a single member and a multilayer with frictionless contacts that has buckled at a critical wavelength of folding free slip between layers is assumed based on the possible existence of mechanically weak interbeds in the ridged plains sequence separating groups of flows the near surface mechanical structure in the area of ridged plains is approximated by a strong layer or layers overlying a weak megaregolith of finite thickness overlying a strong basement buckling of the ridged plains is assumed to be decoupled from the basement by the weak megaregolith decoupling is enhanced if the megaregolith were water or ice rich at the time of deformation the rheologic behavior of the ridged plains and megaregolith is approximated by a linear elastic and linear viscous material the models are examined for a range in 1 the strength contrast between the ridged plains material and the underlying megaregolith 2 thickness of the ridged plains material 3 thickness of the megaregolith and 4 number of layers the elastic model can explain the observed ridge spacing only if the ridged plains are relatively thick 2400 m with multiple layers n 1 and relatively high contrasts in young s modulus e e0 100 the high e e0 required is possible only if the megaregolith was water rich at the time of deformation over the same range in values of the parameters viscous buckling is much less restricted the viscous model can explain the observed ridge spacing over a wide range in ridged plains thickness 250 m to several kilometers megaregolith thickness number of layers n 1 to 8 and contrasts in viscosity 0 10 in addition viscous buckling is viable if the megaregolith were dry water rich or ice rich at the time of deformation the absence of folds with a cross sectional geometry in the shape of a sinusoid anticline syncline pairs may be the result of initial deformation of the ridged plains material into low amplitude folds in infinitesimal strain followed by plastic yielding in the cores of the anticlines in finite strain initial elastic or viscous buckling coupled with plastic yielding confined to the hinge area followed by the development of reverse to thrust faulting could account for the asymmetric fold geometry of many of the wrinkle ridges

the role of arcuate ridges and gullies in the degradation of craters in the newton basin region of mars abstract a survey of craters in the vicinity of newton basin using high resolution images from mars global surveyor and mars odyssey was conducted to find and analyze examples of gullies and arcuate ridges and assess their implications for impact crater degradation processes in the phaethontis quadrangle mc 24 we identified 225 craters that contain these features of these 188 had gullies on some portion of their walls 118 had arcuate ridges at the bases of the crater walls and 104 contained both features typically on the same crater wall a major result is that the pole facing or equator facing orientation of these features is latitude dependent at latitudes 44 s equator facing orientations for both ridges and gullies are prevalent but at latitudes

crustal anisotropy in the bohemian massif czech republic observations based on central european lithospheric experiment based on refraction celebration 2000 1 we study the azimuthal velocity variation of pg waves in the bohemian massif using data collected during central european lithospheric experiment based on refraction celebration 2000 we analyze travel times of waves generated by 28 shots and recorded by 256 portable and 19 permanent seismic stations deployed on the territory of the czech republic and in adjacent areas we use recording offset ranging from 30 to 190 km with azimuths covering the whole interval of angles the observed travel times are inverted for parameters of a velocity model formed by an isotropic low velocity subsurface layer with a varying depth lying on a homogeneous transversely isotropic half space with a horizontal axis of symmetry the recovered velocity displays a systematic azimuthal variation indicating a regional scale intrinsic or effective anisotropy in the bohemian massif the mean minimum and maximum values of the velocity are vmean 6 03 km s vmin 5 98 km s vmax 6 10 km s respectively indicating an anisotropy of 1 5 2 5 the direction of the maximum propagation velocity is n35 e being approximately perpendicular to the present maximum compression in the earth crust in central europe the observed anisotropy cannot be induced by stress aligned cracks in the crust because the crack models predict azimuthal velocity variations completely inconsistent with the observed one therefore we suggest the crustal anisotropy to be induced by a preferred orientation of rock forming minerals and large scale intrusion fabrics developed during a tectonic evolution of the bohemian massif

titaniferous accessory minerals in very low grade metamorphic rocks keweenaw peninsula michigan usa abstract titanite tio 2 and pseudorutile are associated with primary igneous fe oxide grains in basalt and rhyolite clasts from the keweenaw peninsula michigan usa which were metamorphosed to the prehnite pumpellyite facies pseudorutile occurs with titanite tio 2 in broad lamellae within titaniferous magnetites it also occurs as intergrowths with titanite and fe oxide in embayments within primary oxide grains and in composite fe oxide titanite grains that appear to represent nearly complete replacement of original ti bearing fe oxides thin 111 lamellae in titaniferous magnetite grains contain titanite titanite tio 2 and titanite tio 2 fe oxide tio 2 also occurs by itself in networks of closely spaced small elongated lenses in fe ti oxides concentrations of caalsio 4 f caalsio 4 oh in titanite range from 0 to 30 the large variation in titanite compositions suggests that equilibrium was not achieved except on a very local scale a conclusion also supported by local variations in the assemblages of ti bearing secondary minerals textures and mineral assemblages indicate that ulvospinel lamellae were altered to titanite and or tio 2 polymorphs while ilmenite was altered to pseudorutile and titanite tio 2 the relative proportions of tio 2 and titanite appear to reflect local variations in the composition of the metamorphic fluid phase that may be linked to the degree of interaction with a hydrothermal fluid titanite rich regions may indicate a greater degree of fluid flushing than tio 2 rich regions textures and mineral assemblages cannot distinguish between models in which pseudorutile and a tio 2 polymorph formed during weathering or diagenesis followed by conversion of tio 2 to titanite during metamorphism and models in which pseudorutile formed together with titanite and tio 2 during metamorphism in either case pseudorutile was able to persist through prehnite pumpellyite metamorphism suggesting that it can be a significant ti rich accessory mineral in very low grade metamorphic rocks

martian cratering 10 progress in use of crater counts to interpret geological processes examples from two debris aprons abstract recent controversies about systems of crater count dating have been largely resolved and with continuing refinements crater counts will offer a fundamental geological tool to interpret not only ages but also the nature of geological processes altering the surface of mars as an example of the latter technique we present data on two debris aprons east of hellas the aprons show much shorter survival times of small craters than do the nearby contiguous plains the order of magnitude depths of layers involved in the loss process can be judged from the depths of the affected craters we infer that ice rich layers in the top tens of meters of both aprons have lost crater topography within the last few 10 8 yr probably due to flow or sublimation of ice rich materials mantling by ice rich deposits associated with climate change cycles of obliquity change has probably also affected both the aprons and the plains the crater count tool thus adds chronological and vertical dimensional information to purely morphological studies

hadriaca patera insights into its volcanic history from mars express high resolution stereo camera 1 high resolution stereo camera hrsc images of hadriaca patera mars in combination with mars orbiter camera moc mars orbiter laser altimeter mola and thermal infrared imaging system themis data sets reveal morphologic details about this volcano and enable determination of a chronology of the major geologic events through new cratering age assessments new topographic measurements of the hadriaca edifice were also made from a hrsc based high resolution 125 m digital terrain model dtm and compared to the mola dtm we find evidence for a complex formation and erosional history at hadriaca patera in which volcanic fluvial and aeolian processes were all involved crater counts and associated model ages suggest that hadriaca patera formed from early shield building volcanic likely explosive pyroclastic eruptions at 3 7 3 9 ga with caldera formation no later than 3 5 ga a variety of geologic activity occurred in the caldera and on the northern flank and plains at 3 3 3 5 ga likely including pyroclastic flows that partially filled a large crater nw of the caldera and plains to the ne and differential erosion deposition by aeolian and or fluvial activity there were some resurfacing event s in the caldera and on the eastern flank at 2 4 2 6 ga in which the eastern flank s morphology is indicative of fluvial erosion the most recent dateable geologic activity on hadriaca patera includes caldera resurfacing by some process most likely differential aeolian erosion deposition in the amazonian period as recent as 1 5 ga this is coincident with the resurfacing of the heavily channeled south flank by fluvial erosion unlike the tharsis shields major geologic activity ended at hadriaca patera over a billion years ago

degradation of selected terrestrial and martian impact craters degraded craters on mars record the cumulative effects of the complex interplay between erosion transport and deposition by competing intermittent processes fortunately impact craters are instantaneous landforms common to both the earth and mars that are characterized by similar topography and local lithofacies deconvolving the signatures of individual degradation processes around young craters on earth e g drainage scale and density changing wall slope deflation features allows calibrating degradation signatures around craters on mars and places first order limits on controlling processes and perhaps past climates such comparisons are valid despite differences in vegetation cover and time scales over which activity occurs on the two planets analysis of degradation at meteor crater lonar crater and talemzane crater reveals a terrestrial sequence of advancing degradation by fluvial eolian and mass wasting processes at meteor crater fluvial processes currently dominate primary erosion however combined deflation from the ejecta and both alluvium and colluvium make eolian processes most important in overall ejecta degradation lonar and talemzane reveal that advancing fluvial degradation is characterized by larger drainages and decreasing wall slopes at talemzane interior drainages breach the rim crest and pirate headward regions of exterior drainage basins when comparable degradation signatures resolvable at viking resolutions are used in selected areas on mars important differences from the terrestrial sequence are revealed all morphologies of craters in southern ismenius lacus sil are typically incised by small valleys with low drainage densities display rare alluvial deposits possess walls sloped at the angle of repose and are sometimes partially covered by airfall deposit remnants analogy with the terrestrial craters indicates signatures associated with advancing fluvial degradation should be readily detected on mars together with other differences between degraded craters on the two planets the paucity of fluvial signatures in sil implies that mass wasting and eolian activity predominated degradation of martian craters preserved since the hesperian crater statistics for sil indicate most craters were degraded during geologically brief intervals in the noachian and mid hesperian therefore fluvial signatures preserved in sil imply any runoff since the hesperian was short lived locally debouched and unrelated to rainfall

transition from the zeolite to prehnite pumpellyite facies in the karmutsen metabasites vancouver island british columbia

mafic pyroclastic flows at tyrrhena patera mars constraints from observations and models abstract tyrrhena patera 22 s 104 e mars is a low relief 1800 m maximum relief central vent volcano whose flanks are dissected with broad 5 km wide flat floored channels the easily eroded nature of the shield materials combined with extremely low flank slopes 2 0 suggest that tyrrhena patera is composed of pyroclastic materials these shield deposits are observed to crop out 600 km from the volcano s summit with measured thicknesses of 100 150 m at these distances such dimensions strongly suggest emplacement via pyroclastic flows currently available data indicate that these deposits have a mafic composition application of models derived for terrestrial pyroclastic flow emplacement reveals that aside from environmental parameters atmospheric density gravity if all else is held equal a pyroclastic flow should travel a factor of 3 to 4 times farther on mars than on earth the observed tyrrhena patera deposits extend even farther suggesting that some emplacement mechanism may be enhancing pyroclastic flow runout distances on mars

the circum hellas volcanic province mars assessment of wrinkle ridged plains abstract wrinkle ridged plains common on the terrestrial planets are inferred to form by tectonic deformation of volcanic or sedimentary surfaces if wrinkle ridged plains adjacent to volcanic features originated from volcanic activity associated with the features then the plains should have similar ages to the volcanic features as well as other morphological or compositional indicators of volcanism we test this hypothesis on several regions of wrinkle ridged plains bounding the circum hellas volcanic province chvp we constructed themis daytime ir mosaics spatial resolution 100 m pixel and performed crater counts to determined cratering model formation ages of these regions we found ages of 3 4 3 7 ga for se malea planum 3 6 3 7 ga for w promethei terra 3 5 3 7 ga for hesperia planum and 3 6 3 8 ga for the eastern hellas basin floor all of which are contemporaneous with the formation of the major volcanic edifices 3 6 3 8 ga in the chvp although examination of available moc ctx hirise themis and hrsc data shows few examples of features definitive of a volcanic origin of these wrinkle ridged plains hrsc true color images 50 100 m pixel show that large areas of these plains have a dark blue black color consistent with previous viking and mars express hrsc and omega color spectral studies indicative of basaltic compositions however in some areas this color may be due to aeolian mantles rather than underlying bedrock thus we cannot demonstrate unequivocally that these wrinkle ridged plains are volcanic beyond the synchronicity of their formation ages with those of the chvp volcanoes nevertheless if these wrinkle ridged plains were originally formed by volcanic activity or other processes induced by volcanic activity then the inclusion of these regions brings the size of the chvp to 4 86 106 km 2 comparable in size to the elysium volcanic province thus the chvp may have been a dominant source of volcanism early in martian history

geomorphic evidence for the distribution of ground ice on mars high resolution viking orbiter images show evidence for quasi viscous relaxation of topography the relaxation is believed to be due to creep deformation of ice in near surface materials the global distribution of the inferred ground ice shows a pronounced latitudinal dependence the equatorial regions of mars appear to be ice poor while the heavily cratered terrain poleward of 30 latitude appears to be ice rich the style of creep poleward of 30 varies with latitude possibly due to variations in ice rheology with temperature the distribution suggests that ice at low latitudes which is not in equilibrium with the present atmosphere has been lost via sublimation and diffusion through the regolith thereby causing a net poleward transport of ice over martian history

calc silicate mineralization in active geothermal systems detailed study of the calc silicate mineralogy in the cerro prieto geothermal system was used to demonstrate examples for thermodynamic evaluation of phase relations among minerals of variable composition and to calculate the chemical characteristics of hydrothermal solutions compatible with the observed calc silicate assemblages in general there is a close correlation between calculated and observed fluid compositions calculated fugacities of o 2 at about 320 degrees c in the cerro prieto geothermal system are about five orders of magnitude less than those at the nearby salton sea geothermal system this observation is consistent with the occurrence of fe super 3 rich epidotes and andradite garnets in the latter system and the presence of prehnite at cerro prieto modified journal abstract

styles and timing of volatile driven activity in the eastern hellas region of mars 1 recent analyses of mars global surveyor and mars odyssey data sets provide new insights into the geologic evolution of the eastern hellas region of mars in particular the role of volatiles here we present results of our recent work and integrate these with previous studies by various investigators to provide a synthesis of the history of volatile driven activity of the region we utilize high resolution images from the mars orbiter camera and thermal emission imaging system combined with mars orbiter laser altimeter digital elevation models and profiles to examine fluvial systems that dissect the circum hellas highlands to characterize stages in the development of the dao niger harmakhis and reull valles canyon systems and to evaluate evidence for ancient lakes in hellas planitia the occurrence of valley networks dissected highland crater rims and crater interior deposits such as layered plateaus suggests widespread ancient degradation of the circum hellas highlands canyon development which represents subsequent more localized activity may have included an early fluvial phase followed by the collapse and sapping dominated stages that along with recent wall erosion and floor resurfacing produced the currently observed morphologies the prominent role of collapse and sapping along the east rim of hellas along with the presence of numerous channels extending toward the basin and sequences of finely layered deposits along the basin rim suggests a volatile rich substrate across a broad depositional shelf the east rim of the basin was an accumulation zone for atmospheric volatiles and or the edge of volatile rich deposits associated with the basin floor this evidence combined with topographic data and cratered terrain preservation around the basin is consistent with a lacustrine period or periods in early martian history the style magnitude and spatial extent of volatile driven activity in eastern hellas have varied considerably with time and these variations may represent a transition from a water to an ice dominated surface environment

zeolite to prehnite pumpellyite facies metamorphism in the toa baja drill hole puerto rico secondary mineral assemblages in eocene volcanic and volcaniclastic rocks of the toa baja drill hole progressively change as a function of depth four metamorphic zones are delineated with increasing depth caclinoptilolite heulandite laumontite prehnite purnpellyite zone the deepest belongs to the prehnite pumpellyite facies whereas the three zones at shallower depths 2350 m belong to the zeolite facies ca clinoptilolite and heulandite exhibit continuous solid solution with varying si al 2 9 5 2 and ca ca na k ratios 0 45 0 89 pumpellyites are characterized by extensive variation in the fe fe al mg ratio 0 29 0 74 and extreme fe enrichment in the laumontite zone temperatures estimated from mineral assemblages and fades transitions suggest that the north coast basin puerto rico has been subject to a metamorphic field gradient of 50 to 70 c km

discontinuous drainage systems formed by highland precipitation and ground water outflow in the navua valles and southwest hadriacus mons regions mars abstract the navua valles are systems of paleodrainages located north of dao vallis which empty into hellas planitia the largest impact basin on mars in this study we mapped and characterized the navua valles region s individual drainage systems including drainages along the southwestern flank of hadriacus mons and one valley network from the same source as navua valles but flowing in the opposite direction the major drainage systems share morphological characteristics common to both outflow channels and valley networks the slopes in this region are dissected by two major navua drainage systems here navua a and b and several shorter sub parallel valleys formed on the highest gradient approximately 20 m km 1 15 slopes at the lowest part of hellas basin s rim the two major drainage systems originate in the highlands and empty into the basin our mapping suggests that water in navua valles reached the basin floor in a complicated descent and included several episodes of surface ponding surface runoff infiltration subsurface flow and subsequent outflow the most prominent channel system navua a forms a repetitive sequence of deep incision into bedrock followed by a transition into broad channels in erodible materials and then into unconfined deposits this successive erosion transport deposition sequence continues to repeat along the valley s entire length forming a discontinuous pattern that is consistent with classical fluvial process models the channels cut into volcanic plains likely emplaced from the formation of tyrrhenus and hadriacus montes the dendritic source valleys of navua a originate from the rim of a highland crater while the rest of this subsystem consists of a single discontinuous channel which is consistent with a single water source zone that likely supplied water for all channels downslope these drainages may have formed as discontinuous channels revealing the potential existence of subsurface drainage pathways located within an approximately 1 5 10 5 km 2 area water transported underground emerged in segments that are either isolated or aligned downslope from each other we have identified several causes of discontinuities located the zones of potential ground water discharge and recharge and a site of localized precipitation at the headwaters of navua a

geologic evolution of the east rim of the hellas basin mars abstract geomorphic analyses and crater statistics indicate the distribution of materials on the east rim 27 5 42 5 s 260 275 w of the hellas basin and constrain the timing nature and interactions of geologic processes which have modified the hellas region the discernible geologic history of the area began with the formation of the impact basin and the emplacement of highlands that became heavily cratered during the noachian period the tectonic setting of the region was established at this time and basin structures promoted and influenced subsequent volcanic tectonic and fluvial activity degradation of the highland units by fluvial mass wasting and aeolian processes began in the noachian and continued into the hesperian and amazonian periods sedimentary plains covered low lying regions of the highlands their pitted surfaces in some areas suggest subsidence and the presence of volatiles emplacement of lobate debris aprons shed from highland peaks and possibly facilitated by ice creep occurred in the amazonian period the volcanic history of the east rim of the hellas basin began with the formation of the highland paterae the low dissected shields of hadriaca and tyrrhena paterae formed in the late noachian or early hesperian epochs and are older than or coeval with the ridged plains of hesperia planum volcanic activity continued throughout the hesperian period with the emplacement of the caldera filling materials at hadriaca patera and the lava flows of the flank flow unit of tyrrhena patera outflow channels and related channeled plains of the hesperian and amazonian periods suggest an extensive and complex history of volatile driven erosion and sedimentary deposition dao and harmahkis valles are interpreted to be collapsed regions of the older plains a combination of surface and subsurface flow has removed materials with deposition on the floor of the hellas basin the geologic evolution of the region determined from the observed surface morphology and stratigraphic relationships and refined by crater statistics indicates that a combination of diverse geologic processes acted in the degradation of the hellas basin the effects of volcanism and volatile driven processes were prominent throughout the hesperian and well into the amazonian periods the proposed transition from explosive to effusive volcanism in the hellas region is supported by the relative ages indicated by crater statistics the heat released by volcanism may have resulted in the melting of ground ice and contributed to the development of the channeled plains and outflow channels the presence of wrinkle ridges on units that are inferred to be relatively young from their crater size frequency distributions suggests deformation in the late hesperian or early amazonian epoch

geology of the reull vallis region mars abstract the geology and stratigraphy of the reull vallis region 27 5 47 5 s 245 270 w of the southern highlands of mars are documented through geomorphic analyses and geologic mapping at 1 2 000 000 scale crater size frequency distributions are used to constrain relative ages of geologic units and determine the timing and duration of the various geologic events the origin and evolution of the reull vallis outflow system and the extent to which reull vallis and other fluvial features modified the surrounding highlands are also evaluated rugged highland terrains were formed by repeated impact events and were extensively degraded and embayed by a series of plains highland terrains incised with well developed valley networks record some of the earliest fluvial activity in the region reull vallis originates in hesperia planum and dissects units of various types and ages truncated and bisected wrinkle ridges in hesperia planum indicate that the formation of reull vallis postdates ridge formation the morphology of reull vallis suggests it had a long and complex history including subsurface and surface movement of fluids followed by extensive modification by mass wasting volcanic and sedimentary plains units in the region record evidence of erosion by surface flow possibly related to development of reull vallis features produced by mass wasting such as debris aprons and crater fill material and aeolian processes appear to form the youngest deposits exposed in the region

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

lithospheric structure beneath trans carpathian transect from precambrian platform to pannonian basin celebration 2000 seismic profile cel05 1 in 2000 a consortium of european and north american institutions completed a huge active source seismic experiment focused on central europe the central european lithospheric experiment based on refraction or celebration 2000 this experiment primarily consisted of a network of seismic refraction profiles that extended from the east european craton along and across the trans european suture zone region in poland to the bohemian massif and through the carpathians and eastern alps to the pannonian basin the longest profile cel05 1420 km is the focus of this paper the resulting two dimensional tomographic and ray tracing models show strong variations in crustal and lower lithospheric structure clear crustal thickening from the pannonian basin 24 25 km thick to the trans european suture zone region 50 km together with the configuration of the lower lithospheric reflectors suggests northward subduction of mantle underlying carpathian pannonian plate under the european plate this however conflicts with strong geological evidence for southward subduction and we present three tectonic models that are to not totally mutually exclusive to explain the lithospheric structure of the area 1 northward old subduction of the pannonian lithosphere under the east european craton in the jurassic lower cretaceous 2 a collisional zone containing a crocodile structure where carpatho pannonian upper crust is obducting over the crystalline crust of the east european craton and the carpathian pannonian mantle lithosphere is underthrusting cratonic lower crust and 3 lithosphere thinning due to the effects of neogene extension and heating with the slab associated with young subduction southward in the miocene having been either detached and or rolled back to the east in the last case the northwestward dipping in the lithosphere can be interpreted as being due to isotherms that could represent the lithosphere asthenosphere boundary in the pannonian region

geology and landscape evolution of the hellas region of mars hellas basin on mars has been the site of volcanism tectonism and modification by fluvial mass wasting and eolian processes over its more than 4 b y existence our detailed geologic mapping and related studies have resulted in the following new interpretations the asymmetric distribution of highland massifs and other structures that define the uplifted basin rim suggest a formation of the basin by the impact of a low angle bolide having a trajectory heading s60 e during the late noachian the basin was infilled perhaps by lava flows that were sufficiently thick 1 km to produce wrinkle ridges on the fill material and extensional faulting along the west rim of the basin at about the same time deposits buried northern malea planum which are interpreted to be pyroclastic flows from amphitrites and peneus paterae on the basis of their degraded morphology topography and the application of a previous model for pyroclastic volcanism on mars peneus forms a distinctive caldera structure that indicates eruption of massive volumes of magma whereas amphitrites is a less distinct circular feature surrounded by a broad low dissected shield that suggests generally smaller volume eruptions during the early hesperian a 1 to 2 km thick sequence of primarily fined grained eolian material was deposited on the floor of hellas basin subsequently the deposit was deeply eroded except where armored by crater ejecta and it retreated as much as 200 300 km along its western margin leaving behind pedestal craters and knobby outliers of the deposit local debris flows within the deposit attest to concentrations of groundwater perhaps in part brought in by outflow floods along the east rim of the basin these floods may have deposited 100 200 m of sediment subduing wrinkle ridges in the eastern part of the basin floor during the late hesperian and amazonian eolian mantles were emplaced on the basin rim and floor and surrounding highlands their subsequent erosion resulted in pitted and etched plains and crater fill irregular mesas and pedestal craters local evidence occurs for the possible former presence of ground ice or ice sheets 100 km across however we disagree with a hypothesis that suggests that the entire south rim and much of the floor of hellas have been glaciated orientations of dune fields and yardangs in lower parts of hellas basin follow directions of the strongest winds predicted by a recently published general circulation model gcm transient frost and dust splotches in the region are by contrast related to the gcm prediction for the season in which the images they appear in were taken

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

volcanic geology of tyrrhena patera mars tyrrhena patera is a large low relief volcano located in the southern cratered highlands of mars on a proposed ring fracture of the hellas basin the volcano is composed of four or possibly five principal units the oldest and most areally extensive of which are suggested to be ash on the basis of their morphology and erosional characteristics lava flows are observed in a flank flow unit extending from the central caldera to the southwest and apparently cap the summit region models derived from the study of terrestrial pyroclastic flows have been applied to the deposits at tyrrhena patera and indicate that the distribution and lengths of the observed deposits are consistent with an origin by the emplacement of gravity driven ash flows generated by hydromagmatic or magmatic explosive eruptions the hydromagmatic case requires considerable quantities of water 7 5 1016 kg however at volumetric water flow rates determined by other investigators 105 m3 s and calculated from the regional slopes in the hesperia planum region 106 m3 s the amounts necessary could be supplied relatively rapidly in geologic time tyrrhena patera represents the earliest central vent volcanism identified on mars and may reflect a transition from the flood style eruptions which dominated early martian history a hydromagmatic origin for tyrrhena patera is in agreement with suggested climatic changes on mars and may explain the absence of this style of volcanism in later eras alternatively a magmatic origin for tyrrhena patera implies an evolution in the types of magmas produced on mars from hesperian to amazonian time during which the prominent shields in the tharsis region formed

origin and evolution of valleys on martian volcanoes morphological analyses of six martian volcanoes ceraunius tholus hecates tholus alba patera hadriaca patera apollinaris patera and tyrrhena patera indicate that fluvial processes were the dominant influence in the initiation and subsequent development of many dissecting valleys lava processes and possibly volcanic density flows were also important as valley forming processes fluvial valleys are especially well developed on alba patera ceraunius tholus and hecates tholus these valleys are inset into the surrounding landscape they formed in regions of subdued lava flow morphology contain tributaries and tend to widen slightly in the downstream direction lava channels on alba patera are located on the crest of lava flows and have a discontinuous irregular surface morphology and distributary patterns these channels sometimes narrow toward their termini possible volcanic density flow channels are located on the northern flank of ceraunius tholus valleys dissecting apollinaris patera hadriaca patera and tyrrhena patera appear to have a complex evolution probably a mixed fluvial and lava origin they are inset into a subdued possibly mantled surface lack tributaries and either have fairly constant widths or widen slightly downvalley valleys surrounding the caldera of apollinaris appear to have formed by fluvial and possibly by volcanic density flow processes while those on the apollinaris fan structure may have a mixed lava and fluvial origin valleys on tyrrhena have broad flat floors and theater heads which have been extensively enlarged probably by sapping hadriaca valleys have a trough shaped form like those on the fan structure on apollinaris but are more enlarged and have theater heads fluvial valleys on the martian volcanoes generally followed a two stage evolutionary sequence similar to that of the hawaiian volcano valleys including 1 initial formation by surface runoff and 2 subsequent enlargement by groundwater sapping because basalt is highly permeable valleys on hawaii island formed only in regions where lava flows were mantled by less permeable volcanic ash similarly fluvial valleys on the martian volcanoes particularly those on alba patera formed in regions where lava flow morphology is subdued probably by ash mantling thus the presence or absence of this mantling may explain why fluvial valleys are present on some martian volcanoes but not on others of the same age the formation of fluvial or fluvial modified valleys on the older volcanoes ceraunius hecates tyrrhena apollinaris and hadriaca implies that surface and near surface water activity was widespread during late noachian to early hesperian period of heavy bombardment however the presence of anomalously young fluvial valleys on alba patera indicates that fluvial valley activity did not entirely cease near the end of late heavy bombardment but rather persisted in isolated regions until mid to late amazonian

compositional variations in mafic phyllosilicates from regional low grade metabasites and application of the chlorite geothermometer mafic phyllosilicates in metabasites affected by low grade regional metamorphism from wales and eastern north greenland show variations in their structure and chemistry these variations are related to four mineral zones in these metabasites which are recognized on the presence absence of various key calc silicate minerals and also actinolite zones 1 and 2 equate with the zeolite facies zone 3 with the prehnite pumpellyite facies or prehnite actinolite facies in rocks with appropriate bulk rock composition and zone 4 with the greenschist facies whilst variations in fe fe mg in chlorite correlate closely with fe fe mg ratios in the whole rock other chemical variations are clearly unrelated to whole rock compositions contents of aliv are seen to increase systematically in samples from zone 1 through to zone 4 which relate to an increase in temperature calibration of alteration temperatures calculated using the chlorite geothermometer based on aliv contents developed for meta andesites in the los azufres geothermal system mexico against x values an estimate of the proportion of chlorite to swelling component in the mafic phyllosilicates shows a decrease in the swelling component in passing from zone 1 to zone 4 i e with an increase in temperature calculated temperatures compare favourably with published stability estimates for the various key calc silicates and actinolite these data indicate that the chlorite geothermometer although developed for meta andesites from a hydrothermal system does show a correlation with temperatures estimated from calc silicate assemblages in metabasites affected by low grade metamorphism developed on a regional scale

volcanic geology of hadriaca patera and the eastern hellas region of mars hadriaca patera is a low relief volcano in the southern highlands of mars northeast of the hellas basin layered friable deposits composing the extensive channeled flanks of the volcano surround a well defined summit caldera containing late stage eruptive products the morphologic characteristics of the channels suggest erosion by groundwater sapping and surface runoff the erosional morphology of the volcano the lack of lava flow features and the friable nature of the flank materials indicate that hadriaca patera consists predominantly of pyroclastic deposits gravity driven flow models demonstrate that the distribution of flank materials can be attributed to the emplacement of pyroclastic flows both magmatic and hydromagmatic eruption models are viable for the magmatic case the necessary mass eruption rates 107 108 kg s ejection velocities 400 m s and volatile contents 1 5 3 0 wt h2o are consistent with parameters derived for terrestrial plinian eruptions for the hydromagmatic case the required energy conversion efficiencies are comparable to those of laboratory experiments and the inferred permeability of the martian crust allows large amounts of groundwater to be transported rapidly at flow rates of 103 104 m3 s into the region models of cooling during emplacement indicate that welding of pyroclastic flows can occur at large distances hundreds of kilometers from a source vent on mars the layering within hadriaca patera could be attributed to welding of pyroclastic flows that would control its susceptibility to erosion morphologic similarities between hadriaca and tyrrhena paterae suggest a similar volcanic history with an early pyroclastic dominated shield building phase followed by effusive eruptions at their summit calderas and on the flank of tyrrhena patera the formation of the extensive ridged plains of hesperia planum following the formation of the highland paterae supports the interpretation of a transition from explosive to effusive volcanism in the eastern hellas region a progressive depletion of volatiles on mars is consistent with the morphologic properties of highland paterae and other central vent volcanoes a predominance of hydrovolcanic eruptions in the development of hadriaca and tyrrhena paterae would imply that the transition in volcanic eruption style can be attributed to a volatile depletion of the crust whereas magmatic eruptions at the paterae would be indicative of temporal changes in martian magmas

mass transfer and porosity evolution during low temperature water rock interaction in gneisses of the simano nappe arvigo val calanca swiss alps late alpine fissures and fractures in amphibolite facies basement gneisses at arvigo val calanca swiss alps show distinct cm sized reaction selvages parallel to the fracture walls that composed of subgreenschist facies assemblages produced by the interaction of water present in the fracture porosity with the old high grade gneiss assemblages the process of selvage or reaction vein formation occurred in the brittle deformation regime and at temperatures characteristic of first the prehnite pumpellyite facies and then later of the zeolite facies the vein formation occurred during uplift and cooling at very late stages of the alpine orogeny the reaction veins are composed of a selvage of altered gneiss on both sides of the central fracture and a central zone with fissure minerals that have been growing in the open fracture pore space the central zone of the arvigo veins contains an early assemblage with epidote prehnite and chlorite and a late succession sequence of various species of zeolite the veins of the arvigo quarry are convincing evidence that fracture fluids in gneiss and granite have the potential to precipitate ca zeolite this is an important find because many fluids recovered from deep continental drill holes and from geothermal energy exploration are found to be oversaturated in respect to a number of ca zeolite species vein formation during late uplift and cooling of the alps occurred at continuously decreasing t and at hydrostatic pressure 1 coexisting prehnite epidote records temperatures of 330 380 c 2 chlorite formation at temperature of 333 32 c and 3 formation of zeolites 250 c in the selvages the prime reaction is the replacement of plagioclase by albite along a sharp reaction front that separates the selvage from unaltered gneiss in addition to albitisation chloritisation of biotite is the second important reaction in the alteration process the reactions release components for the formation of ca al silicates the water rock interaction is associated with a depletion of al si ca fe and k in the altered wall rock the overall reaction is associated with an increase in porosity of up to 14 2 2 2 in the selvage zone altered wall rock caused by the volume decrease during albitisation and the removal of biotite the propagation of the sharp reaction front through the gneiss matrix occurred via a dissolution reprecipitation mechanism zeolite formation is tied to the plagioclase alteration reaction in the rock matrix which releases components for zeolite formation to a co2 poor aqueous liquid

modification history of the harmakhis vallis outflow channel mars based on ctx scale photogeologic mapping and crater count dating abstract harmakhis vallis is one of the four major outflow channel systems dao niger harmakhis and reull valles that cut the eastern rim region of the hellas basin the largest well preserved impact structure on mars the structure of harmakhis vallis and the volume of its head depression as well as earlier dating studies of the region suggest that the outflow channel formed in the hesperian period by collapsing when a large amount of subsurface fluid was released thus harmakhis vallis as well as the other nearby outflow channels represents a significant stage of the fluvial activity in the regional history on the other hand the outflow channel lies in the martian mid latitude zone where there are several geomorphologic indicators of past and possibly also contemporary ground ice the floor of harmakhis also displays evidence of a later stage ice related activity as the outflow channel has been covered by lineated valley fill deposits and debris apron material the eastern rim region of the hellas impact basin has been the subject of numerous geologic mapping studies at various scales and based on different imaging data sets however harmakhis vallis itself has received less attention and the studies on the outflow channel have focused only on limited parts of the outflow channel or on separated different geologic events in this work the harmakhis vallis floor is mapped and dated from the head depression to the beginning of the terminus based on the mars reconnaissance orbiter s context camera images ctx 6 m pixel our results show that harmakhis vallis has been modified by several processes after its formation age determinations on the small uncovered parts of the outflow channel which possibly represent the original floor of harmakhis imply that harmakhis may have experienced fluvial activity only 780 850 400 600 ma ago the discovered terrace structure instead shows that the on surface activity of the outflow channel has been periodic the most significant of the modification processes on harmakhis vallis has been the formation of lineated valley fill units the lineated valley fills now cover the outflow channel almost entirely they formed not later than 400 ma ago based on stratigraphic analyses and crater counts all the floor units have also been resurfaced several usually two or three times the resurfacing ages of the dated units show that the later modification processes have occurred at least on a local scale in the harmakhis vallis region not only inside the outflow channel this in turn may indicate that the processes resulted from a larger scale change for example in the local climate or endogenic conditions

geological and hydrological histories of the argyre province mars the geologic history of the multi ringed argyre impact basin and surroundings has been reconstructed on the basis of geologic mapping and relative age dating of rock materials and structures the impact formed a primary basin rim materials and a complex basement structural fabric including faults and valleys that are radial and concentric about the primary basin as well as structurally controlled local basins since its formation the basin has been a regional catchment for volatiles and sedimentary materials as well as a dominant influence on the flow of surface ice debris flows and groundwater through and over its basement structures the basin is interpreted to have been occupied by lakes including a possible mediterranean sized sea that formed in the aftermath of the argyre impact event the hypothesized lakes froze and diminished through time though liquid water may have remained beneath the ice cover and sedimentation may have continued for some time at its deepest the main argyre lake may have taken more than a hundred thousand years to freeze to the bottom even absent any heat source besides the sun but with impact induced hydrothermal heat geothermal heat flow due to long lived radioactivities in early martian history and concentration of solutes in sub ice brine liquid water may have persisted beneath thick ice for many millions of years existence of an ice covered sea perhaps was long enough for life to originate and evolve with gradually colder and more hypersaline conditions the argyre rock materials diverse in origin and emplacement mechanisms have been modified by impact magmatic eolian fluvial lacustrine glacial periglacial alluvial colluvial and tectonic processes post impact adjustment of part of the impact generated basement structural fabric such as concentric faults is apparent distinct basin stratigraphic units are interpreted to be linked to large scale geologic activity far from the basin including growth of the tharsis magmatic tectonic complex and the growth into southern middle latitudes of south polar ice sheets along with the migration of surface and sub surface volatiles towards the central part of the primary basin the substantial difference in elevation with respect to the surrounding highlands and tharsis and the thaumasia highlands result in the trapping of atmospheric volatiles within the basin in the form of fog and regional or local precipitation even today in addition the impact event caused long term millions of years hydrothermal activity as well as deep seated basement structures that have tapped the internal heat of mars as conduits for far greater time possibly even today this possibility is raised by the observation of putative open system pingos and nearby gullies that occur in linear depressions with accompanying systems of faults and fractures long term water and heat energy enrichment complemented by the interaction of the nutrient enriched primordial crustal and mantle materials favorable to life excavated to the surface and near surface environs through the argyre impact event has not only resulted in distinct geomorphology but also makes the argyre basin a potential site of exceptional astrobiological significance

major episodes in the geologic history of western promethei terra mars 1 geologic evolution of the western portion of promethei terra 40 50 s 90 105 e consists of two major episodes the first was the formation of a late noachian early hesperian volcanic province during this episode a kilometer thick suite 0 3 106 km3 of lavas accumulated to the south of reull and harmakhis valles within a regional depression that probably was formed earlier in a massive erosion a topographic barrier of the cratered terrains separates the volcanic western promethei plateau from hesperia planum thus the lavas could not originate from hesperia planum the topographic position of western promethei terra excludes a possible lava feeding from hadriaca patera dikes from tyrrhena patera potentially could be the lava source the massive erosion before formation of the lava plateau in western promethei terra is poorly consistent however with the hypothesis that the distal dikes served as the source and favors emplacement of sills or a local source for the lavas the second episode after the lava plateau emplacement was surface modification by glacial fluvial and aeolian processes the time of the episode is poorly known and it could continue from the late hesperian and through the entire amazonian epoch mesas channels and esker like ridges suggest that at the earlier stages of this episode late hesperian early amazonian a glacier or ice dust deposits covered the western promethei terra area studied the 50 60 103 km3 formation could contain 15 18 to 40 50 103 km3 of ice this is comparable with the ice involved into of lobate apron formation 5 13 103 km3 at the later amazonian stages of western promethei terra because of the uncertainties in the ice volume estimates the total amount of water in the earlier glacier and later aprons was approximately the same

constraints on the formation and properties of a martian lobate debris apron insights from high resolution topography sharad radar data and a numerical ice flow model

millochau crater mars infilling and erosion of an ancient highland impact crater the geology and stratigraphy of millochau crater 21 4 s 275 w located in the highlands of tyrrhena terra mars are documented through geomorphic analyses and geologic mapping crater size frequency distributions and superposition relationships are used to constrain relative ages of geologic units and determine the timing and duration of the geologic processes that modified millochau rim materials and emplaced deposits on millochau s floor crater size frequency distributions show a middle noachian age for rim materials and middle noachian to early hesperian ages for most of the interior deposits valley networks and gullies incised within millochau s rim materials and interior wall respectively indicate fluvial activity was an important erosional process millochau contains an interior plateau offset northeast of millochau s center which rises up to 400 m above the surrounding crater floor and slopes downward to the south and west layers exposed along the northern and eastern scarp boundaries of the plateau are tens to hundreds of meters thick and laterally continuous in moc images these layers suggest most materials within millochau were emplaced by sedimentary processes e g fluvial or eolian with the potential for lacustrine deposition in shallow transient bodies of water and contributions of volcanic airfall mass wasting may have also contributed significant quantities of material to millochau s interior especially to the deposits surrounding the plateau superposition relationships combined with impact crater statistics indicate that most deposition and erosion of millochau s interior deposits is ancient which implies that fluvial activity in this part of tyrrhena terra is much older than in the eastern hellas region eolian processes mobilized sediment to form complicated patterns of long and short wavelength dunes whose emplacement is controlled by local topography these deposits are some of the youngest within millochau amazonian and eolian modification may be ongoing

small martian valleys pristine and degraded morphology the equatorial heavily cratered uplands of mars are dissected by two classes of small valleys that are intimately associated in compound networks pristine valleys with steep valley walls preferentially occupy downstream portions of compound basins degraded valleys with eroded walls are laterally more extensive and have higher drainage densities than pristine valleys morphometric and crater counting studies indicate that relatively dense drainage networks were emplaced on mars during the heavy bombardment about 4 0 b y ago over a period of approximately 10 sup 8 years these networks were degraded and subsequently invaded by headwardly extending pristine valleys the pristine valleys locally reactivated the compound networks probably through sapping processes dependent upon high water tables fluvial activity in the heavily cratered uplands generally ceased approximately 3 8 3 9 b y ago coincident with the rapid decline in cratering rates the relict compound valleys on mars are morphometrically distinct from most terrestrial drainage systems the differences might be caused by a martian valley formation episode characterized by hyperaridity by inadequate time for network growth by very permeable rock types or by a combination of factors

sequence and mechanisms of deformation around the hellas and isidis impact basins on mars the distribution and age of early volcanic and tectonic features surrounding the itellas and isidis impact basins are shown to fit a four stage sequence first concentric canyons form outside the basin boundary scarp at or near the time of basin formation followed shortly thereafter by radial troughs extending beyond the boundary scarp after a hiatus concentric graben develop inside the basin within the massif ring finally soon after graben formation widespread volcanic plains are emplaced between the massif ring and the boundary scarp to one side of the basin three models of basin centered deformation are compared io hese observed deformation events elastic flexure due to loading elastic flexure due to uplift and impact fracture a central load of basin fill can account for concentric fractures by elastic flexure around the load formation of the distant concentric canyons however requires lithospheric thicknesses a factor of 5 greater than those indicated by planetary thermal history models and an increase in feature width by an order of magnitude relative to flexural graben identified elsewhere on mars and the moon although inclusion of loading by basin ejecta reduces the required lithospheric thickness to acceptable values flexure still fails to account for the large canyon widths observed impact fracture from a rapid inward flow of asthenosphere during transient cavity collapse however is consistent with the three key observational constraints for the distant canyons their age width and distance from the basin as the basin then undergoes isostatic uplift soon after impact elastic flexure induces a radial pattern of failure consistent with the observed extent and timing of the radial troughs later after a long period of basin infilling elastic failure due to loading of the central basin region can account for the ring grabens in the massif ring the localization of volcanism into a single ridged plains unit on the basin rim indicates a thermal source offset from the basin which is not included in these models and perhaps reflects an additional mechanism unique to mars

tyrrhena patera geologic history derived from mars express high resolution stereo camera 1 we used mars express high resolution stereo camera images of the tyrrhena patera volcano to assign cratering model ages to material units defined in the vikingorbiter based geologic mapping cratering model ages are generally consistent with their stratigraphy we can identify three key intervals of major activity at tyrrhena patera 1 formation of the volcanic edifice in the noachian period 3 7 4 0 ga shortly following the hellas impact 4 ga and coincident with the formation of hadriaca patera 3 9 ga 2 modification of the edifice and formation of the caldera rille and channels in the hesperian period possibly extending into the amazonian period and 3 a final stage of modification in the late amazonian epoch 0 8 1 4 ga early to mid hesperian activity on tyrrhena patera is consistent with similar activity on hadriaca patera at 3 3 3 7 ga the most recent dateable event on tyrrhena patera is modification on the upper shield caldera rille and channel floors at 800 ma this coincidence of resurfacing in three units suggests a widespread process es which we speculate involved preferential aeolian erosion of small craters on these flatter surfaces relative to the other units on the volcano alternatively some combination of pyroclastic flow emplacement on the upper shield and fluvial activity in the caldera rille and channels followed by differential aeolian erosion and deposition could have produced the present surface regardless major geologic resurfacing ended at tyrrhena patera nearly a billion years ago

radar sounding evidence for buried glaciers in the southern mid latitudes of mars lobate features abutting massifs and escarpments in the middle latitudes of mars have been recognized in images for decades but their true nature has been controversial with hypotheses of origin such as ice lubricated debris flows or glaciers covered by a layer of surface debris these models imply an ice content ranging from minor and interstitial to massive and relatively pure soundings of these deposits in the eastern hellas region by the shallow radar on the mars reconnaissance orbiter reveal radar properties entirely consistent with massive water ice supporting the debris covered glacier hypothesis the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes such features may collectively represent the most extensive nonpolar ice yet recognized on mars

regional and local patterns of low grade metamorphism in the north shore volcanic group minnesota usa the north shore volcanic group in northern minnesota is part of the middle proterozoic keweenawan sequence one of the largest plateau lava provinces in the world the primary geochemistry of the basalts suggests that volcanism occurred in an intracontinental rift environment the subaerial lava flows mainly amygdaloidal olivine tholeiites and tholeiites have undergone low grade metamorphism from zeolite to lower greenschist facies on the basis of alteration phases replacing the primary magmatic minerals infilling amygdales and veins and replacing secondary minerals the following zones have been distinguished 1 thomsonite scolecite smectite 2 heulandite stilbite smectite 3 laumontitechlorite albite 4 laumontite chlorite albite prehnite pumpellyite and 5 epidote chlorite albite actinolite zone in addition to the overall zonation based on mineral parageneses zonations in the composition of the ab content of the newly formed albite replacing primary ca rich plagioclase and of the newly formed mafic phyllosilicates are observed within the sequence and within single flows mafic phyllosilicates in the upper part of the sequence mainly smectites and mixed layer smectite chlorites display high si and ca na k contents whereas in the lower part of the sequence the amounts of si and ca na k are markedly lower mainly chlorites and mixed layer chlorite smectites similar zonations are observed within the individual flows the albite content of the newly formed plagioclase is highest and the si and ca na k content of the phyllosilicates lowest in the amygdaloidal flow top while the opposite is true for the massive flow interior the above features suggest that the overall pattern is one of burial type metamorphism associated with extension in the rift setting in detail the mineral assemblages are controlled not only by the stratigraphic position but also by the flow morphology controlling permeability whose effect on the assemblages is most pronounced in the stratigraphically upper parts this suggests that at the first stages of alteration lowest grade the patterns of fluid flow were important effects in controlling the assemblages at greater burial depth assemblages are more homogeneous perhaps representative of a more even and pervasive flow pattern using the observed assemblages at face value to define grade and or facies different conditions would be assigned within the different morphological flow portions thus at low grade metamorphic conditions it is essential to integrate assemblages from different morphological flow portions in order to define satisfactorily the overall metamorphic conditions